Tesla's Model S is known for its long range, with the 100kWh version rated to travel 335 miles (540 km) between charges. On Tuesday, Tesla announced changes to the Model S drivetrain that boosted the range by more than 10 percent to 370 miles (595 km).
Similar improvements have pushed the range of the high-end Model X up to 325 miles (525 km). And that's all without increasing the vehicle's battery capacity. The cars are simply able to go 10 percent further for every kWh of charge—which translates to electricity savings for Tesla customers.
Several factors combined to produce these impressive efficiency gains. Tesla switched one of the motors in the Model S and Model X to a new technology pioneered in the Model 3. The company also announced an improved suspension system and other efficiency tweaks throughout the vehicle. The impressive result: greater than 93 percent energy efficiency.
Permanent magnet synchronous reluctance motors, explained
Until now, the Model S and X used conventional induction motors. In an induction motor, alternating current is run through windings in the stator (the stationary portion of the motor) to produce a rotating magnetic field. This magnetic field induces electric currents in the windings of the rotor (the spinning part of the motor) that generates an opposing magnetic field, causing the rotor to turn in the same direction as the magnetic field.
The Model 3 debuted with an alternative motor technology that Tesla calls a permanent magnet synchronous reluctance motor. A synchronous reluctance motor has a series of electromagnets around the stator, but the rotor doesn't have any windings or permanent magnets. Instead, the rotor contains veins of a magnetic material interspersed with non-magnetic material, arranged so that it has a preferred orientation in the magnetic field created by the stator.
To turn the rotor, the motor activates electromagnets in sequence, creating a rotating magnetic field that pulls the rotor along. This design is known as a synchronized motor because the activation of the electromagnets is synchronized to the rotation speed of the rotor—something that isn't true for an induction motor.
The dual-motor versions of the Model 3 have an induction motor in the front and a permanent magnet synchronous reluctance motor in the back. The Model S and Model X switch this around, putting an induction motor in the back and a PMSRM in the front.
Combining an induction motor with a PMSRM makes sense because the two motor types have different performance characteristics. As Elon Musk put it last year, "one is optimized for power & one for range." Induction motors offer high torque at low speeds, but they're less energy-efficient overall. So dual-motor vehicles can send power to the induction motor when immediate, rapid acceleration is called for, then shift power to the PMSRM as the vehicle gets up to speed.
Tesla says that the Model S and X efficiency gains haven't come at the expense of reduced torque. To the contrary, the company says the latest versions have improved 0-60 times compared to earlier iterations.
Other improvements
Along with the new motor design, Tesla says the latest Model S and X designs have "silicon carbide power electronics, and improved lubrication, cooling, bearings, and gear designs." Tesla says that the new vehicles are also better at regenerative braking, allowing a car to recapture more of its kinetic energy as it decelerates.
Tesla also overhauled the air suspension on the Model S and Model X. The new technology uses a "predictive model to anticipate how the damping will need to be adjusted based on the road, speed, and other vehicle and driver inputs." Tesla says that it has "improved the leveling of the system while cruising, keeping the car low to optimize aerodynamic drag."
Tesla also says that it has dramatically improved supercharging times, with peak charging of 200kW on new V3 Superchargers. Tesla says customers will be able to recharge 50 percent faster.
Correction: This story originally said that a switched reluctance motor was another name for a synchronous reluctance motor, and then had an explanation of how switched reluctance motors work. In fact, these are different types of motors. I have modified the story accordingly and regret the error.
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