Transmission-regulating device for motor vehicle

A device for regulating the operation of the transmission of a motor vehicle having a variator which includes a step-down control element, said device comprising a hydraulic receiver, an element movable in said receiver to define therewith a chamber, means connecting said movable element with the step-down control element of the variator, distributor means associated with said receiver, a slide valve to said distributor means, a source of pressure fluid, a reservoir for pressure fluid, first conduit means adapted to communicate said chamber through said distributor means with said source, second conduit means adapted to communicate said chamber through said distributor means with said reservoir, a centrifugal regulator movable in response to engine speed, connecting means associating the slide valve with the centrifugal regulator resilient means associated with said connecting means, means for controlling said resilient means in response to operation of an accelerator for said engine, said centrifugal regulator, said resilient means and said control means serving to establish three positions for said slide valve, in the first of which the effect of the resilient means predominates and communication is established between said chamber and said source through said first conduit means while preventing communication between said chamber and said reservoir through said second conduit means, in the second of which the effect of said centrifugal regulator predominates and communication is established between said chamber and said reservoir through said second conduit means while preventing communication between said chamber and said source through said first conduit means, and in the third of which the effects of the resilient means and the centrifugal regulator are in equilibrium and communication is prevented between said chamber and both said source and said reservoir, a two position electrically operable valve in said first conduit means and having a normally open position connecting said first conduit means with said source, an energising circuit for said valve, switch means normally holding said energising circuit open, and a device for detecting the rotary speed of the engine when said speed is at least equal to a predetermined value and for closing said switch means thereby to energise said circuit, close said valve and thus close said first conduit means.