International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
Hydraulic Rear Drum Brake System In Two Wheeler
S.NAKKEERAN
Department of Automobile engineering
Bharath University, Chennai
Tamilnadu, India
ABSTRACT:The function of the braking system is to
retard the speed of the moving vehicle or
bring it to rest in a shortest possible distance
whenever required. The vehicle can be held
on an inclined surface against the pull of
gravity by the application of brake.The
effectiveness of the brake has been increased
with the introduction of hydraulic brake
system. With this system the stopping
distance and the braking force required is
considerably less, smooth and easy to
operate also less maintenance compared to
mechanical braking system.Normally in
motor cycle of the current trend employ
mechanical braking system with drum
brakes. We hope to increase the
effectiveness of the braking system in
motorcycle with the application of hydraulic
drum brakes at rear of the motorcycle
INTRODUCTION:-
In the present day scenario of Indian roads,
the number of road accidents is increasing
due to increase in the population of road
vehicles rather than road network, loss of
control in adverse conditions, improper or
inadequate braking, etc., This condition is
more seen in two-wheelers rather than four
wheelers due to the reason that there are
features like Anti-lock Brake System (ABS),
Electronic Brake Distribution (EBD), AntiSpin Regulation (ASR), etc., come to rescue
incase of any emergency or sudden braking
in four wheelers whereas in two wheelers
such features are not implemented due to
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constraints like space, cost and other
complications. In order to increase the
effectiveness of the braking system in twowheelers, we have implemented hydraulic
system in replacement of the existing
mechanical system so as to increase the
response of the braking system and to ease
the operation or application of brakes also
taking care of stability of the rider and
pillion especially in motorcycles.
FLUID CHARACTERISTICS
If a liquid is confined and a force is applied,
pressure is produced. In order to pressurize a
liquid, the liquid must be in a sealed
container. Any leak in the container will
decrease the pressure .The basic principle of
hydraulics
are
based
on
certain
characteristics of liquids. Liquids have no
shape of their own, they acquire the shape of
the container they are put in. In addition
they
always seek a common level.
Therefore, oil in a hydraulic system will
flow in any direction and through any
passage, regardless of size or shape.
Liquids are basically incompressible, which
gives them the ability to transmit force. The
pressure applied to a liquid in sealed
container transmits equally in all directions
and to all areas of the system and acts with
equal force on all areas .As a result, liquids
can provide great increase in the force
available to do work. A liquid under
pressure may also change from a liquid to a
gas in response to temperature changes.
Liquids can be used to transmit movement.
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
Consider two cylinders of the same diameter
are filled with a liquid and connected by a
pipe. If you force piston A downward, the
liquid will push piston B upward. Because
piston A starts the movement, it is called the
apply piston. Piston B is called the output
piston. If the apply piston moves 10 inches,
the output piston also will move 10 inches.
This principle works not only for one output
piston, but for any number of output pistons
.The principle that motion can be
transmitted by a liquid is used in hydraulic
brake systems. A master cylinder piston is
pushed when the driver applies the brakes.
The master cylinder piston is the apply
piston. The brake fluid in the master
cylinder is connected by pipes to pistons in
rear wheel brake units. The wheel brake
piston is an output piston. They move
whenever the master cylinder input piston
moves.
Mechanical advantage with hydraulics is
used to do work in the same way as a lever
or gear does work. All of these systems
transmit energy or force. Because energy
cannot be created or destroyed, these
systems only redirect energy to perform
work and do not create more energy. Work
is the amount of force applied and the
distance over which it is applied. Force is
power working against resistance; it is the
amount of push or pull exerted on an object
needed to cause motion. We usually
measure force in the same units that we use
to measure weight pounds or kilograms.
Pressure is the amount of force exerted onto
a given surface area. Therefore, pressure
equals the applied force (measured in
pounds or kilograms) divided by the surface
area (measured in square inches or square
centimeters) that is receiving the force. In
customary English units, pressure is
measured in pounds per square inch (psi). In
the metric system it can be measured in
kilograms per square centimeter, but the
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preferred metric pressure measurement unit
is the Pascal. The pressure of a liquid in a
closed system such as a brake hydraulic
system is the force exerted against the inner
surface of its container, which is the surface
of all the lines, hoses, valves, and pistons in
the system. Pressure applied to a liquid
exerts force equally in all directions. If the
hydraulic pump provides 100 psi, there will
be 100 pounds of force on every square inch
of the system .When pressure is applied to a
movable output piston, it creates output
force. If the system included a piston with
an area of 30square inches, each square inch
would receive 100 pounds of force. This
means there would be 3,000 pounds of force
applied to that piston .The use of the larger
piston would give the system a mechanical
advantage or increase hydraulic system
mechanical advantage with hydraulics.
