How ME7 calculate airflow at low loads-idle?

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NOTORIOUS VR

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #15 on: July 12, 2011, 10:46:10 AM »

Ok question...

does anyone know how the base 1.70ms inj time is calculated? It clearly seems that it never goes lower then that on my car... There must be some reason the ECU thinks it needs to keep it at least that high.

Does anyone else know what their min inj time is?


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nyet

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #16 on: July 12, 2011, 10:56:48 AM »

I would guess it is latency + requested on time


« Last Edit: July 12, 2011, 10:58:22 AM by nyet »	Logged

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #17 on: July 12, 2011, 12:36:08 PM »

I'm starting to wonder now if my TVUB is just simply too high (even though AFR's are good @ idle and cruise).

Simply because the following:

Warm/Hot start is out of whack (maybe cold start is too rich as well, but the car starts fine when stone cold), I have the issue with light cruise (21+ in. Hg) being too rich, etc.

I got to thinking yesterday that possibly my TVUB values are just too high. Although I would hope that Bosch was smart enough and make other adjustments so that you could make the TVUB's as close to what the inj specs are. It's clear we either haven't found them or know how/what exactly is in calculating the base injection time.


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TTQS

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #18 on: July 20, 2011, 05:00:09 AM »

There is the added complication of the intake manifold model. This is mentioned in Greg Banish's book and I have seen it referred to in the funktionsrahmen. The ECU compares actual readings of airflow with those returned by the MAF sensor and will makes corrections as it deems necessary. I don't know how it works in any detail or which map(s), characteristic(s) and constant(s) define it. Banish does discuss the general difficulties in controlling fuelling at idle for any engine system (e.g. Large percentage error in injector pulse) so it's clearly not a trivial exercise to tune idle parameters.

Doug


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sleeperavant

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #19 on: July 26, 2011, 08:00:39 AM »

Generally in KFKHFM if you raise the values does that increase fueling (richer), and the opposite if lowering values (leaner)?


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TTQS

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #20 on: July 26, 2011, 03:30:51 PM »

Quote from: sleeperavant on July 26, 2011, 08:00:39 AM

Generally in KFKHFM if you raise the values does that increase fueling (richer), and the opposite if lowering values (leaner)?

I'm just finishing up translating the GGHFM 57.60 module and it states the following:

Application of the MAF Correction Map KFKHFM:

In regions of no pulsation, the air mass comparison is carried out via the map KFKHFM. In this way, MAF-sensor errors caused, for example, by a problematic installation position can be corrected. For either, the balancing should maintain lambda of approximately 1.0, so the error in calculating the air mass in the exhaust gas is low. The residual errors (lambda deviation around 1.0) are interpreted as a mixture error and are compensated for by the characteristic curve FKKVS in the RKTI 11.40 module.

The values in KFKHM in one of my files cluster around 1.000 and the GGHFM overview flow diagram shows that the output from KFKHM is the multiplication factor fkhfm which then feeds through as a multiplication factor into an air flow reading in kg/hr.

Therefore increasing the values in KFKHM will correct the metered air flow up which should result in an enrichment correction in FKKVS.

Doug


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nyet

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #21 on: July 26, 2011, 03:43:53 PM »

Quote from: TTQS on July 26, 2011, 03:30:51 PM

The values in KFKHM in one of my files cluster around 1.000 so whether they are lambda values or correction factors to lambda, increasing them will increase lambda (leaner) and decreasing them will decrease lambda (richer).

I thought they were air mass corrections, not lambda corrections, so it would be the opposite ... higher means adjust MAF reading up (adding fuel to a too lean area) and lower means adjust MAF reading down (remove fuel from a too rich area).

Do I have it backwards??


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TTQS

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #22 on: July 27, 2011, 01:21:49 AM »

No, you're right nyet. I must have got confused by the discussion of lambda at the end. The overview flow diagram, clearly shows that the output from KFKHM is the multiplication factor fkhfm which then feeds through as a multiplication factor into an air flow reading in kg/hr.

I shouldn't have been looking at this forum late at night after a busy shift. Sad

I'll edit my original post to reflect that.

Doug


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Giannis

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #23 on: July 27, 2011, 01:43:28 AM »

Also keep in mind that by adjusting KFKHM you are adjusting the load that ECU can read. For example in my car i was getting some severe ignition retard (cf) although i have lowered my basic ignition maps enough. When i adjusted the KFKHM i managed to scale up the load that ecu reads and so my ignition and fueling also restored. This map is related to hardware moddifications that can increase airflow to the engine such as front mound intercooler with custom metal pipes bigger or modyfied airbox bigger valves etc. It is a very smart map and you must play with it in order to fine tune your ecu. Sorry for my english i wish you got the point.


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sleeperavant

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #24 on: July 27, 2011, 06:01:44 AM »

Thanks guys for the good info!


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Tony@NefMoto

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	Re: How ME7 calculate airflow at low loads-idle? « Reply #25 on: September 04, 2011, 04:22:06 PM »

MLHFM - converts the MAF voltage to air mass.
KFKHFM - corrects the air mass based engine speed and load.
KFMLDMN - is the minimum air mass based on engine speed and throttle angle.

There is also a global minimum for air mass, and an offset for the air mass after it has been converted from voltage using MLHFM.

For injection time there is a constant that determines the minimum injection time. Even if you want to inject less than this the ECU never will. This minimum injection time is applied after the calculations for injector scale and injector latency offset.


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