GB2376514A

GB2376514A - A hydraulic damper for a vehicle suspension system

Info

Publication number: GB2376514A
Application number: GB0114383A
Authority: GB
Inventors: Dominguez Gonzalo Bragado; Del Prado Leopoldo Perez; Sambruno Manuel Cherne; Valero Joaquin Vicente
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2001-06-13
Filing date: 2001-06-13
Publication date: 2002-12-18
Anticipated expiration: 2021-06-13
Also published as: GB0114383D0; GB2376514B

Abstract

A hydraulic damper comprises a tube substantially closed at both ends and containing fluid. A piston (42) is slidably mounted in the tube and separates the tube into a compression chamber and a rebound chamber; a piston rod (18) is attached to the piston and extends though the rebound chamber and out of one end of the tube. A compression stroke valve (64) is mounted on the rebound chamber side of the piston for controlling the flow of fluid during a compression stroke through a compression flow passage (60) which extends though the piston. A rebound stroke valve (66) is mounted in the compression chamber side of the piston for controlling the flow of fluid during a rebound stroke through a rebound flow passage (62) which extends through the piston. The rebound stroke valve comprises one or more deflectable discs (70) which cover one end of the rebound flow passage, and a wave spring (74) mounted on the piston which serves to bias the one or more deflectable discs to normally close the rebound flow passage.

Description

HYDRAULIC DAMPER FOR A VEHICLE SUSPENSION SYSTEM Technical Field The present invention relates to a hydraulic damper for the suspension system of a motor vehicle.

Background of the Invention Known hydraulic dampers comprise a tube; a piston sealably slidably mounted in the tube and attached to a piston rod, the piston separating a compression chamber from a rebound chamber within the tube; a compression stroke valve mounted on the piston; and a rebound stroke valve mounted on the piston. The compression stroke valve acts as a one way valve to allow flow of fluid from the compression chamber to the rebound chamber through one or more compression flow passages in the piston during the compression stroke of the hydraulic damper. The rebound stroke valve acts as a one way valve which allows flow of fluid from the rebound chamber to the compression chamber through one or more rebound flow passages in the piston during the rebound stroke of the hydraulic damper. Typically, the valves comprise one or more discs which cover the flow passages and which deflect or move to allow fluid flow. The disc or discs of the compression stroke valve are typically of larger diameter than the disc or discs of the rebound stroke valve. In these known arrangements, the flow passages extend in a direction which is substantially parallel to the longitudinal axis of the piston rod, with the rebound flow passage or passages positioned nearer the longitudinal axis of the piston rod than the compression flow passage or passages. In this arrangement, one or more apertures are formed in the deflectable discs of the compression stroke valve to allow fluid flow through the rebound flow passage or passages during a rebound stroke. GB-A- 1387150 and FR-A-2420060 describe arrangements where the deflectable discs of the rebound stroke valve are biased to a closed position by a coil spring which engages a nut which is screw threaded to the piston rod and a

spring seat which is axially slidable relative to the nut and which engages the deflectable discs. GB-A-2314602 describes an improvement to the design of the rebound stroke valve of these known arrangements. Such known

arrangements provides a blow-off charactcristic during a rebound stroke. afi-ai-igeii-ierits prc,- ; 1% 4 L) li 11 L JL Li % LUX 111r, a I Summary of the Invention It is an object of the present invention to provide a hydraulic damper in which the axial load acting on the disc or discs of the rebound stroke valve is more evenly distributed.

A hydraulic damper in accordance with the present invention comprises a tube substantially closed at both ends and containing fluid; a piston slidably mounted in the tube and making a sealing fit therewith, the piston separating a compression chamber and a rebound chamber within the tube; a piston rod attached to the piston, having a longitudinal axis, and extending through the rebound chamber and out of one end of the tube; a compression stoke valve mounted on the piston on the rebound chamber side thereof for controlling flow of fluid during a compression stroke through a compression flow passage extending through the piston; and a rebound stroke valve mounted on the piston on the compression chamber side thereof for controlling flow of fluid during a rebound stroke through a rebound flow passage extending through the piston; wherein the rebound stroke valve comprises one or more deflectable discs which cover one end of the rebound flow passage, and a wave spring mounted on the piston and acting on the said one or more deflectable discs to normally close the rebound flow passage.

