Audi Q7
Cutting weight and improving emissions were at the top of the agenda for Audi's large SUV
- Published in Vehicle Development.
Altogether greener: New V6 powertrain for the Q7 takes some of the guilt out of owning a large SUV
The death of the SUV has been predicted many times but they’re still with us. Fleet average CO2 targets in Europe, and tightening corporate average fuel economy targets in the US, led some to think that such vehicles didn’t have much of a future.
The financial crisis caused a steep and prolonged drop in sales, and the effect of the global recession was compounded by last year’s spike in oil prices. There are societal pressures too. Neighbours might once have been envious of the big all-wheel drive vehicle in your garage. Now they’re more likely to question its environmental performance and wonder why you didn’t go for a hybrid sedan instead.
Hybridisation of big SUVs is becoming more common. Lexus, Volkswagen and Porsche already have V6 gasoline hybrids on their fleets; Volvo and Land Rover are working on diesels.
Audi is working on hybrids too. But it’s also been working hard to cut the fuel consumption of its biggest SUV – the Q7 Quattro – by optimising conventional powertrains. Consumers going for the 3.0TDI will gain fuel consumption improvements of almost a fifth: this Q7 gets through 7.4litres/100km instead of 9.1; CO2 emissions are now 195g/km instead of 239.
The engine shares its basic dimensions with the outgoing unit and, in this application, power and torque ratings too. But it’s not an overhaul of the original 2003 design; it’s completely new.
“Development started around two and a half years ago – that’s about standard for a new-generation engine,” says Audi V6 diesel project engineer Jörg Juchen. “We benchmarked BMW, Daimler and Jaguar. We always try to get the best in performance and acoustics.”
Fundamental to both targets is the strongest, stiffest engine possible. So Audi dropped the old engine’s grey cast iron crankcase for one made from compacted graphite iron, saving 8kg. “We considered aluminium but if you look at the cylinder pressures, and the complex structures used by some competitors, there’s no weight advantage,” says Juchen.
The cylinder bores are plate-honed: a plate bolted to the block before machining gives the pretension equivalent to that of an assembled engine, reducing geometrical tolerances. As a result, tangential forces in the piston ring pack – a significant source of engine friction – could be reduced by more than a third.
Other weight savings include 3kg from the aluminium cylinder heads and 2kg from the forged steel crankshaft, achieved by deleting centre counterweights. At 193kg, the engine is 25kg lighter than the old one.
