Transistor car ignition: Some clarity please

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Ampdog

R.I.P. 23 June 2022
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Since this is the section for 'all else' ....

I am at present examining the transistorised ignition of a Toyota. The functional elements are fortunately physically separate, so measurements can be done. It typically consists of a trigger coil magnetically actuated, triggering a power transistor 'switch' in the ignition coil primary.

Firstly the coil is quite small (a few cubic centimeters), so I must presume a higher quality transformer to still provide the necessary energy in the spark-plug gap. I have difficulty in finding a discussion of such a small 'coil' (I have not yet taken it out so as to measure inductances; the winding resistances are similar to the larger can type coils).

Then I find the coil energising time ('on' time) about 5x shorter than more regular types. At about 2000 engine rpm it is only 10mS. This seems to be governed by the passing of an actuator tooth past the pick-up coil. As it approaches the coil (power transistor) is switched on, to be turned off only 10mS later by the sharp exit of said tooth. Thus this interval is not really controlable. The spark drawn under room conditions is hardly 5mm long from this short burst of energy deposited into the coil. My only previous experience of transistor ignition was with my Tredia some 10 years ago; it could quite easily generate a free air sperk of 10mm.

I then proceeded to energise/trigger the system from a variable on-time signal generator. Lengthening the coil 'on' time quickly extended the park length to 9mS.

My question then: Is the above typical of modern transistor ignitions? (Not speaking of sophisticated types in high-end cars.) What about the (to me) very short coil energising period of 10mS compared to previous systems (this was at an equivalent engine speed of about 2000 rpm) where the spark energy was definitely increased by lengthening the coil 'on' time? Where can I read about this?

(Oh, in my very ordinary Nissan Exa's ignition system, the 'on' period provided by the power transistor module is fixed, not dependent on the triggering teeth's time spent in the vicinity of the pick-up coil.)

Thanks for any comments. 
 
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