WO1992005970A1

WO1992005970A1 - Arrangement on a vehicle bogie to distribute weight between a driven and non-driven axle

Info

Publication number: WO1992005970A1
Application number: PCT/SE1991/000604
Authority: WO
Inventors: Lars Jung
Original assignee: Saab-Scania Aktiebolag
Priority date: 1990-09-27
Filing date: 1991-09-12
Publication date: 1992-04-16
Also published as: SE467200B; DE4192425T1; DE4192425C2; GB2254057B; SE9003068D0; GB9210271D0; SE9003068L; GB2254057A

Abstract

To distribute weight between a drive axle (3) and a tag axle (5) in a tag axle bogie, a pressure-conducting pipe (22) is installed between the air springs (11) of the two axles (3, 5). In the pipe (22) a pressure limiter (25) is designed to close the pipe (22) when a predetermined pressure is reached in the air springs (11) of the drive axle (3), but to open the pipe (22) when the predetermined pressure is undercut. When the pipe (22) is closed, continued pressure build-up is permitted in the air springs (11) of the drive axle (3), but not in the air springs (11) of the tag axle (5). By varying the predetermined pressure, weight distribution between the two axles (3, 5) can be modified.

Description

Arrangement on a vehicle bogie to distribute weight between a driven and non-driven axie

The present invention relates to an arrangement for a vehicle bogie to distribute weight between a driven and a non-driven axle, which bogie includes at least one first pneumatic spring device mounted between the frame of the vehicle and the driven axle and at least one second pneumatic spring device mounted between the frame and the non-driven axle, which pneumatic spring devices are interconnected as well connected to a pressure source via pressure-conducting piping

Heavy vehicles such as trucks are often equipped with a rear suspension formed as a tag axle bogie, comprising a driven axle and a tag axle. Having dual rear axles, such a vehicle can be subjected to greater loads than a vehicle with only one rear axle. On some vehicle types, e.g. with a short axle distance, bouncing is difficult to avoid during driving if conventional leaf springs are used in the tag axle bogie. Air suspension is therefore often employed on these vehicle types, since this suspension has properties that counteract bouncing and provide a better ride for driver and cargo. The air suspension includes two spring units per axle. Each spring unit comprises a spring bracket attached to the frame, from which one end of a leaf spring assembly is pivoted. The other end of the spring assembly carries one end of an air spring, whose other end is fixed to the frame.

On vehicles with tag axle bogies it is common to load the drive axle somewhat more than the tag axle. To achieve appropriate weight distribution on vehicles with air suspension, both the distance from the spring bracket to the air spring and the size of the air spring must be taken into account. A certain distance between these components, combined with a spring of a certain size, gives a unique weight distribution between the drive axle and the tag axle

The weight distribution between the axles is limited by legislation that stipulates the maximum weight permitted on the drive axle, tag axle and the whole of the bogie. However, regulations differ between countries The permissible drive axle weight therefore varies between 10 and 13 tonnes and that on the tag axle between 6 and 8 tonnes The permissible bogie weight varies between 16 and 21 tonnes, depending on legislatory regulations in individual countries.

Since different countries have different regulations, a vehicle manu¬ factured for one country often does not comply with the regulations in another, where permissible vehicle weights may not be the same. When optimizing vehicles for maximum capacity within the regulations in a country, this means that different air springs would have to be used and different distances be maintained between air spring and spring bracket, vehicle equipment otherwise being identical.

For manufacturers of vehicles sold in different markets a number of different air springs must be used, as well as different leaf spring assemblies adapted to the distance required between the air spring and the spring bracket. The manufacture of air springs and leaf spring assemblies therefore takes place in shorter production runs than would otherwise be possible, while a larger number of different items has to be kept in stock. As a consequence, the cost of air suspension components is comparatively high.

The present invention serves the purpose of eliminating the above- mentioned drawbacks. To this end, the invention is characterized in that a pressure-limiting device is installed in a pressure-conducting pipe be¬ tween the pressure source and the second pneumatic spring device, which pressure-limiting device is designed to close the pressure-conducting pipe when a predetermined pressure's reached in the pneumatic spring device, but which opens the pressure-conducting pipe when the predetermined pressure is undercut, and in which the pressure source, when the pressure exceeds the predetermined value, only has pressure-conducting connection with the first pneumatic spring device.

The invention in a simple and advantageous way solves the problems hitherto associated with the distribution of weight between the drive axle and tag axle in a tag axle bogie. The invention provides, for any load condition, automatic weight distribution between the axles by employing a compressed-air system already present on the vehicle.

Suitably arranged, the invention incorporates a control device in the pressure-limiting device, which enables the predetermined pressure to be varied. This allows the weight distribution to be easily adjusted for different markets, which in turn means that identical air spring and leaf spring assemblies can be used to provide vehicles with different distributions of drive axle and tag axle weights. The manufacture of vehicles optimally adapted for different markets is therefore enabled using identical components, whilst costs can be kept down.

