汽车英语翻译

英文翻译
Braking System
Energy is required when a vehicle is accelerated from rest to a certain speed. A
proportion of that energy is now stored in the vehicle and is called kinetic energy. In
order to reduce the speed of the vehicle, the brakes have to convert the kinetic energy
to heat energy; the speed of conversion governs the rate at which the vehicle slows
down.
The three types of braking systems are in use today: service braking system,
parking braking system and additional retarding-braking system. The service braking
system and the parking braking system have separate control and transmission devices.
The service braking system is normally foot-operated, while the parking braking
system is hand- operated.
Two types of brakes are used in modern cars: drum brakes and disc brakes. Since
1976, all cars have used disc brakes on the front wheels. Most cars use drum brakes
on the rear wheels . In both drum and disc brakes, a hydraulic system applies the
brakes. The hydraulic system connects the brake pedal to the brake parts at each
wheel.
These have two shoes, anchored to a stationary back-plate, which are internally
expanded to contact the drum by hydraulic cylinders or a mechanical linkage.
In the case of the simplex brake, C*(brake factor) is the sum of the values for the
individual shoes, and is ≈2.0（referred to a specific coefficient of friction)．A
disadvantage of this design is the great difference in the braking effect between the
two brake shoes, and the resulting greatly increased wear on the leading shoe. For this
reason, the trailing shoe is often equipped with a much thinner lining than the leading
shoe.
An advantage of this type of brake is the nearly equal brake lining wear on both
shoes and the higher internal transmission ratio in comparison to simplex brakes.
Many cars have 2 L.S. front brakes and L.&T. rear brakes. The more powerful
front brakes take advantage of the transference of weight from the rear to the front
which occurs when the brakes are applied.
Duo-servo drum brake
This type of drum brake has an application mechanism which is simpler, more
reliable and insensitive to temperature. It comprises diaphragm cylinder, automatic
slack adjuster, brake shaft and S-cam.
The main disadvantage of drum brakes is that the friction area is almost entirely
covered by a lining, so most heat must be conducted through the drum to reach the
outside air to cool.
Exposed to the air, disc brakes radiate the heat to the air better than drum brakes:
This means that the brake can be operated continuously for a longer period, i.e. they
have a greater resistance to fade (fall-off in brake efficiency due to heat).
Disc brakes as used in most passenger cars are slowly beginning to be used in
commercial vehicles as well. Aside from their use in fast coaches, current use of disc
brakes in commercial vehicles is primarily limited to front- axle brakes for commercial

vehicles up to a weight of approx. 7.5 t which are driven in a manner similar to
passenger cars.
The master cylinder contains two separate sections, there is a piston in each
section and both pistons are connected to a brake pedal in the driver's compartment.
When the brake pedal is pushed by the driver, the two pistons move in the two
sections of the master cylinder. This forces brake fluid out and through the brake lines,
or tubes, to the brake mechanisms at the wheels. In a typical system, the brake fluid
from one section of the master cylinder goes to the two front-wheel brakes. The brake
fluid from the other section goes to the two rear-wheel brakes. The purpose of this
that, if one section fails, the other section will still provide braking.
he operating principle of the power-assisted system is the same as for a
non-power system. However, braking force is increased through the use of a vacuum
booster unit. Atmospheric pressure helps to push the brake pedal. Thus, less muscle
effort is required.
In SI engines, vacuum is generated via a connection to the engine intake
manifold, and diesel engines use a vacuum pump.
Operation principle (Tandem master cylinder): after passing over snifter holeⅠ,
the push-rod piston forces the brake fluid into brake circuit Ⅰ. The compression of
the spring and the pressure buildup in brake circuit I actuates the intermediate piston,
which passes over snifter hole Ⅱ and builds up pressure in brake circuit Ⅱ
The port for brake circuit I, which supplies the rear drum brakes, has a
pre-pressure valve which assures a residual pressure of approx 150kPa when the
brakes are released. This prevents the entry of air through the wheel-cylinder seals.
The more heavily the driver brakes, the greater is the dynamic shifting of weight
from the rear axle to the front axle. With the vehicle empty, the braking force at the
rear axle may be so great that the rear axle locks before the front axle. This can lead to
instability when braking, i.e. to skidding .Braking stability is obtained when,
irrespective of vehicle loading, the front axle always locks before the rear axle. The
correct braking-force distribution can be achieved by brake–pressure- regulating
valves which are installed in the brake lines to the wheels of the rear axle.
A compressor is used as the energy source, and is usually of the plunger type; the
intake air is compressed via automatic suction and delivery valves.
The combination brake cylinder consists of a single-chamber diaphragm cylinder
for the service brakes and a spring-brake actuator for the parking brakes. The cylinder
and spring brake actuator are in tandem and act on a common pressure rod.
Electrohydraulic braking systems are designed to allow electonic control of
vehicle braking while retaining a reduced hydraulic system. The EHB control unit
receives inputs from sensors connected to the brake pedal. In normal operation, a
backup valve is closed and the controller activates the brakes of the wheel through
an electric motor driven hydraulic pump. When the controller goes into a fail-safe
mode, the backup valve is opened, which allows the brakes to be controlled
through a conventional hydraulic circuit.
In order to brake the vehicle, the field coils are supplied with current (from the
battery or alternator) and generate a magnetic field. Eddy currents are induced in the

