The Audi A4: Engines

Source: Audi AG

Engines

Higher power, lower consumption – the new Audi A4 is being launched with a choice of five vigorous but refined engines. All of them have direct fuel injection: the two petrol engines use FSI technology, the three TDI units the common-rail principle. All the four-cylinder engines are turbocharged. The splendid flow of power from these engines makes driving the new A4 pure pleasure. Yet at the same time they consume an average of nine percent less fuel than the corresponding engines in the previous model. For Audi, power and efficiency always belong together.

The new Audi A4 is being launched with a choice of two petrol engines. The 3.2 FSI is a V6 developing 195 kW (265 bhp). The four-cylinder 1.8 TFSI has a power output of 118 kW (160 bhp). These engines are further proof of Audi’s leading position in engine design. Both of them use the petrol direct injection technology known as FSI, which is superior to anything that their competitors have to offer. The naturally aspirated 3.2 FSI combines FSI with the innovative Audi valvelift system; the 1.8 TFSI has forced aspiration by turbocharger.

FSI injection technology injects fuel directly into the combustion chambers. This principle has thermodynamic advantages and operates at greater efficiency. FSI engines develop higher power and are more dynamic than conventional engines with fuel injection into the intake pipes – and also make more economical use of the fuel. This increase in efficiency once again provides evidence of the technological lead summed up in the Audi slogan “Vorsprung durch Technik”.

Petrol direct injection from Audi first demonstrated its potential for superior performance in June 2001, when an engine featuring petrol direct injection took the Audi R8 sports-car prototype to overall victory in the Le Mans 24 Hours. In the years that followed, the car was entered for 80 races and won 64 of them – evidence not only of the power developed by its engine but also of the refusal to compromise on reliability and quality that is typical of the Audi attitude to both motor sport and series production.

Top petrol-engined model: the 3.2 FSI

In the new Audi A4 model line, the top petrol engine is also new: the 3.2 FSI. This magnificent, highly refined engine has been extensively redesigned in comparison with the previous model. It now incorporates a complete package of high-tech features: the innovative Audi valvelift system, FSI petrol direct injection and various measures aimed at reducing internal friction and thus boosting efficiency still further.

A member of the modern Audi family of vee engines, the 3.2 FSI has a 90-degree included angle between the cylinder banks, compact dimensions and a low weight of just 171 kilograms. Its engine block is made from an aluminium-silicon alloy. This keeps the overall weight of the new Audi A4 low and gives it optimal axle-load distribution. The low weight also makes a direct contribution to the car’s dynamic road performance.

The 3.2 FSI engine, with a displacement of 3197 cc, develops 195 kW (265 bhp) and delivers its maximum torque of 330 Nm all the way from 3000 to 5000 rpm. It can accelerate the Audi A4 3.2 FSI quattro with manual gearbox from 0 to 100 km/h in only 6.2 seconds, and urge it on to its governed top speed of 250 km/h.

This imposing flow of power is linked to remarkably low fuel consumption, for instance only 9.2 litres per 100 kilometres for the 3.2 FSI quattro with manual gearbox.

Compared with the previous model, which had a power output of 188 kW (255 bhp), fuel consumption has been reduced by an impressive 1.2 l/100 km, yet the 0-100 km/h acceleration figure has been cut by two tenths of a second. From 2008 on, the 3.2 FSI quattro will be available with tiptronic six-speed automatic transmission; all versions of this model transmit their power to the road by means of quattro permanent four-wheel drive.

About half of the improvement in fuel consumption is due to the Audi valvelift system: with this new valve operating technology, the engine uses at least five percent less fuel. The Audi valvelift system, which controls valve lift in two stages, ensures excellent combustion chamber filling in all situations.

It regulates the amount of combustion air drawn into the engine by varying inlet valve lift; in most cases the throttle butterfly can therefore remain fully open, which largely eliminates undesirable throttling losses. The engine breathes more freely and develops higher power and torque, but consumes less fuel.

