Abstract:
A shock absorber includes a hydraulic stop. The hydraulic stop includes two housings connected together by a spring. At the end of the stroke of the shock absorber, the piston causes the two housings to approach each other thereby causing fluid disposed between the housings to flow through a bleed passage. The size or total area of the bleed passage will determine the amount of hydraulic damping provided by the hydraulic stop.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a hydraulic damper or shock absorber having rebound damping for use in a suspension system such as the suspension systems used for automotive cars and trucks. More particularly, the present invention relates to a hydraulic damper or shock absorber having rebound damping that provides a hydraulic cushion for the hydraulic damper or shock absorber just prior to full extension of the hydraulic damper or shock absorber.  
       BACKGROUND OF THE INVENTION  
       [0002]     A conventional mono-tube shock absorber comprises a cylinder defining a working chamber having a piston slidably engaging the cylinder within the working chamber. The piston divides the working chamber into an upper working chamber and a lower working chamber. A piston rod is connected to the piston and the piston rod extends through the upper working chamber and through one end of the cylinder. An extension valving system is incorporated into the piston for generating a damping force during an extension stroke of the shock absorber and a compression valving system is incorporated into the piston for generating a damping force during a compression stroke of the shock absorber. In a dual tube shock absorber, a reservoir tube surrounds the pressure tube to define a reservoir chamber. A base valve assembly controls fluid flow between the working chamber and the reservoir chamber. An extension valving system is incorporated into the piston for generating a damping force during an extension stroke of the shock absorber and a compression valving system is incorporated into the base valve assembly for generating a damping force during a compression stroke of the shock absorber. The piston includes a compression valving system to regulate the pressure drop across the piston during the compression stroke and the base valve assembly includes an extension valving system to regulate the pressure drop across the base valve system during the extension stroke.  
         [0003]     In some applications, the shock absorber is required to limit the full extension travel of the vehicle&#39;s suspension system. When the shock absorber is used as an extension stop for the vehicle&#39;s suspension system, it is important to provide some type of mechanism or system which provides a cushion for this stop to avoid the excessive loading and/or noise which occurs when there is a metal to metal stop. Built into the shock absorber, one typical extension stop is a resilient bumper made of some type of elastomeric material. The bumper is designed to cushion the impact between the piston and the top of the pressure tube. While these types of extension stops help to cushion the impact, they still provide an abrupt means for limiting the travel and the elastomeric material may experience heat degradation which reduces its ability to limit the impact.  
         [0004]     Another type of extension stop that has been developed is to provide additional hydraulic damping force acting against the piston during the extension stroke when the piston approaches the end of the pressure tube. These systems are known as “hydraulic extension cut-off” or “stop” and they have been effective at cushioning the impact between the piston and the end of the shock absorber.  
         [0005]     While the prior art hydraulic extension cut-off designs have been effective at reducing both the loads and the noise associated with the impact between the piston and the end of the pressure tube, the costs and complexities of these designs is excessive and easier and less costly designs or systems are needed which can provide the same and/or additional features.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides the art with a simpler and less costly hydraulic extension stop system. The system includes a pair of plastic retainers which define a damping chamber located at the extension end of the shock absorber. When the piston engages the lower retainer, the hydraulic fluid in the damping chamber is forced through a bleed passage to dampen the movement of the piston as it reaches the full extension position. A spring disposed between the pair of plastic retainers returns the lower retainer to its original position upon a compression movement of the shock absorber.  
