Patent ID: 7937195

Claim:
A system for managing a power source in a vehicle including an engine, an electric machine, and an accelerator pedal for indicating a driver demand for power, each of the engine and the electric machine being operable to output torque to at least one vehicle wheel, the engine having an engine-on power requirement for starting the engine, the power source being operable to supply power to the electric machine and having a first operating temperature range, a second operating temperature range above the first operating temperature range, and a third operating temperature range below the first operating temperature range, the system comprising: a sensor for measuring a temperature related to the temperature of the power source; and a control system in communication with the sensor and the accelerator pedal, and including at least one controller, the control system being programmed with first and second discharge limits for the power source, the first discharge limit being at least partly based on an amount of power supplied by the power source for a first predetermined period of time, and being substantially constant over the first operating temperature range and decreasing over the second and third operating temperature ranges, the second discharge limit being higher than the first discharge limit, and at least partly based on the temperature of the power source and an amount of power supplied by the power source for a second predetermined amount of time that is less than the first predetermined amount of time, and which is based on an amount of time required to start the engine, the control system being configured to: determine a buffer value as a function of at least the second discharge limit and the engine-on power requirement, determine a driver demand for power, and start the engine when the engine is off and the driver demand for power exceeds the buffer value.