UNIT 2
ENGINE MECHANICAL
TEXT A
Operation,Main Components and Classification
of the Engine
PROFESSIONAL ENGLISH
UNIT 2
ENGINE MECHANICAL
TEXT A
Operation,Main Components and Classification
of the Engine
Principle of Operation
Main Engine Components
Engine Classification
本次课学习内容本次课学习目标
掌握发动机主要部件的英文名称
掌握各中发动机的英文名称
掌握常用术语（ phrases and
expressions）
了解相关术语（ related terms）
较熟练翻译与发动机工作原理相关的英文文章
NEW WORDS
combustion [k?m'b?s∫?n] n.燃烧
stroke [strouk ] n.冲程
piston ['pist?n] n.活塞
cylinder ['silind?] n.气缸
valve [v?lv ]n.气门，阀门，阀
exhaust [ig'z?:st ]n.排气，废气
intake ['inteik ]n.进气，进（引，吸）入
compression [k?m'pre∫?n ]n.压缩
crankshaft ['krk∫ɑ:ft]n.曲轴
swirl [sw?:l ]n.漩涡，涡流，紊流； v.涡动
churn [t∫?:n ]v.搅拌，搅动
foundation [faun'dei∫?n ]n.基础，基地，基金，机座
camshaft ['k?m∫ɑ:ft]n.凸轮轴
accessory [?k'ses?ri]n.附属品，附件，辅助装置
clutch [kl?t∫]n.离合器
housing ['hauzi?] n.外壳
bolt [boult] n.螺栓； v.用螺栓连接
core [k?:] n.芯，核心，铁心，型芯，沙芯，（电缆）芯线
aluminum ['?lju:min?m]n.铝
liner ['lain?]n.衬套，衬里，衬板
oversize ['ouv?saiz]n.& a.加大尺寸
heavy-duty ['hevi'dju:ti]a.重型的，重载的
oscillate ['?sileit]v.振荡，振动，波动，动摇
bearing ['bri?]n.轴承
journal[':n?l]n.轴颈
throw [?rou]n.& v.投掷，扔； n.投掷距离，偏心距离，摆幅；（ pl.）曲柄
attach [?'t?t∫]v.附着，连接，固定（ to）
reciprocating [ri'sipr?keiti?]a.往复的
mount [mɑunt]v.安装，固定； n.安装件，支架，机座
rim [rim]n.边缘，轮缘，轮辋，齿圈
heat-resistant [hi:t-ri'zist?nt ]a.耐热的
clearance ['kli?r?ns]n.间隙
lifter ['lift?]n.挺杆
harden ['hɑ:d?n]v.硬化，变硬，淬硬
revolution [rev?'lu:∫?n]n.转，回转，大变革
inline ['in'lain]a.直列式的，在一条直线上的
bank [bk]n.（气缸）列，排，银行
rigidity [ri'?iditi]n.刚性
profile ['proufail]n.外形，轮廓
conducive [k?n'dju:siv]a.有助于 … 的，促进 … 的（ to）
sacrifice ['s?krifais]n.牺牲（品），损失
liquefy ['likwifai]v.液化
propane ['proupein]n.丙烷
carburetion [kɑ:bju're∫?n]n.汽化
carburetor [kɑ:bju'ret?]n.化油器
internal combustion engine 内燃机
four-stroke cycle 四冲程循环
spark plug 火花塞
intake stroke 进气行程
power stroke 作功行程
compression stroke 压缩行程
exhaust stroke 排气行程
connecting rod 连杆
automatic transmission 自动变速器
torque converter 液力变矩器
PHRASES AND EXPRESSIONS
insert bearing 镶入式轴承
valve seat 气门座
valve guide 气门导管
valve train 气门机构，气门组
hydraulic valve lifter 液力挺杆
TEXT A Operation,Main Components and
Classification of the Engine
The automotive engine is essentially a heat engine,The
heat engines used in automobiles are internal combustion
engines.
