System Identification Of Electronic Wedge Brake (EWB).
"I hereby declare that I have read this thesis and in my opinion this report is sufficient in terms of
scope and quality for the award of the degree of
Bachelor of Mechanical Engineering (Automotive)"
Signature:
ｾ＠
Supervisor:
Mr. Vauzi.A.hrnad
Date:
21st July 2012
© Unlvetsltl Teknlkal Malaysia Melalal
SYSTEM IDENTIFICATION OF
ELECTRONIC WEDGE BRAKE (EWB)
D.RAVISANKAR AIL DEVARAJEE
This report was submitted in accordance with the partial requirements for honor of
Bachelor of Mechanical Engineering (Automotive)
#
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
MAY2012
© Unlvetsltl Teknlkal Malaysia Melalal
: l
,.
"I hereby declare that the work in this report is my own except for summaries and quotations
which have been duly acknowledged."
Signature:
ﾷ ﾷ ｾ ﾷ＠
Author:
D.Ravisankar AIL Devarajee
Date:
21st July 2012
© Unlvetsltl Teknlkal Malaysia Melalal
For Loving Father and Mother
© Unlverlltl Teknlkal Malaysia Melakll
ACKNOWLEDGEMENT
I would like to take this opportunity to express my gratitude to all the people who
have helped; supported and guided me throughout the completion of Projek Sarjana
Muda (PSM) entitled System Identification of Electronic Wedge Brake (EWB).
First and foremost, my outmost gratitude goes to my project supervisor, Mr
Fauzi Ahmad for the continuous guidance and support given to me. Your constructive
comments help me a lot in PSMl and PSM2 and thanks for spending your precious time
for the meeting despite your busy schedule and commitments.
Secondly, my extended thank you goes to Universiti Teknikal Malaysia Melaka
(UTeM) for creating an opportunity for all final year students to carry out a final year
project. With this final year project, I can apply all the knowledge learned in UTeM
from the very first year till now. My most grateful thanks to my family members who
gave me lots of moral and mental support which means a lot to me.
Last but certainly not the least; I would like to thank you, the reader for taking
your time to read this report.
© Unlvetsltl Teknlkal Malaysia Melalal
ll
ABSTRACT
This study deals with the use of Electronic Wedge Brake (EWB) in improving
driving quality and solving common problems in current vehicle braking systems. This
new electronic brake concept is based on an electric powered controlled friction brake
with high self-reinforcement capability which has performance advantages over
conventional brake systems. The main content of this study is the development of
System Identification of EWB. Modeling is done to study the brake behavior on a real
vehicle through MA TLAB SIMULINK. software. Detail design of EWB mechanism
with CATIA is done followed by test rig which consist of one unit linear variable
displacement transducer (LVDT), one unit load cell, one unit rotation encoder, data
acquisition (DAQ) and EWB actuator. Experimental result are then used to develop the
System Identification of EWB and followed by the EWB modeling. Common problems
in hydraulic braking system vary from few sources such as air in the brake line, brake
fluid leakage, sticking pistons and more. The ideal solution for these problems is the
development and implementation of EWB system in modern vehicles. EWB system are
said to be the perfect system to replace existing hydraulic braking system in vehicles
because of its dominant advantages. This EWB system results low power consumption,
totally silent with no vibration during braking, able to react more quickly and hence
shortening the stopping distance. However this EWB system may fail if power supply to
be this system is disrupted. To take care of this, EWB is to be connected to a main and a
backup power supply. The development of EWB system brings the technology further
advance and providing the perfect platform for X-by-wire technologies. In future, brakeby-wire is predicted to be replaced by wireless braking system .
.
© Unlvetsltl Teknlkal Malaysia Melalal
iii
TABLE OF CONTENTS
ACKN"OWLEDGEMENT............................................................. ....... ... .i
ABSTRACT . .. .... ... ................. .. .. .... . ..... ..... .. ...... .. ....... .. . ............... ........ii
LIST OF FIGURES ... ..... . ... .... .... .... ... . ............ .. ... ....... .. ..... ............... .... vii
LIST OF ABBREVIATIONS .. ...... . ...... . .......... ....... ...... ....... ...... ....... ........ x
CHAPTER 1 ..................................................................................................................... 1
1
INTRODUCTION .................................................................................................... !
1.1
OVERVIEW ........................................................................................................ !
1.2
PROBLEM STATEMENT ..................................................................................3
1.3
BACKGROUND OF STUDY .............................................................................4
1.4
OBJECTIVES ......................................................................................................5
1.5
SCOPES ...............................................................................................................S
1.6
SIGNIFICANCE OF TtiE STUDY ....................................................................6
CHAPTER2
2
LITERATURE REVIEW ........................................................................................7
2.1
HYDRAULIC BRAKING SYSTEM.................................................................. 7
2.2
PNEUMATIC BRAKING SYSTEM ..................................................................9
2.3
ELECTRO-HYDRAULIC BRAKING (EHB) SYSTEM ................................. l2
2.4
ELECTRO-PNEUMATIC BRAKING SYSTEM (EPB) .................................. 14
© Unlvetsltl Teknlkal Malaysia Melalal
iv
2.5
ELECTRO-MECHANICAL BRAKING SYSTEM (EMB) ............................. l5
2.6
ELECTRONIC WEDGE BRAKE (EWB) ........................................................ 18
CHAPTER3
3
METHODOLOGY .................................................................................................22
3.1
FLOW CHART OF EWB PROJECT ............................................................... 24
3.2
GANTT CHART OF EWB PROJECT PLANNING ........................................ 25
CHAPTER4
4
DETAIL DESIGN AND MODELING THE EWB MECHANISM .................. 26
4.1
EWB CALIPER ASSEMBLY DRAWING ......................................................27
4.2
EWB CALIPER EXPLODED DRAWING ......................................................28
4.3
EWB CALIPER COMPONENTS ..................................................................... 29
4.3.1
CALIPER BODY PART A ........................................................................ 29
4.3.2
BRAKE PISTON ....................................................................................... 31
4.3.3
CALIPER BODY PART C ........................................................................ 32
4.3.4
STUD ......................................................................................................... 33
4.3.5
EWB CALIPER WEDGE PART A ...........................................................34
4.3.6
EWB CALIPER WEDGE PART B ...........................................................35
CHAPTERS
5
EWB TESTING ......................................................................................................36
5.1
SENSOR INSTALLATION ............................................................................. .37
5.1.1
LINEAR VARIABLE DISPLACEMENT TRANSDUCER (LVDT) ...... .37
5.1.2
ROTARY ENCODER ................................................................................ 39
5.1.3
LOAD CELL ..............................................................................................40
© Unlvetsltl Teknlkal Malaysia Melalal
v
5.2
TEST APPARATUS AND PROCEDURES .....................................................41
5.3
TEST RESULTS ...............................................................................................42
CHAPTER6
6
SYSTEM IDENTIFICATION OF EWB SYSTEM ........................................... .49
6.1
EWB TEST RESULT ANALYSIS .................................................................. .50
6.2
