边界润滑下表面涂层对活塞裙摩擦学性能影响研究

Study on the Influences of Surface Coatings under Boundary Lubrication on the Frictional Performance of a Piston Skirt

为研究边界润滑条件下表面固体润滑涂层对活塞裙摩擦磨损性能的影响,从而为高强化内燃机活塞裙涂层的设计提供支撑,采用自制往复式摩擦磨损试验机,设计活塞裙–气缸套试样级试验,开展38CrMoAl镜面氮化气缸套分别与石墨、二硫化钨涂层活塞裙(铝硅合金基体)的摩擦磨损试验,获得了不同工况条件下两种活塞裙–气缸套配副的摩擦系数和磨损量结果,并分析了磨损表面情况。结果表明:在所有试验工况下,二硫化钨涂层活塞裙磨损量、摩擦系数均小于石墨涂层活塞裙。在15、25、35 MPa三种强化负荷试验条件下,随着负荷升高,摩擦系数和磨损量整体呈现上升趋势;试验温度由120℃升高到150℃时会促进润滑油中二烷基二硫代磷酸锌(zinc dialkyl dithiophosphate,ZDDP)添加剂的分解,摩擦系数和磨损量总体呈下降趋势;在35 MPa条件下,试验温度由150℃升高到180℃时,摩擦系数和磨损量会再次升高,在高温高载作用下,活塞裙基体硅颗粒露出引起的磨粒磨损程度增加。

The effects of surface solid lubricating coatings on the friction and wear performance of piston skirts under boundary lubrication conditions were studied,so as to provide supports for the design of piston skirt coatings for high-duty internal combustion engines.A self-built reciprocating friction and wear testing machine was utilized for conducting wear experiments with real cylinder liner and piston skirt samples.38CrMoAl steel mirror nitride cylinder liners and two types of coated pistons,namely graphite and tungsten disulfide coated pistons(aluminum-silicon alloy matrix)were used in the experiments.The friction coefficient and wear of the two piston skirt-cylinder liner pairs were obtained under different working conditions,and the wear surface was also analyzed.The results show that under all working conditions,the wear amount and friction coefficient of the tungsten disulfide-coated piston skirts are smaller than those of the graphite-coated piston skirts.Under the three loading conditions of 15,25 and 35 MPa,the friction coefficients and wear amounts show an upward trend for both friction pairs as the load increases.When the test temperature increases from 120℃to 150℃,the decomposition of zinc dialkyl dithiophosphate(ZDDP)additive in the lubricating oil is promoted,and the friction coefficient and wear decreases.Under the load of 35 MPa,the friction coefficient and wear amount increase again when the test temperature increases from 150℃to 180℃.It is considered that the abrasive wear caused by the exposure of silicon particles in the piston skirt increases under the combined action of high temperature and high load.