汽车发动机外文翻译文献Word文件下载.docx
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汽车发动机外文翻译文献Word文件下载.docx
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Attheendofthepowerstrokethecamshaftopenstheexhaustvalve,andtheexhauststrokebegins.Remainingpressureinthecylinder,andupwardmovementofthepiston,forcetheexhaustgasesoutofthecylinder.Attheendoftheexhauststroke,theexhaustvalveclosesandtheintakevalveopens,repeatingtheentirecycleofeventsoverandoveragain.
3EngineBlockandCylinderHead
3.1EngineBlock
Theengineblockisthebasicframeoftheengine.Allotherenginepartseitherfitinsideitorfastentoit.Itholdsthecylinders,waterjacketsandoilgalleries(Fig.2-4).Theengineblockalsoholdsthecrankshaft,whichfastenstothebottomoftheblock.Thecamshaftalsofitsintheblock,exceptonoverhead-camengines.Inmostcars,thisblockismadeofgrayiron,oranalloy(mixture)ofgrayironandothermetals,suchasnickelorchromium.Engineblocksarecastings.
Fig.2-4V6engineblock
Someengineblocks,especiallythoseinsmallercars,aremadeofcastaluminum.Thismetalismuchlighterthaniron.However,ironwearsbetterthanaluminum.Therefore,thecylindersinmostaluminumenginesarelinedwithironorsteelsleeves.Thesesleevesarecalledcylindersleeves.Someengineblocksaremadeentirelyofaluminum.
3.2CylinderSleeves
Cylindersleevesareusedinengineblockstoprovideahardwearingmaterialforpistonsandpistonrings.Theblockcanbemadeofonekindofironthatislightandeasytocastwhilethesleevesusesanotherthatisbetterabletostandupwearandtear.Therearetwomaintypesofsleeves:
dryandwet(Fig.2-5).
DrysleeveWetsleeve
Fig.2-5Cylindersleeve
3.3CylinderHead
Thecylinderheadfastenstothetopoftheblock,justasarooffitsoverahouse.Theundersideformsthecombustionchamberwiththetopofthepiston.In-lineengineoflightvehicleshavejustonecylinderheadforallcylinders;
largerin-lineenginescanhavetwoormore.Justaswithengineblocks,cylinderheadscanbemadeofcastironoraluminumalloy.Thecylinderheadcarriesthevalves,valvespringsandtherockersontherockershaft,thispartofvalvegearbeingworkedbythepushrods.Sometimesthecamshaftisfitteddirectlyintothecylinderheadandoperatesonthevalveswithoutrockers.Thisiscalledanoverheadcamshaftarrangement.
3.4Gasket
Thecylinderheadisattachedtotheblockwithhigh-tensilesteelstuds.Thejointbetweentheblockandtheheadmustbegas-tightsothatnoneoftheburningmixturecanescape.Thisisachievedbyusingcylinderheadgasket.Gasketsarealsousedtosealjoinsbetweentheotherparts,suchasbetweentheoilpan,manifolds,orwaterpumpandtheblocks.
3.5OilPan
Theoilpanisusuallyformedofpressedsteel.Theoilpanandthelowerpartofcylinderblocktogetherarecalledthecrankcase;
theyenclose,orencase,thecrankshaft.Theoilpumpinthelubricatingsystemdrawsoilfromtheoilpanandsendsittoallworkingpartsintheengine.Theoildrainsoffandrundownintothepan.Thus,thereisaconstantcirculationofoilbetweenthepanandtheworkingpartsoftheengine.
4PistonAssembly,piston
rings,The
piston
pin,ConnectingRods,CrankshaftsAndFlywheel
4.1Piston
Pistonringsandthepistonpinaretogethercalledthepistonassembly(Fig.2-6).
Fig.2-6Piston,pistonringsandconnectingrod
The
is
an
important
part
of
a
four-stroke
cycle
engine.
Most
pistons
are
made
from
cast
aluminum.
piston,
through
the
connecting
rod,
transfers
to
crankshaft
force
created
by
burning
fuel
mixture.
This
turns
crankshaft.
To
withstand
heat
combustion
chamber,
must
be
strong.
It
also
light,
since
it
travels
at
high
speeds
as
moves
up
and
down
inside
cylinder.
hollow.
thick
top
where
takes
brunt
expansion
force.
thin
bottom,
there
less
heat.
head,
or
crown.
skirt.
have
three
ring
grooves
top.
sections
between
called
lands.
4.2
rings
rings
fit
into
near
piston.
In
simplest
terms,
thin,
circular
pieces
metal
that
in
tops
pistons.
modern
engines,
each
has
rings.
(Piston
older
engines
sometimes
had
four
rings,
even
five.)
surface
fits
groove
on
ring'
s
outside
presses
against
cylinder
walls.
Rings
provide
needed
seal
That
is,
only
contact
two
keep
gases
compression
lower
one
prevents
oil
splashed
onto
bore
entering
ring.
4.3The
pin
pin
holds
together
rod.
holes
hole
end
rod
much
smaller
than
small
bottom
side
then
other
firmly
place
center
Pins
high-strength
steel
hollow
center.
Many
pins
chrome-plated
help
them
wear
better.A
round
joins
boss.
4.4ConnectingRods
little
connected
pin.
A
bush
soft
metal,
such
bronze,
used
for
this
joint.
journal.
big
end.
For
big-end
bearing,
steel-backed
lead
tin
shell
bearings
used.
These
same
those
main
bearings.
split
angle,
so
enough
withdrawn
bore.
forged
alloy
steel.
4.5Crankshafts
Thecrankshaftisregardedasthe“backbone”oftheengine(Fig.2-7).The
crankshaft,
conjunction
with
converts
reciprocating
motion
th
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