FUZZY LOGIC CONTROLLER...................................................................... 52
6.2.1
SIGMOIDAL FUNCTION ....................................................................... 53
6.2.2
GENERALIZED BELL MEMBERSHIP FUNCTION (MF) ................... 59
6.3
MATHEMATICAL EQUATION OF EWB SYSTEM ....................................64
CHAPTER7
7
TORQUE TRACKING CONTROL ....................................................................65
7.1
STEPPERMOTOR ...........................................................................................65
7.2
TORQUE TRACKING CONTROLLER ..........................................................68
CHAPTERS
8
CONCLUSION AND RECOMMENDATION ...................................................72
8.1
CONCLUSION ................................................................................................. 72
8.2
RECOMMENDATION .....................................................................................73
'
© Unlvetsltl Teknlkal Malaysia Melalal
vi
LIST OF FIGURES
Figure 1: Schematic Diagram ofHydraulic Braking System ............................................ 7
Figure 2 : Typical Automotive Braking System ................................................................ 8
Figure 3 : Typical Pneumatic Brake System .................................................................... 11
Figure 4 : EHB System Block Diagram ........................................................................... 12
Figure 5 : EHB System Model ......................................................................................... 13
Figure 6: Schematic Diagram ofEPB System ................................................................ 14
Figure 7 : Block Diagram ofEMB System ...................................................................... 16
Figure 8: Electro mechanical braking system ................................................................. 17
Figure 9: Working Mechanism ofEWB ......................................................................... 19
Figure 10 : EWB Actuator ...............................................................................................20
Figure 11 : The EWB Test Rig .........................................................................................23
Figure 12: Gantt chart ofEWB ProjecL-.........................................................................25
Figure 13 : The EWB Caliper Assembly Design ............................................................. 27
Figure 14 : The EWB Caliper Exploded Drawing ...........................................................28
Figure 15: EWB Caliper Body Part A ............................................................................ .30
Figure 16 : The Brake Piston ............................................................................................ 31
Figure 17 : The Caliper Body Part C ................................................................................ 32
Figure 18 : Stud ................................................................................................................ 33
Figure 19: The EWB Caliper Wedge Part A ...................................................................34
Figure 20 : The EWB Caliper Wedge Part B ...................................................................35
Figure 21: EWB Test Rig at Autotronic Lab ................................................................... 36
Figure 22: Linear Variable Displacement Transducer (LVDT) ......................................38
Figure 23 : The Rotary Encoder ....................................................................................... 39
Figure 24 : The Load Cell Sensor .................................................................................... 40
.
© Unlvetsltl Teknlkal Malaysia Melalal
vii
Figure 25 : EWB Model on Test Rig ............................................................................... 41
Figure 26: Angle, Displacement and Force from Test 1 .................................................43
Figure 27 : Angle, Displacement and Force from Test 2 .................................................43
Figure 28 :Angle, Displacement and Force from Test 3 ................................................. 44
Figure 29 : Angle, Displacement and Force from Test 4 .................................................44
Figure 30 : Angle, Displacement and Force from Test 5 .................................................45
Figure 31 : Angle, Displacement and Force from Test 6 ................................................ .45
Figure 32 :Angle, Displacement and Force from Test 7 .................................................46
Figure 33 : Angle, Displacement and Force from Test 8 ................................................. 46
Figure 34 : Angle, Displacement and Force from Test 9 .................................................47
Figure 35 :Angle, Displacement and Force from Test 10 ...............................................47
Figure 36 : Control Design Example............................................................................... .49
Figure 37 : Motor Angle Input, 6 ofEWB during Braking Condition .............................50
Figure 38 : Motor Angle Input, 6 ofEWB during release braking condition .................. 51
Figure 39: Clamping Force, F ofEWB during braking condition ..................................51
Figure 40 : Clamping Force, F of EWB during release braking condition ......................52
Figure 4 l : Sigmoidal function modeling under braking condition. .................................54
Figure 42 : Simulink modeling to compare force from Sigmoidal function and EWB test
under braking condition .................................................................... ,.............................. 55
Figure 43 : Graph of Force (N) against time (s) under braking condition ....................... 56
Figure 44 : Sigmoidal function modeling under release braking condition .....................57
Figure 45 : Simulink modeling to compare force from Sigmoidal function and EWB test
under release braking condition ,...................................................................................... 58
Figure 46: Graph of Force (N) against time (s) under release braking condition ........... 58
Figure 47: Generalized Bell function modeling under braking condition ......................60
Figure 48 : Simulink modeling to compare force from Generalized Bell function and
EWB test under braking condition ...................................................................................60
Figure 49 : Graph of Force (N) against time (s) under braking condition ....................... 61
Figure 50 : Generalized Bell function modeling under release braking condition ..........62
Figure 51: Simulink modeling to compare force from Generalized Bell function and
EWB test under release braking condition .......................................................................62
.
© Unlvetsltl Teknlkal Malaysia Melalal
Vlll
Figure 52 : Graph of Force (N) against time (s) under release braking condition ........... 63
Figure 53 : Stepper Motor Control System ...................................................................... 66
Figure 54 : Principle of a 2-phase stepper motor .............................................................66
Figure 55 :2-phase stepper motor (open loop) ................................................................. 67
Figure 56 : Torque Tracking Controller ........................................................................... 68
Figure 57 : EWB Torque in Sine Wave Form ..................................................................69
Figure 58: EWB Torque in Saw Wave Form .................................................................. 70
Figure 59: EWB Torque in Square Wave Form .............................................................. ? I
© Unlvetsltl Teknlkal Malaysia Melalal
ix
LIST OF ADBREVIATIONS
EWB
Electronic Wedge Brake
DAQ
Data Acquisition
EHB
=
ESP
EPB
Electro-Hydraulic Braking
Electronic Stability Program
=
Electro-Pneumatic Braking
EMB
Electro-Mechanical Braking
LVDT=
Linear Variable Displacement Transducer
PID
=
=
=
=
Proportional Integrative Derivative
DOF
=
Degree of Freedom
CAD
DC
RPM
Computer' Aided Drawing
Direct Current
Rotation per Minute
.
