2020年(汽车行业)汽车构造(英文版)

（汽车行业）汽车构造(英文版)

CHAPTER 1 AUTOMOTIVE BASICS


1.1 Principal Components
Today's average car contains more than 15,000 separate, individual parts that must work
together. These parts can grouped into four major categories: engine, body, chassis and
electrical equipment.



1.2 Engine

The engine acts as the power unit. The internal combustion engine is most common: this
obtains its power by burning a liquid fuel inside the engine cylinder. There are two types
of engine :gasoline(also called a spark-ignition engine) and diesel(also called a
compression-ignition engine).Both engines are called heat engines; the burning fuel
generates heat which causes the gas inside the cylinder to increase its pressure and
supply power to rotate a shaft connected to the transmission.

1.3 Body

An automobile body is a sheet metal shell with windows, doors, a hood, and a trunk deck
built into it. It provides a protective covering for the engine, passengers, and cargo. The
body is designed to keep passengers safe and comfortable. The body styling provides an
attractive, colorful, modern appearance for the vehicle.


1.4 Chassis

The chassis is an assembly of those systems that are the major operating part of a vehicle.
The chassis includes the transmission, suspension, steering, and brake systems.

Transmission systems ― conveys the drive to the wheels. The main components are clutch,
gearbox, driveshaft, final drive, and differential.

Suspension― absorbs the road shocks.

Steering― controls the direction of the movement.

Brake― slows down the vehicle.


1.5 Electrical Equipment
The electrical system supplies electricity for the ignition, horn, lights, heater, and starter.
The electricity level is maintained by a charging circuit. This circuit consists of the battery,
alternator (or generator). The battery stores electricity. The alternator changes the
engine's mechanical energy into electrical energy and recharges the battery.

New Words

Principal component 主要部件 category 种类，类型
body 车身 chassis 底盘
layout 布置 power unit 动力装置
internal combustion engine 内燃机 cylinder 汽缸
gasoline 汽油 spark 火
ignition 点燃，点火 diesel 柴油机
compression 压缩 shaft 轴
transmission 传动系 sheet metal 金属板
shell 外壳 hood （发动机）罩

trunk deck 行李舱盖 cargo 货物
styling 样式 assembly 总成，装配
suspension 悬挂，悬置 shock 冲击
steering 转向，操纵 brake 刹车，制动器
clutch 离合器 gearbox 变速器
driveshaft 传动轴 final drive 主减速器，后桥
differential 差速器 slow down （使）慢下来，减速
horn 喇叭 starter 起动机
charge 充电 alternator 交流发电机
Review Questions
1. List the main parts of an automobile?
2. What are the common types of a vehicle according to body styling?
3. Which systems does a chassis include and what are the main functions of the chassis?
4. Why are suspension systems used on vehicles?
CHAPTER2 INTERNAL COMBUSTION ENGINE
2.1 principle of operation
2.1.1 Engine and power

Engine is used to produce power. The chemical energy in fuel is converted to heat by
the burning of the fuel at a controlled rate. This process is called combustion. If engine
combustion occurs with the power chamber. ,the engine is called internal combustion
engine. If combustion takes place outside the cylinder, the engine is called an external
combustion engine.
Engine used in automobiles are internal combustion heat engines. Heat energy

released in the combustion chamber raises the temperature of the combustion gases
with 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.
2.1.2 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 “uses up” the gas , so means must be
provided to expel the burnt gas and recharge the cylinder with a fresh petrol-air
mixture :this control of gas movement is the duty of the valves an inlet valve allows the
new mixture to enter at the right time and an exhaust valve lets out the burnt gas after
the gas has done its job. Engine terms are :
TDC(Top Dead Center):the position of the crank and piston when the piston is farther
away from the crankshaft.
BDC(Bottom Dead Center):the position of the crank and piston when the piston is
nearest to the crankshaft.
Stroke : the distance between BDC and TDC; stroke is controlled by the crankshaft.
Bore : the internal diameter of the cylinder.
Swept volume : the volume between TDC and BDC.
Engine capacity : this is the swept volume of all the cylinder e.g. a four-stroke having a
capacity of two liters(2000cm) has a cylinder swept volume of 50cm.
Clearance volume: the volume of the space above the piston when it is at TDC.
Compression ratio = (swept vol + clearance vol)(clearance vol)

Two-stroke : a power stroke every revolution of the crank.
Four-stroke : a power stroke every other revolution of the crank..

2.1.3 The Four- stroke Spark-ignition Engine Cycle

The spark-ignition engine is an internal-combustion engine with externally supplied
in ignition, which converts the energy contained in the fuel to kinetic energy.
The cycle of operations is spread over four piston strokes. To complete the full cycle it
takes two revolutions of the crankshaft.
The operating strokes are :

This stroke introduces a mixture of atomized gasoline and air into the cylinder. The
stroke starts when the piston moves downward from a position near the top of the
cylinder. As the piston moves downward, a vacuum, or low-pressure area, is created.
During the intake stroke, one of the ports is opened by moving the inlet valve. The
exhaust valve remains tightly closed.

Compression stroke
As the piston moves upward to compress the fuel mixture trapped in the cylinder, the
valves are closed tightly. This compression action heats the airfuel mixture slightly and
confines it within a small area called the combustion chamber.


Power stroke

Just before the piston reaches the top of its compression stroke, an electrical spark is
introduced from a spark plug screwed into the cylinder head.
The spark ignites the compressed, heated mixture of fuel and air in the combustion
chamber to cause rapid burning. The burning fuel produces intense heat that causes
rapid expansion of the gases compressed within the cylinder. This pressure forces the
piston downward. The downward stroke turns the crankshaft with great force.



Exhaust stroke

Just before the bottom of the power stroke, the exhaust valve opens. This allows the
piston, as it moves upward, to push the hot, burned gases out through the open exhaust
valve.
Then, just before the piston reaches its highest point, the exhaust valve closes and the
inlet valve opens. As the piston reaches the highest point in the cylinder, known as TDC,
it starts back down again. Thus, one cycle ends and another begins immediately.
2.1.4 Engine Overall Mechanics
The engine has hundreds of other parts . The major parts of engine are engine block ,
engine heads, pistons, connecting rods, crankshaft and valves. The other parts are joined
to make systems. These systems are the fuel system, intake system, ignition system,
cooling system, lubrication system and exhaust system. Each of these systems has a
definite function. These systems will discussed in detail later.
NEW WORD
Piston 活塞 Connecting rod 连杆
Crankshaft 曲轴 Power stoke 活塞行程

Expel 排出 Valve 气阀
inlet(intake) valve 进气阀 exhaust valve 排气阀
term 术语 TDC 上止点
BDC 下止点 Bore 缸径
swept volume 有效容积 engine capacity 发动机排量
clearance volume 余隙容积,燃烧室容积 compression ratio 压缩比
revolution 旋转,转数 every other 每隔一个
cycle 循环 spread over 分布,遍及
intake stroke 进气行程 compression stroke 压缩行程
knock 敲缸,敲打 exhaust stroke 排气行程
engine block 发动机缸体 lubrication 润滑
2.2 Engine Block and Cylinder Head
2.2.1 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. The camshaft also
fits inside the block, except on overhead-cam engines (OHC). In most cars, this block is
made of gray iron, or an alloy (mixture) of gray iron and other metals, such as nickel or
chromium. Engine blocks are castings.

Some engine blocks, especially those in smaller cars, are made of cast aluminum. This
metal is much lighter than iron. However, iron wears better than aluminum. Therefore,
the cylinders in most aluminum engines are lined with iron or steel sleeves. These sleeves

are called cylinder sleeves. Some engine blocks are made entirely of aluminum.


2.2.2 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. The most common
cylinder head types are the hemi, wedge, and semi-hemi. All three of these terms refer to
the shape of the engine's combustion chamber. The cylinder head carries the valves,
valve springs and the rockers on the rocker shaft, this part of the valve gear being
worked by the push-rods. Sometimes the camshaft is fitted directly into the cylinder
head and operates on the valves without rockers. This is called an overhead camshaft
arrangement. Like the cylinder block, the head is made from either cast iron or
aluminum alloy.


2.2.3 Gasket
The cylinder head is attached to the block with high- tensile steel studs. The joint
between the block and the head must be gas-tight so that none of the burning mixture
can escape. This is achieved by using cylinder head gasket. This is a sandwich gasket, i.e.
a sheet of asbestos between two sheets of copper, both these materials being able to
withstand the high temperature and pressures within the engine.


2.2.4 Oil Pan or Sump
The oil pan is usually formed of pressed steel. The oil pan and the lower part of the
cylinder block together are called the crankcase; they enclose, or encase, the crankshaft.
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.


New Words
engine block 缸体 cylinder head 气缸盖 fasten 使固定
water jacket 水套 oil gallery 油道 camshaft 凸轮轴
overhead-cam(OHC) 顶置凸轮 gray iron 灰铸铁 alloy 合金
nickel 镍 chromium 铬 casting 铸件
head cover 汽缸盖罩 intake manifold 进气总管 distributor 分电
器
oil pan 油底壳 aluminum 铝 be lined with 镶
有
cylinder sleeve 气缸套 hemi 半球形 wedge 楔型，楔入
semi-hemi 准半球形 rocker 摇臂 push-rod 推杆
gasket 衬垫 high-tensile 高强度的 stud 螺栓
gas-tight 密封的 asbestos 石棉 crankcase 曲轴箱，曲柄
箱
encase 封闭，把…包起来 drain off 排出，流出

Review Question
1. What do TDC, BDC, stroke, compression ratio and engine capacity stand for?
2. How do you calculate swept volume and compression ratio?
3. What controls the length of the stroke?
4. List the main parts of the engine overall mechanics?

5. What are the main function of the engine block?

2.3 Piston Connecting Rod and Crankshaft
2.3.1 Piston Assembly

The piston is an important part of a four-stroke cycle engine. Most pistons are made
from cast aluminum. The piston , through the connecting rod, transfers to the crankshaft
the force create by the burning fuel mixture. This force turns the crankshaft .Thin,
circular , steel bands fit into grooves around the piston to seal the bottom of the
combustion chamber. These bands are called piston rings. The grooves into which they
fit are called ring grooves. A piston pin fits into a round hole in the piston . The piston
pin joins the piston to the connecting rod . The thick part of the piston that holds the
piston is the pin boss.
The piston itself , its rings and the piston pin are together called the piston assembly.

