2016 BMW 7 Series Prototype First Drive
Carbon Fingerprint: BMW Pioneers the Carbon-Fiber/Steel/Aluminum Unibody
For those uninterested in the quirky electric i3 or unable to justify or afford the slick i8, BMW's investment in those carbon-fiber-intense green machines is about to start paying off in more mainstream offerings. The next-gen 7 Series will be the world's first and only car to incorporate structural carbon-fiber elements into a conventional metal unibody. Patents are pending and SAE papers await publication, so the engineers are still being coy about some of the details, but they freely admit that these miracle fibers are responsible for a big hunk of the nearly 450 pounds of weight savings realized on the next 7 Series (150 of which went back in as added feature content). A recent visit to BMW's southern European proving ground in Miramas, France, provided an opportunity to learn a lot more about these and other technologies debuting on this flagship, and to spend an hour behind the wheel of a couple prototypes as well.
Lightening any part is a worthy cause, but the higher up those lightened bits are, the more they improve handling dynamics by lowering the car's center of gravity. That's why much of the 7's carbon fiber is found in the roof structure, including two 10-foot long arched tubes supporting the roof and three of the four roof crossbows. For more nitty-gritty details about all 16 carbon-fiber pieces, see sidebar. Aluminum is also used extensively in the unibody. The front crash rails are long rectangular extrusions with three inner webs connecting the long sides. The front and rear spring seats are die-castings, as are the structures that kick up over the rear axle, connecting the rocker rails with the rear crash structure. The doors, hood, and trunk inner panels are also aluminum.
The tricky thing about this construction technique is that when you dip the unibody in the hot electro-coat primer bath and again when you bake the final paint job, the heated metals want to expand but the carbon fiber bits don't, which should stress out the bonds and rivets connecting these parts. We're all awaiting those SAE papers to learn how BMW's bonding techniques and/or paint shop processes were modified to make this work.
The 740's TwinPower straight-six turbo joins the new B-engine architecture (500cc combustion chambers with turbocharging, direct injection, and Valvetronic timing and lift) that began rolling out in the Mini lineup with the 1.5-liter B38 I-3 and the 2.0-liter B48 I-4. No output figures have been released yet, but simply scaling up two cylinders' worth from the Mini JCW's output would suggest 347 hp and 387 lb-ft -- an output level that seems plausible, given the thrust I experienced at Miramas in the 740Li. The sound elicited by this new six is quite muted, thanks in large part to blanketing the entire engine in lightweight foam sound absorbers that permitted a dramatic reduction in firewall sound insulation, saving 26.5 pounds. No further powertrain details were provided, except to say that the rest of the current engine lineup should carry over with minor refinements, there will be a plug-in hybrid model, and the eight-speed automatic will benefit from friction reduction measures. We're told to expect a notably shrunken carbon footprint.
The big news is standard four-corner air suspension with Dynamic Damper Control that's credited with smoothing the ride and improving highway economy slightly by hunkering down at speed. The Driving Experience Control switch now features Comfort and Comfort+ in place of Normal and Comfort (Sport and EcoPro continue). The even more appealing new setting is Adaptive, which senses and reacts to the current driving style, delivering optimum comfort and efficiency when loafing along, then tensing everything up whenever the pace quickens and the lateral gs elevate. The system can even monitor navigation and forward-looking camera data to make anticipatory suspension calibration changes. Sadly, the car defaults to Comfort with every restart for CO2-emissions/CAFE reasons.
Optional Integral Active Steering replaces the former planetary gear setup on the column with a new electric-assist variable-ratio steering rack and electric rear-wheel steering that adds up to 3 degrees of steering in the same or opposite direction at high or low speeds to improve stability or maneuverability respectively. Also new: This system now packages on x-Drive models. The old Dynamic Drive system with the hydraulic anti-roll bars is replaced by a planetary-geared electromechanical active-anti-roll bar system renamed Executive Drive Program (see diagram). There is just one global suspension tuning calibration, with tire choices the only big differentiator between markets.
Unsprung mass is down 15 percent, thanks to refinements such as optimized aluminum rear lateral links (0.6 pound each), redesigned wheel bearings (0.9 pound each), iron rotors with aluminum "hats" (1.1-1.4 pounds each, depending on size), all-aluminum fixed calipers replacing aluminum and steel sliders (5.0-5.5 pounds each), and CAD-optimized die-cast rear knuckles (1 pound each).
Continuing its march toward ever greater ease of use and customer acceptance, the next generation of this pioneering user interface adds choice. Users can now control nearly everything via the central touchscreen, which supports pinch-to-zoom, drag, and press to select. Of course everything still works using the (now) traditional rotary push knob (the top of which also accepts handwriting inputs), or by voice commands that are increasingly conversational. And the simplest tasks, such as like volume control and accepting or ignoring a phone call, can even be accomplished via gesture controls monitored by a tiny camera looking down at the iDrive controller area. The screen designs are also more graphically pleasing and intuitive. When selecting menu items via the rotary knob, a preview of the screen about to be selected is shown on the right half of the central display. When reaching to touch the screen, touch-optimized screens appear -- like a telephone touchpad when dialing a number. Reach down to the side of your seat to make an adjustment, and the function of the button you're blindly touching appears on the center screen -- no more fumbling and wondering.
