Building a better EV motor: The drive for power, efficiency and cost-effectiveness

Editor's note: Japanese supplier Aisin manufacturers traction motors for hybrids and EVs. An earlier version of this story said otherwise.

When it comes to electric vehicles, efficiency is money.

Even a 2 or 3 percent gain in efficiency could save automakers hundreds of dollars per EV — edging them closer to cost parity with internal combustion vehicles and, more importantly, improved profitability.

When the auto industry trains its product development guns on a component, that item usually gets smaller, lighter, simpler, more powerful and more efficient. Oftentimes a component comes through that transformation costing less as engineers find ways to reduce precious metal content and other raw materials and to improve manufacturing efficiency.

That's what's happening today to the electric motor, which is just starting what will likely be a very long journey in the automobile.

"It's all about losses in the motor, and right now we are only at the beginning of optimizing that and the control of the motor," General Motors President Mark Reuss told Automotive News.

GM, like virtually all other automakers and most suppliers, is pouring money into electric motor development. The goal is not only to make them run more efficiently on less power and use fewer rare-earth magnets and copper, but to reduce manufacturing costs.

"As an industry, we can learn from each other, which we always do really well," Reuss said at an event in October introducing the battery-powered, ultra-luxury Cadillac Celestiq.

Tula Technologies, the Silicon Valley startup that created the modern cylinder deactivation system used in GM's big pickups and SUVs, is close to perfecting an energy-saving strategy called Dynamic Motor Drive for EVs. It pulses the electricity to the motor — effectively turning it off and on thousands of times per second.

John Fuerst, senior vice president of Dynamic Motor Drive and engineering at Tula, explained what a 3 percent gain in efficiency could mean for the Chevrolet Bolt. Tula is testing a fleet of Bolts with Dynamic Motor Drive.

"The way the industry really is looking at percentage benefits is battery cost per kilowatt-hour. How big is your battery? And right in our Bolt, that's a $7,200 battery. If you shrink it by 3 percent, it's going to cost you 216 bucks less," Fuerst said.

Automakers struggle to save dimes and quarters. Savings in the hundreds are hard to come by, which is why the race is on to improve electric motors and the power electronics that control them.

The electric motor is nearly 200 years old. In transportation, electric motors power everything from scooters to locomotives. But mostly because of the amount of energy in gasoline and its low cost compared with other fuels, the electric motor — with the exception of hybrids, such as the Toyota Prius and Chevrolet Volt — has only seen fits and starts in the automobile over the last 120 or so years.

Until now, that has prevented the electric motor from being optimized for the unique requirements of passenger vehicles. Things are changing of course, as automakers now race to replace internal combustion engine vehicles with EVs.

Dirk Kesselgruber, president of ePowertrains at GKN, the British supplier best known for its axles and propshafts, believes electric motor development will occur far faster than did the internal combustion engine, which has been under constant development for more than a century.

"I don't expect the electric motor will have such a long journey to be optimum," Kesselgruber said. Like Bosch, American Axle, Dana and other driveline suppliers, GKN has a portfolio of electric drive units, many of which are already in high-volume production.

"Electric machines (motors) are super old, and there's a lot of science and learning around that," Kesselgruber said. "So in the automotive industry, we are looking at two aspects. The efficiency of the motor — 'How much energy do I need to translate into torque?' And, second, is the cost element, which includes everything — the size of the motor, the exposure to critical materials, cooling and thermal management, the high speeds of the electric motor."

The U.S. Department of Energy says a typical electric vehicle drive system is responsible for a 15 to 20 percent energy loss compared with a 64 to 75 percent energy loss for a gasoline engine. Some of those losses are caused by friction, while others are thermal losses.

Engineers at automakers and suppliers are making quick progress raising overall efficiency while lowering costs. Improving efficiency isn't just reducing friction inside the motor and the gearbox it's attached to — it involves such things as reducing the weight and size of the motor, managing heat and optimizing the motor speed to suit the needs of the vehicle.

At 10 hp per pound, the compact motor in the Lucid Air is one of the lightest, most powerful available. In a video presentation explaining how it all works, Lucid officials showed how the company reduced weight and increased the power density compared with two unnamed competitors, described as a "German sports car manufacturer" and "a high-tech American company."

In the motor's stator, the 72 slots are bigger than competitive motors and filled with one heavy strand of copper wire formed as a continuous wave. Most other motors have those slots filled with numerous strands of insulated copper wire, with the air between each causing inefficiency.

"I prize efficiency so highly above all else," Lucid CEO Peter Rawlinson said in the presentation.

