(ELECTRONIC CITY CAMPUS)DEPARTMENT OF MECHANICAL ENGINEERINGDEPARTMENT OF MECHANICAL ENGINEERING

MECHANICAL ENGINEERING SCIENCE (MES)

(UE18ME101)(UE18ME101)

Unit 3Unit – 3

POWER TRANSMISSIONPOWER TRANSMISSION

Power TransmissionPower Transmission

• Rotational motion can be transmitted from onemechanical element to the other with the help ofcertain systems known as transmission system orDrives

• The system used to drive a device directly by a primemovers or transmit the rotational motion to thevarious parts of a machine within itself

• The one that drives is called driving system, otherg y ,which is driven is called driven system

Power transmission Classification Classification Based onDistance between them, Speed and  powerThThey are ‐1. Belt drives                                                                             2. Chain drives

3. Rope drive                                                                                 4. Gear drives

Belt DriveA belt drive is a method of transferring rotary motion between two shafts

which are at a distance (pulleys are attached to the shafts)which are at a distance (pulleys are attached to the shafts)It is a looped strip of flexible material, used to mechanically link two or

more rotating shafts..gBelt drives may be used as a source of motion, to efficiently transmit

power, or to track relative movement.Generally belt drives are friction drives.

ApplicationApplication• Where the rotationalspeeds are different

• Distance between theDistance between theshafts is highM ti th t• Motion or power thatneeds to bet itt d ttransmitted to morenumber of

li tiapplications

Types of beltsTypes of beltsFlat belt                                         V belt

Round belt                                        Timing belt 

Materials used for belt drivesMaterials used for belt drivesBelts are generally made from leather, rubber,Belts are generally made from leather, rubber, canvas and balata

• Leather: Used in both dry and wet conditions• Leather: Used in both dry and wet conditions• Rubber: Used when the belts are exposed to         

damp condition• Canvas: Used when atmospheric conditionsCanvas: Used when atmospheric conditions

affect a leather or rubber beltl h d f d l• Balata: They are made from Cotton and Balata

Used in wet condition

Types of Belt drivesTypes of Belt drives• Open belt driveOpen belt drive• Crossed belt drive

Open belt driveU d f ll l h ft d t b t t d i th• Used for parallel shafts and to be rotated in the samedirection as that of the driver shaft.

• The driver pulley pulls the belt from one side and delivers it• The driver pulley pulls the belt from one side and delivers itto the other side.

• The tension in the former side will be larger and hence calledThe tension in the former side will be larger and hence calledtight side and the other side where the tension is less iscalled slack side.called slack side.

Crossed belt drive• when the driven shaft is to be rotated in the opposite direction as that of the driver shaftopposite direction as that of the driver shaft

• The belt is to be arranged in a crossed manner

V – Belt • These appears in trapezoidal in 

cross section.• These are moulded as endless• These are moulded as endless 

loops from rubber, reinforced with fibrous material

• They run in the V‐ groove pulleys or sleeves of total cone angle 2α

• Multiple V‐ belts are used whenMultiple  V belts are used when the power transmitted  is too greater for a single belt P f 0 5 t 150 kW b• Power from 0.5 to 150 kW can be transmitted. 

TerminologyTerminology

• Length of the belt• Velocity ratioVelocity ratio• Slip• Creep• Ratio of belt tensionsRatio of belt tensions• Power transmitted

Length of Belt DriveO B l D i• Open Belt Drive

Where ‐dr1 and r2 = Radii of the large and small pullysx = Distance between the centres of the pulleys (i.e. O1O2)L = Total length of the beltL = Total length of the beltα = Angle of Lap

Cross Belt Drive

Where ‐dr1 and r2 = Radii of the large and small pullysx = Distance between the centres of the pulleys (i.e. O1O2)L = Total length of the beltL = Total length of the beltα = Angle of Lap

Velocity RatioVelocity Ratio

It is defined as the ratio of the speed ofthe driving pulley (N1) to the speed ofg p y ( 1) pthe driven pulley (N2)

Velocity Ratio  =   N1/N2  = d2/d1 (Negligible belt Thickness)

Velocity Ratio = N1/N2 = (d2+t)/(d1+t)Velocity Ratio      N1/N2  (d2 t)/(d1 t) (Effect of belt Thickness (t))

