The SQ7 TDI is the first production car combining turbocharging with an electrically powered compressor designed to eliminate ‘turbo lag’ and also has electromechanical active roll stabilisation for significantly reduced body roll.
At the heart of the new Audi SQ7 TDI is a redesigned V8 BiTDI engine that now develops 429 BHP and 663.8 lb ft of torque, producing a 0-62 mph sprint time of just 4.8 seconds. Top speed is limited to 155mph, and in the New European Driving Cycle (NEDC), the SQ7 TDI returns up to 38.2 mpg combined, with CO2 emissions of 194 g/km.
“Following the launch of the successful SQ5, we are now also applying the concept of a diesel-engined S model to the Q7 model line. So equipped, the SQ7 TDI with a V8 TDI engine achieves the consumption figures of a six-cylinder. The new technology solution of the electric powered compressor in the SQ7 TDI is a world first in the competitive environment, with which Audi once again underscores its claim Vorsprung durch Technik,” said Dr. Stefan Knirsch, Member of the Board of Management of Audi AG for Technical Development.
Audi says the 3,956cc 4.0 TDI has been redesigned from the ground up, with two exhaust-gas turbochargers which are activated selectively according to the concept of sequential charging, since exhaust gas only flows through one turbocharger at low and intermediate load. The second turbine is only activated at higher loads. The electrically powered compressor (EPC) augments the work of the two turbochargers, particularly in the lower engine speed range. The electrically powered compressor is a world first in a production vehicle. Driven by a compact electric motor, its compressor wheel spins up to 70,000 revolutions per minute.
The Audi valvelift system (AVS) is also making its debut in a diesel model from Audi. The inlet and exhaust cam shafts each have two cam contours per valve. On the inlet side, one cam contour supports starting off in conjunction with the EPC, while the other optimises cylinder filling and thus power at high engine speeds. The AVS system on the exhaust side enables activation of the second exhaust-gas turbocharger. The sequential charging system controls the two exhaust-gas turbochargers so that only one turbocharger is used at low engine speeds. The second is activated additionally at higher loads and engine speeds.
The exhaust streams from the two exhaust valves are hermetically separated, with each driving one of the two turbochargers. In the lower engine speed range, one valve per cylinder remains closed, so that the full exhaust stream flows to the active turbocharger. When load and engine speed increase, the AVS opens the second exhaust valves. This directs flow to and activates the second exhaust-gas turbocharger. The engine achieves its maximum output in this biturbo mode. The switching by the AVS enables fast and precise activation of the second exhaust-gas turbine. The power for the EPC, which reaches a maximum of 7 kW, is provided by a new 48‑volt electrical subsystem.
The Audi SQ7 TDI also has a redesigned eight-speed tiptronic gearbox. A self-locking centre differential is the heart of the quattro permanent all-wheel drive system.