Adjustable bypass shock absorber

Abstract

Shock absorber (1) has a primary tube (3) with a rod (8) protruding therefrom. A rebound bypass tube (14) runs outside of the primary tube and has a rebound bypass adjuster (15) extending therefrom for rebound bypass valving adjustment. Compression bypass tube (16) runs outside of the primary tube and has a compression bypass adjuster 17 for compression bypass valving adjustment. The external reservoir (18) can be fixed to the primary tube (3) and / or to the rebound and compression bypass tubes (14, 16) e.g. part of an extrusion (extruded body (20)) of the shock absorber incorporating the primary tube; the external reservoir formed by a secondary tube (21); the rebound bypass tube forming a rebound bypass passage (22); and the compression bypass tube forming a compression bypass passage (23). The extrusion can have cooling fins 19 e.g. external fins, such as part of the extrusion.

Description

ADJUSTABLE BYPASS SHOCK ABSORBERTECHNICAL FIELD

[0001] The present invention relates to shock absorbers and in particular to bypass shock absorbers which provide different levels of damping between multiple regions within the total stroke.BACKGROUND

[0002] Hydraulic shock absorbers are used in most production vehicles, generally comprising a hydraulic cylinder having a piston on the end of a rod forming a compression chamber and rebound chamber. Valving is typically provided at least on the piston to restrict flow of fluid across the piston between the compression and rebound chambers, the restriction provided by the valving providing a velocity dependent damping force to compression and rebound motions of the shock absorber. A reservoir containing gas is provided in, on or connected to the hydraulic cylinder of the shock absorber to accommodate the displacement of rod volume into and out of the cylinder. In monotube shock absorbers, the reservoir is within the hydraulic cylinder. In twin-tube shock absorbers, the reservoir is within an outer sleeve around the hydraulic cylinder. The reservoir can also be external to the hydraulic cylinder, connected by at least one fluid conduit.

[0003] Bypass shock absorbers provide one or more bypass paths between different locations along the stroke of the shock absorber. So, for example, around the ride height position, at least one bypass tube is connected to the compression and rebound chambers on either side of the piston by holes through the wall of the cylinder. The flow through the or each bypass tube can be controlled to prevent flow being so free that damping control is lost in that bypass region, but still allowing flow between the compression and rebound chambers on either side of the piston, to reduce the damping force generated by velocity in the region when the piston is between the holes to the bypass.

[0004] This reduced damping force around ride height can provide an improved comfortable feeling for low displacements around ride height. However, when the displacements are larger, the piston passes over the bypass holes and outside the bypass zone, into a region of higher damping where larger body and / or wheel motions can be more strongly controlled. This can maintain comfort and safety by controlling for example large heave or roll motions of the body using only the higher damping across the piston when required, while allowing additional fluid to bypass the piston around ride height where lower damping forces are preferable.

[0005] United States patent number 7,628,259 shows a typical bypass shock absorber with external reservoir. It uses a finned aluminium alloy housing to reduce weight and heat build-up. Multiple bypass tubes are provided, each connected at two points by ports between the compression or rebound chamber and the bypass tube, with flow through each bypass tube controlled by a respective adjustable valve. Although this provides multiple bypass zones, the shock absorber is complex to manufacture and install having multiple bypass tubes and a separate external reservoir connected by a flexible hose.

[0006] It would therefore be desirable to provide a shock absorber that alleviates or overcomes one or more disadvantages of the known art, or at least provides an alternative.SUMMARY OF INVENTION

[0007] A first aspect of the invention provides a shock absorber (1 ) comprising a primary tube (3), a piston (31 ), and a rod (8); the primary tube (3) having a cap (4) at a cap end and a rod guide (6) at a rod guide end forming a main volume (30) separated by the piston (31 ) into a compression chamber (32) and a rebound chamber (33), the piston (31 ) being fixed to the rod (8) and the rod passing through at least the rebound chamber (33) and the rod guide (6); the shock absorber further comprising a rebound bypass tube (14), a compression bypass tube (16) and a reservoir (18) external to the primary tube; the reservoir (18) comprising a secondary tube (21 ) having a blank cap (41) at a blank cap end and a charging cap (42) at an opposite charging cap end forming a reservoir volume (40) separated by a moveablewall (43) into a liquid chamber (44) towards the blank cap end and a gas chamber (45) towards the charging cap end; the rebound bypass tube (14) being in fluid communication with the main volume (30) of the primary tube by a rebound bypass in-flow port (51 ) towards the reservoir charging cap end of the rebound bypass tube, and the rebound bypass tube (14) being in fluid communication with the liquid chamber (44) of the reservoir (18) by a reservoir rebound port (52) towards the reservoir blank cap end of the rebound bypass tube, a rebound bypass valve (60) being provided in the rebound bypass tube (14) to provide a restriction to fluid flowing along the rebound bypass tube between the rebound bypass inflow port (51 ) and the reservoir rebound port (52); the compression bypass tube (23) being divided into a first portion (23a) and a second portion (23b), a first compression bypass valve (70) being located in the first portion (23a) and a second compression bypass valve (90) being located in the second portion (23b); the first portion (23a) of the compression bypass tube being in fluid communication with the main volume (30) of the primary tube by a rebound bypass re-flow and first compression bypass in-flow port (56) on one side of the first compression bypass valve (70), and the first portion (23a) of the compression bypass tube being in fluid communication with the liquid chamber (44) of the reservoir (18) by a reservoir compression port (55) on an opposite side of the first compression bypass valve (70); the second portion (23b) of the compression bypass tube being in fluid communication with the main volume (30) of the primary tube by a second compression bypass inflow port (54) and the second portion (23b) of the compression bypass tube being in fluid communication with the main volume (30) of the primary tube by a second compression bypass reflow port (53) on an opposite side of the second compression bypass valve (90).

