US20120305350A1 - Methods and apparatus for position sensitive suspension damping - Google Patents

Abstract

An apparatus and system are disclosed that provide position sensitive suspension damping. A damping unit includes a piston mounted in a fluid-filled cylinder. A vented path in the piston may be fluidly coupled to a bore formed in one end of the piston rod, creating a flow path for fluid to flow from a first side of the piston to a second side of the piston during a compression stroke. The flow path may be blocked by a needle configured to engage the bore as the damping unit is substantially fully compressed, thereby causing the damping rate of the damping unit to increase. In one embodiment, the piston includes multiple bypass flow paths operable during the compression stroke or the rebound stroke of the damping unit. One or more of the bypass flow paths may be restricted by one or more shims mounted on the piston.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/491,858 (Atty. Dkt. No. FOXF/0055USL), filed May 31, 2011, and U.S. Provisional Patent Application Ser. No. 61/645,465, filed May 10, 2012, which are herein incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The invention relates generally to vehicle suspensions and, more specifically, to variable damping rates in vehicle shock absorbers and forks.
• 2. Description of the Related Art
• Vehicle suspension systems typically include a spring component or components and a damping component or components. Often, mechanical springs, like helical springs, are used with some type of viscous fluid-based damping mechanism, the spring and damper being mounted functionally in parallel. In some instances a spring may comprise pressurized gas and features of the damper or spring are user-adjustable, such as by adjusting the air pressure in a gas spring. A damper may be constructed by placing a damping piston in a fluid-filled cylinder (e.g., liquid such as oil). As the damping piston is moved in the cylinder, fluid is compressed and passes from one side of the piston to the other side. Often, the piston includes vents there-through which may be covered by shim stacks to provide for different operational characteristics in compression or extension.
• Conventional damping components provide a constant damping rate during compression or extension through the entire length of the stroke. As the suspension component nears full compression or full extension, the damping piston can “bottom out” against the end of the damping cylinder. Allowing the damping components to “bottom out” may cause the components to deform or break inside the damping cylinder.
• As the foregoing illustrates, what is needed in the art are improved techniques for varying the damping rate including to lessen the risk of the suspension “bottoming out.”
SUMMARY OF THE INVENTION
• One embodiment of the present disclosure sets forth a vehicle suspension damper that includes a cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, where an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and where the piston borders each of the compression chamber and the rebound chamber. The vehicle suspension damper further includes a damping liquid within the cylinder and a bypass fluid flow path connecting the compression chamber and the rebound chamber, which forms a fluid path extending between an inner diameter of the piston and a side surface of the piston directly bordering one of the compression or rebound chambers.
• Another embodiment of the present disclosure sets forth a vehicle suspension damper that includes a cylinder and a damping liquid within the cylinder, the cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, where an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and where the piston borders each of the compression chamber and the rebound chamber. The piston includes multiple flow paths that enable the damping liquid to flow from the compression chamber to the rebound chamber. The multiple flow paths include a damping flow path that comprises a first fluid path extending between a first side surface of the piston directly bordering the compression chamber and a second side surface of the piston directly bordering the rebound chamber and a bypass flow path that comprises a fluid path extending between an inner diameter of the piston and one of the first side surface of the piston or the second side surface of the piston.
