Abstract:
A rotary damper is disclosed. The rotary damper comprises a first and a second plurality of plates disposed within a housing. The first and second pluralities of plates are interleaved and are capable of moving relative to one another. A magnetorheological fluid contained within the housing resides in the interleave of the first and second plurality of plates. A magnetic flux generator drives a magnetic flux through the magnetorheological fluid in the interleave in a direction transverse to the orientation of the plates and is capable of varying the strength of the driven magnetic flux. The magnetic flux aligns the magnetic particles suspended in the magnetorheological fluid, increasing the shear strength of the magnetorheological fluid, which in turn resists motion between the first and second plurality of plates, acting as a damper.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention pertains to a damper, and, more particularly, a magnetorheological (“MR”) rotary damper.  
         [0003]     2. Description of the Related Art  
         [0004]     Numerous types of machines employ rotors, or parts that rotate, for a variety of reasons. Frequently, the designer incorporates a mechanism to help control the movement of the rotor. One mechanism used for this purpose is a “rotary damper”, so-called because it controls motion with regards to angular velocity in a rotary or circular movement.  
         [0005]     A wide variety of rotary dampers are well known to the art. However, as with all technologies, each type of rotary damper has drawbacks as well as advantages. One common problem is achieving a sufficiently rapid response in damping the rotor&#39;s movement for certain types of applications. For many applications, rapid response is not an issue. But, for certain high performance applications, it becomes critical. As the range of applications broadens because of advance in technology, the number of these high performance applications concomitantly increases.  
         [0006]     Consider, for instance, a wheeled vehicle. Some wheeled vehicles include suspension systems employing rotary dampers. A rapid response from the rotary dampers is important in order to provide a smooth, comfortable ride for a passenger. But, there are many other reasons, such as safety, e.g., to help a driver keep control of the vehicle.  
         [0007]     However, as a variety of technologies have improved, robotic vehicles have become more ubiquitous. Robotic vehicles typically rely on numerous sensors to collect data from which the operation of the vehicle is controlled. Poor response from the rotary dampers can lead to operating conditions in which the sensors collect wrong or inaccurate data. For instance, if a robotic vehicle hits a large obstacle in its path, the sensors might acquire data in a direction different from that in which the vehicle is moving. This could lead to even poorer operating conditions as the robotic controller makes decisions on data that does not accurately reflect the terrain over which the vehicle is actually moving.  
         [0008]     Note that this particular consequence is more acute in a robotic vehicle than in a manually operated vehicle. The operator driving a manned vehicle acquires data independently of the operation of the vehicle as a whole through their natural senses, which is untrue of the robotic controller. Granted, a manned operator&#39;s data acquisition may be interrupted by a sufficiently violent perturbation, but the risk is much less than it is for the robotic controller. Thus, the rapid response arguably becomes more critical for the robotic vehicle application and rotary dampers with higher bandwidth may be required as compared to dampers for manned vehicles.  
         [0009]     The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.  
       SUMMARY OF THE INVENTION  
       [0010]     The invention is a rotary damper comprising a first and a second plurality of plates disposed within a housing. The first and second pluralities of plates are interleaved and are capable of moving relative to one another. A magnetorheological fluid contained within the housing resides in the interleave of the first and second plurality of plates. A magnetic flux generator drives a magnetic flux through the magnetorheological fluid in the interleave in a direction transverse to the orientation of the plates and is capable of varying the strength of the driven magnetic flux. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:  
         [0012]      FIG. 1  is a perspective view of one particular embodiment of a rotary damper constructed in accordance with the present invention;  
         [0013]      FIG. 2  is a perspective, section view of the rotary damper of  FIG. 1 ;  
         [0014]      FIG. 3  provides a partial, perspective, section view of the rotary damper of  FIG. 1 ;  
         [0015]      FIG. 4A  and  FIG. 4B  enlarge and detail a portion of the section view of  FIG. 2  in plan and perspective views, respectively;  
         [0016]      FIG. 5A  enlarges and details a portion of the section view in  FIG. 2  alternative to that shown in  FIG. 4A  in a plan view;  
         [0017]      FIG. 5B  illustrates a means for maintaining a predetermined level of the magnetorheological fluid within the housing;  
         [0018]      FIG. 6  illustrates one segment of the segmented flux housing in the embodiment of  FIG. 1  and  FIG. 2 ;  
         [0019]      FIG. 7  depicts a robotic vehicle in which the rotary damper of  FIG. 1 - FIG. 6  may be employed in one particular implementation; and  
         [0020]      FIG. 8  and  FIG. 9  depict, in block diagrams, two alternative control systems that may be used in conjunction with the invention in the robotic vehicle of  FIG. 7 . 
