GM hasn't developed the Hummer EV yet, but its battery tech is ready

Automakers that build off-road vehicles often talk about how their development work has taken them to the far reaches of the globe, over millions of miles. As off-roading becomes electrified, with vehicles like the 2022 GMC Hummer EV just introduced, that need applies more than ever.

Such was the case last month when we spoke with Jeep propulsion chief Micky Bly, who told us that FCA engineers have put 1.5 million miles, around the world, on development versions of its Wrangler 4xe plug-in hybrid so engineers could cover all the conditions. Rivian has been fine-tuning its propulsion systems in its R1T electric pickup and R1S electric SUV in what appear to be near-production-level vehicles for several years. 

That kind of language was missing from the introduction of the Hummer EV. The reason, confirmed in a Q&A following the model’s introduction, is essentially that the Hummer EV is just 18 months into its development cycle. 

One year out, but just now starting physical testing

“Interestingly enough, we don’t have a vehicle yet,” chief engineer Al Oppenheiser confessed. “We’re building our first test vehicle as we speak; the vehicle you see in the video is our display vehicle.”

2022 GMC Hummer EV

2022 GMC Hummer EV

With the project only given the green light in April 2019, and GM aiming for deliveries to start in fall 2021, it’s a record pace for GM—or any company. 

To this seemingly impossible timeline, GM has assigned some of its top engineers. Oppenheiser, who was formerly the Camaro’s chief engineer, now oversees electric vehicle development and as chief engineer for the Hummer EV, is leading a team mostly transplanted from the Corvette program. 

Oppenheiser added that GM has used some of its other trucks to do some off-road work in the area around Gateway, Colorado, where the team was connected with press for the Wednesday Q&A session—and that the more modular EV underpinnings have helped shave some time off development. “The 18 months has been quick-paced, doing a lot of analytical tools in our computer-aided engineering,” he added.

2022 GMC Hummer EV

2022 GMC Hummer EV

2022 GMC Hummer EV

2022 GMC Hummer EV

2022 GMC Hummer EV

2022 GMC Hummer EV

If the Hummer EV is on time, the 30 or so months of development work will be an industry first. The so-called supertruck includes the first double-stack pack ever for GM, and it uses a specific cell that will debut in production form in the Hummer EV. The truck will also be able to accelerate to 60 mph in as little as 3 seconds—a huge test for propulsion systems—and will be GM’s first vehicle to charge at anywhere close to 350-kw DC fast charging, a rate that no model on the market (not even a Tesla) can yet handle.

Battery tech already torture-tested

On the battery side, however, GM says that the Ultium propulsion systems underpinning the Hummer EV are indeed fully developed. The so-called double-stack battery has 24 modules in all—two levels, each with 12 modules—and while it runs at 400 volts it charges at 800 volts, allowing 100 miles of recovered range in just 10 minutes, from low states of charge.

“It’s just not manageable to have the huge power cord at 240 kilowatts at 400 volts,” said Tim Grew, GM’s director of battery cell engineering. “So it’s much more rational to go up to 800 volts to make that happen.”

2022 GMC Hummer EV

2022 GMC Hummer EV

Grew said that essentially amounts to treating the two levels as separate packs—running them in parallel for vehicle operation, but allowing them to be placed in series during DC fast charging. As part of GM’s from-scratch Ultium modular approach, the smart cell-module assembly has the cooling integrated into it, where each module essentially has a plus and a minus that allows for coolant flow. 

“Literally speaking, you load it in, you bolt it down, you hook up our coolers, you hook up your DC bolts, and then the wireless battery management system takes care of everything else for you,” said Grew.

That wireless BMS, which has a transceiver in each module, is already an industry first. GM claims that it will make a wide range of pack variations built for various capacities possible, and that it allows for easy replacement when the technology steps up. 

GM Ultium battery - cell stacking

GM Ultium battery – cell stacking

There’s multiple channels, they can channel-hop, they’re cybersecure, and they all communicate everything you need to handle, whatever happens, either during charging or during the actual drive events or off-road.”

If there’s an issue, the wireless module has the capability not just to talk to the central RF controller but to pass its data through other modules. “There was incredible work done to make sure that the data could get through,” said Grew. 

GM has had independent teams attempt to break the system, Grew said.

2022 GMC Hummer EV

2022 GMC Hummer EV

But so many pieces to bring together

Although those pieces have been pressure-tested, putting all the pieces together into something with its claimed world-leading performance will be something else entirely. Corvette engineers, who reportedly took at least five years to develop the mid-engine C8 Corvette, should be familiar with that. 

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