Simulating Multiple Moving Parts of a Magnetic GearGear with MagNet
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 they allow frictionless torque transmission of potentially larger magnitude than equivalent mechanical gears. This example shows simulations of a magnetic gear system and its 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
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 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 has been used to carry out this study. In this simulation, the inner rotor is being driven at a constant speed of 600 deg/s. As expected, MagNet calculates that the outer rotor settles to a rotational speed of 240 deg/s in the opposite direction (negative speed), which is 2.5 times smaller than the inner rotor's speed.
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ROTATING MAGNETIC FIELD
This animation displays the flux lines and the shaded plot of the magnetic flux density as the gears come up to speed. We can see 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. The torque ripple can be seen in the video.
The torque transmission capability is evaluated with another simulation that runs the inner rotor at constant speed, with gradually higher loads on the outer rotor. The load here is applied in the same direction as the outer rotor rotates. This example is analogous to a situation where the outer rotor drives a pulley or winch to lower a load at a controlled speed. When the load exceeds the torque limit of the magnetic gears, the outer rotor starts to slip. The speed suddenly increases since it can no longer be maintained at 240 deg/s. The outer rotor keeps accelerating due to the external load up to the point where the viscous force, which is proportional to speed, becomes so large that the speed settles to a constant value. This graph shows that this set of gears will start slipping when the load is between 100Nm and 120Nm.
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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.