1,Principle of Operation
The spark-ignition engine is an internal-combustion engine
with externally supplied in ignition,The gasoline engine is a
kind of spark-ignition engines,
The four-stroke-cycle gasoline engine cycle is spread over
four piston strokes,The operation strokes are (figure2-1):
Fig,2-1 The operation of a four-stroke-cycle gasoline engine
The first stroke in your engine is called the intake stroke,
Instead of opening the intake valve after you have drawn
the piston down,you will find it better to open the intake
valve as the piston starts down [1],This allows the air to
draw fuel in the entire time the piston is moving down,
Remember,the intake stroke starts with the piston at the
top of the cylinder (intake valve open and exhaust valve
closed) and stops with the piston at the bottom of its travel
[2],This requires one-half turn of the crankshaft.
[1] Instead of opening the intake valve after you have drawn
the piston down,you will find it better to open the intake
valve as the piston starts down.
Instead of… 的意思是,而不是 …”,,代替着 …” 。 draw…
down的意思是,将 … 向下移,。 better为副词，意思为,更好,,,更多,,,更加,,修饰动词不定式短语 to open
the intake valve。本句译为：在活塞下行之后，进气门不只是已经打开，而是随着活塞的下移，开度还在进一步增大。
[2] Remember,the intake stroke starts with the piston at the
top of the cylinder (intake valve open and exhaust valve
closed) and stops with the piston at the bottom of its travel.
With后面的宾语接有现在分词、过去分词、形容词,甚至是副词,with后面的宾语与现在分词、过去分词、形容词之间具有,主谓,关系。 这时整个 with短语说明附带情况，或者交待细节。本句译为：记住，进气行程在活塞位于气缸顶部
（进气门开启，排气门关闭）时开始，在活塞到达其行程的底部时结束。
As the crankshaft continues to move,the piston is forced up
through the cylinder,If you keep both valves closed,the fuel
mixture will be squeezed,or compressed,as the piston reaches
the top,This is called the compression stroke,It,too,requires a
half turn of the crankshaft,
The compression stroke serves to break up the fuel into even
smaller particles,This happens due to the sudden swirling and
churning of the mixture as it is compressed.
When the air-fuel mixture is subjected to a sudden sharp
compression force,its temperature rises,This increase in
temperature makes the mixture easier to ignite and causes it to
explode with greater force,As the piston reaches the top of its
travel on the compression stroke,it has returned to the proper
position to be pushed back down by the explosion.
Remember,the compression stroke starts with the piston at
the bottom of the cylinder (both valves closed) and stops with the
piston at the top of the cylinder,This requires an additional half
turn of the crankshaft.
As the piston reaches the top of the compression stroke,
the mixture is broken into tiny particles and heated up,
When ignited,it will explode with great force,This is the
right time to explode the mixture,A spark plug provides a
spark inside the combustion chamber,The spark produced
at the plug is formed by the ignition system,This will be
discussed in Unit 6.
Just imagine that a hot spark has been provided in the
fuel mixture,The mixture will explode and,in turn,force the
piston down into the cylinder,This gives the crankshaft a
quick and forceful push,This is the power stroke,Both
valves must be kept closed during the power stroke or the
pressure of the burning fuel will squirt out through the valve
pods,Remember,the power stroke starts with the piston at
the top of the cylinder (both valves closed) and stops with
the piston at the bottom of the cylinder,This requires
another half turn of the crankshaft.
When the piston reaches the bottom of the power stroke,the
exhaust valve opens,The spinning crankshaft forces the piston
up through the cylinder,pushing burned gases out,This is the
exhaust stroke.
Remember,the exhaust stroke starts with the piston at the
bottom of the cylinder (exhaust valve open and intake valve
closed),It stops with the piston at the top of the cylinder,This
requires one more half turn of the crankshaft,
If you count the number of half turns in the intake,compression,
power,and exhaust strokes,you will find you have a total of
four,This gives you two complete turns,or revolutions,of the
crankshaft,While the crankshaft is turning around twice,it is
receiving power only during one half turn,or one fourth of the
time.
As soon as the piston reaches the top of the exhaust stroke,
it starts down on another intake,compression,power,and
exhaust cycle,This cycle is repeated over and over,
Each complete cycle consists of four strokes of the
piston,hence the name four-stroke cycle.
