Abstract:
A shock absorber includes a pressure tube with a piston slidably disposed therein. A separate valve includes a fluid circuit for fluid low in rebound and a fluid circuit for fluid flow in compression. Each fluid circuit includes a variable orifice which allows selection between a firm rebound with a soft compression, a soft rebound with a soft compression, and a soft rebound with a firm compression. Each variable orifice is in communication with a blowoff valve in such a manner that they provide a variable blowoff feature to the blowoff valves.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hydraulic damper or shock absorber adapted for use in a suspension system such as the suspension systems used for automotive vehicles. More particularly, the present invention relates to a hydraulic damper or shock absorber having a continuously variable damping characteristic which is adjustable by a solenoid actuated continuously variable servo valve to vary the damping characteristics between a relatively low level of damping for a soft ride for comfort and a relatively high level of damping for a firm ride for handling. 
     BACKGROUND OF THE INVENTION 
     A conventional prior art hydraulic damper or shock absorber comprises a cylinder which is adapted at one end for attachment to the sprung or unsprung mass of a vehicle. A piston is slidably disposed within the cylinder with the piston separating the interior of the cylinder into two fluid chambers. A piston rod is connected to the piston and extends out of one end of the cylinder where it is adapted for attachment to the other of the sprung or unsprung mass of the vehicle. 
     Various types of adjustment mechanisms have been developed to generate variable damping forces in relation to the speed and/or the amplitude of the displacement of the sprung mass in relation to the unsprung mass. These adjustment mechanisms have mainly been developed to provide a relatively small or low damping characteristic during the normal steady state running of the vehicle and a relatively large or high damping characteristic during vehicle maneuvers requiring extended suspension movements. The normal steady state running of the vehicle is accompanied by small or fine vibrations of the unsprung mass of the vehicle and thus the need for a soft ride or low damping characteristic of the suspension system to isolate the sprung mass from these small 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 movement or vibration which then requires a firm ride or high damping characteristic of the suspension system to support the sprung mass and provide stable handling characteristics to the vehicle. These adjustable mechanisms for the damping rates of a shock absorber offer the advantage of a smooth steady state ride by isolating the high frequency/small amplitude excitations from the unsprung mass while still providing the necessary damping or firm ride for the suspension system during vehicle maneuvers causing low frequency/large excitations of the sprung mass. 
     The continued development of shock absorbers includes the development of adjustment systems which provide the vehicle designer with a continuously variable system which can be specifically tailored to a vehicle to provide a specified amount of damping in relation to various monitored conditions of the vehicle and its suspension system. 
     SUMMARY OF THE INVENTION 
     The present invention provides the art with a continuously variable adjustable hydraulic damper or shock absorber that includes the capability of adjusting the damping rate of the shock absorber between a firm rebound damping force with a soft compression damping force, a soft rebound force with a soft compression damping force and a soft rebound damping force with a firm compression damping force. A solenoid actuated continuously variable servo valve adjusts the damping force characteristics of the shock absorber and has the capability of positioning the damping force characteristics of the shock absorber anywhere between these configurations to provide the continuously variable damping for the shock absorber. 
     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 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
     FIG. 1 is a cross-sectional side view of a shock absorber incorporating the continuously variable damping capabilities in a completely damping fluid filled monotube configuration in accordance with the present invention; 
     FIG. 2 is a schematic side view illustrating the servo valve shown in FIG. 1 when the shock absorber is configured to provide a firm ride during rebound and a soft ride during compression of the shock absorber; 
     FIG. 3 is a cross-sectional side view illustrating the servo valve shown in FIG. 1 when the shock absorber is configured to provide a soft ride during rebound and a soft ride during compression of the shock absorber; 
     FIG. 4 is a cross-sectional side view illustrating the servo valve shown in FIG. 1 when the shock absorber is configured to provide a soft ride during rebound and a firm ride during compression of the shock absorber; 
     FIG. 5 is a schematic view illustrating the hydraulic fluid circuit incorporated into the shock absorber shown in FIG. 1; and 
     FIG. 6 is a cross-sectional side view illustrating a typical poppet valve in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 shock absorber incorporating the continuously variable damping adjustment system in accordance with the present invention which is designated generally by the reference numeral  10 . Shock absorber  10  comprises a piston  12 , a piston rod  14 , a pressure tube  16 , an outer tube  18 , a floating piston  20  and a continuously variable servo valve assembly  22 . Piston  12  is slidingly received within pressure tube  16  and divides pressure tube  16  into an upper working chamber  24  and a lower working chamber  26 . Piston  12  does not allow fluid flow between chambers  24  and  26 . 
