Patent ID: 8047959

Claim:
A method for starting a piston engine of a hybrid drive in an electric travel state, the hybrid drive comprising at least the piston engine, an electric motor, a transmission, a clutch, which is situated between the piston engine and the electric motor, and a converter lockup clutch, the converter lockup clutch being situated between the electric motor and the transmission and being switchable into a slip state, in which it transmits a reduced torque or no torque from the electric motor to the transmission, comprising: setting a slip at the converter lockup clutch, increasing a speed of the electric motor from an initial speed to a starter speed and setting the speed in such a way that the speed and the torque do not change or only change in a predefined range at an output side of the converter lockup clutch, rapidly applying a torque on and off at the clutch situated between the piston engine and the electric motor in such a way that a torque pulse sufficient to overcome a first top dead center of a piston of the piston engine is transmitted to the piston engine, initiating a start of the piston engine at or close to overcoming the first top dead center, and setting a predefined slip and thus a predefined torque at the clutch in such a way that the electric motor, upon reaching its starting speed, both supports a run-up of the piston engine and transmits a positive torque to the converter lockup clutch, slip of the converter lockup clutch being reduced enough that the speed and the torque do not change or only change in a predefined range at the output side of the converter lockup clutch.