Averaging MAP and MAF for input to controller

[themadscientist]

I run a liner progressive controller in my car. I was thinking that because I run the stock turbo and need more cooling in the upper RPM range where the turbo blows the hottest air. I could just use the MAF voltage and that would follow RPM closely. But then I though about averaging MAP and MAF. That way I can run more boost through the whole RPM range and have more water when and where it is needed.

Am I insane? Or would this be a good idea? One big problem I can think of is isolation of the MAP and MAF signal lines.

TMS

[Richard L]

I think you are very sensible, the intercooler efficient will also drop as well at high flow promoting more heat.

[themadscientist]

Do you think I should weight one more than the other?

TMS

[Richard L]

Do you think I should weight one more than the other?

TMS

The map sensor output will level off when the boost pressure reaches wastergate setting but the MAF will continue unless the flow exceeds the MAF sensing range.

Is it possible to incorporate a temperature sensor to modify the MAF sensor output?

[themadscientist]

Do you think I should weight one more than the other?

TMS

The map sensor output will level off when the boost pressure reaches wastergate setting but the MAF will continue unless the flow exceeds the MAF sensing range.

Is it possible to incorporate a temperature sensor to modify the MAF sensor output?

That is my problem. The turbo cannot carry boost to redline. When the boost starts to fall off I get a reduction in the amount of water injected. When the boost starts to fall the heat in the charge starts to rise because the turbo can't flow enough air to keep the pressure up. So when I need the most water I am not getting it because the boost is falling off.

I was looking a a microcontroller for this, but then I found a passive circuit to average the voltages. I like to keep thing simple. How would you intergrate the temp sensor? Would you average all three MAP, MAF, and IAT after the IC? If it would be a straight average of the three the passive circuit could be used.

[Richard L]

Here is a circuit you can rig up yourself for less than 5 dollars.
You need to find a temperture to suit your operating range.

http://www.aquamist.co.uk/forum/summing.png

[themadscientist]

That is the active one that I found. My only concern is that there will be cross talk between the signal lines. I tried to set up the passive version of that circuit today using 2 DC power supplies and a volt meter but the voltage readings did not jive with the average I should be getting.
I am leaning towards using a microcontroller like a STAMP that would allow me to give a weight to each input and would isolate each one from the other signals.

TMS

[Richard L]

That is the active one that I found. My only concern is that there will be cross talk between the signal lines. I tried to set up the passive version of that circuit today using 2 DC power supplies and a volt meter but the voltage readings did not jive with the average I should be getting.
I am leaning towards using a microcontroller like a STAMP that would allow me to give a weight to each input and would isolate each one from the other signals.

TMS


Try this one, no cross talk:

http://www.aquamist.co.uk/forum/summing3.png

[themadscientist]

That was my next idea. Now I just need a quad opamp. I will see what I have at work tomorrow.

TMS

[Richard L]

Slight improvement, you can switch off the sensors you don't need.

The LM324 shouldn't cost you more than 20 cent each.


http://www.aquamist.co.uk/forum/summing4.png

[themadscientist]

I ordered 2 dual single supply opamps today.

Cost with 2-day shipping and eval boards was $0.00. :shock:

It is nice when a company gives out samples so easily.

TMS

[Richard L]

I ordered 2 dual single supply opamps today.

Cost with 2-day shipping and eval boards was $0.00. :shock:

It is nice when a company gives out samples so easily.

TMS

May be we use a different terminology here, the quad op-amp is termed as single supply. The part number is LM324. The price we paid for each is about 15 cent each at 1K qty.

The dual rail supply op amp will not work with the above diagram. Nice company we have been dealing with... :smile:

[themadscientist]

Sorry that was a little confusing.

I ordered 2 @ Dual opamp, single supply
I think that is a little better

TMS