• Yet another embodiment of the present disclosure sets forth a vehicle suspension system that includes a first damper unit. The first damper unit includes a cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, wherein an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and wherein the piston borders each of the compression chamber and the rebound chamber. The first damper unit further includes a damping liquid within the cylinder and a bypass fluid flow path connecting the compression chamber and the rebound chamber, which forms a fluid path extending between an inner diameter of the piston and a side surface of the piston directly bordering one of the compression or rebound chambers.
• One advantage of some disclosed embodiments is that multiple bypass flow paths enable the vehicle suspension damper to be setup such that the damping rate changes (i.e., is increased) as the damper nears full compression. The increased damping rate, caused by fluid being forced through fewer flow paths formed by the multiple bypass flow paths causes the force opposing further compression of the damper to increase, thereby decreasing the chance that the damper “bottoms out.”
BRIEF DESCRIPTION OF THE DRAWINGS
• So that the manner in which the above recited features can be understood in detail, a more particular description, briefly summarized above, may be had by reference to certain example embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting the scope of the claims, which may admit to other equally effective embodiments.
• FIG. 1 shows an asymmetric bicycle fork having a damping leg and a spring leg, according to one example embodiment;
• FIGS. 2A-2C show sectional side elevation views of a needle-type monotube damping unit in different stages of compression, according to one example embodiment;
• FIG. 3 shows a detailed view of the needle and bore at the intermediate position proximate to the “bottom-out” zone, according to one example embodiment;
• FIGS. 4A and 4B illustrate the castellated or slotted valve, according to one example embodiment;
• FIGS. 5A and 5B illustrate a damping unit having a “piggy back” reservoir, according to one example embodiment;
• FIG. 6 illustrates a half section, orthographic view of a damping unit, according to another example embodiment;
• FIGS. 7A through 7E illustrate the piston ofFIG. 6, according to one example embodiment; and
• FIGS. 8A and 8B illustrate the shaft ofFIG. 6, according to one example embodiment.
• For clarity, identical reference numbers have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one example embodiment may be incorporated in other example embodiments without further recitation.
DETAILED DESCRIPTION
• Integrated damper/spring vehicle shock absorbers often include a damper body surrounded by or used in conjunction with a mechanical spring or constructed in conjunction with an air spring or both. The damper often consists of a piston and shaft telescopically mounted in a fluid filled cylinder. The damping fluid (i.e., damping liquid) or damping liquid may be, for example, hydraulic oil. A mechanical spring may be a helically wound spring that surrounds or is mounted in parallel with the damper body. Vehicle suspension systems typically include one or more dampers as well as one or more springs mounted to one or more vehicle axles. As used herein, the terms “down”, “up”, “downward”, “upward”, “lower”, “upper”, and other directional references are relative and are used for reference only.
• FIG. 1 shows anasymmetric bicycle fork100 having a damping leg and a spring leg, according to one example embodiment. The damping leg includes anupper tube105 mounted in telescopic engagement with alower tube110 and having fluid damping components therein. The spring leg includes anupper tube106 mounted in telescopic engagement with alower tube111 and having spring components therein. Theupper legs105,106 may be held centralized within thelower legs110,111 by anannular bushing108. Thefork100 may be included as a component of a bicycle such as a mountain bicycle or an off-road vehicle such as an off-road motorcycle. In some embodiments, thefork100 may be an “upside down” or Motocross-style motorcycle fork.
