UNIT 10
BRAKING SYSTEMS
TEXT A
Basic Braking System and ABS
PROFESSIONAL ENGLISH
UNIT 8
Basic Braking System and ABS
TEXT A
Basic operating principle of the hydraulic
system
Disc brakes
Drum brakes
ABS
Components
Operating principle
Types of Anti-Lock Brakes
本次课学习内容本次课学习目标
掌握制动系统的有关英文专业词汇
掌握制动系统主要部件工作原理
训练快速阅读能力，提高阅读速度
NEW WORDS
kinetic [kai'netik] a.(运 )动的,动力 (学 )的
reservoir ['rez?vwɑ:] n.水库,蓄水池
caliper ['k? lip?] n.卡钳,测径器； v.用卡钳测量
withdraw [wie'dr?:] v,缩回,收回,退出
phonograph ['f?un?grɑ:
f]
n.电唱机,留声机
fade [feid] v.(声音等 )减弱下去,衰减，
枯萎,凋谢
inherently [in'hi?r?ntl
i]
ad.天性地,固有地
lump [l?mp] v.使成块状,混在一起
lining ['laini?] n.衬里,内层,衬套
nerve-
wracking
['n?:v?r? ki
]
a.(=nerve-racking)
极端令人头疼的,非常伤脑筋的
magnetize ['m?gnitaiz] v.使磁化,吸引
magnetic [m? g'netik] a.磁的,有磁性的,有吸引力的
deceleration [di:?sel?'rei
∫?n]
n.减速
algorithm ['? lg?rie?m] n.[数 ]运算法则，算法
scheme [ski:m] n.方案,安排,配置,计划
T-fitting ['ti:fiti?] n.T型管接头
PHRASES AND EXPRESSIONS
service braking 行车制动
parking braking 驻车制动
retarder braking 缓速制动
fluid reservoir 储液室
wheel cylinder 轮缸
master cylinder 主缸
drum brake 鼓式制动器
disc brake 盘式制动器
in a hurry 匆忙
inductive sensor 感应式传感器
magnetic field 磁场
integral with 与 … 成一体
line pressure 管路压力，主油路压力
dash panel 仪表板
instrument panel 仪表板
hydraulic unit 液压单元
hydraulic actuator 液压执行器
Basic Braking System and ABS
In order to reduce the speed of the vehicle,the brakes
have to convert the kinetic energy stored in the vehicle to
heat energy,A braking system consists of an energy-supplying
device,a control device,a transmission device and the brake.
Today,there are three types of braking systems in use,
service braking system,parking braking system and additional
retarder braking system,The service braking system and the
parking braking system have separate control and
transmission devices,The service braking system is normally
foot-operated,while the parking braking system is hand-
operated.
Basic operating principle of the hydraulic system
Hydraulic systems are used to actuate the brakes of all
small cars,The system transports the power required to force
the frictional surfaces of the braking system together from the
pedal to the individual brake units at each wheel,
The master cylinder consists of a fluid reservoir and a
double cylinder and piston assembly,Double type master
cylinders are designed to separate the front and rear braking
systems hydraulically in case of a leak.
Steel lines carry the brake fluid to a point on the vehicle
frame near each of the vehicles wheels,The fluid is then
carried to the calipers and wheel cylinders by flexible tubes in
order to allow for suspension and steering movements.
The hydraulic system operates as follows,When at rest,the
entire system,from the piston(s) in the master cylinder to
those in the wheel cylinders or calipers,is full of brake fluid,
Upon application of the brake pedal,fluid trapped in front of
the master cylinder piston(s) is forced through the lines to the
wheel cylinders,Here,it forces the pistons outward,in the case
of drum brakes,and inward toward the disc,in the case of disc
brakes,The motion of the pistons is opposed by return springs
mounted outside the cylinders in drum brakes,and by spring
seals,in disc brakes,
Upon release of the brake pedal,a spring located inside the
master cylinder immediately returns the master cylinder pistons
to the normal position,The pistons contain check valves and
the master cylinder has compensating ports drilled in it,These
are uncovered as the pistons reach their normal position,The
piston check valves allow fluid to flow toward the wheel
cylinders or calipers as the pistons withdraw,Then,as the
return springs force the brake pads or shoes into the released
position,the excess fluid reservoirs through the compensating
ports,It is during the time the pedal is in the released position
that any fluid that has leaked out of the system will be replaced
through the compensating ports [1].