Brilliantly simple: actuation at the camshafts

Whereas previous valve lift control systems have needed complicated, clumsy elements between the camshafts and the valves, Audi has moved the actuating principle directly to the camshafts – a high-efficiency solution with the simplicity of genius. The V6 engine’s inlet camshafts are provided with splines that carry cylindrical sleeves. These cam elements have two different profiles, one for low valve lift, the other for full valve lift. Metal pins actuated by an extremely rapid electronic shift system engage in spiral grooves on the sides of the revolving cam elements and displace them by seven millimetres along the camshafts.

During part-load operation, the lower cam profiles actuate the valves’ roller cam followers. The valves then open by either 2.0 or 5.7 millimetres. This difference in valve lift introduces a controlled degree of turbulence in the mixture as it forms in the combustion chamber, and ensures particularly clean combustion. At full load, the larger cam profile comes into use, for a valve lift of 11.0 millimetres. The changeover takes place at any engine speed between 700 and 4000 rpm, and is completed within two turns of the crankshaft.

A series of accompanying measures are applied by the new, highly intelligent engine management system to make the transitions smooth and unnoticeable. All the driver senses is an unbroken, turbine-like build-up of power and spontaneous response to the accelerator.

Thanks to its uncomplicated layout, the system is rated for engine speeds up to almost 7200 rpm, so that high power outputs are possible. The Audi valvelift system achieves its greatest potential for fuel economy at constant road speeds in the moderate part-load operating range. If it is driven smoothly at 150 km/h in sixth gear on a motorway, equivalent to an engine speed of approximately 4000 rpm, the engine will operate in the low valve-lift setting.

A technological leap forward: petrol direct injection

FSI petrol direct injection is another major step forward in automotive technology: it injects the fuel directly into the combustion chambers at pressures of up to 100 bar. As the fuel evaporates, it draws heat out of the combustion chamber surface. This permits the high compression ratio of 12.5 : 1 to be used, which greatly increases combustion efficiency. Depending on load and engine speed, an electronically controlled flap in the plastic intake pipe switches over from the longer air-intake path that increases the engine’s pulling power to a shorter path for maximum power output.

Design progress in other areas on the 3.2 FSI engine concerns for instance the timing chains that drive the camshafts. As is typical of Audi vee engines, they are located at the rear of the engine in order to save space. The sprockets and intermediate gears now have more teeth, for quieter running and reduced loads on the chains. A similar effect is achieved by the tri-oval, i.e. very slightly triangular, shape of the chain sprockets. The three single-roller chains are also of new design, for smooth running and maximum wear resistance. They need no routine maintenance and do not have to be changed throughout the engine’s operating life.

The oil pump has also been extensively modified. Its delivery volume has been reduced by 30 percent, and it now operates by varying the volumetric flow according to actual demand. At an engine speed of 4600 rpm, the pump switches from the low to the high pressure stage, after which the oil spray jets for the underside of the piston crowns are brought into action to avoid peak temperatures. A combined coolant radiator/oil cooler is installed immediately adjacent to the pump.

Taken together, all these measures – which include a smaller water pump and reduced piston-ring pressure – have significantly reduced the engine’s friction losses. The mean friction pressure at 2000 rpm has gone down by 0.22 bar, equivalent to 25 percent. This has yielded a fuel saving of approximately five percent.

FSI injection technology and turbocharging: the 1.8 TFSI engine

The smaller of the two petrol engines also underlines Audi’s leading position in engine design. The 1.8 TFSI combines the valuable advantages of direct injection and turbocharging into an ideal technical package that provides sporty driving fun allied to low fuel consumption and emissions. This four-cylinder engine develops 118 kW (160 bhp) and has the high maximum torque of 250 Nm, which remains available over the entire engine-speed range from 1500 to 4500 rpm.

This turbocharged direct-injection engine gives the new Audi A4 ample performance. The version with six-speed manual gearbox has a top speed of 225 km/h and accelerates from a standing start to 100 km/h in 8.6 seconds. Yet the A4 1.8 TFSI limits itself to just 7.1 litres of fuel per 100 kilometres, 1.1 l/100 km less than the previous model. With a compression ratio of 9.8 : 1, the engine is designed to run on super grade petrol (95 RON). As an alternative to the manual gearbox, Audi will be offering multitronic continuously variable transmission on this model from 2008 on; both four-cylinder cars’ transmission options drive the front wheels.