2,Main Engine Components
Engine block
The engine block serves as a rigid metal foundation for
all parts of an engine,It contains the cylinders and supports
the crankshaft and camshaft,In older engines,the valve
seats,ports,and guides are built into the block,Accessory
units and the clutch housing are bolted to it,
Blocks are made of either cast iron or aluminum,The
lighter the block (providing it has sufficient strength),the
better,The modern thin-wall casting process controls core
size and placement much more accurately than the older
casting process,This permits casting the block walls much
thinner,reducing the weight of the block,Since the block
wall thickness is more uniform,block distortion during
service is less severe.
Cylinders
The cylinder is a round hole formed in the block,It forms
a guide for the piston and acts as a container for taking in,
compressing,firing,and exhausting the air-fuel charge,
Cylinders have been made of both steel and cast iron,Cast
iron is by far the most popular.
When steel cylinders are desired in an aluminum block,
they are installed in the form of cylinder sleeves (round,
pipe-like liners),These sleeves may be either cast or
pressed into the block,Some engines use removable
cylinder sleeves,When the cylinder becomes worn,the old
sleeves can be pulled out and new sleeves can be pressed
in,The sleeves are pressed into oversize cylinder holes,
Cylinder sleeves are widely used in heavy-duty truck and
industrial engines,Sleeves can also be used to repair a
worn or cracked cylinder in a cast iron block.
Pistons
The piston must move down through the cylinder to
produce a vacuum to draw a fuel charge into the cylinder,It
then travels up in the cylinder and compresses the mixture,
When the mixture is fired,the pressure of the expanding
gas is transmitted to the top of the piston,This drives the
piston back down through the cylinder with great force,
transmitting the energy of the expanding gas to the
crankshaft,The piston then travels up through the cylinder
and exhausts the burned fuel charge.
Pistons are usually made of aluminum,Often,aluminum
pistons are tin-plated to allow proper break-in when the
engine is started,Aluminum pistons can be forged,but they
are more commonly cast,Cast iron is a good material for
pistons used in a slow-speed engine,It has excellent wear
characteristics and will provide good performance,
Connecting Rods
As the name implies,connecting rods are used to connect
pistons to the crankshaft,The upper end of the rod oscillates
(swings back and forth),while the lower,or big end,bearing
rotates (turns).
Because there is very little bearing movement in the upper end,
the bearing area can be reasonably small,The lower end rotates
very fast,and the crankshaft bearing journal turns inside the
connecting rod,This rotational speed tends to produce heat and
wear,To make the rod wear well,a larger bearing area is
required.
The upper end of the rod has a hole through it for the piston
pin,The bottom of the large end of the connecting rod must be
removed so the rod can be installed on the crankshaft journal,
The section that is removed is called the connecting rod cap.
Connecting rods are normally made of alloy steel,They are
drop-forged to shape and then machined.
Crankshaft
The engine crankshaft provides a constant turning force
to the wheels,It has throws to which connecting rods are
attached,and its function is to change the reciprocating
motion of the piston to a rotary motion to drive the wheels,
Crankshafts are made of alloy steel or cast iron,
The crankshaft is held in position by a series of main
bearings,The maximum number of main bearings for a
crankshaft is one more than the number of cylinders,It may
have fewer main bearings than cylinders,Most engines use
precision insert bearings that are constructed like the
connecting rod bearings,but are somewhat larger,In
addition to supporting the crankshaft,one of the main
bearings must control the forward and backward movement.
Flywheel
A heavy flywheel is attached to the rear of the
crankshaft with bolts,The function of the flywheel is to
smooth out engine speed and keep the crankshaft spinning
between power strokes,in some engines,the flywheel also
serves as a mounting surface for the clutch,The outer rim
of the flywheel has a large ring attached with gear teeth cut
into it,The teeth of the starter motor engage these teeth
and spin the flywheel to crank the engine,When an
automatic transmission is used,the torque converter
assembly works with the flywheel.
