Abstract:
The present invention improves a ball-detent torque-limiting assembly by providing breakout means for maintaining an axial separation distance between opposing pocketed surfaces of the assembly once the balls have rolled out of their pockets, wherein the axial separation distance maintained by the breakout means is at least as great as the diameter of the balls. The breakout means assumes the axially directed spring load that urges the opposing pocketed surfaces together, thereby preventing the balls from entering and exiting the pockets in quick and violent succession following breakout and avoiding damage to the torque-limiting assembly. The torque-limiting assembly is resettable by counter-rotation following a breakout event.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority of U.S. Provisional Patent Application No. 61/724,989 filed Nov. 11, 2012, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to electromechanical actuation of aircraft control surfaces, and more particularly to torque limiters designed to prevent transmission of excessive torque and load after an electromechanical actuator for moving an aircraft control surface has encountered a hard mechanical stop. 
       BACKGROUND OF THE INVENTION 
       [0003]    Aircraft control surfaces, for example flaps located on the trailing edge of a fixed wing, slats located on a leading edge of a fixed wing, spoiler panels, aileron surfaces, and the like, have traditionally been actuated by hydraulic actuation systems. More recently, electromechanical actuators (“EMAs”) have gained acceptance in the aviation industry for adjusting the position of control surfaces. EMAs are designed to sweep through a given stroke, linear or rotary, but must have definite points where the stroke must start and end. In practice, two sets of endpoints are defined: one set defines the electrical stroke and the other the mechanical stroke. In normal operation, EMAs are controlled by sophisticated integral or remote electronics over the electrical stroke. However, conditions may arise where an errant command results in the EMA being driven beyond the normal electrical stroke endpoint into a mechanical stroke endpoint. The endpoints that define the mechanical stroke are usually hard mechanical stops. Aircraft manufacturers require that the EMA contain the EMA stroke to prevent possible damage to the airframe or control surfaces. Because of usual space constraints in aircraft, extra room to include “soft” mechanically cushioned stops is not available. If an EMA is driven at sufficient rate into a mechanical end stop either during an in-flight event or as a result of a rigging error during assembly, significant damage usually occurs. After a “shearout” device is employed, and after an event, the EMA is rendered inoperative. A costly overhaul process is required to replace parts and return the unit to service. 
         [0004]    It is known to use a rotary ball detent mechanism in an EMA system to limit the torque transmitted from an input gear to an output gear to a chosen maximum torque. The input and output gears are axially aligned on a drive shaft. After a stop is encountered, the rotary ball detent mechanism disconnects the driving inertia from the load path at levels that prevent damage. Conventional ball detent mechanisms employ a series of metal balls all in the same plane that are equally spaced around a circumference about the drive shaft. The balls are held between two circular plates each having an array of pockets to hold the balls. The spacing between the plates is therefore the ball diameter less the depth of the opposing ball pockets. A cage between the plates having a thickness slightly less than the plate spacing is usually employed to maintain even angular ball spacing. The plates and balls are held on the drive shaft by relatively heavy axial spring loading. Under normal operation, all parts rotate together at a commanded speed. The magnitude of the spring loading, the size and number of balls, and depth and shape of pocket dictate the torque limit of the device. 
         [0005]    The breakout load or torque limit is selected to be greater than the maximum operating load so that it never “trips” during normal operation, but less than loads that would cause damage to the EMA. With the conventional ball detent mechanism described above, after a breakout or hard stop condition is encountered, one plate is brought to an abrupt stop while the other continues to rotate as the set of balls, in unison due to the cage, roll out of the pockets and onto the flat opposing surfaces of the two circular plates. The shaft is usually rotating at least several hundred—and often up to several thousand—revolutions per minute. The control electronics cannot sense a problem or act on a problem instantaneously, so the EMA&#39;s motor is driven for some fraction of a second after breakout. For example, if initial speed is 2400 RPM and six balls are used, with an assumed time of 200 msec before the motor can be turned OFF, 8 revolutions occur. Therefore, the balls that breakout of the initial pockets then encounter 48 more events of rolling into and out of subsequent pockets in the direction of rotation. With the high spring force and the abrupt shape of the pockets, the continued motion of the balls rolling into and out of pockets results in a very violent series of events. The balls experience very high and repeated impact loading and may fracture. Also, the edges of the pockets in the plates may generate harmful debris. Tests have shown significant damage to ball pockets after several encounters. The audible noise from the conventional approach is a loud chatter that may be described as “machine-gun-like.” 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention solves the damage and noise problems associated with a breakout event experienced by a conventional torque-limiting assembly. Moreover, the present invention provides a torque-limiting assembly that is easily reset for continued operation after a breakout event. 
