Patent Publication Number: US-2010109276-A1

Title: Controllable vehicle suspension system with magneto-rheological fluid device

Description:
CROSS REFERENCE 
     This application is a continuation-in-part of application Ser. No. 11/742,911, filed May 1, 2007, which claims the benefit of U.S. Provisional Application No. 60/796,567, filed May 1, 2006, all of which the benefit are claimed and are herein incorporated by reference. This application is a continuation-in-part of International Application No. PCT/US07/83937, filed Nov. 7, 2007, which claims the benefit of U.S. Provisional Application No. 60/984,212, filed Oct. 31, 2007, and application Ser. No. 11/742,911, filed May 1, 2007, all of which the benefit are claimed and are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of suspension systems for controlling motion. The invention relates to the field of controllable systems for controlling motion and providing support. The invention relates to the field of controllable vehicle systems for controlling vehicle motions. More particularly, the invention relates to vehicle cab suspensions with controllable magneto-rheological fluid device having beneficial motion control. 
     BACKGROUND OF THE INVENTION 
     Magneto-rheological fluid devices such as magneto-rheological fluid dampers and struts are useful in controlling or damping motion in suspension systems such as vehicle suspension systems. A typical magneto-rheological fluid damper includes a damper body with a sliding piston rod received therein. The damper body includes a reservoir that is filled with magneto-rheological fluid, i.e., non-colloidal suspension of micron-sized magnetizable particles. One or more seals are used to retain the magneto-rheological fluid within the reservoir as the piston rod reciprocates within the damper body. The damping characteristics are controlled by applying a magnetic field to the magneto-rheological fluid. A magneto-rheological fluid strut combines a magneto-rheological fluid damper function with the ability to support loads. 
     There is a need for controllable magneto-rheological fluid devices for supporting a load while providing motion control and vibration isolation. There is a need for vehicle cab magneto-rheological fluid devices for isolating vibrations and cab motions. There is a need for controllable magneto-rheological fluid devices which accurately and economically control and minimize vibrations. There is a need for an economically feasible method of making motion control magneto-rheological fluid devices and vehicle suspension systems. There is a need for a robust suspension system and magneto-rheological fluid devices for isolating troublesome vibrations and controlling vehicle motions. There is a need for an economic suspension system providing beneficial controlled motion and vibration isolation. 
     SUMMARY OF THE INVENTION 
     In one aspect, a controllable suspension system for controlling the relative motion between a first body and a second body includes at least one strut. The at least one strut includes a magneto-rheological fluid damper which comprises: a damper body; a piston rod guide disposed within the damper body, the piston rod guide having a passage therein for receiving a piston rod; a piston rod bearing assembly disposed in the piston rod guide to engage with and support reciprocal motion of the piston rod; at least a first piston rod seal and at least a second piston rod seal arranged to seal between the piston rod guide and the piston rod; a fluid chamber defined between the piston rod guide and the piston rod; and a piston rod guide gas charged accumulator arranged between the piston rod and the damper body. 
     In another aspect, a controllable suspension system for controlling the relative motion between a first body and a second body comprises: a damper body; a spring longitudinally aligned with the damper body; a piston rod guide disposed within the damper body, the piston rod guide having a passage therein for receiving a piston rod; a piston rod bearing assembly disposed in the piston rod guide to engage with and support reciprocal motion of the piston rod; at least a first piston rod seal and at least a second piston rod seal arranged to seal between the piston rod guide and the piston rod; a fluid chamber defined between the piston rod guide and the piston rod; and a piston rod guide gas charged accumulator arranged between the piston rod and the damper body. 
     In another aspect, a controllable suspension system for controlling the relative motion between a first body and a second body includes at least one strut. The at least one strut includes a magneto-rheological fluid damper which comprises: a damper body; a piston rod guide disposed within the damper body, the piston rod guide having a passage therein for receiving a piston rod; a piston rod bearing assembly disposed in the piston rod guide to engage with and support reciprocal motion of the piston rod; at least a first piston rod seal and at least a second piston rod seal arranged to seal between the piston rod guide and the piston rod; a fluid chamber defined between the piston rod guide and the piston rod; means for filtering fluid entering the fluid chamber; and a piston rod guide gas charged accumulator arranged between the piston rod and the damper body. 
     In another aspect, a method of making a controllable suspension system for controlling the relative motion between a first body and a second body comprises: providing a damper body having a reservoir for containing the magneto-rheological fluid; providing a piston rod; providing a piston rod guide disposed within the damper body, the piston rod guide having a passage therein for receiving the piston rod; providing a piston rod assembly coupled to the piston rod guide and arranged to engage and support reciprocal motion of the piston rod; providing at least a first piston rod seal and at least a piston rod seal arranged to seal between the piston rod guide and the piston rod; providing a fluid chamber defined between the piston rod guide and the piston rod; providing a piston rod guide filter arranged in a communication path between the fluid chamber and the reservoir to filter particulates out of fluid entering the fluid chamber; and providing an accumulator arranged between the piston rod guide and the damper body. 
     In another aspect, a controllable suspension system for controlling the relative motion between a first body and a second body includes at least one magneto-rheological fluid damper. The at least one magneto-rheological fluid damper comprises: a damper body; a piston rod guide disposed within the damper body, the piston rod guide having a passage therein for receiving a piston rod; a piston rod bearing assembly disposed in the piston rod guide to engage with and support reciprocal motion of the piston rod; at least a first piston rod seal and at least a second piston rod seal arranged to seal between the piston rod guide and the piston rod; and a piston rod guide gas charged accumulator arranged between the piston rod and the damper body. The magneto-rheological fluid damper includes a reservoir for a magneto-rheological fluid provided within the damper body and a piston rod guide filter arranged in a communication path between the fluid chamber and the reservoir to filter particulates out of the magneto-rheological fluid entering the fluid chamber from the reservoir. 
     In another aspect, a vehicle suspension system for controlling the relative motion between a first body and a second body comprises: a damper body; a spring longitudinally aligned with the damper body; a piston rod guide disposed within the damper body, the piston rod guide having a passage therein for receiving a piston rod; a piston rod bearing assembly disposed in the piston rod guide to engage with and support reciprocal motion of the piston rod; at least a first piston rod seal and at least a second piston rod seal arranged to seal between the piston rod guide and the piston rod; a fluid chamber defined between the piston rod guide and the piston rod; a piston rod guide gas charged accumulator, said piston rod guide gas charged accumulator arranged between the piston rod and the damper body; and a piston rod guide filter. 
     In another aspect, a method of controlling motion between a first body and a second body comprises: providing a magneto-rheological damper fluid comprised of a plurality of magnetic particulates in a carrier fluid; providing a damper body having a reservoir for containing the magneto-rheological fluid; providing a piston rod; providing a piston rod guide disposed within the damper body, the piston rod guide having a passage therein for receiving the piston rod; providing a piston rod assembly coupled to the piston rod guide and arranged to engage and support reciprocal motion of the piston rod; providing at an outer piston rod seal arranged to seal against the piston rod; providing a piston rod guide accumulator arranged between the piston rod and the damper body; and inhibiting the magnetic particulates from the magneto-rheological fluid in the reservoir from reaching the outer piston rod seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, described below, illustrate typical embodiments of the invention and are not to be considered limiting of the scope of the invention, for the invention may admit to other equally effective embodiments. The figures are not necessarily to scale, and certain features and certain view of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
         FIG. 1  is a side view of a vehicle with a controllable suspension system including magneto-rheological fluid struts. 
         FIG. 2A  is a side view of a tractor with a controllable suspension system including magneto-rheological fluid struts. 
         FIG. 2B  is an end view of the tractor shown in  FIG. 2A . 
         FIG. 3  is a diagram of a controllable suspension system including magneto-rheological fluid struts. 
         FIG. 4A  is a side view of a magneto-rheological fluid strut including a magneto-rheological fluid damper. 
         FIG. 4B  is an enlarged view of a portion of the magneto-rheological fluid strut shown in  FIG. 4A . 
         FIG. 4C  is another side view of the magneto-rheological fluid strut shown in  FIG. 4A . 
         FIG. 4D  is an end view of the magneto-rheological fluid strut shown in  FIG. 4A . 
         FIG. 5  is a perspective view of a magneto-rheological fluid strut. 
         FIG. 6A  is a side view of the magneto-rheological fluid strut shown in  FIG. 5 . 
         FIG. 6B  is another side view of the magneto-rheological fluid strut shown in  FIG. 5 . 
