WO2000046054A1

WO2000046054A1 - Vehicle suspension system

Info

Publication number: WO2000046054A1
Application number: PCT/GB2000/000295
Authority: WO
Inventors: Richard Granville Townend; Richard Hurdwell; Giles Douglas Muddell
Original assignee: Prodrive Holdings Limited
Priority date: 1999-02-02
Filing date: 2000-02-02
Publication date: 2000-08-10
Also published as: GB0002289D0; GB2346346A; GB9902182D0; GB2346346B; AU2305600A

Abstract

A vehicle suspension system is arranged to be able to locate a vehicle at a predetermined ride position during cornering and acceleration and deceleration. The system includes for each wheel a piston and cylinder (16, 17) connected between the vehicle and the wheel mounting. The fluid supply to each side of the piston is controlled to regulate the net force on the piston and hence the position of the piston in the cylinder. A valve (25) is arranged to operate according to dynamic characteristics of the vehicle to change the fluid pressure to one side of the piston.

Description

VEHICLE SUSPENSION SYSTEM

This invention relates to vehicle suspension systems and in particular, but not exclusively, to so called 'active' suspension systems for road vehicles.

Active suspension systems have been proposed by which the ride characteristics of the vehicle suspension are adjusted according to the desired ride of the vehicle, according to the vehicle roll characteristics, and for other reasons.

An object of the invention is to provide an improved vehicle suspension system.

According to the invention a vehicle suspension system comprises piston and cylinder means associated with the vehicle road wheels, each piston and cylinder means being operatively connected between an associated wheel mounting and the vehicle body, fluid supply means to each side of each piston arranged to regulate the net force on the piston in the associated cylinder, valve means for controlling fluid pressure on one side of the cylinder to control the pressure difference at opposite sides of the piston, and monitoring means for monitoring variable parameters of the moving vehicle such as acceleration, braking, cornering forces, and generating signals derived from said monitored parameters, the signals generated being arranged to operate the valve means to cause the pistons to maintain selected positions within the respective cylinders.

Preferably each piston is operatively connected to the associated wheel mounting means and each cylinder is operatively connected to the vehicle body. The valve means preferably controls fluid supply to and from the associated cylinder to the side of the piston remote from the piston rod.

Conveniently, but not essentially, the cross sectional area of the piston is of the order of twice the cross sectional area of the piston rod for the piston. This enables the control of the piston positions to be more readily achieved by introducing fluid at around half the operative pressure to that side of the piston remote from the piston rod using the valve means for said supply. The other side of the piston carrying the piston rod is then permanently connected to the pressurised fluid supply directly without the need for similar valve means.

The fluid supply to each side of each piston may include fluid flow control means or restrictors for controlling the rate of fluid flow to and from the cylinder.

The fluid supply to either or both sides of the piston may include fluid damping means for damping the fluid flow to and from the cylinder.

The fluid supply is conveniently from a common pump which communicates with each of the piston and cylinders, fluid being arranged to be in communication with each side of the piston.

Preferably, motion in reaction to other inputs such as road undulations is separately controlled by means of springs and/or dampers.

The arrangement may be such that the pressure applied to each side of the piston of each piston and cylinder is kept the same and the piston is biased for movement towards a constant predetermined position. The impact of bumps and road irregularities on the wheels is absorbed by conventional suspension means between the wheel mounting and the vehicle and by damping means for damping movement of the piston in the cylinder.

The monitoring means can be arranged to select the parameters to be monitored so that, for example, during cornering of a vehicle the system can inhibit vehicle roll by monitoring the lateral acceleration forces and, according to detection of these forces, the valve means operates to increase and decrease the pressure applied to the upper surface of the pistons in the piston and cylinder devices at opposite sides of the vehicle. Thus the tendency of the vehicle to lift at one side and lower at the other during cornering is inhibited end the vehicle remains level. Similarly during acceleration and braking of the vehicle the acceleration and deceleration of the vehicle in the longitudinal direction is monitored and signals are transmitted to the respective valve means to increase or decrease pressure in the cylinders at front and rear and maintain the pistons in their selected mean position thereby keeping the vehicle level.

