Abstract: An apparatus and method to determine the relative humidity of a fuel cell system. A controller is cooperative with a first device and a second device to receive a valve signal and a high frequency resistance value. The controller controls the relative humidity of a fuel cell stack based on the estimation of the relative humidity of the fuel cell stack based on one or more algorithms. The controller modifies the relative humidity of the fuel cell stack through changes in the position of a valve based on at least one of the valve signal and the high frequency resistance value. In one form, the relative humidity of the fuel cell system is determined without the need of a humidity sensor.

Abstract: A system and method for reducing the frequency of stack stand-by mode events, if necessary, as a fuel cell stack ages and experiences lower performance. The method determines an irreversible voltage loss of the fuel cell stack at predetermined time intervals and determines a stack voltage degradation variable based on the irreversible voltage loss. The method also determines if the stack voltage degradation variable indicates that the fuel cell stack will not meet predetermined stack end-of-life voltage requirements and calculates a maximum allowed voltage degradation rate of the fuel cell stack. The method calculates a maximum number of stand-by mode events per unit time that can be allowed to prevent the stack from exceeding the maximum allowed degradation rate and controls the number of stand-by mode events based on the calculated maximum number of stand-by mode events.

Abstract: An apparatus and method to determine the relative humidity of a fuel cell system. A controller is cooperative with a first device and a second device to receive a valve signal and a high frequency resistance value. The controller controls the relative humidity of a fuel cell stack based on the estimation of the relative humidity of the fuel cell stack based on one or more algorithms. The controller modifies the relative humidity of the fuel cell stack through changes in the position of a valve based on at least one of the valve signal and the high frequency resistance value. In one form, the relative humidity of the fuel cell system is determined without the need of a humidity sensor.

Abstract: A system and method for reducing the frequency of stack stand-by mode events, if necessary, as a fuel cell stack ages and experiences lower performance. The method determines an irreversible voltage loss of the fuel cell stack at predetermined time intervals and determines a stack voltage degradation variable based on the irreversible voltage loss. The method also determines if the stack voltage degradation variable indicates that the fuel cell stack will not meet predetermined stack end-of-life voltage requirements and calculates a maximum allowed voltage degradation rate of the fuel cell stack. The method calculates a maximum number of stand-by mode events per unit time that can be allowed to prevent the stack from exceeding the maximum allowed degradation rate and controls the number of stand-by mode events based on the calculated maximum number of stand-by mode events.

Abstract: A fuel vapor canister is purged by admitting fuel vapor from the canister to the vehicle engine under control of a solenoid valve, the duty cycle of the valve being controlled to optimize the purge rate. Closed loop fuel correction and block learn fuel correction factors developed by the fuel control system are used to update a learned purge duty cycle which is stored in a keep-alive memory.