         FIG. 6C  is an end view of the magneto-rheological fluid strut shown in  FIG. 5 . 
         FIG. 6D  is an end view of the magneto-rheological fluid strut shown in  FIG. 5 . 
         FIG. 6E  is a side view of the magneto-rheological fluid strut shown in  FIG. 5 . 
         FIG. 6F  is a cross-section of the magneto-rheological fluid strut shown in  FIG. 6E . 
         FIG. 6G  illustrates the relationship between piston rod bearing seal interface, bearing gap, piston head fluid flow interface, piston gap, and stroke length for the magneto-rheological fluid strut shown in  FIG. 6F . 
         FIG. 6H  is an enlarged view of a portion of the cross-section shown in  FIG. 6G . 
         FIG. 6I  is an enlarged view of a portion of a magneto-rheological fluid damper depicted in  FIG. 6G , depicting an upper piston rod bearing assembly. 
         FIG. 6J  is a perspective view of a head portion of the magneto-rheological fluid strut of  FIG. 6G . 
         FIG. 6K  is a perspective view of an end portion of the magneto-rheological fluid damper in the magneto-rheological fluid strut of  FIG. 6G . 
         FIG. 6L  is a perspective view of an electromagnetic coil included in the piston head of the magneto-rheological fluid damper of  FIG. 6G . 
         FIG. 6M  is a cross-section of the electromagnetic coil shown in  FIG. 6L . 
         FIG. 6N  is a perspective view of two overmolded EM coils. 
         FIG. 7A  is an enlarged view of a piston head portion of the magneto-rheological fluid damper shown in  FIG. 6G . 
         FIG. 7B  is a perspective view of an overmolded EM coil. 
         FIGS. 7C through 7N  are end, side, and cross-sectional views of portions or components of an overmolded EM coil. 
         FIG. 8  shows an arrangement of magneto-rheological fluid struts in a suspension system. 
         FIG. 9  is a cross-section of an EM coil. 
         FIG. 10  is a cross-section of a magneto-rheological fluid strut. 
         FIG. 11  is a perspective view of a magneto-rheological fluid damper. 
         FIGS. 12 and 13  depict vertical cross-section views of the magneto-rheological fluid damper of  FIG. 11 . 
         FIGS. 14-16  depict a partial cross-section of the magneto-rheological fluid damper of  FIG. 11 . 
         FIG. 17  is a schematic illustration of a vehicle with a suspension system including magneto-rheological fluid dampers. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described in detail with reference to a few preferred embodiments, as illustrated in the accompanying drawings. In describing the preferred embodiments, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without some or all of these specific details. In other instances, well-known features and/or process steps have not been described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals are used to identify common or similar elements. 
     In an embodiment the invention includes a controllable suspension system for controlling the relative motion between a first body and a second body. Referring to  FIGS. 1-10 , and particularly to  FIGS. 1-3 , a controllable suspension system  20  controls the relative motion between a first body  22  and a second body  24 . In preferred embodiments the controllable suspension system  20  is a vehicle controllable suspension system  20 , most preferably as shown in  FIGS. 1-3  a cab suspension controllable suspension system  20 , with the suspension system controlling motion between the vehicle cab body  22  and the vehicle frame body  24 . In alternative embodiments the controllable suspension system  20  is a non-vehicle suspension system, preferably a stationary suspension system. 
     The controllable suspension system  20  includes at least one magneto-rheological fluid strut ( 30  in  FIGS. 1-6N ). Referring to  FIG. 3 , the controllable suspension system strut  30  includes a single-ended magneto-rheological fluid damper  32 , preferably a cantilevered single-ended magneto-rheological fluid damper. As more clearly shown in  FIG. 6F , the magneto-rheological fluid damper  32  includes a longitudinal damper tubular housing  34  having a longitudinally extending axis  36 . The longitudinal damper tubular housing  34  has an inner wall  38  for containing a magneto-rheological fluid  40  within the tubular housing  34 . Preferably the longitudinal damper tubular housing  34  is comprised of a magnetic metal material, preferably a magnetic low carbon steel as compared with a nonmagnetic metal material such as stainless steel. Preferably the magneto-rheological fluid  40  is a magneto-rheological damper fluid with the fluid containing iron particles wherein the rheology of the damper fluid changes from a free flowing liquid to a flow resistant semi-solid with controllable yield strength when exposed to a magnetic field, such as the LORD MR fluids available from LORD Corporation, Cary, N.C. 
     Referring to  FIG. 6G , the magneto-rheological fluid damper  32  includes a cantilevered damper piston  42 , the damper piston  42  including a piston head  44  movable within the damper tubular housing  34  along a longitudinal length of the tubular housing axis  36 . The damper piston head  44  provides a first upper variable volume magnetorheological fluid chamber  46  and a second lower variable volume magnetorheological fluid chamber  48 . The damper piston head  44  has a fluid flow gap  50  between the first upper variable volume magnetorheological fluid chamber  46  and the second lower variable volume magnetorheological fluid chamber  48  with a piston head fluid flow interface length HL, with the fluid flow gap  50  between the piston head  44  and inner wall surface  38  of the tubular housing  34  with a piston gap Pgap between the OD of the piston head  44  and the ID of the inner wall  38 . The damper piston  42  includes a longitudinal cantilevered piston rod  52  for supporting the piston head  44  within the longitudinal damper tubular housing  34 . 
     The damper piston  42  is supported within the longitudinal damper tubular housing  34  with an upper piston rod bearing assembly  54  disposed between the longitudinal damper tubular housing  34  and the longitudinal piston rod  52 . The piston rod bearing assembly  54  has a piston rod bearing seal interface length BL with BL&gt;HL and contact between the piston head  44  and the damper tubular housing inner wall  38  is inhibited. Preferably the bearing assembly  54  has a minimal bearing gap Bgap between the bearings  56  and the OD of the piston rod  52 . As shown in  FIG. 6G , preferably [Pgap/(HL+Stroke)] is greater than (Bgap/BL). Preferably the piston head  44  is a wear-band-free piston head, with the fluid flow gap  50  maintained between piston head sides OD and tubular housing inner wall ID with no wear band or seal on the piston between piston head  440 D and inner wall  38  ID. In embodiments such as shown in  FIG. 6L-6N , axially aligned coil guides  95  are preferably utilized to maintain fluid flow gap  50  and inhibit contact between the piston head  44  and the housing wall  38 . Preferably the axially aligned coil guides  95  are aligned with axis  36 , and preferably substantially equally spaced around the outside perimeter of EM coil  94 , preferably with at least three coil guides  95 , more preferably at least four guides, more preferably at least five guides, and more preferably at least six guides spaced around the OD of EM coil  94 , preferably with the guides  95  occupying less than 15% of the perimeter of the EM coil, and more preferably no greater than 10% of the perimeter of the EM coil. Preferably the guides  95  are a nonmagnetic material, preferably a polymer, preferably with the guides  95  comprised of injection pressurized polymer  110  with the guides molded integral and simultaneously with their adjacent bobbin polymer overmold  110  that is pressure injected into a overmold  106 , with the nonmagnetic polymer guides and overmold polymer  110  encompassing and covering the underlying wound EM coil wiring  102 . Preferably the axially aligned guides  95  axially extend over the adjacent magnetic poles  96  in  FIG. 6L . Referring again to  FIG. 6G , the cantilevered damper piston  42  preferably minimizes the off state resistance of the damper with a minimized parasitic drag and resistance. Preferably the cantilevered damper piston  42  off state energy dissipation is minimized by substantially inhibiting contact between piston head  44  and housing wall  38  while maintaining the predetermined fluid flow gap  50  and the gap width Pgap, preferably while not utilizing a piston wear band or piston seal that encircles the piston perimeter. 
     Preferably the piston  42  has a constant bearing length in that the piston head  44  has no substantial bearing contact with the housing inner wall  38 , with the cantilevered piston  42  providing a single ended damper  32  as compared to a double-ended damper. Preferably the rod  52  terminates with the piston head  44 , with the piston head unconnected to the housing  34  except for the single bearing assembly  54 . Preferably the rod  52  and the piston head  44  are unconnected to the lower housing end  58  distal from the piston rod bearing  54  and the upper housing end  60 . Preferably the only mechanical connection of the piston head  44  is with the single piston rod  52  extending to the upper bearing assembly  54 , with rod  52  terminating with the piston head  44 , with no contact of piston head  44  with housing inner side walls  38  or the lower damper end  58  distal from the upper damper end  60  with the bearing  54 . In embodiments contact of piston head  44  is inhibited with minimized perimeter occupying axially aligned guides  95 . Preferably the piston head  44  is free of internal fluid flow conduits, preferably with substantially all fluid flow between the piston head  44  and housing  34  through the fluid flow gap  50 , preferably with the fluid flow gap maintained with assistance of guides  95  which assist in ensuring that substantial contact between the piston head  44 , particularly the magnetic poles ( 96  in  FIGS. 6L-6N ), and the housing inner side walls  38  is inhibited. 
