Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1994-09-23
1996-01-09
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60426, 60428, 60494, 60457, 91517, 91518, 91445, 91447, F16D 3102, F15B 1108
Patent
active
054818729
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a hydraulic circuit for operating a plurality of actuators by supplying the delivery pressure oil of a single pump or a plurality of pumps to the plurality of actuators, a pressure compensating valve for distributing the delivery pressure oil of the pump or pumps in accordance with the opening of each operating valve, and a maximum load pressure detector for detecting the maximum load pressure of a plurality of actuators in the hydraulic circuit and using it as a pilot pressure for controlling the discharge of the pump or pumps and the pressure compensating valve, in a hydraulic excavator or the like.
BACKGROUND ART
A generally employed hydraulic circuit for simultaneously driving a plurality of actuators of a construction machine or the like, has all pressure compensating valves set in accordance with the maximum load pressure of the plurality of actuators when a plurality of operating valves are simultaneously operated, thereby making it possible to distribute the oil flow to the plurality of actuators in accordance with the opening area ratio of each operating valve even if the load pressures of the plurality of actuators differ.
In such a hydraulic circuit, when a plurality of actuators are simultaneously operated, the respective pressure compensating valves are set in accordance with the maximum load pressure, and the delivery pressure of the hydraulic pump becomes slightly higher than the set pressure. Therefore, the pressure loss in a pressure compensating valve of an actuator, wherein there is a significant difference between the maximum load pressure and the load pressure of the actuator, becomes high, resulting in a great horsepower loss for the prime mover which drives the hydraulic pump and an increased temperature of the hydraulic oil with consequent quickened deterioration of the hydraulic oil. For instance, when pressurized oil is supplied to a boom cylinder and a swinging motor of a power shovel to lower the boom and to swing the upper body of the power shovel at the same time, the load pressure of the boom is low because the boom lowers automatically due to gravity, while the load pressure of the swinging motor is high because the motor starts and accelerates the upper body, and the pump delivery pressure becomes slightly higher than a set pressure. Therefore, the difference between the high load pressure of the swing motor and the low load pressure of the boom cylinder causes a pressure loss in the pressure compensating valve on the boom cylinder side, resulting in a great pressure loss since the difference in load pressures is great as previously mentioned.
A prior art hydraulic circuit is shown in FIG. 12. More specifically, in FIG. 12, a delivery circuit 1a of a left pump 1 and a delivery circuit 1a of a right pump 1 can be connected together through a flow merging and branching valve 176. A load pressure introduction conduit 178a of a pressure compensating valve 5 of an operating valve 2, which is connected to the delivery circuit 1a of the left pump 1, and a load pressure introduction conduit 178b of the pressure compensating valve 5 of the operating valve 2, which is connected to the delivery circuit 1a of the right pump 1, are connected through a flow merging and branching valve 177. The delivery circuits 1a, 1a and the load introduction conduits 178a, 178b, are made independent by the flow merging and branching valves 176, 177 so that when an actuator 3a, connected to the left delivery circuit 1a, and an actuator 3b, connected to the right delivery circuit 1a, are operated simultaneously, the pressure compensating valve 5 is set in accordance with the load pressures of both actuators, thereby reducing the pressure loss.
In such a hydraulic circuit, however, delivery pressures P.sub.1, P.sub.2 of the pumps are controlled based on a load pressure P.sub.LS, so that they are slightly higher than the load pressure. Therefore, merely providing the delivery passages 1a, 1a of the pumps with relief valves may not allow the hydrau
REFERENCES:
patent: 5005358 (1991-04-01), Hirata et al.
patent: 5083428 (1992-01-01), Kubomoto et al.
patent: 5146747 (1992-09-01), Sugiyama et al.
patent: 5161373 (1992-11-01), Morikawa et al.
Akiyama Teruo
Ishizaki Naoki
Karakama Tadao
Yamashita Kouji
Kabushiki Kaisha Komatsu Seisakusho
Lopez F. Daniel
Nguyen Hoang
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