GB2155584A

GB2155584A - A hydropneumatic vehicle suspension with load-responsive damping

Info

Publication number: GB2155584A
Application number: GB08430444A
Authority: GB
Inventors: Hubert Beck; Heinz Knecht
Original assignee: Boge GmbH
Current assignee: ZF Boge GmbH
Priority date: 1984-02-20
Filing date: 1984-12-03
Publication date: 1985-09-25
Also published as: IT8519482A0; DE3406032A1; GB8430444D0; FR2559716B1; DE3406032C2; IT1183334B; GB2155584B; FR2559716A1

Abstract

A self-levelling hydropneumatic vehicle suspension is arranged to give an automatic increase in the damping of the vehicle on increase in the load and a reduction in the damping when the load on the vehicle is reduced. In addition to conventional damping valves (13, 16) a component has a bypass 14 of variable throttling cross-sectional area 23, 24. This component may be the damping piston 10 of the telescopic suspension strut, 5, or can be connected in the form of a separate component (Fig. 4) to the telescopic suspension strut 5. The fluid pressure in the system and external atmospheric pressure act on a control slide 20, axial displacement of which regulates the effective throttling cross-sectional area of the bypass. The displacement of the control slide 20 is in addition influenced by the spring force of the extension phase damping valve 16 which likewise assists in regulation of the damping in accordance with load. <IMAGE>

Description

SPECIFICATION A hydropneumatic vehicle suspension with height control The invention relates to a hydropneumatic suspension with height control for vehicles, especially motor vehicles, with at least two telescopic suspension struts arranged in the region of the vehicle wheels between the vehicle structure and the wheel axle, the telescopic supension struts being connected by a fluid pipe on the one hand to a pressure fluid pump and a control element for controlling the desired vehicle height and on the other hand to a pressure reservoir, and each spring strut cooperating with a throttling element which regulates a throttling cross-sectional area in accordance with the load on the vehicle.

Such devices for altering the damping force are known (e.g. DE-OS 31 410), in which damping fluid is fed into the strut by the pump through pipes so that the piston rod of the damper is extended by the pressure which builds up and accordingly the rear end of the vehicle is lifted. This device opens up the possibility of the vehicle achieving the desired height despite differences in its condition of loading. A drawback in this arrangement is that the control slide is relatively long and is connected ahead of the pressure reservoir in such a way- that a direct angled take off, as is often necessary because of limited space, is impossible. On the other hand in this design there is the danger that the diaphragm which also gives travel in this case could take up unstable shapes which have an adverse effect on the necessary accuracy of control.Furthermore the throttling cross-section is controlled only by the system pressure, which means that the damping is compression and in extension the control rod produces unwanted reaction forces on the dividing diaphragm in exerting the damping force.

Likewise spring struts are known with integrated load-dependent damping valves (e.g.

DE-PS 1 6 55 094) relating to a closed system.

This system influences the suspension of the vehicle by means of a spring-loaded valve slide. It does not influence the damping of the vehicle. A hydropneumatic suspension of this kind, corresponding to the loading of the vehicle, connects in a cascade manner two or more gas pressure reservoirs of different pressures one behind the other in order to obtain more favourable spring characteristics.

Taking this as its starting point it is the aim of the invention to construct a hydropneumatic suspension to as to provide a simple and reliable height control, achieving automatic raising of the degree of damping of the vehicle on an increase in the load and a reduction in the damping of the vehicle when the load on it is reduced, in order to improve the ride comfort.

To solve this problem it is provided according to the invention that the throttling element comprises a control slide which is axially slidable within the throttling element, that the throttling element has fluid passages of constant area, provided with valves, for the extension and compression phases of the damping, and that a first spring acts on one of the valves and on the control slide, one face of the control slide being exposed to the pressure of the fluid and the opposite face being exposed to atmospheric pressure.

Preferably, the first spring and a second spring both act on the control slide through a common element, and the second spring acts directiy or indirectly on a piston in which the fluid passages are formed.

According to a further important aspect it is provided that the control slide has an axially extending passage which forms at least part of a bypass of variable throttling cross-sectional area. The variable cross-sectional area may be formed by axially displaceable openings. Alternatively, the size of the variable throttling cross-sectional area may be controlled by a conical surface on the control slide.

In such a construction it is of advantage that the damping of the vehicle is regulated automatically by means of the throttling element, and in fact on an increase in the load, representing also an increase in pressure, the throttling cross-sectional area is reduced, and on reduction of the load the cross-sectional area is increased, without having to react to damping pressure influences. By virtue of the increase in damping on an increase in the load on the vehicle the large vehicle masses are more easily stabilised during travel so that a significant improvement in the ride behaviour is achieved. Furthermore excessive rolling movements of the vehicle structure are, for example, more rapidly damped out.

