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UNIT THREE Engine Construction

By Elsie Murray,2014-10-24 15:09
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UNIT THREE Engine Construction

    UNIT THREE

    Engine Construction

    New Words engine 发动机 complicated 复杂的 contain 包含;容纳 aluminum surround 围绕,包围 pour 浇注,浇铸 mole 模子,模具 cool 冷却 remove 除去 rough 粗糙的 machine 加工 difference 区别 pressure 压力 relatively 相对地,比较地 conduct 引导,传导 rapidly 迅速地 soft 软的 wear 磨损 alloy 合金 silicon particle 粒子 manufacturer 制造厂家 sleeve 套管,衬套 hone ,用磨石磨 etch 侵蚀,腐蚀 slide 滑动 minimum 最小的 maximum 最大的 convert 转换 forge 锻造 cylindrical 园柱的 hollow 空的 groove 凹槽 perimeter 周围,周边 snug 紧帖的,紧身的 ensure 保证,确保 require 需要,要求 clearance 缝隙,间隙 mixture 混合物,混合气 compress 压缩

    forged 锻造的 crankpin 曲柄销 attach 安装,装上,附上 assemble 装配 stamp 盖印,打印于 prevent 防止,避免 switch 切换,转换 unbalance 失衡 unwanted 不需要的 vibration 振动

    damage 损害 member 构件,部件 heat-treated 热处理的 reciprocate 往复运动 bend 弯曲

     Phrases and Expressions Gray iron 灰铁 cylinder liner 气缸衬套 cast iron 铸铁 intake stroke 吸气行程 water jacket 水套 power stroke 作功行程 sand form 沙模 load with 掺入,加入 molten metal 金属溶液 treat with 为……涂上保护层 break up 拆除,打碎 be made of 由……制成的 cylinder-block casting 气缸铸件 diesel engine 柴油机 spark-ignition engine 汽油机 exhausted system 排气系统 high-strength steel 高强度钢 Lock bolt 锁销 back and forth 前后 rod-bearing cap 连杆轴承盖

Cylinder Block

    The cylinder block is cast in one piece. Usually, this is the largest and the most

complicated single piece of metal in the automobile.

     The cylinder block is a complicated casting made of gray iron (cast iron ) or aluminum. It contains the cylinders and the water jackets that surround them. To make the cylinder block, a sand form called a moldis made. Then molten metal is poured into the mold. When the metal has cooled the sand mold is broken up and removed. This leaves the rough cylinder-block casting. The casting is then cleaned and machined to make the finished block. Fig.2-1 shows the a finished cylinder block.

    Cylinder blocks for diesel engines are very similar to those for spark-ignition engines. The basic difference is that the diesel-engine cylinder block is heavier and stronger. This is because of the higher pressures developed in the diesel-engine cylinders.

    Several engines have aluminum cylinder blocks. Aluminum is a relatively light metal, weighing much less than cast iron. Also, aluminum conducts heat more rapidly than cast iron. This means there is less chance for hot spots to develop. However, aluminum is too soft to use as cylinder-wall material. It wears too rapidly. Therefore, aluminum cylinder blocks must have cast-iron cylinder liners or be cast from an aluminum alloy that has silicon particles in it.

    Some manufactures make an aluminum cylinder block that does not have cylinder liners, or sleeves. Instead, the aluminum is loaded with silicon particles. Silicon is a very hard material. After the cylinder block is cast, the cylinders are honed. Then they are treated with a chemical that etches eats away the surface aluminum. This leaves only the silicon particles exposed. The piston and rings slide on the silicon with minimum wear.

Piston

    The piston converts the potential energy of the fuel into the kinetic energy that turns the crankshaft. The piston is a cylindrical shaped hollow part that moves up and down inside the engines cylinder. It has grooves around its perimeter near the top where the rings are placed. The piston fits snugly in the cylinder. The pistons are used to ensure a snug air tight fit. See Fig.2-2.

    The piston in your engines cylinder are similar to your legs when you ride a

    bicycle. Think of your legs as pistons; they go up and down on the pedals, providing power. Pedals are like the connecting rods; they are attached to your

    legs. The pedals are attached to the bicycle crank which is like the crank shaft, because it turn the wheels.

    To reverse this, the pistons (legs) are attached to the connecting rods (pedals) which are attached to the crankshaft (the bicycle rank). The power from the combustion in the cylinders powers the piston to push the connecting rods to turn the crankshaft.

    Connecting-rod

    The connecting rod shown in Fig.2-2 is made of forged high-strength steel. It transmits force and motion from the piston to the crank-pin on the crankshaft. A steel piston pin, or wrist pin, connects the rod to the piston. The pin usually is

    pressed into the small end of the connecting-rod. Some rods have a lock bolt in the small end. As the piston moves up and down in the cylinder, the pin rocks back and forth in the hole, or bore, in the piston. The big end of the connecting rod is attached to a crank-pin by a rod bearing cap.

    Connecting rod and rod-bearing caps are assembled during manufacture. Then

    the hole for the bearing is bored with the-cap in place. This is called line-boring. It makes each rod and its cap a matched set. Usually, the same number is stamped on the rod and cap. This prevents the caps setting mixed during engine services. If the caps are mixed, the bearing bore will not be round. An engine assembled with the rod-bearing caps switched will probably lock the crankshaft. If the crankshaft turns, the bearing will probably have improper clearance and early bearing failure will result.

    Another reason for keeping the cap and rod matched is to prevent engine unbalance and unwanted vibration. All connecting rods in an engine must be as light as possible. But they must all weigh the same. If one rod is heavier than the others, the engine will vibrate. This could damage the engine.

    Crankshaft

    The crankshaft shown in Fig.2-3 is the main rotating member, or shaft, in the engine. It has crank-pins, to which the connecting rods from the pistons are attached. During the power strokes, the connecting rods force the crank-pins and therefore the crankshaft to rotate. The reciprocating motion of the pistons is changed to rotary motion as the crankshaft spins. This rotary motion is transmitted through the power train to the car wheels.

    The crankshaft is a strong, one-piece casting, or forging, of heat-treated alloy steel. It must be strong to take the downward force of the power strokes without excessive bending. It must be balanced so the engine will run without excessive vibration.

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