摘要 |
A hydraulic drive system ( 11 ) of the type including a hydrostatic pump-motor unit ( 35 ) having a pumping mode in which the unit pressurizes, from its port (A), a high pressure accumulator ( 41 ), and a motoring mode, in which the unit is driven by pressurized fluid from the high pressure accumulator. The system also includes a source of low pressure ( 39 ) in communication with the opposite port (B) of the pump-motor unit ( 35 ), and a filter circuit ( 107 ) disposed therebetween. The filter circuit ( 107 ) defines an unrestricted first flow path from the source of low pressure ( 39 ) to the port (B) when the unit is in the pumping mode, and a second flow path from the port (B) to the source of low pressure ( 39 ) when the unit is in the motoring mode. The second flow path comprises one path portion ( 125 ) through a filter shut-off valve ( 121 ) and a filter ( 127 ) in series, and in parallel therewith, another path portion through a controlled flow restriction ( 135 ). Thus, filtration occurs during only the motoring mode, and the percentage of fluid being filtered can be predetermined.
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