Hydraulics is used to do work in the same
way as a lever or gear does work. All of
these systems transmit energy or force.
Because energy cannot be created or
destroyed, these systems only redirect
energy to perform work and do not create
more energy. The multiplication of force
through a hydraulic system is directly
proportional to the difference in the piston
sizes throughout the system. By changing
the sizes of the pistons in a hydraulic
system, force is multiplied, and as a result,
low amounts of force are needed to move
heavy objects .The mechanical advantage of
a hydraulic system can be further increased
by the use of levers to increase the force
applied to a piston.. A is smaller than output
piston B. Piston A has an area of 20 square
inches; in the example, we are applying 200
pounds of force.Therefore,200 pounds (F)=
10 psi (P)20 square inches (A)where F is
force, A is area, and P is pressure. If that
same 200 pounds of force is applied to a
piston of 10 square inches, system pressure
is 20 psi because200 pounds (F)= 20 psi
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
(P)10 square inches (A)Therefore, pressure
is inversely related to piston area. The
smaller the piston, the greater the pressure
that is developed. Let us apply the 10 psi of
pressure in the first example to an output
piston with an area of 50 square inches. In
this case, output force equals pressure times
the surface area:
P×A=F
Therefore, 10 psi of pressure on a 50-squareinch piston develops 500 pounds of output
force:
10 × 50 = 500
Brake systems use hydraulics to increase
force for brake application .piston of 10
square inches .A force of 500 pounds is
pushing on the piston .The pressure
throughout the system is 50 psi:500 (F) ÷ 10
(A) = 50 (P).
A pressure gauge in the system shows the 50
psi pressure. There are two output pistons in
the system. One has100 square inches of
area. The 50 psi pressure in the system is
transmitted equally everywhere in the
system. This means that the large output
piston has 50 psi applied to 100 square
inches to deliver an output force of 5000
pounds: 100square-inches × 50 psi = 5000
pounds The other output piston is smaller
than the input piston with a 5-square-inch
area. The 5-square-inch area of this piston
has 50-psi pressure acting on it to develop
an output force of 250 pounds: 5 square
inches × 50 psi = 250 pounds. In a brake
system, a small master cylinder piston is
used to apply pressure to larger pistons at
the wheel brake units to increase braking
force. Importantly, the pistons in the front
brakes have a larger surface area than the
pistons in the rear brakes. This creates
greater braking force at the front and exerts
more force but travels a shorter distance.
The opposite also is true. If the output piston
is smaller than the input piston, it exerts less
force but travels a longer distance. Apply the
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equation to the 5 square inch output piston.
square inches (input piston) 5 square inches
(output piston)=21× 2 inches (input stroke)
= 4.0 inches output motion. In this case, the
smaller output piston applies only half the
force of the input piston, but its stroke
(motion) is twice as long. These
relationships of force, pressure, and motion
in a brake system are easily observed when
you consider the force applied to the master
cylinder’s pistons and the resulting brake
force and piston movement at the wheels.
Wheel cylinder pistons move only a fraction
of an inch to apply hundreds of pounds of
force to the brake shoes, the wheel cylinder
piston travel is quite a bit less than the
movement of the master cylinder piston.
Disc brake caliper pistons move only a few
thousands of an inch but apply great force to
the brake rotors. This demonstrates how the
use of hydraulics provides mechanical
advantage similar to that provided by the use
off levers or gears. Although hydraulic
systems, gears, and levers can accomplish
the same results, hydraulics is preferred
when the size and shape of the system are of
concern. In hydraulics, the force applied to
one piston will transmit through the fluid,
and the opposite piston will have the same
force on it. The distance between the two
pistons in hydraulic system does not affect
the force in a static system. Therefore, the
force applied to one piston can be
transmitted without change to another piston
located somewhere else. A hydraulic system
responds to the pressure or force applied to
it. The mere presence of different sized
pistons does not always result in fluid
power.
The force or pressure applied to the pistons
must be different in order to cause fluid
power. If an equal amount of pressure is
exerted onto both pistons in a system and
both pistons are the same size, neither piston
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
will move; the system is balanced or is at
equilibrium. The pressure inside the
hydraulic system is called static pressure
because there is no fluid motion. When an
unequal amount of pressure is exerted on the
pistons, the piston receiving the least
amount of pressure will move in response to
the difference between the two pressures.