Camshaft
The camshaft is used to open and close the valves,
There is one cam on the camshaft for each valve in the
engine,Generally only one camshaft is used in most
engines,Newer engines are increasingly equipped with two
or more camshafts (figure2-2),
Figure 2-2 Dual overhead camshaft（ DOHC）
driven by a toothed drive belt
Valves
Each engine cylinder ordinarily has two valves,
However,modern engines often use four valves per
cylinder (two intake and two exhaust),A few engines used
in smaller vehicles have three or five valves per cylinder,
two intake valves and one exhaust valve or three intake
valves and two exhaust valves,
Because the head of an exhaust valve operates at
temperatures up to 1300℉ (704℃ ),valves are made of
heat-resistant metal,In order to prevent burning,the valve
must give off heat to the valve seat and to the valve guide,
The valve must make good contact with the seat and must
run with minimum clearance in the guide.
Valve Lifters
Mechanical valve lifters are usually made of cast iron,The
bottom part that contacts the camshaft is hardened,Some lifters
are hollow to reduce weight,Most valve trains that contain
mechanical lifters have some provision for adjusting clearance,
Mechanical valve lifters were used in older engines.
Hydraulic valve lifters perform the same job as mechanical
lifters,However,hydraulic lifters are self-adjusting,operate with
no lifter-to-rocker arm clearance,and uses engine oil under
pressure to operate,Hydraulic lifters are quiet in operation.
3,Engine Classification
Cycle Classification
Engines are often classified according to cycle,Most internal
combustion piston engines use a two- or four-stroke cycle,All
modern automobile engines use the four-stroke cycle engine.
The two-stroke cycle engine performs the intake,compression,
firing,and exhaust sequence in one revolution of the crankshaft,
Cylinder Classification
The inline engine has its cylinders arranged one after
the other in a straight line,They are in a vertical,or near
vertical position,Most modern inline engines are four
cylinders,
A V-type engine places two banks or rows of cylinders
at an angle to each other— generally at 60° or 90°,The
V-type engine has several advantages,short length,extra
block rigidity,a short,heavy crankshaft,and low profile that
is conducive to low hood lines,The shorter block permits a
reduction in vehicle length with no sacrifice in passenger
room.
The horizontal opposed engine is like a V-type engine,
except that both banks lie in a horizontal plane,The
advantage here is an extremely low overall height,which
makes this engine ideally suited to installations where
space is limited.
Cooling Classification
As you have learned,engines are either liquid-cooled or
air-cooled,Most vehicles use liquid-cooled engines,Air-
cooled engines are used in limited numbers on modern
vehicles.
Fuel Classification
Automobile engines can use gasoline,diesel fuel,gasohol
(mixture of gasoline and alcohol),alcohol,LNG (liquefied
natural gas),CNG (compressed natural gas),or LPG
(liquefied propane gas),Gasoline powers the majority of
vehicles,but diesel fuel is used in some vehicles,Gasohol,
LNG,CNG,and LPG are beginning to see wider use,One of
the principal differences in these engines is in method of fuel
delivery and carburetion,Gasoline,LNG,CNG,and LPG
utilize the same basic type of engine,but LNG,CNG,and
LPG utilize a slightly different fuel delivery setup,Diesel
engines do not use a carburetor or an ignition system.
