US20070175676A1 - Vehicle Having Twin Transmissions For Driving Respective Wheels - Google Patents
Vehicle Having Twin Transmissions For Driving Respective Wheels Download PDFInfo
- Publication number
- US20070175676A1 US20070175676A1 US11/697,568 US69756807A US2007175676A1 US 20070175676 A1 US20070175676 A1 US 20070175676A1 US 69756807 A US69756807 A US 69756807A US 2007175676 A1 US2007175676 A1 US 2007175676A1
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- Prior art keywords
- operation device
- vehicle
- steering
- steering operation
- pair
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D11/00—Steering non-deflectable wheels; Steering endless tracks or the like
- B62D11/24—Endless track steering specially adapted for vehicles having both steerable wheels and endless track
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60K17/00—Arrangement or mounting of transmissions in vehicles
- B60K17/04—Arrangement or mounting of transmissions in vehicles characterised by arrangement, location or kind of gearing
- B60K17/10—Arrangement or mounting of transmissions in vehicles characterised by arrangement, location or kind of gearing of fluid gearing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60K17/00—Arrangement or mounting of transmissions in vehicles
- B60K17/34—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles
- B60K17/356—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles having fluid or electric motor, for driving one or more wheels
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
- B60K17/00—Arrangement or mounting of transmissions in vehicles
- B60K17/36—Arrangement or mounting of transmissions in vehicles for driving tandem wheels
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D11/00—Steering non-deflectable wheels; Steering endless tracks or the like
- B62D11/001—Steering non-deflectable wheels; Steering endless tracks or the like control systems
- B62D11/005—Hydraulic control systems
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D11/00—Steering non-deflectable wheels; Steering endless tracks or the like
- B62D11/001—Steering non-deflectable wheels; Steering endless tracks or the like control systems
- B62D11/006—Mechanical control systems
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D3/00—Steering gears
- B62D3/02—Steering gears mechanical
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D7/00—Steering linkage; Stub axles or their mountings
- B62D7/06—Steering linkage; Stub axles or their mountings for individually-pivoted wheels, e.g. on king-pins
- B62D7/08—Steering linkage; Stub axles or their mountings for individually-pivoted wheels, e.g. on king-pins the pivotal axes being situated in a single plane transverse to the longitudinal centre line of the vehicle
- B62D7/09—Steering linkage; Stub axles or their mountings for individually-pivoted wheels, e.g. on king-pins the pivotal axes being situated in a single plane transverse to the longitudinal centre line of the vehicle characterised by means varying the ratio between the steering angles of the steered wheels
Definitions
- the present invention relates to a vehicle equipped with a pair of transmissions, e.g., a pair of hydrostatic transmissions (HSTs), a pair of belt type continuous variable transmissions (CVTs), or a pair of electric motors, for driving respective left and right drive wheels, wherein the pair of transmissions, which surely drive the vehicle straight when they are set so, are operated for left and right turning of the vehicle so that one of the left and right drive wheels is accelerated and the other is decelerated, and wherein each of the left and right turning directions of the vehicle always coincides with the manipulated leftward or rightward direction of a steering operation device whether the vehicle travels forward or rearward.
- a pair of transmissions e.g., a pair of hydrostatic transmissions (HSTs), a pair of belt type continuous variable transmissions (CVTs), or a pair of electric motors, for driving respective left and right drive wheels
- the pair of transmissions which surely drive the vehicle straight when they are set so, are operated for left and right turning of the vehicle so
- HSTs twin parallel transmissions
- HSTs twin parallel transmissions
- one of the transmissions accelerates the corresponding drive wheel (on an outside of turning), and the other decelerates the other drive wheel (on an inside of turning).
- a steering wheel serving as a steering operation device of the vehicle is turned left, one transmission decelerates the left drive wheel, and the other accelerates the right drive wheel, whereby the vehicle turns left.
- the deceleration force applied on the inside drive wheel becomes relatively larger than the traveling force thereof, the rotational direction of the inside drive wheel is reversed. Then, the deceleration force becomes an acceleration force for the rotationally reversed inside drive wheel.
- the traveling speed and direction of the vehicle can be changed by operation of a speed change operation device such as a pedal or a lever so that both the transmissions drive both the drive wheels at equal rotary speed. If the steering wheel is turned for turning, the rotary speed of one drive wheel becomes higher than the equal rotary speed, and that of the other drive wheel becomes lower than the equal rotary speed.
- a speed change operation device such as a pedal or a lever
- the vehicle having the twin transmissions still has such a problem as follows:
- the steering wheel When it is assumed that the left drive wheel is decelerated and the right wheel accelerated by turning the steering wheel leftward during the forward traveling of the vehicle, the steering wheel must be turned rightward for left turning during the rearward traveling of the vehicle because the acceleration force for a forwardly rotating wheel serves as a deceleration force for a rearwardly rotating wheel.
- Such an operation of the steering wheel is so illusional as to cause the vehicle to turn to a wrong side.
- Japanese Laid Open Gazette No. 2000-25,637 discloses mechanical means interposed among a transmission, a steering operation device and a speed changing operation device
- Japanese Patent No. 3,176,237 discloses a hydraulic switching valve provided in an HST for steering.
- each of the two Japanese documents discloses a pair of HSTs for driving two rotors
- one of the HSTs is provided for traveling so as to rotate both the rotors at various equal speeds
- the other HST is provided for steering so as to accelerate one rotor and decelerate the other rotor.
- each of the above-mentioned disclosed means does not correspond to the vehicle driving system comprising a pair of transmissions for driving respective right and left drive wheels. Furthermore, while the rotors disclosed in Japanese Laid Open Gazette No. 2000-25,637 are drive wheels, those disclosed in Japanese Patent No. 3,176,237 are sprockets.
- the performances of the parallel transmissions must be strictly equal to each other so as to ensure a straight traveling when the steering wheel is set in the straight traveling position. If there is a slight performance difference between the transmissions, the drive wheels rotate at different speeds so as to turn the vehicle while the steering wheel is in the straight traveling position, or a complicated and troublesome adjustment of a linkage from the steering wheel to the transmissions must be performed. Moreover, the differential driving of left and right drive wheels is not requested in such a case where the vehicle travels on a rough road or one of the drive wheels slumps into mud.
- U.S. Pat. No. 5,590,737 discloses a crawler vehicle equipped with a driving system comprising a pair of HSTs for driving respective right and left sprockets, wherein a differential-locking clutch is provided so as to lock the sprockets with each other at need.
- An object of the present invention is to provide a vehicle including a prime mover, left and right drive wheels, and twin parallel transmissions for driving the respective drive wheels, wherein the vehicle is made user-friendly by such a driving direction changing system as to ensure that each of left and right turning directions of the vehicle corresponding to the manipulated direction of the steering operation device is constant whether the vehicle travels forward or rearward.
- the reversing means in case that the vehicle includes a common input shaft shared between the transmissions to receive power of the prime mover, the reversing means is preferably interposed among the common input shaft and the pair of input shafts of the respective transmissions.
- the reversing means may be interposed between each of output shafts of the respective transmissions and each of the drive wheels.
- a vehicle includes (1) a prime mover, left and right drive wheels, and twin parallel transmissions for driving the respective drive wheels, (2) a traveling operation device for setting a traveling speed of the vehicle and selecting a traveling direction of the vehicle between forward and rearward, which is operationally connected with the pair of transmissions so as to drive the drive wheels at a common speed and in a common direction, and, (3) a steering operation device for turning the vehicle leftward or rightward, which is operationally connected with the pair of transmissions so as to accelerate one of the drive wheels at outside of the turning vehicle and to decelerate the other drive wheel at inside of the turning vehicle whether the vehicle travels forward or rearward
- a second object of the present invention is to ensure both the drive wheels rotate at the same speed for exact straight traveling of the vehicle when the steering operation device is set so the vehicle travels in a straight direction, in spite of some performance differences between the transmissions.
- the vehicle according to the present invention comprises a differential locking clutch for the drive wheels.
- the differential locking clutch is engaged to lock the drive wheels with each other when the steering operation device is set to make the vehicle travel straight, and wherein the differential locking clutch is disengaged to unlock the drive wheels from each other when the steering operation device is set to make the vehicle travel leftward or rightward.
- FIG. 1 is a schematic plan view of a six-wheel vehicle according to the present invention, including a steering wheel, two front casters, two middle drive wheels, and two rear drive wheels, wherein the middle and rear drive wheels are not steerable.
- FIG. 2 is a schematic plan view of another six-wheel vehicle according to the present invention, including a steering wheel, two steerable front driven wheels, two middle drive wheels, and two rear drive wheels, wherein the middle and rear drive wheels are not steerable.
- FIG. 3 is a schematic plan view of a four-wheel vehicle according to the present invention, including a steering wheel, two front drive wheels, and two rear drive wheels, wherein the four drive wheels are not steerable.
- FIG. 4 is a schematic plan view of another four-wheel vehicle according to the present invention, including a steering wheel, two front drive wheels which are not steerable, and two steerable rear drive wheels.
- FIG. 5 is a diagram of a wheel driving system for a vehicle according to the present invention, including twin transmissions for driving respective left and right drive wheels independently, wherein a differential-locking clutch is provided so as to connect the left and right drive wheels to each other when a steering wheel is set in a straight traveling position.
- FIG. 6 illustrates a perspective view of a mechanical linkage for controlling left and right speed control levers of the respective twin transmissions, together with a diagram of hydraulic and electric circuit for controlling the speed control levers and the differential locking clutch, wherein the linkage and the hydraulic and electric circuit are provided for the wheel driving system shown in FIG. 5 .
- FIG. 7 is a diagram of another wheel driving system for a vehicle according to the present invention, including twin transmissions for driving respective left and right drive wheels independently, wherein a differential-locking clutch is provided so as to connect left and right drive wheels to each other when a steering wheel is set in a straight traveling position, and a reversing mechanism (a reverser) is provided among a primary input shaft and respective input shafts of the twin transmissions.
- a differential-locking clutch is provided so as to connect left and right drive wheels to each other when a steering wheel is set in a straight traveling position
- a reversing mechanism (a reverser) is provided among a primary input shaft and respective input shafts of the twin transmissions.
- FIG. 8 is a diagram of another wheel driving system for a vehicle according to the present invention, including twin transmissions for driving respective left and right drive wheels independently, wherein a differential-locking clutch is provided so as to connect left and right drive wheels to each other when a steering wheel is set in a straight traveling position, and a reverser is interposed between an output shaft of each transmission and each drive wheel.
- FIG. 9 is a perspective view of a mechanical linkage for controlling left and right speed control levers of the respective twin transmissions, together with a diagram of hydraulic and electric circuit for controlling the speed control levers, the differential locking clutch and the reverser, wherein the linkage and the hydraulic and electric circuit are provided for any of the wheel driving systems shown in FIGS. 7 and 8 .
- FIG. 10 is a perspective view of the mechanical linkage of FIG. 9 , having an alternative reverser control system.
- FIG. 11 is a diagram of the wheel driving system of FIG. 7 , having an alternative reverser clutch formation.
- FIG. 12 is a diagram of the wheel driving system of FIG. 8 , having an alternative reverser clutch formation.
- FIG. 13 is a perspective view of a mechanical linkage for controlling left and right speed control levers of the respective twin transmissions, together with a diagram of hydraulic and electric circuit for controlling the speed control levers and the differential locking clutch, wherein the linkage and the hydraulic and electric circuit are provided for any of the wheel driving systems shown in FIGS. 11 and 12 .
- a six-wheel vehicle has a vehicle frame 1 , on which a vertical crankshaft engine 2 , a transmission housing 3 and left and right axle casings 4 L and 4 R are mounted.
- Left and right drive wheels 5 L and 5 R are disposed on left and right sides of transmission housing 3 , respectively.
- Left and right drive wheels 6 L and 6 R are disposed behind respective drive wheels 5 L and 5 R.
- Left and right casters 7 are supported (alternatively, only one caster 7 or more than two casters 7 may be supported) by a front portion of vehicle frame 1 so as to serve as laterally turnable driven wheels, which are free from driving power of engine 2 and turn to a lateral side coinciding with a turning side of a steering wheel 14 serving as a steering operation device.
- casters 7 serve as front wheels, drive wheels 5 L and 5 R as middle wheels, and drive wheels 6 L and 6 R as rear wheels.
- positions of these wheels may be changed in the longitudinal direction of the vehicle, e.g., drive wheels 6 L and 6 R may serve as front wheels, and casters 7 as rear wheels.
- a belt 8 is interposed between an engine output pulley 9 of vertical crankshaft engine 2 and a primary input pulley 10 fixed on a primary input shaft 11 projecting from transmission housing 3 so as to transmit power from engine 2 to a transmission system in transmission housing 3 . Additionally, belt 8 is looped over a tension pulley 12 to be tensioned.
- the transmission system in transmission housing 3 comprises left and right power take-off portions which transmit power to left and right axle casings 4 L and 4 R through respective propeller shafts 13 , thereby driving drive wheels 6 L and 6 R.
- left and right steerable driven wheels 60 serving as the laterally turnable wheels as mentioned above, mechanically interlock with steering wheel 14 .
- a pivot (a king pin) of each driven wheel 60 is connected to a pivot 61 c of each of two small sector gears 61 .
- Each small sector gear 61 has a front edge 61 a and a shorter rear edge 61 b .
- Pivot 61 c is disposed extremely adjacent to an end of gear 61 where both edges 61 a and 61 b are gathered.
- an axle housing for supporting both driven wheels 60 is provided at each of left and right ends thereof with each of two large sector gears 62 supported rotatably around respective vertical pivots.
- Each large sector gear 62 has a front edge 62 a and a longer rear edge 62 b .
- An end of gear 62 where both edges 62 a and 62 b are gathered is pivotally connected to each of left and right ends of a tie rod 63 interlocking with steering wheel 14 .
- a distance of a serrated periphery of each gear 61 from pivot 61 c (hereinafter, the distance is referred to as a “radius”) gradually decreases while it passes from front edge 61 a to rear edge 61 b .
