Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
2000-10-31
2002-04-30
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S452000, C091S445000
Reexamination Certificate
active
06378302
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hydraulic circuit system mounted on a construction machine, such as a hydraulic excavator, including a plurality of hydraulic actuators which are often simultaneously operated, and more particularly to a hydraulic circuit system including a load sensing system and having control valves provided with flow distribution valves which enable a combined operation to be performed without being affected by a difference in load pressure between a plurality of hydraulic actuators.
BACKGROUND ART
JP,C 2721383 discloses a hydraulic circuit system employing a load sensing system in a hydraulic excavator as a typical example of construction machines, and including flow distribution valves which enable a combined operation to be performed. The hydraulic circuit system shown in
FIG. 3
of the known art comprises a variable displacement hydraulic pump, a tilting control cylinder for the hydraulic pump, an LS valve for operating the tilting control cylinder depending on a differential pressure between a delivery pressure of the hydraulic pump and a maximum load pressure, and a flow distribution valve disposed on the outlet side of each meter-in throttle of a plurality of directional control valves. Further, a branch hydraulic line for detecting a load pressure is provided on the outlet side of each flow distribution valve, and a check valve is provided in the branch hydraulic line. With such an arrangement, when the load pressure of the associated hydraulic actuator is a maximum one, that load pressure is detected by the check valve and the detected load pressure is transmitted, as a signal pressure, to the LS valve via a signal transmitting hydraulic line. Also, a hydraulic fluid outgoing from the meter-in throttle is introduced to the hydraulic actuator through the flow distribution valve. The signal pressure is introduced to a control chamber in which a pressure bearing portion of each flow distribution valve acting in the throttling direction is positioned, and an inlet-side pressure of each flow distribution valve is introduced to a space in which a pressure bearing portion of each flow distribution valve on the opposite side (acting in the valve opening direction) is positioned. Thus, the same signal pressure is applied to the pressure bearing portions of all the flow distribution valves acting in the throttling direction, and the flow distribution valve on the lower load pressure side is balanced when the pressure bearing portion of that valve on the opposite side (acting in the valve opening direction) is subjected to the same pressure as the inlet-side pressure of the flow distribution valve on the higher load pressure side. Accordingly, a differential pressure across the meter-in throttle has the same value on both the higher and lower load pressure sides so that the hydraulic fluid delivered from the hydraulic pump is distributed depending on a ratio between valve openings of the meter-in throttles. With such a flow distributing function, the hydraulic actuators can be operated at the same time regardless of the difference in load pressure.
Also, a swing motor and a boom cylinder are provided as the hydraulic actuators, and an on/off valve is disposed in a branch hydraulic line for detecting a load pressure on the swing motor side. The on/off valve is operated by a pilot pressure signal for the boom-raising operation. With that arrangement, when the boom is raised while turning a swing body of the hydraulic excavator, the on/off valve is operated to cut off the load pressure of the swing motor, and the load pressure of the boom-raising operation is detected, as the signal pressure, to operate the LS valve and a pressure compensation valve.
Further, PCT Laid-Open Publication WO98/31940 discloses a control valve for use in a hydraulic circuit system including a load sensing system, the control valve being constructed as a valve assembly in combination of a flow distribution valve and a hold check valve for simplification. In the disclosed control valve, a valve body of the flow distribution valve is partly incorporated in a hollow valve body of the hold check valve, and a load-pressure detecting hydraulic line of the control valve is formed as an internal passage (hydraulic line slit) of the flow distribution valve. The internal passage is utilized to provide a check valve function. As a result, a check valve as a separate valve element is no longer required and the control valve is simplified in its construction.
DISCLOSURE OF INVENTION
Of civil engineering works using a hydraulic excavator, the most popular one is to scoop earth and sand excavated by a front device and to load the earth and sand on a dump truck. Let suppose the case of carrying out the work in such a manner that the truck is on standby with its bed positioned in a direction rotated 90 degrees from the excavating direction of the front device. After scooping the earth and sand by a bucket, the boom is raised to a level of the truck bed and an upper swing body is turned 90 degrees. Then, the work is finished by discharging the earth and sand onto the truck bed. To perform the work quickly, the upper swing body is turned simultaneously with raising of the boom. To avoid the hydraulic excavator from striking against the truck during the work, the bucket at a fore end of the front device must be at a position higher than the level of the truck bed when the upper swing body has been turned 90 degrees. A method of first turning the upper swing body through 90 degrees and then raising the boom accompanies a possibility that the bucket may strike against the truck bed.
In the hydraulic circuit system having the general construction shown in
FIG. 3
of the above-cited JP,C 2721383 with the on/off switch not provided, when remote control valves for swing and boom-raising are both operated at the same time to perform the above-mentioned work, the upper swing body cannot move at once because it is an inertial body and a swing side system has large inertia. Therefore, the pressure detected on the swing side has a value close to a delivery pressure of a hydraulic pump, and the LS valve is operated to increase the pump delivery pressure up to a relief pressure immediately. In spite of that the boom can be operated with a lower pressure than the relief pressure when operated solely, an extra pressure loss (energy loss) is caused in a flow distribution valve portion on the boom side when the boom is operated simultaneously with the upper swing body. If the hydraulic circuit system includes a horsepower control function associated with the hydraulic pump, a pump delivery rate is reduced with an increase in the delivery pressure of the hydraulic pump. Unlike the case of moving an object vertically (i.e., the case where an object cannot be moved by a force less than the weight of the object), a load on the swing side corresponds to the case of moving an object on a horizontal plane. In this case, therefore, the load can be moved by a force greater than a frictional force between the object and the plane. In other words, though slowly accelerated, the upper swing body can be moved with the driving pressure in the boom side. To this end, it is desired that the pressure in the boom side be detected during the combined operation without detecting the pressure in the swing side.
In the hydraulic circuit system shown in
FIG. 3
of the above-cited JP,C 2721383, the above-described function is achieved by operating the on/off valve, which is disposed in the branch hydraulic line for detecting the load pressure on the swing side, by the pilot pressure signal for the boom-raising operation so that the load pressure of the swing motor is not detected. The energy consumption and the working speed are thereby improved. In the disclosed prior art, however, it is required to provide a branch hydraulic line dedicated for detecting the load pressure, and to arrange the check valve in the branch hydraulic line. This raises a problem that a portion for detecting the maximum load pressure is complicated
Nishimura Yoshizumi
Nozawa Yusaku
Takahashi Kinya
Tougasaki Mitsuhisa
Hitachi Construction Machinery Co. Ltd.
Mattingly Stanger & Malur, P.C.
Ryznic John E.
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