© Unlvenltl Teknlklll Malayala Melalal
CHAPTER!
1
1.1
INTRODUCTION
OVERVIEW
System identification is the art of determining a model of a dynamical process by
combining information obtained from experimental data. The purpose of system
identification is to determine states or modes needed to construct a model of the system.
System identification is to model the dynamic behavior of a physical system by
determining the equations of motion.
Automotive brakes provide the means to slow down or stop a vehicle, by using
friction to convert the kinetic energy of a moving vehicle into heat. Numerous braking
systems are available on modern vehicles but passenger vehicles commonly employ
hydraulic braking system. The progress in microelectronics, sensor technology and
actuator technology has led to brake-by-wire whlch replaces mechanical linkage or
hydraulic controls in a motor vehicle resulting in a decrease in vehicle weight, improved
handling and facilitating the implementation of active safety elements.
© Unlvetsltl Teknlkal Malaysia Melalal
2
Over recent years, studies on electronic wedge brake have been increasingly
popular. This modem brake system is a fully controlled electro-mechanical braking
system with a high degree of mechanical self-reinforcement. By intelligently controlling
the wedge, it becomes possible to convert the kinetic energy of the vehicle into actual
braking force. The electronic wedge brake will be far superior to any braking
technologies presently being developed or already on the market in terms of energy
consumption, efficiency, space consumed, weight and price.
Electronic wedge brake can be considered to bring add-on value both to the car
manufacturer as well as to the customer. The car manufacturer will gain not only
financial benefit by producing electronic wedge brake but also a reputation of
technological leadership. The customer will benefit from improved driving comfort as
well as improved driving characteristics and safety.
The goal of this study is to explore the possibility of improving braking system on
passenger vehicles by the use of electronic wedge brake. This is the call for ever more
sophisticated and complex braking and driver assistance systems. Brake-by-wire allows
for branding by tailoring the overall feel of a vehicle through software changes rather
than changing hardware on a vehicle. The main task of this study is to design the system
identification of electronic wedge brake (EWB) and to study the behavior of EWB. The
research begins with the studies on classification in the type of brakes existing in current
market. The electronic wedge brake (EWB) then is designed using CATIA V5Rl6
software. The study then continued with the development of EWB test rig, sensor
installation, experiment and fmally system identification of EWB.
© Unlvetsltl Teknlkal Malaysia Melalal
3
1.2
PROBLEM STATEMENT
This research is ignited by the problems that frequently occur in modem hydraulic
braking system in current vehicles. There are several problems that commonly occur in
commercial braking system. Air in the system is the most common of them all. This is
caused by the brake not being bleed properly after rebuild, or lose connection on the
hose lines or bleed nipple allowing air into the system. Next are the sticking pistons in
the brake caliper allowing the pad to constantly run on the disc, causing friction and
heating the fluid. The fluid boils and generates air bubbles so leading to spongy soft
brakes. Leaking fluid from the master cylinder seals could allow air into-the system too.
Worn out or tired brake hose on the other hand could degrade over a period of time so
leading to greater expansion of the hydraulic fluid and loss of perfonnance.
The ideal solution for all the above problems is by eliminating mechanical parts
and linkage including brake fluid in the braking system. Since EWB system fulfil] the
criteria needed, hence it is the perfect replacement for current conventional braking
system. Developing and integrating EWB system in modern vehicles would be the
perfect solution for the technical problems. However, EWB may fail on road if the
power supply to the system turns flat since the system uses vehicle battery power. This
situation could be avoided if the EWB system is powered by a main vehicle battery and
a secondary backup battery in case the main battery fails .
© Unlvetsltl Teknlkal Malaysia Melalal
4
1.3
BACKGROUND OF STUDY
The electronic wedge brake (EWB) is a new electro-mechanical braking system
with a high self-reinforcement factor. This results in low power consumption, providing
the perfect platform for X-by-wire technologies. In the automotive industry today, there
is a strong tend towards 'power-by-wire technologies', aimed at replacing hydraulic or
pneumatic systems. EWB differs from the conventional braking system that transmits
braking power through hydraulic system such as brake cylinders, hydraulic lines and
brake fluid. EWB also has less mechanical parts and hence totally silent with no
vibration felt through the brake pedal. Its main benefit is that it is able to react more
quickly, resulting in shorter stopping distances and increased safety. Yet another reason
for its increasing number of studies is that it takes up much less physical space, which is
an important factor considering how tight engine compartments have become.
Currently hydraulic, pneumatic, electro-hydraulic, electro-pneumatic and electromechanical braking systems are available in market. Although these braking systems
have been researched and developed extensively, EWB is still an interesting subject to
be studied. In this research, hydraulic connection between brake pedal and individual
brake actuators are eliminated and replaced with electronic system. Caliper, wedge
mechanism, brake pad and brake disc is used as an actuator for EWB to improve the
braking system of vehicles. The effectiveness of this EWB depends on the accuracy of
force sensor, the electronic system and the design of actuator.
In theory, the faster the vehicle travelling when the brakes are applied, the more
powerful they become. When the pad is applied to the disc, the momentum of the
rotating disc draws the pad farther up an interlocking series of wedges, applying greater
braking pressure and increasing stopping efficiency. A series of electric motors push in
and pull out at an extremely high frequency, while a torque sensor controls the braking
force and keeps the wheels from locking up. The distance required to stop the vehicle is
less than half compared to other conventional brakes.
© Unlvetsltl Teknlkal Malaysia Melalal
5
1.4
OBJECTIVES
The primary objective of this study is to identify the system of electronic wedge
brake (EWB). EWB actuator mechanism is designed in detail using CATIA V5R 16
Software. Then, the model was fabricated according to the design and used for the
experimentation purpose. Test rig are also fabricated to test the EWB prototype. Sensors
together with the EWB prototype are fixed on the test rig for experimentation
evaluation. Data of motor input angle, brake piston displacement and clamping force on
disc are obtained from Data Acquisition (DAQ).
The experimental data are processed to two different parts. The first part is the
data during braking and the next is the data during releasing the brake. Next, system
identification and modeling of EWB are done. The simulation is then used to study the
perfonnance of EWB in passenger vehicles. Finally it is also targeted to provide
recommendations to automotive designers and manufacturers on the potential benefits in
the use of the EWB system in improving the braking system perfonnances of the
vehicle. Besides that, EWB are also environmental friendly as there is no oil spillage
that damages the environment and wildlife habitat.