     Preferably the magnetorheological fluid damper  32  includes an upper volume compensator  62 . The magnetorheological fluid damper volume compensator  62  preferably is proximate the piston rod bearing assembly  54 . Preferably the volume compensator  62  is adjacent the upper piston rod bearing  54 . Preferably the bearing holder support structure housing  55  and the volume compensator housing are integrated together to provide an upper bearing gas charged compliance member. Preferably the gas compliance volume compensator  62  is in fluid communication with the first upper variable volume magnetorheological fluid chamber  46 , with the volume compensator proximate the upper bearings  56  and the piston rod  52 , preferably with upper fluid chamber  46  and volume compensator  62  in use in the suspension system  20  oriented on top relative to the force of gravity to allow gas bubble migration into volume compensator  62 . Preferably the damper  32  configuration provides for a dry assembly process with the magnetorheological fluid filled into the damper after the piston  42  is assembled into the housing  34 , and preferably then gas pressure charging of gas compliance volume compensator  62 . 
     Preferably the strut  30  includes a longitudinal air gas spring  64 , with the longitudinal gas spring  64  aligned with the longitudinal damper tubular housing longitudinally extending axis  36 . Preferably the strut  30  includes the strut air spring  64  and the magneto-rheological fluid damper  32  aligned with the common center axis  36  and packaged together with the gas spring  64  encompassing the damper  32 , with the upper end of the damper including the piston rod  52 , substantially housed within the gas spring  64 . Preferably the upper end of the strut  30  includes an upper strut end head member  66  (also shown in  FIG. 6J ) for attachment to the uppermost first body  22 . Referring to  FIGS. 6G and 6J , preferably the upper strut end head member  66  includes an electrical power input  68  and an air compressed gas input  70 . Preferably the upper strut end head member  66  has an internal head cavity housing that includes a strut control system  72  with an electronic control circuit board  74 , gas spring air sleeve leveling valve  76 , and preferably also includes a high speed electrical communications connection  78 , such as a CAN-Bus, for receiving outside the strut signals in addition to electrical power input  68 . Preferably the upper strut end head member  66  includes a strut sensor system  80 , preferably the upper sensor head end of the magneto-strictive longitudinal sensor  80  that is aligned with the piston rod  52  and axis  36  and housed within the piston rod the  52 . Preferably the piston rod  52  is comprised of a nonmagnetic material, preferably a nonmagnetic metal such as stainless steel, wherein the inner housed magneto-strictive longitudinal sensor  80  provides for sensing the stroke position of the piston along the stroke length of the damper. Preferably the upper strut end member housing  66  includes the strut control system with sensors inputs, sensors, current supply, and also the pneumatic leveling valve to control leveling of the gas spring  64  in addition to controlling the magnetorheological fluid damper  32 . 
     Referring again to  FIG. 6G , preferably the upper piston rod bearing assembly  54  includes a bearing holder support structure  55  which receives a first upper bearing  56  and a distal second lower bearing  56  to provide the piston rod bearing seal interface length BL. Preferably the bearing holder support structure  55  receives a bearing seal  53  between the lower bearing  56  and the upper fluid chamber  46 . Preferably the upper piston rod bearing assembly  54  includes the bearing holder support structure  55  which receives the at least first bearing  56  and includes compliance member cavity  82  for receiving a volume compensator gas compliance member  84 , preferably with the gas compliance member flexible fluid gas partition diaphragm  84  flexibly fixed to the support structure  55  allowing expansion and contraction of the gas filled diaphragm cavity to compensate for magnetorheological fluid volume changes, preferably with the gas compliance member flexible elastomer fluid gas partition diaphragm  84  radially expandable between the support structure  55  and the housing  34 . Preferably the upper piston rod bearing assembly  54  includes the bearing holder support structure  55  which receives the at least first bearing  56  and includes a sensor target magnet holder  86  which receives a target magnet  88  for the magnetostrictive sensor  80  in the non-magnetic piston rod  52 . Preferably the upper volume compensator  62  is vertically oriented relative to gravity in operation of the suspension system with the volume compensator proximate the piston rod bearing. 
     Preferably volume compensator  62  is adjacent the upper piston rod bearing assembly  54 , preferably with the bearing holder support structure  55  and volume compensator housing cavity  82  integrated to provide an upper damper rod bearing gas charged compliance member. Preferably the rod bearing gas charged compliance member support structure  55  includes a gas compliance charging conduit  90  for filling the cavity  82  with a pressurized gas, preferably after the piston has been assembled into the housing and bearing and the damper has been filled with the magnetorheological fluid. Preferably the volume compensator  62  is in fluid communication with the adjacent damper fluid chamber  46  through a plurality of fluid volume compensating conduits ( 92  in  FIG. 6K ) between the housing  34  and the piston rod  52 , which allow flow of fluid into and out of the volume compensator, preferably with the conduits  92  providing for greater flow than the piston head gap  50 , preferably a relatively high flow into and out compared to piston head flow, with relatively low resistance to flow into the volume compensator such that it is not dynamically isolated from the rest of the working magnetorheological fluid. 
     Referring to  FIGS. 7A-7N , the piston head  44  includes the electromagnetic coil  94  and an upper and lower magnetic pole  96  for controlling the flow of magneto-rheological fluid  40  between the upper and lower chambers  46  and  48 , preferably with the electromagnetic coil  94  comprised of an electrically insulated encapsulant injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94 . The preferred modular component injected pressurized polymer overmolded electromagnetic magneto-rheological fluid coil  94  is shown in  FIG. 7B . Preferably the EM coil insulated wire ( 102  in  FIGS. 7C ,  7 H- 7 N) is wound on a non-magnetic plastic bobbin ( 104  in  FIGS. 7C ,  7 G- 7 I), with the coiled wire  102  on the bobbin  104  pressure overmolded with an injected pressurized non-magnetic polymer ( 110  in  FIGS. 7C ,  7 D,  7 I) in a pressurized injection overmold  106  under an applied pressure  107 . Preferably the pressurized injection overmolded EM coil  94  includes a first and second wire pins  108  for connection with a current supply wire circuit  100 . Preferably the modular component pressurized injection overmolded EM coil  94  is sandwiched between upper and lower magnetic metal poles  96 , to provide the current controllable EM coil piston head  44 , with the modular component pressurized injection overmolded EM coil  94  overmolded EM coil and poles  96  sized to provide the predetermined gap  50  with the housing inner wall  38 , with the pressurized injection overmolded EM coil magnetic field controlling magnetorheological fluid flow proximate the piston head EM coil, with preferred embodiments molded with axially aligned guides  95  as shown in  FIG. 7L-7N .  FIG. 6N  show two overmolded EM coils with molded guides  95  placed head to head to illustrate how the guides  95  extend beyond the coil top and bottom sides such that they will overlap the adjacent magnetic poles when assembled into the piston head, with the guides equally spaced around the EM coil outer perimeter in a piston axially centering pattern centered and aligned with the longitudinal extending axis  36  of damper  32 . 
     Referring again to  FIG. 3 , preferably the controllable suspension system  20  includes a first strut  30  and at least a second cantilevered magnetorheological fluid damper strut  32  between the first body ( 22  in  FIGS. 1 ,  2 A,  2 B) and the second body ( 24  in  FIGS. 1 ,  2 A,  2 B), preferably with both struts  30  having outer encompassing air spring sleeves  64 . Preferably the controllable suspension system  20  includes a third cantilevered magnetorheological fluid damper strut  30  between the first body and the second body. In one embodiment, at least two of the more than one struts  30  operate independently with their own self contained sensor and control systems in their strut head member housing  66 , preferably with no master control signals communicating between the at least two struts from a suspension system master controller. In one embodiment, the struts  30  are self-contained, self-controlled struts that house their own control systems, preferably with only electrical power and compressed gas supplied from a master suspension system source, such as a vehicle battery electrical power system and a compressed air system. In a preferred embodiment with the more than one strut  30  operating, preferably such as with four struts, a first master controlling strut  30 ″ controls a second controlled dependent strut  30 ′ with master control signals communicating between the at least two struts  30 ″ and  30 ′, such as with the master strut  30 ″ that sends controls to the other dependent strut  30 ″ in addition to its own control. 