Likewise, the fluid will move if the size of
the two pistons is different and an equal
amount of pressure is exerted on the pistons
.The pressure of the fluid while it is in
motion is called dynamic pressure.
Kinetic energy is the force that tends to keep
the vehicle moving. Kinetic energy must be
dissipated as heat by the brakes during
operation. The kinetic energy doubles as the
weight doubles, but it increases four times as
speed doubles. The kinetic energy of a
vehicle is given by
W = (u^2-v^2)
Where W = vehicle gross weight
u = initial velocity
v = final velocity
HYDRAULIC BRAKE SYSTEMS
Co-efficient Of Friction
Engineers must consider these principles of
force, pressure, and motion when designing
a brake system for any vehicle. If an
engineer chooses a master cylinder with
relatively small piston areas, the brake
system can develop very high hydraulic
pressure, but the pedal travel will be
extremely long. Moreover, if the master
cylinder piston travel is not long enough,
this high-pressure system will not move
enough fluid to apply the large area caliper
pistons regardless of pressure. If, on the
other hand, the engineer selects a large area
master cylinder piston, it can move a large
volume of fluid but may not develop enough
pressure to exert adequate braking force at
the wheels. The overall size relationships of
master cylinder pistons, caliper pistons, and
wheel cylinder pistons are balanced to
achieve maximum braking force without
grabbing or fading. Most brake systems with
front discs and rear drums have large
diameter master cylinders (a large piston
area) and a power booster to increase the
input force.
Frictional force opposes the motion of the
vehicle consuming power and producing
heat. Frictional force occurs between the
sliding tyre and the road surface when
brakes lock wheel rotation.
Vehicle’s kinetic energy and its ability to
stop is related to the coefficient of friction
between the rubbing surfaces. Maximum
usable coefficient of friction occurs between
the tyre and road surface, rather than in the
brakes. Two - wheeler brakes have
coefficient of friction 0.3 to 0.5
The Amount Of Energy
BRAKING REQUIREMENTS
The amount of energy the brakes can absorb
is dependent upon the coefficient of friction
of the brake materials, their diameter, their
surface area, shoe geometry, and the
pressure used to actuate them. Stopping a
car quickly means total friction must
begreater, resulting in high brake
temperature.
Kinetic Energy
Brake Balance
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
The stopping distance is same with the same
tyre and road conditions, when the wheels
are locked and skidding, regardless of the
weight, number of wheels or vehicle load.
Maximum braking power occurs when the
wheels are braked just before the locking
point or point of impending skid. Non-skid
brake systems are designed to operate at or
below this point. Changes in load on a wheel
will change the point of impending skid.
The effective braking force of a vehicle
occurs at ground level. Vehicle weight and
kinetic energy of the vehicle act through
center of gravity which is above ground
level. This causes the vehicle to tend to pitch
forward as the brakes are applied. Pitching
forward effectively transfers some of the
vehicle weight from the rear wheels to the
front wheels. The front brakes therefore,
must absorb more kinetic energy than the
rear brakes. The maximum amount of
weight transfer is given by
Wt = µhW/b
Where, Wt = weight transferred, N
µ = coefficient of friction
h = height of C.G from the ground,
shoe-disc combination type, brake size,
lining coefficient of friction, wheel cylinder
size and differential hydraulic actuating
pressures. With full braking it is desirable to
have the front brakes lock up slightly ahead
of the rear brakes. This causes the car to go
straight forward and not to spin out.
Stopping Distance
Stopping distance is extremely important for
emergency braking. The stopping distance is
based on the deceleration rate. Also it is
affected by the tyre deflection, air resistance,
engine braking efforts and the inertia of the
drive line.
Brake Fade
Since brake lining material is a poor
conductors of heat, most of the heat goes
into the brake drum or disc during braking.
Under severe use, brake drums may reach
590k. The coefficient of friction between the
drum and the lining is much lower at these
high temperatures and hence additional
pedal pressure is required. After a number of
severe stops or after holding the brakes on a
long down hill grade, a point is eventually
reached when the coefficient of friction
drops so low that little braking effect is
available. This is called brake fade.
m
W = vehicle gross weight, N
b = wheel base, m
This weight is added to the static weight on
the front wheels and subtracted from th
static weight on the rear wheels. The front
wheel static weight is normally 55% of the
vehicle weight.