1.5
SCOPES
I) Designing the EWB mechanism using CATIA V5Rl6 software.
2) Fabricating the electronic wedge brake (EWB) test rig for system identification
purpose.
3) Sensor installation for experimentation evaluation.
4) System identification of EWB mechanism using MATLAB SIMULfNK
Software by Math Works Inc.
© Unlvetsltl Teknlkal Malaysia Melalal
6
1.6
SIGNIFICANCE OF THE STUDY
The significance of this EWB study is to improve the safety of vehicle in terms of
its braking capabilities by reducing the stopping distance and the reaction time with
appropriate control strategy. Drivers are given more control of their vehicles especially
in case of emergency. The stopping time needed to stop a vehicle with EWB are just I 00
milliseconds compare to conventional brake that takes 140 to 170 milliseconds to
generate full braking power at a speed of I 00 kilometers per hour. The additional benefit
of the study is to develop automotive industries with innovation. EWB is the answer to
future vehicle chassis safety, weight, reliability and space requirements. Continued
developments in the auto industry made it possible for drivers to have more and more
features in their vehicles which make driving a new experience. Thus it is predicted that
this study can reduce the number of accidents on road as well as improving the ride of a
vehicle without sacrificing the comfort level of the passenger in the compartment.
© Unlvetsltl Teknlkal Malaysia Melalal
7
CHAPTER2
2
2.1
LITERATURE REVIEW
HYDRAULIC BRAKING SYSTEM
A simple hydraulic system has liquid, a pump, and lines to carry the liquid, control
valves and an output device. The liquid must be available from a continuous source such
as the brake fluid reservoir or a sump.
Apply piston
Rear
wheel
cylinders
Front
wheel
Master
cylinder
Brake pedal
Figure 1: Schematic Diagram ofHydraulic Braking System
© Unlvetsltl Teknlkal Malaysia Melalal
8
Hydraulic brakes use a special liquid called brake fluid to apply brake pressure to
pad or shoes. The main parts of this system are a chamber called a master cylinder,
which is located near the brake pedal, at least one wheel cylinder at each wheel and
tubes called brake pipes which connect the master cylinder to the wheel cylinders. The
cylinders and brake pipes are filled with brake fluid (James W et al, 1999). Inside the
master cylinder is a piston which can slide back and forth. The brake pedal controls
piston by means of rod or a mechanical link.
In a hydrauHc brake system, the master cylinder serves as the main fluid pump
and moves the liquid through the system. The lines which used to carry the liquid
throughout the system maybe pipes, hoses, or a network of internal bores or passages in
a single housing. Valves are used to regulate hydraulic pressure and direct the flow of
the liquid. The output device is the unit that uses the pressurized liquid to do work. In
this case, the output devices are brake drum wheel cylinders and disc brake calipers.
Typical Disk Brake
Typical Drum Brake
Rear Brakes
Front Brakes
Brake Lines
Figure 2 : Typical Automotive Braking System
When the brake pedal is depressed, the pressure on the brake pedal moves the
piston within the master cylinder, forcing the brake fluid from the master cylinder
through the lines to the wheel cylinder. The wheel cylinders contain two opposed, each
© Unlvetsltl Teknlkal Malaysia Melalal
9
of which is attached to a brake shoe fitted inside the brake drum. Each output piston
pushes the attached brake shoe against the wall of brake drum, thus retarding the rotation
of wheel (Okwuchi E, 2005). When the pressure on the pedal is released, the springs on
the brake shoes return the wheel cylinder pistons to their released positions. This action
forces the displaced brake fluid back through the flexible hose and tubing the master
cylinder. The force applied to the brake pedal produces a proportional force on each of
the output pistons, which in turn apply the brake shoes frictionally to the turning wheels
to retard rotation.
2.2
PNEUMATIC BRAKING SYSTEM
Pneumatic brakes are simply the wheel brakes on the vehicle, but they are
powered by compressed air. Pneumatic brakes use a compressor which is powered by
the engine of the vehicle to compress air, which is stored in tanks, and then used to apply
the braking system and stop the vehicle. Compressor is the pump which draws air from
atmosphere and compresses it for use in brake system. Main reservoir is the storage tank
for braking and other pneumatic systems. The feed valve ensures that brake pipe
pressure remains at required level, a feed valve connected between main reservoir and
brake pipe.
Pneumatic brakes are operated by number of important components such as the
air compressor, governor, air filter drier, alcohol evaporator, air reservoir, protection and
control valves, gauges, brake champers, slack adjusters, brake drums, glad hands, and
warning devices. Below are components in pneumatic braking system with their
respective function.
© Unlvetsltl Teknlkal Malaysia Melalal
10
Air compressor is a machine that pumps the air into a smaller space to produce
compressed air powered by the engine and could be mounted to the engine. Governor is
a controller that limits the air compressor to produce amount of air required. It controls
the compressor cut-in (on) and cut-out (oft) to make sure the compressor produces
enough air but not too much air. Governor is normally located on the compressor. Air
dryer removes moisture and vaporized oil from the compressed air before it enters the
air supply tank. Air dryer is normally located on the air compressor Alcohol
evaporator prevents any moisture in the air brake system to freeze. Air reservoir
system stores compressed air before it's released to the brakes.
Safety valve protects the air tank to over pressure or release access of air in case the
governor fails. Warning devices detects low air pressure and warns the driver when the
air pressure drops below 60 psi. A light and buzzer goes off to warn the driver in the
case of low air pressure. Air pressure gauges located on the dashboard indicates amount
of air pressure in the air tank. Some trucks are equipped with two air pressure gauges,
one for each tank. Brake champers consists of diaphragm, air inlet, push rod, return
springs, and clamp. Air enters the brake champers through the air inlet and pushes
against diaphragm which also pushes the push rod. The push rod is connected to the
slack adjuster. Return spring returns the diaphragm to its original position.
Slack Adjuster is a lever arm attached to the push rod. Glad hands are coupling
devices at the end of the air lines where tractor connects with the trailer. Glad hands are
color coded, service line is normally blue and supply line is red. Service line supplies air
from the brake pedal to the trailer service brakes and supply line supplies air to the
trailer air tank and controls trailer brake.
