Abstract: In a hydromechanical transmission, low and high speed drive power trains are selectively completed in response to variation of the speed ratio between an input shaft and an output shaft. The transmission comprises a speed ratio detecting valve for detecting lower and higher limits of a predetermined speed ratio and a clutch control valve for conducting the switch over between the low and high speed drive power trains when the actual speed ratio reaches a range defined by the lower and higher limits of the predetermined speed ratio.

Abstract: In a hydromechanical transmission, low and high speed drive power trains are selectively completed in response to variation of the speed ratio between an input shaft and an output shaft. The transmission comprises a speed ratio detecting valve for detecting lower and higher limits of a predetermined speed ratio and a clutch control valve for conducting the switchover between the low and high speed drive power trains with a predetermined time lag after the actual speed ratio reaches a range defined by the lower and higher limits of the predetermined speed ratio.

Abstract: In a hydromechanical transmission, low and high range clutches are selectively operated in response to variation of an actual speed ratio between an input shaft and an output shaft to complete low or high speed drive power train. The transmission comprises a speed ratio detecting valve for detecting lower and higher limits of a predetermined speed ratio and a clutch control valve for selectively operating the low and high range clutches when the actual speed ratio reaches in a range defined by the lower and higher limits of the predetermined speed ratio. The operation of the clutch control valve is controlled by a pressure control valve in accordance with a difference in value between a first signal responsive to a throttle opening angle and a second signal responsive to the rotation speed of the input shaft such that the low and high range clutches are selectively operated only when the difference between the first and second signals becomes a predetermined value.

Abstract: A control system for a power dividing type hydraulic transmission in which the motive power supplied from an engine is transmitted mechanically. Part of the motive power is converted to hydraulic power by hydraulic pump motors to obtain infinitely variable speed ratios. The transmission includes a hydraulic pressure control system that operates by the use of electrically controlled solenoid valves. The control system detects the rotational speeds of an input and an output shaft, and when the speed ratio between the shafts is smaller than the mode converting speed ratio, a first solenoid valve is operated to engage a first clutch. When the speed ratio is greater than the mode converting speed ratio, a second solenoid valve is operated to engage a second clutch. The engagement of the clutches is timed so that both clutches are not coincidentally disengaged.