METHOD FOR OPERATING A HYBRID DRIVE SYSTEM OF A MOTOR VEHICLE, HYBRID DRIVE SYSTEM, AND MOTOR VEHICLE

A method for operating a hybrid drive system of a motor vehicle, in which an internal combustion engine with a belt-driven starter generator coupled thereto is operated in an overrun mode for braking of the motor vehicle, wherein, in order to avoid a delivering of air to an exhaust system of the hybrid drive system, the internal combustion engine is configured in such a manner that intake valves and/or exhaust valves of the internal combustion engine remain closed during a rotation of a crankshaft of the internal combustion engine. Also provided is a hybrid drive system for a motor vehicle and to a motor vehicle having a hybrid drive system.