GB2171488A

GB2171488A - Hydro-pneumatic vehicle suspension

Info

Publication number: GB2171488A
Application number: GB08603744A
Authority: GB
Inventors: Rudolf Kopper
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1985-02-15
Filing date: 1986-02-14
Publication date: 1986-08-28
Also published as: FR2577481A1; JPH0571404B2; GB8603744D0; DE3505220C2; GB2171488B; JPS61188211A; FR2577481B1; DE3505220A1

Abstract

In a hydro-pneumatic vehicle suspension having a shock absorber (12) between the wheel axle (10) and the vehicle body (11), and a suspension component (13) which is connected to the shock absorber (12) and which comprises an oil chamber (19) connected to the oil column of the shock absorber (12) and a first gas chamber (20) containing the effective spring volume, there is provided a second gas chamber (21) for the purpose of independently regulating the spring constant in the suspension component (13), the gas chamber (21) being connected to the first gas chamber (20) by way of a restrictor (25) which only transmits quasistatic (very low frequency) pressure changes. A respective fluid volume (37, 38) enclosed in a bladder and isolated from the respective gas volume is disposed in each gas chamber (20, 21). The two fluid volumes (37, 38) are interconnected by way of a bidirectional feed device (34). By varying the fluid volume (37) in the first gas chamber (20), the effective spring volume in the gas chamber (20), and hence the spring characteristic of the vehicle suspension, is varied whilst keeping a constant gas pressure in the suspension component (13). A filling and discharge device (39) enables the gas pressure in the suspension component (13) to be changed. <IMAGE>

Description

SPECIFICATION Hydro-pneumatic vehicle suspension The invention reiates to a hydro-pneumatic vehicle suspension comprising a hydraulic piston and cylinder, a fluid chamber connected thereto via a retraction and a gas chamber separated from the fluid chamber by a membrane.

The spring constant or characteristic and the damping of hydro-pneumatic suspensions of this kind used in passenger motor vehicles are designed in such a way that they offer adequate travelling safety at the maximum velocity. However, at lower velocities, for example in town traffic, this design does not, in general, provide the high travelling comfort which ought to be possible at such reduced velocity.

The present invention resides in a hydropneumatic vehicle suspension having a shock absorber for interconnecting a vehicle wheel axle and the vehicle body, comprising a hydraulic cylinder and a hydraulic piston displaceable therein, a fluid chamber communicating with the hydraulic cylinder, a first gas chamber separated from the fluid chamber by a diaphragm, a second gas chamber connected to the first gas chamber by way of a restrictor which only transmits quasi-static pressure changes, a respective fluid volume disposed in each gas chamber and isolated from the respective gas volume therein, and a feed means interconnecting the two fluid volumes.

This has the advantage that its spring- and damping constant can be varied continuously and independently of one another during travelling operation. As a result, the first gas chamber, upon which the hydraulic cylinder acts by way of the diaphragm and the fluid chamber, forms the effective spring volume as previously, since, as a result of the very narrow throttle between the two gas chambers, dynamic pressure changes in the spring-mass system can only build up in the first gas chamber, and the second gas chamber does not participate in this. On the other hand, quasi-static operations, that is to say, changes taking place at a very low frequency, are transmitted to the second gas chamber. The hardness or characteristic or constant of the spring-mass system is determined by the pressure and the volume of the first gas chamber.The dynamically effective gas volume is changed by the change in the fluid volume in the first gas chamber by, for example, transferring by pumping into or from the fluid volume in the second gas chamber, the sum of the gas volumes in the two gas chambers, and hence the gas pressure, remaining constant as a result of the narrow restrictor. The spring constant varies inversely proportionally by varying the effective gas volume at a constant gas pressure, so that the spring constant may be adjusted very accurately by the transferring of fluid by pumping.

This pumping of quantities of fluid between the two fluid volumes may be considered to be a quasi-static operation, and the consequent quasi-static variation of of the effective spring volume may be performed during travel, for example when changing between various ranges of velocity of the vehicle. The adjustment of the spring constant may be performed by the driver who desires a sporty or soft characteristic of the chassis, or automatically in dependence upon various parameters, such as velocity, inclination or tilt of the vehicle, unevenness of the roadway and the like.

