Patent ID: 8491443

Claim:
A method of controlling a lock-up clutch of a hydrodynamic torque converter having a turbine wheel which connects a drive motor to a transmission having at least two shiftable gears, the lock-up clutch being actuated for engagement to thereby directly connecting an input shaft of the hydrodynamic torque converter to an output shaft of the hydrodynamic torque converter, and being actuated for disengagement to thereby disconnect the direct connection, a turbine rotational speed, a drive torque of the transmission and an engaged gear being determined, and the lock-up clutch being actuated for engagement depending on the drive torque of the transmission, the turbine rotational speed and the engaged gear of the transmission and thereby directly connecting the input shaft to the output shaft of the hydrodynamic torque converter, the method comprising the steps of: when the drive motor is operating under a full load, engaging the lock-up clutch and thereby directly connecting the input shaft of the hydrodynamic torque converter to the output shaft when the torque of the turbine wheel is substantially the same as when the lock-up clutch is actuated for engagement and disengagement, and when the drive motor is operating in a partial load range, engaging the lock-up clutch only when the turbine rotational speed is higher than the turbine rotational speed at which the lock-up clutch is engaged when the drive motor is under the full load, and disengaging the lock-up clutch, when the transmission shifts to a different gear, while the drive motor is operated in the partial load range, and engaging the lock-up clutch when the transmission shifts to a different gear while the drive motor is operated in the full load range.