FIELD

[0001] The present disclosure relates to automotive shock absorbers. More particularly, the present disclosure relates to internal structures of a passive shock absorber operable to provide a different magnitude of damping based on a frequency as well as a velocity of the input to shock absorber.

BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Shock absorbers are typically used in conjunction with automotive suspension systems or other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung (body) and the unsprung (suspension/chassis) masses of the vehicle.

[0004] The most common type of shock absorbers for automobiles may be either mono-tube or a dual-tube dashpot devices. In the mono-tube design, a piston is located within a fluid chamber defined by a pressure tube and is connected to the sprung mass of the vehicle through a piston rod. The pressure tube is connected to the unsprung mass of the vehicle. The piston divides the fluid chamber of the pressure tube into an upper working chamber and a lower working chamber. The piston includes compression valving which limits the flow of damping fluid from the lower working chamber to the upper working chamber during a compression stroke and rebound valving which limits the flow of damping fluid from the upper working chamber to the lower working chamber during a rebound or extension stroke. Because the compression valving and the rebound valving have the ability to limit the flow of damping fluid, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass.

[0005] In a dual-tube shock absorber, a fluid reservoir is defined between the pressure tube and a reservoir tube which is positioned around the pressure tube. A base valve assembly is located between the lower working chamber and the fluid reservoir to control the flow of dampening fluid. The compression valving of the piston is moved to the base valve assembly and is replaced in the piston by a compression check valve assembly. In addition to the compression valving, the base valve assembly includes a rebound check valve assembly. The compression valving of the base valve assembly produces the damping force during a compression stroke, and the rebound valving of the piston produces the damping force during a rebound or extension stroke. Both the compression and rebound check valve assemblies permit fluid flow in one direction, but prohibit fluid flow in an opposite direction and these valves can be designed such that they also generate a damping force.

[0006] The valve assemblies for the shock absorber have the function of controlling fluid flow between two chambers during the stroking of the shock absorber. By controlling the fluid flow between the two chambers, a pressure drop is built up between the two chambers and this contributes to the damping forces of the shock absorber. The valve assemblies can be used to tune the damping forces to control ride and handling as well as noise, vibration and harshness.

[0007] Typical passive shock absorbers provide the same magnitude of damping force regardless of the frequency of the input. For a given input velocity, the damping force generated by a conventional damper/shock remains the same regardless of the frequency of the input. Typically, the primary ride frequency of a passenger vehicle is in the range of 1 -2 Hz. When a vehicle goes over a road surface with a lower frequency input, a higher amount of damping is preferred to manage the road inputs. During handling events (where directional stability is critical), a higher amount of damping is also preferred. A roll mode is subjected to a vehicle handling condition. The roll-mode of the typical passenger vehicle could be in the range of 2- 4Hz depending on the roll-stiffness and CG height of the vehicle. While there are semi-active damping shock absorbers which change the damping of the shock absorber in real-time to address these vehicle inputs, a need exists for a passive shock absorber operable to provide frequency dependent damping without complicated (active) controls.

SUMMARY

[0008] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0009] A damper system for a vehicle includes a piston slidably fitted in a cylinder that separates the cylinder into a first working chamber and a second working chamber. A piston rod is connected to the piston and extends outside of the cylinder. A disc valve assembly is mounted to the piston and controls fluid flow between the first working chamber and the second working chamber. An actuator is coupled to the piston rod and includes a moveable sleeve as well as an accumulation chamber fluidly connected to one of the first working chamber and the second working chamber. The accumulation chamber includes a flexible wall. An increased pressure within the accumulation chamber creates a force on flexible wall to increase a volume of the accumulation chamber and a force on the moveable sleeve which acts on the disc valve assembly to increase resistance to opening the MAIN disc valve assembly.

[0010] The damper of the present disclosure functions by bypassing the flow from the rebound chamber to apply a pressure against the backside of a movable cylinder sleeve. The movable cylinder sleeve applies an additional load on the rebound stack and creates further resistance to the rebound side main valve opening under a low frequency event. Under a high frequency event, fluid entering the accumulation deforms an expansion disc. Reversal of flow occurs much more quickly under a high frequency event and sufficient time is not provided to build a fluid pressure sufficient to preload the plunger. During compression, all damping is provided by a main piston under all frequencies of input and the devices of this disclosure do not provide frequency dependent damping in the compression mode of operation. It should be appreciated, however, that the present disclosure contemplates applying this technology to the compression side, the rebound side, or both.

