| 摘要 |
PURPOSE:To prevent loss of power when a discharging volume is decreased by a method wherein a spool valve is moved in response to a differential pressure across a flow rate direction control valve and hydraulic oil is supplied to and discharged from a large volume port and a low volume port for increasing and decreasing flow rate cylinders of a variable volume type pump. CONSTITUTION:The force of spring 30 and a differential pressure across a flow rate direction control valve 23 are opposed to each other through a spool 31. When forces are balanced, the flow rate increasing and decreasing cylinder 34 is blocked, and in turn if differential pressure is higher than the spring force, the low capacity port 36 is communicated with the variable capacity pump 21, the high capacity port 35 is communicated with the low pressure passage 33, and if the spring force 30 is higher than the differential pressure, the port 36 is communicated with the passage 33 and the port 35 is communicated with the pump 21. No spring is placed in the cylinder 34, no resistive force is generated in accordance with variation in discharged volume of pump, a changed-over pressure in the spool valve 29 becomes constant, and when the pump discharging volume is decreased, the pump discharging pressure is not increased and loss of power can be prevented. Since the volume of cylinder 34 can be reduced, a better response of variation in flow rate can be attained.
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