79
CHAPTER 4
MECHANICAL DESIGN OF DISC BRAKE
4.1
DISC BRAKE DESIGN -1
4.1.1
Components of the Disc Brake Unit
Motorcycle uses the hydraulically operated foot brakes on the rear
wheel. A layout of the proposed braking system is shown in Figure 4.1. The
components of the system are listed below:
Brake lever or pedal. (pushes the master cylinder piston)
Master cylinder. (produces pressure in the brake system)
Hydraulic lines. (transfer hydraulic pressure from master
cylinder to wheel cylinder)
Disc or rotor.
Caliper unit.
Mechanical linkage. (to move the caliper unit in radial
direction)
4.1.2
Caliper Unit
The disc brake unit here employs a single piston floating
caliper type. The cylinder is formed as a mono block with the caliper.
It has one movable piston, pad, and one stationary pad.
80
Figure 4.1 Components of the proposed disc brake unit
When the brake is applied , fluid pressure developed in the
cylinder causes the pad on the piston side to press against the disc. The
floating caliper body is also moved to the right by the fluid pressure
which pulls the pad against the disc and stops the rotation of the wheel
as shown in Figure 1.8. The clearance between the disc and the pads is
maintained automatically by means of viton seal ring between the
piston and the cylinder.
The caliper which is used in the sports motorcycle is exclusively
designed for the rear braking system as shown in Figure 4.2.
Caliper
Disc
Figure 4.2 Single Piston Floating Type Caliper- sports motorcycle
81
4.1.3
Master Cylinder Unit
The master cylinder is an important unit of the entire disc brake
system. The typical master cylinder has two main chambers viz. fluid
reservoir and pressure chamber. The fluid reservoir stores the brake fluid
and compensates for any change in fluid volume in the pipe lines. A
piston operates inside the pressure chamber.
Caliper
Piston
Figure 4.3 Basic master cylinder when brake is applied
Caliper
Piston
Figure 4.4 Basic master cylinder when brake is released
82
In the basic master cylinder design as shown in Figure 4.3,
the fluid reservoir is an integral part of the master cylinder unit. These
types of master cylinder could be easily used in the front disc brakes .
Figure 4.4 shows the brake fluid motion when the brake is released.
4.1.4
Modification on the Existing Master Cylinder
The basic master cylinder is modified and the fluid reservoir
is removed. In India, most of the motorcycles have a disc brake on the front
wheel and a drum brake on the rear wheel. Hence the master cylinder which is
used for the front wheel braking system of the same motorcycle is procured.
The line of action of rider’s force for the front brake is parallel to the road
surface, it is expected that the line of action for the rear brake will be
perpendicular to the road surface. Hence the master cylinder has to rotate at
an angle 90º and fixed for the rear braking system. (Angle between the front
brake mounting to the rear brake mounting). If the master cylinder is rotated
at an angle of 90º, there is a problem of space constraint where the mater
cylinder is fixed for actuating the rear brake in the motorcycle. Furthermore in
general reservoir of the master cylinder is located at an elevated level from the
brake caliper because the gravitational feed is required in case of any brake
fluid loss in the brake line that being compensated by the gravitational feed.
In case of the front brake, master cylinder is located nearer to the handle bar.
So the gravitational feed is possible, even though reservoir is attached with
master cylinder. But in case of rear brake, master cylinder is located almost at
the same level with respect to brake caliper and approximately 0.75m
horizontally apart. So the gravitational feed is not possible. Therefore the
reservoir is removed and located at an elevated level.
If the fluid reservoir is removed, the remaining part is like cylinder
as shown in Figure 4.5 which is given for explanation purpose. The master
83
cylinder inner diameter is 17mm. So it may look like a piston in the top
view.
Caliper
Piston
Figure 4.5 Reservoir is removed from master cylinder (For explanation
purpose)
The edges of the remaining master cylinder block is filed to
get the smooth surface. Then a hole is drilled in an inclined direction on a
bush, before it is fixed over the master cylinder. The hole drilled into the
bush opens the two ports of the pressure chamber . A separate fluid
reservoir is connected to the hole of the bush; thus the fluid reservoir
is connected to the ports.
Figure 4.6 shows the layout of the master cylinder used in the
variable braking force (VBF) system after the modification. The step by step
modification work on the master cylinder is shown in Figure 4.7 and its
assembly drawing is shown in Figure 4.8.
