新版轮机英语unit3dieselengineconstructionppt课件

Lesson 3 Diesel Engine Construction,理解柴油机的主要固定件 理解柴油机的主要运动件 活塞的冷却,Cylinder block,A-Frame (Entablature),Bedplate,Tie rod,Seating,Cylinder cover,Exhaust valve,Inlet valve,Fuel injector,Cylinder,Piston,Piston ring,Connecting rod,Four-stroke diesel engine,Combustion chamber,Piston pin,crankshaft,Crank web,词汇,Bearing; journal; bolt; bore; Clearance; dowel pin,Bedplate(机座) and Frame(机架) The bedplate, which in most cases is of the welded design, is bolted(螺栓） to the seating which forms part of the double bottom of the ship.,Cylinder block,A-Frame (Entablature),Bedplate,Tie rod,Seating,Cylinder cover,It is secured (固定) in the transverse(横向的) direction by means of bolts known as side-chock bolts (侧楔螺栓) and in longitudinal(纵向的) direction by means of end-chock bolt (端楔螺栓).,The crankshaft rests(放置、坐落) in bearing（轴承） built into cross girders(横梁) of the bedplate.,Bearing,Cross girder,Housing,These bearings, known as main bearings, each consist of two shells(轴瓦) which are supported in housings(轴承座) machined（用车床加工） in the bedplate and secured by means of studs(双头螺栓)and bearing caps(轴承盖).,The thrust block or thrust bearing(推力轴承), located at the aft end of the engine, may be integral（整体的） with, or separate from, the bedplate.,*On the flat(平的) upper surface of the bedplate are arranged a number of A-shaped frames or entablatures(机架) which may be manufactured of cast iron or fabricated steel(结构钢).,The frames are mounted on and bolted to the bedplate cross girders.,At the top of the A-frames there is a strong cast iron frame（框架结构） called the scavenging air box,which is built of a number of sections provided with vertical（垂直） flanges(法兰) enabling them to be bolted together to form a block for 1-3 cylinders in front of the chain transmission, and a block with 4-6 cylinders aft of the chain transmission.,The chain transmission, forming the connection between the crankshaft and the camshaft , is enclosed in a cast iron casing（盒，箱体） known as the chain drive casing.,Cylinders and Covers On top of scavenging air box is mounted a strong cast iron frame for each cylinder.,These frames are known as cylinder blocks（汽缸体） or cooling jackets(冷却水套), which are provided with vertical flanges enabling them to be bolted together in the foremost and aftmost groups in the same way as the scavenging air boxes.,The bedplate, frames and cylinder blocks are secured together by long tie-rods（贯穿螺栓） to achieve a greater rigid construction(刚性结构) with less deformation(变形) in service and lower vibration.,The cylinder liners（气缸套） are made of alloyed（合金的） cast iron and the cylinder surfaces are sometimes chromium-plated(镀铬).,The cylinder liners are extend somewhat down in the scavenging air box, and sealing between the liner and the top of the scavenging air box is achieved by the rubber rings（橡胶圈） fitted into the slots（缝，狭槽） machine-turned(机加工的，切削) in the liners.,In the part of the cylinder liner inside the scavenging air box there is a series of openings known as scavenging air ports.,These ports are located at such a height that they are just exposed by the upper edge of the piston when the piston is in the bottom dead-center position.,The ports are drilled in the liners at an angle of approx. 20（倾角）, the result being that the scavenging air is given a rotary movement. （使扫气旋转）,Each cylinder is closed at the top by a cylinder cover, made of a special heat-resistant steel (耐热钢).,The cover is mounted against a flat surface at the top of the cylinder liner and located（定位） on the liner by means of a machine-turned guide edge（机械加工的凸肩）.,A sealing ring is inserted in a groove（凹槽） turned（车削） in the conical(圆锥形的) part of the cover. The fitting of the sealing ring in the conical surface must be carried out with great care.,The cylinder covers and the liners are bolted together by means of studs screwed into the cylinder frames.