Engineering machinery fault diagnosis method - Solutions - Huaqiang Electronic Network

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Fault diagnosis concept and thinking method Fault diagnosis is the process of analyzing and finding the cause of the fault from the fault phenomenon. In actual work, fault diagnosis has two distinct forms: routine diagnosis and deep diagnosis. Routine diagnostics target entities to identify fault locations, and to eliminate faults by repairing and replacing faulty components. The diagnostic results are easy to verify. Deep diagnosis is based on influencing factors to find out the root cause of system failure or component damage, so as to take corresponding preventive measures, it has strong theoretical significance, and its diagnostic conclusion is less certain. more difficult. General faults only require routine diagnosis, while major or recurring faults should be diagnosed in depth.
Certain fault phenomena must be related to certain fault causes. The intrinsic relationship between analysis phenomena and causes is the central task of fault diagnosis. In complex faults, phenomena and causes often appear intricate, which requires the diagnostic personnel to have good analytical reasoning skills. Therefore, reverse analysis, logical reasoning, and gradual imminence are the most basic and practical ideological weapons for fault diagnosis.
Of course, the same fault phenomenon may result from different fault causes, and the same fault cause may also produce different results. For example, air filter plugging may cause malfunctions such as engine power drop, temperature rise, and fuel consumption increase. The above failure phenomenon may also be caused by the oil supply system, the cooling system, the lubrication system malfunctioning, or the wear of the gas distribution mechanism parts is too large. Therefore, the diagnostic personnel must also learn to use dialectical methods to analyze and solve problems, and be good at grasping the main contradictions in complex systems and identifying the main factors. The analysis tool for fault diagnosis helps the diagnostic personnel grasp the overall situation with the aid of the fault analysis tool. It’s easy to go astray simply by “following the feeling”. Common analytical tools include causal maps, fault trees, and flowcharts. For complex faults with multiple phenomena and multiple possible factors at the same time, experienced diagnostic personnel can assign values ​​according to the intimacy between each fault phenomenon and each fault factor, and establish a mathematical model for probability analysis. Diagnostic method preparation phase In the preparation phase, the most important task is to master the principle and clarify the phenomenon. Proficiency in the structural features and working principles of the diagnostic object is the premise for specific diagnosis and analysis, otherwise it can only be a touch. When conducting deep diagnosis, the diagnostic personnel must also have relevant knowledge and comprehensive analytical skills. And figuring out the phenomenon is the basis for diagnosis. The situation reflected by the operator or other personnel should be carefully verified, and the best method is to manually operate the test machine.
After familiarizing with the principle and grasping the phenomenon, the necessary reasoning analysis should be carried out to grasp the key points and narrow the scope of the search. At the same time, it is necessary to make good use of analysis tools such as causal analysis diagrams to assist the reasoning analysis, so as to master the whole situation and avoid omissions.
The search phase (1) adheres to the principle of “from the table to the inside, the first is simple and then the complex”, and in the process of finding faults, the basic principle of simple to complex must be adhered to. The specific requirements are to be done from the table and the inside, first easy and then difficult, first low pressure and high pressure, first control the mainstream. That is, the factors that are easy to find or can be accurately judged are checked in advance to avoid the situation of "small problems". A simple and easy method should also be preferred in the use of measurement and test methods. For hydraulic fault diagnosis, the pressure measurement is prioritized, and finally the flow test is considered. Significant changes in engine speed and changes in exhaust color caused by engine load changes are also fully identifiable by the operator's eyes and ears.
(2) Pay attention to the key points, focus on the breakthrough, pay attention to the string and parallel relationship of the identification system, and be good at sub-regional and sub-paragraph inspection. For inspection items that can accurately judge or eliminate the scope of faults, key inspections can be arranged, which is conducive to narrowing the scope of search as quickly as possible, so as to concentrate and be targeted. During the diagnosis process, the identified or excluded factors and the latest fault phenomena should be further analyzed and judged in order to better select the next action.
(3) Emphasis on measuring and comparing the specified conditions to avoid misjudgment in the process of finding faults. It is often necessary to carry out necessary measurements and tests. However, in actual work, the conditions of measurement and test (such as engine water temperature, oil temperature, rotational speed, hydraulic oil viscosity, temperature, operating state and ambient temperature) are often easily overlooked, which may have a significant impact on the test results. Sometimes it even leads to the opposite conclusion. In addition, in addition to observing and recording the parameters and conditions in a specific operating state during measurement and test, special attention should be paid to observing the changing trend of the monitored parameters during different operating actions and their conversion processes.
The application of the "stethoscope" principle is faulty in the construction of the site. Because of the objective situation, the conditions for the diagnosis of the equipment are often not available, and the maintenance personnel need to use the "stethoscope" principle to carry out the detection with rich experience or with simple tools and instruments. "Stethoscope" is a qualitative judgment of the state of the device based on the human sense and its long-term accumulated emotional experience. That is, any device is diagnosed, and the diagnostic personnel go to the scene to understand the condition of the device by asking, watching, smelling, listening, touching, etc., and obtaining relevant information through the senses, and making a preliminary assessment. However, the biggest flaw in sensory judgment is the lack of evaluation of “quantity”. The problem is analyzed purely by perceptual experience, subjective factors are judged by results, and reliability is poor.
Several simple methods of judgment (1) Partial stop method: that is, a method of artificially causing a certain part of the equipment to stop participating in work and observing changes to conduct a comparative test. For example, the multi-cylinder engine uses the "broken cylinder method" to judge whether a cylinder works well or the abnormal sound comes from that cylinder.
(2) Cross-contrast method: Compare the pipelines of the same nature, or exchange two identical or similar parts, or replace the suspected parts with normal parts to compare whether the parts are in question.

(3) Short-circuit isolation method: the input and output terminals of the suspected component are directly connected for comparison test. This method is suitable for use in a process system. If the filter element is suspected to be clogged, the filter element can be removed for testing.
(4) Cut-off isolation method: a comparative test is carried out by using a cut-off device to perform segmentation isolation at different flow nodes, or to replace the actuator for braking. This method is suitable for process systems. If it is suspected that the working pressure is insufficient due to the leakage of the hydraulic motor, the cut-off plate can be used to block the motor to simulate the “zero internal leakage” of the fuel pipe for comparative test.
(5) Forced state method: For some automatic adjustment components, the automatic method is used to cancel its automatic function, and it is forced to be in a certain state to reduce the variable factors for the comparison test.
(6) Heuristic adjustment method: In the case of suspecting that a certain component is not properly adjusted, heuristic adjustment can be made, but the original state should be restored when the adjustment is invalid.
(7) Contrast method of similar models: When it is not possible to determine whether the characteristic values ​​or conditions are normal, compare them with the corresponding values ​​or conditions of normal similar models.
Intelligent electronic monitoring system This diagnosis method mainly monitors the working condition of the mechanical operation through the sensors installed in various parts of the construction machinery, and cyclically measures the set parameters. When the mechanical working conditions are abnormal, the monitoring system is preset according to the preset conditions. The data (alarm value) is illuminated in three levels by light or sound and light. Its working principle is to convert the working parameters of various parts of the machine (oil path, gas path, etc.) into the electric quantity, voltage or current through the sensor installed in each part, and convert it into a preamplifier. The voltage is input to the corresponding input port of the host. The host uses a single-chip computer as the microprocessor. The computer technology is used to process the input signal in real time, and output corresponding signals to implement display and alarm to remind the operator that it may If a mechanical failure occurs, it needs to be handled in time to prevent the accident.