     In a preferred embodiment the suspension system  20  is a cab suspension system with two back cab struts  30  and the front of the vehicle cab is mounted without such controllable cantilevered magnetorheological fluid damper struts  30 , such as hard mount or mounted with noncontrolled elastomer mounts. In a preferred cab suspension system  20  embodiment with two rear back cab struts  30  and the front of the vehicle cab is mounted without such controllable cantilevered magnetorheological fluid damper struts  30 , the struts  30  are self controlled and autonomous with each having its own circuit board control system, with the strut control system sharing and communicating its sensor data, such as its processed accelerometer information, with each other through the electrical communication connection  78  link to control roll of the cab body. In preferred embodiments the controllable magnetorheological fluid damper struts  30  are self controlled and autonomous with each having its own circuit board control system  72  housed in its upper strut end head member  66 , with the struts control system sharing its sensor data through its electrical communication connection  78  to control a motion of the cab relative to the frame, such as to control roll, or with a four point strut suspension controlling roll and pitch of the cab with the four self controlled sensor data sharing struts  30 . In a preferred embodiment, as illustrated in  FIG. 8 , at least three struts  30  provide for a three point cab suspension system for control of roll and pitch, preferably with three independent self-controlled struts  30 ,  30 , and  30 ′ and one dependent strut  30 ″. 
     In an embodiment the invention includes a controllable damper for controlling motion. The controllable damper  32  provides for the controlling or relative motion between a first body  22  and a second body  24 , preferably with the damper controlling motion in a vehicle, most preferably in a suspension system  20  between a vehicle frame and the vehicles cab. In alternative embodiments the damper  32  provides for controlling motion in non-vehicle stationary suspensions. The controllable damper  32  includes a longitudinal damper tubular housing  34  having a longitudinally extending axis  36 . The longitudinal damper tubular housing  34  has an inner wall  38  for containing a magnetorheological fluid  40  within the tubular housing, with the damper housing having an upper damper end  60  and a lower damper end  58 . The controllable damper  32  includes a cantilevered single ended damper piston  42 . The damper piston  42  includes a piston head  44  movable within the damper tubular housing  34  along a longitudinal stroke length of the tubular housing, with the damper piston head  44  providing a first upper variable volume magnetorheological fluid chamber  46  and a second lower variable volume magnetorheological fluid chamber  48 . The damper piston head  44  has a fluid flow gap  50  between the first upper variable volume magnetorheological fluid chamber  46  and the second lower variable volume magnetorheological fluid chamber  48  with a piston head fluid flow interface length HL, preferably with the gap  50  having a width Pgap between the piston head OD and inner surface ID of the tubular housing  34 . The damper piston  42  has a longitudinal piston rod  52  for supporting the piston head  44  within the longitudinal damper tubular housing  34 . Preferably the cantilevered piston rod  52  is the only mechanical support for supporting the piston head within the damper housing with a bearing. The piston  42  is supported within the longitudinal damper tubular housing with an upper piston rod bearing assembly  54  disposed between the longitudinal damper tubular housing  34  and the longitudinal piston rod  52 . The piston rod bearing assembly  54  having a piston rod bearing seal interface length BL, wherein contact between the piston head  44  and the damper tubular housing inner wall  38  is inhibited. Preferably the piston head  44  is a wearbandfree piston head, with the magnetorheological fluid flow gap width Pgap maintained between piston head OD sides and tubular housing inner wall with no wear band or seal on the piston head or between the piston OD sides and the inner wall. Preferably the damper  32  minimizes off state resistance a minimized parasitic drag and resistance. Preferably the off state energy dissipation of damper  32  when no controlling current is supplied to the piston head EM coil  94  is minimized by inhibiting contact between the piston head and housing wall while maintaining the predetermined magnetorheological fluid flow gap cylindrical shell of length HL and thickness Pgap. Preferably the piston  42  has a constant bearing length BL in that the piston head  44  has no bearing contact with the housing inner wall  38 . Preferably the damper  32  is a single ended damper as compared to a double ended damper, preferably with the rod  52  terminating with the piston head  44 , with the piston head otherwise unconnected to the housing and the lower housing end  58  distal from the piston rod bearing  54 , preferably with the only mechanical connection of the piston head  44  with the single piston rod extending to the upper bearing assembly, with the rod terminating in the piston head. Preferably the piston head  44  is free of internal fluid flow conduits inside the piston head OD, preferably with substantially all fluid flow of the magnetorheological fluid  40  between the piston head and the housing through the magnetorheological fluid flow gap  50 . Preferably the controllable damper  32  cantilevered piston length BL is greater than the piston head cylindrical shell gap length HL. 
     Preferably the controllable magnetorheological fluid damper  32  includes an upper damper volume compensator  62 . The volume compensator  62  is proximate the piston rod bearing assembly  54 . Preferably the gas compliance volume compensator  62  is adjacent the upper piston rod bearing  54 , preferably with the bearing holder support structure  55  and the volume compensator housing cavity  82  integrated into an upper bearing gas charged compliance member. Preferably the gas compliance volume compensator  62  is in fluid communication with the first upper variable volume magnetorheological fluid chamber  46 , with the volume compensator proximate the upper bearing and the piston rod, preferably with upper fluid chamber  46  and volume compensator  62  in use oriented on top of lower fluid chamber  48  relative to the force of gravity to allow gas bubble migration upward into volume compensator  62 . Preferably the damper  32  provides for a dry assembly process with magnetorheological fluid filled after the piston  42  is assembled in the housing  34 , preferably through a lower housing end opening  59 , then gas pressure charging of the gas compliance volume compensator  62  through an upper end conduit  90 . Preferably the piston rod bearing assembly bearing holder support structure  55  includes fluid flow conduits  92  to allow flow of fluid into and out of the volume compensator, preferably with conduits  92  providing for greater flow than the magnetorheological piston head gap  50 , preferably with relatively high flow into and out of the volume compensator as compared to piston head flow, with relatively low resistance to flow into volume compensator. 
     Preferably the controllable magnetorheological fluid damper  32  includes an upper strut end head member  66  with an electrical power input  68 . Preferably the upper strut end head member houses the damper control system  72  with electronic control circuit board  74 . In a preferred embodiment the power input is included with a multiple wire array connector  78 , such as a CAN bus electrical connector  78 , preferably with the multiple wire electrical connection providing for receiving outside the strut damper control signals in addition to electrical power input that generates the magnetorheological fluid controllable magnetic field. Preferably the upper strut end head member houses the damper control sensor system, preferably including the upper head end of the magnetostrictive longitudinal sensor  80  that is aligned axis  36  and housed within the piston rod  52 . Preferably the upper strut end head member housing includes the control system for also controlling leveling with the gas spring with a leveling valve  76  for controlling pneumatic leveling of the strut  30 . Preferably the strut and damper with the upper strut end head member  66  is an intelligent self-contained damper system with the head member containing the electronics control system circuit boards  74  that receives sensor inputs such as from the magnetostrictive sensor  80  and accelerometers  120 , and controls the electrical current supplied to the piston head EM coil  94  through the current supply wire circuit  100  to control the damper  32 , preferably with the control electronics including accelerometer sensors  120 , preferably an at least one accelerometer axis acceleration sensed, preferably with a first accelerometer axis  122  aligned with the damper axis  36  (shown in  FIG. 10 ). Preferably the accelerometer sensor  120  is an at least two axis accelerometer, and most preferably a three axis accelerometer, with the first axis  122  aligned with the damper axis  36 , the second and third axis normal to the damper axis  36 . 
     Preferably the controllable magnetorheological fluid damper upper piston rod bearing assembly  54  includes a bearing holder support structure  55  which receives a first upper bearing  56 , a distal second lower bearing  56 , and a piston rod seal  53  to provide the piston rod bearing seal interface length BL. Preferably the controllable magnetorheological fluid damper upper piston rod bearing assembly  54  includes bearing holder  55  which receives at least first bearing  56  and a compliance member cavity  82  for receiving a volume compensator gas compliance member  84 . Preferably the controllable magnetorheologicai fluid damper upper piston rod bearing assembly  54  includes bearing holder  55  which receives at least first bearing  56  and a sensor target magnet holder  86  which receives a target magnet  88  for producing a sensor signal in the proximate magnetostrictive sensor  80  in the non-magnetic piston rod  52 , to provide a sensed measurement of the location of the target magnet along the length of sensor  80  to provide a measurement of the stroke position of the piston head in the damper housing that is used as an input into the damper electronic control system. 