小结
Principle of Operation
Main Engine Components
Engine Classification
小结
Principle of Operation
The four-stroke-cycle gasoline engine cycle is
spread over four piston strokes,The operation
strokes are,
intake (induction) stroke
compression stroke
power stroke
exhaust stroke
小结
Main Engine Components
Main Engine
Components
小结
Engine Classification
Cycle Classification
Two-stroke cycle engine
Four-stroke cycle engine
Cylinder Classification
In-line engine
V-type engine
Flat engine (horizontal opposed)
Cooling Classification
Liquid-cooled engine
Air-cooled engine
Fuel Classification
Gasoline,diesel fuel,gasohol (mixture of gasoline and alcohol),alcohol,
LNG (liquefied natural gas),CNG (compressed natural gas),or LPG
(liquefied propane gas)
作业
熟记相关专业词汇
P30 EXERCIES Ⅰ
ENGINE MECHANICAL
TEXT A
Operation,Main Components and Classification
of the Engine
PROFESSIONAL ENGLISH
UNIT 2
ENGINE MECHANICAL
TEXT A
Operation,Main Components and Classification
of the Engine
Principle of Operation
Main Engine Components
Engine Classification
本次课学习内容本次课学习目标
掌握发动机主要部件的英文名称
掌握各中发动机的英文名称
掌握常用术语（ phrases and
expressions）
了解相关术语（ related terms）
较熟练翻译与发动机工作原理相关的英文文章
NEW WORDS
combustion [k?m'b?s∫?n] n.燃烧
stroke [strouk ] n.冲程
piston ['pist?n] n.活塞
cylinder ['silind?] n.气缸
valve [v?lv ]n.气门，阀门，阀
exhaust [ig'z?:st ]n.排气，废气
intake ['inteik ]n.进气，进（引，吸）入
compression [k?m'pre∫?n ]n.压缩
crankshaft ['krk∫ɑ:ft]n.曲轴
swirl [sw?:l ]n.漩涡，涡流，紊流； v.涡动
churn [t∫?:n ]v.搅拌，搅动
foundation [faun'dei∫?n ]n.基础，基地，基金，机座
camshaft ['k?m∫ɑ:ft]n.凸轮轴
accessory [?k'ses?ri]n.附属品，附件，辅助装置
clutch [kl?t∫]n.离合器
housing ['hauzi?] n.外壳
bolt [boult] n.螺栓； v.用螺栓连接
core [k?:] n.芯，核心，铁心，型芯，沙芯，（电缆）芯线
aluminum ['?lju:min?m]n.铝
liner ['lain?]n.衬套，衬里，衬板
oversize ['ouv?saiz]n.& a.加大尺寸
heavy-duty ['hevi'dju:ti]a.重型的，重载的
oscillate ['?sileit]v.振荡，振动，波动，动摇
bearing ['bri?]n.轴承
journal[':n?l]n.轴颈
throw [?rou]n.& v.投掷，扔； n.投掷距离，偏心距离，摆幅；（ pl.）曲柄
attach [?'t?t∫]v.附着，连接，固定（ to）
reciprocating [ri'sipr?keiti?]a.往复的
mount [mɑunt]v.安装，固定； n.安装件，支架，机座
rim [rim]n.边缘，轮缘，轮辋，齿圈
heat-resistant [hi:t-ri'zist?nt ]a.耐热的
clearance ['kli?r?ns]n.间隙
lifter ['lift?]n.挺杆
harden ['hɑ:d?n]v.硬化，变硬，淬硬
revolution [rev?'lu:∫?n]n.转，回转，大变革
inline ['in'lain]a.直列式的，在一条直线上的
bank [bk]n.（气缸）列，排，银行
rigidity [ri'?iditi]n.刚性
profile ['proufail]n.外形，轮廓
conducive [k?n'dju:siv]a.有助于 … 的，促进 … 的（ to）
sacrifice ['s?krifais]n.牺牲（品），损失
liquefy ['likwifai]v.液化
propane ['proupein]n.丙烷
carburetion [kɑ:bju're∫?n]n.汽化
carburetor [kɑ:bju'ret?]n.化油器
internal combustion engine 内燃机
four-stroke cycle 四冲程循环
spark plug 火花塞
intake stroke 进气行程
power stroke 作功行程
compression stroke 压缩行程
exhaust stroke 排气行程
connecting rod 连杆
automatic transmission 自动变速器
torque converter 液力变矩器
PHRASES AND EXPRESSIONS
insert bearing 镶入式轴承
valve seat 气门座
valve guide 气门导管
valve train 气门机构，气门组
hydraulic valve lifter 液力挺杆
TEXT A Operation,Main Components and
Classification of the Engine
The automotive engine is essentially a heat engine,The
heat engines used in automobiles are internal combustion
engines.