Dual circuit master cylinders employ two pistons,located one
behind the other,in the cylinder,The primary piston is actuated
directly by mechanical linkage from the brake pedal through
the power booster,The secondary piston is actuated by fluid
trapped between the two pistons,
If a leak develops in front of the secondary piston,it moves
forward until it bottoms against the front of the master
cylinder,and the fluid trapped between the pistons will
operate the rear brakes,If the rear brakes develop a leak,the
primary piston will move forward until direct contact with the
secondary piston takes place,and it will force the secondary
piston to actuate the front brakes,In either case,the brake
pedal moves farther when the brakes are applied,and less
braking power is available.
Disc brakes（自学）
Instead of the traditional expanding brakes that press outward
against a circular drum,disc brake systems utilize a disc (rotor)
with brake pads positioned on either side of it,Braking effect
is achieved in a manner similar to the way you would squeeze
a spinning phonograph record between your fingers,The disc
(rotor) is a casting with cooling fins between the two braking
surfaces,
This enables air to circulate between the braking surfaces
making them less sensitive to heat buildup and more resistant
to fade,Dirt and water do not affect braking action since
contaminants are thrown off by the centrifugal action of the
rotor or scraped off by the pads,Also,the equal clamping
action of the two brake pads tends to ensure uniform,straight
line stops,Disc brakes are inherently self-adjusting,There are
three general types of disc brake,fixed caliper,floating caliper
and sliding caliper.
The fixed caliper design uses two pistons mounted on either
side of the rotor (in each side of the caliper),The caliper is
mounted rigidly and does not move,The sliding and floating
designs are quite similar,In fact,these two types are often
lumped together,In both designs,the pad on the inside of the
rotor is moved into contact with the rotor by hydraulic force,
The caliper,which is not held in a fixed position,moves
slightly,bringing the outside pad into contact with the rotor,
Drum brakes（自学）
Drum brakes employ two brake shoes mounted on a
stationary backing plate,These shoes are positioned inside a
circular drum which rotates with the wheel assembly,The
shoes are held in place by springs,This allows them to slide
toward the drums (when they are applied) while keeping the
linings and drums in alignment,The shoes are actuated by a
wheel cylinder which is mounted at the top of the backing
plate,When the brakes are applied,hydraulic pressure forces
the wheel cylinder's actuating links outward,Since these links
bear directly against the top of the brake shoes,the tops of
the shoes are then forced against the inner side of the drum,
This action forces the bottoms of the two shoes to contact the
brake drum by rotating the entire assembly slightly (known as
servo action),When pressure within the wheel cylinder is
relaxed,return springs pull the shoes back away from the
drum.
ABS
Stopping a car in a hurry on a slippery road can be very
challenging,Anti-lock braking systems (ABS) take a lot of the
challenge out of this sometimes nerve-wracking event,In fact,
on slippery surfaces,even professional drivers can't stop as
quickly without ABS as an average driver can with ABS,
There are four main components to an ABS system,speed
sensors,pump,valves and controller (Fig.10-1).
Fig.10-1 Main components of anti-lock braking system
Components
Speed Sensors
The speed sensors are located at each wheel and provide the
speed reference to the control unit,The speed sensors are
permanently magnetized inductive sensors that read pulses from
a tooth wheel on each hub,A voltage signal is generated as
each tooth passes through the magnetic field,The sensors are
replaceable,The tooth wheels are integral with the wheel hubs
and are replaced with the complete hub.
Control Unit
The control unit contains all the signal conditioning circuitry and
the output circuits,The output circuits control the hydraulic unit
to adjust the line pressure to each caliper,The unit is located
under the dash panel on the left side,above the glove
compartment and in the forward position of the electronic box in
the engine compartment,If a problem is sensed,the control unit
will light the instrument panel warning lamp.