The use of a wave spring provides more even distribution of axial load on the deflectable disc or discs of the rebound stroke valve. This provides improvements in consistency of performance, especially during small openings of the rebound stroke valve.

The present invention is particularly for a hydraulic damper comprising an inner tube and an outer tube (sometimes referred to as a twin tube damper) in which the piston slides in the inner tube, although the

invention may also be used in a hydraulic damper having a single tube (sometimes referred to as a monotube damper).

Brief Description of the Drawings The present invention will now be described, by way of example, with reference to the accompanying drawings, in which :- Figure 1 is a schematic cross-sectional view of a preferred embodiment of hydraulic damper in accordance with the present invention; Figure 2 is an enlarged cross-sectional view of the piston assembly of the hydraulic damper of Figure 1; Figure 3 is an enlarged side view of one wave of the wave spring of the piston assembly of Figure 2; Figures 4a to 4e are side views of alternative configurations for the wave spring; and Figure 5 is a graph of opening force against piston speed for the compression stroke valve and the rebound stroke valve of the hydraulic damper of Figure 1.

Description of the Preferred Embodiment Referring to Figures 1 to 3 of the drawings, the hydraulic damper 10 shown in Figure 1 is of the twin tube damper type, and comprises an outer tube 12, an inner tube 14 substantially coaxial with the outer tube on an axis L, a piston assembly 16, a piston rod 18 having a longitudinal axis on axis L, a compensation valve 20, and a piston rod guide 22. The piston assembly 16 will be described in greater detail below. The compensation valve 20 and the piston rod guide 22 may be any suitable conventional design known to those skilled in the art, and will not be described in detail. The inner tube 14 is substantially closed at one end 24 by the compensation valve 20, and is substantially closed at the other end 26 by the piston rod guide 22.

The outer tube 12 is closed at one end 28 by an integral formation of the outer tube walls, and is substantially closed at the other end 30 by the piston rod

guide 22. The piston rod 18 extends through, and makes a sealing sliding fit with the piston rod guide 22. The piston assembly 16 makes a sealing sliding fit with the inner surface 32 of the inner tube 14. The piston assembly 16 divides the inner area ofme inner mbe 14 imo a rebound chamber 36 and a compression chamber 38. The area between the inner tube 14 and the outer tube 12 defines a compensation chamber 40. The rebound and compression chambers 36 and 38 are substantially filled with fluid to damp reciprocating movement of the piston assembly 16 and piston rod 18 along axis L relative to the outer and inner tubes 12 and 14. The compensating chamber 40 is partly filled with fluid and acts as a reservoir for the fluid in the rebound and compression chambers 36 and 38. The hydraulic damper 10 is mounted in a motor vehicle (not shown) in the standard manner.

The piston assembly 16 is shown in greater detail with reference to Figure 2. The piston 42 of the piston assembly 16 has an annular seal 44 made from Teflon material. The piston 42 is preferably formed from sintered steel. The annular seal 44 is preferably secured to the piston 42 by heat forming and provides a surface which makes a sealing sliding fit with the inner surface 32 of the inner tube 14. The piston 42 is substantially annular and has a through bore 46 comprising a first portion 48, a second portion 50 having a smaller diameter than the first portion, and a shoulder 52 between the first and second portions. A substantially annular channel 54 is formed in the surface of the shoulder 52. A substantially annular channel 56 is formed in an end surface 58 of the piston 42 through which the second portion 50 of the through bore 46 opens. The annular channel 56 has a larger diameter than the annular channel 54. In use, the first portion 48 of the through bore 46 opens into the compression chamber 38, and the end surface 58 of the piston 42 is directed towards the rebound chamber 36. The surfaces 58,52 are contacted by discs 70,82 (described below) respectively.

A number of passages 60 (which define compression flow passages) pass through the piston 42 from the channel 56 to the first portion 48 of the through bore 46. On assembly of the piston assembly 16 to the

piston rod 18, the passages 60 extend in a direction substantially parallel to the axis L. Any suitable number of such passages 60 may be used. The number and size of the passages 60 is predetermined dependent on the required damping characteristics of the hydraulic damper 10.

