Quote:
Originally Posted by swamp2
Again, in theory, if a vehicles drivetrain inertia is known accurately, it appears to me that roller inertia doesn't matter. Putting it into a linear context for simplicity, if you want to know how big a force is, put that force on any mass and measure the acceleration, F=ma. The test mass is irrelevant. That is simplified for sure but the right concept to match the equation.
In practice though, this formula above is NOT used and the drive train inertia is not factored in in anyway and thus this does lead to errors, absolutely.
This also shows very explicitly why an intertial dyno will give different results in different gears and why higher gear numbers will exhibit less error (drivetrain inertia is significantly lower).
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Sorry, I wasn't clear. I was speaking in reference to the fact that most interia dynamometers use a fixed value for drive train inertia. My remarks are meant to highlight the difference in effect of drivetrain inertia between inertial dyno measurement, real world performance, and simulation.
So my point is really: on inertial dynamometers -- which assume a fixed drivetrain mass for all measurements -- wouldn't the
actual difference in drivetrain mass have a more statistically significant effect than we would see in real world performance and simulation?
To make a claim, rather than asking a rhetorical question, it would appear to me that the error in measurement on inertia dynamometers (which use fixed assumptions) would be greater than the figures stated in the paragraph below:
Quote:
Originally Posted by swamp2
Using this as a live spreadsheet we can answer a huge number of what if, sensitivity and accuracy questions about our calculated mass factors. What if the E92 estimated engine inertia is off by a full factor of 1/2? The first and second gear F8X M-DCT mass factors change to 1.361 and 1.135 respectively. 1st gear only changes by 2%. All other mass factors are the same within 1%. What if we underestimated the F8X DCT flywheel radius by 25%? That "whopper" changes the 1st gear mass factor (mf) by nearly 4%. The transmission values were some of the "rougher" estimates I made. What if the transmission has twice this total inertia? This also has about a 4% change in the 1st gear mf and less than a 1% change in gears 3 and above. What is the wheel inertia is actually 25% larger than my estimate? This only makes less than a 1% change in all mf. What if the axles were truly weightless? This would not change any mf out to 3 decimal places.
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