| The piston, with highly complicated structure, is one of the key parts of the internal-combustion engine. It motions under high heat and intensive mechanical load with a high speed. Then its working condition concerns directly the working dependability and durability of the engine. In the initial stages of designing, it brings great significance to the optimization and the improvement of the piston and its working dependability to compute and analyze the its heat load, force field and there coupling field (the heat and the mechanical load act on together in conformity with the force field), which contributes to find out the comprehensive stress distribution situation. Currently, while carrying on a design to the piston, the method of separated analysis of heat and mechanical pressure is widely adopted, which pays no attention to the influence of the interactions of the heat and the mechanical load on the piston. Thus, these methods can't be accurate in imitating and computing the transform of the piston on works.Multidisciplinary Design Optimization (MDO) is a kind of design methodology with universal characteristics. It involves the whole process of the system-wide performance and optimization, utilizing the interaction of each part to achieve the highest possible efficiency of the design options or the best possible overall solution which helps to save the time and the cost. Its ideas and purposes are completely consistent with the requests of modern automotive design and the application of the MDO to the design of cars and their parts will definitely brings great practical significance and highly academic value.Supported by the National Science Foundation of Chongqing Science and Technology Department (project No: CSTC 2007BB3407), this paper optimizes the piston with the methodology of MDO, utilizing Energetic Thermodynamics, Elastic-plastic Theory and Finite Element Method to compute the pressure by coupling the heat and the mechanical load, then to insure its intensity request by choosing its structural shape and size, The main research includes:(1) According to the principles of MDO, the piston is regarded as a simplified hierarchic system with two sub-systems including temperature field and pressure field from which the analysis of the piston begins.(2) The piston temperature field, pressure field and their coupling field are computed and analyzed through the means of 3D graphics Solid Works software to build up piston model, which is transmitted into Finite Element software PATRAN by its non-linearity calculator MARC. The results show that stress of piston under both mechanical load and heat load is the same as the stress of piston under mechanical load alone, which fulfill the intensity requirements of piston. The coupling effect of mechanical load and heat load is not obvious.(3) A Searching Strategy of multidisciplinary design which based on Orthogonal Distributing Design of Experiments(DOE) is put forward. After the optimization, the weight of piston decreased 46%, to 272g. The effect of optimization is obvious. The strategy optimizes the quality of the piston and analyzes the sensitivity of design variables of temperature field, pressure field and their coupling field. The effect of the three factors act on coupling stress of piston and that act on mechanical stress of piston are almost the same. Among the three factors, the effect of field of fire is the most obvious one. The three factors have no obvious effect on the temperature of piston. |
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