Test Benches

[John Lamb]

Just thoughts:
Ok, here's what we do in the industial process control world to prove in
a new PLC control systems: We create a plant model (which in this case
would be the car)on a PC using ViSSim or Simulink, then we interface the
plant model to our control system so we can exercise it in a psuedo-real
world enviroment for debugging and tuning loops etc.
You can buy one of these PC hardware I/O boards for $200-$300. You can
get ViSSim personal student copy pretty cheap. You can make the
plant(car) model as simple or as sophisticated as you want. The wiring
is minimal, just to the I/O board--no pots etc.
JL


"Gregory A. Parmer" wrote:
> 
> A "test bench" is nothing more than a way of faking the ECM into believing
> it's in a running car when it's really not. With a few variable resistors
> (pots) you can see how twiddling inputs affect the ECM even in situations
> that'd be almost impossible to see in real life. Despite having the
> formula in front of me (see the FAQ or archives), my "clue" light didn't
> come on that injector dwell is *much* more closely related to MAP than TPS
> until after I experimented on the bench.
> 
> My super low tech test bench consisted of the harness I intended to
> install, some pots, and a variable speed drill (!) for spinning the dizzy
> to any desired RPM. Injector dwell was read with an old fashioned points
> dwell meter.
>  http://www.aces.edu/~gparmer/efi/harness.jpg
> 
> Bruce (and others too) immediately made mine look downright foolish as he
> graduated to something described at
>  http://www.diy-efi.org/gmecm/projects/ecm_testbench/
> The description there is quite detailed, BTW.
> 
> This works great for verifying that a set of conditions reacts as you
> expect based on your research/guesses, but...
> 
> The next level would be to log data from a running vehicle, then use that
> log file as input to a device which would re-create the signals seen in
> actual on-road conditions. Wondering if your TCC settings may be
> contributing to tranny failures? Verify it safely on the bench!
> 
> It'd be even more useful for cycling through a known set of inputs to see
> how changes affect the outputs. In short, it would make reasonably
> thorough scientific analysis possible.
> 
> One weekend a few years back I got the idea that I could use the LPT port
> and some RC circuits to generate the needed analog (and digital) signals
> based on a log file. I went as far as to prove I could modify an old Boca
> External Modem and that I could possibly learn enough Visual Basic to do
> it before I remembered how much I hated Circuits 101.
> 
> That weekend's hardware modification efforts are reflected in pics at
>  http://www.aces.edu/~gparmer/efi/testbench/
> 
> If you're interested in building TestBench Generation III and like the
> modified modem concept, I'm sure I could round up some more...if you've
> got a better idea, please go for it and share your results.
> 
> -greg
> 
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