HYDRAULIC CIRCUIT FOR PREVENTING POP OUT OF MULTI-STAGE EXPANSION BOOM IN SELF-RUNNING VEHICLE

摘要

PROBLEM TO BE SOLVED: To inhibit unexpected pop out of a multi-stage expansion boom even when a vehicle is quickly braked or stopped during running. ;SOLUTION: In a self-running vehicle having a multi-stage expansion boom which can be freely expanded/contracted by a hydraulic cylinder 10a actuated by hydraulic oil from a first oil pressure source, it comprises a first oil passage 33 connected to a contraction side operating oil chamber 13a of the hydraulic cylinder 10a, a second oil pressure source 25, a selector valve 52 having a communication position A to communicate a first oil passage 33 with a second oil pressure source 25, and a disconnection position B to disconnect this communication, and a changing means 24 to change the selector valve 52 from the disconnection position B to the communication position A during run of a vehicle for communicating the first oil passage 33 with the second oil pressure source.;COPYRIGHT: (C)1999,JPO