Thermal management system for fuel cell vehicle having multiple fuel-cell stacks

1. A vehicle comprising:

first and second fuel-cell stacks;

a first coolant circuit including conduit arranged to circulate coolant through the first fuel-cell stack;

a second coolant circuit including conduit arranged to circulate coolant through the second fuel-cell stack;

a heater in fluid communication with at least the first coolant circuit; and

an isolation valve assembly configured to proportion a flow of coolant between the first and second coolant circuits, the isolation valve assembly including:

a first inlet port connected to the conduit of the first circuit,

a first outlet port connected to the conduit of the first circuit,

a second inlet port connected to the conduit of the second circuit,

a second outlet port connected to the conduit of the second circuit, and

valving having (i) an isolation position in which the first inlet port and the second outlet port are not in fluid communication and the second inlet port and the first outlet port are not in fluid communication so that the first and second circuits are isolated and (ii) at least one mixing position in which the first inlet port and the second outlet port are in fluid communication and the second inlet port and the first outlet port are in fluid communication so that the first and second circuits are in fluid communication.

2. The vehicle of claim 1 , wherein the conduit of the first circuit is further arranged to circulate the coolant through a first radiator and a first pump, and the conduit of the second circuit is further arranged to circulate the coolant through a second radiator and a second pump.

3. The vehicle of claim 2 , wherein the isolation valve assembly is downstream of the first fuel-cell stack and upstream of the first radiator.

4. The vehicle of claim 1 , wherein the valving includes a first valve configured to proportion coolant between the first inlet and the first and second outlets and a second valve configured to proportion coolant between the second inlet and the first and second outlets.

5. The vehicle of claim 4 , wherein the first and second valves are synchronized with each other such that the proportion of coolant circulating between the first inlet and the second outlet is equal to the proportion of coolant circulating between the second inlet and the first outlet.

6. The vehicle of claim 1 further comprising:

a third coolant circuit including conduct arranged to circulate coolant through the heater and a heater core; and

a four-way valve including first and second ports connected to the conduit of the third circuit, a third port connected to conduit of the first circuit, and a fourth port connected to conduit of the second circuit.

7. The vehicle of claim 6 further comprising:

a battery assembly;

a heat exchanger connected to the conduit of the third circuit; and

a battery coolant circuit including conduit connected between the battery assembly and the heat exchanger.

8. The vehicle of claim 1 further comprising a valve selectively connecting the heater in fluid communication with the first and second circuits, the valve including at least a first position in which the heater is in fluid communication with the first circuit and is isolated from the second circuit and a second position in which the heater is in fluid communication with the second circuit and is isolated from the first circuit.

9. The vehicle of claim 1 further comprising a controller in electric communication with the isolation valve assembly, the controller being programmed to:

in response to a request to start the vehicle and temperatures of the coolant in the first and second circuits being less than a threshold, command the isolation valve assembly to the isolation position, connect the heater and the first circuit in fluid communication, and energize the heater,

in response to the coolant in the first circuit exceeding the threshold, start the first fuel-cell stack, isolate the heater and the first circuit, and command the isolation valve assembly to the isolation position, and

in response to the coolant in the first circuit exceeding a second threshold that is greater than the first, command the isolation valve assembly to the at least one mixing position.