Front brakes are designed to absorb this
extra brake effort by selecting shoe-drum or
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In drum brakes, the lining covers a large
portion of the internal drum surface allowing
little cooling space. Therefore, drum brakes
are more susceptible to fade than disc
brakes. As the vehicle moves, cooling air is
directed around the drum and disc to remove
brake heat.
The drum and disc expansion due to brake
temperature is another factor for fade. The
diameter of the drum increases as it gets hot.
The shoe arc no longer will match the drum
and hence lining-to-drum contact surface
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
becomes smaller. The same stopping force
requires higher pedal pressure and this in
turn increases the temperature on the smaller
contact surface. Continued braking increases
the problem until the braking becomes
ineffective, regardless of the pedal force. On
the other hand, expansion of disc has little
effect on braking because the pads apply
braking force on the side of the disc and
hence braking surface area remains constant.
Leading shoes are more susceptible to fade
than trailing shoes.
Fade-resistant drum brakes must limit brake
shoe arc to 110 degree and power absorption
to 28370kW/m^2 of lining. The horsepower
absorbed by the brakes during a stop can be
calculated as
P = KE/1000t, kW
Where, KE = Kinetic energy, N
t = time, s
Braking Torque
The braking torque is the twisting action
caused by the drum or disc on the shoes or
caliper anchors during the application of
brakes. The amount of torque is determined
by the effective axle height and stopping
force between the tyre and the road surface.
Brake torque on the front wheels is absorbed
by the knuckle and suspension control arms.
In rear, it is absorbed by the axle housing
and the leaf spring or control arm. Braking
torque during an emergency stop is much
higher than accelerating torque at full
throttle. Brake supporting and anchoring
members must therefore, have sufficient
strength to withstand and these high braking
loads.
Brake Safety
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All automobiles are equipped with an
emergency brake that would operate
independently from the service brakes.
Safety standards require the emergency
brake to hold the automobile on a 30% slope
indefinitely after the brake has been applied
until the operator releases it.
BRAKING SYSTEM
Classification
The brakes are classified according to the
application of brake shoe to the revolving
brake drum as the internal-expanding or
external-contracting type. They are also
classified as mechanical or hydraulic,
depending upon the way of transferring
braking force from hand lever or foot pedal
to brake shoes, either by means of
mechanical linkage or by hydraulic pressure.
In modern vehicles the service brakes are
generally hydraulically operated, internal expanding type and the hand brakes are
mechanically operated either internal expanding and external - contracting type.
Main Components
The main components of the braking system
are the brake assembly at the wheel and the
mechanism which applies them. The brake
assembly at the wheel comprises of the
following main components. Braking plates
are pressed-steel discs placed on the axle
ends on which the brake shoes are mounted.
Brake shoes are the curved members,
Usually two numbers for a wheel and are
mounted on the braking plates so as to be
concentric with the wheels. They are pivoted
at one end and are moved outward at the
other end (in case of internal expanding)
when brakes are applied. Brake lining of
special asbestos compound is either riveted
or bonded to the faces of these shoes. This
lining comes in contact with the metal brake
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
drum when brakes are applied. Friction
between the lining and the drum resists the
turning of the wheels. The lining withstand
high heat and the dragging force that
develops when the brake shoes are pressed
against the drum. A force of 640 Pa and a
temperature of 480 K is not uncommon
under extreme brake applications. Cooling
fins attached to outside of the drum help in
dissipating this heat to atmosphere. The
brake drums or hubs are made up of
aluminium casting and rotate with the
wheels. In internal expanding shoes, the
brake lining comes in contact at the inside
surface of the drum and in externalcontacting type the lining contacts on the
outside surface of the drum. The pivot pins
at the ends of the shoes outward against the
drum by hydraulic pressure. Whereas
actuating cams spread the shoes in
mechanical operation. When the pressure on
the brake pedal is released, the brake
retracting springs return the shoes to their
‘off’ position.
rear wheel. The master cylinder is connected
to the wheel cylinder by rubber tubing.
The brake application mechanism consists
of brake pedal where force is applied by
operator’s foot. Linkage transmits the
applied by operator’s foot. Linkage
transmits the applied force on brake pedal to
brake shoes in mechanical system. It
consists of rods and levers connected so as
to apply the brake. In hydraulic system the
master cylinder operates the brake shoes by
transmitting the pressure through brake fluid
when the pedal is depressed.
