Abstract:
A rotary vane magnetorheological energy absorber, which enables a longer stroke capability in a more compact configuration than conventional magnetorheological devices, is disclosed. This novel device design is attractive for applications where long stroking capability, high force dynamic range, device size, and device weight are important. The improved magnetorheological energy absorber comprises an internal or external flow valve and a hollow body enclosing fixed and rotary vanes as well as magnetorheological fluid. Fluid flow in the valve is restricted as a solenoid is activated, thus adjusting the capability of the device to react torque. Various flow valve configurations are disclosed, as well as various motion translation mechanisms for translating linear motion to rotary motion for use of the rotary vane magnetorheological energy absorber. The improved design minimizes the amount of magnetorheological fluid required as compared to conventional linear stroke energy absorbers, thus minimizing device weight.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application derives priority from U.S. provisional patent application 61/268,419 filed 12 Jun. 2009, and is a continuation-in-part of U.S. application Ser. Nos. 11/818,582 filed Jun. 15, 2007 now U.S. Pat. No. 7,874,407 and 12/378,275 filed Feb. 12, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to energy absorbers and energy absorption systems, and more particularly, to a rotary magnetorheological damper for shock and vibration energy absorption systems. 
     2. Description of Prior Art 
     The primary function of a shock and vibration protection system is to minimize the potential for equipment damage and/or personnel injury during shock and vibration loading. Such systems are important for vehicular applications, including aircraft, ground vehicles, marine vehicles, etc. Severe shock events may include harsh vertical or crash landings of aircraft, under body explosions of military ground vehicles, horizontal collisions of automobiles, and severe wave-to-hull impact of high speed watercraft. Lower amplitude shock and vibration tend to result from normal operation of such vehicles, including aircraft air loads or rotor loads, ground vehicles traversing rough terrain, etc. The severity of equipment damage and/or personnel injuries can be considerably minimized if the vehicles are equipped with shock and vibration protection systems. 
     Most current shock and vibration protection systems are passive, in that they cannot automatically adapt their energy absorption as a function of payload weight or as a function of real-time environmental measurements such as shock level, impact velocity, vibration levels, etc. Moreover, some energy absorbers are essentially rigid and do not stroke until the load reaches a tuned threshold. Because of this, these systems provide no isolation of vibration. This motivates the development of a shock and vibration protection system that utilizes an electronically adjustable adaptive energy absorber that can provide adaptive energy absorption for enhanced crashworthiness as well as vibration mitigation. 
     Magnetorheological (MR) technology is particularly attractive for shock and vibration protection systems as an MR fluid based device can offer an innovative way to achieve what is effectively a continuously adjustable energy absorber, in combination with a real-time feedback controller, can automatically adapt to payload weight and respond to changing excitation levels. With its ability to smoothly adjust its load-stroke profile, MR energy absorbers can provide the optimum combination of short stroking distance and minimum loading while automatically adjusting for the payload weight and load level. Furthermore, MR energy absorbers offer the unique ability to use the same system for vibration isolation. 
