Abstract:
A two-stage shock absorber has a pressure tube within which a valve assembly is slidably disposed. A piston rod is attached to the valve assembly and extends out of the pressure tube. A ring is slidably disposed within the pressure tube and engages the valve assembly. After a specified amount of movement of the valve assembly with respect to the pressure tube in an extension movement of the shock absorber, the sleeve engages a plurality of spirally positioned bores and reduces the fluid flow through the valve assembly to progressively switch the shock absorber from soft damping to firm damping. In another embodiment the sleeve engages a spiral groove of variable depth to reduce the fluid flow through the valve assembly to progressively switch the shock absorber from soft damping to firm damping.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a hydraulic damper or shock absorber adapted for use in a suspension system such as the systems used for automotive vehicles. More particularly, the present invention relates to a hydraulic damper having a two-stage damping characteristic where a relatively low level damping force is provided for small amplitudes of movement and a relatively high level of damping is provided for large amplitudes of movement.  
       BACKGROUND OF THE INVENTION  
       [0002]     A conventional prior art hydraulic damper or shock absorber comprises a cylinder defining a working chamber having a piston slidably disposed in the working chamber with the piston separating the interior of the cylinder into an upper and a lower working chamber. A piston rod is connected to the piston and extends out of one end of the cylinder. A first valving system is incorporated for generating damping force during the extension stroke of the hydraulic damper and a second valving system is incorporated for generating damping force during the compression stroke of the hydraulic damper.  
         [0003]     Various types of damping force generating devices have been developed to generate desired damping forces in relation to the speed and/or the displacement of the piston within the cylinder. These multi-force damping force generating devices have been developed to provide a relatively small or low damping force during the normal running of the vehicle, and a relatively large or high damping force during maneuvers such as turning or braking. During normal running of the vehicle, the suspension system experiences small or fine vibrations of the un-sprung mass of the vehicle. Thus, there is a need for a soft ride or low damping characteristics of the suspension system to isolate the sprung mass from these vibrations. During a turning or braking maneuver, as an example, the sprung mass of the vehicle will attempt to undergo a relatively slow and/or large vibration which then requires a firm ride or high damping characteristics of the suspension system to support the sprung mass and provide stable handling characteristics to the vehicle. Thus, these multi-force damping force generating devices offer the advantage of a smooth steady state ride by eliminating the high frequency/small excitations from the sprung mass while still providing the necessary damping or firm ride for the suspension system during vehicle maneuvers causing larger excitations of the sprung mass.  
         [0004]     The continued development of hydraulic dampers includes the development of multi-force damping force generating devices which are simpler to manufacture, can be manufactured at a lower cost and which improve the desired force generating characteristics.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides the art with a multi-stage hydraulic damper or shock absorber that provides damping which varies according to the stroke amplitude. Soft damping is provided for small strokes and firm damping is provided for large strokes. The variable damping is provided by a sliding sleeve that is frictionally held in place in the pressure cylinder. While the shock absorber undergoes a small stroke, the sliding sleeve remains inactive and the fluid flows through two separate flow paths to provide a soft damping. When the shock absorber undergoes a large stroke, the sliding sleeve moves to progressively close off one of the two flow paths which in turn provides a firm damping. Various design iterations are disclosed for both mono-tube and double tube shock absorbers.  
