Shock absorber

Abstract

The present invention relates to a position sensitive shock absorber having a bypass passage adapted to communicate a working fluid between two positions in a bore, and an adjustable one-way valve arranged to direct working fluid flowing through the bypass passage, the adjustable one-way valve comprising a resiliently flexible shim having a first end fixed relative to a port, the port being in fluid communication with the bypass passage, and a free end extending from the first end and covering the port, and an adjuster having a fulcrum arranged against the shim to form a pivot, whereby when the working fluid exits the port, the free end is urged away from the port and flexes the shim about the pivot, thereby allowing the working fluid to flow through the port, and when the working fluid enters the port, the free end is urged towards the port and covers the port, thereby substantially preventing the working fluid flowing through the port, and at least one of the shim and adjuster are displaceable relative to each other, thereby moving the pivot relative to the free end.

Claims

1. A shock absorber comprising: a body defining a bore containing a working fluid, the bore having opposed ends and defining a longitudinal axis; a piston slidable within the bore; two apertures arranged at axially spaced apart positions along the bore and extending through a side-wall of the bore; a bypass passage in fluid communication with the two apertures, the bypass passage defining a conduit therebetween; and a first adjustable one-way valve arranged to allow the working fluid to flow through the bypass passage in a single direction, the first adjustable one-way valve comprising: a shim having a curved body arranged to curve at least partially around the longitudinal axis, the curved body having a fixed end fixed relative to a port and a free end extending from the fixed end and covering the port, the shim being resiliently flexible; and an adjuster having a fulcrum arranged against the shim to form a pivot; whereby, in use, responsive to the piston moving towards one end of the bore, the working fluid urges the free end away from the port and flexes the shim about the pivot, thereby allowing the working fluid to flow through the port; and responsive to the piston moving towards the other end of the bore, the working fluid urges the free end towards the port to covers the port, thereby substantially preventing the working fluid flowing through the port; and wherein at least one of the shim and adjuster are displaceable relative to each other to move the pivot relative to the free end.

2. The shock absorber according to claim 1, wherein the port is one of the two apertures.

3. The shock absorber according to claim 1, wherein the adjuster is rotatable about the longitudinal axis to move the pivot relative to the free end.

4. The shock absorber according to claim 1, wherein the curved body is arranged so that the free end flexes about the pivot axially relative to the longitudinal axis.

5. The shock absorber according to claim 1, further comprising: a further two apertures arranged at respective axially spaced apart positions along the bore and extending through the side-wall of the bore; a further bypass passage in fluid communication with the further apertures, the further bypass passage defining a conduit therebetween; and a second adjustable one-way valve arranged to allow the working fluid to flow through the further bypass passage in a single direction, the second adjustable one-way valve comprising features identical to the features of the first adjustable one-way valve.

6. The shock absorber according to claim 5, wherein the second adjustable one-way valve is arranged so that the single direction of the second adjustable one-way valve is opposite to the single direction of the first adjustable one-way valve.

7. The shock absorber according to claim 5, wherein the adjuster of the second adjustable one-way valve is mechanically connected to the adjuster of the first adjustable one-way valve, thereby allowing both adjusters to be moved simultaneously.

8. The shock absorber according to claim 7, wherein the adjusters are mechanically connected to an adjuster ring, the adjuster ring extending at least partially around the bore and being rotatable about the longitudinal axis to move each adjuster relative to the free end of the respective shim.

9. The shock absorber according to claim 1, further comprising: a fluid distributor connected between one of the two apertures and the bypass passage, the fluid distributor defining a second conduit therebetween; and wherein the first adjustable one-way valve is arranged across the second conduit to allow the working fluid to flow through the second conduit along the single direction only.

10. A suspension assembly for a vehicle comprising: the shock absorber according to claim 1: and a coil spring arranged around the shock absorber and connected thereto, the coil spring defining an inside diameter within which the shock absorber is disposed, and wherein the first adjustable one-way valve is dimensioned to fit within the inside diameter.