Moreover by monitoring vehicle speed, the position of the steerable wheels, lateral and other acceleration forces and biasing reaction of the loads one axle and the other(s) it is possible to alter the driving characteristics of the vehicle, such as oversteer and understeer and optimise them for different road speeds and conditions.

The signals generated by the monitoring means are fed to an electrical processor preprogrammed to effect operation of the various valve means to bring about the desired flow of fluid to and from the piston and cylinder means to adjust the pressures inside the cylinder.

Conveniently the system comprises further suspension means acting in parallel to the piston and cylinder means and including a further piston and cylinder operatively connected between the associated wheel mounting and the vehicle body. In said further piston and cylinder the piston may be operatively connected to the wheel mounting and the cylinder to the vehicle body, optionally through a spring, and the cylinder being in fluid connection with one or the other side of the first mentioned piston and cylinder. Alternatively said further piston and cylinder may be arranged with the piston connected to the wheel mounting through a spring and the cylinder is fixed in relation to the vehicle and is in fluid connection with a still further piston and cylinder or gas spring.

Further features of the invention will appear from the following description of embodiments of the invention given by way of example only and with reference to the drawings in which:

Fig 1 is a schematic view of a suspension system as applied to one vehicle wheel, the other wheels each having a similar system associated therewith,

Fig. 2 is a similar view to that of Fig. 1 with variants,

Fig. 3 is a similar view, with further variants,

Figure 4 is a further similar view with further variants, and

Fig. 5 is a further view with further variants.

Referring to Fig 1 a vehicle wheel 10 is mounted for movement about an axis 11 on a suspension arml2. Conventional suspension means 13 is interposed between the vehicle body and the arm 12. In addition a piston and cylinder device 15 is interposed between the arm 12 and the vehicle body. The device 15 includes a cylinder 16 in which is a piston 17 having a piston rod 18 extending from one side of the piston 17 for pivotal connection of the rod 18 to the arm 12 at 19.

The cross sectional area of the piston rod 18 is approximately half of the cross sectional area of the piston 17 and it will be appreciated that the fluid pressure in the volume 20 above the piston need be only half the fluid pressure in the volume 21 below the piston to maintain equal forces on the piston 17.

A hydraulic pump 23 is arranged to supply fluid for each of the four piston and cylinder devices 15 (when there are four wheels on the vehicle) and the supply of fluid from the pump 23 communicates directly with the cylinder space 21 through a restrictor 24. The fluid pressure from the pump 23 communicates with the cylinder volume 20 through a valve 25 and there is also provided a damping restrictor 26 between the valve 25 and the cylinder space 20. A gas spring 27 is provided in the fluid line between the valve 25 and the cylinder space 20 to provide displacement means to accommodate fluid displaced from the cylinder due to bumps, for example. There are also provided for the fluid line communicating with cylinder space 20 a pressure transducer 28 and a temperature sensor 29. Instead of the displacement means being a gas spring, as shown, it may be a spring and piston or other compliant device.

Pressure of fluid from the pump 23 is usually controlled to give a constant pressure output by a pressure controller 35 which may be associated with the pump 23 or with the valve 25.

The valve means 25 is a three porj, proportional spool valve, the valve having a closed position (as shown), a position in which fluid is supplied from the pump 23 to the gas spring 27, and a position in which fluid is returned from the gas spring 27 for return to the pump 23 fluid being admitted and discharged at a variable rate. The position of the valve 25 is controlled electrically and the valve is moved to the appropriate position under the action of signals from an electrical control unit or signal processor 30. The electrical control unit 30 is controlled according to monitoring means 31 which monitors various parameters of the vehicle and which can also receive a manually operated input, if required.

