This presentation provides an overview of mechanical power transmission drives. It discusses different types of drives including shaft and axle drives, belt drives, rope drives, chain drives, and gear drives. For each type of drive, it describes the basic components, materials used, advantages and disadvantages. It also discusses important terminology and considerations for the design and selection of power transmission drives. The presentation aims to explain the basic concepts and components of various mechanical power transmission systems.

1. A
PRESENTATION
ON
MECHANICAL POWER
TRANSMISSION DRIVES
By
Sachin Kumar, Asst. Prof.
ME Deptt. BIT Meerut

2. Power Transmission Drives
• A Machine consists of a power source and
a power transmission system, which
provides controlled application of the
power.
• Transmission Drives are an assembly of
parts including the speed-changing device
and the propeller shaft by which the power
is transmitted from an engine/motor to a
live axle.

3. Why we need Power Transmission
Drives?
• Speed difference between the machine
and prime mover.
• Intermediate change in the velocity of
machine.
• To operate more than one machine.
• No direct coupling due to the consideration
of safety, convenience and maintenance

4. Types of Power Transmission Drives
• Shaft & Axles
• Belt Drives
• Rope Drives
• Chain Drives
• Gear Drives

5. Selection of the Drive
• Velocity Ratio
• Peripheral Velocity
• Transmitted Power
• Losses in Transmission
• Cost of drive

6. Shaft & Axle Drive
Shaft and Axle are the machine members,
mostly cylindrical in section which support
the revolving part of a machine

7. Shaft
• Shaft is the machine
member which not
only supports the
revolving parts but
also transmits the
torsional moment.
• It is subjected to both
bending and torsional
stresses.

8. Propeller Shaft

9. Crank Shaft

10. Line Shaft

11. Flexible Shaft

12. Axle
• Axle is the machine member which only
supports the rotating part of the machine.
• It takes the bending load only and is
subjected to bending stresses only.

13. Axle

14. Materials for the Shaft & Axle
• C-25, C-30, C-35, C-40, C-50
• Alloy Steel
Materials are heat treated to impart high
mechanical properties.
Where wear resistance is the dominating
factor, case hardening is done.

15. Design of Shaft & Axle
• Design for strength
Pure bending load
Pure torsional load
Combined load
• Design for stiffness
• Design for fatigue load

16. Methods of Manufacturing of Shaft
& Axles
• Hot Rolling
• Cold Drawing
• Turning and grinding from rough bars
• Forging
• Casting

17. Belt Drives
• Belt drives are most widely
used in industry for the
transmission of power from
one shaft to another over
considerable distance.
• Belt drive consists of an
endless belt which is
wrapped over two pulleys
known as driving and driven
pulleys which in turn are
mounted on the driving and
driven shafts respectively.

18. Types of Belt Drives
• Light Drives- Belt speed up to 12m/s.
Ex.- agro machines, fitter machines etc.
• Medium Drives- Speed 12-24m/s.
Ex.- machine tools
• Heavy Drives- Speed above 24 m/s.
Ex.- generators, compressors and main
drives.

19. Types of Belts
• Flat Belt
• V-Belt
• Ribbed Belt
• Timing Belt

20. Flat Belt
Flat belts are used in
the machines where a
moderate amount of
power is to be
transmitted when the
pulleys are not more
than 8 meters apart.

21. V-Belt
V belts are used in
machines where a
great amount of
power is transmitted
when the pulleys are
very near to each
other.

22. Types of Flat Belt Drives
• Open belt drives
• Crossed belt drives
• Quarter turn belt drives
• Belt drive with idler pulley
• Compound belt drives
• Stepped pulley drive
• Fast and loose pulley drives

23. Open Belt Drive
In this drive, the
shafts are arranged in
parallel and rotate in
same direction.

24. Crossed Belt Drive
If the shafts are
arranged in parallel
but need to be rotated
in opposite directions,
this type of drive is
used.

25. Quarter Turn Belt Drive
In this drive the shafts
are at right angles.

26. Belt Drive with idler Pulley
• When the high
velocity ratio is
desired in short
centre distance and
• When the required
belt tension can not
be obtained by other
means than this drive
is used.

27. Compound Belt Drive
This type of drive is
used when several
units are to be driven
from one central
shaft.

28. Stepped Pulley Drive
This type of drive is
used for stepped
changing of angular
speed of the driven
shaft when the driving
shaft is at constant
angular speed.

29. Fast and Loose Pulley Drive
This drive is used
when the driven shaft
is to be rotated and
stopped too often,
then two pulleys are
keyed on the shaft as
fast and loose.

