Abstract:
Parallel paths for damping fluid are provided through the piston of a suspension damper, each of which are provided with separate damping valving sets to control damping. Communication through one of the paths is controlled by a movable control valve member, which is controlled by a magnetostrictive element which deforms in response to application of a magnetic field. The control valve member is moved between active and inactive positions in response to changes in a magnetic field applied by a coil mounted within the damper piston. In one position, all communication of damping fluid is through one of the damping valve sets, while in the other positon damping fluid communicates through both valve sets. Accordingly, damping levels may be varied by controlling the magnetic field.

Description:
TECHNICAL FIELD 
     This invention relates to a dual mode suspension damper which is switched between different levels of damping by a magnetostrictive element controlled by a magnetic field. 
     BACKGROUND OF THE INVENTION 
     Vehicle suspension systems require suspension dampers (such as shock absorbers or struts) to control oscillations in the vehicle suspension system. Conventional dampers include a housing filled with damping fluid and a piston slidable in the housing. A piston rod extends from the housing and connects the piston to the sprung mass (body) of the vehicle, while the housing is attached to an unsprung mass of the vehicle. Appropriate valving within the piston controls communication of damping fluid across the piston, to thereby dampen the suspension oscillations. Since conventional dampers have only a single valve in the piston and therefore are able to damp only at a set damping force, such dampers involve compromises in vehicle suspension performance. 
     More recently, variable suspension dampers have been proposed, in which the damping level can be varied between two separate levels in response to varying vehicle operating conditions as sensed by sensors on the vehicle. Such a damper is disclosed in U.S. Pat. No. 5,690,195. In the damper disclosed in this patent, two separate flow paths with separate valving are provided through the piston. A solenoid valve controls communication through one of the flow paths. Accordingly, damping can be adjusted or varied between two different levels, depending upon vehicle operating conditions. 
     SUMMARY OF THE INVENTION 
     According to the present invention, parallel paths are provided through the piston of a suspension damper, each of which are provided with separate damping valving. Communication through one of the paths is controlled by a movable valve element, which is controlled by a magnetostrictive element which deforms in response to application of a magnetic field. The movable valve element responds to changes in the magnetostrictive element as a result of application of a magnetic field to open or close the corresponding path. Magnetostrictive materials used to fabricate the magnetostrictive elements used in this invention include nickel and various other compounds available commercially. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross sectional view of a suspension damper incorporating the present invention; 
     FIG. 2 is an enlarged, longitudinal cross sectional view taken through the piston used in the suspension damper of FIG. 1; 
     FIG. 3 is an exploded view in perspective illustrating some of the components of the piston illustrated in FIG. 2; 
     FIG. 4 is a view similar to FIG. 2, but illustrating another embodiment of the present invention; 
     FIGS. 5 and 6 are views similar to FIGS. 2 and 3 respectively, but illustrating still another embodiment of the invention; 
     FIG. 7 is an exploded view in perspective similar to FIG. 6, but taken from a different angle to illustrate portions of the various components not shown in FIG. 6; 
     FIGS. 8 and 9 are views similar to FIGS. 2 and 3 respectively, but illustrating still another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a suspension damper, such as a shock absorber, is generally indicated by the numeral  10  and includes a cylindrical housing  12  filled with damping fluid. A piston  14  is slidable within the housing  12  and divides the latter into a compression chamber  16  and a rebound chamber  18 . A piston rod  20  extends from the piston  14  through the rebound chamber  18  and closure member  22 . An attachment fitting  24  on piston rod  20  permits the piston rod  20  to be secured to the sprung mass of the vehicle (the vehicle body) and an attachment fitting  26  on housing  12  permits the housing  12  to be secured to an unsprung mass of the vehicle. A conventional gas cap  28  slides in the compression chamber  16  and separates the latter from gas chamber  30 , which is charged with compressed gas in a conventional manner to permit the damper  10  to accommodate changes in volume of the rebound chamber  18  in response to changes in volume of the piston rod within rebound chamber  18  in response to movement of the piston  14 . Gas cap  28  also reduces cavitation of the damping fluid, all in a manner well known to those skilled in the art. 
     Referring now to FIGS. 2 and 3, the piston  14  includes an outer case  32  which defines a cavity therewithin. The outer case is stepped to define a larger diameter portion  34  and a smaller diameter portion  36  so that the cavity includes larger and smaller diameter portions  38 , 40  respectively. The larger portion  34  is closed by a cover  42  through a threaded connection generally indicated by the numeral  44 . The portion of the outer case  32  engaged by the cover  42  terminates in multiple circumferentially spaced tabs  46 , and the corresponding portion of the cover  42  is provided with circumferentially spaced recesses  48 . Accordingly, the cover can be locked in place relative to the outer case  32  by deflecting one or move of the tabs  46  with a corresponding recess  48 , as will hereinafter be explained. The piston rod  20  is secured to the cover  42  through a threaded connection  50 . 