A number of passages 62 (which define rebound flow passages) pass through the piston 42 from the channel 54 to the end surface 58. On assembly of the piston assembly 16 to the piston rod 18, the passages 62 extend at an angle to the axis L and open through the end surface 58 on a circle having a diameter greater than the diameter of the channel 56. Any suitable number of such passages 62 may be used. The number and size of the passages 62 is predetermined dependent on the required damping characteristics of the hydraulic damper 10. With the arrangement of passages 60 and 62 as shown, and using a sintered piston 44, only the passages 62 need to be cut in the piston 44 as the passages 60 can be formed on sintering the piston.

In addition to the piston 42 and seal 44, the piston assembly 16 comprises a compression stroke valve 64 and a rebound stroke valve 66 (see Figure 2). The rebound stroke valve 66 will be described in greater detail below. The compression stroke valve 64 comprises a deflectable disc 82, and a retaining washer 84, both of which are substantially annular. On assembly, the deflectable disc 82 engages the end surface 58 of the piston 42 to substantially cover the annular channel 56, and engages the retaining washer 84. The surface 86 of the retaining washer 84 adjacent the deflectable discs 82 has a flat portion and a convex portion. The deflectable disc 82 is sized so as not to cover the rebound flow passages 62. The deflectable disc 82 may be replaced by a number of similar deflectable discs, including a disc adjacent the end surface 58 of the piston 42 having a number of slots formed in its outer periphery, the slots being of a size so as to form a restricted flow passage between the channel 56 and the rebound chamber 36.

The piston assembly 16 is retained on the end 88 of the piston rod 18 between a shoulder 90 formed on the piston rod and a nut 34 which

makes a threaded connection on the end of the piston rod, as shown in Figure 2, with the end of the piston rod passing through the second portion 50 of the through bore 46. On assembly, the retaining washer 84 engages the shoulder 90 on me piston rod 18.

The rebound stroke valve 66 comprises a deflectable disc 70, a number of spacer discs 71, a cylindrical bushing 72, a cylindrical spring seat 73, and a wave spring 74. The discs 70,71 are substantially annular. The cylindrical bushing 72 has a through bore 75 and a radially directed flange 76 at one end 77. The cylindrical spring seat 73 has a through bore 78 and a radially directed flange 79 at one end 81. On assembly, the deflectable disc 70 engages the surface of the shoulder 52 to substantially cover the annular channel 54, and is positioned between the shoulder 52 and the spacer discs 71.

The end 88 of the piston rod 18 passes through the through bore 75 of the cylindrical bushing 72. The nut 34 engages the end 77 of the bushing 72, and the other end 83 of the bushing 72 engages the spacer discs 71 to clamp the inner peripheral portions of the deflectable disc 70 to the piston 42. The spring seat 73 is positioned around the bushing 72 with the surfaces of the through bore 78 of the spring seat making a sliding fit on the cylindrical outer surface 85 of the bushing. The end 81 of the spring seat 73 engages the deflectable discs 70 at the outer peripheral portion of the deflectable discs.

The wave spring 74 is annular, and positioned around the spring seat 73. The wave spring 74 engages the flange 79 of the spring seat and the flange 76 of the bushing 72. The wave spring 74 biases the spring seat 73 into engagement with the deflectable disc 70. The deflectable disc 70 is sized so as not to cover the compression flow passages 60. The deflectable disc 70 may be replaced by a number of similar deflectable discs, including a disc adjacent the shoulder 52 having a number of slots formed in its outer peripheral edge, the slots being of a size so as to form a restricted flow passage between the channel 54 and the first portion 48 of the through bore 46.

One wave of the wave spring 74 is shown in Figure 3. As can be seen, the wave spring 74 is annular and the waves are undulating, with a

number of adjacent crests 100 and troughs 102. The wave spring 74 is preferably formed from a single continuous piece of material, and formed from any suitable material, such as carbon steel, stainless steel, copper alloy, etc. Various alternative configurations for the wave spring 74 are shown in Figure 4 and include a single turn with a gap 104 (Figure 4a); a single turn with an overlap 106 (Figure 4b); a plurality of turns with the crests of adjacent turns in contact and with plain ends (Figure 4c); a plurality of turns with the crests of adjacent turns in contact and with squared shim ends 108 (Figure 4d); and a plurality of turns with the crests of one turn in contact with the troughs of the adjacent turn in a nested arrangement (Figure 4e). The configuration, size, and material, for the wave spring 74 is selected dependent on the required spring load.

