February 26, 2004

The Audi A8 3.0 TDI quattro: With the World's First Piezo Inline Common Rail Fuel Injection System from Bosch
Text and pictures courtesy of Audi AG

Technical speech
Richard Bauder, Head of Diesel Engine Development

Ladies and Gentlemen,

It was Audi who began the success story of the direct-injection diesel engine for passenger cars in 1989, with its 5-cylinder inline engine. This had a swept volume of 2.5 litres and was available in a series of successful Audi models with power outputs up to 140 bhp. 

The first V6 TDI engine followed in 1997, also a 2.5-litre unit with a power output of 150 bhp and a maximum torque of 310 Nm. This generation of engines is still in active use with power outputs up to 180 bhp and torques of up to 370 Nm in various models, from the Audi A4 Cabriolet to the allroad quattro, and is therefore an important element in the Audi model programme.

Today we are able to present to you our latest development, currently the world's most powerful series-production V6 diesel engine for passenger cars, a 3.0-litre unit developing 233 bhp and 450 Nm of torque. 

Even without a particle filter, this new engine complies with the very tough EU4 exhaust emission limits when installed in luxury-class cars with automatic transmission and permanent all-wheel drive. This is an achievement of which we are particularly proud.

The new V6 TDI is the first diesel in the new generation of Audi vee engines with the distance between cylinders increased from 88 to 90 millimetres. This was necessary in order to obtain the increased swept volume of three litres.

A significant feature of the Audi vee engine family is the novel timing chain positioning at the transmission end of the engine. The chains drive the balancer shaft and the oil pump as well as the camshafts, and of course need no routine maintenance.

This design principle makes the engine extremely short and compact. It is only 444 mm long - an impressive figure when we consider that some competitors' engines are more than 700 mm long.

The cylinder heads contain two overhead camshafts, one each for the inlet and exhaust valves. The valves are actuated by low-friction roller cam followers. To reduce mechanical noise, the camshafts are linked together by special zero-backlash gears.

 The engine block, with a 90-degree included angle between the cylinder banks, is a vermicular graphite iron casting. This material has twice the strength of conventional grey cast iron. As a result, it also weighs about 7 kilograms less than the block used for the previous engine.

In combination with the main bearing deck and the aluminium sump, which is not exposed to ignition loads, this design principle permits optimum weight saving and in particular optimum acoustics. 

The complete engine weighs only 220 kg.

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It has a third-generation common-rail fuel supply system with piezo injectors from Bosch. This is a world first. It has a maximum injection pressure of 1600 bar; the high-pressure pump is located in the vee of the engine and driven by a toothed belt.

The novel piezo inline injectors can perform up to five injection stages on each injection stroke, and are notable for the very small amount of fuel they can deliver if necessary and the very low volumetric tolerances between the fuel deliveries. These are important factors in achieving the lowest possible emissions and an excellent operating noise pattern.

The new 3.0 TDI engine has a turbocharger with variable turbine blade geometry. For the first time, the blades are moved by an electric actuating motor; this permits their position to be controlled more accurately. 

To avoid any unnecessary loss of exhaust heat, the manifolds and compensators have air-gap insulation. The combination of variable-blade turbocharger and air gap insulation ensures a spontaneous build-up of boost pressure and therefore of torque from the engine.

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