     
    
       [0021]     While the invention is susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments herein described in detail by way of example. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
         [0023]     Turning now to the drawings,  FIG. 1 ,  FIG. 2 , and  FIG. 3  illustrate one particular embodiment of a rotary damper  100  constructed in accordance with the present invention. The rotary damper  100  includes an inner housing  110 , a rotor  120 , an outer housing  130 , and a segmented flux housing  140 . The inner housing  110  and outer housing  130  are fabricated from a “soft magnetic” material (a material with magnetic permeability much larger than that of free space), e.g., mild steel. The rotor  120  is made from a “nonmagnetic” material (a material with magnetic permeability close to that of free space), e.g., aluminum. In one embodiment, the segmented flux housing  140  is fabricated from a high performance magnetic core laminating material commercially available under the trademark HIPERCO 50® from: 
        Carpenter Technology Corporation     P.O. Box 14662     Reading, Pa. 19612-4662     U.S.A.     Phone: (610) 208-2000     FAX: (610) 208-3716 
 
 However, other suitable, commercially available soft magnetic materials, such as mild steel, may be used. 
       
 
         [0030]     The rotary damper  100  is affixed to, in this particular embodiment, a vehicle chassis (not shown) by fasteners (also not shown) through a plurality of mounting holes  150  of the inner housing  110 . The rotor  120  is made to rotate with the pivoting element (not shown) with the use of splines or drive dogs (also not shown). Note that the rotary damper  100  may be affixed to the pivot and the chassis in any suitable manner known to the art. The rotary damper  100  damps the rotary movement of the pivot relative to the vehicle chassis in a manner more fully explained below.  
         [0031]     A portion  210  of the rotary damper  100  in the view of  FIG. 2  is enlarged and detailed in  FIG. 4A  and  FIG. 4B . Pluralities of rotor plates  400 , separated by magnetic insulators  405 , are affixed to the rotor  120  by, in this particular embodiment, a fastener  410  screwed into the rotor plate support  415  of the rotor  120 . A plurality of housing plates  420 , also separated by magnetic insulators  405 , are affixed to an assembly of the inner housing  110  and outer housing  130 , in this embodiment, by a fastener  425  in a barrel nut  430 . Note that the assembled rotor plates  400  and the assembled housing plates  420  are interleaved with each other. The number of rotor plates  400  and housing plates  420  is not material to the practice of the invention.  
         [0032]     The rotor plates  400  and the housing plates  420  are fabricated from a soft magnetic material having a high magnetic permeability, e.g., mild steel. The magnetic insulators  405 , the fasteners  410 ,  425 , and the barrel nut  430  are fabricated from nonmagnetic materials, e.g., aluminum or annealed austenitic stainless steel. The nonmagnetic fasteners can be either threaded or permanent, e.g. solid rivets. The rotor plates  400  and the housing plates  420  are, in this particular embodiment, disc-shaped. However, other geometries may be used in alternative embodiments and the invention does not require that the rotor plates  400  and the housing plates  420  have the same geometry.  
         [0033]     Still referring to  FIG. 4A , the assembled inner housing  110 , rotor  120 , and outer housing  130 , define a chamber  435 . A plurality of o-rings  440  provide a fluid seal for the chamber  435  against the rotation of the rotor  120  relative to the assembled inner housing  110  and outer housing  130 . An MR fluid  445  is contained in the chamber  435  and resides in the interleave of the rotor plates  400  and the housing plates  420  previously described above. In one particular embodiment, the MR fluid  445  is MRF132AD, commercially available from: 
        Lord Corporation     Materials Division     406 Gregson Drive     P.O. Box 8012     Cary, N.C. 27512-8012     U.S.A     Ph: 919/469-2500     FAX: 919/481-0349 
 
 However, other commercially available MR fluids may also be used. 
