Hydraulic control for a power transmission

Abstract

A hydraulic control for a power transmission has a regulator valve for controlling the hydraulic system pressure and a plurality of shift valves for controlling the automatic ratio change in the transmission. The shift valves are urged toward the higher ratio position by a governor pressure. The shift valves, except the 1-2 valve, are selectively subjected to separate modulated throttle valve pressures acting in opposition to the governor pressure and depending upon whether the respective shift valve is in the lower or higher ratio position. The modulated pressures are maintained at substantially zero for a portion of the throttle valve pressure range so that upshifting and downshifting will be sensitive to governor pressure and therefore vehicle speed only. The regulator valve is subject to a variable bias pressure which is proportional to throttle valve pressure. The bias pressure is controlled by a valve to be equal to the throttle pressure during the lower pressure portion of the throttle pressure range and to increase at a rate less than the throttle valve pressure during the remainder of the pressure range.