Halbach Array in Model 3

One of the surprising characteristics of electric vehicles is their acceleration. Even the simplest vehicles accelerate faster than comparable combustion engine cars. Tesla’s vehicles have been know for their extremely good acceleration behavior and the Model 3 even more so, due to a small but important detail.

Sandy Munro, who’s the founder of an engineering service providers, and who specializes in buying, disassembling, and analyzing technology trendsetting cars, and did so with the Model 3. And they discovered some interesting details at the electric motor.

Initially, there is the weight, which is at 46 kilogram for the Model 3, below the 48 kilogram of the BMW i3 and the Chevrolet Bolt’s 50 kilogram. And the Model 3’s motor brings about 40 percent more power on the street despite being lighter. That of course raised the engineer’s interests. The Model 3’s permanent magnets gave a first clue of what makes the motors so powerful. Those rectangular magnets a bit larger than the size of a Bazooka chewing gum, had some small rills, which Munro’s engineers couldn’t explain. Until they learned about the Halbach Array.

By arranging the spatially rotating pattern of magnetization by 90° of each magnet, the magnetic flux distribution one one side of the magnet cancels or weakens, while on the opposite side it increases.

Similarly arranged magnets (left) and the Halbach-Array (right) with the visualized magnetic flux.

This leads to the effect that the magnetic force on the side with the increased magnetic flux distribution is much stronger than the sum of the single magnets would allow. One plus one is more than two. That explains why a smaller and lighter electric motor such as in Tesla’s Model 3 can bring more torque and uses less energy.

Such Halbach-Array magnets are, according to Sandy Munro, no commodity. You can’t buy them from the shelf. The glue alone used for keeping the magnets together, is noteworthy. During tests, when they tried to break the magnets at the rills, the loose magnets would fly violently in all directions.

Tesla Model 3 electric motor with visible Halbach-Array-magnets.

Beside fridge magnets, this seems to be the first mass use of Halbach-Arrays, only discovered about 40 years ago, in a consumer product.

Here is the video with the analysis of the tear-down of a Model 3, where Sandy Munro starts talking about the Halbach-Array around the 10 minute mark for about 15 minutes.

This article was also published in German.


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