Diagnostic method for detecting a coolant pump failure in a fuel cell system by temperature measurement

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 temperature that would be expected under the current operating conditions of the fuel cell system in a controller. 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.

BACKGROUND OF THE INVENTION

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. 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.

SUMMARY OF THE INVENTION

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 measured 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.

DETAILED DESCRIPTION OF THE EMBODIMENTS

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.

FIG. 1is a block diagram of a fuel cell system10including a fuel cell stack12. A cooling fluid pump14pumps a cooling fluid through a pipe16external to the stack12and through cooling fluid flow channels between the several fuel cells in the stack12, as is well understood in the art. The cooling fluid is also pumped through a radiator18external to the stack12to dissipate heat from the cooling fluid before it is returned to the stack12. A fan (not shown) could also be provided to force air through the radiator18to remove the waste heat. The speed of the pump14and the speed of the fan provide the desired cooling and are determined from the output load of the stack12and other operating conditions by a controller34so that the temperature of the stack12is maintained at a desirable operating temperature for efficient stack operation.

In the embodiment shown in figure, the stack12, the radiator18and the pump14are shown in a particular configuration or sequence. However, the order of the stack12, the pump14and the radiator18in the coolant loop can be different in other embodiments. Also, the coolant loop can include by-pass paths for providing the cooling fluid to other devices, as is well understood in the art.

According to the invention, a temperature sensor20is positioned in the line16as close as possible to the outlet from the fuel cell stack12. Additionally, a temperature sensor22is positioned in a cathode exhaust line24, also as close as possible to the stack12. Although two temperature sensors20and22are used in the system10, it is within the scope of the present invention that only one of the temperature sensors20or22be used to determine if the pump14has failed. The temperature sensors20and22could also be positioned within the stack12, where the sensor20measures the temperature of the cooling fluid and the sensor22measures the temperature of the cathode exhaust. For example, the sensor20could be positioned within the cooling fluid outlet header and the sensor22could be positioned within the cathode exhaust outlet header.

The temperature sensor20measures the temperature of the cooling fluid exiting the stack12and provides a signal indicative of same to a look-up table26within the controller34. Likewise, the temperature sensor22measures the temperature of the cathode exhaust in the exhaust line24and provides a temperature signal indicative of same to the look-up table26. The look-up table26also receives signals from a sub-system28identifying the current operating conditions of the fuel cell system10, such as ambient temperature, output load of the stack12, stack start-up, etc.

The look-up table26determines 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 system10and outputs the temperature signals to a deviation device30to 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 table26provides the measured temperature signal of the cathode exhaust and the expected temperature of the cathode exhaust if the system10only uses the temperature sensor22to determine if the pump14has failed. Or, the look-up table26provides the measured temperature signal of the cooling fluid and the expected temperature of the cooling fluid if the system10only uses the temperature sensor20to determine if the pump14has failed. Both sensors20and22can be used, where the look-up table26would send the four temperature signals to the deviation device30.

The difference between the two temperature signals is then applied to a comparison device32that compares the difference to a predetermined value. If the difference between the measured temperature from either of the temperature sensors20and22and the calculated temperature is greater than the predetermined value, it is an indication that the cooling fluid is not cooling the stack12. Therefore, the pump14has either completely failed or partially failed and is not providing the desired cooling.

As mentioned above, one of the operating conditions applied to the look-up table26from the sub-system28could be whether the stack12is at start-up. In some applications, such as cold starts, it may be desirable to delay the start of the pump16at system stack start-up to reduce the thermal mass of the system so that it heats up to the operating temperature faster. If the pump14is not immediately started at stack start-up, then the temperature signal provided by the sensors20and22will be lower than if the pump14is immediately started at stack start-up. Thus, the look-up table26needs to adjust the expected temperature if the start of the pump14is delayed at system start-up. Also, once the pump16is started, the temperature increase may be slower than expected for a certain period of time. A logic step may be required to determine if the pump16has recently been started to adjust for the expected temperature in the look-up table26until the temperature reaches a steady-state. Therefore, the logic in the look-up table26may need to calibrated for cold starts in this manner.

It is desirable that the sensors20and22be positioned as close as possible to the active area of the fuel cell stack12, possibly within the stack12itself, so that they respond quickly enough to a rise in temperature. As discussed above, either of the temperature sensors20or22can be used to determine if the pump14has failed. The sensor22may 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 stack12may increase significantly before the temperature of the cooling fluid outside of the stack12where the sensor20is located increases significantly. However, if there are water droplets in the cathode exhaust gas, water on the sensor22could provide evaporative cooling, possibly giving an inaccurate temperature reading.