SE7407540L

An automatic transmission system for use in automotive vehicles wherein the engine shaft drives an output shaft through a medium of a reversing gear and the output shaft carries a disk-shaped clutch element which can drive one flange of a variable-pitch sheave on the output shaft. The sheave forms part of a belt drive the other sheave of which drives one or more wheels. The flanges of the sheave on the output shaft are rotatable relative to the output shaft and are movable axially of the output shaft with and relative to each other by a piston which is reciprocable in a cylinder of the output shaft. A helical spring urges the sheave on the output shaft to a position in which the one flange is disengaged from the clutch element. When the cylinder receives pressurized fluid from a hydraulic regulating unit, the piston causes the one flange to engage the clutch element so that the belt drive rotates the wheel or wheels. A further increase of fluid pressure in the cylinder causes the other flange of the sheave on the output shaft to move toward the one flange and to thus change the speed ratio of the belt drive. The regulating unit has a pressure regulating valve which is controlled by an electromagnet. The latter can be influenced by the speed of the engine shaft, by the position of the gas and/or brake pedal, by the position of the kickdown switch and/or by a device which is actuated when the vehicle travels on a sloping road surface.