Audi’s V6 diesel gets two turbochargers
Dual-stage systems deliver higher torque ratings which increase performance.
PE in Technology.
- Published in Technology.
Raising the bar: More boost lifts torque to 650Nm in Audi’s 3-litre V6 diesel engine
Audi has applied dual-stage turbocharging to its 3-litre V6 diesel. A Honeywell series-sequential system boosts output to 230kW/650Nm – the highest in the class. The first applications are the A7 Sportback and A6 sedan.
Dual-stage systems deliver higher torque ratings, increasing performance. The engine, which Audi calls the TDI Biturbo, cuts the A7 Quattro’s 0-100km/h time by 1s to just 5.3s.
Richard Bauder, Audi’s head of diesel engine development, said: “With the new V6 TDI Biturbo we now have an optimum engine family with efficiency- and performance-oriented variants. The Biturbo has very high torque – the prerequisite was an innovative concept for stepped turbocharging.”
The boosting system features variable turbine geometry on the smaller, high-pressure turbo. The larger turbo is regulated with an electronically controlled wastegate.
The smaller turbo supplies all the boost pressure below 2,300rpm, reducing pumping losses and improving transient response. The two turbos work together in series until 3,400rpm. The larger turbo supplies all the boost after that. Maximum engine speed is 5,200rpm – high for a diesel.
Packaging was one of the biggest development challenges. Audi located the system at the back of the engine. “The low-pressure turbo is positioned transversly; the high-pressure turbo is mounted longitudinally,” said Bauder.
The Bosch commonrail system now operates at 2,000bar and uses eight-hole piezo injectors. A larger piston bowl reduces compression ratio from 16.8 to 16.0:1, reducing NOx emissions. Peak combustion pressure remains unchanged at 185bar but is maintained over a wider range of the engine’s operating map. To cope with the extra thermal loads the cylinder heads get two-part water jackets to improve cooling.
The high torque rating enabled Audi to increase the overall ratio of the eight-speed automatic transmission by 7%, helping to reduce fuel consumption. The increased performance still comes at a price – the A7 Quattro’s CO2 emissions range from the 180kW variant’s 158g/km to 169g/km. The dual-stage system means that the Audi V6’s output is now the highest in the class.
