UNIT 9
AUTOMATIC TRANSMISSIONS
TEXT B/C
Continuously Variable Transmissions
(CVT)
PROFESSIONAL ENGLISH
UNIT 9
AUTOMATIC TRANSMISSIONS
TEXT B-C
Continuously Variable Transmissions
(CVT)
History of the CVT
Driving a car with a CVT
How CVT Works
Advantages of the CVT
Disadvantages of the CVT
本次课学习内容本次课学习目标
掌握无级变速器的有关英文专业词汇
掌握无级变速器的结构与工作原理
训练快速阅读能力，较高的阅读速度
NEW WORDS
sketch [sket∫] v,勾画，绘略图
a.k.a,=also known as又叫，亦称
race [reis] v.赛跑,疾驰,猛转，急转，使空转
acceptance [?k'sept?n
s]
n.接受,赞同,相信
accustom [?'k?st?m] v.使习惯于
floor [fl?:] v.在,..上铺 (地板 ),(被困难 )难倒，
将（加速器等）踩到底
lurch [l?:t∫] n.突然倾斜,摇摆，突然前倾
creep [kri:p] v.爬行,蠕动，蹑手蹑脚，蔓延
robust [r?'b?st] a.精力充沛的，坚固的，耐用的
PHRASES AND EXPRESSIONS
continuously variable
transmission
无级变速器（英文缩写为 CVT）
call up 召唤，提取
Continuously Variable Transmissions (CVT)
A continuously variable transmission,or CVT,is a type of
automatic transmission that provides more useable power,
better fuel economy and a smoother driving experience than a
traditional automatic,
History of the CVT
Leonardo Da Vinci sketched the first CVT in 1490,Dutch
automaker DAF first started using CVTs in their cars in the late
1950s; however technology limitations made CVTs unsuitable
for engines with more than around 100 horsepower,In the
late 80s and early 90s,Subaru offered a CVT in their Justy
mini-car,while Honda used one in the high-mileage Honda
Civic HX of the late 90s,
Improved CVTs capable of handling more powerful engines
were developed in the late 90s and 2000s,and CVTs can now
be found in cars from Nissan,Audi,Honda,Ford,GM,and
other automakers,
Driving a car with a CVT
The controls for a CVT are the same as an automatic,No
clutch pedal and a P-R-N-D-L-style shift pattern,But while
an automatic transmission has a set number of gear ratios
(a.k.a,speeds),usually 4,5 or 6,the CVT can constantly
change the relationship of engine speed to car speed,When
driving a car with a CVT,you never hear or feel the
transmission shift—it simply raises and lowers the engine
speed as needed,calling up higher engine speeds (or RPMs)
for better acceleration and lower RPMs for better fuel
economy while cruising,
When you step on the accelerator,the engine races as it
would with a slipping clutch or a failing automatic
transmission,This is normal—the CVT is adjusting the
engine speed to provide optimal power for acceleration.
How CVT Works
Traditional transmissions use a gearset that provides a given
number of ratios (or speeds),The transmission (or the driver)
shifts gears to provide the most appropriate ratio for a given
situation,Lowest gears for starting out,middle gears for
acceleration and passing,and higher gears for fuel-efficient
cruising.
Fig.9-6
CVT
operation
Though there are several types of CVTs,most cars use a
pair of variable-diameter pulleys,each shaped like a pair of
opposing cones,with a metal belt or chain running
between them(Fig.9-6) [1],One pulley is connected to the
engine (input shaft),the other to the drive wheels (output
shaft),The halves of each pulley are moveable; as the
pulley halves come closer together the belt is forced to ride
higher on the pulley,effectively making the pulley's
diameter larger,Changing the diameter of the pulleys
varies the transmission's ratio (the number of times the
output shaft revolves for revolution of the engine),in the
same way that a 10-speed bike routes the chain over larger
or smaller gears to change the ratio,Making the input
pulley smaller and the output pulley larger gives a low ratio
(a large number of engine revolutions producing a small
number of output revolutions) for better low-speed
acceleration,As the car accelerates,the pulleys vary their
diameter to lower the engine speed as car speed rises,
This is the same thing a conventional automatic or manual
transmission does,but while a conventional transmission
changes the ratio in stages by shifting gears,the CVT
continuously varies the ratio - hence the name "continuously
variable transmission".
