Shock absorber having orifice check disc

A shock absorber for a vehicle includes a pressure tube that defines a fluid chamber and a piston disposed within the fluid chamber. The piston divides the fluid chamber into an upper working chamber and a lower working chamber, and defines a compression passage and a rebound passage. A valve disc assembly of the shock absorber engages the piston and controls the flow of fluid between the upper and lower working chambers. The valve disc assembly includes an orifice check disc and an orifice disc. The orifice disc defines a bleed passage between the upper and lower working chambers. The orifice check disc is disposed between the piston and the orifice disc. The orifice check disc closes the bleed passage as the fluid flows in a first direction and opens the bleed passage as the fluid flows in a second direction opposite of the first direction.

FIELD

The present disclosure relates to shock absorbers. More particularly, the present disclosure relates to a valve disc assembly for controlling damping characteristics of a shock absorber during low hydraulic fluid flow.

BACKGROUND

Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb the unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and the pressure tube is connected to the unsprung portion of tile vehicle. The piston is connected to the sprung portion of the automobile through a piston rod which extends through the pressure tube.

The piston divides the pressure tube into an upper working chamber and a lower working chamber both of which are filled with hydraulic fluid. Because the piston is able through valving, to limit the flow of the hydraulic fluid between the upper and the lower working chambers when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the vehicle of the vehicle. In a dual tube shock absorber, a fluid reservoir or reserve chamber is defined between the pressure tube and a reserve tube. A base valve is located between the lower working chamber and the reserve chamber to control the flow of fluid between the lower working chamber and the reserve chamber.

For a full displacement valving system, all rebound damping forces produced by the shock absorber are the result of piston valving while compression forces are a combination of piston and cylinder end valving. The greater the degree to which the flow of fluid within the shock absorber is restricted by the piston and/or cylinder end, the greater the damping forces which are generated by the shock absorber. Thus, a highly restricted flow of fluid would produce a firm ride while a less restricted flow of fluid would produce a soft ride.

Shock absorbers have been developed to provide different damping characteristics depending on the speed or acceleration of the piston within the pressure tube. Because of the exponential relation between pressure drop and flow rate, it is a difficult task to obtain a damping force at relatively low piston velocities (i.e., low hydraulic fluid speed), particularly at velocities near zero. Low speed damping force is important to vehicle handling since most vehicle handling events are controlled by low speed vehicle body velocities.

Various systems for tuning shock absorbers during low speed movement of the piston include a fixed low speed orifice or orifices which provide a defined leak path which is always open across the piston for both compression and rebound. While a soft ride is generally preferred during compression, a firm ride is generally preferred during rebound.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. The present disclosure relates to a shock absorber for a vehicle, and more particularly, to a valve disc assembly that controls the flow of fluid between an upper working chamber and a lower working chamber during low fluid flow. The shock absorber includes a pressure tube that defines a fluid chamber, a piston that is disposed within the fluid chamber, and a valve disc assembly that engages with the piston.

The piston divides the fluid chamber into an upper working chamber and a lower working chamber, and defines a compression passage and a rebound passage. The compression passage and the rebound passage extend through the piston between the upper working chamber and the lower working chamber.

The valve disc assembly controls the flow of fluid between the upper working chamber and the lower working chamber. The valve disc assembly includes an orifice check disc and an orifice disc. The orifice disc defines a bleed passage. The orifice check disc is flexible and is disposed between the piston and the orifice disc. The orifice check disc controls the flow of fluid through the orifice disc or, in other words, the bleed passage.