To withstand the heat of the combustion chamber, the piston must be strong. It also
must be light, since it travels at high speeds as it moves up and down inside the cylinder.
The piston is hollow. It is thick at the top where it take the brunt of the heat and the
expansion force. It is thin at the bottom, where there is less heat. The top part of the
piston is the head , or crown . The thin part is the skirt The sections between the ring
grooves are called ring lands.
The piston crown may be flat , concave ,dome or recessed . In diesel engine , the
combustion chamber may be formed totally or in part in the piston crown , depending
on the method of injection . So they use pistons with different shapes.

2.3.3Piston Rings
As Fig.2-9 shows , piston rings fit into ring grooves near the of the piston. In simplest
terms, piston rings are thin, circular pieces of metal that fit into grooves in
the tops of the pistons.
In modern engines ,each piston has three rings. (Piston in older engines sometimes
had four rings, or even five.) The ring’s outside surface presses against the cylinder
walls. Rings provide the needed seal between the piston and the cylinder walls. That is,
only the rings contact the cylinder walls. The top two rings are to keep the gases in the
cylinder and are called compression rings. The lower one prevents the oil splashed onto
the cylinder bore from entering the combustion chamber , and is called an oil ring.
Chrome-face cast-iron compression rings are commonly used in automobile engines.
The chrome face provide a very smooth , wear-resistant surface.
During the power stoke , combustion pressure on the combustion rings is very high.
It causes them to untwist . Some of the high-pressure gas gets in back of the rings. This
force the ring face into full contact with the cylinder wall. The combustion pressure also
holds the bottom of the ring tightly against the bottom of the ring groove. Therefore ,
high combustion pressure causes a tighter seal between the ring face and the cylinder
wall.

2.3.4 Piston Pin

The piston pin holds together the piston and the connecting rod . This pin fits into
the piston pin holes and into a hole in the top end of the connecting rod. The top end of
is much smaller than the end that fits on the crankshaft . This small end fits inside the
bottom of the piston . The piston pin fits through one side of the piston , through the
small end of the rod , and then through the other side of the piston . It holds the rod
firmly in place in the center of the piston. Pins are made of high-strengh steel and have a
hollow center . Many pins are chrome-plated to help them wear better.
2.3.3 Connecting rod
The connecting rod is made of forged
high-strength steel . It transmits and motion from the piston to the crankpin on the
crankshaft . 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 fits the crankshaft journal . This is called the big end . For this big-end bearing ,
steel- backed lead or tin shell bearing are used . These are the same as those used for the
main bearings . The split of the big end is sometimes at an angle , so that it is small
enough to be withdrawn through the cylinder bore . The connecting rod is made from
forged alloy steel .


2.3.5 Crankshaft
The crankshaft , in conjunction with the connecting rod , coverts the reciprocating
motion of the piston to the rotary motion needed to drive the vehicle . It is usually made
from carbon steel which is alloyed with a small proportion of nickel .The main bearing

journals fit into the cylinder block and the big end journals align with the connecting
rods .At the rear end of the crankshaft is attached the flywheel , and at the front end are
the driving whells for the timing gears , fan , cooling water and alternator .
The throw of the crankshaft , the distance between the main journal and the big
end centers , controls the length of the stroke . The stroke is double the throw , and the
stroke- length is the distance that the piston travels from TDC to BDC and vice versa .

2.3.6 Flywheel
The flywheel is the made from carbon steel . It fit s onto the rear of the crankshaft . As
well as keeping the engine rotating between power strokes it also carries the clutch ,
which transmits the drive to the transmission , and has the starter ring gear around its
circumference . There is only one working stroke in four so a flywheel is needed to drive
the crankshaft during the time that the engine is performing the non-power strokes .

New Words
Comprise 由。。。。。。。组成，包含 Inter 惯性，惯量 Radius 半径，范围
Circular 圆形的 Steel band 钢圈 Fit into 放入，放进
Groove 凹槽 Piston pin 活塞销 Pin boss 活塞销凸
台
Withstand 抵抗 Hollow 空的 Brunt 冲力
Crown 活塞顶 Skirt 裙部 Ring land 环带
Concave 凹的，凹入的 Dome 圆顶 Recessed 隐蔽的
Cylinder wall 气缸壁 Cylinder bore 缸筒 Splash 飞溅

chrome-face 表面镀银的 Untwist 朝相反方向的 In place 在适当位置
Chrome-plated 镀铬的 Forge 伪造，仿造 Crankpin 曲轴销
Bush 轴瓦，套筒 Bronze 青铜 Crankshaft journal 曲轴轴颈
Steel-backed 钢背的 Lead 铅 Tin 锡
Splint 切口，中断，分配，分离 In conjunction with 连同 Reciprocating motion 往复
运动
Rotary 旋转的 Carbon steel 碳钢 Journal 轴颈
Align with 匹配 Overlap 重叠 Timing gear 正时齿
轮
Throw 摆幅 Vice verse 反之亦然 Impulse 脉冲
Space out 隔开，分隔 Through out 遍及 Diagram 图表
Firing order 点火顺序 Companion 成对 Circumference 圆
周

2.4 Valve System
The valve system is made up of those parts needed to open and close the valves at just
the right time .
2.4.1 Valve Operation

To coordinate the four-stroke cycle , a group parts called the valve train opens and
closes the valves ( moves them down and up , respectively ) . These valve movements
must take place at exactly the right moments . The opening of each valve is controlled by
a camshaft .
1. Camshaft(OHC) Valve Train Overhead

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 , or open an exhaust valve for an
exhaust stroke .
As the camshaft continues to rotate , the high spot moves away from the valve
mechanism . As this occurs , valve spring pull the valve tightly closed against its opening ,
called the valve seat .
Valve in modern car engines are located in the cylinder head at the top the engine .
This is known as an overhead valve (OHC) configuration . In addition , when the camshaft
is located over the cylinder head , the arrangement is known as overhead camshaft (OHC)
design . Some high- performance engine have two separate camshafts , one for each set
of inlet and exhaust valves . These engines are known as overhead-camshaft (DHOC)
engine .
2. Push-rod Valve Train
The camshaft also can be located in the lower part of the engine , within the
engine block . To transfer the motion of the cam upward to the valve , additional parts
are needs .
In this arrangement , the cam lobs push against round metal cylinders called
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 .
Because a push-rod valve train has additional parts , it is more difficult to run at
high speeds . Push-rod engines typically run at slower speeds and , consequently ,
produce less horsepower than overhead- camshaft designs of equal size . ( Remember ,
power is the rate at which work is done .)



2.4.2 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 fill power . Also the valve heads will be liable to be brunt by the passing hot
gases , and there is the likelihood of crown touching an open valve , which can seriously
damage the engine .
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 t 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 taping noise .

2.4.3 Valve Timing

The time at which valves open and close ( valve timing ) and the duration of the
valve opening in stated in degrees of crankshaft rotation . For example , the intake valve

normally begins to open just before the piston has reached the top dead center . The
valve remains open as the piston travels down to BDC and even past BDC . This is intake
valve duration .An example of this could be stated as follows : IO at 17BTDC , IC at
51ABDC ( or , intake opens 17before top dead center , intake closes 51after bottom dead
center ) . Intake valve duration in this case is 248 of crankshaft rotation .
This leaves 129 duration for the compression stroke since compression ends when
the piston reaches TDC . At this point the power stroke begins . The power stroke ends
when the exhaust valve begins to open approximately at 51 before bottom dead center .
The duration of the power stroke in this case is also 129 .
Since the exhaust valve is opening at 51 BBDC , this begins the exhaust stroke . The
exhaust stroke continues as the piston passes BDC and moves upward to past TDC . With
the exhaust valve closing at 17 TTDC , the duration of the exhaust stroke is 248 .
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 stroke overlap for a short period of time .
This is called valve overlap . Valve timing and valve overlap vary on different engines.
Opening the intake valve before TDC and closing it after BDC increase 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 kentia of the moving air-fuel mixture .
This increase volumetric efficiency .
As the piston moves down on the power stroke past the 90 ATDC position ,
pressure in the cylinder has dropped , and the leverage to the crankshaft has decreased

due to connecting rod angle and crankshaft position . This ends the effective length of
the power stroke , and the exhaust valve can now be opened to begin expelling the
burned gases . The exhaust valve remains open until the piston has moved up past the
TDC position . This helps to remove as much of the burned gases as is possible and
increase volumetric efficiency .
2.4.4 Cam Design and Control Dynamics
The function of the cam is to open and close the valves as far as possible , as fast
as possible and as smoothly as possible . The closing force for the valves is applied by
the valve spring which also maintain contact between the cam and the valves . Dynamic
force impose limits on cam and valve lift .
The entire valve-train assembly can be view as a spring mass system in which the
conversion from stored to free energy causes force 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 ) .
For system with valve bottom-mounted camshaft and push rods , a 2-mass
system is being increasingly used .
The maximum permissible contact stress , usually regarded as the parameter
which limits cam-lobe radius and the rate of opening on the flank , currently lies
between 600-700Mpa depending upon the material parings used .
2.4.5 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. The gears are linked in one of three ways:
Drive
A cog- type belt can be used .Such belts are made of synthetic rubber and reinforced
with internal steel or fiberglass strands. The belts have teeth ,or slotted spaces to
engage and drive teeth on gear wheels. A belt typically is used on engines with
overhead-cam valve trains.
Drive
On some engines, a metal chain is used to connect the crankshaft and camshaft
gears. Most push-rod engines and some OHC engines have chains.
Drive
The camshaft and crankshaft gears can be connected directly, or meshed. This type
of operating linkage commonly is used on older six-cylinder, inline engines.
A camshaft driven by a chain or belt turns in the same direction as the crankshaft .
But a Camshaft driven directly by the crankshaft gear turns in the opposite direction.
Timing belts are used because they cost less than chains and operate more quietly. A
typical timing belt is made of neoprene (synthetic rubber) reinforced with fiberglass.

2.4.6 Electronic Valve Control System
An electronic value control (EVC) system replaces the mechanical camshaft,
controlling each value with actuators for independent value timing. The EVC system
controls the opening and closing time and lift amount of each intake and exhaust

valve with independent actuators on each value. Changing from a mechanical
camshaft driven value into independently controlled actuator valves provides a huge
amount of flexibility in engine control strategy. Vehicles utilizing EVC can realize
several benefits including:
1) increases engine power and fuel economy,
2) allows centralized and distributed EVC systems to perform at their full
potential,
3) adapts to engines of varied cylinder counts.
With all of the improved efficiencies and consumer benefits, auto manufacturers
are eager to get their first EVC systems on the road. The EVC system is targeted
to operate in temperatures up to 125, while the actuator is targeted to run up to
6000 rmin. The actuator can be controlled in a centralized system with a
high-speed multiplex bus (up to 10Mbps) or in a distributed system with a
nominal speed bus.
EVC systems must be compact in size, specifically the actuators that must be
small enough to fit in the engine space. A vehicle that uses a 42V system is ideal
for EVC because it requires high voltage to control the value actuators, and EVC
is targeted for V8 and V12 engines. The EVC system is also highly flexible,
allowing adaptability for a number of cylinder engines.

