GB2262585A

GB2262585A - Twin-tube shock absorber

Info

Publication number: GB2262585A
Application number: GB9225189A
Authority: GB
Inventors: Eberhardt Schunck
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-12-03
Filing date: 1992-12-02
Publication date: 1993-06-23
Also published as: GB9225189D0; JPH05215169A; DE4139820A1

Description

2262585

- 1DESCRIPTION TWIN-TUBE SHOCK ABSORBER

The invention relates to a twin-tube shock absorber.

In a known twin-tube shock absorber having a damping piston in the inner tube or cylinder (J. Reimpel "Fahrwerktechnik: "Stossddmpfer", VogelBuchverlag, Wurzburg, 1.983. pages 23 to 29), the damping piston contains a throttle valve and nonreturn valve. The throttle valve throttles the flow of fluid from the upper pressure chamber above the piston into the lower pressure chamber below the piston. The non-return valve permits an unthrottled flow of fluid from the lower pressure chamber to the upper pressure chamber. A bottom valve between the lower pressure chamber and a compensating chamber formed by the annular space between the outer and inner tubes or cylinders comprises a non-return valve having a flow-through direction from the compensating chamber to the lower pressure chamber, and a throttle valve in parallel therewith. Upon deflection of the shock absorber, the damping piston moves downwardly and a portion of the fluid flows from the lower pressure chamber into the upper pressure chamber by way of the non-return valve. The other portion of the fluid, which corresponds to the entering volume of the -2piston rod, is forced in to the compensating chamber by the throttle valve of the bottom valve. The forces required for pressure damping are mainly applied by the throttling action taking place here. Upon extension of the shock absorber, the upwardly moving damping piston causes an excess pressure in the upper pressure chamber. In this connection, the main quantity of fluid is forced through the throttle valve in the damping piston to effect the damping upon extension. The make-up of fluid in the lower pressure chamber is derived from the compensating chamber by way of the non-return valve of the bottom valve.

The introduction of shock absorbers whose damping action is controllable makes it desirable to produce the damping action for both directions of movement by only a single throttle in order to influence the latter by a control unit in the compression and extensions phases. Therefore, in a known twin-tube shock absorber (DE 36 32 562 A1), only one non-return valve has been provided in the bottom valve and one in the damping piston, and its flow-through direction is, directed from the compensating chamber to the lower pressure chamber and from the lower pressure chamber to the upper pressure chamber respectively. The upper pressure chamber is connected to the compensating chamber by way of a line in which is disposed a

1 -3throttle valve which throttles in both flow-through directions. The throttling of the fluid and thus the damping of the shock absorber is adjustable by means of an electric adjusting device acting upon the throttle valve, wherein, advantageously, the damping of the shock absorber in the compression and extension phases may be made equal. A twin-tube shock absorber of this kind is suitable preferably for filling with a so-called electro-rheological fluid, since, owing to the construction of the valve. it allows the fluid to flow in only one direction, whereby the fluid in the compensating chamber is circulated. At the same time.

it is disadvantageous that, although the expenditure on valves is somewhat reduced compared with the firstmentioned known twin-tube shock absorber, it is not yet minimized, and there is only a poor possibility of cabelling from the adjusting device to the throttle valve, since the latter is connected to the outer cylinder of the shock absorber and the shock absorber is coupled to the vehicle axle or to the wheel guides.

The present invention resides in a twin-tube shock absorber having a twintube shock absorber having a fluid-filled inner cylinder with a piston rod extending into it in a sealed manner, a damping piston which is secured to the piston rod and which is axially displaceably guided in the inner cylinder and -4sub-divides the interior of the inner cylinder into an upper and a lower pressure chamber, an outer cylinder which receives the inner cylinder and. together therewith, encloses a compensating chamber partially filled with fluid, a valve disposed in the damping piston and a bottom valve disposed in the bottom, defining the lower pressure chamber, of the inner cylinder for the purpose of releasing a flow of fluid between the various chambers, in which the valve in the piston has a throttling action effective in both flow-through directions, and the bottom valve is in the form of a two-way valve which is controllable by the pressure in the upper pressure chamber and which opens upon a rise in pressure therein and closes again upon a drop in pressure.

Thus the advantage that the damping action for the compression and extension phases of the shock absorber is effected by the same throttle which, moreover, is still formed in the damping piston. Since the damping piston is connected to the vehicle body by way of the piston rod, it is a far simpler matter to lay cables from the vehicle body for the purpose of electrically controlling the throttle. Moreover, the requirement with respect to individual valves is reduced by a further.valve. The tendencyiof the fluid to foam in the shock-absorber in accordance -5with the invention is slight, since no fluid is circulated and is displaced back and forth only through the bottom valve.

The invention is further described. by way of example, with reference to the accompanying drawing, which is a diagrammatic, longitudinal section through a twin-tube shock absorber constructed in accordance with the invention.

