Abstract:
An electromechanical rear derailleur is provided for a bicycle, including a base member for attachment to the bicycle bicycle along a mounting axis. A movable member has a cage assembly attached thereto. A linkage is provided including pivot axes oriented substantially perpendicular to the mounting axis, the linkage coupling the movable member to the base member and operative to enable movement of the movable member relative to the base member in a direction substantially parallel to the mounting axis. A power source powers an electric motor connected thereto and a transmission is coupled to and actuated by the motor to move the movable member.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to bicycles and bicycle derailleurs. In particular the invention relates to electromechanical rear derailleurs for bicycles. 
       SUMMARY OF THE INVENTION 
       [0002]    The invention provides, in one aspect, an electromechanical rear derailleur for a bicycle, including a base member attachable to the bicycle along a mounting axis. A movable member includes a cage assembly attached thereto. A linkage includes pivot axes oriented substantially perpendicular to the mounting axis. The linkage coupling the movable member to the base member is operative to enable movement of the movable member relative to the base member in a direction substantially parallel to the mounting axis. A power source is provided with a motor electrically connected to the power source, and a transmission is coupled to and actuated by the motor to move the movable member. 
         [0003]    Other aspects of the invention provide a rear derailleur wherein the power source is disposed on or in the base member. The linkage may include an outer link member and an inner link member. The linkage may include link pins on which the linkage pivots, the link pins defining the pivot axes. The transmission may include a plurality of gears rotatable about a plurality of gear axes, respectively, wherein the gear axes are substantially parallel to the pivot axes. The transmission may be disposed on or in the base member. The motor may be disposed on or in the base member. The power source may be disposed on or in the base member. The linkage may include an outer link member and an inner link member. The rear derailleur may further include a clutch between the movable member and the transmission, the clutch moving the movable member responsive to operation of the transmission. The clutch may include a drive arm coupled to the transmission and a clutch spring in contact with the drive arm. The transmission may include an output gear and the drive arm is coupled to the output gear. The clutch spring may be disposed on the inner link member. The clutch spring may be disposed about the link pin that attaches the inner link member to the movable member. The motor may have a motor shaft with a motor shaft axis that is perpendicular to the pivot axes. The linkage may include link pins on which the linkage pivots, the link pins defining the pivot axes, wherein the pivot axes are substantially parallel to the mounting axis and the transmission includes a plurality of gears rotatable about a plurality of gear axles, respectively, wherein at least some of the gear axles have gear axle axes that are substantially parallel to the pivot axes. 
         [0004]    The invention also provides in an alternative embodiment an electromechanical rear derailleur for a bicycle, including a base member attachable to the bicycle. A movable member is provided having a cage assembly attached thereto. A linkage is provided coupling the movable member to the base member and operative to enable movement of the movable member relative to the base member. The derailleur includes a power source and a motor electrically connected to the power source. A transmission is coupled to and actuated by operation of the motor to move the movable member and a position detector is provided, including a magnet rotated by the transmission, a sensor to sense rotation of the magnet, a magnet guide sized and shaped to guidingly receive a portion of the magnet and position the magnet within an effective range of the sensor. 
         [0005]    Alternatives include wherein the rear derailleur includes a magnet holder disposed in the rear derailleur, the magnet held by the magnet holder. The magnet holder may be coupled to the transmission. The rear derailleur may further include a PC board positioned in the base member and wherein the sensor is disposed on the PC board in position to sense motion of the magnet. A magnet guide may be disposed on the PC board and the magnet extends from the magnet holder. The magnet holder may be attached to a position detector gear. The position detector gear may be in contact with and actuated by an output gear of the transmission. The rear derailleur may further include a position detector gear biasing gear disposed in the derailleur and coupled to the position detector gear to reduce backlash thereof. 
         [0006]    These and other features and advantages of the present invention will be more fully understood from the following description of one or more embodiments of the invention, taken together with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    In the drawings: 
           [0008]      FIG. 1  is a rear derailleur according to the invention installed on a bicycle. 
           [0009]      FIG. 1   a  is the rear derailleur shown partially-actuated. 
           [0010]      FIGS. 2   a, b  are two top views of a linkage of the derailleur at the outboard and inboard extremes of its travel, respectively. 
