To decrease ventilation loss to make the operation of a retarder effective at the time of braking by providing a switching valve in a pipe between the hydrodynamic center of the retarder and a working medium container and in a pipe between the medium outlet of the retarder and the container, respectively.
During the braking operation, if it is necessary to fill a retarder with a working medium, a valve A communicates a pipe 5.1 with a pipe 5.2 to connect a working medium container 4 with the hydrodynamic center 2.3. Simultaneously, a valve B cuts off the communication between a pipe 6.1 and a pipe 6.2. At this time, the retarder 2 is quickly filled with a required quantity of working medium immediately to enable the braking action. During the non- braking operation, the valve A blocks between the pipe 5.1 and the pipe 5.2, thereby cutting off between the container 4 and the retarder 2. Simultaneously, the valve B communicates the pipe 6.1 with the pipe 6.2 to let the flow free. As the pipe 5.1 is opened to the inside of the hydrodynamic center 2.3, the substantially full quantity of working medium is discharged from the working chamber so as to hold down power loss to the minimum value.
ROSE PETER
OTT HELMUT
HEILINGER PETER
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