UNIT 6
ENGINE ELECTRICAL SYSTEMS
TEXT A
Starting,Charging and Ignition Systems
PROFESSIONAL ENGLISH
UNIT 5
ENGINE ELECTRICAL SYSTEMS
TEXT A
Starting,Charging and Ignition Systems
Charging System
Starter System
Ignition System
本次课学习内容本次课学习目标
掌握发动机电气系统的组成
掌握点火系统的型式及原理
掌握有关的专业名词与术语
了解翻译技巧 — 增词
NEW WORDS
electromagnetic [ilektroum? g'netik] a.电磁的
trio['tri:ou]n.三件一套，三个一组，三重唱
forward-biased ['f?:w?d-'bai?st] 正向偏压的
reverse-biased [ri'v?:s-'bai?st] 反向偏压 [偏置 ]的
capacitor [k?'p?sit?] n.= capacitator 电容器
thermistor [:'mist?] n.热敏电阻
rope [roup] n.绳,索,绳索； v.围起
armature ['ɑ:m?tju?] n.电枢
collaps [k?'l? ps] v.&n.倒塌，塌陷，消失，减弱
high-tension ['hai-'ten∫?n] a.高（电）压的
reluctor [ri'l?kt?] n.磁阻轮
centrifugal [sen'trifjug?l] n.离心的
advent ['?dv?nt] n.出现，到来，来临
charging system 充电系统
keep up with 跟上，不落后于
magnetic field 磁场
field strength 磁场强度
contact points 触点
power transistor 功率晶体管
integrated circuit 集成电路
solid state 固态
diode trio 二极管三件组合
starting motor 起动机
PHRASES AND EXPRESSIONS
transmission housing 变速器壳
responsible for（应）对 … 负责，是造成 … 的（主要）原因，决定着，导致
with the advent of 随着 … 的出现（到来）
in time with 与 … 合拍（同期）
in（ constant） contact with（始终） 与 … 保持接触
pickup coil 传感线圈
electric eye 电眼，光电池
shutter wheel 遮光轮
initial timing 初始点火正时
vacuum advance 真空式点火提前角调节装置
distributorless ignition system 无分电器点火系统
Starting,Charging and Ignition Systems
Charging System
The charging system uses the rotation of the engine to
create electricity,The electricity recharges the battery and
provides power to operate the various vehicle electrical
systems,The modern charging system consists of the
alternator and regulator.
Alternator
The alternator is a belt-driven,electromagnetic device,After
the engine is started,the alternator produces electricity to
meet the needs of the vehicle and to keep the battery charged,
The modern vehicle contains many circuits that place a heavy
load on the electrical system,Since many vehicles are used in
stop-and-go city driving,this makes it difficult to maintain the
battery in a fully charged state,Therefore,the alternator must
be extremely efficient at all speeds,
At idle,when the rotor is turning relatively slowly,the
alternator can keep up with the demands of the vehicle
electrical system,At normal vehicle speeds,the alternator can
produce much more voltage and current than needed,To
protect the alternator and the rest of the electrical system from
damage,a means of reducing the output must be found.
Voltage Regulator
To reduce alternator output,a voltage regulator is used,
The voltage regulator controls the alternator output by
adjusting the amount of current reaching the rotor,This
controls the strength of the magnetic field passing through the
stator windings,The regulator controls the field strength by
reading voltage output from the alternator,If output voltage
becomes too high,the regulator reduces field strength,If the
output voltage drops,the regulator increases field strength.
Electromechanical Voltage Regulator
Older voltage regulators use contact points that are
operated by electromagnetic coils,These were called
electromechanical voltage regulators,
Electronic Voltage Regulator(EVR)
All vehicles made within the last 15 years use an electronic
voltage regulator,The electronic voltage regulator uses power
transistors,integrated circuits,diodes,and other solid state
parts to control alternator output,The electronic voltage
regulator eliminates contact points and moving parts that can
stick,oxidize,or wear,Some electronic regulators are remotely
mounted,However,electronic voltage regulators are reliable,
durable,and small enough to be incorporated into the
alternator itself.