11. A shock absorber for a vehicle comprising: a body defining a bore containing a working fluid, the bore having opposed ends and defining a longitudinal axis; a first bypass passage arranged parallel and adjacent to the bore, the first bypass passage being in fluid communication with the bore; a piston slidable within the bore, the piston dividing the bore into a compression chamber and a rebound chamber; a pair of first apertures arranged at axially spaced apart positions along the bore, each first aperture extending through a side-wall of the bore so that one of the first apertures fluidly couples the first bypass passage and the bore; a fluid distributor connected to the body and adapted to receive a portion of the bore, the fluid distributor defining a first conduit between the other first aperture and the first bypass passage to communicate the working fluid from the bore to the first bypass passage; and an adjustable one-way valve arranged to allow the working fluid to flow through the first conduit in a single direction, the adjustable one way valve comprising: a shim having a curved body arranged to curve at least partially around the longitudinal axis, the curved body having a first end fixed relative to a port and a free end extending from the first end and covering the port, the shim being resiliently flexible; and an adjuster having a fulcrum arranged against the shim to form a pivot; whereby, in use, responsive to the piston moving towards one end of the bore, the working fluid urges the free end away from the port and flexes the shim about the pivot, thereby allowing the working fluid to flow through the port, and responsive to the piston moving towards the other end of the bore, the working fluid urges the free end towards the port to cover the port, thereby substantially preventing the working fluid flowing through the port; and wherein at least one of the shim and adjuster are displaceable relative to each other to move the pivot relative to the free end.

12. The shock absorber according to claim 11, wherein the shock absorber further comprises: a second bypass passage arranged parallel and adjacent to the bore, the second bypass passage being in fluid communication with the bore; and a pair of second apertures arranged at axially spaced apart positions along the bore, each second aperture extending through the side-wall of the bore so that one of the second apertures fluidly couples the second bypass passage and the bore; wherein the fluid distributor defines a second conduit between the other second aperture and the second bypass passage to communicate the working fluid between the bore and the second bypass passage.

13. The shock absorber according to claim 12, wherein the fluid distributor has a further adjustable one-way valve arranged to allow the working fluid to flow through the second conduit in a single direction, the further adjustable one-way valve comprising identical features to the first-mentioned adjustable one-way valve.

14. The shock absorber according to claim 13, wherein the adjustable one-way valve arranged across the first conduit allows the working fluid to flow through the respective port when the piston moves towards the compression chamber, and the further adjustable one-way valve arranged across the second conduit allows the working fluid to flow through the respective port when the piston moves towards the rebound chamber.

15. The shock absorber according to claim 11, wherein the curved body is arranged so that the free end flexes about the pivot axially relative to the bore.

16. A suspension assembly for a vehicle comprising: the shock absorber according to claim 11; and a coil spring arranged around the shock absorber and connected thereto, the coil spring defining an inside diameter within which the shock absorber is disposed, wherein the fluid distributor has an external peripheral region dimensioned to fit within the inside diameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a cross-section view of a shock absorber;

(3) FIG. 2 is a graph of damping force vs. piston displacement provided by the shock absorber;

(4) FIG. 3 is a perspective view of the shock absorber;

(5) FIG. 4 is an exploded perspective view of the shock absorber;

(6) FIG. 5A is a perspective view of an adjuster ring and a plurality of shims;

(7) FIG. 5B is a perspective view of an alternative adjuster ring and alternative plurality of shims;

(8) FIG. 6 is a graph of a range of damping force vs. piston displacement provided the shock absorber;

(9) FIG. 7 is an exploded view of the adjuster rings shown in FIGS. 5A and 5B and a fluid distributor;

(10) FIG. 8A is a cross-section view of the shock absorber, illustrating fluid flow paths during a compression stroke;

(11) FIG. 8B is a cross-section view of the shock absorber, illustrating fluid flow paths during a rebound stroke;

(12) FIG. 9 is an alternative perspective view of the shock absorber;

(13) FIG. 10 is an exploded perspective view of an adjustable one-way valve assembly;