- a distance of a serrated periphery of each gear 62 from the end of gear 62 pivotally connected to tie rod 63 i.e., a radius of gear 62 gradually increases while it passes from front edge 62 a to rear edge 62 b.
- the vehicle can turn on a small circle swiftly even if the angle of steering wheel 14 is not very large.
- the vehicle is more advantageous than a vehicle having a caster in that a driver can comprehend the direction of driven wheels 60 and stably operate the vehicle on a slope because steering wheel 14 is always connected to driven wheels 60 .
- a skid steering type four-wheel vehicle has left and right front drive wheels 5 L and 5 R and left and right rear drive wheels 6 L and 6 R, wherein none of the four wheels are steerable.
- Steering wheel 14 serving as a steering operation device is manipulated so as to locate left and right speed control levers 17 L and 17 R.
- the vehicle selectively travels straight or turns left or right, depending upon whether or not the rotary speed of left drive wheels 5 L and 6 L determined by the location of left speed control lever 17 L coincides with that of right drive wheels 5 R and 6 R determined by the location of right speed control lever 17 R.
- a four-wheel vehicle has left and right front drive wheels 5 L and 5 R and left and right steerable rear drive wheels 6 L and 6 R.
- Steering wheel 14 is operationally connected to drive wheels 6 L and 6 R through a linkage which is similar with that of FIG. 2 .
- HSTs 18 L and 18 R are disposed oppositely to each other.
- Each of HSTs 18 L and 18 R comprises a hydraulic pump 19 including a movable swash plate 19 a , and a hydraulic motor 20 including a fixed swash plate 20 a .
- Hydraulic pump 19 and hydraulic motor 20 are fluidly connected with each other through a center section 21 .
- Speed control levers 17 L and 17 R interlock with respective movable swash plates 19 a (See FIG. 4 ).
- Pump shafts 19 b of both hydraulic pumps 19 are extended toward each other.
- Bevel gears serving as HST input gears 19 c are fixed onto ends of pump shafts 19 b facing each other, respectively.
- An upper wall of transmission housing 3 rotatably supports primary input shaft 11 vertically.
- Above-mentioned primary input pulley 10 is fixed onto the outer end of primary input shaft 11 .
- a bevel gear 22 is fixed onto the other inner end of primary input shaft 11 and meshes with both HST input gears 19 c .
- primary input shaft 11 penetrates charge pump 23 so as to serve as a drive shaft of charge pump 23 .
- primary input shaft 11 is supported horizontally by transmission housing 3 .
- An outer end of horizontal primary input shaft 11 penetrating charge pump 23 may be extended outward from transmission housing 3 so as to serve as a PTO shaft for driving a working machine attached to the vehicle.
- differential locking clutch 24 Motor shafts 20 b of both HSTs 18 L and 18 R are extended toward each other and connected/disconnected through a differential locking clutch 24 .
- each motor shaft 20 b projects from center section 21 so as to be provided thereon with a brake 25 .
- Differential locking clutch 24 is a spring-loaded hydraulic clutch, which is engaged by spring force and disengaged by hydraulic pressure overcoming the spring force. The hydraulic pressure for disengaging differential locking clutch 24 is applied by fluid supplied by a later-discussed electric and hydraulic circuit.
- Each of drive wheels 5 L and 5 R is fixed to each of left and right drive axles 27 rotatably supported by transmission housing 3 .
- Motor shafts 20 b engage with respective counter shafts 26 through deceleration gears 20 c and 26 a .
- Counter shafts 26 engage with respective drive axles 27 through deceleration gears 26 b and 27 a .
- Left and right drive axles 27 project laterally outward from transmission housing 3 oppositely to each other and are provided on their outer ends with respective drive wheels 5 L and 5 R.
- Each counter shaft 26 is extended outward in transmission housing 3 so as to be fixedly provided on its distal end with a bevel gear 26 c , which meshes with a bevel gear 29 a fixed on an inner end of each of left and right PTO shafts 29 .
- Each PTO shaft 29 projects rearward from transmission housing 3 so as to be joined to propelling shaft 13 through a universal joint.
- a horizontal input shaft 31 and a horizontal drive axle 32 are rotatably supported mutually perpendicularly and engage with each other through bevel gears 31 a and 32 a fixed onto respective shafts 31 and 32 .
- Input shaft 31 projects outward from each of axle casings 4 L and 4 R so as to be joined to propelling shaft 13 through a universal joint.
- Drive axles 32 project laterally outward from respective axle casings 4 L and 4 R oppositely to each other and are provided on their outer ends with respective drive wheels 6 L and 6 R.
- Each PTO shaft 29 is intermediately provided with a clutch 30 .
- Clutches 30 are engaged or disengaged so as to put the vehicle into either a four-wheel drive (4WD) mode or a two-wheel drive (2WD) mode.
- a forward traveling shift pedal 33 and a rearward traveling shift pedal 34 (together, the traveling operation device) are juxtaposed above a footboard on the vehicle.
- a pressure-sensing switch 35 F is disposed on forward traveling shift pedal 33 so as to be switched on by a driver's foot when pedal 33 is depressed.
- a pressure-sensing switch 35 R is disposed on rearward traveling shift pedal 34 so as to be switched on by a driver's foot when pedal 34 is depressed.
- a support shaft 36 is disposed horizontally and fixed to a vehicle body such as vehicle frame 1 .
- a sleeve 37 is relatively rotatably disposed around support shaft 36 .
- a shaft 38 is fixedly extended upward from sleeve 37 radially about shaft 36 .
- a sleeve 39 is relatively rotatably provided around shaft 38 .
- a top of shaft 38 projects upward from sleeve 39 .
- An arm 33 a fixedly projects upward from a boss of forward traveling shift pedal 33 serving as a pivot of pedal 33 .
- a link 45 is connected at one end thereof to arm 33 a so as to be pulled by depression of pedal 33 .
- An arm 34 a fixedly projects downward from a boss of rearward traveling shift pedal 34 serving as a pivot of pedal 34 .
- a link 46 is connected at one end thereof to arm 34 a so as to be pushed by depression of pedal 34 .
- Links 45 and 46 are joined at the other ends thereof to the top of shaft 38 .
- sleeve 37 is biased by neutral-returning springs (not shown) interposed in respective links 45 and 46 so as to locate shaft 38 at a neutral position N.
- link 45 pulls the top of shaft 38 so as tilt shaft 38 forward from neutral position N to a maximum forward traveling speed position Fm in forward traveling range F in correspondence to the depth of depressed pedal 33 .
- link 46 pushes the top of shaft 38 so as to tilt shaft 38 rearward from neutral position N to a maximum rearward traveling speed position Rm in rearward traveling range R in correspondence to the depth of depressed pedal 34 .
- shaft 38 is rotated forward or rearward together with sleeve 37 around shaft 36 .
- a pair of opposite traverse bars 39 a are fixedly extended from sleeve 39 radially about shaft 38 .
- Bars 39 a are connected at utmost ends thereof to respective links 16 L and 16 R extended from speed control levers 17 L and 17 R. Consequently, either pedal 33 or 34 is depressed so as to tilt sleeve 39 together with shaft 38 forward or rearward and move the utmost ends of traverse bars 39 a with links 16 L and 16 R forward or rearward, thereby rotating speed control levers 17 L and 17 R to an equal degree.
- both levers 17 L and 17 R are pulled and rotated from their neutral positions through links 16 L and 16 R, thereby rotating movable swash plates 19 a of HSTs 18 L and 18 R so as to accelerate drive wheels 5 L and 5 R forward.
- both levers 17 L and 17 R are pushed and rotated from their neutral positions through links 16 L and 16 R, thereby rotating movable swash plates 19 a of HSTs 18 L and 18 R so as to accelerate drive wheels 5 L and 5 R rearward.
- a double-acting hydraulic cylinder 40 is disposed horizontally in parallel to shaft 36 , and its cylinder casing is fixed to sleeve 37 .
- a piston rod 40 a of cylinder 40 is connected to sleeve 39 through an arm 39 b extended radially (perpendicularly to bars 39 a ) from sleeve 39 .
- Sleeve 39 is rotated in relative to shaft 38 by telescopic motion of piston rod 40 a . Consequently, one bar 39 a pulls corresponding one of levers 17 L and 17 R, and the other bar 39 a pushes the other lever 17 R or 17 L, so that one of drive wheels 5 L and 5 R is accelerated, and the other decelerated. However, if one drive wheel 5 L or 5 R is rotated forward and the other rearward, both drive wheels 5 L and 5 R are accelerated in respective forward and rearward directions.
- piston rod 40 a pushing arm 39 b is defined as extension movement increasing the stroke thereof, and the movement of piston rod 40 a pulling arm 39 b as contraction movement decreasing the stroke thereof.
- the stroke of piston rod 40 a is controlled to correspond to a set rotational position of steering wheel 14 .
- the corresponding position of steering wheel 14 differs due to whether the vehicle travels forward or rearward, i.e., whether pedal 33 or 34 is depressed.
- shaft 38 is disposed in rearward traveling range R where both swash plates 19 a of left and right hydraulic pumps 19 are tilted in their ranges for rearward traveling, forwardly pulled left lever 17 L reduces the tilt angle of swash plate 19 a linked therewith so as to reduce the capacity of left hydraulic pump 19 , thereby decelerating left drive wheel 5 L. Simultaneously, rearwardly pushed right lever 17 R increases the tilt angle of swash plate 19 a linked therewith so as to increase the capacity of right hydraulic pump 19 , thereby accelerating right drive wheel 5 R. Therefore, the vehicle turns left.
- a steering valve 41 connects each of ports 40 b and 40 c of cylinder 40 to either pump 42 or tank 43 .
- Steering valve 41 is an electro-magnetically controlled hydraulic (servo) valve having oppositely active solenoids 41 a and 41 b , which is switched among three positions, i.e., a neutral position N 41 , an extension position E 41 and a contraction position C 41 .
- a neutral position N 41 a neutral position
- E 41 extension position
- C 41 a contraction position
- steering valve 41 By exciting solenoid 41 a , steering valve 41 is located at extension position E 41 , where port 40 b is connected to pump 42 , and port 40 c to tank 43 , thereby extending piston rod 40 a .
- steering valve 41 By exciting solenoid 41 b , steering valve 41 is located at contraction position C 41 , where port 40 c is connected to pump 42 , and port 40 b to tank 43 , thereby contracting piston rod 40 a .
- steering valve 41 When neither solenoid 41 a nor 41 b is excited, steering valve 41 is set at neutral position N 41 so as to block both ports 40 b and 40 c , thereby stopping piston rod 40 a.
- Steering wheel 14 is manually turned from a straight traveling position S14 either rightward in a right turning range RT14 or leftward in a left turning range LT14.
- a switch 14 a inputs a detected positional signal of steering wheel 14 to controller 44 .
- An actual stroke of piston rod 40 a or another actual value corresponding to an actual stroke of piston rod 40 a e.g., an actual rotational angle of sleeve 39 , is detected.
- controller 44 Based on a difference of actual stroke of piston rod 40 a from a stroke of piston rod 40 a corresponding to the detected rotational position of steering wheel 14 , controller 44 outputs an exciting signal to one of solenoids 41 a and 41 b of steering valve 41 and stops the output so as to switch steering valve 41 between neutral position N 41 and either position E 41 or C 41 , thereby telescoping and stopping piston rod 40 a . Therefore, in correspondence to the rotational position of steering wheel 14 , sleeve 39 is rotationally located together with levers 17 R and 17 L so as to locate swash plates 19 a of right and left hydraulic pumps 19 to appropriate slant angles and directions.
- a signal value with respect to a stroke of piston rod 40 a is zero when the stroke is a neutral stroke corresponding to the rotational position of steering wheel 14 in straight traveling position S14, that the signal value is increased in a positive range from zero when piston rod 40 a is extended from the neutral stroke, and that the signal value is decreased in a negative range from zero when piston rod 40 a is contracted from the neutral stroke.
- controller 44 calculates a positive signal value in correspondence to the position of steering wheel 14 .
- controller 44 calculates a negative signal value of the same volume with the positive signal value calculated when forward traveling sensing switch 35 F is turned on.
- piston rod 40 a which is extended to a degree from the neutral stroke during forward traveling of the vehicle, is contracted to the same degree from the neutral stroke during rearward traveling of the vehicle.
- piston rod 40 a which is contracted to a degree from the neutral stroke during forward traveling of the vehicle, is extended to the same degree from the neutral stroke during rearward traveling of the vehicle.
- the stroke of piston rod 40 a is increased to a certain degree from the neutral stroke so as to rotate sleeve 39 counterclockwise around shaft 38 and rotate bars 39 a in ranges LT, whereby left speed control lever 17 L is rotated rearward, and right speed control lever 17 R forward, that is, they are symmetrically rotated from their above-mentioned initial position set for forward straight traveling when viewed along the common pivot of levers 17 L and 17 R. Accordingly, forward rotating left drive wheel 5 L is decelerated, and forward rotating right drive wheel 5 R is accelerated so as to compensate for the reduced speed of left drive wheel 5 L, whereby the forward traveling vehicle turns left.
- shaft 38 and sleeve 39 are located at any position in rearward traveling range R, and both bars 39 a are extended laterally in direction S so as to locate speed control levers 17 L and 17 R rearwardly slantwise in the same angle.
- left and right drive wheels 5 L and 5 R rotate rearward at equal speed.
- steering wheel 14 is turned to the certain rotational position in left turning range LT 14 , which is the same with the above-mentioned certain position of steering wheel 14 when setting forward traveling.
- the stroke of piston rod 40 a is reduced from the neutral stroke to a certain degree as much as the above-mentioned increased degree thereof when setting forward traveling so as to rotate sleeve 39 clockwise around shaft 38 and rotate bars 39 a in ranges RT, whereby left speed control lever 17 L is rotated forward, and right speed control lever 17 R rearward, that is, they are symmetrically rotated from their above-mentioned initial position set for rearward straight traveling when viewed along the common pivot of levers 17 L and 17 R. Accordingly, rearward rotating left drive wheel 5 L is decelerated, and rearward rotating right drive wheel 5 R is accelerated so as to compensate for the reduced speed of left drive wheel 5 L, whereby the rearward traveling vehicle turns left.
