Fault Diagnosis of Excavator Hydraulic Transmission System

Hydraulic transmission is a complex system composed of multiple components, and its maintenance and repair are much more difficult than those of mechanical transmission. Construction units generally lack monitoring and maintenance equipment for hydraulic systems. Therefore, accurately identifying and eliminating faults in the hydraulic transmission system of excavators is an important guarantee for their efficient and safe operation.

The overall structure of a fully hydraulic excavator

Most hydraulic excavators adopt a dual-pump circuit constant power variable hydraulic system. Among them, the majority use a constant power regulator to control two hydraulic pumps. All working mechanisms are divided into two groups (see the base diagram), and the operation is completed by manually controlled mechanical operation valves or pilot systems controlling the operation valves. In addition, when the boom, bucket and boom are operating, a two-pump combined flow is adopted to increase the speed.

The sequence of fault diagnosis

The sequence for diagnosing faults in the hydraulic transmission system of an excavator is as follows: understand the working conditions of the equipment before and after the fault occurs - external inspection - test run observation (fault phenomena, on-board instruments) - internal system inspection (refer to the system schematic diagram) - instrument check of system parameters (flow, temperature, etc.) - logical analysis and judgment - adjustment, disassembly inspection, repair - test Vehicle - Fault summary record.

There are many types of faults with excavators. According to the characteristics of different models, make full use of the monitoring system of the equipment itself, analyze specific problems specifically, master effective fault analysis methods, and divide the main oil circuit into several branches according to the working function by referring to the hydraulic system schematic diagram. According to the fault phenomenon, follow the sequence from outside to inside and from easy to difficult, and eliminate the faults one by one in the corresponding branch. In case of more complex comprehensive faults, the fault phenomena should be carefully analyzed, and the possible causes should be listed and eliminated one by one.

Issues to be noted in troubleshooting

1) Do not blindly disassemble or adjust components by yourself without carefully analyzing and determining the location and scope of the fault, as this may lead to the expansion of the fault range and the creation of new faults.

2) Due to the diversity and complexity of faults, other factors should be taken into account during the process of troubleshooting, such as the effects of mechanical and electrical faults.

3) When adjusting components, pay attention to the quantity and extent of the adjustment. Each time, only one variable should be adjusted to avoid other variables

Interference. If there is no change in the fault after adjustment, it should be reset. The adjustment range should be controlled within a certain range to prevent excessive adjustment.

Statistics show that over 70% of faults in hydraulic systems are caused by contamination of hydraulic oil. Therefore, when conducting maintenance and disassembly, special attention should be paid to the cleanliness of hydraulic components and systems. During diagnosis, the quality and temperature of the oil should be closely observed.

Diagnosis and elimination of common faults

4.1 Whole Machine Failure

The overall machine failure is caused by a malfunction in the common parts. At this time, it is necessary to focus on checking whether the oil level in the hydraulic oil tank, the oil suction filter element and the oil suction pipe are cracked. For servo-controlled excavators, insufficient pilot pressure can cause control failure. Therefore, the pilot oil circuit (pilot pump, filter element, relief valve, oil pipe, etc.) should be inspected. If the entire machine does not move and there is no load sensation when operating the excavator, the power connection parts between the oil pump and the engine, such as splines and gears, should be inspected. If the operation is sluggish, the servo regulation system of the oil pump should be inspected.

4.2 Several actions controlled by a certain group of control valves are abnormal simultaneously

At this point, there is no fault in the common part of the two groups of systems. The fault point lies in the common part of these actions.

1) The main relief valve is faulty. Most of the main relief valves of modern excavators adopt pilot-operated relief valves. If the pressure of the relief valve is not adjusted properly, the valve core does not close tightly, or the spring breaks, it will cause the entire system to have low pressure and small flow. The diagnostic methods can adopt pressure detection and component replacement.

2) Hydraulic pump regulating mechanism of the subsystem. Some excavators adopt a constant power variable regulation system, with each variable pump controlled by its own constant power regulator. If the regulating mechanism malfunctions, such as the valve core being stuck or severely worn, the oil output pressure of the oil pump will not conform to the constant power law, resulting in sluggish and slow operation.

3) Single action failure. It is caused by a malfunction in the connection part between the operation control section and the actuator of this action, including the operation pilot valve, pilot oil circuit, operation directional control valve, overload valve, actuator and other related parts. As mentioned earlier, in order to increase the working speed of excavators, a dual-pump combined flow is adopted when the boom, boom and bucket move. Therefore, when diagnosing faults, it is necessary to pay attention. If the left motor does not move or moves weakly or deviates, the rotation oil circuit of the same side traveling motor should be used for testing to see if it is a single-action fault. If the boom movement is used, it may not be accurate. Because the two pumps supply oil to the bucket rod cylinder simultaneously.

For the judgment of faults in the combined flow operation of the double pumps in the boom, such as "slow boom movement", the main reasons are: large leakage in the cylinder or failure to form a combined flow when the boom rises. At this point, a pressure gauge can be connected to the outlet of each of the front and rear pumps, and the boom can be operated separately. If the pressures of the two pressure gauges are the same, it indicates convergence; if one is high and the other is low, it indicates that no convergence has been formed. In addition, if the pilot valve is a pressure reducing proportional valve (adopted by most excavators), the stroke of its longitudinal lever is directly proportional to the output oil pressure. If this stroke is not adjusted properly, resulting in low control oil pressure and insufficient opening of the main valve, causing insufficient flow, at this time, the outlet pressure of the pilot valve can be detected to determine.

Sometimes it operates on its own without control. This is because the oil circuit that should be closed has compressive oil entering the actuator. The possible cause could be that the pilot valve or operating valve related to this action is stuck, or the joint of the rotary mechanism is leaking.