Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1989-10-23
1992-08-25
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60460, 91461, F16D 3102
Patent
active
051408155
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to valve apparatuses mounted to hydraulic machines such as construction machines or the like, for controlling driving of hydraulic actuators and, particularly, to a valve apparatus for a hydraulic machine, capable of securing a function equivalent to a counter balance valve with small loss of energy.
BACKGROUND ART
Generally, as disclosed in, for example, JP-A 54-12927, a conventional hydraulic circuit for a hydraulic machine comprises a hydraulic pump, an actuator, for example, a hydraulic motor for driving a load (or an inertia body) by hydraulic fluid from the hydraulic pump, a valve apparatus, for example, a directional control valve for controlling flow of hydraulic fluid supplied to the hydraulic motor from the hydraulic pump to control driving of the hydraulic motor, and a counter balance valve arranged between the directional control valve and the hydraulic motor, for preventing a load in the gravitational direction from causing the hydraulic motor to run away.
In the hydraulic circuit constructed as above, when, for example, the directional control valve is neutral, the hydraulic fluid from the hydraulic pump is not supplied to the hydraulic motor. Further, the hydraulic motor attempts to rotate by the load in the gravitational direction. Since, however, main lines through which return fluid from the hydraulic motor is introduced into a tank are shut off by the counter balance valve, it is impossible to discharge the return fluid. Accordingly, the hydraulic motor is maintained stationary.
When the directional control valve is switched to one direction from the neutral, the hydraulic fluid from the hydraulic pump is supplied to the hydraulic motor through the main line. The counter balance valve is also switched to one direction by the actuator driving pressure generated in the main line for driving the load, that is, a hydraulic-motor driving pressure. Thus, the main line on the discharge side, which has been shut off by the counter balance valve, is brought into communication with the tank. Return fluid discharged from the hydraulic motor is introduced into the tank. The hydraulic motor drives the load in a direction corresponding to the switched direction of the directional control valve, for example, in a direction against the force of gravity.
When the directional control valve is switched to the opposite direction, the hydraulic fluid from the hydraulic pump is supplied to the hydraulic motor through the main line. The counter balance valve is also switched to the opposite direction by the hydraulic-motor driving pressure generated in the main line. Thus, the main line on the discharge side is brought into communication with the tank, and the return fluid from the hydraulic motor is introduced into the tank, so that the hydraulic motor drives the load in the gravitational direction. In this case, if the quantity of the return fluid discharged into the discharge-side main line from the hydraulic motor increases more than the quantity of the hydraulic fluid supplied through the supply-side main line, the hydraulic-motor driving pressure within the supply-side main line decreases so that the counter balance valve is moved toward the neutral. Thus, the discharge-side main line is restricted, whereby the quantity of the return fluid discharged from the hydraulic motor is limited.
In the manner described above, when the load is driven in the gravitational direction, the counter balance valve operates in such a manner that hydraulic-motor driving pressure corresponding to a spring of the counter balance valve is generated in the supply-side main line, to restrict the discharge-side main line thereby limiting the return fluid. For this reason, rotation of the hydraulic motor is prevented from being brought to a valve higher than rotation corresponding to the hydraulic fluid supplied to the hydraulic motor through the supply-side main line, making it possible to prevent running-away of the hydraulic motor in the load direction due to the force of gravi
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Hirata Toichi
Nozawa Yusaku
Sugiyama Genroku
Tanaka Hideaki
Yuasa Kazumasa
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Lopez F. Daniel
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