What is an axial flux motor?
Based on the direction of the magnetic flux path, motors can be categorized into axial flux motors and radial flux motors. Although the flux direction differs, both operate according to the fundamental laws of electromagnetism.
Specifically, the motor driver controls the magnetic field strength and direction of the coil (rotor) by altering the direction and magnitude of the current flowing through it. Since the stator poles remain stationary, changes in the rotor's magnetic field direction and intensity induce magnetic interaction, generating the Lorentz force that drives the rotor's rotation.
In axial flux motors, the stator poles are arranged along the axis, while the rotor is typically cylindrical. Magnetic flux passes through the rotor's central axis. When current flows through the stator windings, the generated magnetic field traverses the rotor along the axial direction. According to Lorentz's force law, this magnetic field induces torque within the rotor, driving its rotation.
Axial flux motors feature a planar air gap with a short axial length, resulting in a thin disc-like shape. Hence, they are also known as disc motors.
The topological structure of axial flux motors offers flexible combinations adaptable to specific application scenarios. Based on stator-rotor configurations, axial flux motors can be categorized into four structures:
Single-Stator/Single-Rotor Structure: 1 rotor + 1 stator. Features a simple, compact design but exhibits high unilateral magnetic pull, increased bearing load, significant vibration and noise, and potential stator-rotor friction risks that reduce motor lifespan.
Single-Stator/Dual-Rotor Configuration: 2 outer stators + 1 inner rotor. Features high power density, making it suitable for traction systems, aerospace applications, and similar fields.
Dual-Stator/Single-Rotor Configuration: 2 outer rotors + 1 inner stator. Offers excellent symmetry with relatively lower unilateral magnetic pull force, making it well-suited for wind power generation systems.
Multi-Stator/Multi-Rotor Structure: Multiple stators + multiple rotors, suitable for high-torque applications like marine propulsion systems, large wind turbines, and hydroelectric generators.
Advantages of Axial Flux Motors
Compact size and lightweight: As a pioneer in axial flux motors, YASA reports its axial flux motors measure 5L in volume and weigh 24kg, compared to conventional radial flux automotive motors at 10L volume and 50kg weight. Axial flux motors align with automotive lightweighting trends, offering compact structure, shorter radial length, and greater installation flexibility.
High Torque Density & Power Density: The effective magnetic surface area of an axial flux permanent magnet motor is located on the rotor's surface rather than its outer diameter. Consequently, it typically delivers greater torque within a given volume, thereby enhancing torque density and power density. According to calculations based on YASA's official website data, its axial flux motors achieve torque density and power density of 160 Nm/L and 14.9 kW/kg respectively—four times that of traditional automotive radial flux motors.
High Efficiency: Benefiting from a shorter one-dimensional magnetic path, axial flux motors achieve high efficiency, typically exceeding 96%. This performance rivals or surpasses the best two-dimensional radial flux motors on the market. Across all power ratings, axial flux motors consume approximately 15%-25% less energy than conventional radial motors while sustaining peak power output for longer durations.
Low Noise and Vibration: With uniform magnetic field distribution, axial flux motors generate minimal noise and vibration during operation, making them particularly suitable for applications with stringent noise and vibration requirements.
Energy Savings and Carbon Reduction: The compact size and lighter weight of axial flux motors reduce material consumption—including copper, iron, and permanent magnets—by approximately 50% compared to radial permanent magnet motors during manufacturing. When incorporating ironless PCB stator technology, copper usage in axial motors can drop to just 34% of radial motors.
Simultaneously, their lighter weight and higher efficiency result in lower power consumption and stronger driving capability during operation, contributing to energy conservation and carbon reduction.
Market Applications of Axial Flux Motors
Currently, axial motors are widely adopted in new energy vehicles, aerospace, marine propulsion, robotics, and wind power generation—applications demanding high torque density and compact space utilization.
New Energy Vehicles: A Key Market for Scaled Axial Motor Adoption
The compact size and low theoretical cost of axial flux motors hold promise for resolving the cost and size challenges of wheel-hub motors, driving their large-scale adoption. The power density advantage of axial flux motors enables sufficient torque output while maintaining lightweight construction and reducing unsprung mass, propelling the mass application of hub motors.
Axial flux motors have already played a significant role in optimizing the performance and design of commercial vehicles, with commercial vehicle electrification representing a new blue ocean for axial flux motor technology. According to Global Information projections, the global automotive axial flux motor market is expected to grow from $135 million in 2022 to $497 million by 2027, achieving a CAGR of 29.8%.
