Theoretical And Experimental Research On Lubrication Performance Of Laser Surface Textured Piston Ring

Piston rings in internal combustion engine play crucial role in sealing gas, lubricating and oil scraping, heat transferring and cooling, meanwhile bearing impact and corrosion of high temperature and high pressure combustible mixture in the cylinder. Thus, lubrication, friction, wear and seal problems have been the core of ring technology research and development. With increasingly stringent requirements for energy-saving and emissions in engine, piston ring technology is highly demanded. Surface texture can effectively improve lubrication performance and reduce friction coefficient of mechanical components. Recently, surface texture technology is applied on the surface of piston ring and become an interesting research area. Therefore, a great amount of theoretical and experimental research on textured piston ring is conducive to the development of high-performance novel piston rings and the technical progress.Based on the first ring of a diesel engine, a mixed lubrication theoretical model of surface textured ring-liner system is established in this paper. Firstly, theoretical mechanism of friction reduction and performance improvement in the textured piston ring is explored and clarified. It is found that, when the textured ring slides on liner surface, the flow and direction of lubricant stored in the texture change suddenly, forming partial uneven pressure distribution, thus generating hydrodynamic pressure effect. In this case, oil film with certain thickness and bearing capacity between the cylinder and piston ring is produced. Then, the lubrication performance of the piston ring textured with circular, rectangular, elliptical dimple is analyzed, in which circular textures in the calculation cycle show good tribological performance, and elliptical ones show relatively poor friction reduction effect.Then parametric optimization was performed on the basis of circular textures. Different texture structural parameters were considered on the effect of ring lubrication performance. The results show, the effect of dimple area density on lubrication properties can be ignored, dimple diameter has certain influence, and dimple depth influence most significantly. Then more calculation and analysis for the varying dimple depth was conducted, and compared with the same depth texture. It is indicated that ring with varying depth cavities can meet the lubrication conditions of different working environment in central stroke and TDC area. It is also found that the depth layout of shallow depth on the two ends and deep one on the central part reduced more friction than the opposite one. This is because lubricant stored in the deep cavities volume moves with rough surface, flowing into the shallow holes, and oil file is compressed due to cavities volume changing from large to small. Also, macroscopic hydrodynamic pressure is formed similar to barrel shape.According to the theoretical analysis of the potential value of the derived variable depth textured ring, new and difficult requirements for processing of variable depth textured ring is proposed for determining reasonable process sequence and the relations between dimple parameters and the laser processing parameters. Under the conditions of reasonable single pulse energy and pulse repetition, the dimple diameter is only related to the single pulse energy, and the dimple depth only determined by the pulse repetition frequency.Eventually, tribological performance of the laser textured piston ring is mounted on the diesel engine and verified experimentally by motored engine. In the testing, the friction torque of uniform depth textured ring is lower than that of the barrel shaped ring when the speed is higher, especially for speed of 2100r/min, the reduction for uniformly textured ring approaching peak of 2.88%. But for low speed case, friction torque of uniformly textured ring increased significantly, which also verifies uniform depth on ring face cannot meet the complicated working conditions of this tribo-pair in the whole engine cycle; The tribological performance of cylindrical ring with variable depth pits scheme was significantly improved compared to that of the barrel shaped ring within high speed range with the greatest reduction in friction torque of 6.12% at 2100r/min. When the engine operates on low, the friction torque of variable depth textured tribo-pair was equal to the original one. Therefore, the variable depth textured ring has better overall lubrication performance than that of the barrel shaped ring.