GB2161892A

GB2161892A - A hydropneumatic vehicle suspension system with height control

Info

Publication number: GB2161892A
Application number: GB08513735A
Authority: GB
Inventors: Hubert Beck
Original assignee: Boge GmbH
Current assignee: ZF Boge GmbH
Priority date: 1984-06-01
Filing date: 1985-05-31
Publication date: 1986-01-22
Also published as: GB2161892B; IT8520820A0; IT1183643B; FR2565170A1; IT8521888V0; GB8513735D0

Abstract

In a hydropneumatic vehicle suspension system with height control a telescopic spring cylinder (5) is connected to a fluid pressure medium pump and a control element for controlling the vehicle height and to a pressure reservoir. In addition an extension phase damping valve (16) in a damping piston (10) is acted on by a gas cushion (24) arranged in a closed chamber. In this way the degree of damping in the extension phase automatically increases with the vehicle load. In other embodiments (Figs. 3-6), the gas cushion (24) comprises a tubular body mounted within the piston rod. <IMAGE>

Description

SPECIFICATION A hydropneumatic vehicle suspension system with height control This invention relates to a hydropneumatic suspension system with height control for a vehicle, in particular for a motor vehicle, which comprises at least two telescopic spring cylinders arranged in the region of the vehicle wheels between the vehicle structure and the axle, the cylinders being connected to a fluid pressure pump and a control element for controlling the height of the vehicle and to a reservoir for fluid pressure medium, and each cylinder containing a damping piston.

An arrangement for varying the damping force in such a system is known (e.g. DE OS 31 11 410) in which damping fluid is fed into the cylinder by the fluid pressure pump so that the piston rod of the damper is extended by the pressure that builds up and accordingly the rear end of the vehicle is raised. In this arrangement the vehicle can achieve the desired height despite different conditions of load. However, when such an arrangement includes a diaphragm which can give way, the diaphragm can take up unstable shapes and adversely affect the control and steering of the vehicle.Another version with a dividing piston does overcome the instability, but this version has the drawback that the slide of the control element has to be made relatively long and often cannot be connected above the pressure reservoir in such a way that a direct angled take-off is possible, for reasons of available space. Moreover in both these constructions there is the danger that the escape of gas over long periods can result in the control slide changing its set position, and this has the consequence of an unwanted variation in the damping.

Furthermore closed suspension systems including spring cylinders with integrated damping valves, working in accordance with load, are known. In one such system (DE PS 1 6 55 094) the springing of the vehicle is influenced through a spring-loaded valve slide, but the damping of the vehicle is not affected in this version. A hydropneumatic suspension system of this form switches in two or more gas pressure reservoirs at different pressures in a cascade fashion in accordance with the load on the vehicle in order to achieve more favourable spring characteristics.

An aim of the present invention is to provide a hydropneumatic suspension system with a simple and reliable form of height control that leads to an improvement in the ride comfort, automatic raising of the degree of damping of the vehicle on increase in the load and a reduction in the damping of the vehicle when the load on the vehicle is reduced.

According to the present invention there is provided a hydropneumatic vehicle suspension system with height control comprising at least two telescopic spring cylinders for arrangement in the region of the vehicle wheels between the vehicle structure and the axle, the cylinders being connected to a fluid pressure pump and a control element for controlling the height of the vehicle and to a reservoir for fluid pressure medium, each cylinder containing a damping piston which has constant openings for the through passage of the fluid pressure medium, damping valves, each associated with one of the openings, for damping in the extension phase and in the contraction phase respectively, and a gas cushion contained within a closed chamber which acts on the extension phase damping valve.

An advantage of the suspension system in accordance with the present invention is that it enables the fluid pressure medium to be introduced into the cylinder through the piston rod which may be secured to the vehicle structure.

The present invention enables the damping of the vehicle in the extension phase to be controlled automatically by means of the damping piston and, on an increase in the load and also an increase in the pressure the extension damping valve is given a higher degree of pre-loading, and on a reduction in the load the pre-loading of the extension phase damping valve is reduced.- By increasing the damping in accordance with an increase in the load of the vehicle, the large vehicle masses are taken into account during travel so that a substantial improvement in the quality of the ride is obtained. Furthermore, for example, excessive oscillations of the vehicle structure are more rapidly damped out.

The closed chamber containing the gas cushion may be formed by a metal diaphragm bellows. The diaphragm bellows may be arranged in the neighbourhood of the end of the piston rod so that the prevailing system pressure acts on the quantity of gas trapped in the bellows which acts either directly or indirectly on the extension phase damping valve to ease or hinder the flow of oil through the valve. The diaphragm bellow preferably has the characteristic of a stack of plate springs.

