Date: Wed, 27 Nov 2013 14:45:49 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Arduino and Vanagons
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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
