Throttle Plate Control

Lawrence S. Harris III lharris at crl.com
Mon May 15 01:30:03 GMT 1995


> > I'm currently designing a rev limiter that works by cutting out the
> > spark when the revs exceed a certain limit. I was thinking of
> > progressively cutting out more sparks as the revs go over a certain
> > level to reduce power (eg at 7000 rpm) then all the sparks (eg
> > 7500 rpm) IE:
> In the Bosch Automotive Electronics Handbook they talk about rev 
> limiting by chopping spark, but they use a hysteresis of 80RPM ie
> spark disabled at 7580, and reenabled when revs drop to 7500.  This 
> way you won't skip too many sparks so you won't get a huge backfire.

I'm surprised that with an EFI system that people wouldn't consider 
cutting fuel rather than spark.  Of course hysteresis as mentioned above 
would be a must.  I would guess with too little or no hysteresis, that a 
really lean condidtion may occur as the computer would kind of half 
heartedly feed fuel right around the rev limit.  Sending unburnt fuel out 
into the exaust system seems quite nasty.  Lots of drag racers use this 
technique with a two stage rev limiter where they sit on the line 
limiting the revs on their "launch" RPM.  Some cars will sit on the line 
backfiring through the exaust terribly.  This can only lead to thoughts 
of "There's got to be a better way".

Has anyone out there played with cutting fuel rather than spark?  If no 
one uses this method, why not?

Thanks
Larry Harris  lharris at crl.com (pref) or lharris at msm.mea.com
'86 Mustang LX 5.0 Coupe (149K)  '82 BMW 635CSi Euro (121K)
Meyers Tow'd Dune Buggy (1776cc) '83 Toyota Tercel (180K)




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