The Audi S3: Drivetrain

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August 28, 2006

Source: Audi AG

The TFSI engine in the new S3, with a displacement of 1984 cm3, is the logical evolution of the Audi four-cylinder engine that is one of the group’s most successful engines ever. Compared with the 1.8-litre power unit of its predecessor, in the new S3 it has gained 29 kW (40 bhp) and 70 Nm of torque.

The competition-beating hallmark of the TFSI is the way it creates a synthesis of two performance-boosting technologies that complement each other perfectly – turbocharging, which brought Audi rally driving victories as long as 20 years ago, and FSI petrol direct injection, likewise developed by the Ingolstadt-based manufacturer.

These two technologies transformed the sports car prototype Audi R8 into a record-breaking winner of the Le Mans 24 Hours, making it a legend in its own time. By the time it was superseded by the R10 in summer 2006, it had won 64 of the 80 races in which it had participated.

Double victory: twice “Engine of the Year”

The technology that has caused a sensation in the stiffest challenges in the world is likewise proving a success in production use. A jury of international trade journalists voted the two-litre TFSI engine their “Engine of the Year” on two successive occasions, in 2005 and 2006, in recognition of its innovative technological package.

An FSI engine uses fuel more efficiently than a conventional indirect injection engine. It generates more power on lower fuel consumption when operating at part loads – another typical example of “Vorsprung durch Technik” from Audi.

In the FSI engine, the fuel is injected at a pressure of up to 110 bar into the combustion chambers, where a homogeneous fuel-air mixture of lambda = 1 (one part fuel to 14.7 parts air) is formed. Flaps in the intake tract, which also features a two-stage variable intake manifold, induce a rolling type of movement in the incoming air. The injectors atomise the fuel into this “tumble” inside the combustion chambers.

During direct injection, as the fuel evaporates it extracts heat from the combustion chambers. This effect solves the fundamental problem encountered in conventional turbocharged engines – the high amount of heat generated, and the engine’s resulting tendency to knock, which normally necessitates a reduced compression ratio.

On the TFSI, Audi’s engineers achieved a compression ratio of 9.8:1 – an extremely impressive figure for a turbocharged engine. This substantially improves the engine’s thermodynamic efficiency. The intake camshaft, which can be adjusted continuously through 42 degrees crankshaft angle, contributes towards optimum cylinder charging. Two balancing shafts rotating at twice the crankshaft speed compensate for the second-order mass forces.

Fundamentally stronger: the engine block

Compared with its starting version with an output of 147 kW (200 bhp), the 195 kW (265 bhp) engine of the S3 fundamentally represents another evolutionary leap. Pistons with stronger pins and new rings as well as reinforced connecting rods with new bearings transmit the powerful forces to the crankshaft. The cylinder block has been reinforced at the main-bearing pedestals and the main-bearing cap.

The cylinder head consists of a new, extra-lightweight aluminium-silicon alloy that exhibits high temperature resistance and strength.

The exhaust camshaft timing and the high-pressure injectors with increased cross-section have been adjusted to accommodate the increased power output.

The new turbocharger has a larger turbine and compression rotor than the basic unit. Its cast steel casing – produced as a single piece including the manifold – withstands exhaust gas temperatures of up to 1,050 degrees. The turbocharger generates a boost pressure of 1.2 bar instead of 0.9 bar on the starting version.

The intercooler: 850 kg of air per hour

An intercooler drastically lowers the temperature of the compressed air, thus increasing the amount of air that is necessary for combustion. Both its housing and the mesh through which the air passes are made from aluminium; the depth of the mesh has been increased, resulting in considerably greater efficiency. The intercooler is capable of an air throughput of up to 850 kilograms per hour or, put another way, over 650,000 litres of air.

The new high-performance turbo engine tips the scales at only 152 kilograms, significantly less than comparable engines from direct competitors – with a positive impact on the axle load distribution and therefore on handling characteristics. With its compact dimensions – it is just 652 mm long, 648 mm wide and 666 mm high – the TFSI is ideal for transverse installation.

Whatever tasks the driver wishes the engine to perform, the powerful TFSI accomplishes them with ease, thanks to its 195 kW (265 bhp) at 6,000 rpm. As a high-performance sports engine, it revs up effortlessly, responds intrinsically well to the throttle and produces strikingly sonorous acoustics. The four-valve engine with undersquare configuration is simultaneously impressive for its powerful traction. It puts 350 Nm of torque onto the crankshaft even at engine speeds as low as 2,500 rpm, and is able to maintain this high level of torque up to
5,000 rpm.

Road performance: power and efficiency

The 2.0 TFSI accelerates the new Audi S3 from 0 to 100 km/h in just 5.7 seconds, then on to a governed top speed of 250 km/h. Over the standard driving cycle it consumes just 9.1 litres of fuel over 100 km – further proof of the forward-looking efficiency of TFSI technology developed by Audi.

Like the predecessor model, the new S3 is equipped with a closely spaced six-speed gearbox. Three-shaft technology and the weight-saving magnesium casing mean that it is compact and light – entirely in keeping with its decidedly sporty overall configuration. The gears and shafts have been reinforced with an eye to the higher torques to be transmitted, and gearshift travel is now shorter; gear changes are accomplished swiftly and with ease, along the precise gate.

In common with all other S models, the new S3 has four driven wheels – an advantage that its direct competitors cannot match. The nerve-centre of the quattro drive technology that was developed specifically for transverse engines is an electronically controlled, hydraulically actuated multi-plate clutch: this is where the engine’s power joins forces with the transmission’s intelligence.

This clutch is located at the end of the propshaft, in front of the rear axle differential – the installed position at the rear improves the axle load distribution. A package of plates running in an oil bath within the clutch housing can be pressed together by controlled hydraulic power. The higher the pressure becomes, the more drive torque is diverted continuously to the rear axle.

The hydraulic multi-plate clutch: a pressing matter

The design, with a separate oil supply and two axial piston pumps for a rapid pressure buildup, permits lightning-fast reactions when the driving conditions change – the clutch’s control unit constantly analyses the situation on the basis of a wide range of data.

Depending on the degree of slip between the front and rear axles, an oil pressure that squeezes together the package of plates builds up. At its extreme, as much as 100 percent of the drive torque is diverted to just one set of wheels. The superimposed electronics are able to regulate the oil pressure and therefore the torque distribution as dictated by the situation.

This equips the Audi S3 with maximum traction and slip-free acceleration from the moment it starts to move. It also provides ample reserves for the transmission of cornering forces – S3 drivers consequently know they will benefit from optimum safety and lots of driving fun whatever the conditions. From the clutch to the wheel bearings, the drivetrain has been reinforced in every critical area, thus enabling it to transmit the engine’s high propulsive power with confident ease.

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