Pump and Valves
The hydraulic unit (Fig,10-2),
also known as hydraulic
actuator,located in the engine
compartment contains valves
and a pump,The valves have
3 positions; pressure build-up,
pressure hold and pressure
drop,As the tires locks,the
control unit informs the valve
to hold the pressure,If the
tire remains locked,the
control unit will allow the valve
to drop the pressure until the
tire starts to turn,The control
unit will allow the valve to
start building pressure to start
the cycle over again.
1,Hydraulic control unit
2,Valve relay
3,Motor relay
4,Cover
5,ABS control unit
Fig,10-2 Hydraulic unit of the
anti-lock brake system
The pump returns the brake fluid taken from the wheel
cylinder while the pressure is lowered,The pump is designed to
maintain separation of the 2 braking circuits.
During operation of the anti-lock system,a pulsing may be felt at
the brake pedal and a clicking heard from the hydraulic unit,This
is normal and informs the operator that the ABS is in the
functioning mode.
Operating principle
There are many different variations and control algorithms for
ABS systems,We will discuss how one of the simpler systems
works,
The controller monitors the speed sensors at all times,It is
looking for decelerations in the wheel that are out of the
ordinary,Right before a wheel locks up,it will experience a rapid
deceleration,If left unchecked,the wheel would stop much more
quickly than any car could,It might take a car five seconds to
stop from 60 mph (96.6 kph) under ideal conditions,but a wheel
that locks up could stop spinning in less than a second,
The ABS controller knows that such a rapid deceleration is
impossible,so it reduces the pressure to that brake until it sees
a acceleration,then it increases the pressure until it sees the
deceleration again,It can do this very quickly,before the tire
can actually significantly change speed,The result is that the
tire slows down at the same rate as the car,with the brakes
keeping the tires very near the point at which they will start to
lock up [2],This gives the system maximum braking power,
When the ABS system is in operation you will feel a pulsing in
the brake pedal; this comes from the rapid opening and closing
of the valves,Some ABS systems can cycle up to 15 times per
second,
Types of Anti-Lock Brakes
Anti-lock braking systems use different schemes depending on
the type of brakes in use,We will refer to them by the number
of channels -- that is,how many valves that are individually
controlled -- and the number of speed sensors,
·Four-channel,four-sensor ABS - This is the best scheme,There
is a speed sensor on all four wheels and a separate valve for all
four wheels,With this setup,the controller monitors each wheel
individually to make sure it is achieving maximum braking force,
·Three-channel,three-sensor ABS - This scheme,commonly
found on pickup trucks with four-wheel ABS,has a speed sensor
and a valve for each of the front wheels,with one valve and one
sensor for both rear wheels,The speed sensor for the rear
wheels is located in the rear axle,
This system provides individual control of the front wheels,so
they can both achieve maximum braking force,The rear wheels,
however,are monitored together; they both have to start to lock
up before the ABS will activate on the rear,With this system,it
is possible that one of the rear wheels will lock during a stop,
reducing brake effectiveness,
·One-channel,one-sensor ABS - This system is commonly found
on pickup trucks with rear-wheel ABS,It has one valve,which
controls both rear wheels,and one speed sensor,located in the
rear axle,
This system operates the same as the rear end of a
three-channel system,The rear wheels are monitored
together and they both have to start to lock up before the
ABS kicks in,In this system it is also possible that one of
the rear wheels will lock,reducing brake effectiveness,
This system is easy to identify,Usually there will be one
brake line going through a T-fitting to both rear wheels,
You can locate the speed sensor by looking for an electrical
connection near the differential on the rear-axle housing,
