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Audi puts diesel in TT

Audi TT diesel coupe (copyright image)

Audi TT diesel coupe (copyright image)

A diesel engine is now available in a sports car

Home > News > Audi

19th July, 2009

Audi is setting the standard once again, this time with the new Audi TT and its TDI engine – a model that blends purist sportiness, powerful performance and sensational efficiency.

The Audi TT Coupe 2.0 TDI quattro is the first series-production sports car in the world to use a diesel engine as its power source.

A fascinating combination, the two-litre four-cylinder engine delivers dynamic thrust, with a power output of 125 kW and 350 Nm of torque.

It sprints from zero to 100 km/h in 7.5 seconds and achieves a top speed of 226 km/h. Consumption is just 5.3 litres of fuel on average over 100 km (combined cycle), representing CO2 emissions of only 139 grammes/km.

The engine

The new four-cylinder TDI with its capacity of 1,968 cm3 signals the advent of a new generation of dynamic, ultra-efficient Audi diesel engines. It interprets the consistently impressive qualities of the TDI concept in a fundamentally new way. This latest two-litre power unit, featuring two camshafts, builds on the strengths of its predecessor, once the most-manufactured diesel engine in the world – high pulling power, impressive efficiency and refinement.

The new common rail injection system is run by one of the most advanced control units on the market, and features ultramodern piezo injectors. Its eight-hole injectors can achieve up to five separate injection processes per combustion cycle. This fine-tuned approach produces a gentle pressure increase in the combustion chambers, decisively reducing the noise level. The single-piston high-pressure pump develops a system pressure of 1,800 bar, allowing fuel to form a fine dispersion, enabling precise, highly efficient combustion.

The turbocharger, too, belongs to a new generation. For a swift torque build-up it operates with adjustable vanes, and a special damper reduces its vibration. The engine's intake manifold houses swirl flaps that generate a tumbling action in the inflowing air while electric motors regulate the flaps' position so that this tumble is always adapted perfectly to the load and engine speed. The geometry of the engine's pistons has been optimised, and the acoustics of the camshaft drive belt overhauled. Two balancing shafts reduce the second-degree inertial forces produced by the crankshaft drive.

High exhaust gas recirculation: low nitrogen oxide emissions

The cumulative result of this progress is a high maximum engine speed of 5,400 rpm and, most importantly, a significant improvement in thermodynamics in the combustion chambers. What this means is that the engine can run almost entirely on re-circulated exhaust gas that has been thoroughly cooled by the radiator. The cooler combustion process involving less oxygen drastically reduces engine emissions of nitrogen oxide.

The 2.0 TDI in the Audi TT, with a compression ratio of 16.5:1, delivers 125 kW at 4,200 rpm. It puts a hefty 350 Nm onto the crankshaft at engine speeds ranging from 1,750 to 2,500 rpm – where power really makes a difference to driving.

The four-cylinder power unit runs with little vibration and responds quickly to the accelerator. Its superb pulling power is available from 'rock-bottom' upwards. It gives the 2.0 TDI a very distinctive, very strong character – that of a clever sports engine.

The on-road performance reflects this character with the Audi TT Coupe 2.0 TDI quattro leaving the competition in its wake with equivalent petrol engines, sprinting from zero to 100 km/h in just 7.5 seconds and not looking back until it reaches 226 km/h.

The TT Coupe 2.0 TDI quattro’s average fuel consumption of just 5.3 litres per 100 km, and emissions of 139 grammes of CO2/km also sets a benchmark that represents a veritable quantum leap in the sports car segment.

The operating range of over 1,100 km on a single tank of fuel expresses this superiority in a very tangible way, shrugging off advances from its petrol-engined competitors, when the figures that really count are closely scrutinised.

Its specific output is 63.5 kW per litre of engine capacity, and its specific torque is 177.8 Nm per litre. But the most impressive ratio is power to fuel consumption and CO2 emissions. At just 0.90 kW per gram/km, the TT 2.0 TDI quattro is truly in a league of its own when it comes to efficiency.

The drivetrain

In keeping with the theme of sporty performance, Audi has equipped its diesel-engine sports cars with highly effective manual six-speed gearbox with a short lever travel to allow the driver to shift quickly, easily and precisely. The housing for this transmission is made of lightweight, high-tech magnesium. Relatively long final transmission ratios bring the drivetrain into line with the character of the TDI engine.

In light of its immense torque of 350 Nm, Audi equips its new TT model with quattro all-wheel drive as standard, improving traction, slip-free acceleration, drivability, stability and straight-line running in all weather conditions.

The nerve centre of the quattro drive in the TT is an electronically-controlled, hydraulically-actuated multi-plate clutch located at the end of the prop shaft at the vehicle's rear end – a position that improves the weight distribution. It distributes the torque continuously between the front and rear wheels depending on the driving situation. Thanks to a new pressure reservoir, the clutch works twice as fast as before, within a matter of milliseconds.

