engine speed droop.

[guido]

Here is my question,
On mechanical type flyweights/spring type engine governor:
What is engine speed droop?
What effect speed droop has on an engine RPM'S?
What can be done to change that effect?
Can an engine be controlled to have zero speed droop?

Guido.

 

[LW]

What is usually called high idle is the speed the govenor is set at or governed speed. If it is set a 1600 a mechanical gov. will have a mechanical loss of 200-300 rpm. Due to the weights/springs and clearance the mechanical system has to operate. Swivel eyes and ball ends that have less clearance can help on certain systems in the linkage. When the enigne gets a load it will go down to that lower speed and maintain. Newer power units have electronic/computer gov. that with a speed sensor have little loss they can hold the engine to the set speed with great pecision but are usually for constant speed. Most new equipment is Fly by Wire and there is no mechincal link to the engine. There is a potentiometer in put control and a servo/ solenoid to control rack or butterfly position.

 

[guido]

Hello LW,
Pretty good explanation of what engine speed droop is and how it effects engine RPM'S.
What can be done to change that rpm drop?
Is there a governor that will control the engine regardless of load at zero droop speed?
Guido.

 

[LW]

There is no mechanical gov. that will have no loss. You can make one surge and it will hide some of it, but I can't stand that. Just try to get rid of as much loose motion and clearance in all the connections. You can use ball swivels, or swivel eyes. They don't require the clearance that a rod in a hole does.

 

[guido]

Hello LW,
There is a type of governor that is used to provide zero governor droop. It is called isochronous or zero droop governor.
One application is for GEN SETS, to keep the Hz as close to 60Cycles os possible where required.
To change governor droop on a mechanical flyweight/s governor you change the spring rate/tension.
That will make the throttle more sensitive/ responsive and will take some of the droop out.
The engine will then have more RPM's at full load as a result.
Governor droop in an engine can be calculated with this formula. Here we use an engine with 2250 no load RPM's and 2100 full load RPM'S.As an example. % of an engine
Droop speed can be calculated as follows:
MNL RPM'S - MFL RPM'S / MFL RPM'S
2250-2100 = 150/2100 = 0.07%
If you have modified a governor spring, this formula will tell you how much droop speed you have after the modification. The less the droop speed the better in some application, like pulling a concrete sled.
When the engine hunts or has an erratic idle, if not normal wear or misadjusted engine components tight linkcage, it usually means that the governor weights and the spring/s are not touching.
They are designed to be if contact and counteract and balance each other's force.This is called a state of balance.
Guido.

 

[Superih]

Nice post.

 

[LW]

I'm aware of what causes surge and a not matched weight to spring rate does also, Which is the same as what you have in the above post. The gen. set style gov. is constant speed I thought we were talking about variable speed set-ups. Most all the gen sets of any size now have electronic units.

 

[guido]

Hello LW.
You are correct!. You just missed the last question on my post.It asks if an engine can be controllled to have zero droop speed. You said you know about those governor soooooo good job!
Guido.

 

[LW]

Ok, But really for sake of argument.. They are a frequency moniter that happens to change engine speed to keep the frequency constant. I worked on trying to develop a universal variable speed electronic gov. for a while that could be set to read ignition pulse and control the engine but the servo for variable speed seemed to be the hold up( to fing one thats linear action was fast enough) then to control the over shoot and return required a little more than a basic dc servo drive because it had to ramp up and down. I was shooting to make this for tractors but the cost looked to be to great.

 

[guido]

Hello LW,
Sounds like a good device if you can get around the time delay and make the servo action more responsive. I have a friend who has quite an extensive eletronic background.
He designed for me a device that is used in series with the power on a dc circuit which is intermittently losing power and shows that it has lost power.He drew that circuit in a couple of minutes at lunch time.
Pretty sharp fellow. I would be interested in your progress.
Guido.

 

[LW]

I have a brother that has a PHD EE and I have cornered him for some help, he shunned me and then I went to the older brother he does PLC controls. Now He has found a PLC controller that is 12 volt and tiny that might do the trick. Some of these newer cars have a direct shaft mounted motor in the throttle body that would be the way to go. Might have to wait for the technology to trickle down...

 

[guido]

Hello LW,
Sounds like you are making some progress.
Guido.