Hydraulic pressure control system for an automatic power transmission

Claim 1

A control system for controlling the level of hydraulic pressure supplied to a servo mechanism of a friction element of an automotive automatic power transmission driven by an engine comprising, in combination, a source of hydraulic pressure, a first conduit means hydraulically connected to said source of hydraulic pressure, a regulator valve communicating with said source of hydraulic pressure through said first conduit means and having a valve spool for controlling the level of the hydraulic pressure, a branch conduit hydraulically connected to said first conduit means and communicating with said regulator valve therethrough, a shift valve hydraulically connected to said branch conduit and having a valve spool for controlling the supply of hydraulic pressure to be supplied to said servo mechanism, the movements of the valve spool of said shift valve being controlled by the hydraulic pressure exerted on the valve spool of said shift valve, and a second conduit means hydraulically connected between said shift valve and said regulator valve, said second conduit means passing the hydraulic pressure to be exerted on the valve spool of said shift valve to said regulator valve which hydraulic pressure acts on the valve spool of said regulator valve, whereby the valve spool of said regulator valve is moved in a direction to reduce the level of the hydraulic pressure to be supplied to said servo mechanism simultaneously with the actuation of the valve spool of said shift valve for thereby effecting smooth engagement of said friction element, further comprising an actuating means associated with said shift valve for controlling the hydraulic pressure to be exerted on the valve spool of said shift valve for thereby controlling the movements of the valve spool of said shift valve, wherein said shift valve has a port which is hydraulically connected to said second conduit means, wherein said actuating means includes a pilot valve hydraulically connected between said branch conduit and said second conduit means and having a valve spool to control the hydraulic pressure to be admitted to the port of said shift valve, further comprising first sensing means to sense vehicle speed and a second sensing means to sense on output torque of said engine, and wherein said first sensing means includes a hydraulic governor valve adapted to produce a first pressure signal in dependence on the vehicle speed, said hydRaulic governor valve communicating with said pilot valve for applying said first pressure signal on one end of the valve spool of said pilot valve, and wherein said second sensing means includes a throttle valve adapted to produce a second pressure signal in dependence on the output torque of said engine, said throttle valve communicating with said pilot valve for applying said second pressure signal on the other end of the valve spool of said pilot valve.