         [0006]     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a cross-sectional side view of a mono-tube shock absorber incorporating the multi-force damping force generating device in accordance with the present invention;  
         [0009]      FIG. 2  is a cross-sectional side view illustrating the piston assembly of the shock absorber shown in  FIG. 1  during a small extension stroke of the shock absorber;  
         [0010]      FIG. 3  is a cross-sectional side view illustrating the piston assembly of the shock absorber shown in  FIG. 1  during a larger extension stroke of the shock absorber;  
         [0011]      FIG. 4  is a cross-sectional side view illustrating the piston assembly of the shock absorber shown in  FIG. 1  during an even larger extension stroke of the shock absorber;  
         [0012]      FIG. 5  is a cross-sectional side view illustrating the piston assembly of the shock absorber shown in  FIG. 1  during a small compression stroke of the shock absorber;  
         [0013]      FIG. 6  is a cross-sectional side view illustrating the piston assembly of the shock absorber shown in  FIG. 1  during a large compression stroke of the shock absorber;  
         [0014]      FIG. 7  is a perspective view of the bypass through the piston nut as shown in  FIGS. 1-6 ; and  
         [0015]      FIG. 8  is a perspective view of the bypass through the piston nut in accordance with another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in  FIGS. 1-7 , a two-stage mono-tube shock absorber which incorporates the multi-force damping force generating device in accordance with the present invention and which is designated generally by the reference numeral  10 . Shock absorber  10  is a mono-tube design and comprises a piston rod assembly  12  and a pressure tube  14 . Piston rod assembly  12  includes a piston valve assembly  16  and a piston rod  18 . Valve assembly  16  divides pressure tube  14  into an upper working chamber  20  and a lower working chamber  22 . Piston rod  18  extends out of pressure tube  14 , for attachment to one of the sprung or unsprung mass of the vehicle. Pressure tube  14  is filled with fluid and attaches to the other sprung or unsprung masses of the vehicle. Thus, suspension movements of the vehicle will cause extension or compression movement of piston rod assembly  12  with respect to pressure tube  14  and these movements will be dampened due to the restricted fluid flow between chambers  20  and  22  through piston valve assembly  16 .  
         [0017]     Referring now to  FIG. 2 , piston valve assembly  16  is attached to piston rod  18  and comprises a piston body  40 , a compression valve assembly  42 , an extension or rebound valve assembly  44  and a sliding valve assembly  46 . Piston rod  18  includes a reduced diameter section  48  located on the end of the piston rod  18  disposed within pressure tube  14  to form a shoulder  50  for mounting the remaining components of piston valve assembly  16 . Piston body  40  is located on reduced diameter section  48  with compression valve assembly  42  being located between piston body  40  and shoulder  50  and with rebound valve assembly  44  being located between piston body  40  and a threaded end  52  of piston rod  18 . Piston body  40  defines a plurality of compression flow passages  54  and a plurality of rebound flow passages  56 .  
         [0018]     Compression valve assembly  42  comprises a plurality of compression valve plates  58  and a compression support plate  60 . Valve plates  58  are disposed adjacent to piston body  40  to cover the plurality of compression flow passages  54 . Support plate  60  is disposed between valve plates  58  and shoulder  50  to hold valve plates  58  against piston body  40  to close passages  54 . During a compression stroke of shock absorber  10 , fluid pressure builds up in lower working chamber  22  until the fluid pressure applied to valve plates  58  through passages  54  overcomes the bending load of valve plates  58 . Valve plates  58  elastically deflect around the outer edge of support plate  60  to allow fluid to flow from lower working chamber  22  to upper working chamber  20  as shown by arrows  62  in  FIGS. 5 and 6 .  
         [0019]     Rebound valve assembly  44  comprises a plurality of valve plates  66 , a rebound support plate  68  and a piston nut  70 . Valve plates  66  are disposed adjacent to piston body  40  to cover the plurality of rebound flow passages  56 . Support plate  68  is disposed between piston nut  70  and valve plates  66 . Piston nut  70  is threaded onto end  52  of piston rod  18  to retain support plate  68  and hold valve plates  66  against piston body  40  to close passages  56 . During an extension stroke of shock absorber  10 , fluid pressure builds up in upper working chamber  20  until the fluid pressure applied to valve plates  66  through passages  56  overcomes the bending load of valve plates  66 . Valve plates  66  elastically deflect around the outer edge of support plate  68  to allow fluid to flow from upper working chamber  20  to lower working chamber  22  as shown by arrows  72  in  FIGS. 2-4 .  
         [0020]     Sliding valve assembly  46  comprises a flow passage  74 , a series of bores  86  and a sliding sleeve  78 . Flow passage  74  extends through piston rod  18  and includes a radial passage  80  and an axial passage  82  which opens into a chamber  84  defined by piston rod  18  and piston nut  70 . The series of bores  86  extending radially through piston nut  70 , are created in an evenly spaced, helical pattern, axially along the piston nut  70 . Sliding sleeve  78  is slidingly received within pressure tube  14  and slidingly received on piston nut  70  to provide the multi-stage damping characteristics for shock absorber  10 .  
