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Simulating Multiple Moving Parts of a Magnetic Gear
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Magnetic and mechanical planetary gear systems have been compared recently with regards to their potential applications. It has been shown that magnetic gears could be potential alternatives to mechanical systems as it allows frictionless torque transmission of potentially larger magnitude than equivalent mechanical gears. This example shows simulations of a magnetic gear system and it's performance. In this example, the magnetic planetary gear assembly is analogous to an equivalent mechanical system, with the inner rotor acting as the sun gear, the outer rotor as the ring gear, and the stationary steel pole pieces acting as planetary gears (it is the magnetic field that spins, not the pole pieces themselves). There are 2 pole pairs on the inner rotor and 5 pole pairs on the outer rotor, making the gear ratio of this assembly 2.5:1. The model is shown here.
METHODS and RESULTS
Results
The magnetic gear system has two separated rotary motion components. MagNet can be used to model such disconnected multiple moving systems. A velocity driven inner ring (with external load) is coupled to a load driven outer rotary system with damping. The effect of damping coefficients on the outer rotor has been studied and these results are presented here. Parameterization and scripting has been used to carry out this study using.
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Transient magnetic flux density variations
This animation displays the flux lines and the shaded plot of the magnetic flux density as the gears come up to speed. At the end of this simulation, the inner rotor is being driven at a constant speed of 600 deg/s. The outer rotor is load driven, with a viscous friction applied, and its rotational speed is calculated by MagNet to be -240 deg/s. The torque ripple can be seen in the video.
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Magnetic fields in poles
The operation of the gears can be seen from this animation of the flux lines, which shows the magnetic field in the pole pieces rotating as the rotors turn. The outer rotor rotates in the opposite direction to the inner rotor, and the field in the pole piece completes one revolution as each pair of rotor and stator magnets pass by it.
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TORQUE TRANSMISSION
The torque transmission capability is evaluated with another simulation that runs the inner rotor at constant speed, with gradually higher loads. When the load exceeds the torque limit of the magnetic gears, the outer rotor starts to slip. Before this point, the outer rotor will lag the inner rotor and, in fact, the relation between torque and lag is approximately sinusoidal, with a period equal to twice the rotor magnet spacing (360/5 degrees). This graph shows that this set of gears will start slipping when the load is between 80Nm and 100Nm.
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Reference
Comparative Study Between Mechanical and Magnetic Planetary Gears, E. Gouda, S. Mezani, L. Baghli and A. Rezzoug, IEEE Transactions on Magnetics, Vol. 47, No. 2, pp. 439-450, 2011.
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