GB2189004A

GB2189004A - Hydro-pneumatic spring suspension with load-dependent damping

Info

Publication number: GB2189004A
Application number: GB08707764A
Authority: GB
Inventors: Ludwig Axthammer
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1986-04-09
Filing date: 1987-04-01
Publication date: 1987-10-14
Anticipated expiration: 2007-04-01
Also published as: FR2597033B1; DE3612006A1; FR2597033A1; GB2189004B; GB8707764D0; DE3612006C2

Abstract

A hydro-pneumatic spring suspension with load-dependent damping for vehicles comprises a damping piston 4 axially movably held, between two initially stressed support springs 9, 10, in sealing manner on a cylindrical wall 15 of a housing. The springs 9, 10 are supported on opposite, mutually relatively movable stop discs 11, 12 in operative connection with a control piston 16, while valve springs 7, 8 acting on damping valves 5, 6 of the damping piston 4 likewise are supported on the stop discs 11, 12. The control piston 16 is subject to the action on the inner side of the pressure in the hydro- pneumatic spring suspension and on the outer side to atmospheric pressure and through the stop discs effects a pressure-dependent variation of initial stress of the valve springs 7, 8 acting upon the damping valves 5, 6, both for the traction direction and for the compression direction. The damping device can be located in a piston 20, as shown, or in a connection between a piston/cylinder unit and an accumulator (Figs. 3, 4). <IMAGE>

Description

SPECIFICATION Hydro-pneumatic spring suspension with load-dependently acting damping The invention relates to a hydro-pneumatic spring suspension with load-dependently acting damping according to the opening statement of Claim 1.

Such a hydro-pneumatic spring suspension is known for example from Fed. German Insp.

Doc. No. 3,406,032. For the load-dependent variation of the damping force of a damping valve a control piston is provided which is subject to the action for the one part of the internal pressure of the spring suspension and for the other part of atmospheric pressure, and thus varies the initial stress of a valve spring and enlarges or reduces a by-pass connected in parallel to a damping piston. With such a design it is merely possible to vary the initial stress of only one damping valve, while the adjusting of a passage cross-section bridging over the damping piston is quite problematical, since such a by-pass mostly has only a small passage cross-section which is to be adjusted over a large pressure range, for example between 30 and 90 bars, with sufficient accuracy.Accordingly a finely sensitive, pressure-dependent variation of damping force can be achieved only with a very high construction expense, if at all, with such an arrangement, since the components necessary for the by-pass cross-section control must be produced with maximum precision and adjusted extremely accurately.

It is the problem of the present invention to produce a load-dependently acting damping device for hydro-pneumatic spring suspension which is simple in assembly and renders possible a problem-free adaptation to required damping forces. The damping device should further render possible a finely sensitive, loaddependent damping for the traction and compression directions with simple assembly and without expensive adjustment work.

In accordance with the invention this problem is solved in that the damping piston is axially movable between at least two initially stressed support springs and is guided in sealing manner on a cylindrical wall of a housing, in that the support springs are supported on opposite, mutually relatively movable stop discs in operative connection with the control piston, in that the valve springs acting upon the damping valves of the damping piston are likewise supported on the stop discs or on parts in connection with the stop discs and in that the control piston and possibly a control rod firmly connected with the control piston pass centrally through at least one of the stop discs, the support springs, the valve springs and the damping piston.Here the damping piston is held in equilibrium by the support and valve springs, the initial stress of the springs being pressure-dependently varied by the control piston and the stop discs in operative connection therewith. Thus for the initial stress variation the support springs are connected in series, so that for equal support springs the spring rigidity is halved and accordingly an effective variation of initial stress of the valve springs too is achieved by the force exerted by the control piston. On the other hand a substantially higher force is necessary for the deflection of the damping piston out of its position of equilibrium, for the initially stressed support springs and the valve springs act in parallel connection, since on deflection of the damping piston the one spring is further initially stressed while the other spring is relaxed.With equal support springs the piston is thereby supported by the doubled spring force contrarily of the direction of displacement. Thus by simple components a damping device acting in load dependence in the traction and compression directions is produced which is simple in assembly and by appropriate dimensioning of the valve springs renders possible a problem-free adaptation to required damping force values.

