Friction and Lubrication Characteristics of Piston Pin Boss Bearings of an Automotive Engine

The aim of this research was to analyze the lubrication conditions of piston pin boss bearings used in the press-fit piston pins of automobile gasoline engines. An original pin boss friction measuring device was developed and used to successfully obtain measurements. It was revealed that the friction force peaks twice every cycle at high engine loads, and non-fluid lubrication characteristics are displayed. The friction forces for various differing piston pins and pin boss bearings were analyzed, and it was shown that reducing piston pin length or thickness to reduce piston weight, or reducing the pin boss bearing clearance to reduce noise worsen the friction characteristics and increase the possibility of abnormal bearing friction as well as seizure. In order to improve the friction force and friction characteristics, the effectiveness of reducing the surface roughness of pins, the use of an oil feed groove in the bearing part, and bearing material were investigated, and it was shown that friction can be substantially reduced, especially by changing the bearing material.