The axial flux motor, with its advantages of high power density, high efficiency, and lightweight design, is becoming a solution for many industries. With the continuous development of new materials and processes, axial flux motors will play a greater role in more fields.
Definition of Axial Flux Motor
The magnetic flux direction of an axial flux motor is parallel to the motor’s rotational axis. Due to its flat shape and short axial dimensions, the axial flux motor is also referred to as a “disk motor.”
Axial motors consist of rotor and stator components. The permanent magnets of the motor are fixed to the rotor part and aligned parallel to the rotational axis; the stator houses the coils, which react with the rotor’s magnetic field when energized, generating torque. The stator and rotor are assembled relative to each other in the axial direction. Considering the potentially destructive axial forces due to the mutual attraction between the stator and rotor in the disk structure, axial flux motors typically adopt a dual-stator single-rotor structure or a single-stator dual-rotor structure.
Principle of Axial Flux Motor
The principle of the axial flux motor is similar to that of traditional electric motors, both based on the law of electromagnetic induction. The main difference lies in the direction of the magnetic flux. In traditional radial flux motors, the magnetic field radiates from the center of the motor outward along the radius, while in axial flux motors, the magnetic flux is transmitted along the axis of the motor.
Specifically, the magnetic flux between the rotor and stator flows along the axial direction of the motor. In an axial flux motor, the current through the stator coils generates a magnetic field that interacts with the permanent magnets on the rotor, causing the rotor to rotate. The magnetic field design used in axial flux motors allows for a more uniform distribution of the magnetic field between the rotor and stator, which plays a positive role in improving motor efficiency and reducing energy losses.
Advantages of Axial Flux Motor
| Lightweight: The outer diameter of axial flux motors is comparable to that of radial motors, but their axial length is only about half that of radial flux motors, meaning that the volume of axial motors is more than 50% smaller than that of radial flux motors. Given that the raw materials for the motor do not significantly change, the weight of axial motors is typically only about half that of radial motors. This lightweight design facilitates space-saving installations and overall motor design.
| High Torque Density and Power Density: Axial motors can provide a 30% torque density advantage and a 1% to 2% efficiency advantage compared to traditional radial motors. With both weight and volume about half that of comparable radial motors, the torque density can reach four times that of similar radial motors.
In terms of stator structure, non-stator yoke designs can allow axial motors to have a power density of 2 to 3 times that of radial motors while reducing the iron mass of the stator by 80%. For stator windings, the axial motor’s “concentrated winding” design improves power density through 100% winding effectiveness, compared to a mere 50% utilization rate in radial motor coils.
| Process Flexibility: Axial motors offer a high degree of process flexibility. Depending on the motor’s intended application, the composition of the stator, arrangement of magnetic poles, and winding embedding methods can be adjusted.
Disadvantages of Axial Flux Motor
| High Manufacturing Precision Requirements: Due to the balance of magnetic pulling forces, axial motors must maintain a uniform air gap between the rotor and stator. Adjusting this air gap during motor manufacturing can be challenging, necessitating precise control of the manufacturing tolerances for key components.
| Thermal Management: The axial flux motor employs a sandwich structure, and both the intermediate stator of a dual-rotor axial flux motor and the intermediate rotor of a dual-stator axial flux motor experience difficulties with heat dissipation, requiring complex cooling and sealing structures.
| High Costs: The use of new materials and complex manufacturing processes results in low industrial maturity and high production costs.
Layout of Axial Flux Motor
Based on the number of stators and rotors and their relative positions, axial flux motors can be classified into four types: single stator single rotor structure, dual stator single rotor structure, single stator dual rotor structure, and multi-disk structure. To mitigate the destructive axial forces between stators and rotors in the disk structure, axial flux motors generally adopt a dual-stator single-rotor configuration or a single-stator dual-rotor structure.
Key Materials of Axial Flux Motor
The Core Material of the Rotor
Permanent Magnets: magnets play a core role in axial flux motors, as their high saturation magnetic flux density and high magnetic energy product can enhance magnetic field strength and motor performance. For example, electric motors using high-performance neodymium-iron-boron magnets can increase power density by over 20% compared to traditional magnetic materials. Neodymium magnets are widely used in the field of permanent magnet motors.
Axial flux motors utilize wedge-shaped neodymium magnets or complete ring neodymium magnets that are axially magnetized in sectors on a back iron as a rotor. In some cases, wedge-shaped magnets are laminated to reduce overheating.
Core Material of the Stator
| PCB: Unlike traditional motors, the copper coils are directly etched onto the PCB stator, reducing the motor’s weight and size by 50% compared to conventional designs. In applications within electric vehicle power systems, the drive current from the traction inverter produces axial magnetic flux through fixed PCB stator windings, driving the rotor and propelling the vehicle forward.
Beyond size and weight, the absence of cores also reduces stator hysteresis and eddy current losses, improving efficiency and the physical output per unit input of electricity. By eliminating potential failure points related to copper winding and insulation in traditional motors, PCB stators enhance motor reliability.
Applications of Axial Flux Motor
| Electric Vehicles: The high power density and lightweight characteristics of axial flux motors make them especially prominent in electric vehicle applications. An increasing number of electric vehicle manufacturers are focusing on and developing this type of motor to enhance vehicle performance and range.
| Aerospace: In the aerospace sector, they can be used in drive systems for drones, electric aircraft, and other aviation vehicles, playing a significant role in future aerial mobility due to their lightweight and high-efficiency features.
| Wind Power Generation: Due to their high efficiency and adaptability, axial flux motors are gradually becoming an ideal choice in wind power generation systems. They can improve the efficiency of wind turbine systems and reduce the costs associated with wind energy.
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.
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