As GM enthusiasts, there are things you count on. Robust and enduring engines is likely number one. We questioned what that would mean for electrification, like the GMC Hummer EV and future Chevrolet electric pickups. Thus, GM-Trucks requested an interview with a subject matter expert able to walk us through the current strategy for electrification, specifically the drive units that will give these vehicles their power and torque.

Related Article: GM Shows Off Ultium Drive Motors For Coming Trucks, Cars & Crossovers

Patrick Curran is GM Assistant Chief Engineer, Electric Drive Units. He began our interview with a primer.

“You’ve probably seen our announced suite of five drive units, designed in-house. Each drive unit is powered by one of a family of three electric motors, also designed in-house with the goal of being interchangeable and capable of transitioning our current portfolio into fully electric vehicles, and even additional vehicles in the future.”

Let that last bit sink in, along with another quote from General Motors. “Ultium Drive will help the company transition its current portfolio to a fully electric lineup, providing significant advantages over GM’s previous EVs in performance, scale, speed to market and manufacturing efficiencies.”

 It’s our prediction that your toddler won’t be able to by a non-electric GM vehicle, other than a Heavy-Duty truck, upon graduation.

GM calls these “motors” drive units, each made up of three basic main components.

General Motors’ next-generation EVs are expected to be powered by a family of five interchangeable drive units and three motors, known collectively as “Ultium Drive.” Ultium Drive units left to right: an all-wheel assist motor; a front-wheel drive motor; a rear-wheel drive motor; a truck front-wheel drive / rear-wheel drive motor; a truck dual motor.

“There’s an inverter, which converts DC power from the battery pack into AC. Second, an electric motor takes that AC power and converts it into mechanical energy. Finally, there’s the gear box with a single ratio that provides output speed and output torque to match the application. That’s it in the simplest form, plus a bunch of little bits that you have to have to make things work,” Patrick said.

With the basics outlined, we dug deeper. If you’ve been following current EV technology, there’s a big discussion surrounding PM or permanent magnet motors and induction motors. GM uses both types, and they’re making them in-house. (Note that others follow the same philosophy; Volvo announced this week that it is starting its own electric motor program to supply it and parent Geely.)

Ultium Drive will be powered by three motors that have industry-leading torque and power density across a wide spectrum of different vehicle types. Ultium drive motors left to right: an all-wheel drive motor; a primary front-wheel drive motor; a primary drive motor for rear-wheel drive; the front/rear-wheel drive motor powers several Ultium Drive applications; and a dual-motor.

Patrick, why are you building your own EV motors with so many Tier 1 suppliers like ZF, Borg Warner, Bosch and others designing, building and offering very high quality EV motors?

“General Motors has a lot of experience making transmissions, right? And Ken Morris, GM vice president, Autonomous and Electric Vehicle Programs recently stated, ’Making motors, transmissions, driveline components and systems are among GM’s best-known competencies.”

Hand assembly of an electric motor stator at General Motors Global Propulsion Systems Center in Pontiac, Michigan. (Photo by Jeffrey Sauger for General Motors)

“So, when creating things that are highly complex and contain a lot of intellectual property, it’s best to do them in-house. And also doing it in concert with the vehicle design creates the most efficient system approach. However, there will be opportunities working with other suppliers to take off-the-shelf drive units and plug-and-play them where it makes sense. [Take note of that for announcements far in the future.] I really don’t think we [could outsource] a system like we have with these five interchangeable drive units that can cover the spectrum that we’re going to cover.”

The five drive units; similarities and differences

“They’re very similar in architecture with similar layouts. Of the three motors, two are permanent magnet motors and one is an induction motor. The permanent magnet motors are more primary drive motors. The induction motor is better for a different use case. With an induction motor, you have to actually create the [magnetic field required by all electric motors]. Because of this requirement, it’s a little less efficient if you’re using it all the time, but it’s really good at being turned off because it doesn’t create as much drag. For instance, we’ve got front wheel drive, rear wheel drive, and all-wheel drive which uses that smaller induction motor.

Electric motor parts (stators) at General Motors Global Propulsion Systems Center in Pontiac, Michigan. (Photo by Jeffrey Sauger for General Motors)

That offers various combinations such as for performance or off-road where you can put multiple motors into a drive unit. There’s a lot you can do with the combinations that we’ve announced so far.”

Help us understand the buzz around induction motors versus PM motors?

