VE table interpolation...
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From: Port Tobacco, MD
VE table interpolation... Which cells does the computer use to interpolate the VE table? Does it use cells directly above or on all surrounding corners?
Phil
Phil
It uses an average factor of the neighboring cells, based on how much it is "leaning" towards the next cell. The closer the engine gets to a neighboring cell, the closer the "value" referenced gets to the cell unit value.
The way I understand it (and the way I believe EFI Live uses it) is the value you enter in a given cell is the central point for that cell or "tile" if you will. Imagine the tiles on your bathroom floor and maybe it will help. If you draw a dot in the center of the tile, that represents the location of the value for that VE cell. As your MAP and RPMs fluctuate, you're more often than not off-center in each cell. Let's assume you draw some crosshairs for 1900rpm and 32kPa. This will land you in the corner of the 2000rpm/30kPa cell. Since there's no 1900rpm/32kPa cell in the table, it is my understanding the PCM calculates the value at that point by determining an approximate slope using the centerpoint of the current and surrounding cells/tiles.
Or better yet, imagine you have a flat piece of foam with the VE grid drawn on it and each point in the VE table is represented with a stick that stands vertically in the center of the cells. The value of each cell is in essence the length of the stick. Now, you lay a piece of cloth over the top of the sticks. This is basically what you see in your graphical representation of your VE table. Now, assume you need to know the VE of a spot on the cloth near one of the sticks. Basically, the PCM is calculating how long a stick would be if it were under that part of the cloth based on the length of the surrounding sticks.
That's my understanding of interpolation. Hopefully, I was able to provide a little mental visualization or two...
Or better yet, imagine you have a flat piece of foam with the VE grid drawn on it and each point in the VE table is represented with a stick that stands vertically in the center of the cells. The value of each cell is in essence the length of the stick. Now, you lay a piece of cloth over the top of the sticks. This is basically what you see in your graphical representation of your VE table. Now, assume you need to know the VE of a spot on the cloth near one of the sticks. Basically, the PCM is calculating how long a stick would be if it were under that part of the cloth based on the length of the surrounding sticks.
That's my understanding of interpolation. Hopefully, I was able to provide a little mental visualization or two...
Last edited by SSpdDmon; Apr 18, 2006 at 12:12 PM.
