The Secrets of Electric Cars and Their Motors: It’s Not All About the Battery, Folks
Car nuts know precious little about the motors in electric cars, yet they’re central to innovation.
Internal combustion engines have been around for about 140 years. In that time, we’ve become fully versed in all their nuances. We can chat with our pals about compression ratios and horsepower and valve timing. We know the advantages of displacement and the efficiency of turbos. Car meets quickly turn into oceans of popped hoods. Even the most cutting-edge engine tech in the latest hypercar is parsed out thoroughly in the automotive media. We know engines. We talk engines. We love engines.
We don’t love motors, though—the electric ones, that is. You know, the ones that have been around for almost 250 years and were powering cars in the 1880s, until gasoline engines overtook them due to their range and speedy refueling. (One of the first alternating-current induction motor inventors: Nikola Tesla.) Our collective and virtually absolute lack of knowledge of what actually drives the wheels of all the new electric vehicles on the roads today is, indeed, puzzling. How bad is this problem? Most EV owners probably don’t even know where the motors are in their cars, or how many there are, or what they look like.
Making things worse: Technical information is scarce, and mostly found only in forums and niche technology sites. Consider, as well, the fact that our own Alex Roy just reviewed the brand-new Tesla Model 3, and in the course of 4,000 carefully-crafted words, didn’t mention the motor once.
Not that you could blame him: The Tesla Motors page on the Model 3, which includes a “specs” section, itself makes no mention whatsoever of the motor. Furthermore, the company’s own application to the EPA last year for the car’s Certificate of Conformity dedicated 250 words to describing the battery, but just 20 to the motor. (It’s a “3-phase, 6-pole AC internal permanent-magnet motor” producing 258 hp—or 192 kW—and 317 lb-ft of torque, in case you were wondering.) Similarly, Chevrolet’s page on its new Bolt EV makes no reference to the motor except to say that the car has an “electric drive unit.” Even BMW—a company that literally has "motor" for a middle name—only deigns to reveal on its i3 product page that the motor is “AC synchronous.” Meanwhile, the engine in the base-model 3 Series a few clicks over is described as a “2.0-liter BMW TwinPower Turbo inline 4-cylinder, 16-valve 180-hp engine that combines a twin-scroll turbocharger with variable valve control (Double-VANOS and Valvetronic) and high-precision direct injection.” That's before the site goes on to describe the engine’s electronic throttle control, auto start-stop function, direct ignition system with knock control, electronically controlled engine cooling (map cooling), brake energy regeneration, and driving dynamics control with Eco Pro, Comfort, and Sport settings.
Among reviewers, Roy is far from the only one to give the motor short shrift. Most EV reviews gloss over that key part of the tech, except to note its relative quiet, its torquey response, and its simplicity and long-term low maintenance requirements. Most of the space dedicated to the powertrain focuses instead on the battery—how big, its construction and composition, where it sits, how much range it has, how many days it takes to fully charge, and so forth.
But then, it's hard to blame people for not giving a damn. Most consumers—hell, even car geeks—don’t possess the knowledge or vocabulary to authoritatively converse about electric motors, and on the surface, there would seem to be precious little indication that there’s even anything meaningful to discuss about them. It’s a lot harder to get excited about, say, the difference between permanent magnets and AC induction than it is between V-8s and twin-turbo sixes. The fact that carmakers and the media don’t billboard motor innovation naturally leads the public to assume that there’s nothing much going on there.
Except...that’s just not true.
While the electric motor has its own century of progress under its belt, there’s still much that can be done. Consider, for one thing, that most carmakers have brought motor manufacturing in-house. If there weren’t room for innovation, they’d just order them out of a catalog from external suppliers. Lighter materials in motor construction, new alternative solutions for rare-earth magnets, and optimized overall performance characteristics for different vehicle demands are all very much in the crosshairs of automotive engineers. And that’s just the start, says Venkat Viswanathan, a mechanical engineering professor at Carnegie Mellon University who studies EV performance.
“The motor efficiency map—that is, its efficiency as a function of torque and speed—determines the energy consumption for consumer vehicles, and the peak power characteristics are an important factor for high-performance demands,” Viswanathan said. “In addition, the heating of the motors in-use—at high speeds—is another area with room for innovation and development.”