rotors as they pass through this field. This generates a braking torque whose
magnitude is a function of the excitation of the stator coils.
he function of an anti-lock, or anti-skid, braking system is to prevent the wheels
from locking under hard braking. Maximum braking force is obtained just before the
wheels lock and skid. Such anti-skid systems are useful on slippery surfaces, such as
ice and snow, where the wheels may lock easily.
The wheel-speed sensor monitors the motion of the wheel. If one wheel shows
signs of locking, there is a sharp rise in peripheral wheel deceleration and in wheel
slip. If these exceed defined critical values, the controller sends commands to the
solenoid- valve unit to stop or reduce the buildup of wheel- brake pressure until the
danger of lock-up has passed. The brake pressure must then be built up again in order
to ensure that the wheel is not under-braked.
A wheel-speed sensor consists of a toothed pulse ring and an inductive wheel-
speed pickup. The pulse ring is mounted on the hub and , as the rotates, produces in
the wheel-speed pickup an A.C. voltage, the frequency of which is proportional to the
wheel speed.
From the signals from the wheel-speed pickups, these microcomputers calculate
the wheel speeds as well as the wheel decelerations and accelerations. A vehicle
reference speed is formed from the wheel speeds of two diagonally opposite wheels.
With this reference speed and the individual wheel speeds it is possible to calculate
the brake slip for each wheel. If a wheel has a tendency to lock, this is determined
from the wheel-acceleration and slip signals.
A separate frame must be light yet strong enough to resist the various loads and
road forces. Commercial vehicles normally use a separate steel frame to provide the
rigidity needed to support the various loads. The two long side members of channel
section are riveted to a number of cross members to give a low weight frame which
offers great resistance to bending, twisting.
Most cars use a unitized body construction, a combined body and frame.
Unitized body construction is lighter than bodyframe construction, but noisier.
Rubber mounts are used between the body section and mechanical parts to absorb
vibrations. The floor pan is made of sections that support the rear suspension and the
transmission.
Modern cars have a blend-air system that mixes warm and unwarmed air to heat
the car. The
the radiator, through the water pump hoses, and to the heater core. Therefore, the
heater core is always hot. The temperature of air entering the passenger compartment
is controlled by the amount of air moving through the heater core. This heated air is
blended with fresh, cool air that bypasses the heater. Small doors in the heating
system regulate the air- flow. Control levers on the dash panel open and close these
doors to direct air to the heat ducts and window defrosters
The purpose of venting systems is to draw in fresh air and remove stale air from
the interior of the car. Fresh air venting systems direct air to two different places. First,
they can direct outside air into the heater housing. This air either can bypass the coil
or it can be heated by the coil. Second, the air can move directly into the passenger