New Words

coordinate 协调 valve train 气阀传动
respectively 分别的，各自的 overhead camshaft 顶置凸微轮轴

guide 导管 tappet 挺杆
valve insert 气门座 cotter 锁销，锁片
opening 口 lobe 凸起
spot 点，位置 stem 杆
dual 双的 cam follower 凸轮挺杆
seesaw 跷跷板，杠杆 value clearance 气门间歇
gas-tight seal 气封 liable to 容易
likelihood 可能 tapping 轻敲
valve timing 配气正时 intake valve 进气阀
exhaust valve 排气阀 static 静态的，静力的
kinetic （运）动的，动力（学）的 volumetric 测定体积的
leverage 杠杆作用 offset 偏移量
dynamics 动力学 valve lift 气门挺杆
valve…as… 把…..看成… parameter 参数，参量
radius 半径，范围 flank 侧面
pairing 配对，成对 correspond with 相当于
gear ratio 传动比 cog-type belt 齿型带
synthetic rubber 合成橡胶 reinforce 加强
fiberglass 玻璃纤维 strand 绳，线，绞合
slotted 有槽的，切槽的 mesh 相啮合
linkage 联动 inline engine 直列发动机
neoprene 氯丁（二稀）橡胶 electronic valve control (EVC) 电子式气阀控
制

centralized system 集中系统 distributed system 分布系统
varied cylinder count 可变的汽缸数 architecture 结构，构造
processor 处理器 local node 局域节点
communication layer 通信层 synchronization 同步

Review Question
1. List the main parts of the OHC valve train .
2. How does a push-rod valve train work ?
3. how are the valve clearance adjusted by hand ?
4. Why do the intake valves open before TDC and close after BDC ?
5. What do we mean by “ valve overlap “
6. Why do most cars use timing belts rather than chains ?
7. What are the advantage of the electronic valve control (EVC) ?


2.5 Gasoline Fuel System
2.5.1 Gasoline
Gasoline is distilled from crude petroleum . Gasoline is highly flammable , meaning it
burns easily in the presence of air .
Gasoline must vaporize easily . This characteristic , called volatility , is important .
However , it must not vaporize too easily , or it will turn to vapor inside the fuel tank or
fuel lines . Inside the fuel line , fuel vapor may block the flow of liquid gasoline . This is
called vapor lock . Vapor lock is common in fuel lines where the inlet side of the pump is

exposed to high temperatures .
The flammability of gasoline varies with its quality and the additives mixed with the
gasoline The way gasoline burns inside the combustion chamber is most important .
Increasing the pressure of the fuel mixture in the combustion chamber before
ignition helps to increase the power of an engine . This is done by compression the fuel
mixture to a smaller volume . Higher compression ratio not only boost power but also
give more efficient power . But as the compression ratio goes up , knocking tendency
increase . The octane number of a gasoline is a measure of its antiknock quality or ability
to resist detonation during combustion . Detonation , sometimes referred to as knock ,
can be defined as an uncontrolled explosion of the last portion of the burning fuel-air
mixture due to excessive temperature and pressure condition in the combustion
chamber . Since detonation creates shock pressure waves , and hence audible knock ,
rather tan smooth combustion and expansion of the fuel-air mixture , it result in loss of
power , excessive localized temperatures , and engine damage if sufficiently severe .
There are two commonly used methods of determining the octane number of motor
gasoline the motor method and the research method . Both used the same type of
laboratory single –cylinder engine , which is equipped with a variable head and a knock
meter to indicate knock intensity . Using the test sample as fuel , the engine compression
ratio and the air-fuel mixture are adjusted to develop a specified knock intensity . Two
primary standard reference fuels , normal heptane and iso-octane , arbitrarily assigned 0
and 100 octane numbers , respectively , are then blended to produce the same knock
intensity as the test sample . Thus , if the matching reference blend is made up of 15
n-heptane and 85 iso-octane , the test sample , the test sample is rate 85 motor or

research octane number , according to the test method used .
2.5.2 Adaptation to Operating Condition

In certain operation conditions , the fuel requirement differs greatly from the
basic injection-fuel quantity so that corrective is required in mixture formation .
Start
During a cold start , the air-fuel mixture drawn in by the engine leans off . This is
due to the low turbulence at cranking speeds causing poor mixture of the fuel particles
with the air , and to the minimal evaporation of the fuel and wetting of the cylinder walls
and intake ports with fuel at low temperature . In order to compensate for these
phenomena , and thus facilitate staring of the cold engine , additional fuel must be
injected during cranking .
-start Phase

After staring at low temperatures , it is necessary to enrich the mixture for a short
period in order to compensate for poor mixture formation and wetting of the cylinder
and intake-port walls with fuel . In addition , the rich mixture results in higher torque and
therefore better throttle response when accelerating from idle .

-up

The warm=up phase follows the cold-start and the post-start phase . The engine
needs extra fuel during the warm-up phase because some of the fuel condenses on the
still cold cylinder walls . At low temperatures , mixture formation is poor due to the large
fuel droplets concerned , and due to the inefficient mixing of the fuel with the air drawn
in by the engine , The result is that fuel condenses on the intake valves and in the intake

manifold , and only evaporates at higher temperatures .
The above factors all necessitate an increasing enrichment of the mixture along
with decreasing temperature .
ration

If the throttle is opened abruptly , the air- fuel mixture is momentarily leaned-off ,
and a short period of mixture enrichment is needed to ensure good transitional
response .

5 . Part Load

During part- load operation , achieving maximum air-fuel economy and
observing the emission values are the crucial factors .
Load
The engine delivers maximum power at full load , when the air-fuel mixture must
be enriched compared to that at part load .
This enrichment depends on engine speed and provide maximum possible
torque over the entire engine-speed range . This also ensure optimum fuel-economy
figures during full-load operation .

In addition to the efficiency of the engine , the engine idle speed principally
determines the fuel consumption at idle .
The higher frictional resistances in the cold engine must be overcome by
increasing the air-fuel mixture input . In order to achieve smoother running at idle , the
idle-speed control increases the idle speed . This also leads to more rapid warm-up of
the engine . Close-loop idle-speed control prevents too high an idle speed . The mixture

quantity corresponds to the quantity required for maintaining the idle speed at the
relevant load ( e.g.. cold engine and increased friction ) . It also permits constant
exhaust-gas emission values for a long period without idle adjustment . Closed-loop
idle- speed control also partially compensates for charges in the engine resulting from
aging and ensures stable engine idling throughout the service life .

n
Cutting off the fuel during deceleration reduces fuel consumption not merely
on long downhill runs and during braking , but also in town traffic . Because no fuel is
burnt , there are no emission .

-speed Limiting

When a presser engine speed is reached , the ECU suppresses the fuel-injection
pulses .

tion of the Air-fuel Mixture at High Altitudes

The low density of air at high altitudes necessitates a leaner air- fuel mixture . At
high altitudes , due to the lower air density , the volumetric floe measured by the air-fuel
sensor corresponds to a lower air-mass floe . This error can compensated for by
correcting the fuel quantity . Over-enrichment is avoided and , therefore , excessive fuel
consumption .
2.5.3 Carburetor
As shown in Fig.2-20 , the fuel system has a fuel tank , fuel tank , fuel pump , fuel
filter and carburetor . These parts store gasoline and deliver it to the carburetor as
needed . Stated simply , the fuel tank stores the gasoline . The fuel lines carry the fuel
from the tank to the carburetor . The fuel pump moves gasoline from the tank and

through the fuel lines to carburetor . the fuel filter removes impurities from the gasoline .
Then the carburetor sends the fuel ━ a mixture of air and gasoline ━ into the combustion
chamber .
2.5.4 Motronic Combine Ignition and Fuel Injection System
The carburetor sends the correct air-fuel mixture to the engine . However , not all
cars have carburetors . Fuel-injection systems are used on many modern cars .
Fuel- injection systems have many advantages over carburetors . For example , they
provide more exact fuel control . Thus , they can better match air-fuel ratios to changing
engine conditions . They also provide better economy and emission control .
Furthermore , fuel-injection system do not need many of the parts that carburetor have .
The Motronic system is an engine-management system comprising a control unit
( ECU ) which implements at least the two basic function ignition and fuel injection , but
which , however may contain additional subsystems as required for improves engine
control .
1. Detection of Measured Valves
The combustion process in the cylinder is influenced not only by fuel
management , mixture quantity and air- fuel ratio , but also by the ignition advance and
the energy contained in the ignition spark . An optimized engine control the air-fuel ratio
λ throughout the injection time t ( i.e. the quantity of injected fuel ) as well as the ignition
advance angle α and the dwell angle β . The main parameters which effect the
combustion process are detected as measure values and processed together such that
the optimum ignition and injection timing is calculated for instantaneous engine
operating conditions

2. Actuating VariablesSensors
Engine speed and load are the main actuating variables . Because a specific
ignition advance angle and a specific injection time correspond to each point of the
engine speedload map , it is important that all variables which pertain to the same point
are calculate on the same speed load area . This is only possible if the ignition advance
and the injection time are calculated with the same speed and load valves ( engine speed
detected only once with the same sensors ) .
This avoids statistical errors which can result , for example , from tolerances of
different load sensor devices . Whereas a slightly different allocation in the part-load
rage normally only increases consumption or exhaust emission , at full load near the
knock limit the susceptibility t engine knocking increase . Clear allocation of the ignition
timing angle and the injection time is provide by Motronic Systems , even under
conditions of dynamic engine operation .
3. Motronic System
The Motonic system comprise a series of subsystem , the two basic subsystem
being ignition and fuel injection . The combined system is more flexible and can
implement a greater number of functions than the corresponding individual system . An
important feature of the Motronic system is its implementation of a large number of
freely programmable maps as desired for most sub-functions .
The exhaust gas recirculation (EGR) function has not been used in Europe to date ,
and is therefore provide only as an alternative systems . The lambda control system can
only be considered today if used in conjunction with an adaptive precontrol for reasons
of reduced exhaust emissions .