Built-in Electronic Regulator Operation
A common charging system circuit with a built-in regulator is
illustrated in Fig.6-1,A small amount of current passes from the
stator through the diode trio to the regulator,This equalizes the
voltage on either side of the indicator light,putting it out,and
tries to ground through resistor R3.
When the stator voltage reaches a certain level,voltage going
to ground through resistor R3 will increase to the point that it will
cause Zener diode D1 to conduct,Forward-biased (voltage
applied in direction causing current flow) transistor TR2
conducts and transistor TR3 is reverse-biased off,This turns
transistor TR1 off,The field current and system voltage
immediately decrease with TR1 off.
Fig.6-1 A
charging
system circuit
with a built-in
regulator
When system voltage decreases,voltage through R3
decreases and D1 stops conducting,This causes transistor TR2
to become reverse-biased off and transistors TR1 and TR3
forward-biased on,Output voltage and field current will increase,
This cycle is repeated thousands of times per second,holding
alternator voltage output to a preset level.
Sudden voltage change across R3 is prevented by capacitor
C1,and excessive back current through TR1 at high
temperature is prevented by R4,TR1 is protected by D2 that
prevents a high induced voltage in the field winding when TR1
is off,Voltage control temperature correction is provided by a
thermistor (resistance decreases as temperature increases).
Computer-Controlled Voltage Regulation
Most vehicles today have several electronic control
units (ECUs) or powertrain control modules (PCM) that
control the engine and other systems,ECU can also be
used to control voltage to the field winding,which
eliminates the need for a separate regulator,The
disadvantage of this system is if the portion of the ECU
that controls voltage regulation becomes defective,the
entire ECU must be replaced [1].
Starter System
To start an internal combustion engine,it must be cranked
(rotated by an outside source),Small two-stroke engines are
often cranked by pulling a rope which causes the internal
engine parts to revolve,The first automobiles used a hand
crank rod for starting,However,this method was dangerous
and impractical,A method was soon developed to start the
engine by using an electric starting motor,or starter,The
starter is mounted on the transmission housing and operates a
small gear that can be meshed with a large ring gear attached
to the flywheel,To energize the starter,the driver turns the
ignition switch to start,which completes an electrical circuit to
the starter [2],When the starter motor armature begins to turn,
the starter gear moves out and engages the ring gear,which
spins the crankshaft,When the engine starts,the driver breaks
the starter electrical circuit by releasing the ignition key switch,
This causes the starter gear to move out of mesh with the ring
gear [3].
Ignition System
The purpose of the ignition system is to create a spark that
will ignite the fuel-air mixture in the cylinder of an engine,It
must do this at exactly the right instant and do it at the rate of
up to several thousand times per minute for each cylinder in
the engine,If the timing of that spark is off by a small fraction
of a second,the engine will run poorly or not run at all.
The ignition system sends an extremely high voltage to the
spark plug in each cylinder when the piston is at the top of its
compression stroke,The tip of each spark plug contains a gap
that the voltage must jump across in order to reach ground,
That is where the spark occurs.
The voltage that is available to the spark plug is somewhere
between 20,000 volts and 50,000 volts or better,The job of
the ignition system is to produce that high voltage from a 12
volt source and get it to each cylinder in a specific order,at
exactly the right time.
The ignition system has two tasks to perform,First,it must
create a voltage high enough (20,000+) to arc across the gap of
a spark plug,thus creating a spark strong enough to ignite the
air/fuel mixture for combustion,Second,it must control the
timing of that the spark so it occurs at the exact right time and
send it to the correct cylinder.
The ignition system is divided into two sections,the primary
circuit and the secondary circuit,The low voltage primary circuit
operates at battery voltage (12 to 14.5 volts) and is responsible
for generating the signal to fire the spark plug at the exact right
time and sending that signal to the ignition coil,The ignition coil
is the component that converts the 12 volt signal into the high
20,000+ volt charge,Once the voltage is stepped up,it goes to
the secondary circuit which then directs the charge to the
correct spark plug at the right time.
The basic principle of the electrical spark ignition system has
not changed for over 75 years,What has changed is the
method by which the spark is created and how it is distributed.
