介绍四冲程发动机英文翻译（毕设翻译）

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1. Introduction to the four-stroke engine
Internal Combustion Engine
The engine is a self-contained power unit which converts the heat energy of fuel into mechanical energy for moving the vehicle. Because fuel is burned within the engine, it is known as an internal combustion engine. In the internal combustion engine, air/fuel mixture is introduced into a closed cylinder where it is compressed and then ignited. The burning of the fuel cause a rapid rise in cylinder pressure which is converted to useful mechanical energy by the piston and crankshaft. The most common engine is the four-stroke piston engine. These four strokes are intake stroke, compression stroke, power stroke and exhaust stroke.
Intake Stroke
The intake stroke of a four-stroke engine begins with the piston at top dead center(TDC). The starter causes the crankshaft to rotate in a clockwise direction. The crankshaft, through the connecting rod, forces the piston to move downward. This downward, movement of the piston creates a vacuum, a difference in pressure, in the space above the piston. The engine manufacturer times the intake valve action so that it opens automatically at or slightly before the piston starts down. Therefore, a mixture of gasoline and air, pushed by the atmospheric, pressure outside the engine, rushes through the intake manifold and into the engine cylinder. At the same time, the exhaust valve remains closed during this downward stroke of the piston. This valve closure prevents the entering air/fuel charge from escaping through the exhaust port. After the piston reaches the bottom of its first stroke, the cylinder is practically full of an air/fuel charge. The drawing of an air/fuel charge into the cylinder in this manner, during the downward movement of the piston, constitutes the intake stroke of the piston.
Compression Stroke
After the piston reaches bottom dead center (BDC), it moves upward again as the starter continues to turn the crankshaft in a clockwise direction. As the piston is beginning to move upward, the intake valve closes, and the exhaust valve remains closed. Since both valves are closed, the piston compresses the air/fuel mixture in the small space between the top of the piston and the cylinder head. As the piston reaches TDC again during its upward travel, the compression stroke of the piston is over. The air/fuel charge is now under compression so that it will produce a great deal of power when the spark plug ignites it.
Power Stroke
Just as or slightly before the piston reaches TDC on the compression stroke with the air/fuel mixture fully compressed, a timed electrical spark appears at the spark plug. This spark ignites the compressed air/fuel mixture. The burning mixture begins to expand; the pressure in the combustion chamber above the piston immediately increases. These results in a high pressure applied to the top of the piston. Now, both valves remain closed during the power stroke. This assures that the total force of the expanding gas applied itself to the head of the piston. This tremendous force pushes the piston downward on the power stroke, causing the connecting rod to rotate the crankshaft. In other words, the force resulting from the expansion of the burning air/fuel mixture is turning the crankshaft.
Exhaust Stroke
Near the end of the downward movement of the piston on the power stroke, the camshaft opens the exhaust valve, but the intake valve remains closed. Although much of the gas pressure has expended itself driving the piston downward, some pressure still remains when the exhaust valve opens. This remaining pressurized gas flows comparatively freely from the cylinder through the passage (port) opened by the exhaust valve. Then, as the piston again moves up in the cylinder, it drives any remaining gases out of the cylinder past the open exhaust valve. As the piston travels through the TDC position and starts downward again in the cylinder, a new operating cycle begins. The four strokes are continuously repeated in every cylinder as long as the engine remains running.
Flywheel
The engine cycle has only one power stroke where the piston is actually driving the crankshaft. During the other three strokes, the rotating crankshaft is moving the piston up or down in its cylinder. Thus, during the power stroke, the crankshaft tends to spend up; during the other three strokes, it tends to slow down. To keep the crankshaft turning smoothly between two power strokes, the flywheel is attached to the end of the crankshaft. This wheel resists any effort to change its speed of rotation. When the crankshaft tends to speed up or slow down, flywheel inertia resists it.
Engine Classification
For identification purposes, manufacturers classify automobile engine by their by their cylinder arrangement, valve arrangement, and type of system used to cool the engine.
Engine manufacturers basically use three distinct way to arrange the cylinder in an engine: in-line, V-shape, or opposed.
Automobile engines have their valves arranged in one of three ways. In an L-head engine, the valves are in the block, sitting side by side, adjacent to the cylinder. This engine design was at one time very common, but because of its limited compression ratio, the usage now has been confined. The F-type engine has one valve in the cylinder head and one in the engine block. Modern automotive engines utilize the third type of valve arrangement, with both valves in the cylinder head.