         [0007]     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  
       [0008]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0009]      FIG. 1  is a perspective illustration of an automobile which includes shock absorbers which incorporate the hydraulic extension cut-off in accordance with the present invention;  
         [0010]      FIG. 2  is a cross-sectional side view of a dual tube shock absorber incorporating the hydraulic extension cut-off in accordance with the present invention;  
         [0011]      FIG. 3  is an enlarged cross-sectional view of the extension end of the shock absorber illustrated in  FIG. 2 ;  
         [0012]      FIG. 4  is a cross-sectional side view of a mono-tube shock absorber incorporating they hydraulic extension cut-off in accordance with the present invention;  
         [0013]      FIG. 5  is a view similar to  FIG. 3  but illustrating a hydraulic extension stop in accordance with another embodiment of the present invention;  
         [0014]      FIG. 6  is a view similar to  FIG. 3  but illustrating a hydraulic extension stop in accordance with another embodiment of the present invention;  
         [0015]      FIG. 7  is a view similar to  FIG. 3  but illustrating a hydraulic extension stop in accordance with another embodiment of the present invention; and  
         [0016]      FIG. 8  is an end cross-sectional view of the hydraulic extension stop illustrated in  FIG. 7  taken in the direction  8 - 8  shown in  FIG. 7 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     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 having shock absorbers which include the hydraulic extension stop 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  includes a rear axle assembly (not shown) adapted to operatively support a pair of rear wheels  18 . The rear axle assembly is operatively connected to body  16  by means of a pair of rear shock absorbers  20  and a pair of rear helical coil springs  22 . Similarly, front suspension  14  includes a front axle assembly (not shown) adapted to operatively support a pair of front wheels  24 . The front axle assembly is operatively connected to body  16  by a pair of front shock absorbers  26  and by a pair of front 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) from 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 including, but not limited to, vehicles incorporating independent or non-independent front and rear suspension assemblies. Further, the term “shock absorber” as used herein is meant to refer to dampers in general and thus will include McPherson struts.  
         [0018]     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  also includes the hydraulic extension stop in accordance with the present invention which is described below for rear shock absorber  20 . Front shock absorber  26  only differs from rear shock absorber  20  in the way in which it is adapted to be connected to the sprung and the 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 , a base valve assembly  38  and a hydraulic extension stop  40 .  
         [0019]     Pressure tube  30  defines a working chamber  42 . Piston assembly  32  is slidably disposed within pressure tube  30  and it divides working chamber  42  into an upper working chamber  44  and a lower working-chamber  46 .  
         [0020]     Piston rod  34  is attached to piston assembly  32  and it extends through upper working chamber  44 , through hydraulic extension stop  40  and through an upper end cap  50  which closes the upper end of both pressure tube  30  and reservoir tube  36 . A sealing system  52  seals the interface between upper end cap  50 , pressure tube  30 , reservoir tube  36  and piston rod  34 . The end of piston rod  34  opposite to piston assembly  32  is adapted, in the preferred embodiment, to be secured to the sprung portion of vehicle  10 . Valving within piston assembly  32  creates a damping force by controlling the movement of fluid between upper working chamber  44  and lower working chamber  46  during an extension stroke of piston assembly  32  with respect to 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  from the amount of fluid displaced in lower working chamber  46 . This difference in the amount of fluid displaced is known as the “rod volume” and it flows through base valve assembly  38 . Valving in base valve assembly  38  creates a damping force by controlling the movement of fluid between lower working chamber  46  and a reservoir chamber  54  defined between pressure tube  30  and reservoir tube  36  during a compression stroke of piston assembly  32  with respect to pressure tube  30 . While shock absorber  20  is being illustrated as a dual tube shock absorber having base valve assembly  38 , it is within the scope of the present invention to utilize pressure tube  30  and piston assembly  32  in a mono-tube designed shock absorber as shown in  FIG. 4  and detailed below.  
         [0021]     Reservoir tube  36  surrounds pressure tube  30  to define reservoir chamber  54  located between tubes  30  and  36 . The bottom end of reservoir tube  36  is closed by an end cap  56  which is adapted, in the preferred embodiment, 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  54  to control the flow of fluid between the two chambers. When shock absorber  20  extends in length (extension or rebound), 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  38 . This fluid flow will not create a damping force. The damping force in an extension stroke is created by valving in piston assembly  32 . When shock absorber  20  compresses in length (compression), replacement fluid for upper working chamber  44  flows through piston assembly  32 . This fluid flow also does not create a damping force. An excess amount of fluid must be removed from lower working chamber  46  due to the “rod volume” concept. Thus, fluid flow will flow from lower working chamber  46  to reservoir chamber  54  through valving in base valve assembly  38  to create a damping force during the compression stroke.  
