Abstract:
Disclosed is an air pump for a fuel cell that utilizes a speed-reduction traction drive so that a low speed electric motor can be used to drive a high-speed rotodynamic compressor. The rotodynamic compressor is an efficient air pump, but operates at high speeds that would require a specialized high-speed electric motor. The speed-reduction traction drive couples to the compressor and provides a low-speed output that is connected to a lower speed electric motor.

Description:
BACKGROUND 
       [0001]    Fuel cells are an alternative source of energy to energy provided by batteries for powering electric vehicles. The fuel cell operates by controlling the combination of a fuel, commonly hydrogen, and oxygen in air to produce electricity that is then used to power electric motors that drive the vehicle. Fuel cell pumps can be used to pressurize the air entering the fuel cell to increase the power density and efficiency of the fuel cell. Higher power density allows a reduction in size and cost of the fuel cell. 
       SUMMARY 
       [0002]    An embodiment of the present invention may therefore comprise an air pump for a fuel cell comprising: a rotodynamic compressor that pressurizes intake air for the fuel cell; a high-speed shaft attached to the rotodynamic compressor; a speed-reduction traction drive that interfaces with the high-speed shaft; an electric motor that is attached to a low-speed output of the speed-reduction traction drive that drives the rotodynamic compressor through the speed-reduction traction drive. 
         [0003]    An embodiment of the present invention may therefore further comprise a method of pumping air to create a source of pressurized air for a fuel cell, comprising: rotating a low speed shaft with an electric motor, the low speed shaft connected to a roller; rotating a high speed shaft with the roller using a traction drive that is formed from an interface between a surface of the roller and a surface of the high speed shaft; driving a rotodynamic compressor with the high speed shaft to create the source of pressurized air; applying the source of pressurized air to the fuel cell. 
         [0004]    An embodiment of the present invention may therefore further comprise a method of pumping air to create a source of pressurized air for a fuel cell comprising: rotating a low speed shaft with an electric motor; driving a traction drive with the low speed shaft; driving a high speed shaft with the traction drive; driving a rotodynamic compressor with the high speed shaft to create the source of pressurized air to the fuel cell. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic diagram of a fuel cell system with a fuel cell pump. 
           [0006]      FIG. 2  is an isometric view of a fuel cell pump with a planetary traction drive. 
           [0007]      FIG. 3  is an isometric view of a fuel cell pump with a planetary traction drive and the addition of a turbine. 
           [0008]      FIG. 4  is an isometric view of a fuel cell pump with a planetary traction drive, where the electric motor is integrated into a ring roller of the planetary traction drive. 
           [0009]      FIG. 5  is a schematic diagram of a fuel cell pump with a single roller traction drive. 
           [0010]      FIG. 6  is a schematic diagram of a fuel cell pump with a single roller traction drive and the addition of a turbine. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0011]      FIG. 1  is a schematic diagram of a fuel cell system  100  with a fuel cell pump  102 . Fuel cell pumps can be used to pressurize the air entering the fuel cell to increase the power density and efficiency of the fuel cell. Higher power density allows a reduction in size and cost of the fuel cell. Rotodynamic compressor  104  compresses intake air  106  for fuel cell  108  and is driven by high-speed shaft  110 . The forced charging of intake air  106  allows fuel cell  108  to have a greater power density and efficiency than if ambient air is used for intake air  106 . Fuel cell  108  combines fuel  112  (such as hydrogen) with intake air  106  in a controlled manner to produce electricity, which can be used to power an electric vehicle. Normally, hydrogen is used for fuel  112 , but other types of fuel can be used as well. Rotodynamic compressor  104  can be of a radial or axial design. The use of a rotodynamic compressor  104  enables high efficiency charging of intake air  106  with a small device, but at the cost that rotodynamic compressor  104  must operate at a high rotational speed, commonly in the range of 100,000 to 200,000 RPM. As most devices have difficulty operating at these high rotational speeds, a speed-reduction traction drive  114  is used. Speed-reduction traction drive  114  interfaces with high speed shaft  110 , and provides a fixed ratio speed step-down to a low-speed output  116  of speed-reduction traction drive  114 . This fixed ratio can be in the range of 10:1 to 20:1, reducing the rotational speeds of 100,000 to 200,000 RPM of rotodynamic compressor to speeds in the range of 5,000-20,000 RPM at a low-speed output  116  of speed-reduction traction drive  114 . Electric motor  118  is connected to low-speed output  116  of speed-reduction traction drive  114 , and provides power to fuel cell pump  102  which drives rotodynamic compressor  104  through speed-reduction traction drive  114 . In this way, speed-reduction traction drive  114  allows a more conventional, lower speed electric motor  118  to drive rotodynamic compressor  104  at the high rotational speeds required by rotodynamic compressor  104  to pressurize intake air  106  for fuel cell  108 . Electric motor  118  is controlled and powered by power electronics  120  of fuel cell system  100 . 