Manufacturers also classify engines as being either air- or water-cooled. In these air-cooled engines, the cylinders are cooled by the air flowing around. A liquid-cooled engine uses a liquid coolant as the medium to remove heat from the engine. With this system, the engine has the water jackets in the block and head, which surround the cylinders and combustion chambers and through which coolant circulates freely. This coolant enters the engine from the bottom of the radiator and circulates throughout the engine, where it absorbs heat. Then it exits from the upper water jacket and pours into the upper portion of the radiator. As the coolant passes through the radiator, it picks up the heat contained in the coolant and passes this heat to the air flowing around the radiator passages or tubes. Thus, the coolant leaving the lower tank is cool ready to flow through the engine again.




2 .Engine construction
   Engine Block
The engine block forms the main framework, or foundation, of the engine. The block is cast mainly from gray iron or iron alloyed with other metals such as nickel or chromium. However, some blocks have been made from aluminum. In any case, the block itself has many components.
The cylinders are cast into the block. The cylinders are circular, tube like openings in the block, which act as guides for the pistons as they move up and down. In aluminum blocks, the manufacturer usually installs cast-iron or steel cylinder sleeves (liners). The water jackets are also cast into the block. Finally, the block has cast-in bores for both the camshaft and crankshaft.
Many parts are also attached by fastening devices to the engine block. These items include the water pump, oil pan, the flywheel or clutch housing, the ignition distributor, oil and fuel pump, and the cylinder head.
Cylinder Head
The cylinder head is bolted to the block. The manufacturer casts the cylinder head in one piece from iron, from iron alloyed with other metals, or from aluminum alloy. Aluminum has the advantage of combining lightness with rather high heat conductivity. Depending on the style of engine, the cylinder head serves many functions.
Pistons
The engine manufacturer fits a piston into each cylinder of the engine. The piston is a movable part or plug that receives the pressure from the burning air/fuel mixture and converts this pressure into reciprocating (up-and-down) motion. Manufacturers make most engine pistons from aluminum, which is less than half the weight of iron. Iron pistons were common engines.
Piston Clearance
Piston clearance is the distance between the outer circumference of the piston and the cylinder wall itself. In operation, oil fills this clearance so that the piston moves on films of lubricating oil. If this clearance is too small, several problems can develop. On the other hand, excessively large clearance can result in piston slap as the piston itself operates many degrees hotter than the adjacent cylinder wall and therefore expands more. Manufacturers must control this expansion in order to avoid the loss of adequate piston clearance.
Piston Rings
Some operating clearance must exist between the piston and the cylinder wall; however, some form of seal is necessary between the piston and the cylinder wall to prevent blow by. Consequently, piston rings are used to provide the necessary seal to eliminate blow by and to control oil consumption. Automotive pistons have two kinds of rings: compression and oil control. The compression rings primarily seal against the loss of air/fuel mixture as the piston compresses it and also the combustion pressure as the mixture burns. While the function of the oil control ring is to prevent excessive amounts of oil from working up into the combustion chamber.
Connecting Rods
As mentioned earlier, the piston moves up and down in the cylinder, in a reciprocating motion. In order to rotate the drive wheels, a connecting rod and crankshaft must change reciprocating motion to rotary. The connecting rod itself attaches at one end to the piston and on the other end to the crankpin section of the crankshaft.
Crankshaft
The crankshaft is the main rotating member, or shaft, of the engine. Its function, along with the connecting rod, is to change the reciprocating motion of the piston to rotary. In addition, the crankshaft is responsible for driving the camshaft through timing gears, plus operating the accessories via a system of belts and pulleys. Lastly, the crankshaft carries the total torque-turning or twisting effort and delivers it to the flywheel. From the flywheel the torque then pass either to the friction clutch assembly or to the torque converter.
Designed into the one-piece crankshaft are areas for main bearing journals, crankpins, counterweights, flywheel flange, and driving hub.
Flywheel
The flywheel is a comparatively heavy wheel, bolted to the flange on the rear end of the crankshaft. Its function is to keep the engine running smoothly between power strokes. Its inertia tends to keep the flywheel rotating at a constant speed. The flywheel also has several other functions. For example, the flywheel has gear teeth around its outer circumference. These teeth mesh with teeth located on the starting motor drive pinion in order to crank the engine over. In addition, the rear surface of the flywheel serves as the driving member of the clutch assembly.
