A Comparative Analysis of Multidisciplinary Aspects in Exotic Axial Flux Machine Powertrain Architectures Emphasizing Vehicle Dynamics, Efficiency, and Packaging

This paper presents an analysis for evaluating electric machine and reducer specifications in conjunction with a comprehensive assessment of vehicle dynamics and drivability for an axial flux machine. The refence point for this study is a conventional central drive unit comprising a single electric machine, reducer, and differential. Powertrain architectures configured with two axial flux machines integrated as in-wheel drives as well as one axial flux machine mounted perpendicular to the chassis, are examined in comparison to the reference design. The study begins by establishing wheel-level traction force requirements and minimum power demands for a mid-sized vehicle. Subsequently, requisite machine and reducer specifications are derived based on these findings. Additional considerations encompass packaging constraints and efficiency thresholds. The reference E-axle design adopts a single-stage planetary gearbox, while the perpendicular mounted machine is connected to a bevel gear reducer. The direct in-wheel drive eliminates the need for a reducer. These powertrain architectures undergo a comparative analysis within a vehicle dynamics simulation environment. The vehicle model has six degrees of freedom, along with models for suspension, tires, and roads. Efficiency assessments are conducted using the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). Beyond acceleration and top speed metrics, torque vectoring and cornering performance are examined for the in-wheel drive powertrain. The study highlights the advantages of the advanced powertrain solutions as well as their potential drawbacks including gyroscopic effects and unsprung masses. Conclusively, the research provides insights into the merits and challenges associated with each powertrain solution. Furthermore, the paper categorizes and evaluates the advantages and disadvantages regarding passenger comfort, drivability, and cornering performance. Aspects such as packaging considerations, component requisites, and overall efficiency are considered as well. Ultimately, this investigation offers an integrative perspective on emerging powertrain architectures, shedding light on their potential to revolutionize future vehicle designs and performance standards.