Method and device for adjusting the friction coefficient of a friction clutch situated in a hybrid power train

1. A method for adjusting a torque characteristic curve or a friction coefficient of a friction clutch situated in a hybrid power train between an electric machine and a combustion engine, actuated by a clutch actuator, comprising:

adjusting the torque characteristic curve or friction coefficient by a torque transmitted by the friction clutch, the torque being determined when starting the combustion engine by the electric machine,

wherein the adjusting step includes the following steps:

actuating the friction clutch to crank-start the combustion engine in accordance with an old torque characteristic curve, in such a way that the friction clutch transmits a target torque definitely sufficient to start the combustion engine;

detecting a change in speed of the combustion engine;

determining an actual clutch torque from the change in engine speed, a moment of inertia and a torque of the combustion engine; and

adjusting the old torque characteristic curve or friction coefficient so that the target torque matches an actual torque.

2. The method as recited in claim 1 wherein the actual clutch torque is determined when the combustion engine is not yet firing.

3. The method as recited in claim 2 wherein the combustion engine has a drag torque, the drag torque being taken into account as a function of operating parameters of the combustion engine.

4. The method as recited in claim 1 wherein the actual clutch torque can be determined when the combustion engine is already producing torque.

5. The method as recited in claim 1 wherein the adjustment of the old torque characteristic curve or friction coefficient occurs incrementally.

6. The method as recited in claim 1 wherein the adjustment of the old torque characteristic curve or friction coefficient does not occur until the friction clutch is fully engaged.

7. A device for adjusting the torque characteristic curve or the friction coefficient of a friction clutch situated in a hybrid power train between an electric machine and a combustion engine, actuated by an actuator, the device comprising:

an electronic control device with inputs connected to sensors for detecting operating states of the hybrid power train, and at least one output connected to the actuator, the control device including a torque characteristic curve that specifies a transmissible clutch torque as a function of the setting of the clutch actuator, and a program that adjusts the torque characteristic curve or friction coefficient in accordance with a method as recited in claim 1 .