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Technology Architecture of Audi A8 Hybrid Shown in Geneva Previews the Production Q5 Hybrid, Due This Year

Drivetrain of the Audi A8 parallel hybrid. Click to enlarge.

Audi presented the A8 parallel hybrid as a technology concept at the Geneva Motor Show. (Earlier post.) The technology architecture of the A8 hybrid previews that of the production Q5 hybrid, due to reach the market in late 2010/early 2011, Audi said. A production version of the A8 hybrid is due in late 2011/early 2012 (orders will start in late 2011).

The A8 hybrid is powered by a four-cylinder 2.0 TFSI gasoline engine and an electric motor that together develop a total output of 180 kW (245 hp) of system power and 480 N·m (354 lb-ft) of torque.

This enables the Audi A8 hybrid to accelerate from 0-100 km/h in 7.6 seconds and to achieve a top speed of 235 km/h (146). Average fuel consumption amounts to 6.2 L/100km (38 mpg US), equivalent to 144 grams CO2 per km (231.75 g/mile). In city traffic, the hybrid drive uses about 20% less fuel than a conventional drive. Both the car’s performance and its fuel economy benefit substantially from the A8 series’ lightweight aluminum body based on the Audi Space Frame principle (ASF).

The 2.0 TFSI—which has been named “Engine of the Year” five times in a row since 2005—combines direct fuel injection with turbocharging and the AVS Audi valvelift system, which regulates the valve lift in two stages. In combination with the adjustable intake camshaft, the Audi valvelift system improves cylinder charging and ensures spontaneous and powerful torque build-up. The 2.0 TFSI delivers 155 kW (211 hp) and 350 N·m (258 lb-ft); the torque value remains constant from 1,500 to 4,200 rpm.

In the crankcase of the four-cylinder unit, which has a displacement of 1,984 cc, two balancer shafts offset second-order inertial forces to ensure virtually vibration-free and quiet operation. All components are optimized to minimize friction. The flow-rate-regulated, pressure-controlled oil pump further reduces fuel consumption.

A hydraulically operated wet clutch links the 2.0 TFSI with the electric motor. The synchronous motor, which is continually excited, also serves as a generator that develops 33 kW (45 hp) of power and 211 N·m (156 lb-ft) of torque. Its full power is available practically right from standstill and contributes to a sportily powerful start-up. The motor housing is furnished with cooling ducts.

Interposed between the electric motor and the wheelset of the eight-speed tiptronic, which is controlled entirely by electronics, is an additional cut-out clutch. In conjunction with the electric unit, this functions as a torque converter. The propulsive power of both drive systems is applied to the road through the front wheels.

The lithium-ion battery energy storage system of the Audi A8 hybrid is mounted in the rear section. It is protected by a high-strength housing, and a ventilation module ensures that it always operated within the ideal temperature range. The A8 hybrid provides luggage space of 400 liters (14.13 cubic feet).

Several subsystems that operate on engine power in a conventional car have been modified to run electrically in the Audi A8 hybrid, including the compressor in the climate control system. The steering system is electromechanical as well. The brake booster too is supplied by a demand-controlled electric vacuum pump. During electrical—i.e. regenerative—braking actions, a control system ensures that the ABS and ESP functions operate properly.

The power electronics unit—including the pulse control inverter and DC-DC converter—is located in the engine compartment.

The hybrid drive is designed for fully electric-powered driving up to 65 km/h (40 mph) and for a distance exceeding 2 km (1.2 miles). When conditions permit, the driver can also select the electric mode by actuating a separate e-key in the cockpit.

Above 65 km/h (40 mph) the combustion engine alone does all the propulsive work, while the electric motor supplies onboard users and recharges the battery. When the driver lets up on the gas, the combustion engine is disconnected from the drivetrain, so the Audi A8 hybrid “sails”. In braking and slow-down phases, the e-motor functions as a generator, recuperating energy efficiently and feeding it into the battery.

When the driver floors the pedal, the engine management temporarily controls the entire system power, and the electric motor provides boosting power.


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