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Automobiles and Power Transmission Devices ARUN JOSE TOM, MLMCE, BME

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TYPES OF AUTOMOBILES Purpose • a) Passenger Vehicle: Carries passengers. Eg. Car, jeep, bus • b) Goods Vehicle: Vehicles that carries goods. Eg. Truck Capacity • a) Light Motor Vehicle: Carry light things, less in size and weight. Gross vehicle weight does not exceed 7500kg. Eg. Car, motor cycle, scooter • b) Heavy Motor Vehicle: Can carry very heavy materials and possess large mass. Gross vehicle weight exceeds 12000kg. Eg. Bus, lorry Fuel Used • a) Petrol Vehicles: Car, scooter • b) Diesel Vehicles: jeep, truck, bus • c) Electric Vehicle: electric car, electric buses ARUN JOSE TOM, MLMCE, BME

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d)Gas Vehicles: CNG vehicles

Based on type of transmission • a) Automatic Transmission Vehicle: capable of changing gear automatically • b) Manual Transmission Vehicle: gear have to be changed manually • c) Semi-Automatic Transmission Vehicles: manual and automatic mode, gear changes without a clutch pedal

Drive of the vehicle • a) Rear Wheel Drive: rear wheels are driven by the engine • b) Front Wheel Drive: front wheels are driven by the engine • c) All Wheel Drive: all the wheels are driven by the engine

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Major Components of an Automobile

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• Power transmitted from engine to flywheel through crankshaft • When clutch is in engaged position, power transmitted from flywheel to gear box through clutch

• From gear box, the power is transmitted to the wheels via propeller shaft, differential and axle

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Clutch Engaged ENGINE

→

GEAR BOX

→

PROPELLER SHAFT

→

DIFFERENTIAL

↓ WHEELS

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AXLE

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Clutch Disengaged

ENGINE

→

FLYWHEEL

→ NO POWER TRANSFER

HEELS

No power is transmitted to clutch

Engine is isolated from the wheels

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• Engine and flywheel is connected by a shaft called crank shaft( driver shaft) • Clutch and gear box is connected by a shaft( driven shaft)

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Functions of Major Components of an Automobile

Chassis and Frame It supports the engine, body, braking system, transmission system, steering, passengers…etc

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Chassis

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Frame

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FLYWHEEL

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The main function of a flywheel is to smoothen out variations in the speed of a crankshaft

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GEAR BOX

PROPELLER SHAFT

CLUTCH

TRANSMISSION SYSTEM

AXLE

DIFFERENTIAL

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Transmission System The power developed by the engine is transferred to the wheels by transmission system

It consists of • Clutch • Gear box • Propeller Shaft • Axle • Differential ARUN JOSE TOM, MLMCE, BME

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TRANSMISSION SYSTEM- Clutch • Purpose of the clutch is to allow the driver to couple or decouple the engine and transmission • Clutch is used to engage or disengage the engine to the gear box • When clutch is in engaged position, the engine power flows to the gear box through clutch and from gear box power flows to the wheels

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• When clutch is in disengaged position, the engine power does not reach to gear box • When gears are to be changed while vehicle is running, the clutch permits temporary decoupling of engine and wheels so that gears can be shifted • Engine and flywheel is connected by a shaft called crank shaft ( driver shaft) • Clutch and gear box is connected by a shaft( driven shaft)

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CLUTCH PLATE ARUN JOSE TOM, MLMCE, BME

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SQUARE JAW POSITIVE SPIRAL JAW CLUTCH

CENTRIFUGAL

FRICTION

CONE MULTIPLE PLATE

PLATE SINGLE PLATE

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MAIN PARTS OF A CLUTCH It consists of (a) a driving member, (b) a driven member, and (c) an operating member •Driving member has a flywheel which is mounted on the engine crankshaft. • The driven member is a disc called clutch plate. This plate can slide freely to and fro on the clutch shaft. • The operating member consists of a pedal or lever which can be pressed to disengaged the driving and driven plate.

