In the fast-paced world of engineering, the Axial Flux Permanent Magnet Coupling (AFPMC) system is revolutionizing contactless power transmission, offering efficient and sustainable solutions across various industries.
What is an AFPMC?
The Axial Flux Permanent Magnet coupling transmits torque between shafts contact-free using magnetic fields, avoiding the wear and tear of traditional mechanical couplings. An example of a AFPMC is shown in Figure 1, below:
Figure 1: CAD model of the AFPMC machine and an illustration of the alternation of PM poles.
A low frequency electromagnetic simulation package, like EMWorks-EMS, is indispensable to model and optimize AFPMC machines. Some of the flux dens ity results obtained by EMWorks-EMS for the above machine are shown in Figure 2-3.
Figure 2: Vector plot of Magnetic Flux between similarly magnetized poles for Angle = 0° and 15°.
Figures 2-a) and 2-b) showcase the axial magnetic flux density at coupler angles of 0° and 15°. At 0°, where poles of the same magnetization align, both magnetic reluctance and torque reach their lowest values. In contrast, at a 15° angle, there's a significant increase in magnetic reluctance, leading to the maximum magnetic torque, indicating this as the optimal angle for generating maximum torque.
Figure 3: Fringe plot of Magnetic Flux density on a single rotor for Angle = 0° and 15°.
Why Axial Flux?
Axial flux in PM couplings means the magnetic flux moves parallel to the rotor's axis, unlike in radial flux systems. This allows for a more compact, efficient design ideal for space constrained, and high torque machines. Figure 4 shows a torque vs displacement angle obtained by EMWorks-EMS, for the AFPMC machine shown in Figure 1.
Figure 4: Torque (Tz) versus angular displacement at air gap g=9.5mm
Air Gap in AFPMC
The air gap in AFPMC machines is vital for their efficiency and performance. It influences magnetic flux linkage, affecting torque and overall functionality. Optimizing the air gap is critical; too large decreases efficiency, while too small may cause mechanical issues. Balancing these factors is key to maximizing the machine's effectiveness. Figure 5 shows a plot of torque vs airgap obtained by EMWorks-EMS, for the AFPMC machine shown in Figure 1.
Figure 5: Pull-out torque versus air gap
Figure 5 reveals that the pull-out torque of the magnetic coupling decreases sharply with an increase in the distance between magnets, while maintaining a constant load angle of 15°. Notably, the maximum torque nearly halves as the air gap expands from 2mm to 7mm, underscoring the critical impact of the air gap distance on torque performance.
Advantages of AFPMC
Contactless Operation: No physical contact reduces wear, extends service life, and lowers maintenance.
High Efficiency: Axial flux designs boast high efficiency with optimized circuits reducing losses.
Lightweight: More compact and lighter than radial systems, ideal for space-weight critical applications.
Versatility: Suitable for diverse applications due to adaptable power and torque designs.
Coupling to Motion Analysis
Coupling to motion analysis is vital for AFPMC enabling optimal electromagnetic to mechanical energy conversion. This analysis ensures enhanced torque, minimized losses, and increased reliability by fine-tuning the magnetic and mechanical interactions. It's key to achieving peak operational efficiency and meeting application-specific requirements. Figure 6 shows the coupling to motion results obtained by EMWorks-EMS, for the AFPMC machine shown in Figure 1.