DESIGN & FABRICATION OF TWO SPEED VARIABLE

TRANSMISSION GEARBOX

A PROJECT REPORT

Submitted by

G.ARAVIND (312313114021)

S.ARUN MOZHI THEVAN (3123131140)

In partial fulfilment for the award of the degree

Of

BACHELOR OF ENGINEERING

IN

MECHANICAL ENGINEERING

St. JOSEPH'S COLLEGE OF ENGINEERING

CHENNAI 600 119

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ANNA UNIVERSITY: CHENNAI 600 025

APRIL 2016

BONAFIDE CERTIFICATE

DEPARTMENT OF MECHANICAL ENGINEERING

Certified that this project report “DESIGN AND FABRICATION OF TWO SPEED

VARIABLE TRANSMISSION GEARBOX” is the bonafide work of “G.ARAVIND

(312313114021) & S.ARUN MOZHI THEVAN (3123131140)” who carried out

the project work under my supervision.

SIGNATURE SIGNATURE

Dr S.ARIVAZHAGAN M.E. Ph.D., Mr.M.MUNINATHA KOTA M.E

HEAD OF DEPARTMENT ASSISTANT PROFESSOR

Department of Mechanical Engineering, Department of Mechanical Engineering,

St. Joseph’s College of Engineering., St. Joseph’s College of Engineering,

Jeppiaar Nagar, Jeppiaar Nagar,

Chennai-600119 Chennai-600119.

Submitted for project viva-Voice held on ________________

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CERTIFICATE OF EVALUATION

COLLEGE NAME: ST JOSEPH’S COLLEGE OF ENGINEERING

BRANCH: MECHANICAL ENGINEERING

SEMESTER: VI

S. No. Name of the Students who have

done the project Title of the Project

Name of the

Supervisor with

designation

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2

G.ARAVIND

S.ARUNMOZHITHEVAN

DESIGN AND

FABRICATION

OF TWO SPEED

VARIABLE

TRANSMISSION

GEARBOX

MR.M.MUNINATHA

KOTA M.E

ASSISTANT

PROFESSOR

Department of Mechanical

Engineering.

This report of project work submitted by the above students in partial

fulfilment for the award of Bachelor of Mechanical Engineering Degree in Anna

University were evaluated and conformed to be reports of the work done by the

above students and then evaluated.

Submitted for UNIVERSITY VIVA EXAMINATION held on …………………

INTERNAL EXAMINER EXTERNAL EXAMINER

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ACKNOWLEDGEMENTS

We would like to express our sincere thanks and gratitude to our college

Chairman Col Dr THIRU JEPPIAAR M.A., B.L., Ph.D., Managing Director Dr

BABU MANOHARAN M.A, BL, Ph.D. Director Mr JAIKUMAR

CHRISTHURAJAN B.E, M.B.A.

Principal Dr VADDI SESHAGIRI RAO M.E., Ph.D., F.I.E. for giving us this

opportunity to carry out this project.

We extend our thanks to the Head of the Department of Mechanical

Engineering, Dr S.ARIVAZHAGAN M.E., Ph.D., for his valuable support and

cooperation.

We also thank MR.M.MUNINATHAN KOTA M.E, Lecturer-Department

of Mechanical Engineering for his guidance and timely suggestions which helped us

to complete this project.

Finally, Mr BALAMURUGAN M.E,Ph.d of Mechanical Engineering for

his constant support and guidance throughout the process of the project.

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TABLE OF CONTENTS

TITLE PAGE NO

Abstract 7

1 Introduction 8

2 Literature review 9

3 Description of equipment 11

3.1 Gearbox 11

3.2 Spur gears 11

3.3 Shafts 15

3.4 D.C motor 17

4 Design and drawing 18

4.1 Calculation for gears 19

4.2 Drawing of sliding mesh gearbox 20

4.3 3D Modeling 21

5 Working principle 22

6 Merits & demerits 23

7 Applications 24

8 Material Considerations 24

9 Conclusion 27

10 Bibliography 28

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LIST OF FIGURES1. Figure 1 11

2. Figure 2 16

3. Figure 3 20

4. Figure 4 22

5. figure 5 17

LIST OF TABLES1 Table 1 25

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ABSTRACT

Conventional gearboxes are capable of varying a given input speed. It is

achieved by meshing of gears in various gear ratios. The torque values are different

during different gear ratios. Hybrid gearboxes are capable of transmitting various

torque levels at the same gear ratio. They have a high torque producing capacity

compared to a conventional gearbox. These gearboxes have provisions for several

inputs and several outputs, unlike one input and one output of a conventional

gearbox. It allows the choice of varied speeds to the inputs.

These gearboxes can be used in a lot of practical applications. As they have

very high loading capacities, they can be used in off-road, commercial vehicles,

military vehicles and other specialty vehicles. They can also be used in cranes,

pumps, tractors, lawn mowers etc. Its most important application is that it can be

used in a hybrid car.

