SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015

ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 33

Design and Study of Four Speed Sliding Mesh Gear Box

Atthuru Manikanta Reddy1, Aakash.k2

12

Department of Mechanical Engineering, R.M.K. Engineering college, Anna University, Chennai, India

ABSTRACT: This Paper deals with understanding

of the gear transmission system principles with its

design and working. Different types of gears are

used in automobiles. Gears have teeth which mesh

with each other to transmit the drive. A detailed

CAD(Computer-aided design) model has also been

developed according to the theoretical calculations

to validate the design and an brief study of the four

speed sliding mesh gear box.

Keywords -Gear Transmission, Meshing, CAD,

Drive and Automobiles

I.INTRODUCTION Gearbox is enclosed system of assembled gears that

transmits mechanical energy from a prime mover to

an output device. A gearbox can also change the

speed, direction, or torque of mechanical energy.

Gear box is a device placed between the clutch and

propeller shaft. It allows the engine to run at

different speeds relative to road vehicles, so as to

maintain its power and regulates the torque. The

vehicle requires high torque when climbing hills

and when starting, even though they are performed

at low speeds .On the other hand, when the vehicles

are running at high speeds on the road level, high

torque is not required because of momentum.

PURPOSE OF GEAR BOX An automobile is able to provide varying speed

and torque through its gear box. Various functions

of a gear box are listed below To provide high

torque at the time of starting, vehicle acceleration,

climbing.To provide more forward speeds by

providing more than one gear ratios. In modern

cars, four to five forward gears and reverse gear is

provided. For given engine speed, higher speed can

be obtained by running in higher (4th and 5th)

gears.To provide a reverse gear for driving the

vehicle in reverse direction and To give different

speeds and torques. To get high acceleration from

rest .To drive vehicle at low speeds. In the engine

running conditions the vehicle can be stopped by

changing the gear to neutral condition without

applying brake.

II. WORKING PRINCIPLE OF SLIDING

MESH GEARBOX

It is simplest type of gear box out of the available

gear boxes. In this type of gear box, gears are

changed by sliding one gear on the other. This gear

box consists of three shafts; main shaft, clutch shaft

and a counter shaft. In a four speed gear box

(which includes one reverse gear), the counter shaft

has four gears which are rigidly connected to it.

Clutch shaft has one gear and main shaft has two

gears. The two gears on the main shaft can slide in

the horizontal direction along the splines of the

main shaft. However, the gears on the counter shaft

cannot slide. The clutch gear is rigidly fixed to the

clutch shaft. It is always connected to the counter

shaft drive gear.

The two gears on the main shaft can be slide

by the shifter yoke by operating the shift lever (not

shown in Figures). These two gears are second gear

and low/reverse gear respectively. These gears can

be meshed with corresponding gears on the counter

shaft with the help of shifter yoke and shift lever.

Shift lever is operated by hand in four wheelers for

changing the gears. A reverse idler gear is mounted

on another (third) shaft and is always in mesh with

reverse gear on counter shaft.

Neutral position:

The above figure shows sliding mesh gear box

in neutral position. In this position, the engine is in

running condition, clutch remains engaged and

clutch gear drives the counter shaft drive gear. The

direction of rotation of countershaft is opposite to

that of clutch shaft. In this position Ist, IInd and

IIIrd and reverse gears are free. Thus, main

(transmission) shaft does not rotate and automobile

wheels do not rotate. So vehicle remains stationary

First Gear:

When first gear position is selected by the

shift lever, first gear (large gear) on the main shaft

slides and is connected to first gear on the

countershaft. The direction of rotation of main

SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015

ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 34

shaft is same as that of clutch shaft. In first gear,

small gear of counter shaft meshes with larger gear

on main shaft, speed reduction in the ratio 3: 1

(approximate) is obtained.

Second Gear:

When second gear is selected by the shift

lever, second gear on counter shaft meshes with

second gear (small gear on main shaft) on the main

shaft. The direction of main shaft is same as that of

clutch shaft. Speed reduction of the order of 2: 1 is

obtained in second gear.

Third Gear

In third gear, the main shaft is slides axially

towards the clutch shaft so that main shaft is

directly connected to the clutch shaft. In this

position, the main shaft rotates at the speed of

clutch shaft. Thus, a speed ratio of 1: 1 is obtained.

It can be noted that the clutch gear is directly

connected to engine crankshaft and main shaft is

connected to the wheels through propeller shaft.

Reverse Gear

When the shift lever is operated to engage the

reverse gear, the larger (reverse) gear of the main

shaft meshes with the reverse idler gear. Reverse

idler gear is always connected to reverse gear on

counter shaft. The reverse idler gear between

counter shaft reverse gear and main shaft larger

gear changes the direction of rotation of main shaft.

Thus, the direction of main shaft becomes opposite

to that of clutch shaft. Therefore, wheels of the

automobile start moving in backward direction.

(Note: Countershaft is also known as lay shaft.)

III . COMPONENTS USED IN GEAR BOX

Some of the components used in gear box are:

- Shaft

- Bearing

- Selector Forks

Shafts:

Fig 2.1 Drive Shaft

A drive shaft is a mechanical component for

transmitting torque and rotation, usually used to

connect other components of a drive train that

cannot be connected directly because of distance or

the need to allow for relative movement between

them. Drive shafts are carriers of torque: they are

subject to torsion and shear stress, equivalent to the

difference between the input torque and the load.

They must therefore be strong enough to bear the

stress, whilst avoiding too much additional Weight

as that would in turn increase their inertia.

