A Multiscale Cylinder Bore Honing Pattern Lubrication Model for Improved Engine Friction

Three-dimensional patterns representing crosshatched plateau-honed cylinder bores based on two-dimensional Fast Fourier Transform (FFT) of measured surfaces were generated and used to calculate pressure flow, shear-driven flow, and shear stress factors. Later, the flow and shear stress factors obtained by numerical simulations for various surface patterns were used to calculate lubricant film thickness and friction force between piston ring and cylinder bore contact in typical diesel engine conditions using a mixed lubrication model. The effects of various crosshatch honing angles, such as 30 degrees, 45 degrees, and 60 degrees, and texture heights on engine friction losses, wear, and oil consumption were discussed in detail. It is observed from numerical results that lower lubricant film thickness values are generated with higher honing angles, particularly in mixed lubrication regime where lubricant film thickness is close to the roughness level, mainly due to lower resistance to pressure flow. Although, shear stress values are lower for higher honing angles, significant friction force observed in the expansion stroke with high honing angles is primarily due to metal-to-metal contact and increased viscous shear as a result of lower film thicknesses. It is observed that average asperity contact pressures double with each 15 degrees increase in the crosshatch angle indicating high wear particularly in the ring reversal zones. The results showed that transversal plateau-honing patterns generate resistance to fluid flow and enhance full film hydrodynamic lubrication, reducing friction and asperity contact. However, oil film transported to the combustion chamber also increases with transversal patterns in the complete engine stroke that may result in increased oil consumption.