Abstract:
A dual tube shock absorber has a base valve assembly which includes both low speed control using a bleed type orifice and high speed/high pressure blow off control using a disc spring. The base valve assembly provides this variable damping force characteristic while reducing the dead length of the shock absorber.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to shock absorbers having a unique base valve assembly. More particularly, the present invention relates to a shock absorber having a base valve assembly which includes low speed control in conjunction with a blow off control which reacts to rising pressures. 
     BACKGROUND OF THE INVENTION 
     Shock absorbers are used in conjunction with automotive suspension systems and 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 automobile. 
     The most common type of shock absorbers for automobiles is the dashpot type in which a piston is located within a pressure tube and 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. Because the piston, through valving, has the ability to limit the flow of 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 a reserve tube which is positioned around the pressure tube. A base valve is located between the lower working chamber and the fluid reservoir to also produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the automobile during stroking of the shock absorber. 
     Because the amount of damping forces the shock absorber generates causes variation in driving characteristics, it is often desirable to have a shock absorber in which the amount of damping forces generated by the shock absorber is variable. Various designs in the prior art have provided this variable damping force feature. 
     Shock absorbers which are used to provide variable damping often have a base valve which controls the flow of damping fluid between the lower working chamber and the fluid reservoir. While such base valves generally serve their intended purpose of controlling the flow of damping fluid between the fluid reservoir and the lower working chamber, they often do not adjust the flow of damping fluid in response to the desired damping characteristics which the shock absorber is to provide. In other words, the prior art base valves would typically allow approximately the same amount of damping fluid to flow between the lower working chamber and the fluid reservoir regardless of whether it was desired for the shock absorber to provide firm damping or soft damping. 
     SUMMARY OF THE INVENTION 
     The present invention provides the art with a shock absorber that includes a base valve assembly having both low speed control using an orifice and high speed/high pressure blow off type control using a disc spring. The base valve assembly provides this variable damping force characteristic while reducing the dead length of the shock absorber which is an advantage over the typical blow-off base valve which utilizes a coil spring. 
     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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic representation of a typical automobile which incorporates the unique base valve assembly in accordance with the present invention; 
         FIG. 2  is a side sectional view of the shock absorber in accordance with the present invention; 
         FIG. 3  is an enlarged cross-sectional view of the piston assembly in accordance with the present invention; and 
         FIG. 4  is an enlarged cross-sectional view of the base valve assembly in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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. 
     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 incorporating the shock absorbers in accordance with the present invention and 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 a pair of rear wheels  18  of vehicle  10 . 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 a pair of front wheels  24  of vehicle  10 . 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 mass (i.e., front and rear suspensions  12  and  14 , respectively) and the sprung mass (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. 
     Referring now to  FIG. 2 , shock absorber  20  is shown in greater detail. White  FIG. 2  illustrates only shock absorber  20 , it is to be understood that shock absorber  26  also includes the base valve assembly described below for shock absorber  20 . Shock absorber  26  only differs from shock absorber  20  in the manner in which it is adapted to be connected to the sprung and unsprung masses of vehicle  10 . Shock absorber  20  comprises a pressure tube  30 , a piston assembly  32 , a piston rod  34 , a reserve tube  36  and a base valve assembly  38 . 
     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 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  and 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 assembly  38 . 
     Reserve tube  36  surrounds pressure tube  30  to define a fluid reservoir chamber  52  located between tubes  30  and  36 . The bottom end of reserve tube  36  is closed by an end cap  54  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  38  is disposed between lower working chamber  46  and reservoir chamber  52  to control the flow of fluid between chambers  46  and  52 . 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  52  to lower working chamber  46  through base valve assembly  38  as detailed below. When shock absorber  20  compresses in length, an excess of fluid must be removed from lower working chamber  46  due to the “rod volume” concept. Thus, fluid will flow from working chamber  46  to reservoir chamber  52  through base valve assembly  38  as detailed below. 
     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 . 
     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 . 
     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 to upper working chamber. Typically spring  82  only exerts a light load on valve disc  80  and compression valve assembly  62  acts like a check valve between chambers  46  and  44 . The damping characteristics for shock absorber  20  are controlled by base valve assembly  38  which accommodates the flow of fluid from lower working chamber  46  to reservoir chamber  52  due to the “rod volume” concept as detailed below. During a rebound stroke, compression passages  70  are closed by valve disc  80 . 