The hydraulic brake has the following
advantages over the mechanical brakes
HYDRAULIC BRAKES
ADVANTAGES
AND
ITS
The hydraulic brake system consists of
essentially of a master cylinder with piston
and the wheel cylinder with piston a in the
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The depression of the brake pedal moves the
piston in the master cylinder which displaces
the brake fluid (usually a glycerine
compound) forcing it through the tubing to
the rear wheel. The wheel cylinder consists
of a piston and the brake fluid is forced in
between them, separating them apart. The
outer end of the piston presses the cam lever
which in turn operates the cam inside the
drum causing the brake linings to come in
contact with the drum. When the brake pedal
is released the hydraulic pressure drops and
the return spring in the in the brake shoe
pushes the piston to its original position. At
the same time retracting springs on the
wheel brakes pull the shoes back to their
position, bringing drums out of contact. This
also forces the pistons at the wheel cylinder
inward causing the flow of braking fluid
back to the master cylinder.
Application of equal pressure.
Minimum
moving
parts
and
less
complicated linkage.
Application of brake is smooth and easy.
Maintenance of brake is easy.
BRAKE FLUID
Brake fluid is specifically designed to be
compatible with its environment of high
heat, high pressure and moving parts.
Standards for brake fluid have been
established by the society of automobiles
engineers (SAE) and the Department of
Transportation (DOT).
Requirements of a fluid used in automotive
brake applications must include the
following:
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
affinity for air than polyglycol. Because the
air remains suspended in the fluid it is more
difficult to bleed air from the hydraulic
system.
Remain viscous.
have a high boiling point
act as lubrication for moving parts.
The Federal Motor Vehicle Safety Standard
(FMVSS) states that by law, brake fluid
must be compatible regardless of
manufacturer. Fluids are not necessarily
identical however, any DOT approved brake
fluid can be mixed with any other approved
brake fluid without damaging chemical
reactions. Although the fluid may not effect
the properties of liquid under pressure.
DOT GRADES
Two types of brake fluid are used in
automotive brake application, each having
specific
attributes
and
drawbacks.
Polyglycol is clear to amber in color and is
the most common brake fluid used in the
industry.
wet
One of the negative characteristics of
polyglycol is that it is hygroscopic, that is, it
has a propensity to attract water. Water can
be absorbed through rubber hoses and past
seals and past vent in the master cylinder
reservoir cap. Moisture in the hydraulic
circuit reduces the boiling point of the fluid
and causes it to vaporize. In addition,
moisture causes metal parts to parts to
corrode resulting in leakage and / or frozen
wheel cylinder pistons.
Extra caution should be taken with
containers of brake fluid because it absorbs
moisture from the from the air when the
container is opened. Do not leave the
container uncapped and closed it tightly.
There are three grades of brake fluid which
are determined by Federal Motor Vehicle
Safety Standard 116. Fluid grades are rated
by the minimum boiling point for both fluid
(dry) and water contaminated fluid (wet):
. DOT 3- Polyglcol
. Minimum boiling point - 401ºF dry, 284ºF
. Blends with DOT -4
DRUM BRAKE COMPONENTS
Drum brakes consist of a backing plate,
brake shoes, brake drum, wheel cylinder,
return springs and an automatic or selfadjusting system. When you apply the
brakes, brake fluid is forced, under pressure,
into the wheel cylinder which, in turn,
pushes the brake shoes into contact with the
machined surface on the inside of the drum.
When the pressure is released, return springs
pull the shoes back to their rest position.
As the brake linings wear, the shoes must
travel a greater distance to reach the drum.
When the distance reaches a certain point, a
self-adjusting mechanism automatically
reacts by adjusting the rest position of the
shoes so that they are closer to the drum.
Silicone is purple in colour. It is not
hygroscopic and therefore has virtually no
rust corrosion problems. It has a high boiling
point and can be used in higher heat
applications. It will not harm paint when it
comes in contact with it. Silicone has greater
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
Figure 1 . Drum Brake
BRAKE SHOES
Like the disk pads, brake shoes consist of a
steel shoe with the friction material or lining
riveted or bonded to it. Also like disk pads,
the linings eventually wear out and must be
replaced. If the linings are allowed to wear
through to the bare metal shoe, they will
cause severe damage to the brake drum.
BACKING PLATES
The backing plate is what holds everything
together. It attaches to the axle and forms a
solid surface for the wheel cylinder, brake
shoes and assorted hardware. It rarely
causes any problems.