Lever
Metal bush
Chamber
Figure 4.6 Master cylinder used in the VBF system
84
(a) Existing master cylinder
with fluid reservoir
(b) Master cylinder after removing
fluid reservoir
(c) Hexagonal metal bush is fixed
in pressure chamber
(d) Final modified master cylinder
Figure 4.7 Modification works on master cylinder
Figure 4.8 Assembly drawing (line sketch) of the modified master
cylinder
85
4.1.5
Disc Brake Pads
The existing area of contact of the pad is increased for maintaining
enough area of contact with the disc, when the caliper moves in the
radial direction for loaded conditions . When the pillion load is increased, the
caliper is moved outwards from the disc center with respect to pivot as shown
in Figure 4.15. In that position, brake pads do not have enough area to have
contact with the disc since the disc size (outer diameter) is small when it is
compared with the center of brake pad that is located more than disc size
(diameter). The caliper piston center is more than the brake disc outer radius
with respect to disc center. So the size of the brake pad is increased.
The Figure 4.9 shows the pads (Conventional - 30 mm X 25 mm,
VBF - 30 mm X 30 mm) used in the conventional system and variable
braking force system.
4.1.6
Technical Data and Operating Range of Pads
Table 4.1 Technical Data of the Pads
Modulus in compression
830 MN / m2
Ultimate shear strength
11 MN / m2
Thermal conductivity
5796 Nm/hKm
Brinell hardness
14
Friction coefficient
0.35
Table 4.2 Operating Range of the Pads
Unit pressure
Maximum rubbing speed
Maximum temperature
0.35 – 5 .2 MN /m2
24 m/s
550°C
Maximum continuous temp
250°C
86
Figure 4.9 Pads
4.2
ASSEMBLY OF THE ENTIRE BRAKE SYSTEM TO THE
MOTORCYCLE
4.2.1
Assembly of the Disc to the Wheel Hub
The first step is to assemble the brake disc to the wheel. In general,
an alloy wheel is used in a motorcycle which has a disc brake. The hub of
the alloy wheel has provision for bolting the disc to the hub. But the
wheel which is used for this research work is spoke wheel and does not
have provision for fixing the disc to it. So a separate unit called disc
holder is made. A disc holder is made from a cylindrical plate of dimensions
115 mm × 10mm. The cylindrical plate is gas welded and several
machining processes like drilling, grinding were performed to get a final
shape as shown in the Figure 4.10. The disc holder (a) which is connected
with wheel hub is used to support the brake disc.
The motorcycle has a drum brake at the rear wheel. Hence there are
some modifications to be done to modify the existing drum brake as a disc
brake. But the disc inner diameter does not match with the outer diameter of
the drum. Hence a disc holder is made which has five holes that are located at
the radial position which is equal to radial position of hole in the disc from the
87
centre of the wheel hub. Also, the inner diameter of the disc holder is equal to
the outer diameter of the wheel hub. So, the disc holder is fixed with the
wheel hub and then the disc is fixed with disc holder.
(a) Disc holder
(c) Wheel with disc holder
(b) Brake disc
(d) Wheel with brake disc
Figure 4.10 Assembly of the disc to the wheel hub
88
4.2.2
Location of the Master Cylinder
The location of the master cylinder is very important for the
buildup of the right amount of brake pressure. The master cylinder may
be placed at a higher level than that of the brake pedal. It has been found
out that the suitable place for locating master cylinder is the place of tool box.
Hence the tool box is removed and the master cylinder is located in that
place. Then the master cylinder is screwed to metal strips that are welded
to the chassis frame of the motorcycle as shown in the Figure 4.11. It gives
rigid support to the master cylinder which is located at a height of 187 mm
from the brake pedal. It is not mandatory to locate the master cylinder at the
place of the tool box. Actually, a space is needed near the brake pedal to ease
the operation of the master cylinder linkage. Since the tool box is originally
fitted nearer to brake pedal, that place where the tool box fitted, is selected to
fix the master cylinder.
Figure 4.11 Location of master cylinder
4.2.3
The Brake Pedal Linkage
Initial mechanical advantage is produced by the brake pedal.
Pushing force developing into the master cylinder is increased by the
mechanical leverage of the brake pedal. Here the initial mechanical advantage
89
is provided by the lever ratio of the brake pedal. With a 4: 1 lever ratio, 1N of
force applied to the brake pedal results in 4 N of force acting on the master
cylinder piston as shown in Figure 4.12.
