The first electric motor in the world was made by Michael Faraday over 160 years ago and it was axial flux yet almost all traction motors have been radial flux ever since. That in the 60,000 rpm GKN kinetic energy recovery system KERS in London buses is one of the few exceptions. Nowadays, attention is turning to the development potential of axial flux, which gives pancake formats useful in in-wheel motors for example. At EVS29 in Montreal June 2016, the following paper reflected this for an 1800kg four wheel drive car:
Driving-scenario oriented optimal design of an axial-flux permanent-magnet motor for an electric vehicle
This paper proposes a driving-scenario oriented optimal design of an axial-flux permanent-magnet (AFPM) motor for an electric vehicle. The target torque and speed (TN) curve is defined as three operation zones-constant torque, maximum direct current, and maximum voltage—based on the driving scenario. The AFPM motor is designed to minimize energy consumption based on the motor weight and the frequent operating points of a driving cycle. The final result shows that the electric vehicle driven by the proposed AFPM motor consumes about 15% less energy than motors designed using traditional methods.
In conclusion, the authors said:
This paper proposed a systematic, driving-scenario oriented, multi-objective optimal design process of an AFPM motor for a four-wheel-drive EV. The driving scenario, the modulation method of the motor drive, and basic torque and voltage equations of the motor were used to provide basic information for building a range of target TN curves for three operation zones—constant torque, maximum DC current, and maximum voltage. Thus, the back EMF constant, phase inductance, and phase resistance were used to size and optimize the proposed motor using a quasi-3D magnetic circuit model. The systematic optimal design process for a preliminary motor design was fast and accurate, as verified through FE analysis. First, the resulting TN curve was found to match well with the target TN curve. The corresponding efficiency maps of the FE and magnetic circuit methods were also found to be similar, with a difference of less than 3%. Second, the energy consumption of the proposed motor was 15% less than the energy consumption of the motor designed using a traditional method, which optimized the motor efficiency only at its rated operation point. Finally, the water-cooling duct was designed so that the motor dissipated energy loss during the operation. Moreover, the temperature response and steady-state temperature distributions were investigated, and it was proven that the proposed motor can be operated safely for a continuous driving mode.
For more see the new IDTechEx report, Electric Vehicle Traction Motors, Belt Driven & Integrated Starter Generators 2016-2026.
Top image of Michael Faraday: Wikipedia
