Abstract:
A vehicle including a chassis, a plurality of wheels, a regenerative braking system, a fuel cell, a capacitive energy storage device and a controller. The wheels are coupled to the chassis. The regenerative braking system is operatively connected to the plurality of wheels. The capacitive energy storage device is electrically couplable to the fuel cell. The controller is electrically connected to the fuel cell. The controller routes electrical power from the fuel cell through the regenerative braking system to the capacitive energy storage device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a vehicular fuel cell capacitor charging system, and, more particularly, to a vehicular fuel cell capacitor charging system in a vehicle with a regenerative braking system. 
       BACKGROUND OF THE INVENTION 
       [0002]    A fuel cell is an electrochemical cell that converts chemical energy from fuel into electrical energy. The electrical energy is generated by way of the reaction between a fuel supply and an oxidizing agent. The resulting reactants flowing into the cell and the chemical reaction produces products that flow out of it, while the electrolyte remains within the fuel cell. The fuel cell continues to produce electrical power continuously as long as the necessary reactant and oxidant flows are maintained thereto. Fuel cells are utilized in both stationary and mobile applications. For example, fuel cells are utilized on the type  212  submarine of the German and Italian navies. 
         [0003]    Regenerative braking is utilized in many hybrid vehicles. When the brake pedal is depressed this causes the vehicle to engage a circuit to cause the electric motors that provide power to the wheels to act as generators thereby generating electricity by removing energy from the vehicle thus slowing of the vehicle. Typically the energy generated in the braking maneuver is stored in either an electrochemical device such as a battery or in a capacitive device such as an ultracapacitor. 
         [0004]    The vehicle has been stopped and turned off the capacitive storage device may lose its charge. It is desirous to charge the capacitive energy storage device after starting the vehicle so that energy can be removed or added from it as needed. The discharged capacitive energy storage device will by its very nature act as a current sink until the voltage has reached its charged value. If a high current is drawn directly from the fuel cell by the capacitor bank that may cause the fuel cell to shutdown due to the over current situation. 
         [0005]    Ultracapacitors are often utilized as the passive energy storage device used with the fuel cell in order to buffer transient loads. The charge current of the discharged ultracapacitor bank is higher than the maximum available current from the fuel cell. In order to overcome this difficulty the ultracapacitors must be pre-charged to a voltage close to the fuel cell voltage to prevent a large charging current from being drawn from the fuel cell by the low charged capacitor bank. 
         [0006]    A prior art solution is to charge the capacitor bank but utilizing an external boost converter that receives energy from a 12 V battery. The solution may take a long time, such as 15 min., for the boost converter to provide the charging energy of the ultracapacitor bank. 
         [0007]    What is needed in the art is a apparatus and a method to quickly charge the ultracapacitors without requiring the power to come from a 12 volt battery. 
       SUMMARY 
       [0008]    The invention in one form is directed to a vehicle including a chassis, a plurality of wheels, a regenerative braking system, a fuel cell, a capacitive energy storage device and a controller. The wheels are coupled to the chassis. The regenerative braking system is operatively connected to the plurality of wheels. The capacitive energy storage device is electrically couplable to the fuel cell. The controller is electrically connected to the fuel cell. The controller routes electrical power from the fuel cell through the regenerative braking system to the capacitive energy storage device. 
         [0009]    The invention in another form is directed to a fuel cell control system for use with a vehicle having a regenerative braking system. The control system includes a fuel cell, a capacitive energy storage device and a controller. The capacitive energy storage device is electrically coupled to the fuel cell. The controller is configured to route electrical power from the fuel cell through the regenerative braking system to the capacitive energy storage device. 
         [0010]    The invention in yet another form is directed to a method of charging a capacitive energy storage device of a vehicle having a regenerative braking system. The method includes the step of routing electrical power from a fuel cell through the regenerative braking system to the capacitive energy storage device under the control of the controller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a schematical top view of a vehicle system utilizing an embodiment of a capacitive energy storage device charging system of the present invention; 
           [0013]      FIG. 2  is a schematic of the existing configuration of a capacitive energy storage device charging system; 
           [0014]      FIG. 3  is a schematic of system of a capacitive energy storage device charging system of  FIG. 1 ; and 
           [0015]      FIG. 4  is a schematical view of an embodiment of a method used by the capacitive energy storage device charging system of  FIGS. 1 and 3 . 
       
    
    
       [0016]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0017]    Referring now to the drawings, and more particularly to  FIG. 1 , there is illustrated a vehicle  10  including a chassis  12 , wheels  14 , a regenerative braking system  16 , a capacitive energy storage device  18 , control circuitry  20  and a fuel cell  22 . Capacitive energy storage device  18  may be in the form of a bank of ultracapacitors, which are configured to absorb abrupt changes in the charging or discharging of the unit. Fuel cell  22  is activated when vehicle  10  is started, thereby causing fuel cell  22  to come online and start producing electrical power, which is used to drive wheels  14  and to provide the power to perform other vehicular tasks. During the deacceleration of vehicle  10  regenerative braking system  16  recoups some of the motion energy of vehicle  10  and sends it to capacitive energy storage device  18 . 
         [0018]    Now, additionally referring to  FIG. 2  there is illustrated a schematic diagram showing how a prior art fuel cell system for a vehicle charged capacitive energy storage device  18 . When fuel cell  22  was started, then boost converter  42  was used to charge capacitive energy storage device  18  up to a voltage commensurate with the output voltage of fuel cell  22 . Boost converter  42  obtains energy from a 12 volt battery  44  and a typical charge time is 15 minutes, which significantly delays the direct connection of fuel cell  22  to capacitive energy storage device  18 . 
