Start-up strategy for hybrid powertrain

A method for starting-up a hybrid powertrain for a vehicle comprising an engine, an electric propulsion motor, an over-running clutch coupled to the engine and the electric propulsion motor, an electric oil pump motor coupled to the over-running clutch, and an oil pump coupled to the electric oil pump motor, the method comprising:

• in response to a vehicle start-up command from a vehicle operator, evaluating whether predetermined conditions for a casual start are satisfied, the casual start involving only the electric oil pump motor powering the oil pump to generate a desired oil pressure within a desired start-up time period, the predetermined conditions including oil temperature, and the desired oil pressure being for operation of a transmission of the hybrid powertrain;
• starting the engine when the predetermined conditions are not satisfied;
• activating the electric oil pump motor for the casual start without activating the engine when the predetermined conditions are satisfied:
• calculating the difference between an oil pump target rotations per minute and the rotations per minute of the electric oil pump motor,
• comparing the difference to a threshold value,
• when the vehicle operator issues a transmission shift command, starting the engine and then deactivating the electric oil pump motor once the rotations per minute of the engine equal or exceed the rotations per minute of the electric oil pump when the difference is greater than the threshold value, and
• continuing the casual start when the difference is less than the threshold value or the vehicle operator does not issue a shift command;
• and
• starting the engine and terminating the method after a predetermined amount of time has passed from the start-up command when the difference is greater than the threshold value.

A system for starting up a hybrid powertrain for a vehicle having an engine, an electric propulsion motor, a transmission, an oil pump configured to generate hydraulic fluid pressure for the transmission, and an electric oil pump motor coupled to the oil pump, the system comprising:

• an input device configured to receive a vehicle start-up command from a vehicle operator;
• a temperature sensor configured to measure a temperature indicative of a temperature of the hydraulic fluid;
• and
• a controller configured to, in response to receiving the vehicle start-up command:
• evaluate whether predetermined conditions for a casual start are satisfied, the casual start involving only the electric oil pump motor powering the oil pump to generate the hydraulic fluid pressure within a desired start-up time period, the predetermined conditions including at least the measured temperature being above a temperature threshold;
• start the engine to power the oil pump when the predetermined conditions are not satisfied;
• and
• activating the electric oil pump motor to power the oil pump for the casual start without activating the engine when the predetermined conditions are satisfied.