Removal of running deviation of CAT320BL excavator

A CAT320BL hydraulic excavator appeared following symptoms after working in 5100H: when the machine is walking forward 30m, the machine has shifted to the left 2m; after walking backward 30m, the machine also shifted to the left 2m.

1 、 Analysis and test

The machine is driven and controlled by 3 systems, which are mainly hydraulic system, pilot hydraulic system and electronic control system. The working principle of the hydraulic system is composed of a direct drive engine, variable piston pump and pump, hydraulic oil from the upper and lower pump respectively into the main control valve, the machine without walking and other movements of the operation, hydraulic oil, pump valve into the tank respectively; at the same time, from the main the control valve of the negative feedback signal feedback controller first, pump, pump swashplate control, the swing angle, make the machine idle when hydraulic pump displacement is reduced to the minimum; when walking and other operations, the main control valve in the control of the pilot pressure oil, the pressure oil to the hydraulic pump the left and right walking motor actuator. The system is a pilot negative feedback constant power variable automatic control system. The maximum working pressure is controlled by the main overflow valve, and the pressure is 34.3Mpa when walking.

According to the fault phenomena of the machine, combined with the principle of the hydraulic system, the preliminary judgment of fault should come from the hydraulic system, the position of possible: on the main pump and its control system, the pilot control valve, control valve, the main center of rotary joint and walking motor and other parts. In order to locate the fault more quickly and accurately, we carried out the following tests and measurements.

(1) walking test;

One end of the excavator parked in about 25m long and flat hard on the site (see photo), start the engine, the speed automatic control switch (AEC) is disconnected, and the engine throttle is placed in the "10" position, and pushed down the left and right walking pilot control valve, make the machine to walk straight about 25m, the whole left shifted 1.3m; then, push down the left and right walk first Chi control valve, make the machine back straight walking about 25m, also found the left offset 1.3m.

(2) measurement of system pressure;

The bucket cylinder piston is retracted to the limit position, and the hydraulic system pressure is raised. At this point, the pressure of the system is measured by the pressure gauge 34.3Mpa, which is the setting pressure of the overflow valve

(3) test of walking system pressure;

Release main relief valve locking screw pure, clockwise rotation adjustment screw ring 1.5, raised the main relief valve pressure test valve pressure overload running, test method for plug pin card after the death of the right driving wheel, and hold up the right track hanging bucket and boom, to the control right travel control lever, the pressure gauge system measured pressure is the pressure of the pump (29.5MPa).

(4) oil pipe for rotary joint;

The 4 main oil pipes under the center swivel joint are removed, so that the left and right two pairs of oil pipes are exchanged with each other. After tightening, the two walking control rod is operated, and the test procedure (1) is tested to find the machine left deviation.

(5) changing the tubing between the upper and lower pumps;

The upper and lower two pump out of the oil pipe, so that the upper and lower two pumps out of each other, after tightening, and then step (1) test, found that the machine to the right offset.

(6) testing of complex movements

When the walking control valve is used to make the excavator walk in a straight line, at the same time, other systems on the machine are operated to make them move, and it is found that the machine does not have any left leaning faults.

2 、 diagnosis and elimination

According to the above test and test results, combined with the work amount of hydraulic system, we can deduce the cause of the fault through the "elimination method":

According to: (1), (4), (5) and (6) test results of the steps, it can be concluded that the center rotary joint, the left and right running motors, the pilot control valve and the main control valve do not have any fault. Because the test steps (4) the results of the table, walking around to walk, walk the overload valve balance valve, there is no fault, and test steps (5) the results show that the pilot control valve and travel main control valve does not exist fault.

According to (2), (3), (6) the test results of the steps, can determine the pump no fault, the fault source should be under the pump. The basis is: through the test procedure (2), (3) can determine the initial pump work is normal, after step (6) after the test, there is no fault can be judged on the. Because when walking straight and other system of excavator operating machine only when the pump oil supply, it is further pump fault.

Then, remove the hydraulic pump from the excavator assembly, the pump overhaul, overhaul after the discovery, the pump plunger and the plunger sleeve, the valve plate is no problem; the piston and the cylinder pump regulator has abrasion traces, and has a groove. It can be determined that the cause of the trouble should be here.

According to the above, the failures of the machine can be explained as follows: when the machine is straight line, because the piston pump pump regulator card at a certain position, and the piston pin and the cylinder through the pump mechanical connection, so that the position of maximum angle cylinder cannot go to pump regulator the pump can not be formed, the largest displacement. At the same time, due to severe wear, the internal leakage, so that the system pressure can only reach 29.5Mpa, eventually resulting in the speed of the left side of the motor slowed down, the machine is left offset.

When the pump regulator is replaced, the fault has been eliminated and the machine has been returned to normal after the test table has been reinstalled.

By analysis, the real cause of the fault is: because the machine in the larger sand desert, the oil hydraulic oil pollution; in addition, the Caterpillar Inc provides the models of each core filter industry 500H to replace the hydraulic oil, is found in the inspection and maintenance, maintenance records of the machine, in a a Huanyouzhouqi (2000H) had two times according to the specified time to replace the filter, a total of more than a specified time for 150H. By the failure of the following conclusions can be obtained: Excavator in use, we must choose the qualified fuel requirements according to instructions, pay attention to maintaining the cleanliness of hydraulic oil, to prevent oil pollution; at the same time, according to the provisions of timely replacement of hydraulic oil and filter. Only in this way can the machine be less trouble free and its service life prolonged.