Other characteristics of the invention emerge from the following patent claims and the description below of an embodyment exemplifying the invention. The description makes reference to the attached figures, of which:

Figure 1 shows a side view of the rear section of a truck chassis,

Figure 2 shows a schematic compressed-air diagram of an air suspension system, and

Figure 3 shows a pressure-limiting device intended for installation in an air suspension system.

Figure 1 shows the rear section of a truck chassis. The chassis comprises a frame 1, consisting of twin parallel longitudinal members 2 connected to each other via a number of crossmembers (not shown). The figure shows a side view of the chassis, therefore only one of the side members 2 is visible.

Underneath and across the frame 1 is a drive axle 3 with drive wheels 4 and a non-driven tag axle 5 with tag axle wheels 6.

Between each axle 3, 5 and the frame 1 , an air spring assembly 7 is installed at each frame side member 2. Although the figure only shows the air spring assembly 7 of the drive axle 3 and tag axle 4 at the side member 2 on one side, it is understood that the spring assemblies 7 at the other side member are identical to the ones described.

Each spring assembly 7 comprises a bracket 8 attached to the side member 2. From the lower end of this bracket, one end of a leaf spring assembly 9 is pivoted by means of a bushing 10. The other end of the leaf spring assembly 9 carries one end of a pneumatic spring device 11 , the other end of which is attached to the frame 1.

For the purposes of the remainder of this description, this pneumatic spring device 11 is referred to as an air spring.

Between the bushing 10 and the air spring 11, each axle 3, 5 is attached to the leaf spring assembly 9 using spring clamps 12. Both between the drive axle 3 and the frame 1 and the tag axle 5 and the frame 1, shock absorbers are installed to dampen oscillations of the frame 1 relative to the axles 3, 5. However, the shock absorbers are not represented in the figures.

The air springs 11 are filled with pressure medium, i.e. compressed air, via a compressed-air system 13, which is partly shown in figure 1 and, although schematically, in greater detail in figure 2. The compressed-air system 13 includes a pressure source 14, principally in the form of an accumulating tank, which is supplied with compressed air from a com¬ pressor 15 driven off the power unit of the vehicle, the latter not shown in the figure. The pressure source 14 is connected to a level valve 17 via a pressure pipe 16. The level valve 17 is attached to the frame 1 and connected to the drive axle 3 via an arm 18. The arm 18 pivots upwards and downwards, thus transmitting the movements up and down of the frame 1 relative to the drive axle 3 to the level valve 17. The level valve 17 is arranged to admit pressure via air pipes 19-21 to the air springs 1 1 in order to maintain the frame 1 at constant height relative to the drive axle 3, irrespective of load.

Three pressure-conducting pipes 20, 21, 22 are branched off pipe 19. Two of the pipes 20, 21 are each connected to one of the air springs 11 on the drive axle 3, whereas the third pipe 22 is branched into a pipe 23 connected to one air spring 11 on the tag axle 5 and one pipe 24 to the other air spring 11 on the tag axle 5.

A pressure-limiting device 25 in the form of a pressure reduction valve is installed in pipe 22. From figure 3 it can be seen that the valve 25 com- prises a housing 26 designed to incorporate an inlet port 27 and an outlet port 28. The inlet port 27 communicates with the air springs 1 1 at the driven axle 3 via pipe section 22' (fig.2), while the outlet port 28 communicates with the air springs 11 at the non-driven axle 5 via pipe section 22" (fig. 2). Valve 25 furthermore includes a valve element 29 arranged to slide in the valve housing 26, and which is pushed off a valve seat 30 by a spring 31. The tension of spring 31 is adjustable by means of a control device 32. Via a duct 34 the inlet port 27 is also connected to a cavity above a piston 33 integrated in the lower section of the valve element 29, the underside of piston 33 being subjected to atmospheric pressure and pressure from spring 31. The piston 33 is designed to slide in a cylinder bore in the housing 26, across a seal 35. The control device 32, which is set to a pressure in the pressure-conducting pipe 22 corresponding to the desired weight distribution, maintains the valve element 29 in an open position until the preset pressure is exceeded. In the following typical execution, control device 32 is set to close the pressure-conducting pipe 22 when a pressure of 5 bar is reached in pipe 22, which may correspond to a maximum weight of around 6.5 tonnes on the tag axle 5. It is an advantage if the control device 32 is adjustable for closing pressures of between 3 and 8 bar.

The invention has the following function. The function description is related to a tag axle bogie of a specific geometrical design. For a tag axle bogie of another geometrical design, other pressures than those mentioned in the description naturally apply. However, the principle incorporated in the invention can be applied to all bogies, independently of their geometrical design.