Three Types of Ignition Systems
Currently,there are three distinct types of ignition systems,
The mechanical （ conventional） ignition system was used
prior to 1975,It was mechanical and electrical and used no
electronics,By understanding these early systems,it will be
easier to understand the new electronic and computer
controlled ignition systems,so don't skip over it,The
electronic ignition system started finding its way to production
vehicles during the early '70s and became popular when
better control and improved reliability became important with
the advent of emission controls,Finally,the distributorless
ignition system became available in the mid '80s,This system
was always computer controlled and contained no moving
parts,so reliability was greatly improved,Most of these
systems required no maintenance except replacing the spark
plugs at intervals from 60,000 to over 100,000 miles.
The Mechanical Ignition System
The distributor is the nerve center of the mechanical ignition
system and has two tasks to perform,First,it is responsible for
triggering the ignition coil to generate a spark at the precise
instant,Second,the distributor is responsible for directing that
spark to the proper cylinder,The circuit that powers the ignition
system is simple and straight forward (Fig.6-2),When you insert
the key in the ignition switch and turn the key to the Run
position,you are sending current from the battery through a
wire directly to the positive (+) side of the ignition coil,Inside
the coil is a series of copper windings that loop around the coil
over a hundred times before exiting out the negative (-) side of
the coil,From there,a wire takes this current over to the
distributor and is connected to a special on/off switch,called the
points,When the points are closed,this current goes directly to
ground,When current flows from the ignition switch,through the
windings in the coil,then to ground,it builds a strong magnetic
field inside the coil.
Fig,6-2
A
conventional
ignition
system
The points are made up of a fixed contact point that is
fastened to a plate inside the distributor,and a movable
contact point mounted on the end of a spring loaded arm,The
movable point rides on a 4-,6-,or 8-lobe cam (depending on
the number of cylinders in the engine) that is mounted on a
rotating shaft inside the distributor,This distributor cam
rotates in time with the engine,making one complete
revolution for every two revolutions of the engine,As it rotates,
the cam pushes the points open and closed,Every time the
points open,the flow of current is interrupted through the coil,
thereby collapsing the magnetic field and releasing a high
voltage surge through the secondary coil windings,This
voltage surge goes out the top of the coil and through the
high-tension coil wire.
Now,we have the voltage necessary to fire the spark plug,
but we still have to get it to the correct cylinder,The coil wire
goes from the coil directly to the center of the distributor cap,
Under the cap is a rotor that is mounted on top of the rotating
shaft,The rotor has a metal strip on the top that is in constant
contact with the center terminal of the distributor cap,It
receives the high voltage surge from the coil wire and sends it
to the other end of the rotor which rotates past each spark plug
terminal inside the cap [4],As the rotor turns on the shaft,it
sends the voltage to the correct spark plug wire,which in turn
sends it to the spark plug,The voltage enters the spark plug at
the terminal at the top and travels down the core until it
reaches the tip,It then jumps across the gap at the tip of the
spark plug,creating a spark suitable to ignite the fuel-air
mixture inside that cylinder.
The Electronic Ignition System
In the electronic ignition（ EI） system,the points and
condenser were replaced by electronics,On these systems,
there were several methods used to replace the points and
condenser in order to trigger the coil to fire,One method used
a metal wheel with teeth,usually one for each cylinder,This is
called an armature or reluctor,A magnetic pickup coil senses
when a tooth passes and sends a signal to the control module
to fire the coil.
Other systems used an electric eye with a shutter wheel to
send a signal to the electronics that it was time to trigger the
coil to fire,These systems still need to have the initial timing
adjusted by rotating the distributor housing.
The advantage of this system,aside from the fact that it is
maintenance free,is that the control module can handle much
higher primary voltage than the mechanical points,Voltage
can even be stepped up before sending it to the coil,so the
coil can create a much hotter spark,on the order of 50,000
volts instead of 20,000 volts that is common with the
mechanical systems,These systems only have a single wire
from the ignition switch to the coil since a primary resistor is no
longer needed.
