ABSTRACT
Some researchers found the relationship between the resonance frequency of an in-wheel motor (IWM) drive system and the tire-road friction coefficient (TRFC), and used it to estimate TRFC. This paper tries to establish a similar relation between the road condition and the electric power steering system (EPS) frequency response, by analysing the dynamic characteristics. System modelling is conducted by coupling a lateral-relaxation-length based dynamic tire model and a simplified motor model. Then detailed analysis of the system dynamics in the frequency domain is provided by a deduced frequency response function, considering different system parameters, such as longitudinal velocity and the gear ratio. As a result of analysis, a function of the system resonance frequency (RF) which is related to TRFC is presented. Comparison of the RF is made between EPS and IWM to propose a TRFC estimation idea based on frequency domain data fusion. The correctness of the RF equation is demonstrated using a simulation model.
