Fuzzy Logic

Do I remember correctly that everyone is advised to steer clear of anything with Fuzzy Logic.

I'm looking at the GReddy PRofec A and it looks like its the nuts, but  an alarm bell went off in my head when the blurb mentioned Fuzzy Logic. (isn't that phrase copyrighted by Mitsubishi?)

Is there anything wrong with this product or Fuzzy Logic. It is a Greddy/Trust product after all.

Regards,

Alex

(PS I'm 6ft and 11.5 stone so I'm not too much of a burden to the motor! re: I'm too fat!) :wink:

Hi...

As it happens I was searching the MKIV.com mailing list last night and one of the mails commented that they should update their site as they were now of the opinion that fuzzy logic was okay with the Supra.

Gavin  

I looked into this issue a couple of years ago. My curiosity was aroused because I had just bought an HKS EVC-IV for my own MKIV.

The general concensus, on the MKIV.com site, was that the HKS EVC-IV "fuzzy logic" boost controller was not suited to the MKIV. Some people also mentioned that fuzzy-logic units, per se, were entirely unsuitable and recommended the fitment of a non fuzzy-logic alternative.

However, my own study into this matter specifically concerns the HKS EVC-IV.

One of the procedures in setting up the HKS EVC-IV, following the actual fitment, is to have the unit "learn" your stock boost-curve.

This is done by placing the unit in a certain setup mode and then accelerating the car, under full power, from about 2000 rpm. The unit will detect where boost starts, through to where boost begins to tail off. Then it stores this information into it's memory.

I remember reading an article which said the reason why the HKS EVC-IV fuzzy-logic unit was unsuitable, was that the unit didn't know there was a second turbo about to come on stream. The article went on to say that, because of this, it "confused" the fuzzy logic of the unit... in the sense the unit would think the boost curve, provided by No1 turbo, was the entire turbo boost-curve.

Immediately, the issue begged the *big* question in my mind, which was: What was it, exactly, that was telling the EVC-IV that boost was tailing off prematurely?

You see, ordinarily the EVC-IV would decide that completion of the boost-curve had occured, i.e. your turbos had reached maximum stock boost, when boost stopped rising and/or began to dip.  

Now here's where I was most confused: because the total sequential boost-curve of the MKIV... from No1 turbo first taking exhaust from all 6 cylinders, through to No1 and No2 turbos operating in parallel... is a *very* smooth and continually *upward* surge in boost.

A large part of the reason why this is so, is because, from fairly low-down in the rev range, No2 turbo is "pre-spooled".

What that means is: an exhaust bypass valve opens from around 1800 rpm, to allow a small amount of exhaust to flow through No2 turbo in order to get it spinning *before* it comes on stream. Obviously, this ultimately means No1 turbo gives a tad more lag and makes a little less boost than it would do *if* pre-spool did not take place. However, having No2 turbo actually spinning at quite a high speed, as it comes on stream, avoids creating a big dip in boost (not to mention the increased mechanical stresses) that would occur as a near stationary No2 turbo suddenly came on line.

Upon studying the fitting instructions, I noted that if you were to fit the EVC-IV valve controller exactly as HKS recommend, it was clear that pre-spool of No2 turbo would *not* take place.

The reason why this is so, is because the piping instructions clearly tell you to connect the exhaust bypass valve in *parallel* with the wastegate on No1 turbo. In other words, the exhaust bypass valve, instead of opening at around 1800 rpm in order to pre-spool No2 turbo, will remain shut. And will only open at the same time as the wastegate, i.e. at maximum boost, which obviously occurs much higher in the rev-range.

Under such conditions, the boost curve would initially give a strong rise, then, at around 3500 rpm, there would be a distinct boost dip (as a relatively stationary No2 turbo came in) followed by a continuation of the rise in boost.

This boost dip is not something that can be seen on an ordinary dash-mounted boost gauge. It can only be detected by data-logging the boost curve with a suitable electronic measuring setup.

Problem was, the fuzzy-logic of the EVC-IV was easily fast enough to detect this dip; whereupon the unit would simply decide that was it, end of boost curve, and promptly store the results into it's memory.

On discovering this, my curiosity was aroused yet further and I sought to find an answer to the big question of why HKS would recommend for their EVC-IV to be connected in such a way as to screw up its operation?

However, as this aspect of the issue has led to much contention from certain quarters, I'm not going to say anything more about that in this forum.

Suffice to say, I would speculate the reason why the information on the MKIV website has been recommended for change, is because people have steadily realised what I too realised from my own study. Namely, that it was not the fuzzy-logic aspect, per se, that was causing the problem. It was the way the units were being plumbed in.

Yours,

J

(Edited by Ash at 1:29 pm on June 16, 2001)