[Diy_efi] Re: EMS inputs/output?

[Kent Martin]

Open loop means that it is a feed forward system i.e. no feedback,
predictive.
This means you will predict the amount of fuel required from the given
sensors(not the lambda sensor).
Closed loop means that you will use control input and adjust based on an
output you use.
i.e. the lambda (exhaust gas oxygen) sensor will indicate what portion of
air is left in the
exhaust gasses. To much air means more fuel is needed and vice versa.
Engines generally only
come with a narrow band sensor. Narrow band only gives you a Air/Fuel ratio
applicable to
light to moderate load. This means it can only be used when the car is
cruising or light acceleration.
However wide band ego sensors are available that give a much broader range
of air/fuel ratios so
that you can control the engine in almost all conditions using the sensor.
One drawback lies in all ego sensors though, they must be hot to operate, so
they are
unusable until they reach their operating temperature. Many systems employ a
heater
in the sensor itself to get to temperature faster, but I'm sure how long it
will take.
This mean you may still have to control the engine in open loop when idling
and
when ego sensor is cold.

Ping or knock sensors are usually piezo electric sensors and produce an
oscillating voltage
when excited by vibration. They are very hard to use in a generic manner.
The frequency and
amplitude of the knock and background noise depend on where and how many
sensors there are
and when you sample them (i.e. 5 degrees BTDC) . Filters and timing are
specific for each engine type
and are difficult to calibrate without equipment like a audio spectrum
analyser and some control
of the system to force knock so that you can determine where (frequency) and
when (degrees)
and how long (time period to measure over) to catch the knock.
Not easy to say the least, but is doable if you want to spend the time.

Dwell is a measure of the coil off an on time. I'm not sure of the exact
calculation of it
but it is a hangover from the Kettering (points) ignition system where the
points opened
for a fixed angle. This is not important though, the important thing is that
you turn the
coil on long enough for it to fully charge and off long enough for it to
cause the secondary
winding break down.
I generally just turn the coil off for 1 mS and on for the remainder of the
engine cycle.
I also limit the on time so that it does not exceed 10mS to avoid coil
overheating at
low RPM. This figures may not be accurate but the principle should be.

----- Original Message -----
From: "alex averbuch" <averchoob at hotmail.com>
To: <diy_efi at diy-efi.org>
Sent: Thursday, July 25, 2002 2:52 PM
Subject: [Diy_efi] Re: EMS inputs/output?


> Cheers for the help Huw
> Is the difference between open and closed loop just the ommission of the
> LAMBDA sensor or is there more to it?  If it is then wouldn't a closed
loop
> method just continuosly poll the LAMBDA for changes and
increment/decrement
> the inj-open-time accordingly?
>
> What complications would a Ping sensor introduce if I wanted to use it as
> one of the inputs for the ECU? Isn't it simply an anolog input from a
> microphone,where a frequency (or volume?) over a certain threshold would
> signal that detonation is occuring, or do other problems like calibration
> nightmares also come into play?
>
> This is probably a dumb question but what is Dwell? you mentiond it but
I've
> never heard that term before.
>
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