     Mounted within larger diameter cavity portion  38  immediately inside of the cover  42  is a bobbin  52  which carries coil windings  54 . An electrical connector  56  extends from the bobbin  52  and into a bore  58  that extends through the piston rod  20 . Electrical connector  56  is sealed to piston rod  20  by circumferentially extending seal  57 . An electrical cable (not shown) extends through bore  58  to carry electrical power to the windings  54  through the electrical connector  56 . The piston rod  20  provides an electrical ground to complete the power circuit to the windings  54  in a manner well known to those skilled in the art. The side of the bobbin  52  facing away from the cover is provided with a recess that extends into the portion of the bobbin  52  circumscribed by the windings  54 . This recess which receives a pellet  60  of magnetostrictive material. Accordingly, pellet  60  will be within the magnetic field generated by electrical power transmitted to the windings  54 . The magetostrictive material has been described in more detail above, and has the property of constricting (shrinking) in the axial direction (that is, the direction extending along the axis of the coil) in response to an applied magnetic field. A disc-shaped transfer plate  62  extends across larger cavity portion  38  and is engaged by the pellet  60  and transfers the deformation of the pellet  60  as a result of the magnetic field applied thereto to a transfer medium  64 . The transfer plate  62 , outer case  32  and cover  42  define a magnetic circuit and are made of magnetically soft material. 
     The transfer medium  64  is a disc of a shape compliant elastomer, such as silicone rubber that is contained between the transfer plate  62  and a pin guide  66 . Pin guide  66  rests on shoulder  68  defined between larger and smaller portions of the outer case  32 , and includes an aperture  68  along the axis thereof that slidably receives a pin  70  that projects from a movable valve spool member  72  that is slidable within smaller diameter cavity portion  40 . The spool valve member  72  is urged toward the pin guide  66  by a spring  74 , which is mounted in the cavity portion  40  and is held in place by a clip  76 . The spring  74  bears against the end  78  of the spool valve member  72  opposite the end  80  from which the pin  70  extends. The end  80  includes slot  81  through which damping fluid communicates through the spool valve member  72 . 
     A first set of circumerentially extending valve elements  82  and a second set of circumerentially extending valve elements  84  are each supported on the outer circumferential surface of smaller portion  36  of case  32  and are separated by a circumferentially extending spacer  86 . The valve sets  82  and  84  are described in detail in the above-mentioned U.S. Pat. No. 5,690,195, and, since they form no part of the present invention, will not be described in detail herein. As discussed in U.S. Pat. No. 5,690,195, valve sets  82  and  84  regulate flow of damping fluid across the piston  14  and thus provide damping. For clarity, the valve sets  82 ,  84  and spacer  86  are not shown in FIG. 3. A piston cap  88  is mounted on smaller portion  36  and holds the valve sets  82 ,  84  and spacer  86  in position. The outer circumferential surface of piston cap  88  is provided with seals and sealing grooves  90 , which sealingly engage the inner wall of housing  12 . Circumferentially spaced apertures  92  are provided in the piston cap  88 , and define a portion of a first fluid path indicated by the arrow A that is controlled by valve set  82 . Circumferentially spaced apertures  94  are provided through the smaller portion  36  near the end thereof through which the pin  70  extends. The apertures  94  define a portion of a second fluid path indicated by arrow B, that is controlled by the valve set  84 . Communication through the second fluid path is controlled by the movable spool valve  72 , which in one position closes communication through the aoertyres  94  but is movable to a position which opens communication through the apertures  94 . The movable spool valve  72  is calibrated when the piston  14  is assembled, by advancing the cover  42  on the case  32  until the valve spool  72  attains a predetermined position, at which one or move of the tabs  46  are deflected into a corresponding registering recess  48 , to thereby lock the cover in position. 
     When the windings  54  are energized, the magnetostrictive pellet  60  shrinks or constricts. Accordingly the transfer plate  62  is permitted to move toward the cover  42 , which in turn allows the spring  74  acting through valve spool member  72  to push the pin  70  into transfer medium  64 , thereby moving the valve spool member into a position closing the apertures  94 , thereby preventing communication of damping fluid through apertures  94 . Accordingly, communication of damping fluid through flow path B is prevented, so all damping is provided through flow path A and the first set of valve elements  82 . When the windings  54  are deactivated, the valve spool member  72  is pushed away from valve guide  66 , so that damping is provided through both fluid flow paths A and B and both sets of valve members  82  and  84 . The spool valve element may be designed so that the normal position either blocks or opens the apertures  94 , so that energization of the windings  54  either adds or removes the damping provided by the flow path B through second valve elements  84 . 