compartment through small vent doors in the dash panel or at floor level. Venting also
can take place by opening the windows.
Levers andswitch to regulate air and heat are located on the dash panel. Some
heater controls use small vacuum motors for simpler, more positive action. Others use
cables, while some use a combination of the two. The vacuum to operate the motors
comes from the engine intake manifold.
As the compressor raises the pressure of the refrigerant, it also heats it. The hot
refrigerant is then pumped into the condenser , where it cools by giving off heat to air
passing over the condenser fins. As the refrigerant cools, it condenses into a liquid.
Still under high pressure, the refrigerant passes into the receiver. The receiver acts as a
storage tank to furnish refrigerant to the expansion valve at all times. From the
receiver, the high- pressure liquid refrigerant passes to the expansion valve.
The expansion valve controls the flow of refrigerant into the evaporator, where a
low pressure is maintained by the suction side of the compressor. As it enters the
evaporator, the refrigerant begins to boil by absorbing the heat from the air passing
over the evaporator core. Having given up its heat to boil the refrigerant, the air is
cooled and passes into the passenger compartment. The refrigerant continues to boil
in the evaporator until all the liquid has vaporized. From the evaporator, the
refrigerant flows back to the compressor to repeat the cycle.

Energy and power


Engines used in automobiles are internal combustion heat engines. They convert
the chemical energy of the gasoline into heat within a power chamber that is called a
combustion chamber. Heat energy released in the combustion chamber raises the
temperature of the combustion gases within the chamber. The increase in gas
temperature causes the pressure of the gases to increase. The pressure developed
within the combustion chamber is applied to the head of a piston to produce a usable
mechanical force, which is then converted into useful mechanical power.
Engine terms:
Linking the piston by a connecting rod to a crankshaft causes the gas to rotate the
shaft through half a turn. The power stroke upthe gas, so means must be
provided to expel the burnt gas and recharge the cylinder with a fresh petrol-air
mixture: this control ofgas movement is the duty of the valves;
Engine block:
The engine block is the basic frame of the engine. All other engine parts either fit
inside it or fasten to it. It holds the cylinders, water jackets, and oil galleries. The
engine block also holds the crankshaft, which fastens to the bottom of the block.
Cylinder sleeve:
The dry sleeve can be cast in or pressed into a new block or used to recondition
badly worn or damaged cylinders that cannot easily be rebored.

Cylinder head:
The cylinder head fastens to the top of the block, just as a roof fits over a house.
The underside forms the combustion chamber with the top of the piston. In-line
engines of light vehicles have just one cylinder head for all cylinders; larger in-line
engines can have two or more.
The cylinder head carries the valves, valve springs and the rockers on the rocker
shaft, this part of the valve gear being worked by push-rods.
Oil pan:
The oil pump in the lubricating system draws oil from the oil pan and sends it to
all working parts in the engine. The oil drains off and runs down into the pan.
Thus,there is constant circulation of oil between the pan and the working parts of the
engine.
Piston assembly:
Most pistons are made from cast aluminum. The piston, through the connecting
rod, transfers to the crankshaft the force created by the burning fuel mixture. This
force turns the crankshaft.
Piston :
In disel engines, the combustion chamber may be formed totally or in part in the
piston crown, depending on method of injection.
Piston rings:
In modern engines, each piston has three rings. (Piston in older engines
sometimes had four rings, or even five.) The inside surface of the ring fits in the
groove on the piston. The ring's outside surface presses against the cylinder walls.
Connecting rod:
The connecting rod little end is connected to the piston pin. A bush made from a
soft metal, such as bronze, is used for this joint. The lower end of the connecting rod
fit the crankshaft journal. This is called the big end.
Cylinder number and firing order:
N.B. No.4 piston is always performing the companion stroke to No.1: when the
inlet valve in No.4 cylinder is fully open, No.1 cylinder inlet valve is fully closed ---
this feature is useful to remember when checking valve clearances.
As each cylinder fires, it causes the crank throw to speed up. The inertia of the
rest of shaft cause it to stay slightly behind, resulting in a twisting action on the
crankshaft.
Inertial ring elastomer
The inertia ring is bonded to the hub through a flexible elastomer (rubber
compound) insert. The inertial ring moves slightly in relation to crankshaft rotation as
each cylinder fires, thereby dampening the torsional vibration of the crankshaft over a
wide range of engine speed.
Valve operation:
The cam is an egg-shaped piece of metal on a shaft that rotates in coordination
with the crankshaft. The metal shaft, called the camshaft, typically has individual
cams for each valve in the engine. As the camshaft rotates, the lobe, or high spot of
the cam, pushes against parts connected to the stem of the valve. This action forces

