The Audi TDI – Tech Workshop 2014
The new 3.0 TDI
The 3.0 TDI represents the very latest technology. The Audi bestseller in the large model series is now even cleaner and satisfies the requirements of the Euro 6 emissions standard. Performance has also increased. Output is 200 kW (272 hp), the maximum torque of 580 Nm (427.8 lb-ft) is available between 1,250 and 3,250 rpm.
The updated Audi A7 Sportback, in which the new V6 diesel is being used for the first time, accelerates with quattro all-wheel drive from 0 to 100 km/h (62.1 mph) in 5.7 seconds on its way to an electronically limited top speed of 250 km/h (155.3 mph). Fuel consumption is just 5.2 liters of fuel per 100 km (45.2 US mpg) on average, which corresponds to 136 grams of CO2 per km (218.9 g/mile). The new 3.0 TDI is thus 13 percent more efficient than the previous model.
In the ultra model, the new V6 diesel is even more efficient and delivers new best marks. With 160 kW (218 hp) and 400 Nm (295 lb-ft) of torque, it accelerates in 7.3 seconds from zero to 100 km/h (62.1 mph) and reaches a top speed of 239 km/h (148.5 mph). It consumes just 4.7 liters of fuel per 100 kilometers (50.0 US mpg), a CO2 equivalent of 122 grams per kilometer (196.3 g/mi).
The new 3.0 TDI, which works with ignition pressures of up to 180 bar, has taken over the key dimensions of the two previous generations: the bore of 83.0 millimeters (3.3 in) and the stroke of 91.4 millimeters (3.6 in) for a displacement of 2,967 cc. The cylinder banks arranged at 90 degrees to one another; a balance shift spins in the cylinder crankcase. The cylinder crankcase is made of high-strength, yet lightweight vermicular graphite cast iron. Intensive detail work has shaved some weight from it. The entire engine weighs 192 kilograms (423.3 lb).
The forged crankshaft, which has also been optimized for weight, uses the splint-pin principle for smooth running behavior. The connecting rods of the opposing pistons offset by 30 degrees, resulting in even firing intervals. Cast channels supply the aluminum pistons with cooling oil. To reduce friction, the piston pins received a diamond-like carbon coating. The first piston ring also has a high-end hard coating. The ring package has been completely redeveloped. Tangential tension has been reduced by more than 25 percent, so the rings now slide more easily in the piston sleeves. The compression ratio is 16.0:1.
Elaborate plate honing is used in the production of the 3.0 TDI. A plate, which is bolted to the crankcase prior to the mechanical honing of the piston sleeves, simulates the tension later exerted in operation by the cylinder head and which results in deviations from perfect roundness measured in thousandths of a millimeter.
The V6 diesel uses advanced thermal management. The cylinder crankcase and the cylinder heads each have their own coolant circuits connected to one another by a valve. During the warm-up phase, the coolant is not circulated in the block, so the motor oil heats up quickly. To save energy, the coolant often remains stationary at low load, too. The coolant in the head loop heats the cabin and is also supplied to the intercooler for the exhaust gas recirculation system. The cylinder heads’ cooling jackets are divided into an upper section and a lower section to reduce pressure losses.
Pressures in the common rail system reach up to 2,000 bar. The extremely fast-switching piezo injectors with their eight-hole nozzles can perform up to eight injections per work cycle. The central swirler flap mounted at the entrance to the induction pump helps to minimize pressure losses. At low rpm, the closed intake channel results in greater swirl, which promotes the development of torque. At high rpm, however, the open channel ensures that the combustion chambers are well filled.
The water-cooled turbocharger is a next-generation design. The electrically actuated positioning mechanism on the turbine side (VTG) is now more aerodynamic and precise, so the engine reacts more quickly to the position of the accelerator. Maximum relative boost pressure has increased from 1.6 to 2.0 bar. The exhaust manifold has also been revised. The newly developed oil pump is now load and engine-speed-controlled over a large range of its characteristic, and the oil cooler has been integrated into the loop via a thermostatically controlled bypass.
Thanks to an emissions-control unit compliant with the Euro 6 emissions standard, all versions of the 3.0 TDI bear the “clean diesel” designation. In the new engine, the components have been moved as close as possible to the rear side to enable quick activation. With the 160 kW (218 hp) V6, the enlarged oxi-cat is mounted coaxially downstream of the turbocharger’s turbine outlet. Immediately downstream is a diesel particulate filter. The inner lining of its filters has a coating that removes nitrogen oxides from exhaust emissions by means of selective catalytic reduction (SCR). A metering module injects the additive AdBlue.
The new packaging of the emissions-control components resulted in modifications to the chain drive. The oil/vacuum pump and the high-pressure pump of the common rail system each have their own drives. Intermediate wheels mounted on needle bearings and gear stages replace the large chain wheels in the camshaft drive. As assembled hollow shafts, the camshafts are particularly lightweight. They actuate the valves via extremely rigid roller cam followers. Camshaft bearings with reduced diameters reduce friction.