4.

DRIVES
Contents:
 Introduction
 Methods of drive,
 Power transmission elements
 shaft Spindle and axle
 Belt-drive
 Pulleys
 Power transmitted by a belt, Chain drive,
Friction drive, Gear drive
 Introduction
 Need:
◦ Energy is required to drive the machines &
equipments for variety of applications.
◦ Available energy/power is required to be
transmitted to get desired motion &work. When
the power is transmitted from input to output
using mechanical elements is known as mechanical
power transmission. Mechanical elements like
friction disc, various type of belts, rope, chain,
gears, couplings etc. are used for power
transmission.
Introduction

◦ Every actuation or system need power or

motion to drive itself from source.
◦ Thus transmission of power from a
source(such as an engine or motor) through a
machine to an output actuation is needed to
do all machine tasks.
◦ This task can be achieved by different
methods of drives.
Different Terms of TPM
 Driving member
 Driven member
 Idler member
 Pulley
 Belt
 Chain
 Rope
 Gear
Methods of drive

Belts Used when the distance between

the shaft centers is LARGE

Used when the distance between the

Chains shaft centers is LARGE and no slip is
permitted

Gears Used when the distance between the

shaft centers is adequately less
 Belts and Belt Drive
What is Belt?
 A belt drive is a method of transferring rotary motion between
two shafts.
 A belt drive includes one pulley on each shaft and one or more
continuous belts over the two pulleys.
 The motion of the driving pulley is, generally, transferred to the
driven pulley via the friction between the belt and the pulley.
 Generally belt drives are friction drives.
 A Belt is a looped strip of flexible material, used to mechanically
link two or more rotating shafts.
 A pulley is a wheel with a groove between two flanges around its
circumference. Pulleys are keyed to the shafts.
 The speed of the driven shaft can be varied by varying the
diameter of the two pulleys.
TYPES OF BELTS
There are 4 types belts used in belt drives they are as follows:
Flat belts
shaft distance 5 to 10 meters, low
power, high speed, used for their
simplicity, low bending stress on pu
Round belts
smaller initial tension, absence of vibration
and noise, high power, shaft distance > 5
meters Diameter range is 3 to12 mm but usually from 4 to 8
mm.
V belts
shaft distance < 2 meters, high
power, moderate speed

Timing Belts
positive drives, precise, reliable
FLAT BELTS
 Flat belts find their widest application
where high
high--speed motion, rather than
power, is the main concern
concern..
 Flat belts are made from leather, woven
cotton, rubber, balata (wood gum)
gum)..
ROUND BELT
 Round belts are a circular cross section belt
designed to run in a pulley with a circular (or
near circular) groove
groove..
 The circular belt or rope is mostly used in the
factories where a great amount of power is to
be transmitted from one pulley to another, when
the two pulleys are more than 5 meters apart
apart..
‘V’ BELTS
 The strength of these belts is
obtained by reinforcements with
fibers like steel, polyester.
 V-belts are far superior to flat belts
at small center distances and high
reduction ratios.
 Require larger pulleys than flat belts
because of their greater thickness.
 The "V" shape of the belt tracks in a
mating groove (or sheave) in the
pulley, with the result that the belt
cannot slip off.
TIMING BELTS
 Also known as Toothed, Notch or Cog
belts are a positive transfer belt and can
track relative movement.
 These belts have teeth that fit into a
matching toothed pulley .
 They are often used to replace chains or
gears, reducing noise and avoiding the
lubrication bath or oiling system
requirement.
 Requires the least tension of all belt drives
and are among the most efficient.
 TYPES OF BELT DRIVES
BASED ON
ARRANGEMENT
Types of Belt drives based on the arrangement are

as follows

• OPEN BELT DRIVES

• CROSSED OR TWIST BELT DRIVES

• BELT DRIVE WITH IDLER PULLEYS

• COMPOUND BELT DRIVE

OPEN BELT DRIVE
 The Open belt drive is arranged
with shafts arranged parallel and
rotating in the same direction.
 The driver pulls the belt from one
side and delivers it to the other
side thus the tension in the one
side belt will be more than that in
the other side belt.  ( d 1  d 2) ( r 12  r 22)
 2x 
2 x
Length of the open belt=
d1 d2

