Abstract:
A shock absorber includes a rebound valve assembly which performs the flexing disc function normally required for allowing the passage of fluid from one side of a piston assembly to the opposite side during the stroke of the shock absorber. The rebound valve assembly also incorporates a blow off function which increases the fluid flow through the piston when the fluid pressure being exerted upon the rebound valve assembly exceeds a specified level. The blow off feature utilizes a coil spring to protect both the shock absorber as well as the suspension system into which the shock absorber is assembled.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to shock absorbers having a unique rebound valve. More particularly, the present invention relates to a shock absorber having a rebound valve defined by a valve assembly that combines both the normal valving for the shock absorber and a blow-off function.  
       BACKGROUND OF THE INVENTION  
       [0002]     Shock absorbers are used in connection with automotive suspension systems and other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb this unwanted vibration, automotive shock absorbers are generally connected between the sprung mass (the body) and unsprung mass (the suspension) of the automobile.  
         [0003]     The most common type of shock absorber in automobiles is the dashpot type in which a piston is located within a pressure tube. The piston is connected to the sprung mass of the vehicle through a piston rod. The piston divides the pressure tube into an upper working chamber and a lower working chamber, both of which are filled with a damping fluid. Because the piston, through valving, has the ability to limit the flow of the damping fluid between the upper and lower working chambers within the pressure tube when the shock absorber is compressed or extended, 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. In a dual tube shock absorber, a fluid reservoir is defined between the pressure tube and the reserve tube. A base valve is located between the lower working chamber and the fluid reservoir to produce a damping force which also counteracts the vibration which would otherwise be transmitted from the unsprung mass to the sprung mass of the automobile.  
         [0004]     Automotive shock absorbers are generally provided with bleed orifices which allow the restricted flow of damping fluid from the upper side of the piston, which is know as the rebound side, to the lower side of the piston, which is known as the compression side. These bleed orifices provide the shock absorber with a portion of its damping characteristic. Automotive shock absorbers also may include a blow off valve of some type. The blow off valve is normally in a closed position. However, when fluid pressure within the pressure cylinder reaches a predetermined level, the blow off valve opens reducing considerably the restriction of damping fluid flow between the two sides of the piston.  
         [0005]     Various designs in the prior art combine the conventional piston valving with a blow off valve. For example, U.S. Pat. No. 4,721,130, issued on Jan. 26, 1988 to Hayashi for “Valve Structure of Hydraulic Buffer,” discloses a valve structure used in a hydraulic buffer. A valve body is used for opening and closing ports in the piston. As the piston rod is extended, a free end of the valve body deflects about a first fulcrum point to allow fluid to pass. When the piston is moving at a high rate of speed and the force of the fluid passing through the port exceeds the pre-load set by the spring, the spring seat is depressed so that more fluid flows through the port while deflecting the valve body about a second fulcrum point.  
         [0006]     Additionally, U.S. Pat. No. 2,717,058, issued to Brundreit on Sep. 6, 1955 for “Shock Absorber Control Valve,” discloses a shock absorber control valve for controlling restricted flow of hydraulic fluid between opposite ends of a pressure tube. A valve disk flexes upwardly against a rigid retainer plate as permitted by the angularity of the face portion of the plate. As the requirement for fluid flow increases, the valve member and the retainer are moved against the compression spring to change the fluid flow rate.  
         [0007]     While these prior art systems have performed acceptably, they are relatively complex and they fail to produce optimum results in the terms of efficiency and cost. The continued development of shock absorbers includes the development of systems which combine the flexing disk function of a rebound valve with the blow off function in a system that is less complex and less expensive while providing the necessary damping acquirements.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides the art with a shock absorber that includes a flexing disc assembly which combines the flexing disc function of a rebound valve with the blow off function. The shock absorber of the present invention utilizes a flexing disc assembly for allowing the passage of fluid between the two sides of the piston in the pressure tube. The fluid discs are held against the piston body by a coil spring and a valve retainer. The coil spring biases the valve retainer towards the valve discs by reacting against a nut. The nut is threaded onto the end of the piston rod. A spacer limits the travel of the nut thus controlling the amount of coil spring preload while eliminating tolerance build up and over compression of the discs.  
         [0009]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a schematic representation of the shock absorber in accordance with the present invention in operative association with a typical automobile;  
         [0012]      FIG. 2  is a cross-sectional view of the shock absorber in accordance with the present invention; and  
         [0013]      FIG. 3  is an enlarged cross-sectional view of the piston assembly in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0015]     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 incorporating a suspension system having the shock absorbers in accordance with the present invention which is designated generally by the reference numeral  10 . Vehicle  10  includes 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&#39;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&#39;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 second 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 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.  
         [0016]     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 , a piston rod  34 , a reservoir tube  36  and a base valve assembly  40 .  
         [0017]     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 end cap  50  which closes the upper end of pressure tube  30 . A sealing system seals the interface between upper end cap  50 , reserve tube  36  and piston rod  34 . The end of piston rod  34  opposite to piston assembly  32  is adapted to be secured to the sprung portion of vehicle  10 . 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 . Because piston rod  34  extends only through upper working chamber  44  and not lower working chamber  46 , movement of piston assembly  32  with respect to pressure tube  30  causes a difference in the amount of fluid displaced in upper working chamber  44  than the amount of fluid displaced in lower working chamber  46 . The difference in the amount of fluid displaced is known as the “rod volume” and it flows through base valve assembly  40 .  
