Methods and apparatus for protecting a shock absorber from bottoming

Methods and apparatus for accommodating vehicle suspensions that may bottom out. Some embodiments of the present invention include the secondary shock absorber placed within a primary shock absorber. Yet clear embodiments describe a shock absorber having multiple fluid flowpaths during compression, with one of the flowpaths being active near the bottoming-out condition.

FIELD OF THE INVENTION

The present invention pertains to improvements in shock absorbers, and more particularly to shock absorbers having position-dependent damping force characteristics.

BACKGROUND OF THE INVENTION

Some vehicles travel over surfaces where there are large surface irregularities. One example of such a vehicle would be an all terrain vehicle traveling over an unprepared surface. Yet other vehicles travel at high speeds over hills, with the prospect of becoming airborne at the top of the hill. An example of such a vehicle would be a motorcycle engaged in a motocross race. Yet other vehicles are subjected to relatively infrequent loads that nonetheless fully compress the suspension. An example of such a vehicle is an aircraft landing on an aircraft carrier. In all of these cases, as well as others, there is a need to design the suspension of the vehicle for the possibility that the vehicle suspension will bottom out in compression. Likewise, there is also a need to design vehicle suspensions for the possibility that the suspension will bottom out in rebound.

Various embodiments of the present invention address these situations in novel and unobvious ways.

SUMMARY OF THE INVENTION

Some embodiments of the present invention pertain to shock absorbers having multiple flowpaths for the constrained flow of hydraulic fluid during compression of a vehicle suspension. In some embodiments one or more of these flowpaths are inactive during some portions of the compressive stroke.

Yet other embodiments of the present invention pertain to a shock absorber having within it a second, internal fluid shock absorber comprising a piston and cylinder that are separated by a spring. In some embodiments the spring forces this piston apart from this cylinder. In yet other embodiments there is a mechanical means for keeping the piston within the sliding interior surface of the cylinder.

Some embodiments of the present invention pertain to a shock absorber which has a first, reduced-force compressive characteristic during an initial portion of the compression of the vehicle suspension. There is a second, increased-force characteristic during a latter portion of this compressive stroke.

Yet other embodiments of the present invention pertain to a shock absorber having at least two flowpaths which are active during at least a portion of the compression of the vehicle suspension. A first characteristic provides a relatively constant resisting force during application of a constant compressive stroking velocity. The second compressive characteristic provides a progressively increasing force through a predetermined range of displacement when moved at a relatively constant compressive stroking velocity.

Some embodiments of the present invention pertain to shock absorbers having multiple flowpaths for the constrained flow of hydraulic fluid during rebound of a vehicle suspension. In some embodiments one or more of these flowpaths are inactive during some portions of the rebound stroke.

It will be appreciated that the various apparatus and methods described throughout this application can be expressed as a large number of different combinations and subcombinations. All such combinations and subcombinations are contemplated herein, it being recognized that the explicit expression of each of these myriad combinations is excessive and unnecessary.

These and other features and aspects of different embodiments of the present invention will be apparent from the claims, specification, and drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Some embodiments of the present invention pertain to a shock absorber for a vehicle suspension. The shock absorber includes features that increase the damping force when there is significant travel of the vehicle suspension, such that there is a possibility of the suspension reaching a bottoming out condition in either compression or rebound. In these embodiments, the damping characteristics of the shock absorber depend upon not only the relative velocity of one end of the shock absorber relative to the other end, but also the position of one end of the shock absorber relative to the other position.

In some of these embodiments the shock absorber comprises a main piston slidable within a main cylinder, and further a second shock absorbing apparatus contained within the main cylinder. In some embodiments this second shock absorbing apparatus comprises a secondary piston slidable within a secondary cylinder. This second internal shock absorber is located within the main compression volume of the main cylinder. The secondary piston strokes within the secondary cylinder upon application of a force by the elements of the main shock absorber. In some embodiments, the second shock absorber is active to provide a damping force only during a portion of the compressive stroke of the main shock absorber.

