The V6 retains the basic architecture of the existing engine with the same 90 degree bank angle and bore spacing. However, all of the major components have been reworked with the dual aims of reduced weight and friction. The overall mass of the V6 has been cut by 55 pounds to 425.5 pounds. The use of a thin-wall vermicular graphite cast iron block cut 17.6 pounds. While it might seem counter-intuitive to use an iron block when weight is a priority, the high stresses in a diesel engine would have required more material if it was cast of aluminum, raising the overall weight.
On the friction side, machining of the block comes into play. When the cylinder heads are bolted onto the block, the cylinder bores are distorted toward the bolts. Plates that simulate the heads are now bolted on prior to the finish honing process to pre-distort the bores. The result is that, when the engine is assembled, the bores are now closer to circular. This allows the use of piston rings with lower spring tension, reducing friction.
Additional efficiency improvements come from cooling system changes. When cold, the coolant in the block and heads is not circulated, allowing it to warm up faster. The coolant is also not circulated under some light load conditions. All together these changes cut consumption in the Q7 by 20 percent.
Unfortunately, we won't be seeing this engine arrive in the U.S. for a while because of the additional exhaust after-treatment systems required for diesels here.
Update: Just to be clear, although we won't get the new lighter engine in the U.S. yet, the current engine is in many ways still the most advanced version because of the after-treatment systems to make it meet 50-state emissions standards.
Audi TechDay Drivetrain
A whole new level of efficiency: the new 3.0 TDI
Andreas Fröhlich, Head of Design – 3.0 V6 TDI
The 3.0 TDI that Audi uses in the A8 and now also in the Q7 is a thorough redesign. All that was carried over from the previous version of the engine are the 90 degree V, the cylinder spacing of 90 millimeters (3.54 in), and the displacement of 2,967 cc. All major components are new developments – from the cylinder block to the crankshaft and from the forged connecting rods and the aluminum pistons to the cylinder heads.
The V6 diesel, which operates with an ignition pressure of up to 185 bar combines powerful performance with exemplary efficiency. In the Audi Q7 it produces 176 kW (240 hp) and delivers a constant 550 Nm (405.66 lb-ft) of torque to the crankshaft between 1,750 and 2,500 rpm. Fuel consumption was reduced by 1.7 liters per 100 kilometers, or 20 percent, to 7.4 liters per 100 km (31.79 US mpg). The 3.0 TDI emits only 195 grams CO2 per kilometer (313.82 g/mile). It accelerates the large Q7 from zero to 100 km/h (62.14 mph) in 7.9 seconds on the way to a top speed of 218 km/h (135.46 mph) (with air suspension).
Reducing weight was a central aspect of the redesign. The new V6, which is only 44 centimeters (17.32 in) long, weighs just 193 kilograms (425.49 lb), a full 25 kilograms (55.12 lb) less than its predecessor. Thanks to its high strength, the crankcase of vermicular graphite cast iron permits low wall thicknesses. That alone saved the development engineers eight kilograms (17.64 lb) of weight.
The engineers saved three kilograms (6.61 lb) with the alloy cylinder heads and two kilograms (4.41 lb) with the crankshaft. The majority of the bolts and cooling water lines are made of aluminum rather than steel.
The development engineers also devoted a great deal of attention to friction. Two high-end techniques play a major role in the production of the 3.0 TDI: laser exposure, which improves the strength of the cylinder barrels, and, as a new solution, plate honing, in which a plate is bolted onto the crankcase prior to the mechanical honing of the cylinder barrels. This simulates the pretension that the cylinder head will exert later during operation and which results in deviations from perfect roundness on the scale of just thousandths of a millimeter.
This effect is then accounted for during honing, which is why Audi can fit the pistons with rings with less pretension that slide easily in the barrels. Tangential forces are thus reduced by around 35 percent.
