Influence of numerous start-ups and stops on tribological performance evolution of engine main bearings

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For main bearings of internal combustion engines, most of the wear occurs during the start-ups and stops. The popularity of the start–stop system in automobile engines, which is used to save fuel consumption during idling stage, makes the working condition of main bearings severer because more frequent starts and stops will be generated. Changes in the bearing surface caused by wear will directly affect the bearing’s working performance. So in this study a transient mixed lubrication model and a wear model are coupled to analyze the influence of numerous start-ups and stops on the tribological performance evolution of engine main bearings. Starved lubrication of bearings before the oil supply is considered. The wear process is studied on the scale of surface topography and geometry. A main bearing in a four-stroke four-cylinder gasoline engine is studied under engine start–stop cycle conditions. The effects of temperature and lubricant grade on the transient tribodynamic behavior during the start-ups and stops are first investigated. Then the evolutions of surface characteristics and tribological performance of main bearings after numerous engine start-ups and stops are simulated. Results show that the temperature and lubricant grade can significantly affect the friction and wear of bearings. Hot start–stop condition leads to more serious asperity contact friction in the early stage of start-up, while cold start–stop condition generates more friction loss. The wear process of bearing surface is faster when applying oil with lower viscosity. And the impacts of engine start-ups and stops on bearing working performance are mainly seen in contact friction.