Patent Application
20070104986
1. Field of the Invention
This invention relates generally to a method for detecting cooling fluid pump failure in a fuel cell system and, more particularly, to a method for detecting cooling fluid pump failure in a fuel cell system that includes measuring one or both of the temperature of the cooling fluid at the outlet from the fuel cell stack and the temperature of the cathode exhaust at the outlet from the fuel cell stack, and comparing the measured temperature to a temperature that would be expected based on the operating conditions of the fuel, cell system to determine whether the cooling fluid is flowing through the stack.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cells as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing internal combustion engines.
A hydrogen fuel cell is an electrochemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode. The work acts to operate the vehicle.
Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell for vehicles. The PEMFC generally includes a solid polymer-electrolyte proton-conducting membrane, such as a perfluorosulfonic acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum (Pt), supported on carbon particles and mixed with an ionomer. The catalytic mixture is deposited on opposing sides of the membrane. The combination of the anode catalytic mixture, the cathode catalytic mixture and the membrane define a membrane electrode assembly (MEA). MEAs are relatively expensive to manufacture and require certain conditions for effective operation.
Several fuel cells are typically combined in a fuel cell stack to generate the desired power. For the automotive fuel cell stack mentioned above, the stack may include about two hundred or more fuel cells. The fuel cell stack receives a cathode reactant gas, typically a flow of air forced through the stack by a compressor. Not all of the oxygen is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The fuel cell stack also receives an anode hydrogen reactant gas that flows into the anode side of the stack.
The fuel cell stack includes a series of flow field or bipolar plates positioned between the several MEAs in the stack. The bipolar plates include an anode side and a cathode side for adjacent fuel cells in the stack. Anode gas flow channels are provided on the anode side of the bipolar plates that allow the anode gas to flow to the anode side of the MEA. Cathode gas flow channels are provided on the cathode side of the bipolar plates that allow the cathode gas to flow to the cathode side of the MEA. The bipolar plates also include flow channels through which a cooling fluid flows.
The cooling fluid is pumped through the cooling fluid flow channels in the stack by a pump to maintain the stack at a desirable operating temperature, such as 60°-80° C., for efficient stack operations. However, if the cooling fluid pump fails, then the stack may overheat depending on the output load of the stack, possibly damaging the fuel cell components, such as the membranes. Therefore, it is necessary to monitor whether the cooling fluid pump is pumping the cooling fluid through the cooling fluid flow channels to prevent fuel cell stack failure.
One known technique for determining if the cooling fluid pump is operating is to provide a flow sensor at a suitable location in the cooling fluid flow line outside of the fuel cell stack to measure the flow rate of the cooling fluid. However, such flow sensors are typically expensive devices that add significant cost to the fuel cell system. It would be desirable to eliminate the flow sensor in the fuel cell system used for this purpose.
In accordance with the teachings of the present invention, a technique for determining whether a cooling fluid pump used for pumping a cooling fluid through a fuel cell stack has failed. The technique includes measuring the temperature of the cooling fluid at the output from the stack and/or measuring the cathode exhaust gas temperature as close as possible to the cathode outlet of the stack. The measured temperature is compared to a stack temperature that would be expected under the current operating conditions of the fuel cell system. If the difference between the measuring temperature and the expected temperature is large enough, then the controller provides a warning signal of pump failure, and also possibly reduces the stack outlet power.
Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
The following discussion of the embodiments of the invention directed to a technique for determining whether a cooling fluid pump has failed in a fuel cell system is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.
According to the invention, a temperature sensor 20 is positioned in the line 16 as close as possible to the outlet from the fuel cell stack 12. Additionally, a temperature sensor 22 is positioned in a cathode exhaust line 24, also as close as possible to the stack 12. Although two temperature sensors 20 and 22 are used in the system 10, it is within the scope of the present invention that only one of the temperature sensors 20 or 22 be used to determine if the pump 14 has failed. The temperature sensors 20 and 22 could also be positioned within the stack 12, where the sensor 20 measures the temperature of the cooling fluid and the sensor 22 measures the temperature of the cathode exhaust. For example, the sensor 20 could be positioned within the cooling fluid outlet header and the sensor 22 could be positioned within the cathode exhaust outlet header.
The temperature sensor 20 measures the temperature of the cooling fluid leaving the stack 12 and provides a signal indicative of same to a look-up table 26 within the controller 34. Likewise, the temperature sensor 22 measures the temperature of the cathode exhaust in the exhaust line 24 and provides a temperature signal indicative of same to the look-up table 26. The look-up table 26 also receives signals from a sub-system 28 identifying the current operating conditions of the fuel cell system 10, such as ambient temperature, output load of the stack 12, etc.
The look-up table 26 determines what the temperature of the cooling fluid and/or the cathode exhaust gas should be based on the current operating conditions of the fuel cell system 10 and outputs the temperature signals to a deviation device 30 to determine the difference between the two temperature signals for the cathode exhaust and/or the two temperature signals for the cooling fluid. Particularly, the look-up table 26 provides the measured temperature signal of the cathode exhaust and the expected temperature of the cathode exhaust if the system 10 only uses the temperature sensor 22 to determine if the pump 14 has failed. Or, the look-up table 26 provides the measured temperature signal of the cooling fluid and the expected temperature of the cooling fluid if the system 10 only uses the temperature sensor 20 to determine if the pump 14 has failed. Both sensors 20 and 22 can be used, where the look-up table 26 would send the four temperature signals to the deviation device 30.
The difference between the two temperature signals is then applied to a comparison device 32 that compares the difference to a predetermined value. If the difference between the measured temperature from either of the temperature sensors 20 and 22 and the calculated temperature is greater than the predetermined value, it is an indication that the cooling fluid is not cooling the stack 12. Therefore, the pump 14 has either completely failed or partially failed and is not providing the desired cooling.
It is desirable that the sensors 20 and 22 be positioned as close as possible to the active area of the fuel cell stack 12, possibly within the stack 12 itself, so that they respond quickly enough to a rise in temperature. As discussed above, either of the temperature sensors 20 or 22 can be used to determine if the pump 14 has failed. The sensor 22 may provide a better indication of the stack temperature because if the cooling fluid is not flowing, then the temperature of the cooling fluid within the stack 12 may increase significantly before the temperature of the cooling fluid outside of the stack 12 where the sensor 20 is located increases significantly. However, if there are water droplets in the cathode exhaust gas, water on the sensor 22 could provide evaporative cooling, possibly giving an inaccurate temperature reading.
The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
