Control unit for a transmission and associated operating method

A control unit for regulating the transmission ratio of a transmission which is located in a drive train together with a motor, in order to obtain braking assistance through the braking torque of the motor is disclosed. The control unit comprises several signal inputs for receiving the desired braking torque (MSET) and the number of revolutions (nACT) of the motor and/or the vehicle speed; a calculation unit for determining the suitable transmission ratio (ü) of the transmission for achieving the desired braking torque in accordance with the desired braking torque (MSET) and the number of revolutions (nACT) or the vehicle speed; and a signal output for outputting a control signal (ü) which determines the transmission ratio of the transmission. An electrical generator which feeds a battery and which has an additional braking torque is located in the drive train. A measuring unit is provided for determining the charge status of the battery, this measuring unit being connected to the calculation unit on the output side in order to regulate the transmission ratio of the transmission according to the charge status of the battery.