Abstract:
A rod guide assembly for a shock absorber includes a seal assembly which is biased towards a sealing surface on the rod guide by a biasing member which is located between the seal assembly and the bearing which is assembled to the rod guide housing. The biasing of the seal assembly prohibits movement of the seal assembly during operation of the shock absorber. In addition, a wire circlip which radially biases the seal assembly can be included.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to shock absorbers. More particularly, the present invention relates to a unique slip ring which seals the interface between the piston rod and the rod guide.  
       BACKGROUND OF THE INVENTION  
       [0002]     Shock absorbers are used in conjunction with automobile suspension systems and other vehicle suspension systems to absorb unwanted vibrations which occur during operation of the vehicle. To absorb this unwanted vibrations, shock absorbers are connected between the sprung mass (the body) and the unsprung mass (the suspension system) of the vehicle. A monotube shock absorber has a piston which is located within a pressure tube of the shock absorber and the piston is typically connected to the sprung mass of the vehicle using a piston rod. The pressure tube is typically connected to the unsprung mass of the vehicle and it is typically filled with hydraulic fluid. The piston includes valving systems which have the capability to limit the flow of hydraulic fluid within the pressure tube when the shock absorber is compressed (compression stroke) or extended (rebound stroke). The limiting of fluid flow produces a damping force which counteracts the vibrations which would otherwise be transmitted from the suspension (unsprung mass) to the body (sprung mass) of the vehicle.  
         [0003]     A dual tube shock absorber comprises a pressure tube with a piston disposed therein and a reserve tube surrounding the pressure tube. The piston divides the pressure tube into an upper and lower working chamber. A piston rod is connected to the piston and the piston rod extends through the upper working chamber of the pressure and through the upper end of the reserve tubes. At the lower end of the pressure tube, a base valve is located between the pressure tube and the reserve tube. The base valve controls fluid flow between the working chamber defined by the pressure tube and a reserve chamber defined by the serve tube. Due to the piston rod being located on only one side of the piston within the upper working chamber, a different amount of fluid is displaced between the upper working chamber above the piston and the lower working chamber below the piston when the shock absorber extends or compresses. This difference in the amount of fluid is termed the “rod volume”. During a compression stroke, the “rod volume” flows out of the lower working chamber through the base valve and into the reserve chamber. During a rebound or extension stroke, the “rod volume” flows out of the reserve chamber through the base valve and into the lower working chamber. The piston rod is typically connected to the unsprung mass of the vehicle and the reserve tube is typically secured to the unsprung mass of the vehicle. During an extension or rebound stroke, a valving system in the piston limits the flow of hydraulic fluid within the pressure tube to produce a damping force. A check valve is included in the base valve to accommodate the “rod volume” flow of fluid. During a compression stroke, a valving system in the base valve limits the flow of hydraulic fluid between the lower working chamber and the reserve chamber to produce a damping force. A check valve is included in the piston to allow fluid to flow into the upper working chamber.  
         [0004]     The piston rod of a shock absorber is supported at its lower end by the piston and it is slidingly received at the upper end of the pressure tube, and the reserve tube for a dual tube shock absorber, by a rod guide. The rod guide thus functions as a slide bearing for the piston rod. The rod guide properly positions the piston rod within the pressure tube and also acts as a closure member for both the pressure tube and the reserve tube when present. In order for the smooth sliding of the piston rod through the rod guide, a slight clearance is formed between the inner periphery of the bearing portion of the rod guide and the outer surface of the piston rod. This slight clearance allows for the hydraulic fluid to lubricate the interface between the piston rod and the rod guide.  
         [0005]     In addition to locating the piston rod and closing the pressure tube and the reserve tube when present, the rod guide supports and locates a seal assembly which is designed to keep the hydraulic fluid within the shock absorber and also keep contaminants out of the shock absorber. The seal assembly normally interfaces between the rod guide and the piston rod and its purpose is to seal this interface in both rebound and compression strokes.  