The spring seat 73 and the bushing 72 are preferably formed from sintered material. The use of sintered material provides better control tolerances on dimensions during manufacture of the spring seat 73 and the bushing 72, and better sliding characteristics between the spring seat and the bushing.

As can be seen in this preferred embodiment, the compression flow passages 60 extend from a position inside the outer peripheral edge of the deflectable disc 82 of the compression stroke valve 64 to a position outside the outer peripheral edge of the deflectable disc 70 of the rebound stroke valve 66, and the rebound flow passages 62 extend from a position inside the outer peripheral edge of the deflectable disc 70 of the rebound stroke valve 66 to a position outside the outer peripheral edge of the deflectable disc 82 of the compression stroke valve 64.

On compression stroke of the hydraulic damper 10, fluid flows from the compression chamber 38 through the compression flow passages 60 into the annular channel 56, the deflectable disc 82 deflects away from the annular channel 56 to allow a flow of fluid through the compression flow passages 60 into the rebound chamber 36. The convex portion of the surface 86 on the retaining washer 84 of the compression stroke valve 64 allows for

the deflection of the deflectable disc 82, but restricts the amount of deflection so as to prevent damage to or deformation of the deflectable discs. During a compression stroke, the compensation valve 20 may also open to allow fluid

AO flow from the compression chamber 38 to the compensation chamber 40. The combination of the compression stroke valve 64 and the compensation valve 20 determine the compression damping force.

On rebound stroke of the hydraulic damper 10, fluid flows from the rebound chamber 36 through the rebound flow passages 62 into the annular channel 54, the deflectable disc 70 deflects away from the annular channel 54 to allow a flow of fluid through the rebound flow passages 62 into the compression chamber 38. The deflection of the deflectable disc 70 causes the spring seat 73 to slide in an axial direction relative to the bushing 72 towards the nut 34 against the bias of the wave spring 74. This arrangement provides a blow-off characteristic during rebound stroke to limit the force exerted on the disc 70 as the speed of the rebound stroke increases. During a rebound stroke, the compensation valve 20 is normally closed and acts as a check valve.

Figure 5 shows a plot of opening force (force required to deflect the deflectable discs) against piston speed for the compression stroke valve 64 and the rebound stroke valve 66 during a compression stroke and a rebound stroke respectively. These plots show that the initial opening force for the rebound stroke valve 66 is higher, but then the blow-off characteristics take effect.

The presence of the annular channels 54,56 is optional but provides for better load distribution on the deflectable discs 82,70 during rebound and compression strokes respectively, and better valve seating for the rebound and compression stroke valves 66,64 respectively. A ridge 92 may be formed in the annular channel 56 between the passages 60 to reduce the risk of breakage or deformation of the deflectable disc 82 during rebound stroke due to pressure build-up in the rebound chamber 36. A similar ridge may be formed in the annular channel 54.

The number and size (thickness) of the deflectable discs 70,82 is predetermined dependent on the required damping characteristics of the hydraulic damper 10. Similarly, the configuration and strength of the wave spring 74 is selected to provide the required characteristics for the hydraulic damper 10 during a rebound stroke. The through bore 46 in the piston 42 may be of substantially constant diameter, with the rebound stroke valve 66 being positioned on the end surface of the piston that is remote from the end surface 58. The arrangement of the compression flow passages 60 and the rebound flow passages 62 may be other than that shown in the preferred embodiment.

In the above described embodiment of the present invention, the wave spring 74 does not directly engage the nut 34. This arrangement makes it easier to assembly the components of the rebound stroke valve 66, and also makes it easier to adjust and set the required torque on the nut 34 during the assembly process, when compared to previously known arrangements.

Further, the use of the wave spring 74 rather than a coil spring provides a move even distribution of load (in the axial direction) acting on the deflectable disc 70 of the rebound stroke valve 66. This provides more consistent operating performance during a rebound stroke, especially for small opening of the rebound stroke valve.

