When the new Audi A8 rolls up to a red traffic light, it switches the engine off at a speed of 22 km/h, much earlier than would be the case with a classic start-stop system. The combustion engine regularly shuts itself off even when coasting at speeds between 55 and 160 km/h – and switches itself back on again as soon as the driver wants to accelerate. On the other hand, if it brakes, the A8 converts a large part of the kinetic energy, which normally is converted to heat, into usable electrical energy. This is made possible by a compact belt starter generator with integrated power electronics from Continental.
The system replaces the pinion starter in conventional vehicles. It is connected to the crankshaft of the internal combustion engine via a belt. Together with the lithium-ion battery, it forms the heart of the electrified powertrain that the new Audi A8 has on board as standard. And not only the new A8 – such starter generators are the core element of every powertrain that works according to the micro-hybrid approach.
“The technology offers double-digit fuel savings potential,”said José Avila, head of Continental’s Powertrain Division. Incidentally, Continental competitor Schaeffler makes similar statements, having presented a concept car some time ago that was consistently designed for this technology.
The asynchronous motor developed by Continental delivers a starting power of 8 kW and a maximum torque of up to 60 Nm. The continuous output in generator operation is up to 5kW; for a short time up to 15 kW can be achieved. This becomes possible because the belt starter generator and especially the power electronics are protected from overheating by water cooling. The normal coolant circuit of the internal combustion engine is used; a separate low-temperature circuit is therefore not required.
The combination of zero-emission soaring, early activation of the start-stop function and improved braking energy recovery results in fuel savings of up to 0.7 litres of fuel per 100 kilometres in real-life operation. In addition, the 48-volt main power supply system enables four times higher electrical outputs to be provided for shorter periods, with the same current. This not only has advantages for the powertrain. Adaptive suspension systems such as the forward-looking active suspension of the new Audi A8 are also possible.
Continental has been producing the belt starter generator with integrated power electronics since 2017. It is based on a modular system that can be adapted to the needs of different car manufacturers. Thus, high performance requirements could be met by extending the stator, which is not wound but made of welded copper rods. However, the cooperation with Audi was not limited to hardware alone; the two companies also developed the engine control software.