The orifice check disc closes the bleed passage as the fluid flows from the upper working chamber toward the lower working chamber (i.e., a rebound stroke or first direction of fluid flow) and opens the bleed passage when fluid flows from the lower working chamber toward the upper working chamber (i.e., a compression stroke or second direction of fluid flow). For instance, when the fluid flows in the first direction at low fluid speed, the orifice check disc flexes towards the orifice disc and closes the bleed passage to prevent fluid from flowing through. On the other hand, when the fluid flows in the second direction at low fluid speed, the orifice check disc flexes away from the orifice disc toward the piston and opens the bleed passage to allow fluid to flow through. Thus, the orifice check disc controls the flow of fluid through the bleed passage which controls the damping characteristics of the shock absorbers during low fluid speed.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference to the accompanying drawings. Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views,FIG. 1illustrates a vehicle10incorporating a suspension system with shock absorbers having an orifice check disc in accordance with the present disclosure. Vehicle10includes a rear suspension12, a front suspension14and a body16. Rear suspension12has a transversely extending rear axle assembly (not shown) adapted to operatively support the vehicle's rear wheels18. The rear axle assembly is operatively connected to body16by means of a pair of shock absorbers20and a pair of helical coil springs22. Similarly, front suspension14includes a transversely extending front axle assembly (not shown) to operatively support the vehicle's front wheels24. The front axle assembly is operatively connected to body16by means of a second pair of shock absorbers26and by a pair of helical coil springs28.

Shock absorbers20and26serve to dampen the relative motion of the unsprung portion (i.e., front and rear suspensions12and14, respectively) and the sprung portion (i.e., body16) of vehicle10. While vehicle10has been depicted as a passenger car having front and rear axle assemblies, shock absorbers20and26may be used with other types of vehicles or in other types of applications including, but not limited to, vehicles incorporating independent front and/or independent rear suspension systems.

Referring now toFIG. 2, shock absorber20is shown in greater detail. WhileFIG. 2illustrates only shock absorber20, it is to be understood that shock absorber26includes the same components as shock absorber20. Shock absorber26only differs from shock absorber20in the manner in which it is adapted to be connected to the sprung and unsprung masses of vehicle10. Furthermore, while the shock absorber20is depicted as a dual-tube shock absorber, shock absorber20may also be a mono-tube shock absorber.

Shock absorber20comprises a pressure tube30, a piston assembly32, a piston rod34, a reservoir tube36, and a base valve assembly38. Pressure tube30defines a working chamber42. Piston assembly32is slidably disposed within pressure tube30and divides working chamber42into an upper working chamber44and a lower working chamber46. A seal48, which is shown inFIG. 3, is disposed between piston assembly32and pressure tube30to permit sliding movement of piston assembly32with respect to pressure tube30without generating undue frictional forces as well as sealing upper working chamber44from lower working chamber46.

Piston rod34is attached to piston assembly32and extends through upper working chamber44and through an upper end cap50which closes the upper end of pressure tube30. The end of piston rod34opposite to piston assembly32is adapted to be secured to the sprung portion of vehicle10.

Valving within piston assembly32controls the movement of fluid between upper working chamber44and lower working chamber46during movement of piston assembly32within pressure tube30. Because piston rod34extends only through upper working chamber44and not lower working chamber46, movement of piston assembly32with respect to pressure tube30causes a difference in the amount of fluid displaced in upper working chamber44and the amount of fluid displaced in lower working chamber46. The difference in the amount of fluid displaced flows through the base valve assembly38, the piston assembly32, or a combination thereof.

Reservoir tube36surrounds pressure tube30to define a fluid reservoir chamber52located between tubes30and36. Base valve assembly38is disposed between lower working chamber46and reservoir chamber52to control the flow of fluid between chambers46and52. When shock absorber20extends in length, fluid will flow from reservoir chamber52to lower working chamber46through base valve assembly38. Fluid may also flow from upper working chamber44to lower working chamber46through piston assembly98. When shock absorber20compresses in length, an excess of fluid must be removed from lower working chamber46. Thus, fluid will flow from lower working chamber46to reservoir chamber52through base valve assembly38.

Referring now toFIG. 3, piston assembly32comprises a piston body60, a compression valve assembly62, and a rebound valve assembly64. Piston body60defines a plurality of compression fluid passages66and a plurality of rebound fluid passages68, and includes a compression valve land70and a rebound valve land72. Compression fluid passages66include an inlet74and an outlet76. Rebound fluid passages68include an inlet78and an outlet80. Compression fluid passages66and rebound fluid passages68fluidly couple upper working chamber44and lower working chamber46.

Piston body60abuts with compression valve assembly62which abuts with a shoulder82formed on piston rod34. Piston body60also abuts with rebound valve assembly64which is retained by a retaining nut84. Retaining nut84and a retaining nut86secure piston body60and valve assemblies62and64to piston rod34.

