New Audi SQ5 TDI launched

Audi has tapped the smooth, strong powertrain of the SQ7 sports SUV to finally deliver a diesel version of its fastest Q5 model.

The diesel-powered Audi SQ5 TDI will be launched at next month's Geneva motor show, where it will debut with a crunching 700Nm of torque and a 0-100km/h sprint in only 5.1 seconds.

Like its big brother, the SQ5 will be an internal combustion master class of technology, combining a turbocharged V6 diesel engine with an electric compressor and a mild-hybrid boosting system that adds another 7kW of power.

The 255kW powerhouse is limited to 250km/h, but is claimed to deliver an NEDC fuel-consumption figure of 6.6L/100km and CO2 emissions of 172g/km.

That makes the SQ5 TDI both faster and far more fuel efficient than the petrol-powered SQ5 it will join in Australia mid-year – but only about on-par with the 2013 SQ5 TDI for both speed and economy.

The original SQ5 diesel in 2013 used a twin-turbo 3.0-litre V6 with 230kW and 650Nm to reach 100km/h in 5.1 seconds – the exact performance claim of the new SQ5 TDI – and also used fuel at a rate of 6.8L/100km.

Yet the current SQ5, with a lonely twin-scroll turbocharger nestled into the vee of the 3.0-litre petrol V6, is 0.3 seconds slower than both the old and the new diesel SQ5s and gulps a claimed 8.7L/100km while it’s doing it.

In spite of 260kW of power and 500Nm of torque, the petrol version never got on top of its diesel predecessor, despite jumping up around $10,000 in price.

Alas, the diesel replacement is far more sophisticated than the old SQ5 TDI. The new version uses a 48-Volt electrical system to help its belt-driven alternator-starter motor to feed recovered coasting or braking energy into a dedicated 10Ah lithium-ion battery beneath the luggage area’s floor, and then punches that back into the crankshaft when it can be useful.

Besides that 12kW of helpfulness, there is also a 7kW electric motor that never actually adds energy directly to the powertrain, but is purely dedicated to spinning up the electric compressor.

The electrically-driven compressor sits downwind of the conventional variable-vane turbocharger and its job is to punch in torque at low revs, before the rest of the engine hits its stride.

It also reduces turbo lag and tightens the engine’s responsiveness at less than 1650rpm, delivering up to 1.4 bar of air pressure, which is down on the turbocharger’s 2.4 bar, but still useful.

The end result is a 700Nm torque chunk from 2500 to 3100 revs, but that entire range is above where the electric compressor has finished its work. Like it does in the SQ7, the electric compressor can whizz up to 65,000rpm in just 0.003 seconds.

Then, if the driver lifts off the throttle anywhere between 55 and 160km/h, the SQ5 TDI can either recuperate energy at up to 12kW or coast with the engine switched off for up to 40 seconds – even at 160km/h.

There has been work done on the conventionally oily bits of the V6 diesel, too, including a new crankshaft, new pistons, new connecting rods and an entirely new oil-management system.

Like the petrol-powered version, the TDI SQ5 runs its engine performance through an eight-speed automatic transmission, and then adds permanent all-wheel drive through an old-school Quattro system. It means a standard torque split of 40 per cent to the front axle and 60 per cent to the rear, though its centre differential can switch up to 70 per cent to the front or 85 per cent to the back axle.

There’s also torque vectoring, plus dynamic cornering and an optional sports diff on the rear axle to help out the five-link suspension layouts at both ends.

There is also an option of dynamic steering, though active damper control is standard and can lower the body by 30mm.

It all runs on 20-inch cast alloy wheels and 255/45 rubber, though there is a 21-inch option, and it’s anchored by six-piston front calipers biting on 375mm discs.

Besides a bewildering array of active driver-assistance systems, the SQ5 TDI’s interior uses a combination of Alcantara and leather, with a 12.3-inch digital instrument cluster, an 8.3-inch infotainment screen, Bang & Olufsen audio and wireless smartphone charging.