     One key challenge in vehicular applications involving MR energy absorbers is the device weight and size associated with providing sufficient stroke and force capability. Often, a large and massive energy absorbing device is not a possibility due to design and structural constraints. MR energy absorbers having large controllable range, stroke, and bandwidth are needed to provide adaptation to payload weight, shock energy, speed, and required energy absorption. Many MR energy absorbers for shock and vibration isolation mounts have been disclosed such that the damping level can be controlled in feedback by applying a magnetic field (U.S. Pat. No. 5,277,281 to J. D. Carlson et al., U.S. Pat. No. 6,279,700 to H. Lisenkser et al., U.S. Pat. No. 6,311,810 to P. N. Hopkins et al., U.S. Pat. No. 6,694,856 to P. C. Chen and N. M. Wereley, U.S. Pat. No. 6,953,108 to E. N. Ederfass and B. Banks, U.S. Pat. No. 6,481,546 to M. L. Oliver and W. C. Kruckemeyer, and U.S. Pat. No. 6,983,832 to C. S. Namuduri et al). See also, U.S. Pat. No. 6,694,856 issued Feb. 24, 2004 to Chen et al. which includes test data obtained from a COTS Lord Rheonetics® MR damper including force vs. piston behavior. The size and weight of these conventional linear-piston MR damper designs for such applications can make their use prohibitive. Hence, the development of more compact MR devices with the capability to adapt to shock and vibration conditions is of great interest. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a novel compact rotary vane MR energy absorber in which linear motion is converted into rotary motion so as to increase damper stroke while maintaining a compact profile. In this MR energy absorber, a rotor seated inside a hollow MR-fluid-filled body is equipped with “vanes” that rotate on a shaft inside the hollow body (vane herein being defined as any blade, fin or fluid foil mounted in a fixed position or movable, and extending either radially or axially with respect to an axis and operative on a fluid). The rotating vane(s) operate on the MR fluid interdependently with an internal stator (for example, a fixed vane) to propagate MR fluid flow through defined channel(s). Solenoid coils also mounted within the body control the MR fluid flow through those channels by changing the rheological properties of the fluid with the presence of a magnetic field, allowing control over the a reaction force on rotor vanes which, because the vanes are offset from the shaft, cause a reaction torque-moment on the shaft. The torque-moment serves as a damping force and can be further converted into a linear damping force with a rotary-to-linear motion converting mechanism. 
     A variety of different configurations are possible for the rotating vane(s) and internal stator. 
     In one exemplary embodiment, the internal stator comprises fixed vanes protruding inward from the body. The fixed vanes and rotary vane(s) separate the internal volume into two or more fluid chambers. The rotary vane(s) create a pressure-differential between the chambers. The fluid chambers are in communication with each other through either internal valves enclosed in the vanes or external by-pass valves, allowing MR fluid to flow from chamber to chamber. For example, a throttle valve mode is utilized (see, e.g., U.S. Pat. No. 5,842,547) in order to increase damping force due to a hydro-amplification effect. Different throttle valves including typical tubular or rectilinear flow mode valves and porous valves are disclosed. Electro-magnetic solenoid coils are enclosed in the corresponding valves to provide a variable magnetic field to control the rheology (apparent viscosity) of the MR fluid. As a shaft rotates along the center axis of the cylindrical body, radially-protruding rotary vane(s) mounted thereon force the MR fluid to flow through one or more valves from one fluid chamber to another. Thus, the pressure difference between the valve(s) leads to a resistant torque moment of the MR energy absorber. The torque moment can be further converted into a linear damping force with a rotation/linear motion converting mechanism such as, but not limited to a cable reel, a mechanical gearing, helical screw, etc. The resulting damping force can be varied as the applied electro-magnetic field is varied. 
     In another exemplary embodiment, the rotary vanes are mounted axially on the shaft and the internal stator includes fixed vanes protruding proximate the rotary vanes. The cooperating rotary and fixed vanes operate in shear mode such that, as the shaft and rotary vane(s) rotate, the MR fluid between the rotary vane(s) and the fixed vane(s) and/or body is sheared such that a resistant torque can be applied on the shaft. Electro-magnetic solenoid coils provide a variable magnetic field to control the rheology (apparent viscosity) of the MR fluid and hence the torque moment on the rotary vanes and shaft. Again, the torque moment of the shaft can be further converted into a linear damping force with a rotation/linear motion converting mechanism as described above. The resulting damping force can be varied as the applied electro-magnetic field is varied. 
     The key benefits and payoffs of the proposed rotary vane MR energy absorber technology are as follows:
         increases stroke limit of the energy absorber while maintaining a compact damper profile;   reduces device weight compared to conventional linear stroke MR energy absorbers for a given stroke and force requirement;   provides a controllable damping force for shock and vibration protection applications in which protection for personnel and/or equipment can be significantly enhanced;   eliminates the requirement of the air accumulator (used for compensating rod volume in linear stroke energy absorbers), which increases device size and can provided unwanted stiffness and/or preload force;   passive damping for fail-safe, reduced or no power operation.       