Alternatively, the closed chamber of the gas cushion may be contained within a hollow piston rod, and the gas cushion is sealed off from the interior of the piston rod and acts on the extension phase damping valve through an axially movable slide. In this arrangement the integration of the gas cushion within the piston rod ensures that the space available is fully employed.

Preferably, the closed chamber is formed by a tubular body in the interior of the hollow piston rod. In this way the interior of the piston rod is indeed fully employed, but only insofar as the closed chamber for containing the gas cushion is formed in the tubular body, the remaining spaced in the interior of the piston rod still being available for supply of the fluid pressure medium from the pump and the reservoir. The dimensions of the tube for receiving the gas cushion can be made variable, and generally they depend upon the geometry of the piston rod and/or the pressure at which the gas is to be introduced into the close chamber.

The gas cushion may act indirectly on the extension phase damping valve through an intermediate component or components. The extension phase damping valve may be engaged by such an intermediate component.

For example, the gas cushion may act on the extension phase damping valve through a potshaped component which substantially surrounds the end portion of the piston rod. In such an arrangement with at least one intermediate component the extension phase damping valve and the gas cushion either can be arranged axially one behind the other or indeed can be arranged parallel to one another.

For ease of manufacture and assembly, the diaphragm bellows or the slide of the gas cushion may be rigidly connected to the potshaped component.

Instead of being rigidly connected to a potshaped component which engages the extension phase damping valve, the slide may act on the extension phase damping valve through at least one spring. This has the advantage that the damping is influenced not only be the gas cushion but also by the spring or springs. Furthermore, the damping may also be influenced by another factor if a spring acts between an abutment within the closed chamber and the slide. The provision of such a further spring therefore increases the number of possible variations for influencing damping in the extension phase of such a suspension system.

Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic illustration of a hydropneumatic vehicle suspension system with height control; Figure 2 is a longitudinal section through part of a spring cylinder of a suspension system in accordance with the invention, the cylinder including a piston rod, a damping piston and a gas cushion; Figure 3 is a longitudinal section through an alternative embodiment of the piston rod which has an integrated gas cushion; Figure 4 is a longitudinal section similar to Fig. 3 of a modified piston rod; Figure 5 is a longitudinal section through another modified piston rod similar to that of Fig. 4; and Figure 6 is a longitudinal section through yet another modified piston rod.

The hydropneumatic vehicle suspension system with height control shown in Fig. 1 comprises substantially a fluid pressure medium pump 1, fluid pipes 2, a control element 3, reservoirs 4 containing fluid pressure medium and telescopic spring cylinders 5. Each cylinder 5 comprises a housing 6, an upper working chamber 7 and a lower working chamber 8, and a hollow piston rod 9 for connection to the vehicle structure. The housing 6 is connected to a wheel suspension component, not shown. The upper working chamber 7 and the lower working chamber 8 are separated from one another by a damping piston 10 secured to the piston rod 9. A reservoir 11 serves to provide a sufficient reserve of fluid pressure medium. The medium is fed in through the fluid pipes 2 into the piston rod 9 and from there into the upper and lower working chambers 7 and 8.

In Fig. 2 there is illustrated part of one of the telescopic spring cylinders 5 in which the upper working chamber 7 is separated from the lower working chamber 8 by the damping piston 10. Damping is achieved by means of openings 1 2, 1 5 in the piston 10 and associated damping valves 13, 16. The extension phase damping valve 1 6 is a leaf spring in this embodiment. The supply of fluid pressure medium from the pump 1 and from the pressure reservoir through the pipe 2 takes place through a bore 14 in the upper part of the hollow piston rod 9. From the hollow interior 25 of the piston rod 9 the fluid flows into the lower chamber 8 through recesses 26 in the lower part of the piston rod 9 and through bores 27 provided in a pot-shaped component 21 which substantially surrounds the lower end portion of the piston rod 9.

At the lower end of the piston rod 9 there is a closed chamber 17, sealed off from the interior of the piston rod by a seal 28. The closed chamber 1 7 is made in the form of a diaphragm bellows 1 8 and contains a gas cushion 24. The gas of the gas cushion 24 may, for instance, be nitrogen and may be at substantially atmospheric pressure or at a higher pressure. The gas cushion 24 inside the diaphragm bellows 1 8 exerts an axial force on the extension phase valve 1 6 through the pot-shaped component 21, so that the valve 1 6 is more or less strongly preloaded. In this way the damping force in the extension phase is automatically regulated in accordance with load.

