Magnetic Gear
Recently, a new type of magnetic gear has been proposed by Kais Atallah and Dave Howe in IEEE Transactions on Magnetics, Vol. 37, No. 4, pp. 2844-2846, July 2001. While it is still in the theoretical stage, the simulations presented here confirm that it has the potential to replace conventional mechanical gearboxes in some applications. This example also highlights the advanced capabilities of Infolytica's Transient with Motion solver, which is able to simulate multiple moving parts simultaneously.
The operation of this gear assembly is analogous to a Planetary Gear assembly, 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). Since there are 44 magnets in the outer rotor and 8 in the inner rotor, the gear ratio of this magnetic gearbox is 5.5:1.
Results
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| Click image to see full size version |
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 833 rpm. The outer rotor is load driven, with a viscous friction applied, and its rotational speed is calculated by MagNet to be -151.5 rpm.
- Video - AVI clip - 9012KB
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| Click image to see full size version |
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.
- Video - AVI clip - 3120KB
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| Click image to see full size version |
The torque transmission capability is evaluated with another simulation that runs the inner rotor at constant speed, while gradually increasing the load on the outer rotor. 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 (360/22 degrees). This graph shows that this set of gears is capable of transmitting up to 665 Nm of torque per meter of length of the gears.
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| Click image to see full size version |
Setting up different loads is easy in MagNet, as shown in the dialog box at right which corresponds to the increasing load with time used in the simulation for the previous image. Loads can also be specified as a function of position and speed, to simplify the modeling of non-linear springs and dampers, for example. Loads are also automatically combined so that different types of load can be included in the same simulation.
Recently, a new type of magnetic gear has been proposed by Kais Atallah and Dave Howe in IEEE Transactions on Magnetics, Vol. 37, No. 4, pp. 2844-2846, July 2001. While it is still in the theoretical stage, the simulations presented here confirm that it has the potential to replace conventional mechanical gearboxes in some applications. This example also highlights the advanced capabilities of Infolytica's Transient with Motion solver, which is able to simulate multiple moving parts simultaneously.
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