     Other features, advantages and characteristics of the present invention will become apparent after the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments and certain modifications thereof when taken together with the accompanying drawings in which: 
         FIG. 1  is an isometric view (with a transparent body) of one embodiment of the rotary vane MREA; 
         FIG. 2  is a cross sectional view of the embodiment of the rotary vane MREA in  FIG. 1 ; 
         FIG. 3  is an isometric view (with a transparent body) of one optional embodiment of the rotary vane MREA with a by-pass valve body; 
         FIG. 4  is a cross sectional view of the optional embodiment of the rotary vane MREA in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of a rectilinear flow valve in the by-pass valve body of the optional embodiment; 
         FIG. 6  is a cross-sectional view of a porous flow valve in the by-pass valve body of the optional embodiment. 
         FIG. 7  is a perspective drawing with a sectioned quarter of a fourth embodiment of the rotary vane MREA of the present invention. 
         FIG. 8  is a cross-sectional view of the axial rotary vane structure used in the fourth embodiment of  FIG. 7 . 
         FIG. 9  is a perspective side cross section of the rotary vane MREA incorporating a multiple-concentric-axial rotary vane structure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Generally, the invention disclosed herein is a novel compact rotary vane magnetorheological (MREA) energy absorber in which linear motion is converted into rotary motion and is subjected to a rotary damping force, the rotary configuration allowing increased damper stroke within a compact mechanical profile. A rotor is seated inside a hollow MR-fluid-filled body. The rotor includes vanes mounted on a shaft that together rotate inside the hollow body. The rotating vane(s) operate interdependently with an internal stator (for example, one or more fixed vanes) to propagate MR fluid flow through defined channel(s). Solenoid coils mounted within the body control the rheology (apparent viscosity) of the MR fluid flowing through those channels, allowing control over the reaction force on the vanes. Since the rotary vanes(s) are offset from the shaft, the controllable force allows adjustment of the torque-moment on the shaft. This allows adjustment of the damping force, which can be further converted into a linear damping force with a rotary-to-linear motion converting mechanism. 
     The invention provides a rotary vane MR energy absorber to provide adaptive damping force for shock and vibration protection applications. The conversion of the rotary motion to the linear motion makes it possible to construct a shock absorber to provide a larger stroke within a compact profile. 
     A first embodiment of the rotary vane MREA of the present invention is depicted in  FIG. 1 . In this embodiment, the MREA comprises a cylindrical damper body  10  defining an internal cylindrical volume containing MR fluid. An internal stator comprising one or more fixed vane structures  22  protrudes radially into the internal volume of damper body  10 . A shaft  30  is rotatably mounted in the damper body  10  and traverses the internal volume and one or more rotary vane structures  24  protrude radially from the shaft  30  within the cylindrical volume. In addition, a rotation/linear motion converting mechanism (here a cable reel including a cable reel wheel  52  equipped with a cable  54 ) is coupled to the shaft  30 . Both vanes  22 ,  24  are rectangular structures seated radially across the cylindrical volume, and the rotary vane  24  is driven by the center shaft  30  which is made of magnetic steel. Each vane  22 ,  24  is made of vertical magnetic steel plates  26  arranged in columns and mounted in parallel within a non-magnetic metal frame  21 . The vanes  22 ,  24  partition the internal volume into chambers. Between the steel plates  26  are defined fluid channels, here valve openings  28 , through which MR fluid in the cylindrical volume can communicate from chamber-to-chamber. The boundary edges of the fixed vane  22  may be attached to or integrally formed with the cylindrical body  30 . Each rotary vane  24  as well as the center shaft  30  can rotate along the center axis of the cylindrical body  30 . The edges of the rotary vane  24  in contact with the interior cylinder surfaces may be configured with wiper seals  33 . It should be apparent that turning the shaft  30  counterclockwise will rotate the rotary vane(s)  24  toward the fixed vane  22 , creating a pressure differential in the chambers there between. This pressure differential prompts the MR fluid within the cylindrical volume of body  30  to flow through the valve openings  28  between steel plates  26 , equalizing the chambers. 
