Powertrain with AC brushless starter and sensor/sensorless control method

A hybrid sensor/sensorless control method for use with a system having an alternating current (AC) brushless starter motor selectively connectable to an internal combustion engine, the brushless starter motor having a rotor with a rotor position, a position sensor positioned with respect to the rotor, and a controller in communication with the position sensor, the method comprising:

• below a threshold speed of the starter motor:
• generating measured angular position signals using the position sensor, the measured angular position signals being indicative of the rotor position of the brushless starter motor;
• calibrating sensorless logic of the controller using the measured angular position signals;
• and
• controlling a torque operation the brushless starter motor below the threshold speed using the measured angular position signals;
• and
• above the threshold speed:
• generating an estimated rotor position using the sensorless logic;
• and
• controlling the torque operation of the brushless starter motor solely using the estimated rotor position.

A powertrain comprising:

• an internal combustion engine;
• a transmission connected to the engine;
• a drive axle connected to the transmission;
• a load connected to the drive axle;
• and
• an electric starter system comprising:
• a brushless starter motor electrically connected to an alternating current (AC) voltage bus, the brushless starter motor being selectively connectable to the engine in response to a requested engine start event, the brushless starter motor having a rotor with a rotor position;
• a position sensor positioned with respect to the rotor that is configured to generate measured position signals indicative of the rotor position;
• and
• a controller in communication with the position sensor and programmed with sensorless logic configured to generate an estimated rotor position;
• wherein the controller is configured, below a threshold speed of the brushless starter motor, to:
• calibrate the sensorless logic using the measured position signals;
• and
• control a torque operation of the brushless starter motor during the requested engine start event using the measured position signals;
• and
• wherein the controller is configured to control the torque operation of the brushless starter motor above the threshold speed solely using the estimated rotor position.