the valve to move downward. This action could open an inlet valve for an intake
stroke, or open an exhaust valve for an exhaust stroke.
Valve operation：
In this arrangement, the cam lobes push against round metal cylinders called
cam follower. As the lobe of the cam comes up under the cam follower, it pushes the
cam follower upward (away from the camshaft). The cam follower rides against a
push rod, which pushes against a rocker arm. The rocker arm pivots on a shaft
through its center. As one side of the rocker arm moves up, the other side moves down,
just like a seesaw. The downward-moving side of the rocker arm pushes on the valve
stem to open the valve
Valve clearance:
When the engine runs in compression stroke and power stroke, the valves must
close tightly on their seats to produce a gas-tight seal and thus prevent the gases
escaping from the combustion chamber. If the valves do not close fully the engine will
not develop full power. Also the valve heads will be liable to be burnt by the passing
hot gases, and there is the likelihood of the piston crown touching an open valve,
which can seriously damage the engine.
Valve clearance:
So that the valves can close fully some clearance is needed in the operating
mechanism. This means that the operating mechanism must be able to move
sufficiently far enough away from the valve to allow the valves to be fully closed
against its seat by the valve spring. However, if the clearance is set too great this will
cause a light metallic tapping noise.
Valve timing:
It is apparent from this description that the exhaust valve stays open for a short
period of time during which the intake valve is also open. In other words, the end of
the exhaust stroke and the beginning of the intake stoke overlap for a short period of
time. This is called valve overlap. Valve timing and valve overlap vary on different
engines.
Valve timing:
Opening the intake valve before TDC and closing it after BDC increases the fill
of air-fuel mixture in the cylinder. Opening the intake valve early helps overcome the
static inertia of the air-fuel mixture at the beginning of the intake stroke, while leaving
the intake valve open after BDC takes advantage of the kinetic inertia of the moving
air-fuel mixture. This increases volumetric efficiency.
Cam design and control dynamic:
The entire valve-train assembly can be viewed as a springmass system in which
the conversion from stored to free energy causes forced vibration. Valve-train

assemblies with overhead camshafts can be represented with sufficient accuracy by a
1-mass system (consisting of the moving mass, the valve-train assembly stiffness and
corresponding damping).
Camshaft drive mechanism:
Each cam must revolve once during the four-stroke cycle to open a valve. A
cycle, remember, corresponds with two revolutions of the crankshaft. Therefore, the
camshaft must revolve at exactly half the speed of the crankshaft. This is
accomplished with a 2:1 gear ratio. A gear connected to the camshaft has twice the
number of teeth as a gear connected to the crankshaft.




中文翻译
汽车从原地起步加速到某一速度需要能量。储存在汽 车中的那部分能量 称
为动能。要降低车速,制动器必须把汽车的动能转换为热能；转换的速度决定了
汽车减速的快 慢。
目前使用的制动系统有三种类型：行车制动系，住车制动系 和辅助制动系。
行车制动系 和住车制动系有独立的控制和传动装置．行车制动系通常使用脚刹，
而驻车制动系通常使用手刹。 目前使用的制动器有两种类型：鼓式制动器和盘式制动器。从1976年开始，
所有的汽车前轮都使 用盘式制动器, 大部分汽车后轮使用的是鼓式制动器。 在
盘式制动器和 鼓式制动器中都使用液压系统. 液压系统把制动踏板与每个车轮
的制动部件相连接。这种制动器有两个 固定在制动底板上的制动蹄，通过液压轮
缸或机械杆系作用从内侧向 外推开与制动鼓接触。
这种制动器有两个固定在制动底板上的制动 蹄，通过液压轮缸或机械杆系
作用从内侧向 外推开与制动鼓接触。
就领从蹄而言， C*表示各蹄的值的总数，且≈２.０ (特指某一摩擦系数）．这
种设计的缺点是两个制动蹄 制动效果有很大不同，结果大大增加了领蹄上的摩
擦．因此，从蹄的摩擦衬片比领蹄薄．
这种制动器的优点是两个蹄上制动衬片磨损几乎相 同，与领从蹄制动器相
比它的内传动比较高
多数汽车前轮采用双领蹄式制动器，后轮采 用领从蹄式制动器。前轮制动
器制动力很大 ，充分利用制动时轴荷由后轮向前轮转移的 特点。
凸轮式制动器工作过程