     Piston rod  14  is attached to piston  12  and extends out of pressure tube  16  and outer tube  18  through a rod guide  34 . The outer end of piston rod  14  is adapted to be attached to either the sprung mass or the unsprung mass of the vehicle by means known well in the art. Outer tube  18  surrounds pressure tube  16  and with pressure tube  16  defines an upper intermediate chamber  36  and a lower intermediate chamber  38 . Outer tube  18  is adapted for attachment to the other of the sprung mass or the unsprung mass of the vehicle by methods known well in the art. A sealing ring or housing  40  is sealingly disposed between outer tube  18  and pressure tube  16  to isolate upper intermediate chamber  36  from lower intermediate chamber  38 . As can be seen in FIG. 1, lower working chamber  26  extends out of the lower end of pressure tube  16  to communicate with lower intermediate chamber  38  which is defined by housing  40 , outer tube  18  and floating piston  20 . Floating piston  20  is slidingly and sealingly disposed within outer tube  18  to define the lower boundary of lower intermediate chamber  38  and a gas chamber  42  located below floating piston  20 . Floating piston  20  moves within outer tube  18  to adjust for the rod volume during the stroking of piston  12  as is well know in the art. Outer tube  18  defines a rebound outlet  54  in communication with upper intermediate chamber  36  and a compression outlet  56  in communication with lower intermediate chamber  38 . 
     Referring now to FIGS. 1 and 2, continuously variable servo valve assembly  22  is sealingly secured to outer tube  18 . Continuously variable servo valve assembly  22  comprises a solenoid coil assembly  58 , a valve body assembly  60  and a spool valve  62 . Solenoid coil assembly  58  includes a housing  64  within which is contained a set of windings  66  and a bobbin  68 . A valve member  70  is disposed within the set of windings  66  and moves axially within windings  66  in response to electrical power being supplied to windings  66  as is well known in the art. Solenoid coil assembly  58  is attached to valve body assembly  60 . Spool valve  62  is disposed within a bore  72  extending through valve body assembly  60 . A spring  74  biases spool valve  62  towards solenoid coil assembly  58 . Thus, solenoid coil assembly  58  operates to move spool valve  62  axially within bore  72  of valve body assembly  60 . Spool valve  62  is normally in an upper position as shown in FIG.  2  and is movable to a lower position as shown in FIG. 4 when full power is being supplied to solenoid coil assembly  58 . By the use of pulse width modulation, the position of spool valve  62  can be intermediate the positions shown in FIGS. 2 and 4 which is the position shown in FIG.  3 . 