Once you dig in a bit, it becomes clear how much of said optimization and development is really going on. One of the key choices is the general type of the motor. “Typically, most of the manufacturers use synchronous motors, but whether it is a permanent magnet or electromagnet strongly influences the performance,” said Viswanathan.
Tesla, for instance, while typically very tight-lipped about its innovation, made a significant change with its Model 3 in its decision to use a permanent-magnet electric motor instead of the AC induction motor it has used so far. The key difference is that AC induction motors have to use electricity to generate the magnetic currents inside the motor, which cause the rotor to spin, whereas a permanent magnet motor doesn’t require that additional current since its magnets—created from rare-earth materials—are always “on.” This all means that the Model 3’s motor is more efficient and thus better for smaller and lighter cars, but not ideal for high-performance cars, since an AC induction motor can produce greater power. The Chevy Bolt uses a similar strategy for the same reason.
Other times, the manufacturer will focus on ways of reducing the costs of the motor in order to make EVs more affordable. Heraldo Stefanon, a senior engineering manager at Toyota’s Technical Center in Ann Arbor, Michigan, says the company mostly manufactures its motors in Japan, with an eye toward streamlining manufacturing in mind.
“Our challenge and those of the other carmakers is to find ways to simplify manufacturing while improving motor efficiencies and performance, but at a reduced cost,” he said. “Several motor improvements were introduced with the 2016 Prius, including different materials and controls that minimize costs and power losses. The Toyota Hybrid System II has been reduced to more than one-quarter of the original cost of THS introduced with the first Prius.”
For its own electrification efforts, Honda has been in hot pursuit of both performance and efficiency benefits carefully designed motors can provide. Its Twin Motor Unit deployed in the hybrid systems of the Acura MDX crossover, RLX sedan, and NSX supercar is engineered to be compact, with two small 36-horsepower motors placed back-to-back in a single package positioned between the front (NSX) or rear (MDX, RLX) wheels. This configuration allows for precision torque vectoring in an all-wheel-drive setup, with a conventional or hybrid engine supplying power to the other axle. The performance benefits stem from the motors’ ability to alternately deliver torque or resistance when modulating power to the individual wheels. The motors, like those in other EVs and hybrids, also provide regenerative braking, where the motors act as generators to charge the car’s battery when coasting—or even provide braking action by virtue of the built-in resistance while generating that power, if tuned to do so.
Additionally, Honda made the motors in the new Accord Hybrid smaller by using square copper wires instead of round ones in its stator—the stationary part of an electric motor, which generates the alternating magnetic field to spin the rotor—since square wires nest more compactly and densely. Engineers also used three smaller magnets in place of two larger ones for the motor, which helps improve torque, the company said. All of these changes improved the car’s horsepower by 14.8, to 181, and torque by six lb-ft, to 232.
Honda is also well-known for its integrated electric motosr, which sit between the engine and transmission in hybrid models. “Honda’s drive motors are specifically designed for the applications,” an engineer noted on behalf of the company. “Power and torque characteristics, diameter/length ratio, and speed and cooling performance are optimized for achieving the desired performance while being accommodated into the limited space. They are not off-the-shelf components.”
In the future, motors will naturally continue to grow in performance and efficiency. Some innovators will seek out magnets made using more low-cost and non-rare-earth elements, as Honda recently did in a development project with Daido Steel. Their neodymium magnet contains no heavy rare earth materials, but is still powerful enough for vehicle use. Motor speeds will also improve; right now they range from roughly 12,000–18,000 rpm, but researchers are developing motors that can reach 30,000 rpm—with the benefit that a smaller, lighter motor can do the work of a larger one that spins more slowly.
There will also be improved thermal management that will further enhance efficiency, and completely new motor designs, such as ultra-lightweight in-wheel hub motors—which have been attempted in the past but are usually stymied by heavy hardware. Finally, with Formula E now surging in popularity, and racing powerhouses like McLaren and Andretti Motorsport pushing their motor tech hard—while also honing everything from motor placement to control electronics, even optimizing the placement of wires to minimize electronic interference—it’s only a matter of time before all the machines at the car meets are showing off modded electric motors, too.
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