German Car Zone

Recession? Not in Munich's Engineering Development.

The smaller tunnel is no less interesting. Here, half-scale models are tested, also on a moving ground plane. But while you'd think the half-scale models would imply similarly lower wind speeds, a pesky rule of aerodynamic scaling (the Reynolds Number!) actually requires the wind speed to be doubled, so this has to be a very high-speed tunnel as well. A particularly neat capability of the smaller tunnel is its ability to maneuver two models around on the moving ground (suspended from twin overhead gantries) while the fan is running, to explore the aerodynamic interaction of cars running nose to tail, or even passing each other.

While the tunnel was intended for models, full-sized cars can be tested as well. I was intrigued to learn that when they are, vertical loads on the wheels are measured by repositionable load cells beneath air bearings that support both the wheels and the fast-moving steel belt.

One interesting aerodynamic nugget that came to light during our conversations was that while a car's bodywork is certainly the greatest source of aerodynamic resistance, it isn't the dominant as you might think. Indeed, it accounts for only about 40% of the total, with 30% arising from the wheels and wheel wells, 20% from the car's underbody, and 10% owed to internal air flow (radiator flow and whatnot).

Another morsel: If you can reduce air resistance by 10%, fuel consumption declines by about 2.5 %. And speaking of that startlingly high wheel-well resistance number, the small tunnel's role in experimental, and early-on, development was illustrated by a concept we were shown called an "air curtain." Here, the front air intake of a 50% model of a 3 Series was internally ducted such that its flow was expelled in a sheet from the half of the wheel well, smoothing over the turbulence typically created by the front wheels as it passes.


Full Story: Motor Trend - Driving the BMW 750i xDrive at BMW's Efficient Dynamics Technology Workshop


M

That says it all:

Oh man, I hope they manage to keep this technology from the sportscars just a while longer.

^ lol

Nice! Thank you ENI! I just love X-Drive and Daynamic drive.....
I wonder where is Martin, would like to hear his comment.
My fellow countrymen is quite the expert in this area.

ENI Does the new 7 X-Drive have this Differential used in the X6?

Judging from the quote below indications point to the F01 xDrive possibly employing the DPC differential as part of the Dynamic Drive concept:

I'd be surprised if the F01 didn't use the new torque vectoring differential.

Technologically a very impressive system. I wonder how the system "knows" that the car is mid-corner. Probably uses the yaw and braking sensors to detect the driver coming off the brake, then on neutral throttle followed by the application of throttle (combined with the weight transfer to the rear) to divert the 80% of torque to the rear axle. Impressive, very Playstation.

Too much technology - too little simplicity of communication from the manufacturers though, enthusiasts are always having to dredge through tons of superfluous advertising babble before getting to the key information at hand. Just say it like it is for mercy's sake: "The new BMW 7 Series xDrive uses the new DPC, torque vectoring differential as first seen on the X6." Damn, that would make it so much simpler.

Then we would have no use of you, now would we?

Hey! Martin is back....I asked for you earlier.

Thanks for your input, I knew you could shed more light on the subject.
I know that anybody on this forum will agree with you that they (BMW)could have made it ALOT easier just telling us, the basic principal of the 7er X-Drive is the same as on the X6.

Thanks Dr. But actually what I've said above is based purely on assumption. The real facts are really difficult to get hold of.

Edit: Judging by the poorly worded press release, I'm now doubting that the DPC diff is employed in the F01 xDrive.