           [0011]      FIG. 3  is a section view of two linkage pivot pins located at the “B” knuckle of the derailleur through section E-E of  FIG. 2   a.    
           [0012]      FIG. 4  is a section view of the two linkage pivot pins located at the “P” knuckle through section F-F of  FIG. 2   a.    
           [0013]      FIGS. 5   a, b  are perspective views of the derailleur with the power source installed ( 5   a ) and removed ( 5   b ), respectively. The cage is not shown for clarity. 
           [0014]      FIGS. 6   a, b, c  are mechanical and electrical connections between the power source and the derailleur, and also show the sequential procedure for removing the battery from the derailleur through section D-D of  FIG. 2   a.    
           [0015]      FIG. 7  is an exploded view of a gearbox assembly of the derailleur. 
           [0016]      FIG. 7   a  is a top view of the gearbox assembly. 
           [0017]      FIG. 8  is a perspective view of a motor module of the derailleur. 
           [0018]      FIG. 8   a  is a top view of the motor module. 
           [0019]      FIG. 8   b  is a side view of the motor module. 
           [0020]      FIG. 9  is a section view of the motor module along section H-H of  FIG. 8   b  showing the motor/worm/worm-gear arrangement. 
           [0021]      FIG. 10  is a section view of the gearbox assembly through section K-K of  FIG. 7   a  showing three (3) of the gears/axles. 
           [0022]      FIG. 11  is a section view of the gearbox assembly through section J-J of  FIG. 7   a  showing the parts relating to the position detector/magnet. 
           [0023]      FIG. 12  is a section view of the motor module through section G-G of  FIG. 8   a  showing an element for locating the position detector chip relative to the position detector magnet. 
           [0024]      FIG. 13  is a section view of the gearbox assembly through section A-A of  FIG. 1   a  showing a button and its actuator assembly and, in addition, a LED and lens. 
           [0025]      FIG. 14  is a section view of the derailleur assembly through section B-B of  FIG. 1   a  showing the low limit screw. 
           [0026]      FIG. 15   a  is a section view of the derailleur assembly through section C-C of  FIG. 1   a  showing the clutch in the non-actuated position. 
           [0027]      FIG. 15   b  is a section view of the derailleur assembly through section C-C of  FIG. 1   a  showing the clutch in a partially actuated position. 
           [0028]      FIG. 15   c  is a section view of the derailleur assembly through section C-C of  FIG. 1   a  showing the clutch in its fully actuated position, with further movement prevented by a hard stop between the drive arm and the inner link. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    Embodiments of the invention will herein be described with reference to the drawings. It will be understood that the drawings and descriptions set out herein are provided for illustration only and do not limit the invention as defined by the claims appended hereto and any and all their equivalents. For example, the terms “first” and “second,” “front” and “rear,” or “left” and “right” are used for the sake of clarity and not as terms of limitation. Moreover, the terms refer to bicycle mechanisms conventionally mounted to a bicycle and with the bicycle oriented and used in a standard fashion unless otherwise indicated. 
         [0030]      FIGS. 1 and 1   a  are an overview of the derailleur assembly. The basic structure of the electromechanical rear derailleur or gear changer  20  includes a base member  22 , also referred to as a “b-knuckle,” which is attachable to a bicycle frame  19  in a conventional manner and an outer link  24  and an inner link  26 , which is pivotally attached to the base member by link pins  28   a - d , for example. A moveable member or assembly  30 , also known as a “p-knuckle,” is pivotally connected to the outer and inner links at an end opposite the base member to permit displacement of the moveable assembly relative to the base member  22 . 
         [0031]    The outer link  24  and inner link  26  taken together may be considered components of a linkage or link mechanism  32 , for example a parallelogram-type link mechanism. Cage assembly  34  is pivotally connected to moveable assembly  30  in a conventional manner. A bicycle chain  36  may be engaged with a sprocket of a conventional sprocket assembly  38  and positioned in the cage assembly  34  in a conventional manner and can be shifted from one sprocket to another of the sprocket assembly by the movement of moveable assembly  30  and cage assembly relative to base member  22  in a lateral direction when mounted. 