         [0021]      FIGS. 2 through 6  illustrate the various damping characteristics provided for by piston rod assembly  12  of shock absorber  10 .  FIG. 2  illustrates a small amplitude extension,  FIG. 3  illustrates a larger amplitude extension,  FIG. 4  illustrates an even larger amplitude extension,  FIG. 5  illustrates a small amplitude compression and  FIG. 6  illustrates a large amplitude compression for shock absorber  10 .  
         [0022]     A small amplitude extension of shock absorber  10  is illustrated in  FIG. 2  with arrows  72  and  92  depicting the fluid flow. During small amplitudes of extension, sliding sleeve  78  will only move a small amount with respect to piston nut  70  due to the friction with pressure tube  14  and thus does not restrict fluid flow through passage  74  and bores  86 . Fluid flow from upper chamber  20  of pressure tube  14  into lower chamber  22  of pressure tube  14  occurs through two generally parallel paths. The first path is shown by arrow  72  and it extends from upper chamber  20  of pressure tube  14  through passages  56  unseating valve plates  66  from piston body  40  to enter lower chamber  22  of pressure tube  14 . Simultaneously, fluid flows through the second flow path as depicted by arrows  92 . Fluid flow leaves upper working chamber  20  through passage  74  and enters chamber  84 . Fluid flows from chamber  84  through the series of bores  86  in piston nut  70  to also enter lower chamber  22  of pressure tube  14 . These dual parallel flow paths shown by arrows  72  and  92  will thus provide a relatively soft ride for small movements of shock absorber  10 .  
         [0023]     A larger amplitude extension of shock absorber  10  is illustrated in  FIG. 3  with arrows  72  and  92  depicting fluid flow. During the larger amplitudes of extension, sliding sleeve  78  will move enough to cover one or more of the passageways comprising bores  86 , due to the friction with pressure tube  14  and will progressively close more and more passages comprising bores  86 . As shown in  FIGS. 3 and 7 , the helical series of evenly spaced bores  86  will permit a gradual closing of the entire passage  74  which provides the advantage of the major reduction or elimination of the switching noise typical with a dual-stage damping device. Fluid flow from upper chamber  20  of pressure tube  14  into lower chamber  22  of pressure tube  14  still occurs through the two generally parallel paths shown by arrows  72  and  92  but the second path shown by arrow  92  is progressively being closed off as a function of the amplitude of the stroke. The variable helical pattern of the bores  86  thus provides the shock absorber designer the option of defining the curve between the soft damping characteristics of the shock absorber  10  and the firm damping characteristics of shock absorber  10  and no longer requires him to accept a step function. The first path shown by arrow  72  extends from upper chamber  20  of pressure tube  14  through passages  56  unseating valve plates  66  from piston body  40  to enter lower chamber  22  of pressure tube  14 . Simultaneously, fluid flow through the second flow path shown by arrow  92  by leaving upper working chamber  20  through passage  74  and enters chamber  84 . Fluid flows from chamber  84  through bores  86  to also enter chamber  22  of pressure tube  14 . The amount of fluid flowing through the second flow path shown by arrow  92  will be determined by the position of the sliding sleeve  78  and the number of bores  86  which sliding sleeve  78  covers.  
         [0024]     An even larger amplitude extension of shock absorber  10  is illustrated in  FIG. 4  with arrow  72  depicting fluid flow. During large amplitudes of extension, sliding sleeve  78  remains in position due to friction and entirely covers all bores  86  preventing fluid flow through the flow path depicted by arrow  92  in  FIGS. 2 and 3 . Fluid flow from upper chamber  20  of pressure tube  14  into lower chamber  22  of pressure tube  14  occurs through only one path which is the path depicted by arrow  72 . As stated above, the path depicted by arrow  72  extends from upper chamber  20  of pressure tube  14  through passage  56  unseating valve plates  66  from piston body  40  to enter lower chamber  22  of pressure tube  14 . The flow path depicted by arrow  92 , shown in  FIGS. 2 and 3 , is blocked due to the position of sliding sleeve  78 . The single flow path will thus provide a relatively firm ride for larger movements of shock absorber  10 .  
