Hybrid vehicle propulsion systems and methods

A method of operating a vehicle propulsion system comprising:

• selectively operating at least one of a combustion engine and a first electric machine to provide a propulsion torque, the first electric machine being powered by a high-voltage power source;
• deactivating the combustion engine in response to the vehicle being operated at a speed corresponding to a power draw less than a power threshold for a predetermined amount of time;
• in response to a torque demand that is greater than a torque demand threshold, restarting the combustion engine using torque output from a second electric machine powered by the high voltage power source;
• and
• operating the second electric machine as a generator in response to a fault condition associated with the first electric machine.

A propulsion system for a vehicle, the propulsion system comprising:

• a combustion engine and a first electric machine each configured to selectively provide torque to propel the vehicle;
• a second electric machine coupled to the engine to selectively provide torque;
• a high-voltage power source configured to selectively power the first electric machine and the second electric machine;
• a low-voltage power source configured to selectively power the first electric machine and the second electric machine;
• and
• a controller programmed to:
• selectively operate at least one of the combustion engine and the first electric machine to provide a propulsion torque, the first electric machine being powered by the high-voltage power source;
• deactivate the combustion engine in response to the vehicle being operated at a speed corresponding to a power draw less than a power threshold for a predetermined amount of time;
• in response to a torque demand that is greater than a torque demand threshold, restart the combustion engine using torque output from the second electric machine powered by the high voltage power source;
• and
• power at least one of the first electric machine and the second electric machine using the low-voltage power source in response to a fault condition associated with the high-voltage power source.