Where   

d1  andd2 = Diameters of the pulleys

Slip In Belt DrivesSlip In Belt Drives

• It is a phenomenon of the relative motion between belt and pulley.p y

• Due to insufficient grip of friction between pulley and beltpulley and belt

Creep in the Belt DrivesCreep in the Belt Drives

• The  motion of belt relative to driving and driven pulley due to unequal stretching of the p y q gtwo sides of the drive is known as creep

Ratio of belt tension 

V

T1 = Tension in the tight side T2 = Tension on the slack side µ= coefficient of frictionµ= coefficient of friction θ= angle of contactβ = Angle made by V-section of the Belt

Power TransmittedP = [(T1 - T2 )V] /1000 KW( 1 2 )

» V= velocity of the belt » V= πdN/60 m/s

Stepped Cone  Pulley or Speed Cone

Advantages of belt drive mechanismAdvantages of belt drive mechanism

Th i l Th i lTh i l Th i l•• They are simple. They are economical.They are simple. They are economical.•• Overload and jam protection are provided. Overload and jam protection are provided. •• Noise and vibration are damped out Machinery life isNoise and vibration are damped out Machinery life is•• Noise and vibration are damped out. Machinery life is Noise and vibration are damped out. Machinery life is 

prolonged because load fluctuations are cushioned (shockprolonged because load fluctuations are cushioned (shock‐‐absorbed). absorbed). 

•• They are lubricationThey are lubrication‐‐free. They require only low maintenance. free. They require only low maintenance. •• They are highly efficient (90They are highly efficient (90––98%, usually 95%). Some 98%, usually 95%). Some 

l l bll l blmisalignment is tolerable. misalignment is tolerable. •• They are very economical when shafts are separated by large They are very economical when shafts are separated by large 

distancesdistancesdistances. distances. 

Disadvantage of belt driveDisadvantage of belt drive

• They are not a positive drive• Less efficient due to slip and creepLess efficient due to slip and creep• Not suitable for short centre distance • Not applicable for heavy loads• Belt joints reduce the life of the beltBelt joints reduce the life of the belt 

Comparison of Flat and V belt

Flat Belt V beltTransmit less torque Transmit high torque

Suitable for large center distance Suitable for short center distance

Si b lt St d d SiSize can be alter Standard Size

Suitable for high speed Suitable for optimum speedSuitable for high speed Suitable for optimum speed

Repairable Non repairable

Cost is optimum Cost is more

Real time applicationsReal time applications

• Lathe , drilling  and sewing machines• Compression systemsCompression systems • Automobiles• Water systems• Power generation unitsPower generation units• Air conditioning systems

Problems on Belt DrivesProblems on Belt DrivesProblem : 1

Power is to be transmitted from a shaft to anotherPower is to be transmitted from a shaft to anotherby means of a belt drive. The diameter of the largepulley is 600 mm and that of the small pulley is 300pulley is 600 mm and that of the small pulley is 300mm. the distance between the center of the twopulleys is 3 meter. If the axes of the two shafts arepulleys is 3 meter. If the axes of the two shafts arein the same plane and parallel to each other findthe length of the belt required for:g qi) Open belt drive and ii) Cross belt drive

Problem : 2

An engine is driving a generator bymeans of a belt The pulley on themeans of a belt. The pulley on thedriving shaft has a diameter of 55 cmand runs at 276 rpm. If the radius ofth ll th t i 15the pulley on the generator is 15 cm,find its speed in rpm.find its speed in rpm.

P bl 3Problem : 3

A shaft running at 100 rpm is to drivea parallel shaft at 150 rpm The pulleya parallel shaft at 150 rpm. The pulleyon the driving shaft is 35 cm ingdiameter. Find the diameter of thedriven pulley Calculate the lineardriven pulley. Calculate the linearvelocity of the belt and also thevelocity ratio.

P bl 4Problem : 4

The sum of the diameter of twopulleys A and B connected by a belt is900 mm If they run at 700 and 1400900 mm. If they run at 700 and 1400rpm respectively, determine thep p y,diameter of each pulley

P bl 5Problem : 5

In a belt drive the ratio of tensions is 2and the slack side tension is 500 N. Ifthe speed and diameter of the driventhe speed and diameter of the drivenpulleys are 200 rpm and 120 cmp y prespectively, find the power

i dtransmitted.

P bl 6Problem : 6

In an open belt drive running in theclockwise direction, the tension in thetight side is 3000 N and the arc oftight side is 3000 N and the arc ofcontact is 150°. if the coefficient is 0.3.find the tension on the slack side ofh b lthe belt

P bl 7Problem : 7

In a cross belt the difference intensions between the tight and slacksides of the belt is 1000 N fine thesides of the belt is 1000 N. fine thetension on the slack and tight sides, ifg ,the angle of contact is 160° and the

ffi i f f i i i 0 3coefficient of friction is 0.3.

