US 5,488,787 AGranted

Hydraulic drive system for construction machine

AssigneeHitachi Construction Machinery Co., Ltd.

InventorsYukio Aoyagi, Kazuhiko Otsubo, Gen Yasuda, Koji Fujita, Takayuki Yamakawa, Kazuyoshi Narita

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Abstract

When a prime mover (1) is driven, a controller (25) outputs an open-drive signal for bringing an opening/shutting valve (23) into an open position and, upon a control lever (68, etc.) being operated, a hydraulic fluid is supplied from an auxiliary hydraulic pump (7) through pressure reducing valves to driving sectors of directional control valves (8 to 16) for shifting them. A flow rate and a direction of flow of the hydraulic fluid from main hydraulic pumps (3, 4) are thereby adjusted so that actuators (57A, 57B, 57C, 56A, 54) can be each operated at a speed depending on the amount by which the control lever is operated. When one of the actuators (57A, 57B, 57C, 56A, 54) is to be driven when the prime mover (1) is not driven, an open command is selected in a selection command device (24), whereupon the controller (25) outputs the open-drive signal, causing the opening/shutting valve (23) to open a line interconnecting the accumulator (21) and the pressure reducing valve (17), etc. By now operating the control lever (68), for example, the directional control valve (9) is shifted so that a boom cylinder (57A) is operated with the dead weight of a working unit to allow a descent thereof. When any of the actuators (57A, 57B, 57C, 56A, 54) is not to be driven when the prime mover (1) is in a stopped state, a shut command is selected in the selection command device (24), whereupon the controller (25) outputs a shut-drive signal, causing the opening/shutting valve (23) to shut off the line interconnecting the accumulator (21) and the pressure reducing valve (17). Even if the control lever (68), etc. are touched by a mistake under such a condition, no actuators (57A, 57B, 57C, 56A, 54) are operated and the working unit is not descended. Thus, the actuators are surely prevented from being operated against the intention of an operator.

A hydraulic drive system for a construction machine comprising a prime mover (1), main hydraulic pumps (3, 4) driven by said prime mover (1), actuators (57A, 57B, 57C, 56A, 54) driven by a hydraulic fluid delivered from said main hydraulic pumps (3, 4), directional control valves (8-16) for controlling flows of the hydraulic fluid supplied from said main hydraulic pumps (3, 4) to said actuators (57A, 57B, 57C, 56A, 54), an auxiliary hydraulic pump (7) driven by said prime mover (1), control valve operating means (67, 69;

17-20, 68, 70;
27-30, 31-36, 38) for controlling the hydraulic fluid delivered from said auxiliary hydraulic pump (7) to shift said directional control valves (8-16), and accumulator means (21) disposed in a line interconnecting said auxiliary hydraulic pump (7) and said control valve operating means (67, 69;
17-20, 68, 70;
27-30, 31-36, 38) and used as a hydraulic source for said control valve operating means (67, 69;
17-20, 68, 70;
27-30, 31-36, 38) to shift said directional control valves (8-16) when said prime mover (1) is stopped, wherein:
said hydraulic drive system further comprises stop detecting means (2, 26, 37, 41, 49, 47B, 48B) for detecting that said prime mover (1) is in a stopped state;
selection means (24, 47A, 48A) for selecting whether or not said actuators (57A, 57B, 57C, 56A, 54) are to be driven when said prime mover (1) is in the stopped state;
and
shift control means (23, 39-42, 43-48, 17c-20c, 89;
17a;
25, 38) for enabling said directional control valves (8-16) to be shifted by using said accumulator means (21) when said stop detecting means (2, 26, 37, 41, 49, 47B, 48B;
25, 39) detects that said prime mover (1) is stopped and said selection means (24, 47A, 48A) selects that said actuators (57A, 57B, 57C, 56A, 54) are to be driven, and disabling said directional control valves (8-16) from shifting with the use of said accumulator means (21) when said stop detecting means (2, 26, 37, 41, 49, 47B, 48B;
25, 39) detects that said prime mover (1) is stopped and said selection means (24, 47A, 48A) selects that said actuators (57A, 57B, 57C, 56A, 54) are not to be driven.

11 more elements

Abstract

Claims20