         [0007]    The present invention provides a ball-detent torque-limiting assembly with breakout means for maintaining an axial separation distance between opposing pocketed surfaces of the assembly once the balls have rolled out of their pockets, wherein the axial separation distance maintained by the breakout means is at least as great as the diameter of the balls. The breakout means assumes the axially directed spring load that urges the opposing pocketed surfaces together, thereby preventing the balls from entering and exiting the pockets in quick and violent succession following breakout and avoiding damage to the torque-limiting assembly. 
         [0008]    In one embodiment, the breakout means comprises an angular array of cooperating pairs of ramp members respectively protruding from one of the pocketed surfaces and from a facing surface of a cage retaining the balls. In another embodiment, the breakout means includes a plurality of rollers in an angular array spaced radially relative to the balls and opposing ball pockets to avoid alignment with the ball pockets. In both embodiments, the breakout means is reversible to reset the assembly by commanding a reverse rotation in an angular direction opposite the breakout direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING VIEWS 
         [0009]    Features and advantages of embodiments of the present disclosure will become apparent by reference to the following detailed description and drawings, in which: 
           [0010]      FIG. 1  is a perspective view of a torque-limiting assembly formed in accordance with a first embodiment of the present invention; 
           [0011]      FIG. 2  is an exploded perspective view of the torque-limiting assembly shown in  FIG. 1 , looking generally in a first axial direction; 
           [0012]      FIG. 3  is an exploded perspective view of the torque-limiting assembly shown in  FIG. 1 , looking generally in a second axial direction opposite the first axial direction; 
           [0013]      FIG. 4  is a perspective view of an input gear of the torque-limiting assembly shown in  FIG. 1 ; 
           [0014]      FIG. 5  is an axial plan view of the input gear shown in  FIG. 4 ; 
           [0015]      FIG. 6  is a perspective view of a cage, balls, and backing plate of the torque-limiting assembly shown in  FIG. 1 ; 
           [0016]      FIG. 7  is an axial plan view of the cage, balls, and backing plate shown in  FIG. 8 ; 
           [0017]      FIG. 8  is a cross-sectional view of the torque-limiting assembly shown in  FIG. 1 , in normal operating condition; 
           [0018]      FIG. 9  is a cross-sectional view of the torque-limiting assembly shown in  FIG. 1 , in breakout operating condition; 
           [0019]      FIG. 10  is a perspective view illustrating the torque-limiting assembly of  FIG. 1  after breakout; 
           [0020]      FIG. 11  is another perspective view illustrating the torque-limiting assembly of  FIG. 1  after breakout; 
           [0021]      FIG. 12  is an exploded perspective view of a torque-limiting assembly formed in accordance with a second embodiment of the present invention, looking generally in a first axial direction; 
           [0022]      FIG. 13  is an exploded perspective view of the torque-limiting assembly shown in  FIG. 12 , looking generally in a second axial direction opposite the first axial direction; 
           [0023]      FIG. 14  is a perspective view of an input gear of the torque-limiting assembly shown in  FIGS. 12-13 ; 
           [0024]      FIG. 15  is an axial plan view of the input gear shown in  FIG. 14 ; 
           [0025]      FIG. 16  is an enlarged perspective view of the backing plate shown in  FIG. 12 ; 
           [0026]      FIG. 17  is a perspective view of an outer cage, balls, inner cage, rollers and backing plate of the torque-limiting assembly shown in  FIGS. 12-13 ; 
           [0027]      FIG. 18  is an axial plan view of the outer cage, balls, inner cage, rollers and backing plate shown in  FIG. 17 ; 
           [0028]      FIGS. 19-25  are a sequential series of schematic axial views showing the torque-limiting assembly of the second embodiment as it experiences breakout and then reset. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIG. 1-3  depict a torque-limiting assembly  10  formed in accordance with a first embodiment of the present invention. Assembly  10  has utility in an EMA drive system for actuating an aircraft control surface, e.g. a spoiler panel, flap, slat or other aircraft control surface. 
