| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 91 === Abstract
Oval cross section piston is the most common profile in the present motor industry while designing the piston of engine. However, precision and machining processes for an oval profile are the most difficult things since a cam is introduced to make oval-shaped path during the machining process of piston edge. Since , the cross section of the piston shall be a real circle before and after heating and the strength of some area of the piston should be also considered ,the design of a piston is quite complicated . Therefore, series of analyses and design strategies are discussed in this paper. First, the combustion and thermal conduction phenomena of engine thermal system are analyzed. Engine combustion performance, including gas temperature in combustion chamber and thermal coefficient, are obtained by iteration simulation. Then the finite element model to analyze the temperature distribution of the piston wall is set up. Simulation in different operating conditions of engine RPM, is conducted and the computing result shows that theory analysis is coincident with the experiment data. The thermal deformation analysis is also conducted. From these analysis results, the design of a piston with real circle cross section before and after being heated can be achieved.
The results show us that the thermal displacement caused by heat vary with engine RPM( 800-2200rpm ) and temperature( 134-299c). The ratio of real circle and oval-shaped cross section in this paper is between 75% and 98%. The method of design presented by this research can readily improve the productivity of the engine piston’s manufacture.
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