| 摘要 |
A control including a control valve and an override valve for use with a variable displacement pump or motor unit having a pair of strokers into and out of which fluid must be directed to vary the displacement of the unit. The control valve ports fluid from a high pressure source to a first control passage and from a second control passage to a low pressure source, reverses said flow, and terminates said flow. The override valve is interposed between the control passages and the strokes and defines a pair of override passages therein used to direct fluid from one control passage to one stroker and from the other stroker to the other control passage. The override valve is selectively movable between a first position directing such flow therethrough and a second position in which such flow is terminated between the control passages and the strokers. Upon flow termination, the override valve communicates, via a bore in the override valve, the strokers with one another to allow the pump unit to go to minimum displacement or the motor unit to go to maximum displacement. In the preferred embodiment, the override valve is responsive to the high pressure fluid being ported from or to respectively, the pump or motor unit. The control may also include a centering valve interposed between the control valve and the override valve. The centering valve is responsive to the pressure of the control fluid to define passages between the first and second control passages and the first and second override passages. Upon a loss of control fluid pressure, the centering valve moves to a second position to cross port the control valve passages and the override valve passages. The override valve may also be actuated via external signals such as an electrical, mechanical, or manual input. |