         [0030]    Assembly  10  generally comprises an elongated shaft  12  supporting an input gear  14  and an output gear  16 . Shaft  12  includes a splined end  18  provided with a circumferential retaining groove  19 . Assembly  10  further comprises a spring  20 , washers  22 , a collar  24 , retainer clips  26 , and a backing plate  28  all mounted on shaft  12 . 
         [0031]    Output gear  16  is mounted on shaft  12  for rotation with the shaft. In the context of the present specification, “mounted on” is meant in a broad sense to include a part that is separately manufactured and slid onto shaft  12 , as well as a part that is integrally formed on shaft  12 . 
         [0032]    Input gear  14  is mounted on shaft  12  so as to be rotatable about the shaft axis relative to the shaft, and axially displaceable along the shaft in first and second opposite axial directions. Input gear  14  includes a driving surface  38  facing in a first axial direction toward splined end  18  of shaft  12 . Driving surface  38  may be an integral surface of input gear  14  as shown in  FIG. 3 , or it may be a surface of a drive plate (not shown) that is manufactured separately from input gear  14 . Integrating driving surface  38  with input gear  14  is advantageous because it saves axial space. Driving surface  38  includes a plurality of ball pockets  40  angularly spaced about the axis of shaft  12 . As best seen in  FIG. 2 , input gear  14  may include an annular recess  36  on the side opposite from driving surface  38 , and a cylindrical mounting sleeve  34  extending in a second axial direction away from splined end  18  and toward output gear  16 . 
         [0033]    Backing plate  28  includes a toothed opening  46  enabling the backing plate to be mounted on splined end  18  of shaft  12  such that the backing plate rotates with the shaft about the shaft axis. Backing plate  28  is constrained against axial displacement along shaft  12  in the first axial direction by C-shaped retainer clips  26  received in retaining groove  19 . Backing plate  28  includes a detent surface  48  opposing driving surface  38  and having a plurality of ball pockets  50  angularly spaced about the shaft axis. 
         [0034]    Spring  20 , which may be embodied as a Belleville spring pack, may be mounted over cylindrical sleeve  34  of input gear  14  for partial receipt within annular recess  36  for an axially-compact biasing arrangement. One end of spring  20  bears against axially-fixed output gear  16  by way of washers  22  and collar  24 , while the other end of spring  20  bears against axially-displaceable input gear  14 . As may be understood, spring  20  is arranged to provide an axially-directed load urging input gear  14  in the first axial direction toward backing plate  28 . 
         [0035]    Assembly  10  further comprises a cage  32  having a central mounting hole  52  for mounting the cage on shaft  12 . Cage  32  is mounted on shaft  12  between driving surface  38  and detent surface  48 . Cage  32  includes a driven surface  54  facing driving surface  38 , and a braking surface  56  facing detent surface  48 . Cage  32  further includes a plurality of ball openings  58  therethrough. Ball openings  58  are angularly spaced about the axis of shaft  12 . Assembly  10  also includes a plurality of balls  30  of uniform diameter received in ball openings  58 . The diameter of balls  30  is greater than the axial thickness of cage  32  (i.e. the distance from driven surface  54  to braking surface  56 ), such that protruding spherical caps of each ball  30  project into a ball pocket  40  in driving surface  38  and an opposing ball pocket  50  in detent surface  48 . Under normal torque loading conditions, the bias of spring  20  maintains the assembly in the described arrangement. 
         [0036]    When a hard mechanical stop event results in abrupt rotational stoppage of shaft  12  and output gear  16 , the motor of the EMA momentarily continues to drive input gear  14 . When this occurs, assembly  10  is designed to allow slippage between input gear  14  and shaft  12  to prevent torque transmission to shaft  12  in excess of a predetermined torque limit. In accordance with the present invention, assembly  10  comprises breakout means for causing and maintaining axial separation of driving surface  38  from detent surface  48  by a distance at least as great as the diameter of balls  30  during a mechanical stop event, whereby balls  30  are not repeatedly slammed into pockets  40  and  50  as input gear  14  continues to rotate. 
