| 摘要 |
<p>The invention provides a valve suitable for use in an overdrive unit, to control the rate of build-up and decay of fluid pressure in piston and cylinder mechanisms which move a clutch member of the overdrive between engaged and disengaged positions. The valve comprises a body (10) with a valve member (20) moveable to control communication between an inlet passage (15) and an outlet passage (22), and a piston (24) which is moveable between limiting positions under fluid pressure. A spring (28) is interposed between the piston (24) and valve member (20), which spring becomes loaded during movement of the piston whilst causing a relatively small increase in load on the valve member (20) and thus a period during which pressure in passage (15) increases gradually, thus providing a smooth shift as the overdrive engages. A second spring (34) operates between the piston (24) and valve member (20) when the piston has reached the limit of its travel, and a third spring (30) provides a residual load on the valve member (20) when the piston is in its starting position.</p> |