1,Principle of Operation
The spark-ignition engine is an internal-combustion engine
with externally supplied in ignition,The gasoline engine is a
kind of spark-ignition engines,
The four-stroke-cycle gasoline engine cycle is spread over
four piston strokes,The operation strokes are (figure2-1):
Fig,2-1 The operation of a four-stroke-cycle gasoline engine
The first stroke in your engine is called the intake stroke,
Instead of opening the intake valve after you have drawn
the piston down,you will find it better to open the intake
valve as the piston starts down [1],This allows the air to
draw fuel in the entire time the piston is moving down,
Remember,the intake stroke starts with the piston at the
top of the cylinder (intake valve open and exhaust valve
closed) and stops with the piston at the bottom of its travel
[2],This requires one-half turn of the crankshaft.
[1] Instead of opening the intake valve after you have drawn
the piston down,you will find it better to open the intake
valve as the piston starts down.
Instead of… 的意思是,而不是 …”,,代替着 …” 。 draw…
down的意思是,将 … 向下移,。 better为副词，意思为,更好,,,更多,,,更加,,修饰动词不定式短语 to open
the intake valve。本句译为：在活塞下行之后，进气门不只是已经打开，而是随着活塞的下移，开度还在进一步增大。
[2] Remember,the intake stroke starts with the piston at the
top of the cylinder (intake valve open and exhaust valve
closed) and stops with the piston at the bottom of its travel.
With后面的宾语接有现在分词、过去分词、形容词,甚至是副词,with后面的宾语与现在分词、过去分词、形容词之间具有,主谓,关系。 这时整个 with短语说明附带情况，或者交待细节。本句译为：记住，进气行程在活塞位于气缸顶部
（进气门开启，排气门关闭）时开始，在活塞到达其行程的底部时结束。
As the crankshaft continues to move,the piston is forced up
through the cylinder,If you keep both valves closed,the fuel
mixture will be squeezed,or compressed,as the piston reaches
the top,This is called the compression stroke,It,too,requires a
half turn of the crankshaft,
The compression stroke serves to break up the fuel into even
smaller particles,This happens due to the sudden swirling and
churning of the mixture as it is compressed.
When the air-fuel mixture is subjected to a sudden sharp
compression force,its temperature rises,This increase in
temperature makes the mixture easier to ignite and causes it to
explode with greater force,As the piston reaches the top of its
travel on the compression stroke,it has returned to the proper
position to be pushed back down by the explosion.
Remember,the compression stroke starts with the piston at
the bottom of the cylinder (both valves closed) and stops with the
piston at the top of the cylinder,This requires an additional half
turn of the crankshaft.
As the piston reaches the top of the compression stroke,
the mixture is broken into tiny particles and heated up,
When ignited,it will explode with great force,This is the
right time to explode the mixture,A spark plug provides a
spark inside the combustion chamber,The spark produced
at the plug is formed by the ignition system,This will be
discussed in Unit 6.
Just imagine that a hot spark has been provided in the
fuel mixture,The mixture will explode and,in turn,force the
piston down into the cylinder,This gives the crankshaft a
quick and forceful push,This is the power stroke,Both
valves must be kept closed during the power stroke or the
pressure of the burning fuel will squirt out through the valve
pods,Remember,the power stroke starts with the piston at
the top of the cylinder (both valves closed) and stops with
the piston at the bottom of the cylinder,This requires
another half turn of the crankshaft.
When the piston reaches the bottom of the power stroke,the
exhaust valve opens,The spinning crankshaft forces the piston
up through the cylinder,pushing burned gases out,This is the
exhaust stroke.
Remember,the exhaust stroke starts with the piston at the
bottom of the cylinder (exhaust valve open and intake valve
closed),It stops with the piston at the top of the cylinder,This
requires one more half turn of the crankshaft,
If you count the number of half turns in the intake,compression,
power,and exhaust strokes,you will find you have a total of
four,This gives you two complete turns,or revolutions,of the
crankshaft,While the crankshaft is turning around twice,it is
receiving power only during one half turn,or one fourth of the
time.
As soon as the piston reaches the top of the exhaust stroke,
it starts down on another intake,compression,power,and
exhaust cycle,This cycle is repeated over and over,
Each complete cycle consists of four strokes of the
piston,hence the name four-stroke cycle.