Figure 4.12 Brake pedal linkage
4.3
LOCATION OF CALIPER AND THE MECHANICAL
LINKAGE
The main phase of this design is the construction and the
assembly of the linkage to move the caliper in the radial direction . The
layout of the linkage is shown in Figure 4.13.
Figure 4.13 Caliper position without pillion rider on the motorcycle
90
4.3.1
Constructional Details of Mechanical Linkage
One end of the caliper is bolted to the top end of the steel
plate as shown in Figure 4.13. The other end of the steel plate is being
screwed to the place of torque arm where it is fixed as shown in Figure 4.13.
The other end of the caliper is welded to a metal piece which is fixed at
perpendicular direction to the wheel vertical axis. The lower end of the steel
plate is also welded with a metal piece in perpendicular direction like the
previous one. A hole is drilled in both the metal pieces and a threaded rod
with a knob is inserted into the two holes with a spring as shown in
Figure 4.13. The spring stiffness keeps the caliper in the required position.
The rotation of the knob moves the caliper based on different load conditions
i.e., the movement of the threaded rod causes the caliper to move in the radial
direction.
4.3.2
Working of the Mechanical Linkage
The loading condition in the motorcycle is first with the rider alone
and second is the rider with the pillion rider. When the rider alone is on the
motorcycle, the effective disc radius may be reduced i.e., the caliper may be
moved inwards towards the center of the disc as shown in Figure 4.14. Hence
for unladen condition the knob shown in Figure 4.14 is rotated in clockwise
direction, this causes the caliper to move inwards and thus the effective radius
of the brake disc is reduced.
The maximum braking force developed between the tyre and the
ground is based on the pillion load. When there is a pillion rider on the motor
cycle, the effective disc radius may be increased, i.e. the caliper must be
moved outwards from the center of the disc. So whenever there is a pillion
rider on the motor cycle the knob is rotated in the anticlockwise direction to
reduce the compressive load on the spring that causes the movement of the
caliper outwards as shown in Figure 4.15. The layout of variable braking
force system with the pillion rider is shown in Figure 4.16.
91
Figure 4.14 Layout of the variable braking force system without pillion
rider
Figure 4.15 Caliper position when the motorcycle is loaded
92
Figure 4.16 Layout of the VBF system with the pillion rider
Figure 4.17 VBF System for unloaded
motorcycle
Figure 4.18 VBF System for loaded
motorcycle
The Figures 4.17 and 4.18 show the constructions of the
mechanical linkages that operate the caliper at unladen and laden conditions
respectively. When the motorcycle is in unladen condition, the knob is turned
in the clockwise direction and causes compression on the spring which makes
the caliper move down in the radial direction. Similarly the knob turned in the
93
anticlockwise direction releases the compression of the spring which makes
the caliper move out in the radial direction when the motorcycle is in laden
condition.
Reservoir
Master
cylinder
Figure 4.19 Motorcycle with VBF system
All rear brake components assembled in the motorcycle are shown
in Figure 4.19. After assembling the master cylinder the brake fluid is filled in
the reservoir to the proper level which is located at an elevated level from the
master cylinder as shown in Figure 4.19. Then air bleeding is performed on
the brake system. The brake fluid used for the brake system is Dot 3. The
pedal is checked for free movement of the linkage to operate the master
cylinder.
The brake design-1 is mainly established for knowing how the
mechanism works rather than 30 mm radial movement, since the locus traced
by the center of disc pad is an arc. In India most of the motorcycles have a
drum brake at both the wheels. But some of the motorcycles have a drum
brake at the rear and a disc brake at the front. Moreover, the braking system in
the motorcycle which is selected for this research work is a drum brake. As a
disc brake is needed for establishing variable braking force system, the
existing drum brake is modified as disc brake. So a brake disc and master
cylinder of a front disc brake system are procured and modified because the
disc cannot be fixed on the wheel hub. As the disc’s inner diameter does not
94
match with the outer diameter of the drum, a disc holder is made which has
five holes that are located at the radial position equal to the same radial
position of holes in the disc from the centre of wheel hub as has already been
stated elsewhere in the thesis. Also, the inner diameter of the disc holder is
equal to the outer diameter of the wheel hub. So, the disc holder is fixed to the
wheel hub and then the disc is fixed to disc holder. Space availability for
these modification works is sufficient because the existing rear brake system
(drum brake) is mechanically operated. Hence a reasonable amount of space
is available (torque arm and brake actuating rods are removed as they are not
needed for disc brake). The actuating mechanism of master cylinder is
modified as the line of action of rider’s force for the front brake is parallel to
the road surface and for the rear brake is perpendicular to the road surface.