Valve
Modern engine have cylinder head that contain valves. These valves open and close ports to allow or stop the flow of gases into or from the combustion chamber. Each cylinder requires at least two: an intake and exhaust.
Camshaft
The camshaft is another rotating shaft within the engine; it serves usually three functions. First, the camshaft has a series of cams that can change rotary motion to straight-line motion which cause the intake and exhaust valves to open. The camshaft will have one cam for each valves, or, in most engines, two cams per cylinder. Second, the camshaft has an eccentric, or special cam, designed to operate the fuel pump. Finally, the camshaft has a gear that drives the oil pump and ignition distributor.
Lifters
A lifter is a cylindrical part within an engine that rests on a cam of the camshaft. As the camshaft rotates, the cam raises the lifter, and the lifter in turn opens a valve. The lifter may be in direct contact with the tip of the valve stem, or it may bar against a push rod that functions along with a rocker-arm assembly to open a valve.
Push Rods and Rocker Arms
Along with the camshaft, valves, valve seats, and valve springs, some valve trains have several other components------the push rods and rocker arms. The push rod is a metal rod that fits between the lifter and the rocker arm. Its function is to transmit cam lobe lift from the camshaft to the rocker arm assembly. The rocker arm is nothing more than a precision-designed lever. Its function is to convert the upward motion of a push rod into downward motion that compresses the spring and opens the valve.
Valve Timing
Duration is the length of time a valve is open. The measurement of this open period is not in units of time because the actual time a valve remains open varies with engine speed. Therefore, this measurement is in degrees of crankshaft rotation, which does not change with speed. To lengthen the time and to accelerate the air/fuel mixture flow into the cylinders, both the intake and exhaust valves must be open at the same time for a short period. The overlap is provided in order to take advantage of the inertial forces in the escaping exhaust gases. These gases create strong suction as they rush out of the combustion chamber.
