3. Upper Pilot Valve (remote control valve

Other Circuits

Auto pressure boost circuit (bucket close)

When an attachment is operated, this circuit boosts the control valve main relief set pressure from 34.3 MPa to 37.3 MPa according to the engine load ratio and hydraulic load pressure, then ends the pressure boost after 8 sec.

As an example, this section explains bucket-close operations.

By moving the remote control valve to the bucket-close side, the pilot pressure oil is fed via the cushion valve to the control valve pb7 port and switches the bucket spool to the close side.

At the same time, the output signal from the upper pilot pressure sensor that detected the pressurized oil separated from the pilot internal path is input to computer A, which judges that there is upper operation. Furthermore, computer A judges that there is a boost in the main pump P1 and P2 pressure, outputs the ON (24 V) signal to the pressure boost relief solenoid, switches the valve, and the pilot pressure oil is fed to the control valve main relief valve PH port to hold the pressure boost relief set pressure for 8 sec.

There is no boost for the option circuit and during travel operation.

Pressure line Tank line Pilot pressure line Pilot tank line Electric line

1 Cushion valve 11 Upper pilot pressure sensor 2 Bucket (close) 12 Console lever lock switch 3 Bucket (open) 13 Digging force incresed 4 Remote control valve (boom, bucket) 14 Monitor display 5 Lever lock 15 Computer A 6 Boost pressure relief 16 P1 pressure sensor 7 5 stack solenoid valve 17 P2 pressure sensor 8 Control valve 18 Hydraulic pump 9 Bucket 19 Check valve 10 Bucket cylinder 20 Oil cooler

Overall View

Enlarged View

14