         [0037]    Reference is made to  FIGS. 4-11  for explanation of the breakout means of the first embodiment. In the first embodiment, the breakout means includes a circular series of peaked ramps  42  protruding out of driving surface  38 , and a corresponding circular series of peaked ramps  60  protruding out of driven surface  54 . Peaked ramps  42  are angularly spaced about the axis of shaft  12  and are separated from one another by arc-shaped slots  44 . Likewise, peaked ramps  60  are angularly spaced about the axis of shaft  12  and are separated from one another by arc-shaped slots  62 . The circle defined by ramps  42  and slots  44 , and the circle defined by ramps  60  and slots  62 , have the same radius. In the depicted embodiment, the ramp-slot circles are radially within a circle defined by balls  30 , however an arrangement in which the ramp-slot circles are radially outside the ball circle is within the scope of the invention. Under normal condition, ramps  42  are received in slots  62  and ramps  60  are received in slots  44 ; this condition can be seen in the cross-sectional view of  FIG. 8 . 
         [0038]    When a hard mechanical stop is encountered, backing plate  28  stops rotating along with shaft  12  and output gear  16 . However, input gear  14  continues to be driven momentarily due to delay in stopping the EMA motor, and toque is transmitted to shaft  12 . When the torque limit is exceeded, input gear  14  will rotate relative to shaft  12  and backing plate  28 . As this happens, balls  30  will roll out of pockets  40  in driving surface  38 ; this is best seen in  FIGS. 9 and 11 . The balls will also roll out of pockets  50  in detent surface  48  of backing plate  28  because the backing plate is rotationally stopped with shaft  12 . As the balls  30  roll out onto the flat driving surface  38  and flat detent surface  48 , they displace input gear  14  slightly in the second axial direction (away from splined end  18 ) against the bias of spring  20 . 
         [0039]      FIGS. 9 and 10  show that simultaneously with the breakout of balls  30  from pockets  40 , complementary sloped surfaces of ramps  42  and  60  engage one another, thereby converting the relative rotary motion between input gear  14  and cage  32  into further axial displacement of input gear  14  in the second axial direction. The cooperative engagement of ramps  42  and  60  causes the driving surface  38  and detent surface  48  to be separated by an axial distance greater than the diameter of balls  30 , such that the balls do not bear the load of axial spring  20 . The engaged ramps  42  and  60  also cause cage  32  to rotate in unison with input gear  14  (or with a separate driving plate, if a separate driving plate is used as mentioned above). This prevents the balls from reaching another pocket  40 . The balls  30  are unloaded and rotate with input gear  14  (or with a separate driving plate) and with cage  32 . Cage  32  is also displaced in the first axial direction such that its braking surface  56  comes into frictional contact with detent surface  48  of stationary backing plate  28 , thereby providing braking action which gently slows the rotating parts. 
         [0040]    If a breakout occurs, the control electronics will eventually command the EMA&#39;s motor to stop. The present invention will then allow a simple reset of the assembly  10  by commanding a reverse rotary motion of input gear  14  to cause balls  30  to roll back into the original pockets  40 ,  50 . The invention handles a breakout event with little or no damage to the system. 
         [0041]      FIGS. 12 and 13  illustrate a torque-limiting assembly  110  formed in accordance with a second embodiment of the present invention that employs an alternative breakout means. Assembly  110  comprises an input gear  114 , output gear  16 , a backing plate  128 , a composite cage  132 , and a plurality of balls  30  arranged and mounted on drive shaft  12  and biased by spring  20  in a manner similar to the first embodiment. 
         [0042]      FIGS. 14 and 15  show input gear  114  in detail. Input gear  114  includes a driving surface  138  facing in the first axial direction toward splined end  18  of shaft  12 . As in the first embodiment, driving surface  138  may be an integral surface of input gear  114  as shown in  FIG. 13 , or it may be a surface of a separately-manufactured drive plate (not shown). Driving surface  138  includes a plurality of ball pockets  140  angularly spaced about the axis of shaft  12 . In contrast to driving surface  38  of the first embodiment, driving surface  138  does not have ramps and slots. 
         [0043]    Backing plate  128 , shown in  FIG. 16 , includes a detent surface  148  opposing driving surface  138  and having a plurality of ball pockets  150  angularly spaced about the shaft axis. Detent surface  148  is also provided with a plurality of curved roller pockets  151  angularly spaced about the axis of shaft  12  radially inward from ball pockets  150 . 