• In one embodiment, the damping components inside the damping leg include aninternal piston166 disposed at an upper end of adamper shaft136 and fixed relative thereto. Theinternal piston166 is mounted in telescopic engagement with acartridge tube128 connected to atop cap180 fixed at one end of theupper tube105. The interior volume of the damping leg may be filled with a damping liquid such as hydraulic oil. Thepiston166 may include shim stacks (i.e., valve members) that allow a damping liquid to flow through vented paths in thepiston166 when theupper tube105 is moved relative to thelower tube110. A compression chamber is formed on one side of thepiston166 and a rebound chamber is formed on the other side of thepiston166. The pressure built up in either the compression chamber or the rebound chamber during a compression stroke or a rebound stroke provides a damping force that opposes the motion of thefork100.
• The spring components inside the spring leg include ahelically wound spring115 contained within theupper tube106 and axially restrained betweentop cap181 and aflange165. Theflange165 is disposed at an upper end of theriser tube135 and fixed thereto. The lower end of theriser tube135 is connected to thelower tube111 in the spring leg and fixed relative thereto. Avalve plate155 is positioned within theupper leg tube106 and axially fixed thereto such that theplate155 moves with theupper tube106. Thevalve plate155 is annular in configuration, surrounds an exterior surface of theriser tube135, and is axially moveable in relation thereto. Thevalve plate155 is sealed against an interior surface of theupper tube106 and an exterior surface of theriser tube135. A substantially incompressible lubricant (e.g., oil) may be contained within a portion of thelower tube111 filling a portion of the volume within thelower tube111 below thevalve plate155. The remainder of the volume in thelower tube111 may be filled with gas at atmospheric pressure.
• During compression offork100, the gas in the interior volume of thelower tube111 is compressed between thevalve plate155 and the upper surface of the lubricant as theupper tube106 telescopically extends into thelower tube111. The helically woundspring115 is compressed between thetop cap181 and theflange165, fixed relative to thelower tube111. The volume of the gas in thelower tube111 decreases in a nonlinear fashion as thevalve plate155, fixed relative to theupper tube106, moves into thelower tube111. As the volume of the gas gets small, a rapid build-up in pressure occurs that opposes further travel of thefork100. The high pressure gas greatly augments the spring force ofspring115 proximate to the “bottom-out” position where thefork100 is fully compressed. The level of the incompressible lubricant may be set to a point in thelower tube111 such that the distance between thevalve plate155 and the level of the oil is substantially equal to a maximum desired travel of thefork100.
• FIGS. 2A-2C show sectional side elevation views of a needle-typemonotube damping unit200 in different stages of compression, according to one example embodiment. In one embodiment, the components included in dampingunit200 may be implemented as one half offork100. In another embodiment, dampingunit200 may be implemented as a portion of a shock absorber that includes a helically-wound, mechanical spring mounted substantially coaxially with the dampingunit200. In yet other embodiments, dampingunit200 may be implemented as a component of a vehicle suspension system where a spring component is mounted substantially in parallel with the dampingunit200.
• As shown inFIG. 2A, the dampingunit200 is positioned in a substantially fully extended position. The dampingunit200 includes acylinder202, ashaft205, and apiston266 fixed on one end of theshaft205 and mounted telescopically within thecylinder202. The outer diameter ofpiston266 engages the inner diameter ofcylinder202. In one embodiment, the damping liquid (e.g., hydraulic oil or other viscous damping fluid) meters from one side to the other side of thepiston266 by passing through vented paths formed in thepiston266.Piston266 may include shims (or shim stacks) to partially obstruct the vented paths in each direction (i.e., compression or rebound). By selecting shims having certain desired stiffness characteristics, the damping effects can be increased or decreased and damping rates can be different between the compression and rebound strokes of thepiston266. The dampingunit200 includes an annular floatingpiston275 mounted substantially co-axially around aneedle201 and axially movable relative thereto. Theneedle201 is fixed on one end of thecylinder202 opposite theshaft205. A volume of gas is formed between the floatingpiston275 and the end ofcylinder202. The gas is compressed to compensate for motion ofshaft205 into thecylinder202, which displaces a volume of damping liquid equal to the additional volume of theshaft205 entering thecylinder202.
