Abstract: The methodology of designing for time-varying performance of products is analyzed to overcome the system degradation of products during running. For complex mechanical products, the following three key problems are presented to be solved. First, a benchmark of working condition or system degradation process should be set up to evaluate time-varying performance of different design schemes. Second, the coupling among different disciplines should be analyzed to simulate the transient system behaviors of products. Third, the degradation process of system structure and performance should be predicted and analyzed to provide information for the design decision. The case study on the internal combustion engine demonstrates that the system wear or other system degradation phenomena influence the system performance obviously. So the key factors related with performance should be found out and optimized on the basis of system time-varying performance degradation analysis. The research indicates that the time-varying performance is vital to complex products and the methodology presented in this paper will lay a foundation for improving the time-varying performance of products.

Key words: Complex products, System degradation, Time-varying performance, Transient system behaviors