| 摘要 |
There is disclosed a control system providing manual and also automatic shift control for a multispeed forward and reverse track-laying vehicle transmission. The automatic operation is provided by pilot valves which are controlled by a pressure indicative of vehicle speed and also a pressure indicative of engine torque demand to condition shift valves to effect shifting between all of the forward drives. The manual control is provided by solenoid valve control over the bias of the shift valves to effect manual shifting with downshifting to lower speed range drives being delayed until vehicle speed is suitable for the speed range of the selected lower drive. The transmission includes a torque converter having a lockup clutch whose engagement is effected with the fluid delivery used for the selected drive engagement with the lockup clutch engagement being momentarily interrupted on shifting between certain of the forward drives by shuttle valve operation. A neutral valve whose operation is controlled by solenoid valves operates to deliver fluid to the shift valves for the drive engagements and on interruption of electrical power to its solenoid valves, operates to automatically condition the transmission in neutral but if the transmission is providing drive and there then occurs loss of power to these solenoid valves, the neutral valve continues to permit the establishment of transmission drive. The control system further includes a directional valve which is operated by solenoid valves to control the engagement of devices that are necessary to establish forward and reverse drive. When there is loss of power to the directional valve's solenoid valves, the directional valve remains in its preselected position. A forward-reverse inhibitor valve prevents the directional valve from effecting shifting between forward and reverse above a vehicle speed suitable for such shifting. The control system also includes a brake coolant valve which is controlled by a brake apply valve to deliver fluid to cool the transmission's two output brakes with a normal fluid supply that originates at an input driven pump and is supplemented by operation of a diverter valve that delivers flow from output pump after higher fluid supply priorities are set.
|