• During compression,shaft205 moves into thecylinder202, causing the damping liquid to flow from one side of thepiston266 to the other side of thepiston266 withincylinder202.FIG. 2B shows theneedle201 andshaft205 at an intermediate position as the dampingunit200 has just reached the “bottom-out” zone. In order to prevent the damping components from “bottoming out”, potentially damaging said components, the damping force resisting further compression of the dampingunit200 is substantially increased within the “bottom-out” zone. The needle201 (i.e., a valve member) compresses fluid in abore235, described in more detail below in conjunction withFIG. 3, thereby drastically increasing the damping force opposing further compression of the dampingunit200. Fluid passes out of the bore around the needle through a valve that is restricted significantly more than the vented paths throughpiston266. As shown inFIG. 2C, the damping rate is increased substantially within the “bottom-out” zone until the dampingunit200 reaches a position where the dampingunit200 is substantially fully compressed.
• FIG. 3 shows a detailed view of theneedle201 and bore235 at the intermediate position proximate to the “bottom-out” zone, according to one example embodiment. As shown inFIG. 3, theneedle201 is surrounded by acheck valve220 contained within anut210 fixed on the end ofshaft205. During compression within the “bottom out” zone, thevalve220 is moved, by fluid pressure within thebore235 and flow of fluid out ofbore235, upward againstseat225 ofnut210 and the bulk of escaping fluid must flow through theannular clearance240 that dictates a rate at which theneedle201 may further progress intobore235, thereby substantially increasing the damping rate of the dampingunit200 proximate to the “bottom-out” zone. The amount ofannular clearance240 between the exterior surface of theneedle201 and the interior surface of thevalve220 determines the additional damping rate within the “bottom-out” zone caused by theneedle201 entering thebore235. In one embodiment, theneedle201 is tapered to allow easier entrance of theneedle201 into thebore235 throughvalve220.
• During rebound within the “bottom out” zone, fluid pressure in thebore235 drops as theneedle201 is retracted and fluid flows into thebore235, causing thevalve220 to move toward avalve retainer clip215 that secures thevalve220 within thenut210. In one embodiment, the valve is castellated or slotted on the face of thevalve220 adjacent to theretainer clip215 to prevent sealing the valve against theretainer clip215, thereby forcing all fluid to flow back into thebore235 via theannular clearance240. Instead, the castellation or slot allows ample fluid flow into thebore235 during the rebound stroke to avoid increasing the damping rate during rebound within the “bottom out” zone. Thevalve220 is radially retained within thenut210, which has a recess having a radial clearance between the interior surface of the recess and the exterior surface of thevalve220 that allows for eccentricity of theneedle201 relative to theshaft205 without causing interference that could deform the components of dampingunit200.
• FIGS. 4A and 4B illustrate the castellated or slottedvalve220, according to one example embodiment. As shown inFIGS. 4A and 4B, thevalve220 is a washer or bushing having an interior diameter sized to have anannular clearance240 between the interior surface of thevalve220 and the exterior surface of theneedle201 when theneedle201 passes through thevalve220.Different clearances240 may be achieved by adjusting the interior diameter of thevalve220 in comparison to the diameter of theneedle201, which causes a corresponding change in the damping rate proximate to the “bottom-out” zone. A spiral face groove is machined into one side of thevalve220 to create the castellation orslot230. It will be appreciated that the geometry of theslot230 may be different in alternative embodiments and is not limited to the spiral design illustrated inFIGS. 4A and 4B. For example, theslot230 may be straight (i.e., rectangular) instead of spiral, or the edges of theslot230 may not be perpendicular to the face of thevalve220. In other words, the geometry of theslot230 creates empty space between the surface of theretainer clip215 and the surface of thevalve220 such that fluid may flow between the two surfaces.
