Zf Friedrichshafen Ag

Zf Friedrichshafen

Horst Rogner

Josef Haupt

Siegfried Winkelmann

A method and device for actuating a shift element of an automatic transmission having a start-stop function and a pressure medium pump driven by an internal combustion engine. The shifting elements are clutches or brakes that can be actuated by a piston which is actuated for engagement via pressure supplied to a pressure space. The pressure space is depressurized when the engine stops. To enhance start-stop operation, the shifting elements comprise an additional pressure space that acts, in opposition to the pressure space acting in the engaging direction, as a controllable restoring mechanism which can be rendered inactive, if desired. If the engine stops and the automatic start-stop function is activated, the additional pressure spaces, acting in the restoring direction, are depressurized before the pressure drop in the pressure spaces, acting in the engaging direction, of the pistons, but are otherwise permanently pressurized during driving operation.

Method and device for actuating a shift element of an automatic transmission having a start-stop means

A method for actuating a shift element of an automatic transmission having a start-stop function and a pressure medium pump driven by an internal combustion engine. The shifting elements are clutches or brakes that can be actuated by a piston which is actuated for engagement via pressure supplied to a pressure space. The pressure space is depressurized when the engine stops. To enhance start-stop operation, the shifting elements comprise an additional pressure space that acts, in opposition to the pressure space acting in the engaging direction, as a controllable restoring mechanism which can be rendered inactive, if desired. If the engine stops and the automatic start-stop function is activated, the additional pressure spaces, acting in the restoring direction, are depressurized before the pressure drop in the pressure spaces, acting in the engaging direction, of the pistons, but are otherwise permanently pressurized during driving operation.

A device for controlling a rotating shifting element of an automatic transmission for a start/stop operation. The shifting element is actuated by an axially moving piston which is biased, in a disengaging direction, by a spring and biased, in an engaging direction, by hydraulic pressure supplied to a pressure space. At least one spring-loaded latch, which is able to move in the radial direction, is arranged in the pressure space. The spring-loaded latch, when the combustion engine is operating, rotates with the piston and acts upon the piston such that if the engine stops, the previously engaged shifting element is locked by spring force and, as the pressure decreases, the shifting element disengages, at most only slightly, and when the engine is re-started, the locking action is again released by centrifugal force, in opposition to the spring force, so that the piston remains engaged during the hydraulic pressure build-up in the pressure chamber.

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Oberteuringen, Germany

Horst Rogner