New Audi A8 comes with 48V mHEV standard; plug-in e-tron model with wireless charging

New Audi A8 comes with 48V mHEV standard; plug-in e-tron model with wireless charging

11 July 2017

In a brand event in Barcelona, Audi unveiled its fourth-generation A8 luxury sedan. The new A8 features a new design language, an innovative touchscreen operating concept and a systematically electrified drive. The Audi A8 has also been developed for highly automated driving. From 2018, Audi will gradually be taking piloted driving functions such as parking pilot, garage pilot and traffic jam pilot into production.

All five engines options—3.0 TDI and TFSI; 4.0 TDI and TFSI; and 6.0L W12— operate in conjunction with a 48V mild hybrid (mHEV) belt alternator starter (BAS) system. (Earlier post.) This mHEV technology enables the car to coast with the engine switched off, and to restart smoothly. It also has an extended start/stop function and an energy recovery output of up to 12 kW. The combined effect of these measures is to bring down the fuel consumption by as much as 0.7 liters (0.2 gallons US) per
100 kilometers (62.1 mi) in real driving conditions.

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The A8 L e-tron quattro plug-in hybrid will follow at a later date. The 3.0 TFSI and electric motor deliver 330 kW
(449 hp) of system power and 700 N·m (516.3 lb-ft) of system torque. The lithium-ion battery stores enough power for about 50 kilometers (31.1 mi) of electric driving. It can optionally be charged by Audi Wireless Charging. A pad in the garage floor transfers the power inductively to a receiver coil in the automobile with a power output of 3.6 kW.

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mHEV. Audi’s MHEV technology is based on a newly developed 48-volt primary electrical system; it supplies the 12-volt system that now becomes an electrical subsystem. The 48-volt system is fed by a belt alternator starter (BAS) connected to the engine’s crankshaft by the belt drive. A lithium-ion battery positioned safely beneath the luggage compartment floor serves as the storage unit.

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Due to the higher voltage, the new A8 can coast along silently in a speed range from 55 through 160 km/h (34.2 through 99.4 mph). The automobile then proceeds with zero emissions for up to
40 seconds with the engine off altogether.

As soon as the driver steps on the gas again, the belt alternator starter prompts a swift but soft restart. In addition, start/stop operation is actually active from 22 km/h (13.7 mph).

3.0 TDI and 3.0 TFSI. The 3.0 TDI (earlier post) develops 210 kW (286 hp) from a displacement of 2,995 cm3. Many areas have been extensively reengineered, such as its thermal management. With 600 N·m (442.5 lb-ft) of torque across a rev range from 1,250 to 3,250 rpm, it develops hefty traction. The 3.0 TFSI with a displacement of 2,967 cm3 develops 250 kW (340 hp) and likewise achieves its peak of 500 Nm (368.8 lb-ft) extremely low down the rev range, between 1,370 and 4,500 rpm.

Its exhaust end lies inside the 90° vee, so the short gas paths and the twin scroll charger promote responsiveness. Its combustion principle makes the V6 gasoline engine especially efficient. To support it, the Audi valvelift system (AVS) adjusts the intake valve opening times and stroke in two stages based on demand. (Earlier post.)

4.0 TDI and 4.0 TFSI. The two four-liter, eight-cylinder engines will follow in 2018—the 4.0 TDI with 320 kW (435 hp) and the 4.0 TFSI with 338 kW (460 hp). They share fundamental technical principles, such as biturbo technology and the Audi valvelift system (AVS).

When the gasoline engine is being driven with restraint, the AVS deactivates cylinders 2 3, 5 and 8 by closing their intake and exhaust valves. This reduces fuel consumption and promotes efficiency. On the diesel, AVS operates one exhaust valve in each cylinder. It therefore manages the two turbochargers, which—unlike on the TFSI—are switched sequentially. For better filling of the combustion chambers, there is likewise an intake AVS on the TDI.

Under load, the 4.0 TFSI develops a characteristically sporty sound that is completely free from interfering frequencies. On the V8 gasoline engine, the e-tron and the W12, Active Noise Cancellation (ANC) eradicates these. The system sends specific anti-noise to the sound system’s loudspeakers. In addition, the V8, W12 and 3.0 TDI are fitted with active engine mounts that inhibit the transmission of vibrations to the vehicle body. They, too, generate out-of-phase counterimpulses—their effect is particularly marked when idling.

W12. The W12 will follow in 2018 in the new A8 L as the top engine version. With its two twin scroll turbochargers, it develops 430 kW (585 hp) from a displacement of 5,950 cm3. Its 800 N·m (590.0 lb-ft) of torque is available constantly between 1,300 and 5,000 rpm. Like the 4.0 TFSI, the twelve-cylinder engine features COD (cylinder on demand) technology. At low loads and engine speeds, it shuts down the left-hand cylinder bank to trim fuel consumption.

8-speed. All engines in the A8 deliver their power to a newly developed eight-speed tiptronic. An rpm-adaptive torsion damper (RTD) with a centrifugal force pendulum compensates for undesirable vibrations in the engine. This permits efficient driving from an engine speed range as low as 1,000 revolutions per minute.

The improved tiptronic is now for the first time equipped with an electric oil pump—it is activated whenever the large sedan is coasting with the engine off. As soon as the new A8 is coasting and its engine is either deactivated or idling, a clutch in the central transmission is disengaged to interrupt the power flow. For a faster buildup of pulling power, especially after coasting with the engine deactivated, the engineers in partnership with ZF optimized the engagement logic applied in the gearshift process.

