DIY-WB Output Voltage Scaling

Len Sabatine sabatine at epix.net
Sat Aug 25 19:58:58 GMT 2001 

     Right on , Simple, for OL Tuning and CL Monitoring. One Answer.

     My reference about risk is in relation to the use of the WB input
     to on the fly, modify the PCM's expected NB response to AFR
     in real time, as a relationship. Use in this scenario is not that simple.
     A GM PCM's "expected" NB responses in CL may not line up with
     the WB's responses , fuel curve wise, without additional HW and
     some application software to operate a piggy back system that can
     default  to NB operation for engine protection. The's much to be
     considered..
     Application Software isn't that roll hanging by the commode either.
     What the PCM wants and what we want can be difficult to achieve
     without the controller's source code or use of stealth external devices.
     Another Answer of which I'm sure there's many What If's.
     I clearly see what Mr. Roe is thinking.
     Len

>One answer is very simple.
>Use the WB to tune your car for open loop.
>Install where the NB's are and simply keep it hooked up so you can keep
>an I on it from time to time. This is not that risky and people/cars
>have been running this way long before the electronics were there.
>JL
>
>Len Sabatine wrote:
> >
> >      I believe your cautions here are well placed. Entering into
> >      WB territory could be stepping into a very large can of worms,
> >     depending upon what an individual is going to use the Diy-WB
> >     tool for. In the hands of experienced tuners , as a monitor,  is ,
> >     a basic need. Using this tool to interact directly with and modify
> >     a PCM's expected NB routines is another matter . These operations
> >     need to be carefully tested and developed, IMO.
> >     The age old theory vs practice is especially important in this 
> scenario.
> >     Len
> >
> > >Now that the WB project is off the ground, a potentially
> > >even bigger problem looms: How is it best used?  Here
> > >are some thoughts about that.
> > >
> > >Say I'm changing fuel injector pulse width (changing the
> > >fuel added to a volume of air).  Lets say I make a 1/10 ms
> > >change.  I would expect the output format of my WB unit
> > >to change a certain amount.  If I keep making 1/10 ms
> > >changes (same amount of air), I would expect the WB
> > >output format to keep taking equal sized steps across
> > >the lean to rich scale.  In other words, a linear response.
> > >
> > >I would be annoyed if the WB output showed a huge
> > >step in the lean area, but a small step in the rich area,
> > >for the same size change in injected fuel.
> > >
> > >If you agree with the above, then how might that be
> > >achieved?  The WB output voltage curve faithfully tracks
> > >the sensor, with a continuously changing slope and an
> > >extra bend at stoich.
> > >
> > >What about a direct A/F readout?  The very same
> > >amount of fuel change required to make one A/F division
> > >change at the rich end, will make TWO A/F division changes
> > >at the lean end.  Thats because A/F is NOT directly
> > >proportional to the change in fuel.  A/F has been a handy
> > >handle in the past, but just what IS the linear tuning
> > >function I (and perhaps you) want?
> > >
> > >I have cooked up an output display for the WB project
> > >which (I hope) displays a LINEAR input fuel change to
> > >output display change.  Just how does this work?
> > >
> > >Imagine you have this box of air, and you add a drop of
> > >fuel, say 1 % or 1/100th by weight.  Then more and more
> > >drops.  The ratio of fuel to air (by weight) is increasing
> > >LINEARLY with the number of drops.  Just plot 0/100,
> > >1/100, 2/100, 3/100, 4/100 against 0, 1, 2, 3, 4 etc drops,
> > >and you get a nice straight line.
> > >
> > >So what about A/F?  WAIT A MINUTE, the above is a
> > >description of FUEL/AIR, NOT AIR/FUEL.  F/A is the
> > >inverse of A/F.  OK, lets plot the inverse series,
> > >100/0, 100/1, 100/2, 100/3, 100/4, 100/5  etc against
> > >the number of drops of fuel.  Gee, the first number is