Hence the master cylinder has to rotate at an angle of 90º (Angle between the
front brake mounting to the rear brake mounting) and is so fixed. The total
cost was about Rs. 2000 for purchasing brake disc and master cylinder. The
original size of the brake disc is 120 mm in radius with a thickness of 6 mm.
The normal load acting on the brake disc is 4943N. The theoretical torque
ranges from 186 N-m (unladen) to 285 N-m (laden). As the brake pads are
moved in an arc, the angular movement of the caliper is more when it is
compared with radial movement which is discussed in detail below:
Figure 4.20 Analysis of radial and arc movement of brake pad
95
It is assumed that points ‘A’ and ‘B’ in Figure 4.20 denote the
center of pressure of fluid pressure at low and high radial position
respectively. From the right angled triangle BAD,
sin
BD
AB
2
(4.1)
BD = dr
(4.2)
AB
(4.3)
0A
dr 0A
Where,
sin
2
(4.4)
= Angle subtended at brake pad pivoted point for different pad
position.
dr = Change in effective disc radius.
From the Equation (4.4), the magnitude of the angular movement
( 0A
) is found to be more when it is compared with the radial movement of
the pad. i.e. Radial movement is the product of angular movement and half
the pad subtension angle at the pivot. As the angular movement is more per
unit rise in effective disc radius, the mechanical design-1 may not be suitable
for variable braking force system.
4.4
DISADVANTAGES OF DISC BRAKE DESIGN-1
The effective disc radius could be varied only by 10 mm
since the brake disc face width is only 20mm.
As the brake pad is not moved along the radial direction (it
moves in a locus like an arc with respect to hinged point),
effective disc radius cannot be set exactly as required. The
96
angular movement is more per unit rise in effective disc
radius (radial movement).
Due to leakage problem in the master cylinder, the variable
braking system does not work properly.
A lot of modification works on the master cylinder lead to
brake fluid leaking problem, when high brake pressure is
developed.
4.5
DISC BRAKE DESIGN - 2
4.5.1
Caliper Design
In order to rectify the problem in the previous disc brake design-1,
a new design is developed on another type of two-wheeler. The main
objective of caliper design is to fabricate a caliper to move along the radial
direction over the brake disc around 35 mm. Existing rear brake assembly is
shown in Figure 4.21.
Figure 4.21 Existing rear brake assembly
97
Figure 4.22 Rear brake assembly (next model - same motorcycle)
The existing rear brake in the motorcycle is a drum brake. A disc
brake system is required for incorporating variable braking force system in
the two-wheeler. Hence a disc brake assembly which is available in the next
model of the same motorcycle is procured. The rear brake assembly of next
model of the same motorcycle is shown in Figure 4.22. A lot of reworks are
done on the rear disc brake assembly to achieve variable braking force
system.
The caliper design includes the following reworks
Separate the left and right caliper pistons and clamp design
Modification of hydraulic circuit
Allow the linear travel and provide linear guide (constrain) in
“Y’ axis
Piston stroke
98
4.5.2
Caliper Halves
Figure 4.23 Caliper halves
The caliper split up is shown in Figure 4.23 involving the effective
clamp design to withstand braking force, external hydraulic piping for brake
fluid flow and a calculation of the caliper piston stroke and brake pad
adjustments. In order to provide external piping (caliper split up) both oil
holes in the RH and LH caliper parts are permanently blocked which is shown
in Figure 4.24 by using aluminum welding.
Blocked oil holes
Figure 4.24 Brake caliper
99
4.5.3
‘C’ – clamp (Caliper housing - Mechanical Design 1)
A clamp which holds LH and RH part of the caliper is in ‘C’-shape.
The Figures 4.25 and 4.26 show the orthographic view and 3D model of the
‘C’-clamp.
Figure 4.25 ‘C’-clamp (Caliper housing-Mechanical design-2)
Figure 4.26 3D model of ‘C’-clamp (Mechanical design-2)
100
The caliper hangs on the ends of the C-clamp plates. The two
halves of the caliper are fixed on the C-clamp as shown in Figure 4.27.