The present invention is applicable for any design of rebound stroke valve in which a coil spring can be replaced by a wave spring. The present invention is also applicable for a compensation valve in which a coil spring can be replaced by a wave spring.

Claims

1. A hydraulic damper comprising a tube substantially closed at both ends and containing fluid; a piston slidably mounted in the tube and making a sealing fit therewith, the piston separating a compiession chamber and a rebound chamber within the tube; a piston rod attached to the piston, having a longitudinal axis, and extending through the rebound chamber and out of one end of the tube; a compression stoke valve mounted on the piston on the rebound chamber side thereof for controlling flow of fluid during a compression stroke through a compression flow passage extending through the piston; and a rebound stroke valve mounted on the piston on the compression chamber side thereof for controlling flow of fluid during a rebound stroke through a rebound flow passage extending through the piston; wherein the rebound stroke valve comprises one or more deflectable discs which cover one end of the rebound flow passage, and a wave spring mounted on the piston and acting on the said one or more deflectable discs to normally close the rebound flow passage.

2. A hydraulic damper as claimed in Claim 1, wherein the wave spring is substantially annular and undulating with a number of adjacent crests and troughs.

3. A hydraulic damper as claimed in Claim 2, wherein the wave spring comprises a single turn with a gap between the ends.

4. A hydraulic damper as claimed in Claim 2, wherein the wave spring comprises a single turn with the ends overlapping.

5. A hydraulic damper as claimed in Claim 2, wherein the wave spring comprises a plurality of turns with the crests of adjacent turns in contact with one another.

6. A hydraulic damper as claimed in Claim 2, wherein the wave spring comprises a plurality of turns with the crests of one turn in contact with the troughs of the adjacent turn.

7. A hydraulic damper as claimed in any one of Claims 1 to 6, wherein the rebound stroke valve further comprises a cylindrical bushing mounted on the piston rod in engagement with the said one or more deflectable discs, a nut screw threaded on the piston rod to retain the bushing in position, and a cylindrical spring seat mounted on the bushing and slidable relative thereto in an axial direction, and the wave spring being mounted between a radial flange on the spring seat adjacent the said one or more deflectable discs and a radial flange on the bushing adjacent the nut to bias the spring seat into engagement with the said one or more deflectable discs.

8. A hydraulic damper as claimed in Claim 7, wherein the cylindrical bushing and the cylindrical spring seat are formed from sintered material.

9. A hydraulic damper as claimed in Claim 7 or Claim 8, comprising one or more spacer discs between the said one or more deflectable discs and the cylindrical bushing.

10. A hydraulic damper as claimed in any one of Claims 1 to 9, wherein the compression stoke valve comprises one or more deflectable discs mounted on the piston on the rebound chamber side thereof ; the compression flow passage extends through the piston from a position inside the outer peripheral edge of the deflectable disc or discs of the compression stroke valve to a position outside the outer peripheral edge of the deflectable disc or discs of the rebound stroke valve in a direction substantially parallel to the longitudinal axis of the piston rod; and the rebound flow passage extends through the piston from a position inside the outer peripheral edge of the

deflectable disc or discs of the rebound stroke valve to a position outside the outer peripheral edge of the deflectable disc or discs of the compression stroke valve and at an angle to the longitudinal axis of the piston rod.

11. A hydraulic damper as claimed in any one of Claims 1 to 10, comprising a plurality of rebound flow passages.

12. A hydraulic damper as claimed in Claim 11, wherein the rebound flow passages open into an annular channel formed in the piston adjacent the rebound stroke valve, the deflectable disc or discs of the rebound stroke valve covering the annular channel.

13. A hydraulic damper as claimed in any one of Claims 1 to 12 comprising a plurality of compression flow passages.

14. A hydraulic damper as claimed in Claim 13, wherein the compression flow passages open into an annular channel formed in the piston adjacent the compression stroke valve, the deflectable disc or discs of the compression stroke valve covering the annular channel adjacent the compression stroke valve.

15. A hydraulic damper as claimed in Claim 14, wherein a ridge is formed in the annular channel in the piston adjacent the compression stroke valve.

16. A hydraulic damper substantially as herein described with reference to, and as shown in, the accompanying drawings.