Research On Friction And Wear Characteristic Of Cylinder Liner-Piston Ring For Diesel Engine In Running-in Period Based On Fractal Theory

Mostly the failure of machine parts consists of wear. For the cylinder liner - piston ring — one of most important friction pairs in diesel engine — as the very hard operating condition, including operation status, environment, stress and movement mode etc., the abnormal wear failure has been produced due to insufficient lubrication. It not only reduces its service lifetime, but also causes considerable economic loss. Therefore, the friction and wear characteristic of cylinder liner - piston ring connects directly with the quality of diesel engine.In this paper, the friction and wear of cylinder liner - piston ring during running-in period has been studied. Firstly, the current research situation of the friction and wear relevant to the friction pairs has been summarized, and the insufficiency was pointed out. The quantitative and semiquantitative analysis method based on the fractal theory in tribological research has been proposed. Then, the simulation experiment of the cylinder liner - piston ring friction pair was carried out. The experiment data such as wear loss, surface roughness, friction moment was measured and picked up. The friction and wear characteristic of the cylinder liner - piston ring during running-in period under different lubrications has been discussed. Then, the identity and difference by means of various methods to appraise the wear process of cylinder liner - piston ring have been evaluated. It was shown that the friction process and lubrication condition can be interpreted by traditional analysis methods. But the characteristic information in different wear steps can be accurately reflected by the analysis methods based on fractal theory. Finally, comparing the different analysis methods, it is concluded that the analysis methods of fractal theory are more accurate than the traditional analysis methods in appraising the friction pairs' characteristic.Generally, the serious wear occurs on the top dead center and bottom dead centerof cylinder liner. In this study the experimental parameters (lead and rotation speed) to be closed to operating state of top dead center and bottom dead center were selected. The different lubrication states were simulated by different lubrication modes such as soaking lubrication and dropping lubrication. Therefore, the results of study can provide the reference for understanding the friction pair's characteristic in running-in period, formulating the rational program of running-in procedure, determining the completion of running-in procedure and appraising the quality of running-in.