Advantages of the CVT
Engines do not develop constant power at all speeds;
they have specific speeds where torque,horsepower and
fuel efficiency are at their highest levels,Because there are
no gears to tie a given road speed directly to a given engine
speed,the CVT can vary the engine speed as needed to
access maximum power as well as maximum fuel efficiency,
This allows the CVT to provide quicker acceleration than a
conventional automatic or manual transmission while
delivering superior fuel economy.
Disadvantages of the CVT
The CVT's biggest problem has been user acceptance,
Because the CVT allows the engine to rev at any speed,the
noises coming from under the hood sound odd to ears
accustomed to conventional manual and automatic
transmissions,The gradual changes in engine noice sound like
a sliding transmission or a slipping clutch -- signs of trouble
with a conventional transmission,but perfectly normal for a
CVT,Flooring an automatic car brings a lurch and a sudden
burst of power,whereas CVTs provide a smooth,rapid
increase to maximum power,To some drivers this makes the
car feel slower,while in fact a CVT will generally out-
accelerate an automatic,
Automakers have gone to great lengths to make the CVT
feel more like a conventional transmission,Most CVTs are set
up to creep forward when the driver takes his or her foot off
the brake,This provides a similar feel to a conventional
automatic,and serves as an indicator that the car is in gear,
Other CVTs offer a "manual" mode that simulates manual gear
changes,
Because early automotive CVTs were limited as to how
much horsepower they could handle,there has been some
concern about the long-term reliability of the CVT,Advanced
technology has made the CVT much more robust,Nissan has
more than a million CVTs in service around the world and uses
them in powerful cars such as the 255 horsepower Maxima,
and says their long-term reliability is comparable to
conventional transmissions,
Continuously variable transmissions are more efficient
and provide more torque and power than traditional
transmissions,By 2012,CVTs are expected to have a 20
percent share of the Japanese market,a 4 percent share of
the North American market and less than a 5 percent share
of the European market,
Fig,9-5 An electronic transmission control system
小结
Continuously Variable Transmissions (CVT)
History of the CVT
Driving a car with a CVT
How CVT Works
Advantages of the CVT
Disadvantages of the CVT
作业
熟记相关专业词汇
P215 EXERCIES Ⅰ &Ⅱ
AUTOMATIC TRANSMISSIONS
TEXT B/C
Continuously Variable Transmissions
(CVT)
PROFESSIONAL ENGLISH
UNIT 9
AUTOMATIC TRANSMISSIONS
TEXT B-C
Continuously Variable Transmissions
(CVT)
History of the CVT
Driving a car with a CVT
How CVT Works
Advantages of the CVT
Disadvantages of the CVT
本次课学习内容本次课学习目标
掌握无级变速器的有关英文专业词汇
掌握无级变速器的结构与工作原理
训练快速阅读能力，较高的阅读速度
NEW WORDS
sketch [sket∫] v,勾画，绘略图
a.k.a,=also known as又叫，亦称
race [reis] v.赛跑,疾驰,猛转，急转，使空转
acceptance [?k'sept?n
s]
n.接受,赞同,相信
accustom [?'k?st?m] v.使习惯于
floor [fl?:] v.在,..上铺 (地板 ),(被困难 )难倒，
将（加速器等）踩到底
lurch [l?:t∫] n.突然倾斜,摇摆，突然前倾
creep [kri:p] v.爬行,蠕动，蹑手蹑脚，蔓延
robust [r?'b?st] a.精力充沛的，坚固的，耐用的
PHRASES AND EXPRESSIONS
continuously variable
transmission
无级变速器（英文缩写为 CVT）
call up 召唤，提取
Continuously Variable Transmissions (CVT)
A continuously variable transmission,or CVT,is a type of
automatic transmission that provides more useable power,
better fuel economy and a smoother driving experience than a
traditional automatic,
History of the CVT
Leonardo Da Vinci sketched the first CVT in 1490,Dutch
automaker DAF first started using CVTs in their cars in the late
1950s; however technology limitations made CVTs unsuitable
for engines with more than around 100 horsepower,In the
late 80s and early 90s,Subaru offered a CVT in their Justy
mini-car,while Honda used one in the high-mileage Honda
Civic HX of the late 90s,
Improved CVTs capable of handling more powerful engines
were developed in the late 90s and 2000s,and CVTs can now
be found in cars from Nissan,Audi,Honda,Ford,GM,and
other automakers,
Driving a car with a CVT
The controls for a CVT are the same as an automatic,No
clutch pedal and a P-R-N-D-L-style shift pattern,But while
an automatic transmission has a set number of gear ratios
(a.k.a,speeds),usually 4,5 or 6,the CVT can constantly
change the relationship of engine speed to car speed,When
driving a car with a CVT,you never hear or feel the
transmission shift—it simply raises and lowers the engine
speed as needed,calling up higher engine speeds (or RPMs)
for better acceleration and lower RPMs for better fuel
economy while cruising,
When you step on the accelerator,the engine races as it
would with a slipping clutch or a failing automatic
transmission,This is normal—the CVT is adjusting the
engine speed to provide optimal power for acceleration.
