Exploring the Exotic Realm: A Multidisciplinary Comparison of Axial Flux Machines and Their Alluring Powertrain Alternatives

<div class="section abstract"><div class="htmlview paragraph">This paper evaluates electric machine and reducer specifications along-side vehicle dynamics and drivability for an axial flux machine (AFM). The baseline is a conventional central drive unit with a single electric machine, reducer, and differential. It compares powertrain architectures with two in-wheel AFMs (IWD) and one AFM mounted perpendicular to the chassis against the E-Axle design. The study starts by determining wheel-level traction force and power requirements for a mid-sized vehicle, then derives necessary machine and reducer specifications. It also considers packaging and efficiency constraints. The E-Axle uses a single-stage planetary gearbox, while the perpendicular AFM connects to a bevel gear reducer, and the IWD requires no reducer. These architectures are analysed in a vehicle dynamics simulation with six degrees of freedom, suspension, tire, and road models. Efficiency is assessed using the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). Besides acceleration and top speed, the study examines torque vectoring and cornering for the IWD powertrain. The paper highlights the benefits and drawbacks of advanced powertrain solutions, including gyroscopic effects and unsprung masses, and evaluates passenger comfort, drivability, and cornering performance. Packaging, component needs, and overall efficiency are also considered. The perpendicular AFM powertrain shows high efficiency and good packaging but at a high cost compared to the E-Axle. Overall, the research provides insights into the advantages and challenges of each powertrain solution.</div></div>