小结
Basic Braking System and ABS
Basic operating principle of the
hydraulic system
Disc brakes
Drum brakes
ABS
Components
Operating principle
Types of Anti-Lock Brakes
作业
熟记相关专业词汇
P224 EXERCIES Ⅰ &Ⅱ
BRAKING SYSTEMS
TEXT A
Basic Braking System and ABS
PROFESSIONAL ENGLISH
UNIT 8
Basic Braking System and ABS
TEXT A
Basic operating principle of the hydraulic
system
Disc brakes
Drum brakes
ABS
Components
Operating principle
Types of Anti-Lock Brakes
本次课学习内容本次课学习目标
掌握制动系统的有关英文专业词汇
掌握制动系统主要部件工作原理
训练快速阅读能力，提高阅读速度
NEW WORDS
kinetic [kai'netik] a.(运 )动的,动力 (学 )的
reservoir ['rez?vwɑ:] n.水库,蓄水池
caliper ['k? lip?] n.卡钳,测径器； v.用卡钳测量
withdraw [wie'dr?:] v,缩回,收回,退出
phonograph ['f?un?grɑ:
f]
n.电唱机,留声机
fade [feid] v.(声音等 )减弱下去,衰减，
枯萎,凋谢
inherently [in'hi?r?ntl
i]
ad.天性地,固有地
lump [l?mp] v.使成块状,混在一起
lining ['laini?] n.衬里,内层,衬套
nerve-
wracking
['n?:v?r? ki
]
a.(=nerve-racking)
极端令人头疼的,非常伤脑筋的
magnetize ['m?gnitaiz] v.使磁化,吸引
magnetic [m? g'netik] a.磁的,有磁性的,有吸引力的
deceleration [di:?sel?'rei
∫?n]
n.减速
algorithm ['? lg?rie?m] n.[数 ]运算法则，算法
scheme [ski:m] n.方案,安排,配置,计划
T-fitting ['ti:fiti?] n.T型管接头
PHRASES AND EXPRESSIONS
service braking 行车制动
parking braking 驻车制动
retarder braking 缓速制动
fluid reservoir 储液室
wheel cylinder 轮缸
master cylinder 主缸
drum brake 鼓式制动器
disc brake 盘式制动器
in a hurry 匆忙
inductive sensor 感应式传感器
magnetic field 磁场
integral with 与 … 成一体
line pressure 管路压力，主油路压力
dash panel 仪表板
instrument panel 仪表板
hydraulic unit 液压单元
hydraulic actuator 液压执行器
Basic Braking System and ABS
In order to reduce the speed of the vehicle,the brakes
have to convert the kinetic energy stored in the vehicle to
heat energy,A braking system consists of an energy-supplying
device,a control device,a transmission device and the brake.
Today,there are three types of braking systems in use,
service braking system,parking braking system and additional
retarder braking system,The service braking system and the
parking braking system have separate control and
transmission devices,The service braking system is normally
foot-operated,while the parking braking system is hand-
operated.
Basic operating principle of the hydraulic system
Hydraulic systems are used to actuate the brakes of all
small cars,The system transports the power required to force
the frictional surfaces of the braking system together from the
pedal to the individual brake units at each wheel,
The master cylinder consists of a fluid reservoir and a
double cylinder and piston assembly,Double type master
cylinders are designed to separate the front and rear braking
systems hydraulically in case of a leak.
Steel lines carry the brake fluid to a point on the vehicle
frame near each of the vehicles wheels,The fluid is then
carried to the calipers and wheel cylinders by flexible tubes in
order to allow for suspension and steering movements.
The hydraulic system operates as follows,When at rest,the
entire system,from the piston(s) in the master cylinder to
those in the wheel cylinders or calipers,is full of brake fluid,
Upon application of the brake pedal,fluid trapped in front of
the master cylinder piston(s) is forced through the lines to the
wheel cylinders,Here,it forces the pistons outward,in the case
of drum brakes,and inward toward the disc,in the case of disc
brakes,The motion of the pistons is opposed by return springs
mounted outside the cylinders in drum brakes,and by spring
seals,in disc brakes,
Upon release of the brake pedal,a spring located inside the
master cylinder immediately returns the master cylinder pistons
to the normal position,The pistons contain check valves and
the master cylinder has compensating ports drilled in it,These
are uncovered as the pistons reach their normal position,The
piston check valves allow fluid to flow toward the wheel
cylinders or calipers as the pistons withdraw,Then,as the
return springs force the brake pads or shoes into the released
position,the excess fluid reservoirs through the compensating
ports,It is during the time the pedal is in the released position
that any fluid that has leaked out of the system will be replaced
through the compensating ports [1].