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CHAPTER I

INTRODUCTION

The main objective of our project is to create a gearbox with several inputs and

a single output. For this purpose, we have selected two input shafts and one output

shaft. It is a two speed sliding mesh gear box, controlled by a dog clutch for the

required sliding mechanism. It is simple, effective and a cost efficient design.

It is a hand feed gearbox. Adequate provisions have been given to adapt a

motor or an engine to it. It is designed with utter care to withstand high loading and

has a high factor of safety. The gearbox was fabricated with high accuracy milling

machines and tools with good engineering practices.

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CHAPTER II

LITERATURE REVIEW

TRANSMISSION  An assembly of parts including the speed-changing gears and the propeller

shaft by which the power is transmitted from an engine to a live axle. Often

transmission refers simply to the gearbox that uses gears and gear trains to

provide speed and torque conversions from a rotating power source to another

device.

The most common use is in motor vehicles, where the transmission adapts the

output of the internal combustion engine to the drive wheels. Such engines need to

operate at a relatively high rotational speed, which is inappropriate for starting,

stopping, and slower travel. The transmission reduces the higher engine speed to the

slower wheel speed, increasing torque in the process. Transmissions are also used on

pedal bicycles, fixed machines, and where different rotational speeds and torques are

adapted.

Often, a transmission has multiple gear ratios (or simply "gears"), with the

ability to switch between them as speed varies. This switching may be done manually

(by the operator), or automatically. Directional (forward and reverse) control may

also be provided. Single ratio transmissions also exist, which simply change the

speed and torque (and sometimes direction) of motor output.

In motor vehicles, the transmission generally is connected to the

engine crankshaft via a flywheel and/or clutch and/or fluid coupling, partly because

internal combustion engines cannot run below a particular speed. The output of the

transmission is transmitted via driveshaft to one or more differentials, which in turn,

drive the wheels. While a differential may also provide gear reduction, its primary

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purpose is to permit the wheels at either end of an axle to rotate at different speeds

(essential to avoid wheel slippage on turns) as it changes the direction of rotation.

Early transmissions included the right-angle drives and other gearing in

windmills, horse-powered devices, and steam engines, in support of pumping,

milling, and hoisting.

Most modern gearboxes are used to increase torque while reducing the speed

of a prime mover output shaft (e.g. a motor crankshaft). This means that the output

shaft of a gearbox rotates at a slower rate than the input shaft, and this reduction in

speed produces a mechanical advantage, increasing torque. A gearbox can be set up

to do the opposite and provide an increase in shaft speed with a reduction of torque.

Some of the simplest gearboxes merely change the physical rotational direction of

power transmission.

Many typical automobile transmissions include the ability to select one of

several different gear ratios. In this case, most of the gear ratios (often simply called

"gears") are used to slow down the output speed of the engine and increase torque.

However, the highest gears may be "overdrive" types that increase the output speed.

USES:

Gearboxes have found use in a wide variety of different—often stationary—

applications, such as wind turbines.

Transmissions are also used

in agricultural, industrial, construction, mining and automotive equipment. In

addition to ordinary transmission equipped with gears, such equipment makes

extensive use of the hydrostatic drive and electrical.

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Assembly of parts including the speed changing gears and the propeller shaft

by which the power is transmitted from an engine to a live axle. Often

transmission refers simply to the gearbox that uses gears and gear trains to

provide speed and torque conversions from a rotating power source to another

device.

CHAPTER III

DESCRIPTION OF EQUIPMENTS3.1 GEARBOX

(Figure 1)

3.2 SPUR GEARS

Spur gears or straight-cut gears are the simplest type of gear. They consist of a

cylinder or disk with the teeth projecting radially, and although they are not straight-

sided in form (they are usually of special form to achieve constant drive ratio,

mainly involute), the edge of each tooth is straight and aligned parallel to the axis of

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rotation. These gears can be meshed together correctly only if they are fitted to

parallel shafts.

Number of teeth, N  

How many teeth a gear has, an integer. In the case of worms, it is the number

of thread starts that the worm has.

Gear, wheel 

The larger of two interacting gears or a gear on its own.

Pinion  

The smaller of two interacting gears.

Path of contact  

Path followed by the point of contact between two meshing gear teeth.

Line of action, pressure line  

Line along which the force between two meshing gear teeth is directed. It has

the same direction as the force vector. In general, the line of action changes

from moment to moment during the period of engagement of a pair of teeth.

For involute gears, however, the tooth-to-tooth force is always directed along

the same line—that is, the line of action is constant. This implies that for

involute gears the path of contact is also a straight line, coincident with the line

of action—as is indeed the case.

Axis  

Axis of revolution of the gear; center line of the shaft.

