Hydraulic system fault diagnosis strategy and method skills

1.Fault diagnosis strategy of hydraulic system

The fault diagnosis strategy of hydraulic system is to find out the working principle and structural characteristics of the whole hydraulic system, and judge according to the fault phenomenon with knowledge and experience; Gradually deepen, purposefully, and in a direction, gradually reduce the scope, determine the region, the part, and even a component.

2.Fault diagnosis method of hydraulic system

At present, the commonly used and developed fault diagnosis methods of hydraulic system have two basic methods: qualitative analysis and quantitative analysis. The former can be divided into logical analysis, comparison and replacement method, observation and diagnosis method (simple fault diagnosis method), and the latter can be divided into special inspection method and intelligent diagnosis method. According to the specific fault phenomenon and focus and implementation strategy, these methods are sometimes subdivided into sensory diagnosis method, parameter measurement method, field test method, interception method, layer depth method and rounded to zero comprehensive evaluation method.

1）Qualitative analysis method

①When the logical analysis method is used to diagnose the fault of the hydraulic system, the following two situations should be distinguished.

a.For the hydraulic system with relatively simple function and oil circuit structure, logical analysis can be carried out according to the fault phenomenon and the basic principle of the hydraulic system, in accordance with the order of hydraulic source → control components → executive components, check item by item and exclude other factors according to the existing inspection results, gradually narrow the scope, gradually approach, and finally find out the cause of the fault (location) and eliminate.

b.For the hydraulic system with more complex function and oil circuit structure, it is usually possible to analyze the two parts of the control oil circuit and the main oil circuit according to the fault phenomenon, and remove the fault one by one.

Logic analysis can be subdivided into list method, block diagram method, cause-effect diagram method   and fault tree analysis method.

②Contrast and replacement method
There are two situations: one is to use two hosts of the same model and the same specification to compare the same system test, from which to find the fault, the suspicious components in the test process with new parts or intact mechanical components to replace, and then boot the test, such as the performance becomes better, the fault will be known; Second, for two hydraulic systems with the same functional circuit, the hose is connected to the same host machine for testing, and when suspicious components are encountered, they can be replaced.

③Observation diagnosis (simple fault diagnosis)
This method is one of the most common methods for fault diagnosis of hydraulic system at present, which is convenient and easy to use. It is based on the personal experience of maintenance personnel, the use of simple instruments, objectively according to the "look → smell → ask → cut" process. This method can be carried out both in the working state of hydraulic equipment and in the stopping state.

2）Quantitative analysis method

① Special inspection method of instruments
This method is suitable for some important hydraulic equipment, and it uses instruments to quantitatively detect the relevant parameters of the system (such as pressure, flow rate, temperature, vibration, noise, torque and speed, etc.) to provide a reliable basis for troubleshooting. Some of these methods must be tested on the test bench, while others can be tested online.
② Intelligent diagnosis
This method is a kind of hydraulic equipment fault diagnosis expert system (computer system) based on computer, with the help of computer's powerful logic operation ability and memory ability, the hydraulic fault diagnosis knowledge is systematized and digitized. The expert system usually consists of six parts: knowledge base (rule base), database, inference machine (strategy), interpreter, knowledge acquisition program and man-machine interface.

Knowledge base is one of the core of the expert system, which stores various fault phenomena, fault causes and the relationship between the two, which are from experienced maintenance personnel and experts in the field. The knowledge base concentrates the knowledge of many experts, collects a lot of data, deducts the subjective bias in the solution, and makes the diagnosis result closer to the reality.
Once the hydraulic system fails, the user can send the fault phenomenon to the computer through the man-machine interface, the computer according to the input fault phenomenon and knowledge   in the knowledge base, according to the reasoning method stored in the reasoning machine to introduce the fault cause and report to the user, and can also propose maintenance or preventive measures. The new expert system includes fuzzy expert system, neural network expert system, Internet expert system and so on.