Engine Fault Study Based On Frequency Domain Analysis Of The Torsional Vibration

With economic globalization,world transport more develops, whether sea transport, land transport, or air traffic, are more convenient, At the same time, as the improvement of people's living standards, cars as a convenient means of transport get into thousands of families. All these vehicles must have power plant,.So it must have the following requirements for the power plant.(1)Can provide enough power to meet the long-range transport.(2)Must be safe enough for people to properly control the vehicle to ensure safety of life.(3)If the power unit fails, people can easily find fault, while faults are easy to be repaired.Engine is widely used in transportation industry as power equipment, so people are focusing on its design, diagnosis and maintain increasingly. In the past, people study engine fault from different points, and maintain, like from engine crankshaft mechanical model, including dynamic and static; also from engine instantaneous speed, including time domain and frequency domain. The disadvantage of the former is : This method is based on the specific structural parameters of the engine, so this method is not very universal because of each different engine having different structural parameters. The disadvantage of the latter is :high speed is easy to lead to misdiagnosis.On the engine's high-speed operation, crankshaft contains lots of information which can reflect kinds of state's characteristic signal. Crankshaft torsional vibration signals is one of them, and torsional vibration signal measurement method is simple ,what's more ,measurement equipment is very cheap, so we choose torsional vibration as the engine fault diagnosis signal and it is the main clue of this paper.Extinguishing of engine cylinder is the most common faults, and the most is single cylinder, because if two or more cylinders are extinguishing, the engines will not work, and stop. In this paper, we make fault diagnose through torsional vibration signal. At first, we start from the torsional vibration signal test, then design hardware and software, and design the entire diagnostic system, finally make engine fault diagnosis by the data in the frequency-domain. The main content of this paper as follow:(1) Introducing several commonly used methods of making engine fault diagnosis, and analyzing advantages and disadvantages of diagnostic methods. Comparing of these methods, the advantages of torsional vibration method is nothing with the specific parameters of engine, and the method is very easy and inexpensive.(2)On researching torsional vibration measurement, several torsional vibration measuring instrument are described according to sequence of time. From Mechanical Inertia Torsional Vibration Instrument to Analog torsional vibration instrument, to Digital Torsional Vibration Instrument, and introducing their principles and methods. The common factors that affect the measurement accuracy are discussed. Such as installation of measuring gear eccentric, Speed stability of engine.(3)When designing engine fault diagnosis system, designing ideas are used like this: From the sensor selection to hardware design, and then to software design. Designing hardware circuit, we should consider two points: Basically achieving to measure torsional vibration, at the same time improving the measurement accuracy. High-frequency temperature-controlled crystal oscillator is firstly used within considering the price, at the same time using a combination of high-speed and cache latch body through the realization of computer microprocessors and high-speed USB communications. So ensuring the information is not only high-speed transported but high-precision. Software design is mainly excluding abnormal points and the use of FFT algorithm transforming torsional vibration information from the time domain to the frequency domain.(4)The most sensitive low-frequency harmonics of torsional vibration signals are used to make engine fault diagnosis. Low-harmonic (0.5 sub-harmonics, 1 sub-harmonic, etc.) will be changed significantly when engine is extinguishing. At the end of the above-mentioned Theoretical Study, verifying the fault diagnosis method is feasible through engine experiments measurement torsional vibration.