| 摘要 |
PROBLEM TO BE SOLVED: To ensure safety by suppressing an operating speed only during a slewing operation in a state of switching to crane specifications, and enhance workability by setting a speed at a normal operating speed during other operations, in a hydraulic excavator which allows the switching between excavator specifications and the crane specifications by a switch operation. SOLUTION: Secondary side oil passages 18 and 19 of a remote control valve 17 for a slewing motor 16 are connected together via a shuttle valve 20, and a pressure switch 21 is installed in an outlet oil passage of the shuttle valve 20. A hydraulic pump 11 can increase/decrease a discharge rate by changing a pump tilting angle by the extension/contraction of a hydraulic cylinder 23; and when the pressure switch 21 is put into an on-state by the slewing operation, an electromagnetic selector valve 28 is opened according to a command signal of a controller 22. Either pressure oil from a hydraulic source 24 or pressure oil from a negative control oil passage 25 is selected under high pressure by using the shuttle valve 26, so as to be introduced into the hydraulic cylinder 23, and the discharge rate of the hydraulic pump 11 is changed into a low flow rate. Thus, the amount of the supply of the pressure oil to the slewing motor 16 is reduced so that the slewing motor 16 can run at a low speed, and a safe slewing speed appropriate for crane operations can be secured. COPYRIGHT: (C)2004,JPO
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