The gauge cluster is one big reconfigurable screen as well, with different appearances tailored to Comfort, Sport, and EcoPro drive settings. The right side typically displays a tachometer, but that space will also present sound-system or navigation items when needed, like when selecting a track or station, or when a maneuver is upcoming in navigation. Even the climate-controls are touchscreen operated on their own dedicated display, and the little wheels that allow front-seat occupants to make the vents warmer or cooler than the cabin temperature setting are replaced by capacitive slider switches.
At last -- the moment I've been waiting for. The test cars are rear-drive 740Li models fully equipped with Executive Drive Program and Integral Active Steering, riding on 245/45R19 Pirelli P Zeros. My first laps of a rolling, twisting handling circuit were made in Comfort+ mode, which seemed to provide Benz S-Class levels of isolation, with a bit more float than I'm accustomed to from the Roundel. This is how the Asian markets prefer their chauffeured conveyances to feel. Stepping back down to the default Comfort mode buttons things down to a more familiar Euro-plush connectedness. Steering effort remains light, and negotiating the few near-U-turn maneuvers never requires more than 180 degrees of lock with the help of the rear steering.
Then our convoy quickens the pace and selects Adaptive mode. By the first time I trail-brake into a turn the steering has stiffened up noticeably (while still conveying subtle messages about the level of grip on our damp track), and the transmission is resisting its instinct to grab the highest possible gear. Cornering is flatter and road surface texture is more noticeable. This is the setting I'd use most often. We eventually switch to a different, faster track and try the top Sport mode, which lowers the body by 0.4 inch and further restricts the amount of permissible roll. Ride quality is slightly sharper and the throttle and transmission programming is notably more aggressive, but clearly each setting has been designed to be every day livable -- not just a "hey, look at this" parlor trick of temporary kidney trauma. Brake pedal feel and response is near ideal in the first car I sample, way too grabby in the second, so hopefully the former is closer to production intent.
The second half of the drive provides a chance to sample the new driver-assistance systems. Adaptive cruise control operates from 0 to 130 mph with stop-and-go support, and Driving Assistant Plus provides steering assistance to maintain a position centered in the lane. The two systems operate independently, controlled by two steering wheel buttons. Speed Limit Assist uses the stereo cameras to read speed limit signs (yes, even in the U.S.), alerting the driver to any changes. It then allows you to speed up or slow down to the new limit with a simple tap up or down on the cruise-control rocker switch. (A setting inside iDrive allows you to request that the system maintain an offset of +9 mph when acknowledging these messages.) Even when the steering assistant is switched off, if the radar determines that a lane-change would cause you to collide with a car, it can steer you back into your lane.
The 7's coolest party trick is automatic remote parking, which allows you to drive a car forward into or back out of a tight garage or parking space while standing outside the car, using the fancy interactive key fob (which features its own touchscreen). Sadly, this feature is not yet legal in the U.S. But hey, BMW, how about letting us have the remote start function that comes with automatic parking? That is legal, and highly sought after here in cheap-gas-land.
We'll learn a whole lot more about BMW's new flagship at the official launch in June, but this early look suggests that Munich is doing its best to grow business in Asian who-cares-how-it-drives markets where ride matters most, while trimming and distributing weight to optimize driving dynamics for the rest of us. Oh, and if it's just not sporty enough for you, an M7 variant has been widely rumored. Fingers crossed.
A Deeper Dive on the Carbontech
Two gorgeous curved tubes of woven and infused carbon fiber weighing just 6.6 pounds span from the base of the A-pillars to the base of the C-pillars. These get sandwiched between steel inner panels and the large body-side aperture panel you see when you open the doors. These provide critical roof-crush and rollover protection. Three of the four cross-car roof beams are also carbon. The one connecting the B-pillars is another woven tube, flattened to about 3 inches wide and maybe a half-inch tall and capped with steel end plates. This one bears the side-impact loads. The one behind that mostly supports the roof panel, so it's an open "hat section" piece made of resin-transfer molded carbon fiber. The windshield header is two thin hat section pieces, bonded and riveted along the "brim" flanges to provide more structural support.
The B-pillars are formed of inner and outer high-strength steel, the outer pieces of which get swatches of carbon fiber bonded right into them. The "hat shelf" under the back window, and two panels in the C-pillar area, are made of recycled carbon fiber -- basically the scraps that are cut from the blanks forming the other parts, squeezed together and infused with resin. Two more L-section pieces go inside each side rocker panel, and a another caps the center tunnel. (Forming the entire tunnel of carbon would permit way too much noise intrusion, insulating against which would add too much weight back in.) These last pieces are all made of multi-directional fibers with resin-transfer injection.
What about repairability, you ask? There is no carbon fiber in the front or rear, where cars bear the brunt of most crash damage, and a rollover severe enough to damage the roof bows will likely write off any car, and the same can be said of anything involving the center tunnel. That just leaves the side-impact parts, and damage in these areas is repaired by in much the same way the current car is and by following a simple factory prescribed procedure -- no "flying doctors" required, as with carbon-tub vehicles.