The device has a cover (2) connected to a power intake shaft, and a pump rotor (3) connected to the cover, to form a hydraulic chamber. A turbine rotor (4) inside the chamber is connected to a take-off shaft. A guide rotor (5) is located between pump and turbine rotors. A piston (22) forms a first hydraulic chamber (A) between piston and front cover, and a second hydraulic chamber (B) between piston and turbine rotor. The piston is moved by a fluid pressure differential between the chambers towards and away from the first cover, and has a counter element opposite to the front cover. The piston is connected to the turbine rotor to transmit a torque.