Additional measures for reducing friction target the chain drive. Whereas the previous engine still used four chains and a toothed belt, only two chains are needed now. They drive the four camshafts with their narrow bearings, the balance shaft, the regulated oil pump and the common rail system's efficient high-pressure pump. Pressure of up to 2,000 bar is developed in the rails. The piezo inline injectors are equipped with eight-port nozzles. They activate extremely quickly and can inject fuel up to eight times per work cycle.
At the inlet of the intake manifold, which is made entirely of plastic, is a central swirler flap that swirls the air in the combustion chamber for efficient combustion, particularly at low engine speeds. The new flap replaces the individual swirler flaps in the intake ports of the previous engine, reducing pressure losses. The exhaust system and the charging air path of the turbocharged engine were also designed for low-loss flow.
In the turbocharger, which theoretically can compress more than 600 cubic meters of air, the compressor shaft was mounted in new bearings. The friction-optimized sliding bearings ensure spontaneous initial response, particularly at low engine speeds. A fast electric actuator adjusts the turbine geometry so that the engine reacts spontaneously to the throttle.
The new 3.0 TDI has a particularly sophisticated version of Audi's innovative thermal management system on board. The crankcase and the cylinder heads each have their own cooling water loops connected to one another via a pneumatically actuated valve. During the warm-up phase, the coolant in the block is not circulated so that the cooling water and thus the motor oil heat up quickly. The oil cooler is also bypassed during this phase.
The water also is often not circulated at low load, which saves energy. The coolant circulating through the heads also heats the cabin and feeds the cooler of the exhaust gas recirculation system. Its stainless steel tube bundles are integrated into an aluminum housing.
The new 3.0 TDI is paired standard with a start-stop system. When the car comes to a stop at a traffic light or an intersection and the driver keeps the brake depressed, the system's control unit shuts down the engine. On a hill or a downgrade, the brake system maintains the brake pressure if the slope does not exceed than 10 percent. A powerful starter restarts the engine quickly and conveniently as soon as the driver lets off the brake.
The start-stop system works together with a particularly powerful battery that continues to function even at very low outdoor temperatures. It only allows the engine to continue running during the early warm-up phase so that the oil and the cabin come up to temperature more quickly. Fuel consumption in the EU cycle is reduced by around 0.3 liters per 100 km.
The world's cleanest diesel: the 3.0 TDI clean diesel
The 3.0 TDI clean diesel uses the cleanest diesel technology in the world to comply with the emissions standards of every U.S. state and also the Euro 6 emissions standard announced for 2014. The V6 diesel, which is available for the Audi Q7 and in the A4 model series, is also highly efficient. In the large SUV, it uses only 8.4 liters of fuel per 100 km (28.00 US mpg); in the A4 and the A4 Avant, consumption is only 6.7 and 6.9 liters per 100 km (35.11 US mpg and 34.09 US mpg), respectively.
The technology package of the 3.0 TDI clean diesel quattro comprises the engine itself and the exhaust gas after-treatment system. A common rail injection system that develops pressures of up to 2,000 bar, innovative combustion chamber pressure sensors and an ultra-high-performance exhaust gas recirculation system ensure highly efficient combustion which produces minimal raw emissions from the outset.
Located at the end of the exhaust line is a DeNox catalytic converter, which provides for the chemical reduction of nitrogen oxides. Just upstream of it, a pump injects an aqueous additive named AdBlue into the hot exhaust flow, where this solution decomposes into ammonia, which splits the nitrogen oxides into nitrogen and water. The tank is large enough that the driver never has to refill it. This is done instead by the Audi dealership during scheduled maintenance.
The innovative V6 TDI provides powerful performance. In the Q7, zero to 100 km/h (62.14 mph) takes 8.1 seconds, and top speed is 218 km/h (135.46 mph) (in the version with air suspension). In the A4 and the A4 Avant, the standard sprint takes only 6.2 and 6.3 seconds, respectively. Both mid-size models reach an electronically governed top speed of 250 km/h (155.34 mph).