Electric Turbo, 48V Electrics Onboard New Audi SQ7

INGOLSTADT, Germany – Moving on quickly from the Geneva auto show and the world premiere of the small Q2 CUV, Audi uses its annual press conference at its headquarters Thursday as the setting for the unveiling of its new SQ7 TDI.

The latest addition to the Q7 lineup is the first series production vehicle to receive an electric turbocharger to boost the power of its engine, in this case a new 429-hp 4.0L V-8 diesel that also is destined for the fourth-generation A8 sedan and a new top-of-the-line Q8 CUV, both under intensive development here.

In a first for Audi, the SQ7 also uses an electromechanical active roll-stabilization system to suppress roll during cornering, as well as a dual electrical architecture that combines a 48V system with standard 12V wiring used on other new second-generation Q7 models.

The new model marks the first “S” treatment for the Q7, following the SQ5 that has been on sale in North America since 2014. In the biggest hint yet the performance model will be sold in North America, Audi says the “high torque levels at low revs and low consumption make (the SQ7) ideally suited for markets such as the United States.”

Heading the list of developments brought to the SQ7 TDI is the all-new diesel engine, which is 0.2L smaller than the units it replaces, in keeping with the current trend toward downsizing. It also adopts a new common-rail injection system that generates up to 36,250 psi (2,500 bar) of injection pressure and incorporates Audi’s patented valve-lift system, marking the first time it has been applied to one of the German automaker’s diesels.

In a move that follows the lead of rival BMW’s most powerful 3.0L 6-cyl. diesel, the Audi engine uses three chargers to boost induction. But whereas the BMW powerplant relies on three conventional turbochargers, the new Audi engine employs two exhaust-gas-driven units and a separate electrically driven compressor.

The two conventional turbos, mounted within the 90-degree angle of the cylinder banks, run sequentially, with the smaller one engaged at low and intermediate throttle loads and the larger unit activated at higher loadings. The electrically powered compressor, or EPC, increases pressure within the induction system at the minimum throttle loads to improve overall response.

Modern-day diesel engines tend to drop their revs quite markedly when the driver backs off the throttle, because induction pressure is dramatically reduced as the boosting effect of the turbochargers is halted. The idea behind the new induction process is to use the additional air forced into the induction system by the EPC, whose compressor wheel spins at up to 70,000 rpm, to keep the smaller turbocharger primed and ready to supply maximum boost as fast as possible, so that full torque is available virtually the moment the driver gets back on the throttle.

“The electrically driven compressor in the SQ7 TDI is a world first, with which Audi underscores its claim Vorsprung durch Technik (advancement through technology),” says Stefan Knirsch, in charge of technical development.

SCR System Onboard

In the SQ7 TDI, the new engine’s 429 hp and 663 lb.-ft. (899 Nm) of torque at 1,000-3,250 rpm is 94 hp and 74 lb. ft. (100 Nm) more than Audi’s old twin-turbocharged 4.2L V-8 diesel used in the first-generation Q7.

However, it is not the most powerful diesel ever in the top-of-the-line Audi SUV. That honor rests with the discontinued twin-turbocharged 6.0L V-12, which produced 493 hp and 737 lb.-ft. (999 Nm) in the Q7 6.0 TDI, a model not offered in the U.S.

Predictably, the new V-8 receives a selective catalytic converter, which is integrated into a particulate filter and uses urea injection to reduce nitrogen-oxide levels. In keeping with the sporting pretensions behind the latest Q7 model, it also uses a sound actuator that allows the driver to vary the acoustic qualities, with the synthetic exhaust note played back through the audio system.

Power is fed through an 8-speed automatic gearbox and Audi’s Torsen torque-sensing all-wheel-drive system with a self-locking center differential to all four wheels. Buyers also can specify an optional sport differential, which provides a torque-vectoring effect with a variable amount of drive between each of the individual rear wheels, making it the only Q7 model to offer it.

Audi quotes an official 0-62 mph (100 km/h) time of 4.8 seconds, some 1.3 seconds faster than the most powerful existing Q7, the 328-hp supercharged 3.0L gasoline V-6 model. Top speed is limited to 155 mph (249 km/h). Combined consumption on the European test cycle is 31.8 mpg (7.4 L/100 km), endowing the SQ7 TDI with average carbon-dioxide emissions of 194 g/km.

Although not yet made official, WardsAuto has learned the new V-8 forms the basis for a smaller V-6 diesel featuring a similar EPC-enhanced induction system.

The chassis of the SQ7 TDI is described as the most advanced applied to a road-going Audi yet. Together with the electro-mechanical 4-wheel steering, air suspension and adaptive-damping functions brought over from standard second-generation Q7 models, it also uses a new electromechanical roll stabilization system similar to that available on the latest BMW 7-Series. Fitted with an electric motor boasting a 3-stage planetary gearbox that separates the two halves of the stabilizer bar, it is claimed to significantly reduce body lean. In off-road driving, the stabilizers are decoupled.

Energy to run the EPC and electromechanical active roll-stabilization system is provided by the 48V architecture. Also set to be adopted by the next A8 and upcoming Q8, it uses a 48V lithium-ion battery mounted beneath the luggage compartment boasting an energy content of 0.47 kWh and output of up to 13 kW. A DC/DC converter connects the new 48V and existing 12V systems, the latter using a lead-acid battery.

Originally showcased in Audi’s RS5 TDI concept car, the 48V subsystem requires adoption of a new generator, which Audi says operates with an efficiency level of over 80% at an output of up to 3 kW.

The SQ7 TDI is differentiated from other second-generation Q7 models by a series of subtle exterior design revisions, including a new grille insert, uniquely styled bumpers, aluminum housings for the door mirrors and four rectangular tailpipes. As with its standard sibling, buyers can choose between a 5- or 7-seat interior layout.

The new model will hit European showrooms in the spring.