Frequency comparator - engine sync

[Wiggo]

Actually, the throw isn't that great - only about 4" - but as the controls are conventional Morse Controls wire-in-tube and they are long cable runs (30-35') they would require a lot of mechanical force from an actuator.

The alternative system from Volvo was EDC: electric fly-by-wire throttles operating the big actuators I mentioned. They already have a 'sync' button to lock the revs automatically...

 

[MikeMl]

You want to do this in the digital domain; not analog. If the existing tacho pick-ups produce an analog signal, dont use them; use an inductive or optical pick-up that produces logic levels. This rules out any freq-to-voltage converters, too.

Here is a circuit with two LEDs; one will flash at the beat-frequency if Freq1>Freq2 while the other is off; the other will flash if Freq1<Freq2. You will have to come up with suitable pickups to create the F1/F2 pulse trains...

 

[tcmtech]

What about using the actuators right on the main injector pumps? I have worked around diesel pumps enough and I have yet to see any that took much actual effort to move the mechanical throttle linkage right at the pump itself.

 

[Boncuk]

Actually he'd need just one actuator like a worm drive lengthening or shortening the throttle linkage for a certain range of rpm.

The electronics for that is pretty easy and should include a fail safe logic to prevent the slave engine being pulled to idle if the master engine fails.

I used the system for a twin engine model plane mounting two magnets into the prop spinner (for balancing reasons).

Maximum engine rpm was 18,000 and the modified servo adjusted for ± 1,000rpm. If both throttles are taken into a position having the engines running almost sychronously the actuator can be kept short.

The system should have the option to disengage the sychronizer circuit for maneouverability reasons. (turning with limited space)

Boncuk

 

[ccurtis]

MikeMi, that circuit is a phase comparator. The LED with not flash at the beat frequency. It will flash at one of the input frequencies and the brightness will be erratic even if the input freqs are constant, as the phase varies.

 

[MikeMl]

MikeMi, that circuit is a phase comparator. The LED with not flash at the beat frequency. It will flash at one of the input frequencies and the brightness will be erratic even if the input freqs are constant, as the phase varies.

Nope, I simulated it at various differences, and the rate that the respective (high or low) led cycles through its duty cycle is proportional to the difference between F1 and F2. Look at the sim above and you can clearly see the beat...

If the difference is above the eye's flicker fusion freq, then either the High or Low LED will be lit. Since only one LED is lit at a time, you would know which way to move which throttle. As the engine speeds get close, the LED will flash at the beat frequency; the beat getting slower as the two engines get closer to the same RPM.

 

[Wiggo]

Actually he'd need just one actuator like a worm drive lengthening or shortening the throttle linkage for a certain range of rpm.

The electronics for that is pretty easy and should include a fail safe logic to prevent the slave engine being pulled to idle if the master engine fails.

I used the system for a twin engine model plane mounting two magnets into the prop spinner (for balancing reasons).

Maximum engine rpm was 18,000 and the modified servo adjusted for ± 1,000rpm. If both throttles are taken into a position having the engines running almost sychronously the actuator can be kept short.

The system should have the option to disengage the sychronizer circuit for maneouverability reasons. (turning with limited space)

Boncuk

Nice thoughts, but not what I'm trying to achieve, sadly. One thing I like about my engine setup is that it is entirely mechanical, so I will still get home even if all the electrickery fails.

For close quarters manoeuvring, both engines will often run at very different revs. All I want to be able to do is to have a simple visual check that bnoth engines are pulling the same revs once we have settled down at cruising speed. As they might then sit at that point for several hours, it is important they they are loaded evenly - right now, I often see a 10% difference in fuel burn.

Manually adjusting the throttles till they match is fine.

 

[Boncuk]

Nope, I simulated it at various differences, and the rate that the respective (high or low) led cycles through its duty cycle is proportional to the difference between F1 and F2. Look at the sim above and you can clearly see the beat...

If the difference is above the eye's flicker fusion freq, then either the High or Low LED will be lit. Since only one LED is lit at a time, you would know which way to move which throttle. As the engine speeds get close, the LED will flash at the beat frequency; the beat getting slower as the two engines get closer to the same RPM.

I simulated that exact circuit using Proteus ISIS and the results were the same.

No need for seven LEDs. Just two will suffice.

To MikeMI:

Great little circuit! I like it!

Boncuk

 

[MikeMl]

...

Manually adjusting the throttles till they match is fine.

Then look at the circuit I posted.

 

[Boncuk]

Manually adjusting the throttles till they match is fine.

Can I now put my 1KW servo drive design aside?

 

[Wiggo]

Mike,

as the two engines approach sync, the beat frequency gets lower and lower. At some point, let's say the engines are at the same revs to within 1 rpm, so the beat frequency will be 1/60th Hz. One or other LED will be off, but the other will flash at 1/60th Hz, or 30 seconds on, 30 seconds off. Short of staring at the LEDs for several minutes at a stretch, what would tell me that they are as near as damn it in sync, rather than a) in perfect sync (both LEDs off) or b) miles out (one LED on solid)?

Is there an easy way to indicate sync, or near sync?

 

[crutschow]

I would think syncing within a few rpm (or even 10's of rpms) would be more than adequate. I doubt that the stability of the engine speed is better than that anyway, and thus it would be impossible to maintain any better sync unless you are constantly tweaking the throttle. The resolution on your throttle is probably greater than a few rpm also.

So what do you consider "near sync"?

 

[Wiggo]

So what do you consider "near sync"?

Good question. What prompted all this is uneven fuel burn: cruise speed is about 85-90% of WOT (wide open throttle) or around 3500 rpm but with the tachos reading the same revs I burn about 10% more fuel on one engine. At a guess, if the revs are out by 150rpm that could account for a 10% discrepancy so I guess 'near sync' might be both engines within 40-50 rpm of each other.

 

[mikeReynolds]

Good question. What prompted all this is uneven fuel burn: cruise speed is about 85-90% of WOT (wide open throttle) or around 3500 rpm but with the tachos reading the same revs I burn about 10% more fuel on one engine. At a guess, if the revs are out by 150rpm that could account for a 10% discrepancy so I guess 'near sync' might be both engines within 40-50 rpm of each other.

Have you considered the possibility that the RPMs are matched but one engine is more worn than the other causing the difference in fuel usage ? Twin-screw drive correct ? Find a calm long straight, set tiller (rudder, etc) straight, match RPMs, if you start veering to either side then RPMs are mis-matched, if not one engine is less efficient,usually due to wear.

 

[Wiggo]

It's a possibility, but not likely, Mike. Twin shafts as you say and identical hours on both engines. Differential throttle settings will indeed cause a boat to turn, but only at low speeds; this is a planing hull and at planing speed you wouldn't see any turning effect.

Again, because they are mechanically governed diesels, if one is more worn than the other it would only show up as a drop in output power at equal revs, not an increase in fuel consumption (if the engines are turning at the same revs, barring manufacturing tolerances on the mechanical injection pumps fuel consumption would be equal - it may not all be burnt, but the volume injected into each engine would be the same).

If I can ensure that the revs are the same then I know that the loads will be the same on each engine and therefore any difference in fuel consumption can only be down to problems with the pumps...

 

[Acetronics]

Hi, Wiggo

Did you had a look to this ... ???

WRC Wike R/C Products Twinsync Engine Synchronizer (WRCTWINSYNC) - troybuiltmodels.com

surprised eh ??? ... IT WORKS REALLY FINE !!!

Alain