Abstract:
A rotating power transfer system for an automotive fuel cell vehicle includes one of an impeller and turbine in fluid communication with a fuel cell stack, an electric machine and a shaft operatively associated with the one of impeller and turbine. The system also includes a heating element disposed within the shaft. The heating element is configured to be selectively electrically coupled with a stator coil of the electric machine.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Embodiments of the invention relate to automotive rotatable power transfer systems and methods of operating the same. 
         [0003]    2. Discussion 
         [0004]    Certain techniques are known for heating rotating mechanical elements. U.S. Pat. No. 4,200,784 to Albaric et al. is one such example. Albaric et al. discloses a hollow, rotatable shaft bore heater assembly for heating a shaft. Rotatable shaft heating is provided by a plurality of electrical heaters situated in slots formed on inner surfaces of a plurality of foundation members which are insertable in the hollow shaft and are biased thereagainst by biasing structure. The biasing structure provides biasing force between circumferentially adjacent foundation members so as to maintain contact between the shaft and foundation members during non-rotation of the shaft. 
         [0005]    U.S. Pat. No. 4,329,566 to Hooper is another example. Hooper discloses a heated fuser roll for use in a fuser apparatus for fixing toner images to a support surface. The fuser roll includes a circular sleeve member having at least one heating unit positioned within the sleeve member. Each heating unit includes (i) a plurality of axially disposed thermally conductive members, (ii) a plurality of wafer shaped heating elements and (iii) resilient means. Each of the heating units is separated from each other by an insulating member. A plurality of cavities on flat surfaces of the thermally conductive members is provided. One of the heating elements is positioned within each of the cavities. 
       SUMMARY 
       [0006]    A rotating power transfer system for an automotive fuel cell vehicle including a fuel cell stack includes one of an impeller and turbine in fluid communication with the fuel cell stack, an electric machine including a stator coil and a shaft operatively associated with the one of impeller and turbine. The system also includes a heating element disposed within the shaft and configured to be selectively electrically coupled with the stator coil. 
         [0007]    A rotating power transfer system including a stator coil for an automotive vehicle includes one of an impeller and turbine and a rotatable member mechanically coupled with the one of impeller and turbine. The rotatable member includes a heating element to heat the rotatable member. The system also includes a mechanical governor assembly configured to selectively electrically couple the heating element and the stator coil based on a rotational speed of the rotatable member. 
         [0008]    A method of heating a shaft, including a heating element, of an automotive rotating power transfer device including a stator coil includes electrically coupling the stator coil and heating element if a rotational speed of the shaft is less than a threshold rotational speed and electrically de-coupling the stator coil and heating element if the rotational speed of the shaft is equal to or greater than the threshold rotational speed. 
         [0009]    While example embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the invention. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic view of an embodiment of a fuel cell system for an automotive vehicle. 
           [0011]      FIG. 2  is a schematic view, in cross-section, of a motor driven pump. 
           [0012]      FIG. 3  is an exploded assembly view of a portion of the motor driven pump of  FIG. 2 . 
           [0013]      FIG. 4  is another schematic view, in cross-section, of the motor driven pump of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to  FIG. 1 , an embodiment of an automotive fuel cell system  10  includes a hydrogen tank  12 , pressure regulator  14 , fuel cell stack  16  and motor driven pump  18 . Other embodiments, of course, may have different arrangements and/or configurations and be implemented in different environments, e.g., a stationary fuel cell for home power generation, etc. 
         [0015]    Hydrogen gas (indicated by arrow) flows from the hydrogen tank  12 , through the pressure regulator  14  and to the fuel cell stack  16 . The hydrogen gas reacts with oxygen (not shown) within the fuel cell stack  16  to produce electrical power. This reaction also produces water vapor. In certain proton exchange membrane (PEM) technologies, nitrogen gas crosses over from a cathode to an anode through the PEM. This dilutes the concentration of hydrogen in the anode. In order to maintain a proper concentration of hydrogen, the gas mixture exits the fuel stack  16  and is re-circulated via a recirculation loop  20  powered by a radial-flow impeller  22  of the motor driven pump  18 . In other embodiments, the impeller  22  may act as a turbine, for example, if the flow of fluid causes the impeller  22  to rotate, thus generating electrical power. 
