Agility for the long haul: Audi S6 and S7 now as TDI models with advanced EPS technology
Executive class Audi S models newly adopt TDI power bolstered by a 48volt MHEV drivetrain and ultraresponsive electric compressor
For the first time the executive class Audi S Series models are welcoming TDI power into their ranks – the new Audi S6 and S7 join the recently reinstated SQ5 in offering a torque-rich V6 TDI engine that fully delivers on the promise of the red rhombusbacked S badge but is also in it for the long haul. Thanks to an electrically powered compressor working with a 48-volt primary electrical system, the new MHEV models combine characteristic TDI economy with exceptional throttle response which can be fully exploited with the help of S sport suspension with damping control, dynamic all-wheel steering and the option of ceramic disc-assisted braking.
“Torque kick” - electrically powered compressor and 700 Nm of torque
An impressive 700 newton metres (516.3 lb-ft) of torque available across an engine speed range of 2,500 to 3,100 rpm is the ideal basis for compelling performance in the new executive class S TDI models. They take the very successful configuration of the SQ7 TDI to the next level by pairing an electrically powered compressor with a 48-volt primary electrical system for the first time. This takes the 3.0-litre V6 TDI’s total power output to 350 horsepower, which is transmitted via the eight-speed tiptronic automatic transmission to the quattro allwheel-drive system.
Ever ready: the electrically powered compressor
The electrically powered compressor (EPC) delivers high starting performance. As well as very vigorous acceleration, the electric supercharger provides a repeatable boost function when accelerating. This means the EPC pre-empts any hint of turbo lag, and enables high responsiveness and powerful acceleration in every driving situation.
The EPC’s response time is under 250 milliseconds, its peak output is seven kilowatts and its maximum speed is 70,000 rpm. The electric turbocharger’s boost function extends all the way to an engine speed of 1,650 rpm. Thanks to dual supercharging, in other words the EPC working in tandem with the exhaust turbocharger, the full-size S models achieve a constant torque of 700 newton-metres (516.3 lb-ft) across an engine speed range of 2,500 to 3,100 rpm. The EPC supports the TDI’s turbocharger whenever there is insufficient energy in the exhaust gas for a spontaneous torque build-up – when starting off or accelerating at low load, from a low engine speed.
The EPC, which visually resembles a conventional turbocharger, is mounted directly on the engine in the intake air path behind the intercooler. In most operating statuses it is circumvented by a bypass. However if the load demanded by the accelerator is high and the energy available on the turbine side is low, the bypass valve closes, guiding the intake air to the EPC. The compressed air flows directly into the combustion chamber.
The result: spontaneous response and impressive pulling power when accelerating, overtaking and for changes of load. That places the entire power of the 3.0 TDI engine immediately at the driver’s disposal whenever they require it. In everyday driving, the technology avoids frequent downshifts, keeps the engine speed level low and suppresses the turbo lag to which a conventional exhaust turbocharger is susceptible.
The EPC paves the way for an impressive starting performance. The V6-TDI complete with EPC propels the new S6 Saloon from 0-62mph in 5.0 seconds, with the S6 Avant and S7 Sportback taking a tenth of a second longer
over the standard sprint. The top speed is electronically limited to 155mph.
“Clean power” - coasting for up to 40 seconds: the 48-volt mild-hybrid system
While the EPC boosts the performance, the mild-hybrid system (MHEV) helps to improve fuel efficiency. The 48-volt MHEV system comprises a belt alternator starter (BAS) and a lithium-ion battery with a capacity of 10 Ah housed in the vehicle floor beneath the luggage compartment. The BAS is connected to the crankshaft. During deceleration it can recover up to 8 kW of power, which it then stores in the lithium-ion battery. When the driver accelerates again, the BAS reacts instantly by restarting the engine.
MHEV technology allows for start/stop operation from a speed as low as 13mph. Thanks in part to the integration of the mild-hybrid system and the vehicle sensors, the S models realize a fuel saving of up to 0.4 litres in real driving conditions and can coast for up to 40 seconds with the combustion engine deactivated.
On that basis, the S TDI models combine impressive driving dynamics with high efficiency, low fuel consumption and low emissions. All S TDI models have homologation to the Euro 6d temp emission standard. WLTP fuel economy values for the S6 TDI Saloon range from 35.8 mpg to 36.2 mpg, equating to NEDC-correlated CO2 emissions of 164 g/km. The figures for the S6 Avant are 34.9 mpg to 35.3 mpg and 171 g/km, and for the S7 Sportback 35.3 mpg to 35.8 mpg and 170 g/km.
Concentrated high tech: the engine
The 3.0 TDI is notable for its power delivery and high efficiency. Its displacement of 2,967 cm3 develops 350 metric horsepower. Its specific output is 117.9 hp per litre of engine capacity, and its specific torque is 235.9 Nm (174.0 lb-ft) per litre.