BRAKE DRUM
Brake drums are made of iron and have a
machined surface on the inside where the
shoes make contact. Just as with disk
rotors, brake drums will show signs of wear
as the brake linings seat themselves against
the machined surface of the drum. When
new shoes are installed, the brake drum
should be machined smooth. Brake drums
have a maximum diameter specification that
is stamped on the outside of the drum. When
a drum is machined, it must never exceed
that measurement. If the surface cannot be
machined within that limit, the drum must
be replaced.
WHEEL CYLINDER
The wheel cylinder consists of a cylinder
that has a piston, on one side. Each piston
has a rubber seal and a shaft that connects
the piston with a brake shoe. When brake
pressure is applied, the pistons are forced
out pushing the shoes into contact with the
drum. Wheel cylinders must be rebuilt or
replaced if they show signs of leaking.
RETURN SPRINGS
Return springs pull the brake shoes back to
their rest position after the pressure is
released from the wheel cylinder. If the
springs are weak and do not return the shoes
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all the way, it will cause premature lining
wear because the linings will remain in
contact with the drum. A technician will
examine the springs during a brake job and
recommend their replacement if they show
signs of fatigue.
Figure 2
SELF ADJUSTING SYSTEM
The parts of a self adjusting system should
be clean and move freely to insure that the
brakes maintain their adjustment over the
life of the linings. If the self adjusters stop
working, you will notice that you will have
to step down further and further on the brake
pedal before you feel the brakes begin to
engage. Disk brakes are self adjusting by
nature and do not require any type of
mechanism. When a technician performs a
brake job, aside from checking the return
springs, he will also clean and lubricate the
self adjusting parts where necessary.
TYRE ADHESION
The amount of the force applied on a shoe
against controls the resistance to rotation of
a road wheel. Simultaneously the road
surface has to drive the wheel around. This
driving force attains its limit when the
resistance offered by the brake equals the
maximum frictional force generated between
the tire and road which is known as the
adhesive force. This force can be determined
from the expansion
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Adhesive Force = Load on
wheel *Coefficient of friction
When the limit is reached, the wheel starts
to skid, and extra force on the on the brake
shoe does not increase in the rate of slowing
down the vehicle , no matter how how good
is the braking system. This means that the
adhesion between the tire and the road is the
governing factor for the minimum stopping
distance.
TABLE NO: 1
Adhesion factors for various road surfaces.
No
Road Surface
1.
Concrete,
asphalt dry
Tarmac,
gritted
bitumen dry
Tarmac wet
Ice wet
Gritted
bitumen
Tarmac wet
Gritted
bitumen
Tarmac greasy
Gritted bitumen, snow
compressed dry
Gritted bitumen, snow
compressed wet
Concrete, Coarse
asphalt wet
2.
ROAD ADHESION
Road adhesion depends on
Type of roads surface.
conditions of surface e.g. wet, dry, icy ,
Design of tire tread, composition of tread
material and depth of tread.
The stopping distance of a wheel is greatly
affected by the interaction of the rotating tire
tread and the road surface. The relationship
between the decelerating force and the
vertical load on a wheel is known as the
adhesion factor. This factor is very similar to
the coefficient of friction that occurs when
one surface slides over the other. In the ideal
situation of braking, the wheel should
always rotate right up to the point of
stopping to obtain the greatest retarding
resistance.
It is common thinking that the shortest
stopping distance is achieved when the
wheel is locked to produce a skid. This idea
is incorrect because experiments have
confirmed that the force required to unstuck
the tire is greater than the force required to
skid it over the surface. A wheel held on the
verge of skidding not only provides the
shortest distance, but also allows the driver
to maintain directional control of the
vehicle. Typically adhesion factors for
various road surfaces are given below
3.
4.
5.
6.
7.
8.
9.
Adhesion
Factor
Coarse 0.8
0.6
0.4
0.1
0.3
0.25
0.2
0.15
0.5
DESIGN CALCULATIONS
Following calculations are done to find out
the force required at front and rear wheels
during braking.
1. Retardation.
2. Stopping distance.
3. Stopping force.
4. Brake power.
5. Brake force.
6. Average stopping distance.
7. Average stopping time.
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
8. Average retardation.
= 60 * 5/18 m/s
9. Brake force under extreme conditions.
= 16.67 m/s
10. Weight transfer from rear to front wheels
during braking.