The knock control is either connected to the Motronic system via a defined
interface , or integrated into the system . This combination of subsystem makes sense a
physical standpoint : it enables a basic system ( ignition and fuel injection ) with
open-loop functional control in a management system .
The idle speed control is realized by means of data from the ignition system and
the fuel
emissions .
The knock control is either connected to the Motronic system via a defined
interface , or integrated into the system . This combination of subsystem makes sense a
physical standpoint : it enables a basic system ( ignition and fuel injection ) with
open-loop functional control in a management system .
The idle speed control is realized by means of data from the ignition system and
the fuel injection system and is part of the overall system of control which includes tank
ventilation and camshaft control .
Microcomputer-controlled systems today are required to perform self-diagnosis of
the control unit itself , as well as of the entire system to a certain extent . Motronic
system of the future will thus include a diagnostic feature .
An engine-management system should include at least those function described
here . The addition of other functions is practical if they can be implemented without the
need for a number of additional inputs and outputs . System which use input and output
signals different from those used by the Motronic system are not integrated but rather
are connected with the Motronic system via interfaces . Typical examples of such systems
are the transmission control system and the traction control system which access the

ignition and injection system via corresponding interfaces .
4. System Configuration
Fig 2-22 is a typical Motronic system which shows the fuel circuit and the
acquisition of load and temperature data . The system dose not include the cold-start
valve or the thermo-time switch whose function are performed by the control unit . The
auxiliary-air device has been replaced by the idle-speed actuator . In addition to the
ignition coil , the ignition section also include the high-volt-age distributor which is
normally mounted directly on the camshaft . In contrast to the conventional ignition
distributor , the high-voltage distributor only incorporate the high-voltage distributor
function . The control unit electronically determines the proper ignition timing as a
function of engine speed and load .
5. Control Unit ( ECU )

The ECU detects the instantaneous condition of the engine at very short intervals
( milliseconds ) via a number of sensors . The signals output by the sensors are fed to the
ECU where input circuits remove any signal interference and convert the signals to a
uniform voltage range . An AD converter then transforms these signals to their signal
equivalents . This information is then processed by the microcomputer , which generates
output signals . The output stages amplify the low power lever of microcomputer
outputs to the lever required by the actuators . All programs and maps are resident in a
semiconductor memory . Digital signal level or component tolerance fluctuations .
Digital accuracy is governed by word length , quartz-clock frequency constancy and the
algorithms used for processing . Analog accuracy is determined by constancy and
accuracy of the reference volt- ages , and by the components used in the input circuits .

Program configuration must allow for the extreme real-time requirements of the engine :
the interval between two ignition pulse in a 6-cylinder engine is only about 3ms at
maximum speed . All essential calculation must be performed during this period . In
addition to crankshaft-synchronous control processing , the ECU also has to calculate
time-synchronous events .Both then functions have to wait if an interrupt occurs .

2.6 Engine Cooling
The purpose of the engine’s cooling system is to remove excess heat from the
engine , to keep the engine operation at its most efficient temperature , and to get the
engine up to the correct temperature as soon as possible after staring .Ideally , the
cooling system keeps the engine running at its most efficient temperature no matter
what the operation are .
There are two types of cooling systems liquid cooling and air cooling . Most
auto engines are cooled by the liquid type air cooling is used more frequently for
airplanes , motorcycles and lawnmowers .
2.6.1 Liquid Cooling
This system consists of several interdependent parts that function together to
maintain proper engine temperature . The cooling system of a water –cooled engine
consists of the engine’s water jacket , a thermostat , a water pump , radiator and
radiator cap , a cooling fan ( electric or belt-drive) , hoses , and usually an expansion
( overflow ) tank .
To dissipate excess engine heat , the cooling system performs four function :
1) absorption

2) circulation
3) radiation
4) control
Absorption occurs as coolant moves through the engine block . Heat energy
from the burning fuel in the cylinders passes into the cylinder walls and cylinder head .
Liquid coolant circulates through hollow spaces within the engine block and head to
absorb the heat from the metal parts of the engine . The hollow spaces are known as the
water jacket .
After absorbing the heat , the hot coolant passes out through the cylinder head
and eaters the radiator . As the coolant circulates through the radiator , it gives up its
heat to the metal tubes of the radiator . The radiator is made of brass or aluminum ,
metals that conduct heat well . As air passes through the radiator fins and around the
tubes , heat is transferred to air .
However , if coolant circulated at all times from the engine to radiator , the
engine would run very cool on cold days . Remember that chemical reaction , including
the burning of the fuel , occur more efficiently at high temperature . Thus , for the engine
to operate efficiently , there must be a control mechanism .
This control system is the thermostat . It regulates hoe much coolant is
permitted to flow through the radiator . After you start the engine , it should heat an
efficient operating temperature as quickly as possible and maintain that temperature
without overheating .
2.7 Engine Lubrication

The purpose of the lubrication system is to circulate oil through the engine . An

engine must have a good lubrication system . Without it , the friction heat from the
contact of moving parts would wear the parts and cause power loss . Oil , when placed
between two moving parts , separates them with a film . This oil film prevents the parts
from rubbing against between each other . This oil film also cushions the parts , giving
quieter and smoother engine operating .
Besides lubricating engine parts , oil is also used to :
1) clean the inside of the engine
2) help cool the engine
3) from a seal between the cylinder walls and piston rings .
Friction between engine components is reduced by :
1) boundary lubricating – relies on oil being splashed up onto the surfaces .
2) full film lubricating – an oil film is maintained by forcing the oil between the
surfaces by an oil pump .
The system used on a modern engine combines both methods : pistons are
lubricated by splash and bearing are pressure fed .
The main parts of a lubrication system are : pump , main oil gallery , relief valve
and filters .
2.7.1 Pump
In most cars , the oil pump is in the crankcase above the sump . It draws oil
through a tube that extends downward oil through a tube that extends downward into
the sump .This tube has a filter screen over its bottom end . The screen keeps large
pieces of sludge and dirt from being drawn into the pump . The tube may be hinged on
the pump end so that it can move up and down as the oil level change in the sump .

Thus , the pump always draws oil from the top of the sump , not from the bottom where
the dirt and sludge tend to settle . Modern cars use one of two common types of oil
pump – the gear – type and the rotor – type .

2.7.2 Main Oil Gallery and Relief Valve
This runs the length of the engine . Drilling from the gallery allow oil to be
supplied to the bearing surfaces .
Generally fitted in the gallery , this spring loaded valves opens when the
pressure reaches the maximum allowed .

2.7.3 Filters

Besides the gauze screen that prevents pieces of the metal entering the pump
there is an external filter which can be renewed periodically . A modern engine uses a full
– flow filtering system . In this system , the output of the oil pump flows through the oil
filter before each trip through the engine . When an engine runs at 3000rmin its entire
five quarts of oil pass through the filter at least once every minutes . Thus the oil filter
ensures that only clean oil enters the engine .
New Words

Cushion 缓冲，减振 Relief valve 溢流阀 Sludge 油泥渣，残渣
Hinge 依……..而转移 Gauze screen filter 金属滤网滤清器

Review Question
1. What is the purpose of the cooling system ?
2. List the main parts a liquid – cooling system ?

3. Why is thermostat need is a liquid – cooling system ?
4. What are the main function of the lubrication system ?
5. List the main parts of the lubrication system ?
2.8 Exhaust System

The exhaust system carries exhaust gases from the engine’s combustion chamber to
the atmosphere and reduces , or muffles , engine noise . Exhaust gases leave the engine
the engine in a pipe , traveling through a catalytic converter and a muffler before exiting
through the tailpipe .
2.9.1 The Tailpipe
The tailpipe is a long metal tube attached to the muffler . It sticks out from under the
body of a car , at the rear , in order to discharge the exhaust gases from the muffler of
the engine into the air outside the car .
2.8.2 The Muffler

Exhaust gases leave the engine under extremely high pressure . If these gases
escaped directly from the engine , the noise would be tremendous . For the reason , the
exhaust manifold sends the gases to a muffler where they go through metal plates , or
tubes , with a series of holes . The pressure of the gases is reduced when they pass
through the muffler , so they go out of the tailpipe quietly .
The muffler is made of metal and is located underneath the body a car . it’s
connected between the tailpipe and the catalytic converter .
There are two types of muffler design . One type uses several baffled chambers to
reduce noise . The other type sends the gases straight through perforate pipe wrapped
in metal or fiberglass This type of muffler is designed for the purpose of reducing

backpressure and , consequently , makes slightly more noise .
The muffler quests the noise of the exhaust by “ muffling ” the sound waves
creates by the opening and closing of the exhaust valves . When an exhaust valve opens ,
it discharge the burned gases at high pressures into exhaust pipe , which is at low
pressure . This type of action creates sound waves that travel through the flowing gas ,
moving much faster than the gas itself ( up to 1400 m. p . h . ) that the muffler must
silence . It generally does this by converting the sound wave energy into heat by pasting
the exhaust gas and through perforated chambers of varied sizes . Passing into the
perforation and reflectors within the chamber forces the sound waves to dissipate their
energy .
Car manufacturers are experimenting with an electronic muffler , which uses sensors
to monitor the sound waves of the exhaust noise . The sound wave data are sent to a
computer that controls speaker near the tailpipe . The system generates sound waves
180 degrees of phase with the engine noise . The sound waves from the electronic
muffler collide with the exhaust sound waves and they cancel each other out , leaving
only low – lever heat to emerge from the tailpipe .
2.8.3 The Exhaust Manifold And Header

The exhaust manifold , usually constructed of cast iron , is a pipe that conducts the
exhaust gases from the combustion chambers to the exhaust pipe . It has smooth cures
in it for improving the flow of exhaust .
The exhaust manifold is bolted to the cylinder head , and has entrances for the air
that is injected into it . It is usually is located under the intake manifold .
A header is a different type of manifold , it is made of separate equal – length

tubes .
2.8.4 Manifold to Exhaust Pipe Gasket

There are several types of that connect the exhaust pipe to manifold .
One is a flat surface gasket . Another type uses a ball and socket with spring to
maintain pressure . This type allows some flexibility without breakage of the seal or the
manifold . A third type is the full ball connector type , which also allows a little flexibility .
2.8.5 Exhaust Pipe Hangers
Hangers hold the exhaust system in place . They give the system flexibility and
reduce the noise lever . The hanger system consists of rubber rings , tubes and clamps .
2.8.6 Exhaust pipe
The exhaust pipe is the bent – up or convoluted pipes underneath a car . Some are
shaped to go over the rear axle allowing the rear axle to move up and down without
bumping into the exhaust pipe some are shaped to bend around under the floor of the
car , connecting the catalytic converter with the muffler . Exhaust pipes are usually made
out of stainless steel , since the high heat conditions involved with the muffler system
will cause rust .
2.8.7 Dual Exhaust System
The advantage of a dual exhaust system is that the engine exhausts more
freely ,thereby lowering the backpressure , which is inherent in an exhaust system . With
a dual exhaust system , a sizable increasing in engine horsepower can be obtained
because the “ breathing ” capacity of the engine is improved , leaving less exhaust
gases in the engine at the end of each exhaust stroke . This , in turn , leaves more room
for en extra intake of the air – fuel mixture .