© Unlvetsltl Teknlkal Malaysia Melalal
ll
Figure 3 : Typical Pneumatic Brake System
When the driver presses the brake pedal, they operate a valve which controls the
air pressure release into the brake lines. The harder the brake pedal is pressed, the more
air the tanks release, and the harder the brakes are applied to the disc or drum. There are
two types of air brakes. First type which use pressure to apply the brakes, and the second
that use pressure to hold the brakes open. The main braking system in commercial
vehicles uses air to apply the brakes, and has a secondary system which called
emergency or parking brake that uses springs to apply the brake, and a small air canister
to hold the brakes open. Pneumatic brake system is undoubtedly one of the most
enduring features in commercial vehicles.
© Unlvetsltl Teknlkal Malaysia Melalal
scope and quality for the award of the degree of
Bachelor of Mechanical Engineering (Automotive)"
Signature:
ｾ＠
Supervisor:
Mr. Vauzi.A.hrnad
Date:
21st July 2012
© Unlvetsltl Teknlkal Malaysia Melalal
SYSTEM IDENTIFICATION OF
ELECTRONIC WEDGE BRAKE (EWB)
D.RAVISANKAR AIL DEVARAJEE
This report was submitted in accordance with the partial requirements for honor of
Bachelor of Mechanical Engineering (Automotive)
#
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
MAY2012
© Unlvetsltl Teknlkal Malaysia Melalal
: l
,.
"I hereby declare that the work in this report is my own except for summaries and quotations
which have been duly acknowledged."
Signature:
ﾷ ﾷ ｾ ﾷ＠
Author:
D.Ravisankar AIL Devarajee
Date:
21st July 2012
© Unlvetsltl Teknlkal Malaysia Melalal
For Loving Father and Mother
© Unlverlltl Teknlkal Malaysia Melakll
ACKNOWLEDGEMENT
I would like to take this opportunity to express my gratitude to all the people who
have helped; supported and guided me throughout the completion of Projek Sarjana
Muda (PSM) entitled System Identification of Electronic Wedge Brake (EWB).
First and foremost, my outmost gratitude goes to my project supervisor, Mr
Fauzi Ahmad for the continuous guidance and support given to me. Your constructive
comments help me a lot in PSMl and PSM2 and thanks for spending your precious time
for the meeting despite your busy schedule and commitments.
Secondly, my extended thank you goes to Universiti Teknikal Malaysia Melaka
(UTeM) for creating an opportunity for all final year students to carry out a final year
project. With this final year project, I can apply all the knowledge learned in UTeM
from the very first year till now. My most grateful thanks to my family members who
gave me lots of moral and mental support which means a lot to me.
Last but certainly not the least; I would like to thank you, the reader for taking
your time to read this report.
© Unlvetsltl Teknlkal Malaysia Melalal
ll
ABSTRACT
This study deals with the use of Electronic Wedge Brake (EWB) in improving
driving quality and solving common problems in current vehicle braking systems. This
new electronic brake concept is based on an electric powered controlled friction brake
with high self-reinforcement capability which has performance advantages over
conventional brake systems. The main content of this study is the development of
System Identification of EWB. Modeling is done to study the brake behavior on a real
vehicle through MA TLAB SIMULINK. software. Detail design of EWB mechanism
with CATIA is done followed by test rig which consist of one unit linear variable
displacement transducer (LVDT), one unit load cell, one unit rotation encoder, data
acquisition (DAQ) and EWB actuator. Experimental result are then used to develop the
System Identification of EWB and followed by the EWB modeling. Common problems
in hydraulic braking system vary from few sources such as air in the brake line, brake
fluid leakage, sticking pistons and more. The ideal solution for these problems is the
development and implementation of EWB system in modern vehicles. EWB system are
said to be the perfect system to replace existing hydraulic braking system in vehicles
because of its dominant advantages. This EWB system results low power consumption,
totally silent with no vibration during braking, able to react more quickly and hence
shortening the stopping distance. However this EWB system may fail if power supply to
be this system is disrupted. To take care of this, EWB is to be connected to a main and a
backup power supply. The development of EWB system brings the technology further
advance and providing the perfect platform for X-by-wire technologies. In future, brakeby-wire is predicted to be replaced by wireless braking system .
.
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TABLE OF CONTENTS
ACKN"OWLEDGEMENT............................................................. ....... ... .i
ABSTRACT . .. .... ... ................. .. .. .... . ..... ..... .. ...... .. ....... .. . ............... ........ii
LIST OF FIGURES ... ..... . ... .... .... .... ... . ............ .. ... ....... .. ..... ............... .... vii
LIST OF ABBREVIATIONS .. ...... . ...... . .......... ....... ...... ....... ...... ....... ........ x
CHAPTER 1 ..................................................................................................................... 1
1
INTRODUCTION .................................................................................................... !
1.1
OVERVIEW ........................................................................................................ !
