Hydrodynamic torque-transfer unit, especially a hydrodynamic brake

Abstract

The invention concerns a hydrodynamic torque transfer unit, particularly in the form of a hydrodynamic brake. Flow to the inlet of the working chamber of the transfer unit is controlled by an inlet valve movable between a closed, partially open and fully open position. A first piston moves the valve between its positions. A change over device cooperates with the first piston. The change over device includes a second piston. A first pressure chamber is defined between the first and second pistons. A second pressure chamber is defined behind the second piston. Initially, the first pressure chamber is pressurized, driving the first piston and thus the inlet valve to the fully open position. The second piston is moved by pressurization of the second pressure chamber to cut off pressure to the first pressure chamber and to instead cause communication between the first pressure chamber and the working chamber. Typically, the working chamber is at reduced pressure which thereby permits depressurization of the first pressure chamber. A spring then returns the inlet valve back toward the intermediate open position. The second piston has been shifted by pressurization of the second pressure chamber to prevent the first piston and thus the inlet valve from returning to the fully closed position, and the inlet valve therefore remains at the intermediate open position. There may be an outlet control which also regulates the outlet flow from the working chamber. The first pressure chamber may communicate with the working chamber through the outlet control.