"Tom Walker" wrote to "Charles Angelich" (24 Feb 03  07:10:48)
 --- on the topic of "CMOS battery"

 TW> I believe Saab was the first one to have the Ignition system that
 TW> didn't need the High Voltage wires. They use a minature Ignition Coil
 TW> for each plug. And it is located right at the spark plug taking the
 TW> place of the old Spark plug connector, a bit bigger of course, at the
 TW> plug end of the old High Voltage wire. Then you only have the Computer
 TW> Controlled 12 volt pulse to deal with in the Ignition wiring system.

I think it could work both ways. First as with your description of a
simple ignition coil being fed a current pulse from a central ignition
system. However it could also have an individual ignition system per
plug in the same module as the coil but getting logic signals directly
from the engine controller. With surface mount techniques the trigger
electronics can be very tiny when compared to the size of the coil and
so is easily built-in these days.

The difference between both methods is that with the latter there isn't
as much of a problem with rfi from the high current pulses. Don't forget
the higher the rate of change of current the more leaks out the
conductors as radio waves, i.e. rfi.

Another benefit is that any one plug ingition module may fail but the
remainder will still operate. As a refinement the logic trigger signals
could be transmitted through fibre optics cable for faster response,
zero rfi, and more reliability. BTW faster is better at 20K rpm.

 Mike
 ****

... A computer doesn't do anything smart. It does something stupid fast.
--- Blue Wave/DOS v2.30