         [0018]     Reservoir tube  36  surrounds pressure tube  30  to define a reservoir chamber  54  located between the tubes. The bottom end of reservoir tube  36  is closed by an end cap  56  which is adapted to be connected to the unsprung portion of vehicle  10 . The upper end of reservoir tube  36  is attached to upper end cap  50 . Base valve assembly  40  is disposed between lower working chamber  46  and reservoir chamber  54  to control the flow of fluid between the two chambers. When shock absorber  20  extends in length, an additional volume of fluid is needed in lower working chamber  46  due to the “rod volume” concept. Thus, fluid will flow from reservoir chamber  54  to lower working chamber  46  through base valve assembly  40 . When shock absorber  20  compresses in length, an excess amount of fluid must be removed from lower working chamber  46  due to the “rod volume” concept. Thus, fluid will flow from lower working chamber  46  to reservoir chamber  54  through base valve assembly  40 .  
         [0019]     Referring now to  FIG. 3 , piston assembly  32  comprises a piston body  60 , a compression valve assembly  62  and a rebound valve assembly  64 . Compression valve assembly  62  is assembled against a shoulder  66  on piston rod  34 . Piston body  60  is assembled against compression valve assembly  62  and rebound valve assembly  64  is assembled against piston body  60 . A nut  68  secures these components to piston rod  34 .  
         [0020]     Piston body  60  defines a plurality of compression passages  70  and a plurality of rebound passages  72 . Seal  48  includes a plurality of ribs  74  which mate with a plurality of annular grooves  76  to permit sliding movement of piston assembly  32 .  
         [0021]     Compression valve assembly  62  comprises a retainer  78 , a valve disc  80  and a spring  82 . Retainer  78  abuts shoulder  66  on one end and piston body  60  on the other end. Valve disc  80  abuts piston body  60  and closes compression passages  70  while leaving rebound passages  72  open. Spring  82  is disposed between retainer  78  and valve disc  80  to bias valve disc  80  against piston body  60 . During a compression stroke, fluid in lower working chamber  46  is pressurized causing fluid pressure to react against valve disc  80 . When the fluid pressure against valve disc  80  overcomes the biasing load of spring  82 , valve disc  80  separates from piston body  60  to open compression passages  70  and allow fluid flow from lower working chamber  46  to upper working chamber  44 . In a single-tube shock absorber, the strength of spring  82  and the size of compression passages  70  will determine the damping characteristics for shock absorber  20  in compression. In a dual-tube shock absorber as shown in  FIG. 2 , compression valve assembly  62  is designed as a low load check valve and the damping characteristics for shock absorber  20  in compression is controlled by the design of base valve assembly  40 . During a rebound stroke, compression passages  70  are closed by valve disc  80  while fluid is allowed to flow into rebound passages  72 .  
         [0022]     Rebound valve assembly  64  comprises a spacer  84 , a plurality of valve discs  86 , a spring retainer  88  and a coil spring  90 . Spacer  84  is threadingly or slidingly received on piston rod  34  and is disposed between piston body  60  and nut  68 . Spacer  84  retains piston body  60  and compression valve assembly  62  while permitting the tightening of nut  68  without compressing either valve disc  80  or the plurality of valve discs  86 . Spring retainer  78 , piston body  60  and spacer  84  provide a continuous solid connection between shoulder  66  and nut  68  to facilitate the tightening and securing of nut  68  to piston rod  34 . The plurality of valve discs  86  are slidingly received on spacer  84  and abut piston body  60  to close rebound passages  72  while leaving compression passages  70  open. Retainer  88  is also slidingly received on spacer  84  and abuts the plurality of valve discs  86 . Coil spring  90  is assembled over spacer  84  and over spring retainer  88  to provide stability for coil spring  90 . Coil spring  90  is disposed between spring retainer  88  and nut  68 . Coil spring  90  biases spring retainer  88  against the plurality of valve discs  86  and the plurality of valve discs  86  against piston body  60 . The plurality of valve discs  86  comprise a bleed disc  92 , a valve disc  94 , a spacer disc  96  and a fulcrum disc  98 . Bleed disc  92 , valve disc  94  and spacer disc  96  all have the same outer diameter. Bleed disc  92  includes a plurality of slots  100  which permit a limited amount of bleed flow bypassing rebound valve assembly  64 . Fulcrum disc  98  provides a fulcrum point or bending point for bleed disc  92 , valve disc  94  and spacer disc  96 . When fluid pressure is applied to discs  92 ,  94  and  96 , they will elastically deflect at the outer peripheral edge of fulcrum disc  98  to open rebound valve assembly  64 . The calibration for the blow off feature of rebound valve assembly  64  is separate from compression valve assembly  62  and it is controlled by the design of spacer  84  and nut  68 . Further calibration of the blow off feature can be accomplished by placing one or more shims (not shown) between nut  68  and spacer  84  as illustrated in Assignee&#39;s U.S. Letters Patent 6,371,264, the disclosure of which is incorporated herein by reference.  
         [0023]     During a rebound stroke, fluid in upper working chamber  44  is pressurized causing fluid pressure to react against the plurality of valve discs  86 . When the fluid pressure against the plurality of valve discs  86  overcomes the bending load for the plurality of valve discs  86 , the plurality of valve discs  86  elastically deflects opening rebound passages  72  allowing fluid flow from upper working chamber  44  to lower working chamber  46 . The strength of the plurality of valve discs  86  and the size of rebound passages  72  will determine the damping characteristics for shock absorber  20  in rebound. If the fluid pressure within upper working chamber  44  reaches a predetermined level, the fluid pressure will overcome the biasing load of coil spring  90  causing the axial movement of spring retainer  88  and the plurality of valve discs  86 . The axial movement of spring retainer  88  and the plurality of valve discs  86  fully open rebound passages  72  thus allowing the passage of a significant amount of damping fluid creating a blowing off of the fluid pressure which is required to prevent damage to shock absorber  20  and/or the vehicle.  
         [0024]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.