(14) FIG. 11 is a cross-section view of the shock absorber, illustrating fluid flow paths to a reservoir during a compression stroke;

(15) FIG. 12 is an alternative graph of damping force vs. piston displacement, provided by the shock absorber; and

(16) FIG. 13 is a cross-section of a body of the shock absorber.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(17) The present disclosure generally relates to a shock absorber for a vehicle having one or more bypass passages adapted to communicate a working fluid between different locations in a bore whilst a piston is displaced in a defined portion of the bore, or between a location in a bore and a reservoir of working fluid. In particular, the present invention relates to a position sensitive shock absorber having an adjustable one-way valve arranged in each bypass passage, the one-way valve having a shim which flexes about a pivot to allow the working fluid to flow through the bypass passage in a single direction only, and whereby the position of the pivot can be adjusted to adjust the spring rate of the shim, which adjusts the damping force provided by the bypass passage. The disclosure also relates to the adjustable one-way valve itself, and to an alternative shock absorber having a body that defines a bore and one or more bypass passages, and a fluid distributor component which provides one or more respective conduits between the bore and the bypass passages, and also may house one or more respective one-way valves.

(18) In FIG. 1, a suspension strut 3 is shown in cross-section, the suspension strut 3 comprising a shock absorber 1 housing a coil spring 2. The shock absorber 1 comprises a body 4 having a cylindrical bore 5 containing a working fluid, the body being connected to a vehicle chassis 10. A piston 6 is disposed within the bore 5 having a seal around a peripheral region which seals the piston against side-walls of the bore 5, thereby dividing the bore 5 into two portions; a compression chamber 7, being the portion of bore the piston 6 moves towards during a compression stroke, and a rebound chamber 8, being the portion of the bore 5 the piston 6 moves towards during a rebound stroke. The piston 6 is a conventional vented piston, having one or more valves to control the flow of the working fluid through vents as the piston 6 travels through the bore 5. A rod 9 is connected between the piston 6 and a wheel (not shown).

(19) The bore 5 is in fluid communication with a reservoir 11 via a union 17 and hose 18, in this case being a piston type pressure accumulator. The reservoir 11 comprises a reservoir bore 12 and a floating piston 13, dividing the reservoir bore 12 into a fluid chamber 14, filled with the working fluid, and a gas chamber 15, filled with a gas. The floating piston 13 is displaceable within the reservoir bore 12 dependent on working fluid displaced by the piston 6 from the bore 5. The pressure of the gas in the gas chamber 15 is adjustable using the gas valve 16. Whilst it is preferable that the reservoir is a piston type pressure accumulator, the reservoir could also be a flexible diaphragm type (not shown) or a resilient closed cell foam type (not shown).

(20) A plurality of apertures 41 are arranged through a side-wall of the bore 5, providing a fluid port between the bore 5 and one of a plurality of bypass passages 42 formed in an annular region concentric to the bore 5 in the body 4. Each bypass passage 42 provides a conduit for communicating the working fluid between a pair of apertures 41 arranged in a spaced apart position axially along the bore 5 when the piston 6 moves along the bore 5 between the pair of apertures 41, thereby forcing the working fluid to enter one of the pair of apertures 41 and exit the other. Each pair of apertures 41 and an associated bypass passage 42 defines a bypass zone in which the working fluid flow rate is increased and damping force is reduced accordingly.

(21) FIG. 2 is a graph of damping force vs. piston displacement, illustrating the range of damping force provided by the shock absorber 1 during a compression and rebound stroke. In a compression stroke, the damping force increases in four defined increments, corresponding with four pairs of apertures 41 and four bypass passages 42, towards the maximum displacement of the piston 6. The increase in damping force is due to four bypass passages 42 being operational during the majority of a compression stroke (0-60% displacement of piston) and progressively less bypass passages 42 being operational during the top portion of stroke (60-80% of piston displacement), until no bypass passages function in the end portion of the stroke (80-100% of piston displacement). A similar damping force relationship is provided during a rebound stroke.