On some vehicles,this control module was mounted inside
the distributor where the points used to be mounted,On other
designs,the control module was mounted outside the
distributor with external wiring to connect it to the pickup coil,
On many General Motors engines,the control module was
inside the distributor and the coil was mounted on top of the
distributor for a one piece unitized ignition system,GM called it
High Energy Ignition or HEI for short.
The higher voltage that these systems provided allows the
use of a much wider gap on the spark plugs for a longer,fatter
spark,This larger spark also allows a leaner mixture for better
fuel economy and still insures a smooth running engine.
The early electronic systems had limited or no computing
power,so timing still had to be set manually and there was still
a centrifugal and vacuum advance built into the distributor.
On some of the later systems,the inside of the distributor is
empty and all triggering is performed by a sensor that watches
a notched wheel connected to either the crankshaft or the
camshaft,These devices are called crankshaft position sensor
or camshaft position sensor,In these systems,the job of the
distributor is solely to distribute the spark to the correct
cylinder through the distributor cap and rotor,The computer
handles the timing and any timing advance necessary for the
smooth running of the engine.
The Distributorless Ignition System
Newer automobiles have evolved from a mechanical system
(distributor) to a completely solid state electronic system with
no moving parts,These systems are completely controlled by
the on-board computer,In place of the distributor,there are
multiple coils that each serves one or two spark plugs,A
typical 6-cylinder engine has 3 coils that are mounted together
in a coil "pack",A spark plug wire comes out of each side of
the individual coil and goes to the appropriate spark plug,The
coil fires both spark plugs at the same time,One spark plug
fires on the compression stroke,igniting the fuel-air mixture to
produce power,while the other spark plug fires on the exhaust
stroke and does nothing,On some vehicles,there is an
individual coil for each cylinder mounted directly on top of the
spark plug,This design completely eliminates the high tension
spark plug wires for even better reliability,Most of these
systems use spark plugs that are designed to last over
100,000 miles,which cuts down on maintenance costs.
小结
Charging System
Alternator
Voltage Regulator
Starter System
Ignition System
Mechanical （ Conventional） Ignition System
Electronic Ignition System
Distributorless Ignition System
作业
熟记相关专业词汇
P140 EXERCIES Ⅰ & Ⅱ
ENGINE ELECTRICAL SYSTEMS
TEXT A
Starting,Charging and Ignition Systems
PROFESSIONAL ENGLISH
UNIT 5
ENGINE ELECTRICAL SYSTEMS
TEXT A
Starting,Charging and Ignition Systems
Charging System
Starter System
Ignition System
本次课学习内容本次课学习目标
掌握发动机电气系统的组成
掌握点火系统的型式及原理
掌握有关的专业名词与术语
了解翻译技巧 — 增词
NEW WORDS
electromagnetic [ilektroum? g'netik] a.电磁的
trio['tri:ou]n.三件一套，三个一组，三重唱
forward-biased ['f?:w?d-'bai?st] 正向偏压的
reverse-biased [ri'v?:s-'bai?st] 反向偏压 [偏置 ]的
capacitor [k?'p?sit?] n.= capacitator 电容器
thermistor [:'mist?] n.热敏电阻
rope [roup] n.绳,索,绳索； v.围起
armature ['ɑ:m?tju?] n.电枢
collaps [k?'l? ps] v.&n.倒塌，塌陷，消失，减弱
high-tension ['hai-'ten∫?n] a.高（电）压的
reluctor [ri'l?kt?] n.磁阻轮
centrifugal [sen'trifjug?l] n.离心的
advent ['?dv?nt] n.出现，到来，来临
charging system 充电系统
keep up with 跟上，不落后于
magnetic field 磁场
field strength 磁场强度
contact points 触点
power transistor 功率晶体管
integrated circuit 集成电路
solid state 固态
diode trio 二极管三件组合
starting motor 起动机
PHRASES AND EXPRESSIONS
transmission housing 变速器壳
responsible for（应）对 … 负责，是造成 … 的（主要）原因，决定着，导致
with the advent of 随着 … 的出现（到来）
in time with 与 … 合拍（同期）
in（ constant） contact with（始终） 与 … 保持接触
pickup coil 传感线圈
electric eye 电眼，光电池
shutter wheel 遮光轮
initial timing 初始点火正时
vacuum advance 真空式点火提前角调节装置
distributorless ignition system 无分电器点火系统
Starting,Charging and Ignition Systems
Charging System
The charging system uses the rotation of the engine to
create electricity,The electricity recharges the battery and
provides power to operate the various vehicle electrical
systems,The modern charging system consists of the
alternator and regulator.
