Patent Publication Number: US-2004046395-A1

Title: System and method for recovering potential energy of a hydrogen gas fuel supply for use in a vehicle

Description:
[0001] (1) FIELD OF THE INVENTION  
       [0002] This invention relates to a system and a method for recovering potential energy of a hydrogen gas fuel supply in a vehicle and more particularly, to a system and method which uses an expander, compressor and a motor/generator to utilize the potential energy stored within hydrogen gas that is supplied to a fuel cell in order to provide pressurized air to the fuel cell and to generate electricity, thereby improving the efficiency and the fuel economy of the vehicle.  
       [0003] (2) BACKGROUND OF THE INVENTION  
       [0004] In order to reduce automotive emissions and the demand for fossil fuel, automotive vehicles have been designed that are powered by electrical devices such as fuel cells. These fuel cell-powered electric vehicles reduce emissions and the demand for conventional fossil fuels by eliminating the internal combustion engine (e.g., in completely electric vehicles) or by operating the engine at only its most efficient/preferred operating points (e.g., within hybrid electric vehicles).  
       [0005] Many fuel cells consume hydrogen gas and air (e.g., as a reaction constituent). The consumed hydrogen and air must be properly stored and transferred to the fuel cell at certain pressures in order to allow the fuel cell and vehicle to operate in an efficient manner.  
       [0006] Vehicles employing these types of fuel cells often include systems and/or assemblies for storing and transmitting hydrogen gas and air to the fuel cell. Particularly, the hydrogen gas is typically stored within a tank at a relatively high pressure and with a relatively high amount of potential energy. The hydrogen gas is then transferred to the fuel cell by use of several conduits and several pressure-reducing regulators which lower the pressure of the gas by a desirable amount. While the pressure of the hydrogen gas leaving the fuel tank is substantially lowered prior to entering the fuel cell, it is above normal atmospheric pressures which is required for efficient operation. The air that is communicated from the fuel cell is obtained at atmospheric pressures and must be pressurized or otherwise driven through the system in order to ensure proper and efficient fuel cell operation. This pressurization and/or driving of air through the system is typically performed by use of one or more compressors or turbines. These compressors or turbines require electrical energy for their operation, and therefore drain the vehicle&#39;s battery and use generated electrical energy, which could otherwise be used to power the vehicle&#39;s electrical components and accessories.  
       [0007] There is therefore a need for a new and improved system and method for use with a fuel cell powered vehicle which recovers the potential energy stored within pressurized hydrogen gas and which converts that potential energy to mechanical and electrical energy that can be used to drive a compressor, to supplement the electrical power demands of the vehicle and/or to recharge an electrical storage device.  
       SUMMARY OF THE INVENTION  
       [0008] A first non-limiting advantage of the invention is that it provides a system and method for recovering the potential energy of the compressed gas stored within a fuel cell-powered vehicle.  
       [0009] A second non-limiting advantage of the invention is that it provides a system and method for recovering the potential energy of the hydrogen gas stored within a fuel cell powered vehicle and which selectively converts the potential energy into mechanical and electrical energy which is selectively used to drive a compressor, supplement the electrical power demands of the vehicle, and/or to recharge an electrical storage device.  
       [0010] According to a first aspect of the present invention, a system is provided for recovering potential energy from a hydrogen gas fuel supply that is used to power a fuel cell within a vehicle. The system includes a fuel tank which stores pressurized gas; a first conduit system which selectively and fluidly couples the fuel tank to the fuel cell, effective to allow the pressurized gas to be selectively communicated to the fuel cell; an expander including a turbine which is disposed within the first conduit system and which is selectively and rotatably driven by the pressurized gas, effective to generate torque and lower the pressure of the pressurized gas which is communicated to the fuel cell; a second conduit system which selectively and fluidly couples the fuel cell to a source of air, effective to allow the air to be selectively communicated to the fuel cell; a compressor which is disposed within the second conduit system and which is selectively coupled to and driven by the expander, the compressor being effective to pressurize the air which is communicated to the fuel cell; and an electric machine which is operatively coupled to the expander and the compressor, the electric machine being effective to selectively convert torque generated by the expander into electrical power, and to selectively convert electrical power into mechanical torque for rotating the compressor.  
       [0011] According to a second aspect of the present invention, a method is provided for recovering potential energy stored within a pressurized gas used to power a fuel cell within a vehicle. The method includes the steps of: providing a first conduit system for transferring the pressurized gas to the fuel cell; providing an expander; operatively disposing the expander within the first conduit system; providing a motor/generator for producing electrical power from torque and for producing torque from electrical power; providing a second conduit system for transferring air to the fuel cell; providing a compressor; operatively disposing the compressor within second conduit system; operatively connecting the expander and the compressor to the motor/generator; selectively connecting the expander and the compressor; and channeling the pressurized gas through the expander, effective to rotatably drive the expander, thereby selectively driving the compressor and selectively causing the motor/generator to produce electrical power.  
