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汽车发动机外文翻译文献

(文档含中英文对照即英文原文和中文翻译)

AUTOM OTIVEENGINE

1Engine ClassificationandOverallMechanics

The automobile engines can be classified according to: (1) cycles, (2)coolingsystem, (3) fuel system, (4) ignition method, (5) valve arrangement, (6)cylinderarrangement, (7) enginespeed.

Engines usedin automobilesare the internal combustionheat engines.Theburning of

gasoline inside the engine produces high pressure in the engine combustion

chamber. This high pressure force piston to move, the movement is carried by

connectingrods to the engine crankshaft. The crankshaft is thus made to rotate:therotarymotioniscarriedthroughthepowertraintothecarwheelssothattheyrotateand the carmoves.

Theenginerequiresfourbasicsystemstorun(Fig.2-1).Dieselenginesrequirethree

of

these systems. They are fuelsystem, ignition system (exceptdiesel),lubricating system

and cooling system. However, three other related systems arealsonecessary. These are

the exhaust system, the emission-control system, and thestartingsystem. Each performs a basic job in making the engine run.

Fig. 2-1

Theengineconstruction2EngineOperatingPrinciples

Fig. 2-2 Engineterms

Theterm“stroke”isused to describe the movementof the pistonwithinthe cylinder. The movement of the piston from its uppermost position (TDC, topdeadcenter) to its lowest position (BDC, bottom dead center) is called a stroke.Theoperatingcyclemayrequireeithertwoorfourstrokestocomplete.Mostautomobileenginesoperateonthefourstrokecycle(Fig.2-2).

In four-stroke engine, four strokes of the piston in the cylinder are requiredto

completeone full operating cycle. Each stroke is named after the action. It performs

intake, compression, power, and exhaust in that order (Fig. 2-3).

Intakestroke stroke

1. The intake stroke

Compressionstroke Powerstroke Exhaust

Fig. 2-3 Four-stroke-cycle gasolineengine

The intake stroke begins with the piston near the top of its travel. As the pistonbegins

its descent, the exhaust valve closes fully , the intake valve opens andthevolume of the combustion

chamber

begins

to

increase,

creating

a

vacuum.

Asthepistondescends,anair/fuelmixtureisdrawnfromthecarburetorintothecylinderthrough the intake manifold. The intake stroke ends with the intake valve closejustafter the piston has begun itsupstroke.

2. Compressionstroke

As the piston is moved up by the crankshaft from BDC, the intake valvecloses.The air/fuel mixture is trapped in the cylinder above the piston. Future pistontravelcompressestheair/fuelmixturetoapproximatelyone-eighthofitsoriginalvolume(approximately 8:1 compression ratio) when the piston has

reached TDC.Thiscompletes the compressionstroke.

3. Power stroke

As the piston reaches TDC on the compression stroke, an electric sparkisproduced at the spark plug. The ignition system delivers a high-voltage surgeofelectricitytothesparkplugtoproducethespark.Thesparkignites,orsetsfireto,theair/fuel mixture. It now begins to burn very rapidly, and the cylinderpressureincreases to as much as 3-5MPa or even more. This terrific push against thepistonforces it downward, and

a

powerful

impulse

is

transmitted

through

asthe

the

pistonis

connectingrodtothecrankpinonthecrankshaft.Thecrankshaftisrotated

pusheddown by the pressure aboveit.

4. Exhaust stroke

At the endof the power stroke the camshaft opens the exhaust valve, andthe exhauststrokebegins.Remainingpressureinthecylinder,andupwardmovementofthepiston,forcetheexhaustgasesoutofthecylinder.Attheendoftheexhauststroke,theexhaustvalveclosesandtheintakevalveopens,repeatingtheentirecycleofevents over and overagain.

3 Engine Block and CylinderHead

3.1 EngineBlock

Theengineblockisthebasicframeoftheengine.Allotherenginepartseitherfitinsideitorfaste

ntoit.Itholdsthecylinders,waterjacketsandoilgalleries(Fig.2-4). The engine block also holds

the

crankshaft,

which

fastens

to

the

bottom

oftheblock.Thecamshaftalsofitsintheblock,exceptonoverhead-camengines.Inmostcars,thisblockismadeofgrayiron,oranalloy (mixture) of gray ironand othermetals, such as nickel or chromium. Engine blocksare castings.

Fig. 2-4 V6 engineblock

Someengineblocks,especiallythoseinsmallercars,aremadeofcastaluminum.This metal is

much lighter than iron. However, iron wears better thanaluminum.Therefore, the cylinders in most aluminum engines are lined with iron or steelsleeves.These sleeves are

called cylinder sleeves. Some engine blocks are made entirely ofaluminum.

3.2 CylinderSleeves