Some embodiments of the present invention are adapted and configured to provide a force that opposes compression of the vehicle suspension with a forcing characteristic that increases significantly as the suspension approaches a bottoming condition. In one embodiment, the main shock absorber provides a forcing characteristic that is relatively constant for a constant stroking velocity during the routine movement of the vehicle suspension. However, if the vehicle suspension approaches bottoming out during compression, the forcing characteristic increases (for a constant velocity) as the stroke nears the bottoming condition.

Yet other embodiments of the present invention pertain to shock absorbers adapted and configured as shown and described herein for the protection of a vehicle suspension from bottoming during rebound of the suspension. The embodiments herein can readily be modified to accommodate the main rod that extends through the rebound chamber in some shock absorbers. As one example, the cylindrical inner pistons and inner cylinders can be made annular, such that the rod extends through the central aperture.

Yet other embodiments of the present invention pertaining to a shock absorber having position-dependent forcing characteristics that resist vehicle compression, and which are externally adjustable, and which can include means for externally adjusting a second flow path. In some embodiments there is provided an external adjustment which alters a fixed-orifice flowpath. Yet other embodiments include an external adjustment which changes the relationship of the position-dependent characteristic relative to the stroking position of the main shock absorber.

FIG. 1shows a cross-sectional view of a prior art shock absorber20. A main piston22is coupled to a moveable rod24, piston22being slidably received within the inner diameter26.1of a main cylinder26. Piston22is retained on the end of rod24by a coupling nut24.2. Main piston22generally subdivides the internal volume of cylinder26into a compression volume26.4located between piston22and the compression end28of shock20, and a second rebound volume26.5located between piston22and the rebound end30of shock20. The movement of piston22and rod24toward rebound end32results in a reduction in the size of compression volume26.1, and the subsequent flow of hydraulic fluid20.1through a compression flowpath32in piston22and into the simultaneously enlarging rebound volume26.5. Likewise, movement of piston22toward rebound end30of shock20results in the flow of hydraulic fluid20.1through a rebound flowpath34in piston22and into the simultaneously enlarging compression volume26.4.

In order to compensate for changes in the density of hydraulic fluid20.1, shock absorber20includes a nitrogen chamber separated by a reservoir piston38from the fluid-wetted volume of cylinder26.

Shock absorber20is typically used with the suspension of a vehicle. Rod24includes a first suspension attachment26.3, and end cap26.2of cylinder26includes a second suspension attachment26.3. These suspension attachments26.3permit the pivotal connection of shock absorber20to a portion of the vehicle suspension on one end, and on the other end to a portion of the vehicle frame. It is well known to use shock absorbers on many types of vehicles, including motorcycles, buses, trucks, automobiles, and airplanes. Further, although shock absorber20has been referred to for being used on a vehicle, shock absorbers are also known to be used in other applications where it is beneficial to dampen the movement of one object relative to another object, such as dampers for doors.

Compression flowpath32includes a fluid passageway interconnecting volumes26.4and26.5with a one-way valve in the flowpath32. This one-way valve can be one or more annular shims which are prevented from flexing in one direction (and thus substantially restricting flow), but able to flex in a different direction (and thus allow flow in this opposite direction). Likewise, rebound flowpath34provides fluid communication between volumes26.4and26.5through a one-way valve. Often, the one-way valve of the compression flowpath32has different characteristics than the one-way valve of rebound flowpath34.

FIG. 1bshows a cross-sectional view of a second prior art shock absorber20′. Shock absorber20′ includes a second, separate cylinder37′ which includes gas reservoir40′. A piston38′ slidably received within cylinder37′ separates gas volume40′ from compression volume26.4′. An external fluid connection39′ interconnects the hydraulic fluid end of piston37′ with the compression end of shock absorber20′. Cylinder37′ includes a gas port in one end of cylinder37′ for entry or removal of nitrogen.

Shock absorber20′ includes means for varying the fluid resistance of a flowpath interconnecting compression volume26.4′ and rebound volume26.5′. Rod24′ includes an internal passage24.1′ that extends out one end of shaft24′, and extends in the opposite direction towards attachment26.3′. The open end of internal passage24.1′ is in fluid communication with one or more orifices24.4′ that extend from internal passage24.1′ to rebound volume26.5′. The flow of fluid through this internal passageway between the compression and rebound volumes is restricted by a metering needle24.3′ received within internal passage24.1′. The position of metering needle24.3′ can be altered by a pushrod24.6′ also extending within internal passage24.1′. Push rod24.6′ includes an end24.7′ that is adapted and configured to mate with an internal adjustment screw24.5′. The inward adjustment of screw24.5′ acts on the angled interface to push rod24.6′ and adjustment needle24.3′ toward a position of increased resistance in the internal flowpath.

