From: Hammo on 12 Feb 2007 02:41
On 12/2/07 10:30 AM, in article
"jlittler(a)my-deja.com" <jlittler(a)my-deja.com> wrote:
> On Feb 11, 9:59 pm, Hammo <hbaj2...(a)aapt.net.au> wrote:
>> <j...(a)nowhere.com> wrote:
>>> Hammo wrote:
>>>> QR_yh.5250$sd2.4...(a)news-server.bigpond.net.au, "Knobdoodle"
>>>> <knobdoo...(a)hotmail.com> wrote:
>>>>> "Hammo" <hbaj2...(a)aapt.net.au> wrote in message
>>>>>> "jlitt...(a)my-deja.com" <jlitt...(a)my-deja.com> wrote:
>>>>>>>>> No; it actuates the injector the exact amount that it's been told to
>>>>>>>>> for the
>>>>>>>>> conditions it's measured.
>>>>>>>>> But it doesn't have any idea what a litre actually is and it certainly
>>>>>>>>> doean't have any ability to actually measure one!
>>>>>>>> It's measured, but it can't measure?
>>>>>>> No, it's calculated based on what actually is "measured" (or more
>>>>>>> accurately specified by the efi).
>>>>>>> The efi opens the injector for a period according to what it's lookup
>>>>>>> table tells it is the right amount given the parameters it has sensors
>>>>>>> measuring. It ASSUMES the fuel pressure (and hence fuel flow) is
>>>>>>> correct (unless there has been some new fangled advances in EFI I'm
>>>>>>> not aware of). I know of no cars that measure actual fuel flow, they
>>>>>>> usually calculate your fuel consumption based on the amount of time
>>>>>>> they've opened the injectors, and the number of KM's travelled. Those
>>>>>>> two parameters are based on a number of implicit assumptions:
>>>>>>> - the fuel pressure is correct
>>>>>>> - there are no blockages restricting fuel flow
>>>>>>> - the size of your tyres are as specified and hence the number of K's
>>>>>>> calculated is correct
>>>>>>> etc etc
>>>>>>> it's a reasonably accurate estimate and more than good enough for the
>>>>>>> purposes for which it is used. That doesn't mean the actual fuel flow
>>>>>>> is measured.
>>>>>> It's measured but it doesn't measure?
>>>>> Why do you keep pretending we've said "it's measured" Hammo; when we've
>>>>> quite clearly said the exact opposite!
>>>> How does the efi know how much to squirt?
>>> Because a human told it what to do, if these parameters are measured
>>> (which don't include measuring fuel flow), then do x.
>> A human told it to? That is your explanation of the sophistication of EFI?
> Yup. Pretty much sums it up.
Yes, in the same league
> What amuses me, is that you seem to deliberately be confusing
> measuring with calculating an estimate. If someone else tried that
> obfuscation you'd be up in arms !
Oh dear John. You really are having a hard time understanding what a
measurement and what estimate is. Tell me the difference, or, ask a
physicist, like IK perhaps to explain that any measurement is an
approximation, i.e. The best estimate of the size. If you wish to be so
bold as to be correct 100 percent of the time with the way you measure, it
is quickly going to become pointless.
> The *measured* parameters for the EFI are things like the exhaust gas
> mix (via o2 sensor), duration of injector opening, quantity of air
> flowing through the throttle bodies(MAF) or the postion of the
> butterfly in the throttle (TPS), engine temp etc.
Yes, the better the "measurement" the closer to "correct" or "reproducible"
the value will become. The error in the estimate becomes smaller. Do you
really believe that this is obfuscation, or more doing your best to try and
discredit a fairly well understood paradigm?
> The measure inputs are then used to calculate other things based on
Assumptions. Yes, that is the basis of theories. Some prefer hypothesis as
it makes them sound "scientific" as assumptions has a connotations that
often relates to a rationalisation that is erroneous. The closer the
"assumption" is scrutinised and refreshed, it comes closer to being a real
world applicable and hence increase in accuracy.
> There are lots of assumptions made during the programming of an EFI
> computer, there's also differences in the granularity of the
> measurments and hence how well it can interpolate (finite steps in
> measurement need to be translated into smooth changes in quantity of
> fuel, ignition timing etc).
> When you make assumptions about a variable (rather than measuring it),
> it is inherently more likely to be inaccurate than measuring it. Yes,
> there's also error in measurement, and yes potentially the
> relationship *could* be the other way around, but it's not very
Semantics, see above.
> Fuel flow in Nev's car is a calculated estimate, not measured (to the
> best of my knowledge), the calculation is accurate enough for domestic
> use, but it includes assumptions about the values of some parameters,
> it is therefore not, by definition, a *measurement* of the fuel flow,
> but a reasonably good estimate.
I disagree with you. I have presented my version of how it is determined.
> Please note, I've already said all this once. Please try reading it
> this time.
You may have. That's probably why this discussion is occurring, as, I don't
agree with your "version".
>>>> It must have some idea, after all
>>>> it calcs things to L/100 km. it'd have to be more than just chance.
>>> Uhuh, it sticks it's metaphorical finger in the air and makes it's best
>>> guess, based on the things it does know. It's usually a pretty fair
>>> estimate to, same as when I walk outside, wave my arms around a bit and
>>> say "I think it's about 22, 24 degrees celsius this morning"
>> Yes, you and your "weather station". We have had that discussion before.
> yes and you still seem to think that domestic use requires scientific
> levels of accuracy, the world ain't a lab, get over it.
