governors (1)
TRANSCRIPT
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Governors
Engine Speed controlThis presentation is from Virginia Tech and has not been edited by
Georgia Curriculum Office.
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Performance Objectives
Students will be able to list anddescribe the purpose and types ofgovernors found on small gasolineengines
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Enabling Objectives
Given the instruction in class thestudent will be able to list, describe,and define the purpose of thefollowing small engine governors with80% accuracy.
Pneumatic
Centrifugal
Vacuum
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Interest Approach
What purpose does the governorserve on a small engine?
Have any of you ever unhooked thegovernor on a small engine such ason you go-cart?
What affect did it have?
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Governors
Governors serve three basicpurposes:
Maintain a speed selected by theoperator which is within the range ofthe governor.
Prevent over-speed which may cause
engine damage.
Limit both high and low speeds.
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Governors
Generally governors are used tomaintain a fixed speed not readilyadjustable by the operator or tomaintain a speed selected by meansof a throttle control lever.
In either case, the governor protectsagainst overspeeding.
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How does it work?
If the load is removed on anoperating engine, the governorimmediately closes the throttle.
If the engine load is increased, thethrottle will be opened to preventengine speed form being reduced.
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Example
The governor onyour lawnmowermaintains the
selected enginespeed even whenyou mow through aclump of high grass
or when you mowover no grass atall.
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Pneumatic Governors
Sometimes calledair-vanegovernors, they
are operated bythe stream of airflow created by thecooling fins of the
flywheel.
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Air-Vane Governor
When the engine experiences suddenincreases in load, the flywheel slowscausing the governor to open thethrottle to maintain the desiredspeed.
The same is true when the engine
experiences a decrease in load. Thegovernor compensates and closes thethrottle to prevent overspeeding.
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Centrifugal Governor
Sometimesreferred to as amechanical
governor, it usespivoted flyweightsthat are attachedto a revolving shaft
or gear driven bythe engine.
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Mechanical Governor
With this system, governor rpm is alwaysdirectly proportional to engine rpm.
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Mechanical Governor
If the engine is subjected to a suddenload that reduces rpm, the reductionin speed lessens centrifugal force onthe flyweights.
The weights move inward and lowerthe spool and governor lever, thus
opening the throttle to maintainengine speed.
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Vacuum Governors
Located between the carburetor and theintake manifold.
It senses changes in intake manifold
pressure (vacuum).
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Vacuum Governors
As engine speed increases or decreases thegovernor closes or opens the throttlerespectively to control engine speed.
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Hunting
Hunting is a condition whereby theengine speed fluctuate or is erraticusually when first started.
The engine speeds up and slowsdown over and over as the governortries to regulate the engine speed.
This is usually caused by animproperly adjusted carburetor.
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Stability
Stability is the ability to maintain adesired engine speed withoutfluctuating.
Instability results in hunting oroscillating due to over correction.
Excessive stability results in a dead-
beat governor or one that does notcorrect sufficiently for load changes.
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Sensitivity
Sensitivity is the percent of speedchange required to produce acorrective movement of the fuelcontrol mechanism.
High governor sensitivity will help
keep the engine operating at aconstant speed.
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Summary
Small engine governors are used to:
Maintain selected engine speed.
Prevent over-speeding.
Limit high and low speeds.
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Summary
Governors are usually of the followingtypes:
Air-vane (pneumatic)
Mechanical (centrifugal)
Vacuum
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Summary
The governor must have stability andsensitivity in order to regulate speedsproperly. This will prevent hunting orerratic engine speed changesdepending upon load changes.