> > >infinity, then 100, then 50, then 33 1/3, 25, etc.  This
> > >has a TERRIBLE curve to it, not linear at all.  When
> > >we get into the practical range of 100/5 to 100/10, the
> > >curve is still pretty bad.
> > >
> > >So from the perspective of  tuning aid, what is the
> > >answer?  Here is my proposal.  I have this moving
> > >bar graph of LEDs which is perfectly linear, as
> > >described above.  Along it is a scale of A/F.  Since
> > >A/F is NOT linear, the A/F divisions are twice as far
> > >apart at the rich end, compared to the lean end.  We
> > >have linearity for tuning AND an A/F readout.  Oh
> > >yea, the sensor has a different level of output on
> > >each side of stoich.  That's been taken care of too.
> > >
> > >Is this a good solution?  I'm asking you.  The first
> > >display is already operational at my house.  A
> > >couple of you already have a picture; sorry, I don't
> > >have a scanner.  The sensor limits are not centered
> > >around stoich, so the scale is lopsided.  If we use
> > >a practical operating range of 19:1 to 10:1, the rich
> > >end from stoich will be twice as long as the lean
> > >end.  OR, we could make the scale twice as
> > >responsive at the lean end to equalize the length,
> > >but forget about linear tuning response from end to
> > >end.  Your thoughts please.  This display does not
> > >prevent you from attaching any other output format
> > >devices you like.
> > >
> > >For those interested in the nitty gritty details of this
> > >display device, write me and I'll return the preliminary
> > >(lengthy) writeup.  If you would like to get a better
> > >feel for this, get out that WB output voltage vs A/F
> > >curve.  Calculate the inverse of A/F (divide 1 by the
> > >A/F), and plot these numbers (F/A) against the
> > >voltage.  You will get a straight line, with a bend at S.
> > >The sensor is LINEAR after all, if we could fix that
> > >bend at stoich.  The display design fixes that too.
> > >
> > >Bruce Roe
> > >
> > >
> > >
> > >On Fri, 24 Aug 2001 19:43:50 -0500 jll at edge.net (John Lamb) writes:
> > > > Are you saying that the Display has an embeded PIC that allows you to
> > > > program a segmented curve fit?
> > > > That's what is needed here to linearize the output.
> > > > Another method is to use the an A/D to address memory locations that
> > > > linearize the output.
> > > > Sorry if this is old discussion.
> > > >
> > > > JL
> > > >
> > > > Peter Gargano wrote:
> > > > >
> > > > > It should be pointed out that the current incantation of the
> > > > > DIY-WB unit has a non-linear voltage:AFR transfer function.
> > > > > The actual transfer function is described here:
> > > > >
> > > > >   http://www.diy-efi.org/diy_efi/projects/diy_wb/
> > > > >
> > > > > See "Output voltage/AFR reference". A graphed version is here:
> > > > >
> > > > >   ftp://ftp.diy-efi.org/incoming/DIY_WBafrVolts.gif
> > > > >
> > > > > The curve can be thought of as a series of straight lines
> > > > > for simple interpolation, but it means that a simple digital
> > > > > panel meter connected to the WB output with a simple scaling
> > > > > circuit will not be able to show accurately a large range of
> > > > > AFR ratios. This is why I suggested the Jaycar kit/Silicon Chip
> > > > > kit with 16F84 PIC and 3 digit display that comes with source
> > > > > code that could be modified to scale the DIY-WB's output to the
> > > > > above transfer function.
> > > > >
> > > > > If you're logging the DIY-WB's output and post-processing the
> > > > > logged voltage, then this isn't too much of a problem.
> > > > >
> > > > > For the DIY list, here's the information I posted to GMECM
> > > > > yesterday.
> > > > >
> > > > > Product Name:        DIGITAL FUEL MIXTURE DISPLAY KIT
> > > > > Catalogue Number:    KC5300
> > > > > Price:               AU$62.95  (less than US$35) + freight
> > > > >
> > > > >   http://www.jaycar.com.au/home.htm
> > > > >
> > > > > Peter.
> > >----------------------------------------------------------------------- 
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