Excavating – Ditcher – Condition responsive
Patent
1994-08-03
1996-02-06
Reese, Randolph A.
Excavating
Ditcher
Condition responsive
172 2, 414699, 36442407, F16D 3102, G06F 1520
Patent
active
054887879
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic drive system mounted on construction machines such as hydraulic excavators.
Background Art
A conventionally known hydraulic drive system for hydraulic excavators comprises a prime mover, a main hydraulic pump driven by the prime mover, actuators such as a travel motor, a swing motor, a boom cylinder, an arm cylinder and a bucket cylinder which are driven by a hydraulic fluid delivered from the main hydraulic pump, directional control valves for controlling respective flows of the hydraulic fluid supplied from the main hydraulic pump to the actuators, an auxiliary hydraulic pump driven by the prime mover, and control valve operating means for controlling a hydraulic fluid delivered from the auxiliary hydraulic pump to operate the directional control valves.
In a hydraulic drive system for large-sized hydraulic excavators, it is known to dispose, in addition to the above arrangement, accumulator means or an accumulator in a line branched from a line interconnecting the auxiliary hydraulic pump and the control valve operating means, as disclosed in JP, A, 4-30038, for example. With this arrangement, if any control valve operating means is operated as occasion requires even after stop of the prime mover, the hydraulic fluid from the accumulator serves as a hydraulic source to shift the corresponding directional control valve for driving the corresponding actuator.
Specifically, the above accumulator is utilized, for example, when the corresponding actuator should be driven to operate a working unit which is left suspended in midair upon the prime mover being stopped due to a failure, for descending the working unit down to the ground by its own dead load, or when the directional control valve should be shifted to introduce the hydraulic fluid, which is left in the line connected to the corresponding actuator, to a low-pressure circuit for pressure release before front attachments such as an arm and a boom are disassembled for the purpose of displacement or transportation.
Disclosure of the Invention
In the above-described prior art, however, if an operator or any other person touches the control valve operating means by a mistake after stop of the prime mover, the hydraulic fluid from the accumulator may be supplied to a driving sector of the corresponding directional control valve to shift the same such that the corresponding actuator is brought into an operable state. This results in a disadvantage that the actuator may be operated against the intention of an operator, e.g., that the working unit left suspended in midair, as mentioned above, is descended by gravity.
The present invention has been made in view of the foregoing situation in the prior art, and its object is to provide a hydraulic drive system for a construction machine in which a directional control valve is not shifted even if control valve operating means is touched accidentally while a prime mover is in a stopped state.
To achieve the above object, according to the present invention, there is provided a hydraulic drive system for a construction machine comprising a prime mover, main hydraulic pumps driven by said prime mover, actuators driven by a hydraulic fluid delivered from said main hydraulic pumps, directional control valves for controlling flows of the hydraulic fluid supplied from said main hydraulic pumps to said actuators, an auxiliary hydraulic pump driven by said prime mover, control valve operating means for controlling the hydraulic fluid delivered from said auxiliary hydraulic pump to shift said directional control valves, and accumulator means disposed in a line branched from a line interconnecting said auxiliary hydraulic pump and said control valve operating means, said directional control valves being shifted by using said accumulator means as a hydraulic source for said control valve operating means when said prime mover is in a stopped state, wherein said hydraulic drive system further comprises stop detecting means for detecting that said prime mover is
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Aoyagi Yukio
Fujita Koji
Narita Kazuyoshi
Otsubo Kazuhiko
Yamakawa Takayuki
Hitachi Construction Machinery Co. Ltd.
Pezzuto Robert
Reese Randolph A.
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