GB2314602A

GB2314602A - A damper having a piston valve with blow-off characteristic

Info

Publication number: GB2314602A
Application number: GB9613597A
Authority: GB
Inventors: Felipe Juan Cabezon Rivero
Original assignee: Delphi Automotive Systems Espana SA
Current assignee: Delphi Automotive Systems Espana SA
Priority date: 1996-06-28
Filing date: 1996-06-28
Publication date: 1998-01-07
Anticipated expiration: 2016-06-28
Also published as: DE19725864A1; GB9613597D0; GB2314602B

Abstract

A damper, eg of the twin tube type, comprises a piston 42, eg of sintered steel, having at least one deflectable disc 70, 82 which deflect to allow greater fluid flow through the compression or rebound passages 60, 62, thereby permitting higher piston speed in either the compression or rebound stroke. Discs 70 engage slidable bush 72 which, via coil spring 74, is allowed to slide axially when the discs 70 deflect so as to provide a blow-off characteristic. A nut 34 is threaded on to piston rod 18 to retain the bush 72 in position. The discs 70, 82 are supported by orifice discs 68, 80 which also deflect for high piston velocity and, together with discs 70, 82, are sized so as not to cover their respective passages 60, 62. A convex portion 86 on retaining washer 84 prevent damage when discs 82 deflect. Spring seat 73 and bushing 72 may also be made from sintered material.

Description

2314602 WD/H-197731 SUSPENSION STRUT The present invention relates to a

suspension strut or hydraulic damper or shock absorber for a motor vehicle.

Known suspension struts 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 suspension strut. 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 suspension strut. Typically, the valves comprise a number of discs which cover the flow passages and which deflect to allow fluid flow. The deflectable discs of the compression stroke valve are typically of larger diameter than the deflectable 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-A2420060 describe arrangements where the deflectable discs of the rebound stroke valve are 2 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. Such an arrangement provides a blow-off characteristic during a rebound stroke.

It is an object of the present invention to provide a suspension strut with such a characteristic which is easier to assemble and easier to accurately set the required torque level relative to the previously known arrangements.

The present invention is particularly for a suspension strut 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 suspension strut having a single tube (sometimes referred to as a monotube damper).

A suspension strut 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 3 or more deflectable discs which cover one end of the rebound flow passage, 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, a cylindrical spring seat mounted on the bushing and slidable relative thereto in an axial direction, and a coil spring 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 which biases the spring seat into engagement with the said one or more deflectable discs to normally close the rebound flow passage.

With the present invention, the coil spring is isolated from the nut thereby making it easier to assembly the components of the rebound stroke valve, and easier to adjust and set the required torque on the nut relative to prior known arrangements.

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 suspension strut in accordance with the present invention; 25 Figure 2 is an enlarged cross-sectional view of the piston assembly of the suspension strut of Figure 1; and Figure 3 is a graph of opening force against piston speed for the compression stroke valve and the rebound stroke valve of the suspension strut of Figure Referring to the Figures 1 and 2 of the drawings, the suspension strut 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 4 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 of the inner tube 14 into 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 suspension strut 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. An upstanding substantially annular ridge 57 (in the form of castellations) surrounds the end surface 58 to reduce the risk of accidental damage to the end surface during assembly of the piston assembly 16. Similarly, the first portion 48 of the through bore 46 protects the surface of the shoulder 52. These surfaces 58,52, which are contacted by discs 68,80 (described below) respectively, must remain in good condition in order for the suspension strut 10 to have the required damping characteristics.

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 6 number and size of the passages 60 is predetermined dependent on the required damping characteristics of the suspension strut 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 suspension strut 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 an orifice disc 80, a number of deflectable discs 82, and a retaining washer 84, all of which are substantially annular. on assembly, the orifice disc 80 engages the end surface 58 of the piston 42 to substantially cover the annular channel 56, and the deflectable discs 82 are positioned between the orifice disc and 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 orifice disc 80 has 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 7 and the rebound chamber 36. The orifice disc 80 and deflectable discs 82 are sized so as not to cover the rebound flow passages 62. The piston assembly 16 is retained on the 5 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 the piston rod 18.