(22) The damping force curves shown in FIG. 2 show that the shock absorber 1 is optimised for a vehicle where during on-road use the piston 6 is displaced between 30-60% of the stroke and the damping force is relatively low, providing a comfortable ride. When the vehicle is driven off-road and subjected to much higher impact forces, causing larger amplitude displacement of the piston 6 of higher than 60%, the damping force significantly increases. It will be appreciated that the position of apertures 41 and number of bypass passages 42 may be varied in order to affect the damping force provided as the piston 6 is displaced through the bore 5.

(23) In FIG. 3, a perspective view of the shock absorber 1 is shown, where the shock absorber 1 is disconnected from the spring 2 and vehicle. Two valve adjuster rings 191, 192 are connected to the body 4, each connected to one or more adjustable one-way valves (not shown) in fluid communication with one or more respective bypass passages 42. The upper adjuster ring 192 is connected to each adjustable one-way valve arranged to allow working fluid to flow through a respective bypass passage 42 during a rebound stroke. The lower adjuster ring 191 is connected to each adjustable one-way valve arranged to allow working fluid to flow through a respective bypass passage 42 during a compression stroke. By rotating either ring 191, 192, all of the associated adjustable one-way valves are adjusted simultaneously.

(24) FIG. 4 shows an exploded perspective view of the shock absorber 1 with the reservoir 11, hose 18 and union 17 removed. A fluid distributor 20 is spaced apart from the body 4, having an aperture therethrough adapted to receive a portion of the body 4 housing the bore 5. The fluid distributor 20 defines a plurality of conduits, each conduit adapted to communicate working fluid from one of the apertures 41 to one of the bypass passages 42 (or vice versa). The fluid distributor 20 also engages with each adjuster ring 191, 192, thereby providing a track for each adjuster ring 191, 192 to slide on when rotated.

(25) A plurality of shims 21, 22 are arranged concentric to the bore 5 and connected to the fluid distributor 20, each shim 21, 22 having a planar body having a fixed end 212, 222 fixed to the fluid distributor 20 and a free end 211, 221 arranged over a port 24 formed at an end of one of the conduits. Each shim 21, 22 has at least a portion formed from a resiliently flexible material, such as high strength, high fatigue life steel or stainless steel, thereby when the working fluid is forced through an associated conduit and exits the port 24, the free end 211, 221 flexes away from the port 24, allowing the working fluid to flow through the port 24. Alternatively, when the working fluid is forced in an opposite direction and attempts to enter the port 24, the free end 211, 221 is urged against the fluid distributor ring 20 and covers the port 24, substantially sealing the port 24.

(26) This functionality allows the shims 21, 22 to be used as one-way valves, known as check valves, to control the flow of working fluid through an associated bypass passage 42 in either a compression or rebound stroke of the piston 6. For example, four like shims 21 (compression shims 21) selectively cover the ports 24 of respective conduits in fluid communication with four respective bypass passages 42, thereby allowing the working fluid to flow when the piston 6 is displaced towards the compression chamber only. Similarly, two like shims 22 (rebound shims 22) selectively cover the ports 24 of respective conduits in fluid communication with two further respective bypass passages 42, thereby allowing the working fluid to flow when the piston 6 is displaced towards the rebound chamber only.

(27) Each rebound shim 22 has a free end 221 covering one or more ports 24 in communication with one or more apertures 41 extending through the side-wall of the bore 5. In order to allow the free end 221 to flex away from the one or more ports 24 and allow the working fluid to flow, the planar body of each shim 21 is arranged parallel to the bore 5. Each compression shim 21 has a free end 211 covering one or more ports 42 in the fluid distributor 20 in communication with an end of respective bypass passages 42. In order to allow the free end 211 to flex away from the one or more ports 24 and allow the working fluid to flow, the shims 22 are arranged perpendicular to the bore 5.