The V6 TDI weighs only around 190 kilograms and has concentrated high tech to offer in every department. Its common rail system injects fuel at a pressure of up to 2,500 bar. Crankshaft, pistons, connecting rods and oil management meet high-performance requirements, and sophisticated measures have been taken to reduce friction in the crankshaft and camshaft drive. The cooling circuits of the crankcase and cylinder heads are kept separate so that the engine oil warms up rapidly from a cold start – the heads have dual-section water jackets. The coolant flow is directed to the oil cooler, the EPC, the BAS and the compressor case of the turbocharger as needed.
The exhaust turbocharger, with a turbine wheel measuring 50 millimetres in diameter, generates a relative boost pressure of up to 2.4 bar. Its variable turbine geometry (VTG) is optimized for low-loss flow. The external low-pressure exhaust gas recirculation (EGR) only draws off the exhaust gas after the particulate filter so that the full mass flow can power the supercharger, significantly increasing its effectiveness. Operation of 3.0 TDI is ultra-refined.
Dynamic cornering and high agility: Dynamic allwheel steering makes its entrance in an S model
As on every S model from Audi, quattro permanent all-wheel drive comes as standard. In normal driving conditions, its selflocking centre differential distributes torque between the front and rear axle in a 40:60 ratio. If one wheel encounters slip, most of the drive torque goes to the axle with the better traction. In the extreme, 70 percent can flow to the front wheels and 85 percent to the rear wheels. For sports driving, wheel-selective torque control enhances sporty handling: It brakes the two wheels with reduced load on the inside of a bend slightly before they lose grip.
The standard-fit progressive steering already comes with sports ratios in its basic configuration; the greater the steering lock, the more direct the steering is. Its S-specific electro-mechanical servo assistance filters out rough surfaces but communicates useful information to the driver.
Compared with their predecessor models, the new large S models offer even better transverse dynamics. On request, Audi can supply dynamic all-wheel steering – this combines dynamic steering with a variable ratio of 9.5:1 and 16.5:1 at the front axle with separate rear-axle steering that is operated by spindle drive and track rods. At speeds up to 37mph, the rear wheels turn as much as five degrees in the opposite direction to the front wheels. This reduces the turning circle by up to 1.1 metres. At medium and high speeds above 37mph, they are turned by as much as two degrees in the same direction as the front wheels. This makes the S models much more manoeuvrable and agile at low speeds, and provides more directional stability at high speeds and when changing lanes.
The S sport suspension developed specially for the new S models comes with damping control as standard, highlighting these vehicles’ sporty character. It lowers the body of the S6 by 20 millimetres, and by 10 millimetres in the case of the S7. This gives both S models the same low ride height. Adaptive air suspension – the air suspension version with adjustable damping – makes its first appearance on S models as an explicitly comfort-oriented alternative. It can be set to three modes and includes a “lift” position for poor roads and automatic levelling. In the “auto” mode the body is lowered by a further 10 millimetres at speeds of 75mph and above, and in the “dynamic” mode the vehicle remains always at this low ride height.
For even more dynamic road behaviour, quattro drive can be supplemented with the sport differential on the rear axle. It literally pushes the car into the bend, producing a high level of agility. The driver can adapt the sport differential’s control strategy via Audi drive select.
The dynamics are also aided by the five-link-design suspension, which is made largely from aluminium.
Presence - the design of the S models
The S models are characterized by their striking, distinctive design and sophistication – outside and inside alike. The new Audi design language further emphasises their even more sporty look. A dynamically styled front trim, wide sills and a wide rear diffuser with four tailpipe trims infuse the S models with on-road presence. Distinctive S trim elements in dark chrome and aluminium on the radiator grille lamellas, the front blade, the side air inlet, the exterior mirrors and the rear diffuser signal their intent at a glance.
On the S6, the horizontal splitter in aluminium look creates an enormous feeling of width at the front. It links the two air inlets and ends with the two winglets at the air ducts. At the rear, the S6 features an integrated spoiler that visually extends the boot lid. Aluminum applications in the diffuser link the four S-specific tailpipe trims. These also underline the width of the vehicle.
On the S7, the wide, low Singleframe grille features lamellas in aluminium standard and centre section in dark chrome matt. The air inlets are enlarged, with very bold contours, and their honeycomb-structure inserts come in titanium black. The blade running through them is in a gleaming aluminium look, as are the exterior mirror housings in aluminium. Other features that distinguish the four-door coupé from the S6 models are the funnels in the air inlets and the angular trim strips on the side sills.
Side-on, the sporty appearance of all three cars is enhanced by the large wheels, which are typical features of the S models. A diffuser insert in dark chrome matt adds the finishing touch to the lower rear end. The four tailpipe trims are in gleaming chrome.