For the 1.8 TFSI, Audi’s engineers have carried out intensive development work on the concept first introduced three years ago as the 2.0 TFSI. Since 2005, the two-litre engine has been voted ‘Engine of the Year’ three times in succession by an international jury of journalists. Despite its lower displacement, the turbocharged 1.8 TFSI delivers as much power as a naturally aspirated V6 only a few years ago, but consumes far less fuel.

Weight saving with grey cast iron: the engine block weighs only 33 kg

The 1.8 TFSI engine block has little in common with the previous engine apart from the 88-millimetre cylinder spacing. The crankcase is of grey cast iron, which has good noise-absorbing properties. It weighs only 33 kilograms, and the complete engine tips the scales at a mere 135 kg.

There are two contra-rotating balancer shafts in the crankcase, to suppress the free second-order inertial forces generated by this type of engine. The rigid basic structure of the block and its optimised add-on elements and covers also help to eliminate drumming and vibrations.

The chain that drives the balancer shafts has also been designed for quiet running. A further chain runs to the oil pump: this has volume-regulated delivery and two-stage pressure control, and cuts fuel consumption by 0.2 l/100 km. A third chain drives the two camshafts. A new development is the extremely responsive adjuster that turns the inlet camshaft steplessly through up to 60 degrees of crankshaft rotation. To keep the dimensions compact, the mounting for the auxiliaries holds the oil cooler, the oil filter and the two oil-pressure switches, with the oil filter positioned upright so that it is extremely accessible and time and expense are therefore saved when the car is being serviced.

For the 1.8 TFSI, Audi’s engineers have increased the fuel injection pressure to 150 bar. The high-pressure pump, a new development, is driven by a four-lobe cam on the exhaust camshaft. The six-hole injectors, which are also new, distribute fuel accurately in the combustion chambers so that an efficient combustion process can take place. Double injection strokes (during the induction and compression strokes) are performed after starting a cold engine.

This too is to ensure that combustion is clean and stable, and to raise the ceramic catalytic converters, which are located close to the engine, to their regular operating temperature as quickly as possible.

Combustion air is supplied to the cylinders by a Borg Warner Type K03 water-cooled turbocharger. Its turbine casing is integrated into the exhaust manifold to form a single high-alloy grey cast iron module. An optimised turbine wheel improves initial response at low engine speeds. At 2000 rpm, the 1.8 TFSI needs only 1.2 seconds to build up its maximum torque of 250 Nm. The previous 1.8-litre engine needed 1.7 seconds to reach its maximum torque of 225 Nm.

In the air intake system of the 1.8 TFSI, a new design of charge-movement flap valve generates the turbulence needed to create a high-quality, homogeneous fuel-air mixture. The charge-air intercooler is also a new development and is notable for its high efficiency at low weight and for its compact dimensions. All the turbocharged engines for the new Audi A4 have the intercooler mounted below the front bumper cross-member and ahead of the radiator, a position which locates it in the airflow from the cooling fan.

Drivers of the new Audi A4 1.8 TFSI will experience all these advanced technical features quite simply as pure driving pleasure. The four-cylinder engine responds willingly and unhesitatingly to accelerator pedal movements at all engine speeds. A very smooth-running unit, it pulls lustily from idle speed upwards; it has far more character than its entry-level status would suggest.

A tradition of leading-edge design: Audi TDI engines

For the past 18 years, Audi’s TDI engines have set the standards in every market segment in which they are represented. Their high torque, extremely low fuel consumption and quiet, refined running are evidence that the overall concept is harmonious and convincing. Audi introduced the TDI principle to the market as long ago as 1989, and since then the brand with the four-ring emblem has steadily built up its lead in this technological area. All the TDI engines for the new A4 have diesel particulate filters as standard equipment and are already prepared for compliance with the forthcoming Euro 5 emission limits.

Audi has launched the new A4 with a choice of three diesel engines – two V6 units and a four-cylinder inline engine. The two V6 TDI engines are from the Audi vee engine family, which features a 90-degree included angle between the cylinder banks. With displacements of 3.0 and 2.7 litres, they are compact and light in weight. Their high power and torque makes them ideal for a modern, powerful form of sporty driving, and indeed two Le Mans race wins by the R10 racing car in 2006 and 2007 are ample evidence of the power that the Audi TDI principle can deliver. The four-cylinder, two-litre TDI engine now has a new common-rail injection system using piezo injectors; it too runs quietly, smoothly and efficiently.

