Method for controlling a hybrid drive train of a vehicle

A method of controlling a hybrid drive-train of a motor vehicle, in which the hybrid drive-train comprises an internal combustion engine (VM) with a driveshaft (2), an electric machine (EM) that is operable at least as a motor and which has a rotor (3) that is connectable to the driveshaft (2) of the internal combustion engine (VM) by an automated separator clutch (K0), an automated powershift transmission (LSG, LSG′) with an input element (4, 4′) which is in driving connection with the rotor (3) of the electric machine (EM), and with at least two frictional shifting elements (K1, K2;

• K1′, K2′) for time-overlapped shifting between two gears, such that during electric driving operation with the internal combustion engine (VM) stopped and the separator clutch (K0) disengaged, the internal combustion engine (VM) can be drag-started in combination with a downshift in the powershift transmission (LSG, LSG′), the method comprising the following steps:
• disengaging a frictional shifting element (K_ab) to be disengaged to below its slipping limit;
• engaging the separator clutch (K0) until the internal combustion engine (VM) has at least reached a minimum starting speed (nVM—Start);
• starting the internal combustion engine (VM);
• partially disengaging the separator clutch (K0);
• separately adjusting the internal combustion engine (VM) and the electric machine (EM) to a synchronous speed (nSync—ZielG) of a target gear;
• and
• fully disengaging the frictional shifting element (K_ab) to be disengaged and fully engaging a frictional shifting element (K_zu) to be engaged and the separator clutch (K0).