Tesla Veteran Explains How Electric Motors Crush Gas Engines

November 17, 2015, 4:49 PM UTC
Photograph by Jasper Juinen — Bloomberg via Getty Images

Before leaving this year to join electric bus manufacturer Proterra as director of battery engineering, Dustin Grace spent almost nine years working on drivetrains at Tesla (“TSLA”). Grace sees the electric machines he has helped to perfect as feats of engineering as much as they are agents of environmental redemption. Arguing that electric motors are inherently superior to gasoline engines, he walks through several fundamental advantages that electric motors have over gas:

Electric motors generate motion, not heat. A fossil-fuel engine produces motion, basically, with tiny controlled explosions. Those explosions push interlocking pieces of metal, which connect to a driveshaft. All that metal rubbing together generates a lot of heat, even when the parts are swimming in oil. That’s energy that’s not being used to push a vehicle forward.

The contrast with an electric motor couldn’t be bigger. “There’s zero contact,” Grace says, between the motor and a vehicle’s driveshaft. “Just an air gap. The only thing reacting … is a magnetic field.”

With the driveshaft pushed magnetically instead of mechanically, even a running electric motor is barely warm to the touch, eliminating a major energy waste.

That efficiency has one small downside. The wasted heat from a gas engine becomes free cabin heat in the winter, while electric vehicles have to produce extra heat as needed. Cold also has a negative impact on batteries, meaning that electric systems take hits to range, performance, and charging speed in the cold.

They’re more powerful (most of the times that matter). This one goes against all our images of feral, gas-thirsty Detroit muscle cars. But for proof, look no further than Tesla’s recently introduced “Ludicrous Speed” mode, which makes the car’s acceleration competitive with gas-driven supercars that cost millions of dollars.

That’s possible because at lower speeds, electric motors deliver more torque than gas engines. “Torque is what you need to get a car going,” says Grace, and with more of it, electrics out-accelerate comparable gas engines.

Gas engines do still perform better at very high speeds than electric—so motorsports and law enforcement may stay gas-dependent for longer.

They’re simpler. Electrics’ better torque has a secondary advantage. With less torque at low speeds, gas engines need help from a transmission to get moving. Electric engines by and large don’t need transmissions.

Diesel buses, for example, usually have complex eight- or nine-speed transmissions. Proterra’s buses, by contrast, have a two-speed transmission—and its only role is changing efficiency profiles, not acceleration.

Grace says that ditching the complex gears and fluids of a transmission leads to better efficiency and agility. In effect, he says, “there’s this internal brake inside of a transmission that keeps it from wanting to spin freely.”

They’re (vastly) easier to service. Electric drivetrains have far fewer subsystems—no transmission, no oil tank, no catalytic converter. That means there’s less to break down. (It’s also fairly mind-bending—looking at an electric motor, you might think someone just stole half the machine.)

And the heart of an electric drivetrain—the motor—is much smaller and more streamlined than its gas counterpart. Even the motor that drives Proterra’s full-sized buses is small enough to be lifted by one person. It can be entirely removed by a team of two mechanics, and it’s cheap enough that it can be replaced for purely preventative reasons.

They feed themselves. Every electric motor is also an electric generator. That makes it very simple to implement regenerative braking, which recaptures forward momentum as battery charging. The really amazing part is that this process, just like acceleration, is electrical, not mechanical.

“The rotor is always spinning in the same direction,” says Grace, “but the electrical field reverses.” That sends electrons streaming back into the battery (so to speak), while helping slow the vehicle.

They’re smarter. “Even today’s gasoline cars generate very accurate data,” Grace admits. But electric vehicles give you more and better opportunities to monitor and adjust them. “Your control systems are much more accurate, and probably more transparent as to what’s going on.” As software updates become an increasingly regular part of car ownership, electrics will be that much more flexible.

Better metrics also let manufacturers detect faults in vehicles before they become a big problem. At Proterra, for example, Grace can receive text alerts when buses in operation have certain problems. The team can arrange a fix before the customer notices anything is wrong.

All that adds up to an electric machine that is, in Grace’s words, “a very beautiful, efficient thing.” And now the one big limitation—battery storage—is finally being overcome.


For a look at Toyota’s Mirai fuel-cell vehicle—a possible contender for Tesla’s Model S— watch this Fortune video:

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