Hybrid Drivetrain, Hybrid Gearbox, and Method for Operating Same

A hybrid gearbox has a shift gearbox including at least one fixed ratio gear having a gear ratio both for the internal combustion engine and the electric motor-generator with respect to a power train connection, and speed superposition gearbox which is designed to provide a power-split gear having a variable speed ratio and a fixed torque ratio with respect to the internal combustion engine connection and the power train connection, wherein the variable speed ratio is formed by a modulation of a speed provided by the internal combustion engine on a speed provided by the electric motor-generator. The hybrid gearbox has at least one operating mode in which gear changes are only carried out between the fixed-ratio gear and the power-split gear.