     Preferably the controllable magnetorheological fluid damper piston head  42  includes an insulating encapsulant injected pressurized polymer overmolded electromagnetic coil  94 , with the piston head, overmolded electromagnetic coil and magnetic poles ODs sized to provide the predetermined gap Pgap with the housing inner wall ID, with the gap  50  maintained to inhibit contact with the wall  38  and to provide the fluid flow gap with the coil  94  producing a magnetic field for controlling magnetorheological fluid flow through the gap. The controllable piston head electromagnetic coil  94 , upper and lower magnetic poles  96  with a variable applied current producing a controlling magnetic field for controlling the flow of magnetorheological fluid  40  between the upper and lower chambers  46  and  48 , with the electromagnetic coil  94  comprised of an electrically insulated injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94 . The preferred modular component injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94  is shown in  FIG. 7A-7I . Preferably the EM coil insulated wire  102  is wound on the non-magnetic plastic bobbin  104 , with the coiled wire  102  on the bobbin  104  pressure overmolded with the injected pressurized polymer  110  in the pressurized injection overmold  106  under an applied pressure  107 . Preferably the pressurized injection overmolded EM coil  94  includes first and second wire pins  108  for connection with a current supply wire circuit  100  that supplies the controlling current output by the control system. Preferably the modular component pressurized injection overmolded EM coil  94  is sandwiched between the upper and lower magnetic metal poles  96 , to provide the current controllable EM coil piston head  44 , with the modular component pressurized injection overmolded EM coil  94  overmolded EM coil and poles  96  sized to provide the predetermined gap  50  with the housing inner wall  38 , with the pressurized injection overmolded EM coil magnetic field controlling magnetorheological fluid flow proximate the piston head EM coil. 
     In an embodiment the invention includes a method of making a controllable suspension system for controlling the relative motion between a first body and a second body. Preferably the invention provides a method of making a controllable vehicle suspension system for controlling the relative motion between a first vehicle body and a second vehicle body, most preferably a method of making a vehicle cab suspensions for controlling the motion between a first body cab  22  and a second body frame  24 . The method includes providing the longitudinal damper tubular housing having a longitudinally extending axis, the longitudinal damper tubular housing  34  having inner wall  38  for containing a magnetorheological fluid within the tubular housing. The provided longitudinal damper tubular housing  34  has a first upper end  60  and a second distal lower end  58 , with the housing centered about axis  36 . The method includes providing piston rod bearing assembly  54  having piston rod bearing seal interface length BL for supporting damper piston  42  within the longitudinal damper tubular housing  34 . The method includes providing cantilevered damper piston  42  including piston head  44  and longitudinal piston rod  52 . Cantilever piston rod  52  supports the piston head  44  within the longitudinal damper tubular housing, with the upper piston rod bearing assembly  54  disposed between the longitudinal damper tubular housing and the longitudinal piston rod. The method includes disposing the piston rod bearing assembly  54  in the longitudinal damper tubular housing  34  proximate the first upper end  60 . The method includes receiving the damper piston longitudinal piston rod  53  in the piston rod bearing assembly  54 , wherein the piston head  44  is movable within the damper tubular housing along the longitudinal length of the tubular housing, with the damper piston head providing a first upper variable volume magnetorheological fluid chamber  46  and a second lower variable volume magnetorheological fluid chamber  48 , the damper piston head having a fluid flow gap  50  between the first upper variable volume magnetorheological fluid chamber and the second lower variable volume magnetorheological fluid chamber with a piston head fluid flow interface length HL with contact between the piston head and the damper tubular housing inner wall inhibited. The method includes providing magnetorheological damper fluid  40  and disposing the magnetorheological damper fluid  40  in the damper tubular housing  34 . The damper provides for controlling the relative motion between the first body  22  and the second body  24 . Preferably the method includes providing the longitudinal air strut gas spring  64 , and aligning the longitudinal strut gas spring with the longitudinal damper tubular housing longitudinally extending axis  36  with the strut air spring and magnetorheological damper aligned and packaged together with the gas spring encompassing the magnetorheological damper, preferably with the upper end  60  and the piston rod  52  substantially housed within the gas spring  64 , preferably with the upper end of strut including the upper strut end head member  66  for attachment to the uppermost first or second body. Preferably the upper strut end head member  66  includes the electrical power input and the compressed air gas input, along with the strut control system with electronic control circuit boards  74 , gas spring air sleeve leveling valve  76 . In preferred embodiments the upper strut end head member  66  includes the CAN-Bus electrical connection for receiving outside the strut control signals in addition to electrical power input into the strut. In preferred embodiments the upper strut end head member  66  includes the damper sensor system with the end of magneto-strictive longitudinal sensor  80  that is aligned and housed within the piston rod. Preferably the piston rod bearing assembly  54  is provided with the piston rod bearing seal interface length BL greater than the HL. Preferably the upper volume compensator  62  is provided and disposed proximate the piston rod bearing assembly  54 . Preferably the upper piston rod bearing assembly includes the bearing holder which receives the first upper bearing and the distal second lower bearing to provide the piston rod bearing seal interface length BL. Preferably the upper piston rod bearing assembly includes the bearing holder which receives the at least first bearing and includes the compliance member cavity for receiving the volume compensator gas compliance member. Preferably the upper piston rod bearing assembly includes the bearing holder which receives the at least first bearing and has the sensor target magnet holder which receives the target magnet for the magnetostrictive sensor in the non-magnetic piston rod. Preferably the magnetorheological fluid damper includes the upper volume compensator, with the volume compensator proximate the piston rod bearing. Preferably at least a first cantilevered magnetorheological fluid damper, and at least a second cantilevered magnetorheological fluid damper are disposed between the first body and the second body. Preferably the at least a third cantilevered magnetorheological fluid damper is disposed between the first body and the second body. 
     Preferably the invention includes the method of making the controllable damper for controlling motion. Preferably the method includes providing the longitudinal damper tubular housing having the longitudinally extending axis, the longitudinal damper tubular housing having the inner wall for containing the magnetorheological fluid within the tubular housing, the longitudinal damper tubular housing having the first upper end and the second distal lower end. The method includes providing the piston rod bearing assembly, the piston rod bearing assembly having the piston rod bearing seal interface length BL for supporting the damper piston within the longitudinal damper tubular housing. The method includes providing the cantilevered damper piston, the damper piston including the piston head and the longitudinal piston rod for supporting the piston head within the longitudinal damper tubular housing. The method includes disposing the piston rod bearing assembly in the longitudinal damper tubular housing proximate the first upper end. The method includes receiving the damper piston longitudinal piston rod in the piston rod bearing assembly, wherein the piston head is movable within the damper tubular housing along the longitudinal length of the tubular housing, with the damper piston head providing the first upper variable volume magnetorheological fluid chamber and the second lower variable volume magnetorheological fluid chamber, the damper piston head having the fluid flow gap between the first upper variable volume magnetorheological fluid chamber and the second lower variable volume magnetorheological fluid chamber with the piston head fluid flow interface length HL, with HL&lt;BL and contact between the piston head and the damper tubular housing inner wall inhibited. Preferably the method includes providing the upper volume compensator, and disposing the volume compensator proximate the piston rod bearing assembly. Preferably the method includes providing the upper strut end head member with the electrical power input and disposing the strut end head member proximate the damper tubular housing first end. Preferably the method includes providing the upper piston rod bearing assembly with the bearing holder support structure which receives the first upper bearing and the distal second lower bearing to provide the piston rod bearing seal interface length BL. Preferably the method includes providing the upper piston rod bearing assembly with the bearing holder support structure which receives at least the first bearing and includes the compliance member cavity for receiving the volume compensator gas compliance member. Preferably the method includes providing the upper piston rod bearing assembly with the bearing holder support structure which receives at least the first bearing and includes the sensor target magnet holder which receives the target magnet. Preferably the method includes providing the piston head with the injected pressurized polymer overmolded electromagnetic coil. 