r1  d 1
2 r2  d 2
2 X
 Length of an Open Belt Drive

Let the belt leaves the larger pulley at Eand Gand the smaller pulley at
Fand Has shown inThrough O1draw O2Mparallel to FE.
From the geometry of the figure, we find that O2Mwill be
perpendicular to O1E.
Let the angle MO2O1= αradians.
We know that the length of the belt,
CROSSED OR TWIST BELT DRIVE
 The crossed or twist belt drive
is used with shafts arranged
parallel and rotating in the
opposite directions.
 The tension in the tight side will
X
be more than the slack side. The
point where the belts rubs
against each other and there will r1  d 1 r2  d 2
be excessive wear and tear. 2 2
 To avoid this the shafts should
be placed at a maximum
distance of 20b where b is the
width of the belt and the speed
should be less than 15 m/s.
We have discussed in that in a cross belt drive, both the pulleys rotate in the
opposite
directions as shown inLet r1and r2= Radii of the larger and smaller pulleys,
x = Distance between the centres of two pulleys (i.e. O1O2), and
L= Total length of the belt.
Let the belt leaves the larger pulley at Eand Gand the smaller pulley at Fand Has
shown in Through O2 draw O2Mparallel to FE.
From the geometry of the figure, we find that O2Mwill be perpendicular to
O1E.Let the angle MO2O1= αradians.
We know that the length of the belt,
 Power Transmitted by a Belt
Length of the cross belt =  ( d 1  d 2) (r12  r 22)
 2x 
2 x

Velocity of Belt (V)=

  dN Where ( d=diameter of pulley (mts),
N=Revolutions per minute (RPM), V=velocity
60 of belt in mts/sec )
Effective Tension in the belt (T) = (T1-T2)
Power (P) = T x V = (T 1  T 2)  (  dN )
60
Power (P) = T  dN Here ( d=diameter in meters, N=Speed in
RPM,
45000 P=power in HP (Horse Power),
T= Tension in the belt in Kgs )

Power (P) = Td 1 N 1 Here ( d1=diameter in meters, N1=Speed in RPM,

P1=power in Watts,
60 T= Tension in the belt N )
Fig below shows the driving pulley (or driver) Aand the driven
pulley (or follower) B. As already discussed, the driving pulley
pulls the belt from one side and delivers it to the other side. It is
thus obvious that the tension on the former side (i.e. tight side)
will be greater than the latter side (i.e.slack side)
 Ratio of Driving Tensions for Flat Belt Drive
Consider a driven pulley rotating in the clockwise
direction as shown in Fig. 18.16.
Let T1= Tension in the belt on the tight side,
T2= Tension in the belt on the slack side, and
θ= Angle of contact in radians (i.e. angle subtended
by the arc AB, along which the belt touches the pulley, at
the centre).
 4.1.Following are the details of a crossed belt
Example 4.1.Following
drive. Calculate the length
of the belt?
Diameter of the driver : 200 mm
Diameter of the follower : 400 mm
Center distance of the drive : 2m
Speed of the driver : 400 rpm
Angle of contact : 197.3
Determine the length of the belt.
Solution:
D1 = 200 mm
D2= 400 mm
C = 2m
N1 = 400 rpm
Length of the belt = L =2C+ П / 2 (D1+ D2) + (D1+
D2) / 4C
= (2x2) + П / 2 (0.2+ 0.4) + (0.2+ 0.4) /
4x2
= 4.99 m
Example 4.2.Two pulleys, one 450 mm diameter and the
other 200 mm diameter, on parallel shafts 1.95 m apart
are connected by a crossed belt. Find the length of the
belt required and the angle of contact between the belt
and each pulley. What power can be transmitted by the
belt when the larger pulley rotates at 200 rev/min, if the
maximum permissible tension in the belt is 1 kN, and the
coefficient of friction between the belt and pulley is
0.25?
Velocity Ratio of a Belt Drive
It is the ratio between the velocities of the driver and
the follower or driven. It may be
expressed, mathematically, as discussed below:
Let d1= Diameter of the driver,
d2= Diameter of the follower,
N1= Speed of the driver in r.p.m.,
N2= Speed of the follower in r.p.m.,
Slip of the Belt
In the previous articles we have discussed the motion of
belts and pulleys assuming a firm frictional grip between
the belts and the pulleys. But sometimes, the frictional grip
becomes insufficient.
This may cause some forward motion of the driver without
carrying the belt with it. This is called slip of the belt and is
generally expressed as a percentage.
The result of the belt slipping is to reduce the velocity
ratio of the system. As the slipping of the belt is a common
phenomenon, thus the belt should never be used where a
definite velocity ratio is of importance (as in the case of
hour, minute and second arms in a watch).
Let s1% = Slip between the driver and the belt, and
s2% = Slip between the belt and follower,
Example 4. An engine running at 150 r.p.m. drives a line
shaft by means of a belt. The engine pulley is 750 mm
diameter and the pulley on the line shaft is 450 mm. A
900 mm diameter pulley on the line shaft drives a 150
mm diameter pulley keyed to a dynamo shaft. Fine the
speed of dynamo shaft, when 1. there is no slip, and 2.
there is a slip of 2% at each drive.
 COMPOUND BELT DRIVE

