Engine Management by Banish Greg

Author:Banish, Greg [Banish, Greg]
Language: eng
Format: epub
ISBN: 978-1-934709-71-9
Publisher: CarTech Inc.
Published: 2007-01-01T05:00:00+00:00

Mass Air Flow Modeling

For engines that use an MAF sensor, airflow modeling means making sure that the transfer function in the PCM matches the actual output of the sensor. The ideal method is to have data from the exact MAF sensor to be used, as flowed with the exact intake tract from filter to throttle body, and input this data directly into the PCM’s MAF table. Since this data is rarely available, the next best thing to do is create this data by actual testing on a dynamometer. Something as simple as a change in air filter design or MAF sensor clocking relative to bends in the plumbing can shift MAF output to the PCM by 20% or more. Verifying actual performance on the exact vehicle in question gives the best accuracy.

Actual MAF output calibration is best done by using the dynamometer to hold the engine exactly at one of the calibration points of the MAF sensor, waiting for the engine to stabilize, and finding the error. The calibration points in question may not necessarily line up with fixed RPM or engine loads. All that is needed is a static airflow rate. This means that simply driving the vehicle in a single gear on a chassis dynamometer can yield a wide range of calibration points simply by changing throttle position and consequently speed. Once the engine stabilizes, the MAF table is adjusted at this point and we move on to the next calibration point. This process is repeated for as much of the MAF sensor range as possible, always waiting for the engine to reach steady state operation before making an adjustment to the MAF table values. If it is not possible to adjust the MAF table in real time, make a spreadsheet showing MAF calibration points, target λ, actual λ, and percent error. (Figure 9-1) This makes for fast adjustments to the data tables and a quick return to the dynamometer to confirm or adjust again until error is acceptable.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.