Tesla’s ‘rotor geometry’ patent hints at more efficient electric motors

Tesla has invented a technique for increasing its all-electric vehicles’ power and torque by simply adjusting the shape of some of its electric motor’s components.

A recently published US patent application titled “Geometry of Rotor End Ring and Stator End Turns” describes how Tesla accomplishes this. According to the application, certain internal parts of an electric motor can be modified to reduce power losses from leaks in the magnetic field that effectively make the motor smaller.

The primary components of electric motors – the rotor and the stator – together generate the motion used to operate a vehicle. Simply, a magnetic field produced by electricity running through copper wires in the stator cause the magnetized bars of the rotor to spin. However, when the motor is operating at high speed, some of the electromagnetic force is lost, reducing the motor’s power.

Figure 2 from Tesla’s U.S. Patent Application No. 2019/0097508 | Credit: Tesla

Tesla has identified two places where this loss can be reduced – the end parts of the stator and rotor. The copper wiring in these parts is wrapped around cutout shapes, and after some testing, Tesla’s engineers learned that different shapes give different results. Per the application, “geometries for rotor end ring and stator end turns can be chosen in a way that improves performance or other characteristics of the motor.”

Overall, electric current flow becomes concentrated in different spots on the motor depending on the ‘geometry’ of these parts, thus an opportunity to limit any losses has presented itself by controlling where the concentrations happen. Tesla has filed this application to protect the process (‘method’) of building a motor with the geometry knowledge made part of the design and testing.

The process is described in the application’s Abstract as follows:

“A method of making an AC induction motor includes: providing a rotor and a stator for the AC induction motor; determining, for different geometries of an end ring of the rotor, a location of a first centroid of current density in the end ring; determining, for end turns of the stator, a location of a second centroid of current density in the end turns; selecting a geometry for at least the endring of the rotor so that an axial distance between the first centroid of current density and the second centroid of current density is minimized; and assembling the AC induction motor, wherein the end turns and the end ring have the selected geometries.”

Figure 3 from Tesla’s U.S. Patent Application No. 2019/0097508 | Credit: Tesla

Although the publication was only recently available to the public, this application is related to another patent that was filed in 2015, meaning that Tesla is likely already implementing the findings and invention into their manufacturing process. This is rather unsurprising considering the company’s tendency to constantly improve its vehicles’ components as soon as the upgrades are available. Elon Musk himself has mentioned this on Twitter, stating that Tesla’s electric cars are “partially upgraded every month as soon as a new subsystem is ready for production.” This was also highlighted by President of Automotive Jerome Guillen last December, when he highlighted that the designs of Tesla’s batteries are always evolving.

Automotive teardown expert Sandy Munro concluded following a thorough analysis of an early-production Model 3 that the vehicle’s electric motors are among the best in the industry today. In an appearance at YouTube’s Autoline TV, Munro noted that the Model 3’s electric motors are more efficient and more cost-effective than the motors found in the Chevy Bolt EV and the BMW i3. “They’ve got magic. The electric motor is smaller and lighter than everybody else, but outperforms everybody,” Munro said.

The full text of Tesla’s “Geometry of Rotor End Ring and Stator End Turns” patent can be accessed here.

Tesla’s ‘rotor geometry’ patent hints at more efficient electric motors
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