“As I said, if I’m at a very high level, for a permanent magnet motor you’ve always got the field created by the rare earth magnets, right? So, if you’re coasting down a hill that field is still there, and it’s creating drag. In a battery electric vehicle, you want to use that drag and put energy back into the battery pack—regenerative motion. So, even though it’s regenerating power into the battery pack it’s still creating drag. It’s inefficient. With the induction motor you can just turn the field off, no drag.

Bottom line, with a permanent magnet you get more power, you get more torque. Picking a motor is almost a coin toss. You can make either a permanent magnet or an induction machine work and you can make it work really, really well. So, it’s almost a philosophical choice. You’ll absolutely find situations where a permanent magnet is hands down better and other times where an induction is clearly superior. But when you’re creating a family or suite of drive units that cover a whole product portfolio, you kinda need a mix, not just one.

Technician inserts permanent magnet(s) into PM-type drive motor. Electric motor pre-production assembly and testing at General Motors Global Propulsion Systems Center in Pontiac, Michigan. (Photo by Jeffrey Sauger for General Motors)

Which leads into some of the gritty details, like how you make up your magnets, what your main magnet recipes for permanent magnet motors. However, the cost of the component is marginal compared to the cost of efficiency over the lifetime of the vehicle, right? You need to make the right choice for each vehicle because the battery is so expensive that you want to maximize all the energy that comes out of that battery. Our very first goal was to make the most efficient drive units we possibly could. So, a little bit of additional cost here and there? You absolutely need these drive units to be as efficient as possible.”

We only know of Hummer EV and LYRIQ for certain. Is there a difference between how you structure these drive units?

“It ends up being based on the customers. If you want more of the luxury feel typical in that market, our luxury vehicles can be rear wheel drive or all wheel drive. Obviously, all-wheel drive means you need one [drive unit] in the front and another in the rear. If you want an all-wheel drive super truck, you’ve got to have a drive unit in the front and a drive unit in the rear. For other customer bases, what they’re looking for is front wheel drive. Also, different regions prefer front wheel drive due to weather conditions or just the comfort and competence of a front wheel drive vehicle.

RWD drive unit on display when General Motors revealed its all-new modular platform and battery system, Ultium, Wednesday, March 4, 2020 at the Design Dome on the GM Tech Center campus in Warren, Michigan. (Photo by Steve Fecht for General Motors)

I know I’m belaboring the point, but that was one of the foundation blocks of how we put this all together. We wanted to be able to give any customer what they wanted with our five drive units. If you want a front wheel drive vehicle we’ve got it and the same with rear wheel drive. If you want performance with one on each wheel, well, we can kind of do anything with these five drive units.

When you say five drive units, since you have three motors please explain those five drive units?

“There are, for now, three different (electric) motor sizes—kind of the Goldilocks story, right? You’ve got a big, you got the middle and you got a little one. And the drive unit is built in different configurations for packaging space or for different gear ratios. That’s how we come up with the five different drive units. Clearly, much is shared; the architecture is very, very similar, if not exactly the same. Motors are shared between those five — as is an abundance of technology and the look of them are going to be similar. However, they are different use cases.”

Superimposed, here’s how the motors will fit into various applications.

So, if I were looking at the five units, are we looking at different casing sizes?

“One of the key things you can pick up if you look at those five drive units is, if you look at the front drive unit, it’s a little more vertical because the [under hood area] provides more room. Rear drive units tend to be a bit squattier because they have to exist below the load floor.”

As long-time GM buyers, we have some established small block Chevy motor metrics to compare to e-motors. And, you’re already offering a crate motor based on the Chevrolet Bolt EV, so obviously you have confidence.

“I can tell you that that same due diligence and attention to detail has gone into these electric motors and these drive units. We certainly want to hear stories of people driving Hummer EVs to a million miles. That’ll be a pretty proud day for a lot of us.”

 What have I missed about the process you’re going through and the drive units, the motors?

“I think it is key, and something we’re very proud of, is that these are General Motors designs. We didn’t go out and shop for them, we are making and assembling these drive units and doing the things that General Motors believes are its key competencies. We know how to cast aluminum, we know how machine gears, we know how to machine shafts. Ultimately this is nuts-and-bolts General Motors design, engineering, assembly and manufacturing talent that is going into our drive units.”

An electric motor stator is assembled by hand during pre- production at General Motors Global Propulsion Systems Center in Pontiac, Michigan. (Photo by Jeffrey Sauger for General Motors)