- Hydraulic pump 42 serves as a common hydraulic pressure source for hydraulic cylinder 40 and differential-locking clutch 24 .
- a two-positioned spring-loaded electromagnetic differential-locking valve 60 which is switched between positions I and II. Controller 44 controls the location of differential-locking valve 60 in association with operation of steering wheel 14 .
- differential-locking valve 60 When steering wheel 14 is set in straight traveling position S 14 , differential-locking valve 60 is automatically located in position I so as to engage differential-locking clutch 24 , thereby rotating right and left drive wheels 5 R and 5 L at the perfectly same speed, whereby the vehicle accurately travels straight. Even if the vehicle is on a slope and such an unexpected accident as engine or electric power failure occurs, right and left drive wheels 5 R and 5 L are locked together so as to keep the vehicle in safety.
- controller 44 excites a solenoid of differential-locking valve 60 so that differential-locking valve 60 is located at position II to disengage differential-locking clutch 24 , thereby enabling right and left drive wheels 5 R and 5 L to rotate differentially.
- differential-locking valve 60 may be optionally held at position I by manual operation so as to engage differential-locking clutch 24 whether steering wheel 14 is located at straight traveling position S 14 or not, thereby enabling the vehicle to escape from the ditch.
- FIG. 7 illustrates that transmission housing 3 contains a modification of the transmission system of FIG. 5 .
- a reverser 50 is constituted among primary input shaft 11 and pump shafts 19 b .
- Each of bevel gears 51 and 52 is relatively rotatably provided on primary input shaft 11 and meshes with both HST input gears 19 c fixed on proximal ends of respective pump shafts 19 b .
- a hydraulically controlled reversal clutch 53 for selecting either normal or reversed rotation of pump shafts 19 b is disposed on primary input shaft 11 between bevel gears 51 and 52 .
- Clutch 53 is supplied with oil so as to fix either bevel gear 51 or 52 to primary input shaft 11 .
- brake 25 is provided on each motor shaft 20 b between fixed swash plate 20 a and gear 20 c .
- brakes 25 as shown in FIG. 5 may be employed.
- FIG. 8 illustrates that transmission housing 3 contains a further modification of the transmission system of FIG. 5 , comprising a pair of reversers 50 , each of which is interposed between motor shaft 20 b of each of HST 18 L and 18 R and each of drive axles 27 (drive wheels 5 L and 5 R).
- Primary input shaft 11 and input shafts 19 b interlock with one another through bevel gear 22 and HST input gears 19 c so that the rotational direction of pump shafts 19 b is fixed.
- Left and right counter shafts 26 are extended toward each other so as to be mutually connected or disconnected through differential-locking clutch 24 , which is not interposed between left and right motor shafts 20 b but interposed between left and right counter shafts 26 .
- An idler shaft 54 is interposed between each motor shaft 20 b and each counter shaft 26 .
- Idler shaft 54 always engages with motor shaft 20 b through gears 20 c and 54 a .
- Gears 26 d and 26 e are relatively rotatably provided on counter shaft 26 .
- Hydraulically controlled reversal clutch 53 is disposed on each of left and right counter shafts 26 between gears 26 d and 26 e so as to selectively engage either gear 26 d or 26 e with counter shaft 26 .
- Gear 26 d always meshes with gear 20 c fixed on motor shaft 20 b .
- Gear 26 e always meshes with another gear 54 b fixed on counter shaft 54 .
- Gears 20 c and 26 d constitute a normal gear train for rotating counter shaft 26 in one of opposite directions, i.e., a normal direction.
- Gears 20 c , 54 a , 54 b and 26 e constitute a reversing gear train for rotating counter shaft 26 in the other direction, i.e., a reversed direction.
- left and right clutches 53 opposed with respect to differential-locking clutch 24 are operated simultaneously so that, between both HSTs 18 L and 18 R and both drive axles 27 , both the normal gear trains are selected simultaneously, or alternatively, both the reversing gear trains are selected simultaneously.
- left and right drive wheels 5 L and 5 R are stopped even if left and right HSTs 18 L and 18 R actuate.
- brake 25 is disposed on each counter shaft 26 .
- hydraulic motor 20 with fixed swash plate 20 a is mounted to one surface of center section 21 which is opposite to another surface of center section 21 for mounting hydraulic pump 19 thereon.
- a space for arranging reverser 50 and the normal and reversing gear trains is ensured among motor shaft 20 b and counter shafts 26 and 54 .
- each reversal clutch 53 includes an oil chamber 53 a for normal rotation and an oil chamber 53 b for reversed rotation, as shown in FIG. 9 .
- oil chamber 53 a is supplied with pressure oil to fix one of bevel gears 51 and 52 to primary input shaft 11 so as to rotate pump shafts 19 b in the normal direction corresponding to forward traveling of the vehicle.
- Oil chamber 53 b is supplied with pressure oil to fix the other of bevel gears 51 and 52 to primary input shaft 11 so as to rotate pump shafts 19 b in the reversed direction corresponding to rearward traveling of the vehicle.
- oil chambers 53 a are supplied with pressure oil to engage bevel gears 26 e with respective counter shafts 26 so as to transmit output power of HSTs 18 L and 18 R to the normal gear trains.
- Oil chambers 53 b are supplied with pressure oil to engage bevel gears 26 d with respective counter shafts 26 so as to transmit output power of HSTs 18 L and 18 R to the reversing gear trains.
- Such arrangement of reverser 50 or reversers 50 on the upstream or downstream of twin transmissions for respective drive wheels represented by left and right HSTs 18 L and 18 R is applied for combination of the twin transmissions with a transmission, whose output rotation is nonreversible, such as a variable electric motor or a frictional mechanical continuous variable transmission (CVT) having a toroidal belt or another means.
- the vehicle may have means for unclutching the reverser or reversers 50 so as to stop right and left drive wheels 5 R and 5 L simultaneously at need.
- FIG. 9 Description will be given of a control system of HSTs 18 L and 18 R shown in FIG. 9 , which is adapted to the respective transmission systems shown in FIG. 7 and FIG. 8 .
- the system of FIG. 9 serves as a modification of the control system of HSTs 18 L and 18 R shown in FIG. 6 , description of parts and devices shown in FIG. 9 , which are identical with those in FIG. 6 and marked with the same reference numerals of those in FIG. 6 , will be omitted.
- a steering valve 41 , a reverser valve 55 and differential-locking valve 60 are supplied in parallel with oil from pump 42 .
- Steering wheel 14 is mechanically linked with steering valve 41 , through which ports 40 b and 40 c of cylinder 40 are fluidly connected to pump 42 and tank 43 . Therefore, the different point from the case with steering valve 41 of FIG. 6 is that the stroke of piston rod 40 a , i.e., the rotational direction of sleeve 39 around shaft 38 is constant in relation to the left or right rotational direction of steering wheel 14 from the straight traveling position S 14 whether the vehicle travels forward or rearward.
- steering valve 41 alters the leftward rotation of steering wheel 14 from straight traveling position S 14 into proportional extension of piston rod 40 a from the neutral stroke causing bars 39 a to rotate in ranges LT so as to push left lever 19 L rearward and pull right lever 19 R forward, and it alters the rightward rotation of steering wheel 14 from straight traveling position S 14 into proportional contraction of piston rod 40 a from the neutral stroke causing bars 39 a to rotate in ranges RT so as to pull left lever 19 L forward and push right lever 19 R rearward.
- both pedals 33 and 34 have respective upwardly projecting arms 33 a and 34 a , to which links 45 and 46 extended from shaft 38 are connected. Therefore, whichever pedal 33 or 34 is depressed, shaft 38 and sleeve 39 are tilted only forward in forward traveling range F from neutral position N to maximum forward traveling speed position Fm, that is, swash plates 19 a of both hydraulic pumps 19 are rotated in only their ranges which are essentially provided for forward traveling of the vehicle.
- the leftward rotation of steering wheel 14 from straight raveling position S 14 necessarily reduces the capacity of left hydraulic pump 19 so as to decelerate left drive wheel 5 L, and increases the capacity of right hydraulic pump 19 so as to accelerate right drive wheel 5 R, thereby causing a left turn of the vehicle.
- the rightward rotation of steering wheel 14 from straight traveling position S 14 necessarily increases the capacity of left hydraulic pump 19 so as to accelerate left drive wheel 5 L, and reduces the capacity of right hydraulic pump 19 so as to decelerate right drive wheel 5 R, thereby causing a right turn of the vehicle. Therefore, whether the vehicle travels forward or rearward does not depend upon positional control of swash plates 19 a of hydraulic pumps 19 but needs to depend upon other means for switching the rotational direction of drive wheels 5 L and 5 R between forward and rearward directions.
- reverser valve 55 is a three-positioned electromagnetic solenoid valve, which has opposite directive solenoids 55 a and 55 b and is switched among a neutral position N 55 and other two positions F 55 and R 55 , and interposed between pump 42 and oil chambers 53 a and 53 b of reversal clutch 53 .
- Controller 44 receives the depression signal from switch 35 R and excites solenoid 55 b so as to locate reverser valve 55 to position R 55 , thereby connecting chamber 53 b to pump 42 and connecting chamber 53 a to tank 43 , whereby bevel gear 52 is fixed to primary input shaft 11 so as to rotate pump shafts 19 b in the reversed direction. Therefore, hydraulic motors 20 are rotated in the opposite direction such as to drive the vehicle rearward.
- shaft 38 is tilted only forward in forward traveling range F whichever pedal 33 or 34 is depressed. That is, movable swash plate 19 a of each hydraulic pump 19 can be tilted to only one side for forward traveling from its neutral position so that each hydraulic motor 20 is essentially rotated in only one direction for forward traveling at variable speed.
- reverser 50 is changed so as to reverse the flow of fluid between pump 19 and motor 20 , thereby reversing the rotational direction of motor 20 for rearward traveling.
- controller 44 locates reverser valve 55 to shown neutral position N 55 so as to drain oil from both chambers 53 a and 53 b in reversal clutch 53 to tank 43 , whereby left and right HSTs 18 L and 18 R do not actuated and power transmission to left and right drive wheels 5 L and 5 R is perfectly shut down.
- switch 14 a When steering wheel 14 is rotated rightward or leftward from straight traveling position S 14 , switch 14 a sends controller 44 a signal meaning that steering wheel 14 is rotated apart from straight traveling position S 14 . Therefore, controller 44 switches differential valve 60 to position II so as to disengage differential-locking clutch 24 , similarly with that of FIG. 6 , so that right and left hydraulic motors 20 are allowed to rotate freely from each other.
- steering valve 41 is a spring-center hydraulic change-over valve mechanically linked with steering wheel 14 . Then, according to rotation of steering wheel 14 from straight traveling position S 14 , steering valve 41 is changed from a neutral position N 41 to either an extension position E 41 or a contraction position C 41 so as to telescope piston rod 40 a .
- steering valve 41 returns to neutral position N 41 by springs. Therefore, speed control levers 17 R and 17 L are rotated in mutually opposite directions so as to differentially rotate right and left drive wheels 5 R and 5 L.
- steering wheel 14 is rotated leftward in left turning range LT 14 from straight traveling position S 14 .
- steering valve 41 connects port 40 b to pump 42 , and connects port 40 c to tank 43 so as to rotate sleeve 39 clockwise around shaft 38 and rotate bars 39 a in ranges LT, whereby left link 16 L pushes left speed control lever 17 L, and right link 16 R pulls right speed control lever 17 R.
- forward traveling shift pedal 33 is depressed so as to fix bevel gear 51 to primary input shaft 11
- pulled right lever 17 R causes right HST 18 R to accelerate forwardly rotating right drive wheel SR
- pushed left lever 17 L causes left HST 18 L to decelerate forwardly rotating left drive wheel 5 L.
- steering valve 41 contracts piston rod 40 a from the neutral stroke so as to pull left lever 17 L forward and push right lever 17 R rearward.
- controller 44 excites solenoid 55 b of reverser valve 55 based on the depression of switch 35 R so as to locate reverser valve 55 at position R 55 for setting each of reversal clutches 53 into a state where chamber 53 a is connected to tank 43 and chamber 53 b is connected to pump 42 , thereby fixing gears 26 e to respective counter shafts 26 , i.e., selecting the reversing gear trains for rotating counter shafts 26 in the same rotational direction with respective motor shafts 20 b.
- controller 44 sets reverser valve 55 at neutral position N 55 so as to drain oil from both chambers 53 a and 53 b of reversal clutch 53 to tank 43 . Therefore, both right and left drive wheels 5 R and 5 L are perfectly isolated from power transmission even if neutral location of at least one HST 18 R or 18 L is inaccurately adjusted and a slight output arises from the HST 18 R or 18 L.
- steering wheel 14 is rotated leftward in left turning range LT 14 from straight traveling position S 14 .
- steering valve 41 connects port 40 b to pump 42 , and connects port 40 c to tank 43 , thereby extending piston rod 40 a from the neutral stroke, whereby left link 16 L pushes left lever 17 L rearward and right link 16 R pulls right lever 17 R forward.
- pedal 33 is depressed, switch 35 F is switched on so as to fix gears 26 d to respective counter shafts 26 , pulled right lever 17 R makes right HST 18 R accelerate forwardly rotating right drive wheel 5 R, and pushed left lever 17 L makes left HST 18 L decelerate forwardly rotating left drive wheel 5 L.
- switch 35 R When pedal 34 is depressed, switch 35 R is switched on so as to fix gears 26 e to respective counter shafts 26 , pulled right lever 17 R makes right HST 18 R accelerate rearwardly rotating right drive wheel 5 R, and pushed left lever 17 L makes left HST 18 L decelerate rearwardly rotating left drive wheel 5 L.
- steering wheel 14 when steering wheel 14 is turned left from straight traveling position S 14 , right drive wheel 5 R is accelerated and left drive wheel 5 L is decelerated, or if left drive wheel 5 L is rotated opposite to right drive wheel 5 R, left drive wheel 5 L is accelerated, so that the vehicle turns left whether it travels forward or rearward.
- steering wheel 14 is turned rightward in right turning range RT 14 from straight traveling position S 14 .
