| 摘要 |
PROBLEM TO BE SOLVED: To contrive shock relaxation, stability improvement and operability improvement at the time of operation stop in the neighborhood of a boom maximum height position. SOLUTION: When a boom operation lever 32 is operated and the spool of a boom control valve 34 is advanced, a boom cylinder 16 is expanded, and a boom is risen. Accordingly, the value of a boom angle detection signalθB is increased, and when the value of the angle detection signalθB is larger than a speed decrease start angleθS previously stored in the memory of a controller 25, a drive current signal Iβ(=IBI) is output from a control part to an electromagnetic proportional reducing valve 26. The pilot pressure of boom pilot piping 36 is restricted, and the stroke quantity in the direction of the rise of a spool of the boom control valve 34 is limited.
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