Fluid pressure control system for automatic transmissions

Claim 1

A fluid pressure control system for automatic fluid transmission comprising a fluid pressure source; a fluid pressure regulating valve for regulating the hydraulic fluid from said fluid pressure source to a particular line pressure; a plurality of frictional engaging means actuated by said line pressure from said pressure regulating valve for attaining a particular gear ratio within the gear train of said transmission interposed between an input shaft and an output shaft; a governor valve for governor pressure which is increased or decreased in response to the rotational speed of said output shaft; a manual shift valve operatively connected to said fluid pressure regulating valve for supplying said line pressure to said plurality of frictional engaging means; a throttle valve fluidically connected to said manual shift valve for generating a throttle pressure responsive to an engine throttle valve; a shift valve actuated in response to said governor pressure and said throttle pressure for automatically selectively actuating said plurality of frictional engaging means; and a reducing valve for supplying said throttle pressure to said shift valve when said throttle pressure is below a predetermined value and for supplying a predetermined threshold pressure to said shift valve upon kick-down operation by non-activating said throttle valve in order not to exceed said predetermined valve of throttle pressure.