         [0044]    Reference is now made to  FIGS. 17-18 . Cage  132  of the second embodiment is a two-piece assembly comprising a radially outer cage  133  and a radially inner cage  135 , wherein inner cage  135  is slidably received within an axial hole  152  of outer cage  133  to permit relative rotation between the inner and outer cages. A plurality of ball openings  158  are provided through outer cage  133  for receiving and retaining balls  30  in an angularly spaced arrangement around the shaft axis. A plurality of arc-segment coupling recesses  159  are arranged around an edge of axial hole  152  facing driving surface  138 . 
         [0045]    Inner cage  135  has a central mounting hole  164  for mounting the inner cage on shaft  12 . Inner cage  135  also has a plurality of roller openings  166  angularly spaced about the shaft axis for receiving a plurality of rollers  131 . In the figures, rollers  131  are illustrated as being cylindrical rollers to readily distinguish them from balls  30 , however rollers  131  may also be embodied as spherical rollers (balls). Regardless of the shape that rollers  131  take, the diameter of rollers  131  is selected to be the same as or slightly greater than the diameter of balls  30 . Finally, inner cage  135  includes a plurality of coupling tabs  168  each projecting radially outward for receipt within an associated coupling recess  159  of outer cage  133 . 
         [0046]    Operation of the breakout means of the second embodiment will now be explained with reference to  FIGS. 19-25 .  FIG. 19  shows the relative arrangement of input gear  114 , outer cage  133 , inner cage  135 , and balls  30  in an initial angular “set” position about the axis of shaft  12  prior to a breakout event. Balls  30  are aligned with pockets  140  of input gear  114  and also with pockets  150  of backing plate  128  (not shown in  FIGS. 19-25 ). Outer cage  133  is arranged to contain balls  30  within ball openings  158  Inner cage  135  is arranged such that its coupling tabs  168  extend into respective coupling recesses  159  of outer cage  133  with clearance in both angular directions from ends of the recess  159 . Shaft  12  is rotating CW about its axis at high RPM, e.g. in the neighborhood of 2400 RPM. 
         [0047]      FIG. 20  illustrates the onset of a breakout event when output gear  16 , shaft  12 , and backing plate  128  are unexpectedly and suddenly stopped from rotation when the EMA hits a hard mechanical stop. Input gear  114  continues to rotate in the CW direction (a 30° CW rotation is illustrated). Outer cage  133 , situated between rotating input gear  114  and stationary backing plate  128  and carrying balls  30 , rotates 15° CW. Balls  30  roll out of pockets  140  and  150  and come into rolling contact with driving surface  138  and detent surface  148 . As may be understood, balls  30  now carry the axial load of spring  20 , and input gear  114  is displaced slightly in the second axial direction against the spring force Inner cage  135  carrying rollers  131  remains in the same angular position. 
         [0048]    The breakout event continues in  FIG. 21 . Input gear  114  continues its CW rotation (a further 22° CW rotation is illustrated). Outer cage  133  and balls  30  rotate another 11° in the CW direction. At this point, respective ends of coupling recesses  159  come into contact with coupling tabs  168  of inner cage  135 , which heretofore has been stationary. 
         [0049]      FIG. 22  illustrates continuation of the breakout event. Input gear  114  continues its CW rotation (a further 52° CW rotation is illustrated; total rotation is now 104 ° CW). Outer cage  133  and balls  30  rotate an additional 26° in the CW direction, for a total rotation of 52° CW. As outer cage  133  rotates, the engagement of coupling tabs  168  with ends of coupling recesses  159  causes inner cage  135  to rotate together with outer cage  133 . Thus,  FIG. 22  illustrates 26° CW rotation of inner cage  135  and confined rollers  131 . As may be understood, the rotation of inner cage  135  relative to stationary backing plate  128  causes rollers  131  to roll out of roller pockets  151  in backing plate  128 . When this happens, rollers  131  come into rolling contact with driving surface  138  and detent surface  148 . The diameter of rollers  131  is chosen to be the same as or slightly greater than the diameter of balls  30  so that rollers  131  will assume axial loading of spring  20  from balls  30 . 
