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Plastic surgery

The launch of a new German executive saloon has come to signal one thing at least – technical innovation. At the same time, it is possible to second-guess the car’s basic layout by the badge on the bonnet. So for BMW, rear-wheel drive and in-line engines are a foregone conclusion in this market sector. For Mercedes-Benz rear-wheel drive and a mix of in-line and vee engines can be guaranteed, while for Audi, we can expect a mix of front-wheel drive and quattro four-wheel drive, also with a mix of in-line and vee engines.

The third generation A6 has undergone a major facelift and it is also much larger than the model it succeeds

So the arrival of the third-generation Audi A6 holds few surprises where the driveline is concerned. Otherwise, the body, inside and out, is an evolution of the outgoing model, as is the chassis, but that tends to mask the substantial differences between the old and new models.

Starting from the outside, Audi has opted for steel as the major body material, rather than the aluminium used for the A8 and A2, although aluminium is used to contain weight in specific panels, such as the bonnet and front wings, as it was in the outgoing model. It is also used in extrusion pressings to reinforce the sills, stiffening them for additional safety in a side impact. Audi spokesman Axel Catton maintains that steel was chosen as the basic medium because the car will be built in China. His suggestion was that a Chinese-built car in aluminium would raise quality control issues that Audi was not comfortable with, so steel it is. Audi claims that torsional stiffness is 34 per cent greater than for the outgoing model, benefiting both chassis dynamics and safety.

Following modern trends, the car is larger than the one it replaces – 12.0 cm longer at 4.92 m and 4.5 cm wider at 1.86 m, but height is only marginally greater at 146 cm. The new dimensions mean that the car is now the largest saloon in the executive class, adding to cabin space and raising the boot volume by 112 litres to 546 litres.

While the A6 predecessor was the equal of its German rivals in many respects, it did not always bear favourable comparison in terms of chassis dynamics. This was not lost on Audi’s chassis engineers and to begin with, wheelbase and track are greater than before. The wheelbase has been increased by 8.3 cm to 2.843 m and track is wider both front and rear. At the front it measures 6.7 cm wider at 1.612 m and at the rear, it has been increased by 4.9 cm to 1.618 m.

The same basic four-link, double wishbone design is used for the front suspension as on its predecessor, but has been moved forwards by 83 mm, accounting for the increase in wheelbase and providing better weight distribution over the front axle. Lightweight components help to reduce unsprung weight.

In place of the previous two rear suspension layouts, Audi has adopted one rear suspension system for all front-wheel drive and quattro models. Previously front-wheel drive models were equipped with torsion beam rear suspension and quattro models with double wishbones. Now a trapezoidal link system, featuring passive steer is used across the range. The system’s shell structure is made from high-strength steel plate. Overall spring travel is greater than for the outgoing A6. Both front and rear suspension assemblies are carried on a subframe.

From next year, adaptive air suspension will also be available as an option. Besides offering continuous adjustment to suit the load, this system incorporates speed related ride height, lowering the body at high speeds to offer additional stability. At the other extreme, it can also raise ride height over rough terrain – characteristics shared with the VW Touareg. The system will replicate the arrangement on steel sprung models with strut type suspension at the front, fitted with concentric air bags around the damper strut and separate springs and dampers at the rear.

An ESP electronic stability programme is standard across the range, using the latest Bosch ESP 8 system. Besides the usual electronic brake-force distribution, emergency brake assist and traction control functions, the latest generation ESP also provides a brake disc cleaning function, designed to keep the brake discs dry in wet weather by gently pressing the linings against the discs at regular intervals.

ESP can be disabled in two stages at the press of a button. A short press switches off the traction control system, while pressing the button for longer switches off all functions except ABS and the electronic differential lock.

Electromechanical parking brakes are becoming the norm for executive saloons and the Audi A6 follows the trend, in the footsteps of the A8. It provides an anti-roll back function for starting on a gradient. There is no need to release the brake manually when driving off, pressure on the accelerator is sufficient to ensure a progressive release. Sensors determine the selected gear, engine speed and gradient to release the brake smoothly, clutch position is also monitored on manual transmission models.

The system is not a first stage electronic braking system, like that demonstrated by Delphi last year. The rear service brakes are still applied hydraulically, in the conventional manner, electronics only being applied to application and release of the parking brake. The system is designed to hold the car on gradients up to 30 per cent, with a warning message displayed if the car is parked on steeper gradients.

Standard wheels and tyres are 7.5 x 16 inch wheels with 205/60 R 16 tyres, with 225/55 profile tyres on more powerful six-cylinder models, becoming 225/50 profile on the most powerful V8. Tyre pressure monitoring is offered as an option with PAX run-flat tyres as a further option. This allows continued driving with a puncture for 200 km, at speeds up to 80 km/ (50 mph), even with a completely flat tyre.

Powering the A6 is a range of five engines, three petrol and two diesel. Although several of the engines may appear familiar to Audi drivers, they have all been adapted for use in the A6. The smallest engine and the only four cylinder unit is the 2.0 litre turbocharged and intercooled direct injection 2.0 TDI diesel, already available in several Audi and Volkswagen models. This engine joins the A6 range in mid 2004. Audi’s new 3.0 TDI vee-six diesel supersedes the 2.5TDI V6 of its predecessor, becoming the second common-rail diesel in the Audi engine range. The smallest petrol engine is a 2.4 litre V6, while Audi brings its stratified charge direct injection FSI technology to the larger 3.2 litre V6, the engine making its debut in the A6. Topping the petrol engine range is a “conventional” 4.2 litre V8.