     A solenoid  40  comprising a plurality of coils is wound about the middle of the center shaft  30 , and a protective plastic anti-abrasion tube  42  is placed around the solenoid coils  40 . The center shaft  30 , the vertical plates  26  in the vane structures  22 ,  24 , and the MR fluid in the valve openings  28  constitute a closed-loop magnetic field path. In this configuration, a magnetic field is generated when an electric current is applied to the solenoid coil  40 , and the magnetic field across the valve openings  28  is perpendicular to the flow direction of the MR fluid. The upper and lower end of the center shaft  30  may be supported by ball bearings  31  located in upper and lower end plates of the cylindrical body  10 , respectively. One end of the center shaft  30  is extended out of the upper end plate of the cylindrical body  10  through a rod seal, and is connected with the rotation/linear motion converting mechanism (here a cable reel). As mentioned above, the cable reel comprises a cable reel wheel  52  and a high-strength steel cable  54 , the cable reel wheel  52  being rotatably fixed to the upper end of the center shaft  30 . 
     As shown in the top cross-sectional view of  FIG. 2 , given one fixed vane  22  and one rotary vane  24 , the internal volume of the cylindrical body  10  is divided into two fluid chambers by the vane structure. The MR fluid in the fluid chamber  1  can communicate with the MR fluid in the fluid chamber  2  through the valve openings  28 . As a magnetic field is applied to the MR fluid through the valve openings  28 , the iron particles in the MR fluid form column-like structures along the magnetic field such that its apparent viscosity is increased. Thus the valve opening  28  in this embodiment work as a magnetic field-regulated flow valve. In operation, a linear motion of the cable  54  due to a shock/crash event can is converted into a rotation by the cable reel wheel  52 , and then further transferred to the center shaft  30  and rotary vane  24 . The rotation of the rotary vane  24  in the cylindrical volume forces MR fluids in one fluid chamber to flow through the valve openings  28  into the other fluid chamber. The flow resistance as the MR fluid flows through the valve opening  28  leads to a pressure difference across the flow valve. The pressure difference yields a torsional moment applied to the rotary vane  24  and further a linear stroking force applied to the cable  54  of the reel wheel  52 . The stroking force can be regulated as the current applied to the solenoid coil  40  is varied since the pressure difference required to force the MR fluid to flow through the valve can be influenced by the magnetic field. Since the apparent viscosity of the MR fluid is a monotonic increasing function of the magnetic field, the pressure resistance in the flow valve and then the resultant stroking force can increase as the applied magnetic field increases. 
     One skilled in the art should readily understand that there are other suitable vane structures, as well as mechanical means for conversion of linear motion due to a shock/crash event into rotation. For example, rather than a cable reel wheel  52  and cable  54  a rack and pinion gear may be used, or a shaft and ballscrew may be used, such that linear motion of the rack/shaft or pinion/ballscrew turns the other. 
     Referring to  FIG. 3 , a second embodiment of the invention is a rotary vane MREA with an external by-pass valve body  60 , rather than internal valve openings  28 . This embodiment likewise comprises a cylindrical damper body  10  with an internal cylindrical volume, fixed/rotary vane structures  22 ,  24 , a rotation/linear motion converting mechanism (cable reel  52  and cable  54 ). The by-pass valve body  60  is external to body  30  and forms a conduit in which a rectilinear flow valve  62  is embedded. The vane structure may be identical, similarly including a fixed vane  22  and a rotary vane  24 . Both vanes  22 ,  24  are rectangular and seated across the radial direction of the cylindrical volume, and between the fixed and rotary vane  22 ,  24  is a center shaft  30 . The vane structures  22 ,  24  and center shaft  30  can be made of light metal materials, but there are no valve openings on or in the vanes themselves (as ref.  28  in  FIGS. 1-2 ). The boundary edges of the fixed vane  22  are integrated with the internal surface of the cylindrical volume of the damper body  10 . The rotary vane  24  as well as the center shaft  30  can rotate along the center axis of the shaft  30 . The edges of the rotary vane  24  in contact with the internal wall of damper body  10  are again configured with wiper seals  33 . The by-pass valve body  60  is connected to the cylindrical damper body  10  using hydraulic tubes  72 . One end of the by-pass valve body  60  is connected to the internal volume of the damper body  10  at one side of the fixed vane  22  by a through hole  74 , and the other end of the by-pass valve body is connected to the internal bore at the other side of the fixed vane  22  by the another through hole  74 . The upper and lower end of the center shaft  30  is supported by ball bearings  31  located in the upper and lower end plates of the cylindrical body  10 , respectively. One end of the center shaft  30  is extended out of the upper end plate of the cylindrical body  10  through a rod seal, and is connected with a rotation/linear motion converting mechanism, such as a cable reel as per above. The cable reel may comprise a cable reel wheel  52  and a high-strength steel cable  54 , and the cable reel wheel  52  is fixed to the upper end of the center shaft  30 . 