     Referring now to FIGS. 2 and 5, valve body assembly  60  comprises a valve body  76 , a compression inlet  78 , a compression main poppet  80 , a compression co-poppet  82 , a compression orifice  84 , a rebound inlet  88 , a rebound main poppet  90 , a rebound co-poppet  92  and a rebound orifice  94 . A one-way check valve  96  is disposed between compression inlet  78  and spool valve  62 . Check valve  96  permits flow from spool valve  62  to compression inlet  78  but prohibits fluid flow directly from compression inlet  78  to spool valve  62 . Fluid flow is permitted from compression inlet  78  to spool valve  62  by way of compression main poppet  80 , compression co-poppet  82  and compression orifice  84 . Check valve  96  also permits fluid flow from rebound main poppet  90  and rebound co-poppet  92 . A one way check valve  98  is disposed between rebound inlet  88  and spool valve  62 . Check valve  98  permits flow from spool valve  62  to rebound inlet  88  but prohibits fluid flow directly from rebound inlet  88  to spool valve  62 . Fluid flow is permitted from rebound inlet  88  to spool valve  62  by way of rebound main poppet  90 , rebound co-poppet  92  and rebound orifice  94 . Check valve  98  also permits fluid flow from compression main poppet  80  and compression co-poppet  82 . Valve body assembly  60  is positioned such that valve body  76  sealingly engages outer tube  18  with compression inlet  78  sealingly engaging compression outlet  56  and with rebound inlet  88  sealingly engaging rebound outlet  54 . A fluid passageway  100  extends between and fluidly connects spool valve  62  and lower working chamber  26  through check valve  96 , compression inlet  78 , compression outlet  56  and lower intermediate chamber  38 . A fluid passage  102  extends between and fluidly connects spool valve  62  and upper working chamber  24  through check valve  98 , rebound inlet  88 , rebound outlet  54  and upper intermediate chamber  36 . 
     Referring now to FIG. 5, a fluid schematic diagram is shown. Fluid flow through compression inlet  78  is directed to compression main poppet  80 , compression co-poppet  82  and compression orifice  84 . Fluid flow through compression main poppet  80  and compression co-poppet  82  is directed to upper working chamber  24  through passage  102 . Fluid flow through compression orifice  84  is directed through spool valve  62  and then to upper working chamber  24  through passage  102 . Compression main poppet  80  is urged to a closed position by a biasing member  104  and the fluid pressure present at a point between compression orifice  84  and spool valve  62 . Fluid pressure from compression inlet  78  urges compression main poppet  80  towards an open position. In a similar manner, compression co-poppet  82  is urged into a closed position by a biasing member  106  and the fluid pressure between compression orifice  84  and spool valve  62 . Fluid pressure from compression inlet  78  also urges compression co-poppet  82  toward an open position. Thus by controlling the amount of fluid allowed to pass from compression inlet  78  to upper working chamber  24  through compression orifice  84 , the fluid pressure urging compression main poppet  80  and compression co-poppet  82  towards the open position can be controlled. Fluid flow through rebound inlet  88  is directed to rebound main poppet  90 , rebound co-poppet  92  and rebound orifice  94 . Fluid flow through rebound main poppet  90  and rebound co-poppet  92  is directed to lower working chamber  26  through passage  100 . Fluid flow through rebound orifice  94  is directed through spool valve  62  and then to lower working chamber  26  through passage  100 . Rebound main poppet  90  is urged to a closed position by a biasing member  108  and the fluid pressure present at a point between rebound orifice  94  and spool valve  62 . Fluid pressure from rebound inlet  88  urges rebound main poppet  90  towards an open position. In a similar manner, rebound co-poppet  92  is urged toward a closed position by a biasing member  110  and the fluid pressure present at a position between rebound orifice  94  and spool valve  62 . Fluid pressure from rebound inlet  88  also urges rebound co-poppet  92  towards an open position. Thus by controlling the amount of fluid allowed to pass from rebound inlet  88  to lower working chamber  26  through rebound orifice  94 , the fluid pressure urging rebound main poppet  90  and rebound co-poppet  92  towards the open position can be controlled. 
     During the operation of shock absorber  10 , there is no damping force characteristic in either rebound or compression that is determined by piston  12 . Piston  12  is a solid piston without passages and valving between upper and lower working chambers  24  and  26 , respectively. Continuously variable servo valve assembly  22  determines the damping force characteristics for shock absorber  10 . The damping force characteristics for shock absorber  10  are controllable by continuously variable servo valve assembly  22  such that in any given complete stroke of shock absorber  10  (rebound to compression to rebound) depending on the amount of current given to energize solenoid coil assembly  58 . When little or no current is supplied to solenoid coil assembly  58 , continuously variable servo valve assembly  22  generates a firm rebound damping force with a soft compression damping force for shock absorber  10 . When full current to solenoid coil assembly  58  is supplied, continuously variable servo valve assembly  22  generates a soft rebound damping force with a firm compression damping force for shock absorber  10 . 