(28) It will be appreciated that similar arrangements of the shims 21, 22 in relation to the body 4 and bypass passages 42, such as where the fluid distributor 20 is not present and each shim 21, 22 is fixed directly to the body 4, are within the scope of this disclosure. Similarly, the groups of shims 21, 22 may be spaced apart from each other, for example, the body 4 may include a first group of shims arranged at one end of the bore 5 to control fluid flow during a compression stroke, and a second group of shims arranged at an opposite end of the bore 5 to control fluid flow during a rebound stroke. Furthermore, the fluid distributor 20 may house or be connected to one or more alternative one-way valves to the shim 21, 22 arrangement discussed above, such as a poppet valve, plunger valve or solenoid valve.

(29) In FIG. 5A, the rebound adjuster ring 192 and the two rebound shims 22 are shown. The adjuster ring 192 defines a cavity 25 adapted to receive the free end 221 thereby allowing the free end 221 to flex away from an associated port 24 when the working fluid is force through and exits the port 24. At one side of the cavity is a fulcrum 26, being an edge of the cavity 25. The fulcrum 26 abuts the free end 221 providing a pivot around which the shim 21 flexes when the working fluid exits the port 24. When the adjuster ring 192 is rotated around the bore 5, the fulcrum is moved relative to the free end 221, thereby adjusting the length of the free end 221 able to pivot, consequently adjusting the effective stiffness of the shim 22. Rotation of the adjuster ring 192 therefore adjusts the damping force provided by an associated bypass passage 42. As the fulcrum 26 is moved towards the free end 221, the active length of the shim 22 decreases and the effective stiffness of the shim 22 increases, requiring more force to be exerted by the working fluid to bend the shim 22 away from the port and allow the fluid to flow, consequently increasing the damping force of the associated bypass passage 42. Alternatively, the fulcrum 26 may be fixed relative to the bore 5, for example, formed on the fluid distributor 20, and the adjuster ring 192 is connected to the rebound shims 22. In this arrangement, when the adjuster ring 192 is rotated, the free end 221 of each shim 22 is moved relative to the fulcrum 26, thereby adjusting the active length and effective stiffness of the shim 22.

(30) FIG. 5A shows two rebound shims 22 connected to a common adjuster ring 192, the adjuster ring having two respective cavities 25, providing two respective fulcrums 26. Rotation of the adjuster ring 192 moves each fulcrum 26 simultaneously, thereby adjusting the active length of each shim 22 to simultaneously. It will be appreciated that the range of fulcrum 26 movement affects the range of adjustment of the shim 22. Where the range of fulcrum 26 movement for each shim 22 is identical, the adjustment of each shim 22 will be consistent. However, in some applications, it may be desirable to adjust each shim 22 at a different rate, requiring the range of respective fulcrums 26 to be different, for example, one having a larger range and the other having a smaller range, which may be provided by varying the cavity 25 dimensions.

(31) In FIG. 5B, the compression adjuster ring 191 and a plurality of compression shims 21 are shown. The compression adjuster ring 191 also has a plurality of cavities 28 formed between castellated portions 29, each castellated portion 29 forming a fulcrum 30 at one side thereof. Each compression shim 21 is fixed relative to the adjuster ring 191 having a free end 211 covering one or more ports 24. When the working fluid exits the one or more ports 24 the compression shim flexes about the fulcrum 30 allowing the working fluid to flow. The fulcrum 30 is movable relative to the free end 211, thereby adjusting the active length and effective stiffness of the shim 21, consequently adjusting the damping force provided by an associated bypass passage 42, as described above.

(32) FIG. 6 is an alternative version of the graph shown in FIG. 2, illustrating variations of damping force vs. piston displacement dependent on each adjuster ring 191, 192 being rotated to a first extreme to provide a soft ride, i.e. maximum active length of each shim 21, 22, and a second extreme to provide a stiff ride, i.e. minimum active length of each shim 21, 22.

