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Lucid Motors' Peter Rawlinson Talks E-Car Efficiency

Frugal energy use is just as important as his car's 1,000 horsepower

5 min read
Lucid Air car
Photo: Lucid Motors

Two years ago, our own Lawrence Ulrich wrote that Lucid Motors “might just have a shot at being a viable, smaller-scale competitor to Tesla,” with series production of its fiendishly fast electric car, the Air, then slated for 2019.

Here we are in 2020, and you still can’t buy the Air. But now all systems are go, insists Peter Rawlinson, the chief executive and chief technology officer of Lucid and, in a former incarnation, the chief engineer for the Tesla Model S. He credits last year’s infusion of US $1 billion from the sovereign wealth fund of Saudi Arabia.

“Our target for Job 1 is the end of this year,” he says.

Why build yet another performance e-car? First, consider the performance. The Lucid Air is faster than anything else running on electrons. That means not just the Tesla, which made our 2013 Top Ten Tech Cars, but also the Porsche Taycan, in the 2020 version of that list. “It has more than 1,000 horsepower (750 kilowatts),” Rawlinson says, “and it reached 235 miles per hour (380 kph) in testing.”

But sheer power is so early 21st century. Rawlinson says the critical metric really ought to be efficiency, as defined by the distance you can travel at a given speed using a given number of watt-hours. That metric’s very green, of course, but it also hits another key feature for any e-car: range. The Air can cover 400 miles (640 km) on a charge.

“An efficient electric car today can do 4 miles (6.7 km) per kilowatt-hour (kWh); an inefficient one does less than 3,” he says. He calls Tesla the “undeniable technical leader,” despite the Taycan’s advantage in brute power because Tesla is “pushing toward 4 in some models.”

As for the Taycan Turbo, it has a range of 201 miles and a battery capacity of about 93 kWh. Do the division, Rawlinson says, and “you get a very disappointing number.” 

We did the division. The number is a paltry 2.2 miles/kWh.

Lucid aims to top 4, a level which it says is supported by the testing and validation the company conducted before such activities had to be locked down, in March. Here’s a video of a 400-mile (640-km) road trip between San Francisco and Los Angeles that some of the company’s powertrain engineering staff took back then:

As for the range, you can back that out by multiplying efficiency by battery capacity. Too bad we can’t extract that number from Rawlinson. Lucid will only say that the battery will be on the small side—less than 130 kWh. If, say, it should come to 120 kWh, that would imply a range of about 480 miles.

Rawlinson says there is no one key to high efficiency in an e-car; you need to optimize a lot of things all at once. And in a high-performance car, the importance of some of those things is quite different from what you’d expect in a more modest vehicle.

“The main loss in the battery is from impedance in the battery pack,” Rawlinson says. “Now in an [U.S. Environmental Protection Agency] test, the actual currents drawn are so small that those losses are tiny, so efficiency of the pack doesn’t really come to play. But in high-performance driving it matters: Double the current, you get 4 times the losses.”

So he designed the Lucid around a 900-volt architecture. “It’s the only one I’m aware of,” he says. “Tesla’s round about 400 V. Porsche, they upped the ante last year to 800 V.”

Rawlinson says the auto media have wrongly explained this push toward higher voltages as being chiefly about faster charging. “Our real reason for having a high-voltage system is the greater efficiency of the inverter and the electronics that control the motor,” he says. “The inverter is a high-frequency switch that converts direct current to alternating current; the frequency of that AC determines the frequency of spin of the motor.” 

Lucid’s inverter—which he boasts was built completely in-house—uses a silicon carbide MOSFET chip, which he says “really thrives” on high voltage. He lambastes Porsche for using a high-voltage IGBT (insulated-gate bipolar transistor), which is “probably the worst way to do it—nowhere near as efficient at high voltage as silicon carbide.”

More efficient batteries, inverters, and electronics reduce waste heat; less waste heat to dispel means you can have smaller radiators; smaller radiators lets you mold the car more aerodynamically, reducing losses to wind resistance. It all adds up.

“One big loss [to air resistance] is in the ducts; when the ducts are closed, that’s when manufacturers will disclose their aerodynamics,” he says. “We have one radiator each side of the car, and two vortex [induction systems] feeding into those radiators.”

Rawlinson won’t cite hard numbers just yet, saying only that “in real-world terms, not just in computer simulation” the Air has a lower coefficient of drag than either the Tesla (0.23) or the Taycan (0.22). 

One more plus for aerodynamics: The Air is shorter and narrower than both the Model S and the Taycan. Even so, it has “more interior legroom than a long-wheel-base S class Mercedes,” Rawlinson says.

A big reason why Lucid put so much in such a small package is to be found in the power train. “Here I’ll throw out a figure, because I don’t think anyone else is close,” he says. “The volumetric drive unit—that’s the motor, inverter, and transmission differential—the entire thing is over 16 kW/liter, which is more than double of anything I’m aware of.” 

The motor, he says, is the best of any e-car, using his own standard of excellence, which is rather different from that of the rest of the industry. Efficiency and the power-to-size ratio is crucial, but torque at the engine doesn’t matter, he says. The only torque that counts is the torque at the wheel, and you can get what you need there by using gears.

His motor uses a novel form of the permanent-magnet motor that combines its efficiency advantages with the performance advantages of the alternative design, which uses induction coils. The novel design solves a problem known as cogging torque.

If you take a plain induction motor, switched off, and spin it manually, it’ll  freely spin for a long time because there are no electromagnetic losses. Try that on a permanent-magnet motor and it’ll incur those losses and quickly stop spinning—that’s the cogging torque. Auto engineers have tried to get around the problem by putting induction motors on the rear axle, for good acceleration, and permanent-magnet motors on the front axle, to save energy at slower speeds. 

“We have permanent-magnet motors at both front and rear,” Rawlinson says. “We had a breakthrough where when you spin up that magnetic motor it’ll spin very, very close to the way an induction motor would.”

He won’t say a word, though, on how the breakthrough works.

What’s next, after the Air? Can all this high tech, at what will surely be a high price, ever trickle down to cars that a humble tech writer can afford? Absolutely, Rawlinson asserts. “We can scale down to 100 horsepower and reduce the cost—the technology we’re developing today can power the auto world.”

Hmm. A super-efficient electric drive train and battery system might be even more welcome in the aviation world. Right?

“We’ve got a laser focus on Lucid Air, and I don’t intend Lucid’s going into the aircraft business,” he says. “But just as our batteries power all the field in Formula E racing, I think we could supply power trains to electric plane manufacturers. Oh boy, I can see the potential.” 

Editor’s note: the first reference to the Lucid Air’s electrical architecture mistakenly gave the units in watts; this has been corrected to volts.

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