FIG. 1cis a cross sectional view of a portion of another prior art shock absorber. The apparatus inFIG. 1cshows a piston22″ coupled to a shaft24″ by a coupling nut24.2″. Shaft24″ includes an internal flowpath from orifice22.3″ through internal passage24.1″ and into shaft orifice24.4″. This internal flowpath bypasses piston22″.

Piston22″ includes a pair of shim sets36″, each shim set shown including 4 individual washers. During operation in compression (i.e., movement inFIG. 1ctoward the left) fluid is able to freely enter compression flowpath28.1″. However, fluid is unable to exit through flowpath28.1″ and into the rebound side of the shock absorber unless fluid pressure is sufficiently great to bend the periphery shim stack36C″ away from the shim edge support29.4″ of piston22″. During operation in rebound, (i.e., movement inFIG. 1ctoward the right) fluid is able to freely enter compression flowpath30.1″. However, fluid is unable to exit through flowpath30.1″ and into the compression side of the shock absorber unless fluid pressure is sufficiently great to bend the periphery shim stack36R″ away from the shim edge support29.4″ of piston22″.

A resilient seal22.1″ substantially seals the compressive side of piston22″ from the rebound side of piston22″. An energizing backup seal22.2″ urges seal22.1″ outwardly into contact with the inner wall of the cylinder.

Although what has been shown described is a shock absorber20that is linear in operation, the prior art of shock absorbers further includes rotary dampers, such as the toroidal damper disclosed in U.S. Pat. No. 7,048,098, incorporated herein by reference.

As used herein, the word compression refers to the action and direction of the shock absorber during compression of the wheel suspension, this term being synonymous with the term jounce. Therefore, the end of the shock absorber referred to as a compression end is the end which has a reduction in internal volume (due to movement of the piston relative to the cylinder) during compression of the vehicle suspension. The rebound end of the shock absorber is the end that is opposite of the compression end.

FIGS. 2-5depict a shock absorber120according to one embodiment of the present invention. Shock absorber120is similar to shock absorber20, except for the differences noted herein. The use of an N-series prefix for an element number (NXX) refers to an element that is the same as the non-prefixed element (XX), accept as shown and described thereafter.

Shock absorber120includes a second internal shock absorber100which actively provides damping only during a portion of the c stroke. Internal shock absorber100includes a second piston150located within a second cylinder160. Piston150is coupled to rod24by a piston retaining nut172.2. Piston150is captured within cylinder160with a piston retaining member172.1that is threaded onto the outer diameter of cylinder160after piston150is inserted into the interior of cylinder160. Preferably, a spring170biases piston150relative to cylinder160such that an interior variable volume160.4is formed therebetween. As shown and described herein, shock absorber120includes a second internal shock absorber that provides damping during a portion of the compressive stroke. However, the present invention also contemplates those embodiments in which the second internal shock absorber is adapted and configured to provide damping during the rebound stroke.

The outer diameter of piston150is adapted and configured to support a seal that discourages any leakage of hydraulic fluid between the inner diameter160.1of cylinder160and the outer diameter of piston150. Preferably, seal152is a resilient seal. In some embodiments, seal152comprises multiple members, such as an inner spring or o-ring that forces outward a Teflon© seal.

Internal shock absorber100includes a first fluid flowpath154for the flow of hydraulic fluid during compression of shock100, and a second refill flowpath156for fluid flowing during the refilling of compression volume160.4. Referring toFIG. 4, arrows indicate the general direction of flowpath154. Fluid from compression volume160.4flows through one or more orifices or passageways154.1in piston150. The exit of these passageways from shock100is preferably through one or more one-way valves154.2. In one embodiment, these one-way valves include one or more shims36captured between coupling nut24.2and piston150. These one-way valves are free to flex open to permit fluid flow out of interior160.4into the main compression volume26.4. However, the outer edge of at least one of these shims is supported by piston150, and is therefore unable to flex in the opposite direction, and thus unable to permit the flow of fluid into volume160.4.