The transmission control in the new A8 can for the first time recognize stop and go situations. It now modifies the driving strategy with the emphasis on comfort; for example, it avoids unnecessary gearshifts or starting in second gear. The driver can let the automatic transmission do the work automatically in the E, D and S modes, or can take charge of controlling it in M mode. Selector lever commands are all transmitted electrically.

quattro permanent all-wheel drive is standard in the new Audi flagship model. In normal driving conditions, its self-locking center differential distributes torque between the front and rear axle in a 40:60 ratio. If slip occurs at one axle, it directs up to 70% of the drive torque to the front and up to 85 percent to the rear. Handling benefits from wheel-selective torque control whenever a committed driving style is adopted. The intelligent software function brakes the two wheels on the inside of a bend slightly before they can begin to spin.

Customers can also choose the optional sport differential in conjunction with the two V6 and V8 engines as well as the W12. When cornering dynamically, this redistributes the torque between the rear wheels as required—enhancing traction, stability and dynamics. The driver can view a display of the percentage drive torque per wheel in the MMI of the new A8. Compared with the previous model, the sport differential is around one kilogram (2.2 lb) lighter and offers even faster, higher-precision control. Its management uses the latest generation of the electronic suspension platform (ESP) and is incorporated into the
Audi drive select handling system. This allows the driver to experience a range of chassis settings in one and the same car. The operating principle of the participating systems can be set using the comfort, auto, dynamic, efficiency and individual modes.

Audi A8 L e-tron quattro.
A few months after the debut of the new car line, the A8 L e-tron quattro will join the range as Audi’s third plug-in hybrid after the A3 Sportback e-tron and the Q7 e-tron 3.0 TDI quattro.

The 3.0 TFSI and the electric motor, which is integrated into the eight-speed tiptronic together with the separating clutch, generates 330 kW (449 hp) of system power and
700 N·m (516.3 lb-ft) of system torque. The sprint from zero to 100 km/h (62.1 mph) takes 4.9 seconds, and the top speed is electronically limited to 250 km/h (155.3 mph).

The lithium-ion battery beneath the luggage compartment floor stores 14.1 kWh of energy. It consists of a flat block of 104 cells and barely reduces the space available for luggage. In all-electric mode the A8 L e-tron quattro can cover about 50 kilometers (31.1 mi).

The hybrid management takes charge of the efficiency-optimized management of the combustion engine and electric motor. When started, the A8 L e-tron quattro runs in the all-electric mode; the combustion engine cuts in automatically as the situation requires. The active driving pedal with variable pressure point gives the driver feedback on the maximum available power for electric driving. The driver can select various hybrid modes at the EV button. These affect the driving properties—regardless of whether the driver wants to use the energy stored in the battery straight away or save it for later.

If route guidance is activated in the navigation system, the predictive operating strategy is also activated. It uses map data plus a new standard of real-time traffic information, and adapts energy management to reflect the route ahead. For example, when driving along the freeway it is possible to protect or even increase the amount of electrical energy stored. This will then enable the A8 L e-tron quattro to cover a city driving route with zero local emissions.

The predictive efficiency assistant promotes a fuel-saving driving style by incorporating navigation data, connect information such as traffic sign recognition online, and information from the on-board sensors. The driver sees the recommendations displayed in the Audi virtual cockpit. In addition, pulsating of the driving pedal now draws the driver’s attention to such messages.

In conjunction with the adaptive driving assistant (ADA), the car responds to speed limits, bends, junctions and roundabouts without driver intervention, and now slows down or speeds up accordingly. The driver always ultimately always remains in control—whether using all-electric driving, which is possible at up to 135 km/h (83.9 mph), or the combined power of the electric motor and TFSI.

When the driver’s foot comes off the accelerator, the large sedan starts to coast whenever that is the best energy strategy. During moderate deceleration it uses the electric motor as an alternator and therefore as an engine brake. This enables the Audi A8 to recover a substantial amount of energy. The hydraulic wheel brakes are only called upon for harder brake applications. In the tiptronic’s S program, the electric motor provides maximum boost torque to assist propulsion.

Wireless charging. The market introduction of the A8 L e-tron quattro also marks the debut of Audi Wireless Charging (AWC). This involves a floor pad inducing an alternating current in the secondary coil installed in the car, under the front axle. To facilitate parking for the driver, the MMI shows the position of the charging station. Before the charging process starts at 3.6 kW, the pad is raised to reduce the distance between it and the car, and achieve a high charging efficiency of more than 90% from grid to battery.

Alternatively customers can charge the battery of the A8 L e-tron quattro using cables at 3.6 or 7.2 kW. In the latter case, the A8 L e-tron quattro is fully charged from an industrial power socket in about two hours. The driver starts the charging process conveniently from the MMI system. Alternatively charging can be activated with a smartphone, using the myAudi app that also enables programming of charging timers.

The smartphone also plays an important role in regulating the temperature inside the car. The key component in the automatic air conditioning of the new A8 L e-tron quattro is a heat pump that collects the heat given off by the high-voltage electrical components and provides low-energy heating and cooling. The climate control is highly intelligent. Again using the smartphone app, the driver can specify in detail before setting off how the interior climate should be set.

The same applies to the optional steering wheel, seat and windscreen/rear window heating and the seat cooling. In summer, the auxiliary climate control of the
A8 L e-tron quattro with electric air conditioning compressor establishes pleasant interior temperatures before a journey. Another option is instant startup of the climate control components as soon as the car is unlocked with the vehicle key.

The A8 L e-tron quattro is identifiable from outside by its special daytime running lights and special wheels. Its Audi virtual cockpit and MMI touch display inform the driver of all important drive parameters and of the settings for charging and for e-tron specific climate control functions.

The new Audi A8 and A8 L are being built at the Neckarsulm site and will appear on the German market in late fall 2017. The starting price for the A8 is €90,600 (US$103,354), with the A8 L starting at €94,100 (US$107,347).

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