Date: Thu, 14 Nov 2013 17:24:56 -0800
Reply-To: Brett Ne <brettn777@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Brett Ne <brettn777@GMAIL.COM>
Subject: Re: Arduino and Vanagons
In-Reply-To: <CAFNeVpHhk7aD5cp+6uiPAiqPKXQ3an1e3r7ET1ZNGNcvbsBp8Q@mail.gmail.com>
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Wow! What a nightmare of a board to troubleshoot and service...I am so
thankful that we're living in a time of cheap and plentiful
microcontrollers. I believe that you guys are right; that the inputs from
the PS and AC allow for an instant boost to avoid lag time. By using a
microcontroller, I think that we can monitor and maintain idle speed by
watching engine speed alone and have it perform as well or better than a
stock ICU. At an idle speed of 850 rpm, if I'm calculating correctly,
there will be about 28 peaks from the Hall sensor per second. The
microcontroller wouldn't break a sweat calculating engine speed and
adjusting the PWM duty cycle by measuring the time lapse between each of
those peaks. If we play it a bit more conservatively and measure the time
it takes for 8 pulses to pass, we'll get less jitter in the readings and
still be able to update the PWM duty cycle 4 times a second.
Here's what I propose(we can always fall back & use all the inputs if we
need to):
2 analog inputs: coolant temperature & Hall sensor
1 digital input: throttle valve switch
1 PWM output: idle speed stabilizer valve
The ICU adjusts the PWM signal to the idle air valve about 4 times a second
to maintain an idle speed of about 850 rpm. If the engine is cold, the
target rpm is set at, oh, say 1100 rpm, and as the engine warms up, the
target rpm is gradually decreased until it reaches 850 rpm. The
microcontroller keeps doing that until the throttle valve switch indicates
that the throttle is no longer closed, whereupon the PWM duty cycle reverts
to a set level that approximates 850 rpm at closed throttle, and maintains
that air flow until the throttle valve switch indicates that the throttle
has been released and jumps back into action trying to maintain idle speed.
I think that it would work, and the simplicity would be quite pleasant.
Brett
On Thu, Nov 14, 2013 at 2:14 PM, Tom Carchrae <tom@carchrae.net> wrote:
> Another WAG; the power steering pump, etc (which is not on my van) are
> probably to avoid low engine revs before they happen. Perhaps the impact
> on engine speed happens so quickly that they need to pre-empt it by
> checking sooner?
>
> That board does not look too bad - no custom PLC or IC evident. Those
> chips are just amplifiers http://www.futurlec.com/Linear/LM2902N.shtml
>
> Tom
>
>
>
>
> On Thu, Nov 14, 2013 at 2:09 PM, Neil N <musomuso@gmail.com> wrote:
>
> > This is a WAG but is it b/c the ICU is only using hall input as a
> > measure of a running engine and no more? And-or the ICU will react and
> > control the idle stab. valve faster using switches than it would using
> > engine RPM drop as a reference? Interesting question though.
> >
> > Mark: Thanks. The guts of the ICU look fairly involved (though I
> > appreciate that the electronics are somewhat old school given that
> > IC's aside, you can actually see all the caps, resistors etc.)
> >
> > image
> >
> > http://images.thesamba.com/vw/gallery/pix/1111642.jpg
> >
> > Neil.
> >
> > On 11/14/13, Brett Ne <brettn777@gmail.com> wrote:
> >
> > > Okay, now it's time for a dumb question: why do we need input signals
> > from
> > > the power steering pump and air conditioner?
> >
> >
> >
> > --
> > Neil n
> >
> > Blog: tubaneil.blogspot.ca
> >
> > '88 Westy http://tinyurl.com/c8rlw6p
> >
> > '81 VanaJetta 2.0 "Jaco" http://tubaneil.googlepages.com/
> >
> > Vanagon VAG *Gas* inline-VR Engine Swap Group:
> >
> > http://tinyurl.com/d7gd5ej
> >
>
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