Re: Got VSS . . .

[rrauscher@nni.com]

grumpy, show this to doc, if he's still thinking about
brooms we'll need to get him outa' the holding pattern.
Or maybe off of the '727 onto a '747, they are so much
easier to fly. . . 



The IAC is a complex little beast, no doubt about it. I once
figured the whole thing out, then got busy and wrote very
little of it down.

So, most of this is from memory. . .

(There should already be something in the archives about
the idle control portion. Feb/March?).

Whenever IAC steps are calculated, they go into a ram
location. This location can have sudden changes where
it can go from say 50 steps to 10 steps. To smooth the
IAC operation, this value is then lag filtered into/with
another ram location that is used to control the IAC.

There are also delay values used to slow the action of
the IAC.

The lag filter coefs control how fast the IAC responds
to the calc'd changes. They are at:

LoVss: 0x5e4 (note that a larger val causes faster action)
MdVss: 0x5e5
HiVss: 0x5e6

Decay delays are at (in secs/5):

LoVss: 0x5e7
HiVss: 0x5e8

The Vss thresholds are at (in mph):

LoVss: 0x5ec
HiVss: 0x5ed

(The MdVss val is between these two).

The IAC opens as the TPS value goes up. This is referred to
as the 'throttle follower'. It can improve top end performance,
along with 'hanging' the r's for easier shifting. Also slows
the return to idle on a throttle blip.

The amount of IAC follower is controlled at (in percent of tps):

In pk/neut: 0x5f0
Not pk/neut: 0x5f1

Max follower (in steps): 0x5f2

Naturally, all for the '747.


BobR.

Did you know that upon the engine stopping, the IAC immediately
goes from it's current position to the retract pulse position
(0x5ce), to zero, to the park position (0x5c2). Seems to be an
IAC position calibration each and every time the engine stops.


>Owww, stop it
>Grumpy
>   Doc is just ROFLHS, fell on Sleepy and he's talking about brooms again
>
>
>Subject: Re: Got VSS . . .
>
>
>> It's called "shift anticipation".
>> TK
>
>> > Adding VSS has definitely changed the behavior of the system.  The most

>> > notable effect is adding a "dashpot" effect.  That is, when the car is

>> > still moving, the engine speed is held higher than idle speed (in
>neutral,
>> > foot off throttle) which then settles down to idle after stopping.  The

>> > problem I have is that this is about 2000 RPM (2500 RPM cold) on my
>> > system.  I'm hoping there is an IAC setting(s) to control this (perhaps

>> the
>> > IAC park position?).  The car wants to run way right now.  Does anyone

>> know?
>
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