[0008] This arrangement advantageously provides two compression bypasses and one rebound bypass in just two tubes. It provides these three adjustable bypasses whilst having significant packaging benefits over prior arrangements, being compact and lightweight. It also reduces complexity compared to prior arrangement with multiple bypasses and can eliminate welding while having fewer leak points than conventional welded body bypass shock absorbers.

[0009] The primary tube and the reservoir may be formed from an extrusion. The extrusion may include the primary tube to provide the main volume, a secondary tube to form the reservoir volume and two minor tubes to form the compression bypass tube and rebound bypass tube. The extrusion may include cooling fins, e.g. external fins, such as formed as part of the extrusion.

[0010] The moveable wall in the reservoir may be a piston. Alternatively, the moveable wall in the reservoir may be a bladder, diaphragm or any other known means suitable for separating liquid from gas and allowing the relative volumes of each to vary.

[0011] The rebound bypass valve (60) may include a non-return valve in series or in parallel with at least one restrictive valve.

[0012] The at least one restrictive valve in the rebound bypass valve may be at least partially adjustable by a rebound bypass adjuster. For example, the rebound bypass adjuster may extend out of the rebound bypass tube to enable user adjustment. Additionally or alternatively, the rebound bypass adjuster may include a sprung detent arrangement to provide audible and / or tactile feedback on the adjustment.

[0013] Additionally or alternatively, the at least one restrictive valve in the rebound bypass valve may be or may include a needle valve arrangement.

[0014] A non-return valve (95) may be located in the second portion (23b) of the compression bypass tube to limit or prevent fluid flow from the second compression bypass re-flow port (53) to the second compression bypass in-flow port (54).

[0015] The first compression bypass valve (70) may include at least one restrictive valve (71 ).

[0016] The at least one restrictive valve (71 ) in the first compression bypass valve (70) may be at least partially adjustable by a first compression bypass adjuster. For example, the first compression bypass adjuster may extend out of the compression bypass tube to enable user adjustment. Additionally or alternatively, the firstcompression bypass adjuster may include a sprung detent arrangement to provide audible and / or tactile feedback on the adjustment.

[0017] The at least one restrictive valve in the first compression bypass valve may be or may include a needle valve arrangement. Additionally or alternatively, the first compression bypass valve may include a non-return valve effectively in parallel with the at least one restrictive valve.

[0018] The first compression bypass valve may include a pressure relief valve effectively in parallel with the at least one restrictive valve.

[0019] The second compression bypass valve (90) may include at least one restrictive valve (91).

[0020] The at least one restrictive valve (91 ) in the second compression bypass valve (90) may be at least partially adjustable by a second compression bypass adjuster. For example, the second compression bypass adjuster may extend out of the compression bypass tube to enable user adjustment. Alternatively or additionally, the second compression bypass adjuster may include a sprung detent arrangement to provide audible and / or tactile feedback on the adjustment. Alternatively or additionally, the second bypass adjuster may be part of the first compression bypass adjuster. Combining the first and second compression bypass adjusters allows the first and second compression bypass restrictive valves to be adjusted together.

[0021] The at least one restrictive valve in the second compression bypass valve may be or may include a needle valve arrangement. Alternatively or additionally, the second compression bypass valve may include a non-return valve effectively in parallel or in series with the at least one restrictive valve.

[0022] The rebound bypass valve (60) may be adjustable by a rebound bypass adjuster (15) extending through one end of the rebound bypass tube (14). Additionally or alternatively, the first compression bypass valve (70) and the second compression bypass valve (90) may be adjustable by a compression bypass adjuster(17) extending through one end of the compression bypass tube (16). For example, both the first and second compression bypass valves may be simultaneously adjusted using a single adjuster.

[0023] The rebound bypass valve (60) may be adjustable.

[0024] A shaft (64) may extend from the rebound bypass valve through an end of the rebound bypass tube, said shaft being rotatable to permit adjustment of the rebound bypass valve. The rebound bypass adjuster may thereby be provided.

[0025] The rebound bypass valve may be or may include a needle valve. Additionally, the rebound bypass valve (60) may include a sliding collar (67) able to deflect away from the needle against a spring (68) when flow is in a compression direction to reduce a restriction of the rebound bypass valve or to bypass the rebound bypass valve. This may provide the rebound chamber intake flow path during compression motions. The sliding collar may include a seat (63) for the needle valve, the seat being able to deflect away from the needle against a spring (68) when flow is in a compression direction. Alternatively, the seat (63) for the needle valve may be fixed and the sliding collar may slide to either allow or prevent flow to bypass the restriction of the rebound bypass valve.

[0026] The first compression bypass valve (70) may be adjustable and may include at least one restrictive valve (71 ) adjustable by a compression bypass valve adjuster (17). The compression bypass adjuster (17) may include a shaft (74) and the at least one restrictive valve in the first compression bypass valve may be or may include a needle valve having a needle (72) on the shaft (74), and having a seat (73).

