Reversible hydrostatic transmission pump with drive engine speed control

Claim 1

In a control for a drive assembly such as a power vehicle having a primary power source, an adjusting means for the power source connected with a spring loaded piston movable in an operating cylinder loaded with a control pressure fluid on the side of the piston opposite the spring and a hydrostatic transmission, driven by said power source, which transmission is adjustable in opposite directions of output rotation, a regulating unit for said transmission, a servo piston connected to said regulating unit and slidable in a servo operating cylinder, a control valve controlling the pressure in said servo operating cylinder, a receiver piston connected with said control valve and slidable in a receiving cylinder having pressure chambers on opposite sides of said receiver piston, one of which chambers is capable of being loaded with an arbitrarily adjustable control pressure, first means for applying an arbitrarily adjustable control pressure to said receiver piston chamber, second means for applying a control pressure to the spring loaded piston at the adjusting means for the power source, said second means for applying a control pressure being dependent on the control pressure of the first means, the improvement comprising a final control element on said transmission, a normally closed shut-off valve means having two oppposing elements controlled by the position of the regulating unit for said transmission, said shut-off valve means being connected to the control pressure chambers of the receiving cylinder and engaged by lever means on the final control element for bypassing fluid from one of the receiver chambers, and a connection from said shut-off valve means to the adjusting means of the power source to reduce the speed of said power source until the shut-off valve means closes.