A mixed lubrication model of textured cylinder liner-piston ring was built to investigate the effects of four array modes namely, square array, stagger array, stretching, and shortening along liner axis array of micro-dimples on the tribological properties of cylinder liner-piston ring pair. The simulation results indicate that micro-dimples can enhance the hydrodynamic effects of lube oil, improving the film bearing capability. However, the effects differ significantly under the four dimple array modes: for square array, the cylinder liner-piston ring pair is well lubricated due to the synergistic effects of uniformly spaced micro-dimples that form homogeneous bearing film even around the fired top dead center where the lubrication condition is harsh; while the film of stagger array is the thinnest among the four schemes, which means its lubrication is also the worst. From square array mode, to shortening and stretching along liner axis array, then to stagger array mode, the total friction force of cylinder liner-piston ring shows an upward trend. By utilizing laser surface texturing method, square array, stretching along liner axis array, and stagger array of micro-dimples were textured on the gasoline engine cylinder bores, followed by a set of engine bench tests. The experimental results demonstrate that the engine motored torque of the three array modes increases in turns, which validates that the anti-friction effect of square array is optimal whereas that of stagger array is the most inefficient.
Purpose
This paper aims to find out the tribological performance and self-lubricating mechanism of the laser-textured surface filled with solid lubricant in rolling friction pair.
Design/methodology/approach
The textures on the surfaces of GCr15 bearing steel were produced by acousto-optic Q diode-pumped yttrium aluminum garnet laser with the technology of “single pulse one time, repeating at intervals” and filled with composite solid lubricant. The tribology tests were conducted on the MMW-1A universal friction and wear testing machine.
Findings
It was found that the solid-lubricated micro-textured surface can reduce the friction coefficient effectively. The MoS2/PI composite solid lubricant works better than the single MoS2 solid lubricant, and the ratio of PI/MoS2 + PI at 20 per cent is the best recipe. The friction coefficient of the sample surfaces decreases first and then increases with the increase in texture densities, and a texture density of 19.6 per cent has the best effect on friction reduction. The friction coefficient of the textured surfaces gradually decreases with the increase in both rational speed and load. For the same texture density, the friction coefficient of textured surfaces decreases slightly with the increase in diameter. Furthermore, the mechanism of “rolling-extrusion-accumulation” occurred on the textured surface can collect the solid lubricant, thereby, improve the effect of lubricating and anti-friction.
Originality/value
The results of the experimental studies demonstrated the application prospect of laser surfaces texturing combined with solid lubricant in rolling friction pair.
A combination technology of the solid lubricant and the laser surface texturing (LST) can significantly improve the tribological properties of friction pairs. The plate sample was textured by fiber laser and composite lubricant of polyimide (PI) and molybdenum disulfide (MoS 2 ) powders were filled in the microdimples. Sliding friction performances of micron-sized composite lubricant and nano-sized composite lubricant were investigated by ring-plate tribometer at temperatures ranging from room temperature (RT) to 400 C. On the one hand, the results of the micron-sized composite lubricant show that the friction coefficient of the textured surface filled with composite lubricant (TS) exhibits the lowest level and the highest stability compared to a textured surface without solid lubrication, smooth surface without lubrication, smooth surface burnished with a layer of composite solid lubricant. The better dimple density range is 35-46%. The friction coefficients of the sample surface filled with micron-composite solid lubricant with the texture density of 35% are maintained at a low level (about 0.1) at temperatures ranging from RT to 300 C. On the other hand, the results of the nano-sized composite lubricant show that these friction properties are better than those of MoS 2 -PI micron-sized composite. The friction coefficients of MoS 2 -PI-CNTs nano-sized composite solid lubricant are lower than those of the MoS 2 -PI composite lubricant at temperatures ranging from RT to 400 C. In addition, the possible mechanisms involving the synergetic effect of the surface texture and the solid lubricant are discussed in the present work.
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