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Date:         Tue, 26 Nov 2013 20:59:06 -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

Just want everyone to know that Neil has sent a nice set of photos and measurements of the ICU. As I suspected, each cluster of blades matches a standard relay socket. Nice. Neil also stated that there may be a different pinout for Canadian models. So no need for everyone to go out to the garage and take photos & measurements. Unless you want to; a good excuse to crack open a beer or something.

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


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