A study on optimal design and fatigue life of the common rail pipe

To support the latest automobile technology, the next generation of diesel engines is expected to require higher injection pressures than the third generation which can operate at high injection pressures up to 1,800bar. A component in the common rail system, the common rail pipe must have higher strength because it is directly influenced by the high-pressure fuel. Preform design is very important for preventing the head of the common rail pipe from folding in the heading process. In this study, the angle, curvature and outer diameter of the die and the length of the trapped part are selected as main parameters in the design of the optimal preform shape that minimizes the radius of folding. The optimal design is carried out by finite element analysis and the Taguchi method using the main parameters and then fatigue-life analysis is preformed for predicting fatigue life according to the amount of folding. Also, a closed form equation to predict fatigue life was suggested by Goodman theory and life-prediction method for pressure vessels pursuant to ASME Code. In order to verify the reliability of common rail pipe, fatigue-structural coupled field analysis is performed. The results of the finite element analysis were in good agreement with those of the experiments at the actual site and theoretical analysis.

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