Incorporating tiny cooling slots in the stator laminations where high pressure transmission fluid is routed — which removes heat at the source — is a breakthrough for Lucid. It greatly increases motor power and efficiency, especially at higher speeds. The motor is rated at 670 hp, yet weighs only 67 pounds. Another innovation involves placing the differential that drives both planetary gearsets inside the rotor, making the entire drive unit extremely compact and light.

"The way we achieved such groundbreaking power density and efficiency was by taking a holistic approach," Emad Dlala, Lucid's vice president of powertrain, told Automotive News. "You can't focus on one area. You have to look for improvements everywhere. Where do I see further improvements? The short answer is everywhere. We see the potential for improvements in the inverter, motor and transmission.

"We broke new ground with motor cooling, but we think that further improvements are possible," he said.

"Copper winding technology will continue to evolve and improve. The same is true for the electromechanical architecture. There is also still more that can be done with power electronics — chips, capacitors, etc.

"Each of these will have varying degrees of improvements for power density and efficiency," Dlala said, "but taken together, the potential for improvement across the entire powertrain can be significant. By no means are we resting on our laurels."

Electric motors spin at far faster speeds than internal combustion engines do, and revolutions per minute will likely increase as the technology improves. Some automotive electric motors reach speeds of 20,000 rpm or more, and that means the rotor, stator and magnets have to be extremely strong to keep them from flying apart.

"There's as much tuning and engineering in how to hold those magnets and how to take that high speed as there is in tuning an intake manifold," said Tim Grewe, GM's general director, electrification strategy and cell engineering. Grewe has worked on every EV and hybrid GM has built — from the EV1 in the late '90s to the Cadillac Celestiq, the company's latest electric car arriving in the fourth quarter next year.

GM has devoted much of its EV R&D resources to learning how to optimize the magnets in its electric motors. Improvements the company has made in this area since the 2011 Chevrolet Volt hybrid show just one path GM engineers are taking to increase efficiency and lower costs.

"From the design level, we've made motors even better by using less rare earths. Terbium, neodymium and dysprosium are like the catalyst inside the actual magnet itself," Grewe said. "In the first generation of the Volt, we would just put the terbium and dysprosium everywhere in the magnet. In the second-generation Volt, we basically cut the terbium and dysprosium in half, just putting it where we needed it.

"And now, in our Ultium motors, we've taken it to the next level," he said. "We've further refined our magnetic models and our 3D magnetic computational capability and coat the critical rare earths directly on the magnet only where we need it. You can really dial that in because magnet strength is torque.".

In just three years, engineers at German supplier Bosch reduced the size of one of its electric drive units by almost 50 percent. They did so by integrating the motor, inverter and transmission into one unit made up of a single stamped housing, a strategy that reduces manufacturing and material costs and weight.

Bosch is also searching for ways to reduce rare-earth magnets — the most expensive part of the motor.

"The motor has a lot of potential to be improved," said Arturo Maya, product manager, eMotor/eAxle at Bosch. "The rare-earth materials are very important, and we hope to be able to get the magnets in a way that is more affordable."

The magnets, Maya said, make up as much as half the cost of an electric motor. Bosch engineers are also working on the copper windings in the motor and the metals used in the construction of the components.

Aisin, a Japanese supplier of transmissions and driveline components, is working on EV powertrain efficiency in the form of thermal management. Keeping the batteries and the motor at the optimum temperature improves driving range and prolongs battery life

At the Detroit auto show in September, Aisin displayed a complete EV powertrain with a thermal management system that integrates the vehicle's HVAC system. If the motor needs to be cooled, the car's air conditioning compressor does the job. The HVAC system also keeps the battery at the best temperature.

"Getting direct cooling to the motors themselves keeps them at the right levels of thermal management for driving," said Edward Perosky, Aisin's vice president of powertrain engineering.

With the battery pack being the most expensive part of an EV, greater motor efficiency enables an automaker to reduce its size without affecting driving range or performance.

The speedy efforts to improve electric powertrains are possible, in part, because the electric motor and the drive unit it is attached to are far simpler than a conventional gasoline engine and transmission. The powertrain in a typical front-wheel-drive four-cylinder car has around 200 moving parts. The Chevrolet Bolt has just 13 moving parts.

These efforts to improve EVs touch on all areas of the industry.

Even suppliers making the smaller motors that are used throughout the vehicle — such as Brose, the German company that builds motors for everything from power sliding doors, windows, tailgates, fans and sunroofs — are working to improve their motors. The less electricity motors consume and the less they weigh directly impacts how far an EV can drive on a single charge. Brose recently debuted a lightweight cooling module that integrates the radiator's cooling fan, shroud and motor. The less power drawn by motors that move things in the car can help improve driving range.

As Lucid's Rawlinson puts it, achieving greater efficiency will drive down battery size, drive down costs and lead to the widespread adoption of EVs.