       [0012] These and other features, aspects, and advantages of the invention will become apparent by reading the following specification and by reference to the following drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013]FIG. 1 is a block diagram of a system which is made in accordance with the teachings of the preferred embodiment of the invention, which is adapted for use with a fuel cell powered vehicle and which is effective to recover the potential energy stored within hydrogen gas that is used to power the vehicle&#39;s fuel cell.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION  
     [0014] Referring now to FIG. 1, there is shown a block diagram of a system  10 , which is made in accordance with the teachings of the preferred embodiment of the invention, and which is effective to recover the potential energy which is stored within the hydrogen gas which is supplied to one or more fuel cells  12  within a vehicle  14 . Particularly, system  10  is adapted for use in combination with a vehicle  14  including one or more hydrogen-based fuel cells  12  which provide power to the vehicle  14 . In the preferred embodiment, vehicle  14  is an electric or a hybrid-electric vehicle. In the preferred embodiment, fuel cells  12  utilize a chemical reaction that consumes hydrogen gas to generate electrical power. It should be appreciated that while in the preferred embodiment of the invention, fuel cells  12  are of the type which consume hydrogen gas, in other alternate embodiments, other types of compressed gasses can be used to generate power within the fuel cell  12 , and system  10  would work in a substantially identical manner to recover potential energy stored within those compressed gasses and provide substantially identical benefits.  
     [0015] System  10  includes a conventional storage tank  16  which receives and stores hydrogen gas at a relatively high pressure, an expander turbine  18  and a compressor turbine  20  which are each coupled to an electric machine or motor/generator  76 , pressure regulators  22 ,  24 , a bypass valve  26 , an electrical charge storage device or battery  28 , a controller  30 , vehicle sensors  32  and electrical switches or switching module  34 .  
     [0016] The system  10  further includes a first conduit system having several tubes or conduits that are disposed throughout the vehicle  14  and that selectively carry and transport the hydrogen gas from the tank  16  to the fuel cell  12 . Particularly, fuel tank  16  is fluidly coupled to valve  26  by use of conduit  38 , and valve  26  is fluidly coupled to expander turbine  18  by use of conduit  40  and to regulator  22  by conduit  42 . Expander turbine  18  is fluidly coupled to conduit  42  and to regulator  22  by use of conduit  44 , and regulator  22  is fluidly coupled to fuel cell  12  by conduit  46 .  
     [0017] A second conduit system fluidly couples fuel cell  12  to a source of air. Particularly, compressor turbine  20  is fluidly coupled to and receives air through conduit  48 , and is further fluidly coupled to regulator  24  by use of conduit  50 . Regulator  24  is fluidly coupled to fuel cell  12  by use of conduit  52 . It should be appreciated that the present invention is not limited to the foregoing conduit systems or configurations, and that in alternate embodiments, different and/or additional numbers of conduits may be used to interconnect the various components of system  10 . For example and without limitation, vehicle  14  may further include exhaust and/or return conduit systems (not shown) which are effective to treat and/or remove exhaust gasses from the vehicle  14  and/or to return unused hydrogen gas to the fuel cell  12 .  
     [0018] Controller  30  is respectively, electrically and communicatively coupled to regulators  22 ,  24  by use of electrical buses  54 ,  56 , to switching module  34  by use of electrical bus  58 , to sensors  32  by use of electrical bus  60 , to valve  26  by use of electrical bus  62 , and to motor/generator  76  by use of bus  66 . Switching module  34  is further respectively, electrically and communicatively coupled to motor/generator  76  by use of power bus  64 , to battery  28  by use of power bus  68 , and to vehicle electrical loads and accessories  72  by use of power bus  70 .  
     [0019] In the preferred embodiment, controller  30  is a conventional microprocessor based controller and in one non-limiting embodiment, controller  30  comprises a portion of a conventional engine control unit (“ECU”). In other alternate embodiments, controller  30  is externally coupled to the engine control unit.  
     [0020] Fuel tank  16  is a conventional storage tank which is adapted to receive and store compressed gaseous fuel, such as hydrogen gas, at relatively high pressures. In the preferred embodiment, expander  18  is a conventional turbine which selectively receives and which is rotatably driven by pressurized gas delivered from tank  16 . Expander turbine  18  is selectively and operatively coupled to motor/generator  76  by use of shaft  80  and to compressor turbine  20  by of shaft  80 , a conventional clutch  84  and a shaft  82  which is coupled to compressor turbine  20 . In one alternate embodiment, expander turbine  18  and compressor turbine  20  are connected by a single shaft. When expander turbine  18  and compressor turbine  20  are mechanically coupled together by use of clutch  84 , the rotation or torque produced by expander turbine  18  drives compressor turbine  20 . This rotation/torque can also be selectively used by the motor/generator to generate electrical energy in a conventional manner. After passing through expander turbine  18 , the hydrogen gas is communicated to fuel cell  12  by way of conduits  44 ,  42 ,  46  and regulator  22 .  