FIGS. 2-5depict the action of shock absorber120during compression of a vehicle suspension (not shown). Referring first toFIG. 2, during the initial stages of the compressive stroke, piston22and shock absorber100are both moving toward compression end28by action of rod24. Hydraulic fluid within compression volume26.4is being forced through compression flowpath32within piston22. Piston22is active in providing damping during this initial portion of compression stroke. However, both piston150and cylinder160of shock100are moving in unison, with no relative motion there between. Therefore, fluid within compression volume160.4remains still within that volume, and shock absorber100is inactive during the initial portion of the compression stroke.

Referring toFIG. 3, during an intermediate portion of the compression stroke the forward face164of cylinder160contacts the opposing face26.25of end cap26.2. Preferably, surfaces164and26.25are adapted and configured to provide a seal that discourages fluid flow there between. In some embodiments, a resilient seal such as an o-ring can be placed within a groove on one of the surfaces to further discourage leakage of fluid from volume160.4.

After contact is established between cylinder160and end cap26.2, further movement of rod24toward compression end28results in relative movement of piston150within cylinder160, such that there is a reduction in the internal volume160.4available for fluid20.1. Fluid is forced to leave interior volume160.4by way of compression flowpath154, such that shock absorber100becomes active in providing a force resisting further compression of the vehicle suspension. In some embodiments, piston22is adapted and configured to remain active during the entire stroke in providing a force resisting compression of the suspension, such that the total force opposing compression of the suspension results from the flow characteristics of main compression flowpath32and secondary compression flowpath154. In some embodiments, the forces resulting from the flow of fluid along flowpath154are substantially greater than the forces required to move fluid along main compression flowpath32. Second shock absorber100actively provides a resistive force as piston150slides within cylinder160. This relative motion continues until piston150reaches a mechanical stop, such as an internal stop within cylinder160or bottoming of spring170.

FIG. 5depicts the refilling of internal shock100. As the vehicle suspension moves in the rebound direction, rod24moves toward rebound end30of shock120, and piston160separates from contact with end cap26.2. Since piston150has moved away from the inner lip of retaining member172.1, it is biased back toward contact with this lip by the action of spring170. Spring170biases piston150relative to cylinder160such that compression volume160.4increases. Fluid flows back into this volume by means of a refilling flowpath. In one embodiment, fluid is free to flow into a central orifice165in cylinder160. In some embodiments, there is an alternate refilling flowpath that provides fluid from main rebound volume26.5, through one or more refilling orifices24.4into an internal passageway24.1of rod24, through a refill passageway156.1and piston150, and through a one-way valve156.2. In one embodiment, one-way valve156.2is comprised of one or more annular shims trapped between retaining nut172.2and piston150. However, although one-way valves are described herein comprising one or more shims supported such that they can flex in only one direction, the present invention contemplates other types of one-way valves, including for example a ball in a pocket supported by a spring.

FIGS. 6,7, and8depict a shock absorber220according to another embodiment of the present invention. Shock220includes a second, internal shock absorber200according to another embodiment of the present invention. Internal shock200includes a cylinder260that is coupled to the internal compression end28of shock220. In one embodiment, cylinder260is threadably coupled or otherwise attached to end cap26.2. A retaining lip262of cylinder260captures a piston250therein. A spring270biases piston250away from end28, so as to create an internal compression volume260.4. In some embodiments, the main cylinder26has an inner diameter that is the same as the inner diameter of cylinder260.

Shock220includes a metering needle274having a tip and shaft extending through volume260.4. In one embodiment, needle274is captured by end cap26.2, with the shaft of needle274being coaxial with the centerline of shock220, and thereby being coaxially aligned with rod24and internal passage24.1. Further, piston250includes within it a central orifice255which is adapted and configured to receive within it the tip and shaft of needle274. Piston250is slidable within the inner diameter of cylinder260. Further, in some embodiments, piston250is sealed within the inner diameter of cylinder260by a resilient seal assembly252.

