Quote:
Originally Posted by aerohead
* Sovran distinguished the unknown powertrain mechanical efficiency, only second to unknown BSFC as the two, top-tier unknowns in the eleven unknowns identified in the throttle-stop road test phenomena.
* At equilibrium, the engine is just balancing road load power absorption, plus the drivetrain losses.
* Mechanical efficiency of the driveline components are a function of transmitted power.
* As Road Load varies, so does this efficiency.
* It's an unknown quantity, the crux of the powertrain issue.
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* Rolling resistance is a simple linear function of load and velocity. It's a 'known quantity' once its coefficient is derived. If we had enough data for the test vehicle to reverse-engineer the coefficient of power absorption for the tires, we could just plug that in, with the 'new' velocity, compute the rolling drag and power, and have the value to work with. In this way, it could be isolated from the mix. Better book-keeping.
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So "mechanical efficiency of the driveline components are a function of transmitted power" a linear one? It can certainly be approximated to linear over the 5% speed increase, so it can be incorporated into "rolling resistance"
How much does BSFC actually vary by? It is a tiny amount that is negligible over the small speed increase, and so can be ignored altogether.