Final velocity, v
= 0 m/s
Considering the stopping time = 0.1 second
11. Calculation of centre of gravity of a
vehicle.
12. Force required to actuate the cam.
From equations of motion we know that, v
= u + at
13. Calculation of radius of radius of master
cylinder.
0 = 16.66 + a * 0.1
14. Displacement in master cylinder.
15. Calculation of radius of wheel cylinder.
a = - (16.66/0.1) m/s^2
Retardation
a = 166.6 m/s^2
16. Displacement in wheel cylinder.
2. STOPPING DISTANCE
1. RETARDATION
From equations of motion, we know that,
2 a s = v^2 – u^2
The co-efficient of friction between road and
tyre, µ
= 0.3 to 0.4
2 * 166.67 * s = 0 – 16.66^2
The mass of the vehicle, m
= 98 kg
s = ( 16.66^2/2*166.6)
The acceleration due to gravity, g
= 9.81 m/s
Stopping distance,
The weight of the vehicle N = W = mg =
98*9.81
=
961.38 N
3. STOPPING FORCE
The maximum frictional force at the tyre
road contact, F
= µN
Stopping force
acceleration
=
mass
= 0.4*961.38 N
= ( 250/9.81) * 166.6
= 384.552 N
= 4245.66 Kgf
Considering the bike speed, initial velocity,
u
= 60 Km/hr
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s = 0.833 m
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*
= 41,649.92 N
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
S = (25.48 * 16.66) / 2 * 100)
4. BRAKING POWER
Average stopping distance
S = 35.36 m
Considering the brake power to be thrice of
engine power
7.8 * 3 = 23.4 HP
7. AVERAGE RETARDATION
From equations of motion, we know that
u^2 – v^2 = 2 a s
= 23.4 * 75 Kgf.m/s
= 1755 Kgf.m/s
(16.66^2 – 0) = 2 * a *35.36
Braking power
= 17216.55 N.m/s
a = (16.66^2)/(2*35.36)
5. BRAKING FORCE
Average
a = 3.92 m/s
retardation
8. AVERAGE STOPPING TIME
From equations of motion, we know that
v=u+at
16.66 = 0 + a * t
t = (16.66 / 3.92)
t = 4.25 s
Figure 4
Braking force
9. BRAKING FORCE UNDER EXTREME
CONDITIONS
=µW
= 0.4 * 250
From above, with stopping distance as 0.833
m and time of 0.1s
= 100 N
We
know
F = (mv^2 / 2*s)
6. AVERAGE STOPPING DISTANCE
We know that, F
= (mv^2 / 2*s)
Equating
above
two,
we
100 = (25.48 * 16.66^2 / 2* s )
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that
get
= (25.48 * 16.66^2) / (2 * 0.833)
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
Extreme
= 4244.96 N
braking
force
= 0.5133 m
11. WEIGHT TRANSFER
10. CALCULATION OF CENTRE OF
GRAVITY
Length of wheel base while bike is in level
in m, L1
= 1.217 m
Height of front hub from the ground in m,
H1
= 0.29 m
Height from the rear wheel hub to seat in m,
H2
= 0.52 m
Weight of the front wheel when bike is level
in kg, W1 = 43 kg
Weight of the rear wheel when bike is level
in kg, W2
= 55 kg
Weight of front wheel when bike is lifted in
kg, W3
= 51.5 kg
Total bike weight, W = W1+W2 = 43+55
= 98 kg
Weight added to front wheel because of lift,
Wf = W3-W1 = 49.5 – 42 = 8.5 kg
New wheelbase, Ln
= Sqrt (L1^2-H2^2) m
Figure 5
Maximum braking force, F
= µW
= 0.4*250
= 100 N
Height of centre of gravity, h = 0.5133 m
Couple produced due to deceleration force
= µW*h
= 0.4*250*0.5133
= 51.33 N
Length of the wheelbase, l
= 1.217 m
Weight transferred, w = (µWh)/l
= Sqrt ( 1.217^2 – 0.03^2 )
= ( 0.4*250* 0.5133 )/ 1.217
= 42.1774 Kg
= 1.1003 m
12. FORCE REQUIRED TO ACTUATE
THE CAM
Height of CG along Y axis, h
= H1+(Wf*L1*Ln)/(Wt*H2)
= (0.29) + (8.5*1.217*1.1003)/(98*0.52)
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µWr
1/n-µK+1/n+µK)
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= WaµK(
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
.4*2500*0.30m