     Another characteristic of continuously variable servo valve assembly  22  is that when a continuously variable energy signal (through pulse width modulation) is provided to solenoid coil assembly  58 , a continuously variable sloping bleed and a continuously variable blowoff for poppets  80 ,  82 ,  90  and  92  are provided. The basis for this characteristic is shown in FIG.  6 . 
     FIG. 6 discloses schematically compression main poppet  80 . While FIG. 6 is directed to compression main poppet  80 , it is to be understood that compression co-poppet  82 , rebound main poppet  90  and rebound co-poppet  92  operate in a similar manner to main poppet  80 . Compression main poppet  80  includes a valve member  112  disposed within a bore  114  in valve body  76  of valve body assembly  60 . A spring  116  urges valve member  112  into a closed position as shown in FIG.  6 . Fluid flow from compression inlet  78  is directed to a fluid inlet  118 , through an internal bore  120  in valve member  112 , and then to compression orifice  84 . From compression orifice  84 , fluid flows back to intermediate chamber  36  through a passage  122 . A blowoff passage  124  extends from bore  114  to passage  122  to allow fluid flow when valve member  112  is moved to an open position. 
     The amount of fluid flow allowed through compression orifice  84  and rebound orifice  94  will be determined by the position of spool valve  62  as shown in FIGS. 2-4. In FIGS. 2-4, passage  122  adjacent rebound inlet  88  returns fluid from passage  122  of rebound poppets  90  and  92  as well as from rebound orifice  94 . Passage  122  shown adjacent compression inlet  78  returns fluid from passage  122  of compression poppets  80  and  82  as well as from compression orifice  84 . FIG. 2 shows spool valve  62  positioned to fully open compression orifice  84  and fully close rebound orifice  94 . Thus, a soft compression damping force and a firm rebound damping force are provided. Fluid is free to flow through compression orifice  84 , through a bore  126  extending through spool valve  62 , through bore  72  of valve body assembly  58 , through passageway  102  and into upper working chamber  24  to provide soft compression damping. Fluid is prohibited from flowing through rebound orifice  94  thus providing firm compression damping. FIG. 3 shows spool valve  62  positioned to open both compression orifice  84  and rebound orifice  94 . Thus a soft compression damping force and a soft rebound damping force are provided. Fluid is free to flow through both compression orifice  84  into upper working chamber  24  and through rebound orifice  94  to lower working chamber  26  as described above to provide soft compression and rebound damping. FIG. 4 shows spool valve  62  positioned to fully close compression orifice  84  and fully open rebound orifice  94 . Thus, a firm compression damping force and a soft rebound damping force are provided. Fluid is prohibited from flowing through compression orifice  84  to provide firm compression damping. Fluid is free to flow through rebound orifice  94  into lower working chamber  26  as described above to provide soft rebound damping. The amount of firm and/or soft damping provided will be determined by the position of spool valve  62  which in turn is determined by the amount of current being supplied to solenoid coil assembly  58 . Preferably, the amount of current to solenoid coil assembly  58  is controlled using pulse width modulation. 
     Referring now to FIG. 6, the amount of flow through spool valve  62  also contributes to the damping force blowoff level according to the following formula:        Q   =     α          F     P        (     AS     BH   2       )                                    
     In the above formula: 
     Q=the blowoff level 
     α=flow coefficient of damping fluid 
     F=force 
     P=pressure 
     AS=diameter of bore  114   
     BH=diameter of valve member  112   
     AO=diameter of bore  120   
     BV=area of orifice  84  or  94  which is open 
     By varying the amount of flow through orifice  84  or  94 , a variable amount of back pressure is produced to pressure regulated compression main poppet  80 . The amount of force or fluid pressure required to displace valve member  112  and move it to its open position is determined by the area deferential of the upstream pressure face versus the downstream pressure face. By continuously varying the pressure on the downstream pressure face through the movement of spool valve  62 , the amount of force required to displace valve member  112  can be continuously varied thus resulting in a continuously variable damping force blowoff level. Thus, compression main poppet  80 , as well as compression co-poppet  82 , rebound main poppet  90  and rebound co-poppet  92  operate as blowout valves. 
