Date: Tue, 26 Nov 2013 08:10:00 -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: <CAPAEXFc6Gx9zrnzNVsc1j75MOCwFjJYS8HQ_-H5fAUVsqVt_qw@mail.gmail.com>
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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
On Wed, Nov 20, 2013 at 1:41 PM, Brett Ne <brettn777@gmail.com> wrote:
> Before we can go any further with this project, we need those
> measurements. I'm not interested in investing time, materials, and money
> into a project if it's based on assumptions and guesswork. My Vanagon
> can't be used because it doesn't have the Digifant injection system.
>
> So, we need either:
>
> Someone with an oscilloscope or a digital multimeter w/pwm functions who
> has access to a Vanagon with Digifant FI that has a healthy ICU as well as
> power steering and AC. Bonus points if it's an automatic.
>
> Or,
>
> Someone in the Portland Metro area with a van that fits the above
> description who would be willing to work with me for a couple of hours. I
> do have an oscilloscope and could take the measurements.
>
>
>
>
>
>
> On Wed, Nov 20, 2013 at 1:23 PM, Brett Ne <brettn777@gmail.com> wrote:
>
>>
>>
>>
>>
>>
>>> Assuming a properly functioning engine and IS system, if one measured
>>> current draw at the ISV, loads on and off, at idle, cruising speed and
>>> WOT, could they get a really good idea of when the ISV is used? (valve
>>> changes position). Maybe a graphing meter would be useful in this
>>> regard?
>>
>>
>> Current draw or voltage measurements would be kinda okay. They should be
>> proportional to the duty cycle, but again, knowing the duty cycle tells you
>> exactly what the control unit is doing and is much preferred over indirect
>> measurements.
>>
>>
>>
>>> My guess is that at idle, no loads (PS, AC) the valve is
>>> closed. Or.....
>>>
>>
>> ...or partially open. We can all guess until we're blue in the face, but
>> if we want to create a re-engineered control unit that solidly replaces the
>> old one, we have to establish the behaviors of the old one first
>>
>>
>>>
>>> Isn't the ICU basically taken out of the picture any time the throttle
>>> is just off idle or at WOT? (throttle enrichment switch activated or
>>> not).
>>>
>>
>> Maybe, maybe not. Maybe the idle throttle opens fully under full
>> throttle to help the engine breathe better. I just don't know.
>>
>>
>>>
>>> Did you find the correct "Vanagon" Digifant pro training manual
>>> online? If not, can send more images. There may be some useful in
>>> there for your needs.
>>>
>>
>> No, I haven't, though to be honest, I haven't been looking. Typically
>> training or repair manuals may give enough info to identify a faulty part
>> but don't give all the details on how that part interacts with all the
>> other parts of the system.
>>
>>
>>
>> --
>> Brett in Portland, OR
>> "Albert" '82 VanaFox I4 Riviera
>>
>
>
>
> --
> Brett in Portland, OR
> "Albert" '82 VanaFox I4 Riviera
>
--
Brett in Portland, OR
"Albert" '82 VanaFox I4 Riviera
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