Abstract:
An integrated electric motor and traction drive is disclosed. The device comprises an electric motor and a traction drive. The electric motor provides power at a high angular velocity to a sun roller. The sun roller transfers the power to the traction drive which reduces the power to a lower angular velocity and delivers it via an output shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to U.S. Provisional Patent Application No. 60/433,331 filed, Dec. 13, 2002, from which priority is claimed, hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Electric motors are one of the most widely used machines. The applications range from automobiles to earth movers, from aerospace to marine machinery, from home appliances to medical equipment. Recently, there have been increasing demands for motors with greater power density. For the purposes of this application, power density can be defined as the amount of power delivered either per unit weight or per unit volume, expressed respectively as W/kg or W/liter. One way to increase power density is to elevate the speed of a motor. As the speed of a motor increases, so does its overall power. As a result, there is a trend in machine designs toward using smaller electric motors operating at higher speeds. In some applications, this results in the speed of the motor being higher than the required speed of the driven member. Therefore, it is often deemed necessary to include a speed reduction unit between the motor and the driven member to reduce the speed of the motor to the required speed of the driven member. Although this results in an overall higher power density, the speed reduction unit still limits power density because of the additional weight and volume.  
           [0003]    One solution to this is a so-called gear-head motor where a gear reduction unit is integrated with an electric motor. There are many types of gear-head motors including “precision” gear-head motors, which are capable of running at higher speeds and generally are much more expensive than “regular” gear head motors. However, even with precision-made gear heads, gear-head motors are often limited to operating speeds of 5,000 to 6,000 rpm. This has, to a large degree, prevented the gear-head motors from achieving their ultimate power-density potentials.  
           [0004]    Recent developments in traction drives have demonstrated that a well-built traction drive can operate at higher speeds up to and exceeding 10,000 rpm and cost much less than gear-head drives. Thus, integrating a traction drive with an electric motor can increase the system power-density potential and thus extend the scope of application of electric motors.  
         SUMMARY OF THE INVENTION  
         [0005]    Briefly stated, the invention is a motor supplying power at a high angular velocity integrated with a traction drive for receiving the power at a high angular velocity and delivering the power at a lesser angular velocity. The motor comprises a stator, a rotor that revolves in the stator at a high angular velocity, and a sun roller with a first raceway affixed to the rotor. The traction drive comprises a carrier, an outer ring member with an output shaft and a fourth raceway eccentric to the first raceway of the sun roller, and a loading planetary roller supported by the carrier with a third raceway. The third raceway engages with the first raceway of the sun roller and the fourth raceway of the outer ring in a convergent wedge formed by the first and fourth raceways for transferring power between the sun roller and the outer ring. The output shaft of the outer ring delivers power at a lesser angular velocity. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0006]    In the accompanying drawings which form part of the specification:  
         [0007]    [0007]FIG. 1 is an exploded perspective view showing the front of an embodiment of the invention.  
         [0008]    [0008]FIG. 2 is an exploded perspective view showing the back of the embodiment.  
         [0009]    [0009]FIG. 3 is a cross-sectional view of the embodiment.  
         [0010]    [0010]FIG. 4 is a cross-sectional view of the motor.  
         [0011]    [0011]FIG. 5 is a diagram showing forces at the raceways and at a support shaft of the embodiment. 
     
    
       [0012]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.  
         [0014]    As shown in FIGS. 1 and 2, an embodiment of an integrated electric motor and traction drive  1  comprises an electric motor  100  and a traction drive  200 . As used in this specification, “integrated” is defined as “combining multiple parts to form a single unit.” 
         [0015]    As shown in FIGS.  1 - 3 , the electric motor  100  comprises a motor housing  110 , a motor cover  120 , a bearing cup plate  130 , a stator  140 , a rotor  150 , and a sun roller  153 . The motor housing  110  is a hollow cylinder defining a front face  111  with holes  112  for attaching to the motor cover  120 , a back face  113  with holes  114  for attaching to the speed reducer  200 , an inner surface  115  for affixing to the stator  140 , and cooling fins  116  extending from an outer surface  117  to aid with the dispersal of heat produced during operation. The motor cover  120  is a disk with a raised concentric annulus defining a front face  121  with holes  122  for attaching to the bearing cup plate  130 , a back face  123  with holes  124  for attaching to the front face  111  and respective holes  112  of the motor housing  110 , and a first bore  125  for supporting the sun roller  153  via a bearing  155 . The bearing cup plate  130  is a disk defining a back face  131  with holes  132  for attaching to the front face  121  and respective holes  122  of the motor cover  120 . The stator  140  is a hollow cylinder with an outer surface  141  for affixing to the inner surface  115  of the motor housing  110  and internal poles  142  that are energized by electrical power to form magnetic poles for engaging the rotor  150 . The rotor  150  is a hollow cylinder defining a second bore for affixing to the sun roller  153  and external male poles  152  for engaging the internal female poles  142  of the stator  140 . The sun roller  153  is a shaft defining a first raceway  154  for engaging with the traction drive  200 .  