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1) Positive Clutch In the engaged position, the shafts are rigidly connected and in the disengaged position, the shafts will be disconnected fully

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TYPES OF POSITIVE CLUTCH

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2) Friction Clutch • Basic principle: It operates on the principle of friction. When two surfaces are brought in contact and are held against each other due to friction between them, they can be used to transmit power. If one is rotated, then other also rotates. One surface is connected to engine and other to the transmission system of automobile. Thus, clutch is nothing but a combination of two friction surfaces • Engagement occurs gradually and hence smooth engagement is possible • Working of clutch is based on frictional force, that is, when two frictional surfaces are brought in contact and pressed, they are united and rotate together as a single unit

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SINGLE PLATE CLUTCH

CONE CLUTCH FRICTION CLUTCH

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A) Single Plate Clutch • Single plate with friction surface is connected to a driven shaft • Driven shaft transfer power to gear box

• Flywheel is connected to the driver shaft( crank shaft) • Both the shafts are co-axial

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• During disengagement, a lever keeps the disk(clutch) away from the driving disk(flywheel)

driven

• To engage the clutch, the lever is gradually released • The spring provides the required axial force to press the driven disk against the driver disk • Clutch is nothing but a combination of two friction surfaces

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CLUTCH PLATE ARUN JOSE TOM, MLMCE, BME

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B) Cone Clutch • Inner and outer cone as two working surfaces • Outer cone is fixed to the driving shaft

• Inner cone is free to slide axially on the driven shaft • Spring provides the necessary axial force to the inner cone to press against the outer cone, thus engaging the clutch • Lever is used to disengage the clutch • Inner cone surface is lined with friction material

• Greater torque transmitting capacity ARUN JOSE TOM, MLMCE, BME

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Transmission System – Gear Box • It contains gearing arrangement to get different speeds

• Both mating gears have same number of teeth, both will rotate at same speed • One gear has less teeth than other, the gear with less number of teeth will rotate faster than larger gear • Gear box is used to vary the speed of the propeller shaft

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Gears ARUN JOSE TOM, MLMCE, BME

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• From the diagram, the main shaft and crankshaft have the same speed • Speed of the propeller shaft and main shaft have to be varied using a gear box • Low speed of the propeller shaft means higher torque • High speed of the propeller shaft means less torque

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• From the diagram shown in the previous slide, assume GEAR D is the driver

• GEAR D have higher speed and GEAR A have lower speed, It means that shaft connected to GEAR A have higher torque • Reverse case, gear A is the driver • Then GEAR D have the higher speed, so shaft connected to

the GEAR D have low torque and high speed(speed means RPM, RPM- rotations per minute) ARUN JOSE TOM, MLMCE, BME

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Transmission System – Propeller Shaft Used to transfer power from gear box to differential

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Transmission System – Differential • To distribute power from the propeller shaft to two axles

• Finally the power from the differential is transmitted to wheel via axles • Main function of the differential is to give separate amount of power to each wheels

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Function of differential

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Function of differential

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Transmission System – Axle Used to transmit power from differential to wheels

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Steering System • Front wheels can be turned to left and right by steering system

• It also provides stability to vehicle • Nowadays hydraulic and power steering systems are used to turn the wheels

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Suspension System • Main goals: comfort – contact - control • It separates the wheel and axle assembly of the automobile from its body • Main function of the suspension system is to isolate the body of the vehicle from shocks and vibrations generated due to irregularities on the surface of roads

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Coil spring suspension ARUN JOSE TOM, MLMCE, BME

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Leaf spring suspension

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Coil spring suspension ARUN JOSE TOM, MLMCE, BME

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Braking System • It is used to slow down or stop the vehicle • Brakes commonly use friction between two surfaces pressed together to convert the kinetic energy of the moving object into heat • In brake, there is engagement of moving member to a stationary member

