Audi’s flagship sedan A8 comes with 48V primary power system

June 09, 2017 // By Christoph Hammerschmidt
Powertrain electrification can come as a revolutionary step or as an evolution. For the next version of its top-of-the-line luxury sedan, to be introduced at the Audi Summit in Barcelona on July 11, carmaker Audi has chosen the evolutionary way – with a mild hybrid approach and an 48V main power system.

Mild hybrid, this means that the A8 cannot drive electrically, and insofar, Audi falls short of the potential of the hybrid technology. But the 48V level as the primary electric system, this is already something. Its main components are the 48V lithium ion battery with a capacity of 10Ah and the liquid-cooled belt alternator starter (BAS). Being a starter generator, the latter is engaged continuously. The vehicle still has a conventional pinion starter which however is used only for cold starts. The main benefit of the BAS is smooth engine start and changeover in stop-and-go situations. In addition to the BAS, the actuators associated to undercarriage control are working off the 48V supply.  

The BAS enables the vehicle to recuperate electric energy when the car is in push mode or when the brake is applied. For the sake of fuel efficiency, the car switches to coasting mode when it moves along without acceleration or deceleration. This enables the vehicle to move along up to 40 seconds at speeds between 55 kmph and 160 kph noiselessly and without burning any fuel; as soon as the driver hits the gas pedal, the BSA starts the motor (a V6 TSI engine) on the fly.

The start-stop function is connected to the vehicle’s front camera. Thus, the system can distinguish between different traffic situations. If the road ahead is clear and the driver steps onto the gas pedal, the BAS starts the engine in normal mode. If the vehicle in front of the Audi A8 starts moving (for instance at a traffic light or in a stop-and-go situation), the engine is started even while the brake is pressed. In this scenario, the control strategy concludes that the driver intends to spontaneously will fall in with the flow of traffic.