Dwell Control

[Armand Jordaan]

Correct me if I am wrong, but the DIS only controls the coil current.
That is, the closed loop control that is spoken of is a closed loop current control. (The DIS will ensure that the current does not exceed about 7-8A). This ensures that the coil will not burn out.

The ECM is needed to open loop control the dwell angle (or time if you prefer).

A little math will clear this up:

The current in the primary winding of the coil is:
I = (V/R)*( 1 - exp(-(R/L)*t) )    ..... (1)

The energy for spark is E = 0.5 * L * I^2 .... (2)

where 	R = series resistance of the coil (about 0.5 ohm)
    	L = inductance of the primary winding (about 4.8mH)

Normally you need about 100mJ for good combustion, so from (2) you need about 6-7A of current.
>From eq (1) at 13.8V you need about 3 ms of dwell time.
In fact the only variables in eq (1) are battery voltage, meaning that the dwell time is a function of battery voltage. (The ECM measures the battery voltage and then determines the dwell time to ensure that the primary winding of the coil is charged to 100mJ.)

Depending on the coil type (values of R and L), the dwell times for other coils will differ.

Hope this will clear it up.

Armand Jordaan



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From: 	Bruce Plecan
Sent: 	Saturday, April 10, 1999 4:01 PM
To: 	gmecm at esl.eng.ohio-state.edu
Subject: 	Dwell Control

Well, I posted some time ago about the dwell control being in the module,
and was corrected that it is actually in the ecm program.  Tada, well, I was
correct, as well as the correction.  In the DIS Teachers manual they mention
that the dwell control is in the module, and that it is a closed loop dwell
control.  Meaning if the module doesn't sense that the coil (s) were fully
charged, then the dwell was adjusted.  What the ecm must do is try to
account for this correction, hence it has what looks to be dwell control in
it.  Again all of the above, IMHO, and from the GM DIS Teacher's Manual.
   Bruce
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