Figure 4.27 Mounting of caliper halves on C-Clamp
The area nearer to the 12 mm holes is very weak. But the caliper is
bolted in the holes. So the caliper body would fill the area nearer to these
holes i.e. Load (Brake fluid force - 4986 N) will be distributed nearer to that
area as shown in Figure 4.28. Also, the load (4986 N) is not a point load; it is
distributed around the bottom area of the ‘C’ clamp and not acting only nearer
to the hole.
4.5.4
Design of Bolt for ‘C’ clamp
Bolts are used to fix the caliper in the ‘C’ clamp. They are
subjected to direct compressive stress and the bending stress due to brake
fluid pressure. Two bolts are used to fix each caliper half.
Direct compressive stress at each bolt =
Where,
2
P = Brake fluid force.
d c = Caliper bolt diameter.
P 4
dc dc
(4.5)
101
Compressive stress due to bending moment at each bolt =
Allowable compressive stress of the bolts [
[
cb
]
2
P 4
dc dc
cb]
P 20 32
3
2
dc
= 1550 N/mm2
P 20 32
3
2
dc
(4.7)
P = 4986 N (Brake fluid force)
dc
7mm
Holes are drilled only in diameter basis.
Figure 4.28 Brake fluid pressure distributing area
4.5.5
Modification of Hydraulic Circuit
LH Oil
Hole
(4.6)
RH Oil
Figure 4.29 Oil passage in normal caliper
102
The caliper is separated into two equal halves for incorporating
variable braking force system. If not so while reducing the effective radius of
disc, the caliper would hit the brake disc. Hence the caliper is halved and each
half is connected with the bottom of a ‘C’ clamp as shown in Figure 4.27.
Now the caliper along with ‘C’ clamp can move to various radius without
hitting the brake disc. As the caliper is separated, the end of the brake fluid
line passages shown in Figure 4.29 in the left side half and the starting of the
brake fluid line passage in the right hand side half are welded as shown in
Figure 4.30.
Figure 4.30 Modification on caliper halves (Line sketch)
A ‘T’ joint as shown Figure 4.31, is connected at the starting point of
the fluid passage in the left and right halves of the caliper. In ‘T’ joint, one
passage is used to enter the brake fluid from the brake hose to the left side
half of the caliper and another passage is used to provide the fluid supply to
the another one ‘T’ joint which is connected to the right side caliper half. One
103
more passage in the right side is used for performing brake bleeding
operation. Hence a hole which is already available in the left caliper halve
(Two holes are available-one is blocked and the other one is enlarged) is
enlarged to fix the T’ joints as it is required for variable braking force system.
In the right side caliper half, a drilling operation is performed which connects
the existing fluid passage. Then a ‘T’ joint is fixed.
‘T’ Joints
‘C’ Clamp
Figure 4.31 Caliper with modified assembly
The oil holes are connected with copper piping and connectors.
Finally an external brake fluid passage is provided.
4.5.6
Linear Travel Guide
The existing caliper mounting was provided by an aluminium
bracket which connects caliper (2 mounting bolts – M8) and Swing arm. The
caliper is constrained in all degrees of freedom. But in the new design, the
caliper has to move only in “Y”direction (perpendicular to ground), so that
the bracket has to be designed to move the caliper in ‘Y’ direction and
constrained on remaining all degrees of freedom. This objective of rework
may be achieved by providing new bracket design as shown in Figure 4.32.
104
LINEAR GUIDE
BRACKET
Figure 4.32 Modified rear disc assembly
Similar to C-clamp the linear guide bracket which is shown in the
Figures 4.35 and 4.36 (3D model) is subjected to bending when the braking
pressure is applied to the caliper. Hence the same original design (existing
design in the motor cycle) is used for axle support and spacer. An axle spacer
as shown in the Figures 4.33 and 4.34 (3D model) is used to accommodate the
linear guide bracket.
Figure 4.33 Axle spacer (Mechanical Design-2 - Designed by motorcycle
manufacturer)
105
Figure 4.34 3D model of Axle spacer (Mechanical Design-2)
Figure 4.35 Linear guide – caliper mounting bracket
106
Figure 4.36 3D model of linear guide- caliper mounting bracket
(Mechanical Design -2)
Figure 4.37 3D Assembly drawing (Mechanical Design -2)
107
1. ‘C’ clamp, 2. Linear guide, 3. Axle spacer (Design-1)
Figure 4.38 2D Assembly drawing (Mechanical Design -2)
Three dimensional (3D) and two dimensional (2D) assembly
drawings of mechanical design-2 are given in Figures 4.37 and 4.38
4.5.7
Finding out Piston Stroke
The existing brake pad movement is about 2mm. But the caliper
halves are fixed about 4mm apart into the C-clamp. Hence the stroke of the
piston is to accommodate this difference in the pad movement to make the
108
effective brake pad contact with brake disc. This can be achieved by any one
method as follows:
Increasing the displacement/diameter of master cylinder.
