| 摘要 |
<p>A dual pressure source, or selectively alternative high pressure source, control system for a variable displacement hydraulic unit (MR or ML) servo mechanism (22-28) wherein normal control of the unit is provided by the low pressure source (46), such as a transmission charge pump, and wherein a high pressure source (50) of the control fluid with a restrictive orifice (64) is provided to initiate servo movement, especially under conditions generating high internal friction. The flow restrictive orifice (64) generates a pressure drop in a high pressure control line (50) once the servo mechanism (22) starts to move, inducing flow through such line. Thus, the control system provides a momentary source of high pressure fluid but permits control rate changes which are substantially independent of the hydraulic unit working pressure. Preferably, the high pressure source is a shuttle (60) selected highest pressure of a transmission main loop (56-58) incorporating the hydraulic unit.</p> |