         [0032]    The derailleur  20  is of the “Straight-P” or straight parallelogram type in contrast to a “slant parallelogram” type derailleur. Straight-P derailleurs, or in other words non-slanted parallelogram derailleurs, have a linkage  32  with the pivot axes “PA” of the pins  28  (see  FIG. 5   b ) forming the joints of the linkage substantially perpendicular (i.e., within a few degrees) to the axial A′ direction, e.g., the mounting axis (see  FIG. 2   b ). The mounting axis may be defined by the axis of a mounting bolt “B” of the derailleur or the axis of the hanger opening of the bicycle frame dropout, for example, (not shown). The pivot axes may also be considered parallel to the planes defined by the sprockets  38  ( FIG. 1 ). This causes the moveable assembly  30  to move substantially horizontally. Also, the pivot axes PA may be vertical or non-vertical (see  FIG. 1 ). 
         [0033]    Because derailleur  20  is a straight-P, it has an offset jockey wheel  42 , meaning that the rotational axis of the jockey wheel is not coincident with, i.e., is offset from, the axis of rotation of the cage about the p-knuckle  30 , to accommodate the varying diameters of the sprockets  38 . The derailleur may also be equipped with a damper assembly  40  and a cage lock  41  at the p-knuckle as is known in some mechanical derailleurs. 
         [0034]    A gearbox  44  that is disposed in and/or forms part or all of the b-knuckle  22  drives the linkage  32  and the cage assembly  34  through the range of motion shown in  FIGS. 2   a  and  2   b . The gearbox  44  comprises a transmission  80 . 
         [0035]    Referring to  FIG. 15   a  (which is section C-C of  FIG. 1   a ) the gearbox  44  includes an output shaft  46 . A drive arm  48  is mounted on the output shaft  46  via a castellated geometry that engages with a corresponding castellated geometry on the drive arm. The drive arm  48  and the output shaft  46  are thereby rotatably fixed to one another. 
         [0036]    In order to drive the linkage  32  in the inboard direction, i.e., toward the larger diameter ones of the sprockets  38 , the output shaft  46  and the drive arm  48  is rotated by the gearbox  44  clockwise in  FIG. 15   a , which drives the inner link  26  clockwise Via a direct engagement between the drive arm and a projection  50  on the inner link. In order to drive the linkage  32  in the outboard direction, i.e., toward the smaller diameter sprockets  38 , the output shaft  46  and the drive arm  48  rotate counterclockwise in  FIG. 15   a , which drives the inner link  26  counterclockwise via engagement with a preloaded dutch spring  52 , the position and function of which will be described later. In other words, the drive arm  48  does not directly push on the inner link  26  to drive it in the outboard direction. Rather, the drive arm  48  pushes on the dutch spring  52 , and the dutch spring drives the inner link  26  in the outboard direction. The drive arm  48  and dutch spring  52  are considered a dutch  192 , to move the derailleur or decouple the transmission from the derailleur as will be explained in more detail below. 
         [0037]    As shown in  FIG. 3  (which is section E-E of  FIG. 2   a ), a biasing spring  54  is disposed around one of the linkage pivot pins  28   b . One leg  54   a  of the biasing spring  54  engages the outer link  24 , and the other leg (not shown) engages the base member  22 . The biasing spring  54  may be an extension spring  54 ′ ( FIG. 2   a ). The action of the biasing spring  54  urges the linkage  32  in the outboard direction to take the backlash out of the gearbox  44  and linkage. 
         [0038]      FIG. 14  (which is section B-B of  FIG. 1   a ) shows the low limit screw  56 . The low limit screw  56  is disposed in the gearbox assembly  44 , and by advancing and retracting the screw the inboard range of motion of the inner link  26  is limited. The limit screw  56  is adjusted in a tool-free manner, by turning the limit screw  56  by hand. This tool-free design greatly reduces the maximum torque that the limit screw  56  sees since the human hand can exert a at less torque on the screw than a human hand aided by a screwdriver or other tool, and therefore greatly limits the force exerted on the gears (see  FIG. 7 ) of the gearbox  44  by the limit screw. This is desirable because excessive force on the gears could break them. 
         [0039]      FIG. 7  is an exploded view of the gearbox assembly  44 . The gearbox assembly  44  may form the structural part of the b-knuckle  22 . As shown in  FIG. 7 , a motor module  60  (described in detail later) is received in an opening  62  in the bottom of the housing  64  of the gearbox  44  and is secured with fasteners  66 , for example, six screws. The housing  64  includes a pogo piniseal assembly  68  (described in detail below)) received in a recess  70  in the rear wall  72  of the gearbox housing  64  and is secured with fasteners  74 , for example, two screws. 
