CHAPTER 4 MECHANICAL DESIGN OF DISC BRAKE 4.pdf · wheel. A layout of the proposed braking system is shown in Figure 4.1. The components of the system are listed below: Brake lever

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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.

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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.

Figure 4.2 Single Piston Floating Type Caliper- sports motorcycle

Caliper

Disc

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CaliperPiston

CaliperPiston

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.

Figure 4.3 Basic master cylinder when brake is applied

Figure 4.4 Basic master cylinder when brake is released

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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

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cylinder inner diameter is 17mm. So it may look like a piston in the top view.

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.

Figure 4.6 Master cylinder used in the VBF system

Lever Metal bush Chamber

Caliper Piston

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(a) Existing master cylinder (b) Master cylinder after removing with fluid reservoir fluid reservoir

(c) Hexagonal metal bush is fixed (d) Final modified master cylinder in pressure chamber

Figure 4.7 Modification works on master cylinder

Figure 4.8 Assembly drawing (line sketch) of the modified master

cylinder

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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 0.35 – 5 .2 MN /m2

Maximum rubbing speed 24 m/s Maximum temperature 550°C

Maximum continuous temp 250°C

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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

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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 (b) Brake disc

(c) Wheel with disc holder (d) Wheel with brake disc

Figure 4.10 Assembly of the disc to the wheel hub

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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

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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

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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.

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Figure 4.14 Layout of the variable braking force system without pillion

rider

Figure 4.15 Caliper position when the motorcycle is loaded

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Figure 4.16 Layout of the VBF system with the pillion rider

Figure 4.17 VBF System for unloaded Figure 4.18 VBF System for loaded motorcycle 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

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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.

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

Master cylinder

Reservoir

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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

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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,

ABBD

2sin (4.1)

BD = dr (4.2)

A0AB (4.3)

2sin0Adr (4.4)

Where, = 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

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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

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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

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Blocked oil holes

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.

Figure 4.24 Brake caliper

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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)

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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 = cc dd2

4P (4.5)

Where, P = Brake fluid force.

cd = Caliper bolt diameter.

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Compressive stress due to bending moment at each bolt = 3cd23220P (4.6)

Allowable compressive stress of the bolts [ cb] = 1550 N/mm2

3ccc

cb d23220P

dd24P][ (4.7)

P = 4986 N (Brake fluid force)

7mmdc

Holes are drilled only in diameter basis.

Figure 4.28 Brake fluid pressure distributing area

4.5.5 Modification of Hydraulic Circuit

Figure 4.29 Oil passage in normal caliper

LH Oil Hole

RH Oil

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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

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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.

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.

‘T’ Joints

‘C’ Clamp

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LINEAR GUIDEBRACKET

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)

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Figure 4.34 3D model of Axle spacer (Mechanical Design-2)

Figure 4.35 Linear guide – caliper mounting bracket

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Figure 4.36 3D model of linear guide- caliper mounting bracket

(Mechanical Design -2)

Figure 4.37 3D Assembly drawing (Mechanical Design -2)

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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

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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

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GAP BETWEEN DISC AND HUB

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

Figure 4.40 Rear wheel hub

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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.

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.

MODIFIED HUB FACE

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40 mm GAP FOR CALIPER TRAVEL

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.

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.

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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

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LINEAR GUIDE BRACKET

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.

Figure 4.45 Modified rear brake assembly (view-1)

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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 C-

clamp.

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.

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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)

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Figure 4.48 Caliper housing (C-clamp) design (view-2)

Figure 4.49 Rear disc brake assembly (view-1)

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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.

Caliper guide

‘C’ clamp

Caliper

CaliperactuatingShaft

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Figure 4.52 3D model of axle spacer (Mechanical Design-3)

Figure 4.53 Caliper guide (Mechanical design-3)

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Figure 4.54 3D model of caliper guide (Mechanical design-3)

Figure 4.55 Caliper housing (Mechanical design-3)

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Figure 4.56 3D model of caliper housing (Mechanical design-3 mass = 5kg)

Figure 4.57 Support member of stepper motor (Mechanical design-3)

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Figure 4.58 3D model of support member of stepper motor (Mechanical design-3)

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Figure 4.59 Assembly drawing (3D-Mechanical design-3)

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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

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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.