Effect of Waviness Contact on Sliding Friction of the Piston-Cylinder System in Mixed Lubrication

The piston-cylinder is the main component of the transmission of energy in the vehicle's engine, but it represents a significant source of unavoidable friction, which negatively affects engine performance by reducing piston lifespan and increasing fuel consumption. To determine the effect of lubrication performance and asperity contact on the tribological characteristics, mainly on the friction generated by asperity sliding contact, a numerical model of a real piston cylinder operating in mixed lubrication was developed. The mixed lubrication analysis shows the necessity to take into account the elasticity of the piston skirt-cylinder as well as for cavitation to ensure the consistency of the results. The sliding friction, resulting from the Johnson contact model, is developed, with a new approach, according to the Bowden-Tabor friction model. An experimental method is employed to determine the coefficient of the sliding friction. The results show that the tribological characteristics—contact pressure, sliding contact friction, energy loss, and the coefficient of sliding contact friction—are influenced by the waviness of the contact surface. When the amplitude of the asperities increases from 12 to 16 µm, the coefficient of the sliding friction and the corresponding contact energy loss increase from 0.128 to 0.16 and from 0.054 J to 1.126 J, respectively, representing 25% to 78% of the total energy loss.