         [0019]    Now, additionally referring to  FIG. 3  there is shown an embodiment of the charging apparatus of capacitive energy storage device  18  of the present invention including an inverter/drive system  24 , a contactor  26 , a contactor  28 , a resistor bank  30 , a solid state switch  32 , a diode  34 , a fuse  36 , a solid state switch  38 , a controller  40 , a boost converter  42  and a 12 volt battery  44 . Some of the elements of  FIG. 2  are similar to those in  FIG. 3  and bear the same reference number. Solid state switches  32  and  38  may be in the form of MOSFETs as depicted in the illustrations, although other devices are also contemplated. 
         [0020]    Inverter/drive system  24  schematically represents the power providing apparatus that supplies motive power to wheels  14 , as well as control circuitry associated therewith. The elements therein include a part of regenerative braking system  16  in that the motors that are used as generators when braking are therein. No further details of this system are provided for the sake of clarity and to focus on the present invention. 
         [0021]    Contactor  26  is under the control of controller  40  and may be kept in an open condition to electrically isolate capacitive energy storage device  18  from the rest of the circuitry. Contactor  26  may be closed during normal operation of vehicle  10  allowing capacitive energy storage device  18  to absorb what would otherwise be abrupt changes in the current needed from fuel cell  22 . 
         [0022]    Contactor  28  is the main contactor and is used to isolate fuel cell  22  from the significant power consuming circuitry. This allows fuel cell  22  to be powered-up without a significant load being prematurely applied to fuel cell  22 . During normal operation of vehicle  10  contactor  28  is in a closed position to thereby provide power to the electrical power consuming circuitry. A closing of contactors  26  and  28  at the same time without providing an initial charging of capacitive energy storage device  18  would result in an abrupt flow of current to capacitive energy storage device  18  and the overloading of fuel cell  22 . The overloading of fuel cell  22  will lead to fuel cell  22  shutting down and may lead to damage to fuel cell  22 . 
         [0023]    Resistor bank  30  is part of regenerative braking system  16  and is used to dissipate excess power that is generated by the motor/generators which are also part of inverter/drive system  24 , and could not be otherwise stored. Resistor bank  30  serves to provide a safe way of dissipating the energy that exceeds the capacity of capacitive energy storage device  18  to absorb. 
         [0024]    Solid state switch  32 , diode  34  and fuse  36  provided a circuit path from a power bus of fuel cell  22  to one side of resistor bank  30 . Solid state switch  32  is under the control of controller  40 . Solid state switch  38  provides a controlled connection of resistor bank  30  to the system ground to thereby bleed off and dissipate excess power in the system. Solid state switch  32  is under the control of controller  40 . 
         [0025]    Controller  40  may be a vehicle control unit (VCU)  40  that directs the functions of the present invention. Controller  40  receives power from boost converter  42  so that controller  40  can function to control solid state switches  32  and  38  and contactors  26  and  28 , as well as other functions of vehicle  10 . 
         [0026]    Now, additionally referring to  FIG. 4 , there is illustrated a method  100  having steps  102 - 110  that illustrate a portion of the present invention. At step  102 , a determination is made as to whether capacitive energy storage device  18  needs to be charged. This is done by controller  40  detecting the voltage of capacitive energy storage device  18 , or by simply assuming that capacitive energy storage device  18  needs to be charged upon every starting of vehicle  10 . If the voltage is checked and it is above a predetermined value as determined in step  104 , then method  100  terminates. If the voltage is below the predetermined value then method  100  proceeds to step  106 . 
         [0027]    At step  106 , controller  40  causes electrical power to be routed through resistor bank  30 , which is part of regenerative braking system  16  to capacitive energy storage device  18 . This is accomplished by controller  40  opening solid state switch  38  to ensure there is no direct path to ground, keeping contactor  28  open, closing contactor  26  and closing solid state switch  32 . These settings allow current to flow to capacitive energy storage device  18  as restricted by resistor bank  30 . At step  108 , it is determined if capacitive energy storage device  18  has been adequately charged, which may be to a voltage level that is substantially equal to the voltage output of fuel cell  22 . The determination done at step  108  may be simply allowing the charging of capacitive energy storage device  18  started in step  106  to continue for a predetermined amount of time. Once it is determined that capacitive energy storage device  18  has been substantially charged, then method  100  proceeds to step  110 . 
         [0028]    At step  110 , controller  40  discontinues the routing of a current flow through regenerative braking system  16  by opening solid state switch  32 . The charging of capacitive energy storage device  18  using method  100  is substantially quicker than the prior art method. For example, in a test system the prior art method took 15 minutes to charge capacitive energy storage device  18 , while the method of the present invention charged capacitive energy storage device  18  in approximately 2 minutes. 
         [0029]    Although not shown as a step in method  100 , controller  40  will close contactor  28  to allow a substantially direct connection of fuel cell  22  with capacitive energy storage device  18 . 
         [0030]    Additionally, for purposes of maintenance access and safety, capacitive energy storage device  18  can be discharged through regenerative braking system  16  by opening contactor  28 , closing contactor  26  and closing solid state switch  38  to allow the stored energy in capacitive energy storage device  18  to be bled off. 
         [0031]    The present invention advantageously reduces the charging time for capacitive energy storage device  18 . Additionally the present invention allows boost converter  42  to be made smaller since it is not used to charge capacitive energy storage device  18 . Yet another advantage of the present invention is that the main component to reduce the rush current into capacitive energy storage device  18 , which is resistor bank  30 , is already in place for used with regenerative braking system  16 , thereby only requiring the additional switching of solid state switch  32  and the execution of method  100  by controller  40 . 
         [0032]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.