Preferably, one of the fluid volumes is connected to a fluid reservoir by way of a filling and discharge device. As a result, the gas pressure may be adapted upon a change in the vehicle mass (such as payload) and hence a desired constant level of the vehicle mass above the roadway can be achieved. This is achieved by simply discharging a quantity of fluid from the fluid volumes or by adding a quantity of fluid from a fluid reservoir. The level regulation makes it possible to maintain the natural frequency of the vehicle body constant under extreme differences in the payload.

Advantageously, the hydraulic cylinder and the fluid chamber are additionally interconnected by a regulable damping valve. The damping of the shock absorber can be readily adapted to a changed spring constant of the suspension by the regulable damping valve which is effective in both directions of flow.

The adjustment of the damping valve can also be performed in dependence upon optional parameters during travel, in the same manner as the adjustment of the spring constant. The double-acting, parallel first damping valve serves to maintain basic damping in the spring-mass system.

A non-return valve, opening towards the hydraulic cylinder can be connected in parallel with the damping valve or valves. Such nonreturn valve serves to ease the outward extension of the shock absorber when the wheel is relieved of load, and improves the ground adhesion when the contour of the roadway is extremely uneven.

The invention will be further described, by way of example, with reference to the accompanying drawing which is a diagrammatic illustration of a vehicle suspension in accordance with the invention.

The hydro-pneumatic vehicle suspension shown diagrammatically in the drawing comprises a shock absorber 12 which interconnects the axle of a vehicle wheel 10 and the vehicle body or chassis 11 (vehicle mass), and a suspension component 13. The shock absorber 12 comprises a hydraulic cylinder 14 which is rigidly connected to the vehicle body 11, and hydraulic piston 15 which is displa ceable in the cylinder 14 and which is connected to the axle of the vehicle wheel 10.

One end of the hydraulic piston 15 defines a pressure chamber 16 and its other end defines a relief chamber 18 which communicates with a return flow line 17.

The suspension component 13 comprises a fluid chamber 19, a first gas chamber 20 and a second gas chamber 21 which are enclosed in a common housing 22. The fluid chamber 19 and the first gas chamber 20 are separated by a diaphragm 23, whilst a rigid partition 24 is disposed between the two gas chambers 20, 21 and is provided with a restrictor 25. The restrictor 25 has a very pronounced throttling action, so that only quasistatic operations in the first gas chamber 20, that is to say, operations taking place at a very low frequency, are transmitted to the second gas chamber 21, and not dynamic operations such as pressure changes during action of the suspension system. The fluid chamber 19 is connected to the hydraulic cylinder 14, that is to say, to the pressure chamber 16, by way of three parallel lines 26 to 28.A double-acting damping valve 29 determining the basis damping of the vehicle suspension is provided in the first line 26. A regulable damping valve 30 is disposed in the second line 27 and may be adjusted either manually or automatically in dependence upon various parameters, such as the vehicle velocity, inclination of the vehicle, unevenness of the roadway and the like. A non-return valve 31 is provided in the third line 28 and closes in a direction away from the hydraulic cylinder 14 and towards the fluid chamber 19. The non-return valve 31 serves to ease the outward extension of the shock absorber 12 when the wheel is relieved of load.

A respective bladder type accumulator 32 or 33 is disposed in each gas chamber 20, 21 and each accumulator 32 and 33 is filled with a fluid volume 37 or 38 respectively. The two bladder type accumulators 32, 33 are interconnected by a bi-directional feed device 34.

