A Study On Transient-State Model Of Piston Secondary Motion And Piston Skirt Tribology Behaviours In IC Engine

With increasing public concern about the environmental problems and oil prices, improving fuel economy and reducing engine emissions in modern passenger car engines has become one of the important trends in engine design. It is currently estimated that the piston - cylinder bore friction accounts for up to 25% of the power loss in a typical engine. Therefore, a significant reduction of the piston group friction will lead to considerable improvements of fuel economy and engine emissions. The piston secondary motion has a significant influence on the lubrication in piston - cylinder system. Therefore, better understanding and more accurately modeling piston dynamics plays an important role in piston design for the reduction of friction to improve fuel economy and reduce exhaust emissions. However, existing study on piston secondary motion does not consider the effects of engine dynamics and engine inertia variation on piston secondary motion and piston skirt tribology behaviors, and the existing secondary motion model cannot be used for transient analysis. based on developing a new engine dynamics-piston secondary motion coupling model, this thesis do some deep and comprehensive study on piston secondary motion and piston skirt tribology behaviors. the main work involves:a new engine dynamics-piston secondary motion coupling model is developed which could mathematically describe the interaction between engine inertia variation and piston secondary motion, and this new model can be used for transient analysis.The Average Reynolds Equation is used to describe lubrication behavior of the pistion secondary motion. In terms of piston skirt lubrication, a simplified 1-D Reynolds equation is developed for fast and accurate calculation.The model implementation procedure is established for simulation. Numerical simulation have been conducted with a four stroke single cylinder gasoline engine. The simulation result shows: 1.the effects of system inertia variation on the friction and lubrication behavior cannot be ignored. inertia variation make the piston secondary motion more severe and increases the piston skirt friction and friction loss. 2. The center-of-mass (COM) of the connecting rod have considerable effects on the piston skirt friction and friction loss. 3. With the increase of engine speed, amplitude of the piston secondary motion decrease and piston skirt friction loss increase. 4.With the increase of engine speed, engine inertia variation has a deeper influence on piston secondary motion and piston skirt Tribology behaviors.