| 摘要 |
PROBLEM TO BE SOLVED: To prevent a sudden change of the supplying oil pressure to be generated in case of changing speed in a hydraulic pump unit with the structure for mechanically realizing speed change corresponding to the operating condition of a destination of the oil pressure. SOLUTION: A flow control valve 4 is formed by arranging a cylindrical control spool 4a to be slid along the inside of a spool chamber 40 and an auxiliary spool 4b to be slid in the control spool 4a in the spool chamber 40 provided on the way of a discharge oil passage 16 continued to the destination of the oil pressure so as to divide the spool chamber 40 into a first pressure chamber 40a and a second pressure chamber 40b. When an oil flow is generated in the discharge oil passage 16, the auxiliary spool 4b having the equal pressure receiving area in both sides thereof is moved left with the control spool 4a by the action a differential pressure between before and after passing through a fixed throttle 41, against the spring force of a control spring 45, and an opening area of a drain oil passage 43 is increased so as to maintain the fed oil variable from the discharge oil passage 16 nearly constant. When the oil pressure on a downstream side of the fixed throttle 41 is increased to the predetermined value, the control spool 4a having a large pressure receiving area on the second pressure chamber 40b side, to which the oil pressure is led, is moved right by the action of the oil pressure on the downstream side of the fixed throttle 41, against the spring force of an energizing spring 44, and an opening area of the drain oil passage 43 is reduced, and the fed oil variable and the fed oil pressure are increased. |