[0011] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

[0012] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0013] Figure 1 is an illustration of an exemplary vehicle equipped with a frequency dependent damper in accordance with the teachings of the present disclosure;

[0014] Figure 2 is a fragmentary side view of a shock absorber constructed in accordance with the teachings of the present disclosure; [0015] Figure 3 is a fragmentary cross-sectional view of a shock absorber constructed in accordance with the teachings of the present disclosure;

[0016] Figure 4 is an exploded perspective view of a check valve;

[0017] Figure 5 is an exploded perspective view of a flexible wall of an accumulation chamber of an exemplary shock absorber;

[0018] Figure 6 is a fragmentary cross-sectional view depicting an adaptive damping force generating mechanism including a clamped disc check valve and an accumulation chamber including a flexible wall;

[0019] Figure 7 is a perspective view of a clamped disc check valve;

[0020] Figure 8 is a fragmentary cross-sectional view of a shock absorber equipped with a floating piston;

[0021] Figure 9 is a fragmentary cross-sectional view of another shock absorber equipped with a floating piston and a spring;

[0022] Figure 10 is a graph depicting peak rebound force versus rebound frequency for a frequency dependent damper and a passive damper; and

[0023] Figure 1 1 is a graph providing force versus shock displacement test results associated with a shock absorber constructed in accordance with the teachings of the present disclosure.

[0024] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION

[0025] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0026] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0027] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0028] When an element or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0029] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0030] Spatially relative terms, such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0031] Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a vehicle 10 including a rear suspension 12, a front suspension 14 and a body 16. Rear suspension 12 has a transversely extending rear axle assembly (not shown) adapted to operatively support the vehicle's rear wheels 18. The rear axle assembly is operatively connected to body 16 by means of a pair of shock absorbers 20 and a pair of helical coil springs 22. Similarly, front suspension 14 includes a transversely extending front axle assembly (not shown) to operatively support the vehicle's front wheels 24. The front axle assembly is operatively connected to body 16 by means of a second pair of shock absorbers 26 and by a pair of helical coil springs 28. Shock absorbers 20 and 26 serve to dampen the relative motion of the unsprung portion (i.e. front and rear suspensions 12 and 14, respectively) and the sprung portion (i.e. body 16) of vehicle 10. While vehicle 10 has been depicted as a passenger car having front and rear axle assemblies, shock absorbers 20 and 26 may be used with other types of vehicles or machinery, or in other types of applications such as vehicles incorporating independent front and/or independent rear suspension systems. Further, the term "shock absorber" as used herein is meant to refer to dampers in general and thus will include MacPherson struts.

[0032] Referring now to FIG. 2, shock absorber 20 is shown in greater detail. While FIG. 2 shows only shock absorber 20, it is to be understood that shock absorber 26 also includes the piston assembly described below for shock absorber 20. Shock absorber 26 only differs from shock absorber 20 in the way in which it is adapted to be connected to the sprung and unsprung portions of vehicle 10. Shock absorber 20 comprises a pressure tube 30, a piston assembly 32 and a piston rod 34.

[0033] Pressure tube 30 defines a working chamber 42. Piston assembly 32 is slidably disposed within pressure tube 30 and divides working chamber 42 into an upper working chamber 44 and a lower working chamber 46. A seal 48 is disposed between piston assembly 32 and pressure tube 30 to permit sliding movement of piston assembly 32 with respect to pressure tube 30 without generating undue frictional forces as well as sealing upper working chamber 44 from lower working chamber 46. Piston rod 34 is attached to piston assembly 32 and extends through upper working chamber 44 and through an upper end cap 50 which closes the upper end of pressure tube 30. A sealing system 52 seals the interface between upper end cap 50 and piston rod 34. An end 53 of piston rod 34 opposite to piston assembly 32 is adapted to be secured to the sprung portion of vehicle 10. In the preferred embodiment, piston rod 34 is secured to body 16 or the sprung portion of vehicle 10. Pressure tube 30 is filled with fluid and it includes a fitting 54 for attachment to the other of the sprung or unsprung masses of the vehicle. In the preferred embodiment, fitting 54 is secured to the unsprung mass of the vehicle. Thus, suspension movements of the vehicle will cause extension or compression movements of piston assembly 32 with respect to pressure tube 30. Valving within piston assembly 32 controls the movement of fluid between upper working chamber 44 and lower working chamber 46 during movement of piston assembly 32 within pressure tube 30.