How CVT Works
Traditional transmissions use a gearset that provides a given
number of ratios (or speeds),The transmission (or the driver)
shifts gears to provide the most appropriate ratio for a given
situation,Lowest gears for starting out,middle gears for
acceleration and passing,and higher gears for fuel-efficient
cruising.
Fig.9-6
CVT
operation
Though there are several types of CVTs,most cars use a
pair of variable-diameter pulleys,each shaped like a pair of
opposing cones,with a metal belt or chain running
between them(Fig.9-6) [1],One pulley is connected to the
engine (input shaft),the other to the drive wheels (output
shaft),The halves of each pulley are moveable; as the
pulley halves come closer together the belt is forced to ride
higher on the pulley,effectively making the pulley's
diameter larger,Changing the diameter of the pulleys
varies the transmission's ratio (the number of times the
output shaft revolves for revolution of the engine),in the
same way that a 10-speed bike routes the chain over larger
or smaller gears to change the ratio,Making the input
pulley smaller and the output pulley larger gives a low ratio
(a large number of engine revolutions producing a small
number of output revolutions) for better low-speed
acceleration,As the car accelerates,the pulleys vary their
diameter to lower the engine speed as car speed rises,
This is the same thing a conventional automatic or manual
transmission does,but while a conventional transmission
changes the ratio in stages by shifting gears,the CVT
continuously varies the ratio - hence the name "continuously
variable transmission".
Advantages of the CVT
Engines do not develop constant power at all speeds;
they have specific speeds where torque,horsepower and
fuel efficiency are at their highest levels,Because there are
no gears to tie a given road speed directly to a given engine
speed,the CVT can vary the engine speed as needed to
access maximum power as well as maximum fuel efficiency,
This allows the CVT to provide quicker acceleration than a
conventional automatic or manual transmission while
delivering superior fuel economy.
Disadvantages of the CVT
The CVT's biggest problem has been user acceptance,
Because the CVT allows the engine to rev at any speed,the
noises coming from under the hood sound odd to ears
accustomed to conventional manual and automatic
transmissions,The gradual changes in engine noice sound like
a sliding transmission or a slipping clutch -- signs of trouble
with a conventional transmission,but perfectly normal for a
CVT,Flooring an automatic car brings a lurch and a sudden
burst of power,whereas CVTs provide a smooth,rapid
increase to maximum power,To some drivers this makes the
car feel slower,while in fact a CVT will generally out-
accelerate an automatic,
Automakers have gone to great lengths to make the CVT
feel more like a conventional transmission,Most CVTs are set
up to creep forward when the driver takes his or her foot off
the brake,This provides a similar feel to a conventional
automatic,and serves as an indicator that the car is in gear,
Other CVTs offer a "manual" mode that simulates manual gear
changes,
Because early automotive CVTs were limited as to how
much horsepower they could handle,there has been some
concern about the long-term reliability of the CVT,Advanced
technology has made the CVT much more robust,Nissan has
more than a million CVTs in service around the world and uses
them in powerful cars such as the 255 horsepower Maxima,
and says their long-term reliability is comparable to
conventional transmissions,
Continuously variable transmissions are more efficient
and provide more torque and power than traditional
transmissions,By 2012,CVTs are expected to have a 20
percent share of the Japanese market,a 4 percent share of
the North American market and less than a 5 percent share
of the European market,
Fig,9-5 An electronic transmission control system
小结
Continuously Variable Transmissions (CVT)
History of the CVT
Driving a car with a CVT
How CVT Works
Advantages of the CVT
Disadvantages of the CVT
作业
熟记相关专业词汇
P215 EXERCIES Ⅰ &Ⅱ