Effectively new: the 3.0 TDI

The three-litre diesel has been so thoroughly revised in design that it can be regarded as a largely new engine. It now develops 176 kW (240 bhp) and has an impressive maximum torque of 500 Nm. This ultra-powerful TDI, which has a displacement of 2967 cc, makes the new A4 even more of a sports saloon. It accelerates from 0 to 100 km/h in only 6.1 seconds, and has a top speed of 250 km/h – yet the average fuel consumption is a mere 6.9 l/100 km. The 3.0 TDI is supplied with quattro permanent four-wheel drive and a six-speed manual gearbox.

Compared with the engine in the equivalent preceding model, which developed 171 kW (233 bhp) and consumed 7.5 litres of diesel oil per 100 km, maximum torque is now 50 Nm higher, and is at the driver’s disposal all the way from 1500 to 3000 rpm. This is the key to the surge of power – a wave on which the car, like a surfboard, seems to be carried forward in a relaxed, carefree way. The maximum engine speed is also 400 revolutions per minute higher, with the full rated power output available from 4000 to 4400 rpm.

The V6 TDI has an engine block made from vermicular-graphite cast iron, a lightweight material. It is extremely rigid – an essential for smooth running. The pistons have friction-optimised rings, and the chain drives to the camshafts and auxiliaries have also been improved.

Fuel injection on the V6 TDI engine is by a third-generation common-rail system with eight-hole injectors. It operates at a high pressure (up to 1650 bar, and equivalent to the entire weight of the car resting on a surface only one square centimetre in area), which ensures even finer atomisation of the fuel, better mixture formation and more efficient combustion. The injectors use the piezo principle, which changes the structure of a ceramic element when an electrical voltage is applied. The resulting expansion is transmitted to the injector needle. The injectors close again after only one to two thousandths of a second, so that very small quantities of fuel weighing only 0.8 mg (less than a thousandth of a gram) can be injected reliably.

Thanks to the extremely fast, precise switching action of the piezo injectors, the number of injection strokes per working cycle can be widely varied on the 3.0 TDI engine, up to five are possible. This strategy reduces emissions and makes the combustion process smoother, so that the engine’s noise pattern is also more satisfactory. The three-litre diesel is the best performer in its class in terms of refinement.

New components: turbocharger and charge-air intercooler

The 3.0 TDI engine uses the latest type of VTG (variable turbine geometry) turbocharger. A fast electric adjusting motor moves its guide vanes, so that high torque builds up freely and spontaneously. The turbocharger is located in the vee between the cylinder blocks. The charge-air intercooler is also new. It is installed transversely ahead of the radiator in an ideal position for optimal cooling, and has a high thermal efficiency rating. The charge air supplied to the engine is cooled from 184 down to 69 degrees Celsius. Cooling the airflow compressed by the turbocharger increases the volume of charge air entering the cylinders.

The revised 3.0 TDI is notable not only for its low fuel consumption but also for its especially clean exhaust: the limits that will apply when Euro 5 legislation comes into force are already complied with. A new exhaust gas recirculation concept reduces emissions of oxides of nitrogen. It has a much higher cooling rate, thanks to greater EGR cooler efficiency and reduced flow resistance.

A diesel particulate filter is used to reduce soot emissions: it cuts the already low level of untreated emissions further, by more than 90 percent. The filter is installed close to the engine, so that only a small amount of heating energy is required for its regeneration. A small oxidating catalytic converter is installed ahead of the particulate filter: since it is located directly after the turbocharger, it also benefits from the rapid heat build-up.

When engines are developed, the demand for higher power, lower fuel consumption and reduced pollutant emissions are clearly contradictory. However, with the developed version of the 3.0 TDI Audi demonstrates most impressively that within this conflict of requirements all the main parameters can be improved at the same time – further evidence of the brand’s leading position in the TDI sector.

