31-05-2013, 01:02 PM
Governors
Governors.ppt (Size: 367 KB / Downloads: 212)
Enabling Objectives
Given the instruction in class the student will be able to list, describe, and define the purpose of the following small engine governors with 80% accuracy.
Pneumatic
Centrifugal
Vacuum
Interest Approach
What purpose does the governor serve on a small engine?
Have any of you ever unhooked the governor on a small engine such as on you go-cart?
What affect did it have?
Governors
Governors serve three basic purposes:
Maintain a speed selected by the operator which is within the range of the governor.
Prevent over-speed which may cause engine damage.
Limit both high and low speeds.
Generally governors are used to maintain a fixed speed not readily adjustable by the operator or to maintain a speed selected by means of a throttle control lever.
In either case, the governor protects against overspeeding.
How does it work?
If the load is removed on an operating engine, the governor immediately closes the throttle.
If the engine load is increased, the throttle will be opened to prevent engine speed form being reduced.
Pneumatic Governors
Sometimes called air-vane governors, they are operated by the stream of air flow created by the cooling fins of the flywheel.
Air-Vane Governor
When the engine experiences sudden increases in load, the flywheel slows causing the governor to open the throttle to maintain the desired speed.
The same is true when the engine experiences a decrease in load. The governor compensates and closes the throttle to prevent overspeeding.
Hunting
Hunting is a condition whereby the engine speed fluctuate or is erratic usually when first started.
The engine speeds up and slows down over and over as the governor tries to regulate the engine speed.
This is usually caused by an improperly adjusted carburetor.
Stability
Stability is the ability to maintain a desired engine speed without fluctuating.
Instability results in hunting or oscillating due to over correction.
Excessive stability results in a dead-beat governor or one that does not correct sufficiently for load changes.
Summary
Small engine governors are used to:
Maintain selected engine speed.
Prevent over-speeding.
Limit high and low speeds.
The governor must have stability and sensitivity in order to regulate speeds properly. This will prevent hunting or erratic engine speed changes depending upon load changes.