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• Mainly two types a) Drum Brake b) Disk Brake • In drum and disk brake, a fixed shoe rubs against a moving drum or disc • Friction material is attached to the fixed part

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DRUM BRAKE

DISK BRAKE BRAKES

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Hydraulic Type

Mechanical Type

Drum Brake

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Drum Brake • Commonly used in light vehicles • It consists of two shoes • Outer surface of the shoes are lined with some friction material • Each shoe is pivoted at the bottom end

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A) Mechanical Drum Brake

• Each shoe is pivoted at the bottom end • Top end of the shoes are contact with a cam • When the brake is pressed, cam rotates and the shoes are pushed outwards against the rotating drum • Rotating drum is fixed to the wheel

• Friction between the shoes and the drum causes an reduction in drum speed

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B) Hydraulic Drum Brake • Each shoe is pivoted at the bottom end • Other end of the shoes are contact with a PISTON Arrangement

• When the brake is pressed, piston moves outward and the shoes are pushed outwards against the rotating drum • Rotating drum is fixed to the wheel • Friction between the shoes and the drum causes an reduction in drum speed ARUN JOSE TOM, MLMCE, BME

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FLOATING TYPE

DISC BRAKE

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FIXED TYPE

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DISC BRAKE- floating type

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• The main components are brake pads, caliper and the rotor • Brake pads are the rough friction surface that is pressed against the rotor to stop the wheel • Rotor is a round plate attached to the hub • Hub is attached to the wheel • Piston presses one brake pad against the rotor, while the caliper presses the other(floating type) • As the brake fluid pressure in the cylinder increases, piston moves to left, piston also pushes the caliper to the right. This allows both brake pads to press against the wheel simultaneously

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DISC BRAKE- fixed type • The main components are brake pads, caliper and the rotor • Brake pads are the rough friction surface that is pressed against the rotor to stop the wheel

• Rotor is a round plate attached to the hub • Hub is attached to the wheel • Both Piston presses the brake pads against the rotor due to increase in the fluid pressure inside the cylinder

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Methods of Power Transmission • Mechanical power can be transmitted from one shaft to another by following methods • Belt drive • Rope drive • Chain drive • Gear drive • The shaft from which power is transmitted is called driver shaft and the shaft to which power is transmitted is called driven shaft

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The choice of the type of drive for power transmission depend on many factors such as

• Distance between shafts

• Amount of power to be transmitted • Speed ratio of shafts • Accuracy required

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BELT DRIVE • A belt is a thin inextensible band made of leather, rubber, steel, canvas or balata • Belts are used to transmit power between two parallel shafts, which are at a considerable distance apart • Belts are made endless to run over the pulleys mounted on the shafts • Friction between the belt and the pulley is responsible for transmitting power from one pulley to other • It’s a friction drive

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• It is not a positive drive, since there is always some possibility of slipping between the belt and pulley

Amount of power transmitted depends on • Velocity of the belt • The tension with which the belt is placed under the pulleys

• The arc of contact between the belt and the smaller pulley

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FLAT BELT

V BELT

TYPES OF BELTS ARUN JOSE TOM, MLMCE, BME

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a) Flat Belt

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FLAT BELT DRIVE ARUN JOSE TOM, MLMCE, BME

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FLAT BELT PULLEYS

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• Flat belt are run on flat pulleys • They are used in sawmills, conveyors, electrical generators…etc • Used for moderate amount of power transfer Advantages • Simple in construction, smooth operation, low maintenance and long life • Flexible Disadvantages • Not positive drives • Less efficient • Not suitable for short distances ARUN JOSE TOM, MLMCE, BME

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b) V BELT • V belts have trapezoidal cross section • They run in the V- grooved pulleys • Multiple V belts are used when the power to be transmitted is large for a single belt • V belts are used in automotives and in agricultural purposes

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Advantages • Transmits higher torque than flat belts • Suitable for short distance • Easily installed and removed • Slip is negligible • Operation is quiet • Suitable for large speeds Disadvantages • Not suitable for large distances • Costly • V belts cannot be repaired • Construction is complicated ARUN JOSE TOM, MLMCE, BME

