Abstract: Regenerative braking is one of the key technologies to improve the energy efficiency of electric city bus, but there is no available scientific method to evaluate the effectiveness of regenerative braking for electric city bus. A six-factor contained regenerative braking system efficiency index is introduced based on brake energy flow model of 12 m long electric city bus, a rounded analysis of the influence of aboved six factors on regenerative braking system efficiency is made detailedly. Then a new comprehensive and scientific evaluation index named regenerative braking contribution rate, which takes regenerative braking system efficiency, vehicle parameters and drive cycle into account, is raised to evaluate the effectiveness of regenerative braking system. The evaluation method is helpful to orientate technological approaches to improve the energy efficiency of electric city bus by regenerative braking further.

Key words: Drive cycle, Electric city bus, Energy efficiency, Evaluation method, Regenerative braking, Coupling dynamic stiffness, Frequency response function (FRF), Inverse substructuring, Mechanical assembly