Abstract:
A dual tube shock absorber includes a baffle located in the reservoir chamber to define a non-linear flow path within the reservoir chamber. The baffle extends between the pressure tube and the reservoir tube such that the non-linear flow path is the only flow path between two portions of the reservoir chamber. One embodiment is a T-shaped baffle, and another embodiment has a base section and an upright section with a wire being embedded in the base section.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to dual tube shock absorbers having a unique baffle design located within the reservoir chamber. More particularly, the present invention relates to a dual tube shock absorber having a baffle located within the reservoir chamber which directs fluid flow to a helical path in order to reduce aeration of the damping fluid. 
     BACKGROUND OF THE INVENTION 
     Shock absorbers are used in conjunction with automotive suspension systems and with 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 mass (body) and the unsprung mass (suspension) of the automobile. 
     One of the most common type of shock absorbers for automobiles is the dual tube dashpot type. These shock absorbers have a piston which is located within a pressure tube. The piston is typically connected to the sprung mass of the vehicle using 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 from the upper working chamber to the lower working chamber within the pressure tube when the shock absorber is 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 during the extension stroke. In the dual tube shock absorber, a fluid reservoir chamber 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 reservoir chamber. Because the base valve assembly, through valving, has the ability to limit the flow of damping fluid from the lower working chamber to the reservoir chamber when the shock absorber is compressed, 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 during the compression stroke. 
     Because the piston rod of the shock absorber extends only through the upper working chamber and not through the lower working chamber, movement of the piston with respect to the pressure tube causes a difference in the amount of fluid displaced in the upper working chamber from the amount of fluid displaced in the lower working chamber. This difference in the amount of fluid displaced is known as the rod volume and it flows through the base valve assembly during both the extension stroke and the compression smoke. 
     When the shock absorber extends in length, extension stroke, fluid flows through valving in the piston from the upper working chamber to the lower working chamber to create the damping force but an additional volume of fluid is needed in lower working chamber due to the rod volume concept. Thus, fluid will flow from the reservoir chamber to the lower working chamber through a check valve located within the base valve assembly. The check valve does not generate a damping force. 
     When the shock absorber compresses in length, compression stroke, fluid flows through a check valve in the piston from the lower working chamber to the upper working chamber. The flow through the check valve does not generate a damping force. Due to the rod volume concept, an additional volume of fluid must be removed from the lower working chamber. Thus, fluid will flow from the lower working chamber to the reservoir chamber through valving in the base valve assembly to create the damping force. 
     In some applications, the continuous flow of fluid into and out of the reservoir chamber through the base valve assembly has led to aeration of the damping fluid. In order to decrease the aeration of the damping fluid, baffle springs have been designed for the reservoir chamber. These prior art baffle springs typically are in the form of a helical spring which is disposed on the pressure tube to extend towards the reservoir tube but not to extend to the pressure tube. Thus, an opening is left between the baffle spring and the reservoir tube. 
     While these designs of baffle springs have proven to reduce the amount of aeration in certain applications, there is still uncontrolled damping fluid flow possible between the baffle spring and the reservoir tube which enlarges the oil-gas surface and hence worsens the aeration insensitivity. 
     SUMMARY OF THE INVENTION 
     The present invention provides the art with a baffle spring which spans the entire width of the reservoir. Thus, the baffle spring contacts both the pressure tube and the reservoir tube to define a helical channel for the fluid flow. 
     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 shock absorber which include the unique baffle spring 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; 
         FIG. 4  is an enlarged cross-sectional view of the base valve assembly in accordance with the present invention; 
         FIG. 5  is an enlarged cross-sectional view of the baffle spring located between the pressure tube and the reservoir tube in accordance with the present invention; and 
         FIG. 6  is an enlarged cross-sectional view of a baffle spring located between the pressure tube and the reservoir tube similar to  FIG. 3  but in accordance with another embodiment of 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. While  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 reservoir tube  36 , a base valve assembly  38  and a baffle in the form of a baffle spring  40 . 
     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 , reservoir 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 valve assembly  38 . 
     Reservoir tube  36  surrounds pressure tube  30  to define a fluid reservoir chamber  52  located between tubes  30  and  36 . The bottom end of reservoir 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 lower 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  46  to upper working chamber  44 . Typically spring  82  only exerts a light load on valve disc  80  and compression valve assembly  62  acts as a check valve between chambers  46  and  44 . The damping characteristics for shock absorber  20  during a compression stroke 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  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 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 . 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  72  will determine the damping characteristics for shock absorber  20  in rebound. 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  comprises a valve body  110 , a rebound valve assembly  112 , a compression valve assembly  114  and a bolt  116 . Rebound valve assembly  112  is assembled against the head of bolt  116 . Valve body  110  is assembled against valve body  110 . A nut  118  secures these components to bolt  116 . 
     Valve body  110  defines a plurality of rebound passages  120  and a plurality of compression passages  122 . Valve body  110  is press fit or otherwise attached to the end of pressure tube  30 . 