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Single V belt

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Single V belt drive ARUN JOSE TOM, MLMCE, BME

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Multiple V belt

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Multiple V belt drive ARUN JOSE TOM, MLMCE, BME

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V BELT PULLEYS ARUN JOSE TOM, MLMCE, BME

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V Belt

Flat Belt

Suitable for shorter distance

Suitable for longer distance

Trapezoidal section

Rectangular section

Frictional grip is more

Frictional grip is less

Power transmitted is more

Power transmitted is less

Velocity ratio is high

Velocity ratio is low

Occurrence of slip is seldom possible

Slip occurs easily

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Stepped Or Cone Pulley Drive

Open Belt Drive

Compound Belt Drive

Types of Belt Drives

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Belt Drive With Idler Pulleys

Cross Belt Drive

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1.Open Belt Drive

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• It is used to transmit power when the distance between the shafts is large

• Both shafts are in parallel • Both shafts rotates in the same direction • When the driver rotates in the clockwise direction, the lower side of the belt is tight and the upper side is slack • Upper side of the belt is called the slack side • Lower side of the belt is called the tight side

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2.Cross Belt Drive

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• Shafts are parallel and rotating in the opposite directions • At the point where the belt crosses, it rubs against itself and wears • The drive should operate at low velocity

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3.Belt Drive With Idler Pulleys

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• Shafts arranged in parallel and rotating in same direction • This drive is provided to deliver high velocity

• Idler pulley increases the angle of contact between belt and shaft

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4. Compound Belt Drive

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It is used when power is transmitted from one shaft to another through a number of pulleys

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5. Stepped or Cone Pulley Drive

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Used for changing the speed of driven shaft while the driving shaft is maintained at constant speed

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Stepped or cone pulley

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Calculation of length of belt a) Open Belt Drive

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• X= distance between centers of pulleys • r1, r2 = radii of larger and smaller pulleys respectively • L = total length of belt

L = л(r1+r2) + (r1-r2)2/x + 2x…… α = (r1-r2)/x ARUN JOSE TOM, MLMCE, BME

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b) Cross Belt Drive

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• X= distance between centers of pulleys • r1, r2 = radii of larger and smaller pulleys respectively • L = total length of belt

L = л(r1+r2) + (r1+r2)2/x + 2x…… α = (r1+r2)/x ARUN JOSE TOM, MLMCE, BME

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Ratio of Belt Tensions

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• • • •

T1 = tight side tension T2 = slack side tension Ѳ = angle of contact between the belt and pulley in radians μ = coefficient of friction between the belt and pulley

T1/T2 = e μ Ѳ

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Power Transmitted By Belt Drive • • • • • • • •

T1 = tight side tension, N T2 = slack side tension, N r = radius of pulley, m d = diameter of pulley, m ω = angular velocity, rad/sec V = velocity of belt, m/s N = speed of pulley(rotations per minute, rpm) If d is the diameter of driver pulley then N should be the speed of driver pulley and if d is the diameter of driven pulley then N should be the speed of driven pulley ARUN JOSE TOM, MLMCE, BME

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• Torque exerted on the pulley = (T1 - T2)r • Work done per sec = (T1 - T2)r ω

• Power transmitted = (T1 - T2)V • V=rω • ω = 2лN/60

• Power transmitted = [(T1 - T2) лdN]/60, Watts

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Velocity Ratio of a Belt Drive

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• Velocity ratio, i = speed of driven shaft / speed of driver shaft Also, Velocity ratio, i = diameter of driver pulley / diameter of driven pulley

i = N2/N1 = d1/d2 • • • •

N2= speed of driven shaft N1 = speed of driver shaft d1 = diameter of driver pulley d2 = diameter of driven pulley

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If the thickness of the belt, t is also considered, then

i = N2/N1 = (d1+t)/(d2+t)

