Method for controlling a lock-up clutch of a hydrodynamic torque converter

The invention relates to a method for controlling a lock-up clutch of a hydrodynamic torque converter according to the art further defined in the preamble of claim 1.

Lock-up clutches, in hydrodynamic torque converters, are used to directly connect the input shaft of the hydrodynamic torque converter to its output shaft, which creates a direct through drive of the drive motor to the downstream transmission and can Improve the efficiency of the overall system.

DE 4030811 A1 discloses a method for controlling a lock-up clutch of a hydrodynamic torque converter that is controlled to bring the lock-up clutch into a state of slippage depending on the change of the engine load, wherein a specific degree of slippage is set.

The object of the present invention is to create a method for controlling a lock-up clutch, of a hydrodynamic torque converter, in which the driving behavior of the vehicle, especially a working machine such as a wheel loader, is further improved.

The object is achieved with a generic method for controlling a lock-up clutch of a hydrodynamic torque converter having the characterizing features of the main claim.

According to the invention, the engaged gear of the transmission, the drive torque of the transmission and the turbine speed of the hydrodynamic torque converter are determined and, depending on these parameters, the lockup clutch is actuated for engagement. When the drive motor, for example an internal combustion engine, is operated under a full load, the lock-up clutch of the hydrodynamic torque converter is actuated for engagement when the torque of the turbine wheel of the hydrodynamic torque converter is the same when the lock-up clutch Is engaged and disengaged. The lock-up clutch is thereby engaged, before up shifting to the next gear occurs, and is hence actuated for engagement during this shifting process and, when downshifting to the next gear occurs, the lock-up clutch also remains engaged.

When the drive motor is operated under a partial load, the lock-up clutch only engages once the speed of the turbine wheel is significantly higher which causes shifting to occur in the partial load range of the drive motor when the lock-up clutch is actuated for disengagement. Shifting to the next highest or lowest gear, when the drive motor is in the partial load range, hence occurs when the lock-up clutch is disengaged. The lock-up clutch engages, after the shifting process to the next highest gear, when the defined conditions for engagement exist.

If the shifting points, for actuating the lock-up clutch, are exclusively determined from the difference between the rotational speed of the turbine wheel and the impeller of the hydrodynamic torque converter, the driving behavior changes significantly in the lower gears, especially with a working machine such as a wheel loader at speeds in the range of 12 km/h, from the driving behavior when the vehicle is operated in the higher gears.

By means of the method according to the invention, the driving behavior is adapted, when the working machine is operated at lower gears, to the driving behavior when the working machine is operated at higher gears.

In a further embodiment according to the invention, there is a separate characteristic for each gear to set the switching thresholds at which the transmission input torque and the turbine rotational speed are defined in order to set the optimum shifting points for engaging the lock-up clutch in each gear.

(New) claims

1. A method for controlling a lock-up clutch of a hydrodynamic torque converter having a turbine wheel that connects a drive motor to a transmission having at least two shiftable gears, wherein the lock-up clutch can be actuated for engagement and thereby directly connect the Input shaft of the hydrodynamic torque converter to its output shaft, and it can be actuated for disengagement and thereby severs the connection, characterized in that the turbine rotational speed, the drive torque of the transmission and the engaged gear are determined, and that the lock up clutch Is actuated for engagement depending on the torque of the transmission, the turbine rotational speed and the engaged gear of the transmission and thereby directly connects the input shaft of the hydrodynamic torque converter to its output shaft, wherein when the drive motor is operating under a full load, the lock-up clutch is actuated for engagement and thereby directly connects the input shaft of the hydrodynamic torque converter to its output shaft when the torque of the turbine wheel is substantially the same when the lock-up clutch is actuated for engagement and disengagement, and when the drive motor is operating in a partial load range, the lock-up clutch is actuated for engagement only when the turbine rotational speeds are higher than the turbine rotational speeds at which the lock-up clutch is actuated for engagement when the drive motor is under a full load, whereby the lock-up clutch is actuated for disengagement when the transmission shifts to a different gear while the drive motor is operated in a partial load range, and the lock-up clutch is actuated for engagement when the transmission shifts to a different gear while the drive motor is operated in the full load range.

2. The method for controlling a lock-up clutch according to claim 1, characterized in that with more than two gears of the transmission, for each gear, a torque of the transmission and a turbine rotational speed are defined at which the lock-up clutch is actuated for engagement.

3. The method for controlling a lock-up clutch according to claim 1, characterized in that, when the drive motor is operating under a full load, the lock-up clutch is actuated for engagement when the torque of the turbine wheel is nearly the same when the lock-up clutch is actuated for engagement and disengagement.

4. The method for controlling a lock-up clutch according to claim 1, characterized in that, while the drive motor is operated in a full load range, the lock-up clutch is actuated for engagement when the transmission shifts to a different gear.

5. The method to control a lock-up clutch according to claim 1, characterized in that with the transmission having more than two gears, for each gear, a torque of the transmission and a turbine rotational speed are defined at which the lock-up clutch is actuated for engagement.

6. The method for controlling a lock-up clutch according to claim 1, characterized in that, when the drive motor is operating under a full load, the lock-up clutch is actuated for engagement when the torque of the turbine wheel is substantially the same when the lock-up clutch is actuated for engagement and disengagement.