[oldbeaver]

Hello,

From long time I am trying to find an easy way to retrofit real time fuel consumption estimation for old cars, which are not OBDII and which don't have electronic injection signals. This is the case of many of them.

MPGuino needs two signals only:

VSS = km/h or miles/h
Fuel = km/l or miles/gallon

Many cars have the first but not the second, which is my case, by the way.

To obtain an estimation of the fuel consumed / injected at any time, without the use of two flow sensors which are complicated to handle, or last short or are too expensive, I am trying another method which is to estimate real time fuel consumption, regardless if it is gasoline or diesel as follows:

Fuel used per unit time = f( rpm, tps)

Where rpm is well known and always available or easy to make available.
Tps which is throttle position, preferable close to injection pump or carburator, not at the pedal (for precision).

Tps is a signal sometimes available, sometimes not. But you can instal a linear sensor position to almost any car.

The problem was to have a math model to make the relation between the independent variables rpm and tps and the dependent variable Fuel with precission. Not easy.

But some fellows from Korea did it, (Science and Technology Vol. 4 Nr 4, December, 2011).

The model developed took measurements of fuel used from onboard computer. They were rigorous in using stats to measure the accuracy of the model.

I am attaching a spreadsheet with the model and a surface graph of it. Want to open discussion on it, but more than that, I will implement in my car, using MPGuino as final onboard computer, using the model output as the second signal.

The model requires to be calibrated to one's particular car, for what I added one zero constant that can shift the complete model up and down, and a scale contante which can change the "slope" of the model in a simplified manner.

One should produce some points (fuel, rpm, tps) with the car using a small fuel tank or a complete tank and calibrate the model.

I know it will be not a precise model, but at least will serve as a relative model, to measure mods made to the car or engine, driving strategies and more. The more one calibrate it, the more it will work close to reality.

Anyhow, all onboard computers need callibration.

Any thoughts?

What I need now is a small IC processor to evaluate the polynomial expression in real time, before sending the result to MPguino together with VSS.

Any contributions? I am not electronic, so please easy, practical solutions.

Hope this will be of use to many.

Oldbeaver