         [0012]    Additionally shown in  FIG. 1  is an optional turbine  122  that is attached to high-speed shaft  110 . Turbine  122  can be utilized to help drive rotodynamic compressor  104 , so that the power requirement from electric motor  118  and speed-reduction traction drive  114  can be reduced. Turbine  122  can also be of a radial or axial design, and extracts power from exhaust gases  124  of fuel cell  108  that are produced after fuel  112  and intake air  106  are combined in fuel cell  108 . Turbine  122  could also be powered by exhaust gasses of an internal combustion engine, if fuel cell  108  is used in a hybrid application. 
         [0013]      FIG. 2  is an isometric view of a fuel cell pump  200  with a planetary traction drive  202 . Rotodynamic compressor  204  pressurizes intake air  206  for fuel cell  208  and is attached to high-speed shaft  210 . Rotodynamic compressor  204  is shown as a radial compressor, but can also be of an axial design. High-speed shaft  210  functions as the sun of the planetary traction drive  202 . Planet rollers  230 ,  232 ,  234  transmit torque to high-speed shaft  210  via shaft traction interfaces  236 ,  238 ,  240 . As shown, shaft traction interfaces  236 ,  238 ,  240  can be shaped, as taught in U.S. Pat. No. 9,670,832, issued Jun. 6, 2017, entitled “Thrust Absorbing Planetary Traction Drive Superturbo” which is specifically incorporated herein by reference for all that it discloses and teaches, to locate high-speed shaft  210  axially and absorb thrust forces from rotodynamic compressor  204 . In this case, planetary traction drive  202  is a thrust-absorbing traction drive. Planet rollers  230 ,  232 ,  234  can also be double roller planets as shown, such that each planet  230 ,  232 ,  234  is composed of two rollers that interface with high-speed shaft  210  as taught in U.S. Pat. No. 8,668,614, issued Mar. 11, 2014, entitled “High Torque Traction Drive,” which is specifically incorporated herein by reference for all that it discloses and teaches. In this case, planetary traction drive  202  is a double roller planetary traction drive. Ring roller  242  transmits torque to planets  230 ,  232 ,  234  through ring traction interfaces  244 ,  246 ,  248 . Traction fluid  250  may optionally be used to increase the torque capacity of shaft traction interfaces  236 ,  238 ,  240  and ring traction interfaces  244 ,  246 ,  248 . Ring roller  242  is driven by idler gear  252 , which forms the low-speed output  216  of planetary traction drive  202 . Low-speed output  216  rotates at approximately 5-10% of the speed of high-speed shaft  210 , depending on the design of planetary traction drive  202 . Electric motor  218  is connected to low-speed output  216  of traction drive. In this way, electric motor  218  drives low-speed output  216  of planetary traction drive  202 , which transmits power to high-speed shaft  210  to drive rotodynamic compressor  204 . The fixed ratio speed step-down between high-speed shaft  210  and low-speed output  216  provided by planetary traction drive  202  allows electric motor  218  to rotate a much lower speed than rotodynamic compressor  204 . 
         [0014]      FIG. 3  is an isometric view of a fuel cell pump  300  with a planetary traction drive  302  and the addition of a turbine  322 . As in  FIG. 2 , rotodynamic compressor  304  pressurizes intake air  306  for fuel cell  308 . High-speed shaft  310  is coupled to planetary traction drive  302 , which in turn is coupled to and driven by electric motor  318 . In addition, turbine  322  is connected to high-speed shaft  310 , and is driven by exhaust gases  324  from fuel cell  308 . Turbine  322  provides a portion of the power necessary to drive rotodynamic compressor  304 , so that the power requirement from electric motor  318  supplied through planetary traction drive  302  is decreased. Turbine  322  is shown as a radial turbine, but can also be of an axial design. Turbine  322  can also be coupled to the exhaust gasses  328  of a gasoline, diesel, natural gas, or hydrogen internal combustion  326  engine used in a hybrid system  330 . 
