What is it?

A new quattro four-wheel drive system for Audis with longitudinally-mounted engines – so the A4 and larger vehicles – targeting fuel economy and CO2 emissions close to a two-wheel drive version.

How does it work?

Traditionally, quattro-equipped Audis have had permanent four-wheel drive, with 60% of the power and torque directed to the rear axle. If one of the wheels starts to slip, a mechanical centre differential automatically directs power to the corners with the most grip – up to 70% to the front, or 85% to the rear, as required.

The drawback, in dry conditions, is that the engine is still working to turn the propshaft (which connects the two axles), the rear differential and the driveshafts, with an obvious effect on fuel economy. And that’s something Audi wants to claw back.

This new system works differently. There’s a clutch at the back of the gearbox which can decouple the propshaft, and another which separates the driveshafts from the rear differential. This means the car runs in two-wheel drive when there’s plenty of grip, with only minimal drag from the unused parts of the drivetrain. If it needs extra traction – for example, on a patch of snow or mud – the drivetrain reconnects quickly and the clutches brings idle components up to speed to avoid any shudder as it does so.

But this isn’t just a reactive system. Audi wanted it to feel as sure-footed as traditional quattro technology, so it stays in four-wheel drive when driven aggressively and can even predict when extra traction might be needed based on ambient conditions, ESC sensors and driver inputs. On a winding road route, there was no perceptible difference between the two – the car seamlessly engages four-wheel drive before the driver even knows they need it.

The claims?

Audi is targeting class-best fuel consumption and CO2 emissions for this system. It’s said that this offers a fuel economy benefit of around 0.3l/100km on the combined cycle compared to the outgoing system – equivalent to around 5-7g/km of CO2. The advantages are weighted towards motorway driving, where most of the journey is typically in two-wheel drive.

Further ahead, it’s reckoned that the technology could even be integrated with Audi’s detailed navigation system. Knowing the topography, weather conditions and severity of corners ahead, the car could pre-plan not only opportunities to freewheel, but it could also switch to four-wheel drive in advance.

When?

The new quattro system will form part of Audi’s Ultra line-up, fitted to its most efficient engines, while performance cars will still use the traditional technology. This starts with the new A4 Allroad, only on the 2.0 TFSI petrol engine with S-tronic transmission at first, but will be available on diesel engines and manual gearboxes within a year, starting with the next-generation Q5. As there are no sheet metal changes required, it’s an easy retrofit for current-generation cars. With fleets accounting for half of all A4 quattro volume in the UK, there’s a potentially large business opportunity for it.