CHAPTER 1 AUTOMOTIVE BASICS
1.1 Principal Components 主要构成零部件
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. 现在，一般汽车由大约一万五千多个独立的零部件组成。这些部件分为四大类，即发动机(引擎系统)，车身，底盘和电气设备。
1.5 Electrical Equipment 电气设备
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.
电气设备为汽车点火、喇叭、车灯、发热器和启动器提供电力。通过循环充电来维持电量。
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 火花
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 内燃发动机
2.1 principle of operation 发动机的工作原理/操作原理
2.1.1 Engine and power 发动机与能量
Engine is used to produce power.
发动机产生动能。
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. 汽油燃料通过受控速度的燃烧讲自身的化学能转化为热能。这个过程称作燃烧。如果发动机的内燃在燃料室中发上，发动机被称作内燃发动机。如果内燃发生在汽缸外，发动机则被称作外燃发动机。
Engine used in automobiles are internal combustion heat engines. 汽车的发动机是内燃发动机。
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. 燃烧汽缸中释放的热能将汽缸内的内燃其他温度升高。气体温度的升高导致其他压强增大。汽缸内的压强不断产生以用于活塞头产生可用的机械动力，随后转变成为有用的机械动能。
2.1.2 Engine Terms 发动机术语
Linking the piston by a connecting rod to a crankshaft causes the gas to rotate the shaft through half a turn.
连动杆将汽缸活塞与机轴联接起来，这种连接促使气体
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. 上止点
BDC(Bottom Dead Center):the position of the crank and piston when the piston is nearest to the crankshaft. 下止点
Stroke : the distance between BDC and TDC; stroke is controlled by the crankshaft. 冲程
Bore : the internal diameter of the cylinder. 内孔(汽缸的内直径)
Swept volume : the volume between TDC and BDC. 活塞排量
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 of50cm. 发动机容积
Clearance volume: the volume of the space above the piston when it is at TDC. 汽缸余隙容积
Compression ratio = (swept vol + clearance vol)\(clearance vol) 压缩率
Two-stroke : a power stroke every revolution of the crank. 二冲程–曲柄旋转一圈作功一次。
Four-stroke : a power stroke every other revolution of the crank.四冲程-曲柄旋转两圈作功一次。
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 air/fuel 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.
2.3.2.Piston
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:
1.Belt 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.
2.Chain 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.
3.Gear 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 r/min. 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 .
1.Cold 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 .
2.Post-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 .
3.Warm-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 .
4.Acceleration
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 .
6.Full 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 .
7.Idling
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 .
8.Overrun
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 .
9.Engine-speed Limiting
When a presser engine speed is reached , the ECU suppresses the fuel-injection pulses .
10.Adaptation 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 Variables/Sensors
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 speed/load 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 A/D 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 3000r/min 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 .
2.9.1The 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 to1400 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
Distributorless ignition system 无分电器点火系统
Primary and secondary circuits 初级和次级电路
Magnetic filed 磁场
High tension lead 高压导线
Distributor rotor 分火头
Spark plug 火花塞
