HYDRAULIC DRIVING SYSTEM FOR A CIVIL ENGINEERING OR CONSTRUCTION MACHINE.

摘要

Provided are hydraulic pumps 1,2, a control valve group 15a connected to the pump 1 and including a bypass on/off valve 7, a control valve group 15b connected to the pump 2 and including a reserve-actuator-controlling, directional control valve 11, a communication line 13 communicating a most upstream side of the control valve group 15a with a supply line 11a to the reserve-actuator-controlling, directional control valve 11, a merge control valve 14 for communicating or cutting off the communication line 13, an interlocked control means for changing over the merge control valve 14 to an open position and the bypass on/off valve 7 to a closed position in association with a change-over operation of the reserve-actuator-controlling, directional control valve 11, and a selective control valve 28 capable of taking one of a state, in which the operation to change over the merge control valve 14 by the interlocked control means is feasible, and another state in which the operation to change over the merge control valve by the interlocked control means is infeasible. The control valve group 15a, the control valve group 15b, the communication line 13 and the merge control valve 14 are arranged in a housing 15 such that a change or the like in a maximum value of an operating speed of an actuator, said operating speed being controlled by the reserve directional control valve, can be achieved. <IMAGE>