In this article, we leverage PicoScope’s Math channels to perform a detailed comparison of 12 V and 48 V cranking systems, using the Audi A8 as our test vehicle. We’ll analyze power consumption, torque, and cranking speed to highlight the benefits of 48 V technology.
Following on from our Pico Practical engine evaluation Q&A 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, given that it can be cranked 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.
Analyzing the 12 V system with PicoScope #
Starting with the 12 V system, below we have the crank & start of the V6 3.0 TDI engine using a conventional starter motor:
Above, I have calculated the power consumption 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, Watt hour (Wh) using power and “Time”, and finally Watt seconds (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.
Note: Simply download the .psdata file here. You will then need to only save each Math channel to your computer.
The power of 48 V: A direct comparison #
Now, looking at the same engine starting via the 48 V MG system.
Once again, looking at Torque (Nm), Watt hour (Wh) and finally 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
Initial test results #
I need to revisit the results for Energy via “Time” for the 12 V system, as they do not appear to be true. This may be due to the fact that the couture contains 3 x crank and start events in one capture, where the 48 V system contains just 1 crank and start event. I will provide 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 can 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.