         [0006]     The prior art seal assemblies function well during a rebound stroke but they can be susceptible to leakage during a compression stroke. When the seal assembly is at zero velocity during the transition between rebound and compression, there is no residual force acting on the seal assembly. When the piston rod starts displacing in compression, the only initial force acting on the seal assembly is friction. This friction pulls the seal assembly down away from the rod guide until it meets the bearing bushing assembled with the rod guide. Depending on how well the bearing bushing is assembled, the dimensions of the bearing bushing and other related dimensions, the seal assembly then seals on the bearing bushing. The effectiveness of the seal is determined by how well the seal assembly and the bearing bushing are manufactured and the acting pressure (velocity) on the seal assembly. When the piston then displaces in rebound, the seal assembly will again be pushed upward against the sealing surface of the rod guide. This movement of the seal assembly between the rod guide and the bearing bushing provides a slight leaking of the hydraulic fluid. Typically, this leak is uncontrollable.  
         [0007]     In addition to the problems associated with seal assembly movement, the problems associated with higher temperatures can cause leaking of the seal assembly. In applications which use the friction properties of the seal assembly for sealing, when higher temperatures are encountered, the seal assembly is again susceptible to leakage.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides the art with a seal assembly which is always biased towards the rod guide sealing surface using a biasing member disposed between the seal assembly and the bearing bushing. The biasing of the seal assembly prohibits movement of the seal assembly during operation of the shock absorber and during the transitions between compression and rebound strokes. The present invention also provides a wire circlip which radially preloads the seal assembly. The radial preloading of the seal assembly maintains a constant friction/sealing relationship with the piston rod to compensate for temperature differences.  
         [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 an illustration of an automobile using the dual action slip ring in accordance with the present invention;  
         [0012]      FIG. 2  is a cross-sectional view of a shock absorber shown in  FIG. 1  incorporating the dual action slip ring in accordance with the present invention;  
         [0013]      FIG. 3  is an enlarged cross-sectional view of the rod guide for the shock absorber shown in  FIG. 2 ;  
         [0014]      FIG. 4  is an enlarged cross-sectional view of a rod guide incorporating of dual action slip ring in accordance with another embodiment of the present invention; and  
         [0015]      FIG. 5  is an enlarged cross-sectional view of a rod guide incorporating of dual action slip ring in accordance with another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views. 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. There is shown in  FIG. 1 , a vehicle incorporating shock absorbers which include the unique slip ring design in accordance with the present invention and which is designated generally by the reference numeral  10 . Vehicle  10  includes a rear suspension system  12 , a front suspension  14  and a body  16 . Rear suspension system  12  includes a pair of rear suspension arms adapted to operatively support a pair of rear wheels  18 . Each rear suspension arm is attached to body  16  by means of a shock absorber  20  and a helical coil spring  22 . Similarly, front suspension system  14  includes a pair of suspension arms adapted to operatively support a pair of front wheels  24 . Each suspension arm is attached to body  16  by means of a shock absorber  26  and a helical coil spring  28 . Rear shock absorbers  20  and front shock absorbers  26  serve to dampen the relative movement of the unsprung portion of vehicle  10  (i.e., front and rear suspension systems  12 ,  14 ) with respect to the sprung portion (i.e., body  16 ) of vehicle  10 . While vehicle  10  has been depicted as a passenger vehicle having independent front and rear suspension  12  and  14 , shock absorbers  20  and  26  may be used with other types of vehicles having other types of suspension and springs or in other types of applications including, but not limited to, vehicles incorporating air springs, leaf springs, non-independent front and/or non-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, spring seat units as well as other shock absorber designs known in the art.  
         [0017]     Referring now to  FIG. 2 , rear shock absorber  20  is shown in greater detail. While  FIG. 2  shows only rear shock absorber  20 , it is to be understood that front shock absorber  26  is also designed to include the slip ring in accordance with the present invention. Front shock absorber  26  only differs from rear shock absorber  20  in the way 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  32 , a piston rod  34 , a reserve tube  36  and a base valve assembly  38 .  