     As shown in the top cross-sectional view of the second embodiment in  FIG. 4 , the internal bore in the cylindrical body  10  is divided into two fluid chambers  1 ,  2  by the vane structure  22 ,  24 . At each side of the fixed vane  22 , there is a through hole  74  on the wall of the cylindrical damper body  10 . On the outer surface of the cylindrical body  10 , each hole  74  is connected with one end of the by-pass valve body  60 , respectively. Given this configuration, the MR fluid in the fluid chamber  1  can communicate with the fluid in the fluid chamber  2  through the by-pass valve  62 . 
       FIG. 5  is a cross-sectional view of a rectilinear flow valve  62  in the by-pass valve body  60  as in  FIGS. 3-4 . In the by-pass valve body  60  as shown in  FIG. 5 , a typical rectilinear valve  62  is included. The rectilinear valve  62  comprises a coil bobbin  64 , a flux return tube  65  and an electro-magnetic solenoid of one or more coils  66 . Both the coil bobbin  64  and flux return tube  65  are made of magnetic steel. The flow valve  62  is configured such that the coil bobbin  64 , flux return tube  65  and the MR fluid flowing through the flow path constitute a closed-loop magnetic field path, and the magnetic field generated by the solenoid  66  is perpendicular to the flow direction of the MR fluid. In operation, a linear motion of the cable ( FIG. 3 , ref.  54 ) due to a shock/crash event can be converted into a rotation by the cable reel wheel  52  and further transferred to the center shaft  30  and rotary vane  24 . The rotation of the rotary vane  24  in the cylindrical volume forces MR fluids in one fluid chamber to flow through the by-pass flow valve(s)  62  into the other fluid chamber. The flow resistance as the MR fluid flows through the by-pass valve(s)  62  leads to a pressure difference across the flow valve  62 . The pressure difference yields a torsional moment applied to the rotary vane  24  and further a linear stroking force applied to the cable  54  of the reel wheel  52 . The stroking force can be regulated as the current applied to the solenoid coil  66  is varied since the pressure difference required to force the MR fluid to flow through the valve  62  can be influenced by the magnetic field. As the applied magnetic field is stronger, the pressure resistance in the flow valve  62  is bigger since the apparent viscosity of the MR fluid is a increasing monotonic function of the magnetic field. 