       
 
         [0042]      FIG. 6  illustrates one segment  600  of the segmented housing  140  in the illustrated embodiment. A number of segments such as the segment  600  are assembled together to fabricate the magnetic flux housing  140 . The segments  600  are fabricated from a soft magnetic material, e.g., mild steel or Hiperco 50®, using any suitable technology. High performance soft magnetic materials (which saturate at magnetic flux densities greater than 1.5 Tesla) can yield a flux housing  140  of reduced mass. Suitable assembly techniques may include, but are not limited to, fastening (e.g., by screws, bolts, or bands), adhering (e.g. by glue or epoxy), and metallurgy (e.g., welding or brazing). The precise number segments  600  will be implementation specific depending on, e.g., the thickness of the segments  600  and the diameter of the rotary damper  100 . The segmented construction was selected for a number of reasons. For instance, the materials desired for the illustrated embodiment is only commercially available in thin strips. From a performance standpoint, the segmented construction should improve the transient behavior of the rotary damper  100  by reducing the effects of eddy current component core losses, which should be a substantial concern for high performance applications.  
         [0043]     The segmented flux housing  140  contains a coil  450 , the segmented flux housing  140  and coil  450  together comprising an electromagnet. The coil  450 , when powered, generates a magnetic flux in a direction transverse to the orientation of the rotor plates  400  and the housing plates  420 , as represented by the arrow  455 . Alternatively, as shown in  FIG. 5A , a permanent magnetic  500  could be incorporated into the flux housing  140  to bias the magnetic flux  455 . The coil  450  drives the magnetic flux through the MR fluid  445  and across the faces of the rotor plates  400  and the housing plates  420 . The sign of the magnetic flux is not material to the practice of the invention.  
         [0044]     The magnetic flux aligns the magnetic particles suspended in the MR fluid  445  in the direction of the magnetic flux. This magnetic alignment of the fluid particles increases the shear strength of the MR fluid  445 , which resists motion between the rotor plates  400  and the housing plates  420 . When the magnetic flux is removed, the suspended magnetic particles return to their unaligned orientation, thereby decreasing or removing the concomitant force retarding the movement of the rotor plates  400 .  
         [0045]     Note that it will generally be desirable to ensure a full supply of the MR fluid  445 . Some embodiments may therefore include some mechanism for accomplishing this. For instance, some embodiments may include a small fluid reservoir to hold an extra supply of the MR fluid  445  to compensate for leakage and a compressible medium for expansion of the MR fluid  445 . The compressible medium might include, for example, a gas charged accumulator—a flexible diaphragm with compressed gas on one side and a small reservoir of MR fluid  445  on the other. Nitrogen would be one suitable gas for this purpose. Such a device would also ensure a full supply of the MR fluid  445  over a wider temperature range. However, this is not necessary to the practice of the invention.  
         [0046]     However, one such device is shown in  FIG. 5B . In this particular embodiment, a soft, closed-cell foam  505  is employed as the compressible medium. The reservoir chamber  510  is created inside the rotor  120 , which has been sealed off by a tube  515  that is bonded and sealed into the rotor  120 . A channel  520  is fabricated between the reservoir chamber  510  and the active MR fluid chamber  435  by drilling holes through the rotor  120  or some other suitable technique. A drain plug  525  plug  525  has been added so that the MR fluid  445  can be added or removed from the MR rotary damper  100 .  
         [0047]     In operation, the illustrated embodiment employs a control system (not shown) to sense the relative movement between the rotary plates  400  and the housing plates  420  and other variables relating to the system using a plurality of sensors (not shown). Note that this, too, is not necessary to the practice of the invention. Some embodiments may, for instance, infer the relative movement from some other sensed quantity. One exemplary sensed quantity would be the speed of a vehicle of which the rotary damper  100  is a part.  
         [0048]     Returning to the illustrated embodiment, the control system commands an electrical current to be supplied to the coil  450 . This electric current then creates a magnetic flux  455  and the rotary damper  100  resists relative motion between the housings  110 ,  130  and the rotor  120 . Depending on the geometry of the rotary damper  100  and the materials of its construction, there is a relationship between the electric current, the relative angular velocity between the housings  110 ,  130  and the rotor  120 , and the resistive torque created by the rotary damper  100 . In general this resistive torque created by the rotary damper  100  increases with the relative angular motion between the housings  110 ,  130  and the rotor  120  and larger magnetic flux density through the fluid as generated by the coil electric current.  
