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As the quick development of Chinese vehicle market, more and more vehicle manufacturing plants were founded in China. Engine, as one of the most important components of vehicle, has been equipped with advanced production line and made in large quantity. However, in many domestic engine plants, designer mainly borrows ideas from old experience regardless of actual production condition. Meanwhile, producer only cares about the tolerance control plan, no considering the influence of quality of product on engine performance. There is no good combination between engine design and production, thus the tolerance of some components is too small, which results in high rejection rate and high cost, while the tolerance of other components is too large , resulting in bad assembly quality and big performance fluctuation.Based on the above problems, the influence of key dimension tolerance on engine performance is analyzed in this thesis. Be aimed at an engine , the sensitiveness of key dimension tolerance to compression ratio is researched, the BOOST simulation model is constructed, which is proved by bench test, then the correlation between compression ratio and engine performance is obtained. Thus the correlation between key dimension tolerance and engine performance is obtained and the engine performance fluctuation is analyzed. In addition, the actual fluctuation of key dimension which affects compression ratio is analyzed and tolerance-cost model is deduced, the tolerance optimization program is raised. Finally, the impact of key dimension on friction power loss is researched specially with regard to piston assembly, which provides theoretical basis for tolerance design and optimization of an engine.
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