- steering valve 41 contracts piston rod 40 a from the neutral stroke so as to pull left lever 17 L forward and push right lever 17 R rearward.
- An operation system shown in FIG. 10 is adapted for a vehicle transmission system having any of reversers 50 shown in FIGS. 7 and 8 , which is not operated based on turning of a switch provided on a traveling shift pedal as shown in FIG. 9 , but is manually operable with a mechanical link.
- a reverser valve 55 is mechanically linked with a reverser lever (not shown) provided in a driver's portion of a vehicle. Accordingly, only a single pedal 33 serves as an operation device for changing traveling speed of the vehicle.
- a pressure-sensing switch 35 is provided on a depressed surface of pedal 33 .
- a clutch valve 61 which is electro-magnetically controlled by controller 44 based on ON/OFF signal from switch 35 , is interposed among reverser valve 55 , pump 42 and tank 43 .
- clutch valve 61 When pedal 33 is not depressed and switch 35 is turned off, clutch valve 61 is located at a shown position 161 so that any reversal clutch 53 having oil chambers 53 a and 53 b , from which oil is drained to tank 43 , is unclutched wherever reverser valve 55 is located. If pedal 33 is depressed, reverser valve 61 is shifted to a position II 61 so as to be applied for supplying oil to either oil chamber 53 a or 53 b in any reversal clutch 53 through reverser valve 55 .
- reverser valve 55 is set to either forward traveling position F 55 or rearward traveling position R 55 .
- the forward tilt angle of sleeve 39 is changed according to depression of pedal 33 so as to equally change the capacities of both left and right hydraulic pumps 19 , thereby changing the traveling speed of a vehicle.
- hydraulic cylinder 40 telescopes piston rod 40 a so as to rotate sleeve 39 around shaft 38 . Therefore, the capacity of hydraulic pump 19 on one side of the vehicle corresponding to the rotational direction of steering wheel 14 is reduced so as to reduce the output power of hydraulic motor 20 fluidly connected thereto, thereby decelerating corresponding drive wheel 5 L or 5 R. Simultaneously, the capacity of hydraulic pump 19 on the other side of the vehicle opposite to the rotational direction of steering wheel 14 is relatively increased so as to increase the output power of hydraulic motor 20 fluidly connected thereto, thereby accelerating corresponding drive wheel 5 R or 5 L.
- Reverser (or reversers) 50 maintains the relation of deceleration and acceleration of drive wheels 5 L and 5 R to rotational direction of steering wheel 14 so as to coincide turning direction of the vehicle to the rotational direction of steering wheel 14 whether the vehicle travels forward or rearward.
- reverser 50 is interposed between primary input shaft 11 and pump shafts 19 b , similarly with FIG. 7 .
- reverser 50 shown in FIG. 11 is provided with a mechanical reversal dog clutch 53 ′ instead of hydraulic reversal clutch 53 .
- Clutch 53 ′ is provided with a clutch slider 53 ′ a , which is not relatively rotatably but axially slidably disposed on primary input shaft 11 so as to selectively engage with one of opposite bevel gears 51 and 52 freely rotatably provided on primary input shaft 11 .
- Clutch slider 53 ′ a is mechanically linked with a reverser lever (with reference to a reverser lever 72 shown in FIG. 12 ) provided in a driver's portion of a vehicle.
- clutch slider 53 ′ a of reversal clutch 53 ′ slides on primary input shaft 11 and engages with one of bevel gears 51 and 52 so as to rotate pump shafts 19 b in either one direction for forward traveling or the other direction for rearward traveling.
- clutch slider 53 ′ a may be disengaged from both bevel gears 51 and 52 so that reversal clutch 53 ′ may be unclutched to isolate both pump shafts 19 b from rotational force of primary input shaft 11 .
- a main clutch 71 which may be integrally provided on output pulley 9 as shown in FIG. 11 , is temporarily disengaged to isolate primary input shaft 11 from power of engine 2 before switching reversal clutch 53 ′.
- Main clutch 71 may be electro-magnetically controlled so as to be automatically switched depending upon whether later-discussed traveling shift pedal 33 is depressed or not, for example.
- reversers 50 are provided on respective counter shafts 26 on the downstream of respective hydraulic motors 20 , similarly with FIG. 8 .
- reversers 50 shown in FIG. 12 are provided with respective mechanical reversal dog clutches 53 ′ instead of hydraulic reversal clutches 53 .
- Each reversal clutch 53 ′ is provided with a clutch slider 53 ′ a , which is not relatively rotatably but axially slidably disposed on counter shaft 26 so as to selectively engage with one of opposite gears 26 d and 26 e freely rotatably provided on counter shaft 26 .
- Both clutch sliders 53 ′ a are engaged to a common fork shaft 53 ′ b through respective forks 53 ′ c .
- Fork shaft 53 ′ b is mechanically linked with a reverser lever 72 provided in a driver's portion of a vehicle.
- both clutch sliders 53 ′ a of reversal clutches 53 ′ slide on respective counter shafts 26 and engage with either gears 26 d or 26 e so as to rotate counter shafts 26 in either one direction for forward traveling or the other direction for rearward traveling.
- each clutch slider 53 ′ a may be disengaged from both gears 26 d and 26 e so that both reversal clutches 53 ′ may be unclutched to isolate counter shafts 26 from rotational force of motor shafts 20 b.
- Main clutch 71 which may be integrally provided on output pulley 9 as shown in FIG. 12 , is temporarily disengaged to isolate primary input shaft 11 from power of engine 2 before switching reversal clutches 53 ′.
- Main clutch 71 may be electro-magnetically controlled so as to be automatically switched depending upon whether later-discussed traveling shift pedal 33 is depressed or not, for example.
- FIG. 13 illustrates a structure with electric and hydraulic circuits for controlling tilt angles of swash plates 19 a of left and right hydraulic pumps 19 , which is adapted for each of the transmission systems of FIGS. 11 and 12 , and functions similarly with the structure of FIG. 10 .
- controller 44 electro-magnetically controls main clutch 71 to engage.
- Either forward or rearward traveling direction of the vehicle is determined by setting mechanical reverser 50 . While the vehicle travels in the set forward or rearward direction, the forward tilt angle of sleeve 39 with shaft 38 is changed according to depression of pedal 33 so as to change the capacities of left and right hydraulic pumps 19 , thereby changing traveling speed of the vehicle.
- piston rod 40 a of hydraulic cylinder 40 is telescoped so as to rotate sleeve 39 around shaft 38 , whereby the capacity of hydraulic pump 19 on one side of the vehicle corresponding to the rotational direction of steering wheel 14 is reduced so as to decelerate corresponding drive wheel 5 L or 5 R, and the capacity of hydraulic pump 19 on the other side of the vehicle opposite to the rotational direction of steering wheel 14 is increased so as to accelerate corresponding drive wheel 5 R or 5 L.
- Reverser (or reversers) 50 maintains the relation of deceleration and acceleration of drive wheels 5 L and 5 R to rotational direction of steering wheel 14 so as to coincide turning direction of the vehicle to the rotational direction of steering wheel 14 whether the vehicle travels forward or rearward.
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Abstract
A vehicle comprises a vehicle frame, a prime mover mounted on the vehicle frame, a laterally turnable wheel disposed at one side of the vehicle frame, a pair of drive wheels disposed at the other side of the vehicle frame, a steering operation device, a traveling operation device for setting the traveling speed and direction of the vehicle, and a pair of transmissions for controlling the rotary speed and direction of the respective drive wheels. The transmissions are operationally connected with the steering operation device so as to create a difference of rotary speed between the drive wheels according to operation of the steering operation device. The transmissions are operationally connected with the traveling operation device so as to drive the drive wheels in a common rotary direction from their stationary state according to operation of the traveling operation device. A clutch is interposed between the transmissions so as to connect the drive wheels with each other when the steering operation device is set in a straight traveling position. Based on setting of a switching device for switching the traveling direction of the vehicle between forward and rearward, a reverser decides the rotational direction of the drive wheels.
Description
- The present application is continuation of U.S. application Ser. No. 11/327,415, filed Jan. 9, 2006, which is a divisional of U.S. application Ser. No. 10/455,306, filed Jun. 6, 2003, now U.S. Pat. No. 7,004,268, the entire disclosures of which are incorporated in their entirety herein by reference thereto.
- 1. Field of the Invention
- The present invention relates to a vehicle equipped with a pair of transmissions, e.g., a pair of hydrostatic transmissions (HSTs), a pair of belt type continuous variable transmissions (CVTs), or a pair of electric motors, for driving respective left and right drive wheels, wherein the pair of transmissions, which surely drive the vehicle straight when they are set so, are operated for left and right turning of the vehicle so that one of the left and right drive wheels is accelerated and the other is decelerated, and wherein each of the left and right turning directions of the vehicle always coincides with the manipulated leftward or rightward direction of a steering operation device whether the vehicle travels forward or rearward.
- 2. Related Art
- There is a well-known vehicle having twin parallel transmissions, such as HSTs, for driving respective left and right drive wheels. For left and right turning of the vehicle, one of the transmissions accelerates the corresponding drive wheel (on an outside of turning), and the other decelerates the other drive wheel (on an inside of turning). For example, if a steering wheel serving as a steering operation device of the vehicle is turned left, one transmission decelerates the left drive wheel, and the other accelerates the right drive wheel, whereby the vehicle turns left.
- Incidentally, if the deceleration force applied on the inside drive wheel becomes relatively larger than the traveling force thereof, the rotational direction of the inside drive wheel is reversed. Then, the deceleration force becomes an acceleration force for the rotationally reversed inside drive wheel.
- Also, unless the steering wheel is operated for turning, the traveling speed and direction of the vehicle can be changed by operation of a speed change operation device such as a pedal or a lever so that both the transmissions drive both the drive wheels at equal rotary speed. If the steering wheel is turned for turning, the rotary speed of one drive wheel becomes higher than the equal rotary speed, and that of the other drive wheel becomes lower than the equal rotary speed.
- However, the vehicle having the twin transmissions still has such a problem as follows: When it is assumed that the left drive wheel is decelerated and the right wheel accelerated by turning the steering wheel leftward during the forward traveling of the vehicle, the steering wheel must be turned rightward for left turning during the rearward traveling of the vehicle because the acceleration force for a forwardly rotating wheel serves as a deceleration force for a rearwardly rotating wheel. Such an operation of the steering wheel is so illusional as to cause the vehicle to turn to a wrong side.
- As means for coincidence of turning side of a vehicle with a steering direction whether the vehicle travels forward or rearward, Japanese Laid Open Gazette No. 2000-25,637 discloses mechanical means interposed among a transmission, a steering operation device and a speed changing operation device, and Japanese Patent No. 3,176,237 discloses a hydraulic switching valve provided in an HST for steering. However, while each of the two Japanese documents discloses a pair of HSTs for driving two rotors, one of the HSTs is provided for traveling so as to rotate both the rotors at various equal speeds, and the other HST is provided for steering so as to accelerate one rotor and decelerate the other rotor. Therefore, each of the above-mentioned disclosed means does not correspond to the vehicle driving system comprising a pair of transmissions for driving respective right and left drive wheels. Furthermore, while the rotors disclosed in Japanese Laid Open Gazette No. 2000-25,637 are drive wheels, those disclosed in Japanese Patent No. 3,176,237 are sprockets.
- For another problem of the vehicle comprising the twin transmissions for driving respective drive wheels, even if the vehicle is provided with a driving direction changing system which ensures that one drive wheel on inside of the turning vehicle is decelerated and the other on outside thereof is accelerated in correspondence to the turning side of the steering operation device such as a steering wheel whether the vehicle travels forward and rearward, the performances of the parallel transmissions must be strictly equal to each other so as to ensure a straight traveling when the steering wheel is set in the straight traveling position. If there is a slight performance difference between the transmissions, the drive wheels rotate at different speeds so as to turn the vehicle while the steering wheel is in the straight traveling position, or a complicated and troublesome adjustment of a linkage from the steering wheel to the transmissions must be performed. Moreover, the differential driving of left and right drive wheels is not requested in such a case where the vehicle travels on a rough road or one of the drive wheels slumps into mud.
- For solving this kind of problem, U.S. Pat. No. 5,590,737 discloses a crawler vehicle equipped with a driving system comprising a pair of HSTs for driving respective right and left sprockets, wherein a differential-locking clutch is provided so as to lock the sprockets with each other at need.
- However, this U.S. Patent does not disclose a pair of transmissions for driving respective right and left drive wheels.
- An object of the present invention is to provide a vehicle including a prime mover, left and right drive wheels, and twin parallel transmissions for driving the respective drive wheels, wherein the vehicle is made user-friendly by such a driving direction changing system as to ensure that each of left and right turning directions of the vehicle corresponding to the manipulated direction of the steering operation device is constant whether the vehicle travels forward or rearward.
- To achieve the object, the vehicle according to the present invention comprises a traveling operation device for setting a traveling speed of the vehicle and selecting a traveling direction of the vehicle between forward and rearward, which is operationally connected with the pair of transmissions so as to drive the drive wheels at a common speed and in a common direction, and a steering operation device for turning the vehicle leftward or rightward, wherein the steering operation device is operationally connected with the pair of transmissions so as to accelerate one of drive wheels at outside of the turning vehicle and to decelerate the other drive wheel at inside of the turning vehicle. The vehicle further comprises switching means for switching the traveling direction of the vehicle between forward and rearward selected by the traveling operation device, and reversing means provided to the pair of transmissions so as to reverse driving directions of the respective drive wheels in correspondence to the switching operation of the switching means.
- As an aspect for arrangement of the reversing means, in case that the vehicle includes a common input shaft shared between the transmissions to receive power of the prime mover, the reversing means is preferably interposed among the common input shaft and the pair of input shafts of the respective transmissions.
- As another aspect for arrangement of the reversing means, the reversing means may be interposed between each of output shafts of the respective transmissions and each of the drive wheels.
