Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1994-07-11
1995-08-22
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60468, 60494, 91517, 91518, 91461, F16D 3102, F15B 1116
Patent
active
054429129
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic recovery device with which, when driving working members such as a boom, arm and bucket of a hydraulic excavator, for example, hydraulic force of a hydraulic fluid returned from a hydraulic actuator to a reservoir is reused to increase a speed of the working member, and more particularly to a hydraulic recovery device with which hydraulic force can be efficiently reused even upon, e.g., abrupt variations in pressure.
BACKGROUND ART
One of prior art hydraulic recovery devices equipped in hydraulic drive systems is described in JP-B-4-57881, for example. This hydraulic recovery device is equipped in a hydraulic drive system comprising a plurality of actuators operated by a hydraulic fluid supplied from a variable displacement type hydraulic pump, and a plurality of directional control valves disposed between the hydraulic pump and the plurality of actuators for controlling respective flows of the hydraulic fluid supplied to the associated actuators. The hydraulic recovery device comprises variadisposed in a first line communicating a reservoir port of at least one of the plurality of directional control valves and a reservoir, a third line communicating a portion of the first line upstream of the recovery control valve and a second line connected to a pump port of the directional control valve, and a check valve disposed in the third line for allowing-the hydraulic fluid to flow only in a direction from the first line toward the second line.
The recovery control valve comprises a spool formed with a variable throttle, a hydraulic driving sector to which the pressure in the second line is introduced as a condition variable related to the operation of a hydraulic cylinder for driving the spool in the valve opening direction, and a set spring for urging the spool in the valve closing direction. An opening area (an amount of restriction) of the variable throttle is set at the position where the pressure introduced to the hydraulic driving sector and the urging force of the set spring are balanced.
When the directional control valve is operated in a direction to extend a rod of the hydraulic cylinder as the associated actuator, the hydraulic fluid from the hydraulic pump is introduced to a bottom side hydraulic chamber of the hydraulic cylinder via the first line and the directional control valve. On the other hand, the hydraulic fluid delivered from a rod side hydraulic chamber with the operation of the hydraulic cylinder flows into the directional control valve and is then introduced to the reservoir via the first line and the variable throttle of the recovery control valve. At this time, while the load of the hydraulic cylinder is small and pressing force due to the pressure in the second line introduced to the hydraulic driving sector of the recovery control valve is smaller than the pressing force of the set spring, the variable throttle is held at its closed or throttled position and, therefore, a pressure corresponding to the amount of restriction is generated in the first line. At the time the pressure so generated in the first line exceeds the pressure in the second line, a part of the return fluid flowing out of the directional control valve to the first line is allowed to pass into the second line via the third line and the check valve for recovery, and is then supplied to the directional control valve after joining with the hydraulic fluid from the hydraulic pump. Thus, the flow rate of the hydraulic fluid supplied to the bottom side hydraulic chamber of the hydraulic cylinder is increased by an amount corresponding to the recovered flow rate introduced from the first line, thereby increasing a moving speed of the hydraulic cylinder accordingly.
On the other hand, when the load of the hydraulic cylinder is increased and the pressure in the bottom side hydraulic chamber is raised, the delivery pressure of the hydraulic pump is raised and so is the pressure in the second line introduced to the hydraulic driving sector of the recovery contr
REFERENCES:
patent: 4845947 (1989-07-01), Persson et al.
patent: 4901812 (1990-02-01), Ferguson
patent: 4967557 (1990-11-01), Izumi et al.
patent: 5046309 (1991-09-01), Yoshino
patent: 5129230 (1992-07-01), Izumi et al.
patent: 5168705 (1992-12-01), Hirata et al.
Hirata Toichi
Ochiai Masami
Sugiyama Genroku
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Nguyen Hoang
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