GB2191263A

GB2191263A - Hydraulic oscillation damper for vehicles

Info

Publication number: GB2191263A
Application number: GB08712509A
Authority: GB
Inventors: Felix Wossner
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1986-06-03
Filing date: 1987-05-28
Publication date: 1987-12-09
Also published as: FR2599449A1; GB8712509D0; DE3618654A1; GB2191263B; FR2599449B1; DE3618654C2

Abstract

A variable damping force device of simple construction is provided by an external damping valve unit 18 connected in parallel with the damping valves 5,6 of an oscillation damper 1. The connection of the damping valve unit 18 to the oscillation damper 1 is effected via the piston rod 3. In this respect, there is disposed in a bore in the piston rod a central tube 13 which communicates with a working space 11 in the oscillation damper while an annular space 16 bounded by the central tube and the piston rod bore is connected to the other working space 10. The two passages 13,16 disposed in the piston rod are connected across the external damping valve unit 18, which has an adjustable throttle. <IMAGE>

Description

SPECIFICATION Hydraulic oscillation damper for vehicles The invention relates to a hydraulic oscillation damper for vehicles in accordance with the preamble to Claim 1.

In the case of a hydropneumatic suspension system with an automatic level adjustment and oscillation damping facility, it is known from DE-OS 1 680 680 to provide two separate passages in the piston rod. One passage is constituted by a tube located in the piston rod bore while the second passage is created by the space which forms between the tube and the piston rod bore. Both passages discharge into a working space remote from the piston rod and which is defined by a piston supporting the damping valves and connected to the piston rod. The annular space in the piston rod is in this case connected to a spring space, while the second passage, formed by the tube, communicates with a pressurised storage space through pump valves with the working space remote from the piston rod.This prior are construction cannot provide any indication of the use of these passages which are disposed in the piston rod for the connection of a damping valve.

The object of the present invention is to provide a hydraulic oscillation damper which, to vary the damping force, can easily be connected to a damping valve unit disposed outside of the oscillation damper and which permits of a functionally reliable and problem-free assembly in the vehicle.

According to the invention, this probiem is resolved in that the central tube communicates with one of the working spaces while the annular space communicates with the other working space, while at the piston rod end, the central tube is connected on the one hand and the annular space on the other to an external damping valve unit which acts parallel with the damping valves of the piston. The possibility of connecting the external damping valve unit at the piston rod end makes for a very simple construction of the oscillating damper into the vehicle, because connection to the external damping valve unit becomes very simple and can be fitted extremely easily.

Although the two working spaces are connected in fluid-conductive manner to the external damping valve unit, there is no relative movement between the connections on the oscillating damper since they do not have to compensate for any travel motion and are protected from mechanical damage by being disposed at the piston rod end.

A very advantageous embodiment is, according to one feature of the invention, obtained in that the central tube is connected in fluid-conductive fashion to the working space which is remote from the piston rod and the annular space is connected through a throughflow cross-section to the working space at the piston rod end. Substantial freedom of movement for the external damping valve unit is guaranteed so that it can easily be adapted to whatever needs prevail. Thus, it is readily possible affording to the invention for the external damping valve unit to comprise an adjusting device for varying the damping force. According to the invention, the adjusting device can be controlled as a function of various variables such as speed, crossacceleration, deceleration of the vehicle.Variation of the damping force is thus variable via the individual measured values at the vehicle or a combination thereof without any changes being needed to the component unit incorporated between the vehicle' superstructure and the axle. Accordingly, in terms of location and size of the damper valve unit, no great demands are imposed because according to the invention these can be connected to the piston rod end by connecting lines and can thus be disposed at any suitable location in the vehicle.

According to a further embodiment of the invention, the oscillation damper is constructed as a single-tube oscillation damper and is provided with a separate pressure storage means acting as a compensating space and connected to a connecting line. As the invention shows, the pressure storage means is connected to the working space remote from the piston rod, but there is no constriction in the connections so that a perfect damping action with no interference to the damping force is possible in both directions of piston rod movement.

