Research On Method Of Fault Diagnosis For Diesel Using Torsional Vibration Signal

The torsional vibration measuring system of diesel plant has several good qualities such as:measuring easy,without making direct contact,sensor cheap and long life. Three dangerous faults of diesel:one cylinder misfire,crack on crankshaft,cylinder score are be caring by people for a long time. After reading many references,how to diagnose these faults using torsional vibration signal is studied in this paper .Some satisfactory results are achieved in this paper:1. In this paper,a new method of diagnosing cylinder misfire by using kurtosisness of torsional vibration is first introduced. kurtosisness is a parameter which is sensitive to pulse. Assume combustion pressure as pulse force,the kurtosisness of torsional vibration of diesel is steady when engine is "healthy" . Simulation and experiment show:the kurtosisness will minish when one cylinder misfire.2. The principle that cylinder misfire is diagnosed using torsional vibration harmonic analysis is illustrated by calculation of vectorsummation. Calculation and experiment show:low harmonic will increase highly and main harmonic will decrease little when one cylinder is misfiring .3. A method to convert the torsional vibration into individual cylinder combustion pressure using IMS adaptive algorithm is putted forward . The position of misfire cylinder can pointed immediately using this method.4. In this paper,the crack on crankshaft in diesel is first diagnosed by using torsional vibration analysis. Stiffness will decrease because of crack. The stiffness of crankshaft is changing due toopen-close of crack under alternating load of crankshaft. A open-close mathematic model is introduced into calculation of torsional vibration .results show:kurtosisness and high harmonic will increase when crankshaft have crack.5. Cylinder score is also diagnosed by torsional vibration in this paper,when cylinder score occurring,the friction of piston will decrease the action of air pressure. Speed of engine also decrease because of large friction. Two models of friction are proposed,the simulation results show together:kurtosisness of torsional vibration will decrease,low harmonic and main harmonic of torsional vibration will increase when cylinder scoring.6. A diesel fault diagnosis system(IETVDS) using torsional vibration is invented in this paper . there are two parts in the system,one is measuring part,the other is diagnosis part. Torsional vibration can be measured by a 40MHz crystal oscillator. The frequency of oscillator is the highest in China now. Cylinder misfire,crack on crankshaft and cylinder score can be diagnosed by diagnosis part.7. In order to calibrate IETVDS,an electronic torsional vibration calibrater is ameliorated . Compare to other kindred products,besides adjustment of speed,the new calibrater can adjust teeth number and voltage of fanout. The new calibrater can also output a pulse one cycle which simulate cylinder top dead center.