     In an embodiment the invention includes a method of making a controllable damper for controlling motion. The method includes providing a longitudinal damper tubular housing  34  having a longitudinally extending axis  36 . The provided longitudinal damper tubular housing  34  has an inner wall  38  for containing a magnetorheological fluid  40  within the tubular housing. The longitudinal damper tubular housing  34  has a first upper end  60  and a second distal lower end  58 . The method includes providing a piston rod bearing assembly  54 , the piston rod bearing assembly having a piston rod bearing seal interface length BL for supporting a damper piston  42  within the longitudinal damper tubular housing  34 . The method includes providing a damper piston  42 , the damper piston including a magnetorheological fluid piston head  44  and a longitudinal piston rod  52  for supporting the piston head within the longitudinal damper tubular housing  34 . The magnetorheological fluid piston head  44  includes an insulating injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94 . The controllable magnetorheological fluid damper piston insulating encapsulant injected pressurized polymer overmolded electromagnetic coil  94  and magnetic poles  96  preferably having ODs sized to provide the predetermined gap  50  Pgap with the housing inner wall ID, with the gap  50  maintained to inhibit contact with the wall  38  and to provide the fluid flow gap  50  with the coil  94  producing a magnetic field for controlling magnetorheological fluid flow through the gap. The controllable piston head electromagnetic coil  94 , upper and lower magnetic poles  96  with a variable applied current producing a controlling magnetic field for controlling the flow of magnetorheological fluid  40  between the upper and lower chambers  46  and  48 , with the electromagnetic coil  94  comprised of the modular component electrically insulated injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94 . The preferred modular component injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94  is shown in  FIG. 7A-7I . Preferably the EM coil insulated wire  102  is wound on the non-magnetic plastic polymer bobbin  104 , with the coiled wire  102  on the bobbin  104  pressure overmolded with the injected pressurized polymer  110  in the pressurized injection overmold  106  under an applied pressure  107 . Preferably the non-magnetic plastic polymer bobbin  104  and the injected pressurized polymer  110  are comprised of substantially the same base polymer, in a preferred embodiment the bobbin  104  and the pressurized injection overmold polymer  110  are comprised of nylon. In a preferred embodiment the bobbin  104  is comprised of a glass filled nylon and the pressurized injection overmold polymer  110  is comprised of a nylon, preferably a non-glass-filled nylon. In a preferred embodiment the bobbin  104  and the overmold polymer  110  are comprised of a common polymer, preferably with the common polymer comprised of a nylon. Preferably the pressurized injection overmolded EM coil  94  includes first and second wire pins  108  for connection with a current supply wire circuit  100  that supplies the controlling current outputted by the damper control system. Preferably the modular component pressurized injection overmolded EM coil  94  is sandwiched between the upper and lower magnetic metal poles  96 , to provide the current controllable EM coil piston head  44 . The modular component pressurized injection overmolded EM coil  94  overmolded EM coil and poles  96  provide a magnetic field for controlling magnetorheological fluid flow proximate the piston head EM coil. The method includes disposing the piston rod bearing assembly  54  in the longitudinal damper tubular housing  34  proximate the first upper end  60 . The method includes receiving the damper piston longitudinal piston rod  52  in the piston rod bearing assembly  54 , wherein the magnetorheological fluid piston head  44  is movable within the damper tubular housing along the longitudinal stroke length of the tubular housing and the axis  36 , with the damper piston head  44  providing first upper variable volume magnetorheological fluid chamber  46 , second lower variable volume magnetorheological fluid chamber  48 , and the fluid flow gap between the first upper variable volume magnetorheological fluid chamber and the second lower variable volume magnetorheological fluid chamber. The method includes providing a magnetorheological damper fluid  40  and disposing the magnetorheological damper fluid  40  in the damper tubular housing  34  wherein a current supplied to the injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94  controls the flow of the magnetorheological damper fluid  40  proximate the injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94 . The method includes injection molding a polymer  110  with a positive pressure into a overmold  106  containing the wire wrapped electromagnetic coil nonmagnetic plastic bobbin  104  to provide the plastic modular injected pressurized polymer overmolded electromagnetic magnetorheological fluid coil  94  for assembly into the piston head  44 . Preferably the EM coil insulated wire  102  is wound on a non-magnetic plastic bobbin  104  with the coiled wire and bobbin pressure overmolded with an injected pressurized polymer  110  in a predetermined sized cavity overmold  106  under pressure. Preferably the overmolded EM coil  94  includes first and second wire pins  108  for connection with a current supply circuit  100 . Preferably the modular component EM coil  94  is sized and shaped to be sandwiched between upper and lower magnetic metal poles  96 . Preferably the wire  102  is wound on non-magnetic plastic bobbin  104 , and then placed in coil overmold  106 , with insulating injected pressurized polymer nylon polymer  110  overmolded around the bobbin and wire. Preferably the piston head  44  and its overmolded EM coil  94  and poles  96  are sized to provide predetermined gap  50  with the housing inner wall  38 , with the EM coil magnetic field controlling fluid flow  40  proximate the piston head EM coil  94 . Preferably the damper overmolded EM coil  94  in damper  32  provides for controlling the relative motion between first body  22  and the second body  24 , preferably with the damper  32  providing a controllable strut  30 . Preferably the damper overmolded EM coil  94  is utilized in the making of single ended dampers  32  as compared to double ended dampers, preferably with the rod  52  terminating with the piston head  44  that contains the coil  94 . Preferably the piston head  44  is free of internal fluid flow conduits, preferably substantially all fluid flow is between piston head and housing through the magnetorheological fluid flow gap proximate the EM coil OD, preferably with the piston  42  having a constant bearing length with the piston head  44  having no bearing contact with the housing inner wall  38 . In alternative preferred embodiments the piston head  44  has a wear band and contact with the housing wall  38 . Preferably the method includes providing upper volume compensator  62 , and disposing the volume compensator  62  proximate the piston rod bearing assembly  54 . Preferably the volume compensator  62  is adjacent the upper piston rod bearing  54 , preferably with the bearing holder support structure and volume compensator housing integrated into an upper bearing gas charged compliance member. Preferably the gas compliance volume compensator  62  is in fluid communication with the first upper variable volume magnetorheological fluid chamber  46 , with the volume compensator proximate the upper bearing  56  and the piston rod  52 , preferably with the upper fluid chamber  46  and volume compensator  62  in use oriented on the top end of the damper relative to the force of gravity. Preferably the damper components provide for dry assembly of the damper piston in the housing with magnetorheological fluid  40  disposed into the damper after the piston is assembled into the housing, and then gas pressure charging of gas compliance volume compensator  62 . Preferably the piston rod bearing assembly bearing holder support structure  55  includes fluid flow conduits  92  to allow flow of fluid  40  into and out of the volume compensator  62 , preferably with the conduits providing for greater flow than the magnetorheological piston head gap  50 . Preferably the method includes providing upper strut end head member  66  with an electrical power input  68  and disposing the strut end head member  66  proximate the damper tubular housing first end  60 , with the head member providing the controlling current to the EM coil  94  through circuit  100 . Preferably the strut end head member  66  includes the control system  72  with electronic control circuit boards  74 , preferably also including CAN-Bus electrical connection  78  for receiving outside the strut control signals in addition to electrical power input  68 . Preferably the head member  66  includes a damper sensor system, preferably with the end of the magneto-strictive longitudinal sensor  80  that is aligned and housed within the piston rod  52 . Preferably the upper strut end head member housing  66  includes the control system of the magnetorheological damper  32  and the gas spring  64  for controlling pneumatic leveling of the strut. Preferably the damper is an intelligent self-contained damper system with the head member  66  containing the electronics control system that receives sensor inputs and control the electrical current supplied to the EM coil in the piston head to control the damper, preferably with control electronics including accelerometer sensors  120 , preferably with a 2-axis alignment oriented with the axis  36 . Preferably the upper strut end head member housing cavity  66  houses the electronic control sensor system circuit board or boards  74 , preferably with the circuit board plane in alignment with the damper longitudinal axis  36  so the circuit board  74  is substantially vertically oriented in use with a lower end and an upper end, with the circuit board having a first accelerometer  120  and a second accelerometer  120  normal to the first, preferably with first accelerometer sensing axis  122  in alignment with the damper longitudinal axis  36  and the second accelerometer sensing axis  122  oriented perpendicular thereto. Preferably the provided upper piston rod bearing assembly  54  includes bearing holder support structure  55  which receives first upper bearing  56  and distal second lower bearing  56  to provide the piston rod bearing seal interface length BL. Preferably the upper piston rod bearing assembly  54  includes a bearing holder support structure  55  which receives at least a first bearing  56  and includes a compliance member cavity  82  for a volume compensator gas compliance member  84 . Preferably the upper piston rod bearing assembly  54  includes a bearing holder support structure  55  which receives at least a first bearing  56  and includes a sensor target magnet holder  86  which receives a target magnet  88  for the magnetostrictive sensor  80  in the non-magnetic piston rod  52 . Preferably the damper is dry assembled, then filled with magnetorheological fluid  40 , then closed and sealed, preferably through the second lower end  58 , preferably with a lower end stopper member which closes off and seal the damper and provides a lower end attachment member for attaching to the lower moving body  22 , 24 . Preferably the piston rod  52  is hollow with an inner longitudinal chamber which includes a longitudinal magnetostrictive sensor  80 , preferably with the piston rod nonmagnetic such that the permanent magnet target  88  produces a magnetic field sensed along the length of the sensor  80  and detected by the sensor head end preferably in the upper strut end head member  66 . Preferably the piston rod inner longitudinal chamber includes the current supply connection circuit  100 , preferably insulated wires providing connections from the current source in upper strut end head member down through rod and connected to the overmolded EM coil pins  108 . Preferably the lower end of the piston rod inner longitudinal chamber is sealed off, preferably with a sealing member  98  between the lower rod end and piston head, preferably integrated with the rod and piston head attachment joint. Preferably the overmolded EM coil  94  includes an inner overmolded core receiving chamber  112 , overmolded to receive a ferromagnetic core member  114 , preferably with the magnetic metal core member  114  that is received in the inner overmolded core receiving chamber including an extending pole member  116  that extends out of the receiving chamber  112 , preferably having an OD substantially matching the OD of the overmolded coil and the OD of the piston head, with the extending pole member  116  providing the upper magnetic pole member  96  of the piston head  44 . Preferably the OD of the piston head and the overmolded coil are sized to provide the piston gap Pgap between the OD and the damper tubular housing inner wall ID. Preferably the overmolded coil includes the coil guides  95 , preferably with the guides extending longitudinally along the axis  36  such that they extend over the magnetic pole members  96 , with the guides  95  extending radially outward from the OD into the piston gap Pgap towards the damper tubular housing inner wall ID. 
