Hydrodynamic retarder

The hydrodynamic retarder comprises a control circuit including incorporating a hydraulic pump (10), a heat exchanger (3), inlet (4) and outlet (5) valves, and a control and regulating unit (6). The hydraulic pump is driven by an electric motor (2) which is controllable. A filter is connected to the hydraulic pump, and a control valve (13) is provided to regulate the retarder's control pressure which can be carried out on the outlet side or inlet side. The control unit is connected to temperature sensors (7,8) to monitor the temperature in the vehicle's cooling system and the viscosity influence or temperature influence of the braking medium. An Independent claim is included for a method for the controlling of a hydrodynamic retarder.