         [0016]    As well known to those skilled in the art, electric connections are provided to supply electric power to and from the windings of the internal poles  142  of the stator  140 . For easier viewing, the windings are not shown in the drawings. While the embodiment in FIGS.  1 - 3  discloses a typical switched reluctance motor, other types of motors may be used such as, brushless motors, DC motors, and AC induction motors. While the embodiment in FIGS.  1 - 3  discloses a rotor  150  that is formed by laminated plates, other types of rotors may be used.  
         [0017]    As shown in FIGS.  1 - 3 , the traction drive  200  comprises a carrier  210 , a loading planetary roller  230 , supporting planetary rollers  245 , an outer ring member  250 , a double row bearing  260 , and a traction drive housing  270 . The carrier  210  comprises a base plate  211  and a cover plate  220 . The base plate  211  is a disk with a raised concentric annulus defining a front face  212 , a back face  213 , holes  214  for attaching to the motor housing  110  and the traction drive housing  270 , an obround pinhole  215  for supporting the loading planetary roller  230 , pinholes  216  for supporting the supporting planetary rollers  245 , a third bore  217  for supporting the sun roller  153 , and arcuately shaped wedges on the back face  213 , hereby referred to as islands  218 . The islands  218  act as spacers between the base plate  211  and cover plate  220  defining cavities for receiving supporting planetary rollers  245  and the loading planetary roller  230 . The cover plate  220  is a disk defining an obround pinhole  221  for supporting the loading planetary roller  230 , pin holes  222  for supporting the supporting planetary rollers  245 , and a through hole  223  for hosting the sun roller  153 .  
         [0018]    The supporting planetary rollers  245  comprise pin shafts  246  and bearings  247 . The bearings  247  define second raceways  248  for engaging with the first raceway  154  of the sun roller  153 . The bearings  247  affix to the pin shafts  246  so that the second raceways  248  rotates freely. The pin shafts  246  insert into the pinholes  216  of the base plate  211  and the pinholes  222  of the cover plate  220  so that the supporting planetary rollers  245  reside within the cavities defined by the islands  218 .  
         [0019]    The loading planetary roller  230  comprises a pin shaft  231 , an elastic insert  232 , a support bearing  235  and a roller  238 . The elastic insert  232  is circularly shaped with an outer surface  233  and a center hole  234 . The support bearing  235  is a circular anti-friction bearing, such as a ball bearing, with an inner race  236  and an outer race  237 . The roller  238  is also circularly shaped with an inner surface  239  and a third raceway  240 . When assembled, the support bearing  235  affixes to the elastic insert  232  with its inner race  236  fitted tightly over the outer surface  233  of the insert  232 . The roller  238  is fitted to the support bearing  235  with an interference fit between its inner surface  239  and the outer race  237  of the support bearing  235  so that the roller  238  can rotate freely. Next, the elastic insert  232  is affixed to the pin shaft  231  by inserting the pin shaft  231  through the center hole  234  of the elastic insert  232 . The pin shaft  231  is inserted into the pinhole  215  of the base plate  211  and the pinhole  221  of the cover plate  220  so that the third raceway  240  engages the first raceway  154  of the sun roller  153  and a fourth raceway  251  of the outer ring  250 . The obround shape of the pinholes  215  and  221  allow the pin shaft  231  to slide back and forth slightly. During operation, this allows the loading roller  238  to automatically shift to an effective position for the third raceway  240  of the loading roller  238  to engage in a convergent wedge between the first raceway  154  of the sun roller  153  and a fourth raceway  251  of the outer ring  250  allowing power to be transferred between the sun roller  153  and the outer ring  250 . While the pinshaft  231  shown in FIGS.  1 - 3  is shown to be supported by pinholes  215  and  221 , it is also possible to have the pinshaft  231  supported by the carrier  210  through springs or elastomers.  
