Abstract: A method for operating a cooling system for a fuel cell stack in a vehicle is provided. The method includes the steps of: determining a fan request for a variable speed fan disposed in the cooling system; employing a noise-comfort function to select a fan comfort request; and adjusting a speed of the variable speed fan in response to the fan request; wherein a noise emission by the variable speed fan is militated against. A cooling system for a fuel cell stack in a vehicle that employs the noise-comfort function is also provided.

Abstract: A sensor determines the absolute angular position of a body that can rotate through rotations. The sensor includes two code wheels which rotate as the body rotates. The code wheels are driven at a different gear ratio such that the code wheels rotate faster than the body and the code wheels rotate at different rates. Two sensor elements respectively determine the rotational angle positions of the code wheels. The difference between the rotational angle positions is a beat angle. The different gear ratio is selected such that beat angle periods are in an angular measuring range of the sensor and the absolute angular positions of the code wheels in the beat angle periods is different. The absolute angular positions of the code wheels in successive beat angle periods is offset by the nth part of the measuring range of a sensor element, where n is number of beat angle periods.

Abstract: A system and method for reducing RH cycling of the membranes in a fuel cell stack. A control algorithm damps a power request signal using a first order filter during low power transients so that the fuel cell stack continues generating power at a higher rate than is requested. The excess power generated by the stack is used to recharge a battery in the fuel cell system. The damped power signal is weighted so that more fuel cell stack power is provided for a low battery state of charge unless stack power is provided for a high battery state of charge.

Abstract: A diagnostic system for determining whether a rotor shaft of a compressor is unbalanced. The compressor includes a displacement sensor that measures the displacement of the rotor shaft as it is rotating. The sensor dynamic frequency signal is sent to a bandpass filter that filters out an eigen-frequency frequency that is a function of shaft elasticity and rotor dynamics. The filtered frequency signal is then rectified by a rectifier to make the filtered frequency signal positive. The rectified signal is then passed through a low pass filter that converts the rectified signal to a DC signal. The DC signal is then sent to a controller that determines if the amplitude of the signal is above a predetermined threshold, which indicates a problem with the balance of the compressor.

Abstract: A system for controlling the power output of a fuel cell stack and a battery in a hybrid fuel cell system. The system includes a power damping filter that receives a power request signal, and damps the request to reduce large changes in the power request. A battery state of charge controller receives the difference between a battery state of charge set-point and the actual battery state of charge, and provides a battery power signal that attempts to maintain the battery state of charge at the set-point. The damped power signal and the battery power signal are added to generate a system power demand signal that satisfies the driver power request using the battery power and fuel cell stack power, and uses the fuel cell stack power to charge the battery during low power transients or if the battery state of charge is below the set-point.

Abstract: A method for correcting a characteristic curve having values corresponding to displacement between a magnetic sensor element and a magnetic ruler of a sensor within a displacement range includes determining whether the characteristic curve has a jump discontinuity by comparing a first value at a first range end to a second value at a second range end and by comparing values between the range ends. Upon determining that the characteristic curve has a jump discontinuity, the method further includes determining the magnitude of the jump discontinuity, defining a decision threshold lying between the first and second values, identifying the values within the range which are lower than the decision threshold, and offsetting the identified values by the magnitude of the jump discontinuity such that the characteristic curve is corrected to eliminate the jump discontinuity, whereby subsequent measurements made by the MR sensor take into account the jump discontinuity magnitude offset.

Abstract: A pressure management system that balances pressure between first and second fluid circuits of a fuel cell system includes a first fluid reservoir associated with the first fluid circuit and a second fluid reservoir associated with the second fluid circuit. The second fluid reservoir is in fluid communication with the first fluid reservoir. A fluid is transferred from the first fluid reservoir to the second fluid reservoir during an over-pressure condition within the first fluid circuit.

Abstract: A technique for determining the relative humidity of the cathode input airflow to a fuel cell stack that eliminates the need for a dew-point sensor. The cathode input airflow is humidified by a water vapor transfer unit that uses water in the cathode exhaust gas. The technique employs an algorithm that determines the flow of water into the cathode inlet of the stack. In one embodiment, the algorithm determines the volume flow of water through the water vapor transfer unit using the Arrhenius equation, and then converts the water volume flow to a water mole flow. The algorithm then uses the water mole flow through the water vapor transfer unit and the water mole flow of ambient air to determine the water mole flow into the cathode inlet. The algorithm then uses the water mole flow into the cathode inlet to determine the relative humidity of the cathode airflow.

