Critical Review of Direct-Drive In-Wheel Motors in Electric Vehicles

The primary challenge for electric vehicles in replacing oil-fueled vehicles today is their limited range, despite significant advancements in energy storage technology and alternative fuel vehicles over the past few decades. Direct-drive in-wheel motors (IWMs) can achieve higher efficiency by eliminating components such as gearboxes, differentials, and clutches, allowing for longer mileage with the same battery capacity. This positions them as a promising technology for the future of electric vehicles. This article primarily analyzes the key challenges that limit the widespread application of direct-drive IWMs in electric vehicles, including torque density, cost, reliability, efficiency, and ease of production. The article also investigates and compares the electromagnetic performance of the most representative motor topologies studied in direct-drive IWMs within both industrial and academic settings, and comprehensively evaluates the performance of these motor architectures with respect to the aforementioned performance requirements. Based on these investigations, this article aims to provide guidance and reference for the electromagnetic design and analysis of direct-drive IWMs.