--Plenty of push at low revs: One of the most important characteristics of the new V6 TDI is the power it develops at low engine speeds. This is one of the special attractions of the TDI and differentiates it clearly from all 6-cylinder petrol engines of similar capacity. Even at 220 km/h this engine is still running at less than 4000 rpm. At motorway speeds of 130 km/h and in sixth gear it turns over at a gentle 2200 rpm. On a country road at 100 km/h and also in sixth gear the engine speed goes down to 1700 rpm. Because of the high torque at low revs, the six-speed automatic gearbox can extremely often be left in top gear without any risk of stalling or dropping into the turbo lag zone – since there is none.
--Compact and light: The Phaeton's new V6 TDI engine is extremely compact, with a length of only 440 mm. A 90° V-angle is the distinguishing feature of the highly rigid but still very light cylinder crankcase; it is cast in vermicular graphite cast iron, which delivers all the rigidity of grey cast iron at 15 percent less weight. This engine weighs a mere 220 kilos, the distance between cylinder centres is 90 mm and its compression ratio is 17:1.
--Runs as quietly as a petrol engine: The 24 valves of this 6-cylinder engine are actuated by low-friction roller finger followers with hydraulic valve-play compensation, a technique that, like the piezo technology, contributes to reducing consumption and exhaust emissions substantially. The engine's acoustics and quiet-running characteristics are also outstanding and are certainly comparable to those of a 6-cylinder petrol engine. Combined with the new common rail system and the highly rigid construction of the cylinder crankshaft housing, the use of roller finger followers also reduces motor noise levels perceptibly. In detail, together with the stress-free and almost play-free camshaft drive gears, they make it possible to reduce the mechanical noise of the valve drive – a fundamental prerequisite for the excellent quiet-running properties of the V6 TDI 3.0, which bear comparison with those of a 6-cylinder petrol engine.
--1600 bar injection pressure: A state-of-the-art common rail system, the Bosch CRIP II+, is responsible for fuel-air mixing. It consists of a high-pressure pump, which can produce an injection pressure of up to 1600 bar, one distribution rail per cylinder bank, the low-pressure system with a fuel pump and a filter, the piezo injectors and an electronic control unit complete with sensors. This is a very high injection pressure for a common rail engine and means that the fuel can be sprayed more finely, which also makes for the best possible mixture and for more efficient combustion. The results can be felt and measured: output (in kW or h.p.) and torque (in Nm) rise just as significantly as consumption and exhaust emissions fall.
--Piezo technology instead of magnetic valves: One key function within this newly designed common rail system is taken over by the piezo injectors. The background to this is that, up to now, electronically controlled magnetic valves have been used in the injectors to control the timing and the duration of injection into each cylinder. The job of the magnetic valves is now handled in the V6 TDI 3.0 and, for the first time ever, by the piezo inline injectors, which operate far faster.
In these new injectors, the injection valves are in turn controlled by units referred to as piezo actuators. Each of these consists of piezo crystals that change their structure and enlarge under electrical voltage. This results in a minimal geometrical change that, with the assistance of a hydraulic element, mechanically actuates the aperture of the injection nozzle needle.
--Faster and lighter: Piezo technology has a large number of practical advantages to offer. The electronically controlled piezo actuator switches five times more quickly that a conventional magnetic valve. Because it is integrated directly into the injector, the movement is transferred directly to the nozzle needle without any mechanical element or any friction, and the moving mass of the nozzle needle has been reduced by 75 percent, from 16 to only 4 grams. Compared with magnetic valves, piezo technology also delivers double the nozzle needle speed. The actual injection goes through a 7-hole nozzle; it contributes to homogenous fuel distribution in the combustion chamber and to reducing emissions by achieving more efficient combustion.