• When assembled, thevalve200 is oriented such that the side with theslot230 is proximate to the upper face of thevalve retainer clip215, thereby preventing the surface of thevalve220 from creating a seal against theretainer clip215. Theslot230 is configured to allow fluid to flow fromcylinder202 to bore235 around the exterior surface of thevalve220, which has a larger clearance than theannular clearance240 between thevalve220 and theneedle201. In one embodiment, two ormore slots230 may be machined in the face of thevalve220. In some embodiments, thevalve220 is constructed from high-strength yellow brass (i.e., a manganese bronze alloy) that has good characteristics enabling low friction between thevalve220 and theneedle201. In alternate embodiments, thevalve220 may be constructed from other materials having suitable characteristics of strength or coefficients of friction.
• FIGS. 5A and 5B illustrate a dampingunit300 having a “piggy back”reservoir350, according to another example embodiment. As shown inFIG. 5A, dampingunit300, shown fully extended, includes acylinder302 with ashaft305 and apiston366 fixed on one end of theshaft305 and mounted telescopically within thecylinder302. Dampingunit300 also includes aneedle301 configured to enter abore335 inshaft305. However, unlike dampingunit200, dampingunit300 does not include an annular floating piston mounted substantially co-axially around theneedle301 and axially movable relative thereto. Instead, the piggy backreservoir350 includes a floatingpiston375 configured to perform a similar function to that of floatingpiston275. A volume of gas is formed between the floatingpiston375 and one end of the piggy backreservoir350. The gas is compressed to compensate for motion ofshaft305 into thecylinder302. Excess damping liquid may enter orexit cylinder302 from the piggy backreservoir350 as the volume of fluid changes due to ingress or egress ofshaft305 from thecylinder302. InFIG. 5B, the dampingunit300 is shown proximate to the “bottom out” zone whereneedle301 has enteredbore335.
• FIG. 6 illustrates a half section, orthographic view of a dampingunit400, according to another example embodiment. As shown inFIG. 6, dampingunit400 includes apiston466 fixed on one end of ashaft405 and mounted telescopically within acylinder402. Theshaft405 includes abore435 that enables ingress of a needle (e.g.,201,301) to change the damping characteristics of the dampingunit400 proximate to the “bottom out” zone. The piston assembly includes atop shim stack481 and abottom shim stack482 attached to the top face and bottom face of thepiston466, respectively, which enable different damping resistances to be set during the compression stroke and the rebound stroke. During operation, where a needle has not enteredbore435, the damping liquid flows from one side of thepiston466 to the other side throughmultiple flow paths451,452, and453. In compression, a first flow path451 (i.e., a damping flow path) allows the damping liquid to flow from an upper portion of thecylinder402 through vented paths in thepiston466 and into a lower portion of thecylinder402, forcing thebottom shim stack482 away from the bottom face of thepiston466. A second flow path452 (i.e., a bypass flow path) allows the damping liquid to flow from an upper portion of thecylinder402 through thebore435 andshaft ports440 inshaft405 and into additional vented paths in thepiston466 through thebottom shim stack482 and into the lower portion of thecylinder402. In rebound, a third flow path453 (i.e., a rebound flow path, not shown inFIG. 6) allows the damping liquid to flow from a lower portion of thecylinder402, through different vented paths in thepiston466, through thetop shim stack481, and into an upper portion of thecylinder402. In some embodiments, thefirst flow path451 and thesecond flow path452 may be associated with separate and distinct shim stacks. For example, thebottom shim stack482 may be replaced by two shim stacks configured in a clover pattern and arranged such that a first shim stack covers the vented paths in thepiston466 corresponding to thefirst flow path451 and a second shim stack covers the additional vented paths in thepiston466 corresponding to thesecond flow path452.
