Method for actuating a clutch of a hydrodynamic torque converter

The invention relates to a method for actuating a clutch of a hydrodynamic torque converter, of the type defined in more detail in the preamble of Claim 1.

Clutches of this type in torque converters are actuated in the engaging direction in order to cormect the drive input of the torque converter with its drive output, such that direct through-drive from the drive input to the drive output takes place, which results in improved efficiency. These clutches are often actuated in the engaging direction when the turbine torque is of the same size as the pump torque with the clutch engaged or disengaged. The shift-point concerned is determined by the rotational speed difference between the pump impeller wheel and the turbine wheel of the hydrodynamic torque converter.

DE 29 44 410 C2 discloses a bridging clutch of a hydrodynamic torque converter, which remains actuated in the engagement direction until a service brake is actuated, in order reliably to avoid stalling the engine as a result of blocking the wheels.

The purpose of the present invention is to provide a method for actuating a clutch of a hydrodynamic torque converter, which further improves the operating reliability of the vehicle.

This objective is achieved by a method for actuating a clutch of a hydrodynamic torque converter, which also includes the characterizing features of the principal claim.

According to the invention, the clutch of the hydrodynamic torque converter is actuated in the engaging direction by virtue of vehicle status parameters, and also remains actuated in the engaging direction when a service brake is actuated and a device for recognizing the vehicle status detects that the vehicle is driving downhill. Since the clutch remains engaged even when driving downhill, the vehicle can be retarded by means of both the service brake and the engine brake. On the other hand, if the vehicle is not driving downhill the engaged clutch is actuated in the disengaging direction when the service brake is actuated. This makes it possible, for example in the case of a working machine such as a wheel loader, to increase the speed of the drive engine substantially and at the same time to retard the vehicle, in order to be able to obtain sufficient speed at the hydraulic pump for the working hydraulic system, for example in order to raise a scoop of the wheel loader rapidly.

In another version of the invention, the clutch is again actuated in the engaging direction when the service brake is no longer actuated and corresponding shift-points, for example related to the turbine and pump speeds, have been reached. The clutch is actuated by a transmission control unit, which receives signals, for example speed signals from the turbine wheel and the pump wheel of the hydrodynamic torque converter or characteristic signals from the drive engine, for example the torque provided by the drive engine. The transmission control unit evaluates the signals and actuates the clutch as a function of the operating parameters of the vehicle.

In a further embodiment of the invention the clutch is actuated in the disengaging direction even though the service brake is actuated and the vehicle is driving "downhill", if the speed of the vehicle is lower than a defined value.

The downhill driving situation can for example be recognized from the drive engine torque detected, or by means of a level switch. Actuation of the service brake can be recognized for example from the brake pedal position or from the brake pressure.

Since the clutch can be actuated in the engaging direction, the efficiency can be improved. By actuating the clutch in the disengaging direction when the brake pedal is actuated, it is possible to increase the speed of the drive engine and hence that of the working pump of the working machine, even if the criteria for engaging the clutch are fulfilled. Since the clutch remains actuated in the engaging direction even when the service brake is actuated while driving downhill, some of the load on the service brake can be relieved because braking of the vehicle can be assisted by the engine brake.

(New) Claims

1. Method for actuating a clutch of a hydrodynamic torque converter in a self-propelling working machine such as a wheel loader, such that when the clutch is actuated in the closing direction it closes and thereby connects the drive input of the hydrodynamic torque converter to the drive output of the hydrodynamic torque converter, and when a service brake is actuated the clutch is actuated in the opening direction, characterized in that when the service brake is actuated, the clutch remains actuated in the closing direction and therefore remains closed if a device for recognizing the driving status of the vehicle detects that the vehicle is driving downhill.

2. Method for actuating a clutch according to Claim 1, chiaracterized in that when the service brake is actuated and driving downhill is detected, the clutch is actuated in the opening direction if the speed of the vehicle is lower than a defined value,

3. Method for actuating a clutch according to Claim 1, characterized in that when the service brake is actuated and driving downhill is detected, the clutch is actuated in the opening direction if the torque on the drive input shaft is above a define d value.

4. Method for actuating a clutch according to Claim 1, characterized in that downhill driving is detected with the help of the torque of a drive engine.

5. Method for actuating a clutch according to Claim 1, characterized in that the actuation of the service brake is detected from the brake pedal position or the brake pressure.

6. Method for actuating a clutch according to Claim 1, characterized in that after actuating the clutch in the opening direction, it is actuated in the closing direction if the service brake has not been actuated and the speed of the drive input in in the range of the speed of the drive output

7. Method for actuating a clutch according to Claim 1, characterized in that a transmission electronic system determines the speed of the drive input, the speed of the drive output, the brake pedal position or brake pressure and the torque delivered by a drive engine, and controls the clutch accordingly.

8. Method for actuating a clutch according to Claim 1, characterized in that the torque delivered by a drive engine is transmitted by means of a CAN signal to a transmission control unit, which loses it for detecting a downhill driving situation.