| 摘要 |
A closed loop hydrostatic transmission including a pump (11) having a charge pump (23) and an assembly (25). The assembly (25) includes a pair of relief and check valve assemblies (65,67), and each one includes a check valve poppet (71) relatively fixed to a washer member (83) in the absence of high pressure. The washer member (83) moves within a bore to define a chamber (85) in which is the spring (87) biasing the check poppet (71) closed. A drain valve (97) has its inlet in fluid communication with the spring chambers (85), and in response to a predetermined input, such as an electrical input signal (101), the drain valve opens (FIG. 3), and drains the chambers (85). In this condition, both check poppets (71) open, and fluid can flow freely within the closed loop so that, for example, the vehicle may be towed a short distance, without overheating the fluid, and without the need to mechanically unseat the check valves as has been common practice.
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