Abstract: In an exemplary embodiment, a method to control excessive temperature changes in a coolant circuit includes providing a coolant circuit including a bypass flow pathway bypassing a heat exchanger, said coolant circuit at an elevated operating temperature; providing an adjustable coolant flow through said bypass flow pathway and said heat exchanger; providing a coolant pump in said coolant circuit; determining a temperature change in said coolant circuit in response to initiating a coolant flow from said heat exchanger into said coolant circuit, said temperature change greater than predetermined limit; and in response to said determined temperature change, adjusting at least one or more of said coolant pump speed and said coolant flow to maintain said coolant circuit within a predetermined temperature range.

Abstract: A humidity sensing device for determining the amount of humidity in at least one primary fluid stream that is passed to a fuel cell stack is provided. The sensing device includes an outer housing and an inner housing. The outer housing is positioned within at least one conduit such that the outer housing and the conduit coact with each other to generate at least one secondary fluid stream from the primary fluid stream. The inner housing is positioned within the outer housing such that the inner housing is configured to receive the secondary fluid stream and to measure an amount of water present in the secondary fluid stream to determine the amount of humidity in the primary fluid stream.

Abstract: A system and method to control the coolant temperature of two independent cooling loops of a fuel cell vehicle by adjusting system pump speed, fan speed and radiator bypass valve position. Multiple feedback controllers coordinated by robust flip-flop logic are used, to minimize energy consumption and provide optimal control system performance even in the case of substantially different plant responses with respect to fan speed and valve position plant inputs. The system also includes a feed forward disturbance compensator, which reacts immediately to change in net power and vehicle speed disturbance variables, thereby reducing the variance of the temperature control error. Additionally, a feedback controller preset strategy is used to compensate for distinctive plant nonlinear effects such as bypass valve dead-zone and air-conditioning system's request for abrupt change of fan speed.