The twin-tube shock absorber for a vehicle has an outer tube or cylinder 10 and an inner tube or cylinder 11 disposed concentrically therewith. The outer cylinder 10 is closed all round and includes oil its top end remote from the bottom a coaxial guide 12 for a piston rod 13. A fluidtight lead-through for the piston rod 13 is ensured by a sealing ring 14 fitted in the guide 12. The bottom end of the outer cylinder 10 is connected to a vehicle axle or to a wheel guide 15. The free end of the piston rod 13 projecting from the outer cylinder 10 is connected to the vehicle body. The piston rod 13 passes through an opening 17 into the inner cylinder 11 coaxial with the guide 12 in the outer cylinder 10, and its end extending into the inner cylinder 11 carries a damping piston 18. The top surface 181 of the damping piston 18 defines an upper pressure chamber 19, and the bottom surface 182 of the damping piston 18 defines a -6lower pressure chamber 20. Furthermore, the upper pressure chamber 19 is defined by the top end of the inner cylinder 11 containing the opening 17, while the lower pressure chamber 20 is closed by a bottom plate 21 secured in the inner cylinder 11. The two pressure chambers 19, 20 are filled with a fluid, for example hydraulic oil. The annular space enclosed between the outer cylinder 10 and the inner cylinder 11 forms a compensating chamber 22, which, however, is only partially filled with the same fluid. The damping piston 18 is provided with an axial through passage 23 in which is disposed a valve 24 having a restricting or throttling action in both flow-through directions and hereinafter identified as the piston valve. The piston valve 24 may be in the form of, for example, a throttling or pressure-regulating valve. It may comprise a single valve or a plurality of individual valves. The individual valves may be constructed in such a way that at least one is responsible for one flow-through direction and at least one further one is responsible for the opposite flow-through direction. According to the individual valves used, non-return valves may still be necessary in the through passage 23 and conduct the fluid through the individual valve responsible at any given time. The piston valve 24_ may be electrically adjustable and its control leads -7can be accommodated in the piston rod 13.

A bottom valve 25 is disposed in the bottom plate 21 and is constructed as a two-way valve, controllable by the pressure in the upper pressure chamber 19, in such a way that it opens upon an increase in pressure in the upper pressure chamber 19 and closes again upon a drop in pressure. For this purpose, a central valve orifice 26 is provided in the bottom plate 21 and is surrounded by a valve seat 27 which is formed on that surface of the bottom plate 21 which is remote from the lower pressure chamber 20. A valve member 28 cooperates with the valve seat 27 for the purpose of opening and closing the valve orifice 26. A control chamber 29 is provided below, and at a distance from, the valve member 28 and is defined towards the valve member 28 by a fixed wall 30 and on the opposite side by a diaphragm 31. The diaphragm 31 may be, for example, a resilient plastics plate. A control passage 32 opens into the control chamber 29 and connects the control chamber 29 to the upper pressure chamber 19 into which it opens in the vicinity of the top end of the inner cylinder 11 remote from the damping piston 18. This control passage 32 may be in the form of a tube which leads from the control chamber 29 to the upper pressure chamber 19. In the present embodiment, the control passage 32 is formed -8as an annular passage in that the inner cylinder 11 is surrounded at a short distance therefrom by a further cylinder 33 which is sealed at both ends to the inner cylinder 11 in a fluid-tight manner. The inner cylinder 11 has, in the top region of the upper pressure chamber 19, one or a plurality of radial bores 34 through which the annular control passage 32, enclosed between the inner cylinder 11 and the cylinder 33, is connected to the upper pressure chamber 19. The cylinder 33 projects downwardly beyond the region of the bottom plate 21 and overlaps the control chamber 29 whose fixed wall 30 and diaphragm 31 are held in a region of the inner cylinder 11 projecting beyond the bottom plate 21. The inner cylinder 11 in turn carries, in the region of the control chamber 29, at least one radial bore 35 through which the control chamber 29 communicates with the annular control passage 32.

The fixed wall 30 held on the inner cylinder 11 is provided, outside the control chamber 29, with a slot 36 through which, on the one hand, the chamber portion between the bottom plate 21 and the fixed wall 30 communicates with the compensating chamber 22 in a fluid-conducting manner and through which, on the other hand, a plate of U-shaped cross section-passes. The plate 37 extends parallel to the bottom plate 21, -9and its upper limb 371 extends above and parallel to the wall 30 and its lower limb 372 extends below and parallel to the diaphragm 31. The valve member 28 is rigidly connected to the upper limb 371, and the diaphragm 31 is rigidly connected to the lower limb 372. Furthermore. the lower limb 372 is loaded by a valve closure spring 38 which is in the form of a compression spring and which is supported at one end on the lower limb 372 and at the other end on the bottom of the outer cylinder 10. The force of the valve closure spring 38 is transmitted as a closing force to the valve member 28 by way of the plate 37, so that the valve member 28 is applied to the valve seat 27 under initial spring stress.