     Rebound valve assembly  64  comprises a spacer  84 , a plurality of valve discs  86 , a retainer  88  and a Belleville spring  90 . Spacer  84  is threadingly received on piston rod  34  and is disposed between piston body  160  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 valve discs  86 . 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 spacer  84  and thus to piston rod  34 . 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 it abuts valve discs  86 . Belleville spring  90  is assembled over spacer  84  and is disposed between retainer  88  and nut  68  which is threadingly received on spacer  84 . Belleville spring  90  biases retainer  88  against valve discs  86  and 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  includes at least one slot  100  which permits a limited amount of bleed flow bypassing rebound valve assembly  64 . Fulcrum disc  98  provides a fulcrum or bending point for bleed disc  92 , valve disc  94  and spacer disc  96 . When fluid pressure is applied to discs  92  and  94 , they will elastically deflect at the outer peripheral edge of spacer disc  96  and fulcrum disc  98  to open rebound valve assembly  64 . A shim  102  is located between nut  68  and Belleville spring  90  to control the preload for Belleville spring  90  and thus the blow off pressure as described below. Thus, the calibration for the blow off feature of rebound valve assembly  64  is separate from the calibration for compression valve assembly  62 . 
     During a rebound stroke, fluid in upper working chamber  44  is pressurized causing fluid pressure to react against valve discs  86 . When the fluid pressure reacting against valve discs  86  overcomes the bending load for valve discs  86 , valve discs  86  elastically deflect opening rebound passages  72  allowing fluid flow from upper working chamber  44  to lower working chamber  46 . The strength of valve discs  86  and the size of rebound passages will determine the damping characteristics for shock absorber  20  in rebound. Prior to the deflection of valve discs  86 , a controlled amount of fluid flows from upper working chamber  44  to lower working chamber  46  through slot  100  to provide low speed tunability. When the fluid pressure within upper working chamber  44  reaches a predetermined level, the fluid pressure will overcome the biasing load of Belleville spring  90  causing axial movement of retainer  88  and the plurality of valve discs  86 . The axial movement of retainer  88  and valve discs  86  fully opens 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 vehicle  10 . 
     Referring now to  FIG. 4 , base valve assembly  38  is illustrated. Base valve assembly  38  comprises a cylinder end  110 , an intake valve  112 , a bolt  114 , a Belleville or disc spring  116 , a nut  118  and an intake spring  120 . Cylinder end  110  is attached to pressure tube  30  and separates lower working chamber  46  from reservoir chamber  52 . Cylinder end  110  also engages reserve tube and it defines a plurality of fluid passages  122  open to reservoir chamber  52 . Cylinder end  110  defines a central fluid passage  124  extending between lower working chamber  46  and reservoir chamber  52  through fluid passages  122 . 
     Intake valve  112  is disposed within central fluid passage  124  and abuts a generally annular land  126  formed on cylinder end  110  to close central fluid passage  124 . Intake valve  112  defines a plurality of compression passages  128  extending between lower working chamber  46  and reservoir chamber  52 . Bolt  114  extends through a central bore  130  defined by intake valve  112  to attach Belleville spring  116  at a position adjacent intake valve  112 . Nut  118  is threadingly received on bolt  114  in order to bias Belleville spring  116  against intake valve  112  to close compression passages  128 . A seat disc  132  is disposed between nut  118  and Belleville spring  116  to provide a surface against which Belleville spring  116  reacts. 
     Intake spring  120  is disposed between intake valve  112  and bolt  114  to bias intake valve  112  against annular land  126  to close central fluid passage  124 . Intake spring  120  defines a plurality of apertures  134  extending through intake spring  120  to allow fluid within lower working chamber  46  to flow into compression passages  128 . 
     During a rebound stroke of shock absorber  20 , fluid flows through rebound valve assembly  64  of piston assembly  32  as described above. Due to the “rod volume” concept described above, fluid is required to flow from reservoir chamber  52  to lower working chamber  46  through base valve assembly  38 . The pressure differential between lower working chamber  46  and reservoir chamber  52  deflects intake spring  120  to move intake valve  112  away from annular land  126  to open central fluid passage  124  to allow fluid flow from reservoir chamber  52  into lower working chamber  46 . Intake spring  120 : is designed to exert a minimum load against bolt  114  such that base valve assembly  38  acts like a check valve during a rebound stroke. The damping load during a rebound stroke is primarily controlled by rebound valve assembly  64  of piston assembly  32 . 
     During a compression stroke of shock absorber  20 , a minimal amount of damping load is generated by compression valve assembly  62  of piston assembly  32 . The majority of damping force created by shock absorber  20  during a compression stroke of shock absorber  20  is generated by base valve assembly  38 . Due to the “rod volume” concept, fluid needs to flow from lower working chamber  46  to reservoir chamber  52  through base valve assembly  38 . During the compression stroke of shock absorber  20 , fluid in lower working chamber  46  is pressurized and fluid flows from lower working chamber  46  through a bleed orifice  140  formed in annular land  126  or intake valve  112 . As the pressure within lower working chamber  46  increases, the fluid pressure reacts against Belleville spring  116  through compression passages  128 . When the fluid pressure within lower working chamber reaches a predetermined value, the fluid pressure will overcome the biasing load of Belleville spring  116  causing deflection of Belleville spring  116  allowing the passage of fluid through compression passage  128  creating a blow off of the fluid pressure within lower working chamber  46 . 
     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.