这类凸轮制动器有一套简单，稳定，恒温机构．它包 括膜片弹簧制动器室，
自动调整臂，制动轴和S凸轮.
鼓式制动器的主要缺点是它的摩擦面几乎 完全被摩擦衬片覆盖了，制动过
程中大多 数的热要通过制动鼓传给大气进行冷却。
由于暴露于空气中，盘式制动器的散热效果 比鼓式的要好：这意味着盘式
制动器能持续 使用更长的时间，也就是说其抗热衰退性 （因受热导致制动效能
下降）要好得多。
常用在许多乘用车上的盘式制动器正逐渐被用于商用车。 它们 除用于快速
客车外, 目前盘式制动器在商用车上的用途基本限 制在前轴制动, 因为商用车
重量约等于7.5吨时驱动方式与乘用车相似。
制动主缸由两个分开的部分组成，每个部分都有 一个活塞，两个活塞都与驾驶
室里的制动踏板相 连接。
当驾驶员踩下制动踏板时，主缸两套管路中的两活塞移动．迫 使制动液流
出经过制动管路进入各车轮的制动装置中．在标准 制动系统中，主缸的一条管
路中的制动液流向两个前轮制动装 置中，另一条管路的制动液流向两个后轮制
动装置．其目的 是，如果其中一套管路失灵，另一条管路仍然能够提供制动．
伺服制动系的工作原理与人力制动系相同。然而，伺 服制动系通过采用真空助
力装置来增加制动力。大气 压力有助于踩下制动踏板。这样，制动时几乎不需
要 人力。
火花点火式发动机通过连接发动机的进气支管产生 真空，而柴油发动机使
用真空泵．
工作原理(串联式制动主缸）：推杆活塞经过补偿孔Ⅰ迫使制动 液流入制动
回路Ⅰ．弹簧压缩力及制动回路Ⅰ上的压力促动中 间活塞，使它经过补偿孔Ⅱ
并在制动回路Ⅱ上产生压力
制动回路I上的孔为后轮鼓式制动器提供制动液．其内有 一个预压阀，它保证
制动踏板释放时有150kPa残余压力, 阻止空气通过轮缸密封处进入．
驾驶员制动力越大，从后轴到前轴的转移的重量越大．汽车空载时，后轴上 制
动力很大以至后轴在前轴之前抱死．这导致制动不稳定，即发生滑动．当 前轴
总在后轴之前抱死时可获得制动稳定性，它与汽车载重无关．通过安装 在连接
后轮的制动管路上的制动压力调节装置可以得到正确的制动力分配
空压机用做能源一般是活塞型的．通过自动进 气阀进入的空气在其内被压缩
复合式制动室由行车制动器的单室膜片弹簧制动气室和驻车 制动器弹簧助力装
置组成．制动气室和弹簧助力装置串联在 一起并对压力杆作用．
电液制动系统允许电子控制汽车制动,同时保留了简化的液压系 统.电液制动
系统控制单元接受与制动踏板连接的传感器的输入. 正常工作时, 后备阀关闭,