2,Main Engine Components
Engine block
The engine block serves as a rigid metal foundation for
all parts of an engine,It contains the cylinders and supports
the crankshaft and camshaft,In older engines,the valve
seats,ports,and guides are built into the block,Accessory
units and the clutch housing are bolted to it,
Blocks are made of either cast iron or aluminum,The
lighter the block (providing it has sufficient strength),the
better,The modern thin-wall casting process controls core
size and placement much more accurately than the older
casting process,This permits casting the block walls much
thinner,reducing the weight of the block,Since the block
wall thickness is more uniform,block distortion during
service is less severe.
Cylinders
The cylinder is a round hole formed in the block,It forms
a guide for the piston and acts as a container for taking in,
compressing,firing,and exhausting the air-fuel charge,
Cylinders have been made of both steel and cast iron,Cast
iron is by far the most popular.
When steel cylinders are desired in an aluminum block,
they are installed in the form of cylinder sleeves (round,
pipe-like liners),These sleeves may be either cast or
pressed into the block,Some engines use removable
cylinder sleeves,When the cylinder becomes worn,the old
sleeves can be pulled out and new sleeves can be pressed
in,The sleeves are pressed into oversize cylinder holes,
Cylinder sleeves are widely used in heavy-duty truck and
industrial engines,Sleeves can also be used to repair a
worn or cracked cylinder in a cast iron block.
Pistons
The piston must move down through the cylinder to
produce a vacuum to draw a fuel charge into the cylinder,It
then travels up in the cylinder and compresses the mixture,
When the mixture is fired,the pressure of the expanding
gas is transmitted to the top of the piston,This drives the
piston back down through the cylinder with great force,
transmitting the energy of the expanding gas to the
crankshaft,The piston then travels up through the cylinder
and exhausts the burned fuel charge.
Pistons are usually made of aluminum,Often,aluminum
pistons are tin-plated to allow proper break-in when the
engine is started,Aluminum pistons can be forged,but they
are more commonly cast,Cast iron is a good material for
pistons used in a slow-speed engine,It has excellent wear
characteristics and will provide good performance,
Connecting Rods
As the name implies,connecting rods are used to connect
pistons to the crankshaft,The upper end of the rod oscillates
(swings back and forth),while the lower,or big end,bearing
rotates (turns).
Because there is very little bearing movement in the upper end,
the bearing area can be reasonably small,The lower end rotates
very fast,and the crankshaft bearing journal turns inside the
connecting rod,This rotational speed tends to produce heat and
wear,To make the rod wear well,a larger bearing area is
required.
The upper end of the rod has a hole through it for the piston
pin,The bottom of the large end of the connecting rod must be
removed so the rod can be installed on the crankshaft journal,
The section that is removed is called the connecting rod cap.
Connecting rods are normally made of alloy steel,They are
drop-forged to shape and then machined.
Crankshaft
The engine crankshaft provides a constant turning force
to the wheels,It has throws to which connecting rods are
attached,and its function is to change the reciprocating
motion of the piston to a rotary motion to drive the wheels,
Crankshafts are made of alloy steel or cast iron,
The crankshaft is held in position by a series of main
bearings,The maximum number of main bearings for a
crankshaft is one more than the number of cylinders,It may
have fewer main bearings than cylinders,Most engines use
precision insert bearings that are constructed like the
connecting rod bearings,but are somewhat larger,In
addition to supporting the crankshaft,one of the main
bearings must control the forward and backward movement.
Flywheel
A heavy flywheel is attached to the rear of the
crankshaft with bolts,The function of the flywheel is to
smooth out engine speed and keep the crankshaft spinning
between power strokes,in some engines,the flywheel also
serves as a mounting surface for the clutch,The outer rim
of the flywheel has a large ring attached with gear teeth cut
into it,The teeth of the starter motor engage these teeth
and spin the flywheel to crank the engine,When an
automatic transmission is used,the torque converter
assembly works with the flywheel.