To maintain substantially constant pressure within the fluid supply system under operational conditions there is provided an accumulator 32 communicating with the pump 33. The accumulator 32 also allows the flow of fluid in and out of the cylinder if the wheel encounters bumps in the road. In order to reduce energy consumption the fluid pressure in the system may be modulated.

It will be appreciated that the valve 25 controls the fluid pressure above the piston 17 in the cylinder volume 20 only and that this is sufficient to be able to ensure that the force applied to the piston 17 from above and from below can be controlled by operation of the valve 25 having regard to the operational state of the other piston and cylinder devices on the vehicle. This is best illustrated by reference to the vehicle in specific driving modes. Thus, for example, when the vehicle is turning a corner and there is a tendency for the vehicle to roll, that is pivot about its central longitudinal axis, the monitoring means 31 can detect the cornering forces by measuring the lateral acceleration forces on the vehicle or the steering input may be measured. A signal is generated according to the lateral acceleration forces which is processed by the processing means 30 and the processed signal is transmitted to each of the valves 25 associated with one of the vehicle wheels 10. To the vehicle wheels at the outside of the turn will be transmitted increased pressure to the volume 20 above the piston 17 whilst the vehicle wheels on the inside of the corner will transmit decreased pressure to the volume 20 of the associated cylinder. By operation of the associated valves 25 fluid is released and introduced into the gas spring 27 raising and lowering the pressure in the cylinders 16 at the outside and inside respectively of the vehicle thereby maintaining the pistons 17 in their mean position within the cylinders 16.

Similarly under acceleration and deceleration of the vehicle the acceleration and deceleration forces on the vehicle can be monitored by the monitoring means 31 , the signals produced are processed by the electrical processor 30 and the necessary action to maintain the respective piston 17 in position in the cylinder 16 is achieved by the valves 25 to maintain the vehicle substantially level under these conditions.

Thus in each case the pressure above and below the piston 17 are controlled according to the mean pressure difference to counteract the dynamic forces on the vehicle.

At the same time the wheels are free to ride over bumps in the road surface since these movements are controlled by the suspension 13 for each wheel, the gas spring 27 and the damping valves 26 and 24.

The pressure transducer 28 and temperature sensor 29 are provided to enable further monitoring of the system in operation and pressure and temperature signals are fed to the processor 30. The pressure of fluid in the system may also be measured. From a measurement of pressure downstream from the gas spring 32 and the position of the piston 17 and the pressure measured at 28 a measurement of load between the road wheel and road can be obtained. The arrangement may be used to redistribute the load of each wheel, including having zero load on one wheel. During travel of the vehicle over bumps the piston 17 will be displaced in the cylinder and thereby affect the pressures above and below the piston for brief periods. To compensate for these variations the position of the piston 17 in the cylinder is monitored, for example by a positional detector, to determine predicted pressure changes due to movement of the piston arising because of bumps. The predicted pressure changes are used to correct the overall measured pressures and to ignore changes in pressures due to such changes in the position of the piston.

Moreover the pressures of fluid in the piston 17 and cylinder 16 and, more particularly in the gas spring 27, are affected by the temperature so the temperature of the fluid is detected and the measurement is used to minimise any effect that variation in temperature may cause.

As well as controlling the roll of the vehicle, the pitch under acceleration and dive under braking, the suspension system can also be used as a means for controlling the ride height of the vehicle. To achieve this the pressure in the cylinder 16 may be changed to adjust the position of the piston 17 in the cylinder.

Monitoring of acceleration and deceleration parameters coupled with speed of travel and the attitude of the steerable wheels can also be used to improve the drive characteristics of the vehicle for example the extent of oversteer and understeer of the vehicle. The processing unit 30 can use the signals produced from monitoring these parameters to adjust the suspension system to give the desired results. Thus stability control may be provided to act in conjunction with existing stability control means or as a replacement therefor.

The effect of compression of tyres of the vehicle during cornering can also be accommodated by changing the position of the piston 17 in the cylinder to keep the vehicle level.

