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Saturday, January 26, 2008

Audi Q7 V12 TDI

Ultra-modern injection technology

Like most Audi V-engines, the maintenance-free chain drive is located on the back of the engine in a space-saving arrangement. A new layout is used in the new V12 TDI. The chain wheel of the crankshaft locks into the gearwheel. From here two simplex chains drive the camshaft. Two further chains drive the oil pump and both high-pressure pumps in the common rail injection system.

Both new double stamped high-pressure pumps are part of the new common rail injection system developed by the specialists at Bosch. Both pumps amass up to 2,000 bar of pressure in the rails; only 1,600 bar was usually achieved up to now.

The piezo injectors, with their eight-hole jets, have also been radically updated.An optimal spray is created in the combustion chamber through the high pressure. This in turn allows the ignition process to take place quicker and more homogenously, leading to a much better sound. The efficient combustion also improves performance whilst reducing emissions and fuel consumption.

The current generation of inline injectors use the piezo effect. When an electric current is created, piezo crystals expand in milliseconds. This expansion is then directly transported (inline) by the V12 TDI injectors – containing over one hundred piezo plates – to the injection nozzle needles without the use of mechanisms in between.

The number of injection processes per power stroke can be widely varied using piezo technology, in the case of the V12 TDI up to five injections.

In addition to the main injection, pre and post-injections are possible. Pre-injections reduce the acoustic hardness of the combustion procedure. Post-injections serve to increase the temperature of the emissions, helping regeneration of both standard-fit particulate filters.

Both turbochargers can be found on the exterior of the V-engine, each supplied with a cylinder bank. Thanks to its adjustable guide vane geometry, the complete gas emission stream is always fed through the turbines. The chargers respond even at low levels of revolution and reach high levels of efficiency.

Both turbochargers amass a charge pressure of up to 2.6 bar and are a key aspect of the exceptional torque levels of 1,000 Nm that are supplied to the V12 TDI constantly between 1,750 and 3,000 rpm. With its 368 kW (500 bhp), the diesel reaches a specific performance of 62 kW (84.3 bhp) per litre of engine capacity.

Two large charge air coolers reduce the temperature of the compressed air. The V12 comes with a double-flow exhaust system with two particulate filters. The suction unit is built in a similar way – each cylinder bank contains an air filter behind which an air mass meter is stored. Two control units manage what happens within the engine according to the master-slave concept.

The Audi Q7 V12 TDI will conform to the Euro 5 emissions class which will come into force in 2010 and demand a reduction of nitrogen oxide emissions. Aside from the precise analysis of the fuel injection system through the common rail system, the Audi engineers have focused especially on exhaust gas recirculation. At partial load, up to 50 % of emissions are recirculated through the air intake in order to reduce nitrogen oxide emissions. The large-dimension recirculation system is stored in the upper section of the V cylinder and includes a water cooler which reduces emission temperature significantly.

The design

The Audi Q7 V12 TDI is impressive not only with regard to technology but also in terms of appearance. The most striking visual changes to the Audi Q7 are the underbody panels at the front and rear. The chrome-plated single-frame radiator grille evokes the tradition of the Audi S6 and S8. These two cars, with their

V10 FSI engines, are the top sports models in their class. The V12 TDI features a powerful braking system which is every bit its equal.

Vorsprung durch Technik: Diesel milestones from Audi

A further milestone in diesel technology has been reached with the advent of the new V12 TDI. The Ingolstadt brand has been the pioneer in the diesel domain for over three decades. In 1978, Audi introduced the Audi 100, the world’s first five-cylinder diesel. The first TDI engine in motoring history was introduced in the successor model in 1989. The 2.5-litre five-cylinder engine offered 88 kW (120 bhp) and 261 Nm of torque, and catapulted diesel motoring into whole new dimensions.

In 1994, an expanded version was produced with 103 kW (140 bhp). The engine was also available with the option of four-wheel drive – the first TDI quattro. At the same time, a new four-cylinder diesel engine was introduced in the Audi 100 and Audi 80, the now legendary 1.9 TDI with 66 kW (90 bhp).

Towards the end of 1995, the four-cylinder achieved new heights of 85 kW (115 bhp) through the use of pump-jet injection. Just over a year later at the beginning of 1997, the world’s first 2.5 V6 TDI made its debut. This engine came with four valves per cylinder and reached 110 kW (150 bhp). With a top speed of 220 km/h the Audi A8 became the quickest series-production diesel on the market. The first eight-cylinder TDI followed in 1999, a V8 with a displacement of 3.3 litres. The 3.0 TDI was introduced in the spring of 2004, the first V6 diesel engine with inline piezo injectors in the common rail system.

The 4.2-litre TDI currently spearheads the TDI range from Audi. It was first introduced last year in the A8. Every third A8 buyer in Germany decided opted for the V8. The V8 TDI will also become available for the Audi Q7 during the first half of 2007.

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

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Related entries:

Audi Q7 In Depth
Audi Q7 V12 TDI Concept at NAIAS
Audi Q7 V12 TDI to launch in 2008
Leaked: Audi R8 V12 TDI Study for Detroit


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