     A third embodiment of the rotary vane MREA is similar to the second embodiment except that a porous flow valve  82  is employed in the by-pass valve body  60  instead of a rectilinear valve  62  as in  FIG. 5 . As shown in  FIG. 6 , the by-pass valve body  60  here contains a porous flow valve  82  comprising a nonmagnetic metal tube  84  internal to the valve body  60 , a solenoid coil  86  about the tube  84 , a flux return tube  87 , porous media  88  and valve-to-body hydraulic tube connections  72  as above. The porous media  88  may comprise multiple sphere beads or other fillers randomly or orderly-packed inside the non-magnetic metal tube  84 . The solenoid coil  86  is wrapped around the metal tube  84 , and the flux return tube  87  is placed around the solenoid coil  86 . The hydraulic tubes  72  are used to connect the by-pass valve body  60  to the cylindrical damper body  10  as previously described. An important feature of the porous valve of  FIG. 6  is that both the MR fluid and the porous media  88  are placed in the center of the solenoid and function as a magnetic flux guide. Since a tortuous flow path exists through the packed porous media  88 , the flow of the MR fluid through the porous valve  82  is not unidirectional and the local magnetic field has various orientations relative to the velocity of the MR fluid. In such a configuration, mean values of the magnetic field applied to the MR fluid depend on material properties and the geometric shape of the porous media  88 , and the valve design is flexible. Comparatively, in conventional rectilinear flow mode valves, the fluid channel has to be configured so that the MR fluid flows perpendicular to the magnetic field, which places numerous geometric constraints on valve and magnetic coil design. Another feature of the porous valve  82  that improves efficiency and effectiveness is the tortuous fluid channels existing in the porous media. First, the active fluid channel length can be increased by the curvedness of the fluid channel, and second, both yield and viscous behavior of the MR fluid can be affected by the applied magnetic field due to the capillary style of channel. 
     One skilled in the art should readily understand that there are other suitable configurations for the porous valve. For example, rather than porous media included in center nonmetal tube and a coil wrapped around the tube, a tubular valve may be use, in which the porous media is sandwiched between an inner tube and a outer tube and the coil is wrapped around the inner tube. A variety of porous valve configurations are shown and described in Applicant&#39;s co-pending U.S. application Ser. No. 11/818,582, which is herein incorporated by reference. 
     In operation, when the cable reel wheel  52  rotates due to a shock/crash event, the rotary vane  24  pushes the MR fluid from, for example, the MR fluid chamber into one end of the by-pass valve body  60  through the hydraulic tube. As the MR fluid flows into the porous valve  82 , the MR fluid passes through the packed porous media  88  and is exposed by an applied magnetic field. The MR fluid then exits the porous valve  82  and enters the MR fluid chamber  2  through the hydraulic tube  72 . As shown above, when the rotary vane  24  rotates, the MR fluid must pass through the flow path in the porous media  88  in which the yield stress and viscosity of the MR fluid therein are controlled by an applied magnetic field. 
     A fourth embodiment of the rotary vane MREA comprises one or more axially-mounted rotary vane(s) mounted on the shaft (rather than radial vanes  24 , and a cooperating stator structure, which operate by a shear motion rather than pressure differential. The axially-mounted rotary vane(s) shear through the MR fluid, and shear resistance creates a torque-moment and damping force. A solenoid-induced magnetic field controls the shear resistance to rotation of the axially-mounted rotary vane(s), as before allowing control over the torque moment on rotor and shaft. The torque-moment can be further converted into a linear damping force with a rotary-to-linear motion converting mechanism. 
     The fourth embodiment of the rotary vane MREA of the present invention is depicted in the perspective drawing of  FIG. 7 . In this embodiment, the MREA comprises a cylindrical damper body  10  defining an internal cylindrical volume containing MR fluid. The cylindrical damper body  10  may or may not be equipped (or formed) with an internal stator structure as described below. In the illustrated embodiment the damper body  10  is comprises of three separate parts: a cylindrical midsection  11 , and opposing disk end plates  13  screwed or otherwise attached to midsection  11 . 
     As above, a shaft  30  is rotatably mounted in the damper body  10  via shaft bearings  31  (and/or bearing seals) and traverses the internal volume. At least one axially-oriented (generally cup-shaped) rotary vane structure  124  is driven by the shaft  30  within the cylindrical volume, and may be attached to the shaft  30  by its closed end. As described below, a plurality of progressively smaller rotary vane structures  124  may optionally be mounted on the same shaft  30  in a concentric manner. 
       FIG. 8  is a cross-sectional view of the axial rotary vane structure  124  including a closed end  128  with keyed aperture  129  for attachment to shaft  30 , and annular sidewalls  126  that rotate within the confines of the cylindrical body  10 . The axial rotary vane structure  124  is defined by a plurality of annular grooves  130  spaced along the interior surface of the annular sidewalls  126 . 