- Assuming that a vehicle includes (1) a prime mover, left and right drive wheels, and twin parallel transmissions for driving the respective drive wheels, (2) a traveling operation device for setting a traveling speed of the vehicle and selecting a traveling direction of the vehicle between forward and rearward, which is operationally connected with the pair of transmissions so as to drive the drive wheels at a common speed and in a common direction, and, (3) a steering operation device for turning the vehicle leftward or rightward, which is operationally connected with the pair of transmissions so as to accelerate one of the drive wheels at outside of the turning vehicle and to decelerate the other drive wheel at inside of the turning vehicle whether the vehicle travels forward or rearward, a second object of the present invention is to ensure both the drive wheels rotate at the same speed for exact straight traveling of the vehicle when the steering operation device is set so the vehicle travels in a straight direction, in spite of some performance differences between the transmissions.
- To achieve the second object, the vehicle according to the present invention comprises a differential locking clutch for the drive wheels. The differential locking clutch is engaged to lock the drive wheels with each other when the steering operation device is set to make the vehicle travel straight, and wherein the differential locking clutch is disengaged to unlock the drive wheels from each other when the steering operation device is set to make the vehicle travel leftward or rightward.
- These, further and other objects, features and advantages will appear more fully from the following description taken in connection with the accompanying drawing.
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FIG. 1 is a schematic plan view of a six-wheel vehicle according to the present invention, including a steering wheel, two front casters, two middle drive wheels, and two rear drive wheels, wherein the middle and rear drive wheels are not steerable. -
FIG. 2 is a schematic plan view of another six-wheel vehicle according to the present invention, including a steering wheel, two steerable front driven wheels, two middle drive wheels, and two rear drive wheels, wherein the middle and rear drive wheels are not steerable. -
FIG. 3 is a schematic plan view of a four-wheel vehicle according to the present invention, including a steering wheel, two front drive wheels, and two rear drive wheels, wherein the four drive wheels are not steerable. -
FIG. 4 is a schematic plan view of another four-wheel vehicle according to the present invention, including a steering wheel, two front drive wheels which are not steerable, and two steerable rear drive wheels. -
FIG. 5 is a diagram of a wheel driving system for a vehicle according to the present invention, including twin transmissions for driving respective left and right drive wheels independently, wherein a differential-locking clutch is provided so as to connect the left and right drive wheels to each other when a steering wheel is set in a straight traveling position. -
FIG. 6 illustrates a perspective view of a mechanical linkage for controlling left and right speed control levers of the respective twin transmissions, together with a diagram of hydraulic and electric circuit for controlling the speed control levers and the differential locking clutch, wherein the linkage and the hydraulic and electric circuit are provided for the wheel driving system shown inFIG. 5 . -
FIG. 7 is a diagram of another wheel driving system for a vehicle according to the present invention, including twin transmissions for driving respective left and right drive wheels independently, wherein a differential-locking clutch is provided so as to connect left and right drive wheels to each other when a steering wheel is set in a straight traveling position, and a reversing mechanism (a reverser) is provided among a primary input shaft and respective input shafts of the twin transmissions. -
FIG. 8 is a diagram of another wheel driving system for a vehicle according to the present invention, including twin transmissions for driving respective left and right drive wheels independently, wherein a differential-locking clutch is provided so as to connect left and right drive wheels to each other when a steering wheel is set in a straight traveling position, and a reverser is interposed between an output shaft of each transmission and each drive wheel. -
FIG. 9 is a perspective view of a mechanical linkage for controlling left and right speed control levers of the respective twin transmissions, together with a diagram of hydraulic and electric circuit for controlling the speed control levers, the differential locking clutch and the reverser, wherein the linkage and the hydraulic and electric circuit are provided for any of the wheel driving systems shown inFIGS. 7 and 8 . -
FIG. 10 is a perspective view of the mechanical linkage ofFIG. 9 , having an alternative reverser control system. -
FIG. 11 is a diagram of the wheel driving system ofFIG. 7 , having an alternative reverser clutch formation. -
FIG. 12 is a diagram of the wheel driving system ofFIG. 8 , having an alternative reverser clutch formation. -
FIG. 13 is a perspective view of a mechanical linkage for controlling left and right speed control levers of the respective twin transmissions, together with a diagram of hydraulic and electric circuit for controlling the speed control levers and the differential locking clutch, wherein the linkage and the hydraulic and electric circuit are provided for any of the wheel driving systems shown inFIGS. 11 and 12 . - Referring to
FIG. 1 , a six-wheel vehicle has avehicle frame 1, on which avertical crankshaft engine 2, atransmission housing 3 and left andright axle casings right drive wheels transmission housing 3, respectively. Left andright drive wheels respective drive wheels vehicle frame 1 so as to serve as laterally turnable driven wheels, which are free from driving power ofengine 2 and turn to a lateral side coinciding with a turning side of asteering wheel 14 serving as a steering operation device. Thus, in this vehicle, casters 7 serve as front wheels,drive wheels wheels drive wheels - A
belt 8 is interposed between anengine output pulley 9 ofvertical crankshaft engine 2 and aprimary input pulley 10 fixed on aprimary input shaft 11 projecting fromtransmission housing 3 so as to transmit power fromengine 2 to a transmission system intransmission housing 3. Additionally,belt 8 is looped over atension pulley 12 to be tensioned. - The transmission system in
transmission housing 3 comprises left and right power take-off portions which transmit power to left andright axle casings respective propeller shafts 13, thereby drivingdrive wheels - Left and right speed control levers 17L and 17R are pivoted on
transmission housing 3.Steering wheel 14 is operationally connected to speedcontrol levers power steering system 15 andrespective links - Referring to
FIG. 2 , left and right steerable drivenwheels 60, serving as the laterally turnable wheels as mentioned above, mechanically interlock withsteering wheel 14. A pivot (a king pin) of each drivenwheel 60 is connected to apivot 61 c of each of two small sector gears 61. Eachsmall sector gear 61 has afront edge 61 a and a shorter rear edge 61 b.Pivot 61 c is disposed extremely adjacent to an end ofgear 61 where bothedges 61 a and 61 b are gathered. On the other hand, an axle housing for supporting both drivenwheels 60 is provided at each of left and right ends thereof with each of two large sector gears 62 supported rotatably around respective vertical pivots. Eachlarge sector gear 62 has afront edge 62 a and a longerrear edge 62 b. An end ofgear 62 where bothedges tie rod 63 interlocking withsteering wheel 14. - Large sector gears 62 serving as drive gears mesh with respective small sector gears 61 serving as follower gears. A distance of a serrated periphery of each
gear 61 frompivot 61 c (hereinafter, the distance is referred to as a “radius”) gradually decreases while it passes fromfront edge 61 a to rear edge 61 b. As compensating for the decrease of the radius ofgear 61, a distance of a serrated periphery of eachgear 62 from the end ofgear 62 pivotally connected totie rod 63, i.e., a radius ofgear 62 gradually increases while it passes fromfront edge 62 a torear edge 62 b. - As each driven
wheel 60 laterally turns so as to turn its front end to the proximal side of the vehicle, meshing gears 61 and 62 are rotated so that front edges 61 a and 62 a approach each other, whereby a gear ratio ofsmall sector gear 61 tolarge sector gear 62 increases. On the contrary, as the rear end of drivenwheel 60 turns proximally, rear edges 61 b and 62 b approach each other so as to decrease the gear ratio ofgear 61 to gear 62. Consequently, during the turning of the vehicle, drivenwheel 60 on lateral inside of the turning vehicle is turned at a larger angle than drivenwheel 60 on lateral outside of the turning vehicle. Thus, similarly to a vehicle having a caster, the vehicle can turn on a small circle swiftly even if the angle ofsteering wheel 14 is not very large. Moreover, the vehicle is more advantageous than a vehicle having a caster in that a driver can comprehend the direction of drivenwheels 60 and stably operate the vehicle on a slope becausesteering wheel 14 is always connected to drivenwheels 60. - Referring to
FIG. 3 , a skid steering type four-wheel vehicle has left and rightfront drive wheels rear drive wheels Steering wheel 14 serving as a steering operation device is manipulated so as to locate left and rightspeed control levers left drive wheels speed control lever 17L coincides with that ofright drive wheels speed control lever 17R. - Referring to
FIG. 4 , a four-wheel vehicle has left and rightfront drive wheels rear drive wheels Steering wheel 14 is operationally connected to drivewheels FIG. 2 . - Referring to
FIG. 5 , intransmission housing 3, left andright HSTs HSTs hydraulic pump 19 including amovable swash plate 19 a, and ahydraulic motor 20 including a fixedswash plate 20 a.Hydraulic pump 19 andhydraulic motor 20 are fluidly connected with each other through acenter section 21.Speed control levers movable swash plates 19 a (SeeFIG. 4 ). -
Pump shafts 19 b of bothhydraulic pumps 19 are extended toward each other. Bevel gears serving as HST input gears 19 c are fixed onto ends ofpump shafts 19 b facing each other, respectively. An upper wall oftransmission housing 3 rotatably supportsprimary input shaft 11 vertically. Above-mentionedprimary input pulley 10 is fixed onto the outer end ofprimary input shaft 11. Abevel gear 22 is fixed onto the other inner end ofprimary input shaft 11 and meshes with both HST input gears 19 c. Incidentally,primary input shaft 11 penetratescharge pump 23 so as to serve as a drive shaft ofcharge pump 23. - Alternatively, if an engine has a horizontal crankshaft,
primary input shaft 11 is supported horizontally bytransmission housing 3. An outer end of horizontalprimary input shaft 11 penetratingcharge pump 23 may be extended outward fromtransmission housing 3 so as to serve as a PTO shaft for driving a working machine attached to the vehicle. -
Motor shafts 20 b of bothHSTs clutch 24. Oppositely to differential lockingclutch 24, eachmotor shaft 20 b projects fromcenter section 21 so as to be provided thereon with abrake 25.Differential locking clutch 24 is a spring-loaded hydraulic clutch, which is engaged by spring force and disengaged by hydraulic pressure overcoming the spring force. The hydraulic pressure for disengaging differential lockingclutch 24 is applied by fluid supplied by a later-discussed electric and hydraulic circuit. - Each of
drive wheels right drive axles 27 rotatably supported bytransmission housing 3.Motor shafts 20 b engage withrespective counter shafts 26 through deceleration gears 20 c and 26 a.Counter shafts 26 engage withrespective drive axles 27 through deceleration gears 26 b and 27 a. Left andright drive axles 27 project laterally outward fromtransmission housing 3 oppositely to each other and are provided on their outer ends withrespective drive wheels - Each
counter shaft 26 is extended outward intransmission housing 3 so as to be fixedly provided on its distal end with abevel gear 26 c, which meshes with abevel gear 29 a fixed on an inner end of each of left andright PTO shafts 29. EachPTO shaft 29 projects rearward fromtransmission housing 3 so as to be joined to propellingshaft 13 through a universal joint. - In each of
axle casings horizontal input shaft 31 and ahorizontal drive axle 32 are rotatably supported mutually perpendicularly and engage with each other throughbevel gears respective shafts Input shaft 31 projects outward from each ofaxle casings shaft 13 through a universal joint. Driveaxles 32 project laterally outward fromrespective axle casings respective drive wheels - Each
PTO shaft 29 is intermediately provided with a clutch 30.Clutches 30 are engaged or disengaged so as to put the vehicle into either a four-wheel drive (4WD) mode or a two-wheel drive (2WD) mode. - Referring to
FIG. 6 , a structure of power steering system 15 (seeFIG. 1 ) for controllingspeed control levers shift pedal 33 and a rearward traveling shift pedal 34 (together, the traveling operation device) are juxtaposed above a footboard on the vehicle. A pressure-sensing switch 35F is disposed on forward travelingshift pedal 33 so as to be switched on by a driver's foot when pedal 33 is depressed. A pressure-sensing switch 35R is disposed on rearward travelingshift pedal 34 so as to be switched on by a driver's foot when pedal 34 is depressed. - A
support shaft 36 is disposed horizontally and fixed to a vehicle body such asvehicle frame 1. Asleeve 37 is relatively rotatably disposed aroundsupport shaft 36. Ashaft 38 is fixedly extended upward fromsleeve 37 radially aboutshaft 36. Asleeve 39 is relatively rotatably provided aroundshaft 38. A top ofshaft 38 projects upward fromsleeve 39. - An
arm 33 a fixedly projects upward from a boss of forward travelingshift pedal 33 serving as a pivot ofpedal 33. Alink 45 is connected at one end thereof toarm 33a so as to be pulled by depression ofpedal 33. Anarm 34 a fixedly projects downward from a boss of rearward travelingshift pedal 34 serving as a pivot ofpedal 34. Alink 46 is connected at one end thereof to arm 34 a so as to be pushed by depression ofpedal 34.Links shaft 38. - When neither pedal 33 nor 34 is depressed,
sleeve 37 is biased by neutral-returning springs (not shown) interposed inrespective links shaft 38 at a neutral position N. By depressingpedal 33, link 45 pulls the top ofshaft 38 so astilt shaft 38 forward from neutral position N to a maximum forward traveling speed position Fm in forward traveling range F in correspondence to the depth ofdepressed pedal 33. By depressingpedal 34, link 46 pushes the top ofshaft 38 so as to tiltshaft 38 rearward from neutral position N to a maximum rearward traveling speed position Rm in rearward traveling range R in correspondence to the depth ofdepressed pedal 34. Thus, by depressing either pedal 33 or 34,shaft 38 is rotated forward or rearward together withsleeve 37 aroundshaft 36. - A pair of opposite traverse bars 39 a are fixedly extended from
