Motor vehicles – Power – Electric
Reexamination Certificate
1998-02-12
2001-02-13
Swann, J. J. (Department: 3611)
Motor vehicles
Power
Electric
C180S165000, C429S006000
Reexamination Certificate
active
06186254
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a temperature regulating system for a motor vehicle. More particularly, the present invention relates to a temperature regulating system for a motor vehicle that receives power from a fuel cell system.
BACKGROUND OF THE INVENTION
Internal combustion engines have contributed greatly to the advancement of society. Vehicles powered by these engines have shortened the travel times between us by making long distance road travel routine. Such engines, however, have also greatly contributed to the pollution of our environment. The combustion of petroleum products in these engines results in unwanted byproducts such as carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen oxides, etc., that are exhausted into the atmosphere.
Vehicles powered by alternative energy sources are under development. One such alternative energy source is the fuel cell. Fuel cells generate electric power through, for example, reaction of hydrogen and oxygen. The electric power that is generated is used to drive an electric motor that, in turn, drives the wheels of the vehicle. The product of the chemical reaction in a fuel cell utilizing hydrogen and oxygen is water, a product which is essential to our environment and which is easily disposed of.
Regulation of the temperature of the fuel cell is an important consideration for fuel cell powered vehicles. For example, fuel cell performance (and sometimes, lifetime) depends on the temperature at which the fuel cell is operating. Without proper temperature regulation, the fuel cell stack may not be able to supply adequate power to the electric motor of the vehicle and, as such, may not deliver the performance levels that are demanded by the consuming public.
Merritt et al. U.S. Pat. No. 5,366,821 discloses a fuel cell system which includes a coolant circuit having an electrical coil heater to raise the fuel cell stack to operating temperature and maintain that temperature (see column 2, lines 25-30 and column 8, line 50-column 9, line 23).
Mizuno et al. U.S. Pat. No. 5,193,635 discloses several embodiments of a fuel cell powered wheeled vehicle.
Sanderson U.S. Pat. No. 3,507,702 discloses a compact fuel cell system which includes a coolant circuit having an electrical heater to raise the fuel cell stack to operating temperature and maintain that temperature (see column 6, lines 28-66).
Patent Abstracts Of Japan, vol. 16, no. 230 (JA 04-043568) discloses a fuel cell that allows stable control of the cooling water temperature, and promotes water heat recovery without substantial loss, by performing the proportional control of a flow control electric valve, or controlling the speed of a pump and a blower in a fuel cell cooling system.
PCT/International Publication No. WO 94/10716 (Application No. PCT/US93/10333) discloses solid polymer fuel cell systems with a conventional coolant subsystem extending through the fuel cell stack.
SUMMARY OF THE INVENTION
A temperature regulating system for a fuel cell powered motor vehicle is disclosed that assists in maintaining the temperature of the fuel cell within a temperature range which provides satisfactory fuel cell performance. In accordance with a first embodiment of the system, the system includes an electric motor for propelling the vehicle and at least one fuel cell stack for generating electrical power to the electric motor. Each fuel cell stack is provided with temperature regulation means, including at least one heat transfer fluid inlet port and at least one heat transfer fluid outlet port to allow flow of a heat transfer fluid, hereinafter referred to as a “cooling medium” or “coolant”, through the fuel cell stack. The cooling medium may be used to raise or lower the temperature of the fuel cells in the stack. The system is further provided with one or more pipes or conduits external to the fuel cell stack. The pipes or conduits define a coolant path for carrying the cooling medium, for example, water, glycol, or any other heat transfer medium, from the coolant outlet port to the coolant inlet port of the fuel cell stack. A resistor, connected to at least one source of electrical power, is disposed in the coolant path in thermal communication with the cooling medium. The resistor can be used to raise the temperature of the cooling medium, when it is desirable to raise the temperature of the fuel cells in the stack. The resistor is optionally disposed in a housing. The resistor may be electrically connected to the electric motor, via a suitable power conditioning system, so as to dissipate regenerative energy upon braking of the vehicle. The foregoing temperature regulating system topology has several advantageous aspects. First, the thermal energy generated by the regenerative braking is dissipated by the cooling medium within the temperature regulating system. Second, regenerative braking energy is converted into heat that is communicated to the cooling medium. Heating of the cooling medium may be desirable to maintain the fuel cell stack within a proper operating temperature range when the motor vehicle is operated in cool ambient temperatures or at start-up.
Alternatively, or in addition, the resistor may be electrically connected to receive electricity from shore power, thereby acting as a block heater that prevents the fuel cell system from freezing and facilitates start-up in cool ambient temperatures.
Alternatively, or in addition to one or both of the aforementioned sources of electrical power, fuel cell power may be used to supply electricity to the resistor. Fuel cell power may be advantageously used to power the resistor soon after start-up to bring the fuel cell stack within the preferred operating temperature range and during operation to improve fuel cell performance by maintaining the fuel cell stack within the preferred temperature range especially when the motor vehicle is operated in cool ambient temperatures. Fuel cell power may also be advantageously dissipated through the resistor at shut down, the resistor thereby acting as a bleed resistor consuming reactants remaining in the fuel cell stack and causing the stack voltage to fall so that the fuel cell stack is left in an electrically safe state. Other advantages also flow from the foregoing topology.
In accordance with a second embodiment of the system, the system includes an electric motor for propelling the vehicle and at least one fuel cell stack for generating electrical power to the electric motor. The fuel cell stack is provided with at least one coolant inlet port and coolant outlet port. One or more pipes or conduits external to the fuel cell stack are provided and define a coolant path for carrying a cooling medium from the coolant outlet port to the coolant inlet port of the fuel cell stack. The cooling medium is pumped through the coolant path by a main cooling pump that is disposed in the coolant path. Heat dissipation from the cooling medium is facilitated by a radiator disposed in the coolant path and optionally an air flow device that provides a cooling airflow over the radiator to cool the cooling medium. The main cooling pump and the air flow device are independently controllable. Such independent control of the coolant pump and the air flow over the radiator provides a great degree of coolant temperature control and, as a result, of the fuel cell temperature.
In accordance with a third embodiment of the system, the system includes at least one fuel cell stack for generating electrical power. The fuel cell stack is provided with at least one coolant inlet port and coolant outlet port. One or more pipes or conduits external to the fuel cell stack are provided and define a coolant path for carrying a cooling medium from the coolant outlet port to the coolant inlet port of the fuel cell stack. A temperature sensor is disposed to measure temperature of the cooling medium preferably proximate the outlet or inlet coolant port of the fuel cell stack and optionally a current sensor is disposed to measure electrical current flowing from the fuel cell stack. A control circuit
Gorbell Brian N.
Mufford W. Edward
Strasky Douglas G.
Dunn David R.
McAndrews Held & Malloy Ltd.
Swann J. J.
Xcelliss Fuel Cell Engines Inc.
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