In further development of the invention one stop disc lies against a support face arranged in the housing, while the other stop disc cooperates with a stop arranged on the end of the control rod and with a stop face fast with the housing. The assembly of the damping device and its fitting are thus substantially simplified.

According to one form of embodiment a stop disc is held in sealing manner in the housing and forms the guide and seal of the control piston. As additional function this stop disc constitutes the partition between pressure chamber in the interior of the housing and atmosphere.

A further simplification as regards fitting is obtained according to the invention in that the control piston, the control rod, the support springs, the valve springs, the stop discs and the damping piston provided with the damping valves form one construction unit.

There is great freedom in the arrangement of the load-dependently acting damping device in the spring suspension system, for in accordance with the invention the housing accommodating the contruction unit can be formed by a hollow piston rod or the damping device can be accommodated in a separate housing which is in communication through connection leads with the displacement cylinder and the spring accumulator. A combination with an additional damping device is also readily possible.

in further development of the invention the two support springs are made with equal spring rigidities. However it is readily possible to use support springs with different spring rigidities, if a desired damping force attunement requires this. In that case according to one feature the valve spring allocated to the damping valve can also have a damping force different from the valve spring of the traction valve. Thus is can readily be seen that this design renders extensive freedom possible concerning the adaptation to required damping force values.

A simple centring of the valve spring and an adaptation to a specific desired spring length can be obtained in a simple manner in that a centring sleeve supported on the stop disc and guided by the control rod is arranged for the valve spring.

As shown by a further feature of the invention the damping piston comprises a seal, formed by synthetic plastics material discs and arranged between the valve discs of the traction and compression damping valves, in relation to the piston rod. Thus a very simple seal is obtained between damping piston and control rod.

In order to achieve the object that even in the case of very high displacement forces acting upon the damping piston a slight axial displacement of the damping piston occurs and the support springs act in parallel arrangement, it is provided in accordance with the invention that the support springs have an initial stress force which is greater than the force acting upon the damping piston as a result of pressure difference.

The invention will be explained in greater detail below by reference to the forms of embodiment as represented in the drawing, wherein: Figure 1 shows a longitudinal section through the hydro-pneumatic spring suspension according to the invention in diagrammatic representation; Figure 2 shows a form of embodiment in which the guide piston connected with the piston rod is additionally provided with damping devices; Figure 3 shows a form of embodiment of the load-dependently acting damping device which is arranged in a separate housing and is in communication through appropriate connections with the displacement cylinder and the spring accumulator; Figure 4 shows a further form of embodiment for the load-dependently acting damping device.

The hydro-pneumatic spring suspension according to Fig. 1 consists of a displacement cylinder 1, the interior of which is filled with hydraulic medium and is connected in fluidconducting manner with a spring accumulator 2. In the spring accumulator 2 the hydraulic medium is separated by an elastic partition from a gas cushion under pressure. The displacement cylinder 1 is for example connected with a wheel axle (not shown) and a piston rod 13 is connected with a vehicle body (likewise not shown). For adjustment to a predetermined level position in dependence upon vehicle loading for example the spring accumu lator 2 is connected with an ordinary level regulating device (not shown) which-as generally known-brings the vehicle body to the desired level position on variation of the vehicle loading, by supply or discharge of hydraulic medium.For such a hydro-pneumatic spring suspension the damping of the vertical wheel movement in relation to the vehicle body is to be varied in pressure dependence, that is to say in the case of addition to the loading and thus increased pressure of the hydraulic medium the damping should be increased and on unloading and correspondingly decreasing pressure the damping is to be reduced. For this purpose in the cavity of the piston rod 13 a load-dependently acting damping device 3 is provided which comprises a damping piston 4, the compression valve 5 of which is loaded by the valve spring 7 and the traction valve 6 of which is loaded by a valve spring 8. A support spring 9 acts on one side and a support spring 10 on the other side upon the damping piston 4, the support spring 9 being supported on the stop disc 11 and the support spring 10 on a stop disc 12.The stop disc 11 separates the hydraulic-medium-filled interior space of the displacement cylinder 1 from the cavity of the piston rod 13, which is connected through a bore with atmosphere. At the same time this stop disc 11 serves for the guidance and sealing of a control piston 16 which is firmly connected with a control rod 17 which carries at its lower end a stop 18 for the stop disc 12.