[0027] The seat (73) may be provided on a sliding collar (78). The sliding collar (78) may be able to displace in a rebound flow direction against a non-return spring (77) to allow flow directly from the reservoir compression port (55) to the rebound bypass re-flow and first compression bypass in-flow port (56). This may provide an intake valve, i.e. a low restriction effective bypass of the at least one restrictive valve (71 ) in a rebound flow direction, while the sliding collar blocks compression directionflow from the rebound bypass re-flow and first compression bypass in-flow port (56) directly to the reservoir compression port (55), instead forcing said compression direction flow through the at least one restrictive valve (71 ).

[0028] Alternatively, the seat (73) may be fixed relative to the compression bypass tube. For example, the seat may be on the sleeve. A sliding collar (78) may be provided, displaceable in a rebound flow direction against a non-return spring (77) to allow flow directly from the reservoir compression port (55) to the rebound bypass reflow and first compression bypass in-flow port (56). Again, this may provide an intake valve, i.e. a low restriction bypass of the at least one restrictive valve (71 ) in a rebound flow direction, while the sliding collar blocks compression direction flow from the rebound bypass re-flow and first compression bypass in-flow port (56) directly to the reservoir compression port (55), instead forcing said compression direction flow through the at least one restrictive valve (71 ).

[0029] A sliding collar (78) may be provided to prevent fluid communication between the reservoir compression port (55) to the rebound bypass re-flow and first compression bypass in-flow port (56) in a default position, the sliding collar displaceable in the compression flow direction against a pressure relief spring when pressure in the compression chamber (32) exceeds a predetermined pressure, allowing flow directly from the rebound bypass re-flow and first compression bypass in-flow port (56) to the reservoir compression port (55). This may provide a pressure relief valve. The sliding collar may be the same sliding collar as in the intake valve around the restrictive valve 71 .

[0030] The second compression bypass valve (90) may be adjustable and may include at least one restrictive valve (91 ) adjustable by the compression bypass valve adjuster (17). The at least one restrictive valve (91 ) of the second compression bypass valve may be or may include a needle valve. Additionally or alternatively, the second portion (23b) of the compression bypass tube may include a non-return valve in series with the second compression bypass valve (90).

[0031] A sleeve (81 ) may be located within the compression bypass tube (16), the sleeve including a flange (82) having a seal (84) between the sleeve and thecompression bypass tube 16 to provide the divide between the first portion (23a) and the second portion (23b) of the compression bypass tube.

[0032] The sliding collar may be located around the sleeve. Alternatively or additionally, the sleeve may include holes (85) to allow flow from the restrictive valve (71 ) to the reservoir compression port (55). Alternatively or additionally, a seal may be provided between the shaft (74) and the sleeve (81 ) as part of the divide between the first portion 23a and the second portion 23b of the compression bypass tube.BRIEF DESCRIPTION OF DRAWINGS

[0033] In the drawings:

[0034] Figure 1 shows a perspective view of a shock absorber of an embodiment of the present invention.

[0035] Figure 2 shows an extrusion for the body of the shock absorber of Figure 1 .

[0036] Figure 3 shows a cross-section through the shock absorber of Figure 1 , as indicated in Figure 2.

[0037] Figure 4 shows the cross-section of Figure 3 viewed from the other side.

[0038] Figure 5 shows a cross-section through the bypass tubes of the shock absorber of Figure 1 , as indicated in Figure 2.

[0039] Figure 6 is a detailed view of a valve in the rebound bypass tube of Figure 5.

[0040] Figure 7 is a detailed view of a valve in the compression bypass tube ofFigure 5.

[0041] Figure 8 is a fluid schematic drawing of the shock absorber of Figures 1 to 7.

[0042] Figure 9 is a constant velocity force-displacement graph for the shock absorber of Figures 1 to 8.DESCRIPTION OF PREFERRED EMBODIMENT

[0043] Throughout the specification, common reference numerals are used to denote the same, similar or equivalent features.

[0044] Referring initially to Figure 1 there is shown a shock absorber 1 having a primary tube 3 closed at a first or cap end by a cap 4 which includes or has attached a cap end mount 10 for mounting a first end of the shock absorber. At the opposite end of the primary tube is a rod guide 6 which closes the rod guide end of the primary tube around the rod 8 protruding therefrom. At the end of the rod 8, a rod end mount 11 is provided for mounting the second end of the shock absorber. For example, the cap end mount may be used to connect the shock absorber to a body of a vehicle and the rod end mount may be used to connect the shock absorber to a portion of a wheel assembly or to an axle of the vehicle. In this way, the mass of the body of the shock absorber is connected to the sprung mass of the vehicle, although the shock absorber can be mounted the other way up, with the cap end mount connected to the wheel assembly or axle and the rod end mount connected to the body.

[0045] A rebound bypass tube 14 runs along a portion of the outside of the primary tube 3 and has a rebound bypass adjuster 15 extending from one end to allow adjustment of the rebound bypass valving. Similarly, a compression bypass tube 16 runs along a portion of the outside of the primary tube and has a compression bypass adjuster 17 extending from one end to allow adjustment of the compression bypass valving.

[0046] An external reservoir 18 is shown, formed in part by a secondary tube 21 . The external reservoir can be fixed to the primary tube 3 and / or the rebound and compression bypass tubes 14, 16 and in this example is part of the extruded body 20.

[0047] Fins 19 can be added to assist with cooling. These fins can be added to the outside of the primary tube 3, the secondary tube 21 or any other part of the extruded body 20.

