Ignition Trigger Delay???? Does it exist??? 1

[MRSSPOCK]

I wonder has anyone ever come across a device that enables a simple shift in ignition timing?

What I mean is, some piece of circuitry that can be introduced on, lets say, a single cylinder motorcycle engine, whereby the user can quickly change ignition timing, via lets say a potentiometer.

I do realise it might be a tall order that such a device can cater for any single cylinder motorcycle engine, but at least for those that employ a simple VR sensor, (as opposed to a Hall effect).

I imagined that if the default static ignition was advanced mechanically, lets say by slotting the stator plate, and moving the ignition to a position past a realistic advance, then by somehow simply delaying the triggering electronically, it would let the user tune the ignition live.

I know certain ignitions trigger at a certain part of the VR sinewave voltage level, nevertheless, I though somebody somewhere would have by now created some device to enable this?

I know someone is going to say, "they have, it's called a digital ignition such as a Power Commander", but I'm thinking of something you simply place in line within an already existing ignition system, with only the static advance adjustment, as already mentioned, needing to be executed, to achieve the range of delays required.

 

[IceStationZebra]

Some ideas.....

I though about using the charge time of a capacitor (aka condensor), but the effect would vary according to engine speed. This is because the charge time of the cap would be fairly constant, but the time offset required for 5 degrees for example, would be 833ms @ 1000rpm but only 278ms @ 3000rpm. So you would get little change at low rpm but big changes as the rpm climbs. Also not adjustable.

"I know certain ignitions trigger at a certain part of the VR sinewave voltage level, nevertheless, I though somebody somewhere would have by now created some device to enable this?"
If this is the way your ignition works you might be able to rig in a simple voltage divider circuit. You could use a pot in the circuit to provide the variability you want. Also be aware that it would cut the voltage at all points in the wave, so make sure you have still have enough voltage at low rpm to prevent misfires.

Another way to do this is rig up two triggers and switch between them. Not infinitely variable, but simple in principle.

And lastly I have seen distributors set up with a pick-up that can be adjusted from outside the case by means of a screw and thumb wheel. It is difficult to know where you are without using a timing light, but it does make adjustment easy.

ISZ

 

[waross]

The old school solution.
Harleys in the thirties and forties and automobiles back in the thirties just moved the distributar housing to adjust the spark timing. The MCs used a twist grip and a cable to the distributor housing. The old cars generally used rods and bell cranks to move the distributor.
The old speeders on the railroads had a lot of mechanical advance and retard on the single cylinder two cycle engines. To reverse the operator would kill the ignition and advance the spark all the way. When the engine had coasted almost to a stop he would turn on the ignition. The engine would backfire and commence to run in the other direction. More than one biker and more than one peson hand cranking an early engine was injured trying to start the engine with too much advance when a backfire would send the kick starter or crank back at them.
It won't hurt to look at the bike to see if the distributor will be easy to move. It may be more dependable than a home brew electronic solution.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MRSSPOCK]

Thanks, however this need is a recurring issue which shows up pretty regularly among people I know who race classic 500cc two stroke singles. People seem to be fiddling with ignition timing on a regular basis. One bloke was telling me of a time when he went over the handlebars, after giving her the welly in 1st gear, whilst not realising the engine was running in reverse! I was therefore thinking more of a global solution as opposed to making mechanical changes to any one particular machine. That was why I was looking for an electronic solution. I am surprised such a sinewave phase shift device doesn't exist, which simply reads the wave from the VR sensor, waits a predetermined period, then releases the temporarily held wave to carry on its way. I think it would be a good seller if such an inline add on device could be developed. The rollers could be left at home, at it would make restarting the motor after a fall off so much simpler.

 

[patprimmer]

Hand adjustable distributors went back well before the 30s Our 1912 model has it and I am sure earlier models since around 1900 had it. They actually had a lever on the steering column and you retarded it to fire AFTER TDC as you cranked it. The idea was for it not to start running backwards and smash your arm as it fired.

I think they all did it by rotating the points plate as they had solid mounted magnetos normally.

Regards
Pat
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[IRstuff]

Ignition timing is usually required to be a function of rpm, since there are finite and relatively fixed delays in the ignition flamefronts and pressure waves.

I can't see how a manual adjustment, without any correlation to actual timing could be a significant improvement, overall, since the fixed delay must wind up compromising the performance at some rpm.

TTFN

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[MRSSPOCK]

IRSTUFF. The idea isn't to make a spark curve adjustment device. It's simply enable a quick way to make adjustments at specific engine speeds, not through the range. This would enable fine tuning at specific engine speeds/throttle postions. It would also make starting easier. Just like they used 100 years ago. IT worked then to prevent broken wrists, so can also work now to prevent broken ankles.