For the durability of the piston rod journal, on which the piston is mounted, it is particularly advantageous if, according to the invention, the central tube is guided and sealed in a shoulder formed by the inner space in the piston rod and is connected in fluid-conductive manner to the working space remote from the piston rod by an axial bore traversing the piston rod journal. The throughflow cross-section for connecting the working space on the piston rod side to the annular space is, according to the invention, easily provided by at least one radial bore disposed in the piston rod.

The invention will be explained in greater detail hereinafter with reference to embodiments shown in the accompanying drawings, in which: Figure 1 shows a twin-tube oscillation damper with an external damping valve unit, and Figure 2 shows a single tube oscillation damper in longitudinal section with an external damping valve unit and external pressure storage means.

The hydraulic oscillation damper 1 shown in Fig. 1 is constructed as a twin-tube damper and comprises a barrel 2 in which is fitted a piston rod 3 which is connected to a piston 4. The piston 4 comprises a damping valve 5 which operates during the traction phase while a bottom valve 6 predominantly determines damping in the compression stage. A container 7 encloses and is at a radial distance from the barrel 2 and forms a compensating space 12 which can be connected in fluidconductive manner to a working space 11 remote from the piston rod, through the bottom valve 4. Provided in the compensating space 12 is a liquid and gas filling, while the working space 11 remote from the piston rod and a working space 10 on the piston rod side are filled with damping fluid.The piston rod 3 is guided in the hydraulic oscillation damper 1 by means of a piston rod guide means 8 and is sealed vis-a-vis the outside by the piston rod seal 9. A central tube 13 is disposed in a bore in the piston rod 3 and is guided and sealed by a shoulder 14. Via an axial bore 15 which traverses the piston rod journal, the fluid-conductive connection of the interior of the tube 13 with the working space 11 is established. The working space 10 on the piston rod side communicates via a throughflow cross-section 17 with an annular space 16 formed by the outside wall of the central tube 13 and the bore in the piston rod 3. An external damping valve unit 18 communicates on the one hand through a connecting line 19 with the interior of the central tube 13 and on the other through a connecting line 20 to the annular space 16.The external damping valve unit 18 consists, for instance, of a throttling through valve with any desired number of intermediate positions 21, an electromagnetic drive 22 and an adjusting device 23 which has abutments in both directions, the valve device being subject to the action of a restoring spring 24.

The external damping valve unit 18 is disposed to act in parallel with the damping valve 5 so that when the damping valve unit 18 is cut in, damping is diminished. Accordingly, maximum damping in the traction phase is achieved by the damping valve 5, whereas when the damping valve unit 18 is cut in, damping for the traction phase diminishes.

Since this damping valve unit 18 can either comprise a plurality of stages or have any desired number of intermediate settings, a substantial variation in damping force is possible with a hydraulic oscillation damper which is constructed in this manner. The damping valves 5 and 6 are constructed as standard valves and are designed in accordance with the maximum desired damping force in the traction and compression directions. The desired variation in damping force, on the other hand, is brought about by the external damping valve unit 18 so that no intervention is necessary into the component unit which is constructed as a hydraulic oscillation damper 1, this component unit consisting of well-proven standard parts, with the exception of the piston rod 3.The connecting lines 19 and 20 which lead to the damping valve unit 18 may be very short since they do not perform any movement relative to each other. Fitment in the vehicle is very simple, since the connections of the connecting lines 19 and 20 at the top end of the piston rod 3 are easily accessible and can be readily fitted. Correspondingly, relative movement between the end of the piston rod 3 which is articulated on the bodywork, for instance, by a rubber cushioning member, and the damping valve unit 18 which is, for example, mounted on a bodywork part, is extremely small. If any damage occurs at the damping valve unit 18 or the hydraulic oscillation damper 1, it is necessary only to exchange the faulty component so that the object of the invention permits of favourably costed repairs.For the durability of the piston rod 3, it is advantageous for the central tube 13 to be guided and sealed in a projection 14 since then the piston rod journal which accommodates the piston is only slightly weakened by the axial bore 15.

