HYDRAULIC CIRCUIT OF WORK MACHINE

PROBLEM TO BE SOLVED: To provide a hydraulic circuit of a work machine capable of achieving excellent interlocking operability of a fluid pressure motor and each fluid pressure actuator while securing steering performance in traveling.SOLUTION: Distributions of hydraulic fluids from a pair of discharge ports of a first pump 15 to first control valves 31a, 31b and a second control valve 37 are respectively controlled by travel priority valves 32a, 32b. When front-rear differential pressures of the first control valves 31a, 31b become a prescribed value or less, the travel priority valves 32a, 32b are switched to travel priority positions Pb for blocking the hydraulic fluid to a second control valve 37 side. At least a part of the hydraulic fluid discharged from a second pump is joined by a switch valve to a supply passage 60 for joining the hydraulic fluids passing through the travel priority valves 32a, 32b at a downstream side of the first control valves 31a, 31b and supplying the same to the second control valve 37, in a state that both of the travel priority valves 32a, 32b are switched to the travel priority positions Pb.SELECTED DRAWING: Figure 1 【課題】走行の操舵性を確保しつつ、流体圧モータと各流体圧アクチュエータとの良好な連動操作性を得ることが可能な作業機械の油圧回路を提供する。【解決手段】第１の制御弁31a，31bと第２の制御弁37とに対する第１のポンプ15の一対の吐出ポートからの作動油の配分を走行優先弁32a，32bによりそれぞれ制御する。第１の制御弁31a，31bの前後差圧が所定値以下となったときには走行優先弁32a，32bが第２の制御弁37側への作動油を遮断する走行優先位置Pbに切り換わる。走行優先弁32a，32bを通過した作動油を第１の制御弁31a，31bの下流側で合流させて第２の制御弁37に供給する供給通路60に対して、走行優先弁32a，32bがともに走行優先位置Pbに切り換わった状態で第２のポンプから吐出した作動油の少なくとも一部を切換弁により合流させる。【選択図】図１