Vehicle power transmitting system with continuously variable transmission and hydraulic control apparatus, capable of producing adequate engine braking during low-speed reverse running of vehicle

摘要

A vehicle power transmitting system having a continuously variable transmission (14), a reversing device (16) disposed downstream of the transmission, and a hydraulic control apparatus for controlling the transmission. The system comprises a device (114) for producing a required output pressure indicative of a currently required vehicle acceleration value, a shift control valve (330, 460, 490) for changing the speed ratio of the transmission, based on at least the required output pressure, such that the input shaft speed of the transmission increases with the currently required acceleration value and is higher when the shift lever is placed in a low-gear position than in a high-gear position, a device (374) for producing a modified speed-ratio pressure which varies with the speed ratio when the speed ratio is higher than a predetermined value and held constant when the speed ratio is lower than the predetermined value, and a device (382) for applying the modified speed-ratio pressure to the shift control valve device in place of the required output pressure while the shift lever is placed in the low-gear position and when the required output pressure is lower than the modified speed-ratio pressure.