It will be appreciated that the piston arrangement does not permit passage of any fluid between the cylinder volumes 20 and 21. The use of a half fluid pressure system in the volume 20 with full fluid pressure in the volume 21, enables control of the system to be readily achieved although, in practice, there may be some variation from the half pressure arrangement to allow for pressure losses within the system.

Figs. 2-5 show schematically various alternative arrangements whereby the stiffness or softness of the road spring 13 of each wheel suspension may be modified. The arrangement described with reference to Fig. 1 requires minimum energy input at the piston 15 to control dynamic load changes if the gas spring 27 has high stiffness. In this way less fluid flow is required to increase or decrease the control pressure above the piston 17. This stiffness adds to the stiffness rate of the road spring 13 and has a tendency to harden the ride characteristics.

Referring now in particular to Fig. 2 the road spring stiffness can be altered by the replacement of the road spring arrangement 13 of Fig. 1 with that shown. In this arrangement a piston and cylinder 36 is connected with its piston rod or other connection to the piston bearing on a spring or compliant member 37 and the piston 38 of the piston and cylinder 36 is operatively connected to a spring 39 interposed between the piston 38 and the vehicle. A fluid connection is then made between the cylinder 40 of the piston and cylinder 36 and the cylinder 16 above the piston 17, the connection having a restrictor 40.

It will be seen that if the cylinder 40 is depressurised the road spring 39 acts directly on the suspension. When pressurised the spring 39 is lifted away from the suspension support and is connected hydraulically via the piston 38. This arrangement reduces the flow requirements of the fluid in the cylinder 16 and provides support if the power to the suspension system is turned off or fails. In this arrangement the gas spring 27 may be omitted.

Referring now to Fig. 3 a similar arrangement to that in Fig. 2 is provided but in this case the cylinder 40 is arranged to communicate with the fluid supplied to the lower part of the cylinder 16 below the piston 70. When the cylinder 40 is pressurised the road spring 39 is fully retracted and when the cylinder 16 is depressurised or the suspension system fails the road spring 38 acts directly on the suspension. Passive springing in this arrangement is provided by the gas spring 27. Referring now to Fig.4 a road spring 39 remains, connected between the arm 12 and a piston and cylinder device 42 of which the cylinder 43 is attached to a fixed part of the vehicle and the piston 44 to the road spring 39. The cylinder 43 communicates with a further piston and cylinder device of which the piston 46 is attached to the vehicle through a further spring 47.

Thus the arrangement provides an additional spring arrangement in series with the road spring to lower the suspension rate to or below normal passive suspension levels. Instead of the piston and cylinder arrangement 45 a gas spring 48 (shown in outline) may be employed in fluid communication with the cylinder 43.

Referring now to Fig. 5 a similar arrangement to that of Fig. 4 is shown employing a piston and cylinder 42 of which the piston 44 is connected to a road spring 39. Instead of the cylinder 43 being in communication with a further cylinder 45 or gas spring 48, the cylinder 43 communicates with the fluid inlet to the upper side of the piston 17. By the suspension acting on both the spring 39 and the piston and cylinder 42 less pressure change is needed to compensate for dynamic forces. If desired a pressure trapping valve can be introduced to ensure a pre-charge of fluid to support the vehicle when the fluid supply is turned off or fails.

In each of these arrangements the gas spring 27 may be replaced by a piston and cylinder communicating with the fluid input, the piston being spring mounted within the cylinder.

The provision of the suspension system of the invention can provide improved cornering performance for vehicles and give an improved handling response. There may be improved primary and cornering ride comfort with improved secondary ride comfort. It also provides the ability to tune and control vehicle handling and may compliment existing brake or traction stability control systems.

A pump pressure control 35 and operation of the valve 25 may be arranged to be combined to produce control of differential pressures in the piston 15. The system is capable of restraining roll of the vehicle without the need for anti-roll bars which can provide noise and vibration problems. The absence of roll in the handling of the vehicle gives rise to numerous benefits including improved comfort and reduced disturbance of cargo, by reducing or eliminating body roll while optimising vertical ride stiffness for individual wheels.