     Preferably the received core member  114  includes an inner core center chamber  118  centered inside the core and extending pole member OD, the inner core center chamber  118  receiving the lower piston rod end and preferably the overmolded coil wire pin connectors  108 , preferably with the sealing member  98  between the lower rod end and overmolded coil  94 , preferably with the inner core center chamber and the lower piston rod end having mating attachment means, preferably such as matching threads for attaching the piston rod  52  with the piston head  44 . Preferably the overmolded EM coil  94  includes a longitudinal center axis hub member  124  with the EM coil wire pins  108  and a radially extending wire coil connecting arm structure spokes ( 126  in  FIG. 9 ) which provides a containment structure for the coil connection wire leads leading from the longitudinal extending wire pins  108  radially outward to the wound coil on the bobbin, and the received core member  114  includes lower end arm receiving radially extending channels  115  for receiving the extending wire coil connecting arms structure  126  including the overmold encapsulated radially extending wire leads. Preferably the overmolded coil includes the coil guides  95  centered around the axis  36  and extending longitudinally along the axis  36  such that they extend partially over an adjacent part of the magnetic pole members  96  proximate the overmolded coil, with the guides  95  extending radially outward from the OD into the piston gap Pgap towards the damper tubular housing inner wall ID, with the guide radial height from the OD sized to the piston gap dimension Pgap. 
       FIG. 11  depicts a magneto-rheological fluid damper  200  according to another embodiment of the invention. In the magneto-rheological fluid strut described above, the magneto-rheological fluid damper  200  may replace the previously-described magneto-rheological fluid damper ( 32  in  FIGS. 1-10 ). Alternatively, the magneto-rheological fluid damper  200  may be used alone to control motion in a suspension system. For example, the magneto-rheological fluid damper  200  may be connected between the body and wheel of a vehicle, in a manner similar to that depicted for the magneto-rheological fluid strut ( 30  in  FIGS. 1-3 ), as illustrated in  FIG. 12 . The vehicle may be a land vehicle or any other type of vehicle. The magneto-rheological fluid damper may be used in a primary vehicle suspension system or in a secondary vehicle suspension system of a vehicle, such as for the suspension system for the vehicle cab or the vehicle seat. Alternatively, the magneto-rheological fluid damper may be used in a semi-active system not coupled to a vehicle. In a primary suspension system, the magneto-rheological fluid damper would be positioned between the tire and chassis of the vehicle. 
     The magneto-rheological fluid damper  200  includes a damper body  202 . In this example, the damper body  202  is made of several parts, including a cylinder part  202   a  and end caps  202   b ,  202   c . However, these parts may be integrated to form a unitary body in alternate embodiments. The end caps  202   b ,  202   c  are coupled to distal ends of the cylinder part  202   a . The cylinder part  202   a  is preferably a hydraulic cylinder. The cylinder part  202   a  contains a reservoir of magneto-rheological fluid (not shown) and a piston (not shown). The piston is coupled to a piston rod  214 , which extends through the end cap  202   b . The piston rod  214  extends through the end cap  202   b  and includes a rod end  203  for coupling to a frame or other devices. 
     In  FIGS. 12 and 13 , the magneto-rheological fluid damper  200  includes a damper body  202 . As in the case of the magneto-rheological fluid damper ( 32  in  FIG. 6F ), in a strut assembly, the longitudinal axis of the damper body  202  would be aligned with a strut spring, such as the longitudinal axis gas spring ( 64  in  FIG. 6F ). The damper body  202  has a hollow interior  204  in which a piston rod guide  206  is arranged. The damper body  202  may be made of a magnetic metal material, preferably a low magnetic metal material such as carbon steel. The magneto-rheological fluid damper  200  may be a monotube damper having a single reservoir  208 , defined below the piston rod guide  206 , for containing a magneto-rheological fluid, with the single reservoir  208  being divided by a piston  215  into a first variable volume magneto-rheological fluid damper chamber  208   a  and a second variable volume magneto-rheological fluid damper chamber  208   b  with at least one EM coil controllable magneto-rheological fluid flow conduit  213  between the first and second chambers for controlling the fluid flow (controllable current supplied to EM coil  219  produces controllable magnetic field strength for a controllable yield strength of the magneto-rheological fluid). The magneto-rheological fluid contains micron-sized magnetizable particles in a carrier fluid. Such magneto-rheological fluid is available from, for example, Lord Corporation, Cary, N.C. In one example, the magneto-rheological fluid contains iron particles and is such that the rheology of the fluid changes from a free flowing liquid to a flow resistant semi-solid with controllable yield strength when exposed to a magnetic field. In one example, the magneto-rheological fluid contains magnetizable particles having a mean particle size of about 1 micron. 
       FIGS. 14-16  show an enlargement of an end portion of the magneto-rheological fluid damper  200 . In comparison to the magneto-rheological fluid damper  32  in  FIG. 6G , this would be the end portion including the upper piston rod bearing assembly ( 54  in  FIG. 6G ). The remaining portions of the magneto-rheological fluid damper  200  not shown may be the same as depicted in  FIGS. 12 and 13 , or may be as shown for the magneto-rheological fluid damper  32  in  FIG. 6G . 
     Referring to  FIG. 14 , the piston rod guide  206  has an annular body  210  with a passage  212  for receiving the piston rod  214 . In an embodiment the piston rod  214  is made of a nonmagnetic material, such as stainless steel. A position sensor  216  is housed within the piston rod  214 . In one example, the position sensor  216  is a magnetostrictive sensor which senses stroke position of the piston along the stroke length of the damper. The position sensor  216  may communicate with an external control system or may include an internal control system. A magnetic field generator  217  may be provided proximate the piston rod  214  to create a magnetic field around the position sensor  216 . The magnetic field generator  217  in one example may be a permanent magnet, which may be in the form of a ring circumscribing the piston rod  214  or position sensor  216 . Alternatively, the magnetic field generator  217  may be an electromagnetic coil that is supplied with current to generate a magnetic field for the position sensor  216 . 
