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, wherein the hybrid drive system comprises an internal combustion engine with a belt-driven starter generator coupled thereto, a transmission, a drivetrain generator, an exhaust system for the internal combustion engine, a control device, and an output, a first clutch is arranged between the internal combustion engine and the transmission, the method comprising:

• bringing, via the control device, the motor vehicle to a first speed by controlling the hybrid drive system;
• bringing, via the control device, about an operating state of the hybrid drive system in which the first clutch is disengaged;
• shutting off, via the control device, the internal combustion engine;
• detecting, via the control device, a braking demand for braking of the motor vehicle;
• engaging, via the control device, the first clutch for overrunning the internal combustion engine as well as for operating the belt-driven starter generator in a recuperation mode;
• and
• configuring, via the control device, the internal combustion engine such 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.