Following on from our Pico Practical engine evaluation Q&A which you can watch here, I wanted to dig a little deeper into the benefits of 48 V MHEV in comparison to 12 V systems.
The current Audi A8 proved to be the perfect vehicle for such an experiment as 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 and 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 and 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). Read more about how to do this here.
Below we have added multiple math channels now looking at Torque (Nm) using power and engine speed, Energy in Watt-hours (Wh) using power and time, and energy again but in Watt-seconds (Ws) using the integral of power (Integral being the area under the power math channel).
The first item that stands out to me is the cranking time of the 48 V system at 277 ms compared to the 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. It achieves over 600 rpm in a quarter of a second!
INITIAL TEST RESULTS
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 three crank and start events in one waveform buffer, where the 48 V system contains just one 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.