New Word

Tremendous 巨大的，极大的 Perforated 多孔的 Muffler 消音器
Tailpipe 尾管 Hanger 吊耳，吊钩 Manifold 歧管
Fiberglass 玻璃纤维 Speaker 扬声器 Header 集气管
Baffled 用挡板隔开的 Convoluted 回旋状的 Flat 平面
Sizable 相当大的，大小相当的 Room 空间 Bump 碰撞
Catalytic converter 催化转换器 Backpressure 背压

2.9The Ignition System

There are many different ignition systems . Most of these systems can be placed
into one of three distinct : the conventional breaker point type ignition systems ( in use
since the early 1900s ) the electronic ignition systems ( popular since the mid 70s ) and
the distributorless ignition system ( introduces in the mid 80s ) .
The automotive ignition system has two basic functions it must control the spark
and timing of the spark plug firing to match varying engine requirements , and it must
increase battery voltage to a point where it will overcome the resistance offered by the
spark plug gap and fire the plug .
2.9.1 Point – Type Ignition System
An automotive ignition system is divided into two electrical circuits – the primary
and secondary circuits . The primary circuit carries low voltage . This circuit operates only
on battery current and is controlled by the breaker points and the ignition switch . The
secondary circuit coil ( commonly called the coil wire ) , the distributor cap the

distributor rotor , the spark plug leads and the spark plugs .
The distributor is the controlling element of the system . It switches the primary
current on and off and distributes the current to the proper spark plug each time a spark
is needed . The distributor is a stationary housing surrounding a rotating shaft . The shaft
is driven at one – half engine speed by the engine’s camshaft through the distributor
drive gears . A cam near the top of the distributor shaft has on lobe for each cylinder of
the engine . The cam operates the contact points , which are mounted on a plate within
the distributor housing .
A rotor is attached to the top of the distributor shaft . When the distributor cap is
in place , a spring – loaded piece of metal in the center of the cap makes contact with a
metal strip on top of the rotor . The outer end of the rotor passes very close to the
contacts connected to the spark plug leads around the outside of the distributor cap .
The coil is the heart of the ignition system . Essentially , it is nothing more than a
transformer which takes the relatively low voltage ( 12 volts ) available from the battery
and increasing it to a point where it will fire the plug as much as 40000 volts . The term
“coil” is perhaps a misnomer since there are actually two coils of wire wound about an
iron cone . These coils are insulated from each other and the whole assembly is enclosed
in an oil – filled case . The primary coil , which consists of relatively few turns of heavy
wire , is connected to the two primary terminals located on top of the coil . The
secondary coil consists of many turns of fine wire. It is connected to the high – tension
connection on top of the coil ( the tower into which the coil wire from the distributor is
plugged ) .
Under normal operating conditions , power from the battery is fed through a

resistor or resistance wire to the primary circuit of the coil and is then grounded through
the ignition points in the distributor ( the points are closed ) . Energizing the coil primary
circuit with battery voltage produces current flow through the primary winding , which
induces a very large , intense magnetic filed . This magnetic filed remains as long as
current flows and the points remain closed .
As the distributor cam rotates , the points are pushed apart , breaking the primary
circuit and stopping the flow of current . Interrupting the flow of primary current causes
the magnetic filed to collapse . Just as current flowing through a wire produces a
magnetic filed , moving a magnetic filed across a wire will produce a current . As the
magnetic filed collapses , its lines of wire in the secondary winding , inducing a current in
them . Since there are many more turns of wire in the secondary windings , the voltage
from the primary winding is magnified considerably up to 40000volts .
The voltage from the coil secondary winding flows through the coil high – tension
lead to the center of the distributor cap , where it is distributed by the rotor to one of the
outer terminals in the cap . From there , it flows through the spark plug lead to the spark
plug . This process occurs in a split second and is repeated every time the points open
and close , which is up to 1500 times a minute in a 4 – cylinder engine at idle .
2.9.2 Electronic Ignition Systems
The need for higher mileage , reduced emissions and greater reliability has led to
the development of the electronic ignition system . These system generate a much
stronger spark , which is needed to ignite leaner fuel Breaker point system needed a
resistor to reduce the operating voltage of the primary circuit in order to prolong the life
of the points . The primary circuit of the electronic ignition system operates on full

battery voltage , which helps to develop a stronger spark . Spark plug gaps have winded
due to the ability of the increased voltage to jump the large gap . Cleaner combustion
and less deposits have led to longer spark plug life .
On some systems , the ignition coil has moved inside the distributor cap . This
system is said to have an internal coil opposed to the complicated external .
Electronic ignition systems are not as complicated as they may first appear . In fact ,
they differ only slightly from conventional point ignition systems . Like conventional
ignition systems , electronic systems have two circuits : a primary circuit and a secondary
circuit . The entire secondary circuit is the same as in a conventional ignition system . In
addition , the section of the primary circuit from the battery to the battery terminal at
the coil is the same as in a conventional ignition system .
Electronic ignition system differ from conventional ignition system in the
distributor component area . Instead of a distributor cam , breaker plate , points , and
condenser , an electronic ignition system has an armature ( called by various names such
as a trigger wheel , redactor , etc . ) , a pickup coil ( stator , sensor , etc. ) , and an
electronic module .
2.9.3 Distributorless Ignition System ( DIS )
The third type of ignition system is the distributorless ignition . The spark plugs are
fired directly from the coils . The spark timing is controlled by an Ignition Control Unit (
ICU ) and the Engine Control Unit ( ECU ) . The distributorless ignition system may
have one coil per cylinder , or one coil for each pair of cylinders .
Some popular systems use one ignition coil per two cylinders . This type of system
is often known as the waste spark distribution method . In this system , each cylinder is

paired with the cylinder opposite it in the firing order ( usually 1 – 4 – 2 – 3 on 4 –
cylinder engines or 1 – 4 – 2 – 5 – 3 – 6 on V6 engines ) . The ends of each coil secondary
leads are attached to spark plugs for the paired opposites . These two plugs are on
companion cylinder , cylinders that are at Top Dead Center ( TDC ) at the sane time . But ,
they are paired opposites , because they are always at opposing ends of the 4 – stroke
engine cycle . When one is at TDC of the compression stroke , the other is at TDC of the
exhaust stroke . The one that is on compression is said to be the event cylinder and one
on the exhaust stroke , the waste cylinder . When the coil discharges , both plugs fire at
the same time to complete the series circuit .
Since the polarity of the primary and the secondary windings are fixed , one plug
always fires in a forward direction and the other in reverse . This is different than a
conventional system firing all plugs the same direction each time . Because of the
demand for additional energy the coil design , saturation time and primary current flow
are also different . This redesign of the system allows higher energy to be available from
the distributorless coils , greater than 40 kilovolts at the rpm ranges .
The distributorless ignition system uses either a magnetic crankshaft sensor ,
camshaft position sensor , or both , to determine crankshaft position and engine speed .
This signal is sent to the ignition control module or engine control module , which then
energizes the appropriate coil .
The advantage of no distributor , in theory , is :
1. No timing adjustments .
2. No distributor cap and rotor .
3. No moving parts to wear out .

4. No distributor to accumulate moisture and cause staring problems .
5. No distributor to drive thus providing less engine drag .
The major components of a distributorless ignition are :
1. ECU or Engine Control Unit .
2. ICU or Ignition Control Unit .
3. Magnetic Triggering Device such as the Crankshaft Position Sensor and the
Camshaft position Sensor .
4. Coil Pack .
New Words

Distributor 分电器 Condenser 电容器 Wear 磨损
Saturation 磁饱和 Series 串联 Wind 缠绕 Coil （ 点火 ）线
圈
Transformer 变压器 Turn 匝数 Term 术语， 学期，条件
Breaker point type ignition system 触点型点火系统 High tension lead 高压导
线
Distributorless ignition system 无分电器点火系统 Spark plug 火花塞
Primary and secondary circuits 初级和次级电路 Magnetic filed 磁场
Distributor rotor 分火头

Chaper3 Chassis
3.1clutch
The engine produces the power to drive the vehicle . The drive line or drive train

transfer the power of the engine to the wheels . The drive train consists of the parts from
the back of the flywheel to the wheels . These parts include the clutch , the
transmission ,the drive shaft ,and the final drive assembly .
The clutch which includes the flywheel ,clutch disc , pressure plate , springs , pressure
plate cover and the linkage necessary to operate the clutch is a rotating mechanism
between the engine and the transmission . It operates through friction which comes
from contact between the parts . That is the reason why the clutch is called a friction
mechanism . After engagement, the clutch must continue to transmit all engine torque
to transmission depending on the friction without slippage . The clutch is also used to
disengage the engine from the drive train whenever the gears in the transmission are
being shifted from gear ratio to another .
To start the engine or shift the gears , the driver has to depress the clutch pedal with
the purpose of disengagement the transmission from the engine . At that time , the
driven members connected to the transmission input shaft are either stationary or
rotating at a speed that is slower of faster than the driving members connected to
engine crankshaft . There is no spring pressure on the clutch assembly parts . So there is
no friction between the driving members and driven members . As the driver lets loose
the clutch pedal , spring pressure increase on the clutch parts . Friction between the
parts also increases . The pressure exerted by the springs on the driven members is
controlled by the driver through the clutch pedal and linkage . The positive engagement
of the driving and driven members is made possible the friction between the surfaces of
the members . When full spring pressure is applied , the speed of the driving and driven
members should be the same . At the moment , the clutch must act as a coupling device