sleeve 39 radially aboutshaft 38.Bars 39 a are connected at utmost ends thereof torespective links speed control levers sleeve 39 together withshaft 38 forward or rearward and move the utmost ends of traverse bars 39 a withlinks speed control levers - By depressing forward traveling
shift pedal 33, bothlevers links movable swash plates 19 a ofHSTs drive wheels shift pedal 34, bothlevers links movable swash plates 19 a ofHSTs drive wheels - A double-acting
hydraulic cylinder 40 is disposed horizontally in parallel toshaft 36, and its cylinder casing is fixed tosleeve 37. Apiston rod 40 a ofcylinder 40 is connected tosleeve 39 through anarm 39 b extended radially (perpendicularly tobars 39 a) fromsleeve 39.Sleeve 39 is rotated in relative toshaft 38 by telescopic motion ofpiston rod 40 a. Consequently, onebar 39 a pulls corresponding one oflevers other bar 39 a pushes theother lever drive wheels drive wheel wheels - Hereinafter, the movement of
piston rod 40 a pushingarm 39 b is defined as extension movement increasing the stroke thereof, and the movement ofpiston rod 40 a pullingarm 39 b as contraction movement decreasing the stroke thereof. - By a later-discussed
steering valve 41, the stroke ofpiston rod 40 a is controlled to correspond to a set rotational position ofsteering wheel 14. However, the corresponding position ofsteering wheel 14 differs due to whether the vehicle travels forward or rearward, i.e., whetherpedal - When steering
wheel 14 is set at a straighttraveling position S 14 , thestroke piston rod 40 a becomes a neutral stroke. At this time, bars 39 a are oriented in a direction S for straight traveling of the vehicle relative toshaft 38 at any place. - When
piston rod 40 a is extended from the neutral stroke to increase the stroke thereof,sleeve 39 is rotated so thatbars 39 a are rotated in shown ranges LT to respective maximum rotational positions. LTm symmetrically with respect toshaft 38. That is,left bar 39 a rotates rearward from direction S so as to push leftspeed control lever 17L rearward, andright bar 39 a rotates forward from direction S so as to pull rightspeed control lever 17R forward. - If
shaft 38 is disposed in forward traveling range F where bothswash plates 19 a of left and righthydraulic pumps 19 are tilted in their ranges for forward traveling, rearwardly pushedleft lever 17L reduces the tilt angle ofswash plate 19 a linked therewith so as to reduce the capacity of lefthydraulic pump 19, thereby deceleratingleft drive wheel 5L. Simultaneously, forwardly pulledright lever 17R increases the tilt angle ofswash plate 19 a linked therewith so as to increase the capacity of righthydraulic pump 19, thereby acceleratingright drive wheel 5R. Therefore, the vehicle turns left. - If
shaft 38 is disposed in rearward traveling range R where bothswash plates 19 a of left and righthydraulic pumps 19 are tilted in their ranges for rearward traveling, rearwardly pushedleft lever 17L increases the tilt angle ofswash plate 19 a linked therewith so as to increase the capacity of lefthydraulic pump 19, thereby acceleratingleft drive wheel 5L. Simultaneously, forwardly pulledright lever 17R reduces the tilt angle ofswash plate 19 a linked therewith so as to reduce the capacity of righthydraulic pump 19, thereby deceleratingright drive wheel 5R. Therefore, the vehicle turns right. - When
piston rod 40 a is contracted from the neutral stroke to decrease the stroke thereof,sleeve 39 is rotated so thatbars 39 a are rotated in shown ranges RT to respective maximum rotational positions RTm symmetrically with respect toshaft 38. That is,left bar 39 a rotates forward from direction S so as to pull leftspeed control lever 17L forward, andright bar 39 a rotates rearward from direction S so as to push rightspeed control lever 17R rearward. - If
shaft 38 is disposed in forward traveling range F where bothswash plates 19 a of left and righthydraulic pumps 19 are tilted in their ranges for forward traveling, forwardly pulledleft lever 17L increases the tilt angle ofswash plate 19 a linked therewith so as to increase the capacity of lefthydraulic pump 19, thereby acceleratingleft drive wheel 5L. Simultaneously, rearwardly pushedright lever 17R reduces the tilt angle ofswash plate 19 a linked therewith so as to reduce the capacity of righthydraulic pump 19, thereby deceleratingright drive wheel 5R. Therefore, the vehicle turns right. - If
shaft 38 is disposed in rearward traveling range R where bothswash plates 19 a of left and righthydraulic pumps 19 are tilted in their ranges for rearward traveling, forwardly pulledleft lever 17L reduces the tilt angle ofswash plate 19 a linked therewith so as to reduce the capacity of lefthydraulic pump 19, thereby deceleratingleft drive wheel 5L. Simultaneously, rearwardly pushedright lever 17R increases the tilt angle ofswash plate 19 a linked therewith so as to increase the capacity of righthydraulic pump 19, thereby acceleratingright drive wheel 5R. Therefore, the vehicle turns left. - A steering
valve 41 connects each ofports cylinder 40 to either pump 42 ortank 43. Steeringvalve 41 is an electro-magnetically controlled hydraulic (servo) valve having oppositely active solenoids 41 a and 41 b, which is switched among three positions, i.e., aneutral position N 41 , anextension position E 41 and acontraction position C 41 . In this regard, if a detected value about an actual position (stroke) ofpiston rod 40 a is different from a value corresponding to its requested position, steeringvalve 41 is set to eitherextension position E 41 orcontraction position C 41 , and if it becomes no further different, steeringvalve 41 is returned toneutral position N 41 by springs. - By exciting solenoid 41 a, steering
valve 41 is located atextension position E 41 , whereport 40 b is connected to pump 42, andport 40 c totank 43, thereby extendingpiston rod 40 a. By exciting solenoid 41 b, steeringvalve 41 is located atcontraction position C 41 , whereport 40 c is connected to pump 42, andport 40 b totank 43, thereby contractingpiston rod 40 a. When neither solenoid 41 a nor 41 b is excited, steeringvalve 41 is set atneutral position N 41 so as to block bothports piston rod 40 a. -
Steering wheel 14 is manually turned from a straight traveling position S14 either rightward in a right turning range RT14 or leftward in a left turning range LT14. Aswitch 14 a inputs a detected positional signal ofsteering wheel 14 tocontroller 44. An actual stroke ofpiston rod 40 a or another actual value corresponding to an actual stroke ofpiston rod 40 a, e.g., an actual rotational angle ofsleeve 39, is detected. Based on a difference of actual stroke ofpiston rod 40 a from a stroke ofpiston rod 40 a corresponding to the detected rotational position ofsteering wheel 14,controller 44 outputs an exciting signal to one of solenoids 41 a and 41 b of steeringvalve 41 and stops the output so as to switch steeringvalve 41 betweenneutral position N 41 and eitherposition E 41 orC 41 , thereby telescoping and stoppingpiston rod 40 a. Therefore, in correspondence to the rotational position ofsteering wheel 14,sleeve 39 is rotationally located together withlevers swash plates 19 a of right and lefthydraulic pumps 19 to appropriate slant angles and directions. - It is temporarily assumed that a signal value with respect to a stroke of
piston rod 40 a is zero when the stroke is a neutral stroke corresponding to the rotational position ofsteering wheel 14 in straight traveling position S14, that the signal value is increased in a positive range from zero whenpiston rod 40 a is extended from the neutral stroke, and that the signal value is decreased in a negative range from zero whenpiston rod 40 a is contracted from the neutral stroke. When forward traveling sensingswitch 35F is turned on andsteering wheel 14 is rotationally located at a position,controller 44 calculates a positive signal value in correspondence to the position ofsteering wheel 14. On this assumption, if rearward travelingsensing switch 35R is turned off andsteering wheel 14 is rotationally located at the same position,controller 44 calculates a negative signal value of the same volume with the positive signal value calculated when forward traveling sensingswitch 35F is turned on. In other words,piston rod 40 a, which is extended to a degree from the neutral stroke during forward traveling of the vehicle, is contracted to the same degree from the neutral stroke during rearward traveling of the vehicle. Similarly, in correspondence to a rotational position ofsteering wheel 14,piston rod 40 a, which is contracted to a degree from the neutral stroke during forward traveling of the vehicle, is extended to the same degree from the neutral stroke during rearward traveling of the vehicle. - Movement of
speed control levers shaft 38 andsleeve 39 are located at any position in forward traveling range F, and bothbars 39 a are extended laterally in direction S so as to locatespeed control levers right drive wheels steering wheel 14 is turned to a certain rotational position in leftturning range LT 14 . The stroke ofpiston rod 40 a is increased to a certain degree from the neutral stroke so as to rotatesleeve 39 counterclockwise aroundshaft 38 and rotatebars 39 a in ranges LT, whereby leftspeed control lever 17L is rotated rearward, and rightspeed control lever 17R forward, that is, they are symmetrically rotated from their above-mentioned initial position set for forward straight traveling when viewed along the common pivot oflevers left drive wheel 5L is decelerated, and forward rotatingright drive wheel 5R is accelerated so as to compensate for the reduced speed ofleft drive wheel 5L, whereby the forward traveling vehicle turns left. - On the other hand, when setting rearward straight traveling of the vehicle,
shaft 38 andsleeve 39 are located at any position in rearward traveling range R, and bothbars 39 a are extended laterally in direction S so as to locatespeed control levers right drive wheels steering wheel 14 is turned to the certain rotational position in leftturning range LT 14 , which is the same with the above-mentioned certain position ofsteering wheel 14 when setting forward traveling. The stroke ofpiston rod 40 a is reduced from the neutral stroke to a certain degree as much as the above-mentioned increased degree thereof when setting forward traveling so as to rotatesleeve 39 clockwise aroundshaft 38 and rotatebars 39 a in ranges RT, whereby leftspeed control lever 17L is rotated forward, and rightspeed control lever 17R rearward, that is, they are symmetrically rotated from their above-mentioned initial position set for rearward straight traveling when viewed along the common pivot oflevers left drive wheel 5L is decelerated, and rearward rotatingright drive wheel 5R is accelerated so as to compensate for the reduced speed ofleft drive wheel 5L, whereby the rearward traveling vehicle turns left. - In this way, by rotating
steering wheel 14 leftward from straight travelingposition S 14 , the vehicle turns left whether the vehicle travels forward or rearward. The same is true when steeringwheel 14 is rotated rightward from straight travelingposition S 14 . Consequently, the rotational direction ofsteering wheel 14 from straight travelingposition S 14 agrees with turning direction of the vehicle whether the vehicle travels forward or rearward. -
Hydraulic pump 42 serves as a common hydraulic pressure source forhydraulic cylinder 40 and differential-lockingclutch 24. On a hydraulic oil circuit betweenhydraulic pump 42 and differential-lockingclutch 24 is provided a two-positioned spring-loaded electromagnetic differential-lockingvalve 60 which is switched between positions I and II.Controller 44 controls the location of differential-lockingvalve 60 in association with operation ofsteering wheel 14. - When steering
wheel 14 is set in straighttraveling position S 14 , differential-lockingvalve 60 is automatically located in position I so as to engage differential-lockingclutch 24, thereby rotating right and leftdrive wheels drive wheels - When steering
wheel 14 is rotated right or left from straighttraveling position S 14 so as to turn the vehicle,controller 44 excites a solenoid of differential-lockingvalve 60 so that differential-lockingvalve 60 is located at position II to disengage differential-lockingclutch 24, thereby enabling right and leftdrive wheels drive wheels valve 60 may be optionally held at position I by manual operation so as to engage differential-lockingclutch 24 whethersteering wheel 14 is located at straighttraveling position S 14 or not, thereby enabling the vehicle to escape from the ditch. -
FIG. 7 illustrates thattransmission housing 3 contains a modification of the transmission system ofFIG. 5 . Areverser 50 is constituted amongprimary input shaft 11 andpump shafts 19 b. Each ofbevel gears primary input shaft 11 and meshes with both HST input gears 19 c fixed on proximal ends ofrespective pump shafts 19 b. A hydraulically controlled reversal clutch 53 for selecting either normal or reversed rotation ofpump shafts 19 b is disposed onprimary input shaft 11 betweenbevel gears Clutch 53 is supplied with oil so as to fix eitherbevel gear primary input shaft 11. Whichdirection pump shafts 19 b are rotated in depends upon whichbevel gear primary input shaft 11 byreversal clutch 53. When oil is not supplied to clutch 53,hydraulic pumps 19 of both right and leftHSTs - Incidentally,
brake 25 is provided on eachmotor shaft 20 b between fixedswash plate 20 a andgear 20 c. Alternatively, such an arrangement ofbrakes 25 as shown inFIG. 5 may be employed. -
FIG. 8 illustrates thattransmission housing 3 contains a further modification of the transmission system ofFIG. 5 , comprising a pair ofreversers 50, each of which is interposed betweenmotor shaft 20 b of each ofHST drive wheels Primary input shaft 11 andinput shafts 19 b interlock with one another throughbevel gear 22 and HST input gears 19 c so that the rotational direction ofpump shafts 19 b is fixed. - Left and
right counter shafts 26 are extended toward each other so as to be mutually connected or disconnected through differential-lockingclutch 24, which is not interposed between left andright motor shafts 20 b but interposed between left andright counter shafts 26. - An
idler shaft 54 is interposed between eachmotor shaft 20 b and eachcounter shaft 26.Idler shaft 54 always engages withmotor shaft 20 b throughgears Gears counter shaft 26. Hydraulically controlled reversal clutch 53 is disposed on each of left andright counter shafts 26 betweengears gear counter shaft 26.Gear 26 d always meshes withgear 20 c fixed onmotor shaft 20 b.Gear 26 e always meshes with anothergear 54 b fixed oncounter shaft 54.Gears rotating counter shaft 26 in one of opposite directions, i.e., a normal direction.Gears rotating counter shaft 26 in the other direction, i.e., a reversed direction. - Basically, left and
right clutches 53 opposed with respect to differential-lockingclutch 24 are operated simultaneously so that, between bothHSTs axles 27, both the normal gear trains are selected simultaneously, or alternatively, both the reversing gear trains are selected simultaneously. By stopping oil supply to reversal clutch 53, left andright drive wheels right HSTs - Incidentally,
brake 25 is disposed on eachcounter shaft 26. Further, in each ofHSTs hydraulic motor 20 with fixedswash plate 20 a is mounted to one surface ofcenter section 21 which is opposite to another surface ofcenter section 21 for mountinghydraulic pump 19 thereon. Thus, a space for arrangingreverser 50 and the normal and reversing gear trains is ensured amongmotor shaft 20 b andcounter shafts - In any of