 A compound belt drive is used when

power is transmitted from one shaft
to another through a number of
pulleys.

 The belts are connected in such a

way that the driver moving one
system of drives is simultaneously
moving the other connected system.
IDLER PULLEY
1) Adjust tension and slack in the belt
2) Increase the belt contact area with pulley
3) To make drive compact
 APPLICATIONS

DRILLING MACHINE LATHE MACHINE

A OPEN BELT DRIVE IN A
WITH SPEED CONE WITH SPEED CONES
JIG--SAW MACHINE
JIG
PULLEYS AND TIMING BELT

SKIVING
MACHINE
 A GUIDE PULLEY BELT DRIVE
IN SPINDLE MOULD MACHINE
A PLANAR MACHINE
WITH GUIDE PULLEYS

A FLAT BELT IN A CIRCULAR

A TIMING BELT IN LATHE MACHINE SAW MACHINE
TIMING BELT OF AN AUTOMOBILES
Open belt drive Vs. Close belt drive

Open Belt Drive Closed Belt Drive

Both driver and the driven rotates in the Driver and driven rotates in opposite
same direction direction

When the shafts are horizontal, inclined Even if the shafts are vertical it is
it is effective to transmit the power effective to transmit the power

As there is no rubbing point, the life of Due to the rubbing point, the life of the
the belt is more belt reduces.

Require less length of the belt compared Require more length of belt compared to
to crossed belt drive for same centre open belt drive for the same centre
distance, pulley diameters. distance, pulley diameters.
Chains and Chain Drive
◦ What is chain?
A chain consists of links connected by joints
which provide for flexibility for chain.
 Chains and Chain Drive…
◦ Chain drive:
 A chain drive consists of two sprockets and
chain
 Most often, the power is conveyed by a roller
chain, known as the drive chain, passing over a
sprocket gear, with the teeth of the gear
meshing with the holes in the links of the chain.
 The gear is turned, and this pulls the chain
putting mechanical force into the system
 Chains and Chain Drive…
 Advantages of Chain Drives
◦ Do not slip
◦ Maintain constant and precise speed.
◦ Good service life
◦ Easy to install and repair
 Disadvantages of Chain Drives
◦ Noisy
◦ Need lubrication
◦ Weight of the chain
 Chains and Chain Drive…
 Roller Chain Drive:
◦ The hollow rollers are held inside two flat link
plates which are joined together by sleeves or
bushing passing inside the rollers.
 Chains and Chain Drive…
 Roller Chain Drive:
◦ Consecutive sets of such assemblies are connected
together with another pair of plates called pin link plates,
which in turn are held by central pins passing through the
sleeves. Rivets are used to join the link plates. Sometimes
the roller link plates are joined together by rollers
themselves and no sleeves are used.
 Chains and Chain Drive…
 Silent Chain Drive:

