Date:         Wed, 27 Nov 2013 06:33:47 -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:  <BLU177-W360ADD5FC57F1C8EA104C1E0EF0@phx.gbl>
Content-Type: text/plain; charset=ISO-8859-1

A member pmailed results of some testing last night:

"...just checked a spare ISV using DC, operation is proportional to applied
voltage.  Starts opening somewhere around 3 VDC, fully open somewhere
around 8 VDC."

So we can treat it as if it's a dc motor operating against spring
pressure.  Keep in mind that we are feeding it a modulated signal, so even
at 11.5 v and a 50% duty cycle, the valve will operate as if it's receiving
a constant 5.75 v steady signal(11.5 x 50%) and will not be fully open.



So lets crunch some numbers to see what's going on during cranking.  I'm
going to calculate the power (watts) going to the idle valve during cold
idle and during cold cranking and compare.

First, let's calculate the resistance that the idle valve provides so that
we can determine current flow for different voltages.  We know that at 9v
and 29.4% duty cycle the valve draws .157 A, so we can get amperage @ 100%
duty by dividing .157/29.4% = .534 A.
Resistance = Voltage/Current = 9v/.534A = 16.85 ohms of resistance

Now that we know the resistance of the valve, we can calculate the current
flow and power being supplied at different voltages and duty cycles.

Cold Idle:
At cold idle, the ICU is outputting 10.5 volts with a 25% duty cycle.  The
current draw at 100% would be:
Current = Voltage/Resistance = 10.5v/16.85 ohms = .623A
Now calculate the power:
Power = Voltage x Current = 10.5v x .623A = 6.54 watts
Finally, adjust for the 25 % duty cycle to see the power being sent to the
idle valve during cold idle:
6.54W x 25% = 1.64 watts during cold idle

Cold Cranking:
At cold cranking, the ICU is outputting 6 volts with a 55% duty cycle.  The
current draw at 100% would be:
Current = Voltage/Resistance = 6v/16.85 ohms = .356A
Now calculate the power:
Power = Voltage x Current = 6v x .356A = 2.14 watts
Finally, adjust for the 25 % duty cycle to see the power being sent to the
idle valve during cold idle:
2.14W x 55% = 1.18 watts during cold cranking


This was quite surprising to me; the power going to the idle valve is less
during cold cranking than during fast idle.  I was thinking that it would
receive more power during cranking to get a good supply of air & fuel into
the engine to really get things going.  Then I thought maybe it's trying to
restrict the air a bit to richen the mixture, but the ECU knows when the
engine is cold cranking and fuel mixture is one of its main jobs.  Maybe by
restricting airflow, it effectively lessens the compression ratio to make
starting easier.  Or maybe I'm just overthinking this and it's trying to
put out the same airflow as cold idle but isn't able to accurately make up
for voltage drop during cranking.

I think that it would be best to aim for the same airflow for both cold
idle and cold cranking and adjust as real world results suggest.


I think later this weekend I'll work on building an Arduino based
tachometer using the Hall sensor output.  That would be a good first step.


Brett


On Tue, Nov 26, 2013 at 7:23 PM, James <jk_eaton@hotmail.com> wrote:

