Design And Experiment Research On Variable Compression Ratio Piston

Accompanied by the increasing requirements on emissions and fuel economy, the modern engines have been pursuing lower fuel consumption, higher performance, lower pollution, longer life, diversification and new structures. Nevertheless, the problems of the poor performance of the engines at low load conditions, and at the idle condition and at starting condition are not well resolved. Therefore, the current research on engines focus on low energy consumption and low emission.In this study, a VCR (Variable Compression Ratio) piston, which is the piston with a VCR mechanism, is introduced. The project selection and the structural design of the VCR piston are discussed, and the parts of the mechanism are machined. The validation of the technical feasibility of the VCR piston is conducted against static simulation test and dynamic simulation test.The VCR piston consists of the piston head, piston skirt, and a VCR mechanism installed between them. There is higher compression ratio for the VCR engine in advance, allowing the VCR engine with higher compression ratio runs at low load conditions to improve the economy, and to reduce the emissions. And at high load conditions, the VCR piston enables to control the explosion pressure in the cylinders to ensure the reliability of the engine.The design of the VCR piston includes several jobs such as the selection of the elastic elements, and the design of the displacement mechanism with a variable arm, and the design of the auxiliary mechanism. The force analysis of VCR piston has been performed theoretically. The relationship of the position and the geometric dimensioning among the parts VCR piston are initially identified. The calculation and comparison of the elastic elements are discussed, and the types and combination of the disc spring are selected. The basic dimensions of auxiliary mechanism are determined and verified. All parts’drawings are finished, and the requirements for the parts’machining and heat treatment are presented.Several experiments of the VCR mechanism have been conducted. The static mechanical simulation tests are carried out by means of a hydraulic universal testing machine in order to inspect if the structure of the VCR piston is reasonable, and if the components of the VCR piston are reliable. The dynamic simulation experiments are conducted with MTS testing machine in order to examine the stability and deformation of the elastic mechanism under dynamic loading.Experimental results show that:the proposed technical solution of VCR piston mechanism is reasonable and practicable, and the control strategy of VCR can be achieved. The VCR piston is basically stable and reliable, and the design of the parts and components can fulfill the requirements.