It consist of a number of flat links, tooth shaped at ends

and joined together by long cross pins. The sprockets
are usually wider than those of the roller chain and have
a central groove which holds retained plates provided in
the central links for keeping the chain on the sprocket
securely.
 Chains and Chain Drive…
 Use of chain drive:
◦ Motorcycles
◦ Bicycles
◦ Automobiles
◦ Conveyers
◦ Agricultural machinery
◦ Oil-well drilling machines
◦ Machine tools
  Pulley pulley drives
 Pulleys are used to transmit power from one
shaft to another with the help of belt or rope
running over them.
 Pulleys are made from cast iron,cast steel,
wrought iron or aluminium.
 The main part of pulley
 Rim
 Hub or
boss
 Arms or
rib
  Rim

 It is the periphery of the pulley on which

the belt runs.
 The outer face of the rim is made slightly
convex which is called crowning.
 This keep belts at centre when pulley is
misaligned.
  Hub or boss

 It is the central hollow cylindrical portion

of pulley as shown in figure.
 The size of bore on hub is corresponds to
the diameter of the shaft.
 It is mounted on shaft.
 A keyway is provided to fasten the pulley
to the shaft with the help of a key.
  Arms or rib
 It is joining member of the hub and the
rib of pulley.
 It may be straight or curved.
 It’s cross section may be circular or
elliptical.
 Pulleys with smaller diameter are
provided with a rib which is like a circular
disc joining hub and rim.
  Types of pulley
 Solid pulley
 Split pulley
 Stepped or cone pulley
 Fast and loose pulley
 Jockey pulley
 Guide pulley
 Grooved pulley
Gear and Gear Drives
IT IS A TOOTHED WHEEL WITH TEETH CUT ON
ITSPHERIPHERY.
POWER OR MOTION IS TRANSMITTED FROM ONE
SHAFT TO ANOTHER WITH GEAR DRIVE.
 Gears and Gear Drive…
 What is Gear?
◦ A gear is wheel provided with teeth which mesh with
the teethe on another wheel, or on to a rack, so as
to give a positive transmission of motion from one
component to another.
Gears and Gear Drive…
Types of Gears:
According to the position of axes of the shafts.
a. Parallel
1.Spur Gear
2.Helical Gear
3.Rack and Pinion
b. Intersecting
Bevel Gear
c. Non-intersecting and Non-parallel
worm and worm gears
Terms of Gear Drives
Types of Gears
 Spur Gears: If the  Helical Gears: The
teeth of Gear are teeth of helical
parallel to axis of gears are cut in
wheel that gear is form of Helix.
called Spur gear.
 Worm and Worm Wheel
Gears:A worm is a screw
and has one or more
number of helical threads.
 Worm wheel is a gear
wheel with tooth profile
of small helical segment.
 Rack and Pinion Gears:
Rack is a rectangular bar
consisting of series of
straight teeth cut on it.
Gears and Gear Drive…
 Rack and pinion
Rack is a spur gear of infinite diameter. The rack is
mesh with another small gear known as pinion