1.2
PROBLEM STATEMENT ..................................................................................3
1.3
BACKGROUND OF STUDY .............................................................................4
1.4
OBJECTIVES ......................................................................................................5
1.5
SCOPES ...............................................................................................................S
1.6
SIGNIFICANCE OF TtiE STUDY ....................................................................6
CHAPTER2
2
LITERATURE REVIEW ........................................................................................7
2.1
HYDRAULIC BRAKING SYSTEM.................................................................. 7
2.2
PNEUMATIC BRAKING SYSTEM ..................................................................9
2.3
ELECTRO-HYDRAULIC BRAKING (EHB) SYSTEM ................................. l2
2.4
ELECTRO-PNEUMATIC BRAKING SYSTEM (EPB) .................................. 14
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2.5
ELECTRO-MECHANICAL BRAKING SYSTEM (EMB) ............................. l5
2.6
ELECTRONIC WEDGE BRAKE (EWB) ........................................................ 18
CHAPTER3
3
METHODOLOGY .................................................................................................22
3.1
FLOW CHART OF EWB PROJECT ............................................................... 24
3.2
GANTT CHART OF EWB PROJECT PLANNING ........................................ 25
CHAPTER4
4
DETAIL DESIGN AND MODELING THE EWB MECHANISM .................. 26
4.1
EWB CALIPER ASSEMBLY DRAWING ......................................................27
4.2
EWB CALIPER EXPLODED DRAWING ......................................................28
4.3
EWB CALIPER COMPONENTS ..................................................................... 29
4.3.1
CALIPER BODY PART A ........................................................................ 29
4.3.2
BRAKE PISTON ....................................................................................... 31
4.3.3
CALIPER BODY PART C ........................................................................ 32
4.3.4
STUD ......................................................................................................... 33
4.3.5
EWB CALIPER WEDGE PART A ...........................................................34
4.3.6
EWB CALIPER WEDGE PART B ...........................................................35
CHAPTERS
5
EWB TESTING ......................................................................................................36
5.1
SENSOR INSTALLATION ............................................................................. .37
5.1.1
LINEAR VARIABLE DISPLACEMENT TRANSDUCER (LVDT) ...... .37
5.1.2
ROTARY ENCODER ................................................................................ 39
5.1.3
LOAD CELL ..............................................................................................40
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5.2
TEST APPARATUS AND PROCEDURES .....................................................41
5.3
TEST RESULTS ...............................................................................................42
CHAPTER6
6
SYSTEM IDENTIFICATION OF EWB SYSTEM ........................................... .49
6.1
EWB TEST RESULT ANALYSIS .................................................................. .50
6.2
FUZZY LOGIC CONTROLLER...................................................................... 52
6.2.1
SIGMOIDAL FUNCTION ....................................................................... 53
6.2.2
GENERALIZED BELL MEMBERSHIP FUNCTION (MF) ................... 59
6.3
MATHEMATICAL EQUATION OF EWB SYSTEM ....................................64
CHAPTER7
7
TORQUE TRACKING CONTROL ....................................................................65
7.1
STEPPERMOTOR ...........................................................................................65
7.2
TORQUE TRACKING CONTROLLER ..........................................................68
CHAPTERS
8
CONCLUSION AND RECOMMENDATION ...................................................72
8.1
CONCLUSION ................................................................................................. 72
8.2
RECOMMENDATION .....................................................................................73
'
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LIST OF FIGURES
Figure 1: Schematic Diagram ofHydraulic Braking System ............................................ 7
Figure 2 : Typical Automotive Braking System ................................................................ 8
Figure 3 : Typical Pneumatic Brake System .................................................................... 11
Figure 4 : EHB System Block Diagram ........................................................................... 12
Figure 5 : EHB System Model ......................................................................................... 13
Figure 6: Schematic Diagram ofEPB System ................................................................ 14
Figure 7 : Block Diagram ofEMB System ...................................................................... 16
Figure 8: Electro mechanical braking system ................................................................. 17
Figure 9: Working Mechanism ofEWB ......................................................................... 19
Figure 10 : EWB Actuator ...............................................................................................20
Figure 11 : The EWB Test Rig .........................................................................................23
Figure 12: Gantt chart ofEWB ProjecL-.........................................................................25
Figure 13 : The EWB Caliper Assembly Design ............................................................. 27
Figure 14 : The EWB Caliper Exploded Drawing ...........................................................28
Figure 15: EWB Caliper Body Part A ............................................................................ .30
Figure 16 : The Brake Piston ............................................................................................ 31
Figure 17 : The Caliper Body Part C ................................................................................ 32
Figure 18 : Stud ................................................................................................................ 33
Figure 19: The EWB Caliper Wedge Part A ...................................................................34
Figure 20 : The EWB Caliper Wedge Part B ...................................................................35
Figure 21: EWB Test Rig at Autotronic Lab ................................................................... 36
Figure 22: Linear Variable Displacement Transducer (LVDT) ......................................38
Figure 23 : The Rotary Encoder ....................................................................................... 39
Figure 24 : The Load Cell Sensor .................................................................................... 40
.
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Figure 25 : EWB Model on Test Rig ............................................................................... 41
Figure 26: Angle, Displacement and Force from Test 1 .................................................43
Figure 27 : Angle, Displacement and Force from Test 2 .................................................43
Figure 28 :Angle, Displacement and Force from Test 3 ................................................. 44
Figure 29 : Angle, Displacement and Force from Test 4 .................................................44
Figure 30 : Angle, Displacement and Force from Test 5 .................................................45
Figure 31 : Angle, Displacement and Force from Test 6 ................................................ .45
Figure 32 :Angle, Displacement and Force from Test 7 .................................................46
Figure 33 : Angle, Displacement and Force from Test 8 ................................................. 46
Figure 34 : Angle, Displacement and Force from Test 9 .................................................47
Figure 35 :Angle, Displacement and Force from Test 10 ...............................................47
Figure 36 : Control Design Example............................................................................... .49
Figure 37 : Motor Angle Input, 6 ofEWB during Braking Condition .............................50
Figure 38 : Motor Angle Input, 6 ofEWB during release braking condition .................. 51
Figure 39: Clamping Force, F ofEWB during braking condition ..................................51
Figure 40 : Clamping Force, F of EWB during release braking condition ......................52
Figure 4 l : Sigmoidal function modeling under braking condition. .................................54
Figure 42 : Simulink modeling to compare force from Sigmoidal function and EWB test
under braking condition .................................................................... ,.............................. 55
Figure 43 : Graph of Force (N) against time (s) under braking condition ....................... 56
Figure 44 : Sigmoidal function modeling under release braking condition .....................57
Figure 45 : Simulink modeling to compare force from Sigmoidal function and EWB test
under release braking condition ,...................................................................................... 58
Figure 46: Graph of Force (N) against time (s) under release braking condition ........... 58
Figure 47: Generalized Bell function modeling under braking condition ......................60
Figure 48 : Simulink modeling to compare force from Generalized Bell function and
EWB test under braking condition ...................................................................................60
Figure 49 : Graph of Force (N) against time (s) under braking condition ....................... 61
Figure 50 : Generalized Bell function modeling under release braking condition ..........62
Figure 51: Simulink modeling to compare force from Generalized Bell function and
EWB test under release braking condition .......................................................................62
.
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Figure 52 : Graph of Force (N) against time (s) under release braking condition ........... 63
Figure 53 : Stepper Motor Control System ...................................................................... 66
Figure 54 : Principle of a 2-phase stepper motor .............................................................66
Figure 55 :2-phase stepper motor (open loop) ................................................................. 67
Figure 56 : Torque Tracking Controller ........................................................................... 68
Figure 57 : EWB Torque in Sine Wave Form ..................................................................69
Figure 58: EWB Torque in Saw Wave Form .................................................................. 70
Figure 59: EWB Torque in Square Wave Form .............................................................. ? I
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LIST OF ADBREVIATIONS
EWB
Electronic Wedge Brake
DAQ
Data Acquisition
EHB
=
ESP
EPB
Electro-Hydraulic Braking
Electronic Stability Program
=
Electro-Pneumatic Braking
EMB
Electro-Mechanical Braking
LVDT=
Linear Variable Displacement Transducer
PID
=
=
=
=
Proportional Integrative Derivative
DOF
=
Degree of Freedom
CAD
DC
RPM
Computer' Aided Drawing
Direct Current
Rotation per Minute
.
