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What is ignition delay?

 
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How easy is it to understand the MoTeC software and control
Not easy at all - its way too confusing
13%
 13%  [ 3 ]
Its easy to understand once someone explains it
86%
 86%  [ 19 ]
Total Votes : 22

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motecusa



Joined: 22 Jan 2004
Posts: 116
Location: Huntington Beach, CA

PostPosted: Thu Dec 08, 2005 4:18 pm    Post subject: What is ignition delay? Reply with quote

I am just posting this up here because for what ever reason in the last couple of days I have gotten a rash of questions about the Ignition Delay parameter in the MoTeC ECUs.

Basically it takes a finite amount of time for a signal sent from the MoTec ECU to the Ignitor, from the ignitor to the coil, and from the coil to the spark plug gap. This amount of time is built in to any ignition system and is referred to in a MoTeC ECU as the Ignition Delay. The lag exists because the signals are sent at the speed of light but - there is a distance that the signal must travel before spark occurs. This time lag is constant regardless of the rpm. Typically we find that the delay time is around 40 - 50 micro-seconds. This is a very small amount of time, however since it is a fixed period, the number of crankshaft degrees that this delay lasts for is dependant on the RPM which means as the RPM goes up - the delay becomes a proportionally larger number of crank degrees.

At idle lets say 1000 RPM the error in timing might only be .3 degrees but at 10000 rpm this become 3 degees and 4.5 degrees at 15000 which means you will have high speed retard if this delay is not accounted for.

In order to properly adjust your ignition delay we recommend that you monitor your crankshaft position sensor and the spark through an inductive pickup using a labscope. You will want to command a fixed spark advance (the CRip set screen works well for this) and check the offset at 1000 versus 5000 and maybe 10000 if you dare. You can adjust the delay parameter to achieve 0 lag or the same lag at 1000 as 5000 or 10000.

The ignition delay parameter is not supposed to be used as a timing retard advance - that is supposed to be done in the Main ignition table.

Hope this makes sense and answers a few questions.

Regards,
Shane
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John at J&S



Joined: 12 Nov 2005
Posts: 288
Location: GARDEN GROVE, CA

PostPosted: Sat Jan 07, 2006 4:55 am    Post subject: Reply with quote

Ignition delay varies with the type of igniter being used. Piggyback timing controllers add more delay.

Ignition background: http://www.st.com/stonline/products/literature/an/3722.pdf

A typical igniter is a transistor switch. The ECU sends a dwell pulse to the igniter, which turns the switch on. At spark time, the ECU turns off the dwell pulse, but the transistor switch cannot instantly turn off. Depending on the type of ignition transistor used, turn off times can be several usec.

Table 4 in this link shows 15usec storage time, meaning that the transistor remains on, even though the drive pulse has been removed.http://www.st.com/stonline/products/literature/ds/1008.pdf

Piggyback timing controllers add more delay, since they usually employ a micro processor to calculate timing retard. Most of this delay is due to software.

For example, the minimum software delay (no retard) in the J&S knock controller is about 35 usec, between the time when the spark is commanded by the ECU, to the time that the micro processor produces a corresponding output pulse. If the J&S has a coil driver transistor, add another 35 usec delay.

To compensate, add 70 usec to the ignition delay value in the MoTeC set up window.

Dr. Chris Jacobs' book has a useful formula for calculating the amount of retard, based on the delay time (if you have a scope to measure it). Note the the formula is independant of the number of cylinders:

Retard angle = 6 x delay x RPM.

For example:

6 x 70 E-6 x 7000 RPM = 2.94 degrees unintended retard.

At 1000 RPM, the same 70 usec produces 0.42 degrees, so you wouldn't see it with your timing light.

After changing the ignition delay value, the MoTeC software will subtract 70usec from the spark calculation, to remove the unintended retard.
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Pantera EFI



Joined: 12 Feb 2005
Posts: 1718
Location: So. California

PostPosted: Sat Jan 07, 2006 12:04 pm    Post subject: Cranksaft encoding vs ignition delay Reply with quote

A crankshaft target with 2, 4, 6, even 12 teeth will exibit a much greater delay than stated by the earlier equation. When the advance data is added to the ignition " event " the timing lag may be over 10 degrees when the cranshaft is accelerated.

A more modern crankshat target of 24 teeth, 36 teeth, 60 teeth will not exhibit this problem. The lag of a 24=1-2 degrees, 36=.3 to 1 degree and 60=.125 to .25 degrees is goverened by the acceleration rate (change of RPM per second) . A greater number of teeth on the target will not see much gain and the switching speed of the sensor may reach a limit.