Bearings:

Fig 2.2 Bearings

Bearings are highly engineered, precision-made

components that enable machinery to move at

extremely high speeds and carry remarkable loads

with ease and efficiency. It must be able to offer

high precision, reliability and durability, as well as

the ability to rotate at high speeds with minimal

noise and vibration. Bearings are found in

applications ranging from automobiles, airplanes,

computers, construction equipment, machine tools,

DVD players, refrigerators and ceiling fans. If

something twists, turns or moves, it probably has a

bearing in it.

Selector fork:

Fig 2.3 Selector Fork

The shifter fork and fork rods have a

mechanism using a plunger with a ball in it and is

supported with a slide able ball bearing. The detent

mechanisms give the driver distinctive detent

SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015

ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 35

feeling and the sliding ball bearings help reduce the

shift lever operating force. All shifter forks are

made of aluminium die casting and the shifter arm

shaft is formed as a hollow type to minimize the

overall weight of the transmission. Gear double

meshing is prevented by a mechanism that uses

interlock blocks. The select return mechanism

(which returns the selector lever to the neutral

position) uses a U shaped leaf spring.

IV . DESIGN CALCULATION OF GEAR BOX

For design calculation of the spur gear,

Power : 3kw

Speed (N) : 750 rpm

Speed ratio : 2

STEP-1

TO FIND THE GEAR RATIO:

i =2 (assumed); Hence, = 2;

= 375 rpm

STEP-2

TO SELECT THE MATERIAL

For gear and pinion, let us select the

same material. i.e., C45 (STEEL)

STEP-3

INITIAL DESIGN TORQUE

[ ] = [ ]. k.

[ ] = = 389.68 kgf.cm

Assume, k. =1.3;

[ ] = 50.6 X N.mm

STEP -4

TO FIND BENDING AND CRUSHING

SRESSES

FROM DESIGN DATA BOOK

Bending stress: 140

Crushing stress: 500

STEP-5

TO FIND MINUIMUM CENTRE DISTANCE

a (i+1) Assume, = 0.3

a 88 mm.

STEP -6

TO FIND THE MODULE

m 1.26

Assume, =10; = 10; = 20 and

y = 0.3890

m 3

STEP – 7

TO FIND THE NUMBER OF TEETH

= 33

= 22

STEP – 8

TO FIND THE PITCH CIRCLE DIAMETER

= 52.5 mm

= 36 mm.

STEP – 9

TO FIND THE ACTUAL CENTER

DISTANCE

a = m. = 83.

Initial centre distance is less than

actual centre distance.

So, the design is feasible.

STEP -10

TO FIND THE FACE WIDTH

=

= 0.3(83)

b= 25 mm

STEP – 11

TO FIND THE ACTUAL DESIGN TORQUE

[ ] = [ ]. k.

SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015

ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 36

=

= 0.6

From design data book for , k=1.06

V =

V= 1.143

From design data book, for velocity 1.143m/s the

corresponding = 1.3

Therefore the actual design torque [Mt] (actual) =

50.6 X N.mm

STEP- 12:

TO CHECK THE INDUCED STRESSES:

Crushing stress =

= 92.5

The Crushing stress is less than the assumed

crushing stress and so the design is safe.

Bending stress =

= 68.8

The Bending stress is less than the assumed

bending stress and so the design is safe

STEP- 13:

TO FIND THE OTHER DIMENSIONS

Take ( ) = 1

BOTTOM CLEARENCE

C =0.25 (m)

= 0.25 (3)

= 0.75 mm

TIP DIAMETER

= ( + 2 ) m

= 72mm

= ( + 2 ) m

= 75 mm

ROOT DIAMETER

= ( - 2 ) m

= 60 mm

= ( - 2 ) m

= 93 mm.

STEP-14:

DESIGN CALCULATION FOR SHAFT, KEY

FOR SHAFT

50.6 X = ; [ = 140

; F.O.S = 2 (assumed)]

D = 14.76 mm

D (Std) = 15 mm diameter.

FOR KEY

For the calculated diameter the size of key chosen

is 6mm X 3mm X 100mm.

CAD MODELLING PHOTOGRAPHY:

Fig 4.1 Model diagram of Four Speed Sliding

Mesh Gear Box

SSRG International Journal of Mechanical Engineering (SSRG-IJME) – volume 2 Issue 6–June 2015

ISSN: 2348 – 8360 www.internationaljournalssrg.org Page 37

Fig 4.2 Design of Four Speed Sliding Mesh

Gear Box

V. CONCLUSION

The aim of our paper is that we have

undertaken in our engineering course is to improve

our practical knowledge in design and fabrication

of a particular component in a technical manner.

This improves not only our practical skills, but also

our various managing functions such as planning

the project design, fabrication and erection and cost

analysis etc. This paper is planned and completed

as per the schedule and regulations. And In

addition to that, by accomplishing this project of

“FOUR SPEED GEAR BOX” successfully we felt

that we have obtained enough knowledge regarding

this topic, with full of satisfaction and forward the

project to concerned.

REFERENCES

[1] A Text Book of Machine Design(S.I.Unit)2005

Edition By R.S.KHURMI & GHUPTA.

[2] Design of Spur Gears for Improved Efficiency by N.E.Anderson and S.H.Loewenthal

[3] Design of Spur Gear and Its tools by MR.A

.Gopichand

[4] Design of Machine Elements by V. B. Bhandari.

[5] Book of Gear design By William Alfred Tuplin.

[6] Dudleys Handbook of Practical Gear Design and

Manufacturing,Second Edition Hardcopy - 10 May

2012 By Stephan P.Radzevich.

[7] Wear of Spur and Helical Gears by Anders Flodin.

[8] Stress and deformations in involute Gears by Zeping Wei.

[9] Wikipedia (www.wikipedia.org)

[10] what-when-howInDepthTutorialsand

Informationhttp://what-when-

how.com/automobile/sliding-mesh-gearbox-automobile

[11] How Stuff Works(www.howstuffworks.com