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Governors

o Engine Speed controlThis presentation is from Virginia Tech and has not been edited by

Georgia Curriculum Office.

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Performance Objectives

o Students will be able to list anddescribe the purpose and types ofgovernors found on small gasolineengines

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Enabling Objectives

o Given the instruction in class thestudent will be able to list,describe, and define the purpose ofthe following small enginegovernors with 80% accuracy.

o Pneumatic

o Centrifugal

o Vacuum

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Interest Approach

o What purpose does the governorserve on a small engine?

o

o Have any of you ever unhooked thegovernor on a small engine such ason you go-cart?

o

o What affect did it have?

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Governors

o Governors serve three basicpurposes:

o

Maintain a speed selected by theoperator which is within the rangeof the governor.

o Prevent over-speed which may causeengine damage.

o Limit both high and low speeds.

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Governors

o Generally governors are used tomaintain a fixed speed not readilyadjustable by the operator or tomaintain a speed selected bymeans of a throttle control lever.

o

o In either case, the governor protectsagainst overspeeding.

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How does it work?

o If the load is removed on anoperating engine, the governorimmediately closes the throttle.

o If the engine load is increased, thethrottle will be opened to preventengine speed form being reduced.

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Example

o The governor onyour lawnmower

maintains the

selected enginespeed even

when you mowthrough a clump

of high grass orwhen you mowover no grass at

all.

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Pneumatic Governors

o Sometimes calledair-vane

governors, they

are operated bythe stream of air

flow created bythe cooling fins

of the flywheel.

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Air-Vane Governor

o When the engine experiences suddenincreases in load, the flywheelslows causing the governor to openthe throttle to maintain the desiredspeed.

o The same is true when the engine

experiences a decrease in load.The governor compensates andcloses the throttle to prevent

overspeeding.

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Centrifugal Governor

o Sometimesreferred to as a

mechanical

governor, ituses pivoted

flyweights thatare attached to

a revolving shaftor gear drivenby the engine.

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Vacuum Governors

o Located between the carburetor and theintake manifold.

o It senses changes in intake manifold

pressure (vacuum).

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Vacuum Governors

o As engine speed increases or decreases thegovernor closes or opens the throttle

respectively to control engine speed.

o

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Hunting

o Hunting is a condition whereby theengine speed fluctuate or is erraticusually when first started.

o The engine speeds up and slowsdown over and over as thegovernor tries to regulate the

engine speed.o This is usually caused by an

improperly adjusted carburetor.

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Stability

o Stability is the ability to maintain adesired engine speed withoutfluctuating.

o Instability results in hunting oroscillating due to over correction.

o Excessive stability results in a dead-beat governor or one that does notcorrect sufficiently for loadchanges.

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Sensitivity

o Sensitivity is the percent of speedchange required to produce acorrective movement of the fuelcontrol mechanism.

o

o High governor sensitivity will help

keep the engine operating at aconstant speed.

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Summary

o Small engine governors are used to:

n

Maintain selected engine speed.n Prevent over-speeding.

n Limit high and low speeds.

n

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