and transmit all engine power to the transmission , without slipping .
However , the transmission should be engaged to the engine gradually in order to
operate the car smoothly and minimize torsional shock on the drive train because an
engine at idle just develop little power . Otherwise , the driving members are connected
with the driven members too quickly and the engine would be stalled .
The flywheel is a major part of the clutch . The flywheel mounts to the engine’s
crankshaft and transmits engine torque to the clutch assembly . The flywheel , when
coupled with the clutch disc and pressure plate makes and breaks the flow of power the
engine to the transmission .
The flywheel provides a mounting location for the clutch assembly as well . When the
clutch is applied , the flywheel transfers engine torque to the clutch disc . Because of its
weight , the flywheel helps to smooth engine operation . The flywheel also has a large
ring gear at its outer edge , which engages with a pinion gear on the starter motor
during engine cranking .
The clutch disc fits between the flywheel and the pressure plate . The clutch disc has a
splined hub that fits over splines on the transmission input shaft . A splined hub has
grooves that match splines on the shaft . These splines fit in the grooves . Thus , the two
parts held together . However , back – and – forth movement of the disc on the shaft is
possible . Attached to the input shaft , the disc turns at the speed of the shaft .
The clutch pressure plate is generally made of cast iron . It is round and about the
same diameter as the clutch disc . One side of the pressure plate is machined smooth .
This side will press the clutch disc facing are against the flywheel . The outer side has
shapes to facilitate attachment of spring and release mechanism . The two primary types

of pressure plate assemblies are coil spring assembly and diaphragm spring .
In a coil spring clutch the pressure plate is backed by a number of coil springs and
housed with them in a pressed – steed cover bolted to the flywheel . The spring push
against the cover . Neither the driven plate nor the pressure plate is connected rigidly to
the flywheel and both can move either towards it o away . When the clutch pedal is
depressed a thrust pad riding on a carbon or ball thrust bearing is forced towards the
flywheel . Levers pivoted so that they engage with the thrust pad at one end and the
pressure plate tat the other end pull the pressure plate back against its springs . This
releases pressure on the driven plate disconnecting the gearbox from the engine .
Diaphragm spring pressure plate assemblies are widely used in most modern cars .
The diaphragm spring is a single thin sheet of metal which yields when pressure is
applied to it . When pressure is removed the metal spring back to its original shape . The
center portion of the diaphragm spring is slit into numerous fingers that act as release
levers . When the clutch assembly rotates with the engine these weights are flung
outwards by centrifugal plate and cause the levers to press against the pressure plate .
During disengagement of the clutch the fingers are moved forward by the release
bearing . The spring pivots over the fulcrum ring and its outer rim moves away from the
flywheel . The retracting spring pulls the pressure plate away from the clutch plate thus
disengaging the clutch .
When engaged the release bearing and the fingers of the diaphragm spring move
towards the transmission . As the diaphragm pivots over the pivot ring its outer rim
forces the pressure plate against the clutch disc so that the clutch plate is engaged to
flywheel .

The advantages of a diaphragm type pressure plate assembly are its compactness ,
lower weight , fewer moving parts , less effort to engage , reduces rotational imbalance
by providing a balanced force around the pressure plate and less chances of clutch
slippage .
The clutch pedal is connected to the disengagement mechanism either by a cable or ,
more commonly , by a hydraulic system . Either way , pushing the pedal down operates
the disengagement mechanism which puts pressure on the fingers of the clutch
diaphragm via a release bearing and causes the diaphragm to release the clutch plate .
With a hydraulic mechanism , the clutch pedal arm operates a piston in the clutch master
cylinder . This forces hydraulic fluid through a pipe to the cutch release cylinder where
another operates the clutch disengagement mechanism by a cable .
The other parts including the clutch fork , release bearing , bell – housing , bell
housing cover , and pilot bushing are needed to couple and uncouple the transmission .
The clutch fork , which connects to the linkage , actually operates the clutch . The release
bearing fits between the clutch fork and the pressure plate assembly . The bell housing
covers the clutch assembly . The bell housing cover fastens to the bottom of the bell
housing . This removable cover allows a mechanic to inspect the clutch without
removing the transmission and bell housing . A pilot bushing fits into the back of the
crankshaft and holds the transmission input shaft .
New Word

Clutch 离合器 Flywheel 飞轮 Stationary 静止的，不动的，不变的，固定的
Torsional 扭转的，扭力的 Crankshaft 曲轴，机轴 Stall 停止，停转，迟延

Mount 安放，设置，装上 Groove 凹槽，沟 Lever 杆，杠杆，控制杆
Pivot 支点 Gearbox 变速器 Retract 缩回，缩进，收回，
Compactness 紧密，简洁 Drive train 传动系 Drive shaft 传动轴
Pressure plate 压盘 Clutch disc 离合器从动盘，离合器摩擦片
Gear ratio 传动比 Release bearing 分离轴承 Release fork 分离拨叉
Master cylinder 主缸 Clutch pedal 离合器踏板 Coupling device 结合装
置
At idle 空转。空闲 Couple with 与。。。。。。。结合 Ring gear 外形齿轮，齿圈
Pinion gear 小齿轮 Splined hub 花键毂 Cast iron 铸铁
Diaphragm spring 膜片弹簧 Thrust pad 止推片 Engage with 结合
Centrifugal force 离心力 Fulcrum ring 支撑环 Pilot bushing 导轴衬
Bell housing 钟形外壳，离合器壳

3.2 AUTOMATIC TRANSMISSION
The modern automatic transmission is by far , the most complicated mechanical
component in today’s automobile . It is a type of transmission that sifts itself . A fluid
coupling or torque converter is used instead of a manually operated clutch to connect
the transmission to the engine .
There are two basic types of automatic transmission based on whether the vehicle is
rear wheel drive or front wheel drive . On a rear wheel drive car , the transmission is
usually mounted to the back of the engine and is located under the hump in the center
of the floorboard alongside the gas pedal position . A drive shaft connects the
transmission to the final drive which is located in the rear axle and is used to send power

to the rear wheels . Power flow on this system is simple and straight forward going from
the engine , through the torque converter , then trough the transmission and drive shaft
until it reaches the final drive where it is split and sent to the two rear transmission .
On a front wheel drive car , the transmission is usually combined with the final drive to
form what is called a transaxle . The engine on a front wheel drive car is usually mounted
sideways in the car with the transaxle tucked under it on the side of the engine facing the
rear of the car . Front axles are connected directly to the transaxle and provide power to
front wheels . In this example , power floes from the engine , through the torque
converter to a larger chain that sends the power through a 180 degree turn to the
transmission that is along side the engine . From there , the power is routed through the
transmission to the final drive where it is split and sent to the two front wheels through
the drive axles .
There are a number of other arrangements including front drive vehicles where the
engine is mounted front to back instead of sideways and there are other systems that
drive all four wheels but the two systems described here are by far the most popular . A
much less popular rear and is connected by a drive shaft to the torque converter which is
still mounted on the engine . This system is found on the new Corvette and is used in
order to balance the weight evenly between the front and rear wheels for improved
performance and handling . Another rear drive system mounts everything , the engine ,
transmission and final drive in the rear . This rear engine arrangement is popular on the
Porsche.
The modern automatic transmission consists of many components and systems that
designed to work together in a symphony of planetary gear sets , the hydraulic system,

seals and gaskets , the torque converter , the governor and the modulator or throttle
cable and computer controls that has evolved over the years into what many mechanical
inclined individuals consider to be an art from . Here try to used simple , generic
explanation where possible to describe these systems .
3.2.1 Planetary gear sets
Automatic transmission contain many gears in various combinations . In a manual
transmission , gears slide along shafts as you move the shift lever from one position to
another , engaging various sizes gears as required in order to provide the correct gear
ratio . In an automatic transmission , how ever , the gears are never physically moved and
are always engaged to the same gears . This is accomplished through the use of
planetary gear sets .
The basic planetary gear set consists of a sun gear , a ring and two or more planet
gears , all remaining in constant mesh . The planet gears are connected to each other
through a common carrier which allows the gears to spin on shafts called “pinions”
which are attached to the carrier .
One example of a way that this system can be used is by connecting the ring gear to
the input shaft coming from the engine , connecting the planet carrier to the output
shaft , and locking the sun gear so that it can’t move . In this scenario , when we turn
the ring gear , the planets will “walk” along the sun gear ( which is held stationary )
causing the planet carrier to turn the output shaft in the same direction as the input
shaft but at a slower speed causing gear reduction ( similar to a car in first gear ) .
If we unlock the sun gear and lock any two elements together , this will cause all three
elements to turn at the same speed so that to output shaft will turn at the same rate of

speed as the input shaft . This is like a car that is third or high gear . Another way we can
use a planetary gear set is by locking the planet carrier from moving , then applying
power to the ring gear which will cause the sun gear to turn in opposite direction giving
us reverse gear .
The illustration in Figure shows how the simple system described above would look in
an actual transmission . The input shaft is connected to the ring gear , the output shaft is
connected to the planet carrier which is also connected to a “Multi-disk” clutch pack .
The sun gear is connected to drum which is also connected to the other half of the clutch
pack . Surrounding the outside of the drum is a band that can be tightened around the
drum when required to prevent the drum with the attached sun gear from turning .
The clutch pack is used , in this instance , to lock the planet carrier with the sun gear
forcing both to turn at the same speed . If both the clutch pack and the band were
released , the system would be in neutral . Turning the input shaft would turn the planet
gears against the sun gear , but since noting is holding the sun gear , it will just spin free
and have no effect on the output shaft . To place the unit in first gear , the band is
applied to hold the sun gear from moving . To shift from first to high gear , the band is
released and the clutch is applied causing the output shaft to turn at the same speed as
the input shaft .
Many more combinations are possible using two or more planetary sets connected in
various way to provide the different forward speeds and reverse that are found in
modern automatic transmission .
3.2.2
Clutch pack
A clutch pack consists of alternating disks that fit inside a clutch drum . Half of the

disks are steel and have splines that fit into groves on the inside of the drum . The other
half have a friction material bonded to their surface and have splines on the inside edge
that fit groves on the outer surface of the adjoining hub . There is a piston inside the
drum that is activated by oil pressure at the appropriate time to squeeze the clutch pack
together so that the two components become locked and turn as one .
3.2.3 One-way Clutch
A one-way clutch ( also known as a “sprag” clutch ) is a device that will allow a
component such as ring gear to turn freely in one direction but not in the other . This
effect is just like that bicycle , where the pedals will turn the wheel when pedaling
forward , but will spin free when pedaling backward .
A common place where a one-way clutch is used is in first gear when the shifter is in
the drive position . When you begin to accelerate from a stop , the transmission starts
out in first gear . But have you ever noticed what happens if you release the gas while it
is still in first gear ? The vehicle continues to coast as if you were in neutral . Now , shift
into Low gear instead of Drive . When you let go of the gas in this case , you will feel the
engine slow you down just like a standard shift car . The reason for this is that in Drive ,
one-way clutch is used whereas in Low , a clutch pack or a band is used .
3.2.4 Torque Converter
On automatic transmission , the torque converter takes the place of the clutch found
on standard shift vehicles . It is there to allow the engine to continue running when the
vehicle comes to a stop . The principle behind a torque converter is like taking a fan that
is plugged into the wall and blowing air into another fan which is unplugged . If you grab
the blade on the unplugged fan , you are able to hold it from turning but as soon as you

