Abstract: After systematic analysis of function description methods, an extended function modeling strategy for product conceptual design is proposed. The extended functional basis model as well as its ontology representation strategy is given. The function-connecting model including the logic relationship model, the semantic relationship model and the composition relationship model is established. The idea of introducing extended function structure units into conceptual design stage is proposed. The proposed function structure units are strongly connected parts aggregations, which are obtained by extracting the essential characteristics of parts regardless of their concrete structures. The combinatorial explosion of function-connecting graph in the process of function-structure mapping can be avoided by using those units, as well, those defects which are caused by restricting the product structure too early by the use of conventional structure during conceptual design process can be eliminated. The basic principles for function reasoning are proposed, in which three aspects are involved, they are principles for the solvability of functional unit, positive and reverse rules for functional space expansion. A design example is used to demonstrate the successful and effective application of the proposed function representation method in the conceptual design stage.

Key words: Conceptual design, Extended functional basis, Extended functional structure units, Extended function-connecting models, Function reasoning