[0048] Figure 2 shows the extruded body 20 of the shock absorber incorporating: the primary tube 3; the reservoir 18 formed by the secondary tube 21 ; the rebound bypass tube 14 forming a rebound bypass passage 22; and the compression bypass tube 16 forming a compression bypass passage 23. The fins 19 are only shown on the outside of the primary and secondary tubes 3 and 21 in this example, but could be added to the outside of the bypass passages. Also indicated in Figure 2 are the section plane positions for the whole shock absorber sections shown in Figures 3, 4 and 5.

[0049] In the sections shown in Figures 3 and 4, the main volume 30 can be seen, formed by the closing of the primary tube 3 by the cap 4 and the rod guide 6. The main volume 30 is separated by the piston 31 into a compression chamber 32 and a rebound chamber 33. The rod 8 is fixed to the piston 31 and extends through the rebound chamber 33 and out through the rod guide 6. Conventional shim stack type piston compression valving 34 and piston rebound valving 35 are shown on opposing sides of the piston, although other known types of piston compression valving and / or piston rebound valving can be used.

[0050] The secondary tube 21 of the reservoir 18 is closed at one end by a blank cap 41 and at the opposite end by a charging cap 42 to form the reservoir volume 40. Within the secondary tube 21 is a movable wall 43 which is shown as a piston, but can be a bladder or other known moveable dividing means. The movable wall 43 divides the reservoir volume 40 into a liquid chamber 44 and a gas chamber 45. A charging valve 46 is shown in the charging cap 42 to enable the gas charge in the gas volume to the be provided. A cover 47 is shown over the charging valve 46 to prevent dust and dirt ingress. While this arrangement is readily serviceable, other gas charging arrangements are known and may be used in volume production.

[0051] In Figure 3, the rebound bypass inflow port 51 (shown as two holes, but could be one or more slots, or other numbers of holes such as four smaller holes to achieve the required flow area) is visible in the main volume 30, part way between the rod guide 6 and the piston 31 . The bypass effects are displacement dependent, some being inactive for example, when the piston 31 is between the rod guide 6 andthe rebound inflow port 51 . The rebound bypass inflow port connects the main chamber 30 with the rebound bypass passage of the rebound bypass tube (not visible in this section). Similarly adjacent the blank cap 41 end of the liquid chamber 44 in the reservoir volume 40 is the reservoir rebound port 52, shown as two holes which connect the reservoir liquid chamber 44 to the rebound bypass passage 22 of the rebound bypass tube 14.

[0052] In Figure 4, the second compression bypass re-flow port 53 is visible in the main volume 30, part way between the rod guide 6 and the piston 31 . The second compression bypass in-flow port 54 is visible in the main volume 30, part way between the piston 31 and the cap 4. The combined rebound bypass re-flow and first compression bypass in-flow port 56 (coincidentally shown as two holes, but could be one or more slots, or other numbers of holes such as four smaller holes to achieve the required flow area) is visible in the main volume 30, part way between the second compression bypass in-flow port 54 and the cap 4. These three ports, the second compression bypass re-flow port 53, the second compression bypass inflow port 54 and the combined rebound bypass re-flow and first compression bypass in-flow port 56 all connect the main volume 30 to various points along the compression bypass passage 23 of the compression bypass tube 16.

[0053] Adjacent the blank cap 41 end of the liquid chamber 44 in the reservoir volume 40 is the reservoir compression port 55, shown as two holes which connect the reservoir liquid chamber 44 to a point on the compression bypass passage 23 of the compression bypass tube 16.

[0054] Figure 5 shows a sectional view of the shock absorber 1 , cut through the rebound and compression bypass tubes 14, 16 as indicated in Figure 2. Referring to Figure 5, the twin holes of the rebound bypass in-flow port 51 from the main volume of the primary tube can be seen entering the rebound bypass passage 22 of the rebound bypass tube 14 towards the rod guide end of the rebound bypass tube. Towards the cap end of the rebound bypass tube is the rebound bypass valve 60 and the rebound bypass adjuster 15 which are shown in more detail in Figure 6.

[0055] On the opposite side is the compression bypass tube 16 with the first compression bypass valve 70 and the second compression bypass valve 90 towards the cap end. Protruding through the end of the compression bypass tube is the compression bypass adjuster 17. The compression bypass passage formed by the compression bypass tube is divided into a first portion 23a and a second portion 23b. The first compression bypass valve 70 is located in the first portion 23a of the compression bypass tube and the second compression bypass valve 90 is located in the second portion 23b of the compression bypass tube, which is shown in more detail in Figure 7. At the opposite end of the compression bypass tube 16 is the second compression bypass re-flow port 53, connecting the second portion 23b of the compression bypass passage 23 to the main volume of the primary tube. In the compression bypass tube 16, between the second compression bypass re-flow port 53 and the second compression bypass valve 90 is a non-return valve 95.

[0056] Figure 6 shows the rebound bypass valve 60 which includes a restrictive valve 61 , shown as a needle valve comprising a needle 62 forming a gap to a seat 63. The rebound bypass adjuster 15, which extends out of the end of the rebound bypass tube 14, includes a shaft 64 at the end of which is the needle 62. Rotating the threaded rebound bypass adjuster varies the gap between the needle 62 and the seat 63 to adjust the restriction provided by the restrictive valve and thereby adjust the restriction within the rebound bypass passage 22.

[0057] A portion of an optional detent 65 is shown in the rebound bypass adjuster 15. Detents are beneficially used to enable tactile feedback when rotating the rebound bypass adjuster. For example, counting the number of clicks of a detent mechanism is a typical method of determining the setting of an adjustable shock absorber, so the adjuster may be wound all the way in, then a number of clicks counted as the adjuster is wound out to a desired adjustment point. Similarly, making an adjustment can be a known number of clicks from an initial adjuster position to a new adjuster position, so the size of the adjustment made is known, to some degree, by the operator.