I am amused that when accurate measurement is not required in your view, I
am pedantic and anal and need to "get over things". Yet you want to know
how much accuracy is in this system, can't find it and so conclude it is not
accurate and therefore flawed.
> Nev's car does stick it's metaphorical finger in the air - it doesn't
> KNOW how much fuel has flowed through it (ie no flow measured). It
> DOES know that it held the injectors open for N milliseconds X times
> over the last 5 minutes, and *IF* it's assumption that it's fuel rail
> pressure is Y PSI is correct then it has flowed Z ml of petrol. Of
> course that also assumes the temp of the fuel and all sorts of other
> trivial assumptions that would make minor differences to the
> calculated result. Doesn't matter though because for the purposes it's
> being used the estimate's going to be close enough.
No, see above.
> And just for the record, same goes for the "weather station" temp
> measurement in a domestic situation is mostly for the purposes of
> considering your physical well being, so the thermometer saying 21 vs
> 22c doesn't really matter much, I know it means jeans and a tshirt.
Domestic. Oh, this is your escape clause?
>> What does EFI do
>> that makes it so special?
> Nothing, it's not at all special, it's just a way of adding fuel to an
> internal combustion engine, that's nothing special. It does it a bit
> more accurately nowadays than the old analogue based carbies, but
> there was a fair while there when it didn't. It's no more special;
> than any other computer controlled system - why do you think it's
> special ?
Rhetorical question or you'd like an answer? Amusing that the topic of
waste is what generated this discussion and yet you don't see the link.
>> Why are EFI motors getting cleaner and having
>> lower emissions (despite their inherent inefficiencies)?
> Better EFI programming, smaller steps between measurement intervals,
> more powerful CPUs able to interpolate faster and more often per
> second, ability to manage a greater amount of data over a longer
> period to calculate more effectively given a wider range of paramerts.
> The ability to monitor the gas mix in the exhaust in a fairly
> primitive way to be able to then say "oh no lean off the mixture, it's
> too rich" (feedback loop on the result)
> Also, outside of the efi piece - better engine design - cylinder head
> design has come a long way in the last 15 years.
Interesting to note you didn't include better quality fuel.
From: Knobdoodle on 12 Feb 2007 03:25
"sharkey" <sharkey(a)zoic.org> wrote:
> .....any time it starts knocking.
Dammit; now I've got the Dave Edmunds* song in my head!
(*the last concert I ever went to at Brisbane's iconic "Cloudland Ballroom"
was Dave Edmunds and Nick Low's "Rockpile")
From: Knobdoodle on 12 Feb 2007 03:41
> There's also a feedback loop from O2 sensor and knock sensor where
> fitted which moves around in the tables according to the feedback (if
> the o2 says it's a bit rich, knock n milliseconds off the injector
> times), if knock sensor says it's knocking retard injector and
> ignition timing etc
Yep; and this is the strength of EMS/EFI.
It doesn't have to rely on vacuum, bi-metallic strips, centrifical force and
spring tension to do what's needed exactly; it can make a rough guess; check
against "optimum" and then adjust on the run.
As you pointed out earlier (or later if I'm reading this in the wrong order)
the smaller the increments and the faster the processing just makes this all
the more efficient (provided the preset "optimums" are correct of course).
From: Knobdoodle on 12 Feb 2007 03:46
"Hammo" <hbaj2006(a)aapt.net.au> wrote in message
> On 12/2/07 10:43 AM, in article
> <jlittler(a)my-deja.com> wrote:
>> On Feb 11, 11:50 pm, Hammo <hbaj2...(a)aapt.net.au> wrote:
>>> <knobdoo...(a)hotmail.com> wrote:
>>>> "Hammo" <hbaj2...(a)aapt.net.au> wrote:
>>> Now fuel systems are all about air to fuel ratio. Best situation is
>>> the ratio is adjusted for all situations. Hence EFI becoming better and
>>> better wrt emissions. Why? It's not magic, it is due to the monitoring
>>> the system and adjustments that are made via many circuits many times
>>> second. What is based on? What measurement could possibly do this,
>>> principle? Stoichiometry.
>>> I.e. The equation for combustion wrt air:fuel ratio. That monitors how
>>> fuel is required. It is calculated via moles of fuel based on the RON.
>>> This is why some cars run better, or require higher octane fuels (wrt
>>> If you have a running total of fuel used based on the chemical reaction,
>>> have a better indication than fuel flow as it relates to the chemistry,
>>> irreversible chemical reaction that converts fuel to energy.
>> <doubtful look> maybe the F1 teams do this, but too bloody expensive
>> for a run of the mill road car.
> No, I don't think so, and I this is why the focus on the need for a "fuel
> flow measure" to be utter bollocks. Clem claims it to be obfuscation.
Or diversion Hammo; you take your pick!
Totally irrelevant in the "does using headlights unnecessarily waste fuel"
(and the "is Nev's fuel-usage display totally accurate") debate anyway.
From: G-S on 12 Feb 2007 04:10
> Knobdoodle wrote:
>> [crinkles brow]
>> What's this new diversion you're trying now Hammo?
>> "the inefficiencies of the internal combustion engine."?!!?
>> What the hell has that got to do with the fuel waste through
>> unnecessary use of driving lights?
> Eh? I thought we'd already established that there was no waste, or, if
> there was, it was only measurable at a theoretical level.
No we established that you car fuel measuring device wasn't sensitive
enough to measure it but that practical measurment devices for measuring
the effect did in fact exist :)