let go , it will begin to speed up until it comes close to speed of the powered fan . The
difference with a torque converter is that instead of using air it used oil or transmission
fluid , to be more precise .
A torque converter is a lager doughnut shaped device that is mounted between the
engine and the transmission . It consists of three internal elements that work together to
transmit power to the transmission . The three elements of the torque converter are the
pump , the Turbine , and the Stator . The pump is mounted directly to the torque housing
which in turn is bolted directly to the engine’s crankshaft and turns at engine speed .
The turbine is inside the housing and is connected directly to the input shaft of the
transmission providing power to move the vehicle . The stator is mounted to a one- way
clutch so that it can spin freely in one direction but not in the other . Each of the three
elements has fins mounted in them to precisely direct the flow of oil through the
converter .
With the engine running , transmission fluid is pulled into the pump section and is
pushed outward by centrifugal force until it reaches the turbine section which stars it
running . The fluid continues in a circular motion back towards the center of the turbine
where it enters the stator . If the turbine is moving considerably slower than the pump ,
the fluid will make contact with the front of the stator fins which push the stator into the
one way clutch and prevent it from turning . With the stator stopped , the fluid is
directed by the stator fins to re-enter the pump at a “help” angle providing a torque
increase . As the speed of the turbine catches up with the pump , the fluid starts hitting
the stator blades on the back-side causing the stator to turn in the same direction as the
pump and turbine . As the speed increase , all three elements begin to turn at

approximately the same speed . Sine the ‘80s , in order to improve fuel economy ,
torque converters have been equipped with a lockup clutch which locks the turbine to
the pump as the vehicle reaches approximately 40-50 mph . This lockup is controlled by
computer and usually won’t engage unless the transmission is in 3
rd
or 4
th
gear .
3.2.5 Hydraulic System
The hydraulic system is a complex maze of passage and tubes that sends that sends
transmission fluid and under pressure to all parts of the transmission and torque
converter and . Transmission fluid serves a number of purpose including : shift
control ,general lubrication and transmission cooling . Unlike the engine ,which uses oil
primary for lubrication ,every aspect of a transmission ‘s function is dependant on a
constant supply of fluid is send pressure . In order to keep the transmission at normal
operating temperature , a portion of the fluid is send to through one of two steel tubes
to a special chamber that is submerged in anti-freeze in the radiator . Fluid passing
through this chamber is cooled and then returned to the transmission through the other
steel tube . A typical transmission has an avenge of ten quarts of fluid between the
transmission , torque converter , and cooler tank , In fact , most of the components of a
transmission are constantly submerged in fluid including the clutch packs and bands .
The friction surfaces on these parts are designed to operate properly only when they are
submerged in oil .
3.2.6 Oil Pump
The transmission oil pump ( not to confused with the pump element inside the
torque converter ) is responsible for producing all the oil pressure that is required in the
transmission . The oil pump is mounted to front of the transmission case and is directly

connected to a flange on the engine crankshaft , the pump will produce pressure
whenever the engine is running as there is a sufficient amount of transmission fluid
available . The oil enters the pump through a filter that is located at bottom of the
transmission oil pan and travels up a pickup tube directly to the oil pump . The oil is then
sent , under pressure to the pressure regulator , the valve body and the rest of the
components , as required .
3.2.7 Valve Body
The valve body is the control center of the automatic transmission . It contains a maze
of channels and passages that direct hydraulic fluid to the numerous valves which when
activate the appropriate clutch pack of band servo to smoothly shift to the appropriate
gear for each driving situation . Each of the many valves in the valve body has a specific
purpose and is named for that function . For example the 2-3 shift valve activates the 2
nd
gear up-shift or the 3-2 shift timing valve which determines when a downshift should
occur .
The most important valve and the one that you have direct control over is the manual
valve. The manual valve is directly connected to the gear shift handle and covers and
uncovers various passages depending on what position the gear shift is paced in . When
you place the gear shift in Drive , for instance , the manual valve directs fluid to the clutch
pack ( s ) that activates 1
st
gear . It also sets up to monitor vehicle speed and throttle
position so that it can determine the optimal time and the force for the 1-2 shift . On
computer controlled transmission , you will also have electrical solenoids that are
mounted in the valve body to direct fluid to the appropriate clutch packs or bands under
computer control to more precisely control shift points .

3.2.8 Computer Controls
The computer uses sensors on the engine and transmission to detect such things as
throttle position , vehicle speed , engine speed , engine load , stop light switch position ,
etc . to control exact shift points as well as how soft or firm the shift should be . Some
computerized transmission even learn your driving style and constantly adapt to it so
that every shift is timed precisely when you would need it .
Because of computer controls , sports models are coming out with the ability to take
manual control of the transmission as through it were a stick shift lever through a special
gate , then tapping it in one direction or the other in order to up-shift at will . The
computer monitors this activity to make sure that the driver dose not select a gear that
could over speed the engine and damage it .
Another advantage to these “ smart” transmission is that they have a self diagnostic
mode which can detect a problem early on and warn you with an indicator light on the
dash . A technician can then plug test equipment in and retrieve a list of trouble codes
that will help pinpoint where the problem is .
3.2.9 Seals and Gaskets
An automatic transmission has many seals and gaskets to control the flow of hydraulic
fluid and to keep it from leaking out . There are two main external seals : the front seal
and the rear seal . The front seal seals the point where the torque converter mounts to
the transmission case . This seal allows fluid to freely move from the converter to the
transmission but keeps the fluid from leaking out . The rear seal keeps fluid from leaking
past the output shaft .
A seal is usually made of rubber ( similar to the rubber in a windshield wiper blade )

and is used to keep oil from leaking past a moving part such as a spinning shaft . In some
cases , the rubber is assisted by a spring that holds he rubber in close contact with the
spinning shaft .
A gasket is a type of seal used to seal two stationary parts that are fasted together .
Some common gasket materials are : paper , cork , rubber , silicone and soft metal .
Aside from the main seals , there are also a number of other seals and gasket that vary
from transmission to transmission . A common example is the rubber O-ring that seals
the shaft for the shift control lever . This is the shaft that you move when you manipulate
the gear shifter . Another example that is common to most transmission is the oil pan
gasket . In fact , seals are required anywhere that a device needs to pass through the
transmission case with each one being a potential source for leaks .
New Words

Hump 圆形隆起 Transaxle 变速器驱动桥 Tuck 把一端塞进
Gasket 垫圈 Governor 油压调节器 Modulator 调制器
Spline 花键 Bond 结合 Strap 带,皮带
Doughnut 圆环图 Stator 定子,固定片 Maze 曲径
Submerge 浸没,淹没 Quart 夸脱 Downshift 调低速档
Optimal 最佳的 Solenoid 螺线管 Retrieve 重新得到
Cork 塞住 Manipulate 操作,使用 Fluid coupling 液力偶
合器
Torque converter 液力变矩器 Planetary converter 行星齿轮组 Throttle cable 节气门
拉线

Ring gear 齿圈 High gear 高速档 Reverse gear 倒档
Sprag clutch 锲块式单向离合器 Centrifugal force 离心力 Gear up 促进
Stick shift 顶杆档 Vacuum hose 真空软管 Throttle valve 节气阀
Leak out 泄露 Windshield wiper 风窗玻璃刮水器

3.3 The Differential System
When a vehicle is cornered the inner wheel moves through a shorter distance than
the outer wheel . This means that the inner wheel must slow down and the outer wheel
must speed up . During this period it is desirable that each driving maintains its driving
action . The differential performs these two tasks . The principle of the bevel type
differential can be seen if the unit is considered as two discs and a lever .
When the vehicle is traveling straight , the lever will divide the diving force equally and
both discs will move the same amount .
When the vehicle corners , the driving will still be divided equally but the inner disc will
now move through a smaller distance this will cause the lever to pivot about its center
which will prize forward the outer disc to give it a greater movement . This action shows
that the torque applied to each driving wheel is always equal – hence the differential is
sometimes called a torque equalizer .
New Word

Desirable 想知道的 Disc 盘片,轮盘,轮圈 Prize 撬动,推动 Equalizer 平衡装置

3.4 Brake System

The breaking system is the most important system in cars . If the brakes fail , the result
can be disastrous . Brakes are actually energy conversion devices , which convert the
kinetic energy ( momentum ) of the vehicle into thermal ( heat ) . When stepping on the
brakes , the driver commands a stopping force ten times as powerful as the force that
puts the car in motion . The braking system can exert thousands of pounds of pressure
on each of the four brakes .
The brake system is composed of the following basic components : the “master
cylinder” which is located under the hood , and is directly connected to the brake pedal ,
converts driver foot’s mechanical pressure into hydraulic pressure . Steel “brake
lines” and flexible “brake hoses” connect the master cylinder to the “slave
cylinders” located at each wheel . Brake fluid , specially designed to work in extreme
condition , fills the system . “Shoes” and “Pads” are pushed by the salve cylinders to
contact the “drum” and “rotors” thus causing drag , which ( hopefully ) slows the
car .
The typical brake system consists of disk brakes in front and either disk or drum brakes
in the rear connected by a system of tubes and hoses that link the brake at each wheel to
the master cylinder .
Stepping on the brake pedal , a plunger is actually been pushing against in the master
cylinder which forces hydraulic oil ( brake fluid ) through a series of tubes and hoses to
the braking unit at each wheel . Since hydraulic fluid ( or any fluid for that matter )
cannot be compressed , pushing fluid through a pipe is just like pushing a steel bar
through pipe . Unlike a steel bar , however , fluid can be directed through many twists
and turns on its way to its destination , arriving with the exact same motion and pressure

that it started with . It is very important that the fluid is pure liquid and that there are no
air bubbles in it . Air can compress , which causes a sponginess to the pedal and severely
reduced braking efficiency . If air is suspected , then the system must be bled to remove
the air . There are “bleeder screws” at each wheel and caliper for this purpose .
On a disk brakes , the fluid from the master cylinder is forced into a caliper where it
pressure against a piston . The piton , in- turn , squeezes two brake pads against the disk
( rotor ) which is attached to the wheel , forcing it to slow down or stop . This process is
similar to the wheel ,causing the wheel to stop . In either case , the friction surface of the
pads on a disk brake system , on the shoes on a drum brake convert the forward motion
of the vehicle into heat . Heat is what causes the friction surfaces ( lining ) of the pads
and shoes to eventually wear out and require replacement .
Brake fluid is a special oil that has specifics properties . It is designed to withstand cold
temperatures without thickening as well as very high temperatures without boiling . ( If
the brake fluid should boil , it will cause you to have a spongy pedal and the car will be
hard to stop ) .
The brake fluid reservoir is on top of the master cylinder . Most cars today have a
transparent reservoir so that you can see the level without opening the cover . The brake
fluid lever will drop slightly as the brake pads wear . This is a normal condition and no
cause for concern . If the lever drops noticeably over a short period of time or goes down
to about two thirds full , have your brakes checked as soon as possible . Keep the
reservoir covered expect for the amount of time you need to fill it and never leave a can
of brake fluid uncovered . Brake fluid must maintain a very high boiling point . Exposure
to air will cause the fluid to absorb moisture which will lower that boiling point .

