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Engineering The Q7

Because Audi developed its SUV after the VW Touareg and Porsche Cayenne, they were able to make the changes necessary to make theirs distinctly Audi.
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According to Dr. Ulrich Hackenberg, head of Concept Development, Body Development, and Electronics at Audi AG, “The Q7 was not part of the original VW Touareg/Porsche Cayenne program. It was added after the fact.” Although the Q7 shares the same platform as the Touareg and Cayenne, because Audi was late to the party it was able to develop a version more in keeping with its brand attributes–including its distinctive all-wheel-drive system–while providing dealers with a long-wheelbase seven-passenger vehicle. Plus, it gives Audi a base upon which it can pull an even sportier (and reportedly V10-powered) version for its Lamborghini sibling.

It took approximately 25 months for the Q7 to move from the decision to build to production. In that time, the engineering team designed the larger structure, developed a new rear suspension, repositioned the fuel tank, designed a new load floor, fitted quattro all-wheel-drive and mated Audi powertrains to the platform. In North America, those powertrains begin with a direct-injection 4.2-liter V8 and end with a direct-injection 3.6-liter V6. They produce 350 hp/325 lb-ft and 280 hp/265 lb-ft, respectively. In Europe, there is an additional choice, a common-rail 3.0-liter TDI V6 with 233 hp and a massive 365 lb-ft @ 1,750 rpm. All are mated to a six-speed automatic.

The 4.2-liter V8 has three single-row roller chains to drive the four camshafts, and these are located on the back of the engine. A fourth chain is located low on the front of the motor to drive the ancillaries. “The drive is on the back of the block to keep engine height down at the front of the engine,” says Hackenberg. “This is so it can fit under the hood of the RS 4 sport sedan.” A side benefit of designing the motor to fit in Audi’s smallest sedan is that it’s easier to provide the space necessary between the hood and engine to meet European pedestrian impact standards without having to resort to either a higher hood line or a hood that rises upon impact with a pedestrian. The block of the V8 is cast from aluminum-silicon alloy and does not use separate cylinder liners. This allows the bridge width between cylinders to be just 5.5 mm, which also helps to save weight.

The 3.6-liter V6 is an enlarged version of the narrow-angle 3.2-liter engine founding the Audi TT and A3. Its 10.6? cylinder bank angle reduces engine width, and the block is grey cast iron topped by aluminum heads. The twin turbo direct-injection 3.0-liter diesel, on the other hand, is made of high-strength vermicular cast iron that is 15% lighter than grey cast iron. That engine is 17.3-in. long, weighs 498 lb, and its quick-start glow plugs heat up to 1000?C in two seconds.

Audi has switched from symmetric (50:50 torque split) to asymmetric (40:60 in the case of the nose-heavy Q7) all-wheel drive in order to give its vehicles more stability, and to reduce torque steer. The Q7’s VTG750 transfer case contains a Torsen self-locking center differential that sends power aft down the driveshaft and forward–via chain from the differential’s sun gear to the front driveshaft, and on to the front wheels. This mechanical unit only locks under power, which allows speed differences between the wheels under braking or while cornering. “The center differential can shift 65% of the power forward, or 85% to the rear under some off-road conditions,” says Hackenberg. In addition, the electronic differential lock intervenes by braking the offending wheel if it starts to spin.

The front suspension is similar to that of the Touareg and Cayenne, but Audi added aluminum upper and lower A-arms (cast and forged, respectively). The mounting for the spring strut and upper A-arm also is made from aluminum. Since the optional third rear seat folds flat into the floor, Audi engineers had to start from scratch with the rear suspension, jettisoning the four-link independent VW/Porsche design, and substituting a new unit with separate aluminum upper A-arms and steel lower wishbones. Both the front and rear suspensions are mounted on high-strength steel subframes. Buyers have a choice of standard steel springs or an optional air-spring suspension supplied by Continental, as on the VW and Porsche.

The body structure uses ultra-high strength steel in the inner rockers, longitudinal frame rails, the lower cross-car rails in the main passenger compartment, B-pillar, and the roof rail from the A-pillar to the C-pillar. It makes up 32% of the materials used in the structure. High-strength steel is used in the lower A-post, upper cross-car beams, lower windshield support, and is found in 26% of the materials in the body-in-white. Aluminum–just 6% of the total–is used in the front fenders, hood, and tailgate. The remaining 36% of the structure is stamped from standard steel grades. “The bodyshell,” says Hackenberg, “uses a continuous laser weld where the roof and side ring join [a total of 174 in.], so there is no need for a separate finisher piece since you have no spot welds to hide.” Hackenberg also says the Q7 has adhesive bonds totaling 3,142-in., 57-in. of plasmatron brazing, 5,403 spot welds, and 15,272 MAG (Metal Active Gas) welds. ArvinMeritor supplies the Open Sky roof system that has a full perimeter frame welded to the main body structure. Though it stretches 5.6-ft. front to back, the roof reduces body rigidity by “1 Hz at most” according to Hackenberg when compared to non-sunroof Q7s. The full perimeter frame, he claims, “is good for side-crash performance.”

The Q7 offers a blind spot detection system called “Side Assist” that utilizes two 24-GHz radar sensors in the rear bumper to determine if a vehicle is next to, or behind, the Q7. If a vehicle moves into this zone at approximately the same speed, or is approaching quickly from the rear, yellow LEDs in the side mirror housings light up. Though the driver should see the lights only if he is looking at the mirror, those with good peripheral vision will notice them, but not be distracted by their presence, if looking ahead. The sensors have a range of up to 16.5 ft., the unit becomes active at 35 mph, and it can be turned off if the driver wishes.

A 130? view rear camera is incorporated into the handle of the tailgate, and displays its image on the Multimedia Interface (MMI) screen in the dash. Various lines and boxes are overlaid on the image to assist the driver when backing into a parking space, and a blue area is superimposed to show how much space the Q7 needs for parallel parking. The camera also shows the rear bumper and trailer hitch to make maneuvering into place when attaching a trailer that much easier.

The only cruise control system offered on the Q7 is a radar-assisted adaptive cruise control that controls distance and speed from 0 to 90 mph. This means it is able to brake the car to a standstill behind the vehicle ahead, which Audi views as a great benefit in traffic jams and bumper-to-bumper traffic since it also can keep the Q7 rolling at crawling speeds without intervention. The 76.5-GHz radar looks 600 ft. ahead of the vehicle and at an angle of eight degrees. Should the driver ahead suddenly brake hard, the unit has a two-stage response if the driver does not react within a specified time. Stage one activates an acoustic signal accompanied by a red flashing signal on the instrument panel. If there is still no response, the system triggers a short burst of braking that jolts the passengers, and fills the brake system to full pressure so there is no delay when braking is initiated. “Taken together,” says Hackenberg, “it’s why we refer to the Q7 as the world’s first performance SUV.”