Increasing the thickness of brake pad.
Fixing the caliper halves 2mm apart.
Increasing the thickness of disc by 2 mm.
The caliper stroke is determined and compensated for effective
braking, with a simple fluid volume calculation i.e. the volume of brake fluid
displaced at master cylinder is equal to volume of fluid occupied in the caliper
cylinder due to the movement of brake pad. Figure 4.39 shows the modified
assembly of disc and caliper in a line sketch.
The actual designed displacement of caliper piston is calculated as
follows:
Caliper piston diameter = 32 mm
Master cylinder stroke = 15 mm
Master cylinder diameter = 17 mm
Volume of brake fluid displaced per master cylinder full stroke (Vc) = (Area
of master cylinder X Stroke of master cylinder)
Vc = (3.14*8.52) * (15) = 3404.701 mm3
(4.4)
Volume of fluid displaced per caliper caliper (V2):
Vc/2 = 1702.3505 mm3
(4.5)
Brake pad movement per stroke (Xp) = (V2 / Area of Caliper cylinder)
(4.6)
Xp = 1702.3505 / (3.14*162) = 2.116 mm
109
Not in scale
Figure 4.39 Modified assembly of disc and caliper in line sketch
The additional stroke required for the caliper piston by changing
master cylinder stroke/diameter makes tedious process and requires a lot of
reworks on master cylinder piston, bush, and check valve. Hence it is decided
that the brake pad thickness is modified to additional 2mm. It is also possible
to make the ‘C’ clamp in such a manner that there is a gap of 2 mm between
the clamp and the brake disc and another alternative is a thicker disc. But both
methods lead to bring the disc and the caliper halves closer. Hence there may
be a chance of mechanical contact between the brake disc and the caliper
halves.
4.6
WHEEL HUB DESIGN
GAP BETWEEN DISC
AND HUB
Figure 4.40 Rear wheel hub
110
The gap between the disc and the hub is 15mm as shown in Figure
4.40. But the linear movement of caliper requires at least 35 mm to
accommodate caliper LH part travel between the hub and the disc. To make
this possible the following modifications are required in the existing wheel
hub:
Wheel hub/ rim – facing
Additional spacer
New Axle bush
4.6.1
Wheel Hub Modification
The wheel hub before and after modification work, is shown in
Figure 4.41. About 20 mm facing operation was performed on wheel hub.
MODIFIED HUB
FACE
Figure 4.41 Wheel hub modifications
After modification, the hub face is drilled and tapped for the same
pitch circle diameter (PCD-125mm) to provide mounting for the spacer. The
original wheel hub setup is retained after the facing operation.
111
4.6.2
Wheel Hub Spacer
A new spacer connected with wheel hub is designed to hold the
disc and to provide space for caliper movement. The modified wheel hub is
shown in Figure 4.42.
40 mm GAP FOR CALIPER
TRAVEL
Figure 4.42 Wheel hub spacer
4.6.3
Disc Design
A new disc is designed to provide various disc radii. The existing
disc is having only 20mm face width. Hence a new disc is designed and
manufactured to provide various disc radii based on the pillion load on the
two - wheeler. Figures 4.43 and 4.44 show the existing and the new disc
respectively.
112
Figure 4.43 Existing disc
Figure 4.44 Modified disc
4.7
CONSTRUCTION
AND
OPERATING
METHOD
OF
CALIPER
As the brake pad is attached with caliper, the pad cannot be moved
separately. Hence it is decided to move caliper to get various effective disc
radii. The existing caliper has two pistons. Both sides of the brake disc have
one piston. If the caliper is moved downward to decrease the effective radius
of disc, it would hit the brake disc as well as the wheel hub. In order to avoid
113
the hitting of the caliper with the brake disc and the wheel hub, it is made into
two halves (bifurcated into two halves) and internal brake fluid line is
blocked. The width of the wheel hub is reduced to accommodate new caliper
housing and to prevent the hitting of new caliper housing and the wheel hub,
when the effective disc radius is reduced. An external brake line is provided
to the caliper. In this design, the nuts that are used to connect the linear guide
bracket and caliper, are loosened and the entire assembly is moved to set the
required effective disc radius. After setting the required effective disc radius,
the nut is tightened. Figures 4.45 and 4.46 show the modified rear brake
assembly of view-1 and view-2 respectively.
