Open loop vs closed loop in stand alone: Is there a point?
11-23-2005, 06:45 PM
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Open loop vs closed loop in stand alone: Is there a point?
I am considering going to stand alone ECU on my racer, DTA like.
Now there is a Q i have been asking myself: These new ECU can be fully closed loop, so you can put in a required A/F ratio, boost level, and fuel and timing can be regulated. Systems like DTA used to have Closed Loop only control.
Now I saw, that recent developement is that they add open loop control to the functions. DTA data sheet
I allways thought that open loop was due to the shortcomings of 15 y old electronics/ sensors/ algorithms.
Does anybody know if there is a real benefit to open loop control? Why should we want it?
H.
Now there is a Q i have been asking myself: These new ECU can be fully closed loop, so you can put in a required A/F ratio, boost level, and fuel and timing can be regulated. Systems like DTA used to have Closed Loop only control.
Now I saw, that recent developement is that they add open loop control to the functions. DTA data sheet
I allways thought that open loop was due to the shortcomings of 15 y old electronics/ sensors/ algorithms.
Does anybody know if there is a real benefit to open loop control? Why should we want it?
H.
11-23-2005, 07:07 PM
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Hans
Are you sure you dont have open-loop and closed-loop confused?
http://www.customefis.com/GMEFI.html
Are you sure you dont have open-loop and closed-loop confused?
http://www.customefis.com/GMEFI.html
11-23-2005, 08:25 PM
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DTA is a good system. They just released a new box not so long ago. Under load I prefer open loop and have the car tuned once. The reason I prefer open loop under WOT is to take the O2/WB sensor out of the equation.. O2 sensors do fail, I wouldn't want to rely on them under WOT. If they fail and read rich, the DME will try to lean out the mixture, this could damage the engine under LOAD..
Closed loop at Idle, PT is not bad as the effect could be easily detected and you will be able to tell when the O2 sensor is bad as drivability would suffer.. Under WOT/LOAD you do not have this luxury.
Closed loop at Idle, PT is not bad as the effect could be easily detected and you will be able to tell when the O2 sensor is bad as drivability would suffer.. Under WOT/LOAD you do not have this luxury.
11-23-2005, 08:41 PM
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In principle, the closed loop operation looks great, always adjusts to the correct AFR even under changing conditions. But it has a problem, what if one of the sensors in the feedback loop fails and reports incorrect values.
Open loop basically a lookup table, little can go wrong. The closed loop uses a Wide band O2 sensor to adjust the AFR. If the sensor fails, is incorrectly located, or just get to hot, it will report an incorrect AFR to the computer and the computer will adjust timing/fuel and move the AFR to the wrong value. This can cause bad thing to happen, detonation.
The new feature is:
"Turn off closed loop above TPS & RPM NEW"
The open loop trigger point could be set to a RPM level of say 3K just before boost starts. Below 3K it is in closed loop so the AFR is correct for the cat. Not even sure if the Netherlands requires a cat.
The computer in the 951 is very capable despite rumors you read. The engine speed (RPM <7K) is slow enough for the computer to do lots of calculations and lookups before any action needs to be taken. The only thing that was missing when the DME was developed was affordable Wide Band O2 sensors.
Looks like Fast951 bet me to this, got to learn to type faster.
Open loop basically a lookup table, little can go wrong. The closed loop uses a Wide band O2 sensor to adjust the AFR. If the sensor fails, is incorrectly located, or just get to hot, it will report an incorrect AFR to the computer and the computer will adjust timing/fuel and move the AFR to the wrong value. This can cause bad thing to happen, detonation.
The new feature is:
"Turn off closed loop above TPS & RPM NEW"
The open loop trigger point could be set to a RPM level of say 3K just before boost starts. Below 3K it is in closed loop so the AFR is correct for the cat. Not even sure if the Netherlands requires a cat.
The computer in the 951 is very capable despite rumors you read. The engine speed (RPM <7K) is slow enough for the computer to do lots of calculations and lookups before any action needs to be taken. The only thing that was missing when the DME was developed was affordable Wide Band O2 sensors.
Looks like Fast951 bet me to this, got to learn to type faster.
12-04-2005, 07:10 AM
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Thx guys, really helpfull.
Just looking for ways to avoid having to re-dyno my car every time we change some setting.. Probably need an engine dyno to get it properly set up from scratch anyway.
Just looking for ways to avoid having to re-dyno my car every time we change some setting.. Probably need an engine dyno to get it properly set up from scratch anyway.
12-04-2005, 01:42 PM
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Hans,
Your car, a data logging (and/or real time display) system, two active feet and possibly a friend, substitutes very well for a dyno.
Using one foot on the brake and the other gradually increasing the load (accelerator) should enable you to fill out all rpm-load combinations of the AFR and ignition tables, based on the oxygen sensor readouts and beginning audible detonation. One set of brake pads is much cheaper than 10 dyno sessions and the tuning done this way is with "real life" airflow to the engine.
The Electromotive TEC-3 unit has options of setting the closed loop authority range and going to open loop configuration at specified rpm and load ranges. The DTA may have the same features.
Laust
Your car, a data logging (and/or real time display) system, two active feet and possibly a friend, substitutes very well for a dyno.
Using one foot on the brake and the other gradually increasing the load (accelerator) should enable you to fill out all rpm-load combinations of the AFR and ignition tables, based on the oxygen sensor readouts and beginning audible detonation. One set of brake pads is much cheaper than 10 dyno sessions and the tuning done this way is with "real life" airflow to the engine.
The Electromotive TEC-3 unit has options of setting the closed loop authority range and going to open loop configuration at specified rpm and load ranges. The DTA may have the same features.
Laust