 

[IRstuff]

"enable fine tuning at specific engine speeds/throttle postions"

It seems you are asking for an electronic ignition module. Unless you have perfect pitch, it would seem unlikely that you could tell the exact engine rpm by ear, so what kind of "fine tuning" could you do by a relatively crude hand adjustment?

TTFN

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[MRSSPOCK]

IRSTUFF. I don't need perfect pitch to hear detonation. The fine tuning would be every bit as accurate as making 0.1mm incremental adjustments by means of using a DTI and rotating the stator plate etc, but a WHOLE lot simpler than removing a casing, removing a crankshaft nut using a flywheel holder, removing the flywheel using a flywheel puller, fitting a DTI, blah blah blah. I don't know if you have ever had to optomise an ignition on such a two stroke in the way Joe Average has to. i.e its a simple matter of suck it and see. Its simply a matter of making the adjustment and trying it out, right through the relevant rev range, until I'm happy with the best compromise. Its never going to be perfect. I can see a big advantage as I'm sure anyone would, who has personally had to do it the long winded way, but if you can't see the benefit, sorry I can't manke it any plainer. Is there anyone there who gets my drift?

 

[IRstuff]

Nothing to do with what I see; if you can't find the device you're looking for, then maybe no one else sees a benefit.

TTFN

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[MikeHalloran]

The spec kind of drifted during the discussion, so I'm no longer sure what you want:
- delay adjustable in time
- delay adjustable in crank angle
- delay adjustable in time, different at different RPM.
- delay adjustable in crank angle, different at different RPM.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Oh. Adding throttle position is just one more permutation.
All eminently possible.
All would result in instant retaliation by CARB, of course.

Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

On a not unrelated note, I once postulated that I could save a little energy with predictive switching of an ignition coil. I.e., instead of switching the coil on when the breaker points closed, I would instead switch it on electronically, about 2ms before the points opened, so the coil would be on only long enough to saturate it, not half the time.

The trick was to use a free running up-counter to measure the length of the 'previous' points cycle, and have it count down to a number representing 2ms, not zero. It required two such counters, working in alternation. The CMOS breadboard worked as designed on the bench. The intended recipient car had to be junked for other reasons before I got around to installing it, and by then, none of the new cars had points anyway.

Nowadays, you can build whatever behavior you want into a little box with a microprocessor in it.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

"sinewave phase shift device doesn't exist" This requires a bit of electronics, and in the limited market that this probably is, would cost about $200, I'm guessing, assuming someone wanted to actually broach that market.

To store and delay:
> ADC with lots of input protection
> Waveform memory
> FPGA control circuit
> DAC with lots of output protection
> power source/regulator

If other inputs are required, that's just more ADC inputs, and probably going to a microcontroller, like an Arduino:

http://www.sparkfun.com/products/9949

Here is someone who used it for their car ignition controller:

http://thedeltaecho.wordpress.com/2jzduino/

TTFN

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[MRSSPOCK]

"The spec kind of drifted during the discussion, so I'm no longer sure what you want"

Mike, what I want is a means to mimic the old time advance/retard cable unit which mechanically rotated the distributor, but by means of a device which is added INLINE to the trigger sinewave output from a VR sensor, whereby the said sinewave can be temporarily restrained, before being released after the dialled in delay time has elapsed.


"On a not unrelated note" Mike, with your 2ms saturation time set up, did you mean that the 2ms was a constant, no matter the engine speed was? Would that be sort of like a variable dwell angle in reality?

"then maybe no one else sees a benefit" nor did these blokes who were in the know quite amusing (the first 5 quotes)

http://ifaq.wap.org/computers/famousquotes.html

 

[MikeHalloran]

Yes, the 2ms was a constant, set by a digital comparator and a clock, ISTR, selected to give a reasonable minimum dwell at all reasonable engine speeds. It would be simple enough to extend the idea to shift a pulse in time, forward or back, say in response to a pot that a microprocessor could read.

Even if the micro didn't have analog inputs. I've used 555 timers to 'read' analog pots with an 8741. Things like that are much easier now.





Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

What's your point? Most of the quotes were made before computers existed in the form they do now. Electronic ignition systems and retarders have been in existence for over 30 yrs.

"a device which is added INLINE to the trigger sinewave output from a VR sensor, whereby the said sinewave can be temporarily restrained, before being released after the dialled in delay time has elapsed." which I've already described, and provided links to devices that you can build.

TTFN

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[GregLocock]

This is a fairly trivial circuit, the trick is not to store the sine wave, but to initiate a new wave a certain time (or crank angle) after the arrival of the first one. Any keen 16 year old with a spotty face and a soldering iron should be able to knock one up. The number 555 will probably feature in the design.



Cheers

Greg Locock


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[IRstuff]

555 hizzzzz... ;-)

TTFN

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[LionelHutz]

I think you'll find a constant delay time is sadly lacking. After you try a constant delay time, I'm betting you'll find that you actually want to advance or retard based on the number of crank degrees.