Hydraulic pressure control means for automatic fluid speed change mechanism

Claim 1

An automatic control means for a vehicle automatic speed change mechanism, said automatic speed change mechanism including a driving shaft, a driven shaft, a multistage speed change gearing mechanism drivingly connected between said drive and driven shafts, a plurality of hydraulically actuated frictionally engageable means operatively connected to said speed change gearing mechanism for providing a plurality of speed change ratios between said drive and driven shafts upon the application of hydraulic pressure thereto, said hydraulically actuated frictionally engageable means providing a selected one of said plurality of speed change ratios, said automatic control means comprising, a hydraulic pressure source, hydraulic conduit means for communicating the output of said hydraulic pressure source with said hydraulically actuated frictionally engageable means, hydraulic pressure regulating means in communication with said hydraulic conduit means for regulating the line pressure supplied by said hydraulic pressure source, shift valve means hydraulically connected in said conduit means for selectively controlling the distribution of hydraulic line pressure to said hydraulically actuated frictionally engageable means, a throttle control valve communicating with the output of said hydraulic pressure source for generating a hydraulic pressure in response to an engine throttle position and load condition, a hydraulic governor valve for gEnerating a hydraulic pressure which varies as a function of the speed of said driven shaft, a first hydraulic pressure conduit communicating the output of said throttle valve with the input of said governor valve, a second hydraulic conduit communicating the output of said hydraulic pressure source with the output of said governor valve, said output of said governor valve being further communicated with said shift valve means for automatically controlling the operation of said shift valve means depending on the speed of said driven shaft, the output of said governor valve being caused to decrease with an increase in the output pressure of said throttle valve, whereby the shift valve means is caused to downshift to a lower speed change gear ratio due to the rapid decrease in the governor valve output pressure.