Alternator
The alternator is a belt-driven,electromagnetic device,After
the engine is started,the alternator produces electricity to
meet the needs of the vehicle and to keep the battery charged,
The modern vehicle contains many circuits that place a heavy
load on the electrical system,Since many vehicles are used in
stop-and-go city driving,this makes it difficult to maintain the
battery in a fully charged state,Therefore,the alternator must
be extremely efficient at all speeds,
At idle,when the rotor is turning relatively slowly,the
alternator can keep up with the demands of the vehicle
electrical system,At normal vehicle speeds,the alternator can
produce much more voltage and current than needed,To
protect the alternator and the rest of the electrical system from
damage,a means of reducing the output must be found.
Voltage Regulator
To reduce alternator output,a voltage regulator is used,
The voltage regulator controls the alternator output by
adjusting the amount of current reaching the rotor,This
controls the strength of the magnetic field passing through the
stator windings,The regulator controls the field strength by
reading voltage output from the alternator,If output voltage
becomes too high,the regulator reduces field strength,If the
output voltage drops,the regulator increases field strength.
Electromechanical Voltage Regulator
Older voltage regulators use contact points that are
operated by electromagnetic coils,These were called
electromechanical voltage regulators,
Electronic Voltage Regulator(EVR)
All vehicles made within the last 15 years use an electronic
voltage regulator,The electronic voltage regulator uses power
transistors,integrated circuits,diodes,and other solid state
parts to control alternator output,The electronic voltage
regulator eliminates contact points and moving parts that can
stick,oxidize,or wear,Some electronic regulators are remotely
mounted,However,electronic voltage regulators are reliable,
durable,and small enough to be incorporated into the
alternator itself.
Built-in Electronic Regulator Operation
A common charging system circuit with a built-in regulator is
illustrated in Fig.6-1,A small amount of current passes from the
stator through the diode trio to the regulator,This equalizes the
voltage on either side of the indicator light,putting it out,and
tries to ground through resistor R3.
When the stator voltage reaches a certain level,voltage going
to ground through resistor R3 will increase to the point that it will
cause Zener diode D1 to conduct,Forward-biased (voltage
applied in direction causing current flow) transistor TR2
conducts and transistor TR3 is reverse-biased off,This turns
transistor TR1 off,The field current and system voltage
immediately decrease with TR1 off.
Fig.6-1 A
charging
system circuit
with a built-in
regulator
When system voltage decreases,voltage through R3
decreases and D1 stops conducting,This causes transistor TR2
to become reverse-biased off and transistors TR1 and TR3
forward-biased on,Output voltage and field current will increase,
This cycle is repeated thousands of times per second,holding
alternator voltage output to a preset level.
Sudden voltage change across R3 is prevented by capacitor
C1,and excessive back current through TR1 at high
temperature is prevented by R4,TR1 is protected by D2 that
prevents a high induced voltage in the field winding when TR1
is off,Voltage control temperature correction is provided by a
thermistor (resistance decreases as temperature increases).
Computer-Controlled Voltage Regulation
Most vehicles today have several electronic control
units (ECUs) or powertrain control modules (PCM) that
control the engine and other systems,ECU can also be
used to control voltage to the field winding,which
eliminates the need for a separate regulator,The
disadvantage of this system is if the portion of the ECU
that controls voltage regulation becomes defective,the
entire ECU must be replaced [1].
Starter System
To start an internal combustion engine,it must be cranked
(rotated by an outside source),Small two-stroke engines are
often cranked by pulling a rope which causes the internal
engine parts to revolve,The first automobiles used a hand
crank rod for starting,However,this method was dangerous
and impractical,A method was soon developed to start the
engine by using an electric starting motor,or starter,The
starter is mounted on the transmission housing and operates a
small gear that can be meshed with a large ring gear attached
to the flywheel,To energize the starter,the driver turns the
ignition switch to start,which completes an electrical circuit to
the starter [2],When the starter motor armature begins to turn,
the starter gear moves out and engages the ring gear,which
spins the crankshaft,When the engine starts,the driver breaks
the starter electrical circuit by releasing the ignition key switch,
This causes the starter gear to move out of mesh with the ring
gear [3].
