Preface: very much a novice, but have garnered a lot of info over the last few months & here are some personal observations on what I have learned.
I welcome your feedback & opinions.
What is closed loop operation anyway? In the perfect control system, there would a real-time control that could adjust primarily A/F ratio & ignition timing to changing load conditions. The critical factor in creating a system that can do that is in the capability of the various feedback sensors accurately reflecting what is going on. (remember the old saying, garbage in = garbage out!) The most limiting of these is the use of O2 sensors to determine the Air/Fuel ratio. Most systems work under open-loop condition, with look-up tables processed for different load conditions: they may have partial closed-loop operation to trim conditions from the table within a certain degree under certain operating conditions (usually not under WOT)
With more engine management systems (EMS or ECU) having capability for closed-loop operation, a dependable O2 sensing system is essential to have it operate effectively. The newly released AEM for example appears to be an affordable package that incorporates that capability. Now, the std. equipment on most vehicles (NSX included) is narrow band, little more than a digital switch around the stochiometric point (~14.7), either "low" for lean, or "high" for rich, with very little descernability over the say, 10-14.7 range; that's exactly where you want to really know what's going on, particularly in a boosted application where you want to run richer than the "ideal" stochiometric 14.7, typically the 12.5 range.
So, enter wide-band onto the scene, which, while not exactly completely linear, gives a predictable curve related to the fuel ratio.
Courtesy of FJO, Inc.
Now, you can see from the graph, why you need wide-band to offer any possibility of closed-loop response based on the O2 detector.
As you look around the available(affordable) O2 controller options, there are surprisingly few to choose from: TechEdge & FJO are the popular choices.
I came across one operation, however, EGOR Technology, Inc. & had a very lengthy & most enlightening conversation with its principal, Gar Willis.
I learned much, but one of the most interesting phenomena that is mostly overlooked by the low cost alternatives, is the impact that the operating environment pressure has wrt the O2 sensor calibration: this becomes critical in a turbo application particularly, where the exhaust back pressure can have dramatic effect, in the most damaging direction!
EGOR has compensation circuitry in its controller that operate in conjunction with O2 sensors that come complete with calibration curve & exhaust pressure sensors that factor in the result automatically! Clever stuff!
Also available is a dual input/output controller, that would be ideal for the TT application.
This would seem to be an ideal complement to the new generation of closed loop engine controllers. It would appear a requirement for all controllers to have whatever corrections are necessary for true closed-loop operation. I would expect the other low cost outfits to incorporate this before long.
On the NSX, typical location for the bung is pre-turbo, either on the header or the collector - w/o any pressure correction however, a much better solution for accurate response would be to locate the sensor after the turbo.
I believe the stand-alone controller boxes will ultimately be replaced by integrated wide-band control w/in the EMS or ECU itself (some may already have this feature)
So, it will be interesting to watch the development of closed loop technology over the coming year or so: with the available processing technology & improvements in the sensing devices, the self-calibrating system is maybe not just a pipe-dream!
Just not quite there yet!
[This message has been edited by D'Ecosse (edited 03 January 2003).]
I welcome your feedback & opinions.
What is closed loop operation anyway? In the perfect control system, there would a real-time control that could adjust primarily A/F ratio & ignition timing to changing load conditions. The critical factor in creating a system that can do that is in the capability of the various feedback sensors accurately reflecting what is going on. (remember the old saying, garbage in = garbage out!) The most limiting of these is the use of O2 sensors to determine the Air/Fuel ratio. Most systems work under open-loop condition, with look-up tables processed for different load conditions: they may have partial closed-loop operation to trim conditions from the table within a certain degree under certain operating conditions (usually not under WOT)
With more engine management systems (EMS or ECU) having capability for closed-loop operation, a dependable O2 sensing system is essential to have it operate effectively. The newly released AEM for example appears to be an affordable package that incorporates that capability. Now, the std. equipment on most vehicles (NSX included) is narrow band, little more than a digital switch around the stochiometric point (~14.7), either "low" for lean, or "high" for rich, with very little descernability over the say, 10-14.7 range; that's exactly where you want to really know what's going on, particularly in a boosted application where you want to run richer than the "ideal" stochiometric 14.7, typically the 12.5 range.
So, enter wide-band onto the scene, which, while not exactly completely linear, gives a predictable curve related to the fuel ratio.
Courtesy of FJO, Inc.
Now, you can see from the graph, why you need wide-band to offer any possibility of closed-loop response based on the O2 detector.
As you look around the available(affordable) O2 controller options, there are surprisingly few to choose from: TechEdge & FJO are the popular choices.
I came across one operation, however, EGOR Technology, Inc. & had a very lengthy & most enlightening conversation with its principal, Gar Willis.
I learned much, but one of the most interesting phenomena that is mostly overlooked by the low cost alternatives, is the impact that the operating environment pressure has wrt the O2 sensor calibration: this becomes critical in a turbo application particularly, where the exhaust back pressure can have dramatic effect, in the most damaging direction!
From Egor Technology:
Especially if you are measuring AFR pre-turbo, our exclusive built-in EBP Exhaust Back Pressure correction is a must-have; AFR errors due to exhaust pressure can be as high as 30% of F.S.! depending on how much EBP you're running.
And these errors are in the worst possible direction; they can mislead you into thinking the AFR is much lower/richer than it actually is! Under boost, NO other AFR meter will tell you the true AFR, and may indicate as much as 2+(yes, two+) AFR richer than actual! Ouch.
EGOR has compensation circuitry in its controller that operate in conjunction with O2 sensors that come complete with calibration curve & exhaust pressure sensors that factor in the result automatically! Clever stuff!
Also available is a dual input/output controller, that would be ideal for the TT application.
This would seem to be an ideal complement to the new generation of closed loop engine controllers. It would appear a requirement for all controllers to have whatever corrections are necessary for true closed-loop operation. I would expect the other low cost outfits to incorporate this before long.
On the NSX, typical location for the bung is pre-turbo, either on the header or the collector - w/o any pressure correction however, a much better solution for accurate response would be to locate the sensor after the turbo.
I believe the stand-alone controller boxes will ultimately be replaced by integrated wide-band control w/in the EMS or ECU itself (some may already have this feature)
So, it will be interesting to watch the development of closed loop technology over the coming year or so: with the available processing technology & improvements in the sensing devices, the self-calibrating system is maybe not just a pipe-dream!
Just not quite there yet!
[This message has been edited by D'Ecosse (edited 03 January 2003).]