All the dirt on the 2022 GMC Hummer EV’s terrain control modes

As General Motors moves the GMC Hummer into the EV category, the company has learned a new set of skills as it develops the rugged pickup’s crucial off-road capabilities.

Where the old Hummer H2 relied on sophisticated control of differentials and traction control, the new Hummer EV gets traction and control through the highly accurate measurement of the power of the truck’s electric motors.

To ensure the right control program for the circumstances, Hummer engineers developed two different options for off-road driving, off-road mode and off-road mode. Design News spoke with Hummer EV vehicle dynamics engineer Drew Mitchell about the challenges of developing these systems.

Design News: What was the most difficult challenge you faced while developing this vehicle’s dynamic system?

Drew Mitchell: Terrain mode was one of the biggest areas of focus for me. This is our rock crawl mode. We had to balance torque placement, slip control, which allows you to safely climb a rock or ledge, we also use the brake control to apply mechanical brakes to give you that left foot brake feel without actually using the brake. It’s all pedal control.

It’s not EV one-pedal drive, which we have in all other modes, the traditional EV solution. This is a one-pedal drive where you come off the accelerator, the brakes engage and it gives you that instant deceleration.

We tried to make it as accessible to beginners as possible. For many people, their first time riding off-road, left braking can be a very jerky affair. You can still brake the truck with your left foot if you want. It is a slow, gradual stop. We also have a more aggressive one if you put it in low range.

It comes into play when climbing over certain obstacles, especially blind peaks or ledges where you’re not quite sure what’s on the back.

What we spent a lot of time working on was the refinement of the brake setup. You can get a good, fast, confidence-inspiring grip to stop you before you fall off a ledge or down a log or something without being too jerky. If you pull on the brakes too much they will get hot and you will start to smell brakes. What we really wanted to focus on was refining it.

Design News: What was the solution to the brake calibration challenge?

Drew Mitchell: Just a lot of climbing up and down the grades. We actually had quite a few tests. We had a truck, we had a local terrain park where they had an obstacle that was supposed to mimic a lot of the rock formations in Moab, and we would just climb up and down it. Down it in the first place, get that feeling. It was just a matter of playing with the gains in the braking system and how progressive the controls brake. Not just ramp them in but also ramp them out. If you don’t ramp them out fast enough, you’ll feel like you’re holding the brake with your foot.

It was going through a test matrix to find corner cases and trying to stress test the system.

Trail Mode is all about giving you choices, giving you the ability to drive the way you want to drive off-road. Off-Road mode meant to be more for bombing down a two-track [trail] or a gravel road so the ride control calibrations will prioritize ride comfort. We also open up the slip thresholds and yaw thresholds in the stability and traction control calibrations to give you the sense that if you want to drift mid-corner, we’re giving you a drift angle meter for a reason. I’ve maxed it once or twice!

Image courtesy of General Motors Co.2022-GMC-HUMMER-EV-004.jpg

Design News: What were the corner cases and hard problems you were targeting?

Drew Mitchell: The propulsion system is completely new. We started with a blank slate. The Ultium drives, the batteries. We invented our propulsion control system, the whole algorithms, all the torque distribution, all of that was invented on the fly as we went along. This was nothing off the shelf.

For the first four months, every day was discovery. Every day was “Oh, we didn’t predict that in our simulation” or “We had to make a change somewhere and it’s driven a change here that we didn’t expect.” It was the first four months where we winter tested in the snow and ice and really tried to wrap it up.

We check wheel slippage. How do you check wheel slip? You control the torque. In this case we have three motors, we control the torque at each individual motor and move it around as needed.

Probably the first third of the program was just getting the torque distribution and slip control system in place.

There are a few aspects to it. You have to be efficient in how you place that torque

Design News: What were some of the flaws in your simulations?

Drew Mitchell: Snow is difficult to simulate because it is a deformable surface. Like gravel. It wasn’t that we didn’t think about it in the simulations. We just found the flaws in the simulations right away. We were like, “OK, we made some very basic assumptions about snow.” We could go back and catch it.

What we ended up doing was predicting how much slip the engines would produce on snow and ice. We saw in the simulation that we would have wheel flares everywhere. We got out and realized that the tire is more grippy than we thought it would be.

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