         [0018]     Pressure tube  30  defines a working chamber  42 . Piston  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  32  and pressure tube  30  to permit sliding movement of piston  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  32  and extends through upper working chamber  44  and through an upper rod guide  50  which closes the upper end of both pressure tube  30  and reserve tube  36 . A unique sealing system  52  seals the interface between rod guide  50 , reserve tube  36  and piston rod  34 . The end of piston rod  34  opposite to piston  32  is adapted to be secured to the sprung portion of vehicle  10 . Valving within piston  32  controls the movement of fluid between upper working chamber  44  and lower working chamber  46  during movement of piston  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  32  with respect to pressure tube  30  causes a difference in the amount of fluid displaced in upper working chamber  44  when compared with the amount of fluid displaced in lower working chamber  46 . This difference in the amount of fluid displaced is termed the “rod volume” and it flows through base valve assembly  38 .  
         [0019]     Reserve tube  36  surrounds pressure tube  30  to define a reserve chamber  54  located between the tubes. The bottom end of reserve 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 reserve tube  36  is attached to rod guide  50  by mechanically deforming the open end of reserve tube  36  to form a retaining flange  58 . Base valve assembly  38  is disposed between lower working chamber  46  and reserve chamber  54  to control the flow of fluid, the “rod volume” of fluid between the two chambers. When shock absorber  20  extends in length (rebound), an additional amount of fluid, the “rod volume”, is needed in lower working chamber  46 . Thus, fluid will flow from reserve chamber  54  to lower working chamber  46  through base valve assembly  40 . When shock absorber  20  shortens in length (compression), and excess of fluid, the “rod volume”, must be removed from lower working chamber  46 . Thus, fluid will flow from lower working chamber  46  to reserve chamber  54  through base valve assembly  40 .  
         [0020]     The present invention is directed to the unique sealing system  52  which operates to keep hydraulic fluid within shock absorber  20  while keeping dirt and other contaminants from entering shock absorber  20 .  
         [0021]     Referring now to  FIG. 3 , sealing system  52  comprises an upper seal assembly  60  and a lower seal assembly  62 . Upper seal assembly  60  comprises a positioning ring  64 , a damper seal  66  and a dirt wiper  68 . Positioning ring  64  is a metal or a plastic positioning ring which is seated on an annular shoulder  70  defined by rod guide  50 .  
         [0022]     Damper seal  66  is an elastomeric seal which defines an annular groove  72  within which positioning ring  64  is located. Positioning ring  64  can be a separate component or positioning ring  64  can be bonded to damper seal  66  during or after the molding operation for damper seal  66 . The outer diameter of damper seal  66  sealingly engages rod guide  50 . Damper seal  66  defines a lower annular seal lip  74  that engages piston rod  34  at a position below shoulder  70  of rod guide  50  and an upper annular seal lip  76  that engages piston rod  34  at a position above shoulder  70  of rod guide  50 . Lower annular seal lip  74  acts primarily as a seal which keeps hydraulic fluid within shock absorber  20 . Any hydraulic fluid which may adhere to the outer surface of piston rod  34  after having past lower seal assembly  62  will be wiped off of piston rod  34  and returned to reserve chamber  54  through a fluid de-aeration passage  82  extending through rod guide  50 . While acting as a secondary oil seal, lower annular seal lip  74  will also act to stop dirt and contamination from entering shock absorber  20 . Upper annular seal  76  acts primarily as a seal which keeps dirt and other contaminants out of shock absorber  20 . Any dirt or contaminants located on the outer surface of piston rod  34  will be wiped off by upper annular seal lip  76 . While acting primarily as a dirt seal, upper annular seal clip  76  will also act as an oil seal to keep hydraulic fluid within shock absorber  20 .  
