13082013113202-mechanical-governer (1).pptx
TRANSCRIPT
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SEMIN R ON
GOVERNOR
PRESENTED BY-
RAHUL KUMARME 7TH SEM
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Performance Objectives
Students will be able to list and describe thepurpose and types of governors found onsmall gasoline engines
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Enabling Objectives
Given the instruction in class the student willbe able to list, describe, and define thepurpose of the following small enginegovernors with 80% accuracy.PneumaticCentrifugalVacuum
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Interest Approach
What purpose does the governor serve on asmall engine?
Have any of you ever unhooked the governoron a small engine such as on you go-cart?
What affect did it have?
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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 enginedamage.
Limit both high and low speeds.
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Governors
Generally governors are used to maintain afixed speed not readily adjustable by theoperator or to maintain a speed selected bymeans of a throttle control lever.
In either case, the governor protects againstoverspeeding.
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How does it work?
If the load is removed on an operatingengine, the governor immediately closes thethrottle.If the engine load is increased, the throttlewill be opened to prevent engine speed formbeing reduced.
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Example
The governor on yourlawnmower maintainsthe selected engine
speed even when youmow through a clumpof high grass or whenyou mow over no grass
at all.
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Pneumatic Governors
Sometimes called air-vane governors, theyare operated by the
stream of air flowcreated by the coolingfins of the flywheel.
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Air-Vane Governor
When the engine experiences suddenincreases in load, the flywheel slows causingthe governor to open the throttle to maintainthe desired speed.The same is true when the engineexperiences a decrease in load. The governorcompensates and closes the throttle toprevent overspeeding.
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Centrifugal Governor
Sometimes referred toas a mechanicalgovernor, it uses
pivoted flyweights thatare attached to arevolving shaft or geardriven by the engine.
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Mechanical Governor
With this system, governor rpm is always directlyproportional to engine rpm.
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Mechanical Governor
If the engine is subjected to a sudden loadthat reduces rpm, the reduction in speedlessens centrifugal force on the flyweights.The weights move inward and lower thespool and governor lever, thus opening thethrottle to maintain engine speed.
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Vacuum Governors
Located between the carburetor and the intakemanifold.It senses changes in intake manifold pressure(vacuum).
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Vacuum Governors
As engine speed increases or decreases the governorcloses or opens the throttle respectively to controlengine speed.
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Hunting
Hunting is a condition whereby the enginespeed fluctuate or is erratic usually when firststarted.The engine speeds up and slows down overand over as the governor tries to regulate theengine speed.This is usually caused by an improperlyadjusted carburetor.
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Stability
Stability is the ability to maintain a desiredengine speed without fluctuating.
Instability results in hunting or oscillating dueto over correction.Excessive stability results in a dead-beatgovernor or one that does not correctsufficiently for load changes.
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Sensitivity
Sensitivity is the percent of speed changerequired to produce a corrective movementof the fuel control mechanism.
High governor sensitivity will help keep theengine operating at a constant 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 following types: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 or erraticengine speed changes depending upon loadchanges.