Every gram counts – The Audi ultra lightweight construction principle

Ultra lightweight construction is not simply a mandatory task at Audi, rather it is an attitude and a mode of thinking – for many years now it has been one of the brand’s core competences. As early as 1994, Audi pioneered the use of aluminum as a body material: The first A8 was the first production sedan to have a full aluminum body in Audi Space Frame (ASF) technology. In today’s range of models, the A8 and R8 car bodies are built entirely of aluminum according to the ASF principle, the sole exception being the steel B-pillars of the large sedan. In the TT series, the lightweight metal makes up about two-thirds of the body superstructures, while the figure is about 20 percent aluminum for the A6 model series. In the future, each new Audi model will be lighter in weight than the previous model.

The Audi ultra lightweight construction principle is not limited to the body or to specific subassemblies and parts – developers always consider the vehicle as a whole, and in their work every gram counts. In the new A3, they were able to reduce the car’s curb weight by up to 80 kg (176.37 lb) compared to the previous model, reversing the upward weight spiral on a second model after reducing the weight of the A6.

This achievement is especially noteworthy for two reasons: due to the vehicle’s compact size and because it is accompanied by improved vehicle qualities. The new A3 is sportier, safer and even better equipped than the previous model.

The Group’s new modular transverse platform (MQB) and the Audi ultra lightweight construction principle achieve a clear synergy. For one, the modular transverse platform includes many new and lightweight components, and for another it reduces development and production costs by standardization. This has made it possible for the brand with the four rings to invest in new lightweight construction technologies, materials and components more than ever before – extending its competitive lead.

Body
Body developers at Audi have broad-based engineering expertise spanning all relevant materials. By no means is this know-how limited to just a specific material, rather the motto is: “The right material at the right place for optimal function.” The multimaterial body of the Audi A3 lives up to this maxim.

Forming the backbone of the occupant cell are what are known as form-hardened steels. An extreme temperature change during forming operations gives these steels extremely high strength; the parts can be designed with relatively thin walls, making them lightweight. Form-hardened steels represent a 26 percent share of body materials. They are used in the transition from the front of the vehicle to the occupant cell, in the A-pillars, B-pillars, roof arch, center tunnel, side sills and floor panels. Altogether, they lower the car’s weight by 18 kg
(39.68 lb). In total, the occupant cell is 25 kg (55.12 lb) lighter than in the previous model.

High-strength and ultra-high-strength steel grades are used in many other body areas, such as the floor; some of these components are known as tailored blanks, which are blanks whose thickness varies within their component geometry. Large parts at the front of the vehicle are made of aluminum – including the engine hood and fenders which were made 7 kg (15.43 lb) and 2.2 kg (4.85 lb) lighter in weight, respectively. An aluminum profile behind the front apron serves as a crash absorber; it saves 1.5 kg (3.31 lb). Weight reduction in the front body section leads to a more balanced distribution of axle loads – A3 drivers experience this in the car’s sporty handling.

Processing aluminum components in body construction and joining these components with steel components are challenging tasks. The same is true of welding form-hardened components, which are coated with a corrosion-inhibiting aluminum-silicon alloy. Here, Audi benefits from its know-how in ultra-lightweight construction – in models like the TT, such joining technologies have been practice-proven for years now.

The body of the Audi A3 exhibits yet other strengths. It is extremely crash-resistant, rigid and acoustically comfortable. A noise-insulating windshield is standard equipment; despite the addition of an intermediate film layer, it is no heavier than the previous windshield. Many other measures have been implemented to reduce interior noise in the new A3, including wheel housing shells made of an acoustically insulating fleece material – its weight impact is 0.5 kg (1.10 lb).

Engines and chassis
The engines of the new A3 have shed a lot of weight as well. The 1.8 TFSI, for example, weighs just a little over 140 kg (308.65 lb), while the 1.4 TFSI weighs in at just 107 kg (235.89 lb) – 21 kg (46.30 lb) less than the previous engine. At 15 kg (33.07 lb), the aluminum crankcase accounts for a large share of reductions, but progress has also been made in many small engine details – e.g. in the aluminum pistons and hollow bored connecting rod pins.

In the 1.8 TFSI, the thin-wall technology of the crankcase reduces weight by 2.4 kg (5.29 lb). In the 2.0 TDI, the balancer shafts are mounted in the engine block, which accounts for 3.0 kg (6.61 lb) of savings, while modified sound dampers in the exhaust system save an additional 2.0 kg (4.41 lb). The exhaust system was made leaner in all engine versions.

In the chassis area, the new one-piece aluminum subframe and aluminum swivel hubs (depending on the engine) reduced weight by about 6.0 kg (13.23 lb). The optional 18-inch alloy wheels are no heavier than the 17-inch wheels; they are produced by a complex flow-forming technology. In this process, the rim well is rolled out over a cylinder under high pressure and at high temperature. The production system forms the wheel blank in a single work step that strengthens the material as well, permitting thinner walls – each wheel is 0.8 kg (1.76 lb) lighter and yet stronger.

Interior
The Audi ultra lightweight construction principle is a mode of working that is lived by its engineers – and they also eliminated every superfluous gram in the interior of the new A3. The redesigned seats contribute a 4.0 kg (8.82 lb) weight savings; lightweight plastic inserts replace the previously used steel wire in the frame of the rear bench seat.

A new layout of electronic control modules eliminated a number of wire harnesses, reducing wiring weight by 1.5 kg (3.31 lb). The blower motor needed fewer coils, and the entire air conditioning system is 4.0 kg (8.82 lb) lighter. The front passenger airbag housing is made of plastic, and the bracket of the MMI monitor is magnesium. Together they yield a weight savings of 640 grams (1.41 lb). On the previous model, interior trim panels were fastened with steel screws; in the new A3, plastic expanding rivets are used for this purpose – the weight savings is 4 grams (0.14 ounce) per fastening point. When it comes to the Audi ultra lightweight construction principle, every gram counts.

The equipment, data, and prices specified refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.