Timing Gears
The manufacturer machines a cam lobe into a given shape that produces a given amount of valve-open duration and overlap. Furthermore, meshing the timing gear or installing the chain onto the sprockets at a specific place will time the valves to open and close at the proper moment in the engine’s cycle.


翻译
1介绍四冲程发动机
内燃机
发动机是一个独立的动力装置，将燃料燃烧释放的热能转化为移动汽车所需要的机械能。因为燃料在发动机内燃烧，故被称为内燃机。在内燃机中，空气和燃料混合物被吸入到一个封闭的气缸内进行压缩，然后点燃。燃料的燃烧导致气缸气体压力急剧升高，活塞和曲轴将其转化为有用的机械能。最常见的发动机是四冲程活塞式发动机。这四冲程是指进气行程，压缩行程，做功行程和排气行程。
进气行程
四冲程发动机进气行程始于活塞上止点中心（TDC）。点火系统令曲轴在顺时针方向旋转。曲轴通过连杆使活塞向下移动。由于活塞下降，在活塞的上方空间产生压力差，从而使运动的活塞内形成真空状态。发动机制造商记录进气阀的规律，以便活塞开始下降时或稍前它会自动打开。因此，汽油和空气的混合物，在大气和发动机以外的压力推动下，穿过进气歧管进入发动机气缸。同时，保持排气阀门关闭，直到活塞向下运动行程结束。阀门关闭防止空气/燃料通过排气口进入空气。活塞到达下止点后，气缸实际上充满了空气/燃料。空气/燃料以这种方式进入汽缸，活塞向下运动期间，构成了活塞进气行程。
压缩行程
活塞到达下止点（BDC）后，当点火开关继续令曲轴以顺时针方向转动时，它又一次向上运动。当活塞开始向上移动，进气门关闭，排气门仍然关闭。由于这两个阀门关闭，活塞在活塞顶部与气缸盖这个狭小的空间中压缩空气/燃料混合物。当活塞上行过程中再次到达活塞上止点中心（TDC）时，活塞的压缩行程结束。空气/燃料此时在高压下以便当火花塞点燃它时产生一个很大的力。
做功行程
在压缩行程中空气/燃料混合物完全压缩活，活塞到达上止点时或稍前时，定时电火花出现在火花塞上进行点火。火花点燃压缩的空气/燃料混合物。燃烧混合物开始膨胀，活塞上方的燃烧室内压力立即增加。结果最高压力作用于活塞顶部。现在，两个阀门在做功行程中仍处于关闭状态。这确保了不断膨胀的气体总力作用到活塞头顶部。这巨大的力量推动活塞下行做功行程，致使连杆曲轴旋转。换句话说，该力的产生从燃烧的空气/燃料混合物膨胀到转动的曲轴。
排气行程
在活塞做功冲程向下运动快结束时，通过凸轮轴打开排气阀，但进气阀仍然关闭。虽然许多压缩气体膨胀导致活塞下行，但当排气阀门打开时，有些压力依然存在。加压气体比较自由的通过气缸从打开的排气门中流出。然后，当活塞在汽缸中再次向上移动时，它推动了所有剩余气体从打开了排气阀中流出。当活塞穿过上止点中心（TDC）时，开始在汽缸内再次下行，新的运行周期就开始了。只要发动机的每一个汽缸保持运行，四行程是不断重复的。
飞轮
发动机周期中只有一个做功冲程，那是在活塞完全推动曲轴时。在其他三个行程中，活塞在汽缸中上下移动曲轴做旋转运动。因此，在做功冲程中，曲轴往往消耗能量，在其他三个冲程中，它往往慢下来。为了保证曲轴在两个做功行程之间顺利转动，飞轮帮助曲轴转动。飞轮抵制任何想改变其旋转速度的力。飞轮的惯性可以阻止曲轴的加快或减慢速度。
发动机的分类
为了便于识别，制造商靠气缸排列、阀门的安排，以及用于发动机冷却系统类型为发动机分类。
发动机制造商基本上采用三种不同的方式来安排在一个发动机汽缸：直插式，V形，或对插式。
汽车发动机的阀门安排是三种方式之一。在一个L头发动机上，阀门并排在缸盖上。这台发动机的设计很常见，但由于其压缩比的原因，现在已经在限制使用。F -型发动机有一个阀门在缸盖和缸体上。现代汽车发动机利用第三类气门安排方式，两个阀门都在气缸盖上。