         [0040]    An overview of the motor module  60  is shown in  FIG. 8 . A motor  76  is attached to a motor module base  78 , which may be a plastic injection-molded element or elements of any suitable material, and the majority of the transmission  80  is built up on axles  82  that are received in the base  78 . A plate  104 , which may be stamped metal or any suitable material, is attached to the base  78 , by screws for example, and supports the other end of the axles  82  of one or more of the gears, for example three of the gears. 
         [0041]    The gearbox  44  includes a position detector  84  (see  FIGS. 10 ,  11 ). Gears associated with the position detector, which will be described in more detail hereinbelow, are located on or near the motor module base  78 . PC boards  86  comprising circuitry for operating various functions of the derailleur  20  are connected together by flexible cables  88 . The PC boards  86  may be three rigid boards or any suitable number of boards. Two of the three PC boards  86  may be screwed to the base  78 , and the other PC board may be soldered to the back of the motor  76 , for example. A flexible seal  90  is provided on the base  78  to seal between the base and a motor module housing  92  after the base is assembled to the motor module housing. 
         [0042]      FIG. 9  is a section view of the motor module  60 , showing a cross section of the motor  76  (section H-H of  FIG. 8   b ). Referring to  FIG. 9 , the motor  76  may be attached to the motor module base  78  with two screws (not visible in this view). A worm  94  is fixed to a shaft  96  of the motor  76 , and a distal end  98  of the motor shaft is received in a bearing  100 , such as a ball bearing, which is, in turn, received in the motor module base  78 . A worm wheel  102  is engaged with the worm  94 . 
         [0043]      FIG. 10  is a section view of the gearbox  44 , showing three of the gear assemblies (section K-K of  FIG. 7   a ). Referring to  FIG. 10 , one end of each of the three axles  82  may each be rotatably received in the motor module base  78 , and the other end of each axe is received in a corresponding hole in the previously discussed metal plate  104 . Three gear assemblies  106   a - c  of the transmission  80  are rotatably received on the three axles  82 , respectively. The gear assembly  106   a  on the right in  FIG. 10  has the worm wheel  102  on the bottom. The worm wheel  102 , as discussed earlier, is engaged with the worm  94  on the motor shaft  96  (see  FIG. 7   a ). The worm wheel  102  is rigidly attached to a first pinion gear  108  that is coaxial therewith. The first pinion gear  108  is engaged with a spur gear  110  that is rotatably received on the middle of the three axles  82   b . This spur gear  110  is rigidly attached to a second pinion gear  112  that is coaxial therewith. The second pinion gear  112  is engaged with a second spur gear  114  that is rotatably received on the axle  82   c  shown on the left in  FIG. 10 . The second spur gear  114  is rigidly attached to a third pinion gear  116  that is coaxial therewith. The third pinion gear  116  is engaged with an output gear  118  (see  FIG. 7   a ) of the gearbox  44  (not visible in this section view). It should also be noted that the axle  82   c  shown on the left in  FIG. 10  has its top end supported in a bearing  120  in the motor module housing  92 , which adds a substantial amount of support to the metal plate  104 . In other words, the metal plate  104  is supported by the leftmost axle  82   c , which in turn is supported by the bearing  120  in the motor module housing  92 . 
         [0044]      FIG. 3  is a section view of the derailleur  20 , showing a cross section of the two linkage pivot pins  28   a, b  located by the b-knuckle  22  (section EE of  FIG. 2   a ). Referring to the right hand side of  FIG. 3 , the output gear  118  of the gearbox  44  has a toothed portion  122  and two tubular portions  124   a, b  projecting from either side of the toothed portion. The lower tubular portion  124   a  is rotatably received in a bearing in the motor module base  78 , and the upper tubular portion  124   b  is rotatably received in a bearing in the motor module housing  92 . The end of the lower tubular portion  124   a  has the aforementioned castellated geometry that engages the drive arm  48  as previously described (see  FIG. 15   a ). The inner link  26  has two arms  126   a, b , one of which is located above the upper tubular portion  124   b  of the output gear  118 , and the other of which is located below the lower tubular portion  124   a  of the output gear. A hole  128  in the inner link arms  126   a, b  is coaxial with a hole  130  in the output gear  118 , and the associated link pin  28   a  is received in these holes. The link pin  28   a  is rotatable relative to the output gear  118 , but is preferably rotatably fixed to the inner link  26 . 