Where the embodiment according to Fig. 2 is concerned, the hydraulic oscillation damper is constructed as a single-tube oscillation damper 25, the piston 4 connected to the piston rod 3 carrying the damping valve 5 for the traction phase and the damping valve 6 for the compression phase. The interior of the barrel 2 is completely filled with fluid and consists of the working spaces 10 and 11 which are isolated by the piston 4. The central passage which is connected in fluid-conductive manner to the working space 11 which is remote from the piston rod and constituted by the axial bore 15 and the central tubes 13 is connected by a sleeve 26 to the connecting line 19 leading to the damping valve unit 18 into which discharges a connecting line 27 which at the other end is connected to a pressure storage means 28.This pressure storage means 28 comprises, for example, a gas filling which is pressurised and which is isolated from the fluid filling by a diaphragm and forms the compensating space of the single tube oscillation damper 25, the unthrottled connection of the pressure storage means 28 to the working space 11 remote from the piston rod guaranteeing that the damping force characteristics which take effect via the piston stroke are effective without intervention. The damping valve unit 18 communicates on the other hand with the connecting line 20 via the annular space 16 and the throughflow crosssection 17 to the working space 10 on the piston rod side, and so is connected in parallei with the damping valves 5 and 6 and-as already described in Fig. 1-according to the operative damping cross-section of the damping valve unit 18, produces a diminution in the effective damping forces, a closed damping valve 18 providing the maximum damping forces constituted by the damping valves 5 and 6.

Claims

1. Hydraulic oscillation damper for vehicles, comprising a barrel in which a piston connected to a hollow piston rod and provided with at least one damping valve sub-divides the damping fluid-filled interior of the barrel into two working spaces, while the piston rod comprises, for the fluid-conductive connection of external fittings, two lines which are constituted by a central tube disposed in the hollow cavity inside the piston rod and an annular space defined by the outside diameter of this tube and the inside diameter of the piston rod, characterised in that the central tube (13) communicates with one (11) of the working spaces (10, 11) while the annular space (16) communicates with the other working space (10) and, at the piston rod end, the central tube (13) is connected on one side and the annular space (16) on the other to an external damping valve unit (18) which acts in parallel with at least one damping valve (5).

2. Hydraulic oscillation damper according to Claim 1, characterised in that the central tube (13) is connected in fluid-conductive manner to a working space (11) remote from the piston rod and the annular space (16) is connected via a throughflow cross-section (17) to a working space (10) on the piston rod side.

3. Hydraulic oscillation damper according to Claims 1 or 2, characterised in that the exter nal damping valve unit (18) comprises an adjusting device (23) for varying the damping force.

4. Hydraulic oscillation damper according to one of Claims 1 to 3, characterised in that the adjusting device (23)-drive (22)-can be controlled as a function of various variables such as speed, cross-acceleration, deceleration of the vehicle.

5. Hydraulic oscillation damper according to one of Claims 1 to 4, characterised in that the damping valve unit (18) is connected to the piston rod end by connecting lines (19, 20).

6. Hydraulic oscillation damper according to one of Claims 1 to 5, characterised in that the oscillation damper is constructed as a single tube oscillation damper (25) and is provided with a separate pressure storage means (28) which acts as a compensating space and which is connected to a connecting line (19).

7. Hydraulic oscillation damper according to Claim 6, characterised in that the pressure storage means (28) is connected in unthrottled manner to a working space (11) remote from the piston rod.

8. Hydraulic oscillation damper according to one of Claims 1 to 7, characterised in that the central tube (13) is guided and sealed in a projection (14) constituted by the interior of the piston rod (3) and is connected in fluidconductive manner to a working space (11) remote from the piston rod, through an axial bore which traverses a piston rod journal.

9. Hydraulic oscillation damper according to one of Claims 2 to 8, characterised in that the throughflow cross-section (17) is constituted by at least one radial bore in the piston rod (3), leading to the annular space (16).

10. Hydraulic oscillation damper as claimed in Claim 1 substantially as described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.