[0034] Referring now to FIGS. 3 and 4, piston assembly 32 is attached to piston rod 34 and comprises a piston body 60, a compression valve assembly 62, an extension or rebound valve assembly 64, and an adaptive damping force generating mechanism 66. Piston rod 34 includes a reduced diameter section 68 located on the end of piston rod 34 disposed within pressure tube 30 to form a shoulder 70 for mounting the remaining components of piston assembly 32. Piston body 60 is located on reduced diameter section 68 with compression valve assembly 62 being located between piston body 60 and shoulder 70 and with rebound valve assembly 64 being located between piston body 60 and a threaded end 72 of piston rod 34. Piston body 60 defines a plurality of compression flow passages 74 and a plurality of rebound flow passages 76.

[0035] Compression valve assembly 62 comprises a plurality of compression valve plates 78 and a valve stop 80. Valve plates 78 are disposed adjacent to piston body 60 to cover the plurality of compression flow passages 74. Valve stop 80 is disposed between valve plates 78 and shoulder 70 to limit the deflection of valve plates 78. During a compression stroke of shock absorber 20, fluid pressure builds up in lower working chamber 46 until the fluid pressure applied to valve plates 78 through passages 74 overcomes the load required to deflect valve plates 78. Valve plates 78 elastically deflect to open passages 74 and allow fluid to flow from lower working chamber 46 to upper working chamber 44 as shown by arrows 82 in FIG. 3.

[0036] Rebound valve assembly 64 comprises a plurality of valve plates 86. Valve plates 86 are disposed adjacent to piston body 60 to cover the plurality of rebound flow passages 76. Adaptive damping force generating mechanism 66 is threaded onto end 72 of piston rod 34 to retain valve plates 86 against piston body 60 to close passages 76. During an extension stroke of shock absorber 20, fluid pressure builds up in upper working chamber 44 until the fluid pressure applied to valve plates 86 through passages 76 overcomes the load required to deflect valve plates 86. Valve plates 86 elastically deflect thereby opening passages 76 to allow fluid to flow from upper working chamber 44 to lower working chamber 46 as shown by arrows 92 in FIG. 3.

[0037] As adaptive damping force generating mechanism 66 is fixed to piston rod 34, the entire adaptive damping force generating mechanism 66 translates during rebound and compression movement of piston rod 34. Adaptive damping force generating mechanism 66 is rigidly connected with piston assembly 32 but doesn't function to provide sealing within pressure tube 30 in which it is positioned. A frequency dependent damper (FDD) is provided by a combination of components including adaptive damping force generating mechanism 66.

[0038] Adaptive damping force generating mechanism 66 comprises a valve housing 100, a plunger or axially translatable sleeve 102, a check valve 104, and a deformable wall 106. A flow passage 1 10 is in fluid communication with upper working chamber 44 and a staging chamber 1 12. Staging chamber 1 12 is partially defined by valve housing 100 and check valve 104. More particularly, check valve 104 includes a cup-shaped retainer 1 14 positioned within a counter bore 1 16 of valve housing 100. Retainer 1 14 is sealingly fixed to valve housing 100. Retainer 1 14 includes an aperture 1 18 extending therethrough. A flexible check disc 120 and a flexible orifice disc 122 cover aperture 1 18 while a coil spring 124 biases check disc 120 and orifice disc 122 into a seated position engaging retainer 1 14 as depicted in FIG. 3. At the seated position, fluid communication between staging chamber 1 12 and an accumulation chamber 130 is provided only via a slot 134 extending through orifice disc 122. As will be described in detail, orifice disc 122 and check disc may be urged away from the seated position toward piston rod 34 when the pressure within accumulation chamber 130 exceeds the pressure in staging chamber 1 12. [0039] Flexible wall 106 is comprised of a stack of discs depicted in FIG. 5. A support disc 140 is positioned closest to accumulation chamber 130. A spacer disc 142 is sandwiched between support disc 140 and an upper surface of an expansion disc 144. Expansion disc 144 is a continuous uninterrupted member sealingly associated with valve housing 100 to prevent fluid from passing from accumulation chamber 130 to lower working chamber 42. One or more additional spacer discs 148 are positioned between a lower surface of the expansion disc 144 and a restriction disc 150. Flexible wall 106 is retained within a counter bore 160 of valve housing 100. Any number of conventional retaining means may be used such as circlips, adhesive bonding, swaging, etc. Expansion disc 144, spacer discs 142, 148 and discs 140, 150 may be formed from aluminum, steel, plastic, etc. Each of support disc 140 and restriction disc 150 includes several apertures 164 to allow fluid to pass therethrough while maintaining the structural rigidity of each disc.

