Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1992-05-04
1993-12-07
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60427, 60452, 60459, 60484, 91448, 91461, 91517, 91518, 91529, 91531, F16D 3102, F15B 1108, F15B 1300
Patent
active
052674401
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
1. Technical Field
The present invention relates to a hydraulic control system for construction machines, and more particularly to a hydraulic control system for construction machines, such as hydraulic excavators, having a plurality of actuators.
2. Background Art
A hydraulic control system for construction machines, such as hydraulic excavators, comprises a hydraulic pump, a plurality of actuators driven by a hydraulic fluid supplied from the hydraulic pump, and a plurality of valve apparatus for controlling flow rates of the hydraulic fluid respectively supplied to the plurality of actuators from the hydraulic pump. For this type of hydraulic control system, load sensing system is used to control the delivery pressure of the hydraulic pump dependent upon the load pressure. One example of the load sensing system is WO90/00683. This prior art system includes pump control means for controlling the displacement volume of the hydraulic pump so that the delivery pressure of the hydraulic pump is kept higher by a predetermined value than a maximum load pressure among the plurality of actuators. The plurality of valve apparatus each comprise a flow control valve provided with a variable throttle to change its opening dependent upon an operation signal from a control lever unit, and a pressure compensating valve (auxiliary valve) disposed upstream of the variable throttle in series to control a differential pressure across the variable throttle. By controlling the differential pressures across the variable throttles by the associated pressure compensating valves, the hydraulic fluid is positively supplied to the actuator(s) on the low load side as well, thereby enabling driving of the plurality of actuators.
The prior art disclosed in WO90/00683 also comprises a sensor for detecting the differential pressure between the pump delivery pressure and the maximum load pressure (hereinafter referred to as "LS differential pressure") to output a corresponding differential pressure signal, and means for storing an output pattern of the pressure compensating valve control amount corresponding to the differential pressure signal for each actuator and calculating the proper control amount based on the output pattern dependent upon the differential pressure signal from the sensor. The pressure compensating valves are separately controlled in accordance with the calculated control amounts. By so controlling the pressure compensating valve, the supply flow rate is controlled by not only the variable throttle, but also the pressure compensating valve additionally. With this additional flow rate control, during combined operation in which a plurality of actuators are driven simultaneously, it is possible to positively supply the hydraulic fluid to the actuator(s) on the low load side even in a saturation state when the delivery rate of the hydraulic pump becomes insufficient, and also to provide the optimum distribution ratio dependent upon the types of actuators, thereby improving system operability.
Further, in the prior art as illustrated in FIGS. 15 and 16 of WO90/00683, operation signals outputted from control lever units of the swing and boom are electrically detected, and a plurality of output patterns of the pressure compensating valve control amount corresponding to the differential pressure signal are stored in relation to the detected operation signal. When the operation signal is outputted from the control lever unit, the output pattern corresponding to the operation signal is selected and the control amount dependent upon the differential pressure signal is calculated from the selected output pattern. By so calculating the pressure compensating valve control amount in accordance with the operation signal, the additional flow rate control can be effected by the pressure compensating valve dependent upon the operation pattern of the actuator, which further improves the operability.
The prior art disclosed in WO90/00683 has suffered from the following problem.
In the prior art, as mentioned above, the
REFERENCES:
patent: 4967557 (1990-11-01), Izumi et al.
patent: 5048293 (1991-09-01), Aoyagi
patent: 5056312 (1991-10-01), Hirata et al.
patent: 5079919 (1992-01-01), Nakamura et al.
Patent Abstracts of Japan 59047504 Mar. 17, 1984.
Haga Masakazu
Hirata Toichi
Kajita Yusuke
Nakamura Kazunori
Onoue Hiroshi
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Ryznic John
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