Load and speed dependent gear change hydraulic pressure generator

Claim 1

Apparatus supplying a gear changing or switching pressure, for use in vehicle transmissions, comprising: a pump (40) driven by the engine of the vehicle with a speed representative of engine speed, and a switching pressure line (33) connected to the pump and having arising therein a fluid switching pressure proportional to engine speed; a pressure controller (10) having a main valve slider (12), and feedback means (35, 14, 16) connected thereto and controlling the switching pressure; displaceable means (21, 28, 23, 37) changing position as a function of the change of position of the controller for the engine which controls engine speed and providing a force acting on the main valve slider (12) of the pressure controller, representative of engine controller position, the improvement comprising: a Venturi (41) located in the switching pressure line; and a control pressure line (38) branched off the throat of the Venturi to provide a pressure signal representative of flow of pressure fluid at the control pressure through the constriction; said control pressure line (38) and the displaceable means (21, 28, 23, 24, 37) providing a force representative of engine controller position acting on the main valve slider (12) such that the force representative of the control pressure and the force representative of engine controller position are applied to the main valve slider (12) in additive relation to change the position of the main valve slider as a function of the sum of said forces.