         [0045]      FIG. 11  is a section view of the gearbox  44 , showing a cross section of the position detector  84 . The position detector  84  is used to determine the position of the derailleur by sensing rotation of the transmission  80  (see  FIG. 8 ). The position detector  84  includes a sensor in the form of a position detector chip  132 , a position detector gear  134 , a position detector magnet  136 , and an optional position detector gear biasing gear  138  (section J-J of  FIG. 7   a ). Referring to  FIG. 11 , the position detector gear  134  is rotatably mounted on a position detector axle  140 , which is supported by the motor module base  78 . The position detector gear  134  engages the output gear  118 . A magnet holder  142  is fixed to the position detector gear  134 , and the position detector magnet  136  is fixed to the magnet holder. Thus, the position detector gear  134 , magnet holder  142 , and magnet  136  all rotate together as a unit. 
         [0046]    A position detector gear biasing gear axle  144  is supported by the motor module base  78 . The position detector gear biasing gear  138  is rotatably received on the position detector gear biasing gear axle  144 . One leg of a torsion spring  146  is engaged with the motor module base  78 , and the other leg of the torsion spring is engaged with the position detector gear biasing gear  138 . Thus, the torsion spring  146  exerts a torque on the position detector gear biasing gear  138 , which in turn exerts a torque on the position detector gear  134  to effectively eliminate any play or backlash between the position detector gear and the output gear  118 . 
         [0047]      FIG. 12  is a section view of the motor module  60 , showing a cross section of the means by which the position detector chip  132  is accurately located relative to the position detector magnet  136  (section G-G of  FIG. 8   a ). Referring to  FIG. 12 , a position detector chip  132  is disposed on one of the three PC boards  86 . A magnet guide  148  has two projections  150 , which may be cylindrical, and which fit into two corresponding holes  152  in the PC board  86 . Two fasteners, e.g., screws, are inserted into the projections  150  to fasten the magnet guide  148  in place on the PC board  86 . Thus, the PC board  86 , position detector chip  132 , magnet guide  148 , and two screws form a subassembly. During assembly of the motor module  60 , this subassembly is assembled to the motor module such that the magnet  136  is received in the magnet guide  148 . Thus, the axis of the position detector chip  132  is accurately aligned to the axis of the position detector magnet  136 . 
         [0048]    In order to prevent rotation of the PC board  86  relative to the motor module  60 , a slot  154  in the other end of the PC board engages a boss  156  on the motor module base  78  (see  FIG. 11 ). Again referring to  FIG. 11 , a screw  158  is then screwed into a hole in the boss  156  until the screw bottoms out on the boss. In this manner, the alignment between the position detector chip  132  and the position detector magnet  136  is held very accurately. An optional compression spring  160  biases the PC board assembly  86  downwards in  FIG. 11 . Alternatively, the magnet guide  148  could have geometry that locates directly on the position detector chip  132 , rather than locating in two holes  152  in the PC board  86 , 
         [0049]      FIG. 13  is a section view of the gearbox  44 , showing a cross section of a button  162  and its actuator assembly  164  (section A-A of  FIG. 1   a ). The button  162  may be an electrical component on the PC board  86 . The actuator assembly  164  includes a plunger  166 , return spring  168 , O-ring seal  170 , and retaining clip  172 . When the plunger  166  is pressed by the user, it actuates the button  162 . Also visible towards the bottom of  FIG. 13  is an LED  174 , which is another component on the PC board  86 . This LED  174  shines through a dear lens  176  (also partially visible in  FIG. 13 ) in the motor module base  78 , 
         [0050]      FIGS. 5   a  and  5   b  show the derailleur  20  with a power source  178 , which may be a battery, installed ( FIG. 5   a ) and with the power source removed ( FIG. 5   b ). The cage assembly is omitted in these views for clarity. The battery may be a rechargeable battery and may be of the lithium-polymer variety. 
