This paper studies the effect of design improvements generally prescribed for the piston pin hole on induced stresses with the help of finite element analysis techniques. This decade has seen a very significant increase in the load rating of internal combustion engines. The engines develop a pressure to the tune of 180 bar and more, which needs to be supported by the pin hole, which rests on the piston pin. Predictions of the effect of the increased load on the pin hole and design modifications to support the higher load have become very important activities during the course of piston development. Two design modification options are studied in this paper. The first modification is based on reducing stress concentration by suitably machining a taper profile for a pre-calculated distance at the inner boss zone. The second modification is carried out by having pin hole longitudinal relieves, popularly known as lube slots. Any modification carried out in the pin hole has an influence on the stress distribution at the bowl zone. Therefore, in addition to the pin hole stress, a thorough study on the stress distribution in the bowl zone is also carried out. The numerical results obtained for the modified designs are compared with the base line configuration and the effects of the modifications are discussed in detail. The modifications are found to have a significant effect in reducing the pin hole hoop stress, which is tensile in nature. But at the same time, it has been observed that the tensile hoop stress value in the bowl area increases. Therefore, it is concluded that the suggested pin hole improvements can be carried out if the induced hoop stress values do not exceed the prescribed values for the selected material. Further studies were made to analyze the influence of thermal loading on the stress induced and also to analyze the influence of combined (mechanical and thermal) loading on the induced stress. The thermal hoop stress were compressive in nature and hence its influence on the combined loading is significant. In this paper the results are normalized and shown as tables and figures.

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