(33) FIG. 7 is an exploded view of the valve adjuster rings 191, 192 spaced apart from the fluid distributor 20. A plurality of the ports 24 are arranged through a side wall of the fluid distributor 20 and in communication with a fluid inlet 27 on an opposing side wall, the fluid inlet 27 adapted to be fluidly coupled over a bypass aperture 41 and funnel the working fluid to the ports 24. Similarly, a plurality of alternative fluid inlets 31 are arranged on a top surface of the fluid distributor 21, the alternative fluid inlets 31 adapted to direct the working fluid from a bypass passage 42 to further ports 24 arranged on a bottom surface of the fluid distributor 20.

(34) FIGS. 8A and 8B are cross-sections of the shock absorber 1, illustrating the working fluid flow paths during a compression stroke and a rebound stroke.

(35) In FIG. 8A, the piston 6 is shown moving vertically upwards, in a compression stroke, between two bypass apertures 411, 412, thereby displacing working fluid through an upper aperture 412, through a bypass passage 421 and returning to the bore 5 through a lower aperture 411. Fluid also passes through the piston 6 through a main valve or vent. Adjacent to each lower bypass aperture 411 a compression shim 21 flexes away from the one or more associated fluid ports 24, allowing the working fluid to flow into the bore 5.

(36) In FIG. 8B, the piston 6 is shown moving vertically downwards, in a rebound stroke, between two further bypass apertures 413, 414, thereby displacing working fluid through a lower aperture 413, through a further bypass passage 422 and returning to the bore 5 through an upper aperture 414. Adjacent to each lower bypass aperture 413 a rebound shim 22 flexes away from the one or more associated fluid ports 24, allowing the working fluid to flow into the bypass passage 422. During the stroke, the piston 6 also displaces the working fluid into the lower compressions apertures 411, urging the compression shims 21 against the associated ports 24 and covering the ports 41, thereby preventing the working fluid from flowing through the associated compression bypass passages 421 during a rebound stroke.

(37) FIG. 9 is a perspective view of the shock absorber 1 connected to the reservoir 11 by a reservoir mount 31. The reservoir has an end cap 32, through which a valve actuator 33 extends, connected to a plurality of adjustable one-way reservoir valves (not shown) within the reservoir 11.

(38) FIG. 10 shows an exploded view of the adjustable one-way reservoir valve assembly located within the reservoir, the assembly adapted to control the working fluid flowing into and out of the reservoir bore 14. The assembly comprises a body 34 which defines a plurality of inlet conduits 35 and outlet conduits 42, and to which a plurality of inlet shims 36 are fixed. An adjuster 38 is connected to the valve actuator 33 and has a plurality of castellated portions 39 which abut the inlet shims 36 and provide a fulcrum 40 at one side thereof. One or more outlet shims 43 are secured over the outlet conduits 42 and urged against the conduits 42 by a resilient member 44, being a spring.

(39) In use, when the working fluid is displaced from the bore 5 to the inlet conduits 35, the shims 36 bend about the associated fulcrums 40 allowing the fluid to flow into the reservoir 11. The positions of the fulcrums 40 relative to the free ends of the inlet shims 36 is adjusted by rotating the actuator 33, thereby affecting the active length and effective stiffness of each shim 36, consequently adjusting the damping force. This action is essentially identical to the compression shims 21 described above.

(40) When the working fluid is withdrawn from the reservoir 11 to the bore 5, provided the force exceeds the force exerted by the resilient member 44, the outlet shims 43 are forced away from the outlet conduits 42 allowing the working fluid to flow. However, this valve arrangement may be replaced with a shim arrangement as described above, thereby providing an adjustable one-way valve.

(41) It will be appreciated that the adjustable one-way reservoir valve assembly may be readily adapted to cooperate with the piston 6, providing one or more adjustable one-way valves over the vents extending through the piston 6.

