Injector Dynamic Range

[Peter Wales]

Ed Lansinger wrote...[snip]

I replied to the question in the manner I did because I thought the
questioner was asking a wrongly phrased question. I do not believe the
questioner considered the non linear region, but was simply asking whether
an 8 bit counter would cover the entire fuelling requirements of the car
given that the injector was correctly sized for maximum power. Please
forgive me, Mr questioner, for not calling you by name, but a computer crash
wiped out all of my archives and I can't recall the original posting. Please
join in! 

Injectors are digital devices. They are either on or off! I agree that there
are areas in the off /on transition and the on/off transition where they are
non linear due to the fact that they are mechanical devices. I have always
believed that manufacturers stay out of this area for fuel control because
it is undefineable in its characteristics. You may be able to correct me on
that matter.

I am sure that there are injectors which can deliver full flow in under 1 mS
and I am equally sure that there are injectors which will not be fully open
in 2 mS. I was simply trying to explain that working in this area was IMHO
undesireable and should be avoided. The 1.5 mS was a safe average for most
injectors.

Consider the sitaution when the engine is cranking. It requires a pulse of
1.5 mS or longer to inject some fuel (bear with me). Hence, we have an on
pulse requirement of 1.5 mS. Now, when the injector is fully open at 6000
RPM the inejctor is powered continuously. Thus any reduction in fuel flow
rate can be considered as switching the injector off, or pulsing it off,
because as soon as the next injection comes it is going to be switched on
again. Now it requires an off pulse of 1.5 mS. I was simplistically stating
that it takes as long to close the injector as it does to open it and 1.5 mS
is a good average time. Therefore switching it off for less than 1.5 mS will
not reduce the fuel flow rate. OK? Now, I have ignored the non linear areas
for simplicity and the fact that you should not be working it that area, so
please leave that out of the argument.

Finally, as to dynamic range, again ignoring the non linear area. In order
to settle arguments, I like to take things to extremes as it tends to bring
things into focus. So lets take the range of a)not starting the engine -
(flow rate  = 0) to b)running at 100% duty cycle at full power - (flow rate
= full). Now thats a dynamic range of ... erm ... err .... quite a lot of dB :)

If you look at it from the other aspect, if the full flow rate is say
500cc/min then what is the minimum flow rate, it depends on the duty cycle,
again assuming the minimum pluse is in the non linear region. ie a 2mS pulse
at 500 RPM injecting every second revolution gives a pulse of ..... not very
many cc and a dynamic range of ....erm .... err .... lots of dB

Now, the posting of Ed Lansinger sparks some interest from a commercial
point of view. Why were the Japanese investigating the non linear region?
Could it be that Japanese manufacturing skills allow them to make injectors
which will accurately reproduce flow in the non linear region. If so is this
a method of manufacturing in the Japanese tradition of just big
enough/strong enough to do the job and no more. Can they save a yen by
making an injector smaller? Will this bring down the price of Japanese cars?

Peter Wales