Despite the challenges faced by the Volkswagen Group over its diesel emissions scandal, it appears diesel isn’t a dirty word for the automaker as it's just announced a mighty V-8 diesel engine that delivers 429 horsepower and 663 pound-feet of torque. The engine’s first application is in a new Audi SQ7 TDI performance SUV and we’ll eventually see it used by other VW Group brands, including Bentley.
The big news is that the engine is equipped with an electric compressor, essentially a small electric motor that spins a compressor up to 70,000 rpm and provides boost pressure to the engine instantaneously. Audi previewed an early version of the technology in an RS 5 TDI concept. The latest version is slightly different as it consists of a standalone electric compressor which generates boost pressure on its own (the previous version spooled a turbocharger’s compressor at low revs).
The engine in the SQ7 TDI is a twin-turbocharged 4.0-liter V-8 diesel, which is mated to an 8-speed automatic and all-wheel-drive system. Two turbochargers are arranged in a sequential setup and add boost pressure in a conventional way, i.e. by relying on exhaust gasses to spool up their compressor wheels. This, of course, suffers from turbo lag at low engine speeds.
2017 Audi SQ7 TDI
That’s where the new electric compressor comes into the equation. It sits in the air path downstream of the intercooler, close to the engine. Because it relies on an electric motor to develop boost pressure, it can be used at any time, thus making it the solution for the traditional weaknesses of the classic exhaust-gas turbocharger. It’s claimed boost pressure arrives in less than 250 milliseconds.
The result is an engine that delivers peak torque of 663 lb-ft from just 1,000 rpm and maintains this up to 3,250 rpm. This sees the SQ7 TDI accelerate from 0-62 mph in just 4.8 seconds. Top speed is limited to 155 mph.
There’s other innovations on the SQ7 TDI than just the electric compressor. For example, the juice for the electric motor—approximately 10 horsepower at maximum—comes from a new 48-volt electrical subsystem instead of the typical 12-volt system found in most cars. The SQ7 TDI uses this higher-power electrical system to meet the high power and energy requirements of the electric compressor as well as a new electromechanical active roll stabilization system.
2017 Audi SQ7 TDI
The new roll stabilization system relies on a compact electric motor with a three-stage planetary gearbox that separates the two halves of the stabilizer bars. On an uneven road surface, they are actively decoupled from one another, resulting in a soft, supple ride. During sporty driving, the bars are interconnected. That significantly stiffens them, reducing body roll.
Being a top-of-the-range Audi, the SQ7 TDI is also loaded with luxuries. Examples include LED headlights, 20-inch wheels, sportily contored bumpers and door trim strips, adaptive air suspension with S-specific tuning, electrically adjustable and heated sport seats in Alcantara and leather, brushed aluminum inlays, and a multifunction sports steering wheel with shift paddles.
The SQ7 TDI will go on sale in Europe this spring. Audi is yet to mention whether we'll see the SQ7 TDI in the United States, though the automaker states that its engine is legal in the United States.