     The annular body  210  includes an inner annular recess  218  circumscribing the passage  212  for receiving the piston rod  214 . A filtering media  220 , which may be annular in shape, is disposed within the annular recess  218 . The magnetic field generator  217  described above may be included in the filtering media  220 , for example, arranged in a pocket or otherwise supported on or in the filtering media  220 . In one example, the filtering media  220  is made of a porous non-magnetic, corrosion-resistant material. In one example, the porous filtering media  220  has pore size less than or equal to 250 nm. In one example, the porous filtering media  220  is made of porous stainless steel having pore size less than or equal to 250 nm. The filtering media  220  includes a pocket  222  inside of which is disposed an inner piston rod seal  224 . The annular body  210  includes a pocket  226  inside of which is disposed an outer piston rod seal  228 . The inner and outer piston rod seals  224 ,  228  are arranged to engage the wall of the piston rod  214 , thereby forming inner and outer seals between the piston rod guide  206  (or annular body  210 ) and the piston rod  214 . The seals  224 ,  228  may be made of suitable sealing materials such as elastomeric materials. 
     The filtering media  220  may include a pocket  230  for receiving a piston rod bearing assembly  232 . When the piston rod  214  is received in the passage  212 , the piston rod bearing  232  is arranged between the piston rod  214  and the filtering media  220 . Further, the piston rod bearing  232  engages with and supports reciprocal motion of the piston rod  214 . Any suitable piston rod bearing  232  capable of supporting reciprocal motion of the piston rod  214  may be used. For example, Glacier Garlock DU or DP-4 bearings, available from AHR International, may be used. These bearings offer a smooth low friction bearing surface and are self-lubricating. The permanent magnet  217  or other suitable magnetic field generating component may be placed above the piston rod bearing  232 , as shown in  FIG. 14 , or may be placed between the piston rod bearing  232  and the inner seal  224 , as shown in  FIGS. 15 and 16 . 
     A fluid chamber  234  is formed between the filtering media  220 , the inner piston rod seal  224 , the piston rod bearing  232 , and the piston rod  214 . The fluid chamber  234  is in communication with the reservoir  208  containing the magneto-rheological fluid. Preferably in operation, magneto-rheological fluid enters the inner annular recess  218  through ports  236  in the base of the piston rod guide  106  and flows through the filtering media  220  into the filtered fluid chamber  234 . That is, the filtering media  220  is disposed in a communication path between the reservoir  108  and the fluid chamber  234 . The filtering media  220  strains or filters out the magnetizable particles in the magneto-rheological fluid and allows the filtered carrier fluid to enter the fluid chamber  234 . In a preferred embodiment, the permanent magnet  217  is mounted at an end of the filtering media  220  to collect magnetic particle dust left unfiltered by the filtering media  220 , preferably providing magnetic filtering of magnetic particles thereby ensuring that the outer piston rod seal  228  is exposed to only filtered non-particulate clear carrier fluid. Protecting the outer seal  228  from particulates prolongs the useful life of the seal. In a preferred embodiment, the filtering media  220  inhibits the migration of magnetic particles from the inner piston rod seal  224  to the outer seal  228 , with the outer seal filtered non-particulate clear carrier fluid having less than one percent of the magnetizable (iron) particle fraction of the magneto-rheological fluid contacting the inner piston rod seal  224 . The filtering media  220  preferably provides a static charge pressure between the two seals  224 ,  228 , and preferably provides that the inner seal  224  is only exposed to fluid dynamic pressure and that the outer seal  228  is only exposed to static pressure. By exposing the outer seal  228  to only static fluid pressure, air ingestion into the reservoir  108  is prevented. 
     The annular body  210  of the piston rod guide  206  further includes an outer annular recess  238 . A diaphragm or bladder  240  is mounted in the outer annular recess  238  and abuts an inner wall  242  of the damper body  202  of the damper body  202 . The diaphragm  240  defines an air-volume which functions as an accumulator  242 . In use, the accumulator  244  is charged with an inert gas such as nitrogen. Although not shown, a port may be provided in the inner wall  242  of the damper body  202  or in the annular body  210  through which gas can be supplied into the accumulator  244 . The diaphragm  240  is exposed to the magneto-rheological fluid in the reservoir  208  through a gap between the annular body  210  of the piston rod guide  206  and the inner wall  242  of the damper body  202 . The accumulator  242  serves to minimize pressure transients in the magneto-rheological fluid in the reservoir  208 , thereby minimizing the risk of cavitation or negative pressure. Thus, the accumulator  244  minimizes pressure transients while the porous filter media  220  filters out pressure transients from the outer piston rod seal  228 . The combined effect is low charge pressures, e.g., on the order of 200 to 300 psig, without risk of air ingestion and with minimal risk of cavitation. Preferably the piston rod guide  206  includes and houses an accumulator, preferably a gas charged accumulator. 
       FIG. 16  shows an alternative example of the magneto-rheological fluid damper  200 . In this example, the annular body  210  of the piston rod guide  206  includes inner annular recesses  260 ,  262 , which hold inner piston rod seal  224  and outer piston rod seal  228 , respectively. This embodiment includes the piston rod guide  206  with a gas charged accumulator. A fluid conduit or passage  264  extends from the base of the annular body  210  and terminates in an inner surface  266  of the annular body  210  adjacent to the piston rod  214 . A filtering media  266 , having properties described for the filtering media  220  ( FIGS. 14 and 15 ) above, is disposed in the passage  264  to filter magnetizable particles from fluid entering the fluid chamber  234  defined between the piston rod  214 , the inner surface  216  of the annular body  210 , and the seals  224 ,  228 . In this example, the annular body  210  includes an outer annular recess  268  which is open at the outer surface  270  of the annular body  210 . The outer surface  270  of the annular body  210  abuts the inner wall  242  of the damper body  202 , thereby defining a chamber  272 , which serves as an accumulator. A piston  274  is disposed in the chamber  272  and can slide within the chamber  272  in response to pressure differential across it. The piston  274  includes sealing members  276 , which engage an inner wall  278  of the annular body  210  and the inner wall  242  of the damper body  202 , thereby partitioning the chamber  272  into a gas chamber  278  and a magneto-rheological fluid chamber  280 . The gas chamber  278  may be filled with an inert gas such as nitrogen. Although not shown, a port may be provided in the damper body  202  or annular body  210  through which gas can be supplied to the gas chamber  278 . The magneto-rheological fluid chamber  280  is in communication with the reservoir  208  through a gap between the base of the annular body  210  and the inner wall  242  of the damper body  202  or through ports in the base of the annular body  210 . The accumulator provided by the chamber  272  and piston  274  serves the same purpose as described for the accumulator  244  ( FIGS. 14 and 15 ) above. Preferably the piston rod guides include and house a gas charged accumulator, preferably between the piston rod  214  and the damper body  202 , and preferably proximate the seal  224 . 
       FIG. 17  depicts an exemplary vehicle  314  with magneto-rheological fluid dampers  200  between the body  310  and the wheels  312  of the vehicle. The magneto-rheological fluid dampers  200  are in communication with a suspension control system  316  including a control unit  318 . In one example, the control unit  318  receives sensor signals from sensors, which may reside in the dampers  200 , on the vehicle  314  and calculates forces at the dampers  200 . These desired force values are converted and amplified into current, e.g., via closed loop current control, to the dampers  200 . In one example, the sensors (not shown) are accelerometers, and the control unit  318  receives signals from the accelerometers and uses those signals to calculate forces at the dampers  200 . In a preferred embodiment, five or six accelerometers are arranged in different locations and orientations in the vehicle in order to provide the sensor signals to the control unit  318 . In another example, the sensors include accelerometers and roll-rate sensors, and the control unit  318  receives signals from the accelerometers and roll-rate sensors and uses those signals to calculate forces at the dampers  200 . In a preferred embodiment, three accelerometers and two roll-rate sensors are arranged in different locations in the vehicle in order to provide the sensor signals to the control unit  318 . The vehicle  314  in preferred embodiments is a land vehicle, preferably a wheeled land vehicle which preferably transports variable payloads over varied land conditions, such as a truck or off-road vehicle, as shown in  FIG. 17 , or may be another type of vehicle. In preferred embodiments the magneto-rheological fluid dampers are primary vehicle suspension magneto-rheological fluid dampers in the primary suspension of the vehicle between the vehicle body  310  and the wheels  312 . In alternative embodiments the magneto-rheological fluid dampers are secondary vehicle suspension magneto-rheological fluid dampers in the secondary suspension systems of vehicles, such as for the suspension system for the vehicle cab or the vehicle seat. Alternatively, the magneto-rheological fluid dampers  200  may be used in a semi-active suspension system that is not coupled to a vehicle. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from the spirit and scope of the invention. Thus, it is intended that the invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. It is intended that the scope of differing terms or phrases in the claims may be fulfilled by the same or different structure(s) or step(s).