         [0023]     Dirt wiper  68  is a hard plastic component, preferably Teflon®, which includes an annular section  84  and a frusto-conical section  86 . Annular section  84  rests within an annular groove formed in the upper surface of damper seal  66 . Frusto-conical section  86  extends upward from annular section  84  over upper annular seal  76  to provide protection for damper seal  66 . The upper end of frusto-conical section  86  defines a lip which rides against piston rod  34  and operates to wipe or remove any dirt, water or contaminants adhering to piston rod  34 . The stiffness of the hard plastic of dirt wiper  68  enables it to remove contaminants which could possibly damage portions of damper seal  66 .  
         [0024]     Lower seal assembly  62  comprises a slip ring  92  and a biasing member  94 . The present invention optimizes the function of slip ring  92  under all temperature conditions and/or it guarantees full function of slip ring  92  in both rebound and compression strokes of shock absorber  20 . Slip ring  92  is positioned above a bearing  96  press fitted into rod guide  50 . Biasing member  94  biases slip ring  92  against rod guide  50  to provide the necessary sealing for shock absorber  20 . While biasing member  94  is illustrated as a wave washer, other biasing members including, but not limited to, rubber washers or coil springs could be utilized for the biasing of slip ring  92 .  
         [0025]     Slip ring  92  slidingly engages piston rod  34  to provide the primary oil seal for shock absorber  20 . Typically, the prior art refers to a slip ring as being a component sealing the rod guide-piston rod leak during both a rebound stroke and a compression stroke. The inventors of the present invention have found that while a slip ring functions well during a rebound stroke, it does not function adequately during a compression stroke.  
         [0026]     The inventors of the present invention determined that when piston rod  34  is at zero velocity during the transition between rebound and compression, there is no residual force acting on slip ring  92 . When piston rod  34  starts displacing in compression, the only initial force acting on slip ring  92  is the friction with piston rod  34 . This friction will pull slip ring  92  down until it meets bearing  96 . Depending on how well bearing  96  is assembled, the dimensions of bearing  96  and the like, slip ring  92  will engage and seal against bearing  96  after a small movement of piston rod  34 . Depending on how well this slip ring-bearing seal is and the acting pressure of engagement between slip ring  92  and bearing  96  due to the velocity of piston rod  34 , the fluid pressure within shock absorber  20  will push slip ring  92  back against the sealing surface of rod guide  50  again. This cyclical movement of slip ring  92  creates a leak. The cracking point for the leak is very uncontrollable as well as the leak itself when attempting to seal the slip ring-bearing interface. In practice, the leak in compression is uncontrollable.  
         [0027]     Biasing member  94  preloads slip ring  92  against the sealing surface of rod guide  50 . Thus, during the transitions between rebound and compression, and during the entire operation of shock absorber  20 , slip ring  92  does not move. This guarantees a controllable sealing interface between slip ring  92  and piston rod  34  with de-aeration passage  82  returning the hydraulic fluid bypassing slip ring  92  to reserve chamber  54 .  
         [0028]     Referring now to  FIG. 4 , a lower seal assembly  162  in accordance with another embodiment of the present invention is illustrated. Lower seal assembly  162  comprises a slip ring  192 , a biasing member  194  and a retainer  196 . Biasing member  194  is a circlip which is located in a groove  198  defined by the outer surface of slip ring  192 . Biasing member  194  urges slip ring  192  into engagement with piston rod  34 . The use of biasing member  194  allows for control of the friction/sealing between piston rod  34  and slip ring  192 . Retainer  196  positions slip ring  192  with respect to rod guide  50  to control the slip ring to rod guide sealing as described above for slip ring  92 . As illustrated in  FIG. 5 , it is within the scope of the present invention to utilize biasing member  194  in conjunction with biasing member  94  in place of retainer  196 .  
         [0029]     Due to the properties required to seal under high pressures, slip ring  192 , which is preferably manufactured from bronze filled Teflon®, changes its sealing/friction properties with the changes in temperature. The incorporate of biasing member  194  allows for consistency in the friction/sealing interface between slip ring  192  and piston rod  34  by radially preloading slip ring  192 .  
         [0030]     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.