USES
It is used to convert
rotary motion into linear
motion.
Such as lathe , drilling ,
planning machines.
Gear Trains
 Simple gear train:  Compound gear
Series of gear are train: In compound
mounted on different gear train
shafts and between intermediate shafts
driving and driven carries more than
shaft. one gear.
 Reverted gear train: The
first and the last gears
are on the same axis. The
back gear arrangement in
lathe machines this gears
are used.
 Epicyclic gear train: The
axis of rotation of gears
are not fixed at all. Used
in gear boxes of
automobile vehicles.
 Advantages
1. It transmits exact velocity ratio.
2. It may be used to transmit large power.
3. It may be used for small centre distances of shafts.
4. It has high efficiency.
5. It has reliable service.
6. It has compact layout.
Disadvantages
1. Since the manufacture of gears require special tools and
equipment, therefore it is costlier than
other drives.
2.The error in cutting teeth may cause vibrations and noise
during operation.
3. It requires suitable lubricant and reliable method of
applying it, for the proper operation of gear drives.
NOMENCLATURE OF SPUR GEARS

5
 Pitch circle. It is an imaginary circle which by pure rolling
action would give the same motion as the actual gear.
 Pitch circle diameter. It is the diameter of the pitch circle.
The size of the gear is usually specified by the pitch circle
diameter. It is also known as pitch diameter.
 Pitch point. It is a common point of contact between two pitch
circles.
 Pitch surface. It is the surface of the rolling discs which the
meshing gears have replaced at the pitch circle.
 Pressure angle or angle of obliquity. It is the angle
between the common normal to two gear teeth at the point of
contact and the common tangent at the pitch point. It is
usually denoted by φ. The standard pressure angles are 14
1/2 ° and 20°.
 Addendum. It is the radial distance of a tooth from the pitch
circle to the top of the tooth.
 Dedendum. It is the radial distance of a tooth from the pitch
circle to the bottom of the tooth.
 Addendum circle. It is the circle drawn through the top of the
teeth and is concentric with the pitch circle.
 Dedendum circle. It is the circle drawn through the bottom of
the teeth. It is also called root circle.

Note : Root circle diameter = Pitch circle

diameter × cos φ , where φ is the pressure
angle.
Circular pitch. It is the distance measured on the circumference of the
pitch circle from a point of one tooth to the corresponding point on
the next tooth. It is usually denoted by Pc ,Mathematically,

A little consideration will show that the two gears will mesh together
correctly, if the two wheels have the same circular pitch.
Note : If D1 and D2 are the diameters of the two meshing gears having
the teeth T1 and T2 respectively, then for them to mesh correctly,
Diametral pitch. It is the ratio of number of teeth to the pitch circle
diameter in millimetres. It is denoted by pd. Mathematically,

Module. It is the ratio of the pitch circle diameter in millimeters to the

number of teeth. It is usually denoted by m. Mathematically,

Clearance. It is the radial distance from the top of the tooth to the bottom
of the tooth, in a meshing gear. A circle passing through the top of the
meshing gear is known as clearance circle.
Total depth. It is the radial distance between the addendum and the
dedendum circles of a gear. It is equal to the sum of the addendum and
dedendum.
Working depth. It is the radial distance from the addendum
circle to the clearance circle. It is equal to the sum of the
addendum of the two meshing gears.
Tooth thickness. It is the width of the tooth measured along the
pitch circle.
Tooth space . It is the width of space between the two adjacent
teeth measured along the pitch circle.
Backlash. It is the difference between the tooth space and the
tooth thickness, as measured along the pitch circle.
Theoretically, the backlash should be zero, but in actual
practice some backlash must be allowed to prevent
jamming of the teeth due to tooth errors and thermal
expansion.
Face of tooth. It is the surface of the gear tooth above
the pitch surface.
Flank of tooth. It is the surface of the gear tooth below
the pitch surface.
Top land. It is the surface of the top of the tooth.
Face width. It is the width of the gear tooth measured
parallel to its axis.
Profile. It is the curve formed by the face and flank of
the tooth.
Fillet radius. It is the radius that connects the root circle
to the profile of the tooth.
Path of contact. It is the path traced by the point of contact
of two teeth from the beginning to the end of engagement.
Length of the path of contact. It is the length of the
common normal cut-off by the addendum circles of the
wheel and pinion.
Arc of contact. It is the path traced by a point on the pitch
circle from the beginning to the end of engagement of a
given pair of teeth. The arc of contact consists of two
parts, i.e.
(a) Arc of approach. It is the portion of the path of contact
from the beginning of the engagement to the pitch point.
(b) Arc of recess. It is the portion of the path of contact
from the pitch point to the end of the engagement of a pair
of teeth.
Pressure Angle
Pressure
Direction of angle
tooth to
tooth push