For the limitation of the axial movement of the stop disc 12 a stop face 19 is provided in the piston rod 13, which carries a guide piston 20. A centring sleeve 27 is provided for the centring of the valve spring 8 and its supporting on the stop disc 12. The lower working chamber, separated by the piston 20 and the damping piston 4, is in communication, through a bore in the piston rod 13, with an annular working chamber between the inner wall of the displacement cylinder 1 and the outer surface of the piston rod 13.

A higher loading of the vehicle effects a rise of the pressure of the hydraulic medium in the displacement cylinder 1. This pressure acts upon the control piston 16 which transmits a force, corresponding to the pressure multiplied by the cross-sectional area through the control rod 17 and the stop 18 to the stop disc 12, since the other side of the control piston is loaded with the atmospheric pressure. The support springs 9 and 10 and the valve springs 7 and 8 are initially stressed by this force exerted by the control piston 16. In the initial stressing of the springs these act as series-connected, so that the displacement force exerted by the control piston 16 results in a good adaptation for the load-dependently acting damping of the traction and compression stages.By reason of the movement of the piston rod 13 in relation to the displacement cylinder 1 a pressure difference occurs between the working chambers filled with pressure medium and separated by the piston 4. As a result of this pressure difference the piston 4, hitherto held in equilibrium by the springs, is shifted axially, and an increase of initial stress of the spring system arranged on the one piston side effects a reduction of initial stress on the other piston side. Correspondingly on displacement of the piston 4 the support springs 9 and 10 and the valve springs 7 and 8 act as connected in parallel, so that even higher forces acting upon the piston result in only a slight longitudinal movement of the damping piston.

For the adaptation of the load-dependent damping to pre-determined damping values the springs can readily be made accordingly, and in each case the basis is to be adopted that the support springs 9 and 10 serve essentially for the production of the position of equilibrium of the piston while the valve springs 7 and 8, of weaker formation, serve for the variation of the application pressures for the valve discs of the compression damping valve 5 and the traction damping valve 6 respectively.

The form of embodiment according to Fig.

2 differs from that according to Fig. 1 essentially in that the guide piston 20 connected with the piston rod 13 is provided with additional damping devices. These damping devices of the guide piston 20 are connected in parallel with the load-dependently acting damping device 3. In place of such a parallel arrangement a series arrangement can also readily be provided.

A further form of embodiment of the loaddependently acting damping is shown in Fig.

3. In a housing 21 arranged separately from or directly connected with a displacement cylinder the load-dependently acting damping device 3 is arranged in this case. By way of example the displacement cylinder is connected through a connection piece 22 and the spring accumulator is connected through a connection piece 23. Hydraulic medium is expelled or drawn in, in the displacement cylinder, by movement of the vehicle wheels in relation to the vehicle body, and flows through the load-dependently acting damping device 3 to the spring accumulator 2 or is returned from the spring accumulator 2. In this form of embodiment again the load-dependently acting damping device 3 consists of the damping piston 4 which carries damping valves formed from valve discs, namely the compression damping valve 5 and the traction damping valve 6.The construction unit formed from the control piston 16, the control rod 17, the stop discs 11 and 12, the support springs 9 and 10, the valve springs 7 and 8 with the centring sleeves 27, the piston 4 with the damping valves 5 and 6, can be fitted separately and is then introduced from above into the housing 21, then the screw ring formed as spring accumulator connection is screwed in. The control piston 16 here passes through the control piston guide 26, which is mounted in sealing manner in the housing 21 and carries the dynamic seal for the control piston 16.Synthetic plastics material discs 24 and 25 are arranged, for the sealing of the damping piston 4 in relation to the control rod 17, between the valve plates which form the compression damping valve 5 and the traction damping valve 6, while the valve springs 7 and 8 acting upon the damping valves 5 and 6 rest on centring sleeves 27 and these are supported on the stop discs 11 and 12. The manner of operation of this load-dependently acting damping device corresponds to that according to Fig. 1.