         [0016]    Water vapor may also exit the fuel cell stack  16  and enter the recirculation loop  20 . In some embodiments, a water separator (not shown) and purge valve (not shown) may be provided in the recirculation loop  20  to facilitate the removal of some of the water vapor. If the fuel cell system  10  is deactivated in cold environments, water vapor may condense and freeze in the motor driven pump  18  preventing the impeller  22  from moving. In certain prior art systems, a heater (not shown) separate from the motor driven pump  18  is used to melt ice that may have formed in the motor driven pump  18 . 
         [0017]    Referring now to  FIG. 2 , electrical power is provided to stator coils  24  of an electric machine  26  to produce an electromagnetic field. The stator coils  24  are fixedly attached with a housing  28  of the motor driven pump  18 . This electromagnetic field causes a rotor  30  to rotate relative to the stator coils  24 . A hollow shaft  32  is fixedly attached with the rotor  30 . The impeller  22  is fixedly attached, e.g. press fit, with the shaft  32 . In the embodiment of  FIG. 2 , a collar  34  and cap  35  are fixedly attached, e.g. press fit, onto an end of the shaft  32  opposite the impeller  22 . While rotating, the shaft  32  and collar  34  are rotatably supported on bearings  36 ,  38  mounted within the housing  28 . 
         [0018]    An electrically conductive ring  40  may be electrically connected with the stator coils  24  such that electrical current provided to the stator coils  24  may pass through the ring  40 . In the embodiment of  FIG. 2 , electrical leads  42  electrically connect the stator coils  24  and the ring  40 . Any suitable electrical connection, however, may be used. 
         [0019]    An electrically conductive plate  44  may be drivingly engaged with and axially free in the shaft  32  via a key  46  provided on the plate  44  and a key way  48  provided on the shaft  32 . The plate  44  may thus move axially relative to the shaft  32 . In other embodiments, the key  46  may be provided on the shaft  32  and the keyway  48  may be provided on the plate  44 . Multiple keys  46  and keyways  48  circumferentially spaced apart may be also provided. Other configurations and arrangement are, of course, also possible. 
         [0020]    A heating element  50  is disposed within a passageway  52  of the shaft  32 . The heating element  50 , when activated, heats the shaft  32  to, for example, melt any ice formed on an exterior of the shaft  50 . In addition, heat is conducted into the impeller  22  (e.g. aluminum material), which may also melt any ice dams between the impeller profile and surrounding housing. 
         [0021]    The shaft  32  includes an aperture  54  adjacent to the plate  44  though which an end  56  of the heating element  50  passes. The end  56  terminates in an electrical contact  58 , e.g., electrically conductive foil, that is at least partially carried by the exterior of the shaft  50 . The electrical contact  58  and plate  44  may be positioned in contact with one another such that electrical current may pass from the plate  44  to the electrical contact  58 . 
         [0022]    Referring now to  FIGS. 2 and 3 , four governors  60  are spaced at approximately 90° intervals around the plate  44 . In other embodiments, however, any suitable number of governors  60  may be used. For example, three governors may be spaced at approximately 120° intervals around the plate  44 . Because the plate  44  rotates, it may be desirable to approximately equally space the governors  60  around the plate  44  to minimize vibration. The governors  60 , however, may be spaced as desired. 
         [0023]    As explained below, the governors  60  may move the plate  44  relative to the shaft  32  based on the rotational speed of the shaft  32  to selectively electrically connect the stator coils  24  and heating element  50 . In other embodiments, however, a switch electrically connected with the stator coils  24  and heating element  50  may be used instead of the plate  44 /governor  60  configuration described above. For example, a controller and sensor (not shown) may monitor the rotational speed of the shaft  32  and command the switch closed if the rotational speed is less than a threshold rotational speed. The controller and sensor may command the switch open if the rotational speed is greater than or equal to the threshold rotational speed. Other configurations and arrangements are, of course, also possible. 
