Author Topic: Throttle governed engine  (Read 7926 times)

Offline Brian Rupnow

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Throttle governed engine
« on: December 18, 2019, 11:37:12 PM »
This is going to be something a bit different. Most of you will have a fairly good knowledge of how a hit and miss engine runs. On a hit and miss engine, the governor disables the exhaust valve when the pre-set rpm is surpassed, holding the exhaust valve open and letting the engine coast until the engine slows down, at which point the governor allows the exhaust valve to close and the engine will once more be able to build compression and fire.  However, there is a different way of governing an engines speed for engines which are not "hit and miss" types. In this type of governing, the governor opens and closes the butterfly valve in the carburetor to adjust the engine speed. In a perfect world, you "dial in" the speed at which you want the engine to run. If the engine speed slows beyond that point, a linkage from the governor opens the butterfly valve in the carburetor and admits more air/fuel mix to bring the engine back up to the "dialed in" rpm setting. If the engine rpm exceeds the "dialed in" speed setting, the governor closes the butterfly valve, thus starving the engine for fuel until it slows down to the dialed in rpm. I have a twin cylinder opposed engine that I built a few years ago, which has a manually controlled butterfly valve in the carburetor.  I also have a governor which was salvaged from the very first "hit and miss" engine which I designed and built. (The engine ran, but was horribly unbalanced). Over the course of the next few weeks, I am going to try and "marry" the two bits of technology to end up with a "throttle controlled" engine. Follow along. It should be interesting.---Brian

Online crueby

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Re: Throttle governed engine
« Reply #1 on: December 19, 2019, 12:04:01 AM »
Is that sort of the same effect (but very different mechanism) that the cruise control on a car has, where it pushes the gas pedal down/up as it senses the speed change?

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #2 on: December 19, 2019, 01:08:31 AM »
It is the same end result, but I don't know how they do it on a car.

Offline RonGinger

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Re: Throttle governed engine
« Reply #3 on: December 19, 2019, 04:06:24 AM »
Most lawn mower engines are regulated like that- a vane is in the cooling air flow path and is moved  by the velocity of the air. These things can be very tricky to get right- they are more likely to hunt up and down in speed.

 Many steam engine models have flyball governors, and they almost never really work. The balls are to light and the speeds to slow.

This should be an interesting project.

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #4 on: December 19, 2019, 01:29:22 PM »
Before I dive into this one, I want to set up the twin cylinder engine and make sure that I can tweak it manually to give a high speed of 2000 rpm and a low speed of about 1500 rpm.  I have a laser tachometer and can measure rpm quite accurately. Last night I lay in bed thinking about this. If I don't want the engine to ever exceed 2000 rpm, that can be accomplished by a hard-stop on the throttle linkage which doesn't really involve the governor. I would like to have a "mode" where the governor is disengaged so I can start the engine with the throttle closed and the governor completely "locked out" where the engine will run at about 850 to 1000 rpm . When I have the engine started and do engage the governor, I would like the governor to take the rpm up to around 1500 and hold it there under a "no load" condition. As soon as a load comes onto the engine and the flywheel shows the smallest inclination to slow down, I want the governor to immediately open the throttle fully, not incrementally, and take the speed up to full 2000 rpm and hold it there until the flywheels are no longer seeing a load and the engine can drop back to 1500 rpm until the next load is applied.

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #5 on: December 19, 2019, 04:26:12 PM »
Since my twin cylinder engine is a few years old now, and has ran a lot, the first thing to do is to run a few diagnostic checks. The attached drawing and explanation will give a pretty good way to check the valves and rings on each cylinder.



« Last Edit: December 19, 2019, 04:45:00 PM by Brian Rupnow »

Offline ddmckee54

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Re: Throttle governed engine
« Reply #6 on: December 19, 2019, 04:44:54 PM »
Ummmm…..  Couple of questions:
You are using the governor to sense engine load correct?  Engine rpm drops then the engine is under load - right?
You plan on using the governor to then increase the engine rpm to full throttle, right? I believe you said this is about 2000 rpm.
When the governor is engaged and your engine is at full throttle, how are you going to sense the no load condition with the governor?

Just had a Brain Fart.  What if you didn't go full throttle but set a mechanical latch to hold the throttle open enough to hold the engine at about 1900 rpm under load.  Then when the load went away, the engine would overspeed to 2000 and you could use the governor to reset the mechanical latch letting the engine throttle back to the 1500 rpm setting.

This is assuming that the 1500 rpm setting would be a mechanical latch which would move the low throttle limit.  I'm assuming that this is set/reset by your governor engaged/disengaged lever/whatever.

Don

 
« Last Edit: December 19, 2019, 04:58:48 PM by ddmckee54 »

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #7 on: December 19, 2019, 04:49:52 PM »
Don--All will be revealed as I figure it out.---Brian

Online Jasonb

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Re: Throttle governed engine
« Reply #8 on: December 19, 2019, 05:19:09 PM »
I don't think you really want the speed to change as most governors are set to keep speed constant under load.

Think about if you are driving your car at say 50mph on a flat road, you are only applying light throttle pressure so small opening of the carb. You now start to go up hill but want to stay at 50mph what do you do open the throttle due to the increased load but speed of the engine stays the same.

having stood and watched a few engines running a saw bench they don't speed up when the wood is fed in, there is a momentary drop in speed then back to what has been set yet the sound of the engine is quite different as it runs under load, as steam engine will go from a docile chuf, chuf to a real bark if the load is high

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #9 on: December 19, 2019, 07:04:32 PM »
So, now I have something to screw into the sparkplug hole and do my valve and ring testing. Now it's out into the blizzard to get my good wife some cold medicine from the drug store.

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #10 on: December 19, 2019, 07:08:48 PM »
Jason--based on what I have seen so far, the load goes immediately from no load to high load. There is no smooth transition of load forces. Thus I want the engine to go immediately from fast idle to "wide open throttle".

Offline AlexS

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Re: Throttle governed engine
« Reply #11 on: December 19, 2019, 07:27:26 PM »
It is the same end result, but I don't know how they do it on a car.

Modern cars has electrical controlled throttle. So not a direct/lineair linkage between amount of opening pedel vs throttle body. So full pedal on low speed (manual) get a small % opening throttle and on a higher rpm larger % opening.
Indeed for cruise control, it is similar to Governor speed controlling system, but then with electrical controlled PID system that accurate the throttle valve to get to the desired speed measured by a speedsensor.
You can compare it with adjust a potmeter by hand to control the brightness of a led or the speed of a dc motor.

But I am looking forward in this governor valve controlled build Brain. What is the displacement of your twin?

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #12 on: December 19, 2019, 08:49:51 PM »
The engine is 7/8" bore x 3/4" stroke
« Last Edit: December 19, 2019, 08:53:00 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #13 on: December 19, 2019, 09:08:09 PM »
Testing the left side cylinder at 40 psi shows no leakage of either valve and no leakage at the piston. Now I will move over and test the other cylinder.

Offline Brian Rupnow

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Re: Throttle governed engine
« Reply #14 on: December 19, 2019, 09:49:43 PM »
After checking the right side cylinder and discovering no leaking valves or rings, I went ahead and started the engine. It needs a bit of run time to clear itself out, but appears to be working okay. Tomorrow I will test the rpm range with my laser tachometer before starting any modifications to make it a governor throttled engine.