Audi tackles 'huge challenge' of lightweighting the A3

  • 18-Jun-2012 02:58 EDT
Audi6-12 A3 C A3120065.jpg

The focus for the new Audi A3 was expressly on quality and reduced weight. Reduced engine weight further complemented savings throughout the car.

“Never mind the quality, feel the width” is an old sales adage that is total anathema to Audi’s engineering ethic. A variation for the company might be: “We mind the quality and also mind the weight.” Light weight, that is, because Audi has not only given its new compact premium A3 hatchback (and sedan that will follow) a cabin ambiance that closely matches that of its upmarket A6 and A8 siblings, but it has also achieved a weight loss that takes it close to the original 1996 A3’s number.

“With this model, we have broken through the weight spiral while adding to safety and equipment,” said Dr. Olaf Köhler, Head of Lightweight Design. “At Audi, reducing weight is a mindset and a core competence. With each new model, we seek to reduce weight still further; we look at every gram, and the new car is 80 kg lighter than its predecessor. It was a huge challenge.”

The gasoline A3 TFSI in basic trim has a curb mass of 1175 kg (2590 lb).

Although the new A3 continues the overall styling signature of the outgoing model, its visual cues have been sharpened and its overall build standard enhanced, says Audi.

The company is so emphatic about its achievements with the new car that it gave this AEI Editor access to its design and quality development inner sanctum (usually a no-go area for the media) at Ingolstadt to reveal what the company is doing to reach its new compact car targets. “To save on quality is always the most expensive solution,” said Werner Zimmermann, Head of Audi Quality Assurance, which employs more than 2000 specialists. The department reports directly to Audi’s chairman. “Achieving required quality in series production means continually raising the bar higher,” added Zimmermann.

Based on the Volkswagen Group’s new MQB modular transverse platform, which will be used for a wide range of model sizes across several brands, the new car has similar overall dimensions to its predecessor, but its wheelbase is longer by 23 mm (0.91 in) to reach 2601 mm (102.4 in) and the car has a shortened front end. The front axle is further forward, achieving better crashworthiness, and distribution of axle loads is improved. The A3 will be available with front-wheel drive or quattro 4x4.

Köhler emphasized that Audi applies “the right material at the right place for optimal function.” This means using relatively thin walled, form-hardened steels that make up 26% of an A3’s body materials, including A- and B-pillars, roof arch, center tunnel, sills, and floor panels. The material saves some 18 kg (40 lb), and the occupant cell is now 25 kg (55 lb) lighter than that of the previous model.

Aluminum use saves 7 kg (15 lb) for the hood and 2.2 kg (4.9 lb) for the fenders. A front-end aluminum crash absorber cuts 1.5 kg (3.3 lb). The use of wheel housing shells using an acoustically insulating fleece material saves 0.5 kg (1.1 lb).

Depending on engine version, mass saving via the use of aluminum is as much as 21 kg (46 lb). As well as a 15 kg (33 lb) lighter aluminum crankcase for the 1.4-L TFSI, detail savings include balancer shafts mounted in the engine block for 3.0 kg (6.6 lb) less on the 2.0-L TDI and different sound dampers in the exhaust system for 2.0 kg (4.4 lb) savings on the 2.0-L TDI.

Power units at launch are diesel TDI and gasoline TFSI driving through six-speed manual or seven-speed twin-clutch S-tronic gearboxes depending on model. Cylinder deactivation technology, which Audi terms Cylinder On Demand (COD), will also be offered on the 1.4-L TFSI engine. A 1.6-L TDI will cut CO2 emissions to 99 g/km and will have a combined fuel consumption of 3.8 L/100km. A hybrid version of the A3 is slated for 2014.

The A3 is being cited by some North American industry analysts as an example of the right vehicle size, weight, and powertrain likely to constitute the “average” U.S. passenger car needed to meet the 2005 54.5-mpg CAFE requirement.

The new chassis also brings weight benefits via a one-piece aluminum subframe and aluminum swivel hubs for A3 versions, saving 6.0 kg (13.2 lb), and 18-in road wheels are the same weight as the previous 17-in ones. Flow forming technology is being used for the wheels. The wheel blank is formed in a single work step, which strengthens the material again making for thin walling and a saving of 0.8 kg (1.8 lb) per wheel.

Mass savings for the seats amounts to 4.0 kg (8.8 lb), while 640 g (23 oz) are shaved off via use of plastic for the front passenger airbag housing and magnesium for the MMI human-machine interface monitor bracket. Instead of steel screws, plastic expanding rivets secure interior trim, saving 4 g per fastening point.

While mass cutting is an admirable—and essential—achievement, end users may be concerned that this could mean some reduction in quality, with paring of materials to the detriment of durability and tactility leading to a general decay in the finer points of vehicle Audi’s build.

But that, said Hans-Lothar Schollinski, Head of the Central Quality Department, is totally incorrect. A detail example is the introduction of an inlay (fillet) for the dashboard and doors to give a 3D glass look via a “unique” process. Multiple layers of polycarbonate film are imprinted on the trim part with a pattern of very small triangles.

This is then reformed by vacuum deep drawing, the molded part backsprayed with a substrate material before being oversprayed with a 5 mm (0.2 in) thick highly transparent plastic layer to amplify the 3D look (no bubbles allowed!) Finally comes painting with a UV-curing clearcoat. The resultant premium look also saves a few grams against regular aluminum trim.

Each of the car’s air vents now comprise 31 parts. The center axis can be pushed or pulled to spread airflow from draft-free to targeted.

Panel/component gap size is a very serious part of Audi’s quality drive. The first A3 had gaps of about 3 mm (0.1 in); the new car generally 1.3-1.4 mm (0.0501-0.055 in) with some down to 1 mm (0.04 in) and these take into account visual compensation, which is why they may be a fraction wider, by perhaps 0.3 mm (0.01 in), at the top than the bottom of some angled components.

A master jig maintained at a constant 22ºC (72ºF) is an essential part of Audi’s dimensional fine-tuning for very accurate sheet-metal panel fit and exterior trim parts such as taillight alignment between tailgate and rear fenders. Master jigs are used for both exterior and interior calibration 9 months before Job One.

The A3 has 115 sheet-metal components incorporated in its underbody that need to be checked for dimensional conformity to ascertain that components may be joined without creating any tension that could affect other elements of the car’s structure—this creating a domino effect.

Exterior function cubes are used to analyze parts, with resulting correction data being applied to optimize and fine-tune components.

The effects of paint and sealing gaps are checked, too. “You need to be obsessed with attention to detail,” said Claus Ross, Audi’s exterior master jig manager.

There are 4500 measurement points on a pre-series production A3 and 700 on a door inner alone. The A3 door jig is milled from solid aluminum and costs, according to Audi, “about the same as a German house.”

Quality is a largely precise, objective science, but Zimmermann pointed out that some of it has to be subjective. Quality involves seeing, sensing, smelling, and hearing, he said. “As impressive as the measured values may be, if the sensory perception is not right, then the quality is not right for Audi either.”

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