reversers 50 shown inFIGS. 7 and 8 , eachreversal clutch 53 includes anoil chamber 53 a for normal rotation and anoil chamber 53 b for reversed rotation, as shown inFIG. 9 . Regarding reversal clutch 53 shown inFIG. 7 ,oil chamber 53 a is supplied with pressure oil to fix one ofbevel gears primary input shaft 11 so as to rotatepump shafts 19 b in the normal direction corresponding to forward traveling of the vehicle.Oil chamber 53 b is supplied with pressure oil to fix the other ofbevel gears primary input shaft 11 so as to rotatepump shafts 19 b in the reversed direction corresponding to rearward traveling of the vehicle. Regardingclutches 53 shown inFIG. 8 ,oil chambers 53 a are supplied with pressure oil to engagebevel gears 26 e withrespective counter shafts 26 so as to transmit output power ofHSTs Oil chambers 53 b are supplied with pressure oil to engagebevel gears 26 d withrespective counter shafts 26 so as to transmit output power ofHSTs - Such arrangement of
reverser 50 orreversers 50 on the upstream or downstream of twin transmissions for respective drive wheels represented by left andright HSTs reversers 50 so as to stop right and leftdrive wheels - Description will be given of a control system of
HSTs FIG. 9 , which is adapted to the respective transmission systems shown inFIG. 7 andFIG. 8 . As the system ofFIG. 9 serves as a modification of the control system ofHSTs FIG. 6 , description of parts and devices shown inFIG. 9 , which are identical with those inFIG. 6 and marked with the same reference numerals of those inFIG. 6 , will be omitted. - Referring to
FIG. 9 , a steeringvalve 41, areverser valve 55 and differential-lockingvalve 60 are supplied in parallel with oil frompump 42.Steering wheel 14 is mechanically linked with steeringvalve 41, through whichports cylinder 40 are fluidly connected to pump 42 andtank 43. Therefore, the different point from the case with steeringvalve 41 ofFIG. 6 is that the stroke ofpiston rod 40 a, i.e., the rotational direction ofsleeve 39 aroundshaft 38 is constant in relation to the left or right rotational direction ofsteering wheel 14 from the straighttraveling position S 14 whether the vehicle travels forward or rearward. That is, whether the vehicle travels forward or rearward, steeringvalve 41 alters the leftward rotation ofsteering wheel 14 from straight travelingposition S 14 into proportional extension ofpiston rod 40 a from the neutralstroke causing bars 39 a to rotate in ranges LT so as to push left lever 19L rearward and pull right lever 19R forward, and it alters the rightward rotation ofsteering wheel 14 from straight travelingposition S 14 into proportional contraction ofpiston rod 40 a from the neutralstroke causing bars 39 a to rotate in ranges RT so as to pull left lever 19L forward and push right lever 19R rearward. - Furthermore, both
pedals arms shaft 38 are connected. Therefore, whicheverpedal shaft 38 andsleeve 39 are tilted only forward in forward traveling range F from neutral position N to maximum forward traveling speed position Fm, that is,swash plates 19 a of bothhydraulic pumps 19 are rotated in only their ranges which are essentially provided for forward traveling of the vehicle. - Consequently, the leftward rotation of
steering wheel 14 from straightraveling position S 14 necessarily reduces the capacity of lefthydraulic pump 19 so as to decelerateleft drive wheel 5L, and increases the capacity of righthydraulic pump 19 so as to accelerateright drive wheel 5R, thereby causing a left turn of the vehicle. The rightward rotation ofsteering wheel 14 from straight travelingposition S 14 necessarily increases the capacity of lefthydraulic pump 19 so as to accelerateleft drive wheel 5L, and reduces the capacity of righthydraulic pump 19 so as to decelerateright drive wheel 5R, thereby causing a right turn of the vehicle. Therefore, whether the vehicle travels forward or rearward does not depend upon positional control ofswash plates 19 a ofhydraulic pumps 19 but needs to depend upon other means for switching the rotational direction ofdrive wheels - As means for changing the rotational direction of
drive wheels reverser valve 55 is a three-positioned electromagnetic solenoid valve, which has oppositedirective solenoids 55 a and 55 b and is switched among aneutral position N 55 and other twopositions F 55 andR 55 , and interposed betweenpump 42 andoil chambers reversal clutch 53. - Description will now be given of the case where the transmission system shown in
FIG. 7 is associated with the control system shown inFIG. 9 . For forward straight traveling of the vehicle, forward travelingshift pedal 33 is depressed together withswitch 35F andsteering wheel 14 is located in straighttraveling position S 14 .Controller 44 receives the depression signal fromswitch 35F and excitessolenoid 55 a so as to locatereverser valve 55 to positionF 55 , thereby connectingchamber 53 a to pump 42 and connectingchamber 53 b totank 43, wherebybevel gear 51 is fixed toprimary input shaft 11 so as to rotatepump shafts 19 b in the normal direction. Therefore,hydraulic motors 20 are rotated in one direction such as to drive the vehicle forward. - For rearward straight traveling of the vehicle, rearward traveling
shift pedal 34 is depressed together withswitch 35R andsteering wheel 14 is located in straighttraveling position S 14 .Controller 44 receives the depression signal fromswitch 35R and excites solenoid 55 b so as to locatereverser valve 55 to positionR 55 , thereby connectingchamber 53 b to pump 42 and connectingchamber 53 a totank 43, wherebybevel gear 52 is fixed toprimary input shaft 11 so as to rotatepump shafts 19 b in the reversed direction. Therefore,hydraulic motors 20 are rotated in the opposite direction such as to drive the vehicle rearward. - As shown in
FIG. 9 ,shaft 38 is tilted only forward in forward traveling range F whichever pedal 33 or 34 is depressed. That is,movable swash plate 19 a of eachhydraulic pump 19 can be tilted to only one side for forward traveling from its neutral position so that eachhydraulic motor 20 is essentially rotated in only one direction for forward traveling at variable speed. However, when pedal 34 is depressed,reverser 50 is changed so as to reverse the flow of fluid betweenpump 19 andmotor 20, thereby reversing the rotational direction ofmotor 20 for rearward traveling. - Incidentally, if neither pedal 33 nor 34 is depressed,
controller 44 locatesreverser valve 55 to shownneutral position N 55 so as to drain oil from bothchambers tank 43, whereby left andright HSTs right drive wheels - When steering
wheel 14 is rotated rightward or leftward from straight travelingposition S 14 , switch 14 a sends controller 44 a signal meaning thatsteering wheel 14 is rotated apart from straight travelingposition S 14 . Therefore,controller 44 switchesdifferential valve 60 to position II so as to disengage differential-lockingclutch 24, similarly with that ofFIG. 6 , so that right and lefthydraulic motors 20 are allowed to rotate freely from each other. - In this embodiment, steering
valve 41 is a spring-center hydraulic change-over valve mechanically linked withsteering wheel 14. Then, according to rotation ofsteering wheel 14 from straight travelingposition S 14 , steeringvalve 41 is changed from aneutral position N 41 to either anextension position E 41 or acontraction position C 41 so as totelescope piston rod 40 a. When the stroke ofpiston rod 40 a ofhydraulic cylinder 40 becomes correspondent to the rotational position ofsteering wheel 14, steeringvalve 41 returns toneutral position N 41 by springs. Therefore,speed control levers drive wheels - By returning
steering wheel 14 to straighttraveling position S 14 , the stroke ofpiston rod 40 a becomes the neutral stroke. At this time, bars 39 a are oriented in direction S so as to equalize directions and angles ofspeed control levers hydraulic motors 20. Furthermore, switch 14 a sends controller 44 a signal meaning thatsteering wheel 14 is set in straighttraveling position S 14 , so thatcontroller 44 switchesdifferential locking valve 60 to position I so as to engage differential-lockingclutch 24. Therefore, the vehicle travels perfectly straight. - It is assumed that
steering wheel 14 is rotated leftward in leftturning range LT 14 from straight travelingposition S 14 . In this case, steeringvalve 41 connectsport 40 b to pump 42, and connectsport 40 c totank 43 so as to rotatesleeve 39 clockwise aroundshaft 38 and rotatebars 39 a in ranges LT, wherebyleft link 16L pushes leftspeed control lever 17L, andright link 16R pulls rightspeed control lever 17R. At this time, when forward travelingshift pedal 33 is depressed so as to fixbevel gear 51 toprimary input shaft 11, pulledright lever 17R causesright HST 18R to accelerate forwardly rotating right drive wheel SR, and pushedleft lever 17L causes leftHST 18L to decelerate forwardly rotatingleft drive wheel 5L. On the contrary, if rearward travelingshift pedal 34 is depressed in the assumed leftward rotated state of thesteering wheel 14,switch 35R is switched on so as to fixbevel gear 52 toprimary input shaft 11. Therefore,right lever 17R is pulled so as to causeright HST 18R to accelerate rearwardly rotatingright drive wheel 5R, and leftlever 17L is pushed so as to cause leftHST 18L to decelerate rearwardly rotatingleft drive wheel 5L. Consequently, when steeringwheel 14 is rotated leftward from straight travelingposition S 14 ,right drive wheel 5R is accelerated, and leftdrive wheel 5L is decelerated, so that the vehicle turns left whether it travels forward or rearward. When steeringwheel 14 is rotated rightward in rightturning range RT 14 from straight travelingposition S 14 , vise versa. In this case, steeringvalve 41contracts piston rod 40 a from the neutral stroke so as to pullleft lever 17L forward and pushright lever 17R rearward. - Description will now be given of the case where the transmission system shown in
FIG. 8 is associated with the control system shown inFIG. 9 . For straight traveling of the vehicle, forward travelingshift pedal 33 is depressed together withswitch 35F, andsteering wheel 14 is located at straighttraveling position S 14 . Based on depression ofswitch 35F,controller 44 excitessolenoid 55 a ofreverser valve 55 so as to locatereverser valve 55 atposition F 55 for setting each ofreversal clutches 53 into a state wherechamber 53 a is connected to pump 42 andchamber 53 b is connected totank 43, thereby fixinggears 26 d torespective counter shafts 26, i.e., selecting the normal gear trains for rotatingcounter shafts 26 opposite torespective motor shafts 20 b. - When rearward traveling
shift pedal 34 is depressed together withswitch 35R,controller 44 excites solenoid 55 b ofreverser valve 55 based on the depression ofswitch 35R so as to locatereverser valve 55 atposition R 55 for setting each ofreversal clutches 53 into a state wherechamber 53 a is connected totank 43 andchamber 53 b is connected to pump 42, thereby fixinggears 26 e torespective counter shafts 26, i.e., selecting the reversing gear trains for rotatingcounter shafts 26 in the same rotational direction withrespective motor shafts 20 b. - Whether
pedal shaft 38 andsleeve 39 are tilted only forward in forward traveling range F so that, in each ofHSTs movable swash plate 19 a ofpump 19 is rotated to only one side from its neutral position so as to accelerate or decelerate output rotation ofmotor 20 in a constant direction for essential forward rotation ofdrive wheels shift pedal 34, reversers 50 actuate to rotatedrive wheels motors 20 is still constant. - When none of
pedals controller 44 sets reverservalve 55 atneutral position N 55 so as to drain oil from bothchambers tank 43. Therefore, both right and leftdrive wheels HST HST - It is assumed that
steering wheel 14 is rotated leftward in leftturning range LT 14 from straight travelingposition S 14 . At this time, steeringvalve 41 connectsport 40 b to pump 42, and connectsport 40 c totank 43, thereby extendingpiston rod 40 a from the neutral stroke, wherebyleft link 16L pushes leftlever 17L rearward andright link 16R pullsright lever 17R forward. When pedal 33 is depressed,switch 35F is switched on so as to fixgears 26 d torespective counter shafts 26, pulledright lever 17R makesright HST 18R accelerate forwardly rotatingright drive wheel 5R, and pushedleft lever 17L makes leftHST 18L decelerate forwardly rotatingleft drive wheel 5L. When pedal 34 is depressed,switch 35R is switched on so as to fixgears 26 e torespective counter shafts 26, pulledright lever 17R makesright HST 18R accelerate rearwardly rotatingright drive wheel 5R, and pushedleft lever 17L makes leftHST 18L decelerate rearwardly rotatingleft drive wheel 5L. - Consequently, when steering
wheel 14 is turned left from straighttraveling position S 14 ,right drive wheel 5R is accelerated andleft drive wheel 5L is decelerated, or ifleft drive wheel 5L is rotated opposite toright drive wheel 5R,left drive wheel 5L is accelerated, so that the vehicle turns left whether it travels forward or rearward. The same is true when steeringwheel 14 is turned rightward in rightturning range RT 14 from straight travelingposition S 14 . In this case, steeringvalve 41contracts piston rod 40 a from the neutral stroke so as to pullleft lever 17L forward and pushright lever 17R rearward. - An operation system shown in
FIG. 10 is adapted for a vehicle transmission system having any ofreversers 50 shown inFIGS. 7 and 8 , which is not operated based on turning of a switch provided on a traveling shift pedal as shown inFIG. 9 , but is manually operable with a mechanical link. Areverser valve 55 is mechanically linked with a reverser lever (not shown) provided in a driver's portion of a vehicle. Accordingly, only asingle pedal 33 serves as an operation device for changing traveling speed of the vehicle. A pressure-sensing switch 35 is provided on a depressed surface ofpedal 33. - A
clutch valve 61, which is electro-magnetically controlled bycontroller 44 based on ON/OFF signal fromswitch 35, is interposed amongreverser valve 55, pump 42 andtank 43. When pedal 33 is not depressed and switch 35 is turned off,clutch valve 61 is located at a shown position 161 so that any reversal clutch 53 havingoil chambers tank 43, is unclutched whereverreverser valve 55 is located. Ifpedal 33 is depressed,reverser valve 61 is shifted to a position II 61 so as to be applied for supplying oil to eitheroil chamber reverser valve 55. - According to setting the above-mentioned reverser lever to either a forward traveling position or a rearward traveling position,
reverser valve 55 is set to either forward travelingposition F 55 or rearward travelingposition R 55 . The forward tilt angle ofsleeve 39 is changed according to depression ofpedal 33 so as to equally change the capacities of both left and righthydraulic pumps 19, thereby changing the traveling speed of a vehicle. - When steering
wheel 14 is rotated rightward or leftward from straight travelingposition S 14 ,hydraulic cylinder 40telescopes piston rod 40 a so as to rotatesleeve 39 aroundshaft 38. Therefore, the capacity ofhydraulic pump 19 on one side of the vehicle corresponding to the rotational direction ofsteering wheel 14 is reduced so as to reduce the output power ofhydraulic motor 20 fluidly connected thereto, thereby deceleratingcorresponding drive wheel hydraulic pump 19 on the other side of the vehicle opposite to the rotational direction ofsteering wheel 14 is relatively increased so as to increase the output power ofhydraulic motor 20 fluidly connected thereto, thereby acceleratingcorresponding drive wheel - Reverser (or reversers) 50 maintains the relation of deceleration and acceleration of