Ignition System
The purpose of the ignition system is to create a spark that
will ignite the fuel-air mixture in the cylinder of an engine,It
must do this at exactly the right instant and do it at the rate of
up to several thousand times per minute for each cylinder in
the engine,If the timing of that spark is off by a small fraction
of a second,the engine will run poorly or not run at all.
The ignition system sends an extremely high voltage to the
spark plug in each cylinder when the piston is at the top of its
compression stroke,The tip of each spark plug contains a gap
that the voltage must jump across in order to reach ground,
That is where the spark occurs.
The voltage that is available to the spark plug is somewhere
between 20,000 volts and 50,000 volts or better,The job of
the ignition system is to produce that high voltage from a 12
volt source and get it to each cylinder in a specific order,at
exactly the right time.
The ignition system has two tasks to perform,First,it must
create a voltage high enough (20,000+) to arc across the gap of
a spark plug,thus creating a spark strong enough to ignite the
air/fuel mixture for combustion,Second,it must control the
timing of that the spark so it occurs at the exact right time and
send it to the correct cylinder.
The ignition system is divided into two sections,the primary
circuit and the secondary circuit,The low voltage primary circuit
operates at battery voltage (12 to 14.5 volts) and is responsible
for generating the signal to fire the spark plug at the exact right
time and sending that signal to the ignition coil,The ignition coil
is the component that converts the 12 volt signal into the high
20,000+ volt charge,Once the voltage is stepped up,it goes to
the secondary circuit which then directs the charge to the
correct spark plug at the right time.
The basic principle of the electrical spark ignition system has
not changed for over 75 years,What has changed is the
method by which the spark is created and how it is distributed.
Three Types of Ignition Systems
Currently,there are three distinct types of ignition systems,
The mechanical （ conventional） ignition system was used
prior to 1975,It was mechanical and electrical and used no
electronics,By understanding these early systems,it will be
easier to understand the new electronic and computer
controlled ignition systems,so don't skip over it,The
electronic ignition system started finding its way to production
vehicles during the early '70s and became popular when
better control and improved reliability became important with
the advent of emission controls,Finally,the distributorless
ignition system became available in the mid '80s,This system
was always computer controlled and contained no moving
parts,so reliability was greatly improved,Most of these
systems required no maintenance except replacing the spark
plugs at intervals from 60,000 to over 100,000 miles.
The Mechanical Ignition System
The distributor is the nerve center of the mechanical ignition
system and has two tasks to perform,First,it is responsible for
triggering the ignition coil to generate a spark at the precise
instant,Second,the distributor is responsible for directing that
spark to the proper cylinder,The circuit that powers the ignition
system is simple and straight forward (Fig.6-2),When you insert
the key in the ignition switch and turn the key to the Run
position,you are sending current from the battery through a
wire directly to the positive (+) side of the ignition coil,Inside
the coil is a series of copper windings that loop around the coil
over a hundred times before exiting out the negative (-) side of
the coil,From there,a wire takes this current over to the
distributor and is connected to a special on/off switch,called the
points,When the points are closed,this current goes directly to
ground,When current flows from the ignition switch,through the
windings in the coil,then to ground,it builds a strong magnetic
field inside the coil.
Fig,6-2
A
conventional
ignition
system
The points are made up of a fixed contact point that is
fastened to a plate inside the distributor,and a movable
contact point mounted on the end of a spring loaded arm,The
movable point rides on a 4-,6-,or 8-lobe cam (depending on
the number of cylinders in the engine) that is mounted on a
rotating shaft inside the distributor,This distributor cam
rotates in time with the engine,making one complete
revolution for every two revolutions of the engine,As it rotates,
the cam pushes the points open and closed,Every time the
points open,the flow of current is interrupted through the coil,
thereby collapsing the magnetic field and releasing a high
voltage surge through the secondary coil windings,This
voltage surge goes out the top of the coil and through the
high-tension coil wire.