LINEAR GUIDE
BRACKET
Figure 4.45 Modified rear brake assembly (view-1)
114
Figure 4.46 Modified rear brake assembly (view-2)
4.8
DISADVANTAGES OF DISC BRAKE DESIGN- 2
Brake force is not effective because the entire C-clamp unit
starts to bend when the brake is applied. Hence the required
amount of braking force is not developed due to bending of Cclamp.
It is also found that the thickness of C-clamp does not withstand
the bending effect. Hence the thickness of C-clamp may be
increased.
115
The effective disc radius could not be possible to set exact value
since there is no proper guide way. (Both the sides can be
moved independently because of bolt and nut mechanism.)
4.9
DISC BRAKE DESIGN-3
When the brake is applied, the entire caliper unit starts bending.
The amount of brake pressure developed inside the caliper cylinder is less
because of the caliper bending. Hence the braking is not effective. In order to
sort out the problem in the mechanical brake design-2, a new design is
developed. In the new design, the thickness of the C-clamp is increased and a
proper guide way is provided to caliper for the smooth movement along the Y
direction (Perpendicular to the road surface). Figure 4.47 and Figure 4.48
show the caliper housing (C-clamp) with guide weighs 7kg. Figures 4.49 and
4.50 show the modified rear brake assembly of view-1 and view-2
respectively. ‘C’ clamp design is given in Appendix 11.
Figure 4.47 Caliper housing (C-clamp) design (view -1)
116
Figure 4.48 Caliper housing (C-clamp) design (view-2)
Figure 4.49 Rear disc brake assembly (view-1)
117
Caliper guide
‘C’ clamp
Caliper
Caliper
actuating
Shaft
Figure 4.50 Rear disc brake assembly (view-2)
Computer aided drafting (CAD) 2D and 3D drawings of parts are
used in mechanical design-3 as follows:
Axle spacer (Mechanical Design-3)
3D model of axle spacer (Mechanical Design-3)
Caliper guide (Mechanical design-3)
3D model of caliper guide (Mechanical design-3)
Caliper housing (Mechanical design-3)
3D model of caliper housing (Mechanical design-3)
Support member of stepper motor (Mechanical design-3)
3D model of support member of stepper motor (Mechanical
design-3)
The CAD drawings which are drawn using PRO-E modeling
software are shown in Figures 4.51 to 4.60.
119
Figure 4.52 3D model of axle spacer (Mechanical Design-3)
Figure 4.53 Caliper guide (Mechanical design-3)
120
Figure 4.54 3D model of caliper guide (Mechanical design-3)
Figure 4.55 Caliper housing (Mechanical design-3)
121
Figure 4.56 3D model of caliper housing (Mechanical design-3
mass = 5kg)
Figure 4.57 Support member of stepper motor (Mechanical design-3)
122
Figure 4.58 3D model of support member of stepper motor (Mechanical
design-3)
123
Figure 4.59 Assembly drawing (3D-Mechanical design-3)
124
Figure 4.60 Assembly drawing (2D-Mechanical design-3)
1.
Caliper housing
2. Caliper guide
3. Axle spacer
4. Support member of stepper motor
5. Stepper motor
125
4.10
ADVANTAGES OF DISC BRAKE DESIGN- 3
Design-3 is more rigid. Hence ‘C’ clamp bending is reduced
that leads to effective braking.
Caliper pads can be placed at required effective radius as one
rotation of stepper motor moves the caliper 1.75 mm linearly.
4.11
DISADVANTAGE OF DISC BRAKE DESIGN- 3
Total weight of the mechanical design-3 is 10kg
4.12
SUMMARY
In this chapter, three different types of brake design and their
disadvantages are presented. The modification works on the motorcycle wheel
and existing disc brake components like caliper, disc and hydraulic brake line
are discussed for variable braking force system. A new design is incorporated
for holding the caliper halves. Out of three mechanical designs, design-3 is
selected as a suitable design for automating variable braking force system.