Looking Deeper Inside GM’s Ultium Propulsion System

It’s not their first kick at the can, if you’ll recall the EV1 of the late 1990s. It’s not even their second kick at the EV can, which was the Spark EV (don’t remind us of the 1960s EV testbeds). And the automaker has plenty of EVs in China now. But now General Motors is going big on electrification everywhere, with a slew of new top-shelf products coming like the Cadillac Lyriq, GMC Hummer EV, and more. They’re doing it with a driveline and power system called Ultium and now we’ve spoken with the engineering head of Ultium to find out more about what the General has in store.

Mike Harpster is the Global Chief Engineer for Ultium Propulsion Systems. He was the head of the Bolt’s system, the Volt’s system, and the director of the GM Propulsion Systems Research Lab.

“From day one, it was all about going back to this battery cell and coming up with a great cell, that we turned into a great cell, that we turned into a great battery with great propulsion system,” Harpster said, adding that uniquely, the team “started with a clean sheet of paper both in the drive unit and the battery and the vehicle.”

The Ultium name covers the battery, the electronic systems, and the motors, like if the LS name applied to the V8, 6L80, and the ECU instead of just a block. Designing the whole thing together makes the system more flexible. Like the LS that saw duty everywhere from one-ton pickups to full-size front-drive sedans, only this time GM can do the equivalent of dropping and adding cylinders as they please. The battery cells themselves aren’t the cylinder-shape of traditional cells, but are large flat panels (still a pouch-type, but much larger than traditional).

The cells can be stacked on their side or flat, and then are put into modules for installation in the battery pack. GM’s illustrations show the cells to be nearly as long as the width of the vehicle platform, so these are large cells.

Modules come in large and medium sizes, even a small-size that can put 22 kWh under a second-row seat. They can support prismatic cylinder cells if GM changes tack.

Like putting reams of paper in a box (though thinner and longer), GM can put more cell modules in the battery pack or less. They can lay them flat or stack them on edge, the former for low-height sports cars and sedans, the latter allowing for more capacity where height doesn’t matter like under a truck. The current packs can run from 50 kWh all the way to 200 kWh just by changing the number of modules in the same-size pack, allowing ranges of more than 400 miles. They can put 6, 8, 10, or 12 modules into a single pack, up to about 100 kWh, and can also double stack in large trucks and SUVs, allowing for 24 modules in one enclosure. All using the same cells and modules.

Without modules installed, the battery pack itself is an integral part of the vehicle’s structure, designed by the structural team not the electronics team. That protects the cells in a crash and makes the vehicles stiffer.

The chemistry of the cells is called Nickel Cobalt Manganese Aluminum, or NCMA. This chemistry, which sounds like an all-new type but adds aluminum to the NCM chemistry (a common Lithium-ion battery type), and uses 70 percent less cobalt than the pack in the Bolt EV, a major savings of a hard to get, ethically questionable rare earth metal. GM expects to hit $100 per kWh battery costs with Ultium, a place where they expect EVs to be profitable and $45 less than Bolt.

Next are the drive units, with the front unit needing 57 percent fewer high-voltage connections than Bolt. This means less complexity and reduced costs. Add a big drive unit in the rear and the vehicles have AWD or can even just be RWD as well as the FWD. GM will also have a smaller rear drive unit for “people that just want to get unstuck.” Like the rear-drive that Toyota uses for AWD hybrids, which is an excellent option for a non-performance vehicle for most buyers that’ll see snow, ice, or sand. The inverter, DC-DC electronics, and even the battery charging electronics are all built into the drive unit, further simplifying and shrinking the package volume by half. Our presentation was actually about the Lyriq, so Harpster pointed out that while all of these combinations are available with Ultium, that doesn’t mean Lyriq will have all of them.

On the Lyriq, Ultium will be able to charge at “over 150 kW” on DC fast chargers, plus GM is planning to build more than 2,700 of those over the next few years, open to all EVs that use the same charging standard. At home on Level 2 AC, the Lyriq will charge at up to 19 kW, close to three times the rate of a standard Tesla Model 3. That could mean home charging rates closer to 80-90 miles per hour instead of current 25-30 per hour times.

If you’re wondering if Ultium will mean new GM PHEVs, the answer is not really. Harpster says that a PHEV or hybrid would have less energy and more power per cell than one designed for an EV. Ultium cells are EV-specific. The modules themselves, though, and the packs, would support that with the right battery cells.

The modular Ultium system supports vehicles from tiny front-drive crossovers to large trucks and SUVs. Replacing as many as 500 combinations of engine and transmission with just 19 battery and driveline pairings. Using a modular system also helps the automaker to decrease costs on an ongoing basis and to work to improve energy density and range.

Now we’re just waiting for the first Ultium vehicles to actually see production. While we’ve seen the Lyriq, and the Hummer is coming soon, it will still be September 2021 for the first Hummer EV to roll out of Hamtramck. But while both will use the Ultium Propulsion System, only the Cadillac will use GM’s new modular architecture that can support vehicles tiny and large.

Oh, and the Lyriq won’t have a frunk. GM says that consumers liked one optimized space more, so they moved all the electronic bits to the nose instead of spreading them front and rear. We can’t deny we’re not at least a little disappointed.