         [0022]     The present invention is directed to a unique hydraulic extension stop  40  which is engaged by piston assembly  32  as piston assembly  32  approaches upper end cap  50 . Hydraulic extension stop  40  cushions any impact that may occur between piston assembly  32  and upper end cap  50 .  
         [0023]     Referring now to  FIGS. 2 and 3 , hydraulic extension stop  40  comprises a first or an upper retainer  60 , a second or a lower retainer  62 , a coil spring  64  and a collar  66 . Upper retainer  60  is slidingly disposed within pressure tube  30  at a position where it abuts upper end cap  50 . Coil spring  64  is press fit within pressure tube  30  and it engages upper retainer  60  to keep upper retainer  60  positioned against upper end cap  50 . The press fitting of coil spring  64  within pressure tube  30  prevents hydraulic extension stop  40  from coming down during the normal functioning of shock absorber  20 .  
         [0024]     Coil spring  64  is also press fitted onto lower retainer  62 . Upper retainer  60  and lower retainer  62  are preferably manufactured from plastic and they are designed to prevent coil spring  64  from reaching its fully collapsed position. The end of the extension stroke for shock absorber  20  will be defined when piston assembly  32  contacts collar  66 , when collar  66  contacts lower retainer  62 , when lower retainer  62  contacts upper retainer  60  and when upper retainer  60  contacts upper end cap  50 . The initial point of contact between collar  66  and lower retainer  62  can be changed by changing the free length of coil spring  64 .  
         [0025]     Upper retainer  60  and lower retainer  62  define a damping chamber  70  disposed within upper working chamber  44  of working chamber  42 . An O-ring  72  seals damping chamber  70  from the rest of upper working chamber  44 . A fluid passage  74  is defined between lower retainer  62  and piston rod  34  and between upper retainer  60  and piston rod  34 . Lower retainer  62  defines one or more radially extending slots or bleed passages  76  that extend between fluid passage  74  and upper working chamber  44 . Collar  66  is slidingly received on piston rod  34 . Collar  66  has a generally flat upper surface such that once collar  66  engages the lower surface of lower retainer  62 , fluid flow from fluid passages  74  can only flow through bleed passages  76 .  
         [0026]     During an extension stroke of shock absorber  20 , piston assembly  32  will contact collar  66  which will then contact lower retainer  62  to limit the fluid flow from damper chamber  70  to only fluid flow through bleed passages  76 . As shock absorber  20  continues its extension stroke and piston assembly  32  is moved towards end cap  50 , lower retainer  62  will be moved toward upper retainer  60  against the force of coil spring  64  to reduce the volume of damping chamber  70 . The fluid within damping chamber  70  will be forced to flow through fluid passages  74  and through bleed passages  76 . The restricted fluid flow through bleed passages  76  creates an additional damping force which will cushion the impact when shock absorber  20  reaches its fully extended position. The amount of fluid flow and thus the additional damping force can be adjusted by adjusting the size and number and thus the total area of bleed passages  76 .  
         [0027]     When shock absorber  20  moves in compression from the fully extended position back towards its working height, coil spring  64  will again separate lower retainer  62  from upper retainer  60  to bring the volume of damping chamber  70  back to its original size. Due to the ability of collar  66  to move with piston rod  34  during the compression stroke, fluid flow may not be restricted to bleed passages  76  during this compression stroke and fluid flow may be able to flow directly through fluid passages  74  when lower retainer  62  moves back to its original position. If collar  66  remains in contact with lower retainer  62 , fluid flow will only occur through bleed passages  76 .  
         [0028]     Referring now to  FIG. 4 , a rear shock absorber  120  in accordance with another embodiment of the present invention is illustrated. Shock absorber  120  can replace rear shock absorber  20  or with the same modifications that would have to be made to rear shock absorber  20 , shock absorber  120  could replace front shock absorber  26 . Shock absorber  120  is a mono-tube design and it comprises a pressure tube  130 , piston assembly  132 , a piston rod  134  and hydraulic extension stop  40 .  