     [0021] In the preferred embodiment, compressor turbine  20  is selectively coupled to and rotatably driven by motor/generator  76  and expander turbine  18 . Turbine  20  is in fluid communication with conduit  48  and is effective to “draw in” air through conduit  48  (e.g., from the environment external to the vehicle), to compress or pressurize the air and to communicate the pressurized air to fuel cell  12  by use of conduits  50 ,  52  and regulator  24 .  
     [0022] Motor/generator  76  is a conventional electric machine which is capable of both generating electrical power from mechanical torque, and generating torque from electrical power. Particularly, motor/generator  76  is capable of operating in an “electrical power-generating mode” in which the motor/generator  76  receives torque from the rotating expander turbine  18  and converts some of that torque into electrical power (the remainder of the torque is used to drive compressor  20 ). Motor/generator  76  is also capable of operating in a “torque-producing mode” in which motor/generator  76  receives electrical power (e.g., from battery  28 ) and converts the electrical power into torque for rotating compressor turbine  20 . In the preferred embodiment, motor/generator  76  disconnects compressor  20  from expander  18  (e.g., by deactivating clutch  84 ) during torque-producing operation and delivers torque only to compressor  20 , thereby reducing the amount of torque and electrical power required to drive compressor  20 .  
     [0023] In the preferred embodiment, regulators  22 ,  24  are conventional electronically controlled pressure regulators which respectively control the pressure of hydrogen gas and air which entering into fuel cell  12 . Particularly, regulators  22  and  24  receive signals from controller  30  which are effective to control the operation of regulators  22 ,  24 . Controller  30  controls the amount that the regulators  22 ,  24  decrease the pressure of gas and air entering into fuel cell  12  based upon vehicle operating data that is received from conventional vehicle operating sensors  32 . In alternate embodiments, regulators  22 ,  24  are mechanically controlled or set regulators.  
     [0024] Sensors  32  comprise conventional and commercially available vehicle operating sensors which measure and/or estimate various vehicle operating attributes, such as the pressure of the hydrogen gas and air within various locations in the system (i.e., within various conduits), the vehicle speed, the torque provided by turbine  18  to motor/generator  76 , the engine speed, the amount of fuel remaining in tank  16 , the pressure of the fuel within tank  16 , and/or the state of charge of battery  28 . Sensors  32  measure and/or estimate these attributes and communicate signals representing the measured and/or estimated values to controller  30  which uses the signals to operate electrical switches  34 , regulators  22 ,  24 , motor/generator  76  and bypass valve  26  in a desired manner.  
     [0025] Bypass valve  26  is a conventional electronically controlled (e.g., solenoid) valve which allows pressurized gas from fuel tank  16  to be selectively communicated to expander turbine  18  through conduit  40  or to be selectively communicated directly to regulator  22  through conduit  42 . Valve  26  may also be selectively disposed in a closed position in which no gas is allowed to escape from tank  16  through either of conduits  40  or  42 .  
     [0026] Electrical switches or switching module  34  includes several conventional electrical switches (e.g., transistors and/or relays) which operate in response to signals received from controller  30  and which allow motor/generator  76  to be selectively and operatively connected to electrical components and accessories  72  and to battery  28 . In one non-limiting embodiment, switching module  34  may be integral with controller  30 . In another alternate embodiment, switching module  34  may comprise several disparate switches or devices which are each independently connected to controller  30  and which individually receive command signals from controller  30 .  
     [0027] In operation, system  10  utilizes the potential energy stored within the hydrogen gas fuel to generate torque and electrical power. Particularly, when the tank  16  is filled, the hydrogen gas is at a relatively high pressure. When the vehicle  14  is operated, the pressure of the hydrogen gas must be substantially reduced prior to being transferred to fuel cell  12 . When the tank  16  is substantially filled, this pressure reduction is performed by channeling the pressurized gas through expander turbine  18 . Particularly, controller  30  sends a signal to valve  26 , effective to cause valve  26  to channel the gas through conduit  40 . When the pressurized gas flows through expander  18 , it is effective to both desirably reduce the pressure of the gas and to generate torque and rotatably drive expander  18 , thereby driving compressor  20  and generating power within motor/generator  76 . In this manner, the potential energy stored within the compressed gas is desirably captured and converted into mechanical and electrical energy. Based upon vehicle attribute or operating data received from sensors  32 , controller  30  sends signals to motor/generator  76 , effective to control the amount of electrical energy generated by the motor/generator  76 . For example and without limitation, when tank  16  is substantially filled, motor/generator  76  is allowed to operate with a relatively high electrical power output. As the pressure of the hydrogen gas within tank  16  and conduits  38 ,  40  begins to decrease, a higher percentage of the torque generated by expander  18  is used to rotatably drive compressor  20  in order to maintain a desired air pressure value within conduits  50  and  52  (e.g., less torque is converted into electrical power).  