30. Materials used for Belts
• Leather belt
• Cotton belt
• Rubber belt
• Balata belt

31. Pulleys
Two pulleys are used
in power transmission
by belt drives, one is
driving and another is
driven pulley.
Velocity ratio between
them is not constant.

32. Materials used for Pulleys
• Cast Iron
• Steel
• All wood
• Moulded Plastic
• Die cast Aluminium

33. Power Transmitted by Belt Drives
• Power transmitted between a belt and a pulley is
expressed as the product of difference of tension and
belt velocity
P = (T1 − T2)v
where, T1 and T2 are tensions in the tight side and
slack side of the belt respectively.
• They are related as:
T1 /T2=exp(μθ)
where, μ is the coefficient of friction, and θ is the angle
subtended by contact surface at the centre of the
pulley.

34. Advantages of Belt Drives
• Easy, flexible equipment design, as
tolerances are not important.
• Isolation from shock and vibration between
driver and driven system.
• Driven shaft speed conveniently changed by
changing pulley sizes.
• Belt drives require no lubrication.
• Maintenance is relatively convenient
• Very quiet compared to chain drives, and
direct spur gear drives

35. Disadvantages of Belt Drives
• The angular velocity ratio is not necessarily
constant or equal to the ratio of pulley
diameters, because of belt slip and stretch.
• Heat buildup occurs. Speed is limited to 35
meters per second. Power transmission is
also very less.
• Operating temperatures are usually restricted
to –35 to 85°C.
• Some adjustment of center distance or use of
an idler pulley is necessary for wear and
stretch compensation.
• A means of disassembly must be provided to
install endless belts.

36. Rope Drive
Rope drives are used
when large amount of
power is transmitted
over a considerable
distance.

37. Types of Ropes
• Fibre Ropes
 Hemp Rope
 Manila Rope
 Cotton Rope
• Wire Ropes

38. Manila Rope

39. Materials for Rope Drives
• Fibre Ropes
 Fibre
 Cotton
 Leather, Nylon
 Rubberized fabric
• Wire Ropes
 Wrought Iron
 Cast Steel
 Alloy Steel

40. Design of Rope Drives
• Direct Stress is found out.
• Bending Stress is found out.
• Stresses due to starting are found out.
• Stresses due to change in speed are
found out.

41. Application of Rope Drives
• Hoisting and lifting of loads
• Elevators
• Oil Well drilling
• Cranes
• Suspension Bridges

42. Advantages of Rope Drives
• High mechanical efficiency
• Economy of operation
• Smooth, steady and quiet operation
• The ropes are little affected by outdoor
operation
• Lighter weight
• Less danger of damage due to jerk

43. Disadvantages of Rope Drives
• This method has been largely superseded
by Electrical power transmission.
• Machines are becoming compact so this
drive is finding less use.

44. Chain Drive
Chain drive consists
of an endless chain
running over two
sprockets.

45. Chain Drive
• Chain drive is a way of transmitting mechanical
power from one place to another.
• It is often used to convey power to the wheels of a
vehicle, particularly bicycles and motorcycles.
• It is also used in a wide variety of machines
besides vehicles.
• 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..

46. Types of Chain Drives
• Roller Chain
• Bush Chain
• Silent Chain

47. Design of Chain Drives
• Select the type of chain
• Find the no. of teeth of the smaller
sprocket
• Select the chain pitch
• Find the total load on the driving side
• Check the chain for wear

48. Advantages of Chain Drives
• No slippage between chain and sprocket teeth.
• Negligible stretch, allowing chains to carry heavy loads.
• Long operating life expectancy because flexure and friction
contact occur between hardened bearing surfaces separated
by an oil film.
• Operates in hostile environment such as high temperatures,
high moisture or oily areas, dusty, dirty, and corrosive
atmospheres etc.
• Long shelf life because metal chain ordinarily doesn’t
deteriorate with age and is unaffected by sun, reasonable
ranges of heat, moisture, and oil.
• Easy replacement
• High Efficiency

49. Disadvantages of Chain Drives
• Noise is usually higher than with belts or
gears.
• Chain drives can elongate due to wearing
of link and sprocket teeth contact surfaces.
• High Production cost
• Usually limited to somewhat lower-speed
applications compared to belts or gears.
• Sprockets needs to be replaced because of
wear when worn chain is replaced. V-belt
sheaves exhibit very low wear.

50. Gear Drive
A gear can be defined
as the mechanical
element used for
transmitting power
and rotary motion
from one shaft to
another by means of
progressive
engagement of
projections called
teeth.

