[mikeayles]

Although this has dropped off the FP now, I wanted to finish my response, but wanted to follow up with some data:

https://www.mikeayles.com/torque-rpm-time.png

So, here is approximately a weeks worth of data (around 700l of diesel), looking at the histogram on the right hand side, theres an awful lot of time spent at 0-10% this is around 60% of the trucks time.

https://www.mikeayles.com/torque-rpm-volume.png

However, when you multiply the time by the fuel consumption within that same time period, you get a volumetric chart, where we can see that 60% of the time, accounts for only 2% of the fuel use.

So, for idling, whilst it's noisy, produces CO2, a 5% improvement at highway speed will get you so much more of a fuel and co2 saving than eliminating idle. although, both, do both.

[niwtsol]

Roger that - thanks for the OC graphs. In the first chart, the sloping cluster of data points, is that just the max torque output of the engine then? And the vertical clusters at ~950, ~1050, and ~1110 - can we assume those are some sort of cruise control or gearing outcome?

Also, your 28.5M+ miles driven is such a great stat - thanks for sharing this knowledge!

[mikeayles]

Correct, the engines will have a peak reported torque at one particular RPM, usually quite low (maybe 900RPM off the top of my head), at higher RPM, the peak torque may only be 90% of the peak torque, but at 50% more RPM, you end up with (100 * 0.9 * 1.5)=35% more 'power' despite the torque being lower.

This is detailed in J1939 (canbus protocol) PGN (parameter group number) EC1 (engine configuration 1) if you fancy a rabbit hole.

The vertical clusters will be a combination of gearing and cruise control, exactly. At the vehicle speed limit in the top gear (usually 12) most trucks will cruise around 1200rpm (exception being the scanias with supercruise). It's likely this truck did a lot of urban driving or was in average speed zones.

You also get a lot of drivers (suprisingly more younger than older drivers) that are happy to set it at 53mph, get the green tick for the telemetry to try and get a bonus, but then have a really low stress drive. It creates a bigger speed differential so they can be overtaken by other trucks easier, and realistically results in 10-20mins over a 10hr shift, to some, a 10hr chilled out shift is better than 9hr40mins of pushing it.

[jfim]

What are the axes on the chart? Rpm?

[mikeayles]

Correct, RPM and Torque (%)

edit: images may be down for 5mins, migrating my blog to astro.