         [0049]     Note that, in addition to the relative angular rate and the magnitude of the magnetic flux, other factors influence the performance of the rotary damper  100 . The resistive torque is also related to the total surface area of the MR fluid  445  being sheared, the radius of this area from the pivot center, the thickness of the sheared fluid, and the properties of the MR fluid  445  used. This fluid shear area is related to the number of rotor plates  400 , housing plates  420  and the overlapping area between these plates. The fluid thickness is equal to the gap between each of these plates in the device assembly. In general, the larger the fluid shear area, the larger the average radius of this area, and the smaller the fluid thickness, the higher the rotary damper resistive torque in the device. This applies to the full range of tenderization of the device, from the “maximum on-state”, the un-energized “off-state” and for any other energized states between these extremes.  
         [0050]     As is known in the art, the properties of an MR fluid can be greatly influenced depending on the base fluid, the type and particle size distribution of the magnetic particles and the magnetic particle loading of the fluid, among others. For example, a fluid with a higher magnetic particle loading will improve both the maximum fluid yield shear stress as well as the magnetic permeability of the fluid, although there is a corresponding increases in fluid “off-state” viscous drag (typically an MR fluid is a non-Newtonian fluid and the apparent fluid viscosity is related to the shear rate applied on the fluid with higher shear rates resulting in lower apparent fluid viscosity). This change in fluid properties would result in an MR rotary damper  100  with higher controllable resistive torque capability at slightly less commanded coil electric currents, although when turned off, the device would also have higher resistive torque.  
         [0051]     The magnetic and corresponding electrical properties of the device are strongly dependent on the fluid and the device geometry. These design elements define the magnetic energy storage of the device when energized, which in turn relates to the device inductance depending of the number of wire turns in the electrical coil. A large electrical inductance (L) may reduce the speed of response or bandwidth, of the rotary damper, since this inductance relates the rate of change in coil current (i) with respect to time (t) to the voltage (e) applied to the coil (di/dt=e/L for a device with constant inductance). For a typical MR damper the inductance tends to have the largest value at low currents and magnetic saturation effects reduce the apparent inductance at larger device currents.  
         [0052]     Unfortunately, the MR rotary damper tends to have a high inductance. This problem can be mitigated with the use of high control voltages which allow for high rates of change in damper current (di/dt), although this may lead to increased power demands and higher levels of inefficiency depending on the design and the software control driving the rotary damper  100 . Another technique, which may improve the bandwidth and efficiency of the MR rotary damper, uses multiple coil windings. One such system could use two coil windings; one high inductance, slow coil with a high number of turns of small diameter wire and a second low inductance, fast coil with a low number of turns of larger diameter wire. The slow coil would be used to bias the rotary damper  100  while the fast coil could be used to control around this bias. However, the two coil windings may be highly coupled due to the mutual inductance between them in some implementations, which would be undesirable.  
         [0053]     The present invention admits wide variation and enjoys a wide range of applications.  FIG. 7  illustrates one such application, i.e., as part of the suspension system for a robotic vehicle  700 . The robotic vehicle  700  is designed to be airdropped into an operational theater and then traverse the local terrain, which may be quite rugged. The robotic vehicle  700  employs six rotary dampers  100  to control the rotation of the arms  710  to which the wheels  720  are mounted relative to the chassis  730 . Thus, the arms  710  and the chassis  730  constitute the pivot to which the rotary damper  100  is affixed and the vehicle chassis, respectively, discussed above.  
         [0054]     The robotic vehicle  700  employs an arm positions sensor  735  (only three shown) for each arm  710 . The arm position sensors  735  measure the relative position of the respective arms  710  to the vehicle chassis  730 . From this measurement the relative angular velocity of the arms  710  could also be determined. As a simple damper, the MR rotary damper  100  would be commanded (e.g., a control system  740 ) to produce a torque proportional to and against the arm angular velocity. More advanced control algorithms could command the MR rotary damper  100  to produce a resistive torque related to other variables such as: the positions of the arms  710  relative to the chassis  730 , the vertical acceleration on the vehicle chassis  730 , the vehicle roll and pitch angles and angular rates, and the wheel hub motor torques (these would be determined by the vehicle control for controlling vehicle speed and turning). The illustrated embodiments also employs an inertial sensor  745  to help measure some of these variables.  
