Transmission oil pressure control during engine autostart

A vehicle comprising:

• an internal combustion engine having non driver-requested autostart functionality;
• an auxiliary pump operable to provide fluid pressure at a first level when the engine is off;
• a flow control solenoid in fluid communication with the auxiliary pump that is configured to output a variable clutch pressure;
• a transmission having a stationary member, a gear set, an output member, and a designated clutch in fluid communication with the flow control solenoid, wherein the designated clutch is applied via the variable clutch pressure at a second level to connect the gear set to the stationary member and establish a 1st gear launch state of the transmission;
• a hydrodynamic torque converter having an impeller connected to the engine and a turbine connected to an input member of the transmission;
• a sensor configured to measure a rotational speed of the turbine;
• a high-voltage rechargeable energy storage system (RESS);
• a high-voltage electric motor powered via the high-voltage RESS, wherein the high-voltage electric motor and the high-voltage RESS are rated for at least 60 VDC and the high-voltage electric motor is connected to the engine via a belt;
• drive wheels;
• and
• a controller having a processor and tangible, non-transitory memory on which is recorded instructions for controlling the clutch pressure to the designated clutch during the non driver-requested engine autostart event, wherein execution of the instructions by the processor causes the controller to:
• transmit a set of pulse width modulation (PWM) control signals to the flow control solenoid upon detection, by the controller, of a predetermined set of conditions triggering the non-driver requested autostart event to thereby lower the variable clutch pressure to the first level, including detecting an apply pressure to each of a brake pedal and an accelerator pedal and a state of charge of the high-voltage RESS;
• command an automatic restart of the engine, including applying torque to the belt via the high-voltage electric motor;
• determine the turbine speed by processing speed signals from the sensor, via the processor of the controller, while the engine is actively increasing in speed;
• and
• discontinue transmitting the set of PWM control signals to the flow control solenoid while increasing the variable clutch pressure at a calibrated rate to full line pressure, thereby applying the designated clutch to connect a node of the gear set to the stationary member to transmit output torque from the output member of the transmission, via another node of the gear set, to the drive wheels and thereby launch the vehicle in 1st gear when the turbine speed exceeds a calibrated threshold.

A method comprising

• detecting a set of conditions in a vehicle having a transmission and an engine with autostart functionality;
• transmitting a set of pulse width modulation (PWM) control signals to a flow control solenoid in the transmission upon detection, by the controller, of the set of conditions, wherein the flow control solenoid is in fluid communication with a source of fluid pressure;
• lowering a variable clutch pressure to a designated braking clutch of the transmission to a calibrated first level via the PWM control signals;
• commanding an automatic restart the engine via an electric motor;
• determining an input speed to the transmission while the engine is actively increasing in speed;
• increasing the variable clutch pressure to a second level while engine speed is increasing;
• and
• discontinuing the set of PWM control signals to the control solenoid while increasing the variable clutch pressure at a calibrated rate to full line pressure when the input speed to the transmission exceeds a calibrated threshold such that the clutch pressure is set at the second level, thereby applying the braking clutch, wherein applying the braking clutch connects a node of a gear set of the transmission to a stationary member to transmit output torque, via another node of the gear set, to drive wheels of the vehicle via an output member of the transmission.