Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Patent
1991-08-15
1994-02-15
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
60494, F16D 3102
Patent
active
052856437
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to hydraulic drive systems for civil-engineering and construction machines, such as hydraulic excavators and the like and, more particularly, to a hydraulic drive system comprising a pair of reverse-motion check valves for preventing a reverse motion of an inertial body from occurring upon stopping halting movement of the inertial body.
BACKGROUND ART
A hydraulic excavator, which is a typical example of a civil-engineering or construction machines, comprises a swing as one of a plurality of working elements. A hydraulic drive system for the swing generally comprises a hydraulic pump constituting a hydraulic-fluid source, a hydraulic motor for driving the swing, a directional control valve for controlling flow of hydraulic fluid supplied from the hydraulic pump to the hydraulic motor, a pair of main lines through which the directional control valve and the hydraulic motor are connected to each other, the pair of main lines serving selectively as a fluid supply line and a fluid return line by switching of the directional control valve, and a pair of relief valves provide respectively in lines through which the pair of main lines are connected to each other. Further, since the swing is an inertial body, it is necessary to brake the hydraulic motor upon halting movement of the swing and, accordingly, brake means utilizing back pressure of the hydraulic motor is incorporated in the hydraulic drive system. The brake means is a counter balance valve arranged in the pair of main lines, for example.
The counter balance valve operates such that the hydraulic fluid is prevented from being returned to a tank from the main lines when the directional control valve is returned to a neutral position in order to halt the swing from a condition under which the swing is driven. When the hydraulic motor tends to be rotated by an inertial force of the swing, the hydraulic fluid is prevented from being returned from the main line on a return side of the hydraulic motor by the counter balance valve. By doing so, a pressure (back pressure) in the main line increases abruptly by a pumping action of the hydraulic motor. When a magnitude of the pressure exceeds a set pressure of a corresponding one of the relief valves, the relief valve is moved to an open position. Thus, the hydraulic fluid is recirculated through a closed circuit composed of the relief valve, the hydraulic motor and the main lines, so that the hydraulic motor is braked.
By the way, in the hydraulic drive system provided with such brake means, there is such a problem that a reverse motion of the inertial body occurs due to the action of the back pressure upon halt of the inertial body.
That is, as described above, the pressure in the main line on the return side of the hydraulic motor increases abruptly to the set pressure of each of the relief valves to brake the hydraulic motor. When the hydraulic motor is halted, however, each of the relief valves is moved to the closed position so that the pressure in the main line is brought to a condition maintained at high pressure. Accordingly, a differential pressure occurs between outlet and inlet ports of the hydraulic motor. The hydraulic motor begins to rotated reversely by the differential pressure. Thus, the differential pressure between the outlet and inlet ports of the hydraulic motor is nullified. However, the hydraulic motor continues to be further rotated in the same direction by the inertial force of the swing. Thus, this time, the pressure in the main line on the reverse side is brought to a high pressure so that a differential pressure occurs across the hydraulic motor. The hydraulic motor again begins to rotate. In this manner, in the case where the brake means utilizing the back pressure is provided, a reverse motion occurs in which the swing is swung a plurality of times, by the inertial force of the swing, in spite of the fact that halt of the swing is intended.
In order to solve the above-described problem, JP,A, 57-25570 has proposed a pair of reverse-mo
REFERENCES:
patent: 3633359 (1972-01-01), Worn
patent: 4317331 (1982-03-01), Aruga et al.
patent: 4694647 (1987-09-01), Yoshida
patent: 4958494 (1990-09-01), Maki et al.
patent: 5048294 (1991-09-01), Oshina et al.
patent: 5063742 (1991-11-01), Yoshimatsu
patent: 5159813 (1992-11-01), Yoshimatsu
Hirata Toichi
Onoue Hiroshi
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Nguyen Hoang
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