Breakthrough: the world’s cleanest diesel

The new Audi A4 3.0 TDI with ultra-low emission system is a further step forward that demonstrates the potential of the Audi TDI principle: from mid-2008 on, the world’s cleanest diesel will be available in the sportiest midsize saloon. It will arouse enthusiasm not only because of the dynamism promised by a power output of 176 kW (240 bhp) and the outstanding torque of 500 Nm, but also because of its modest fuel consumption and extremely low emissions. The A4 3.0 TDI with ultra-low emission system complies with statutory limits that will not become compulsory until 2014.

The ultra-low emission system raises the principle of the direct-injection turbocharged diesel to a new level. In developing it, Audi’s engineers have combined a whole package of innovative measures. A new common-rail fuel supply system, piezo injectors operating at a pressure of 2000 bar, high-efficiency exhaust gas recirculation and further optimised forced aspiration join forces to achieve a significant reduction in untreated emissions. A further Audi innovation introduced for the first time are pressure sensors in the combustion chambers: they permit combustion processes to be controlled even more precisely.

A further technical breakthrough is the actual exhaust purification system, which cuts emissions of oxides of nitrogen (NOx) by as much as 90 percent. This system operates with the additive AdBlue, an aqueous 32.5-percent solution of carbonic acid diamide, small amounts of which are injected ahead of the DeNOx catalytic converter. This injection process is precisely timed, since for a high conversion rate it is important for the AdBlue solution and the gas flow reaching the entry surface in the converter to be continually matched. In the hot exhaust gas, the solution decomposes into ammonia, which breaks the oxides of nitrogen down into nitrogen and water.

For the winter: heated pipes

The complete system consists of the catalytic converter, the metering module and the AdBlue tank. The AdBlue solution has a freezing point of -11 °C, so that both the active tank and the metering line and pump have to be heated at low outside temperatures. This function is activated automatically by temperature sensors. The regulating sensors are also complex: two NOx sensors measure the concentration of the oxides of nitrogen ahead of the diesel particulate filter and after the ultra-low emission system; system functions are also monitored by pressure and temperature sensors.

The AdBlue tank, like the fuel tank, is filled at the fuel filler flap. The reservoir volume of approximately 22.5 litres is divided between two tanks: the active tank below the fuel filler flap has a capacity of 7 litres, the passive tank under the floor holds 15.5 litres. The AdBlue solution, which is biodegradable, is added as a routine operation each time the car is serviced, without the customer having to take any action. Since consumption of the solution is very low, Audi can guarantee that the amount carried on the car will be sufficient from one workshop visit to the next. The system is rated to perform reliably for the car’s entire operating life.

The exhaust system is completed by two conventional catalytic converters, installed ahead of the ultra-low emission system. The oxidating converter transforms hydrocarbons and carbon monoxide into carbon dioxide and water. The diesel particulate traps particles in the gas flow and collects them in the structure of the filter.

Thanks to their extremely low emissions, Audi is able to sell its clean direct-injection diesels all over the world, even in the US states of California, Massachusetts, Maine, New York and Vermont where extremely stringent emission limits apply. From 2010 on, Audi will be offering this new technology in further car and power-output classes. The brand is pursuing a systematic work strategy aimed at lowering fuel consumption and pollutant emissions still further. By 2012, Audi will have reduced its models’ CO2 emissions by some 20 percent – yet their sporty character will be enhanced at the same time.

Highly efficient: the 2.7 TDI

The second TDI for the new A4 model line is slightly more economical than even the 3.0 TDI, with an average fuel consumption of no more than 6.6 litres per 100 kilometres. Like the 3.0 TDI, the 2.7 TDI already complies with future EU 5 limits. A major element in achieving this has been the Bosch piezo common-rail system, which uses injection pressures of up to 1800 bar. The 2.7-litre engine, like the larger unit, is from the Audi vee-engine family. It has a power output of 140 kW (190 bhp) and delivers a massive 400 Nm of torque all the way from 1400 to 3250 rpm.

