Solutions for heat dissipation of axial flux motors are the main topic of this article. We will provide several solutions for readers.
What Are the Axial Flux Motors?
Axial flux motors are a special type of motor, with structural and operational principles differing from traditional radial flux motors. In axial flux motors, the magnetic circuit direction of the stator and rotor is arranged along the motor axis, meaning that the magnetic field flows axially.
The stator core and rotor core of axial flux motors are typically constructed using a multilayer disk structure, with certain gaps or non-magnetic materials separating them. When the stator winding is connected to an AC power source, a changing magnetic field is generated.
This magnetic field interacts with the permanent magnets (or electromagnetic fields) on the rotor, forming an axially rotating magnetic field at the interface between the two. According to electromagnetic induction laws, this rotating magnetic field drives the rotor to rotate in the direction of the magnetic field, thus outputting mechanical power.
Advantages of Axial Flux Motors
| Compact Size and Lightweight: Axial flux motors have a volume and weight of 5L and 24kg, respectively, while typical radial flux motors for vehicles have a volume and weight of 10L and 50kg.
| High Torque Density & Power Density: The effective magnetic surface area of axial flux permanent magnet motors is located on the rotor’s surface rather than the outer diameter, allowing for greater torque generation within a certain volume.
| High Efficiency: The efficiency of axial flux motors typically exceeds 96%, surpassing traditional 2D radial flux motors. Axial flux motors are about 15%-25% more energy-efficient than conventional radial motors across various power levels.
Heat Dissipation of Axial Flux Motors
Despite axial flux motors’ technical advantages, several challenges must be overcome, one of which is the difficulty of heat dissipation. The heat dissipation challenge arises because axial flux motors often utilize a sandwich structure, making it difficult for the middle stator of dual-rotor axial flux motors and the middle rotor of double-stator axial flux motors to dissipate heat. Additionally, the high specific power characteristics of axial flux motors lead to low thermal capacity, resulting in serious heating issues.
Solutions for Heat Dissipation of Axial Flux Motors
Air Cooling
Utilizing Rotor-Blade Design: Place blades and ventilation openings on the rotor side that is away from the stator. As the rotor spins, the blades create airflow, which passes through the rotor and blows towards the stator, achieving air cooling for both components.
Installing Air Duct Structures: Install guiding rings on both sides of the stator that have first and second convex edges facing the stator and rotor respectively, to direct the gas within the air gaps along annular paths. A fan at the bottom end of the outer shell utilizes the motor’s shaft to rotate, effectively using airflow to carry away the heat generated within the motor without increasing the motor’s axial thickness.
Optimized Motor Structure
Optimizing motor structure is another way of heat dissipation of axial flux motors.
| Segmented Design of Stator Cores: Segment the stator core axially or radially, ensuring a certain gap or using low thermal conductivity materials between segments. This design reduces internal heat transfer pathways, lowering heat generated from eddy current and hysteresis losses, while allowing the placement of cooling channels or filling with thermal materials in the gaps to further enhance cooling.
| Optimizing Rotor Ventilation Hole Designs: Design uniquely shaped and distributed ventilation holes on the rotor, like asymmetrical or spiral arrangements, to create more complex airflow paths inside the rotor. This increases the heat exchange area and time between the air and the rotor, thus improving cooling efficiency.
| Optimizing Stator Design: Place thermal conductive materials at the axial center of the stator teeth. These conductive materials can be metal, forming unidirectional cooling channels along their path. They provide easy embedding for windings without affecting the connecting arrangements while directly contacting stator teeth and windings to dissipate heat, indirectly cooling the rotor assembly and effectively enhancing heat dissipation capability.
Liquid Cooling
Setting Up Liquid Cooling Channels: Create flow paths on the outer wall of the stator bracket and the interior of support rods for cooling fluid to pass through and cool the stator core and the coils arranged around it. Alternatively, use strip-shaped aluminum plate water channels with multiple small holes, placing the core winding coil within these channels to maximize heat absorption while sealing and transferring heat from the windings.
Form stator cooling channels comprised of support from the stator, the stator itself, flow channel plates, outer leads, and gaps with the housing, creating a “Z”-shaped channel structure that includes radial, inner peripheral, and outer peripheral cooling channels. The outer surface of the inner housing has cooling channels that form a housing cooling channel. Insulating cooling media flowing through both the stator cooling channels and housing cooling channels extends the flow distance and increases the contact area between the motor and cooling media, effectively reducing temperature rise.
New Materials
| Carbon Nanotubes: Carbon nanotubes exhibit ultra-high thermal conductivity. Combining them with components like the stator winding or rotor significantly improves heat dissipation performance, quickly transferring heat away. For instance, adding carbon nanotubes into the insulation layer of stator windings ensures insulation performance alongside enhanced heat dissipation.
| Paraffin/Metal Composite Phase Change Materials: Paraffin is a common phase change material with large latent heat; its low thermal conductivity can be enhanced by combining it with high-conductivity metal particles, forming composite phase change materials. During motor operation, once the temperature rises to the phase change temperature of paraffin, it absorbs significant heat, while metal particles quickly conduct the heat away, achieving effective cooling.
Encapsulating phase change materials within microcapsules and adding them to the motor’s cooling media or directly filling them within the cooling structures allows the phase change material to absorb heat during temperature rises, providing cooling. The encapsulation prevents leakage and corrosion of motor components.
Other Cooling Technologies of Heat Dissipation of Axial Flux Motors
| Heat Pipe Cooling: Install heat pipes on hot components such as the stator or rotor, utilizing their efficient thermal transfer characteristics. The working fluid inside the heat pipe evaporates upon heating and condenses in the cooling section, quickly transferring heat from hot areas to cooling areas through this phase change cycle.
| Magnetic Field Modulation Cooling: By applying a specific magnetic field externally, the internal magnetic field distribution and flux pathways can be modified, thus reducing heat generated from eddy current and hysteresis losses. Additionally, changes in the magnetic field may also influence the flow of cooling media, further boosting cooling efficiency.
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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