My opinion, It is better to let the processor do its do its job correctly than to compensate for a " low resolution " cranksahft target.
Lance
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John at J&S



Joined: 12 Nov 2005
Posts: 288
Location: GARDEN GROVE, CA

PostPosted: Sat Jan 07, 2006 5:43 pm    Post subject: Reply with quote

Lance: I know you know this, but to clarify for other readers, the timing lag that you are describing is due to processing of the trigger wheel signal, and is separate from the delay that Shane and I are describing.

The "Ignition Delay" described by Shane is in the ignitor or piggy back timing controller, and occurs after the "ECU" ends the dwell pulse, to make the spark. This delay can be subtracted out with the "ignition delay" parameter.
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Pantera EFI



Joined: 12 Feb 2005
Posts: 1718
Location: So. California

PostPosted: Sat Jan 07, 2006 7:01 pm    Post subject: Event based delay OK Reply with quote

I do agree with your statement, though ALL must be reminded, this problem occurs only with an" event " based spark insant or when using a "piggy back" spark control.
Lance
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motecusa



Joined: 22 Jan 2004
Posts: 116
Location: Huntington Beach, CA

PostPosted: Mon Jan 09, 2006 1:33 am    Post subject: Reply with quote

Lance,

It occurs to me that this delay occurs all the time no matter what type of timing trigger you have feeding information into the processor (which by the way introduces its own set of delays which are accounted for before the ignition output pulse is sent by the MoTeC to an ignitor. Ignition Delay in the MoTeC is specifically intended to deal with delay from ignition output command to spark plug gap as John and I are suggesting.

If say for example some other company has an system which directly fires the coils from the controller (which of course has the disadvantage of increased heat dissapation and heat saturation and reduced speed in components like the processor) they have no doubt accounted for the delay which is built in to their ignition amplifier and therefore dont require an ignition delay parameter.

John,
thank you for adding additional information to the original post.
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Hugh



Joined: 03 Dec 2005
Posts: 426
Location: Scotland

PostPosted: Mon Jan 09, 2006 4:04 am    Post subject: Reply with quote

It's all a bit academic though as when you are tuning your engine you are looking for the map numbers that give you maximum power.

Whether you subtract an ignition delay from your map number or have zero ignition delay will have no bearing on the power produced by your engine at the end of a tuning session.

If you subsequently changed your ignition system in favour of another and you knew the new delay you could possibly use the number to good effect, but maybe the new system would be better / worse at igniting the fuel mixture which would still require a re-map session.
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John at J&S



Joined: 12 Nov 2005
Posts: 288
Location: GARDEN GROVE, CA

PostPosted: Mon Jan 09, 2006 6:28 am    Post subject: Reply with quote

Hugh:

You are correct, it has no bearing on the end result, but if you were to check the timing with a light at various RPM's, you would shut down the run to figure out why the timing doesn't match what's displayed on your laptop.

The ignition delay parameter ensures that there is no unintended "RPM retard" due to the ignition module itself.
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Hugh



Joined: 03 Dec 2005
Posts: 426
Location: Scotland

PostPosted: Mon Jan 09, 2006 9:36 am    Post subject: Reply with quote

Thanks John,

Good point
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motecusa



Joined: 22 Jan 2004
Posts: 116
Location: Huntington Beach, CA

PostPosted: Mon Jan 09, 2006 11:30 am    Post subject: Reply with quote

John again is right on here.

Incidentally we are not talking about the delay for the kernel to form and ignite the mixture in the cylinder - only the electronic delay in the parts used to fire the coil.

If you are tuning the engine to peak performance, you will tune into your ignition map the delay if you dont correct for it. At the end of the day - you are right the engine wont care - but if you are a high end engine developer - you would want to know if the timing the engine wants is due to electronic drift or what the engine actually wants. This is the whole basis of the MoTeC design and why there are so many parameters. Every attempt is made to ensure that what you command is what you get.

REgards,
Shane
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Johnny_9



Joined: 17 May 2006
Posts: 303

PostPosted: Fri Jan 11, 2013 8:57 am    Post subject: Reply with quote

Well explained.
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Hugh



Joined: 03 Dec 2005
Posts: 426
Location: Scotland

PostPosted: Fri Jan 11, 2013 9:14 am    Post subject: Reply with quote

Nice to see old posts being read, they are just as relevant today as they were 6 years ago
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