| 摘要 |
<p>A hydrostatic transmission has a variable displacement pump which is driven by the vehicle engine and hydraulically coupled to a fluid motor that operates the drive wheels. An operator's control member may be adjusted from a neutral position to increase pump displacement and thereby effect progressively higher vehicle speeds in a forward direction and if the control member is shifted in an opposite direction, pump displacement passes through neutral and reverses to reverse vehicle direction. The manual control adjustment is realized through a pair of coaxial sleeve valves which also provide follow-up action to normally limit any change of pump displacement to that dictated by the movement of the operator's control. The sleeve valves also counteract a tendency of operators to increase pump displacement when stalling is imminent, by automatically overriding the manual control and decreasing pump displacement when increased loading of the vehicle causes the pump output pressure to rise to a predetermined high level.</p> |