Problem : 8Problem : 8

A V b l d i i d iA V‐belt drive is used to transmit powerbetween two shafts. The powertransmitted is 8000 W at a speed of 300rpm. If the semi‐groove angle of the V‐p g gbelt is 20°, the mean radius of thegrooved pulley is 500 mm, and the angleg p y , gof lap is 160°, calculate the tension onthe either sides of the belt. (Assumethe either sides of the belt. (Assumecoefficient of friction is 0.25)

P bl 9Problem : 9

A V‐ belt drive transmits 10 kW powerat 240 rpm. The grooved pulley has amean diameter of 1 2 m and groovemean diameter of 1.2 m and grooveangle 45°. Taking µ = 0.3 and angle ofg g µ glap π radian, determine the tension on

h id f h b leach side of the belt.

P bl 10Problem : 10

An engine shaft running at 200 rpm isi d d i 300required to drive a generator at 300rpm

by flat belt drive. Pulley on the drivingy y gshaft has 500 mm diameter. Determineth di t f th ll ththe diameter of the pulley on thegenerator shaft, if the belt thickness isg ,8mm and slip is 4%

CHAIN DRIVES1.1. Chain drive Chain drive is a way of transmitting is a way of transmitting 

mechanical power from one place tomechanical power from one place tomechanical power from one place to mechanical power from one place to another. another. 

22 i f di f d2.2. It is often used to It is often used to convey power convey power to to the wheels of a vehicle, particularly the wheels of a vehicle, particularly bicycles and motorcycles. bicycles and motorcycles. 

3.3. It is also used in a wide It is also used in a wide variety of variety of machines machines besides vehicles.besides vehicles.

4.4. Most often, the power is conveyed by Most often, the power is conveyed by aa roller chainroller chain, known as the, known as the drivedrivea a roller chainroller chain, known as the , known as the drive drive chainchain, passing over a , passing over a sprocket gearsprocket gear, , with the teeth of the gear meshing with the teeth of the gear meshing with the holes in the links of the with the holes in the links of the chain. chain. 

Chain LengthChain Lengthh ( ) bPitch (P) : Distance between two consecutive

roller centerPitch Circle : The circle draw though the rollerPitch Circle : The circle draw though the roller

center of a wrapped chain arounda sprocket

ApplicationsApplications

• Where slippage needs to be reduced to a considerable amount

• Initial torque developed is moreS ll di• Smaller center distance

• Agro machinery , automobiles, cranesg y , ,

ProblemProblem 

A chain drive is used for reduction of speedfrom 300 rpm to 100 rpm. The number ofteeth on driving sprocket is 18. Find thenumber of teeth on driven sprocket. If thepP. C. D (Pitch Circle Diameter) of the drivensprocket is 600 mm and center to centersprocket is 600 mm and center to centerdistance between the sprocket is 700 mm.determine the pitch and length of the chaindetermine the pitch and length of the chain.

Answer

T2 = 54 2

P = 34.89 mmL = 2756.31 mm = 2.756 m

Rope DriveRope Drive

• They are similar to belt drive• They are classified as:They are classified as:

a) Fibre Rope – Made of Manila or Cottonb) Wi R M d f S l ib) Wire Rope – Made of Steel wires

Gear systemsGear systems

• Machine elements that transmit the motion and power between the rotating shafts by p g ymeans of successively engaging teeth .

• Compact than the other drive systems• Compact than the other drive systems• More accurate power transmission • Less slippage 

Common forms of gear configurationCommon forms of gear configuration

• Gears for connecting parallel shafts• Gears for connecting intersecting shaftsGears for connecting intersecting shafts• Gears for connecting neither parallel nor i i h fintersecting shafts

Gear types for connecting parallel shafts

• Spur gears (internal and external)• Parallel helical gearsParallel helical gears• Double Helical/Herringbone gear 

SPUR GEAR• Teeth are parallel to the axis of shaft• Internal gearing & External gearing• Easy to find, inexpensive and efficient• Can not be used when a direction change 

between the two shafts is requiredbetween the two shafts is required• Used for smaller speed due to noise creation 

at higher Speed g p• Examples‐ Gear boxes, Machine tools, Watches

Automobiles, Precision Measuring Instruments etc.