Camshaft
The camshaft is used to open and close the valves,
There is one cam on the camshaft for each valve in the
engine,Generally only one camshaft is used in most
engines,Newer engines are increasingly equipped with two
or more camshafts (figure2-2),
Figure 2-2 Dual overhead camshaft（ DOHC）
driven by a toothed drive belt
Valves
Each engine cylinder ordinarily has two valves,
However,modern engines often use four valves per
cylinder (two intake and two exhaust),A few engines used
in smaller vehicles have three or five valves per cylinder,
two intake valves and one exhaust valve or three intake
valves and two exhaust valves,
Because the head of an exhaust valve operates at
temperatures up to 1300℉ (704℃ ),valves are made of
heat-resistant metal,In order to prevent burning,the valve
must give off heat to the valve seat and to the valve guide,
The valve must make good contact with the seat and must
run with minimum clearance in the guide.
Valve Lifters
Mechanical valve lifters are usually made of cast iron,The
bottom part that contacts the camshaft is hardened,Some lifters
are hollow to reduce weight,Most valve trains that contain
mechanical lifters have some provision for adjusting clearance,
Mechanical valve lifters were used in older engines.
Hydraulic valve lifters perform the same job as mechanical
lifters,However,hydraulic lifters are self-adjusting,operate with
no lifter-to-rocker arm clearance,and uses engine oil under
pressure to operate,Hydraulic lifters are quiet in operation.
3,Engine Classification
Cycle Classification
Engines are often classified according to cycle,Most internal
combustion piston engines use a two- or four-stroke cycle,All
modern automobile engines use the four-stroke cycle engine.
The two-stroke cycle engine performs the intake,compression,
firing,and exhaust sequence in one revolution of the crankshaft,
Cylinder Classification
The inline engine has its cylinders arranged one after
the other in a straight line,They are in a vertical,or near
vertical position,Most modern inline engines are four
cylinders,
A V-type engine places two banks or rows of cylinders
at an angle to each other— generally at 60° or 90°,The
V-type engine has several advantages,short length,extra
block rigidity,a short,heavy crankshaft,and low profile that
is conducive to low hood lines,The shorter block permits a
reduction in vehicle length with no sacrifice in passenger
room.
The horizontal opposed engine is like a V-type engine,
except that both banks lie in a horizontal plane,The
advantage here is an extremely low overall height,which
makes this engine ideally suited to installations where
space is limited.
Cooling Classification
As you have learned,engines are either liquid-cooled or
air-cooled,Most vehicles use liquid-cooled engines,Air-
cooled engines are used in limited numbers on modern
vehicles.
Fuel Classification
Automobile engines can use gasoline,diesel fuel,gasohol
(mixture of gasoline and alcohol),alcohol,LNG (liquefied
natural gas),CNG (compressed natural gas),or LPG
(liquefied propane gas),Gasoline powers the majority of
vehicles,but diesel fuel is used in some vehicles,Gasohol,
LNG,CNG,and LPG are beginning to see wider use,One of
the principal differences in these engines is in method of fuel
delivery and carburetion,Gasoline,LNG,CNG,and LPG
utilize the same basic type of engine,but LNG,CNG,and
LPG utilize a slightly different fuel delivery setup,Diesel
engines do not use a carburetor or an ignition system.
小结
Principle of Operation
Main Engine Components
Engine Classification
小结
Principle of Operation
The four-stroke-cycle gasoline engine cycle is
spread over four piston strokes,The operation
strokes are,
intake (induction) stroke
compression stroke
power stroke
exhaust stroke
小结
Main Engine Components
Main Engine
Components
小结
Engine Classification
Cycle Classification
Two-stroke cycle engine
Four-stroke cycle engine
Cylinder Classification
In-line engine
V-type engine
Flat engine (horizontal opposed)
Cooling Classification
Liquid-cooled engine
Air-cooled engine
Fuel Classification
Gasoline,diesel fuel,gasohol (mixture of gasoline and alcohol),alcohol,
LNG (liquefied natural gas),CNG (compressed natural gas),or LPG
(liquefied propane gas)
作业
熟记相关专业词汇
P30 EXERCIES Ⅰ
