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(11) | EP 1 193 400 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Hydraulic circuit of construction machine |
| (57) To provide a way to prevent sharp decrease in the speed of main body actuators by
ensuring a sufficient amount of hydraulic fluid to be fed to the main body actuators
even if the pressure in the attachment circuit of a hydraulic shovel approaches the
relief pressure. When the pressure in an independent attachment circuit 37, which
is adapted to control an attachment of a hydraulic shovel, approaches a given relief
pressure in the course of operating the attachment together with other main body actuators,
a controller 71 detects the increase of the pressure by means of a pressure sensor
66 and shifts an electromagnetic selector valve 68 to the channel-communicating position
so that priority hydraulic fluid branching off from a pressure compensation flow dividing
valve 38 to an external channel 67 flows through the electromagnetic selector valve
68 into a tank 39. As a result, the discharge rate of a pump 33 is increased by the
amount equivalent to the decrease in the discharge pressure so that a greater amount
of hydraulic fluid is fed from the independent attachment circuit 37 into a main circuit
36 of the main body actuators. Therefore, sharp decrease in the speed of the main
body actuators is prevented. |