drive wheels steering wheel 14 so as to coincide turning direction of the vehicle to the rotational direction ofsteering wheel 14 whether the vehicle travels forward or rearward. - Referring to
FIG. 11 ,reverser 50 is interposed betweenprimary input shaft 11 andpump shafts 19 b, similarly withFIG. 7 . However,reverser 50 shown inFIG. 11 is provided with a mechanicalreversal dog clutch 53′ instead ofhydraulic reversal clutch 53.Clutch 53′ is provided with aclutch slider 53′a, which is not relatively rotatably but axially slidably disposed onprimary input shaft 11 so as to selectively engage with one ofopposite bevel gears primary input shaft 11.Clutch slider 53′a is mechanically linked with a reverser lever (with reference to a reverser lever 72 shown inFIG. 12 ) provided in a driver's portion of a vehicle. - By manual operating the reverser lever,
clutch slider 53′a of reversal clutch 53′ slides onprimary input shaft 11 and engages with one ofbevel gears pump shafts 19 b in either one direction for forward traveling or the other direction for rearward traveling. In addition,clutch slider 53′a may be disengaged from bothbevel gears pump shafts 19 b from rotational force ofprimary input shaft 11. - A main clutch 71, which may be integrally provided on
output pulley 9 as shown inFIG. 11 , is temporarily disengaged to isolateprimary input shaft 11 from power ofengine 2 before switching reversal clutch 53′. Main clutch 71 may be electro-magnetically controlled so as to be automatically switched depending upon whether later-discussed travelingshift pedal 33 is depressed or not, for example. - Referring to
FIG. 12 ,reversers 50 are provided onrespective counter shafts 26 on the downstream of respectivehydraulic motors 20, similarly withFIG. 8 . However, reversers 50 shown inFIG. 12 are provided with respective mechanicalreversal dog clutches 53′ instead ofhydraulic reversal clutches 53. Each reversal clutch 53′ is provided with aclutch slider 53′a, which is not relatively rotatably but axially slidably disposed oncounter shaft 26 so as to selectively engage with one ofopposite gears counter shaft 26. Bothclutch sliders 53′a are engaged to acommon fork shaft 53′b throughrespective forks 53′c.Fork shaft 53′b is mechanically linked with a reverser lever 72 provided in a driver's portion of a vehicle. - By manual operating reverser lever 72, both
clutch sliders 53′a ofreversal clutches 53′ slide onrespective counter shafts 26 and engage with eithergears counter shafts 26 in either one direction for forward traveling or the other direction for rearward traveling. In addition, eachclutch slider 53′a may be disengaged from bothgears reversal clutches 53′ may be unclutched to isolatecounter shafts 26 from rotational force ofmotor shafts 20 b. - Main clutch 71, which may be integrally provided on
output pulley 9 as shown inFIG. 12 , is temporarily disengaged to isolateprimary input shaft 11 from power ofengine 2 before switchingreversal clutches 53′. Main clutch 71 may be electro-magnetically controlled so as to be automatically switched depending upon whether later-discussed travelingshift pedal 33 is depressed or not, for example. -
FIG. 13 illustrates a structure with electric and hydraulic circuits for controlling tilt angles ofswash plates 19 a of left and righthydraulic pumps 19, which is adapted for each of the transmission systems ofFIGS. 11 and 12 , and functions similarly with the structure ofFIG. 10 . When pressure-sensing switch 35 detects depression of single travelingshift pedal 33,controller 44 electro-magnetically controls main clutch 71 to engage. Either forward or rearward traveling direction of the vehicle is determined by settingmechanical reverser 50. While the vehicle travels in the set forward or rearward direction, the forward tilt angle ofsleeve 39 withshaft 38 is changed according to depression ofpedal 33 so as to change the capacities of left and righthydraulic pumps 19, thereby changing traveling speed of the vehicle. - When steering
wheel 14 is rotated leftward or rightward from straight travelingposition S 14 ,piston rod 40 a ofhydraulic cylinder 40 is telescoped so as to rotatesleeve 39 aroundshaft 38, whereby the capacity ofhydraulic pump 19 on one side of the vehicle corresponding to the rotational direction ofsteering wheel 14 is reduced so as to deceleratecorresponding drive wheel hydraulic pump 19 on the other side of the vehicle opposite to the rotational direction ofsteering wheel 14 is increased so as to acceleratecorresponding drive wheel drive wheels steering wheel 14 so as to coincide turning direction of the vehicle to the rotational direction ofsteering wheel 14 whether the vehicle travels forward or rearward. - Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.
Claims (9)
1. A vehicle comprising:
a prime mover;
a pair of left and right steerable wheels;
a steering operation device for steering the pair of left and right steerable wheels;
a pair of left and right gear assemblies interposed between the steering operation device and the respective left and right steerable wheels, wherein, in each of the gear assemblies, a first non-circular gear operatively connected to the steering operation device meshes with a second non-circular gear operatively connected to each of the left and right steerable wheels;
a pair of left and right unsteerable driving wheels;
a speed control operation device for controlling rotational speeds of the unsteerable driving wheels; and
a pair of continuously variable transmissions driven by the prime mover so as to drive the respective unsteerable driving wheels, wherein the speed control operation device is operatively connected to the continuously variable transmissions so as to substantially evenly control output rotational speeds of the continuously variable transmissions, and wherein the steering operation device is operatively connected to the continuously variable transmissions so that a differential rotational speed of the unsteerable driving wheels is increased according to increase of an operation degree of the steering operation device.
2. The vehicle according to claim 1 , wherein the speed control operation device is a foot pedal, and wherein the steering operation device is a steering wheel.
3. The vehicle according to claim 1 , wherein the continuously variable transmissions are operatively connected to the speed control operation device and the steering operation device so that a turning direction of the vehicle coincides to an operation direction of the steering operation device regardless of whether the speed control operation device is operated for forward traveling of the vehicle or for backward traveling of the vehicle.
4. A vehicle comprising:
a prime mover;
a pair of left and right steerable wheels;
a steering operation device for steering the pair of left and right steerable wheels;
a pair of left and right gear assemblies interposed between the steering operation device and the respective left and right steerable wheels, wherein, in each of the gear assemblies, a first non-circular gear operatively connected to the steering operation device meshes with a second non-circular gear operatively connected to each of the left and right steerable wheels;
a pair of left and right unsteerable driving wheels;
a speed control operation device for controlling rotational speeds of the unsteerable driving wheels; and
a pair of hydrostatic continuously variable transmissions driven by the prime mover so as to drive the respective unsteerable driving wheels, wherein the speed control operation device is operatively connected to the hydrostatic continuously variable transmissions so as to substantially evenly control output rotational speeds of the hydrostatic continuously variable transmissions, and wherein the steering operation device is operatively connected to the hydrostatic continuously variable transmissions so that a differential rotational speed of the unsteerable driving wheels is increased according to increase of an operation degree of the steering operation device.
5. The vehicle according to claim 4 , wherein the speed control operation device is a foot pedal, and wherein the steering operation device is a steering wheel.
6. The vehicle according to claim 4 , wherein the hydrostatic continuously variable transmissions are operatively connected to the speed control operation device and the steering operation device so that a turning direction of the vehicle coincides to an operation direction of the steering operation device regardless of whether the speed control operation device is operated for forward traveling of the vehicle or for backward traveling of the vehicle.
7. A vehicle comprising:
a prime mover;
a pair of left and right steerable wheels;
a steering operation device for steering the pair of left and right steerable wheels;
a pair of left and right gear assemblies interposed between the steering operation device and the respective left and right steerable wheels, wherein, in each of the gear assemblies, a first non-circular gear operatively connected to the steering operation device meshes with a second non-circular gear operatively connected to each of the left and right steerable wheels;
a pair of left and right unsteerable driving wheels;
a speed control operation device for controlling rotational speeds of the unsteerable driving wheels; and
a pair of hydraulic units for driving the respective unsteerable driving wheels, each of the hydraulic units including a variable displacement hydraulic pump driven by the prime mover and a fixed displacement hydraulic motor fluidly connected to the hydraulic pump so as to drive the corresponding unsteerable driving wheel, wherein the speed control operation device is operatively connected to the hydraulic pumps so as to substantially evenly control output rotational speeds of the hydraulic motors, and wherein the steering operation device is operatively connected to the hydraulic pumps so that, as an operation degree of the steering operation device is increased, a displacement of one hydraulic pump is increased, and simultaneously, a displacement of the other hydraulic pump is reduced, so as to increase a differential rotational speed of the unsteerable driving wheels.
8. The vehicle according to claim 7 , wherein the speed control operation device is a foot pedal, and wherein the steering operation device is a steering wheel.
9. The vehicle according to claim 7 , wherein the hydraulic pumps are operatively connected to the speed control operation device and the steering operation device so that a turning direction of the vehicle coincides to an operation direction of the steering operation device regardless of whether the speed control operation device is operated for forward traveling of the vehicle or for backward traveling of the vehicle.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US11/697,568 US20070175676A1 (en) | 2003-06-06 | 2007-04-06 | Vehicle Having Twin Transmissions For Driving Respective Wheels |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/455,306 US7004268B2 (en) | 2003-06-06 | 2003-06-06 | Vehicle having twin transmissions for driving respective wheels |
US11/327,415 US7331412B2 (en) | 2003-06-06 | 2006-01-09 | Vehicle having twin transmissions for driving respective wheels |
US11/697,568 US20070175676A1 (en) | 2003-06-06 | 2007-04-06 | Vehicle Having Twin Transmissions For Driving Respective Wheels |
Related Parent Applications (1)
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US11/327,415 Continuation US7331412B2 (en) | 2003-06-06 | 2006-01-09 | Vehicle having twin transmissions for driving respective wheels |
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US20070175676A1 true US20070175676A1 (en) | 2007-08-02 |
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US11/327,415 Expired - Fee Related US7331412B2 (en) | 2003-06-06 | 2006-01-09 | Vehicle having twin transmissions for driving respective wheels |
US11/697,568 Abandoned US20070175676A1 (en) | 2003-06-06 | 2007-04-06 | Vehicle Having Twin Transmissions For Driving Respective Wheels |
US11/750,877 Expired - Fee Related US7455130B2 (en) | 2003-06-06 | 2007-05-18 | Vehicle having twin transmissions for driving respective wheels |
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US11/327,415 Expired - Fee Related US7331412B2 (en) | 2003-06-06 | 2006-01-09 | Vehicle having twin transmissions for driving respective wheels |
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US11/750,877 Expired - Fee Related US7455130B2 (en) | 2003-06-06 | 2007-05-18 | Vehicle having twin transmissions for driving respective wheels |
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US20010040057A1 (en) * | 1998-03-12 | 2001-11-15 | Toshiyuki Hasegawa | Multi-wheel vehicle with transmission for driving-steering |
US20020092685A1 (en) * | 2000-08-15 | 2002-07-18 | Mtd Products Inc | ZTR vehicle with a one-pump two-motor mechanism |
US6601663B2 (en) * | 2000-08-15 | 2003-08-05 | Mtd Products Inc. | Zero turn radius or ZTR vehicle with a one-pump two motor mechanism |
US20030102171A1 (en) * | 2001-09-17 | 2003-06-05 | Hans Hauser | Mechanical ZTR system with steering wheel |
US20030201134A1 (en) * | 2002-04-24 | 2003-10-30 | Norihiro Ishii | Hydraulic driving apparatus for a wheeled vehicle |
US20040060745A1 (en) * | 2002-09-26 | 2004-04-01 | Kubota Corporation | Self-propelled working vehicle |
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US20110248462A1 (en) * | 2005-07-22 | 2011-10-13 | Infinitrak, Llc | Steering systems, steering and speed coordination systems, and associated vehicles |
US9409596B2 (en) * | 2005-07-22 | 2016-08-09 | Mtd Products Inc | Steering systems, steering and speed coordination systems, and associated vehicles |
US10780917B2 (en) | 2005-07-22 | 2020-09-22 | Mtd Products Inc | Steering systems, steering and speed coordination systems and associated vehicles |
US20110053731A1 (en) * | 2005-08-22 | 2011-03-03 | Christopher John Greenwood | Arrangements for Driving and Steering of Motor Vehicles |
US8919464B2 (en) | 2005-08-22 | 2014-12-30 | Mtd Products Inc. | Arrangements for driving and steering of motor vehicles |
US10766521B2 (en) | 2006-10-17 | 2020-09-08 | Mtd Products Inc | Vehicle control systems and methods |
US8944191B2 (en) | 2008-03-26 | 2015-02-03 | Mtd Products Inc | Vehicle control systems and methods |
US10046797B2 (en) | 2008-03-26 | 2018-08-14 | Mtd Products Inc | Vehicle control systems and methods |
US10745048B2 (en) | 2008-03-26 | 2020-08-18 | Mtd Products Inc | Vehicle control systems and methods |
US10780918B2 (en) | 2011-09-22 | 2020-09-22 | Mtd Products Inc | Vehicle control systems and methods and related vehicles |
US11958558B2 (en) | 2011-09-22 | 2024-04-16 | Mtd Products Inc | Vehicle control systems and methods and related vehicles |
Also Published As
Publication number | Publication date |
---|---|
US7004268B2 (en) | 2006-02-28 |
US20070215403A1 (en) | 2007-09-20 |
US20040245029A1 (en) | 2004-12-09 |
US7331412B2 (en) | 2008-02-19 |
US20060108155A1 (en) | 2006-05-25 |
US7455130B2 (en) | 2008-11-25 |
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