         [0029]     Pressure tube  130  defines a working chamber  142 . Piston assembly  132  is slidably disposed within pressure tube  130  and it divides working chamber  142  into an upper working chamber  144  and a lower working chamber  146 .  
         [0030]     Piston rod  134  is attached to piston assembly  132  and it extends through upper working chamber  144 , through hydraulic extension stop  40  and through an upper end cap  150  which closes the upper end of pressure tube  130 . A sealing system  152  seals the interface between upper end cap  150 , pressure tube  130  and piston rod  134 . The end of piston rod  134  opposite to piston assembly  132  is adapted, in the preferred embodiment, to be secured to the sprung portion of vehicle  10 . Valving within piston assembly  132  creates a damping force for controlling the movement of fluid between upper working chamber  144  and lower working chamber  146  during both an extension stroke of piston assembly  132  with respect to pressure tube  130  and a compression stroke of piston assembly  132  with respect to pressure tube  130 .. Because piston rod  134  extends only through upper working chamber  144  and not lower working chamber  146 , movement of piston assembly  132  with respect to pressure tube  130  causes a difference in the amount of fluid displaced in upper working chamber  144  from the amount of fluid displaced in lower working chamber  146 . This difference in the amount of fluid displaced is known as the “rod volume” and it is accommodated for by an additional piston disposed within lower working chamber  146  as is known in the art or by any other method of accommodating the rod flow which is known in the art. The bottom of pressure tube  130  is closed by an end cap  156  which is adapted, in the preferred embodiment, to be connected to the unspurng portion of vehicle  10 .  
         [0031]     Hydraulic extension stop  40  is engaged by piston assembly  132  as piston assembly  132  approaches upper end cap  150  in the same manner as described above for piston assembly  32  and upper end cap  50 . The function, operation and features of hydraulic extension stop  40  and shock absorber  120  are the same as described above for hydraulic extension stop  40  and shock absorber  20 .  
         [0032]     Referring now to  FIG. 5 , a hydraulic extension stop  140  in accordance with another embodiment of the present invention is illustrated. Hydraulic extension stop  140  comprises an upper retainer  160 , lower retainer  62 , a coil spring  164  and collar  66 . Upper retainer  160 , similar to upper retainer  60 , is preferably manufactured from plastic. Hydraulic extension stop  140  is the same as hydraulic extension stop  40  except for the method used to keep hydraulic extension stop  140  adjacent upper end cap  50 .  
         [0033]     As described above for hydraulic extension stop  40 , upper retainer  60  is slidingly disposed within pressure tube  30  and coil spring  64  is press fit within pressure tube  30  to keep hydraulic extension stop  40  adjacent upper end cap  50 .  
         [0034]     Hydraulic extension stop  140  has upper retainer  160  press fit within pressure tube  30  and coil spring  164  is press fit over upper retainer  160  to keep hydraulic extension stop  140  adjacent upper end cap  50 . The features, function, operation and advantages for hydraulic extension stop- 140  are the same as those detailed above for hydraulic extension stop  40 . Also, while hydraulic stop  140  is illustrated in conjunction with a mono tube shock absorber, it is within the scope of the present invention to use hydraulic extension stop  140  with a dual tube shock absorber.  
         [0035]     Referring now to  FIG. 6 , a hydraulic extension stop  240  in accordance with another embodiment of the present invention is illustrated. Hydraulic extension stop  240  comprises upper retainer  60 , a lower retainer  262 , coil spring  64  and collar  66 . Hydraulic extension stop  240  is the same as hydraulic extension stop  40  except that lower retainer  62  has been replaced by lower retainer  262 . Lower retainer  262 , similar to lower retainer  62 , is preferably manufactured from plastic.  
         [0036]     Coil spring  64  is press fit onto lower retainer  262 . Fluid passage  74  is defined between lower retainer  262  and piston rod  34 . Lower retainer  262  defines one or more radially extending holes or bleed passages  276  that extend between fluid passage  74  and upper working chamber  44 . Collar  66  has a generally flat upper surface such that once collar  66  engages the lower surface of lower retainer  262 , fluid flows from fluid passages  74  can only flow through bleed passages  276 . Thus, lower retainer  262  is the same as lower retainer  62  except that bleed passages  76  have been replaced by bleed passages  276 . The features, function, operation and advantage of lower retainer  262  and hydraulic extension stop  240  are the same as detailed above for lower retainer  62  and hydraulic extension stop  40 . Also, while hydraulic extension stop  240  is illustrated in conjunction with a dual tube shock absorber, it is within the scope of the present invention to use hydraulic stop  240  with a mono tube shock absorber.  
