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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.