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How is crank position calculated


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Hey down under.

I have troubled my head with how ViPEC actual keeps track off the cranks position.

Is there somebody that have some information that could answer the following questions.

1) Is there a advantage by using a multi tooth trigger wheel over 1 tooth per firing event.

2) How is crank position calculated.

:geek:

Jan

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Jan,

Is there a advantage by using a multi tooth trigger wheel over 1 tooth per firing event.

It depends on the number of cylinder and the weight of the flywheel. On a single cylinder engine with very light flywheel, one tooth per TDC is useless. The engine accelerates and decelerates so much at low rpm the ignition timing will jump all over the place. Using multi teeth (24) will overcome this.

If you have a six or eight cylinder engine without a light flywheel, then one tooth per TDC works perfectly. Four cylinder engines with light flywheels should use multi tooth.

How is crank position calculated.

How it does this, depends on the type of crank and cam trigger patterns. These are the basic triggers.

Group fire and wasted spark operation only:

One pulse per TDC with distributor:- ECU knows were each cylinder TDC is located as you have a crank tooth at every TDC

Missing tooth with multi coil or distributor:- ECU uses the missing teeth and the trigger offset value to know where TDC is for the first group.

Sequential operation:

Multi tooth with cam trigger signal:- Cam trigger signal is used. The trigger offset value tells the ECU which tooth on the crank is TDC No1 cylinder.

Missing tooth with cam trigger signal:- Cam trigger signal is used. The trigger offset value tells the ECU which tooth on the crank is TDC No1 cylinder.

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Ray, if I understand this right then:

If an engine have one tooth per ignition event, the ECU will calculate the ignition timing by calculate the time it takes the crank to rotate from previous tooth to next ignition event.

And

On an engine with multi tooth per ignition event, the ECU will count the number of teeth from last trigger tooth, and only the amount between the last tooth and the desired timing is based on time.

Is this correct

Jan

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If an engine have one tooth per ignition event, the ECU will calculate the ignition timing by calculate the time it takes the crank to rotate from previous tooth to next ignition event.

Yes..and this is why the timing is not accurate on engines with low inertia.

On an engine with multi tooth per ignition event, the ECU will count the number of teeth from last trigger tooth, and only the amount between the last tooth and the desired timing is based on time.

Yes, timing accuracy is based on the time between teeth, and not the first and last tooth of a group that is counted.

Ray.

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