=
Wa*0.4*0.063m[1/0.065(0.4*0.063)+1/0.065+(0.4*0.063)]
300
Wa*0.0252*(25.12+11.086)
=
Wa
300/0.0252(36.20)
=
r = 2.8740 cm
14. DISPLACEMENT IN MASTER
CYLINDER
Wa
= 331.49 N
13. CALCULATION OF RADIUS OF
MASTER CYLINDER
Pedal ratio
=7:1
Distance traveled by the pedal by the
application of foot
= 9cm
Pressure exerted by the fluid = ρgh
= 1.027 *10^-3
* 9.81 * 27
Therefore travel in master cylinder
= 7/1 = 9/x
= 0.2720
Kg/cm^2
x = 9/7 = 1.2857 cm
Total pressure = Atmospheric pressure +
fluid pressure
Total pressure
pressure + fluid pressure
15. CALCULATION OF RADIUS OF
WHEEL CYLINDER
= Atmospheric
Volume of master cylinder
= Пr^2h
= 1.03 Kg/cm^2
+ 0.2720 Kg/cm^2
= П * 802601 * 0.07
= 1.302
Kg/cm^2
We know that,
= 15.0043 cm^3
Force = pressure * area
33.79Kg f = 1.302 * area
Volume of the fluid displaced will be same
in master cylinder as well as in wheel
cylinder.
Hence we equate their volumes
Area = 33.79/1.302 =
П r^2 h = 15.0043
25.95 cm^2
Пr^2 = 25.95
r^2
= 15.0043/ П * 1.2857 = 3.7311 cm
r^2 = 25.95/П =
8.2601 cm
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
r
Effective radius of the
rear wheel
Effective radius of the
rear drum
Tangential braking
force at the rear drum
Normal force at the
rear wheel brake drum
Actual normal force
required at each brake
shoe
= 1.9316 cm
16. DISPLACEMENT IN WHEEL
CYLINDER
Length of the cam linkage
= 6.5 cm
Angle of turn in cam, θ
=7º
Rr
r
Br
Nfb
0.3042
m
0.065 m
435.837
N
871.674
N
435.837
N
We know that , Sin θ = opposite/
hypotenuse
Sin 7 º = opposite/ 6.5
Displacement = Sin 7 º * 6.5
= 0.7921 cm
= 7.921 mm
CONCLUSION
COMMON RESULTS
Parameters
Symbol
New wheel base after
the rear wheel lifted
Height of CG from
the ground
Weight transfer
during braking
Pedal ratio
Ln
H
w
P
Value
obtained
1.1003
m
0.5133
m
42.1774
Kg
7:1
RESULTS FOR THE REAR WHEEL
Parameters
Symbol
Maximum retarding
force at the rear
REFERENCES
Fr
Value
obtained
384.552
N
The design of the braking system for motor
cycle is to improve the braking performance
and stability at all road conditions. The
fabrication of this hydraulic brake system
has enabled us to know more about practical
working of braking system and its
components. While comparing with the
existing mechanical drum brake system,
hydraulic brake system has more effective
braking, lesser stopping distance and smooth
operation.
Thus by this project we had fabricated the
hydraulic braking system, which is more
effective than the conventional braking
system and in the near future we hope to see
this system in reality.
Dr.N.K.Giri, “ Automobile Technology ”,
First edition 2004, Khanna Publishers
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International Journal of Engineering Trends and Technology (IJETT) – Volume2 Issue 2 Number1–Sep 2011
ISBN No 81-7409-178-5.
Dr.N.K.Giri, “ Automobile Mechanics ”,
Seventh edition 1996, Khanna Publishers.
J.Y.Wong, “ Theory Of Ground Vehicles ”,
Third edition, John Wiley & sons,
Inc 2001 ISBN No 0-471-35461-9.
Kirpal Singh, “ Automobile Engineering ”,
Standard Publishers, Distributors, Delhi,
1971.
R.B.Gupta, “ Auto Design ”, Satya
Prakashan,1999.
Dr.T.J.Prabhu, “ Engineering Mechanics ”,
Scitech Publications, 2003.
Thomas.D.Gillespie, “ Fundamentals Of
Vehicle Dynamics ” SAE, USA, 1992.
Anthony Esposito, “ Fluid Power With
Applications ” Prentice Hall, 1980.
Hajra Choudhury S.K. “ The Fundamentals
Of Workshop Technology ”,Volume I &
Volume II, Media Publishers, 1997.
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