Abstract: A technique for controlling the relative humidity of a cathode airflow to a fuel cell stack that includes compensating for valve non-linearities. The cathode input air flows through a water vapor transfer unit where it is humidified. The humidified cathode exhaust from the fuel cell stack is output to the water vapor transfer unit to provide the water vapor for humidifying the cathode input airflow. A first control valve controls the flow of the cathode exhaust through the water vapor transfer unit and a second control valve controls the flow of the cathode exhaust that by-passes the water vapor transfer unit to control both the relative humidity of the cathode input airflow and the pressure within the stack. By compensating for the non-linearity, the first and second valves control the relative humidity of the cathode airflow without changing the cathode output resistance.

Abstract: A thermal sub-system for a fuel cell system that employs an algorithm using feed-forward control. The algorithm calculates a Reynolds number based on the velocity of the cooling fluid, a diameter of a coolant loop pipe and a kinematic viscosity (temperature) of a cooling fluid. The algorithm also uses a pressure loss number based on the Reynolds number and a position of a by-pass valve. The algorithm also defines a pressure loss value based on the pressure loss number, the density of the cooling fluid and the velocity of the cooling fluid. The algorithm then calculates a delivery head value based on the pressure loss value, the fluid density and a gravitational acceleration. The algorithm then uses the delivery head value and a predetermined set-point value of the volume flow to determine a desired pump speed based on the current operating parameters of the system.

Abstract: A thermal sub-system for a fuel cell system that uses pump characteristics to determine a required cooling fluid volume flow. An algorithm controls the speed of the pump to provide the desired volume flow of the cooling fluid for the system parameters. The algorithm determines a motor efficiency value based on a pump input power value and a pump speed value. The algorithm then determines a coefficient of power value based on the motor efficiency value, the pump input power value and the pump speed value. The algorithm then uses a look-up table to convert the coefficient of power value to a coefficient of flow value. The algorithm then calculates the volume flow based on the coefficient of flow value and the pump speed value.

Abstract: A thermal sub-system for a fuel cell system that calculates a desired volume flow or mass flow of a cooling fluid pumped through a fuel cell stack solely on thermal stack power loss and cooling fluid temperature. An algorithm calculates a power loss of the stack and then calculates the temperature of the stack based on the power loss and dissipated heat power from the stack. The algorithm uses the temperature of the stack and the temperature of the cooling fluid out of the stack to determine the dissipated heat power. The algorithm then uses the temperature of the stack, the temperature of the cooling fluid into the stack and the temperature of the cooling fluid out of the stack to determine the flow.

Abstract: A control algorithm for a by-pass valve in a thermal sub-system of a fuel cell system, where the by-pass valve includes a wax element that is heated by a heating element. A stack power loss is applied to a PDT1 controller that associates a PDT dynamic function to the loss. The difference between the desired temperature of the stack and the actual temperature of the stack is applied to a PI controller that provides an error value of the difference. The actual temperature of the stack is applied to a look-up table that provides a value based on how close the actual temperature is to the opening temperature of the wax element. The values from the PDT1 controller, the PI controller and the look-up table are added to provide an output signal to control the current applied to the heater element, and thus, the heat applied to the wax element.

Abstract: A method for correcting a characteristic curve having values corresponding to displacement between a magnetic sensor element and a magnetic ruler of a sensor within a displacement range includes determining whether the characteristic curve has a jump discontinuity by comparing a first value at a first range end to a second value at a second range end and by comparing values between the range ends. Upon determining that the characteristic curve has a jump discontinuity, the method further includes determining the magnitude of the jump discontinuity, defining a decision threshold lying between the first and second values, identifying the values within the range which are lower than the decision threshold, and offsetting the identified values by the magnitude of the jump discontinuity such that the characteristic curve is corrected to eliminate the jump discontinuity, whereby subsequent measurements made by the MR sensor take into account the jump discontinuity magnitude offset.

Abstract: A pressure management system that balances pressure between first and second fluid circuits of a fuel cell system includes a first fluid reservoir associated with the first fluid circuit and a second fluid reservoir associated with the second fluid circuit. The second fluid reservoir is in fluid communication with the first fluid reservoir. A fluid is transferred from the first fluid reservoir to the second fluid reservoir during an over-pressure condition within the first fluid circuit.