Date: Wed, 27 Nov 2013 15:38:50 -0500
Reply-To: Tom Buese <tantonbz@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Buese <tantonbz@GMAIL.COM>
Subject: Re: Arduino and Vanagons
In-Reply-To: <52964c11.c5a1ec0a.7427.fffff362@mx.google.com>
Content-Type: text/plain; charset=ISO-8859-1
Hang in there David! Good to see your input!
Cheers,
Tom
On Wed, Nov 27, 2013 at 2:45 PM, David Beierl <dbeierl@attglobal.net> wrote:
> At 09:33 AM 11/27/2013, Brett Ne wrote:
>
>> A member pmailed results of some testing last night:
>>
>
> Ok, I'll 'fess up. I'm the guy who's been supplying numbers for
> this. I've been going through a very rough patch over the summer and
> not wanting to talk to anybody, but at least for the moment this and
> some other things happening here are bringing me out of my hole to some
> degree.
>
>
> "...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.
>>
>
> Here are some better numbers for the spare valve, which is a bit
> sticky at the extremes (maybe they all are, I don't know):
>
> Resistance 4.0 ohms.
>
> Impedance at 150 Hz (sine wave) using a signal generator with 50-ohm
> output: 1.0 Vrms --> ~25 mA so ~40 ohms.
> Impedance at 1000 Hz ditto: 1.0 Vrms --> ~9 mA so ~110 ohms.
> My generator couldn't maintain a square wave while driving the valve
> because of its higher output impedance (result was a set of spikes
> with smoothly declining tails) but the numbers at 150 Hz were similar.
>
> I may be able to hook up an amplifier to the generator and actually
> drive the valve at operating levels, but in the meantime, using a DC
> supply with max 1300 mA output:
> On increasing voltage valve jumps open slightly at about 2.4V / 500 mA.
> On decreasing voltage valve closes at about 1.5V / 325 mA.
> On suddenly applying 6.5V / ~1300 mA valve snaps fully open.**
> On suddenly applying 5.8V / ~1100 mA valve does not fully open.
>
> **The open-circuit voltage is probably somewhat higher since I'm
> driving the supply at its current limit here.
>
> 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
>>
>
> Actually you can't extrapolate to DC this way because the valve is
> highly inductive. As your duty cycle approaches 100% the valve
> effective impedance will get closer and closer to its four ohm
> resistance. If I can get the amplifier hooked up and delivering some
> approximation of a square wave I'll be able to vary the duty cycle
> directly and provide more numbers.
>
> Also bear in mind that the 6V/9V/10-11V numbers I supplied for peak
> voltages in the system while operating a) are very approximate,
> eyeballed off a tiny pocket oscilloscope screen at two volts per
> division and b) need to be increased by about a volt each because the
> baseline was about a volt negative. The ~10-~11 range was
> immediately after starting vs after running a few minutes; probably
> because B+ was recovering after extended cranking with the ignition
> disabled.
>
> Vrms and duty-cycle numbers are from a fancy 4-1/2 digit Fluke meter
> with flat response well above our frequencies of interest and IIRC
> four measurement cycles per second. If I indicate a ~n.whatever on
> one of those readings it's because it's fluctuating. You shouldn't
> use any more decimal places in calculation than the least that I
> provide (i.e. if I give you ~9 for an input, a calculation from that
> resulting in n.nn has to be trimmed to ~n to be meaningful).
>
> The white wire on the ISV is less than an ohm to the alternator case,
> so you're right that it's grounded.
>
> Duty cycle at a cold start at 60F ambient was down to around 23% by
> the time I could leave the front of the van, walk through the house
> to avoid the soaking wet cedar tree and reach the back. Quickly got
> down to 21% or less. I don't think I've yet seen it below 20%.
>
> I've not yet been able to catch the duty cycle for the short
> excursion above 1000 rpm that happens a few seconds after a cold
> start. But I think a more important number is the rpm reached
> (guessing 1100) and duration and how this is affected by
> ambient/engine initial temp. And is this normal system behavior or
> an oddity of mine? Like the short period above 1000 when I idle down
> while driving, it's consistent among different ECUs both 022D and
> 022F, but unknown if consistent among different ICUs since I have no spare.
>
> Playing with the throttle plate as it was beginning to warm up it
> seemed to vary between about 22-24% without any particular systematic
> behavior. It's hissing down with rain so I'm not going to wait for
> full warmup at this point. I think the changes are some artifact of
> system operation and don't matter.
>
> Stabbing the throttle produced slightly wider variations up to maybe
> 20-25% but I have trouble seeing how it can matter given the input
> from the driver's foot swamping everything else.
>
> 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 suspect the last. It would be answered by doing cold cranking with
> a booster to keep the voltage up, but I'm not equipped to do that
> (though I'm probably going to have to replace the tired battery soon
> if I want to drive at all this winter). This engine has always
> seemed to crank hard since I've had the van, and replacing the
> starter didn't change it. Sometimes it cranks fine and sometimes it
> goes to its knees on the first revolution, then recovers.
>
>
> 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 that's sensible.
>
> Yrs,
> d
>
--
Tom Buese
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