Mid Michigan Research (United States)

In recent years several efforts have been made to model piston secondary dynamics in an attempt to assess piston performance accurately. In all these efforts, piston translation along the wrist-pin was ignored, and the piston land interactions with the cylinder bore were not considered. In this paper the authors present a model for piston secondary dynamics that considers piston translation along the wrist-pin and piston land interactions with the cylinder bore. A previously developed piston finite element program has been refined further to incorporate piston secondary dynamics. As its predecessor this model uses a full piston model to perform the analysis over a four-stroke cycle. The model is capable of considering an elastic skirt with deformations induced by thermal, inertial, combustive, hydrodynamic and contact effects. In the current model only the interactions of the second land with the cylinder bore are considered. Unlike the skirt, the land is assumed to be rigid. A brief discussion on the model development is presented. Piston secondary dynamics, hydrodynamic and contact forces, and piston wear results are shown. A comparison is made between the results obtained via three different piston secondary dynamics modeling approaches; no translation along the wrist-pin, translation along the writ-pin, and translation along the wrist-pin as well as second land-cylinder bore interactions.

<div class="htmlview paragraph">Elastohydrodynamic lubrication, piston dynamics and friction are important characteristics determining the performance and efficiency of an internal combustion engine. This paper presents a finite element analysis on a production piston of a gasoline engine performed using commercial software, the COSMOSDesignStar, and a comprehensive cylinder-kit simulation software, the CASE, to demonstrate the advantages of using a reduced, parameterized model analysis in the assessment of piston design characteristics. The full piston model is parameterized according to the CASE specifications. The two are analyzed and compared in the COSMOSDesignStar, considering thermal and mechanical loads. The region of interest is the skirt area on the thrust and anti-thrust sides of the piston. The results are compared with the CASE results and a discussion follows on how the piston model simplification approach can help significantly reduce computation time without losing valuable information on piston performance. The piston characteristics are evaluated with the reduced model thus allowing for a faster analysis and optimization than would be possible with a complete FEA piston model. The results demonstrate that the simplified model agrees qualitatively and quantitatively with the full model; the maximum temperature and calculated distortions on the skirt face are comparable. Computation time difference between the full model and simplified model is not significant for a single analysis; however it becomes very significant when a cyclical analysis is performed at every crank angle degree.</div>