控制器通过由液压泵驱动的电动机控 制制动器. 当控制器进入失效安全模式
时,后备阀打开, 并允许传 统的液压回路控制制动器.
为了刹车，用电池或发电机给励磁线圈供电从而产生磁 场．当转子经过磁
场时感应生成感应电涡流．这样产生的 制动力矩的大小是定子线圈中励磁电流
的函数．
防抱死制动系统的作用是防止在强制动条件下 车轮抱死。只在车轮抱死拖滑时才
会获得最大制动力。 这类防滑系统在冰、雪等光滑路面非常实用，因为 在这些
路面上车轮容易抱死。
轮速传感器监控着车轮的运动，如果一个车轮出现抱死信号， 也就是外车
轮减速度急剧增大且车轮开始滑动。如果超出临界 值，控制器给电磁阀发送命
令来停止或降低制动压力，直到抱 死的危险消除。然后制动力再增大确保车轮
制动力不会不足。
轮速传感器由运动的齿圈和磁感应传感头构成。齿圈安装在 轮毂上，车轮转动
时，在传感头上产生频率与车速成正比的交流电压。
通过来自传感头的信号 ，微机不仅计算出车速而且还计算出减速度和加速度．参
考车速由两对角线位置车轮的轮速构成。用这个 参考速度和单胎速度可以计算出
每个 车轮的滑动率。车轮是否有抱死趋势决定于车轮的加速度和滑动信号。
分离式车架必须足够轻巧而且结实，以承受变化的 载荷和路面作用力。商
用车通常使用分离式钢质车架 ，以获得较好的刚度来承受变化的载荷。两根槽形
的长纵梁铆接着很多横梁，这使车架重量较轻， 具有较好的抗弯和抗扭能力
多数轿车采用承载式车身，也就是车身和车架融为一体。承载式车身比非承 载式
车身质量轻，但噪声大。在车身和机械部件之间安装橡胶块以吸收振动 。地板
由一些支撑后悬架和变速器的部件组成。
多数汽车采用加热过的或未加热过的空气的混合起来加热汽车。 暖风系统的核
心是热芯。热的冷却水来自散热器，通过水泵软管 流到热芯。这样，热芯总是
热的。流经热芯的空气数量控制着进 入车厢的空气温度。加热后的空气同流经
加热器的新鲜冷空气混 合。加热系统中的一些小风门控制空气的流量。前围板
上的控制 杆开启和关闭这些风门，从而将空气引入输热管和风窗除霜器。
通风系统吸入新鲜的空气，排除车内不新鲜的空气。 通风系统将新鲜空气
引入两个地方。首先，通风系统 将外部空气引入加热器壳里，空气从线圈旁流
过或被 线圈加热。其次，空气可通过前围板或地板上的小风 门直接将空气引入
车厢. 打开车窗也可实现通风。
控制空气和热量的杠杆和按钮安装在仪表板上。一 些加热器的控制器使用
真空电动机提供简单可靠的 工作。另一些使用缆线，还有一些两者兼用。驱动 电
动机的真空来自发动机的进气管。

压缩机增加制冷剂的压力，对制冷剂进行加热。高温的制 冷剂被吸入冷凝
器中，将热量释放给流经冷凝器散热片的 空气而得到冷却。制冷剂冷却时冷凝
为液体。在高压作用 下，制冷剂进入储液器。储液器不断地给膨胀阀供应制冷
剂。高压液态的制冷剂从储液器流向膨胀阀。
膨胀阀控制着进入蒸发器的制冷剂流量，在蒸发器里压缩 机吸入端保持低
压。制冷剂进入蒸发器时，吸收流经蒸发 器芯的空气的热量而沸腾。空气释放
热量使制冷剂沸腾， 得到冷却后进入车厢。制冷剂在蒸发器里持续沸腾直到液
体完全蒸发为止。制冷剂从蒸发器流回压缩机，重复吸热 制冷循环。


能源和动力
能源是用于生产电力。化工能源是转化为燃料的燃烧的热量，这个过程被称
为燃烧。如果发动机燃烧发生在气缸内的地方，被称为发动机内部燃烧发动机。
如果燃烧发生在气缸外 的地方，被称为发动机外部燃烧发动机。用于汽车的能源
叫内部燃烧高能源，高温能源在燃烧室里降低能 缓解气体燃烧在气缸内的温度。
燃烧气体温度的升高引起气压变大，燃烧室内发展应用到了活塞产生一个 可用的
机械力，然后将其转换成有用的机械能。
活塞通过连杆和曲轴连接，使得气体带动曲轴旋转半 圈。作功冲程耗尽了
所有的气体，这样就必须采取相 应的措施排出废气以及向气缸内充入新鲜的可
燃混合 气：气体的运动由气门来控制。
气缸体是发动机的基体。发动机其它的部件 都安装在缸体内或固定在缸体
上，它包容了 气缸、水套和油道，以及固定在缸体底部的 曲轴等。
干缸套可以铸在或压入新缸体中 ，或者用于严重磨损或损坏而又 不易重镗
的缸体的修复。
气缸盖扣在缸体的顶部，就像屋顶安在房子上 一样。缸盖的下方和活塞顶
部形成燃烧室。轻 型车的直列发动机所有缸仅有一个气缸盖 ，较 大的直列发
动机有两个或更多缸盖。
缸盖上坐有气门、气门弹簧和摇臂轴上的摇臂 ，推杆推动这部分气门传动
机构工作。
润滑系的机油泵从油底壳抽出机油 ，并把机油输送给发动机的所有工 作部
件。机油从油底壳流进流出。 因而在油底壳和发动机的工作部件 之间有机油定
向循环流动。
大多数活塞由铝铸造而成。 通过连杆，活塞把可燃混合 气燃烧所产生的力
传递给曲 轴，并带动曲轴旋转。
柴油机发动机根据喷油方法不同，活塞 头部可以形成全部燃烧室，也可以

