Title: Hydraulic control system for use in automatic transmission

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Abstract: A hydraulic control system for use in an automatic transmission including a fluid coupling type torque converter, and a gear system provided with two or more frictional engaging devices adapted to establish two or more speed conditions. The hydraulic system further includes a hydraulic pressure source, a line pressure control valve for supplying a regulated line pressure, by receiving a hydraulic pressure from the hydraulic pressure source, a throttle pressure control valve for generating a throttle pressure commensurate with an intake throttle opening, a governor pressure control valve for generating a governor pressure commensurate with vehicle speed, a manual change-over valve for enabling manual change-over of the transmission, two or more shift valves for shifting the path of the line pressure to be supplied to the frictional engaging devices in response to abalancing of the relationship between the throttle pressure and the governor pressure, the shift valves including one shift valve operative to establish the highest speed ratio for the transmission, and a highest speed control device for controlling to a low-speed-side shift position the one shift valve of the aforementioned shift valves which is operative to establish the highest speed ratio irrespective of the governor pressure resulting when the intake throttle opening remains over a given valve.


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