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1
1.1
INTRODUCTION
OVERVIEW
System identification is the art of determining a model of a dynamical process by
combining information obtained from experimental data. The purpose of system
identification is to determine states or modes needed to construct a model of the system.
System identification is to model the dynamic behavior of a physical system by
determining the equations of motion.
Automotive brakes provide the means to slow down or stop a vehicle, by using
friction to convert the kinetic energy of a moving vehicle into heat. Numerous braking
systems are available on modern vehicles but passenger vehicles commonly employ
hydraulic braking system. The progress in microelectronics, sensor technology and
actuator technology has led to brake-by-wire whlch replaces mechanical linkage or
hydraulic controls in a motor vehicle resulting in a decrease in vehicle weight, improved
handling and facilitating the implementation of active safety elements.
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Over recent years, studies on electronic wedge brake have been increasingly
popular. This modem brake system is a fully controlled electro-mechanical braking
system with a high degree of mechanical self-reinforcement. By intelligently controlling
the wedge, it becomes possible to convert the kinetic energy of the vehicle into actual
braking force. The electronic wedge brake will be far superior to any braking
technologies presently being developed or already on the market in terms of energy
consumption, efficiency, space consumed, weight and price.
Electronic wedge brake can be considered to bring add-on value both to the car
manufacturer as well as to the customer. The car manufacturer will gain not only
financial benefit by producing electronic wedge brake but also a reputation of
technological leadership. The customer will benefit from improved driving comfort as
well as improved driving characteristics and safety.
The goal of this study is to explore the possibility of improving braking system on
passenger vehicles by the use of electronic wedge brake. This is the call for ever more
sophisticated and complex braking and driver assistance systems. Brake-by-wire allows
for branding by tailoring the overall feel of a vehicle through software changes rather
than changing hardware on a vehicle. The main task of this study is to design the system
identification of electronic wedge brake (EWB) and to study the behavior of EWB. The
research begins with the studies on classification in the type of brakes existing in current
market. The electronic wedge brake (EWB) then is designed using CATIA V5Rl6
software. The study then continued with the development of EWB test rig, sensor
installation, experiment and fmally system identification of EWB.
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1.2
PROBLEM STATEMENT
This research is ignited by the problems that frequently occur in modem hydraulic
braking system in current vehicles. There are several problems that commonly occur in
commercial braking system. Air in the system is the most common of them all. This is
caused by the brake not being bleed properly after rebuild, or lose connection on the
hose lines or bleed nipple allowing air into the system. Next are the sticking pistons in
the brake caliper allowing the pad to constantly run on the disc, causing friction and
heating the fluid. The fluid boils and generates air bubbles so leading to spongy soft
brakes. Leaking fluid from the master cylinder seals could allow air into-the system too.
Worn out or tired brake hose on the other hand could degrade over a period of time so
leading to greater expansion of the hydraulic fluid and loss of perfonnance.
The ideal solution for all the above problems is by eliminating mechanical parts
and linkage including brake fluid in the braking system. Since EWB system fulfil] the
criteria needed, hence it is the perfect replacement for current conventional braking
system. Developing and integrating EWB system in modern vehicles would be the
perfect solution for the technical problems. However, EWB may fail on road if the
power supply to the system turns flat since the system uses vehicle battery power. This
situation could be avoided if the EWB system is powered by a main vehicle battery and
a secondary backup battery in case the main battery fails .
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1.3
BACKGROUND OF STUDY
The electronic wedge brake (EWB) is a new electro-mechanical braking system
with a high self-reinforcement factor. This results in low power consumption, providing
the perfect platform for X-by-wire technologies. In the automotive industry today, there
is a strong tend towards 'power-by-wire technologies', aimed at replacing hydraulic or
pneumatic systems. EWB differs from the conventional braking system that transmits
braking power through hydraulic system such as brake cylinders, hydraulic lines and
brake fluid. EWB also has less mechanical parts and hence totally silent with no
vibration felt through the brake pedal. Its main benefit is that it is able to react more
quickly, resulting in shorter stopping distances and increased safety. Yet another reason
for its increasing number of studies is that it takes up much less physical space, which is
an important factor considering how tight engine compartments have become.
Currently hydraulic, pneumatic, electro-hydraulic, electro-pneumatic and electromechanical braking systems are available in market. Although these braking systems
have been researched and developed extensively, EWB is still an interesting subject to
be studied. In this research, hydraulic connection between brake pedal and individual
brake actuators are eliminated and replaced with electronic system. Caliper, wedge
mechanism, brake pad and brake disc is used as an actuator for EWB to improve the
braking system of vehicles. The effectiveness of this EWB depends on the accuracy of
force sensor, the electronic system and the design of actuator.
In theory, the faster the vehicle travelling when the brakes are applied, the more
powerful they become. When the pad is applied to the disc, the momentum of the
rotating disc draws the pad farther up an interlocking series of wedges, applying greater
braking pressure and increasing stopping efficiency. A series of electric motors push in
and pull out at an extremely high frequency, while a torque sensor controls the braking
force and keeps the wheels from locking up. The distance required to stop the vehicle is
less than half compared to other conventional brakes.
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1.4
OBJECTIVES
The primary objective of this study is to identify the system of electronic wedge
brake (EWB). EWB actuator mechanism is designed in detail using CATIA V5R 16
Software. Then, the model was fabricated according to the design and used for the
experimentation purpose. Test rig are also fabricated to test the EWB prototype. Sensors
together with the EWB prototype are fixed on the test rig for experimentation
evaluation. Data of motor input angle, brake piston displacement and clamping force on
disc are obtained from Data Acquisition (DAQ).
The experimental data are processed to two different parts. The first part is the
data during braking and the next is the data during releasing the brake. Next, system
identification and modeling of EWB are done. The simulation is then used to study the
perfonnance of EWB in passenger vehicles. Finally it is also targeted to provide
recommendations to automotive designers and manufacturers on the potential benefits in
the use of the EWB system in improving the braking system perfonnances of the
vehicle. Besides that, EWB are also environmental friendly as there is no oil spillage
that damages the environment and wildlife habitat.
