1. POWER TRAINS

2. UNIT-5
POWER TRAINS:
General Arrangement of Clutch, Principle of Friction clutches, Torque transmitted, Constructional details, Fluid flywheel, Single plate, Multi plate and Centrifugal clutches
Gear box: Necessity for gear ratios in transmission, Synchronous gear boxes, 3,4 and 5 speed gear boxes, Free Wheeling mechanism, Planetary gears systems, over drives, fluid coupling and torque converters, Epicyclic gear box, principle of automatic transmission, calculation of gear ratios, Numerical calculations for torque transmission by clutches.

3. Introduction
A Transmission system uses a clutch, gear box, propeller shaft and a differential gear to transmit power from engine to the road wheels
The power may be transmitted to rear or front or all four wheels depending on the drive used
The clutch and gear box varies the ratio of torque output to torque input
The propeller shaft transmits final torque to the rear axle from gear box
A differential gear equally distributes the final torque between the road wheels.

4. Functions of Transmission System
It disconnects engine from driving wheels when required
The engine is connected to driving wheels when required
It changes ratio of torque output to torque input, as desired
It turns the drive through a right angle

5. Clutch A clutch is a mechanical device which transmits motion
from one shaft to the other which are along a straight line or same axis of rotation.
A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped when ever needed, without stopping the driving shaft.

6. Location of The Clutch

9. Requirements of a clutch
1. Torque transmission.---The clutch must be able to transmit maximum torque of the engine 2. Gradual engagement----The clutch should engage gradually to avoid sudden jerks 3. Heat dissipation---The clutch should be able to dissipate large quantity of heat which is generated during the clutch operation due to friction 4. Dynamic balancing---The clutch should be dynamically balanced. This is particularly required incase of high speed engine clutches. 5. Vibration damping ---The clutch should have suitable mechanism to damp vibrations and to eliminate noise produced during power transmitted. 6. Size---The clutch should be as small as possible so that it occupies minimum space

10. 7. Inertia -- clutch rotating parts should have minimum inertia 8
7. Inertia -- clutch rotating parts should have minimum inertia 8. Clutch free pedal play – to reduce effective clamping load on carbon thrust bearing 9. Ease of operation – as clutch transmits higher torque , its disengagement should not tiresome the driver 10. Lightness

11. Used Disconnecting the engine with gear box When starting the engine
When changing the gears
When stopping the engine

12. Principle of friction clutch operation

13. Principle of Operation
The clutch works on the principle of friction.
When two surfaces are brought in contact with each other and pressed they are united due to friction between them.
The friction depends on area of contact, pressure applied upon them and coefficient of friction on the surface of the material.
The two surfaces can be separated and brought in contact when required.
One is considered driving member and other driven member. The driving member is kept rotating. When the driven member is brought in contact with the driving member it also start rotating.
When the driven member is separated from the driving member, it does not revolve .

14. T=µWR Where, W- axial load applied µ-Coefficient of friction
T- torque transmitted
R- effective mean radius of friction surface

15. Working of a clutch
Clutch for a drive shaft: The clutch disc (center) spins with the flywheel (left). To disengage, the lever is pulled (black arrow), causing a white pressure plate (right) to disengage the green clutch disc from turning the drive shaft, which turns within the thrust-bearing ring of the lever. Never will all 3 rings connect, with no gaps.

16. The Clutch

18. Types of Clutches
1. Friction Clutches: a. Single plate clutch b. Multi plate clutch----i)Wet ii)Dry c. Cone clutch---i)External ii) Internal 2. Centrifugal Clutch 3. Semi-centrifugal clutch 4. Conical spring clutch or diaphragm clutch a. Tapered finger type b. Crown spring type 5. Positive Clutch—Dog and spline clutch 6.Hydraulic clutch 7.Electro magnetic clutch 8.Vaccum clutch 9. Over running clutch or free wheel clutch

19. Single Plate Clutch

20. Working
It has only one clutch plate mounted on the splines of clutch shaft.
Pressure plate is bolted to the flywheel through clutch springs and is free to slide on the clutch shaft when the clutch pedal is operated.
When the clutch pedal is pressed, the pressure plate moves back against the force of the springs and clutch plate becomes free between the flywheel and the pressure plate.
Thus, the flywheel remains rotating as long as the engine is running and the clutch shaft speed reduces slowly and finally stops rotating.
As soon as the pedal is pressed, clutch is said to be disengaged otherwise it remains engaged due to spring forces.
Used in Ford V8 truck, Tata trucks, Premier President, Hindustan Ambassador, Bajaj Matador, Mahindra Jeep

21. Cover assembly of single plate clutch

22. Multiplate Clutch

23. Working
Multiplate clutch consist of a number of clutch plates, instead of
only one clutch plate as incase of single plate clutch.
As the number of clutch plates increased number of friction surfaces which increases the capacity of the clutch to transmit torque.
The plates are alternately fixed to the engine shaft and gearbox shaft.
They are firmly pressed by strong coil springs and assembled in a drum.
Each of the alternate plate slides in the grooves on the flywheel and other slides on the splines on the pressure plate. Thus each alternate plates have inner and outer splines.
The multi-plate clutch works in the same way as single plate clutch, by operating the clutch pedal. Multiplate clutch is used in heavy vehicles, racing cars etc, where more torque is to be transmitted.