[0040] Axially translatable sleeve 102 is a substantially tubular member including a reduced diameter portion 170 and an enlarged diameter portion 172. Valve housing 100 includes a similarly stepped structure with a reduced diameter portion 176, an enlarged diameter portion 178 and an intermediate diameter portion 180 positioned axially between reduced diameter portion 176 and enlarged diameter portion 178. A first seal 182 is positioned within a groove 184 of valve housing 100. A second seal 186 is positioned within a second groove 188 of valve housing 100. Based on the axial position of first seal 182, second seal 186 and intermediate portion 180, a plunger chamber 190 is provided. A radially extending aperture 192 places plunger chamber 190 in fluid communication with accumulation chamber 130. When plunger chamber 190 is pressurized, sleeve 102 is urged toward rebound valve assembly 64. A magnitude of force applied by sleeve 102 is based on the pressure within plunger chamber 190 and the effective surface area on an annular land 196 on sleeve 102. It should be appreciated that the effective area of land 196 may be relatively easily varied by changing the geometrical relationship between second seal 186 and first seal 182.

[0041] In the embodiment depicted in FIG. 3, sleeve 102 is engageable with a support washer 200. Support washer 200 is free to axially move relative to rebound valve assembly 64. Support washer 200 includes an engagement face 202 positioned at an outer circumferential extent of support washer 200. In the example depicted in FIG. 3, support disc 200 is supporting the rebound disc stack on an outer periphery. This ensures that a given amount of plunger force generates a maximum amount of resistance to the rebound opening. The design of sleeve 102 includes a smaller effective area of land 196 which in turns allows a smaller outer diameter of enlarged diameter portion 172, which in turn affects the packaging. Optimization of the components also allows a single design to be applied to multiple bores to reduce the manufacturing complexity. A manufacturer may achieve a scale on most of the additional components.

[0042] It should be noted that the radial position of engagement face 202 may be varied to apply a force to different portions of rebound valve assembly 64, thereby producing a different modification to the performance of rebound valve assembly 64. To individually tune suspension characteristics to a particular vehicular application, it may be desirable to modify the system response and operation of rebound valve assembly 64 based on vehicle type and configuration. Through the use of a number of different support washers 200 having engagement face 202 positioned at different radial positions, a common valve housing 100 and sleeve 102 may be employed throughout the family of dampers. Another feature pertaining to support washer 200 relates to its axial translation degree of freedom which allows rebound valve assembly 64 blow off.

[0043] To address a possible concern of an impact of washer 200 to the rebound valve assembly 64 being a source of NVH and/or durability concern, sleeve 102 may be spring loaded toward rebound valve assembly 64. A spring may be placed at an end of sleeve 102 or within plunger chamber 190. It should also be appreciated that support washer 200 is optional. Sleeve 102 may directly engage rebound valve assembly 64 when support washer 200 is not present.

[0044] FIG. 3 depicts sleeve 102 in a retracted position where force is not applied to rebound valve assembly 64. The axial movement of sleeve 102 in one direction is limited by a stop face 208. It should be appreciated that stop face 208 need not be a complete uninterrupted annular land but may also be defined by circumferentially spaced apart protrusions or other mechanical structures.

[0045] Operation of shock absorber 20 varies based on the direction and frequency of input forces. A low frequency rebund mode of operation will now be described. During the rebound stroke, fluid in upper working chamber 44 is compressed and fluid flows between upper working chamber 44 and lower working chamber 46 through passages 76 overcoming the load required to deflect valve plates 86 of rebound valve assembly 64 thereby allowing fluid to flow as depicted by arrows 92. Fluid pressure within upper working chamber 44 also flows through passage 1 10 of piston rod 34 and into staging chamber 1 12. From staging chamber 1 12, fluid passess through slot 134 of orifice disc 122 and enters into accumlation chamber 130. As a result, pressure in accumluation chamber 130 downstream from orifice disc 122 will be lower compared to rebound chamber pressure found in staging chamber 1 12.