Rod24of shock220includes a central passage24.1which provides fluid communication with rebound volume26.5, through a pair of orifices24.4and an adjustable main metering needle24.3. This central passageway24.1is open through the end of rod24and through a ram276attached to the end of rod24. One or more coupling nuts24.2hold ram276in place. Piston250preferably includes a pocket adapted and configured to receive ram276.

In those embodiments of the present invention pertaining to protection for bottoming during rebound of the suspension, piston250and cylinder260are annular, with rod24extending through an inner aperture of cylinder260. Preferably, the piston seals against the inside surfaces of both the inner wall and outer wall of the cylinder. Preferably, there are a plurality of metering needles274equally spaced around the cylinder.

During the initial portion of the compression stroke, the damping forces of shock absorber220are provided by a main compression flowpath32. As best seen inFIG. 6, this compression flowpath extends from the central passageway of rod24within compression volume26.4, past metering needle24.3, through orifices24.4, and into rebound volume26.5. During the initial portion of the compression stroke, second shock absorber200is inactive, and does not provide any damping force.

As the vehicle suspension continues to compress, ram276of rod24comes into contact with the complimentary-shaped pocket of piston250. Further, the central passageway24.1through rod assembly24generally aligns with central orifice255of piston250. As shock absorber220continues in the compression stroke, ram276pushes piston250relative to cylinder260. This relative motion results in a reduction in compression volume260.4, and hydraulic fluid20.1flows through an annular orifice formed between the outer surface of needle274and the central passage255of piston250. The hydraulic fluid flowing past needle274and orifice255continues to flow along alternate compression flowpaths254. One flowpath flows through a series of orifices in the sidewalls of ram276and into compression volume26.4. Yet another flowpath continues down central passage24.1and into rebound volume26.5.

In some embodiments, needle274has an exterior shape adapted and configured to provide variable damping characteristics. In one embodiment, the distal end of the metering needle starts with a conical tip, transitions to a generally cylindrical shape, which transitions to a tapered, conical shape over a central portion of needle274, and finally to a larger, generally cylindrical final diameter near the end of the needle.

As an illustrative example, in one embodiment the initial diameter of needle274is about ½ of the inner diameter of central orifice255. The final diameter of the needle is approximately 80% to 95% of the inner diameter of orifice255. These two regions of the needle are interconnected with a taper between about 5 degrees to about 11 degrees.

The damping characteristics of one version of this illustrative example are shown inFIG. 9. The graph ofFIG. 9shows the normalized compressive stroke forces as a function of the normalized displacement of rod24as the rod is oscillated at a constant rate. During the initial part of the compression stroke, there is a first compression force characteristic210which is relatively constant between 0.2 and 0.25 in a non-dimensional displacement range from about 0.3 to about 0.6. During this initial range, compressive forces are provided by the flow of hydraulic fluid through the main compression flowpath32.

At a non-dimensional displacement of about 0.6 to 0.7, contact is achieved between ram276and piston250. Through the non-dimensional displacement range of about 0.7 to 1.0, there is a much steeper compression characteristic212which is a result of the flow of hydraulic fluid through both main compression flowpath32and second compression flowpath254.

As rod24and ram276retract away from piston250, spring270biases piston250away from the compression end28of shock220. As the piston continues to move under the action of spring270, compression volume260.4refills with hydraulic fluid flowing in the reverse direction along flowpath254. A retaining lip262of cylinder260keeps piston250captured within cylinder260.

FIGS. 10-11depict a portion of a shock absorber320according to another embodiment of the present invention. Shock absorber320includes a second internal shock absorber300which is coupled to the end of rod24. Shock absorber300includes a piston350outwardly biased by a spring370from the bottom of a cylinder360. The bottom end of cylinder360is coupled to the end of rod24. Piston360is captured within cylinder360by a piston retaining member372.1. Piston350and cylinder360form a compression volume360.4therebetween. Piston360includes a one-way valve354.2preferably formed by one or more shims in a manner as previously described. One-way valve354.2provides controlled resistance to the flow of fluid out of chamber360.4, and the discouragement of fluid flow into chamber360.4.

