Audi has become the first automaker to introduce a production engine equipped with an electric supercharger. The technology is making its global debut under the hood of the SQ7 TDI, a hot-rodded version of the second-generation Q7.
Power comes from what might well be the most advanced compression-ignition engine ever fitted to a road-legal car. This 4.0-liter V-8 sends 435 horsepower and a stout 664 pound-feet of torque to all four wheels via an eight-speed automatic transmission and two turbochargers that operate sequentially, the second adding boost above 2200 rpm.
The turbines are fed by a novel split-exhaust system that uses Audi’s AVS valve-lift system, a first for a diesel engine. Each variable-geometry turbo is fed by one of the exhaust valves of each cylinder; to bring the second on-stream, a sleeve moves on the camshaft to activate that valve.
Clever, but not clever enough for Audi, as the SQ7 also marks the first appearance of the company’s 48-volt electrically powered supercharger. The electric supercharger (called electric-powered compressor, or EPC, in Audi-speak) spools up at low engine speeds to virtually eliminate turbo lag by providing boost right off the line. This utilizes a nine-horsepower motor that sits downstream of the intercooler, as close to the engine as possible, to spin its compressor wheel up to 70,000 rpm in less than a quarter of a second, filling in the lag-inducing gap as the conventional turbochargers gather momentum at low revs. As a result, the torque peak of 664 lb-ft is available from just 1000 rpm through 3250 rpm.
The setup allows the SQ7 to hit 60 mph from a stop in 4.5 seconds — and reach a top speed that’s electronically limited to 155 mph. In spite of its impressive performance credentials, the SUV returns nearly 32 mpg on average.
Power for the EPC comes from a 48-volt lithium-ion battery that’s located under the trunk floor and connected to the SQ7’s standard 12-volt electrical system by a DC/DC converter. Using a 48-volt sub-system allowed engineers to ensure the EPC always has the seven kilowatts of juice it needs to spool up, and it helps reduce the load placed on the regular 12-volt lead battery that powers the SUV’s other accessories.
The 48-volt system also feeds an electro-mechanical active body roll stabilization system that’s similar to the one that equips the Bentley Bentayga. Consisting of an electric motor and a three-stage planetary gearbox, the system improves handling by reducing body roll and understeer, and it maximizes comfort on rough roads by keeping bumps and vibrations out of the cabin. Audi promises it’s maintenance-free because, unlike the hydraulic setup it replaces, it doesn’t require any oil.
48 volts and an electric turbo are just the tip of the iceberg. The SQ7 features four-wheel steering, a trick valve-lift system that’s never been fitted to an Audi diesel before, and a sound actuator that lets the driver manually select how much of the engine’s grunt is shared with other motorists.
The Audi SQ7 TDI will go on sale across Europe in the spring with a base price of €89,900, a sum that converts to approximately $100,000. Audi suggests that the SQ7’s 4.0-liter TDI is ideally suited for markets like ours, but it hasn’t announced plans to sell the hot-rodded SUV on these shores.. yet.