[0046] As pressure within accumulation chamber 130 increases, expansion disc 144 starts deforming about spacer disc 148. As pressure further increases, deformation of expansion disc 144 increases until it reaches a maximum when expansion disc 144 contacts restriction disc 150. The purpose of restriction disc 150 is to provide support to support disc 140 under high pressure. For the purpose of operating rebound valve assembly 64, it is important that expansion disc 144 maintains a seal between accumulation chamber 130 and lower working chamber 42. Without restriction disc 150, expansion disc 144 may "blow out" under very high pressures encountered during a rebound stroke. Spacer discs 148 are provided between expansion disc 144 and restriction disc 150 to provide a tuning feature to define an amount of travel that expansion disc 144 may deflect before contacting restriction disc 150.

[0047] As the pressure within accumulation chamber 130 rises, fluid starts flowing through passage 192 to pressurize plunger chamber 190 and land 196. The pressure on land 196 causes sleeve 102 to translate and apply a load to support washer 200. The force applied by the sleeve 102 and support washer 200 is applied as an additional force to valve plates 86 and creates an increased resistance to rebound valve assembly 64 opening under low frequency conditions. It should be appreciated that a certain amount of time is required for fluid to pass from staging chamber 1 12 to accumulation chamber 130. Time is also required to deform flexible wall 106. The time delay in deforming expansion disc 144 and providing the controlled pressure build up through orifice disc 122 provides frequency dependent damping.

[0048] As the damper goes into rebound during a high frequency input mode, fluid passes through passage 1 10 of piston rod 34 into staging chamber 1 12. From there, fluid passess through orifice disc 122 and enters into accumlation chamber 130. As a result, pressure in accumluation chamber 130 will be lower than the pressure in staging chamber 1 12. As pressure in accumulation chamber 130 increases, expansion disc 144 starts deforming about spacer disc 148. Due to the nature of the high frequency input, a piston rod stroke reversal occurs before the fluid has time to build pressure within plunger chamber 190. This time requirement and the flexibility of the accumulation chamber wall 106 causes no additional load to be applied to sleeve 102. The flexibility or expansibility of accumulation chamber 130 is tunable with different stiffnesses of expansion disc 144. In other words, the pressure in plunger chamber 190 that may drive movement of sleeve 102 compared to the pressure within accumulation chamber 130 determines the amount of preload that sleeve 102 will generate. This in turn depends on the frequency of the input. At a higher frequency, pressure builds up in accumulation chamber 130 and energy is directed towards flexing expansion disc 144 but insufficient time is provided to charge plunger chamber 190. At lower frequencies, fluid pressure builds in plunger chamber 190 and acts on land 196 of sleeve 102.

[0049] It should be noted that during a rebound stroke of either high or low frequency, the fluid flow path through piston assembly 32 along arrows 82 remains the same. The only change is the amount of preload on valve plates 86 to restrict opening rebound valve assembly 64.

[0050] As shock absorber 20 goes into jounce, or compression, pressure in the upper working chamber 44 will be lower than the pressure within accumulation chamber 130. Fluid flows out of accumulation chamber 130 through check valve 104. The functionality of the check valve ensures that during quick stroke reversal, accumulation chamber 130 remains ready to build a pressure. During the compression stroke, fluid within lower working chamber 42 also presses against expansion disc 144. Expansion disc 144 deflects and is supported by support disc 140, as necessary.

[0051] A number of features of shock absorber 20 may be varied to tune the operating characteristics exhibited during frequency dependent damping. For example, orifice disc 122 provides restriction for flow through piston rod 34 to accumulation chamber 130. The orifice size and/or number of apertures through orifice disc 122 are tunable and result in different frequency dependent damping. It should be appreciated that orifice disc 122 may be shaped as desired and does not need to be configured as a flexible cylindrical element having a diameter greater than its height. The orifice disc 122 may be referred to as an orifice wall at least partially defining an expansible accumulation chamber. The orifice wall separates the first working chamber from the accumulation chamber and may be a rigid member.

[0052] Expansion disc 144 stiffness may be tuned to allow for a change in accumulation chamber 130 volume. Accumulation chamber 130 is expansible based on expansion disc 144 deflection. The size of an aperture 210 (FIG. 5) extending through spacer disc 148 defines where expansion disc 144 deflects.

