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Audi debuts electric anti-lag in V8 diesel SQ7

Under pressure: The Audi SQ7’s electric compressor spins up to 70,000 rpm in just 250 milliseconds, giving the diesel V8’s two exhaust-driven turbos a huff to eliminate lag.

Turbo lag banished with 900Nm from 1000rpm in Audi’s SQ7 hi-po SUV tech-fest


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4 Mar 2016

PROMISING to consign turbo lag to the history books is Audi’s new diesel-powered SQ7 performance SUV, which develops its stump-pulling peak torque of 900Nm from just 1000 rpm courtesy of an electric compressor supporting the V8 engine’s two sequential boost-producers.

Revealed at the annual Audi press conference in Ingolstadt overnight, the SQ7 is confirmed for Australian release and will arrive in local showrooms before the end of this year. GoAuto understands pricing will be in the region of $180,000 plus on-road costs, a hefty increase over the $103,900 base Q7.

With maximum torque available from barely above idle, this new flagship of Audi’ s seven-seat SUV range promises the kind of instant thrust usually reserved for electric vehicles – and the claimed 0-100km/h acceleration time of just 4.8 seconds backs up that expectation.

Displacing 4.0 litres, the all-new diesel V8 also churns out a healthy 320kW, enabling the SQ7 to hit an electronically limited 250km/h top speed.

But despite its size and performance, Audi estimates this hot family hauler will consume just 7.4 litres of fuel per 100 kilometres and emit 194 grams of carbon dioxide per kilometre when subjected to New European Driving Cycle testing.

For comparison, Audi’s first-generation Q7 flagship, the $254,900 V12 TDI, produced 368kW and 1000Nm but was slower to 100km/h at 5.5 seconds. In addition to being more expensive than the SQ7 will be to buy, its 11.3L/100km thirst made it a bit of a bowser-buster.

Central to the SQ7’s impressive combination of performance and economy is the electric powered compressor (EPC), which is powered by a 48-volt electrical system that also runs an adaptive suspension setup similar to that of the Bentley Bentayga.

The EPC draws up to 7kW of power from the 48V system, spinning up to its maximum 70,000rpm in just 250 milliseconds and giving the engine’s exhaust-driven turbos a boost-building head start. The load on the engine and electrical system is significantly less than more conventional mechanically-driven superchargers.

Audi says the system is a production car world-first, but this claim could be disputed by Volvo, which late last year announced PowerPulse, which stores electrically compressed air in a cylinder for lag-busting release into the turbos of its D5 diesel drivetrain – and will soon be fitted to the XC90 SUV along with the just-unveiled V90 wagon.

Power for the Audi EPC comes from a 48-volt lithium-ion battery pack beneath the boot floor, with a 470 watt-hour capacity, maximum output of 13kW and DC-DC converter linking it to – and enabling it to reduce loads on – the vehicle’s standard 12-volt electrical engine starting and accessory power system.

Charging these systems is taken care of by an 80 per cent efficient 3kW Metal Oxide Semiconductor Field Effect generator.

Back in the mechanical world, the new Audi diesel V8 features valve-control technology that helps control the flow of exhaust gases to its sequential turbochargers.

Based on engine speed and load, one of each cylinder’s two exhaust valves can remain closed to ensure maximum efficiency for the EPC while shutting off exhaust gas flow to the second, larger turbo.

Once the big turbo is required, both valves open, which increases the precision with which the second blower comes on-stream and, according to Audi, “optimises cylinder filling and thus power at high engine speeds”.

The result is no perceptible turbo lag plus, as Audi puts it, “very good torque delivery and dynamic response across the entire engine speed range”.

As with most recent high-performance V-configuration engines, the turbos are nestled in the gap between the two cylinder banks, providing the shortest possible distance for exhaust gases to travel into the turbochargers and emissions control hardware, aiding efficiency.

By locating the brace of turbos in the 'valley' of the engine, Audi is following the lead of its main rivals, after BMW started the trend and was later copied by Mercedes-Benz.

The common-rail diesel injection system also runs at pressures of up to 2500 bar.

Despite all the technology, Audi promises the SQ7 will still provide a “sporty, unmistakeable V8 sound”.

Also helping the SQ7’s emotional appeal is the sports-tuned hi-tech chassis control, which in addition to the Bentayga-like 48-volt anti-body-roll system, networks the adaptive shock absorbers, air springs, differentials and all-wheel steering to provide “outstanding handling in any situation”.

The roll-control system can exert up to 1200Nm of force on the front and rear stabiliser bars – each one independently – to counter body-roll during cornering or relax to improve ride comfort on poor surfaces.

Being a 48-volt electromechanical system, it is said to react more quickly, with greater power, than a hydraulic set-up while having the maintenance and environmental advantages of being oil-free.

Distinguishing the SQ7 from letter variants are a new matte-grey radiator grille and rear bash plate separating the quad rectangular exhaust tips, a sports bodykit, 20-inch alloy wheels, LED headlights and aluminium trim for the side air vents, mirror housings and door inlays.

Inside are a choice of two front sports seat designs (trimmed as standard in Alcantara and leather) along with aluminium trim strips, a three-spoke multifunction sports steering wheel with paddle-shifters and S branding, with the option of a Kodiak brown upholstery theme comprising full contrast-stitched leather, black Alcantara headlining, velour floor mats, two-piece aluminium and carbon twill copper trim strips and premium Valcona leather for the front ‘sports seats plus’.

Audi hinted at the potential of its electric turbo technology in 2014 with a diesel version of its RS5 coupe and previewed a 48-volt suspension set-up in an A6 sedan, although that system used compressed air rather than electromechanics.

Several automotive component suppliers are touting 48-volt systems as the fuel-saving technology of the future, with applications from mild-hybrid drivetrains to engine ancillaries such as air-conditioning compressors and water pumps.

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