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New Audi S6 and S7 diesel TDI models pair 48V system with electric compressor

The new Audi S6 and S7 models in Europe are making their entrance with a torquey V6 TDI engine. For the first time, Audi has combined an electric-powered compressor (EPC) with a 48-volt primary electrical system.

The pairing of an electric compressor with a 48-volt primary electrical system takes the three-liter V6 TDI’s total power output to 257 kW (349 hp). Power transmission is handled by the eight-speed tiptronic automatic transmission, which always operates in tandem with quattro permanent all-wheel drive.

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The electric compressor delivers high starting performance. As well as very vigorous acceleration, the electric supercharger provides a repeatable boost function when accelerating. The EPC preempts any hint of turbo lag, and enables high responsiveness and powerful acceleration in every driving situation.

The EPC’s response time is less than 250 milliseconds, peak output is 7 kW 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.

With dual supercharging—i.e., with the EPC working in tandem with the exhaust turbocharger—the full-size S models achieve a constant torque of 700 N·m 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 buildup—e.g., 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 is 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 required. 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 Sedan from 0 to 100 km/h (62.1 mph) 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 250 km/h (155.3 mph).

  • Audi S6 Sedan: Combined fuel consumption in l/100 km: 6.3 – 6.2 (37.3 – 37.9 US mpg);

  • Audi S6 Avant: Combined fuel consumption in l/100 km: 6.5 (36.2 US mpg);

  • Audi S7 Sportback: Combined fuel consumption in l/100 km: 6.5(36.2 US mpg).

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 22 km/h (13.7 mph). Due 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 liters 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.

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Audi S7 Sportback TDI

3.0 TDI. The 3.0 TDI is notable for its power delivery and high efficiency. Its displacement of 2,967 cm3 develops 257 kW (349 hp) of power. Its specific output is 117.9 hp per liter of engine capacity, and its specific torque is 235.9 N·m (174.0 lb-ft) per liter.

The V6 TDI weighs only around 190 kilograms (418.9 lb) 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 millimeters (2.0 in) 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 all-wheel steering. As on every S model from Audi, quattro permanent all-wheel drive comes as standard. In normal driving conditions, its self-locking center 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% can flow to the front wheels and 85% 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 disagreeable bumps 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 60 km/h (37.3 mph), 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 meter (3.3 ft). At medium and high speeds above 60 km/h (37.3 mph), they are turned by as much as two degrees in the same direction as the front wheels. This makes the S models much more maneuverable 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 millimeters (0.8 in), and by 10 millimeters (0.4 in) 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 leveling. In the “auto” mode the body is lowered by a further 10 millimeters (0.4 in) at speeds of 120 km/h (74.6 mph) upwards, and in the “dynamic” mode the vehicle remains always at this low ride height.

For even sportier road behavior, quattro drive can be supplemented with the sport differential on the rear axle. On bends taken dynamically, the sport differential veritably 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 sporty road behavior is also aided by the five-link-design axles, which are made largely from aluminum. Two subframes connect the links with the vehicle body—the elastokinematics are firmly tuned.

All chassis components are controlled by the electronic chassis platform (ECP). It coordinates the shock absorbers’ action at intervals of milliseconds. The ECP collects comprehensive information about the movement of the car and the data from the chassis control systems involved.

From these, it calculates and precisely coordinates the optimal function of these components in an integrated handling controller. Drivers of the new S models experience this progress in the form of precise handling and high transverse dynamics. As well as the dampers, the EPC controls the dynamic all-wheel steering and sport differential. The driver can configure the effect of these modules in the Audi drive select dynamic handling system. It comes with an S-specific setup and offers the diverse modes “comfort”, “auto”, “dynamic”, “efficiency” and “individual.”

The new large S models will be making their debut in European markets in summer 2019. The starting prices in Germany are: €76,500 for the S6 Sedan, €79,000 for the S6 Avant and €82,750 for the S7 Sportback.