HELICAL GEAR• Teeth are at an angle to the shaft• They are longer than the teeth on spur gear• Tooth strength is greater than spurg g p• Carry more load• Due to longer length reduce efficiencyAdvantagesAdvantagesIt can be used on non parallel and even perpendicularShafts and can carry higher load than spurDisadvantagesMore expensive and difficult to manufacturing

Double Helical/Herringbone gear / g g

• They have a right hand helix and left hand helix• The teeth of two rows separated by groove used for tool run out• The teeth of two rows separated by groove used for tool run out• Run at high speed with less noise and vibration• They eliminate thrust load as in case of single helix

Gears for connecting interesting shafts

Bevel gear• Transmit power between intersecting shaft• Teeth of these gears are formed on conical surface• More application in Automobile• More application in Automobile• It can not be used for parallel shaft and becomes noisy at high speed

Neither interesting nor parallel ShaftNeither interesting nor parallel Shaft 

Hypoid GearHypoid Gear• They are resembles spiral bevels• There axes of the shafts do not intersect

U d l th h ft f d i i t ti d ll l• Used only the shafts of drive are non intersecting and non parallel• Used in Automobile differential unit

Warm Gear• It is combination of screw with helical gear• The screw with one or more threads is called Worm• They are used to achieve high velocity ratio• That is they are mainly used to either increase or decrease speed.• Used in Lathe milling drilling machines etc• Used in Lathe, milling drilling machines etc

Rack and Pinion• It  is a type of linear actuator that comprises a pair of gears which convert 

rotational motion into linear motion.rotational motion into linear motion.• A circular gear called  pinion, engages teeth on a linear gear called the 

rack• Rotational motion applied to the pinion causes the rack to move relative 

to the pinion, thereby translating the rotational motion of the pinion into linear motion.

Gear TerminologyGear Terminology

Velocity ratio of gearVelocity ratio of gear

• Ratio of speed of driving gear to the speed of driven gearg

Types of gear trainsTypes of gear trains

• Simple gear train • Compound gear trainCompound gear train• Reverted gear train• Epicyclic gear train • Planetary gear trainPlanetary gear train 

Simple gear trainSimple gear train 

P bl 1Problem ‐ 1

Two gear wheels having 80 teeth and30 teeth mesh with each other. If thesmaller gear wheel run at 480 rpmsmaller gear wheel run at 480 rpm,find the speed of large wheelp g

P bl 2Problem ‐ 2

A gear wheel of 20 teeth drivesanother gear wheel having 36 teethrunning at 200 rpm Find the speed ofrunning at 200 rpm. Find the speed ofthe driving wheel and the velocityg yratio

Problem 3Problem ‐ 3

A simple gear train is made up of four gearsA, B, C, and D having 20, 40, 60 and 70 teethrespectively. If gear A is main driver rotatingat 500 rpm clockwise, calculate thep ,following:1 Speed of the intermediate gears1. Speed of the intermediate gears2. Speed and direction of the last follower3. Train Value

P bl 4Problem ‐ 4

Two spur gears A and B connect twoparallel shafts that are 500 mm apart.Gear A runs at 400 rpm and gear B atGear A runs at 400 rpm and gear B at200 rpm. If the circular pitch is givenp p gto be 30 mm, calculate the number of

h A d Bteeth on gear A and B.

Compound gear trainCompound gear train 

P bl 1Problem ‐ 1

A compound gear train consists of 4gears A B C and D and they have 20gears , A, B, C, and D, and they have 20,30, 40 and 60 respectively. A is keyed toth d i i h ft d D i k d t ththe driving shaft, and D is keyed to thedriven shaft, B and C are compoundgears, B meshes with A, and C mesheswith D. if A rotates at 180 rpm, find thewith D. if A rotates at 180 rpm, find therpm of D

Reverted Gear TrainReverted Gear Train

Epicyclic Gear TrainEpicyclic Gear Train

Planetary gear trainPlanetary gear train

• Also termed a epicyclical gear

Gears in real time applicationGears in real time application 

• Automobiles• Machine systemsMachine systems• Pumping systems• Machine tools• Timing and related equipmentsTiming and related equipments

Merits and DemeritsMerits and Demerits

Merits:• CompactnessCompactness• Greater speed amplification and reduction of 

dspeeds• Less slipp• Direct contact with the driver

Merits and DemeritsMerits and Demerits

Demerits• Wear and tearWear and tear• Required coolant for reduction of heat d l ddeveloped

• Back lash • Noise and vibration