1. Dept of Mechanical Engg.
CHAPTER -2
POWER TRANSMISSION By
Vasanthkumar.ch
M tech (Robotics)
Dept of Mechanical Engg.

2. Power transmission (rotational power)
Belt drives
Chain drives
Gear drives

3. BELT DRIVE
A belt drive is a method of transferring rotary motion between two shafts(attached with pulleys).
It is a looped strip of flexible material, used to mechanically link two or more rotating shafts.
Belt drives may be used as a source of motion, to efficiently transmit power, or to track relative movement.
Generally belt drives are friction drives.

4. Simple belt drive system

5. Application Where the rotational speeds are different
Distance between the shafts is high
Motion or power that needs to be transmitted to more number of applications

6. Types of belts
Flat belt
V belt
Round belt
Timing belt

7. Pictorial view of belts
Flat belt

8. Round belt

9. V belt

10. Timing or grooved belt

11. Pictorial view

12. Pictorial view

13. Materials used for belt drives
Oak tanned leather – fairly stiff
Chrome leather belt – for oil and steam environment
Fabric belts - (Canvas or cotton duck)
Rubber belts – layers of fabric impregnated with rubber or vulcanized rubber

14. Types of Belt drives
Open belt drive
Crossed belt drive

15. Open belt drive

16. Crossed belt drive

17. Terminology Length of the belt Velocity ratio Slip
Tight side and slack side
Angle of contact
Ratio between the belt tensions
Power transmitted

18. Ratios b/w belt tension and Power
R= T1/T2 =eµθ
T1 = Tension in the tight side
T2 = Tension on the slack side
µ= coefficient of friction
θ= angle of contact
Power transmitted P = (T1-T2 )V
V= velocity of the belt
V= πd1 * N/60 m/s

19. Merits of belt drive mechanism
They are simple. They are economical.
Parallel shafts are not required.
Overload and jam protection are provided.
Noise and vibration are damped out. Machinery life is prolonged because load fluctuations are cushioned (shock-absorbed).
They are lubrication-free. They require only low maintenance.
They are highly efficient (90–98%, usually 95%). Some misalignment is tolerable.
They are very economical when shafts are separated by large distances.

20. Demerits of belt drive Non compact
Constant velocity cannot be obtained
Slippage
Not applicable for heavy loads

21. Real time applications
Lathe , drilling and sewing machines
Compression systems
Automobiles
Water systems
Power generation units
Air conditioning systems

22. Example
An engine running at 300 rpm drives a line shaft by means of belt drive. The engine pulley is 600mm in diameter and the pulley on the shaft is 400mm in diameter. Determine the speed of the line shaft.(assume no slip).

23. Example Following details of the cross and open belt drive
Diameter of the driver= 300mm
Diameter of the follower = 600mm
Center distance of the drive is =3mts
Speed of the drive is = 500rpm
Angle of contact = °
Determine the length of the belt required for both of the drive systems

24. Example
For the example in the previous slide the tension on the tight side is 1.3KN and the coefficient of friction between the pulley is 0.25 find the power capacity of the drive.

25. CHAIN DRIVES

26. Animated view

27. Applications
Where slippage needs to be reduced to a considerable amount
Initial torque developed is more
Continuous drive systems
Smaller center distance
Agro machinery , automobiles,cranes

28. Gear systems
Machine elements that transmit the motion and power between the rotating shafts by means of successively engaging teeth .
Compact than the other drive systems
More accurate power transmission
Less slippage or little backlash

29. Common forms of gear configuration
Gears for connecting parallel shafts
Gears for connecting intersecting shafts
Gears for connecting neither parallel nor intersecting shafts

31. Gear types for connecting parallel shafts
Spur gears (internal and external)
Parallel helical gears
Rack and pinion arrangement

32. Spur gear

33. Helical gear

34. Herring bone gear

35. Rack and pinion

36. Gears for connecting interesting shafts
Straight bevel gear

37. Neither interesting nor parallel

38. Nomenclature

39. Terminologies Pitch circle Tooth space Addendum circle Backlash
Root circle Circular pitch
Addendum Diametral pitch
Dedundum Module
Clearance
Face of the tooth
Flank of tooth
Tooth space
Tooth thickness or circular thickness

40. Velocity ratio of the Gear Drive
Angular speeds of two gears
ω1 = 2π N1
ω2 = 2π N2.
Peripheral velocity of the Driver gear
Vp = ω1 d1 /N1 = π d1N1 = ω2d2 /N2 = π d2N2
Velocity ratio = n= ω1/ ω2=N1/N2

41. Gear trains
A combination of two or more gears for transmission of energy.
Size /number of teeth makes a speed change(reduction or increment).
Preferred when large speed change is required in a compact space.

42. Types of gear trains Simple gear train Compound gear train
Planetary gear train

43. Simple gear train

44. Compound gear train

45. Velocity ratio of Gear trains
ω1 = angular velocity of Gear 1
ω2 = angular velocity of Gear 2
ω3 = angular velocity of Gear 3
N1= speed of gear 1
N2 = speed of gear 2
N3 = speed of gear 3
T1= teeth of gear 1
T2= teeth of gear 2
T3= teeth of gear 3
ω1/ ω2= N1/N2 = T2/T1; ω2/ ω3 = N2/N3 =T3/T2
ω1/ ω3= ω1/ ω2 * ω2/ ω3 = N1/N2* N2/N3 = T2/T1* T3/T2

46. Planetary gear train
Also termed a epicyclical gear

49. Gears in real time application
Automobiles
Machine systems
Pumping systems
Machine tools
Timing and related equipments

50. Merits and Demerits Merits: Compactness
Greater speed amplification and reduction of speeds
Less slip
Direct contact with the driver

51. Merits and Demerits Demerits Wear and tear
Required coolant for reduction of heat developed
Back lash
Noise and vibration