Axial flux motors in electric vehicles play a very important role in the revolutionary solution for electric vehicle drive systems due to their high power density, high efficiency, and lightweight advantages.
Principles of Axial Flux Motors
The principle of axial flux motors is significantly different from that of traditional radial flux motors. In radial flux motors, the magnetic field direction is perpendicular to the motor shaft, with the magnetic flux path radially passing from the rotor through the air gap to the stator, then returning to the rotor to form a closed loop. In contrast, the magnetic field direction in axial flux motors is parallel to the motor shaft, with the magnetic flux path axially passing from the rotor through the air gap to the stator and back to the rotor to close the loop.
The structure of an axial flux motor typically consists of a stator, a rotor, and an air gap. The stator and rotor are usually disk-shaped, with windings arranged on the stator and permanent magnets or electromagnets mounted on the rotor. When current flows through the stator winding, the generated magnetic field interacts with the permanent magnet on the rotor, producing torque that drives the rotor to rotate.
Advantages of Axial Flux Motors in Electric Vehicles
| High Power Density and Torque Density: The primary advantage of axial flux motors lies in their high power density and torque density. Since the magnetic field direction is parallel to the motor shaft, the magnetic flux path is shorter, leading to higher utilization of the magnetic field. This allows for greater torque and power generation in a smaller volume, substantially enhancing vehicle acceleration and handling.
| Lightweight Design: The disk-shaped structure of axial flux motors provides significant advantages in terms of size and weight. This lightweight design not only reduces the material cost of the motor but also facilitates the overall lightweight design of electric vehicles.
Design of Axial Flux Motors in Electric Vehicles
| Topology Configuration Design: According to the number of stator and rotor components, their relative positions, and the main magnetic circuit classification, the basic topological structures can be divided into four types: single stator-single rotor structure, double stator-single rotor structure, single stator-double rotor structure, and multi-disk structure.
The appropriate structural topology should be assessed based on specific application scenarios, processes, and cost factors. Currently, the automotive electric drive industry conducts a comprehensive analysis of the performance, process feasibility, and costs of various axial flux motor topologies, with a focus on the double stator-single rotor and single stator-double rotor structures.
Materials and Processes for Axial Flux Motors in Electric Vehicles
Materials
Develop high-strength, high-thermal-conductivity epoxy resin encapsulation materials for heat dissipation, enhancing the motor’s heat dissipation capabilities and preventing demagnetization of permanent magnets at high temperatures.
The application of PCB stator technology can significantly reduce the motor’s weight and losses, improving the reliability and efficiency of electric vehicle motors.
Develop carbon fiber winding reinforcement techniques to meet high-strength rotor and stator requirements, addressing the poor tensile strength of permanent magnets.
Use high magnetic permeability, low-loss materials such as SMC composite materials, amorphous alloys, and oriented silicon steel for the rotor and stator cores. SMC materials are easy to mold and have simple heat treatment processes, suitable for mass production, and can also be adapted for 3D printing, making innovative motor designs more flexible and diverse.
Processes
| For windings, use flat coils, spiral concentrated windings, and multi-pole connected winding processes.
| For permanent magnets, develop low-loss segment mounting and magnetic pole demagnetization protection processes.
| For stator cores, develop sectioned armature splicing without yokes, bolt-free connections with end caps, and powder metallurgy manufacturing processes.
For mass production requirements, develop automated assembly technologies for rotors and stators, automated production of the flat conductor formed coils, and flexible automated production line processes.
Applications of Axial Flux Motors in Electric Vehicles
| High-Performance Electric Vehicles: The high power density and torque density of axial flux motors make them an ideal choice for high-performance electric vehicles. Many high-performance electric vehicles have adopted axial flux motors as their drive systems. These motors not only provide powerful output but also significantly enhance the vehicle’s acceleration performance and handling.
| Wheel Hub Motors and Distributed Drive Systems: The compact structure and lightweight design of axial flux motors are well-suited for use as wheel hub motors. Wheel hub motors are installed directly inside the wheels, eliminating the need for traditional drive shafts and differentials, which can significantly improve vehicle drive efficiency and handling. Additionally, wheel hub motors can achieve torque vector control, further enhancing vehicle dynamic performance.
| Range-Extended Electric Vehicles: The high efficiency and high torque characteristics of axial flux motors make them ideal for generator systems in range-extended electric vehicles. Axial flux range extenders can reduce size by one-third compared to mainstream products, with a weight reduction of 30%, significantly improving the generator’s efficiency and system integration.
Development Trends of Axial Flux Motors in Electric Vehicles
| Multi-Disk Structure: Multi-disk axial flux motors and modular designs will become important development directions in future motor technology. By increasing the number of disks in the stator and rotor, the power density and torque output of the motors can be significantly enhanced. Moreover, modular designs can flexibly adjust the motor’s power and torque according to application needs, catering to different electric vehicle platforms.
| Intelligence: With the advancement of smart electric vehicles, axial flux motors will be highly integrated with other electric control systems to form intelligent drive systems. For example, axial flux motors can be integrated with inverters, battery management systems, etc., to achieve efficient energy management and power distribution. Additionally, axial flux motors can be combined with autonomous driving systems for more precise torque control and vehicle dynamic management.
Provider of Magnets, Soft magnetic composites, and Coils
At Tengye, We provide magnets, soft magnetic composites, and coils, improving the efficiency of customers’ research and development of axial flux motors. Customized materials according to customer needs are also available.
At Tengye, we’re thrilled to be early participants in your new projects. Our passion for magnets extends from material selection and design optimization to providing magnetic solutions. We hope to bring our knowledge and experience to the forefront by actively engaging in your upcoming projects. Work with our magnet experts to get the right magnet solution.
Image Source: Emobility-engineering & Evreporter & Focus & Oemoffhighway & Semanticscholar