Dual circuit master cylinders employ two pistons,located one
behind the other,in the cylinder,The primary piston is actuated
directly by mechanical linkage from the brake pedal through
the power booster,The secondary piston is actuated by fluid
trapped between the two pistons,
If a leak develops in front of the secondary piston,it moves
forward until it bottoms against the front of the master
cylinder,and the fluid trapped between the pistons will
operate the rear brakes,If the rear brakes develop a leak,the
primary piston will move forward until direct contact with the
secondary piston takes place,and it will force the secondary
piston to actuate the front brakes,In either case,the brake
pedal moves farther when the brakes are applied,and less
braking power is available.
Disc brakes（自学）
Instead of the traditional expanding brakes that press outward
against a circular drum,disc brake systems utilize a disc (rotor)
with brake pads positioned on either side of it,Braking effect
is achieved in a manner similar to the way you would squeeze
a spinning phonograph record between your fingers,The disc
(rotor) is a casting with cooling fins between the two braking
surfaces,
This enables air to circulate between the braking surfaces
making them less sensitive to heat buildup and more resistant
to fade,Dirt and water do not affect braking action since
contaminants are thrown off by the centrifugal action of the
rotor or scraped off by the pads,Also,the equal clamping
action of the two brake pads tends to ensure uniform,straight
line stops,Disc brakes are inherently self-adjusting,There are
three general types of disc brake,fixed caliper,floating caliper
and sliding caliper.
The fixed caliper design uses two pistons mounted on either
side of the rotor (in each side of the caliper),The caliper is
mounted rigidly and does not move,The sliding and floating
designs are quite similar,In fact,these two types are often
lumped together,In both designs,the pad on the inside of the
rotor is moved into contact with the rotor by hydraulic force,
The caliper,which is not held in a fixed position,moves
slightly,bringing the outside pad into contact with the rotor,
Drum brakes（自学）
Drum brakes employ two brake shoes mounted on a
stationary backing plate,These shoes are positioned inside a
circular drum which rotates with the wheel assembly,The
shoes are held in place by springs,This allows them to slide
toward the drums (when they are applied) while keeping the
linings and drums in alignment,The shoes are actuated by a
wheel cylinder which is mounted at the top of the backing
plate,When the brakes are applied,hydraulic pressure forces
the wheel cylinder's actuating links outward,Since these links
bear directly against the top of the brake shoes,the tops of
the shoes are then forced against the inner side of the drum,
This action forces the bottoms of the two shoes to contact the
brake drum by rotating the entire assembly slightly (known as
servo action),When pressure within the wheel cylinder is
relaxed,return springs pull the shoes back away from the
drum.
ABS
Stopping a car in a hurry on a slippery road can be very
challenging,Anti-lock braking systems (ABS) take a lot of the
challenge out of this sometimes nerve-wracking event,In fact,
on slippery surfaces,even professional drivers can't stop as
quickly without ABS as an average driver can with ABS,
There are four main components to an ABS system,speed
sensors,pump,valves and controller (Fig.10-1).
Fig.10-1 Main components of anti-lock braking system
Components
Speed Sensors
The speed sensors are located at each wheel and provide the
speed reference to the control unit,The speed sensors are
permanently magnetized inductive sensors that read pulses from
a tooth wheel on each hub,A voltage signal is generated as
each tooth passes through the magnetic field,The sensors are
replaceable,The tooth wheels are integral with the wheel hubs
and are replaced with the complete hub.
Control Unit
The control unit contains all the signal conditioning circuitry and
the output circuits,The output circuits control the hydraulic unit
to adjust the line pressure to each caliper,The unit is located
under the dash panel on the left side,above the glove
compartment and in the forward position of the electronic box in
the engine compartment,If a problem is sensed,the control unit
will light the instrument panel warning lamp.
