Research On Multi-physical Coupling Nonlinear Problem And Improved Design Of Ring-pack Lubricating Oil Consumption

The design of piston group exerts great impact on vibration noise performance, friction loss and emission performance of internal combustion engine. This dissertation focuses on multi-physical nonlinear problems of the piston group experimentally and numerically, improves the design of piston group, and solves practical engineering problems based on a diesel engine.This dissertation mainly consists of two parts. The first part investigates the mechanical characteristics of piston group. The temperature field, strength and high cycle fatigue problems of the piston are studied systematically. The calculation model for the piston thermal boundary condition is established and calibrated by test data. The3d coupling strength analysis model for piston group is built, analyzing the piston stress and radial deformation condition under various loads and predicting piston high cycle fatigue results. The dynamic simulation model for piston secondary motion is built, analyzing the slap of piston on cylinder liner and its evaluation index, and the influence of piston parameters on its secondary motion characteristics. This dissertation systematically investigates the transmission path of piston excitation and engine structure characteristics and designs innovative experiments to explore the transmission path between piston and gas excitations, to analyze the inherent properties of engine components and the whole engine, and to study the effects of main excitations on the vibration and noise radiation of engine, which provides reference for engine low noise design.The second part investigates the sealing of piston group and subsequent lubricating oil consumption (LOC). The sealing principle of piston ring pack and the theory of piston ring dynamics are carried out, and the simulation model for ring pack sealing characteristics and ring dynamics is established, analyzing gas flow characteristics of piston ring surfaces and verified by flow-by test. The total LOC and flow-by of engine are obtained through the LOC experiments by weighing method, then the relationship between engine working conditions and LOC is gotten. The generation mechanism of LOC and related theory of ring-pack are expounded, and the LOC predication model for ring-pack is established and calibrated by the test data according to the method proposed in this dissertation. In addition, through the calibrated simulation model, the LOC under different working conditions is predicated and the influence factors of LOC are studied. Combined with simulation results, the size of piston land and skirt profile are modified, and the first ring is modified in order to reduce the engine LOC. The comparison test of many sample engines shows that the LOC of modified engine drops significantly, satisfies the design requirements, and fits the CAE predication very well.The studies in this dissertation expand the researches on multi-physical nonlinear problems of the piston group of internal combustion engine, improve and enrich the structure design of piston group using the numeral simulation technology, and achieve several innovative models with great engineering application value, which provides important reference for piston ring low noise, low friction and low LOC design.