Pressure
Angle Pressure
angle

14 ½ ° 20°
Rotation
Line of
action

74
Pitch Diameter and Center
Distance
Pitch Pitch
Diameter D2 Diameter D1

Center Distance
C
D1  D 2 D1  2C  D 2
C
2 D 2  2C  D1
75
Circular/Diametrical Pitch

Circular
Pitch

3.1416”

1 2 3 4 5 6 7 8 9 10

76
 Names of Gear Parts
Pitch
Circle

Clearance
Addendum
Pitch
Circle
Dedendum Working Thickness
Whole depth Circular
Addendum Thickness depth pitch
Pitch
Line

Dedendum Whole Circular

depth pitch
77
Backlash

Backlash

Pitch
Line

78
Design Considerations for a Gear Drive
In the design of a gear drive, the following data is usually given :
1.The power to be transmitted.
2.The speed of the driving gear,
3.The speed of the driven gear or the velocity ratio, and
4.The centre distance.
The following requirements must be met in the design of a gear drive :
(a) The gear teeth should have sufficient strength so that they will not
fail under static loading
or dynamic loading during normal running conditions.
(b) The gear teeth should have wear characteristics so that their life is
satisfactory.
(c) The use of space and material should be economical.
(d) The alignment of the gears and deflections of the shafts must be
considered because they
effect on the performance of the gears.
(e) The lubrication of the gears must be satisfactory.
Gear Trains
 When two or more gears are made to mesh with
each other to transmit power from one shaft to
other. Such an arrangement is called gear train.

Types:
 Simple gear train
 Compound gear train
 Epicyclic gear train
Simple gear train
 When there is only one gear on each shaft,
then it is known as simple gear train.

6
Simple gear train…
 When the distance between the two gears is large and
we need Constant velocity ratio:
 The motion from one gear to another, in such a case,
may be transmitted by either of the following two
methods

1. By providing the large sized gear

2. By providing one or more intermediate gears.

The first method (i.e. providing large sized gears) is very

inconvenient and uneconomical method
whereas the latter method (i.e. providing one or more
intermediate gear) is very convenient and economical.
Simple gear train…
Intermediate gears:
Intermediate gears are called idle
gears, as they do not effect the
speed ratio or train value of the
system.
1. To connect gears where a large
centre distance is required
2. To obtain the desired direction
of motion of the driven gear(i.e.
clockwise or anticlockwise)
 Simple gear train…
 Intermediate gears:
when the number of intermediate gears are odd, the
motion of both the gears (i.e. driver and driven or
follower) is like.
If the number of intermediate gears are even, the
motion of the driven or follower will be in the opposite
direction of the driver.
adVantaGes of simple Gear train
 to connect gears where a large center distance is
required
 to obtain desired direction of motion of the driven
gear ( CW or CCW)
 to obtain high speed ratio

Compound gear train

When there are more than one gear on a shaft , then
the gear train is called a compound train of gear.
adVantaGes of Compound Gear
train
 A much larger speed reduction from the first
shaft to the last shaft can be obtained with small
gear.
 If a simple gear trains used to give a large speed
reduction, the last gear has to be very large.
 Epicyclic Gear Train

 When there is relative

motion between two or
more of the axes of
wheels, such arrangement
is called epicyclic gear
train.
 A small gear at the center
called the sun, several
medium sized gears called
the planets and a large
external gear called the
ring gear.
ADVANTAGES of Epicyclic Gear Train

•They have higher gear ratios.

•They are popular for automatic transmissions in
automobiles.
•They are also used in bicycles for controlling power of
pedaling automatically or manually.
•They are also used for power transmission between
internal combustion engine and an electric motor.
any Question ?
EXIT