The feed device 34 comprises a feed pump 35 having a reversible feed direction, and a reversible motor 36 which drives the feed pump 35. Quantities of fluid may be pumped into the bladder type accumulators 32, 33 by means of the feed device 34, so that the two volumes of fluid 37, 38 of the two bladder type accumulators 32, 33 may be optionaliy adjusted. A filling and discharge device 39, comprising a reversible feed pump 40 and a motor 41 for driving the feed pump 40, is connected between the bladder type accumulator 33 and a fluid reservoir 42.A non-return valve 43 prevents fluid from flowing out of the bladder type accumulators 32, 33 during pumping of the feed device 34, but enables fluid to be intrpduced into the bladder type accumulators 32, 33 from the fluid reservoir 42 and enables fluid to be discharged from the bladder type accumulators 32, 33 into the fluid reservoir 42. Preferably, oil is used as fluid in the hydro-pneumatic vehicle suspension.

The mode of operation of the hydro-pneumatic vehicle suspension described is as follows: The fluid column or oil column in the pressure chamber 16, in the lines 26 to 28 and in the fluid chamber 19, together with the mass of the vehicle body 11 and the gas volume in the first gas chamber 20 form a spring-mass system. The basic damping of this springmass system is determined by the double-acting damping valve 29. 3y virtue of the fact that the restrictor 25 between the two gas chambers 20, 21 only transmits quasi-static pressure changes, only the gas chamber 20 constitutes the effective spring volume.The spring hardness C or the spring constant of the active gas chamber 20, and hence the spring constant C of the vehicle suspension, is determined by F2.P, . C= V, in which F represents the effective surface area of the hydraulic piston 15, P, represents the gas pressure in the active gas chamber 20, V, represents the volume in the active gas chamber 20, and is a constant.

The gas volume V in the gas chamber may now be varied as required by pumping quantities of fluid from the bladder type accumulator 32 into the bladder type accumulator 33 and vice versa, the sum of the gas volumes in the two gas chambers 20, 21, and hence also the gas pressure P1, remaining constant. The spring hardness C is varied by varying the dynamically effective gas volume V,.

In the case of a variable vehicle mass, for example, a variation in loading, the gas pressure P1 must be adapted to the changed mass of the vehicle in order that the natural frequency of the vehicle body may be kept constant. This is achieved by means of the filling and discharge device 39 by filling or discharging fluid (when loading or unloading the vehicle) into or from the bladder type accumulators 32, 33.

The spring constant may be varied during travel. At the same time, damping can be adapted to the changed spring constant by means of the regulable damping valve 30 in the line 27. The two adjustments may be performed in dependence upon any desired parameters; for example by the driver who desires a sporty or soft chassis characteristic, or automatically by the velocity of the vehicle, the tilt of the vehicle, unevenness of the roadway and the like.

Claims

1. A hydro-pneumatic vehicle suspension having a shock absorber for interconnecting a vehicle wheel axle and the vehicle body, comprising a hydraulic cylinder and a hydraulic piston displaceable therein, a fluid chamber communicating with the hydraulic cylinder, a first gas chamber separated from the fluid chamber by a diaphragm, a second gas chamber connected to the first gas chamber by way of a restrictor which only transmits quasi-static pressure changes, a respective fluid volume disposed in each gas chamber, and isolated from the respective gas volume therein, and a feed means interconnecting the two fluid volumes.

2. A vehicle suspension as claimed in claim 1, in which the first and second gas chambers are integrated in a suspension component and are separated from one another by a rigid partition in which said restrictor is provided.

3. A vehicle suspension as claimed in claim 1 or 2, in which at least one of the fluid volumes is connected to a fluid reservoir by way of a filling and discharge device.

4. A vehicle suspension as claimed in any of claims 1 to 3, in which each volume is enclosed in a bladder type accumulator.

5. A vehicle suspension as claimed in any of claims 1 to 4, in which said fluid chamber and said hydraulic cylinder are interconnected by way of regulable damping valve connected in parallel with the first-mentioned damping valve.

6. A vehicle suspension as claimed in any of claims 1 to 5, in which said fluid chamber and said hydraulic cylinder are interconnected by way of a non-return valve which is connected in parallel with the damping valve and which closes in a direction away from the hydraulic cylunder and towards the fluid chamber.

7. A hydro-pneumatic vehicle suspension constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.