Pole and Segment Combination in Concentric Magnetic Gears: Vibrations and Acoustic Signature

This paper studies the influence of cogging torque and unbalanced radial magnetic forces on vibrations and acoustic noise properties in concentric magnetic gears. The study involves three physical demonstrators, each with unique properties that make them interesting study cases. The first magnetic gear have pronounced cogging torque due to the pole and segment combination. In the second magnetic gear very low cogging torque is obtained by choosing an odd number of segments, but at the expense of unbalanced radial magnetic forces. The fact that these two magnetic gears are designed to identical specifications and into the same system makes this study unique, as this yields a direct and very clear comparison of the influence of cogging torque and unbalance radial forces. The third gear is designed with a pole and segment combination that has a good balance between minimizing cogging torque and avoiding unbalanced radial forces. Acoustic and vibrational signatures are presented and the characteristics are discussed in each case. It is shown that both cogging torque and unbalanced radial forces in concentric magnetic gears dominate both acoustic and vibrational properties and it is shown how it makes the magnetic gears very sensitive to the eigenfrequencies of the system. Even though cogging torque and unbalanced radial forces are dominant, it is also shown how other excitation mechanisms such as eccentricity, segment passing frequency and pole passing frequency are clearly visible in the acoustic and vibrational signatures.