Six and eight cylinder engines, both petrol and diesel, all share the same basic architecture – a 90 degree vee angle, with the same bore centres, giving 90mm between cylinders. Cam drive is by chain.

With diesel accounting for an ever larger share of executive car sales, the 3.0 TDI is likely to be one of the most significant engines for the A6. As we have indicated, it is a completely new engine, sharing no components with the previous 2.5 TDI range.
Displacing 2,967 cc, the DOHC engine produces maximum power of 225 PS (165 kW) at 4,000rpm and 450 Nm (332 lb ft) of torque between 1,400 and 3,250 rpm. The engine employs conventional undersquare bore and stroke dimensions of 83.0mm x 91.4mm and operates with a compression ratio of 17.0:1. In place of the high-pressure rotary Bosch VP 44 fuel pump of the 2.5TDI, Audi has switched to Bosch common rail injection, with a separate rail for each bank of cylinders. Like all new A6 engines, it conforms to the Euro-IV emissions standard. Weighing in at a lightweight 219 kg, the engine is also compact, measuring 44.4 cm in length.

Right and below right: The 3.2 is the V6 to which Audi has applied its FSI technology
The 3.0 TDI engine which is likely to be one of the most significant for the A6

With the common-rail system, operating at 1,600 bar injection pressure, Audi has chosen piezo-electric injectors. The principal advantages are light weight – the injector needles weighing four grammes instead of 16 grammes for solenoid types - and high-speed operation. This permits a variable injection pattern, depending on speed and load, with up to two pilot injection pulses and a post injection pulse when necessary. Double pilot injection at low speeds drops to a single pulse at medium speeds, while the single post injection pulse operates below around 2,500rpm and maximum part load.

To control emissions, cooled EGR is employed while exhaust after-treatment is limited to a close-coupled pilot catalyst and main catalyst further downstream. There is no particulate filter. Quattro transmission, via Audi’s trademark self-locking worm gear Torsen centre differential is standard with the 3.0TDI engine, driving through a six-speed tiptronic automatic gearbox. So equipped, the A6 3.0 TDI returns 8.3 lit/100km (34.0mpg) on the EU combined test cycle and emits 223g/km of carbon dioxide.

The 3.2 V6 FSI direct injection petrol engine is the first time Audi has applied its FSI technology to a six-cylinder engine. So far, the system has only been seen in four-cylinder 2.0 and 1.6 litre engines. Maximum output is 255 ps(188kW) at 6,500rpm, while peak torque of 330 Nm (243 lb ft) is generated at 3,250 rpm. The DOHC engine uses the same technology as the smaller FSI engines – a common-rail fuel system operating at up to 100 bar and a variable swirl intake system with a high 12.5:1 compression ratio.

In conjunction with variable valve timing via cam phasing of both inlet and exhaust cams, engine efficiency can be greatly improved. When driving through the six-speed manual transmission, the engine returns 9.7 lit/100km (29.1 mpg) on the EU combined cycle and emits 233 g/km of carbon dioxide. Like the diesel, the high compression ratio is achieved with undersquare bore/stroke dimensions of 84.5mm/92.8mm.

The more conventional 2.4 litre V6 is also a brand new engine, despite the similar capacity to the previous small Audi vee-six. This engine is based on the 3.2 litre FSI engine but has a smaller bore and stroke – with oversquare bore/stroke measurements of 81.0 mm/77.4 mm. Cam phasing variable valve timing is applied to the inlet camshaft. The result is 177 ps(130 kW) at 6,000 rpm and 230 Nm (170 lb ft) of torque between 3,000 and 5,000 rpm, while fuel consumption and exhaust emissions match the 3.2 FSI engine.

The 4.2 litre V8 is a retuned version of the five-valve-per-cylinder engine launched in the Audi S4 in 2002. In A6 form it produces 335 ps (246 kW) at 6,600 rpm and 420 Nm (310 lb ft) of torque at 3,500 rpm. Driving through a six-speed Tiptronic automatic and quattro drivetrain it returns 11.6 l/100km (24.3 mpg) on the EU combined cycle and emits 278 g/km of carbon dioxide.

Transmission choices for the range include a new six-speed manual, tiptronic automatic and multitronic CVT. In its latest incarnation for the A6, multitronic now has a torque capacity of 330 Nm (243 lb ft) enabling it to be mated to the 3.2 FSI engine, but not the 3.0 TDI. It also incorporates seven simulated fixed ratios for manual gear changes. Quattro four-wheel drive is standard with both the 3.0TDI and 4.2 litre V8.

The A6 incorporates features previewed by Audi two years ago, including its dynamic cornering lights, available with the optional xenon headlamps. Using steering angle and road speed sensors, the low and high beam units move with the steering to improve illumination on bends. A low powered xenon lamp also provides daytime running lights for the A6.

Light and rain sensors are also standard equipment. Audi has used a new design of light sensor, using two separate sensors mounted behind the windscreen, one pointing upwards to monitor the ambient light and the other straight ahead to monitor light in the direction of travel. It is able to respond much more swiftly to light changes than current systems. Radar adaptive cruise control will be added to the options list next year.

The outgoing A6 won praise for its dashboard design and Audi has retained many of those elements in the new car, which incorporates the multimedia interface, or MMI, from the A8. The basics of the system are a rotary push button control on the centre console with four large push buttons at each quadrant. This layout is replicated on a visual display unit at the top centre of the dash panel.

The four large buttons control the audio/TV system, telephone, navigation/trip computer and the car’s programmable features. Using the controls in combination allows the user to access a range of features and information. The system comes with a black and white LCD screen or full colour screen with options including CD autochanger and DVD navigation.