| 摘要 |
PROBLEM TO BE SOLVED: To satisfy the required pressure characteristic of a power cylinder and reduce the pressure loss at the time of the neutral by setting the underlap angle of the first control valve section within two control valve sections constituting a control valve larger than the underlap angle and the overlap angle of the second control valve section. SOLUTION: The underlap angleθA of the first control valve section 23 is set larger than the overlap angle and the underlap angleθB of the second control valve section 24. When the valve rotation angle exceedsθB, one variable throttle V6 on the pump side of the second control valve section 24 starts to be opened, the pressure of one oil chamber of a power cylinder is increased because a variable throttle V8 is shrunk at this time, the other oil chamber is opened to a reservoir via a variable throttle V7 kept at the expanded state, a differential pressure is generated between both oil chambers of the power cylinder, and handle steering is assisted. When the variable throttle V6 starts to be opened, the variable throttle V8 is shifted to the overlap state, and the throttle area of the variable throttle in the second control valve section 24 is limited.
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