--Four injections in each stroke: Because of these technical conditions it is possible to vary the number of injection cycles in order ideally to match the immediate operating conditions. In the case of the new V6 TDI 3.0, Volkswagen uses up to four injections per working stroke: in addition to the main injection there is a double pre-injection in the low rev range and a single one at medium revs, and there is also a single post-injection at engine speeds up to about 2500 rpm. This sequence of injections guarantees on the one hand the best possible emissions behaviour and on the other hand “softer” combustion, which results in extremely agreeable engine noise levels. The V6 TDI 3.0 can claim a leading position in this respect, and in the passenger compartment of the Phaeton it will hardly be perceived as a diesel engine; on the contrary, the engine noise levels and quiet-running properties are exactly the same as those of a 6-cylinder petrol engine.
--Centrally integrated turbocharger, two intercoolers: In the interests of making the most economical use of space, the turbocharger is located centrally within the V-angle of the engine. In order to achieve the best possible efficiency from the turbocharger, the temperature of the intake air is effectively lowered through two parallel intercoolers with a minimal loss in pressure. The variable turbine geometry of the exhaust turbocharger is controlled in the new V6 TDI 3.0 by aunit referred to as an electric actuator, which enables the guide blades to be set more quickly and precisely. At low engine speeds in particular this results in a faster build-up of turbocharger pressure and thus contributes to a significantly better response behaviour. This direct implementation of acceleration commands is effectively supported by the optimised shapes of the compressor and turbocharger fans.
--Variable intake: There are also three infinitely variable swirl flaps integrated directly into the air intake with which the air movement can be adjusted to suit the immediate engine speed and load. The background to this is that a high degree of swirl at a low engine load optimises combustion just as, conversely, low swirl does at a high motor load. This means in practice that a closed channel at a low load increases the swirl whilst an open channel at a high load make it possible to fill the cylinders to a high level.
--Exhaust gas recirculation: The emissions of the V6 TDI are almost entirely reduced back at the combustion stage. Any exhaust gases that are left are rendered harmless in the next stage. One example is exhaust gas recirculation. The exhaust manifold is designed with double walls and is air-gap insulated, so that the exhaust gases can be sent for treatment without any appreciable heat loss. Effective cooling is necessary, on the other hand, for the actual exhaust recirculation so that, for instance, the emissions of NOx and particles can be effectively reduced. The exhaust gas therefore passes through an exhaust gas recirculation (EGR) cooler with a water through-flow; this is controlled in relation to temperature and load and located in the internal V-angle of the engine, thus achieving an optimum economy of space. In the cold-start phase, however, the exhaust gases “squeeze through” via a bypass channel ahead of the cooler so that the catalytic converters can work more quickly at their ideal operating temperature. Once the engine and the catalytic converters have warmed up the exhaust gas comes directly back into the area of the EGR cooler.
--Catalytic converter and DPF: The exhaust gas is cleaned by a pre-converter located close to the engine (and near to the turbocharger) and the main catalytic converter in the under-floor. Soot particles are then screened out by a diesel particle filter (DPF), a standard feature on the Phaeton V6 TDI 3.0.
Diesel particle filters generally serve the purpose of picking up and eliminating diesel soot before it can be sent out into the environment with the exhaust gases. A system is in use on the Phaeton V6 TDI 3.0 that uses the latest state-of-the-art technology. It is called the “Catalysed Soot Filter” (CSF) and uses a filter coating containing stainless steel that works in two different ways: passive regeneration, in which the soot accumulating in the catalytic converter is converted slowly and gently into CO2, a process that occurs at temperatures between 350 °C and 500 °C and runs continually without any special effort, mainly on long stretches of motorway driving; and active regeneration, during longer period of operation on low load such as in big cities, when the exhaust temperature is actively raised to about 600 °C every 1000 to 1200 kilometres for additional filter regeneration. The particulates accumulating in the filter are burnt off at this temperature.
--Motor management: All these processes have to be perfectly controlled and monitored. In the Phaeton V6 TDI 3.0 this task is handled by the highly efficient Bosch EDC 16 engine management system, which co-ordinates the fuel quantities and the start of fuel injection, the turbo-charger pressure and the exhaust recycling. The electronic system in the Phaeton also provides for a push-button engine start and thus for the use of the optional keyless access unlocking and starting system. To ensure that this start-up works as quickly in the winter as it does in the summer, the engine also has a high-speed pre-heating system with ceramic glow plugs.