Remedying Slow Travel Speed on a PC200-7 Excavator
2013-07-05
612
0人评论
The fault symptom of a PC200-7 excavator was: after 300 hours of operation, the forward travel speed became slow and the machine lacked travel power.
First, the speeds of the boom, arm, bucket and swing as well as the relief pressure were checked; all values were within the standard range, so it was judged that the hydraulic pump, self-pressure reducing valve, main relief valve, main control valve, etc. had no faults.
Next, the right track was raised, and at maximum throttle the time required for the track to rotate 5 turns was measured; the result was abnormal forward travel and normal reverse travel.
From this it could be judged that the travel motor, motor reducer, travel speed solenoid valve, etc. had no faults.
Then a swap test was carried out between the travel pilot lines and the work equipment pilot lines. That is, the boom-lowering pilot line was swapped with the left travel forward pilot line, and the arm-digging pilot line was swapped with the right travel forward pilot line. At the same time, the boom-lowering and arm-digging pilot valves were operated, and it was found that the forward travel speed and force were normal, but the arm digging speed became slow. From this it could be judged that the travel pilot valve was faulty. After replacing this valve, both forward and reverse travel speeds returned to normal.
After 800 hours of operation, the machine lacked power during straight travel and had only the low-speed range. During on-site inspection, it was found that the automatic speed reduction function would automatically activate after the machine had traveled straight for 4 s. Fault codes 019 and 021 were retrieved on the monitor, and it was found that during straight travel the travel oil pressure switch in 019 was OFF while the travel deviation (i.e., steering) oil pressure switch in 021 was ON. During steering, however, both oil pressure switches were ON, from which it could be judged that the circuits of the two pressure switches were faulty. The cab floor plate was removed and the circuits of the pressure switches were checked, and the two connectors were found to be connected in reverse. The cause was that after the travel signal oil pressure switch S30 connector (see attached figure) and the travel steering signal oil pressure switch S31 connector were connected in reverse, during straight travel, although the travel oil pressure switch was closed and conducting, its electrical signal was sent to the controller through the steering oil pressure switch connector S31. At this time, the steering oil pressure switch was not closed, so no electrical signal was sent to the controller through the travel oil pressure switch connector S30. On this basis, the governor and pump controller judged that the machine was not performing a travel operation and executed the automatic speed reduction function through the governor motor. At the same time, the governor and pump controller reduced the pump displacement to the minimum. At this time, even if the high-speed travel range was selected, no electrical signal was sent from the governor and pump controller to the travel speed solenoid valve. Since the travel speed solenoid valve was not energized, the machine had no high-speed travel range. After the two connectors were swapped, the fault disappeared.
评论 （0）