According to a further important feature it is provided that the throttling element is mounted in the working cylinder of the telescopic suspension strut and in the form of a damping piston it is connected to the piston rod, the bypass connecting together the upper and lower working chambers on opposite sides of the throttling element.

In this arrangement it is of advantage that a simple and favourable integration of the throttling element inside the telescopic suspension strut is achieved. A particularly compact unit can be obtained, taking up no significant constructional space in relation to the axial overall length of the assembly. For making further favourable use of the space available the geometry of the telescopic suspension strut and the piston rod are fully employed. According to an advantageous embodiment it is provided that the control slide is slidably received for axial movement in the hollow interior of the piston rod which is open to atmosphere.

A further important embodiment of the invention envisages that the throttling element should be connected in the fluid pipe as a separate component from the telescopic suspension strut. In this embodiment it is of advantage that the throttling element can be arranged as an independent component if desired between the telescopic suspension strut and the pipe. Such an arrangement also gives the advantage that when necessary the throttling element can be exchanged both more rapidly and cheaply, than would be the case with the whole of the telescopic spring strut.

Where a separate throttling element is used, which can simultaneously be used as the damping component, the telescopic suspension strut can immediately be simpiified in that, according to a further feature of the invention, it is provided that the piston of the telescopic suspension strut may either be provided with passages of constant area or with passages and damping valves or it may be of closed form. This gives the advantage that the telescopic suspension strut can be made of substantially smaller diameter as the damping piston or the piston rod only needs to take care of movement of oil within the system.

Some preferred embodiments by way of example are illustrated diagrammatically in the drawings, in which: Figure 1 is a diagrammatic iilustration of a full or part load-supporting hydropneumatic suspension with height control, Figure 2 shows a telescopic suspension strut in section with a piston which inciudes as usual extension and contraction valves and a load-dependent or pressure-dependent automatic control, Figure 3 shows a telescopic suspension strut in section with a guide piston, the regulation of the damping in accordance with load or pressure being achieved in the accompanying separate throttling element, Figure 4 shows the separate throttling element as an individual component in section, Figure 5 shows a telescopic suspension strut in principle like that of Fig. 3 but with additional valves on the piston of the strut, Figure 6 shows a telescopic suspension strut in section and in principle like that of Fig. 3 but with a guiding and displacement piston which is closed, i.e. provided with no passages, Figure 7 shows a telescopic suspension strut in principle like that of Fig. 2 but with the variable cross-sectional area of the bypass controlled by a conical surface, and Figure 8 shows a separate throttling element like that of Fig. 4 but with the varaible cross-sectional area of the bypass controlled by a conical surface.

The diagrammatic illustration in Fig. 1 shows a full or part-load-carrying hydropneumatic suspension with height control for vehicles and comprising substantially a pressure fluid pump 1, fluid pipes 2, a control element 3, a pressure reservoir 4 and telescopic suspension struts 5. The struts 5 comprise a housing 6, an upper working chamber 7 and a lower working chamber 8, and a piston rod 9 pivotally connected to a wheelguiding member (not shown); the housing 6 being connected to the vehicle structure. The upper working chamber 7 and the lower working chamber 8 are separated from one another by a damper piston 10 mounted on the piston rod 9. A reservoir 11 provides an adequate reserve of fluid pressure medium.

Fig. 2 shows a telescopic suspension strut 5 in which the upper working chamber 7 is separated from the lower chamber 8 by the damper piston 10. Basic damping takes place through passages 12, 1 5 in the damper piston and associated damping valves 13, 16. A control slide 20 of a throttling element is slidably received for axial movement in the hollow piston rod 9. The control slide 20 has an axial passage 14 which forms part of a bypass of variable throttling cross-sectional area. Damping dependent upon load is achieved by the effective throttling cross-sectional area between an opening 23 in the control slide 20 and an opening 24 in the piston rod 9. A connection 26 is provided for connecting the strut 5 to the fluid pressure pipe 2.

The bypass has a path for fluid flow from the upper working chamber 7 through the passage 14, the opening 23 in the control slide 20, the opening 24 in the piston rod 9 and into the lower working chamber 8. The effective throttling cross-sectional area is controlled by the pressure in the upper chamber 7 and by.atmospheric pressure which prevails in the interior 1 9 of the piston rod 9. The action of the atmospheric pressure on the control slide 20 is achieved an opening 27 which serves as a communication between the interior 1 9 of the piston rod 9 and atmosphere.

