Hydraulic control system for continuously variable V-belt transmission

Claim 1

A hydraulic control system for controlling a continuously variable transmission having a V-belt connecting a drive and a driven pulley, the drive pulley having a first cylinder chamber and first and second conical discs, the driven pulley having a second cylinder chamber and third and fourth conical discs, the first conical disc being secured to a drive shaft, the third conical disc being secured to a driven shaft, the second conical disc being controllably movable in an axial direction with respect to the drive shaft in response to a fluid pressure in the first cylinder chamber, the fourth conical disc being controllably movable in an axial direction with respect to the driven shaft in response to a fluid pressure in the second cylinder chamber, the hydraulic control system comprising: a source of hydraulic fluid pressure; a line pressure regulator valve means for receiving and regulating said hydraulic fluid pressure and for generating a line pressure, said line pressure regulator valve means comprising a pressure regulating element having a pressure acting area exposed to said line pressure and being loaded by said line pressure in one direction, a member movable relative to said pressure regulating element, and spring means acting between said pressure regulating element and said member to bias said pressure regulating element in the opposite direction against said line pressure, said member being movable relative to said pressure regulating element to vary a length of said spring means, said spring means being constructed and arranged such that a force by which said spring means biases said pressure regulating element varies at a rate for a unit variation in said length thereof, which rate varies as said length varies, said pressure regulating element being movable in response to said force and said line pressure for effecting said regulation of said hydraulic fluid pressure thereby to generate said line pressure variable with said force; a shift control valve means connected to said line pressure regulator valve means for receiving said line pressure and hydraulically controlling a reduction ratio between the drive and driven pulley; and means responsive to said reduction ratio between the drive and driven pulley for urging said member toward said pressure regulating element so as to decrease said length of said spring means as said reduction ratio increases.