In overseas markets—the United States, Asia and Middle East—to reflect local customer preferences and driving profiles, the S6 and S7 will be available as the 2.9 TFSI with an output of 450 hp and 600 N·m (442.5 lb-ft) of torque. Like the TDI models, the V6 gasoline version will be equipped with both the EPC and the 48-volt MHEV system, for more performance and efficiency.

Comments

SJC

They could use this to make hybrid delivery trucks.

HarveyD

And hybrid pick-ups?

Lad

Looks like VW is taking out all the stops on the Audi, i.e., 48v start/stop, integrated electric compressor, all-wheel steering, high performance diesel, 450 HP gasoline engine...all the great electro mechanical engineering waiting in the back room is being pulled up into production...leaves me with the question; 'Do you really need all this complexity to drive to town and back or will a simple EV do?

yoatmon

The higher the complexity of an engine rises, the higher the possibility of engine failure rises. The increase of failure increases maintenance and repair (MTBF); that's excellent for business. An EV decreases complexity and subsequently lowers the possibility of failure and maintenance and repair; that's bad for business.
Mechanical complexity is the credo for MFRCs; simplicity is the credo for users and the environment.

Peter_XX

Mercedes has the 2,9-liter 400d engine with 340 hp and 700 Nm torque. Performance and fuel consumption in the E-class is similar (slightly better FC, actually for the Mercedes) to the S6. The Mercedes engine has conventional twin-turbo supercharging. So, what makes the Audi engine more advanced than the Mercedes engine? I cannot find a giant leap anywhere. Moreover, the specific power of the twin-turbo Mercedes 4-cylinder engine, at 245 hp, is much higher, so here we have a hint that the conventional twin-turbo technology has more potential also on a 6-cylinder engine.

Talking about hybrids... Mercedes already has the 300de.

SJC

With all the miles put on for delivery it is good to save fuel.
Think of the latest trend in online shopping with home delivery.

Peter_XX

We could compare this car with the Mercedes 400 d engine, for example, used in the E class, with an output of 340 hp and 700 Nm. This car accelerates from 0 to 100 km/h in 4,9 s and its fuel consumption is 5.7-6.0 l/100 km. The cars are roughly comparable, and they have similar performance. The Audi engine has a gain of 7 hp and the torque, at 700 Nm, is identical for both engines. Note that the Mercedes engine, at 2.9 liters, is somewhat smaller and already has been in production for some time, so it would not be surprising with an update shortly. The main difference is in the turbocharging. The Mercedes engine has “conventional” turbocharging, albeit twin turbo, while the Audi engine has one turbocharger plus the electric compressor. This, BTW, requires a 48 V electric system.

It is difficult to claim that the Audi engine is superior to a twin-turbo “conventional” in-line 6-cylinder engine. However, one could note that opting for a twin-turbo system on a V6 engine would be a concept that is not ideal and would have some significant drawbacks. With three cylinders on each bank, it would be a plumber’s nightmare and it would sacrifice efficiency due to the plumbing. You could perhaps imagine turning cylinder heads to get exhaust manifold(s) in the V of the engine, but this is difficult from a packaging viewpoint. It could perhaps be done on a single turbo engine but hardly on a twin-turbo engine. Well, you could perhaps have one single turbo on each bank (as on some gasoline V8 engines) but that would not give the gain that sequential and two-stage turbocharging has but would be more comparable with a single-stage turbo on an in-line 6-cylinder engine. Two smaller turbos instead of a big one. Faced with the difficulties mentioned, Audi has managed to get a similar result in power density with an additional electric compressor, as for a conventional twin-turbo engine (such as Mercedes). So, where is the progress? Well, perhaps they get somewhat improved drivability due to the low response time of the electrical compressor. It does not show in acceleration performance, but it might give a small improvement in responsiveness.

So, what would be needed as the next step in charging of a diesel engine? Well, we have the quad turbo of the BMW 6-cylinder engine as an example. This engine provides 400 hp but the whole system screams for simplification. Something that gives at least as much bang for the buck should be found. I will leave that discussion for later...

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