Abstract: Function decomposition is adopted in engineering design, and the heart of functional decomposition uses the principle of bond graphs. It decides physical parameters by analyzing functional relations in engineering design system; It establishes the transform model of the system according to energy transmit and changes it into functional parameter transform matrix, then reasons out a function means tree by additional constraints; it founds system matching component base, gives evaluation factors and decides matching relations; Finally, showing special plasticbox sealing and cutting machine as an example, a critical technology is discussed about the automatic production of function means tree, and multi – solution production and evaluation by means of software.

Key words: Bond graphs, Function means tree, Mechanical product design, Transform matrix, Compensation, Hysteresis behavior, Linear motor, Thermal deformation