The Secrets of Electric Cars and Their Motors: It's Not All About the
January 9, 2018 Eric Adams
Tesla Model 3 -- /CHEATSHEET
The electric motor placement of the Tesla Model S P 90D / Tesla
The Chevrolet Bolt's electric motor / General Motors
The placement of the front-mounted motors in the Acura NSX / Honda
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
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
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.
[© 2018 Time]
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