A number of months in the past, when the Silverado EV was introduced, I obtained into an fascinating dialog with Jo Borrás, considered one of my colleagues right here at CleanTechnica. In an article I referred to as the Silverado EV a unibody, just like the Honda Ridgeline or the Ford Maverick. He informed me I might made a rookie mistake by calling it that, and that it is actually extra of a body-on-frame design, however with no separate mattress module like most body-on-frame vehicles. This is able to make it extra of a body-on-frame automobile, which largely died out when Ford stopped making Crown Vics for police forces.
For individuals who solely care about whether or not a automobile is an EV or an ICE automobile, this distinction could appear a bit foolish. Any EV is healthier than a nasty ICE truck, proper? However there are vital variations between these platform designs. A body-on-frame automobile is extra immune to torsional forces, making it carry out higher in duties equivalent to off-roading or towing. They’re additionally nice for modularity and collision restore, as you may simply unlock closely broken components of the automobile and bolt on one other one, so long as the body is not severely affected.
However they’re additionally costlier to supply than unibody automobiles and are usually much less environment friendly, making them a tricky alternative for EVs (which want as a lot vary as potential).
Unibody automobiles are sometimes derided as “cola cans” by lovers as a result of their energy is extra like an aluminum can. They give the impression of being extra like an insect’s exoskeleton than a mammal’s spine on the subject of construction. However they’re cheaper to construct, and unibody automobiles are inclined to weigh lower than body-on-frame automobiles.
However this dichotomy has not at all times lasted within the automotive trade. There have been some eccentric automobiles that used parts of each body-on-frame and unibody design. Like when Wall-E could not work out whether or not the spork ought to be within the spoon cup or the fork cup, these automobiles wanted one other cup to categorize them. A major instance could be the Pontiac Fiero’s “house body” design, which was later adopted by GM’s now-defunct Saturn model.
GM’s Unibody Heresy with the BEV2 Platform
What began to fret me about that is that I’ve seen some very fascinating issues about the way in which my Chevy Bolt EUV drives and handles. Not like most unibody vehicles I’ve owned over time, the EUV feels a lot sturdier. I can really feel when the suspension flexes, however I do not really feel the additional little bit of twist in my pant leg torsion gauge. Whereas most unibody automobiles have gotten stiffer in recent times to raised survive crashes and defend automobile occupants, I may nonetheless really feel a distinction between them and vehicles/SUVs.
So I began to delve into it. It seems that the GM BEV2 platform, the unique 2017 Bolt EV and its newer cousins (the EUV and Chinese language market automobiles just like the Buick Velite 7, Chevy Menlo) are all based mostly on a little bit of a departure from the unibody orthodoxy within the design section .
Clearly they’re nonetheless unibody’s and never body-on-frame or spaceframe automobiles, however they’ve added an additional subframe that almost all unibody automobiles haven’t got. For these unfamiliar, subframes are small components of the body that bolt to the physique of a unibody automobile to comprise issues just like the drivetrain and maybe the rear suspension. This helps distribute the burden of the engine and suspension forces over a wider a part of the automobile and make every thing stiffer. Subframes may assist isolate vibrations from the principle physique so you do not really feel them.
The additional subframe that the Bolt EV and its cousins have is for the battery. GM has informed a number of media shops that this subframe contributes 28% to the automobile’s general torsional rigidity. This concentrates extra of the stiffness within the decrease a part of the unibody + subframe meeting, giving it a barely completely different really feel than even stiff fashionable unibodys.
Comparable issues have occurred within the designs of different battery pack unibody vehicles just like the Nissan LEAF and to some extent Tesla automobiles, so this departure appears to be the one option to get a unibody EV proper. However for some motive the EUV simply feels stiffer than these different automobiles, however once more, simply by a pocket really feel, which might be exhausting to calibrate.
The BT1 platform deviates farther from the Physique-On-Body & Unibody orthodoxy than these different EVs
As I researched extra, I found: an article from earlier this yr on GM Authority that confirmed GM was doing one thing much more radical. Their writers famous that the GM BT1 platform did not appear to suit both class, defying categorization in methods nicely past the Bolt and its cousins. When requested what sort of platform the Silverado EV was constructed on, GM’s chief engineer, Battery Electrical Vehicles, Nichole Kraatz mentioned:
“It isn’t a unibody and it isn’t a body-on-frame. We designed one other sort of structure the place we’ve a physique with a flooring, but in addition the Ultium battery construction is definitely a part of the construction and people two are linked after the physique exits the physique shaft. So we have outlined a sort of new automobile class that does not have that conventional physique and body method.”
When she pushed additional and requested what their groups name their platform, she mentioned it is referred to internally because the “Ultibody,” a reference to the Ultium platform. A later advert for the truck has an amazing cutaway video exhibiting the varied physique and body parts exhibiting how the automobile is neither and each on the identical time:
In some methods it is only a unibody platform, however with the entrance, rear and battery subframes tied collectively. However after they’re tied collectively, it is sort of like a body, although it isn’t inbuilt one piece like most truck frames. However the bodywork supplies a lot of the rigidity, making it a unibody. It actually defies categorization.
Is it a sturdier Bolt EV with the subframes tied collectively and extra body components? Effectively, sure. However really, no.
Is it a Silverado with a multi-piece body? Effectively no. However really sure. However no.
Ought to we name this unibody-on-frame? Or is that simply extra subframes?
EVs result in a really completely different automotive future
The reality is that EVs have modified automobile design eternally. What was as soon as a really stable distinction turned out to be powered solely by the wants of ICE engines. As engineers started to seek out methods to optimize for a battery pack fairly than a primitive stack of pistons (apologies to Dr. Smith of the previous Misplaced in House), new issues turned not solely potential, however fascinating.
Appears to be like like GM’s journey of embracing front-drive unibodys for many automobiles took a left flip in Albuquerque when it got here time so as to add batteries to a unibody platformand the remaining was historical past.
One factor is for certain, the trade will proceed to supply fascinating issues because the EV transition progresses.
Featured Picture: A screenshot of an internet advert for the Silverado EV, exhibiting its construct.
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