In operation, as the piston rod 9 moves inwards the fluid is forced from the upper chamber 7 through the passage 12, and against the action of the valve 13, into the lower chamber 8. At the same time fluid flows through the passage 1 4. When the piston rod 9 is extended fluid flows through the passage 1 5 against the opposition of the valve 1 6 and discharges into the upper chamber 7. The valve 1 6 is in the form of a leaf spring and is acted on through a disc 1 7 which is displaceable towards a stop and on which the force of a first spring 1 8 is exerted. At the same time the fluid again flows through the opening 14 in the extension phase. If the load on the vehicle is increased further, the pump 1 delivers a corresponding additional amount of fluid into the installation. The supply of fluid con tinues until the vehicle reaches the desired height. The necessarily higher pressure which arises as a consequence acts on the face of the control slide 20 which is sealed off from atmosphere so that the slide 20 takes up a corresponding position against the force of the first spring 1 8 and a second spring 21. This reduces the throttling cross-sectional area as the opening 23 is displaced axially relative to the opening 24 and simultaneously the spring 18 is subjected to a higher loading.

Increase in the damping is determined by the reduction in the cross-sectional area and the higher loading of the spring 18, whereby the damping in the extension phase is controlled not only by the reduction in crosssectional area of the throttling point but also by a corresponding variation in the compression of the spring 1 8.

On higher loading of the motor vehicle the throttle point between the opening 23 and the opening 24 therefore becomes completely closed so that the fluid can only flow through the openings 1 2 and 1 5 and the associated valves 1 3 and 16. The increased force applied by the spring 18 to the extension phase valve 1 6 makes this still harder for the flow to pass to'rough it. 7hue spring 21 is not absolutely essential but it can be used for varying the range of adjustment of the damping (tuning of the valve loading and maintaining constant openings).

In Fig. 3 there is illustrated a telescopic suspension strut 5 which is connected through the pipe 2 to a throttling element (Fig. 4) which is formed as a separate component 25. The strut 5 comprises a housing 6, a piston rod 9 and a damping piston 10. The piston 10 has passages of constant crosssectional area and divides the cylinder of the strut into an upper working chamber 7 and a lower working chamber 8. In the use of such a strut the damping is performed by the separate component 25 illustrated in Fig. 4.

Fig. 4 shows the throttling element as the separate component 25 which is integrated into the fluid pipe 2. A piston 29 of the throttling element 25 corresponds to the damping piston 10 illustrated in Fig. 2, both in its construction and also in its manner of operation. The throttling element has passages 12 and 15 and valves 16 and 13. The control slide 20 is provided with an axial passage 14, and an opening 23 in the slide 20 cooperates with an opening 24 to form a throttling cross-sectional area. On the one hand the control slide 20 has a first face 30 exposed to the fluid under pressure through a pipe 22 and on the other hand the opposite face 31 is exposed to atmospheric pressure in a cavity 32 in the throttling element which communicates with atmosphere through a bore 33.The end of the axial passage 1 4 which is opposite the throttling point communicates with the pipe 2 which leads to the strut through a connection 34 in the control slide so that the bypass is formed by the opening 24, the opening 23, the axial passage 14 and the connection 34.

Arranging the component 25 as a separate member brings the advantage that this component 25 can be rapidly and cheaply exchanged when necessary. The overall unit can for example also be used in the form of a cartridge with a screwed ring or quick connection, arranged so that on the replacement of such a cartridge the system pressure is automatically retained by a non-return valve and after installation of a new cartridge it automatically opens the non-return valve so that the flow is reestablished.

In Fig. 5 there is illustrated a telescopic suspension strut 5 which corresponds in principle to that of Fig. 3. For basic damping which may be required the system is simply provided with additional valves 35 and 36.

Apart from this, this embodiment corresponds in principle to the embodiment shown in Figs.

3 and 4 both in its construction and manner of operation. Such valves 35 and 36 are necessary with the employment of small piston rod diameters since in this case correspondingly less oil is forced through the component 25 so that, according to the use to which it is put, the damping piston 10 can be subjected to basic damping through the valves 35 and 36.