     Referring back to  FIG. 7 , the rotary vane structure  124  rotates about an internal stator which is herein formed as solenoid coils  40  wound about a bobbin  150 . Bobbin  150  is stationery with respect to the body  10  and may be attached or integrally formed with end plate  12 . Bobbin  150  is defined by a plurality of annular grooves  160  for winding the solenoid coils, and the grooves  160  in bobbin  150  correspond to the annular grooves  130  spaced along the interior surface of the annular sidewalls  126 . The rotary vane structure  124  is very slightly smaller in diameter than the interior of the body  10  to allow free rotation and to define an MR fluid gap  140  between the rotary vane structure  124  and body  10 . Similarly, the rotary vane structure  124  is very slightly larger in diameter than the bobbin  150  to allow free rotation there about and to define an MR fluid gap  140  between the rotary vane structure  124  and bobbin  150 . The solenoid coils  40  in the grooves  160  of bobbin  150  may be connected externally through a central wire path  172  through the bobbin  150 , and sealed by a wire seal plug  174  or suitable filler to prevent fluid leakage between the wire and cylindrical body  10 . In this manner, the coils  40  may be connected to an external power supply. The shaft  30  protrudes out at one end of the body  10 , here through side plate  13 . 
     In operation, fluid shear flow occurs down the entire axial length of the rotary vane structure  124  within MR fluid gap  140  occurring between the rotary vane  124  and the cylindrical body  10  as well as the gap  140  between the rotary vane structure  124  and the bobbin  150 . 
     As above, a rotation/linear motion converting mechanism such as a cable reel may be coupled to the protruding end for linear-to-rotary motion translation. The axial rotary vane  124  is made of magnetic steel, and rotates along with the center shaft  30  along the center axis of the cylindrical body  10 . Turning the shaft  30  will turn the rotary vane  124  and create a shearing effect against the MR fluid resident in the gap  140  between the rotary vane structure  124  and body  10 , as well as that between the rotary vane structure  124  and bobbin  150 . Thus, both internal and external surfaces of the rotary vane structure  124  contact the MR fluid. 
     The cylindrical body  10 , the rotary vane  124 , and the MR fluid in the in the MR fluid gaps  140  constitutes a closed-loop magnetic flux path around each coil  40  (shown by arrows). In this configuration, a magnetic field is generated when an electric current is applied to the solenoid coils  40  in the grooves  160  of bobbin  150 , and the magnetic field across the rotary vane  124  is perpendicular to the flow direction of the MR fluid in the flow gaps between the rotor vane and the body/fixed vane  130 . As the magnetic field is applied to the MR fluid in the MR fluid gaps  140 , the iron particles in the MR fluid form column-like structures along the magnetic field such that its apparent viscosity is increased. In operation, a linear motion imparted to the rotation/linear motion converting mechanism (such as cable reel, not shown) is converted to rotary motion transmitted to the center shaft  30  and axial rotary vane  124 . The rotation of the rotary vane  124  in the cylindrical volume creates a shearing action against the MR fluids in flow gaps  140 . The shear resistance of the MR fluid yields a torsional moment applied to the rotary vane  124  and further a linear stroking force applied to the rotation/linear motion converting mechanism. The stroking force can be regulated as the current applied to the solenoid coils  40  is varied since the MR fluid shear resistance can be influenced by the magnetic field. 
     The annular grooves  130  in the rotary vane  124  serve to increase the flux density in the outer gap  140  between the rotary vane structure  124  and body  10 . 
     The number of solenoid coils  40  is preferably a multiple of the number of the grooves  130  in vane  124 , and may be equal in number. The variable magnetic field leads to a controllable shear stress in the MR fluid and a controllable resistive torque of the damper. 
     If desired, optional features such as a fluid level indicator (window) may be provided in body  10  to monitor the quantity of the MR fluid in the damper, and/or an MR fluid vent may be employed to compensate fluid volume variation due to temperature fluctuation. 
