Welcome to my Governor Operations and Tips page.
The governor's purpose on a gasoline engine is to determine MAXIMUM speed at which an engine will operate, and to attempt to maintain an even, set speed. Engine wear/condition and load determine minimum speed. Below, we will attempt to explain engine governor operation and principals.
Volume Control, or "Throttle Governing"
|Gas engine governors are based on the principal of controlling engine speed by balancing spring pressure or tension
against a force based on or controlled by engine speed. With a mechanical governor, spring pressure is balanced
against the pressure from the force of spinning flyweights. Where the balance between the two is achieved is where
the engine speed will be maintained. This is called the "governed speed". If the spring tension is increased,
the result is an increase in throttle opening, and thus, engine speed.
If the spring tension is decreased, the throttle is closed, reducing engine speed until the balance is again restored.
In the example to the left, as engine speed increases, the weights, (B), move outward, causing collar, (D), to shift to the left, or outward, pulling fork, (F) with it. (F) is attached to link (E) through a lever, and pushes UP on (E). (E) is attached to the throttle at(C) and causes it to close. This action continues until the force of the spinning weights is equal to the force of springs (A). This will be the governed speed. The governor will maintain this position until either the spring pressure is changed, or the speed of the engine is changed by a change in the load placed on it. At that time, the system forces will re balance.
In summary, when spring tension is increased, it takes more force from the weights to overcome the extra spring force. The increase in spring tension opens the throttle, causing the engine to run faster until the force of the weights again equals the springs force, preventing the throttle from opening further, achieving the balance which is governed speed.
"Hit and Miss" Governing
Hit and Miss governing works on the same basic principals explained above, except that the control is achieved
by locking and unlocking the exhaust valve operation. When governed speed is reached, the exhaust valve is locked
in the open position, preventing further intake of fuel/air mixture, and preventing the engine from doing anything
more than "coasting" until more speed/power is called for. As speed drops, the governor releases the
exhaust valve, intake of fresh fuel mixture is allowed, and normal operations take place until governed speed is
again attained. Hit and miss governing is obviously more fuel efficient, but doesn't allow for as close a control
of speed. "H & M" governing is also more battery efficient - in cases where battery ignition was
used, the governor would also generally break the ground to the ignition system, stopping ignition system functions,
and saving on battery use when power/speed wasn't needed.
A Chapman pamphlet from the early 1920's explains that engines equipped with battery ignition had hit and miss governing, while magneto equipped engines had volume governing (throttling governor).
In the example below, as engine speed increases, weights (A) move outward against spring tension, causing cone shaped sleeve (B) to move away from engine, lifting governor lever (C) which in turn pushes governor finger (D) downward, locking the exhaust pushrod (E) in the extended position, preventing exhaust valve from closing.
As engine speed decreases, springs pull weights (A) inward, which in turn push the cone (B) in toward engine, allowing lever (C) to drop (assisted by return spring), releasing the exhaust push rod (E).
- To slow down a hit and miss governed engine, use looser springs on the flyweights. Using only one spring will also work, but in theory, may cause uneven wear, or binding of the weights, so use two light springs when you can.
- Keep all moving parts lubricated, especially surfaces where levers or forks meet the spinning "hub", "sleeve" or "cone". This is a high speed/high friction area.
- Too much wear causes "pounding", increases the rate of wear, and causes uneven governor operation or speed control. All parts should move freely by hand, but not have "slop".
- Make sure weights are free to move, and that the latch or lever that moves to lock the exhaust push-rod is easily moved into latch position - test it by moving the lever inward toward the push-rod and making sure that it will indeed hold the valve open.
- If you paint your engine, be sure that no paint is on the pins that governor parts pivot on - it may get gummy and inhibit free movement. I usually sand paint off of all pivot points to insure free movement. Also make sure that no parts are "painted in position" - try all parts for free movement after the paint is dry.
Make sure that the catch mechanism that locks the enhaust valve open isn't worn, that it properly catches - the finger should be sharp, and should have a slight angle back to help lock. There should be a matching angle on the catch block. See "Fig. III" on right.
Now, take a little trip over to my governor test page to see how well you do!