Pump and Valves
The hydraulic unit (Fig,10-2),
also known as hydraulic
actuator,located in the engine
compartment contains valves
and a pump,The valves have
3 positions; pressure build-up,
pressure hold and pressure
drop,As the tires locks,the
control unit informs the valve
to hold the pressure,If the
tire remains locked,the
control unit will allow the valve
to drop the pressure until the
tire starts to turn,The control
unit will allow the valve to
start building pressure to start
the cycle over again.
1,Hydraulic control unit
2,Valve relay
3,Motor relay
4,Cover
5,ABS control unit
Fig,10-2 Hydraulic unit of the
anti-lock brake system
The pump returns the brake fluid taken from the wheel
cylinder while the pressure is lowered,The pump is designed to
maintain separation of the 2 braking circuits.
During operation of the anti-lock system,a pulsing may be felt at
the brake pedal and a clicking heard from the hydraulic unit,This
is normal and informs the operator that the ABS is in the
functioning mode.
Operating principle
There are many different variations and control algorithms for
ABS systems,We will discuss how one of the simpler systems
works,
The controller monitors the speed sensors at all times,It is
looking for decelerations in the wheel that are out of the
ordinary,Right before a wheel locks up,it will experience a rapid
deceleration,If left unchecked,the wheel would stop much more
quickly than any car could,It might take a car five seconds to
stop from 60 mph (96.6 kph) under ideal conditions,but a wheel
that locks up could stop spinning in less than a second,
The ABS controller knows that such a rapid deceleration is
impossible,so it reduces the pressure to that brake until it sees
a acceleration,then it increases the pressure until it sees the
deceleration again,It can do this very quickly,before the tire
can actually significantly change speed,The result is that the
tire slows down at the same rate as the car,with the brakes
keeping the tires very near the point at which they will start to
lock up [2],This gives the system maximum braking power,
When the ABS system is in operation you will feel a pulsing in
the brake pedal; this comes from the rapid opening and closing
of the valves,Some ABS systems can cycle up to 15 times per
second,
Types of Anti-Lock Brakes
Anti-lock braking systems use different schemes depending on
the type of brakes in use,We will refer to them by the number
of channels -- that is,how many valves that are individually
controlled -- and the number of speed sensors,
·Four-channel,four-sensor ABS - This is the best scheme,There
is a speed sensor on all four wheels and a separate valve for all
four wheels,With this setup,the controller monitors each wheel
individually to make sure it is achieving maximum braking force,
·Three-channel,three-sensor ABS - This scheme,commonly
found on pickup trucks with four-wheel ABS,has a speed sensor
and a valve for each of the front wheels,with one valve and one
sensor for both rear wheels,The speed sensor for the rear
wheels is located in the rear axle,
This system provides individual control of the front wheels,so
they can both achieve maximum braking force,The rear wheels,
however,are monitored together; they both have to start to lock
up before the ABS will activate on the rear,With this system,it
is possible that one of the rear wheels will lock during a stop,
reducing brake effectiveness,
·One-channel,one-sensor ABS - This system is commonly found
on pickup trucks with rear-wheel ABS,It has one valve,which
controls both rear wheels,and one speed sensor,located in the
rear axle,
This system operates the same as the rear end of a
three-channel system,The rear wheels are monitored
together and they both have to start to lock up before the
ABS kicks in,In this system it is also possible that one of
the rear wheels will lock,reducing brake effectiveness,
This system is easy to identify,Usually there will be one
brake line going through a T-fitting to both rear wheels,
You can locate the speed sensor by looking for an electrical
connection near the differential on the rear-axle housing,
小结
Basic Braking System and ABS
Basic operating principle of the
hydraulic system
Disc brakes
Drum brakes
ABS
Components
Operating principle
Types of Anti-Lock Brakes
作业
熟记相关专业词汇
P224 EXERCIES Ⅰ &Ⅱ
