Fault analysis is an observation, hypothesis, reasoning, verification, modification, hypothesis, revalidation, and so on. In order to accurately determine the process of failure, it means to use various philosophical methods, logical methods and mathematical methods to scientifically demonstrate or deduct the acquired fault information so as to reveal its essence through the surface phenomena of things.
1. analysis, induction and logical reasoning
According to the fault information, we first analyze all kinds of fault hypothesis (cause) that cause a fault phenomenon (the result), then compare and verify from the possible fault hypothesis, eliminate the false components and seek the real reason.
For complex situations, we can make clear and clear thinking by means of causality diagram, fishbone diagram, fault tree and so on.
Induction means the method of introducing general conclusions from a few facts. In general, we can only use incomplete induction. For example, a hydraulic excavator, its moving arm mechanism does not move, the bucket mechanism does not move, and the rotary mechanism does not move. We can get the conclusion by induction: the main oil pump or pilot at the same time controls the movements of the 3 mechanisms. The oil pump is faulty. Of course, this conclusion needs further proof.
2. proof and refutation
All kinds of fault hypothesis are exploratory and subjective conjecture. To achieve the purpose of the argument, the argument must be true and sufficient, and the individual information we obtain can only provide weak support to it and find negative evidence that the refutation evidence will be more powerful for the fault diagnosis.
In the above example, one of the hydraulic excavators' moving arm mechanism does not move. One of the possible failure hypotheses is that the hydraulic pump is damaged, that is, the main oil pump is damaged - the moving arm mechanism does not move. In turn, the reverse proposition is not set up, and other negative evidence must be found, for example, the main oil pump is damaged - the rotary mechanism can not move, and now it is observed back. If the rotating mechanism works normally, it can be proved that the main oil pump is not damaged, that is, the failure hypothesis of the main oil pump is not valid.
3. substitution method
In the practice of excavator fault diagnosis and maintenance, replacement method replaces the parts with the same type of parts and parts, and compares the working condition of the new and old parts and parts, so as to achieve the purpose of determining the fault location, also known as the prototype replacement. Apply a similar analog signal or load to a local system or part (such as a prescribed pilot variable pressure imposed on a hydraulic pump for a fluid controlled variable), and then compare the working conditions. This method should be used to pay attention to the appropriateness of the new, old parts or analog signals used to replace them, which can not be blindly replaced to cause a failure to expand or produce new reasons. Barrier.
4. deductive method
Deductive method refers to the thinking method of introducing special circumstances from the general principle, its main form is the "syllogism" composed of the big premise, the small premise and the conclusion. It is a kind of inevitable reasoning, the form is that all A has the property C (big premise), B is one of the A (small forward), then B- has the property C (conclusion).
For example, when the hydraulic plunger pump works under rated load, its volume efficiency is not less than 800/0 (large premise). A hydraulic excavator uses a plunger oil pump (small premise), so the volume efficiency should not be less than 80% (conclusion) when working under the rated load. If we pass the test, the displacement efficiency of the plunger pump is less than 80010, then it is less than 80010. It can be judged that the plunger oil pump may have a failure (but it may not be the only reason for the abnormal work of the hydraulic excavator, because there may be some new things out of the "large premise").