Shock absorber320includes a ram376attached to piston360. Preferably, ram376includes a central flow passage in fluid communication with a one-way valve356.2that form part of a refill flowpath356for refilling chamber360.4during rebound.

As best seen inFIG. 10, during the initial portion of the compressive stroke, the resistive force applied by shock absorber320is provided by the flow of fluid through a main compression flowpath32as previously described. Internal shock absorber300is not active during the initial portion of the stroke.

Referring toFIG. 11, as ram376contacts end cap26.2located on the compression end of shock320(FIG. 11showing a portion of ram376being received within a pocket of end cap26.2), further compressive motion of rod24results in the motion of cylinder360relative to piston350. This relative motion reduces the size of compression volume360.4, with fluid20.1subsequently flowing through compression flowpath354, out of one-way valve354.2, and into a reservoir366formed by cylinder360, end cap26.2, and piston350. As piston350moves relative to cylinder360, second shock absorber300becomes active and adds to the force of shock absorber320which resists compression of the vehicle suspension.

FIGS. 12a,12b, and12care cutaway views of a shock absorber420according to another embodiment of the present invention. Shock absorber420is the same as shock absorber220as previously described, except for the changes which are shown and described herein. Shock absorber420includes means for externally adjusting the second flow path as is shown and will be described.

Shock absorber420includes one or more features for externally adjusting the damping characteristics of second internal shock absorber400. In one embodiment, shock absorber400includes two features for externally adjusting the damping of the second compression characteristic (i.e., when the internal shock absorber400is active). However, some embodiments include only one of these features to be described.

Shock absorber400includes an auxiliary compression flowpath454.3that is externally adjustable. As best seen inFIGS. 12aand12c, auxiliary path454.3includes a first passageway in end cap26.2interconnecting compression volume460.4with an adjustment screw478. The external end of screw478is sealed from the fluid environment, and includes an adjustment feature such as an internal hex head or external hex head. The other end of screw478is in fluid communication with the first passageway previously described, and also with a second passageway that is in fluid communication with compression volume26.4. Screw478is threadably received within end cap26.2. As the screw is turned along the threads, a nose of screw478projects more or less into the second flow passage, and thereby forms more or less of a restriction to flow. Adjustment of screw478results in a fixed-characteristic fluid bypass.

In some embodiments, shock absorber420includes a second external adjustment feature, as best seen inFIGS. 12aand12b. Metering needle474is threadably received within end cap26.2. One end of the body of needle474projects into a slotted adjuster wheel474.5. Adjuster wheel474.5is externally accessible and turnable by a person's hand. Turning of wheel474.5results in axial movement of needle474relative to end cap26.2. By this axial movement of needle474, the metering portions of the shaft are displaced, with a subsequent change in the displacement characteristics of shock absorber420. Referring toFIG. 9, the second compression characteristic of shock420can be moved laterally along the displacement axis.

FIGS. 13aand13bdepict portions of a shock absorber520according to another embodiment of the present invention. A shock520includes a second internal shock absorber500which provides damping during a portion of the stroke of the rod relative to the shock absorber cylinder. Shock520is shown partly compressed, with ram576making contact with second internal shock absorber500. Internal shock500includes a cylinder560that is coupled to the internal compression and the28of shock520. In one embodiment, cylinder560is threadably coupled to end cap26.2. Internal shock absorber500includes second piston550located within a second cylinder560. A retaining ridge562of cylinder560captures piston550therein. A spring570biased piston550away from end28, so as create an internal compression volume560.4. A circumferential seal552is outwardly biased by a circumferential spring into sealing contact with the inner diameter of piston560.

Piston550includes a central passage550.1through which fluid from volume560.4can flow. Further, piston550includes a plurality of shims554.2which provide a restriction to flow from volume560.4through passageway554.1, as indicated by compression flowpath arrow554. However, valve554.2does not present appreciable restriction to a refilling flowpath556. Instead, a shim556.2, retained on the opposite side of piston550, deflects to allow a refilling flow to chamber560.4, but substantially prevents flow out of chamber560.4. Piston550includes a threaded insert550.2that includes a central orifice555in fluid communication with passageway550.1and internal volume560.4. As best seen inFIG. 13b, insert550.2is adapted and configured to abut against the end of ram576.