         [0055]     The versatility of the present invention is particularly evident from this implementation. The robotic vehicle  700  operates under software control, in this particular embodiment, in eight modes: air drop, high speed suspension, arm articulation, sensor stabilization, low power, optimized traction, drive reaction torque opposition, and off. The software control optimizes the suspension system, through the rotary dampers  100 , by controlling the current supplied in the coil, which creates a resistive torque applied to the suspension arm in some form of optimal way. The rotary dampers  100  are employed in a semi-active suspension system, although alternative embodiments may employ the rotary dampers  100  in an active suspension system.  
                                                   TABLE 1                           Operational Modes of MR Rotary Damper       and Operational Optimizations                Optimized for:   Performance            Mode   Torque   Response   Power   Description               Air Drop   X           Rotary dampers dissipate                       kinetic energy of falling                       vehicle-very high                       resultant torques at the                       rotary damper.       High Speed   X   X       Rotary dampers quickly       Suspension               increase damping force to                       absorb impact from                       encountering a large                       obstacle.       Arm   X   X   X   Rotary dampers       Articulation               efficiently facilitate rapid                       changes in holding torque                       to stabilize the vehicle                       sprung mass.       Sensor       X       Rotary dampers support       Stabilization               higher bandwidth than                       wheel frequency for                       preferred sensor isolation.       Low Power           X   Rotary dampers                       optimized for efficiency                       over primary or                       secondary roads.       Optimized       X       Rotary dampers support       Traction               higher bandwidth than                       wheel frequency for tire                       traction optimization.       Drive       X   X   Rotary dampers quickly       Reaction               yet efficiently adapt to       torque               changing drive torques to       opposition               reduce coupling between                       drive torque and                       suspension motion.       Off               Rotary dampers have a                       low off-state torque.                  
 
         [0056]     Of the eight modes, the air drop mode should require the highest reaction torque by the rotary dampers  100 , while the high speed suspension mode should require the fastest response of the damper control system. In the Air Drop mode, the suspension position is set for maximal energy absorption and all of the rotary dampers  100  are turned fully on during the fall so that speed of response is not an issue for this operational mode. The highest peak torque occurs on the middle set of suspension arms  710  just after landing, and requiring a peak torque of 22,000 in lb (2500 N m). The middle arms  710  also have the highest arm velocities with a peak around 1400 deg/sec or 25 radian/sec. One difference between the air drop and high speed suspension modes is that, in the high speed suspension mode, the robotic vehicle  700  does not necessarily have knowledge about upcoming bumps and other disturbances. The suspension system therefore should have adequate bandwidth and reaction torque capability for the rotary damper  100  to absorb these impacts with minimal effect on is the robotic vehicle  700 . Generally, in encountering an obstacle, the front suspension arm  710  has the highest reaction torque, 7500 in lb (850 N m), and also the highest arm velocities, 500 deg/sec or 9 radian/sec.  
         [0057]      FIG. 8  and  FIG. 9  depict, in block diagrams, two alternative control systems  800  and  900 , respectively, that may be used in conjunction with the invention in the robotic vehicle  700  of  FIG. 7 . Each of the control systems  800 ,  900 , controls one or more rotary dampers  100 . In the illustrated embodiment, each rotary damper  100  is accompanied by an electromagnet  810  used to generate a magnetic flux from the coil  450  (shown first in  FIG. 4A ) of the rotary damper  100 .  
         [0058]     In both the control systems  800 ,  900 , a control mechanism (not shown) makes some determination, directly or indirectly, of how much torque is to be applied by the rotary damper  100  onto the suspension. For instance, the robotic vehicle  700  in  FIG. 7  could be remotely controlled by a person or under the autonomous control of an on-board processor. The decision of this control mechanism can be communicated by, e.g., a switch  815 , a control algorithm  820 ,  825 , or some combination of these. For instance, a processor (not shown) on the vehicle  700 , responsive to sensor inputs, could decide that the vehicle  700  should operate in one of the modes discussed above and presented in Table 1. This decision could be communicated through the control algorithm  820 , for instance. However, any suitable technique known to the art may be used to perform this aspect of the illustrated embodiment.  
         [0059]     This concludes the detailed description. The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.