是燃 烧室的一部分．
在新型发动机上，每个活塞有三个活塞 环。（在老式发动机上，每个活塞有
四 个甚至五个活塞环。）环的内边面紧贴 在活塞的环槽里，环的外表面紧压在
气 缸壁上。
连杆小头与活塞销连接，小头孔处压有诸 如青铜这种较软材料所制成的衬
套，连杆 下端连接在曲轴的连杆轴径处，称为连杆 大头。
注意4号活塞和1号活塞总是成对运行：4号 气缸进气门全闭时，1号气缸
进气门全开— 这个特点在检查气门间隙时是很有用的。
当一缸点火时，使曲轴摆幅的速度提高，而其它轴的惯 性阻碍它，使其滞
后，从而导致曲轴扭转。
惯性盘通过一层由橡胶合成的可变形人 造橡胶层与减振器圆盘相连．在每
个汽 缸点火时，惯性盘相对于曲轴运动做微 小转动，用以削减发动机较大速度
范围 内的曲轴扭转振动．
凸轮是一个蛋形的金属块，它安装在同曲轴 协调运转的一根金属轴上，该
轴称为凸轮轴 ，其上有同发动机每一个气门对应的凸轮。 当凸轮轴旋转时，凸
轮的最高点，也就是凸 圆，推动连接气门杆的部件，使得气门向下 运动，在进
气冲程打开进气门，在排气冲程 打开排气门。
在这种方案中，凸轮基圆推动圆形的金属筒 ，也就是挺柱。凸轮凸圆运动
到挺柱下方时 ，推动挺柱远离凸轮轴向上运动。挺柱带着 推杆，推杆推动摇臂，
摇臂绕摇臂轴的中心 转动。摇臂的一端升起，另一端就落下，这 类似于跷跷板。
摇臂向下运动的一端推动气 门杆打开气门。
当发动机在压缩冲程和作功冲程工作时，气门必须紧贴在气门 座上，形成
良好的气密性以防止燃烧室漏气。如果气门关闭不 严，发动机就不能发挥出全
部的功率。而且气门头部容易被经 过的高温气体烧蚀，活塞顶部也可能会碰到
气门使发动机严重 损坏。
所以在气门传动机构中要预留一些间隙使气 门得以完全关闭。这就是说，
气门传动机构 运动要与气门有一个充分远的距离，使得气 门在气门弹簧作用下
紧闭气门座。可是如果 间隙过大，会引起轻微的金属敲打声。
由上显而易见，排气门在进气门打开的一小段时间内也打开着。换 句话说，
排气冲程终了和进气冲程初期有一小段时间的重叠，这称 为气门重叠。不同的
发动机，其配气相位和气门重叠是不一样。
在上止点前打开进气门和在下 止点后关闭进气门可增加气缸内可燃混合气
的进气量。提前打开进气门有助于克服进气冲程初 期的惯性，同时在下止点后
打开进气门可充分利用可燃混合气 运动时的惯性，这可增加容积效率。
整个气门机构可看成一个弹簧-质量系统，其储存的 能量转化为自由能量时

会引起受迫振动。带有顶置凸 轮轴的气门机构可非常精确地用单质量系统来表
示， 由运动质量、气门机构的刚度和相应的阻尼组成。
在一个四冲程的循环里，每个凸轮转动 一次来打开一个气门。在一个循环
里曲 轴是转动两圈的。因此，凸轮轴正好以 曲轴转速的一半旋转，这是由2:1
的传动 比来实现的。连接凸轮轴的齿轮齿数是 连接曲轴的齿轮齿数的两倍。