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Purpose – This study aims at proposing an approach for optimizing the shape of the top piston ring face for minimum friction force using an inverse method. The shape of the top piston ring face determines the amount of oil distribution in the interface of the ring and liner. Therefore, the shape has a significant impact on the tribological performance of this interface. Design/methodology/approach – The shape of the ring face is represented by a polynomial function and is based on the load analysis of the ring. The optimization of the shape was performed using the Sequential Quadratic Programming method. The minimizing of the friction parameter at the interface was considered during the solving process to obtain an optimum ring shape. Findings – The optimized high degree of the shape of the ring face could lead to a reduced friction parameter. The proposed method could be applied for the tribological design and optimization of the piston rings. Research limitations/implications – There still need effort to investigate the effect of design parameters (e.g. property of lubricant)on the optimization of the ring face. Originality/value – The subject matter is important and the method has practical value. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to study the real-time change of surface roughness at different small regions of piston rings during running-in process. Meanwhile, the effects of real-time change of the rough surface topography on the lubrication and friction of piston rings are investigated. Design/methodology/approach – An uneven wear model has been developed to research the running-in behavior at the different small regions of piston rings. The model is verified by comparing the simulation results with the experimental results on a reciprocating friction and wear test rig. Findings – This research shows that the wear process of piston ring surface is uneven during running-in. At most time of the operating cycle except the vicinity of top dead center and bottom dead center, the minimum oil film thickness ratio increases while the friction force and power loss decrease after the running-in period. Originality/value – Through this research, the running-in behavior of piston rings is investigated in detail. The interaction between the running-in and the lubrication and friction of piston rings is understood more deeply. [ABSTRACT FROM AUTHOR]