（缸体）,The cylinder liner has drillings for cylinder lubrication（润滑）, and, in later types（新型）, has drillings for cooling water at the uppermost part of it.,In each cylinder cover is a large central opening for mounting the exhaust valve, and two or three holes for the fuel valves.,The cylinder cover is also provided with holes for: the starting valve; the safety valve; the indicator cock(示功器旋塞); the cooling-water inlet and the cooling-water outlet to the exhaust valve cooling chamber（冷却水腔）.,A piston consists of a lower partpiston skirt(活塞裙) of cast iron（铸铁） and an upper part or crown(活塞头) made of a special heat-resistant steel. They are bolted together and fixed to the piston rod.,1.Pistons and Piston rods,Piston crown,Piston skirt,Piston rod,Piston ring,The position of the piston parts in relation to each other is secured by means of machine-turned（车削） recesses(凹槽) and a dowel pin(定位销) in the crown.,Each piston is provided with five or six piston rings fitted in chromium plated（镀铬） grooves in the crown.,The two or three topmost rings are narrow rings having diagonal cuts(斜切口式), while the next two are broad and are provided with overlapping end joints （重叠搭口）.,The lowest ring is an oil distributor ring.,Diagonal cuts,Overlapping end joint,All the rings are slightly rounded on their external top and bottom edges to keep the oil film on the cylinder liner during the running-in period(跑合期、磨合期) for new piston rings.,External top,External bottom,In order to control thermal stresses（热应力）, thin-wall intensively（集中的，强烈的） cooled pistons(薄壁集中冷却式活塞) are used for some types of modern engines.,In this case, the piston has an internal insert（插件） in the piston crown, which serves only to direct（导向） the cooling liquid flow and, thereby, to intensify the conventional cocktail shaker(鸡尾振荡冷却) effect.,The piston rods are bored（镗孔） from the top flange to a point opposite the center of the crosshead(十字头). Through this bore, a long pipe is inserted which goes nearly to the bottom of the bore.,Pipe,The outside diameter of the pipe is less than the diameter of the bore, the result being that an annular space（环形空间） is formed between the piston rod and the pipe.,Annular space,The lower end of each piston rod is reduced in diameter to fit a bore in the crosshead, this being secured to the piston rod by a nut.,The piston rods are provided with dowel pins（定位销） to ensure the correct assembly of the components（部件）.,Piston rod,Crosshead,On each of the two journals（轴颈） of the crosshead, crosshead shoes(十字头滑板) are mounted which are guided in the built-in crosshead guides(十字头导板) of the engine frame.,Crosshead,Crosshead shoe,Engine frame,Crosshead guide,The position of the crosshead shoes on the crosshead is determined by dowel pins. The guide shoes are secured to the crosshead by means of tap-bolts(锥体螺钉).,The crosshead shoes are white metal lined(白合金衬里), grooves（沟槽） being cut horizontally in the face of the white metal to ensure an adequate supply of lubricating oil.,The crosshead is short and rigid（刚性的） and the bearings are so constructed（结构） that the bearing pressure between the journal and bearing is distributed evenly over the entire length of the bearing.,In order to improve the working conditions of the bearings, the bearing pressure is made smaller and the peripheral（周围的） speed (is made) higher in later designs.,The pistons are cooled by oil supplied from the forced lubrication system.,The cooling oil is admitted through the pipe, from which the oil is led to the cooling spaces of the piston through telescopic pipes(伸缩管) or articulated pipe(铰接管), and round the internal pipes of the piston rods.,The cooling oil is conducted from the piston through the internal pipes of the piston rods and the ducts in the crossheads, as well as the slotted pipes（开槽管） from which the oil is led to “control boxes” with sight glasses(观察镜) on the engine.,Sealing between the crankcase and scavenging air boxes is achieved by means of the piston rod stuffing boxes, located in the bottom of the scavenging air boxes. Each stuffing is provided with two sealing rings and three scraper rings（刮油环）.,The sealing rings, which are mounted uppermost are in four parts and pressed together around the piston rods by means of coil springs(圈簧).,Connecting Rod and Main Bearings The crosshead and crankpin bearings (曲柄销轴承) are made of cast steel and each consist of an upper and a lower part secured to the connecting rod by means of fitted bolts(紧配螺栓), the nut of which are secured（防松）.,Compression shims（压缩比调整片） are provided between the bottom end bearing and the palm（手掌） of the connecting rod. Shim 薄垫片,The bearings have white metal bearing surfaces provided with lubrication grooves for the necessary supply of lubricating and cooling oil.,Shims(垫片,调整片) of different thickness are inserted between the shells（轴瓦） to enable adjustment of the bearing clearances (approx. 0.20-0.30mm).,The main bearings, which support the crankshaft, each consist