Compression valve assembly62includes a retainer90, one or more spacers92, and a valve disc assembly94. Retainer90is disposed above piston body60and abuts with shoulder82. Spacers92are disposed between valve disc assembly94and retainer90and between valve disc assembly94and piston body60. Valve disc assembly94abuts with compression valve land70and closes outlet76of compression fluid passages66.

Rebound valve assembly64also includes a retainer100, one or more spacers102, and a valve disc assembly104. Retainer100is disposed below piston body60and abuts with retaining nut84. Spacers102are disposed between valve disc assembly104and retaining nut84and between valve disc assembly104and piston body60. Valve disc assembly104abuts with rebound valve land72and closes outlet80of rebound fluid passages68.

The damping characteristics for both rebound (extension) and compression for shock absorber20are determined by the piston assembly32. More particularly, piston assembly32is provided as a full flow piston assembly which includes valving for mid/high fluid speeds and an independent valving for low piston speeds (i.e., low hydraulic fluid flow or low fluid speed). During mid/high level speed, damping is controlled by the deflection of valve disc assembly94of compression valve assembly62and valve disc assembly104of rebound valve assembly64. During low level speeds, damping is controlled by bleed passages. In the following, valve disc assembly94for compression valve assembly62is referred to as compression valve disc assembly94and valve disc assembly104for rebound valve assembly64is referred to as rebound valve disc assembly104.

Fluid flowing through compression fluid passages66is controlled by compression valve assembly62. During a compression stroke, fluid in lower working chamber46is pressurized and flows from lower working chamber46to compression fluid passages66. The fluid pressure within compression fluid passage66eventually opens compression valve assembly62by deflecting compression valve disc assembly94. Thus, fluid flows through compression fluid passages66into upper working chamber44. Prior to the deflection of compression valve disc assembly94, a controlled amount of fluid flows between upper working chamber44and lower working chamber46through a bleed passage which provides damping at low fluid speeds, as described herein.

Fluid flowing through rebound fluid passages68is controlled by rebound valve assembly64. During the compression stroke, rebound valve assembly64restricts the flow of fluid through rebound fluid passages68. Fluid in lower working chamber46exerts a force onto the rebound valve assembly64. Rebound valve assembly64seals against land72of piston body60, thereby preventing fluid from entering rebound fluid passages68from lower working chamber46at mid/high fluid speed.

During a rebound stroke, fluid in upper working chamber44is pressurized, and fluid flows from upper working chamber44to rebound fluid passages68. The fluid pressure within rebound fluid passages68eventually opens rebound valve assembly64by deflecting rebound valve disc assembly104. Thus, fluid flows through rebound fluid passages68into lower working chamber46. Compression valve assembly62restricts the flow of fluid through compression fluid passages66during the rebound stroke. Fluid in upper working chamber44exerts a force onto compression valve assembly62. Compression valve assembly62seals against land70of piston body60, thereby preventing fluid from flowing through compression fluid passages66. Prior to the deflection of rebound valve disc assembly104, a controlled amount of fluid flows from lower working chamber46to upper working chamber44through a bleed passage which provides damping at low fluid speeds, as described herein.

Referring now toFIGS. 4A and 4B, valve disc assembly94and valve disc assembly104include a plurality of discs which control flow of fluid through piston body60. Compression valve disc assembly94includes an orifice disc110, one or more solid discs112, and a spring disc114. Orifice disc110defines one or more orifices116, and may also be referred to as a bleed disc. Solid discs112are disposed over orifice disc110to cover orifices116of orifice disc110. Spring disc114is disposed over solid discs112.

Orifice disc110, solid discs112, and spring disc114are positioned at land70of piston body60. Orifice disc110abuts with land70of piston body60. Orifice116forms a bleed passage referenced by arrow118for allowing fluid to flow between upper working chamber44and lower working chamber46, at low piston speeds. Bleed passage118is open during compression and rebound, thereby allowing fluid to flow from lower working chamber46to upper working chamber44and vice versa.