     Rebound valve assembly  112  comprises a valve disc  130  and a spring  132 . Valve disc  130  abuts valve body  110  and closes rebound passages  120  while leaving compression passages  122  open. Spring  132  is disposed between the head of bolt  116  and valve disc  130  to bias valve disc  130  against valve body  110 . During a rebound stroke due to the “rod volume” concept, fluid in lower working chamber  46  is reduced in pressure causing fluid pressure from within reservoir chamber  52  to react against valve disc  130 . When the fluid pressure against valve disc  130  overcomes the biasing load of spring  132 , valve disc  130  separates from valve body  110  to open rebound passages  120  and allow fluid flow from reservoir chamber  52  to lower working chamber  46 . Typically, spring  132  only exerts a light load on valve disc  130  and rebound valve assembly  112  acts as a check valve between chambers  52  and  46 . The damping characteristics for shock absorber  20  during a rebound stroke are controlled by rebound valve assembly  64  as detailed above. During a compression stroke, rebound passages  120  are closed by valve disc  130 . 
     Compression valve assembly  114  comprises a spacer  134 , a plurality of valve discs  136 , a retainer  138  and a Belleville spring  140 . Spacer  134  is threadingly received on bolt  116  and is disposed between valve body  110  and nut  118 . Spacer  134  retains valve body  110  and rebound valve assembly  112  while permitting the tightening of nut  118  without compressing either valve disc  130  or valve discs  136 . Valve body  110  and spacer  134  provide a continuous solid connection between the head of bolt  116  and nut  118  to facilitate the tightening and securing of nut  118  to spacer  134  and thus to bolt  118 . Valve discs  136  are slidingly received on spacer  134  and abut valve body  110  to close compression passages  122  while leaving rebound passages  120  open. Retainer  138  is also slidingly received on spacer  134  and it abuts valve discs  136 . Belleville spring  140  biases retainer  138  against valve discs  136  and valve discs  136  against valve body  110 . A shim  152  is located between nut  118  and Belleville spring  140  to control the preload for Belleville spring  140  and thus the blow off pressure as described below. Thus, the calibration for the blow off feature of compression valve assembly  114  is separate from the calibration of rebound valve assembly  112 . 
     During a compression stroke, fluid in lower working chamber  46  is pressurized causing fluid to react against valve discs  136 . When the fluid pressure reacting against valve discs  136  overcomes the bending load for valve discs  136 , valve discs  136  with elastically deflect to open compression passages  122  allowing fluid flow from lower working chamber  46  to reservoir chamber  52 . Fluid flow will also occur through compression valve assembly  62  in piston assembly  32  from lower working chamber  46  to upper working chamber  44 . The flow of fluid through compression valve assembly  114  occurs due to the “rod volume” concept. The strength of valve discs  136  and the size of compression passages  122  will determine the damping characteristics for shock absorber  20  in compression. When the fluid pressure within lower working chamber  46  reaches a predetermined level, the fluid pressure will overcome the biasing load of Belleville spring  140  causing axial movement of retainer  138  and the plurality of valve discs  136 . The axial movement of retainer  138  and valve discs  136  fully opens compression passages  122  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 . 
     In some applications, the movement of fluid into and out of reservoir chamber  52  causes aeration of the hydraulic fluid. The amount of aeration for each application is different with certain applications being very sensitive to the aeration problem. For these applications extremely sensitive to aeration, the performance of the prior art baffle springs has been found to be insufficient. 
     Baffle spring  40  has proven to reduce the sensitivity to aeration by a wide margin. Baffle spring  40  has a T-shape cross section as illustrated in FIG.  5 . T-shaped baffle spring  40  comprises a base section  180  which engages pressure tube  30  and an upright section  182  which extends from base section  180  to engage reservoir tube  36 . Baffle spring  40  is an elastomeric or rubber molding that is helicoidally wound around pressure tube  30  and is attached to pressure tube  30  using an adhesive or by other methods known well in the art. The height of upright section  182  is such that baffle spring  40  is slightly oversize relative to the inside diameter of reservoir tube  36 . The oversize dimensioning of baffle spring  40  in relation to reservoir tube  36  ensures a sufficient clinching of baffle spring  40  between pressure tube  30  and reservoir tube  36 . 
     Baffle spring  40  forces the fluid flow within reservoir chamber  52  to follow the helical channel that is formed by the space created between baffle spring  40 , pressure tube  30  and reservoir tube  36 . The oversize nature of baffle spring  40  in relation to the inner diameter of reservoir tube  36  provides a sufficient degree of sealing between baffle spring  40  and tubes  30  and  36 . 
     Referring now to  FIG. 6 , a baffle spring  240  in accordance with an other embodiment of the present invention is illustrated. Baffle spring  240  comprises a base section  242  having a metal wire  244  disposed within base section  242  and an upright section  246  extending from base section  240  to engage reservoir tube  36 . Baffle spring  240  is an elastomeric or rubber molding that is reinforced by metal wire  244 . Baffle spring  240  is helicoidally wound around pressure tube  30  and is attached to pressure tube  30  using the resiliency of metal wire  244 . The height of upright section  246  is such that baffle spring  240  is slightly oversize relative to the inside diameter of reservoir tube  36 . the oversize dimensioning of baffle spring  240  in relation to reservoir tube  36  ensures a sufficient clinching of baffle spring  240  between pressure tube  30  and reservoir tube  36 . 
     Baffle spring  240  forces the fluid flow within reservoir chamber  52  to follow the helical channel that is formed by the space created between baffle spring  240 , pressure tube  30  and reservoir tube  36 . The oversize nature of baffle spring  240  in relation to the inside diameter of reservoir tube  36  provides a sufficient degree of sealing between baffle spring  240  and tubes  30  and  36 . 
     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.