One design will accommodate a carbon fiber roof, a metal roof, or a sunroof. It's up to you.
When you buy a new car, you get access to various options. If you order a new BMW 3 Series, for example, you can have the standard metal roof, or you can opt for a sunroof. In Germany, you can even get the car with a carbon fiber roof panel like that of the range-topping M3. Some cars also offer a panoramic glass roof, but because of the differences in structural rigidity, each option requires different construction methods, which is part of why a sunroof costs so much more than a regular roof.
But what if there was a way to simplify the manufacturing process and thereby reduce the cost of a charged roof option? In patent filings uncovered by CarBuzz, the German automaker has proposed just that and more.
In your typical construction process, each roof has structural bracing at different points depending on the application. These roof structures are cast in specific molds, and you need a new casting for each new roof design. For example, a glass sunroof adds weight and requires beefier supports to maintain the soundness of the structure, while a carbon fiber roof does not. Moreover, a sliding sunroof requires additional channels for the slides, cabling, and other roof-mounted items.
What BMW is suggesting boils down to playing with Lego. The patent refers to a single modular roof design that, regardless of the final roof panel type, would be mounted on one type of reinforcement frame with transverse frame sections running across the top of the windshield area. The same supports run across the area atop the rear window.
But unlike traditional frames, this one would incorporate a longitudinal "web" down the center that would act as a supporting structural section between the front and rear transverse windshield braces.
This longitudinal bar would connect the two transverse (side-to-side) supporting mounts down the middle. But what if you choose a sunroof? BMW says that the central longitudinal (front-to-back) bar would extend up to the rear of the opening before 90-degree, perpendicular arms would extend outward, connecting to additional longitudinal supports on either side of the sunroof that run from the front windshield's transverse bar, down the sides of the sunroof, and back toward the rear of the opening.
For a full glass roof, the standard modular roof design would continue, meaning the structural bar would be visible. From the inside, it would probably look like a T-top roof with glass portals.
Essentially, the patent depicts one basic design for the roof structure with no supports above the side windows. Regardless of your roof panel type, the location of the longitudinal supports would remain the same unless you have a sunroof, in which case the central bar would be the only part that would be lightly modified to connect to bars on both sides of the opening.
Whichever roof panel is fitted, each would have identical mounting points and slots, which means that the factory would be able to assemble each type of panel on one assembly line because the structure of the car's body before roof panel installation would remain the same in all applications.
BMW notes that this would be an ideal design for a vehicle with at least two rows of seats, so it's not intended for coupes and convertibles. For vehicles like the X7, for example, the modular design would support any feature that would be fitted to the roof. This could include sunroof/s, ambient lighting, a touchscreen, air-conditioning, and more. BMW says this idea could improve the utilization of installation space, simplify the assembly process, and reduce cost.
What's more, although not specifically referenced, this design could potentially accommodate unique new roof designs like the open-top, "falcon-wing" roof that BMW patented last year, making access to the interior easier. With more extreme design ideas previewed by the Concept XM, it's only a matter of time before BMW starts experimenting with the roof of your next car.