[0053] Restriction disc 150 supports expansion disc 144 and prevents its failure under high accumulation pressure. Spacer discs 148 define the amount of travel expansion disc 144 is allowed to travel before contacting restriction disc 144. A surface area of land 196 acted on by the pressurized fluid creates a preload. Varying the surface area changes the force applied by sleeve 102.

[0054] During rebound, check disc 120 and orifice disc 122 stay "seated" in retainer 1 14 and fluid flows around the check disc outer diameter to accumulation chamber 130 through slot 134 on orifice disc 122.

[0055] During a compression damper stroke, pressure in upper working chamber 44, passage 1 10 and staging chamber 1 12 is lower than the pressure in accumulation chamber 130, allowing fluid to flow from high pressure to low pressure through orifice disc slot 134. Fluid pushes check disc 120 against the spring force and a release of pressure within accumulation chamber 130 takes place. This allows accumulation chamber 130 to be depressurized.

[0056] FIGS. 6 and 7 depict an alternate check valve as a clamped disc check valve 280. Use of a clamped disc design provides efficient use of space and provides a packaging advantage. Clamped disc check valve 280 includes a support disc 284, a spacer disc 286, a check disc 288, and a support disc 290. Each of the discs of clamped disc check valve 280 are positioned adjacent one another and clamped under a preload in counter bore 1 16 of valve housing 100.

[0057] Check disc 288 includes a moveable flap 292 connected to an outer ring 294 via a hinge 296. Deflection of flap 292 toward accumulation chamber 130 is restricted by support disc 290. During a rebound damper stroke, fluid passes through apertures 295 of support disc 284. Fluid passes through an orifice 298 in the center of check disc 288.

[0058] Check disc 288 is constructed from an elastomeric material such that flap 292 may move relative to outer ring 294 during a compression stroke. Spacer disc 286 includes an enlarged aperture 299 as compared to an aperture 301 of support disc 290. During a compression stroke, flap 292 is biased into aperture 299 to allow fluid flow from accumulation chamber 130 through clamped disc check valve 280 and into staging chamber 1 12.

[0059] An alternate embodiment damper or shock absorber 300 is depicted in FIG. 8. Shock absorber 300 is substantially similar to shock absorber 20 with the main exception being flexible wall 106 is replaced with a floating piston 304. As such, a member movable to allow a volume of the accumulation chamber to increase may include expansion disc 144 or piston 304. Piston 304 is slidably positioned within a bore 306. A seal 308 prevents fluid from passing from an accumulation chamber 310 to lower working chamber 46. The amount of axial travel that floating piston 304 may experience may be varied based on the placement of a stop 312 formed on a valve housing 314 as well as the relative position of an end plate 318 fixed to housing 314. By varying the position of these components, the total maximum volume of accumulation chamber 310 maintained to effect low frequency delay.

[0060] FIG. 9 shows a variant of shock absorber 300 as shock absorber 300'. Shock absorber 300' is substantially similar to shock absorber 300 with the addition of a spring 320 urging floating piston 304 toward a check valve 322. Spring 320 assists transferring fluid from accumulation chamber 310 during a compression stroke when the pressure of fluid within upper working chamber 44 is less than the pressure within accumulation chamber 310. The preload and spring rate of spring 320 also defines the performance characteristics of the frequency dependent damping provided by shock absorber 300' when operating in the low frequency rebound mode. A spring 320 with a relatively high rate would charge the accumulation chamber 310 in less time than a damper equipped with a spring 320 having a lesser rate.

[0061] Other variants include positioning another spring on the opposite of floating piston 304 to position floating piston 304 in a desired location within bore 306 while tuning the operational characteristics of the frequency dependent damper as previously discussed. Another alternate embodiment would include positioning the biasing spring only on the side of floating piston 304 as check valve 322 and removing spring 320.

[0062] FIGS. 10 and 1 1 present typical output results comparing response characteristics between a shock absorber equipped with a typical passive valve and a shock absorber equipped with the frequency dependent damping mechanism including the previously discussed actuator operable to increase resistance to fluid passing through rebound valve assembly 64. FIG. 10 illustrates a reduction in peak rebound force provided by shock absorber 20 as rebound frequency increases. FIG. 1 1 depicts test results on a shock absorber constructed in accordance with the teachings of the present disclosure comparing force versus shock absorber displacement. A negative force is indicative of rebound and a positive force being generated in compression. Frequency dependency can be visually appreciated based on the varying peak force in the rebound direction. The test was conducted by displacing the shock absorber at a constant velocity.

[0063] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.