A further example of use in accordance with Fig. 3 is shown in Fig. 6. In this embodiment the telescopic suspension strut 5 is provided with a piston 10 and a piston rod 9 which divides the working cylinder into an upper cylinder 7 and a lower cylinder 8. Here the piston 10 is of closed form, in the form of a disc and is sealed by means of a seal 37. The lower working chamber 8 is empty and is vented to atmosphere through a venting hole 38. This embodiment is needed for the case where for example the spring strut 5 has to support a particularly large weight and accordingly needs to make use of the entire surface area of the piston. As the quantity of flow of the fluid is correspondingly large, one can do without any basic damping in the strut 5. The damping is then achieved solely in the separate component 25.

The telescopic spring strut illustrated in Fig.

7 is in principle like that already illustrated in Fig. 2, but with the difference that the bypass is not formed in the control slide 20 by a central bore but the control of the quantity of fluid is achieved by a conical surface 41 around which the fluid flows through the passage 40 into the lower chamber.

Fig. 8 shows a separate throttling element, in principle like that already illustrated in Fig.

4, except that like the embodiment of Fig. 7 the control of the fluid is obtained by means of a conical surface 41, and the passage 40 is introduced as a connection for achieving the bypass. The passage 40 may be formed as a groove or channel but also could be formed as a portion ground into the outer surface of the slide 20. The passage 41 thereby fulfills the same requirements as the central passage 14 such as is illustrated in Fig. 2 or also in Fig.

Claims

1. A hydropneumatic vehicle suspension with height control comprising at least two telescopic spring suspension struts arranged in the region of the vehicle wheels between the vehicle structure and the wheel axle, each telescopic suspension strut being connected by a fluid pipe on the one hand to a pressure fluid pump and a control element for controlling the desired vehicle height and on the other hand to a pressure reservoir, and each suspension strut cylinder cooperating with a throttling element which regulates a throttling cross-sectional area in accordance with the load on the vehicle, the throttling element comprising a control slide which is axially slid able within the throttling element, the throttling element having fluid passages of constant area, with valves, for damping on extension and compression, a first spring engaging one of the valves and acting on the control slide, one face of the control slide being exposed to the pressure of the fluid and the opposite face being exposed to atmospheric pressure.

2. A hydropneumatic vehicle suspension according to claim 1 in which the first spring and a second spring both act on the control slide'through a common element, the second spring acting directly or indirectly on a piston in which the fluid passages are formed.

3. A hydropneumatic vehicle suspension according to claim 1 or claim 2 in which the throttling element has a bypass of variable throttling cross-sectional area formed at least partly by an axially extending passage in or around the control slide.

4. A hydropneumatic vehicle suspension according to claim 3, in which axially displaceable openings form the variable throttling cross-sectional area of the bypass.

5. A hydropneumatic vehicle suspension according to claim 3, in which the size of the variable throttling cross-sectional area is controlled by a conical surface on the control slide.

6. A hydropneumatic vehicle suspension according to any of claims 3 to 5 in which the throttling element is mounted in the working cylinder of the telescopic suspension strut and is connected in the form of a damping piston to the piston rod, the bypass connecting together the upper working chamber and the lower working chamber on opposite sides of the throttling element.

7. A hydropneumatic vehicle suspension according to claim 6, in which the control slide is slidably received for axial movement in the interior of the piston rod which is open to atmosphere.

8. A hydropneumatic vehicle suspension according to any of claims 1 to 5, in which the throttling element is connected in the fluid pipe as a separate component from the telescopic suspension strut.

9. A hydropneumatic vehicle suspension according to claim 8, in which the damping piston of the telescopic suspension strut is provided with passages of constant cross-sectional area.

10. A hydropneumatic vehicle suspension according to claim 8, in which the damping piston of the telescopic spring strut is provided with passages and damping valves.

11. A hydropneumatic vehicle suspension according to claim 8, in which the piston of the telescopic spring strut is of closed form.

1 2. A hydropneumatic vehicle suspension with height control substantially as described herein with reference to and as illustrated by Figs. 1 and 2 of the accompanying drawings.

1 3. A hydropneumatic vehicle suspension with height control substantially as described herein with reference to and as illustrated by Figs. 1, 3 and 4 of the accompanying drawings.

14. A hydropneumatic vehicle suspension with height control according to claim 13, but incorporating the modification illustrated in Fig. 5 of the accompanying drawings.

1 5. A hydropneumatic vehicle suspension with height control according to claim 13, but incorporating the modification illustrated in Fig. 6 of the accompanying drawings.

1 6. A hydropneumatic vehicle suspension with height control according to claim 12, but incorporating the modification illustrated in Fig. 7 of the accompanying drawings.

1 7. A hydropneumatic vehicle suspension with height control according to claim 13, but incorporating the modification illustrated in Fig. 8 of the accompanying drawings.