     Referring now to the embodiment of FIG. 4, where elements the same or substantially the same as those in the embodiment of FIGS. 2 and 3 retain the same reference numeral, the effect of the magnetostrictive pellet is enhanced by using a telescoping structure in which another magnetostrictive pellet  96  is nested within a cavity  98  formed in magnetostrictive pellet  100  and held in place by a support member  102 , which is made of a non-magnetostrictive material. The displacement generated by the combined pellets  96  and  100  is the same as that of a single element with an axial length equal to the sum of the axial lengths of the two nested pellets, but the package size is smaller. 
     The embodiments of FIGS. 2,  3 , and  4  may also be used with a magnetostrictive pellet that expands upon application of a magnetic field, in which case the effect of the magnetic field on the postion of the valving would be reversed; in other words,the position of the valve  72  attained with a strong magnetic field with a constricting pellet  72  will require a weak magnetic field with an expanding pellet. Alternatively, if an expanding pellet is used, the valve  72  may be provided with slots on the circumferentially extending surface thereof instead of the slot on end  81  may be used so that the valve  72  will be moved into the position allowing communication through flow path B by applying a magnetic field thereto. 
     Referring now to the embodiment of FIGS. 5,  6  and  7 , where elements the same or substantially the same as those in the embodiment of FIGS. 2 and 3 retain the same reference numeral, the spool valve member  72  is replaced by a rotary valve member  104 , which is rotatable within the cavity smaller portion  40  and supported by a spacer/thrust bearing  105 , which is retained by clip  106 . The rotary valve member  104  is provided with multiple, circumferentially spaced, axially extending slots  108 . The slots  108  are designed so that in a predetermined angular orientation of the rotary valve member  104  the slots  108  are aligned with the apertures  94 , to thus permit communication of damping fluid through the second set of valve members  84  and flow bath B. However, upon rotation of the rotary valve member  104 , communication through the apertures  94  and the valve set  84  is blocked, to thereby remove the damping provided by the valve set  84 . 
     The rotary valve member  104  is operated by a spiral wound bimetalic element generally indicated by the numeral  110 . Spiral bimetallic element  110  is made by bonding a sheet of magnetostrictive material to a sheet of non-magnetostrictive material of similar thickness, cutting the material into strips of an appropriate length, and then winding the strips into the spiral  110 . The outer end  112  is secured to a pin  114 , which is rigidly secured to a support plate  116 , which is held against rotation relative to case  32  by projection  118 . Support plate  116  supports the spiral element  110  nested within coil windings  54 . The inner end  120  of spiral bimetallic element  110  is rigidly secured to a drive pin  122  which extends through a central aperture in support plate  116  and is rotatable relative thereto. Flats  124  are provided on the end of drive pin  122  engage corresponding flats  125  on the rotary valve member  104 , to permit spiral  110  to drive the rotary valve member  104 . The spiral bimetallic element  110  reacts to a magnetic field generated by coil windings  54  to rotate the rotary valve member  104  between positions permitting and blocking communication through the second set of valve elements  82  in flow path B, thereby changing the damper  10  between the mode in which all damping is provided by valve set  82  and the mode in which damping is provided by both the valve set  82  and the valve set  84 . 
     Referring now to the embodiment of FIGS. 8 and 9, where elements the same or substantially the same as those in the embodiment of FIGS. 2 and 3 retain the same reference numeral, a movable spool valve member  126  is provided with slot  128  that, depending upon the axial position of the spool valve member  126  within smaller cavity portion  40 , either blocks communication through apertures  94  or permits communication through apertures  94 . Spring  74  urges spool valve member  126  into enggagement with a bimetallic coil spring  128 , so that the spool valve member  126  remains engaged with coil spring  128  as spring  128  expands and contracts. Spring  128  is within the magnetic field of coil windings  54  and is made of a magnetostrictive material  130  bonded to a non-magnetostrictive material  132 . Spring  128  is made of two elongate strips, one of the strips being a magnetostrictive material and the other strip being a non-magnetostrictive material. The two strips are then bonded together to form a bimetallic wire having a circular cross-section. This wire is then twisted about its axis, to form a straight wire with the two materials spiraling about the wire. The wire is then coiled to form coil spring  128 . The spring  128  expands and contracts in response to the magnetic field applied by coil windings  54 , to thereby move the spool valve member  128  between the positions blocking or enabling communication through apertures  94 . Alternatively, one end of spring  128  may be fixted to the piston and the other end secured to the spool valve member  128 , thereby eliminating the spring  76 .