(42) In FIG. 11, the shock absorber 1 is shown in cross-section, illustrating the working fluid flowing from the bore 5 to the reservoir 11 during a compression stroke. The body 4 has further apertures 415 extending through the side-wall of the bore 5 in fluid communication with further bypass passages 423. The bypass passages 423 are also in fluid communication with the reservoir 11, via the union 17 and hose 18. It is preferable that the union 17 and hose 18 are arranged external to the spring 2 arranged around the shock absorber 1 to decrease the likelihood of either component being damaged by the spring 2. Similarly, it is convenient for the reservoir 11 to be located at the chassis end of the shock absorber 1, to allow the reservoir 11 to be connected to the vehicle chassis remotely from the shock absorber 1.

(43) The piston 6 is shown moving vertically upwards in a compression stroke through the bore 5 towards the compression chamber, increasing the pressure of the fluid in the compression chamber and causing the working fluid to flow through the main vent in the piston 6 and/or a bypass passage 421 into the rebound chamber. Due to the presence of the shaft 9 in the rebound chamber, a volume of the working fluid equivalent to the volume of the shaft 9 in the rebound chamber is displaced through the reservoir apertures 415 and through the reservoir bypass passages 423 into the reservoir 11.

(44) Following the compression stroke, the piston 6 moves vertically downwards through the bore 5 in a rebound stroke. As the working fluid was previously displaced into the rebound chamber in the compression stroke, the pressure of the fluid in the rebound chamber (or, as the piston 6 is now travelling in a rebound stroke, the pressure of the fluid in the compression chamber) is maintained above the threshold necessary to cause the working fluid to vaporise, commonly known as cavitation. The maintained working fluid pressure therefore reduces or prevents gas bubbles forming in the working fluid and provides consistent resistance to the motion of the piston 6 through the bore 5 in the rebound stroke.

(45) The location of each reservoir bypass aperture 415 axially along the bore 5 determines which portion of a stroke of the piston 6 the working fluid is displaced into the reservoir 11 in. For example, in FIG. 11, two reservoir bypass apertures 415 are shown immediately adjacent to an end of the bore 5. This arrangement is optimised for compression damping as the position of the apertures 415 ensures that throughout the entire length of a compression stroke, working fluid is displaced into the reservoir 11 and the pressure of the working fluid in the rebound chamber is maintained at the reservoir charge pressure, thereby decreasing or preventing cavitation which may affect the motion of the piston 6 during a subsequent rebound stroke. However, during the entire rebound stroke, the pressure will decrease in the compression chamber, potentially causing cavitation of the fluid.

(46) In FIG. 12, the relationship between the location of the reservoir bypass aperture 415 in the bore 5 is illustrated in a graph of damping force vs. piston displacement. In the example shown, the reservoir bypass aperture 415 is located in an alternative position to FIG. 11, being at approximately 20% of the displacement of the piston 6 in the bore 5. In this arrangement, the working fluid pressure is maintained by the reservoir 11 as the piston 6 is displaced through sectors 2 and 4. However, during displacement through sectors 1 and 3, the aperture 415 is upstream of the piston 6 (in the direction of travel) which deactivates the bypass passage 423 and which may result in the working fluid in the portion of the bore 5 downstream of the piston 6 to reduce in pressure. This could mean that cavitation is more likely to occur when the piston 6 is displaced through sectors 1 and 3. However, as cavitation relates to charge pressure, the location of the reservoir bypass aperture 415 in a region of low compression or rebound damping would require high shaft velocity speeds to generate the required pressure to cause cavitation, which is less likely to occur.

(47) In FIG. 13, a cross-section of the body 4 is shown. The body 4 defines the bore 5 and eight bypass passages 421, 422, 423 in an annular region to the bore 5. The bypass passages are preferably configured as four compression bypass passages 421, two rebound bypass passages 422 and two reservoir bypass passages 423. Each bypass passage 421, 422, 423 has a kidney-shaped cross-sectional profile in order to optimise the bore 5 diameter in a given outside diameter of the body 4, which is typically limited by the spring 2.

(48) It will be apparent that obvious variations or modifications may be made to the present invention that are in accordance with the spirit of the invention and which are intended to be part of the invention. Although the invention is described above with reference to specific embodiments, it will be appreciated that it is not limited to those embodiments and may be embodied in other forms.