制造商也将发动机按照气冷和水冷分类。在气冷发动机中，气缸冷却靠周围的空气流动。水冷发动机采用冷却液为媒介消除发动机热量。有了这个系统，发动机在缸体和缸盖上环绕着冷却水套，冷却液通过该冷却水套在汽缸和燃烧室内自由流通。冷却液从散热器底部进入到整个发动机来吸收热量并循环。然后，它从上部水套出口流入到散热器的上部。当冷却液通过散热器时，冷却液带走热量并把这些热量传递给散热器周围的空气。因此，冷却液通过水槽流向发动机，准备再次冷却发动机。




























2发动机构造
发动机缸体
发动机缸体主要的基础框架。缸体主要由灰铸铁或铁合金和其他金属如镍或铬的合金。一些缸体由铝制成。在任何情况下，缸体本身有很多组成部分。
气缸被铸成缸体。气缸是圆形的，管像缸体的开口，容易使他们充当引导活塞上下移动的物质。在铝制缸体上，制造商通常安装铸铁或钢（衬）气缸套。水套也被放进缸体里。最后，在凸轮轴和曲轴中缸体埋入水孔。
许多部分也紧固在发动机缸体上。这些部分包括水泵，油底壳，飞轮或离合器壳体，点火配电盘，油和燃料泵，汽缸头。
缸盖
汽缸盖用螺栓连接到缸体上。制造商用一块铁、铁合金和其他金属或者用铝合金铸造缸盖。铝具有相结合亮度相当高的导热度的优势。取决于发动机的风格，缸盖还能提供许多功能。
活塞组
发动机制造商安装活塞到每个发动机的气缸。活塞是一个可移动的部分或塞住，受到来自燃烧空气/燃油混合物燃烧膨胀所带来的压力，并将其转换为往复式（向上和向下）运动的能量。大多数发动机生产商使用铝制造发动机活塞，它的重量不到铁制活塞的一半。铁活塞是常见的发动机活塞。
活塞间隙
活塞间隙是活塞在外圆周到汽缸壁的距离。在运行中，石油填补这一间隙，以便活塞在润滑油膜中运动。如果此间隙过小，可引发几个问题。另一方面，过大的间隙会导致活塞撞击内壁导致活塞比其相邻的活塞温度高并产生撞击使其扩张。制造商必须控制这种扩张，以避免足够的活塞间隙损失。
活塞环
有些操作系统之间必须存在间隙，像活塞和汽缸壁，但一些结构之间需要密封活塞和汽缸壁，以防止撞击。因此，活塞环是用来提供必要的密封，消除了撞击并控制燃油消费。汽车活塞环有两种：压缩控制和燃油控制。压缩环密封主要靠活塞压缩时损失的空气/燃料混合物，并为混合燃烧时产生燃烧压力。油控环的功能是防止工作时进入燃烧室过量的油。
连杆
如前所述，活塞在汽缸内以往复运动上下移动。为了旋转驱动车轮，连杆和曲轴必须改变往复运动来改变旋转。连杆本身连接在活塞的一端，另一端接到曲轴连杆轴部分。
曲轴
曲轴是发动机主要的旋转结构或旋转轴。它的功能是通过连杆将活塞的往复运动传递成旋转运动。此外，曲轴负责通过定时齿轮推动凸轮轴，在加上通过滑轮组系统操作一个皮带和滑轮系统的配件。最后，曲轴通过总扭矩旋转或扭曲力，并提供给飞轮。然后对摩擦离合器总成或液力变矩器飞轮转矩传递。
将曲柄，平衡力，飞轮边缘，推进中心设计成一体化的曲轴是该领域的主要课题，。
飞轮
飞轮是一个比较沉重的轮，用螺栓固定在曲轴后端的边缘上。它的功能是在做工行程中保证发动机顺利运行。其惯性往往会保持飞轮在一个恒定的高速的范围内旋转。飞轮也有一些其他功能。例如，飞轮的外圆周有齿。这些齿网与齿在启动电机驱动小齿轮上啮合，为了是转动引擎的曲柄停止。此外，在飞轮后表面作为离合器总成的驱动部件。
阀门
现代发动机的缸盖包含阀门。这些阀门开启或者关闭来允许或阻止气体流动到燃烧室。每个气缸至少需要两个阀门：一个进气一个排气。
凸轮轴
凸轮轴是发动机内的另一个旋转轴，它通常提供三种功能。第一，凸轮轴有一连串的凸轮，他可以将旋转运动改成直线运动致使进气和排气阀门打开。凸轮轴为每个阀门设定一个凸轮，或在大多数发动机每缸有两凸轮。第二，有一个偏心凸轮轴，或特殊凸轮，专为操作燃料泵而设计。最后，凸轮轴有一个驱动油泵和点火分配器的齿轮。
推杆
推杆是在一个发动机内的基于一种凸轮轴的凸轮的圆柱。当凸轮轴旋转时，凸轮顶起推杆，推杆转而打开一个阀门。推杆可能直接接触阀杆的顶端，也可能挨着一个随着弹动杆组装的推杆来打开阀门。
推杆和摇臂
随着凸轮轴，阀，阀座，阀弹簧，阀列车以及一些其他几个组件------推杆和摇臂。推杆是安装在推杆和摇臂杆的一根金属杆。它的功能是使凸轮凸角从凸轮轴的摇臂杆中升起。摇臂只不过是一个设计精密的杠杆。它的功能是把向上运动的推杆转换成向下运动的过程，这个过程能够压缩弹簧并且打开阀门。
气门正时
持续时间是一个阀门打开时间的长短。这个开放时期的测量不是在一个单位时间，因为这段时间的时间阀门随着发动机的转速保持开放。因此，这种方法适用于不与速度变化的曲轴旋转情况下。为了延长时间并且加速空气/燃料混合气体流入缸体，进排气阀必须同时打开一段时间。重叠的情况下以便采取提供的惯性力将废气排出的优势。当他们急于冲出燃烧室的外时，这些气体产生强大吸力。
定时齿轮
机器制造商将一个凸轮突起做成一个特定的能在某一个给定的时间或时间重叠的使阀门打开形状。此外，在某一个特定时间啮合一个定时齿轮或者将链安装在链轮上来正时阀门并在发动机周期中的恰当时间打开或关闭

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