The brake fluid travels from the master cylinder to the wheels through a series of steel
tubes and reinforced rubber hoses . Rubber hoses are only used in places that require
flexibility , such as at the front wheels , which move up and down as well as steer . The
rest of the system uses non-corrosive seamless steel tubing with special fittings at
attachment points . If a steel line requires a repair , the best procedure is to replace the
complete line . If this is nit practical , a line can be repaired using special splice fittings
that are made for brake system repair . You must never use brass “compression”
fittings or copper tubing repair a brake system . They are dangerous and illegal .
3.4.1 Other Components in the Hydraulic System
Proportioning Valve or Equalizer Valve
These valves are mounted between the master cylinder and the rear wheels . They are
designed to adjust the pressure between the front and the rear brakes depending on
how hard you are stopping . The shorter you stop , the more of the vehicle’s weight is
transferred to the front wheels , in some cases , causing the rear to lift and the front to
dive . These valves are designed to direct more pressure to the front and less pressure to
the harder you stop . This minimizes the chance of premature lockup at the rear wheels .
Pressure Differential Valve
This valve is usually mounted just below the master and is responsible for turning the
brake warning light on when it detects a malfunction . It measures the pressure from the
two sections of the master cylinder and compares them . Since it is mounted ahead of
the proportioning or equalizer valve , the two pressure it detects should be equal . If it
detects a difference , it means that there is probably a brake fluid leak somewhere in the
system .

Combination Valve
The Combination valve is simply a proportioning valve and a pressure differential
valve that is combine into one unit .
The parking brake system controls the rear brakes through a series of steel cables that
are connected to either a hand lever or a foot pedal . The ideal is that the system is fully
mechanical and completely bypasses the hydraulic system so that the vehicle can be
brought to a stop even if there is a total brake failure .
New Word

Disastrous 灾难性的 Hood 发动机罩 Plunger 活塞,柱塞
Sponginess 轻软有弹性的 Malfunction 故障 Bypass 设旁路,与会
Corkscrew 活塞推杆 Inoperative 不起作用的 Booster 调压器,助力器
Slam 砰地踏下 Screech 发出尖锐的声音 Thumping 极大的
Momentarily 即刻 Thermal energy 热能 Master cylinder 制动主缸
Brake pedal 制动踏板 Brake hose 制动软管 Salve cylinder 轮缸
Drum brake 鼓式制动器 Brake shoe 制动蹄 Bleeder screw 放气螺钉
Spongy pedal 踏板发软 Panic stop 紧急停车,紧急制动 Friction lining 摩擦衬片
Proportioning valve 比列阀 Equalizer valve 平衡阀
Pressure differential valve 差压阀 Combination valve 组合阀
3.5 Steering System
3.5.1 Basic Parts of Steering System
The steering converts the steering –wheel rotary motion into a turn motion of the
steered wheels of the vehicle .

The basic steering system in most cars is the same . The steering gear of steering box
is the heart of the steering system .This is usually next to the engine . A shaft extends
from the back of the steering gear . This shaft is connected to the steering column or
steering shaft . The steering wheel is at the top of the steering column . Another shaft
comes from the bottom of the steering gear . This shaft connects to the arms , rods , and
links . This parts assembly , called the steering linkage , connects the steering gear to the
parts at the wheels . The wheels and tires mount to the steering knuckles , As shown in
fig , the knuckles are pivoted at the top and bottom . Thus , the wheels and rites can turn
from side top side .
While the steering system may look complicated , it works quite simply . When a
driver drives a car straight down the road , the steering gear is centered . The gear holds
the linkage centered so that the wheels and tires point straight ahead . When the driver
turns the steering wheel , the steering shaft rotates and the steering gear moves toward
that side . The shaft coming out the bottom of the steering gear turns , as well . When
the shaft turns , it pulls the linkage to one side and makes the steering knuckles turn
slightly about their pivot points . Thus , the steering knuckle , spindle , wheels , and tires
turn to one side , causing the car to turn .
The type of steering layout depends on the suspension system . The beam axle used
on heavy commercial vehicle has a king pin fitted at each end of the axle and this pin is
the pivot which allows the wheels to be steered . Cars have independent suspension and
this system has ball joints to allow for wheel movement .
New Word

Steering box 转向器 Steering column 转向柱管 Steering linkage 转向传动机构
Steering knuckle 转向节 King pin 主销 Track rod 转向杆
Drop arm 摇臂 Stub axle 转向轴 Turn about 绕…….转动
Spindle 转向节(轴端) Swivel joint 转向节

Types of Steering System
A steering box must have the following qualities :
1) no play in the straight-ahead position
2)low friction , resulting in high efficiency
3)high rigidity ,
4 readjust ability
For these reasons, these are several different types of steering gears . However , there
are only two types of steering systems : manual steering systems and power steering
systems . In the manual type , the driver dose all the work of turning the steering wheel ,
steering gear , wheels and tires . In the power , hydraulic fluid assists the operation so
that driver effort is reduced .
On today’s cars , two types of steering systems commonly are used to provide
steering control :
1) Recirculation ball 2) rack and pinion
Either of these two types of steering mechanisms may be a fully mechanical systems or
a power –assisted system .
3.6 Front Suspension
The front suspension is more complicated than the rear suspension . This is because the

front wheels must move in several different directions . The wheels must move up and
down with the suspension and turn left to right with the steering . Since the car goes in
the direction in which the front wheels point , the alignment of the front wheels is
important . The wheels must point in just the right direction for the car to move straight
down the road and turn properly .
Modern cars uses an independent front suspension . In this system , each wheel
mounts separately to the frame and has its own individual spring and shock absorber .
Thus , the wheels act independently of one another . When one wheel hits a bump or
hole in the road , the other wheel dose no9t deflect .
3.6.1 Front Wheel Alignment
As a car moves down the high-way , the suspension moves the front wheels up and
down . At the same time , the steering mechanism moves the front wheels , sometimes
to make turns and sometimes to make the travel straight . The angular relationship
between the wheels and suspension parts during this motion is the front-end geometry .
Since the geometry can change the alignment of front wheels is adjustable . You can
change the adjustment to compensate for spring sag .
The alignment of the front wheels affects the operation of a car . Poor alignment ca
make a car pull to one side and stop the front wheels from returning to the
straight-ahead position after a turn . The three normally adjustable angles are caster ,
camber , and toe .
1. Toe-in
Toe- in specifies the degree to which non-parallel front wheels are closer together at
the front than at the rear measured at the edges of the rims at the wheel center height .

front non-driven wheels , toe-in is approximately 2-3 mm , and between +3mm and-2
mm for driven wheels . Toe-in reduces the tendency of the wheels to shimmy .
2. Kingpin Angle
The kingpin angle is the inclination of the steering axis relative to the longitudinal
plane , measured in the transverse plane of the vehicle . Kingpin angle is 2°-16°and
determines the steering aligning torque in conjunction with steering offset and wheel
caster . It is measured only with the vehicle loaded .
3. Camber
Camber is the inward or outward tilt of the wheel at the top . Inward tilt is negative
camber and outward tilt is positive camber . The tilt of the wheel is measured inn
degrees and is adjustable on many vehicles .
4. Caster
Caster is the forward or backward of spindle or steering the knuckle at the top when
viewed from the side . Forward tilt is negative caster and backward tilt positive caster .
Caster is measured in the number of degrees that it is forward or backward from true
vertical and is adjustable on many vehicle .
New Word

Front wheel alignment 前轮定位 Sag 倾斜 Caster 主销倾角
Camber 车轮倾角 Toe 轮胎缘距 Toe-in 轮胎前束
Kingpin 主销 Align 矫正,对准 Positive camber 车轮外倾角
Negative camber 车轮内倾角 Deviate 偏离 Positive caster 主销正倾角
Negative caster 主销负倾角

3.6.2 Rear Suspension
The purpose of the rear suspension is to support the weight of the rear of the vehicle .
As with the front suspension , this system contributes to the stability and ride of the
vehicle . Rear suspension may be of the solid axle or independent design . Many cars
have solid axle rear suspension . Either design may have different kinds of springs ,
including torsion bars . However , the coil spring and leaf spring types are most popular .
3.7 Wheels and Tires
To maintain grip when a vehicle is traveling at speed over a bumpy surface , a wheel
must be light in weight . Also it must be strong , cheap to produce , easy to clan and
simple to remove .
3.7.1. Wheels
The structure of the wheel is shown in Fig . The rim is made in one piece , with the
wheel center welded or riveted to it . Most modern vehicles use the drop center type .
This drop center provides a well for tire bead to drop into for tire removal . A slight hump
at the head ledge holds the tire in place should it go flat while driving .
3.7.2. tires
Tires are important to your safety and comfort . They transmit the driving and braking
power to the road . The car’s directional control , road-ability and riding comfort are
greatly dependent on the tires . Tires should be selected and maintained with great care .
There are two basic types of tires – those with inner tubes and those without ( called
“tubeless” tires ) . Most modern automobile tires are of the tubeless type . Truck and
bus tire are usually of the tube type .

Tires are made of several layers of nylon , rayon , or polyester fabric bonded together
with belts of rayon , fiberglass , or steel cord . The rubber used in tires is a blend of
natural and synthetic rubber .
Rim 轮缘
Inner tube 内胎
Casing plies 帘布层

New Words

Bead 胎边,轮缘
Rayon 人造丝
Rubber chafer 橡胶胎圈
Hump 凸起
多元脂

Polyester