Pitch point 

Point where the line of action crosses a line joining the two gear axes.

Pitch circle, pitch line  

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Circle centered on and perpendicular to the axis, and passing through the pitch

point. A predefined diametric position on the gear where the circular tooth

thickness, pressure angle and helix angles are defined.

Pitch diameter, d  

A predefined diametric position on the gear where the circular tooth thickness,

pressure angle and helix angles are defined. The standard pitch diameter is a

basic dimension and cannot be measured, but is a location where other

measurements are made. Its value is based on the number of teeth, the normal

module (or normal diametric pitch), and the helix angle. It is calculated as:

 in metric units or   in imperial units.

Module or modulus, m  

Since it is impractical to calculate circular pitch with irrational numbers,

mechanical engineers usually use a scaling factor that replaces it with a regular

value instead. This is known as the module or modulus of the wheel and is

simply defined as

where m is the module and p the circular pitch. The units of module are

customarily millimeters; an English Module is sometimes used with the units

of inches. When the diametric pitch, DP, is in English units,

 in conventional metric units.

The distance between the two axis becomes

where a is the axis distance, z1 and z2 are the number of cogs (teeth) for each of

the two wheels (gears). These numbers (or at least one of them) is often chosen

among primes to create an even contact between every cog of both wheels, and

thereby avoid unnecessary wear and damage. An even uniform gear wear is

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achieved by ensuring the tooth counts of the two gears meshing together

are relatively prime to each other; this occurs when the greatest common

divisor (GCD) of each gear tooth count equals 1, e.g. GCD(16,25)=1; If a 1:1

gear ratio is desired a relatively prime gear may be inserted in between the two

gears; this maintains the 1:1 ratio but reverses the gear direction; a second

relatively prime gear could also be inserted to restore the original rotational

direction while maintaining uniform wear with all 4 gears in this case.

Mechanic engineers at least in continental Europe use the module instead of

circular pitch. The module, just like the circular pitch, can be used for all types

of cogs, not just evolving based straight cogs.

Operating pitch diameters  

Diameters determined from the number of teeth and the center distance at

which gears operation.

Pitch surface  

In cylindrical gears, cylinder formed by projecting a pitch circle in the axial

direction. More generally, the surface formed by the sum of all the pitch

circles as one moves along the axis. For bevel gears it is a cone.

Angle of action  

Angle with vertex at the gear center, one leg on the point where mating teeth

first make contact, the other leg on the point where they disengage.

Addendum

Radial distance from the pitch surface to the outermost point of the

tooth. 

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Dedendum  

Radial distance from the depth of the tooth trough to the pitch

surface. 

Whole depth  

The distance from the top of the tooth to the root; it is equal to addendum plus

dedendum or to working depth plus clearance.

Diametric pitch

D

Ratio of the number of teeth to the pitch diameter. Could be measured in teeth

per inch or teeth per centimeter, but conventionally has units of per inch of

diameter. Where the module, m, is in metric units

 In English units.

3.3 SHAFTS

Shafts are rotating members that transmit power through them. They are

splined or slotted for a properly transmitting power and also acts as a coupling

medium.

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(Figure 2)

Shaft

Spur gear SHAFT LOCK RING

3.4 D.C MOTOR SPECIFICATIONS

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300 RPM at 12V D.C motor with Metal Gearbox

18000 RPM base motor

6mm shaft diameter

Gearbox diameter: 37 mm.

Motor Diameter: 28.5 mm

Length 63 mm without shaft

Shaft length 15mm

300gm weight

10kgcm torque

No-load current = 800 mA(Max), Load current = upto 9.5

A(Max)

CHAPTER IV

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DESIGN AND DRAWING

4.1 DESIGN CALCULATIONS

Using Buckingham’s and Lewis Equations:

1) Selection of Material:

Gears, pinion and shafts are made of mild steel.

2) Calculation of Transmissibility Ratio:

I = (Z2/Z1) = (30/20) = 1.5

3) Calculation of tangential load:

Ft = (K0*103*W) / Vm

K0 = 1.5 (for median life)

= (1.5*750)/Vm

Vm = (П d1N1)/60 = (ПmZ1N1)/ (60*1000)

= (П*m*20*300)/ (60*1000)

Vm = 0.314m

Which implies,

Ft = (1.5*750)/Vm

= (3582.8)/m

4) Calculation of initial dynamic load:

Fd = Ft * Cv

Cv = (6 + Vm)/ 6 = 3 (Assume Vm = 12)

Fd = (3*3582.8)/m = 10748.4/m

5) Calculation of Beam Strength:

b= 10m

FB= [σb] by*Pa = 720*10*m*y*П*m

Y = 0.154 – (0.912/Z) (20 ̊ involute)

Y=0.1084

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FB = 2450.70 m2

6) Calculation of module:

