Axial Flux Motor for Electric Vehicles: A Comprehensive Overview Brogen axial flux motor A new type of electric motor — the axial flux motor — is gaining increasing attention in the electric vehicle industry. For years, axial flux motors have been used in stationary applications such as elevators and agriculture machinery. However, over the past decade, many developers have been working to refine this technology, making it suitable for a wide range of applications, including electric motorcycles, airport shuttles, cargo trucks, electric vehicles, and even aircraft. The Emergence of Axial Flux Motor: The World’s First Generator Faraday motor In 1831, British physicist Michael Faraday harnessed the phenomenon of electromagnetic induction to invent the world’s first true electric generator, known as the Faraday disk generator. This invention can be seen as the prototype of the axial flux motor. The Faraday disk generator consisted of a disk, brushes, and a horseshoe magnet. Faraday placed a rotatable metal disk within the magnetic field of the magnet and used a galvanometer to measure the current between the edge of the disk and its center. The experiment demonstrated that when the disk rotated, the galvanometer deflected, confirming the presence of current in the circuit—thus achieving the conversion of mechanical energy into electrical energy. Faraday generator reconstruction However, due to limitations in materials, structure, and manufacturing techniques, as well as the late emergence of demand for mobile electric equipment such as electric vehicles, axial flux motors remained largely undeveloped for nearly 200 years. The primary challenges included difficulties in electromagnetic calculations, material selection, complex manufacturing processes, and the intricate coupling between materials, structure, and techniques—all of which exponentially increased the difficulty of industrializing this technology. Axial Flux Motor in the Era of Automotive Electrification While radial flux motors have driven the automotive industry into the electrical age, axial flux motors outperform them in several key areas. Not only are they lighter and more compact, but they also deliver greater torque and power. This groundbreaking technology enables a smaller and lighter motor to generate more powerful force, opening up a world of new possibilities for automotive designers. The most significant difference between axial flux motors and traditional radial flux motors lies in the direction of the magnetic flux. In axial flux motors, the magnetic flux is parallel to the motor’s axis, unlike in radial flux motors where it is perpendicular to the axis. This fundamental difference leads to a considerable change in the stator’s structure. Below are some structural diagrams to help illustrate this concept. A New Benchmark in Performance Traditional radial flux motors, which use permanent magnets or induction in the electric field, are currently being widely developed to optimize weight and cost. However, there is a limit to how much can be improved within this design. Therefore, switching to a completely different type of motor, like the axial flux motor, could be a promising alternative. The torque in a radial flux motor is proportional to the square of the rotor radius, while in an axial flux motor, torque is proportional to the cube of the rotor radius. This means axial flux motors can produce significantly higher torque. For instance, with the same output power, an axial flux motor is 50% smaller and 50% lighter than a radial flux motor. A prime example is the axial flux motor in the Mercedes Vision One-Eleven all-electric concept car, which weighs only one-third of a conventional motor with the same power output. Mercedes Vision One-Eleven Design and Efficiency Advantages The size and weight advantages of axial flux motors not only greatly reduce the use of materials like copper, iron, and permanent magnets in production, but also allow for more flexible placement in tighter spaces, such as the recesses of car wheels. this reduces the need for components like transmissions and drive shafts, minimizing kinetic energy loss and improving drive efficiency. The direct torque compensation further enhances performance. Streamlined Structure and Enhanced System Benefits Due to their compact and lightweight design, axial flux motors require fewer structural elements for installation, saving even more weight. Additionally, their rotational speed does not reach the high levels seen in traditional radial flux motors, eliminating the need for reduction gears. This further reduces the overall system weight, benefiting other subsystems like braking and cooling. Overall, this can lead to a 5-10% improvement in both efficiency and range. Technical Challenges for The Axial Flux Motor Despite the technical advantages of axial flux motors and the significant progress made over the years, the industry has now grasped the working principles of these motors and has largely overcome key challenges in configuration and structural design, electromagnetic performance, thermal performance, and the development of calibration and control strategies. However, the large-scale application remains a challenge due to several design and production hurdles that must be addressed: 1. Immature Manufacturing Equipment The industry’s understanding of axial flux motor manufacturing methods is still limited due to a lack of research and experience. Manufacturing equipment is not readily available, and the supply chain is underdeveloped. 2. High Manufacturing Precision Requirements Axial flux motors must maintain a uniform air gap between the rotor and stator, as the magnetic force is much stronger than in radial flux motors. Adjusting the air gap during the motor manufacturing process is challenging, making it crucial to precisely control the tolerance of key components. 3. Thermal management and Design Complexity Axial flux motors feature a sandwich structure, making it difficult to dissipate heat from the central stator in dual-rotor designs or the central rotor in dual-designs. Additionally, due to their high power density, axial flux motors have a small heat capacity, leading to overheating issues. Innovative cooling methods, such as immersion oil cooling, oil-water hybrid cooling, liquid nitrogen cooling, and phase-change material cooling, are needed, along with the design of complex cooling and sealing structures. 4. High Costs Due to Complex Materials and Processes For radial flux motors, the costs of magnets, silicon steel, copper, and structural components, as well as the manufacturing processes for mass
