Why do we use gearboxes?

  • Most important metrics of electric machines are generally proportional to torque rating (rather than power)

  • Main ways to increase the torque of a electric machine are:

    • Supply more current

    • Make the machine bigger

  • Both of these solutions come with increased cost

  • For high-torque, low-speed applications, gearboxes allow the use of a smaller, lighter, cheaper high-speed machine to be used

    • As compared to more expensive and larger direct-drive machine

  • Mechanical gearboxes have some issues stemming from the interlocking teeth such as acoustic noise, no overload protection, lubrication/maintenance

What is the difference between mechanical and magnetic gears (MGs)?

In the top image you can see a traditional mechanical spur gear. They operate by the teeth interlocking with one another. If you wanted to make a magnetic equivalent of this, the logical step is to replace the teeth with permanent magnets of alternating polarity (north then south etc.). This is what the middle image shows. The problem with this design is that the only magnetic interaction that is occurring is highlighted by the black rectangle. The magnets on the left side of the larger gear and right side of the smaller gear are not interacting at all. Thus when these types of gears have been built and tested, their performance has been very poor. A solution to this is found by placing the smaller gear inside the larger gear and then adding a ring of ferromagnetic blocks. This is shown in the bottom image and represents the most prevalent magnetic gear design in research. It is refereed to as a coaxial radial flux magnetic gear.

What are the benefits and drawbacks of magnetic gears?

Since we have removed the physical contact between “teeth” by utilizing magnets, magnetic gears come with a wide array of potential benefits such as:

  • Increased efficiency

  • Higher reliability

  • Lower acoustic noise

  • Built in overload protection

But of course there is no such thing as a free lunch, so they also do have some drawbacks. They currently cost more to produce, and with the current materials (both for the magnets and ferromagnetic portions) it is hard to get the same performance as mechanical gears. But it is important to remember that mechanical gears have been around for hundreds of year while magnetic gears are only around 30 years old.

What types of magnetic gears are there?

Magnetic gears, just like mechanical gears, come in many different types (usually called “topologies”). There is the aforementioned magnetic spur gear and coaxial magnetic gear, but there are also cycloidal MGs, magnetic screws, transverse flux MGs, etc. The images on the left show some of the different toplogies of MGs and their mechanical counterparts.