| 摘要 |
<p>Power transmissions (16) incorporate gear ratios including a plurality of forward ratios, a neutral condition and at least one reverse ratio. The establishment of each ratio is controlled by selectively engageable hydraulically operated friction devices (C1-C5), such as clutches and brakes. The interchange between forward ratios is controlled by the interchange of at least one friction device. The control elements to accomplish the establishment and interchange of the ratios include a pressure source (50), shift valve (64,66,88), solenoid control valves (74,76,78) and pressure control valves (54,56). The solenoid valves are electrically actuated and the hydraulic portion of the control includes elements that permit continued operation of the transmission in selected ratios in the event of electrical discontinuance. Also provided within the hydraulic control is a pressure knockdown or pressure reducing valve element (120) which operates with one of the shift valves (64) to establish a maximum pressure level in the forward ratios that is less than the maximum pressure level in the reverse ratio. <IMAGE></p> |
