Apple Car research focusing on use of Tesla-style induction motor
Apple is working on a three-phase AC induction motor suitable for an Apple Car, implementing the same basic engineering and motor design principles that Tesla uses.
Apple will still not say that it is making a car, despite filing legally-required documentation, and also countless patents regarding the interior and exterior. Now, though, those countless patents include one that details how Apple intends to use an electrical motor that is designed for cars.
The patent details specifically a three-phrase AC induction motor, which is only one of several possible electrical motor systems for cars. However, it uses the same squirrel cage motor technology that Tesla does.
Apple will have chosen this technology specifically for the same reasons that Tesla has. It can generate a high starting torque when the voltage/frequency is controlled, it's cheaper, and is also useful over rugged terrain. These motors can be also be expected to have a longer life, and need less maintenance, than, for instance, a permanent magnet drive.
In comparison, hybrid vehicles from Ford and Nissan use permanent magnet synchronous motors. They are more efficient than induction motors, but they also cost more and need greater maintenance. Plus their magnets tend to wear out and need replacement over time.
Three-phase induction motors are likely chosen because the technology is relatively cheap to build, requires little maintenance, and can generate a high starting torque when voltage/frequency is controlled. When properly controlled, a three-phase AC induction motor can be made to be 90% efficient. The problem is in the complexity of that control, though the patent does not explicitly detail Apple's systems for handling this.
Instead, Apple's patent concentrates on the motor technology paired with a method for dissipating heat from the engine. "[A] cooling structure [is] disposed in a thermally conductive relationship with at least one of the upper exterior ring surface or the lower exterior ring surface for receiving heat from the end turn ring," it says.
The patent is credited to five inventors, Dillon J. Thomasson, Kan Zhou, Rui Guan, Yateendra B. Deshpande, and William M. Prince. Thomasson, Zhou, and Guan are all previously credited on the related patent "Electric motor with shielded phase windings."