System and method for operating a hybrid vehicle

A method of operating a hybrid vehicle on a terrain, the method comprising:

• determining, by the hybrid vehicle, a grade or slope of the terrain that the hybrid vehicle is operating on;
• determining, by the hybrid vehicle, a retarding capability of a hybrid powertrain within the hybrid vehicle, wherein the retarding capability of the hybrid powertrain is determined based on a state of charge of the battery and at least one of a weight of the vehicle or a rolling resistance of the vehicle, the hybrid powertrain including:
• a motor-generator unit,
• a battery electrically connected to a motor-generator unit,
• an engine, and
• a transmission engageably connected to the engine and the motor-generator unit, the transmission having a plurality of gears;
• and
• determining, by the hybrid vehicle, an appropriate gear of the hybrid powertrain based on the retarding capability of the hybrid powertrain and the grade or slope of the terrain.

A controller for a hybrid vehicle, the controller configured to:

• determine a grade or slope of a terrain that the hybrid vehicle is operating on;
• determine a retarding capability a hybrid powertrain within the hybrid vehicle, wherein the retarding capability is determined based on a state of charge of the battery and at least one of a weight of the vehicle or a rolling resistance of the vehicle, the hybrid vehicle including:
• a motor-generator unit,
• a battery electrically connected to the motor-generator unit,
• an engine and, and
• a transmission engageably connected to the engine and the motor-generator unit;
• and
• determine an appropriate gear of the hybrid powertrain based on the retarding capability of the hybrid powertrain and the grade or slope of a terrain upon which the hybrid vehicle is operating.