24. Cone clutch
Contact surface is in the form of cone

25. Centrifugal clutch

26. Working
The centrifugal clutch uses centrifugal force instead of spring force for keeping it in the engaged position. Also it does not require clutch pedal to operate it.
The clutch is operated automatically depending upon the engine speed. The engine can be stopped in gear without stalling the engine.
Similarly vehicle can be started in any gear pressing the accelerator pedal.
It consists of weight A pivoted at B. When the engine speed increases the weights fly off due to the centrifugal force, operating the bell crank lever P which presses the plate C.
The movement of the plate C presses the spring E Which ultimately presses the clutch plate D on the flywheel against spring G. This makes the Clutch engaged.
The spring G keeps the clutch disengaged at low speeds at about 500 rpm. Stop H limits the movement of the weights due to the centrifugal force.

27. Semi-Centrifugal clutch

28. Clutch operation methods
Mechanically
Electromagnetic operation
Hydraulic operation
Vacuum operation
Clutch by wire

30. Electromagnetic clutch

31. Hydraulically operated single plate clutch

32. Vacuum operation clutch

33. Clutch by wire
In this system there is no mechanical link between the clutch and the pedal
The clutch pedal is electronically controlled by means of an Electronic Control Unit (ECU) and an actuator
A sensor on the pedal measures its exact position which is transmitted to ECU
Information about the car’s behavior from other sensors is also transmitted to ECU, which then operates the clutch through the actuator
Advantages are improved drive ability, better pedal feel and less wear due to absence of mechanical linkage

34. Wet clutch

35. Description Wet clutch Dry clutch
Heat dissipation
Good
Bad
Life
Longer life
Short
Torque transmission
Lower
Higher
Clamping force
More
Less
Coefficient of friction
Less due to oil presence

36. Coil spring single plate clutch

37. Diaphragm clutch

38. Advantages of diaphragm w.r.t coil spring
More compact means of storing energy
Less affected by the centrifugal forces, it can withstand higher rotational speeds whereas coil springs distort transversely at higher speeds
Diaphragm acts as both clamping spring and release lever

39. Clutch Components Clutch plate Clutch facing Pressure plate Springs
Bearing

40. Clutch plate

41. Torsional springs and cushioning springs

42. Clutch facing Requirement of a good clutch facing
Good wearing properties
Presence of good binders in it
Cheap and easy to manufacture
High co-efficient of friction
High resistance to heat

43. Types of Friction materials
Millboard type- asbestos sheet treated with certain impregnants
Moulded type- mixed asbestos fibers with a binding material
Woven type- cloth with certain binders
Solid woven variety- cloth is woven to required thickness
Laminated variety- layers of cloth one upon the other are held together by a binder. Stitches are provided in addition to binders

44. Common clutch facing materials are;
Leather- coefficient of friction- 0.27
Cork -0.32
Fabric-0.4
Asbestos -0.2
Reybestos and Ferodo- 0.35
Non-asbestos clutch facing

45. Design details of single plate clutch
Uniform Pressure Intensity: P= constant
Total axial load on clutch W= πPr(ro2 -ri2 )
Total Torque Transmitted
T= 2 /3 µ W(ro3-ri3)/(ro2-ri2)
T= µWR
Effective Mean Radius R=2/3(ro3-ri3)/(ro2-ri2)

46. T=2µWR Uniform Rate of Wear: Pr= constant
Axial load on clutch W= 2πPr(ro -ri)
Torque Transmitted
T= µ W(ro+ri)/2
T= µWR
Effective Mean Radius R= (ro+ri)/2
T=2µWR

47. Problem-1
The engine of a car employing a single plate friction clutch develops maximum torque of 150Nm. External diameter of the clutch plate is 1.2 times its internal diameter. Determine the dimensions of the clutch plate and the axial force provided by the springs. The maximum allowable pressure intensity for the clutch facings is 100KPa and coefficient of friction is Assume uniform wear.

48. Problem-2
An automobile clutch has a clutch plate of 160mm inside and 240 mm outside diameter. Six springs in the clutch provide a total force of 4.8KN, when the clutch is new and each spring is compressed 5 mm. the maximum torque developed by the automobile engine is 250 Nm. Determine
Factor of safety for the new clutch and
The amount of wear of the clutch facing that will take place before the clutch starts slipping. Assume coefficient of friction for the facing is 0.3

49. Problem-3
Determine the size of the clutch plate suitable for an Ambassador car employing a single plate type of friction clutch and developing 37.5 KW at 4200rpm. The inside diameter of the clutch plate is 0.6 times its outside diameter and it is to be ensured that even after a loss of 30% of the engine torque due to wear of the clutch facing, the clutch does not slip. The intensity of pressure on the facing is not to exceed 70kPa. Assume µ=0.3

50. Problem-4
Single plate friction clutch is to be designed for an Ashok Leyland bus developing kW at 2400 rpm. The maximum torque developed however is 376 Nm at rpm. A maximum wear of clutch facing of 3 mm is to be allowed, when the clutch must transmit at least 25% excess torque. A pressure intensity of 190kPa can be safely allowed and ratio Inside dia/ outside dia= 0.6 is considered reasonable.
Calculate clutch plate dimensions
If 9 springs are used and initial spring force is to be 1.2 times the spring force after allowable wear of 3 mm, find out the spring stiffness. Assume µ=0.35.

51. Design details of Multi plate clutch
If n= total number of friction plates in the multi plate clutch, then number of pairs of contact surfaces= (n-1) then, Torque T= (n-1) µWR i) For uniform pressure intensity, T= (n-1)2 /3 µ W(ro3-ri3)/(ro2-ri2) ii) For uniform wear rate, T=(n-1)W(ri +ro)/2

52. Problem on Multi plate clutch
A multi plate clutch is to be designed for a motor cycle whose engine develops maximum torque of 13Nm at 3500rpm. The external diameter of the clutch facings is limited to 100mm and the inner diameter may be assumed to be 0.2 times the external diameter. The maximum intensity of pressure may be taken as 80kPa and µ=0.3. Calculate the number of plates.