• When a needle just enters bore435, the needle impedes the damping liquid in the upper portion of thecylinder402 from flowing through thesecond flow path452 due to the “plugging” effect of the needle blocking the entrance to thebore435. However, the damping liquid may continue to pass through thepiston466 through thefirst flow path451. In addition, some damping liquid may continue to flow out ofports440 frombore435 as the needle continues ingress intobore435 and decreases the fluid volume inside thebore435. It will be appreciated that the damping rate will increase as the needle blocks thesecond flow path452, thereby forcing substantially all damping liquid in the upper portion of thecylinder402 to move throughpiston466 via thefirst flow path451. At some point during ingress of the needle, the full diameter of the needle is adjacent to theshaft ports440, substantially blocking additional damping liquid from leavingbore435 through theshaft ports440. Again, the damping rate will increase as the needle blocks theshaft ports440 and fluid pressure rapidly builds up withinbore435 and acts on the needle to oppose any further compression of the dampingunit400.
• FIGS. 7A through 7E illustrate thepiston466 ofFIG. 6, according to one example embodiment. As shown inFIGS. 7A and 7B, thepiston466 includes two vented paths (i.e.,421,422) that allow damping liquid to flow from the upper portion of thecylinder402 to the lower portion of thecylinder402 via the first flow path451 (i.e., bypassing the top shim stack and entering thepiston466 proximate to the inner surface of cylinder402). Thepiston466 also includes two additional vented paths (i.e.,423,424) that allow damping liquid to flow from the upper portion of thecylinder402 to the lower portion of thecylinder402 via the second flow path452 (i.e, through thebore435 and shaft ports440). The additional vented paths are connected to thebore435 viachannels425 that fluidly couple the additional vented paths to theshaft ports440 inshaft405 through a surface on the inner diameter of thepiston466. The four vented paths described above (i.e.,421-424) allow damping liquid to flow from an upper portion of thecylinder402 to a lower portion of thecylinder402 during a compression stroke. In rebound, yet another set of four vented paths (i.e.,426,427,428,429) allow damping liquid to flow from the lower portion of thecylinder402 to the upper portion of thecylinder402 via the third flow path453 (i.e., bypassing thebottom shim stack482 and passing into the upper portion of thecylinder402 through the top shim stack481).FIG. 7C shows a side view of thepiston466 ofFIGS. 7A and 7B.FIG. 7D shows a cross section of thepiston466 showing the inner diameter that is fit overshaft405 as well as onechannel425 connected to one of the additional vented paths in the piston corresponding to the firstsecond flow path452.FIG. 7E shows a cross section of thepiston466 showing ventedpaths423 and424.
• FIGS. 8A and 8B illustrate theshaft405 ofFIG. 6, according to one example embodiment. As shown inFIGS. 8A and 8B, theshaft405 includes abore435 formed (e.g., drilled, milled, etc.) into a top portion of the shaft. In one embodiment, the top portion of the shaft may have a smaller diameter than the body of theshaft405, forming a seat a particular distance from one end of theshaft405. The piston assembly including thepiston466 and the shim stacks may be mounted over the top portion of theshaft405 and secured with a nut threaded onto the end of theshaft405. In alternative embodiments, the nut may be press fit onto theshaft405 or secured in any other technically feasible manner.
• Shaft ports440 may be formed through an outer face of the top portion of theshaft405 proximate a surface on the inner diameter of thepiston466 when mounted on theshaft405. Theshaft ports440 fluidly couple thebore435 in theshaft405 with the additional vented paths (i.e.,423,424) in thepiston466 such that fluid may flow through thebore435 via thesecond flow path452. In other words, thesecond flow path452 enables additional fluid to flow through the bottom shim stacks482 when a needle is not blocking thebore435.
• It should be noted that any of the features disclosed herein may be used alone or in combination. While the foregoing is directed to embodiments of the present disclosure, other and further embodiments may be implemented without departing from the scope of the disclosure, the scope thereof being determined by the claims that follow.