         [0024]    The governors  60  of  FIGS. 2 and 3  each include a weight  62  on an end of a governor shaft  64 , as apparent to those of ordinary skill. The governor shafts  64  are each mounted within (and may move relative to) a governor housing  66  mechanically attached with the plate  44 . Springs (not shown) within each of the governor housings  66  spring bias one of the governor shafts  64  toward a stop collar  68  fixedly attached with the housing  28 . That is, if the plate  44  is not moving, the weights  62  will rest against the collar  68  (as shown in solid line in  FIG. 2 .) As explained in more detail below, the weights  62  move away from the collar  68  if the plate  44  achieves a threshold rotational speed (as shown in phantom line in  FIG. 2 .) 
         [0025]    An end of a coil spring  70  is seated within a recess  72  formed on a side of the plate  44  adjacent to the governors  60 . Another end of the spring  70  is seated within a spring collar  74  fixedly attached, e.g., bolted, bonded, etc., with the collar  34 . The collar  74  of  FIG. 2  includes a guide portion  75  surrounded by the spring  70  and a seat portion  76  that retains the another end of the spring  70 . 
         [0026]    In the embodiment of  FIG. 2 , the spring  70  biases the plate  44  towards the ring  40 . The spring  70  has a tendency to resist compression. In other embodiments, the spring  70  may be located between the electric machine  26  and the plate  44  (and thus have a tendency to resist extension.) In some of these other embodiments, the collar  74  may be fixedly attached with the rotor  30  and the spring  70  seated therein accordingly. Alternatively, the spring  70  may be seated against the shaft  32 . Other arrangements are also possible. 
         [0027]    A ramping surface  77  on which the weights  62  may travel is provided by a ramping element  78 . In the embodiment of  FIG. 2 , the ramping element  78  comprises a plate fixedly attached, e.g., bolted, with the housing  28 . The ramping surface  77  is formed by a chamfered aperture in the plate  78 . In other embodiments, the ramping element  78  may take any suitable shape and/or configuration. 
         [0028]    As explained above, water vapor may condense and freeze around the shaft  32  thus preventing its movement if, for example, the system  10  illustrated in  FIG. 1  is deactivated in freezing conditions. If reactivated, electrical current provided to the stator coils  24  will pass through the electrical leads  42 , the ring  40 , the plate  44  and the electrical contact  56  to energize the heating element  50  (even though the shaft  32  is frozen in place). The heating element  50  will melt any ice around the shaft  32  to free its movement. As the shaft  32  begins to rotate, the plate  44  keyed to the shaft  32  will also rotate. As the plate  44  rotates, the weights  62  will begin to move away from the collar  68  and, once the plate  44  achieves a threshold rotational speed, make contact with the ramping surface  77 . 
         [0029]    The threshold rotational speed may be dictated by, for example, the number of governors  60 , the mass of the weights  62 , the length of the governor shafts  64 , etc., as apparent to those of ordinary skill from the appropriate equations of motion. In the embodiment of  FIG. 2 , the threshold rotational speed is approximately 5% of a maximum rotational speed of the shaft  32 . The threshold rotational speed for other embodiments may be different and driven by design and/or packaging considerations. 
         [0030]    Referring now to  FIG. 4 , as the plate  44  continues to increase in rotational speed, forces generated by the rotating weights  62  will permit the weights  62  to “climb” the ramping surface  77  (thus overcoming the biasing force of the spring  70 ) and move the plate  44  away from the ring  40 . The electrical connection between the stator coils  24  and the heating element  50  will be broken once the plate  44  no longer contacts the ring  40 . The plate  44  may continue to travel away from the ring  40  until it makes contact with the ramping element  78 . In other embodiments, a stiffness of the spring  70 , or other suitable mechanism/element, may be used to limit the travel of the plate  44 . 
         [0031]    The plate  44  will return to the position illustrated in  FIG. 2  if, for example, the turbo machine  18  is deactivated or the rotational speed of the shaft  32  is less than the threshold rotational speed. 
         [0032]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.