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1、Lesson4DieselEngineConstruction(2)第4课柴油机结构(2)Pistonsandpistonrods活塞及活塞杆Apistonconsistsofalowerpart-pistonskirtofcastiron-andaupperpartorcrownmadeofaspecialheat-resistantsteel.活塞由其下部——铸铁制成的活塞裙,以及上部——耐热钢制成的活塞头组成。Theyareboltedtogetherandfixedtothepistonrod.它们用螺栓连在一起并固定在活塞杆上。
2、Thepositionofthepistonpartsinrelationtoeachotherissecuredbymeansofmachine-turnedrecessesandadowelpininthecrown.活塞部件相互间的位置由活塞头上车削的凹槽和定位销来固定。Eachpistonisprovidedwithfiveorsixpistonringsfittedinchromiumplatedgroovesinthecrown.每个活塞装有五至六道活塞环,活塞环装在头部镀铬的环槽中。Thetwoorthreetopmostr
3、ingsarenarrowringshavingdiagonalcuts,whilethenexttwoarebroadandareprovidedwithoverlappingendjoints.最上面的两三道活塞环是带斜切口的窄环,紧接下去的两道活塞环是带有重叠搭口的宽环。Thelowestringisanoildistributorring.最下面的那道环是刮油环。Alltheringsareslightlyroundedontheexternaltopandbottomedgestokeeptheoilfilmonthecylin
4、derlinerduringtherunning-inperiodfornewpistonrings.所有活塞环顶部和底部的外缘都稍有倒角,以便在新活塞环磨合期间缸套上留有油膜。Inordertocontrolthermalstresses,thinwallintensivelycooledpistonsareusedforsometypesofmodernengines.为了控制热应力,某些现代柴油机采用薄壁集中冷却活塞。Inthiscase,thepistonhasaninternalinsertinthepistoncrown,wh
5、ichservesonlytodirectthecoolingliquidflowand在这种情况下,活塞头内部有一插件,它用来对冷却液流导向thereby,tointensifytheconventionalcocktailshaker'effect.由此可增强传统的“鸡尾震荡”效应。Thepistonrodsareboredfromthetopflangetoapointoppositethecenterofthecrosshead.活塞杆从顶部法兰到与十字头中心相对位置处锉孔。Throughthisbore,alongpipeisi
6、nsertedwhichgoesnearlytothebottomofthebore.一根长管从此插入接近孔底。Theoutsidediameterofthepipeislessthanthediameterofthebore,theresultbeingthatanannularspaceisformedbetweenthepistonrodandthepipe.管的外径小于孔的直径,因此在活塞杆和管子之间形成一个环形空间。Thelowerendofthepistonrodisreducedindiametertofitaboreint
7、hecrosshead,thisbeingsecuredtothepistonrodbyanut.活塞杆的下端直径减小,插入十字头内孔中,并用螺帽将十字头与活塞杆紧固。Thepistonrodsareprovidedwithdowelpinstoensurethecorrectassemblyofthecomponents.活塞杆上装有定位销,以确保各部件的正确装配。Oneachofthetwojournalsofthecrosshead,crossheadshoesaremountedwhichareguidedinthebuilt-i
8、ncrossheadguidesoftheengineframe.在十字头两端轴颈处,各装有十字头滑块。十字头滑块由发动机机架内的一十字头导板导向。Thepositionofthecrossh
