HYDRAULIC DRIVING DEVICE FOR A CONSTRUCTION MACHINE

摘要

When an engine (1) is in a driven state, a control device (25) outputs an opening driving signal so as to put an on-off valve (23) in an open state, and when operation levers (68 and so forth) are operated, the pressure oil of an auxiliary hydraulic pump (7) is supplied to the driving portions of switching valves (8-16) via a pressure reducing valve for switching. This regulates the flow rate and direction of the pressure oil from main hydraulic pumps (3, 4) and actuators (57A, 57B, 57C, 56A, 54) can be operated at a speed corresponding to the amount of the operation. When driving the actuators (57A, 57B, 57C, 56A, 54) while the engine (1) is in a non-driven state and if an opening command is selected by means of a selection command device (24), the control device (25) outputs an opening driving signal to cause the on-off valve (23) to open a pipe line connecting an accumulator (21) and a pressure reducing valve (17) and so forth, whereby when, for instance, the operation lever (68) is operated, the switching valve (9) is switched, and the boom cylinder (57A) is activated by the weight of a working machine, thereby making it possible to lower the working machine. In contrast, in a case where the actuators (57A, 57B, 57C, 56A, 54) are not driven with the engine (1) in a halt state and if a closing command is selected with the selection command device (24), the control device (25) outputs a closing driving signal to cause the on-off valve (23) to close the pipe line connecting the accumulator (21) to the pressure reducing valve (17). Even if the operation lever (68) or the like is accidentally operated, the actuators (57A, 57B, 57C, 56A, 54) will not operate, and therefore the working machine will not lower, whereby any operation against the operator's intention can securely be prevented.