[0058] The rebound bypass valve shown in Figure 6 includes a non-return valve 66. The non-return valve comprises a sliding collar 67 and a non-return spring 68. The seat 63 of the restrictive valve can be fixed within the rebound bypass tube 14 or located on the sliding collar 67. When flow is in the compression direction, flowing into the rebound bypass tube 14 at the reservoir rebound port 52, the sliding collar 67 is pushed away from the needle 62 and the restriction of the restrictive valve 61 is significantly reduced or bypassed allowing fluid to flow relatively freely through the rebound bypass passage 22 and on into the rebound chamber of the shock absorber. Conversely, when flow is in the rebound direction, flowing from the rebound bypass passage 22, through the rebound bypass valve and out through the reservoir rebound port 52, the sliding collar is pushed towards the needle 62, with the travel of the sliding collar being limited to achieve an operation position of the seat 63 and therefore the gap between the seat 63 and the needle 62 is the flow path, so the restrictive valve 61 is no bypassed and all rebound bypass flow must then pass through the restrictive valve 61 of the rebound bypass valve 60. When there is zero flow through the rebound bypass passage 22, the non-return spring 68 also pushes the sliding collar 67 towards the needle 62. Typically, the non-return spring is a weak spring that provides the function of returning the sliding collar to its default position towards the needle, but provides very little resistance to movement of the collar away from the needle when there is compression direction flow.

[0059] Figure 7 shows the first compression bypass valve 70 and the second compression bypass valve 90. The compression bypass adjuster 17, which extends out of the end of the compression bypass tube 16, includes a shaft 74 and the optional detent 75 for again providing tactile feedback on adjustments being made by a user, as with the rebound bypass adjuster. A sleeve 81 is screwed into the compression bypass passage 16, the sleeve 81 having a flange 82 at which a seal 84 is provided between the sleeve 81 and the wall of the compression bypass tube 16 to divide the compression bypass tube into the first portion 23a and the second portion 23b. The shaft 74 passes inside the sleeve and a seal 83 between the shaft 74 and the sleeve 81 to maintain the separation between the first portion 23a and the second portion 23b of the compression bypass tube.

[0060] The first compression bypass valve 70 is provided in the first portion 23a of the compression bypass tube 16 and includes a restrictive valve 71 formed by a gap between the needle surface 72 on the shaft 74 and the seat 73 on the end of the sleeve 81 . Flow in the compression direction enters the first portion 23a of the compression bypass tube 16 at the rebound bypass re-flow and first compression bypass in-flow port 56. The flow then passes through the restrictive valve 71 and inside the sleeve 81 around the shaft 74, exiting the sleeve through first holes 85 in the sleeve, to then pass out of the first portion 23a of the compression bypass tube 16 at the reservoir compression port 55.

[0061] The first compression bypass valve includes a non-return valve 76 comprising the sliding collar 78 and the non-return spring 77. When there is no flow or normal range compression flow, the widest portion of the sliding collar 78 sits between the rebound bypass re-flow and first compression bypass in-flow port 56 and the reservoir compression port 55, so all flow then passes through the restrictive valve 71 . However, when flow in the rebound direction, the sliding collar 78 is pushed against the non-return spring 77, the widest portion of the sliding collar 78 moves at least partially past the rebound bypass re-flow and first compression bypass in-flow port 56, thus allowing direct flow from the reservoir compression port 55 to the rebound bypass re-flow and first compression bypass in-flow port 56, effectively bypassing the restrictive valve 71 of the first compression bypass valve 70.

[0062] The first compression bypass valve also optionally includes a pressure relief valve 79 comprising the sliding collar 78 and the pressure relief spring 80. Flow in the compression direction pushed the sliding collar 78 against the pressure relief spring 80. When the pressure difference across the restrictive valve in the compression direction is sufficiently high, the sliding collar compresses the pressure relief spring 80, allowing the widest portion of the sliding collar 78 to move at least partially past the reservoir compression port 55, allowing direct flow from the rebound bypass re-flow and first compression bypass in-flow port 56 to the reservoir compression port 55, effectively bypassing the restrictive valve 71 of the first compression bypass valve 70.

[0063] The second compression bypass valve 90 is provided in the second portion 23b of the compression bypass tube 16 and includes a restrictive valve 91 formed by a gap between the needle surface 92 on the end of the shaft 74 and the seat 93 on the sleeve 81 . Flow in the compression direction enters the second portion 23b of the compression bypass tube 16 at the second compression bypass in-flow port 54. The flow then passes through the second holes 86 into the sleeve 81 , then through restrictive valve 91 , exiting into the second remainder of the second portion 23a of the compression bypass tube 16, heading past the non-return valve towards the second compression bypass re-flow port and into the main volume of the primary tube of the shock absorber.

[0064] Figure 8 schematically illustrates the hydraulic arrangement provided by the embodiment discussed above and shown in Figures 1 to 7. The second compression bypass valve 90 solely communicates with the second compression bypass re-flow port 53 (via the non-return valve 95) and the second compression bypass in-low port 54, in the second portion 23b of the compression bypass tube. However the first portion 23a of the compression bypass tube, the liquid chamber 44 of the reservoir 18 and the rebound bypass passage 22 are all used in both the rebound bypass flow path and the first compression bypass flow path.

