[Diy_efi] Re: Minimalist micro based EFI ?

[Greg Hermann]

At 11:29 PM 3/11/03, Mike wrote:

The basic control theory element you are skirting around here is "dynamic
range".

The ratio between an engine's minimum and maximum output power is a pretty
fair definition of the dynamic range which ANY fuel delivery system must
cover.

Next question is, how much granularity in fuel flow control rate can the
engine tolerate without getting into either emission problems (an
artificial constraint), excessive fuel consumption, including plug fouling
and/or bore washing (valid concerns) , or detonation (a very real and
immediately expensive concern).

With a boosted engine, the engine's dynamic range is generally wider, and
the higher the boost level goes, the wider the dynamic range gets--so more
precision (more bits) MAY well be necessary in measurement of inputs
critical to controlling the fuel flow rate fpr boosted engines without
getting into excessive fuel control granularity.

In fact--the need for more precision in fuel metering may well increase
_geometrically_ with boost, since boosted engines are so much more
sensitive to detonation than NA engines are !

Greg

>Yes Mos, but not from the perspective of a design decision to
>run an engine over a certain power come boost range...
>
>ie. A Gen III 5.7L V8 uses a MAF sensor 5v max output, 300Kw
>
>A RB30 N/A puts out 120 Kw and uses a different MAF sensor also
>with a max 5v output.
>
>Case 1 above at say 100Kw flow has less MAF voltage than the
>case 2 with 100Kw flow as its a sensor sizing throat/voltage issue.
>
>So clearly the sensor is chosen for the range and the a/d resolution
>is chosen under some other metric, other than the difference in
>vintage between the 2 samples above, is there a compelling reason
>the 5.7L V8 *needs* higher resolution if emissions is not an issue,
>
>rgds
>
>mike
>
>
>
>At 02:06 AM 3/12/03 +1100, you wrote:
>>On Tue, 11 Mar 2003, Mike wrote:
>>
>>> At 01:38 AM 3/12/03 +1100, you wrote:
>>> >> <cough> I dont see how boost has anything to do with the number of bits.
>>>
>>> So now you are saying air flow voltage is related to boost pressure
>>> rather intimately ?
>>
>>There's no standard (that I was referring to). I was referring to MAP and
>>atmo - hence 5V/1bar (yes, very generally). As another poster stated,
>>there's 5V/3bar (and also 5V/2bar).
>>
>>It doesn't matter what you're measuring, but if your range increases, your
>>resolution will decrease if you use the same number of bits, period. Your
>>10 bits will not give you the same resolution with 2 bar as they will with
>>1 bar.
>>
>>I was in no way saying that it was insufficient - merely stating that
>>boost *can* affect the number of required bits - so yes, boost does have a
>>lot to do with the number of bits.
>>
>>Air flow voltage is related to air flow (obviously), and air flow is very
>>intimately related to boost pressure.
>>
>>Mos.
>>
>>--
>>84 AE86, 90 ST185GrpA, 91 MX83Gr, Sydney, Oz.
>>
>>
>>
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>
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