The mode of operation of the shock absorber described is as follows:- In the extension phase of the shock absorber, the damping piston 18 moves upwardly and the fluid in the upper pressure chamber 19 is compressed. The pressure in the control chamber 29 also rises as the pressure in the upper pressure chamber 19 increases. The diaphragm 31 displaces the plate 37 against the force of the valve closure spring 38, and the plate 37 removes the valve member 28 from the valve seat 27. Thus, the valve orifice 26 is opened and fluid flows in an unthrottled manner from the compensating chamber -1022 into the lower pressure chamber 20. Fluid flows from the upper pressure chamber 18 into the lower pressure chamber 20 by way of the valve 24 in the damping piston 18. The piston valve 24 at the same time determines the damping force of the shock absorber in the extension phase.

The fluid in the lower pressure chamber 20 is compressed in the compression phase. Fluid flows from the lower pressure chamber 20 into the upper pressure chamber 19 by way of the valve 24 in the damping piston 18. Due to the piston rod 13 retracting into the upper pressure chamber 19, the latter cannot accommodate the entire volume of fluid displaced, so that the pressure also increases in the upper pressure chamber 19. Thus, the pressure in the control chamber 29 in turn increases, and the bottom valve 25 is opened by way of the diaphragm 31 and the plate 37. An additional opening force on the bottom valve 25 results from the pressure in the lower pressure chamber 20 and the effective surface of the valve member 28. Fluid can then flow off into the compensating chamber 22 from the lower pressure chamber 20. The pressure in the two pressure chambers 20,19 drops until no substantial excess pressure relative to the compensating chamber 22 prevails in the upper pressure chamber 19. During.this Z1 -11compression phase of the shock absorber, the damping force of the shock absorber is again determined by the valve 24 in the damping piston 18. The quantity of fluid, predetermined by the piston stroke and the cross section of the annular chamber remaining between the inner cylinder 11 and the piston rod 13. flows off by way of the valve 24 in the damping piston 18 both in the extension phase and in the compression phase. The displaced fluid flows through the piston valve 24 in opposite directions during the extension phase and the compression phase respectively.

The invention is not limited to the embodiment described. Thus, the diaphragm 31 may be in the form of an initially-stressed steel diaphragm, whereby it also assumes the function of the valve closure spring 38. Thus, the latter may be omitted or may be of weaker construction. The diaphragm 31 may also be replaced by a sealed piston, one surface of which defines the control chamber 29 in the same manner as the diaphragm 31.

Claims

-12CLAIMS

1. A twin-tube shock absorber having a fluidfilled inner cylinder with a piston rod extending into it in a sealed manner, a damping piston which is secured to the piston rod and which is axially displaceably guided in the inner cylinder and subdivides the interior of the inner cylinder into an upper and a lower pressure chamber, an outer cylinder which receives the inner cylinder and, together therewith, encloses a compensating chamber partially filled with fluid, a valve disposed in the damping piston and a bottom valve disposed in the bottom, defining the lower pressure chamber, of the inner cylinder for the purpose of releasing a flow of fluid between the various chambers, in which the valve in the piston has a throttling action effective in both flow-through directions', and the bottom valve is in the form of a two-way valve which is controllable by the pressure in the upper pressure chamber and which opens upon a rise in pressure therein and closes again upon a drop in pressure.

2. A shock absorber as claimed in claim 1, in which the two-way valve has a valve seat surrounding a valve orifice in the bottom of the inner cylinder anda valve member seating on the valve seat with a closing force, and in which the valve member is -13connected to a pressure impingement surface which is displaceable in the opening direction of the valve and which defines a control chamber connected to the upper pressure chamber.

3. A shock absorber as claimed in claim 2, in which the pressure impingement surface is formed by one surface of a diaphragm which seals the control chamber and to which the valve member is connected by way of a coupling member.

4. A shock absorber as claimed in claim 3, in which the diaphragm is in the form of a steel-spring diaphragm having an initial stress acting in the closing direction of the valve.

5. A shock absorber as claimed in claim 3 or 4, in which a valve closure spring, supported on the bottom of the outer cylinder acts upon the coupling member and has an initial stress acting in the closing direction of the valve.

6. A shock absorber as claimed in any of claims 3 to 5, in which the coupling member is in the form of a plate of U-shaped cross section which overlaps the control chamber at both sides and one limb of which is rigidly connected to the valve member and the other limb of which is rigidly connected to the diaphragm.

7. A shock absorber as claimed in any of claims 2 to 6, in which a control passage, opening into the -14upper pressure chamber in the vicinity of that end of the inner cylinder which is remote from the damping piston, emanates from the control chamber.

8. A shock absorber as claimed in any of claims 2 to 7, in which the valve in the damping piston is in the form of a throttle valve or pressure-regulating valve.

9. A shock absorber as claimed in any of claims 2 to 7, in which the valve in the damping piston has at least two individual valves, one of which effects a throttling action in one flow-through direction and the other of which effects a throttling action in the opposite flow-through direction.

10. A shock absorber as claimed in any preceding claim, in which the valve in the damping piston is adjustable electically.

11. A shock absorber as claimed in claim 10, in which a control lead from the valve in the damping piston passes through the piston rod.

12. A twin-tube shock absorber, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.

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