The rebound stroke valve 66 comprises an orifice disc 68, a number of deflectable discs 70, a number of spacer discs 71, a cylindrical bushing 72, a cylindrical spring seat 73, and a coil spring 74. The discs 68,70,71 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 orifice disc 68 engages the surface of the shoulder 52 to substantially cover the annular channel 54, and the deflectable discs 70 are positioned between the orifice disc 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 discs 70 and orifice disc 68 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 8 at the outer peripheral portion of the deflectable discs. The coil spring 74 is positioned around the spring seat 73 and engages the flange 79 of the spring seat and the flange 76 of the bushing 72. The coil spring 74 biases the spring seat 73 into engagement with the deflectable discs 70. The orifice disc 68 and deflectable discs 70 have substantially the same diameter and are sized so as not to cover the compression flow passages 60. The orifice disc 68 has 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.

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 orifice disc 80 and deflectable discs 82 of the compression stroke valve 64 to a position outside the outer peripheral edge of the orifice disc 68 and deflectable discs 70 of the rebound stroke valve 66, and the rebound flow passages 62 extend from a position inside the outer peripheral edge of the orifice disc 68 and deflectable discs 70 of the rebound stroke valve 66 to a position outside the outer peripheral edge of the orifice disc 80 and deflectable discs 82 of the compression stroke valve 64.

On compression stroke of the suspension strut 10, fluid flows from the compression chamber 38 9 through the compression flow passages 60 into the annular channel 56 and out through the slots in the orifice disc 80 of the compression stroke valve 64 into the rebound chamber 36. For compression strokes of higher speeds, the orifice disc 80 and deflectable discs 82 can deflect away from the annular channel 56 to allow a larger flow of fluid through the compression flow passages 60. 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 discs 82, but restricts the amount of deflection so as to prevent damage to or deformation of the deflectable discs. GB-A-2287299, incorporated herein by reference, provides additional details of the compression stroke valve 64 and its operation.

On rebound stroke of the suspension strut 10, fluid flows from the rebound chamber 36 through the rebound flow passages 62 into the annular channel 54 and out through the slots in the orifice disc 68 of the rebound stroke valve 66 into the compression chamber 38. For rebound strokes of higher speeds, the orifice disc 68 and deflectable discs 70 will deflect away from the annular channel 54 to allow a larger flow of fluid through the rebound flow passages 62. The deflection of the orifice disc 68 and the deflectable discs 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 coil spring 74. This arrangement provides a blow-off characteristic during rebound stroke to limit the force exerted on the discs 68,70 as the speed of the rebound stroke increases.

Figure 3 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 orifice disc 80 and deflectable discs 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 presence of one or both of the orifice discs 68,80 is optional, and fluid flow through the passages 60,62 can be controlled solely by deflection of the deflectable discs 70,82. The number and size (thickness) of the deflectable discs 70, 82 is predetermined dependent on the required damping characteristics of the suspension strut 10.

Similarly, the strength of the coil spring 74 is selected to provide the required characteristics for the suspension strut 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.

11 In the present invention, the coil 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.

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Claims

Claims: -

1. A suspension strut 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 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, 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, a cylindrical spring seat mounted on the bushing and slidable relative thereto in an axial direction, and a coil spring 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 which biases the spring seat into engagement with the said one or more deflectable discs to normally close the rebound flow passage.

2. A suspension strut as claimed in Claim 1, wherein the cylindrical bushing and the cylindrical spring seat are formed from sintered material.

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3. A suspension strut as claimed in Claim 1 or Claim 2, comprising one or more spacer discs between the said one or more deflectable discs and the cylindrical bushing.

4. A suspension strut as claimed in any one of Claims 1 to 3, 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.

5. A suspension strut as claimed in any one of Claims 1 to 4, comprising a plurality of rebound flow passages.

6. A suspension strut as claimed in Claim 5, 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.

7. A suspension strut as claimed in any one of Claims 1 to 6 comprising a plurality of compression flow passages.

8. A suspension strut as claimed in Claim 7, wherein the compression flow passages open into an 14 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. 5

9. A suspension strut as claimed in Claim 8, wherein a ridge is formed in the annular channel in the piston adjacent the compression stroke valve.

10. A suspension strut substantially as herein described with reference to, and as shown in, the accompanying drawings.