Fig. 4 shows a further load-dependently acting damping device 3 of simplified assembly, including the control piston guide 26 in the construction unit. The stop disc 11 on which the support spring 10 is supported is of potshaped formation and for the one part forms a part of the sealing groove for the seal cooperating with the control piston 16. For the other part the valve spring 8, which is guided by the control rod 17, lies on the bottom part. The fitting of the load-dependently acting damping device 3 becomes especially simple here, since all the parts situated in the housing 21 can be assembled outside and fitted by introduction from beneath and subsequent screwing on of the control piston guide 26. In manner of operation this load-dependently acting damping device too corresponds to that according to Fig. 1.

Claims

1. Hydro-pneumatic spring suspension with load-dependently acting damping and preferably with level regulation for vehicles, in which hydraulic-medium-filled displacement cylinders are arranged between a vehicle body and the vehicle wheels, which cylinders are in operative connection with a spring accumulator and a load-dependent damping device, in which further the damping device comprises a damping piston with spring-loaded damping valves for traction damping and compression damping, and in which a control piston which varies the initial stress of valve springs of the damping valves in dependence upon pressure is subject to the action for the one part of the hydraulic medium and for the other part of atmospheric pressure, characterised in that the damping piston (4) is axially movable between at leastftwo initially stressed support springs (9, 10) and is guided in sealing manner on a cylindrical wall of a housing (15, 21), in that the support springs (9, 10) are supported on opposite, mutually relatively movable stop discs (11, 12) in operative connection with the control piston (16), in that the valve springs (7, 8) acting upon the damping valves (5, 6) of the damping piston (4) are likewise supported on the stop discs (11, 12) or on parts (centring sleeves 27) connected with the stop discs (11, 12) and in that the control piston (16) and possibly a control rod (17) connected fast with the control piston (16) pass centrally through at least one of the stop discs (11, 12), the support springs (9, 10), the valve springs (7, 8) and the damping piston (4).

2. Hydro-pneumatic spring suspension according to Claim 1, characterised in that one stop disc (11) rests on a support face (14) arranged in the housing (15, 21), while the other stop disc (12) co-operates with a stop (18) arranged on the end of the control rod (17) and with a stop face (19) fast with the housing.

3. Hydro-pneumatic spring suspension according to Claim 1 or 2, characterised in that one stop disc (11) is held in sealing manner in the housing (15, 21) and forms a guide and seal of the control piston (16).

4. Hydro-pneumatic spring suspension according to one of Claims 1 to 3, characterised in that the control piston (16), the control rod (17), the support springs (9, 10), the valve springs (7, 8), the stop discs (11, 12) and the damping piston (4), provided with the damping valves (5, 6), form one construction unit.

5. Hydro-pneumatic spring suspension according to one of Claims 1-4, characterised in that the damping device (3) is accommodated in a hollow piston rod (13) of a displacement cylinder (1).

6. Hydro-pneumatic spring suspension according to one of Claims 1 to 5, characterised in that the two support springs (9, 10) are made with equal spring rigidities.

7. Hydro-pneumatic spring suspension according to one of Claims 1 to 6, characterised in that a piston rod (13) of the displacement cylinder (1) carries a guide piston (20) provided with additional damping devices.

8. Hydro-pneumatic spring suspension according to one of Claims 1 to 7, characterised in that the valve spring (7) allocated to the compression valve (5) has a spring force different from that of the valve spring (8) of the traction valve (6).

9. Hydro-pneumatic spring suspension according to one of Claims 1 to 8, characterised in that a centring sleeve (27) supported on a pertinent stop disc (11, 12) and guided by the control rod (17) is provided for the centring of at least one valve spring (7, 8).

10. Hydro-pneumatic spring suspension according to one of Claims 1 to 9, characterised in that the damping piston (4) comprises a seal against the control rod, which seal is formed by synthetic plastics material discs and arranged between the valve discs of the traction and compression damping valves (5, 6).

11. Hydro-pneumatic spring suspension according to one of Claims 1 to 10, characterised in that the support springs (9, 10) have an initial stress force which is greater than the force acting upon the damping piston (4) as a result of pressure difference.

12. Hydro-pneumatic spring suspension as claimed in Claim 1, substantially as described with reference to any one of the Figs. 1-4 of the accompanying drawings.