Analysis of the Causes and Maintenance of the deviation Fault of Crawler Crane Travel

Deviation during movement is a common fault of crawler cranes. There are many reasons for this, especially on construction sites, where the lack of measuring instruments and testing devices makes analysis rather difficult. The following introduces the causes and judgment methods of the deviation of crawler cranes with examples.

The fault phenomenon of a certain crawler crane is that it veers to the right when moving forward, does not veer when moving backward, and veers severely when the throttle is large.

The traveling system of a crawler crane mainly consists of mechanical parts (including drive wheels, guide wheels, idler wheels, support wheels and tracks) and hydraulic drive parts. When conducting maintenance, the principle of starting with the easier tasks and moving on to the more difficult ones should be followed. First, analyze the mechanical part.

The mechanical part mainly checks two aspects. One is whether the two tracks are parallel. The second is whether the centerlines of the drive wheel, guide wheel, idler wheel and support wheel coincide. If either of the two has a problem, it will cause the vehicle to deviate during movement. However, the phenomenon should be that it deviates both when moving forward and backward. But this vehicle only deviates when moving forward. Therefore, it can be determined that the fault is not caused by the mechanical part. At this point, an analysis of the hydraulic part is required.

When the control handle 5 is pushed, the control handle supplies pressure oil to the brake 1, which opens the brake. At the same time, the control handle supplies pressure oil to the main valve 4, pushing the valve core of the main valve to act. The main valve supplies pressure oil to the motor 2, and the motor rotates, thereby driving the traveling reducer to rotate and achieving the traveling of the crawler crane. The brake valve serves functions such as hydraulic braking when parking and speed limiting when going downhill. From the perspective of the entire walking hydraulic system, any malfunction of components such as the motor, brake valve, main valve and control handle will cause the walking to deviate. Based on experience, the order of failure rates from high to low is motor, control handle, main valve and brake valve. The following is an analysis in sequence.

The main manifestation of motor failure is large internal leakage. If the internal leakage of the right motor is large and the volumetric efficiency decreases, it will cause the speed of the right motor to be lower than that of the left motor. In this case, both forward and backward movements will deviate to the right. Therefore, it can be determined that it is not a motor failure. To verify this determination, the oil drain port of the right motor was opened for a walking test. It was found that the hydraulic oil slowly overflowed from the oil drain port, indicating that the internal leakage was normal and confirming that the motor was not faulty.

The common faults of the control handle are large internal leakage of the valve, low pilot pressure provided to the main valve, resulting in the main valve not being fully opened, and small flow of hydraulic oil delivered to the motor, causing deviation. The forward and backward movement is controlled by two independent valve cores in the control handle. Swap the two oil outlets that control the forward and backward movement on the control handle. If the reverse movement deviates but the forward movement does not, it indicates that there is a fault with the control handle. After the swap, the test found that it still deviated to the right when moving forward but did not deviate when moving backward, indicating that it was not a problem with the control handle.

The common faults of the main valve are large leakage inside the valve, resulting in significant flow loss. Or the hydraulic system is not clean, causing the valve core to be stuck, the valve port to be not fully opened, and the flow rate to be small. Since both the forward and backward movements are accomplished by the same valve core in the main valve, if there is a large leakage inside the valve, both the forward and backward movements should deviate. Therefore, it can be determined that the possibility of a large leakage inside the main valve is very small. To analyze whether the main valve core is stuck, the pipeline was swapped. The oil outlet of the main valve controlling the left motor was connected to the right motor, and the oil outlet of the main valve controlling the right motor was connected to the left motor. If there is a problem with the main valve, the deviation direction will change. After the walking test, there is no change in the fault phenomenon, which can prove that the main valve is fine.

The common faults of brake valves are excessive leakage inside the valve or incomplete action of the valve core. If the leakage inside the valve is large, both the forward and backward movements should deviate. After determination, the possibility of a large leakage inside the valve fault is very small. If the valve core is stuck by debris or the throttle port inside the valve is blocked, causing the valve core to fail to act properly, the valve port opening will be small, and the flow of hydraulic oil will be small, resulting in deviation. When the throttle is large, the pressure and flow loss will be large, and the deviation will be severe.

For this purpose, a pressure gauge was connected to each of the oil inlet ports (P port) of the left and right main valves for a walking test. It was found that the pressures on the left and right were basically the same when reversing. However, when moving forward with a small throttle, the pressure difference between the left and right sides is not significant. If the throttle is heavily pressed, the pressure on the right side is several megapascals higher than that on the left. This indicates that the valve core of the brake valve that controls the forward direction does not act properly, resulting in poor oil flow. When the throttle is small, the hydraulic oil flow is small, and the pressure and flow loss are relatively small. When the throttle is large, the pressure and flow loss are relatively large. Therefore, it causes the fault phenomenon that the vehicle deviates to the right when moving forward, does not deviate when moving backward, and deviates severely when the throttle is large.

When disassembling and inspecting the brake valve, it was found that the throttle port controlling the forward direction was blocked by debris. After cleaning, the fault disappeared immediately.

From the above analysis, it can be seen that there are many reasons for the walking deviation fault of crawler cranes. All possible factors can be comprehensively considered, then analyzed and determined item by item, and confirmed through measurement and testing, and eliminated item by item to find the true cause.