| 摘要 |
A fluid pressure control system for controlling an automatic transmission, which includes a gear transmission mechanism and several fluid pressure actuated friction engaging mechanisms, and which is shifted to various speed stages including an overdrive speed stage, a directly connected speed stage, and a reduction geared speed stage which is the closest speed stage below the directly connected speed stage, according to selective supply of actuating fluid pressure to the friction engaging mechanisms. The control system includes a governor pressure control valve, a throttle pressure control valve, a first shift valve for upshifting and downshifting between the directly connected speed stage and the overdrive speed stage, and a second shift valve for upshifting and downshifting between the reduction geared speed stage and the directly connected speed stage. These shift valves shift according to balance relationships between the throttle pressure and the governor pressure. The direct/overdrive shift valve has very considerable hysteresis in its operation, so that in the shift diagram the downshift line from the overdrive speed stage to the directly connected speed stage is generally to the high throttle opening low vehicle speed side of the upshift line from the reduction geared stage to the directly connected speed stage. |