Now,we have the voltage necessary to fire the spark plug,
but we still have to get it to the correct cylinder,The coil wire
goes from the coil directly to the center of the distributor cap,
Under the cap is a rotor that is mounted on top of the rotating
shaft,The rotor has a metal strip on the top that is in constant
contact with the center terminal of the distributor cap,It
receives the high voltage surge from the coil wire and sends it
to the other end of the rotor which rotates past each spark plug
terminal inside the cap [4],As the rotor turns on the shaft,it
sends the voltage to the correct spark plug wire,which in turn
sends it to the spark plug,The voltage enters the spark plug at
the terminal at the top and travels down the core until it
reaches the tip,It then jumps across the gap at the tip of the
spark plug,creating a spark suitable to ignite the fuel-air
mixture inside that cylinder.
The Electronic Ignition System
In the electronic ignition（ EI） system,the points and
condenser were replaced by electronics,On these systems,
there were several methods used to replace the points and
condenser in order to trigger the coil to fire,One method used
a metal wheel with teeth,usually one for each cylinder,This is
called an armature or reluctor,A magnetic pickup coil senses
when a tooth passes and sends a signal to the control module
to fire the coil.
Other systems used an electric eye with a shutter wheel to
send a signal to the electronics that it was time to trigger the
coil to fire,These systems still need to have the initial timing
adjusted by rotating the distributor housing.
The advantage of this system,aside from the fact that it is
maintenance free,is that the control module can handle much
higher primary voltage than the mechanical points,Voltage
can even be stepped up before sending it to the coil,so the
coil can create a much hotter spark,on the order of 50,000
volts instead of 20,000 volts that is common with the
mechanical systems,These systems only have a single wire
from the ignition switch to the coil since a primary resistor is no
longer needed.
On some vehicles,this control module was mounted inside
the distributor where the points used to be mounted,On other
designs,the control module was mounted outside the
distributor with external wiring to connect it to the pickup coil,
On many General Motors engines,the control module was
inside the distributor and the coil was mounted on top of the
distributor for a one piece unitized ignition system,GM called it
High Energy Ignition or HEI for short.
The higher voltage that these systems provided allows the
use of a much wider gap on the spark plugs for a longer,fatter
spark,This larger spark also allows a leaner mixture for better
fuel economy and still insures a smooth running engine.
The early electronic systems had limited or no computing
power,so timing still had to be set manually and there was still
a centrifugal and vacuum advance built into the distributor.
On some of the later systems,the inside of the distributor is
empty and all triggering is performed by a sensor that watches
a notched wheel connected to either the crankshaft or the
camshaft,These devices are called crankshaft position sensor
or camshaft position sensor,In these systems,the job of the
distributor is solely to distribute the spark to the correct
cylinder through the distributor cap and rotor,The computer
handles the timing and any timing advance necessary for the
smooth running of the engine.
The Distributorless Ignition System
Newer automobiles have evolved from a mechanical system
(distributor) to a completely solid state electronic system with
no moving parts,These systems are completely controlled by
the on-board computer,In place of the distributor,there are
multiple coils that each serves one or two spark plugs,A
typical 6-cylinder engine has 3 coils that are mounted together
in a coil "pack",A spark plug wire comes out of each side of
the individual coil and goes to the appropriate spark plug,The
coil fires both spark plugs at the same time,One spark plug
fires on the compression stroke,igniting the fuel-air mixture to
produce power,while the other spark plug fires on the exhaust
stroke and does nothing,On some vehicles,there is an
individual coil for each cylinder mounted directly on top of the
spark plug,This design completely eliminates the high tension
spark plug wires for even better reliability,Most of these
systems use spark plugs that are designed to last over
100,000 miles,which cuts down on maintenance costs.
小结
Charging System
Alternator
Voltage Regulator
Starter System
Ignition System
Mechanical （ Conventional） Ignition System
Electronic Ignition System
Distributorless Ignition System
作业
熟记相关专业词汇
P140 EXERCIES Ⅰ & Ⅱ