Importantly, the system can accommodate any arrangement of suspension since the system essentially replaces the function of a hydraulic damper.

The suspension system may also permit the scope for improved conventional suspension components or system of operation, or elastic and kinematic behaviour.

The system may also be arranged to raise and lower selected wheels of a vehicle, for example trucks which have wheel pairs, to lift selected wheels out of contact with the road to reduce rolling resistance when travelling unloaded.

Claims

1. A vehicle suspension system comprising piston and cylinder means associated with the vehicle road wheels, each piston and cylinder means being operatively connected between an associated wheel mounting and the vehicle body, fluid supply means to each side of each piston arranged to regulate the net force on the piston in the associated cylinder, valve means for controlling fluid pressure on one side of the cylinder to control the pressure difference at opposite sides of the piston, and monitoring means for monitoring variable parameters of the moving vehicle, such as acceleration, braking and cornering forces, and generating signals derived from said monitored parameters, the signals generated being arranged to operate the valve means to cause the pistons to maintain selected positions within the respective cylinders.

2. A vehicle suspension system according to claim 1 wherein each piston is operatively connected to the associated wheel mounting means and each cylinder is operatively connected to the vehicle body.

3. A vehicle suspension system according to claim 1 or 2 wherein the valve means controls fluid supply to and from the associated cylinder to the side of the piston remote from the piston rod.

4. A vehicle suspension system according to any one of the preceding claims wherein the cross-sectional area of the piston is of the order of twice the cross-sectional area of the piston rod for the piston.

5. A vehicle suspension system according to claim 4 wherein the fluid supply means is arranged to introduce fluid at around half the operative pressure to that side of the piston remote from the piston rod and the other side of the piston carrying the piston rod is connected directly to a pressurised fluid supply.

6. A vehicle suspension system according to any one of the preceding claims wherein the fluid supply to each side of each piston includes fluid flow control means or restrictors for controlling the rate of fluid flow to and from the cylinder.

7. A vehicle suspension system according to any one of the preceding claims wherein the fluid supply to either or both sides of the piston includes fluid damping means for damping the fluid flow to and from the cylinder.

8. A vehicle suspension system according to any one of the preceding claims wherein the fluid supply is from a common pump which communicates with each of the piston and cylinder, fluid from the pump being arranged to be in communication with each side of the piston.

9. A vehicle suspension system according to any one of the preceding claims wherein motion in reaction to inputs such as road undulations is controlled by means of springs, dampers or other means, operating in parallel to the piston and cylinder means.

10. A vehicle suspension system according to any one of the preceding claims wherein the monitoring means is arranged to select the parameters to be monitored according to the status of the vehicle whereby during cornering of a vehicle the system inhibits vehicle roll by monitoring lateral acceleration forces and during acceleration and braking of the vehicle the acceleration and deceleration of the vehicle in the longitudinal direction is monitored, and the valve means is operated to effect the necessary operation of the valve means.

11. A vehicle suspension system according to any one of the preceding claims wherein the signals generated by the monitoring means are fed to an electrical processor preprogrammed to effect operation of the valve means to bring about the desired flow of fluid to and from the piston and cylinder means to adjust the pressures inside the cylinders.

12. A vehicle suspension system according to any one of the preceding claims comprising further suspension means acting in parallel to the piston and cylinder means and including a further piston and cylinder operatively connected between the associated wheel mounting and the vehicle body.

13. A suspension system according to claim 12 in which in said further piston and cylinder the piston is operatively connected to the wheel mounting and the cylinder to the vehicle body, optionally through a spring, and the cylinder being in fluid connection with one or the other side of the first mentioned piston and cylinder.

14. A suspension system according to claim 12 wherein said further piston and cylinder is arranged with the piston "bearing on the wheel mounting through a spring, and the cylinder is fixed in relation to the vehicle and is in fluid connection with a still further piston and cylinder or gas spring.