[0065] The reservoir liquid chamber 44 is in the rebound flow path that replenishes the compression chamber 32 and in the compression flow path that replenishes the rebound chamber 33.

[0066] Figure 9 shows a graph illustrating the function of the bypasses through the stroke of the shock absorber, in the form of a constant velocity force displacement graph. The shaft displacement zero position on the graph corresponds to the piston position shown in Figures 3 and 4.

[0067] Looking initially at the compression force characteristics in the graph of Figure 9, with reference to the shock absorber features in the schematic of Figure 8, at full extension, the compression damping force is a maximum, as essentially only the piston compression valving 34 is in the flow path. This is because the piston is extended past the second compression bypass re-flow port 53 (indicated in Figure 9by the dashed line 153), so neither the first nor the second compression bypasses are in operation.

[0068] As the shock absorber contracts and the piston passes the second compression bypass re-flow port 53 indicated in Figure 9 by the dashed line 153, the second compression bypass becomes operational, with fluid in the compression chamber 32 now also being pushed into the second compression bypass in-flow port 53, past the second compression bypass valve 90 in the second portion 23b of the compression bypass tube, past the non-return valve 95 and through the second compression bypass re-flow port 53 into the rebound chamber 33. So the compression damping force of the shock absorber, when the piston is in a region between the second compression bypass re-flow port 53 (indicated by dashed line 153) and the rebound bypass in-flow port 51 (indicated by dashed line 151 ), is determined by the combination of the piston compression valving 34 and the second compression bypass valve 90 in parallel.

[0069] As the shock absorber contracts further and the piston passes the rebound bypass in-flow port 51 at the stroke position or shaft displacement indicated in Figure 9 by the dashed line 151 , the first compression bypass also becomes operational, with fluid in the compression chamber 32 now also being pushed into the rebound bypass re-flow and first compression bypass in-flow port 56, past the first compression bypass valve 70 in the first portion 23a of the compression bypass tube and into the liquid chamber 44 of the reservoir 18. While the reservoir absorbs the volume of rod displaced into the main volume 30, the remainder of the liquid flows through the non-return valve 66 around (bypassing) the rebound bypass valve 60 and flowing through the rebound bypass passage 22 back into the rebound chamber 33. So the compression damping force of the shock absorber, when the piston is in a region between the rebound bypass in-flow port 51 (indicated by dashed line 151) and the second compression bypass in-flow port 54 (indicated by dashed line 154), is determined by the combination of the piston compression valving 34, the second compression bypass valve 90 and the first compression bypass valve 70, all in parallel.

[0070] With three parallel flow paths when the piston is in the region between the rebound bypass in-flow port 51 (indicated by dashed line 151) and the second compression bypass in-flow port 54 (indicated by dashed line 154), the compression damping force provided within this region is at its lowest. The shaft displacement position at the ride height of the vehicle may be at a different point to the shaft displacement zero position on the graph in Figure 9, but it is preferably within this lowest compression damping force region. An alternative is to design the positions of the ports at different heights to provide the desired low compression force region relative to the shaft position of the shock absorber at ride height.

[0071] As the shock absorber continues to contract further and the piston passes the second compression bypass in-flow port 54 at the stroke position or shaft displacement indicated in Figure 9 by the dashed line 154, the second compression bypass ceases to be operational. However, the first compression bypass is still in operation until the piston reaches the rebound bypass re-flow and first compression bypass in-flow port 56. So the compression damping force of the shock absorber, when the piston is in a region between the second compression bypass in-flow port 54 (indicated by dashed line 154) and the rebound bypass re-flow and first compression bypass inflow port 56 (indicated by dashed line 156), is determined by the combination of the piston compression valving 34 and the first compression bypass valve 70 in parallel.

[0072] Finally, as the shock absorber contracts further again and the piston passes the rebound bypass re-flow and first compression bypass inflow port 56 at the stroke position or shaft displacement indicated in Figure 9 by the dashed line 156, the first compression bypass also ceases to be operational. Essentially, now only the piston compression valving 34 is in operation up to full compression. So the compression damping force of the shock absorber, when the piston is in a region between the rebound bypass re-flow and first compression bypass inflow port 56 (indicated by dashed line 156) and full contraction, is determined by the only the compression piston damping valve 34 as no bypasses are in operation. In this region approaching full contraction, the compression damping force returns to the same maximum force at full extension when likewise only the piston valving was effectively in operation.

[0073] Looking now at the rebound force characteristics in the graph of Figure 9, with reference to the shock absorber features in the schematic of Figure 8, at full contraction, the rebound damping force is a maximum, as essentially only the piston rebound valving 35 is in the flow path. This is because the piston is contracted past the rebound bypass re-flow and first compression bypass in-flow port 56, indicated in Figure 9 by the dashed line 165. In this region, between the cap of the shock absorber and the rebound bypass re-flow and first compression bypass in-flow port 56, neither the first nor the second compression bypasses are in operation, so the rebound damping force is determined by the piston rebound valving 35.