1.5
SCOPES
I) Designing the EWB mechanism using CATIA V5Rl6 software.
2) Fabricating the electronic wedge brake (EWB) test rig for system identification
purpose.
3) Sensor installation for experimentation evaluation.
4) System identification of EWB mechanism using MATLAB SIMULfNK
Software by Math Works Inc.
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1.6
SIGNIFICANCE OF THE STUDY
The significance of this EWB study is to improve the safety of vehicle in terms of
its braking capabilities by reducing the stopping distance and the reaction time with
appropriate control strategy. Drivers are given more control of their vehicles especially
in case of emergency. The stopping time needed to stop a vehicle with EWB are just I 00
milliseconds compare to conventional brake that takes 140 to 170 milliseconds to
generate full braking power at a speed of I 00 kilometers per hour. The additional benefit
of the study is to develop automotive industries with innovation. EWB is the answer to
future vehicle chassis safety, weight, reliability and space requirements. Continued
developments in the auto industry made it possible for drivers to have more and more
features in their vehicles which make driving a new experience. Thus it is predicted that
this study can reduce the number of accidents on road as well as improving the ride of a
vehicle without sacrificing the comfort level of the passenger in the compartment.
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CHAPTER2
2
2.1
LITERATURE REVIEW
HYDRAULIC BRAKING SYSTEM
A simple hydraulic system has liquid, a pump, and lines to carry the liquid, control
valves and an output device. The liquid must be available from a continuous source such
as the brake fluid reservoir or a sump.
Apply piston
Rear
wheel
cylinders
Front
wheel
Master
cylinder
Brake pedal
Figure 1: Schematic Diagram ofHydraulic Braking System
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Hydraulic brakes use a special liquid called brake fluid to apply brake pressure to
pad or shoes. The main parts of this system are a chamber called a master cylinder,
which is located near the brake pedal, at least one wheel cylinder at each wheel and
tubes called brake pipes which connect the master cylinder to the wheel cylinders. The
cylinders and brake pipes are filled with brake fluid (James W et al, 1999). Inside the
master cylinder is a piston which can slide back and forth. The brake pedal controls
piston by means of rod or a mechanical link.
In a hydrauHc brake system, the master cylinder serves as the main fluid pump
and moves the liquid through the system. The lines which used to carry the liquid
throughout the system maybe pipes, hoses, or a network of internal bores or passages in
a single housing. Valves are used to regulate hydraulic pressure and direct the flow of
the liquid. The output device is the unit that uses the pressurized liquid to do work. In
this case, the output devices are brake drum wheel cylinders and disc brake calipers.
Typical Disk Brake
Typical Drum Brake
Rear Brakes
Front Brakes
Brake Lines
Figure 2 : Typical Automotive Braking System
When the brake pedal is depressed, the pressure on the brake pedal moves the
piston within the master cylinder, forcing the brake fluid from the master cylinder
through the lines to the wheel cylinder. The wheel cylinders contain two opposed, each
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of which is attached to a brake shoe fitted inside the brake drum. Each output piston
pushes the attached brake shoe against the wall of brake drum, thus retarding the rotation
of wheel (Okwuchi E, 2005). When the pressure on the pedal is released, the springs on
the brake shoes return the wheel cylinder pistons to their released positions. This action
forces the displaced brake fluid back through the flexible hose and tubing the master
cylinder. The force applied to the brake pedal produces a proportional force on each of
the output pistons, which in turn apply the brake shoes frictionally to the turning wheels
to retard rotation.
2.2
PNEUMATIC BRAKING SYSTEM
Pneumatic brakes are simply the wheel brakes on the vehicle, but they are
powered by compressed air. Pneumatic brakes use a compressor which is powered by
the engine of the vehicle to compress air, which is stored in tanks, and then used to apply
the braking system and stop the vehicle. Compressor is the pump which draws air from
atmosphere and compresses it for use in brake system. Main reservoir is the storage tank
for braking and other pneumatic systems. The feed valve ensures that brake pipe
pressure remains at required level, a feed valve connected between main reservoir and
brake pipe.
Pneumatic brakes are operated by number of important components such as the
air compressor, governor, air filter drier, alcohol evaporator, air reservoir, protection and
control valves, gauges, brake champers, slack adjusters, brake drums, glad hands, and
warning devices. Below are components in pneumatic braking system with their
respective function.
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Air compressor is a machine that pumps the air into a smaller space to produce
compressed air powered by the engine and could be mounted to the engine. Governor is
a controller that limits the air compressor to produce amount of air required. It controls
the compressor cut-in (on) and cut-out (oft) to make sure the compressor produces
enough air but not too much air. Governor is normally located on the compressor. Air
dryer removes moisture and vaporized oil from the compressed air before it enters the
air supply tank. Air dryer is normally located on the air compressor Alcohol
evaporator prevents any moisture in the air brake system to freeze. Air reservoir
system stores compressed air before it's released to the brakes.
Safety valve protects the air tank to over pressure or release access of air in case the
governor fails. Warning devices detects low air pressure and warns the driver when the
air pressure drops below 60 psi. A light and buzzer goes off to warn the driver in the
case of low air pressure. Air pressure gauges located on the dashboard indicates amount
of air pressure in the air tank. Some trucks are equipped with two air pressure gauges,
one for each tank. Brake champers consists of diaphragm, air inlet, push rod, return
springs, and clamp. Air enters the brake champers through the air inlet and pushes
against diaphragm which also pushes the push rod. The push rod is connected to the
slack adjuster. Return spring returns the diaphragm to its original position.
Slack Adjuster is a lever arm attached to the push rod. Glad hands are coupling
devices at the end of the air lines where tractor connects with the trailer. Glad hands are
color coded, service line is normally blue and supply line is red. Service line supplies air
from the brake pedal to the trailer service brakes and supply line supplies air to the
trailer air tank and controls trailer brake.
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Figure 3 : Typical Pneumatic Brake System
When the driver presses the brake pedal, they operate a valve which controls the
air pressure release into the brake lines. The harder the brake pedal is pressed, the more
air the tanks release, and the harder the brakes are applied to the disc or drum. There are
two types of air brakes. First type which use pressure to apply the brakes, and the second
that use pressure to hold the brakes open. The main braking system in commercial
vehicles uses air to apply the brakes, and has a secondary system which called
emergency or parking brake that uses springs to apply the brake, and a small air canister
to hold the brakes open. Pneumatic brake system is undoubtedly one of the most
enduring features in commercial vehicles.
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