Hybrid electric vehicle energy management during extreme operating conditions

An energy management method for an electrified vehicle having an electrified powertrain including an internal combustion engine and an electric motor, the energy management method comprising:

• providing (i) a fuel level sensor configured to measure an amount of fuel remaining in a fuel tank, wherein the fuel is used for combustion by the engine, and (ii) a state of charge (SOC) sensor configured to measure a SOC of a battery system configured to power the electric motor;
• determining, by a controller of the electrified vehicle, a fuel reserve to maintain in the fuel tank, wherein the fuel reserve is only to be used by the engine to support a heating system of the electrified vehicle configured for at least window heating and/or defrosting;
• controlling, by the controller, the electrified powertrain to maintain the fuel reserve in the fuel tank, wherein the fuel reserve is a threshold amount above a minimum amount of fuel that is kept in the fuel tank while indicating that the fuel tank is fully depleted;
• detecting, by the controller, an operating condition of the electrified vehicle when (i) the fuel tank is depleted down to the fuel reserve, (ii) the battery system SOC is at or below a minimum SOC propulsion threshold, and (iii) an ambient temperature is at or below a cold soak temperature threshold;
• and
• in response to detecting the electrified vehicle operating condition, temporarily powering, by the controller, the engine using the fuel reserve in the fuel tank and utilizing, by the controller, the engine to support the heating system for at least window heating and/or defrosting.