     In order to completely separate the operation of continuously variable servo valve assembly  22  from rebound to compression, a complete separation of the fluid flow of the rebound to the fluid flow of the compression of the shock absorber  10  is required. A description of fluid flow during the rebound stroke and the compression stroke is detailed below. 
     Referring now to FIGS. 1 and 5, during the rebound stroke, because there is no valving in piston  12 , fluid is forced through a passage  130  formed in rod guide  34  and into upper intermediate chamber  36 . The fluid enters upper intermediate chamber  36  which is concentric with working chambers  24  and  26 . Fluid exits through rebound outlet  54  and enters rebound inlet  88  of continuously variable servo valve assembly  22 . After entering rebound inlet  88 , fluid flows to rebound main poppet  90 , to rebound co-poppet  92  and to rebound orifice  94 . As described above, the amount of flow through rebound orifice  94  is controlled by the position of spool valve  62  to control the damping characteristics from a soft ride to a firm ride. Fluid flowing through continuously variable servo valve assembly  22  is directed to lower intermediate chamber  38  and lower working chamber  26 . The rebound movement of piston  12  creates a low pressure within lower working chamber  26  and intermediate chamber  38 . Fluid leaving continuously variable servo valve assembly  22  through compression inlet  78  is allowed to enter lower working chamber  26  to replenish the fluid on the bottom side of piston  12 . Floating piston  20  moves axially within outer tube  18  to compensate for the rod volume. 
     During the compression stroke, because there is no valving in piston  12 , fluid is forced from lower working chamber  26  into lower intermediate chamber  38 . The fluid enters lower intermediate chamber  38  which is concentric with working chambers  24  and  26 . Fluid exits through compression outlet  56  and enters compression inlet  78  of continuously variable servo valve assembly  22 . After entering compression inlet  78 , fluid flows to compression main poppet  80 , compression co-poppet  82  and to compression orifice  84 . As described above, the amount of flow through compression orifice  84  is controlled by the position of spool valve  62  to control the damping characteristics from a soft ride to a firm ride. Fluid flowing through continuously variable servo valve assembly  22  is directed to upper intermediate chamber  36  and upper working chamber  24 . The compression movement of piston  12  creates a low pressure within upper working chamber  24  and upper intermediate chamber  36 . Fluid leaving continuously variable servo valve assembly  22  through rebound inlet  88  is allowed to enter upper intermediate chamber  36  to replenish the fluid on the top side of piston  12  via passage  130  in rod guide  34  which extends between upper working chamber  24  and upper intermediate chamber  36 . Floating piston  20  moves axially within outer tube  18  to compensate for the rod volume. 
     The above construction for shock absorber  10  thus provides an infinitely variable solenoid actuated continuously variable shock absorber. Some, but not all of the advantages of this contraction are given below. First, shock absorber  10  provides a greater differentiation from soft to firm damping forces in compression due to the introduction of separate compression flow passages and check valves. Second, shock absorber  10  provides for a separately tunable rebound and compression valving. Third, shock absorber  10  provides soft compression damping forces and firm rebound damping forces during the same stroke. Conversely, firm compression damping forces and soft rebound damping forces during the same stroke are also available. In addition, shock absorber  10  does not require any piston valving system. Fifth, shock absorber  10  allows for continuously variable bleed and blowoff features. Sixth, continuously variable servo valve assembly  22  differentiates between compression strokes and rebound strokes. 
     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.