> I think having this data is great - I could pretty much write the
> progamming now, if I make a guess/assumption about the ISV's behavior at
> speeds above idle.   ( Which one could do, as the amount of air being
> admitted is only a small fraction of the total air intake when the
> waterboxer is working.)  Thanks to those who took the time to make the
> measurements.
>
> I wonder if the jump to 55% duty cycle is really to compensate for lower
> available voltage while starting, or to aid starting itself?  I guess I can
> better rephrase my question as, does the ISV open more at higher voltages
> (i.e., is there any connection between the amount of air it lets in and the
> voltage applied to it?).  If the ISV were a motor, of course there would
> be, but I wonder if it is more like a pneumatic valve - and the pneumatic
> valves I'm familiar with don't open more with higher voltages, as long as
> the minimum voltage is met.  (I teach pneumatics as well, using German
> Festo equipment, and consult on pneumatic factory equipment.)  Pneumatic
> valves are rather 'digital' in operation - either they're on, or off, with
> no intermediate positions.  The vibraion the ISV produces reminds me of a
> Festo pneumatic valve in 'flutter' operation.
>
> The PIC microcontrollers I teach all have 10 bit (or 1024 step) PWM, so
> having a fine control over the ISV wouldn't be a problem, if we wanted
> something with a finer control than the 256 step.  For a cleaner design and
> possibly more reliability I'd avoid a separate PWM controller, if I could.
>
> James
> Ottawa ON
> '91 Westfalia Weekender
>
> > Date: Tue, 26 Nov 2013 08:10:00 -0800
> > From: brettn777@GMAIL.COM
> > Subject: Re: Arduino and Vanagons
> > To: vanagon@GERRY.VANAGON.COM
> >
> > We have some data to work with!  One of our members has generously put in
> > the time and effort to gather most of the readings we need.  Here is what
> > we have so far:
> >
> >     *Duty Cycle Under Various Engine Conditions*
> >
> >   *Condition* *Duty Cycle* *Peak Voltage*
> >   Engine Cold, Key On, Engine Off 34.0% 9
> >  Engine Warm, Key On, Engine Off 29.4% 9 @ 157 mA  Engine Cold & Starter
> > cranking (45 F) 55.0% 6
> >  Engine Cold & Idling 25.0% 10.5
> >  Engine Warm & Idling 20.5% 10.5
> >  Engine Warm & Running 2000 RPM
> >
> >  Engine Warm, WOT Signal
> >
> >  *Duty Cycle Under Various Load Conditions*
> >
> >  *Load* *Engine Cold* *Engine Warm*
> >  None 23.0% 20.5%
> >  AT in Gear 25.5% 23.0%
> >  PS 27.0% 25.0%
> >  AT in Gear & PS 30.0% 27.0%
> >
> >
> >  *Miscellaneous:*
> >
> >  PWM Frequency constant at 148.2 Hz
> >
> >
> >  Yellow Wire (11/ST1) PWM Power to Idle Stabilizer Valve
> > >
> >  White Wire (4/ST2) Ground Connection? (Needs to be confirmed)
> >
> > From this we can conclude:
> > **The idle air valve is very sensitive.  A 7% increase in duty cycle is
> > able to overcome the combined loads of AT in gear and PS at full
> pressure.
> > The built-in PWM output on the Arduino only has 256 settings, which would
> > give use increments of 0.4% in the duty cycle output.  This would work,
> but
> > I think that there would be a noticeable unevenness in idle speed.  Not a
> > big deal, it just means that we will need to use a timer interrupt to
> gain
> > fine control over the duty cycle(the percentage of "on" time of the
> pulse)
> > of the PWM.  It's just not as fun and easy as using the built-in PWM
> > functions.  I'll explain interrupts in more detail when we get to the
> > programming stage, but it basically is just a way to grab the computer's
> > attention and make it suspend its current operations while it attends to
> a
> > time-critical event, like a new hall sensor pulse coming in.
> >
> > **Most of the time, the duty cycle is pretty low, around 25%, but that
> > changes during starting.  While the engine is cranking, the duty cycle
> > jumps to around 55%.  When I first saw this figure I thought, "Wow, it's
> > really increasing the airflow a lot while the engine is cranking."  But I
> > don't think that is true because the current draw from the starter motor
> > drops the available battery voltage considerably.  The stock ICU output
> > voltage drops from 9v with engine not running to 6v with starter
> cranking.
> > I think the dramatic increase in duty cycle is not for increasing
> airflow,
> > but rather to compensate for the expected voltage drop during cranking.
> >
> > **The ICU apparently makes no attempt to send a fixed voltage to the idle
> > air valve.  With engine off, it sends 9v.  With engine running, it sends
> > 10.5v, which matches the increase in voltage from the alternator.  With
> > engine cranking, the output drops to 6v, reflecting the battery voltage
> > drop under the heavy load of the starter.  For running conditions, we
> don't
> > need to worry about the output voltage level because it will be
> > automatically compensated for by the engine speed feedback.  But for
> > starting, we could have the Arduino measure the voltage coming from the
> > battery and calculate the appropriate duty cycle change to have better
> > control over the airflow.
> >
> > **The idle air valve draws 157 mA when supplied with a 9v 29% duty cycle.
> > This translates to a 535 mA draw @ 100% & 9v or 4.8 W of power.  The
> final
> > drive transistor in our circuit should be chosen to handle 1A of current
> to
> > assure durability.  Lots of options here.
> >
> >
> >
> > What we're still looking for:
> >
> > What happens above idle speed?  Does the idle air flow shut down, or stay
> > at some predetermined level?
> > What happens at Wide Open Throttle?
> > What does the Hall sensor output signal look like?  I haven't found
> > anything definitive on the internet.  There are hints that it is a square
> > wave and that the peak pulses are up near battery voltage.  I would like
> to
> > know peak and base voltages and confirm that it's a clean square wave.
> > Also, has anyone taken apart an idle air valve?  Is it just a motor
> > operating against a spring?
> >
> >
> > Brett
> >
>
>
>



--
Brett in Portland, OR
"Albert" '82 VanaFox I4 Riviera