How does Auto-Tune or M-Tronic work?

[joecool85]

I know what it monitors and that it adjusts the carb, but how? Are there little screws and the computer activates servos to turn them? Some sort of fuel pump system and it adjusts the pressure? What's going on in there?

 

[BloodOnTheIce]

Something like this...

"A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster." Jeremy Clarkson

 

[Saw Dr.]

Very well, thank you!

 

[Jimmy in NC]

I'm curious too as to how they are monitoring the change in performance / exhaust to know what to do...

 

[Mike-M]

Id like to take one apart as well.

 

[04titanse]

Something like this...

"A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster." Jeremy Clarkson

I always wondered why much truck goes through rear tires so fast....must be that turbo/witchcraft!

 

[blsnelling]

It's all based off RPM. Fuel is pulled, the RPMs checked. If the RPMs are higher, it figures it was rich and pulls more fuel. If the RPMs drop, it adds fuel. This happens several times/second. It's a regular carb, except that the H needle is replaced with a small servo. Everything is in the coil and the carb.

 

[Jimmy in NC]

Except with this one...

Whole thread on it coming later tonight or in the AM.

Kind of what I was thinking Brad but thanks for confirming. I wonder how long until they utilize an Oxygen sensor and get real tight on it.

 

[SawTroll]

Very well, as I understand it! :cool2:

However, the current AutoTune is a bit more advanced than the original one, and the Stihl version.....

 

[joecool85]

It's all based off RPM. Fuel is pulled, the RPMs checked. If the RPMs are higher, it figures it was rich and pulls more fuel. If the RPMs drop, it adds fuel. This happens several times/second. It's a regular carb, except that the H needle is replaced with a small servo. Everything is in the coil and the carb.

Ok, so it is a servo turning a screw then. What about the L screw though? And for that matter, it must have an idle screw it adjusts....

 

[mweba]

No screw. The micro actively adjusts a valve controlling fuel mixture through one circuit. When the saw is at idle, no low pressure over the main nozzle leaving it closed, the micro adjusts for idle. As the throttle is opened the throttle position sensor prompts the micro to add more fuel as the pressure drops over the main nozzle, inturn opening it for full throttle mixture. The micro then tests for max power by leaning out several times a second.

Simple really

 

[SawTroll]

How about temp and air pressure sensors?

 

[mweba]

How about temp and air pressure sensors?

Carb temp sensor to aid in mixture. No pressure test.

 

[joecool85]

So it is a rotating assembly of some sort? Whether you call it a valve or a screw doesn't matter to me so much, I was just curious if it was adjusting the flow of a needle or if it was modulating pulse on an injector or something.

Neat.

 

[blsnelling]

The Husky system is different than the Stihl system. IIRC, Stihl does not use a TPS.

 

[mweba]

Old videos. My understanding of the system is better now


[video=youtube;7NNMeKIfUK4]http://www.youtube.com/watch?v=7NNMeKIfUK4&feature=share&list=UUXrUSTTnD1KfjS6rJBCxhhg[/video]

 

[mweba]

Ya one video per response limit is well....


[video=youtube;E18quXUqOz0]http://www.youtube.com/watch?v=E18quXUqOz0&feature=share&list=UUXrUSTTnD1KfjS6rJBCxhhg[/video]

 

[joecool85]

Great videos. Interesting how it uses a magnet coil similar to a voicecoil on a speaker to move the "needle" that adjusts the fuel flow. Great idea.

So I guess the computer etc gets all it's power from a small generator coil on the saw or something? Is there a small battery that will need replacement at some point or is it all just capacitors evening out the voltage flow etc?

 

[Chris-PA]

I've been trying to figure out if it is a stepper motor or simply and on/off solenoid valve that is pulse width modulated to control fuel volume (like an automotive fuel injector is controlled).

Regardless, feedback is by doing a periodic momentary lean out test and looking at the rpm. Depending on what the rpm does they can tell whether it is rich or lean and adjust accordingly.

By doing it this way they do not need to look at a host of input sensors, instead they look at the output results and adjust. The "programming" is going to be mostly to set the initial open loop settings, once in feedback mode it will be looking primarily at the lean out test/rpm - so the fuel/air ratio is not pre-programmed, it is whatever the engine needs right now.

 

[blsnelling]

Great videos. Interesting how it uses a magnet coil similar to a voicecoil on a speaker to move the "needle" that adjusts the fuel flow. Great idea.

So I guess the computer etc gets all it's power from a small generator coil on the saw or something? Is there a small battery that will need replacement at some point or is it all just capacitors evening out the voltage flow etc?

It's all in the coil and carb.