Method for operating a drive train

A method of operating a drivetrain of a motor vehicle, the drivetrain comprising at least a hybrid drive with an internal combustion engine and an electric motor, a clutch connected between the internal combustion engine and the electric motor, the internal combustion engine being an ignited internal combustion engine when operating and being a non-ignited internal combustion engine when not operating, a transmission arranged between the hybrid drive and a drive output, and either a transmission-internal or a transmission-external starting element, the method comprising the steps of:

• partially engaging the clutch connected between the non-ignited internal combustion engine and the electric motor delivering a constant electric motor torque to a slipping condition to entrain the internal combustion engine into motion with help of the electric motor such that as a function of time and starting from a first initial value, the clutch torque transmitted by the clutch is increased linearly up to a first final value;
• determining a break-away torque of the internal combustion engine, if the non-ignited internal combustion engine begins turning during the linear increase of the clutch torque transmitted by the clutch up to the first final value;
• and
• further engaging the clutch, connected between the non-ignited internal combustion engine and the electric motor, to a slipping condition as a function of time and starting from a second initial value, if the non-ignited internal combustion engine does not begin turning during the linear increase of the clutch torque transmitted by the clutch up to the first final value, such that the clutch torque transmitted by the clutch is increased linearly until the non-ignited internal combustion engine begins turning, and determining the break-away torque of the internal combustion engine from the clutch torque at which the internal combustion engine begins turning.