Friction Characteristics of Piston Pin Made of Carbon/Carbon Composite Under Starved Lubrication

Abstract Some high-power density diesel engines employ unstable splash lubrication for connecting rod small ends, driven by structural strength considerations. However, the shrink-fitted bushing may loosen as a result of the high temperatures generated under starved lubrication. This article investigates the friction characteristics of piston pins made of carbon/carbon (C/C) composites under starved lubrication. The coefficient of friction, bushing temperature, and surface morphology were analyzed. Three piston pins made of C/C composite were graphitized at different temperatures and then tested. The results indicate that C/C composites, predominantly composed of smooth laminar pyrolytic carbon, exhibit lower temperatures and coefficients of friction while maintaining surface stability. The friction characteristics of the C/C piston pin were then compared to those of an AISI 4120 piston pin. It is found that the C/C piston pin has a lower coefficient of friction and superior anti-seizure capacity at high swing frequencies. This not only effectively reduces bushing temperature but also avoids significant friction forces generated by severe adhesion, helping prevent bushing looseness. These results offer valuable insights for the design of friction pairs under starved lubrication.