Claims (20)

1. A vehicle suspension damper comprising:

a cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, wherein an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and wherein the piston borders each of the compression chamber and the rebound chamber;

a damping liquid within the cylinder; and

a bypass fluid flow path connecting the compression chamber and the rebound chamber, wherein the bypass flow path comprises a fluid path extending between an inner diameter of the piston and a side surface of the piston directly bordering one of the compression or rebound chambers.

2. The vehicle suspension damper ofclaim 1, wherein the bypass flow path further comprises a valve member restricting fluid flow through the piston.

3. The vehicle suspension damper ofclaim 2, wherein the piston further comprises a damping flow path extending between a first side surface of the piston and a second side surface of the piston, the damping flow path comprising the valve member.

4. The vehicle suspension damper ofclaim 1, wherein the piston further comprises a damping flow path extending between a first side surface of the piston and a second side surface of the piston and including a valve member.

5. The vehicle suspension damper ofclaim 1, further comprising a second valve member connected to the cylinder and operable to restrict the bypass flow path at predetermined positions during a stroke of the damper and to be unrestrictive of the bypass flow path at other positions during the stroke.

6. The vehicle suspension damper ofclaim 5, wherein the second valve member comprises a needle.

7. The vehicle suspension damper ofclaim 6, further comprising a floating piston mounted in fluid communication with an interior of the cylinder, the floating piston separating the damping liquid from a volume of gas contained adjacent a second side of the floating piston.

8. The vehicle suspension damper ofclaim 7, further comprising a reservoir, the reservoir comprising:

a reservoir cylinder having a first end and a second end, wherein the first end of the reservoir cylinder is fluidly coupled to the cylinder; and

the floating piston mounted inside the reservoir cylinder and axially movable relative thereto, the floating piston forming a reserve volume of damping liquid between a first side of the floating piston and the first end of the reservoir cylinder and forming a volume of gas between a second side of the floating piston and the second end of the reservoir cylinder.

9. The vehicle suspension damper ofclaim 7, wherein the floating piston surrounds and moves relative to a needle.

10. The vehicle suspension damper ofclaim 7, wherein the needle restricts an opening of the bypass flow path proximate the inner diameter of the piston at predetermined positions during a stroke of the damper.

11. A vehicle suspension damper comprising:

a cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, wherein an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and wherein the piston borders each of the compression chamber and the rebound chamber; and

a damping liquid within the cylinder,

wherein the piston includes multiple flow paths that enable the damping liquid to flow from the compression chamber to the rebound chamber, the multiple flow paths including:

a damping flow path that comprises a first fluid path extending between a first side surface of the piston directly bordering the compression chamber and a second side surface of the piston directly bordering the rebound chamber, and

a bypass flow path that comprises a second fluid path extending between an inner diameter of the piston and one of the first side surface of the piston or the second side surface of the piston.

12. The vehicle suspension damper ofclaim 11, wherein the multiple flow paths further include a rebound flow path that comprises a fluid path extending between an inner diameter of the piston and one of the first side surface or the second side surface.

13. The vehicle suspension damper ofclaim 12, wherein the damping liquid is forced through the damping flow path and the bypass flow path during a compression stroke of the vehicle suspension damper, and wherein the damping liquid is forced through the rebound flow path during a rebound stroke of the vehicle suspension damper.

14. The vehicle suspension damper ofclaim 12, wherein the bypass flow path further comprises a valve member restricting fluid flow through the piston and a second valve member connected to the cylinder and operable to restrict the bypass flow path at predetermined positions during a stroke of the damper and to be unrestrictive of the bypass flow path at other positions during the stroke.

15. A vehicle suspension system comprising:

a first damper unit that includes:

a cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, wherein an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and wherein the piston borders each of the compression chamber and the rebound chamber,

a damping liquid within the cylinder, and

a bypass flow path connecting the compression chamber and the rebound chamber, wherein the bypass flow path comprises a fluid path extending between an inner diameter of the piston and a side surface of the piston directly bordering one of the compression or rebound chambers.

16. The vehicle suspension system ofclaim 15, wherein the bypass flow path further comprises a valve member restricting fluid flow through the piston.

17. The vehicle suspension system ofclaim 15, wherein the piston further comprises a damping flow path extending between a first side surface of the piston directly bordering the compression chamber and a second side surface of the piston directly bordering the rebound chamber, and wherein the piston includes a valve member.

18. The vehicle suspension system ofclaim 15, further comprising a spring mounted coaxially with the first damper unit.

19. The vehicle suspension system ofclaim 15, wherein the first damper unit is included in a leg of a fork.

20. The vehicle suspension system ofclaim 15, further comprising:

a second damper unit substantially similar to the first damper unit; and

one or more springs mounted substantially in parallel with the first and second damper units.

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