A method is described for determining a reference value of an actuating current that corresponds to a defined operating point of an electro-hydraulically actuated frictional shifting element of a continuously variable power-branched transmission, at which the shifting element transmission capacity is zero, and starting from which an increase of actuating force immediately increases the transmission capacity. The actuating current reference value of the shifting element, when closed with a further shifting element decoupled from the transmission output and when a transmission input rotational speed is higher than a defined threshold, is reduced until a rotational speed difference between the rotational speeds of the shifting element halves exceeds a predefined limit value such that, at the time when the limit value is exceeded, the reference value of the actuating current is the reference value of the actuating current that corresponds to the defined operating point of the shifting element.

When a state of a vehicle is a predetermined state of the vehicle where vehicle vibration occurs, weak circulating torque is generated to fill backlash inside an automatic transmission and in a power transmission path by half-engaging a second clutch for establishing a second power transmission path while a first power transmission path remains established in the automatic transmission. A speed ratio of the second power transmission path is alternatively set to a lower vehicle speed-side speed ratio with respect to a speed ratio of the first power transmission path or a higher vehicle speed-side speed ratio with respect to the speed ratio of the first power transmission path in response to a traveling state. It is possible to generate weak circulating torque in a direction to increase an input shaft rotation speed or in a direction to reduce the input shaft rotation speed in accordance with the traveling state.

When a state of a vehicle is a predetermined state of the vehicle where vehicle vibration occurs, weak circulating torque is generated to fill backlash inside an automatic transmission and in a power transmission path by half-engaging a second clutch for establishing a second power transmission path while a first power transmission path remains established in the automatic transmission. A speed ratio of the second power transmission path is alternatively set to a lower vehicle speed-side speed ratio with respect to a speed ratio of the first power transmission path or a higher vehicle speed-side speed ratio with respect to the speed ratio of the first power transmission path in response to a traveling state. It is possible to generate weak circulating torque in a direction to increase an input shaft rotation speed or in a direction to reduce the input shaft rotation speed in accordance with the traveling state.