[0074] As the shock absorber extends and the piston passes the rebound bypass re-flow and first compression bypass in-flow port 56 indicated in Figure 9 by the dashed line 156, the rebound bypass becomes operational, with fluid in the rebound chamber 33 now also being pushed into the rebound bypass in-flow port 51 , through the rebound bypass valve 60 in the rebound bypass passage 23 in the rebound bypass tube, into the liquid chamber 44 of the reservoir 18. That flow, plus additional liquid to compensate for rod volume leaving the main volume 30, flows through the non-return valve 76, effectively bypassing the restrictive valve 71 of the first compression bypass valve in the first portion 23a of the compression bypass tube, then through the rebound bypass re-flow and first compression bypass in-flow port 56 into the compression chamber 32. So the rebound damping force of the shock absorber, when the piston is in a region between the rebound bypass re-flow and first compression bypass in-flow port 56 (indicated by dashed line 156) and the rebound bypass in-flow port 51 (indicated by dashed line 151), is determined by the combination of the piston rebound valve 35 and the rebound bypass valve 90, acting in parallel.

[0075] Finally, as the shock absorber continues to extend and the piston passes the rebound bypass in-flow port 51 (indicated by dashed line 151), the rebound bypass ceases to operates and the rebound damping force returns to the higher force provided by only having the piston rebound valving 35 in the flow path.

[0076] There are several advantages to the first portion 23a of the compression bypass tube, the liquid chamber 44 of the reservoir 18 and the rebound bypass passage 22 all being used in both the rebound bypass flow path and the first compression bypass flow path. For example, three bypasses can be provided using only two bypass tubes. Another example is the ability to adjust both the first compression bypass valve 70 and the second compression bypass valve 90 using a single compression bypass adjuster 17. However, if desired the first compression bypass valve 70 can be adjusted using a first compression bypass adjuster and the second compression bypass valve 90 can be adjusted using a second compression bypass adjuster which may be separate from the first compression bypass adjuster.

[0077] As can be seen in Figure 8, the non-return valves 66 and 76 that bypass the restrictive valves between the reservoir and the compression and rebound chambers can ensure that both chambers always contain a positive pressure. That is, the arrangement should resist cavitation which causes less of damping force when it occurs and also accelerates the break down of the damping liquid.

[0078] The rebound and compression bypass adjusters are shown exiting the bypass tubes towards the cap end of the primary tube. However, one or more of the bypass adjusters may alternatively or additionally extend out of the associated bypass tube towards the rod guide end of the primary tube.

[0079] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. For example, where any of the rebound bypass in-flow port 51 , reservoir rebound port 52, second compression bypass re-flow port 53, second compression bypass in-flow port 54, reservoir compression port 55 or the combined rebound bypass re-flow and first compression bypass in-flow port 56 are shown as either one or two holes in the drawings, they can be any number of holes or slots. The area of the holes is the primary factor determining the pressure drop through the port, so if a single tool is used to form the holes of the ports inside a bore, such as the primary tube or the secondary tube, all the ports in said tube may be formed from holes of the same size, but the number of holes for each port may vary to provides the required area in the relevant flow path.

[0080] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

CLAIMS:1 . A shock absorber (1 ) comprising a primary tube (3), a piston (31 ), and a rod (8), the primary tube (3) having a cap (4) at a cap end and a rod guide (6) at a rod guide end forming a main volume (30) separated by the piston (31 ) into a compression chamber (32) and a rebound chamber (33), the piston (31 ) being fixed to the rod (8) and the rod passing through at least the rebound chamber (33) and the rod guide (6), the shock absorber further comprising a rebound bypass tube (14), a compression bypass tube (16) and a reservoir (18) external to the primary tube, the reservoir (18) comprising a secondary tube (21) having a blank cap (41 ) at a blank cap end and a charging cap (42) at an opposite charging cap end forming a reservoir volume (40) separated by a moveable wall (43) into a liquid chamber (44) towards the blank cap end and a gas chamber (45) towards the charging cap end, the rebound bypass tube (14) being in fluid communication with the main volume (30) of the primary tube by a rebound bypass in-flow port (51 ) towards the reservoir charging cap end of the rebound bypass tube, and the rebound bypass tube (14) being in fluid communication with the liquid chamber (44) of the reservoir (18) by a reservoir rebound port (52) towards the reservoir blank cap end of the rebound bypass tube, a rebound bypass valve (60) being provided in the rebound bypass tube (14) to provide a restriction to fluid flowing along the rebound bypass tube between the rebound bypass inflow port (51) and the reservoir rebound port (52), the compression bypass tube (23) being divided into a first portion (23a) and a second portion (23b), a first compression bypass valve (70) being located in the first portion (23a) and a second compression bypass valve (90) being located in the second portion (23b), the first portion (23a) of the compression bypass tube being in fluid communication with the main volume (30) of the primary tube by a rebound bypass re-flow and first compression bypass in-flow port (56) on one side of the first compression bypass valve (70), and the first portion (23a) of the compression bypass tube being in fluid communication with the liquid chamber (44) of thereservoir (18) by a reservoir compression port (55) on an opposite side of the first compression bypass valve (70), the second portion (23b) of the compression bypass tube being in fluid communication with the main volume (30) of the primary tube by a second compression bypass inflow port (54) and the second portion (23b) of the compression bypass tube being in fluid communication with the main volume (30) of the primary tube by a second compression bypass re-flow port (53) on an opposite side of the second compression bypass valve (90).

2. A shock absorber as claimed in claim 1 wherein the primary tube and the reservoir are formed from an extrusion.

3. A shock absorber as claimed in claim 2 wherein the extrusion includes the primary tube to provide the main volume, a secondary tube to form the reservoir volume and two minor tubes to form the compression bypass tube and rebound bypass tube.

4. A shock absorber as claimed in claim 1 wherein the moveable wall in the reservoir is a piston.

5. A shock absorber as claimed in claim 1 wherein the rebound bypass valve (60) includes a non-return valve in series or in parallel with at least one restrictive valve.