With a lightly loaded (e.g.4 tonnes) vehicle, for example a heavy truck, air at a pressure considerably lower than 5 bar is transmitted from the pres¬ sure source 14 via pipe 16 to level valve 17. The level valve 17 by means of the arm 18 senses the position of the frame 1 relative to the drive axle 3, admitting sufficient air pressure to maintain the frame 1 at a constant height relative to the drive axle 3. The pressure admitted is partly supplied via pipes 19, 20 and 21 to the air springs 11 of the drive axle 3, and partly via pipe section 22' to the inlet port 27 of the pressure-limiting device 25. As shown in figure 3, the air pressure continues via duct 34 inside the pressure-limiting device 25 to act against the top surface of the piston 33, which is subjected to spring pressure. Since the spring is set to close valve element 29 at a pressure of 5 bar, air pressure is insufficient to affect the open position of valve element 29, and for this reason air pressure is led on via valve seat 30 and valve element 29 through outlet port 28, pipe section 22" and pipes 23, 24 to the air springs 11 of the tag axle 5. The same air pressure is thus obtained in all air springs 11. The bogie weight of 4 tonnes is thereby distributed between the drive axle 3 and the tag axle 5 according to the geometrical design of the tag axle bogie, for example with 2.5 tonnes on the drive axle 3 and 1.5 tonnes on the tag axle 5.

If, on the other hand, the vehicle is heavily loaded -to a bogie weight of 18 tonnes, for instance - level valve 17 will instead admit a pressure of 6 bar on the vehicle exemplified above. As before, the pressure is supplied to the air springs 11 of the drive axle 3 and the inlet port 27 of the pressure-limiting device 25, past valve element 29, which during the initial phase of the pressurizing stage is maintained open by spring 30, and on through outlet port 28 to the air springs 11 of the tag axle 5. When pressure builds up in the air springs 11 of the drive axle 3 and tag axle 5 and ultimately exceeds the pressure of 5 bar preset with spring 31, the pressure induced on the top surface of piston 33 via duct 34 will overcome the force of spring 30. Piston 33 is then pushed down together with valve element 29, closing valve seat 30 and preventing further build-up of pressure in the air springs 11 of the tag axle 5. The pressure in the air springs 11 of the drive axle 3 continues to increase, however, until a pressure corresponding to the load has been reached. On the vehicle in the example, the bogie weight of 18 tonnes is thereby distributed with 12 tonnes on the drive axle 3 and only 6 tonnes on the tag axle 5.

When the vehicle is unloaded, the position of the frame 1 relative to the drive axle 3 is altered. The arm 18 of the level valve 17 senses the new position and vents the air springs 11 of the drive axle 3 to a pressure corresponding to the new load, i.e. the weight of the rear section of the vehicle. When the pressure in the air springs 11 of the drive axle 3 has dropped to a level below the closing pressure of pressure-limiting device 25, the pressure-conducting pipe 22 is opened, thus also allowing the air springs 11 of the tag axle 5 to be vented via level valve 17.

By setting the control device 32 on the pressure- limiting device 25 to provide different spring forces, weight distribution can be varied between the axles 3 and 5. Depending on the setting of control device 32, distribution in the example with a bogie weight of 18 tonnes can be adjusted to 11 tonnes on the drive axle 3 and 7 tonnes on the tag axle 5, or 13 tonnes on the drive axle 3 and 5 tonnes on the tag axle 5, etc.

Within the scope of the present invention, the tag axle bogie can be differently designed, e.g. using other spring designs and a tag axle that can be lifted and lowered automatically or manually, etc., without affecting the principle of the invention.

Claims

1. Arrangement for a vehicle bogie to distribute weight between a driven (3) and non-driven axle (5), which bogie includes at least one first pneumatic spring device (11) mounted between the frame (1) of the vehicle and the driven axle (3) and at least one second pneumatic spring device (11) mounted between the frame (1) and the non-driven axle (5), which pneumatic spring devices (11) are interconnected as well as connected to a pressure source (14) via pressure-conducting piping (16, 19- 24), characterized in that a pressure-limiting device (25) is installed in a pressure-conducting pipe (22) between the pressure source (14) and the second pneumatic spring device, which pressure-limiting device (25) is designed to close the pressure-conducting pipe (22) when a predetermined pressure is reached in the pneumatic spring devices (11), but which opens the pressure-conducting pipe (22) when the pre¬ determined pressure is undercut, and in which the pressure source (14) when the pressure exceeds the predetermined value only has a pressure- conducting connection with the first pneumatic spring device (11).

2. Arrangement according to claim 1, characterized in thatthe pressure- limiting device (25) incorporates a control device (32) which can be used to vary the predetermined pressure.

3. Arrangement according to claim 1 and 2 applied to a heavy vehicle characterized in thatthe predetermined pressure is between 3 and 8 bar, but preferably around 5 bar.

4. Arrangement according to claim 3 characterized in that a load-sensing level valve (17) is connected to the pressure source (14) to regulate the pressure admitted to the pressure-limiting device (25).

5. Arrangement according to claim 1 characterized in that both the first and second pneumatic spring devices (11) are mounted on leaf spring assemblies (9) in a familiar manner, but where the pneumatic spring devices are identical.