The chassis

The front suspension – a classic McPherson layout – is pivoted on an aluminium subframe. A highly precise rack-and-pinion steering system with a direct steering ratio provides an intimate link between the driver and the road. Power steering with servo assist, which decreases as speed increases, is generated by an electromechanical drive far more efficient than a hydraulic pump.

The coil springs and shock absorbers in the four-link rear axle are situated in separate areas. The control arms, too, are carefully configured. The trailing links, which absorb the propulsive and braking forces, have a relatively soft characteristic to promote ride comfort. The connections to the three transverse links per wheel, on the other hand, are rigid in order to direct transverse forces into the body with precision.

The large disc brakes with pads that support high coefficients of friction measure 312 mm at the front and 286 mm at the rear, and the front discs are ventilated. The ESP electronic stabilisation programme is optimised for dynamic driving. A brief press of a button at lower speeds is all it takes to increase wheel slip, while a longer press of the button takes the TT driver into a second, sporty operating plane in which the ESP permits controlled sideslip angles. The brakes intervene later than normal and engine manipulation is suppressed.

Audi magnetic ride, a high-tech shock-absorber system available as an option, is an adaptive system that resolves the traditional conflict of interests between comfort and handling. A magneto-rheological fluid circulating in the shock absorbers changes its flow properties within milliseconds when a voltage is applied and this, in turn, alters the damping characteristic. The driver can choose between "Normal" and "Sport" programmes by flipping a switch.

The body and interior

The intelligent lightweight design of the Audi TT 2.0 TDI quattro is a key factor in its sporty performance. The 2+2-seater Coupe tips the scales at only 1,370 kilogrammes. The low weight is the result of an innovative hybrid-design body developed by Audi. The forward structure is made of light aluminium components assembled using the space frame principle. Steel is used for the rear structure.

This solution guarantees that the frame is as rigid as possible and optimises load distribution between the axles. The body shell of the Coupe weighs 206 kilogrammes.

The design

The TT’s emotional design, all the way along its 4,178 mm body, is 'muscular' and dynamic. The nose end is dominated by the large single-frame grille, and there is an automatically extending spoiler integrated at the rear. Subtle quattro badges identify it as a fundamentally all-wheel-drive vehicle. With a drag coefficient of 0.30, Audi demonstrates how good design can produce a low drag coefficient, translating into a higher top speed and better fuel efficiency.

The flowing dynamic style is echoed in the car's interior. The driving area boasts clear-cut instruments that make reference to the classic circle motif, as do the air vents and rotary controls for the automatic air conditioning. The sports steering wheel with the flat-bottomed rim rests snugly in the hands. Perfect ergonomics and uncompromisingly high standards of build quality are always present in any Audi.

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The height-adjustable sport seats are deep-set, providing a sporty seated position and firm lateral support. The backs of both rear seats fold down in the TT Coupe, making the boot space grow from 290 to 700 cubic litres.

TDI engines in motor racing

Since first appearing in 1989, Audi's TDI engines have been setting trends for the rest of the automotive industry to follow. With their power, refinement and efficiency, they have come to represent a modern, smart interpretation of sportiness. The run of victories celebrated by the Audi R10 TDI diesel race car at the Le Mans 24 Hours and in the American Le Mans Series is impressive evidence of the tremendous potential of this technology.

The Audi R10 TDI has been blazing a trail since early 2006 – with its twelve-cylinder diesel engine it has entered an entirely new dimension. The 5.5 litre TDI is a race engine of superior pedigree. Its torque far surpasses that of any petrol engine, developing more than 1,100 Nm.

At nominal engine speed it delivers over 650 horsepower, producing a top speed of around 330 kilometres per hour.

The only minor problem encountered right at the start was due to the specific nature of the twelve-cylinder TDI – its very quiet running. The drivers of the open-top prototype – including multiple Le Mans winners such as the Dane Tom Kristensen and the German Frank Biela – had to get used to this fundamentally different attribute. Whereas they had previously been able to rely on the engine's sound as a guide to its performance, above a given speed it was now no longer audible. They soon adapted to the new situation, and the diesel engine has since been demonstrating its strengths with resounding success. Among its virtues is fuel efficiency.

Compared with its predecessor, the already very efficient R8 with petrol direct injection, the Le Mans version of the R10 TDI was markedly more economical. Furthermore the Le Mans circuit, with its long straights and scope for 75 per cent use of full throttle, does not provide a true reflection of its strengths.

Fewer stops for refuelling mean faster times – so high efficiency was the key to two successive victories in the tradition-steeped French endurance race. In 2006 Frank Biela, Emanuele Pirro (Italy) and Marco Werner (Germany) emerged as clear winners, completing 380 laps equivalent to 5,187 km at an average speed of 215.409 km/h . The same team of drivers again won in 2007, even though the organisers had capped the tank capacity of the R10 TDI. In difficult weather conditions Biela/Pirro/Werner clocked up 369 laps at an average speed of 209.152 km/h.


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