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Fault Elimination Of CAT320 Series Excavator Travel Device Deviation


A CAT320 hydraulic excavator appears the following symptoms after 5100H of work: When the machine walks 30m forward, the whole machine has left deviation 2m; After 30m backward, the machine also moves 2m to the left.

1. Analysis and testing

The machine is driven and controlled by three systems, namely the main hydraulic system, the pilot hydraulic system and the electronic control system. The working principle of the hydraulic system is: directly driven by the engine, the lower variable piston pump and pilot pump, hydraulic oil from the upper and lower pump respectively into the main control valve, the machine is not walking and other actions of the operation, the upper and lower pump hydraulic oil respectively through the valve body into the tank; At this time, the negative feedback signal of the independent control valve is fed back into the controller of the upper and lower pumps to control the swash plate swing Angle of the upper and lower pumps, so that the displacement of the hydraulic pump is minimized when the machine is idling; When walking and other operations, the main control valve under the control of the corresponding pilot pressure oil, the pressure oil of the hydraulic pump to the left, right walking motor and other executive components. The system is a pilot negative feedback constant power variable automatic control system, its maximum working pressure is controlled by the main relief valve, and the set pressure is 34 when walking. 3 mpa.

In view of the fault phenomenon of the machine, combined with the original work of the hydraulic system, the preliminary judgment of the fault should be from the hydraulic system, the possible parts are: the upper and lower main pump and its control system, pilot control valve, main control valve, central rotary joint and walking motor and other parts. In order to find out the fault location more quickly and accurately, we carried out the following steps of test and measurement.

(1) Straight line walking test

Will excavator parked in about 25 m long and level off one end of the hard ground (see chart), start the engine, the speed will automatically control switch (AEC) disconnected, and the engine throttle placed in the position of the "10", walking and push her left and right pilot control valve, the machine to walk straight ahead about 25 m, the results of the machine left offset the 1.3 m; Then, push down the left and right walking control valve, so that the machine goes straight back about 25m, and it is found that the whole machine is also shifted to the left 1.3m.

(2) Measurement of system pressure

The bucket cylinder piston is retracted to the limit position, so that the pressure of the hydraulic system increases. At this time, the pressure of the system measured by the pressure gauge is 34.3Mpa, which is the set pressure of the relief valve

(3) Test the pressure of the walking system

Loosen the lock screw of the main relief valve and turn the adjusting screw 1.5 turns clockwise to increase the pressure of the main relief valve and test the pressure of the walking overload valve. The test method is as follows: After clamping the right driving wheel with the stopper pin, use the bucket and the boom to support the right track to make it suspended, and then operate the right walking lever forward. At this time, the system pressure measured by the pressure gauge is the pressure of the lower pump (29.5mpa).

(4) Change the tubing of rotary joint

Remove the four main oil pipes under the central rotary joint, make the left and right two pairs of oil pipes change with each other, tighten them, and then operate the two running levers to test step (1). It is found that the machine is deviated to the left.

(5) Change and lower the pump tubing

Remove the outlet pipes of the upper and lower pumps and make the outlet pipes of the upper and lower pumps exchange with each other. After tightening, perform the test of Step (1) and find that the machine deviates to the right.

(6) Test of compound action

When the walking control valve is manipulated to make the excavator walk in a straight line, other systems on the machine are manipulated at the same time to make them move. The result shows that the machine does not have the fault of left deviation.

2. Diagnosis and exclusion

According to the above test and detection results and combined with the original work of the hydraulic system, the cause of the failure can be inferred through the "elimination method".