2450.70m2 = (10748.4)/m

m= 1.6 ᴝ 2mm (standard)

7) Revaluation of Beam strength:

FB = 98028 N

Ft = 1791.4 N

8) Calculation of Dynamic load:

Vm = 0.628mm

d1 = mZ1

= 2*20= 40mm

Fd = 1796.17 N

Fs > Fd (Hence design is safe)

Fw = d1*Q*Kb

= 20*1.2*1.1*20

= 528 N

Q = 2(1.5)/ (1.5+1) = 1.2

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(Figure 3)

Drawing of sliding mesh gearbox

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3-D MODELLING

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IMAGES ATTACHED

(figure4)

CHAPTER V

WORKING PRINCIPLE The spur gears in the gearbox having same pitch mesh against each other. The speed

and torque produced depend upon the gear ratios. The input power of the gearbox is

usually constant, thus the output power too is constant.

The gear ratios are changed by changing the gears using a gear shifting mechanism

by the use of a dog clutch. The dog clutch is connected to a handle or knob for the

gear selection.

CHAPTER VI

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MERITS & DEMERITS

MERITS

Quicker operation.

Easy transmission.

Low cost machine.

It is used for carrying out multiple operations in a single machine.

Both Forward and reverse speeds can be obtained

DEMERITS

Suitable only for small purpose applications.

Heavy weight(around kgs)

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CHAPTER VII

APPLICATIONS

Used in automobile workshops for drilling carburetor holes .

Used in small scale industries that work on a tight budget.

In robots for locomotion

For performing the operations in huge parts which cannot be done in ordinary

machines.

In such places where frequent changes in operation are required.

CHAPTER VIII

MATERIAL CONSIDERATIONS

FACTORS DETERMINING THE CHOICE OF MATERIALSThe various factors which determine the choice of material are discussed

below.

1. Properties:

The material selected must posses the necessary properties for the proposed

application. The various requirements to be satisfied

Can be weight, surface finish, rigidity, ability to withstand environmental attack

from chemicals, service life, reliability etc.

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The following four types of principle properties of materials decisively affect

their selection

a. Physical

b. Mechanical

c. From manufacturing point of view

d. Chemical

The various physical properties concerned are melting point, thermal

Conductivity, specific heat, coefficient of thermal expansion, specific gravity,

electrical conductivity, magnetic purposes etc.

The various Mechanical properties Concerned are strength in tensile,

Compressive shear, bending, torsional and buckling load, fatigue resistance, impact

resistance, eleastic limit, endurance limit, and modulus of elasticity, hardness, wear

resistance and sliding properties.

The various properties concerned from the manufacturing point of view are,

Cast ability

Weld ability

Surface properties

Shrinkage

Deep drawing etc.

2. MANUFACTURING COST:

Sometimes the demand for lowest possible manufacturing cost or surface qualities

obtainable by the application of suitable coating substances may demand the use of

special materials.

3. QUALITY REQUIRED:

This generally affects the manufacturing process and ultimately the material.

For example, it would never be desirable to go casting of a less number of

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components which can be fabricated much more economically by welding or hand

forging the steel.

4. AVAILABILITY OF MATERIAL:

Some materials may be scarce or in short supply; it then becomes obligatory

for the designer to use some other material which may not be a perfect substitute for

the material designed. The delivery of materials and the delivery date of product

should also be kept in mind.

5. SPACE CONSIDERATION:

Sometimes high strength materials have to be selected because the forces involved

are high. In such cases it is of extreme importance to ensure that the space

optimization is not compromised on in the venture to impart high strength and

rigidity.

6. COST:

Factors like scrap utilization, appearance, and non-maintenance of the

designed part are involved in the selection of proper materials.

(Table 1)

S.No DESCIRPTION QTY Material

1 Spur Gears 4 Mild Steel

2 Shafts 3 Mild Steel

3 D.C Motor 1

4 Dog Clutch 1 C.I

5 Gear Box 200mm*200mm Mild Steel

6 Shaft lock rings 6 Mild Steel

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CHAPTER IX

CONCLUSION

This project is made with pre planning, that it provides flexibility in operation.

Smoother and easy handling operation by the principle of “Gear Mechanics”

The comparative gain that can be accomplished is the utilization of roller bar.

This innovation has made the more desirable

This project “Design and fabrication of Hybrid Gearbox” is designed with the

hope that it is very much economical and help full to many industries and workshops

This project helped us to know the periodic steps in completing a project work.

Thus we have completed the project successfully.

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BIBLIOGRAPHY

1. Design data book -P.S.G.Tech.

2. Automobile Engineering - Dr. Kirpal Sen

3. Machine tool design handbook –Central machine tool Institute,

Bangalore.

4. Strength of Materials -R.S.Kurmi

5. Manufaturing Technology -M.Haslehurst.

6.Design of machine elements- R.s.kurmi

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