51. Classifications of Gears
• Parallel Axes - Spur gear, Helical gear,
Herringbone gear, Internal gear.
• Intersecting Axes - Bevel Gears- straight or
spiral bevel
• Non-parallel and Non-intersecting Axes -
Worm gear, Helical gear

52. Spur Gear
In these gears teeth
are straight and
parallel to the axis of
the shaft.

53. Helical Gear
In these gears the
teeth are inclined to
the axis of the shaft
and are in the form of
helix.

54. Herringbone Gear
These gears have two
sets of opposite
helical teeth.

55. Internal Gear
These gears have
teeth cut on the
internal side of the
gear wheel.

56. Bevel Gear
Gear blanks are
conical in shape and
mounted on shafts at
any angle.

57. Rack and Pinion
Gear is rotated over a
long bar of metal
having teeth cut on
the surface.

58. Worm Gear
In these gears one
gear has the screw
threads and another
gear has the
corresponding mating
threads.

59. Fundamental Law of Gearing
wG / wP =constt.
(constant speed
ratio)
Common
normal have to
intersect at the
same point P

60. Gear Terminology

61. Gear Terminology
• Pitch Circle: It is an imaginary circle which by pure rolling action
would transmit same motion as the actual gear .
• Pitch Circle Diameter(d) : It is diameter of pitch circle .
• Pressure Angle: It is the angle between the common normal to the
two gear teeth at point of contact and common tangent to two pitch
circles at pitch point.
• Circular Pitch: It is the distance measured along the circumference
of the pitch circle ,from point on one tooth to corresponding point on
next tooth.

62. Gear Terminology
• Module: It is ratio of pitch circle in mm to the number of teeth.
• Addendum (ha): It is radial distance between top land of the teeth
and pitch circle.
• Dedendum (hf): It is radial distance between bottom land of the teeth
and pitch circle.
• Total depth: It is radial distance between Addendum circle and
dedendum circle. It is sum of addendum and dedendum.
• Base Circle: It is the circle on which the involute profile of the gear
tooth is generated. Face width: It is length of gear tooth measured
along line parallel to gear axes.

63. Gear Terminology
• Backlash: Backlash is the freedom of one gear to move while
the mating teeth is held stationary. Backlash allows room for
an oil film under all conditions of thermal expansion or
contraction and is influenced by deviation of centre distance
,tooth thickness, pitch profile and lead errors.
• Tooth Thickness: It is width of tooth measured along pitch
circle.
• Velocity ratio: It is ratio of pinion speed to gear speed.
• Contact Ratio: Contact ratio can be visualised as the average
number of tooth pairs in contact during mesh. This means
more the contact ratio, smoother will be the operation.

64. Gear Terminology
Contact ratio for helical gears is sum of transverse contact
ratio and face contact ratio. The transverse contact ratio is
contact ratio in plane of rotation, whereas face contact ratio is
contact ratio in axial plane . For spur gears, face contact ratio
is zero.
• Root diameter: It is diameter of base of tooth space.
• Outside diameter: It is diameter of Addendum circle.
• Fillet radius: The curved surface of the tooth flank joining it to
bottom land.

65. Gear Terminology
• Undercut : A condition in generated gear teeth , when part of
fillet curve lies inside of a line drawn tangent to true involute
form at its lowest point . Undercut may be deliberately
introduced to facilitate finishing operation.
• Path of contact :The curve on either tooth surface along which
contact occurs in gears which normally engage with only
single point contact.
• Interference :The contact between mating teeth at some other
point than along line of action .

66. Gear Nomenclature
m= Module
a =Centre distance
z =Number of teeth
i =Gear Ratio
α =Helix Angle
α (b)= Base helix angle
Φ= Pressure Angle
p= Normal pitch
d =Reference Diameter
mt= Transverse Module
Pt= Transverse Pitch
Pb= Base Pitch

67. Gear Nomenclature
Pb=Base Pitch
db= Base Diameter
df= Root Diameter
da= Tip Diameter

68. Gear Materials
Desirable properties for gear material are as
follows:
a) Endurance strength in bending to avoid
bending failure.
b) Surface endurance strength to avoid
destructive pitting.
c) Low coefficient of friction to avoid scoring.
d) Low and consistent thermal distortion during
Heat treatment