6. A shock absorber as claimed in claim 5 wherein the at least one restrictive valve in the rebound bypass valve is at least partially adjustable by a rebound bypass adjuster.

7. A shock absorber as claimed in claim 5 wherein the at least one restrictive valve in the rebound bypass valve is or includes a needle valve arrangement.

8. A shock absorber as claimed in claim 1 wherein a non-return valve (95) is located in the second portion (23b) of the compression bypass tube to limit or prevent fluidflow from the second compression bypass re-flow port (53) to the second compression bypass in-flow port (54).

9. A shock absorber as claimed in claim 1 wherein the first compression bypass valve (70) includes at least one restrictive valve (71 ).

10. A shock absorber as claimed in claim 9 wherein the at least one restrictive valve (71 ) in the first compression bypass valve (70) is at least partially adjustable by a first compression bypass adjuster.

11. A shock absorber as claimed in claim 9 wherein the at least one restrictive valve in the first compression bypass valve is or includes a needle valve arrangement.

12. A shock absorber as claimed in claim 9 wherein the first compression bypass valve includes a non-return valve effectively in parallel with the at least one restrictive valve.

13. A shock absorber as claimed in claim 9 wherein the first compression bypass valve includes a pressure relief valve effectively in parallel with the at least one restrictive valve.

14. A shock absorber as claimed in claim 1 or any of claims 9 to 13, wherein the second compression bypass valve (90) includes at least one restrictive valve (91 ).

15. A shock absorber as claimed in claim 14 wherein the at least one restrictive valve (91 ) in the second compression bypass valve (90) is at least partially adjustable by a second compression bypass adjuster.

16. A shock absorber as claimed in claim 14 wherein the at least one restrictive valve in the second compression bypass valve is or includes a needle valve arrangement.

17. A shock absorber as claimed in claim 14 wherein the second compression bypass valve includes a non-return valve effectively in parallel or in series with the at least one restrictive valve.

18. A shock absorber as claimed in claim 1 wherein the rebound bypass valve (60) is adjustable by a rebound bypass adjuster (15) extending through one end of the rebound bypass tube (14).

19. A shock absorber as claimed in claim 1 or claim 18 wherein the first compression bypass valve (70) and the second compression bypass valve (90) are adjustable by a compression bypass adjuster (17) extending through one end of the compression bypass tube (16).

20. A shock absorber as claimed in claim 1 wherein the rebound bypass valve (60) is adjustable.

21. A shock absorber as claimed in claim 20 wherein a shaft (64) extends from the rebound bypass valve through an end of the rebound bypass tube, said shaft being rotatable to permit adjustment of the rebound bypass valve.

22. A shock absorber as claimed in claim 20 wherein the rebound bypass valve is or includes a needle valve.

23. A shock absorber as claimed in claim 22 wherein the rebound bypass valve (60) includes a sliding collar (67) able to deflect away from the needle against a spring (68) when flow is in a compression direction to reduce a restriction of the rebound bypass valve or to bypass the rebound bypass valve.

24. A shock absorber as claimed in claim 1 , wherein the first compression bypass valve (70) is adjustable and includes at least one restrictive valve (71) adjustable by a compression bypass valve adjuster (17).

25. A shock absorber as claimed in claim 24 wherein the compression bypass adjuster (17) includes a shaft (74) and the at least one restrictive valve in the first compression bypass valve is or includes a needle valve having a needle (72) on the shaft (74), and a seat (73).

26. A shock absorber as claimed in claim 25 wherein the seat (73) is provided on a sliding collar (78).

27. A shock absorber as claimed in claim 26 wherein the sliding collar (78) can displace in a rebound flow direction against a non-return spring (77) to allow flow directly from the reservoir compression port (55) to the rebound bypass re-flow and first compression bypass in-flow port (56).

28. A shock absorber as claimed in claim 25 wherein the seat (73) is fixed relative to the compression bypass tube.

29. A shock absorber as claimed in claim 28 wherein a sliding collar (78) is provided, displaceable in a rebound flow direction against a non-return spring (77) to allow flow directly from the reservoir compression port (55) to the rebound bypass reflow and first compression bypass in-flow port (56).

30. A shock absorber as claimed in claim 1 or claim 24 wherein a sliding collar (78) is provided to prevent fluid communication between the reservoir compression port (55) to the rebound bypass re-flow and first compression bypass in-flow port (56) in a default position, the sliding collar displaceable in the compression flow direction against a pressure relief spring when pressure in the compression chamber (32) exceeds a predetermined pressure, allowing flow directly from the rebound bypass re-flow and first compression bypass in-flow port (56) to the reservoir compression port (55).

31. A shock absorber as claimed in claim 24, wherein the second compression bypass valve (90) is adjustable and includes at least one restrictive valve (91 ) adjustable by the compression bypass valve adjuster (17).

32. A shock absorber as claimed in claim 31 , wherein the at least one restrictive valve (91 ) of the second compression bypass valve is or includes a needle valve.

33. A shock absorber as claimed in claim 31 , wherein the second portion (23b) of the compression bypass tube includes a non-return valve in series with the second compression bypass valve (90).

34. A shock absorber as claimed in claim 1 , wherein a sleeve (81 ) is located within the compression bypass tube (16), the sleeve including a flange (82) having a seal (84) between the sleeve and the compression bypass tube 16 to provide the divide between the first portion (23a) and the second portion (23b) of the compression bypass tube.

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