     As mentioned briefly above, multiple co-axial rotary vanes  124  may be mounted concentrically on the shaft  30  for combined rotation. In this case to ensure maximum shear resistance, the stator structure is preferably expanded to extend a stationery vane between each concentric pair of rotary vanes. 
       FIG. 9  is a perspective side cross section of a rotary vane MREA incorporating a multiple-concentric-axial rotary vane structure. A shaft  30  is rotatably mounted in the damper body  10  via shaft bearings  31  and bearing seals  32 , and traverses the internal volume. The rotary vane structure  224  here comprises three concentric cup-shaped annular sidewalls  225 - a,b,c  riding on the shaft  30  within the cylindrical volume, all attached to the shaft  30  by their closed end in a concentric manner for common rotation within the confines of the cylindrical body  10 . Both walls of the innermost sidewalls  225 - b,c , plus the inner wall of the outermost sidewall  225 - a  are defined by grooves  230  spaced along the surface which provide increased magnetic flux density. The rotary vane structure  124  rotates about an internal stator structure which is herein formed as solenoid coils  40  wound about a bobbin  150 . Bobbin  150  is stationery with respect to the body  10  and may be attached or integrally formed with end plate  12 . Bobbin  150  is defined by a plurality of annular grooves  160  for winding the solenoid coils, and the grooves  160  in bobbin  150  correspond to the grooves  230  in annular sidewalls  225 - a,b,c . Sidewalls  225 - a,b,c  are progressively smaller in diameter to allow free rotation and to define an MR fluid flow path between each and body  10 . The stator structure also includes one or more stationary vanes  222 - a,b  (here two) each fixed to the cylinder body  10  and each dividing the interim space between sidewalls  225 - a,b,c  into two gaps. Similar grooves  260  are applied in stationary vanes  222 - a,b  to increase flux density in the gaps. The increased shear area of the rotary vane structure  224  increases the output resistant torque or damping force while maintaining a compact damper volume. 
     The solenoid coils  40  in the grooves  160  of bobbin  150  may be connected externally through a central wire path  172  and sealed by a wire seal plug  174  for connection to an external power supply. If necessary, additional bearings  250  may be provided to support the rotor vane structure  224 . The shaft  30  protrudes out at one end of the body  10  and a rotation/linear motion converting mechanism as per above may be connected. Turning the shaft  30  will turn all the annular sidewalls  225 - a,b,c  of rotary vane  224  and will create an enhanced shearing effect against the MR fluid between the rotary vane structure  224 , body  10 , and bobbin  150 . The cylindrical body  10 , the rotary vane  224 , and the MR fluid the in the MR fluid flow paths  140  constitutes a closed-loop magnetic flux path (shown by arrows). The magnetic field is generated when an electric current is applied to the solenoid coils  40  in the grooves  160  of bobbin  150 , and the magnetic field across the rotary vane  124  is perpendicular to the flow direction of the MR fluid in the flow gaps between the annular sidewalls  225 - a,b,c  of rotary vane  224  and the interim fixed vanes  222 - a,b  and bobbin  150 . Operation is similar to the embodiment of  FIG. 7 . The rotation of the rotary vane  224  in the cylindrical volume creates a shearing action against the MR fluids, the shear resistance of the MR fluid yields a torsional moment applied to the rotary vane  224  and a stroking force applied to the rotation/linear motion converting mechanism. The stroking force can be regulated as the current applied to the solenoid coils  40  is varied since the MR fluid shear resistance can be influenced by the magnetic field. 
     Other optional features for this embodiment are similar to the single rotary vane damper of  FIG. 7 . 
     In all the above-embodiments, a rotary MR energy absorber is disclosed that increases stroke limit of the energy absorber while maintaining a compact damper profile, thereby reducing weight compared to conventional linear stroke MR energy absorbers for a given stroke and force requirement. 
     Therefore, having now fully set forth the preferred embodiment and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept. It is to be understood, therefore, that the invention may be practiced otherwise than as specifically set forth in the appended claims.