During compression of shock absorber520, ram576(which is threadably captured to rod24) makes contact with threaded insert550.2, and any further increase in compression stroke pushes piston550relative to cylinder560. During this stroking of second internal shock absorber500, hydraulic fluid within chamber560.4can flow out through parallel compression flowpaths.

One flowpath for hydraulic fluid is through central passage550.1, through central orifice555, and into internal passage24.1of rod24. This fluid can pass into compression volume26.4by way of flow passages within ram576(as indicated by compression flowpath arrow554.4), and further through internal passage24.1, past the restriction of metering needled24.3, and into rebound volume26.5(as best seen inFIG. 13a). In addition, fluid expelled from volume560.4during stroking of piston550, can flow via flowpath554into compression volume26.4. This flowpath is open when the pressure differential across piston550is large enough to deflect the one-way valve554.2.

When rod24retracts, piston550is biased to move and refill volume560.4and refill volume560.4by spring570. Hydraulic fluid refills volume560.4by way of flowpath556past one-way valve556.2. Fluid can also refill in a parallel flowpath through orifice555and passage550.1.

One embodiment of the present invention pertains to an hydraulic shock absorber for damping compression and rebound of a vehicle suspension. The embodiment also includes a first piston coupled to a rod and slidably received within a first cylinder, the first piston and the first cylinder defining a first variable hydraulic volume that reduces in size during rebound of the suspension. A second piston is slidably received and captured within a second cylinder, the second piston and the second cylinder defining a second variable hydraulic volume that reduces in size during rebound of the suspension, the second cylinder being located within the first fluid volume. The second volume refills with hydraulic fluid during compression of the suspension.

Another embodiment of the present invention pertains to a method for damping rebound of a vehicle suspension. The embodiment includes providing a first piston slidably received within a first cylinder and a second piston slidably received within a second cylinder, the second cylinder being located within the first cylinder, the first piston being in fluid communication with a first flowpath for hydraulic fluid, the second piston being in fluid communication with a second flowpath for the hydraulic fluid. The embodiment includes rebounding the vehicle suspension by a first amount and sliding the first piston relative to the first cylinder during the rebounding by a first amount. The embodiment includes forcing hydraulic fluid through the first flowpath by sliding the first piston during the rebounding by a first amount, and not sliding the second piston relative to the second cylinder during the rebounding by a first amount. The embodiment includes rebounding the vehicle suspension by a second amount following the first amount, sliding the first piston relative to the first cylinder during the rebounding by a second amount, and sliding the second piston relative to the second cylinder during the rebounding by a second amount. The embodiment includes forcing hydraulic fluid through the second flowpath by sliding the second piston during the rebounding by a second amount.

Another embodiment of the present invention pertains to a hydraulic shock absorber for damping compression and rebound of a vehicle suspension. The embodiment includes a first piston coupled to a rod and slidably received within a first cylinder, the first piston and the first cylinder defining a first variable hydraulic volume that reduces in size during rebound of the suspension. The embodiment includes a second piston slidably received within a second cylinder, the second piston and the second cylinder defining a second variable hydraulic volume that reduces in size during rebound of the suspension. The second cylinder is located within the first fluid volume. There is a sealing member between the second piston and the second cylinder for sealing the second volume, wherein the second volume refills with hydraulic fluid during compression of the suspension.

Another embodiment of the present invention pertains to a hydraulic shock absorber for damping rebound of a vehicle suspension which compresses and rebounds. The embodiment includes a first piston coupled to a rod and slidably received within a first cylinder, the first piston and the first cylinder defining a first variable hydraulic volume that reduces in size during rebound of the suspension, at least one of the first piston or the first cylinder defining a first flowpath for fluid during rebound of the suspension. The embodiment includes a second piston slidably received within a second cylinder, the second piston and the second cylinder defining a second variable hydraulic volume that reduces in size during rebound of the suspension, at least one of the second piston or the second cylinder defining a second flowpath for fluid during rebound of the suspension. The embodiment includes a means for externally adjusting the second flowpath independently of the first flowpath.