         [0050]    As may be understood, input gear  114  will continue to rotate in the CW direction until the EMA&#39;s control electronics have received a signal that actuator output is not moving and sent a motor stop command to cease driving input gear  114 . This may take on the order of 100-200 msec. Assuming an initial speed of 2400 RPM (40 revs per second), approximately eight revolutions of input gear  114  may be expected. During these revolutions, outer cage  133  and inner cage  135  will also rotate about shaft  12  such that rollers  131  will periodically reenter roller pockets  151  and spring loading will be momentary transferred back onto balls  30 . Thus, balls  30  and rollers  131  will alternate in taking up the spring load during post-breakout rotations. In order to prevent damage or at least reduce the risk of damage, it may be advantageous to use special non-galling stainless steel (Nitronic 60) or another material suitable for braking or sustained frictional heating for inner cage  135 , which is spring loaded against the backing plate  128  with about 600 pounds of force. An oil bath lubrication of assembly  110  may also be used to prevent or minimize damage to moving parts. 
         [0051]      FIG. 23  shows an arbitrary rotational position at which rotation of input gear  114  is stopped by the EMA control electronics. Input gear  114  is at an angular position 120° CW from its original set position. Outer cage  133  and balls  30  are at a an angular position 60° CW from their original set position. Inner cage  135  and rollers  131  are at an angular position 34° CW from their original set position. In the position, outer cage  133  and balls  30  are centered over both sets of pockets  140  and  150 , and rollers  131  carry all the axial spring load. With input gear  114  stopped, the breakout event is complete. In accordance with the present invention, assembly  110  can be reset in a relatively simple manner by commanding reverse rotation of input gear  114 . 
         [0052]      FIG. 24  depicts the beginning of the reset process in which input gear  114  is rotated CCW by 60° from its stopped position in  FIG. 23  by commanding the EMA. Outer cage  133 , balls  30 , inner cage  135  and rollers  131  are rotated CCW by 30° from their stopped position in  FIG. 23 . At this point, rollers  131  return to roller pockets  151  and balls  30  assume the axial spring load. 
         [0053]      FIG. 25  shows the completed reset position achieved by commanding an additional 60° CCW rotation of input gear  114 . Outer cage  133  and balls  30  rotate another 30° CCW, whereas inner cage  135  is left in the position shown in  FIG. 24 , thereby substantially centering coupling tabs  168  in the associated coupling recesses  159 . The outer cage  133  and balls  30  are aligned with ball pockets  140  and  150 , and spring  20  resets the mechanism so that the EMA is once again operational. 
         [0054]    It will be appreciated that the present invention prevents repeated events in which the balls roll out of their pockets and are then slammed back into another pocket. This improvement is accomplished in a very compact space envelope. Other approaches may accomplish the same functionality, but they use mechanisms requiring larger physical volume. 
       LIST OF REFERENCE SIGNS 
       [0055]      10  torque-limiting assembly, first embodiment 
         [0056]      12  shaft 
         [0057]      14  input gear 
         [0058]      16  output gear 
         [0059]      18  splined end of shaft 
         [0060]      19  retaining groove of shaft 
         [0061]      20  spring 
         [0062]      22  washers 
         [0063]      24  collar 
         [0064]      26  retainer clips 
         [0065]      28  backing plate 
         [0066]      30  balls 
         [0067]      32  cage 
         [0068]      34  input gear mounting sleeve 
         [0069]      36  input gear annular recess 
         [0070]      38  input gear driving surface 
         [0071]      40  input gear ball pockets 
         [0072]      42  input gear ramps 
         [0073]      44  input gear slots 
         [0074]      46  backing plate toothed opening 
         [0075]      48  backing plate detent surface 
         [0076]      50  backing plate ball pockets 
         [0077]      52  cage mounting hole 
         [0078]      54  cage driven surface 
         [0079]      56  cage braking surface 
         [0080]      58  cage ball openings 
         [0081]      60  cage ramps 
         [0082]      62  cage slots 
         [0083]      110  torque-limiting assembly, second embodiment 
         [0084]      114  input gear, second embodiment 
         [0085]      128  backing plate, second embodiment 
         [0086]      131  rollers 
         [0087]      132  composite cage 
         [0088]      133  outer cage 
         [0089]      135  inner cage 
         [0090]      138  input gear driving surface, second embodiment 
         [0091]      140  input gear ball pockets, second embodiment 
         [0092]      148  backing plate ball detent surface, second embodiment 
         [0093]      150  backing plate ball pockets, second embodiment 
         [0094]      151  backing plate roller pockets 
         [0095]      152  outer cage axial hole 
         [0096]      158  outer cage ball openings 
         [0097]      159  outer cage coupling recesses 
         [0098]      164  inner cage mounting hole 
         [0099]      166  inner cage roller openings 
         [0100]      168  inner cage coupling tabs