• Tesla relies on innovative Plaid drive
• German researchers see a clear performance advantage
• The competition is likely to follow suit
“Due to the limited installation space available in vehicles, traction drives with high torque densities are an essential goal of machine design in the automotive sector. In order to be able to do without a multi-speed gearbox and still achieve high vehicle speeds, there is also the design goal of a high engine speed,” explained Maximilian Claauer and Andreas Binder from the Technical University of Darmstadt in a recently published article.
Plaid Drive
In its Model S and Model X, the e-car pioneer Tesla is now using the Plaid drive. Instead of two engines, these vehicles now have three with, according to the company, a total of 1,020 hp. In addition, the drive units have been newly developed and are based on permanent magnets “buried” in the rotor. Iron bars in the rotor are usually required for mechanical stabilization at high speeds, but with Tesla the rotors are given a carbon fiber cover so that they do not expand too much at high speeds. The rotors are wrapped with carbon fibers under extreme pretension. For this purpose, Tesla has had a new type of machine developed, which comes from Germany, like Tesla CEO Elon Musk revealed in a tweet.
Tesla Automation (Germany) built a specialized machine to wrap the rotor with carbon fiber at precise tension.
If too low, it would come loose at low temp, due to CTE differences. If too high, it would snap at high temp & rpm.
– Elon Musk (@elonmusk) August 6, 2021
Analysis of the German researchers
This technology attracted a lot of attention, which is why the research associate Claauer and his institute director Binder are now taking a closer look at it. They investigated “a rotor concept as a combination of buried rotor magnets and carbon fiber bandage […]in order to eliminate the radial and tangential rotor iron webs”. As Clauer explained to “Teslamag”, the two researchers did not physically build their own Tesla motor, but instead worked with simulations based on an electric motor that is basically the same.
The reduction in magnetic stray flux achieved with this concept in combination with high mechanical strength leads to increased magnet utilization for the air gap field and thus allows a high torque density with a high maximum speed at the same time,” said the summary of the technical article. Compared to a conventional motor, the simulated Tesla drive was characterized by a 50 percent higher maximum speed, 8 percent more power and approximately the same maximum torque.
With their engine simulation, Clauer and his professor achieved a torque of 270 Newton meters and a maximum speed of 15,000 revolutions per minute. But the real Plaid unit from Tesla is larger and therefore more powerful. Clauer therefore believes that Elon Musk’s statement that the Model S Plaid can achieve 20,000 revolutions per minute “and possibly a little more” is correct. For comparison: Conventional electric motors currently available on the market would only achieve 16,000 to 18,000 revolutions per minute.
“Innovative” technology
However, the analysis identified the increased “manufacturing effort for the production and assembly of the carbon fiber bandage” as a disadvantage. Nevertheless, Tesla’s Plaid drive is “very innovative” and according to Teslamag, Clauer expects that the competition will follow suit, at least in the upper performance range with Plaid engines like the e-car pioneer. To his knowledge, Tesla is currently the only manufacturer that produces this technology in series.
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