Study On Frictional Vibration Of Diesel Cylinder Liner-Piston By Using Quantification Analysis Methods

Excess weardown of the cylinder-piston ring pair in diesel engine is one of the main causes of engine failure. A great deal of qualitative study on cylinder - piston ring's friction, wear and lubrication has been conducted by researchers, using surface topography analysis and oil analysis techniques. However, it is difficult to achieve quantitative, continuous, real-time and on-line monitoring and assessment of friction and wear state.Frictional vibration, containing a wealth of information about the interface's fault state and friction wear state, would be produced inevitably in the process of mechanical friction and wear. And on-line monitoring of friction and wear state can be achieved with the collection and analysis of frictional vibration, without affecting the normal operation of contact surface. The key point is to extract the characteristic parameters of frictional vibration signals for quantitative characterization of frictional vibration. Study of this problem has been conducted by many scholars and researchers, and series of methods have been proposed. However, accurate and effective extraction of frictional vibration's characteristic parameters is difficult to achieve. Therefore, research on quantification method of frictional vibration has significant meaning in engineering application value and theoretical study importance.Firstly, the study on frictional vibration signals produced by cylinder and piston ring samples sampled from 6S50MC marine diesel engine under different lubrication statuses were conducted at MMW-1 vertical universal friction and wear testing machine. A method called secondary image analysis in this thesis was developed to extract features of frictional vibration signals, using continuous wavelet transform (CWT) time-frequency image (TFI) and image processing in order to quantitatively describe and evaluate the running-in process of cylinder liner - piston ring under tester condition. TFIs were generated by CWT theory from the vibration signals and characteristic parameters were obtained by image segmentation of TFIs. Study in testing machine showed that: characteristic parameters of different conditions present significant differences. And they can comprehensively reflect friction and wear state of the cylinder- piston ring. Characteristic parameters V, Gmean, Hv, Mtf, N and e were extracted, and characteristic parameters V, Gmean, Hv and N describe the complexity and intensity of wear behavior, and parameters Mtf and e show the state of the worn surface. The CWT TFI characteristic parameters of cylinder-piston ring frictional vibration signals can be used to quantitatively describe vibration signal characteristic.Secondly, frictional vibration produced by cylinder-piston ring of motoring diesel engine was studied based on harmonic wavelet analysis and secondary image analysis. The characteristic parameters of frictional vibration were extracted and analyzed. The study results show that:Harmonic wavelet analysis method can effectively filter out the strong background noise, and extract weak signals. Reciprocating inertia impact signal was filtered out, and the weak target of frictional vibration was isolated from a 4100 diesel engine vibration signal under motoring condition. With the motoring condition, variations of characteristic parameters V, Hv and N can sensitively reflect uncompressed cold running-in process of 4100 diesel engine under conditions of different speed and lubrication, can describe the working state of piston ring with different piston ring breaking failure, and can characterize the cylinder scoring process of 4100 diesel engine under dry friction conditions. The CWT TFI characteristic parameters V, Hv, N and e of 4100 diesel engine frictional vibration signals can be used to quantitatively describe vibration signal features under motoring condition.In summary, experimental research and discussion on quantitative analysis of frictional vibration produced by diesel engine cylinder - piston ring were carried out. And secondary image analysis theory was developed to extract characteristic parameters of frictional vibration signals and to quantitatively characterize the vibrations and wear behavior of diesel engine cylinder-piston ring effectively. This provides a new way for the evaluation of cylinder-piston ring friction and wear process using vibration signals.