         [0020]    The outer ring member  250  is an annular ring defining the fourth raceway  251  eccentric to the first raceway  154  of the sun roller  153  for engaging the third raceway  240  of the loading planetary roller  230  and the second raceways  248  of the supporting planetary rollers  245 , an output shaft  252  for transferring power, and spokes  253  connecting the fourth raceway  251  and output shaft  252  to accommodate any possible misalignment between the fourth raceway  251  and output shaft  252 . The output shaft  252  is supported by a back-to-back arranged double-row bearing  260 .  
         [0021]    The traction drive housing  270  is a hollow cylinder with a raised concentric annulus defining a front face  271  with holes  272  for attaching to the base plate  211  and respective holes  214 , a fourth bore  273  for receiving the double row bearing  260 , and a back face  274  for external mounting.  
         [0022]    To assemble the embodiment, the back face  131  of the bearing cup plate  130  is attached to the front face  121  of the motor cover  120  by aligning holes  132  with respective holes  122  and using appropriate mechanical means, such as bolts or rivets. Similarly, the back face  123  of the motor cover  120  is attached to the front face  111  of the motor housing  110  by aligning holes  124  with respective holes  112  and using appropriate mechanical means, such as bolts or rivets. The stator  140  is inserted in to the motor housing  110  so that the outer surface  141  of the stator  140  is affixed to the inner surface  115  of the motor housing  110 .  
         [0023]    Bearing  156  is affixed to the sun roller  153  adjacent to the first raceway  154  for rotational support. A sleeve spacer  159  is affixed adjacent to the bearing  156 . The rotor  150  is affixed to the sun roller  153  adjacent to the sleeve spacer  159 . A nut  157  is affixed to the sun roller  153  to secure the rotor  150 . Bearing  155  is affixed to the end of the sun roller  153  opposite the first raceway  154  for rotational support. As shown in FIGS. 3 and 4, the sun roller  153  and rotor  150  insert into the stator  140  so that the bearing  155  affixes to the first bore  125  of the motor cover  120  and the bearing  156  affixes to the third bore  217  of the base plate  211 . In this position, the sun roller  153  and the rotor  150  rotate freely within the stator  140 . In addition, the first raceway  154  extends past the base plate  211  so that the first raceway  154  rotates within the carrier  210 .  
         [0024]    To assemble the carrier  210 , the cover plate  220  attaches to the islands  218  of the base plate  211 . The pinshafts  246  of the supporting planetary rollers  245  are inserted into the pinholes  216  of the base plate  211  and the pinholes  222  of the cover plate  220  so that the second raceways  248  frictionally engage the first raceway  154  of the sun roller  153 . The pinshaft  231  of the loading planetary roller  230  is inserted into the pinhole  215  of the base plate  211  and the pinhole  221  of the cover plate  220  so that the third raceway  240  frictionally engages the first raceway  154  of the sun roller  153 .  
         [0025]    The double row bearing  260  affixes to the fourth bore  273  of the traction drive housing  270 . To further secure the double row bearing  260 , a snap ring  275  may be used. The double row bearing  260  affixes to the output shaft  252  of the outer ring member  250  so that the outer ring member  250  can rotate freely. The front face  271  of the traction drive housing  270  attaches to the back face  213  of the base plate  211  by aligning holes  272  with respective holes  214  and using appropriate mechanical means, such as bolts or rivets. In this position, the fourth raceway  251  of the outer ring member  250  frictionally engages the third raceway  240  of the loading planetary roller  230  and the second raceways  248  of the supporting planetary rollers  245 .  
         [0026]    In operation, electric power is supplied to the windings of the internal female poles  142  causing the rotor  150  and sun roller  153  to rotate and transfer power at a high angular velocity. Power is transferred from the first raceway  154  of the sun roller  153  to the second raceways  248  of the supporting rollers  245  and the third raceway  240  of the loading planetary roller  230 . Then, power is transferred from the second raceways  248  and the third raceway  240  to the fourth raceway  251  of the outer ring  250 . Finally, power is transferred via the spokes  253  of the outer ring  250  to the output shaft  252  where it is output at a lesser angular velocity.  