         [0025]     A small amplitude compression of shock absorber  10  is illustrated in  FIG. 5  with arrows  62  and  94  depicting the fluid flow. During small amplitudes of compression, sliding sleeve  78  will move only a small amount with respect to piston nut  70  due to the friction due with pressure tube  14 . Fluid flow from lower chamber  22  of pressure tube  14  into upper chamber  20  of pressure tube  14  occurs through two generally parallel paths shown by arrows  62  and  94 . The first path is shown by arrow  62  and it extends from lower chamber  22  of pressure tube  14  through passages  54  unseating valve plate  58  from piston body  40  to enter upper chamber  20  of pressure tube  14 . Simultaneously, fluid flows through a second flow path as depicted by arrows  94 . Fluid flow leaves lower chamber  22  through bores  86  into chamber  84  and through passage  74  to enter upper chamber  20  of pressure tube  14 .  
         [0026]     A large amplitude compression of shock absorber  10  is illustrated in  FIG. 6  with arrows  62  and  94  depicting fluid flow. During large amplitudes of compression, sliding sleeve  78  remains in position due to friction and support plate  68  contacts sliding sleeve  78 . Fluid flow from the lower chamber  22  of pressure tube  14  into upper chamber  20  of pressure tube  14  occurs through the same two flow paths described above for small compression movement of shock absorber  10  as shown in  FIG. 5 . The multi-force damping characteristics for shock absorber  10  of this embodiment only effect extension movement of shock absorber  10  and not compression movements.  
         [0027]     Referring now to  FIG. 8 , a piston nut  170  in accordance with another embodiment of the present invention is illustrated. Piston nut  170  is designed to replace piston nut  70  in shock absorber  10  and thus the discussion above of shock absorber  10  also applies to piston nut  170 . The difference between piston nut  170  and piston nut  70  is in the manner that the fluid flows through passage  74 .  
         [0028]     Piston nut  170  defines a single through bore  186  and a helical groove  188  extending axially along the outer surface of piston nut  170 . Helical groove  188  has a depth that varies continuously over the length of helical groove  188 . The depth of helical groove  188  is at its maximum valve adjacent bore  186  and at its minimum valve at its opposing terminal end. Sliding sleeve  78  is slidingly received within pressure tube  14  and slidingly received on piston nut  170 , similar to piston nut  70 , to provide the multi-stage damping characteristics for shock absorber  10 .  
         [0029]     During small amplitude extensions of shock absorber  10 , sliding sleeve  78  will only move a small amount with respect to piston nut  170  due to the friction with pressure tube  14  and thus does not restrict fluid flow through passage  74 , bore  186  and groove  188 . The fluid flow is similar to that shown in  FIG. 2  for piston nut  70 .  
         [0030]     During larger amplitude extensions of shock absorber  10 , sliding sleeve  78  will move enough to cover bore  186  and a portion of groove  188 . The movement of sliding sleeve  78  with respect to piston nut  170  will cover more and more of groove  188 . Fluid flow will flow from chamber  84 , through bore  186  and through groove  188 . The continuously varying depth of groove  188  will permit a gradual closing of the entire passage  74  which provides the advantage of the major reduction or elimination of the switching noise typical with a dual-stage damping device. Fluid flow from upper chamber  20  of pressure tube  14  into cover chamber  22  of pressure tube  14  still occurs through the two generally parallel paths depicted by arrows  72  and  92  but the second path depicted by arrow  92  is progressively being closed off as a function of the amplitude of the stroke. The variable depth of groove  188  thus provides the shock absorber designer the option of defining the curve between the soft damping characteristics of shock absorber  10  and the firm damping characteristics of shock absorber  10  and no longer requires him to accept a step function. The fluid flow is similar to that shown in  FIG. 3  for piston nut  70 .  
         [0031]     During even larger amplitude extensions of shock absorber  10  causes sliding sleeve  78  to cover bore  186  and all of groove  188  to close fluid passage  74 . Fluid flow from upper chamber  20  of pressure tube  14  into lower chamber  22  of pressure tube  14  occurs only through the path depicted by arrows  72 . This single flow path will thus provide a relatively firm ride. The fluid flow is similar to that shown in  FIG. 4  for piston nut  70 .  
         [0032]     Small amplitude compression and large amplitude compression of shock absorber is similar to that illustrated above in  FIGS. 5 and 6 , respectively, for piston nut  70 . During compression strokes for shock absorber  10 , bores  186  and  188  are both open providing for the dual path fluid flow as depicted by arrows  62  and  94 . The fluid flow is similar to that shown in  FIGS. 5 and 6  for piston nut  70 .  
         [0033]     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.