Temperature monitoring of magnets in permanent magnet motors used in vehicle drivetrains

A method of monitoring a magnet temperature of magnets of a rotor of a permanent magnet motor used for propelling a vehicle, the method comprising:

• determining an open circuit voltage of the permanent magnet motor;
• wherein the open circuit voltage is determined while the rotor of the permanent magnet motor rotates,
• determining a rotational speed of the rotor of the permanent magnet motor,
• the rotational speed corresponding to the open circuit voltage;
• and
• determining the magnet temperature of the magnets on the rotor of the permanent magnet motor based on the open circuit voltage and based the rotational speed, wherein determining the magnet temperature is performed from calibration data for the permanent magnet motor, the calibration data comprising at least a calibration temperature, a calibration speed, and a calibration voltage corresponding to the calibration temperature and the calibration speed.

A vehicle drivetrain comprising:

• a permanent magnet motor comprising a rotor,
• the rotor comprising permanent magnets;
• an inverter electrically coupled to the permanent magnet motor and controlling electrical power applied to the permanent magnet motor and operable to determine an open circuit voltage of the permanent magnet motor;
• a sensor for determining a rotational speed of the rotor of the permanent magnet motor;
• and
• a controller communicatively coupled to the inverter and to the sensor,
• wherein the controller is operable to determine a magnet temperature of the permanent magnets from the open circuit voltage and the rotational speed, and
• wherein the controller comprises calibration data for the permanent magnet motor, the calibration data comprising at least a calibration temperature, a calibration speed, and a calibration voltage corresponding to the calibration temperature and the calibration speed.