The current Audi A8 proved to be the perfect vehicle for such an experiment given it has the ability to crank either by a conventional 12 V starter motor or a 48 V Motor/Generator (MG) system.

From a cranking perspective, the 48 V system offers more torque & power without the accompanying lag of the 12 V system during the Stop/Start phase

With this in mind, I thought it would be great to do these comparisons with maths and incorporate “Time” into our math channel equations

Starting with the 12 V system, below we have crank & start of the V6 3.0 TDI engine using a conventional starter motor

Above I have calculated the power of the starter motor using the math channel Voltage x Current and the engine RPM via the frequency of the crankshaft sensor signal (incorporating a filter) see here.

Below we have added multiple math channels now looking at Torque (Nm) using power & engine speed, Energy (Wh) using power and “Time”, and Energy again (Ws) using the integral of power (Integral being the area under the power math channel)

Looking at the included measurements above, we can paint a picture of the events taking place during the 460 ms of cranking required to start the engine.

Now looking at the same engine starting via the 48 V MG system.

Once again looking at Torque (Nm), Energy Watt hour (Wh) and finally Energy Watt seconds (Ws) in order to draw a direct comparison between both systems.

The first item that “stands out” is the cranking time of the 48 V system at 277 ms compared to 460 ms of the 12 V system. Let’s be honest, 460 ms is good but note the dramatic increase in cranking speed from zero rpm to idle speed with the 48 V system.

Here we achieve over 600 rpm in a quarter of a second!

**To summarize**

I need to revisit the results for Energy via “Time” for the 12 V system as they do not appear true! This may be due to the fact that the capture contains 3 x crank and start events in one waveform buffer, where the 48 V system contains just 1 crank and start event. I will feedback ASAP

All in all these additional benefits of power, torque and speed originate from a totally independent power source (48 V system) resulting in the absolute minimal impact on the 12 V system during the Stop/Start phase.

Couple this to the fact that fuel consumption, emissions, energy recuperation and starting torque all improve I can now see the benefits.

Another interesting fact is that the 48 V MG system has the ability to compensate for the effects of typical engine vibration orders such as E3 with this V6 engine which is mind boggling!

Another

**BIG**thank you to our Math Guru Pico Martyn for all his support on this adventure

I hope this helps, take care…..Steve