[Diy_efi] RE: Throttling intake air -- references

Djfreggens at aol.com Djfreggens at aol.com
Wed Jan 15 16:56:40 GMT 2003


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In a message dated 1/15/2003 11:12:59 AM Eastern Standard Time, 
erazmus at iinet.net.au writes:


> I have seen occasional reference to this method but many years ago
> when ECU's werent explicity set up to do it compounded by the
> ready availability of casting which included a wastegate causing
> a market 'critical mass' and hence momentum for that approach
> and probably influenced by the feedforward aspect of the control
> systems complexity...
> 
> >Trying to control boost at 2500 revs using throttle only is more difficult
> >than at 5000 on the same engine, as the boost rises and falls over a much
> >smaller throttle movement? What sort of (boost controlling) linkage would
> >you use that could control boost via the (blow through) throttle plate, 
> but
> >alter the 'sensitivity' of the throttle so as the boost came and went over
> >the same amount of pedal travel?
> 
> Oh yes, I can appreciate that point and its well put. I've not yet
> considered the linkage issue but should (I expect) be containable
> via various leverage mechanisms, PID stability plays a major part.
> 
> These days with extremely powerful 25mips processors for USD$5 and
> development in sensors and control electronics it might be feasible to
> revisit the issue armoured with much better implementation tools
> capable of handling what you well describe - vis a vis the positional
> nonlinearity or rather angular nonlinearity issue in respect of
> control dynamic for boost pressure via existing throttle body mechanics.
> 
> >For the same engine, is the exhaust backpressure in the manifold the same
> >when running wide open throttle and wastegate part open as it is when
> >running wastegate shut and throttle part open?
> 
> Well I have recalled, from a magazine sponsored article some years ago,
> that once the wastegate opens (and stays open) the higher pressure on
> the pre-turbine side is vented to the post-turbine side, therefore
> its logical to interpret that the EBP must be higher. These days its
> easy to measure and when i get time I'll set up a pair of gauges
> to report what I find.
> 
> Its common sense to some major degree, if the wastegate needs to
> be opened and stays open to dump pressure one would expect the
> pressure post-turbine to be higher - for some other posters to suggest
> it might be the opposite is ludicrous, sure the turbine will spin
> down a tad *but* if the need is still there to bypass the turbine
> then the region post-turbine must be seeing pressures that exist
> on the pre-turbine side as the wastegate is open and this must
> be higher as its not all going through the damn turbine <sigh>
> 
> I also think there is tradition in seeing the wastegate as a control
> (proportional) element when its really more akin to a digital
> relief valve, hence is discontinuous in its reponse to dumping
> exhaust energy and therefore should be logical to control the fuel/air
> more precisely some time before its combusted. Historically this has
> been difficult and more expensive, these days it should be much
> easier if people can intellectualise the control systems
> algorithms and that was the impetus for this thread in the first
> place,
> 
> ;-)
> 
> 
> rgds
> 
> mike
> 
> 

for all this conjecture why not go look at a chrysler draw thru system ???you 
have a Throttlebody then turbo then the engine. it keeps the turbo spooled 
quite nicely. and you wont have to worry about turbo backpressure. my 2cents 
cuase ive been watching this whole thing and shaking my head. 

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<HTML><FONT FACE=arial,helvetica><FONT  SIZE=2>In a message dated 1/15/2003 11:12:59 AM Eastern Standard Time, erazmus at iinet.net.au writes:<BR>
<BR>
<BR>
<BLOCKQUOTE TYPE=CITE style="BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">I have seen occasional reference to this method but many years ago<BR>
when ECU's werent explicity set up to do it compounded by the<BR>
ready availability of casting which included a wastegate causing<BR>
a market 'critical mass' and hence momentum for that approach<BR>
and probably influenced by the feedforward aspect of the control<BR>
systems complexity...<BR>
<BR>
&gt;Trying to control boost at 2500 revs using throttle only is more difficult<BR>
&gt;than at 5000 on the same engine, as the boost rises and falls over a much<BR>
&gt;smaller throttle movement? What sort of (boost controlling) linkage would<BR>
&gt;you use that could control boost via the (blow through) throttle plate, but<BR>
&gt;alter the 'sensitivity' of the throttle so as the boost came and went over<BR>
&gt;the same amount of pedal travel?<BR>
<BR>
Oh yes, I can appreciate that point and its well put. I've not yet<BR>
considered the linkage issue but should (I expect) be containable<BR>
via various leverage mechanisms, PID stability plays a major part.<BR>
<BR>
These days with extremely powerful 25mips processors for USD$5 and<BR>
development in sensors and control electronics it might be feasible to<BR>
revisit the issue armoured with much better implementation tools<BR>
capable of handling what you well describe - vis a vis the positional<BR>
nonlinearity or rather angular nonlinearity issue in respect of<BR>
control dynamic for boost pressure via existing throttle body mechanics.<BR>
<BR>
&gt;For the same engine, is the exhaust backpressure in the manifold the same<BR>
&gt;when running wide open throttle and wastegate part open as it is when<BR>
&gt;running wastegate shut and throttle part open?<BR>
<BR>
Well I have recalled, from a magazine sponsored article some years ago,<BR>
that once the wastegate opens (and stays open) the higher pressure on<BR>
the pre-turbine side is vented to the post-turbine side, therefore<BR>
its logical to interpret that the EBP must be higher. These days its<BR>
easy to measure and when i get time I'll set up a pair of gauges<BR>
to report what I find.<BR>
<BR>
Its common sense to some major degree, if the wastegate needs to<BR>
be opened and stays open to dump pressure one would expect the<BR>
pressure post-turbine to be higher - for some other posters to suggest<BR>
it might be the opposite is ludicrous, sure the turbine will spin<BR>
down a tad *but* if the need is still there to bypass the turbine<BR>
then the region post-turbine must be seeing pressures that exist<BR>
on the pre-turbine side as the wastegate is open and this must<BR>
be higher as its not all going through the damn turbine &lt;sigh&gt;<BR>
<BR>
I also think there is tradition in seeing the wastegate as a control<BR>
(proportional) element when its really more akin to a digital<BR>
relief valve, hence is discontinuous in its reponse to dumping<BR>
exhaust energy and therefore should be logical to control the fuel/air<BR>
more precisely some time before its combusted. Historically this has<BR>
been difficult and more expensive, these days it should be much<BR>
easier if people can intellectualise the control systems<BR>
algorithms and that was the impetus for this thread in the first<BR>
place,<BR>
<BR>
;-)<BR>
<BR>
<BR>
rgds<BR>
<BR>
mike<BR>
<BR>
</BLOCKQUOTE><BR>
<BR>
for all this conjecture why not go look at a chrysler draw thru system ???you have a Throttlebody then turbo then the engine. it keeps the turbo spooled quite nicely. and you wont have to worry about turbo backpressure. my 2cents cuase ive been watching this whole thing and shaking my head. </FONT></HTML>

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