The 2.7-litre engine has a stroke of 83.1 millimetres, 8.3 less than the 3.0 TDI. With the unchanged bore of 83.0 mm, this yields a displacement of 2698 cc. The engine’s performance has also been boosted beyond the previous version’s figures of 132 kW (180 bhp) and 380 Nm, yet at the same time its fuel consumption has gone down by 0.2 l/100 km. The A4 2.7 TDI reaches 100 km/h in a brisk 7.7 seconds from a standing start, and has a top speed of 226 km/h. It has multitronic continuously variable transmission and front-wheel drive – a technical package for customers who value a car with an easy-to-operate, relaxed, refined driveline.

Further improvements all round: the 2.0 TDI

The 1968 cc four-cylinder TDI ushers in a new generation of efficient, dynamic diesel engines from Audi; it is a new interpretation of the TDI concept’s outstanding qualities. This two-litre unit builds on the characteristic strengths of its predecessor, which was the highest-volume production diesel in the world, and offers customers even more driving fun, economy and refinement.

For use in the new A4 the 2.0 TDI has been given common-rail fuel injection, the piezo injectors of which operate at a maximum pressure of 1800 bar, and a whole series of additional innovations as well. This two-litre engine also complies with future EU 5 emission limits.

The 2.0 TDI is both refined and powerful: it develops 105 kW (143 bhp) and delivers its maximum torque of 320 Nm at all engine speeds between 1750 and 2500 rpm – enough to hustle the Audi A4 in 9.4 seconds from a standing start to 100 km/h and for it to reach a top speed of 215 km/h.

With a six-speed manual gearbox, the 2.0 TDI is content with an average fuel consumption of 5.5 l/100 km – 0.5 l less than the previous model. From 2008 on, this four-cylinder diesel will be available with multitronic continuously variable transmission. Both this and the manual-gearbox version drive the front wheels.

In the new Audi A4 the 2.0 TDI engine is installed at an angle of 20 degrees to the right, which has necessitated certain changes to the oil sump and crankshaft. The most interesting development, however, concerns the cylinder head, in which the two overhead camshafts operate 16 valves, and common-rail injection controlled by one of the most modern engine-management systems on the market supersedes the previous pump-injector units.

Like the 3.0 TDI, the 2.0 TDI features modern piezo injectors and eight-hole injector nozzles. The degree of precision to which up to five injection strokes per operating cycle can be modulated has the effect of audibly reducing the noise level. The single-piston high-pressure pump builds up a full system pressure of 1800 bar, which results in very fine atomisation of the fuel and accurate, efficient combustion.

The acoustics of the toothed belt drive have also received attention, with additional noise-reducing structures on the belt cover. As on the previous engine, two balancer shafts reduce the vibration generated by the crankshaft and reciprocating parts.

The 2.0 TDI, which has a 16.5 : 1 compression ratio, has a number of other special features that also improve its performance potential. Its turbocharger is from a new design generation. So that torque builds up more rapidly, it has adjustable guide vanes on the turbine side, and a pulsation damper to reduce vibration. Electric motors control the position of the swirl flaps in the intake pipe: these modify the incoming airflow continuously to match engine load and speed.

Free-revving: the limit is not reached until 5000 rpm

Optimised intake-air management and modified piston geometry have put the maximum engine speed up to 5000 rpm, and have in particular improved the thermodynamic situation in the combustion chambers. As a result of these measures, the two-litre TDI can be operated with a high rate of exhaust gas recirculation (up to 60 percent); combustion takes place at a lower temperature and oxygen level, so that untreated emissions of oxides of nitrogen are lower. To achieve this, Audi has given the four-cylinder engine a switchable EGR (exhaust gas recirculation) system that has a high cooling rate. The oxidating catalytic converter has been improved and combined into a single unit with the maintenance-free diesel particulate filter. Both of them are located close to the engine and therefore reach their operating temperature quickly.

The 2.0 TDI already complies with the EU 5 emission limits that will probably come into force in 2010, and which will call for a further reduction in the level of oxides of nitrogen. This makes it necessary to reduce the combustion temperature, although this in turn has a negative effect on efficiency. By concentrated attention to design details, however, Audi’s engineers succeeded in averting the risk of poorer fuel consumption and in fact achieved a slight improvement in this respect.

The equipment, data and prices stated here refer to the model range offered for sale in Germany. Subject to amendment; errors and omissions excepted.