The BMW i3: Deconstructed

Gary S. Vasilash

The engineers at Munro & Associates have taken a perfectly sound BMW i3 and taken it apart. Completely apart. And they are impressed with what they’ve discovered about how the EV is engineered.

Sandy Munro, the day before I visited him, was visited by his banker.

And his banker was a bit. . .well, perhaps “puzzled” is a good word in this context.

You see, Munro, founder and CEO of Munro & Associates, a consultancy that helps companies save rather significant amounts of money in developing and manufacturing products, had purchased a BMW i3 for some $53,000.

And the banker saw, as I did, what Munro and his colleagues had done with the car at their facility in Troy, Michigan.

Which was to completely disassemble it.  Completely.  As in you wouldn’t know that it was a car unless someone told you that that is what those pieces are.

Not that they’re taken apart willy-nilly.  But they are taken apart completely.

It isn’t the first time that Munro and his team have disassembled and analyzed vehicles.  Far from it.

But arguably this is one of the most impressive cars that Munro has ever taken apart.

“From an engineering standpoint,” he says, “this is an engineered car.  Most of what I have seen are accounting-driven, finance-driven cars.  Kluges.”

For Munro to suggest that something is “engineered” is high praise.  And he has pretty much nothing but praise for the BMW engineers who have developed the i3.

For example, he points to a section of the frame, where there is an aluminum die casting welded to an extrusion.  “Talk to any engineers who knows anything, and they’ll tell you it can’t be done.”  [Pause.]  “Including me, until I saw that.”  (The issue: hydrogen embrittlement.  Says Mark Ellis, senior associate at Munro: “When you try to weld the two together, the die casting material tends to crumble.  Whatever changes they made to the die casting to allow it to be welded like that is marvelous.”

About the i3
BMW launched the i3 electric vehicle near the end of 2013.  It was a clean-sheet approach for the company, not a modification of an existing product (i.e., it’s an “engineered car.”)

There are two primary components of the i3: the Life Module, which is essentially the cabin or passenger cell, and the Drive Module, which consists of the 22-kWh, 450-lb., lithium-ion battery; electric drive train (132-kW AC synchronous electric motor); MacPherson strut and five-link rear suspension system; and structural and crash components. The Life Module is based on carbon-fiber reinforced plastics (CFRP); the Drive Module is dominated by aluminum.  (The instrument panel cross car beam, for example, is magnesium.)

The vehicle is manufactured at a BMW plant in Leipzig, Germany.  The electric motor is produced at a BMW plant in Landshut, Germany, and the rest of the Drive Module (including the battery) at a BMW plant in Dingolfing, Germany.  The carbon fiber comes from an SGL Group plant in Moses Lake, Washington.

There is attention paid to recycling (e.g., >10% of the carbon fiber needed to make the car is from recycled sources) and sustainability (e.g., the dashboard is made of sustainably sourced eucalyptus; kenaf fibers are used for interior trim and panel components).

The i3’s curb weight is 2,860 lb.

It has an EPA range of 81 miles. So it’s a carbon-fiber-intensive electric vehicle.
And Sandy Munro thinks it defies pretty much all of the accepted wisdom about carbon-fiber-intensive electric vehicles.

The Alternative Approach
“You’ve probably heard, ‘Oh, those guys can’t make any money with that car.’  This is a money-maker.  For real,” Munro insists.

For several reasons. First of all, with the Life Module on top of the Drive Module, the i3 is not a unibody vehicle.

“This is designed for a production of less than 50,000 units a year,” Munro says.  “This is where everybody makes a mistake.  Everybody wants a unibody.  Why?  Because they’re planning on making a million—a gazillion.”

And if past is prologue, those high expectations don’t necessarily work out so well. “What happens when you want to make a tooling change?  Or want to have something different in the marketplace?”

Mark Ellis estimates that the investment in the Leipzig plant is about a third of what it would be for a steel body-in-white facility.

Munro maintains that it is. . .unwise to “do anything but body-on-frame if you’re under 50,000 or want a lot of flexibility.”

In the case of the i3, the body is glued to the frame.  “The frame is the crash-worthy component,” Munro points out.  It takes all of the shock.  All of the load.  “Put a different body on top of it, and it will crash the same way.”

In addition to working in the auto industry, Munro & Associates has done extensive work in aerospace. Which means they’re quite familiar with composite materials.
Munro admits that it is beneficial that BMW has a 51% share of a joint venture with SGL Group, SGL Automotive Carbon Fibers.  But just because they own the factory doesn’t mean that they’re getting an economic edge in terms of carbon fiber use.

“They’re not using the standard number, $42-a-pound, aircraft-quality carbon fiber,” Munro says.  Rather, “They’re using different compounds all over the place.”

For example, aircraft-grade carbon fiber doesn’t flex.  This does.  Which is beneficial in crash situations.  Not every section of the vehicle needs the same level of strength.  So they use material appropriate to the situation.  “They are clever about what materials they use in compounding the carbon fiber,” Munro says.  It isn’t a “one-material-fits-all.”

What’s more, Ellis points out that the BMW engineers paid careful attention to even things like the scrap that is generated during the Life Module production.  It is engineered scrap.   One of the things they do with it is use it to produce the roof.  They arrange the pieces, sew them together with plastic thread, place it in the mold, and through heating, molding and resin injection, produce the roof.

“When we first got into this, I thought we’d do a report about the carbon fiber,” Munro says (yes, they are producing a report on their findings; after all, they’ve got to amortize that $53,000, to say nothing of all of the people-hours invested in the careful deconstruction).  “But once we got into it—wow!  The adhesives are out of this world.  Then there’s the battery.  Then the electric motor.  Then. . . .”

In other words, an “engineered car.”  All of it.

Ellis spent 30 years in the battery industry, set up 17 plants, and he finds the battery pack, which consists of eight modules, each with 12 cells, to be impressive.  He says, “It is designed so that it can be repaired.  If a cell goes bad, then you remove a module and put a new module in.  The genius behind what they did is that there is a circuit board on each module that is daisy chained to a motherboard to keep track of the cells charge and discharge.”

The laminates for the motor are carefully designed to create power in a small package. Again, Munro and Ellis have great respect for the execution.

As we speak amid the i3 unplugged and unconstructed, gasoline prices in the U.S. are falling toward the $2 level.  Doesn’t this mean that there is a possibility that electric vehicles won’t be in much demand?  Munro answers that even if that is the case, the structures are designed such that putting in an internal combustion engine would not require a huge modification of what is already in place—as though the engineers thought of it as a possibility ahead of time.

What’s more, Munro is confident that BMW will use the technology developed for the i3 on other vehicles (and not just the i8).

“It’s easy for them to move ahead from here.  All of the heavy lifting has been done.”

All of the heavy engineering for a lightweight car.