With additional reference toFIG. 5, rebound valve disc assembly96includes an orifice check disc120, an orifice disc122, a solid disc124, and a spring disc126. Orifice check disc120abuts with land72(FIG. 4B). Orifice disc122is disposed between orifice check disc120and solid disc124. Solid disc124is disposed under orifice disc122, and spring disc126is disposed under solid disc126.

Orifice disc122defines an orifice128which forms a bleed passage referenced by arrow130inFIG. 4B. Bleed passage130and bleed passage118control damping characteristics of shock absorber20during low fluid speeds by permitting a limited amount of fluid to flow between upper working chamber44and lower working chamber46. Unlike bleed passage118which is open during compression and rebound, bleed passage130is open during compression but is closed during rebound. That is, orifice check disc120controls the flow of fluid between upper working chamber44and lower working chamber by permitting fluid to flow from lower working chamber46to upper working chamber44and prohibiting fluid to flow from upper working chamber44to lower working chamber46.

With additional reference toFIG. 6, orifice check disc120includes a portion that is flexible or moveable to block fluid flow in one direction and allow fluid flow in the other direction. In the example embodiment, one or more cuts142form four arc-shaped tabs140. Tabs140are moveable and form the flexible portion of orifice check disc120. That is, tabs140flex toward piston body60or toward orifice disc122based on the direction of the fluid.

InFIG. 7A, orifice disc120is in a normal state in which fluid is not exerting a pressure on the rebound valve assembly64and tabs140are not flexing.FIG. 7Billustrates a rebound condition in which fluid from upper working chamber44flows through piston60via rebound fluid passages68and exerts a force onto rebound disc valve assembly94, as indicated by arrow144. Tabs140of orifice check disc120flex towards orifice disc122and exert a force onto orifice disc122. Dotted line inFIG. 7Brepresents position of tabs140in the normal state of orifice check disc120.

In a normal state, orifice check disc120may abut with orifice disc122. In the rebound condition, tabs140exert a force onto orifice disc122which causes orifice disc122to press against solid disc124. Tabs140of orifice check disc120seal orifice disc122to close bleed passage130formed by orifice128. Accordingly, orifice check disc120and orifice disc122function as a solid disc, and fluid does not flow from rebound fluid passages68through orifice128into lower working chamber46during low fluid speeds.

FIG. 7Cillustrates a compression condition at low fluid speeds, in which fluid from lower working chamber46flows toward upper working chamber44, as indicated by arrow146. Fluid flows into orifice128and exerts a force onto tabs140of orifice check disc120. Tabs140flex toward piston body60or, in other words, away from orifice disc122, thereby opening bleed passage130. Fluid from lower working chamber46flows through rebound fluid passages68and into upper working chamber44via bleed passage130.

While orifice check disc120is illustrated as having tabs140, orifice check disc may have other suitable configuration and is not limited to the configuration depicted. For example,FIGS. 8 and 9illustrate an orifice check disc200. Orifice check disc200defines a cuts202that has a swirl like shape for allowing portions of orifice check disc200to flex. Orifice check disc200is disposed within piston lands72and does not abut against land72like orifice check disc120.

Similar to orifice check disc120, during compression, orifice check disc200flexes due to fluid entering orifice128and pressing against orifice check disc200, thereby opening bleed passage130. Dotted line204represents movement of orifice check disc200. During rebound, orifice check disc200presses against orifice disc122to seal orifice128and close bleed passage130, thereby preventing fluid from flowing from upper working chamber44to lower working chamber46. Dotted line206represents movement of orifice check disc200during rebound.

Orifice check disc (120,200) controls bleed passage130formed by orifice128of orifice disc122such that during rebound, bleed passage130is closed and during compression, bleed passage130is open. Accordingly, bleed passage118and bleed passage130provide damping during compression at low fluid speeds, and during rebound, bleed passage118provides damping at low fluid speeds. By having orifice check disc120,200, shock absorbers20,26provide soft damping characteristics for low speed compression and hard damping characteristics for low speed rebound. Thus, the damping characteristics of shock absorbers20,26may be tuned independently for rebound and compression for low fluid speeds. In the example embodiments, orifice check disc is disposed with the rebound valve disc assembly. It is readily understood that the orifice check disc may be disposed in the compression valve disc assembly for controlling the bleed passage on the compression side.