Fig. 3 shows an alternative piston rod in which a tubular body 20 is mounted within the hollow interior of the piston rod 9. The hollow piston rod again provides a path for supplying the damping fluid medium to the cylinder through the bore 14 and through an annular passage 29 surrounding the tubular body 20, the body 20 being hermetically sealed off at its upper end portion by a closure plug 30 and having in the region of the damping piston an axially displaceable slide 1 9. In this embodiment the gas cushion 24 is formed within the closed chamber of the tubular body 20.The slide 1 9 is displaced axially to a greater or lesser extent according to the internal pressure of the gas cushion 24 so that a pre-load is applied to the extension phase damping valve 1 6 through a potshaped component 21 similar to that of Fig.

2. Both the closure plug 30 and also the slide 19 are provided with seals 31 and 32. The slide 1 9 is rigidly connected to the pot-shaped component 21 by a retaining disc 33. The damping fluid which reaches the annular passage 29 through the bore 14 can pass through the recesses 26 provided in the piston rod and the bore 27 in the pot-shaped component 21 and into the lower working chamber 8.

Fig. 4 shows a modified piston rod 9 similar to that of Fig. 3 but in which the potshaped component 21 is replaced by a compression spring 22. The gas cushion 24 acts on the slide 1 9 which, in turn, acts on the compression spring 22 through a plate 34.

The spring 22 acts on the valve 1 6 and an additional valve-limiting plate 35 limits the movement of the valve 1 6 in an axial direction. Also, in this embodiment the fluid pressure medium is fed through the bore 14 and the annular passage 29 and the openings 26 into the lower working chamber.

Fig. 5 shows another modified piston rod 9 similar to that of Fig. 4, but in which the slide 1 9 acts on the extension phase damping valve through an additional spring 23. The additional spring provides a further means for varying the damping in the extension phase.

By the use of springs with different characteristics the behaviour of the valve 1 6 can be modified as desired.

Fig. 6 shows a further modified piston rod in which a compression spring 22 is supported in the interior 25 of the piston rod 9 and acts between an abutment or a stop 36 and the slide. The spring 22 corresponds to the spring in Fig. 4 and also acts on the valve 1 6 in the same direction, through the potshaped component 21.

Claims

1. A hydropneumatic vehicle suspension system with height control comprising at least two telescopic spring cylinders for arrangement in the region of the vehicle wheels between the vehicle structure and the axle, the cylinders being connected to a fluid pressure pump and a control element for controlling the height of the vehicle and to a reservoir for fluid pressure medium, each cylinder containing a damping piston which has constant openings for the through passage of the fluid pressure medium, damping valves, each associated with one of the openings, for damping in the extension phase and in the contraction phase respectively, and a gas cushion contained within a closed chamber which acts on the extension phase damping valve.

2. A suspension system according to claim 1, in which the closed chamber is formed by a metal diaphragm bellows.

3. A suspension system according to claim 1, in which the closed chamber is contained within a hollow piston rod of the damping piston, and the gas cushion is sealed off from the interior of the piston rod and act on the extension phase damping valve through an axially movable slide.

4. A suspension system according to claim 3 in which the closed chamber is formed by a tubular body within the piston rod.

5. A suspension system according to any of the preceding claims in which the gas cushion acts on the extension phase damping valve through a pot-shaped component which substantially surrounds an end portion of the piston rod.

6. A suspension system according to claim 5, as appended to claim 2, in which the diaphragm bellows is rigidly connected to the pot-shaped component.

7. A suspension system according to claim 5, as appended to claim 3 or claim 4, in which the slide is rigidly connected to the potshaped component.

8. A suspension system according to claim 3 or claim 4, in which the slide acts on the extension phase damping valve through at least one spring.

9. A suspension system according to claim 3 or claim 4, or to claim 5 as appended to claim 3 or claim 4, in which a spring acts between an abutment within the closed chamber and the slide.

1 0. A hydropneumatic vehicle suspension system with height control substantially as described herein with reference to Fig. 1 and including a piston rod substantially as described herein and as illustrated by Fig. 2 of the accompanying drawings.

11. A suspension system according to claim 10 but which includes a modified piston rod substantially as described herein with reference to and as illustrated by Fig. 3 of the accompanying drawings.

1 2. A suspension system according to claim 10 but which includes a modified piston rod substantially as described herein with reference to and as illustrated by Fig. 4 of the accompanying drawings.

1 3. A suspension system according to claim 10 but which includes a modified piston rod substantially as described herein with reference to and as illustrated by Fig. 5 of the accompanying drawings.

14. A suspension system according to claim 10 but which includes a modified piston rod substantially as described herein with reference to and as illustrated by Fig. 6 of the accompanying drawings.