         [0027]    As the sun roller  153  rotates in FIG. 5, the friction force F R  (traction) generated at the contact between the first raceway  154  and third raceway  240  of the loading planetary roller  230  tends to rotate the loading roller  230  and generate a reaction friction force F R  at the contact between the third raceway  240  and the fourth raceway  251  of the outer ring  250 . These friction forces pull the loading roller  230  into a converged wedge gap between the sun roller  153  and the outer ring  250  in either direction depending upon the rotation direction of the sun roller  153 . The friction forces FR are balanced by normal contact forces N at the contacts between the first raceway  154  and third raceway  240  and between the fourth raceway  251  and third raceway  240 , and by a supporting force F S  provided from carrier  210  via pin shaft  231 , elastic insert  232 , and support bearing  235  to the loading roller  238 .  
         [0028]    The amount of normal force N generated in response to friction force F R  is controlled by the supporting stiffness K S  of the loading roller  230  assembly in relationship with the contact stiffness at the contacts along with the structural flexibility of outer ring  250  and the flexibility of other relevant components. Assume the lumped effective contact stiffness, representing Hertzian contact stiffness, structural flexibility of outer ring  250  and all other relevant components, be denoted as K R . The following relationship generally holds true.  
                 K   S       K   R       =         μ   o        sin                 δ     -     2          sin   2          (     δ   2     )                   (   1   )                               
 
         [0029]    where  
         [0030]    K S =effective support stiffness of loading roller  
         [0031]    K R =effective contact stiffness between the loading roller and the sun roller and between the loading roller and the outer ring  
         [0032]    μ o =operating traction coefficient  
         [0033]    δ=operating wedge angle (different from initial wedge angle)  
         [0034]    To prevent the traction drive  200  from excessive slip at the contacts, the following inequality must be held.  
                 K   S       K   R       =           μ   o        sin                 δ     -     2          sin   2          (     δ   2     )           ≤         μ   m        sin                 δ     -     2          sin   2          (     δ   2     )                     (   2   )                               
 
         [0035]    where  
         [0036]    μ m =maximum available traction coefficient.  
         [0037]    The second raceways  248  of the supporting rollers  245  are placed between and in contact with the first raceway  154  of the sun roller  153  and fourth raceways  251  of the outer ring  250 . The supporting rollers  245  provide appropriate forces at the contacts between the outer ring  250  and the respective supporting rollers  245  to balance out the contact forces at the contact between the outer ring  250  and the loading roller  230 . Likewise, the supporting rollers  245  provide appropriate forces at contacts between the sun roller  153  and the supporting rollers  245  to balance out the contact forces at the contact between the sun roller  153  and the loading roller  230 . Thus, forces acting on the outer ring  250  and the sun roller  153  are internally self-balanced.  
         [0038]    As can be appreciated, the frictional forces may also be generated at the contacts between the supporting rollers  245  and the outer ring  250  and between the supporting rollers  245  and the sun roller  153 . These friction forces can also help to transmit torque and power between the sun roller  153  and outer ring  250 .  
         [0039]    For efficiency considerations, conventional traction drives have to operate with a wedge angle smaller but close to the so-called friction angle δ f  defined as:  
         δ ƒ =2 Arc tan μ  (3)  
         [0040]    where μ is the friction coefficient at the contact.  
         [0041]    This imposes an undesirable design constraint on the azimuth position of the loading roller  230  since the wedge angle δ is directly related to the azimuth position α of the loading roller  230  in relation to the eccentricity e of the sun roller&#39;s first raceway  153  with respect to the outer ring&#39;s fourth raceway  251 .  
         [0042]    As indicated by equation (2), by choosing appropriate ratio of effective supporting stiffness K S  to effective contact stiffness K R  it is possible to operate the traction drive  200  at a wide range of given operating wedge angle regardless of the friction coefficient, without sacrificing the drive&#39;s efficiency. That is to say, the traction drive  200  is capable of operating with operating traction coefficient close to the maximum available value even at a small wedge angle. This allows the loading roller  230  to be placed at or in vicinity to the azimuth position corresponding to the widest wedge gap. Consequently, the same loading roller  230  can be used as a bi-directional loading mechanism, substantially simplifying the design and construction of the traction drive  200 .  
         [0043]    As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.