Smooth and powerful
The combustion engine of the Audi A8 hybrid is the 2.0 TFSI – a high-tech powerplant. This four-cylinder unit, which has been named “Engine of the Year” five times in a row since 2005, is an example of Audi’s downsizing philosophy. It 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 Nm (258.15 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 pleasantly quiet operation that goes well with the luxurious character of the A8. All components are optimized to minimize friction. The flow-rate-regulated, pressure-controlled oil pump further reduces fuel consumption.
Electric motor with ample propulsive power
A hydraulically operated wet clutch links the 2.0 TFSI with the electric motor. Its control requires the utmost precision, and a great deal of know-how has been expended to achieve its smooth, precise and swift operation. The synchronous motor, which is continually excited, also serves as a generator that develops 33 kW (45 hp) of power and 211 Nm (155.63 lb-ft) of torque. Its full power is available practically right from standstill and contributes to a sportily powerful start-up. Since an electric motor also develops heat, its 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.
Lithium-ion technology – the battery
The energy storage system of the Audi A8 hybrid is mounted in the rear section. This state-of-the-art lithium-ion battery is more compact and weighs less than other types but is substantially more powerful. It is protected by a high-strength housing, and a ventilation module ensures that it always operated within the ideal temperature range. Yet the A8 hybrid also provides ample luggage space of 400 liters (14.13 cubic feet)
Several subsystems that operate on engine power in a conventional car have been modified right from the start for use in the Audi A8 hybrid. The compressor in the climate control system runs entirely on electric power. The steering system is electromechanical as well. The brake booster too is supplied by a demand-controlled electric vacuum pump. During electrical – i.e. recuperative – braking actions, a sophisticated control system ensures that the ABS and ESP functions operate properly.
The power electronics unit manages the interaction of the systems. Its pulse control inverter regulates the interplay of the battery and the electric motor. The DC-DC converter supplies power to users on the onboard network. The power electronics unit, which is connected to the battery and the electric motor by high-voltage cables, is located in the engine compartment.
The smooth interaction of these components and their high level of integration attest to the specialized know-how Audi has accumulated. The technology architecture already provides a glimpse of a future production model – the Audi Q5 hybrid, which will be introduced later this year.