         [0037]     Referring now to  FIGS. 7 and 8 , a hydraulic extension stop  340  in accordance with another embodiment of the present invention is illustrated. Hydraulic extension stop  340  comprises upper retainer  60 , a lower retainer  362 , coil spring  64 , collar  66  and a valve assembly  368 . Hydraulic extension stop  340  is the same as hydraulic extension stop  40  except that lower retainer  62  has been replaced by lower retainer  362  and that valve assembly  368  has been added to hydraulic extension stop  340 . Lower retainer  362 , similar to lower retainer  62 , is preferably manufactured from plastic.  
         [0038]     Coil spring  64  is press fit onto lower retainer  362 . Fluid passage  74  is defined between lower retainer  362  and piston rod  34 . Lower retainer  362  defines radially extending bleed passages  76  as well as a fluid chamber  376 . Valve assembly  368  comprises a valve disc  380  and a fulcrum disc  382 . Valve disc  380  closes fluid chamber  376  to prohibit fluid flow from damping chamber  70 , through fluid passages  74 , through fluid chamber  376  and into upper working chamber  44 . Valve disc  380  and fulcrum disc  382  are slidingly received on piston rod  34 .  
         [0039]     During an extension stroke of shock absorber  20 , piston assembly  32  will contact collar  66  which will then contact fulcrum disc  382  which will then contact valve disc  380 . When valve disc  380  contacts lower retainer  362 , valve disc  380  will close fluid chamber  376  to limit the fluid flow from damper chamber  70  to only fluid flow through bleed passages  76 . As shock absorber  20  continues its extension stroke and piston assembly is moved towards upper end cap  50 , lower retainer  362  will be moved toward upper retainer  60  against the force of coil spring  64  to reduce the volume of damper chamber  70 . The fluid within damper chamber  70  will be forced to flow through fluid passages  74  and through bleed passages  76 . The restricted fluid flow through bleed passages  76  creates an additional damping force which will cushion the impact when shock absorber  20  reaches its fully extended position. If the velocity of piston rod  34  and piston assembly  32  is sufficient to saturate the flow of fluid through bleed passages  76 , fluid pressure will increase in damper chamber  70  as well as within fluid chamber  376 . The increase in pressure within fluid chamber  376  will eventually bend valve disc  380  over fulcrum disc  382  to release the fluid pressure proportional with the velocity of piston rod  34  and piston assembly  32 . The amount of fluid flow through bleed passages  76  as well as the pressure at which valve disc  380  bends and the flow rate past valve disc  380  will be determined by the total area of bleed passages  76 , the strength of valve disc  380 , the size of fulcrum disc  382  and the size of fluid chamber  376 .  
         [0040]     When shock absorber  20  moves in compression from the fully extended position back towards its working height, coil spring  64  will again separate lower retainer  362  from upper retainer  60  to bring the volume of damping chamber  70  back to its original size. Due to the ability of collar  66 , valve disc  380  and fulcrum disc  382  to move with piston rod  34  during the compression stroke, fluid flow may not be restricted to bleed passages  76  during this compression stroke and fluid flow may be able to flow directly through fluid passages  74  when lower retainer  362  moves back to its original position. If valve disc  380  remains in contact with lower retainer  362 , fluid flow will only occur through bleed passages  76 .  
         [0041]     The features, function, operation and advantage of lower retainer  362  and hydraulic extension stop  340  are the same as detailed above for lower retainer  62  and hydraulic extension stop  40 . Also, while hydraulic extension stop  340  is illustrated in conjunction with the dual tube shock absorber, it is within the scope of the present invention to utilize hydraulic extension stop  340  in a mono-tube shock absorber.  
         [0042]     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.