Research On Lubrication And Anti-wear Mechanism Of Low Friction Heat Treatment Technology And Application For Piston Assembly

As one of the key components in the internal combustion engine,piston assembly is the biggest source of engine mechanical loss,and its work efficiency and operation condition have great influence on the comprehensive performance of the internal combustion engine.With the continuous upgrading of fuel consumption standards and emission regulations,the technology demand for energy saving and emission reduction of internal combustion engines is becoming more and more prominent,which sets higher requirements for the technology of piston components.In this paper,the application of a low friction heat treatment technology on a diesel engine is studied.The application potential of the technology is discussed through the analysis of physical and chemical characteristics of the piston assembly,the mechanical properties test,the basic tribology test,the related theoretical calculation,the small fit clearance design and the engine installation verification.First,the physical and chemical properties of material surface after the low friction heat treatment of the piston assembly are analyzed.The scanning electron microscopy analysis found that the surface of component specimen has a transition coating with a thickness of about 40?m,mainly composed of C,O,Si,P,Cr,Mn,Cu,Mo,S,La,V and other elements.At the same time,Mo,S,La,V and other elements were detected in the matrix material,and the penetration depth was about 30?m.The microstructure of piston ring matrix remains unchanged,the hardness of ring surface is increased,the hardness of the chromium layer in ring face is unchanged,and the linear expansion coefficient decreases by 5-8%.The silicon phase grain in the piston sample is refined,the surface hardness is reduced,and the linear expansion coefficient decreases by 13-15%.In the rotary tribological test of different material plate specimens,it is found that the friction coefficient of the aluminum alloy specimen is obviously reduced after heat treatment,the maximum decrease is 30%,but its wear resistance is slightly weakened;the friction coefficient of the steel sample is basically unchanged,and its wear resistance is obviously higher;the friction and wear properties of cast iron sample varies little.The reciprocating friction test of the piston component samples is further carried out.The friction coefficient of the piston ring and cylinder liner is slightly reduced;the friction coefficient of the piston cylinder liner is obviously reduced,especially in the small load and the high frequency condition,and the decrease is more than 40%.The basic tribological tests show that the transition coating formed by low friction heat treatment has the effect of lubrication and antifriction,in which the polymer formed by S,La and other elements improves the tribological properties of surface.Secondly,the theoretical calculation model of lubrication and dynamics of piston assembly with low friction heat treatment is established by Ricardo-Pisdyn&Ringpak software.The calculation results show that the friction power of piston ring and cylinder liner is reduced by 8%,and the wear of piston ring is reduced.Then friction power of piston skirt and cylinder liner is reduced by about 13%,the wear change of thrust surface of skirt is smaller,and the wear area and load of the anti-thrust face are increasing.According to the linear expansion change of the piston assembly material after heat treatment,the design and optimization of the coupling clearance(closed gap and cylinder clearance)of the heat treatment and low friction heat treatment is carried out in this paper.It is found that the improved piston assembly scheme has the comprehensive function of reducing friction and wear resistance after the optimization.Finally,the final performance test of the piston assembly after optimization is carried out in a diesel engine.The results show that the towing power decreased to a maximum of 16.36% after the optimization,the fuel consumption rate on the external characteristic curve is reduced,the maximum drop is 2.78%,and the coverage range of low fuel consumption area in the universal characteristic curve has a wider coverage.Meanwhile,the cylinder sealing performance of the whole machine is better,and the piston blowby and oil consumption are all decreasing,and the cylinder gas pressure has been improved.