         [0015]      FIG. 4  is an isometric view of a fuel cell pump  400  with a planetary traction drive  402 , where electric motor  418  is integrated into ring roller  442  of planetary traction drive  402 . The function of planetary traction drive  402  to drive high-speed shaft  410  and rotodynamic compressor  404  is the same as shown in  FIG. 3 , but the low-speed output  416  of planetary traction drive  402  is reconfigured to be integrated into ring roller  442 . Electric motor rotor  454  is combined with ring roller  442 , and together form low-speed output  416  of planetary traction drive  402 , so no additional parts or gearing is necessary. Electric motor stator  456  is arranged around electric motor rotor  454  and electrically drives electric motor rotor  454 . If planetary traction drive  402  is designed to run dry, without use of traction fluid, then the lack of additional gears allows for the entire fuel cell pump  400  to operate without lubrication fluid. The ability to operate fuel cell pump  400  without any circulating fluids simplifies the sealing of fuel cell pump  400  to keep any fluids from entering intake air  406  and contaminating fuel cell  408 . 
         [0016]      FIG. 5  is a schematic diagram of a fuel cell pump  500  with a single roller traction drive  502 . Rotodynamic compressor  504  pressurizes intake air  506  for fuel cell  508 , and is attached to high-speed shaft  510 . Rotodynamic compressor  504  is shown as an axial compressor, but can also be of a radial design. Roller  560  transmits torque to high-speed shaft  510  through traction interface  562 , which forms single roller traction drive  502 . Single roller traction drive  502  can be of a variety of designs, as taught in U.S. patent application Ser. No. 14/885,781, filed Oct. 16, 2015, entitled “Speed Reduced Driven Turbocharger” which is specifically incorporated herein by reference for all that it discloses and teaches. Roller  560  is of a larger diameter than high-speed shaft  510 , so that it spins at a lower speed than high-speed shaft  510 . As an example, a roller  560  of diameter of 10 cm could interface with a high-speed shaft  510  of a diameter of 1 cm to form a 10:1 reduction ratio. Low-speed output  516  of single roller traction drive  502  is attached to roller  560 . Electric motor  518  is attached to low-speed output  516  of single roller traction drive  502 , and provides power at a lower rotational speed to single roller traction drive  502  that drives high-speed shaft  510  and rotodynamic compressor  504  at a high rotational speed. 
         [0017]      FIG. 6  is a schematic diagram of a fuel cell pump  600  with a single roller traction drive  602  and the addition of a turbine  622 . As in  FIG. 5 , rotodynamic compressor  604  pressurizes intake air  606  for fuel cell  608  and is connected to high-speed shaft  610 . Turbine  622  is also connected to high-speed shaft  610 , and extracts power from exhaust gases  624  of fuel cell  608  to help power rotodynamic compressor  604 . Turbine  622  is shown as an axial design, but can also be of a radial design. High-speed shaft  610  is also driven by roller  660  through shaped traction interface  662 . Shaped traction interface  662  locates high-speed shaft  610  axially and absorbs thrust forces from rotodynamic compressor  604  and turbine  622 . Roller  660  is connected to low-speed output  616  of single roller traction drive  602 , which is driven by electric motor  618 . Together, turbine  622  and electric motor  618  power rotodynamic compressor  604  to provide additional air flow to fuel cell  608 . The use of single roller traction drive  602  allows electric motor  618  to rotate at a lower speed than high-speed shaft  610  and rotodynamic compressor  604 . 
         [0018]    Hence, higher power density can be achieved by providing a source of compressed air to fuel cells. A rotodynamic compressor can be driven by an electric motor and, optionally, a turbine. This increases efficiency of the overall system. Because rotodynamic compressors, including radial and axial compressors, operate at very high rotational speeds, a way to drive the rotodynamic compressors is required. Since traction drives are capable of operating at high rotational speeds, rotodynamic compressors can be driven by traction drives that provide a low speed shaft that can be driven by an electric motor, or a motor from a hybrid drive system. As such, rotodynamic compressors can be driven by standard electric motors and the rotational speed of the electric motor can be multiplied by a traction drive to drive the rotodynamic compressor. 
         [0019]    The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.