         [0051]      FIGS. 6   a, b, c  (section D-D of  FIG. 2   a ) show the electrical and mechanical connectivity between the battery  178  and the derailleur  20 , and also show the procedure for removing the battery from the derailleur. Referring to  FIGS. 6   a, b, c , and  FIG. 7 , the pogo pin assembly  68  includes a pogo pin base  180 , a pogo pin base seal member  182 , and two pogo pins  184  (only one visible), two return springs  186  (one visible), and two O-rings  188  (one visible). The pogo pin assembly  68  may be attached to the motor module housing  92  with two screws as shown in  FIG. 7 . Referring to  FIGS. 6   a, b, c , one end of the return springs  186  contacts the pogo pin  184 , and the other end of the return springs contacts electrical contact pads  190  ( FIG. 7 ) on a PC board  86 . Thus, when the battery  178  is installed as shown in  FIG. 6   a , electricity can flow from the battery, through the pogo pin  184 , through the return spring  186 , and into the PC board  86 . The power supply  178  may be mechanically retained on the derailleur  20  with a catch  196 . 
         [0052]    Turning to  FIGS. 15   a - c , and also  FIG. 4 , the derailleur  20  is equipped with a breakaway mechanism or dutch  192  that protects the gears  106  of the transmission  80  in the gearbox  44  ( FIG. 8 ) in the event of a crash or other side impact to the derailleur.  FIGS. 15   a, b  and  c , show a section view of the derailleur  20  (section C-C of  FIG. 1   a ) with the dutch  192  in its non-actuated (i.e. normal) position ( FIG. 15   a ), its partially actuated position ( FIG. 15   b ), and its fully actuated position ( FIG. 15   c ). During normal riding, the elements of the dutch  192  are arranged as shown in  FIG. 15   a , comprising the spring  52  and drive arm  48 . 
         [0053]    In the event of a crash or other side impact (a force directed from left to right in  FIGS. 15   a, b  and  c ), if the force of the impact overcomes the preload in the torsion-type dutch spring  52 , the links of the linkage  32  rotate clockwise about their pivot pins  28 , deflecting the leg  52   a  of the spring as shown in  FIG. 15   b . Thus, the linkage  32  is able to move without imparting any movement to the gears  106  in the gearbox  44 . When the impact force is removed from the derailleur  20 , the spring leg  52   a  will push against the drive arm  48  and cause the derailleur to go back to its normal state shown in  FIG. 15   a.    
         [0054]    In the event of a more forceful crash or side impact, the links of linkage  32  can rotate clockwise about their pivot pins  28  all the way to the position shown in  FIG. 15   c . In this position, further clockwise rotation of the links  32  is prevented when the drive arm  48  and projection  50  interact and any additional force imparted to the links will be transferred to the gears  106 . 
         [0055]    Another aspect of the invention that protects the gears  106  is the straight-P arrangement of the derailleur  20 . When a bicycle is moving over rough terrain, the p-knuckle  30  of the derailleur  20  experiences forces in the vertical direction. In a slant P derailleur, the axes of the link pins are angled relative to the vertical direction, and these forces can be transmitted through the linkage/parallelogram, imparting undesired forces to the gears in the transmission, since the linkage is able to move in a direction that has a substantial vertical component. The motion of the linkage  32  of the present invention, however, is substantially lateral, rather than vertical, at least because of the vertical orientation of the link pins  28 , and therefore the elements of the derailleur are relatively isolated from the vertical forces created when the bicycle is moving over rough terrain, thereby protecting the gears  106  of the transmission  80  from damage. Preferably, the axes of the link pins  28  are all within 30 degrees of vertical (in addition to being normal to the axial A′ direction). 
         [0056]    A radio chip  194  is positioned on the PC board  86  in such a way to maximize radio signals transmitted between the derailleur  20  and a shifter (or other control devices). Referring to  FIG. 11 , the radio chip  194  is positioned on the lower portion of the rightmost PC board  86  such that it is substantially housed in the motor module base  78 , which may be made of plastic, or any suitable material that does not interfere with the transmission of radio signals. In other words, the radio chip  194  is preferably not positioned on the upper portion of the PC board  86 , because the upper portion of the PC board is substantially housed in the motor module housing  92 , which is preferably made of aluminum, which is a material that is not conducive to transmitting radio signals. 
         [0057]    While this invention has been described by reference to a particular embodiment, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.