69. Gear Materials
• Ferrous Metals
 Cast Iron Material: FG 260 of IS 210 , SG 400/12 of IS -
1865:1991
 Steels:
1)Case Hardening steel- 17CrNiMo6 of DIN 17210 or En 36B
or C of BS 970 or 15Ni2Cr1Mo15 of IS 4432 or equivalent
Nitriding Steel En40C , En41A, En41B of BS 970, 34CrAlMo5
as per DIN, 40Cr2Al1Mo18 of IS 1570 etc.
2) Plain carbon steel
3)Alloy Steel- En 24 or En 19 of BS 970, 45C8 ,
40Ni2Cr1Mo28 of IS 5517-1978 or 42Cr Mo4 of DIN etc.
• Non Ferrous Metals: Copper, Zinc, Aluminium etc.
• Sintered metals: Gears in washing machine, mixtures, toys
etc.
• Non metallic gears : Nylon and Bakelite

70. Basic Design Considerations
In order to drive in a given direction and to transmit power smoothly and without
loss of energy, gears should have following properties
1) Before one pair of teeth goes out of contact during mesh , second pair will
have to pick up its share of load. This is called ‘continuity of action’
2) The angular velocity of driving member is smoothly imparted to the driven
member and transmission ratio should be constant at every instant of
engagement. Gears which meet this requirement are called conjugate
gears.

71. Condition 2 is confirmed by basic law of gearing which states
that ‘Normals to the profiles of mating teeth must , at all points
of contact , pass through a fixed point located on the line of
centres called pitch point. Pitch point is on the line joining the
centres of two gears and divides it in the proportion of number
of teeth on the gears. Tooth profile which meet this conjugacy
requirement are
• Involute profile
• Cycloidal profile

72. Involute Profile
This is most
commonly used
profile . Involute is
path traced by end of
inextensible cord as
unwound over base
circle.

73. Cycloidal Profile
Cycloidal is profile
traced by a point on
the circumference of
a circle as it rolls on a
line without slipping.

74. Steps for Gear Design
• Inputs for gear design are Velocity ratio, input
speed, torque to be transmitted, type of
loading, ambient condition etc.
• Decide centre distance and gear geometric
parameters based on above parameters.
• Based on installation requirements, decide
gearing arrangement required i.e. spur/helical
or bevel
• Depending upon pitch line velocity and
application decide class of accuracy.

75. Helical gears are preferred over spur gear due to
• Greater tooth strength due to helical wrap around.
• Increased contact ratio which gives smooth
operational characteristics.
• Higher load carrying capacity than comparable
spur gear. Spur and helical gears can be used to
transmit large power. However because of low
efficiency, worm gear drive is not preferred for high
power transmission. Spur gears are easy to
manufacture and cheapest, followed by helical and
bevel gears . Due to bimetallic construction of
worm wheel and specialized manufacturing
method, worm gears are costlier.

76. Advantages of Gear drives
• Compact as compared to belt or chain
drive.
• Transmits higher power and speed as
compared to belt or chain drive.
• Transmits power between shafts which are
parallel/non-parallel, intersecting / non-
intersecting.
• Used for wide range of speed ratios.
• Gear drives are positive drives.

77. Limitations of Gear Drives
• Gear drives are costlier than belt or chain
drives.
• Require continuous lubrication and precise
alignment.
• Can not be used for transmitting power over
very long distance.

78. Factors to be considered for
selecting the gear drive
• The relative position of input and output shaft
• Speed ratio
• Efficiency
• Input speed
• Power to be transmitted
• Cost

79. Comparison of Different
Mechanical Power
Transmission Drives

80. Velocity Ratio
Drive Velocity Ratio
Open belt drive Upto 5
V belt drive 8-15
Roller chain 6-10
Toothed gear 4-20

81. Peripheral Velocity
Drive Peripheral Velocity (m/s)
Flat Belts Max. Velocity < 25
V Belts Max. Velocity= 25-30 m/s
Chain Drive Max. Velocity= 25-30 m/s
Spur Gear v >10
Helical Gear V = 120-150

82. Transmitted Power
Drive Transmitted Power( kW)
V Belt Maximum Power = 735-1100
Flat Belt Maximum Power=1835
Chain Drive Maximum Power=3670
Toothed Gear Maximum Power=36775

83. Losses in Transmission
Drive Losses
Flat Belt 2.5%
V-Belt 4%
Chain Drive 2%
Toothed Gear 1%
Worm Gear 10-25%

84. Cost of Drives
Drive Drive Cost w.r.t. V- Belt Cost
Flat Belt 1.06
Flat belt with idler Pulley 1.25
Chain Drive 1.40
Toothed Gear 1.65
Worm Gear 1.25

85. Advances in Power Transmission
• Continuously Variable Transmission
• Dual Clutch Transmission

86. Continuously Variable Transmission

87. Dual Clutch Transmission

88. THANK YOU !