     [0028] Controller  30  also controls switches  34 , in order to direct the generated power to electrical components and accessories  72 , effective to provide electrical power to one or more conventional vehicle electrical loads or accessories  72  and/or to battery  28 , effective to recharge the battery  28 . Controller  30  determines where to direct the generated electrical power based upon the amount or level of power being generated, and the power requirements or needs of the various components  72  and the state of charge of battery  28 . The priority and/or sequence in which the various components  72  and battery  28  receive power may be selectively programmed into controller  30  and may be based upon any desirable design considerations. Controller  30  will also source electrical power directly from the battery  28  to the motor/generator  76  in the event that sufficient torque is not being received from the expander  18  to drive compressor  20  at a certain desired level.  
     [0029] After the compressed hydrogen gas passes through expander  18 , it traverses conduits  44  and  42  and enters “low pressure” pressure-reducing regulator  22  which lowers the pressure of the gas to a predetermined and/or calibratable level which is necessary for the optimal performance of fuel cell  12  and which may be determined based upon the attributes of fuel cell  12 . In the preferred embodiment, controller  30  selectively alters the amount that pressure-reducing regulator  22  lowers the pressure of the hydrogen gas, based upon vehicle attribute or operation condition data, and based upon the pressure of the gas after it traverses expander turbine  18 , which can be sensed in a conventional manner (e.g., by use of conventional pressure sensors (not shown)).  
     [0030] Controller  30  further controls the operation of “low pressure” pressure-reducing regulator  24  which ensures that the pressure of the compressed air entering fuel cell  12  is equal to a predetermined value which is necessary for optimal performance of fuel cell  12 .  
     [0031] As the vehicle  14  is driven and the fuel supply is depleted, the pressure of the hydrogen gas within the system decreases. Controller  30  monitors this pressure by use of sensors  32  and when the pressure falls below a certain predetermined and/or calibratable level, controller  30  generates a signal to valve  26  effective to cause the hydrogen gas from tank  16  to bypass expander  18  and to flow directly to pressure-reducing regulator  22  through conduit  42 . System  10  performs this “bypass” function to ensure that pressure of the hydrogen gas entering fuel cell  12  is sufficient for optimal performance of the fuel cell  12 . That is, when the pressure of the gas in tank  16  falls below a certain level, the pressure drop over the expander turbine  18  may cause the pressure of the hydrogen gas to fall below a value which is required for optimal performance of the fuel cell  12 . In these situations expander  18  is bypassed and pressure-reducing regulator  22  is accordingly adjusted to provide the desired pressure decrease. Additionally, during these “bypass” operating modes, controller  30  communicates signals to switches  34  and motor/generator  76 , effective to source electrical power from battery  28  to motor/generator  76  and to cause motor/generator  76  to operate in a torque-producing mode (e.g., as a motor), thereby driving compressor  20  at a desired level. In the preferred embodiment, controller  30  also signals motor/generator  76  to deactivate clutch  84 , effective to disconnect compressor  20  from expander  18 , thereby allowing all of the motor-generated torque to be used to drive compressor  20 .  
     [0032] In this manner, system  10  efficiently utilizes and recovers the potential energy stored within the compressed hydrogen gas by use of expander turbine  18  and motor/generator  76 . This potential energy is selectively converted into mechanical torque and electrical power which is used to drive compressor  20  and to selectively power various components and/or to recharge the vehicle&#39;s battery  28 . System  10  further eliminates the need for a “high-pressure” pressure-reducing regulator, by desirably lowering the pressure of the hydrogen gas by a substantial amount (e.g., by at least a factor of 10) prior to the gas passing through low pressure step-down regulator  22  and into fuel cell  12 . System  10  also provides the flexibility to bypass the expander  18  in certain situations, thereby substantially guaranteeing that the gas entering fuel cell  12  will be of a sufficient pressure for optimal performance.  
     [0033] It is to be understood that the invention is not to be limited to the exact construction and/or method which has been illustrated and discussed above, but that various changes and/or modifications may be made without departing from the spirit and the scope of the invention.