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Slip of Belt Drive • Slip is measured as a difference between the linear speeds of the pulley rim and the belt over it • Generally it is expressed as a percentage Slip occurs due to  Friction between the belt and pulley decreases  When the smoothness of pulley surface is high  Difference between tensions in the tight and slack sides are very large

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• • • •

S1= % slip between the driver pulley and belt S2 = % slip between the driven pulley and belt d1 = diameter of driver pulley d2 = diameter of driven pulley

• S = S1 + S2, S- total slip 1) Effect of total slip on velocity ratio(neglecting the belt thickness) i = N2/N1 =

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2) Effect of total slip on velocity ratio(considering the belt thickness)

i = N2/N1 =

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ROPE DRIVE

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Ropes

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• Rope drives are used for transmission of large amount of power over long distances • For a rope drive, groove angle of the pulley is usually 45⁰ • Fibre ropes and wire ropes are used Advantages • Smooth and silent operation • Less weight • Longer life • Efficiency is high • More reliable • Low cost ARUN JOSE TOM, MLMCE, BME

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CHAIN DRIVE

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CHAIN

SPROCKET

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• Chain drive consists of an endless chain running over special profile toothed wheels called sprockets • One of the sprockets will be the driver and the other driven • Smaller sprocket is called pinion and the bigger one is

called wheel

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Advantages • It is a non-slip drive • Very high efficiency • Occupies less space Disadvantages • High cost • More weight • Needs accurate mountings • Lubrication is critical

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SILENT OR INVERTED TOOTH CHAIN

ROLLER CHAIN

TYPES OF CHAIN

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ROLLER CHAIN

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SILENT/INVERTED TOOTH CHAIN

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GEAR DRIVE

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• A gear is a toothed wheel • One gear is mounted on the driving shaft and another one on the driven shaft, their teeth meshing with each other • It is a positive drive(no slip) • The axes of the shafts may be parallel or non-parallel • When two gears of different sizes mesh, the smaller one is called pinion and the larger one is called gear • When pinion(smaller gear) is the driver, output speed(driver speed) decreases and torque increases • When the gear(larger gear) is the driver, output speed(driver speed) increases and torque decreases

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Double Helical gears

Bevel gears

Helical gears

Spur gears

Worm gears

Types of gears

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1.SPUR GEAR

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SPUR GEAR DRIVE

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• SPUR gears are those which have teeth cut parallel to the

axis of the shaft • Spur gears are used to transmit power between parallel shafts • They are used in high speed and high load applications

Two types External gear and internal gear

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Internal Spur Gear

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• Internal gears have teeth on the inner periphery • Two gears rotate in same direction

• Pinion or smaller gear is inside the spur gear • Internal gears are used in heavy duty tractors, where much torque is required

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External Spur Gear

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External gears have teeth on the outer surfaces

and the two shafts rotate in opposite directions

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2.HELICAL GEAR

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• In helical gear, the teeth cut on the periphery are of helical screw form • Helical tooth is inclined at an angle to the axis of the shaft • Helical gears are used to transmit power between parallel shafts • The two shafts rotate in opposite directions • They have higher load carrying capacity • They operate smoother and quieter than spur gears

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3.Herringbone Gear or Double-Helical Gears

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• Herringbone gears have opposing helical teeth which nullify two axial thrusts • Load carrying capacity is very high • These gears are used to transmit power between two parallel shafts at high speeds • The two shafts rotate in opposite directions

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4.BEVEL GEAR

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STRAIGHT BEVEL GEAR

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SPIRAL BEVEL GEAR

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• Bevel gears are used to connect two non-parallel shafts with intersecting axes

• Teeth of these gears are formed on a conical surface • These gears are used to transmit power between two shafts at any angle, generally the shafts are at right angles • They are used to slow speed applications

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5.WORM GEAR D

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• Worm gears are used for power transmission between non-intersecting shafts that are generally at right angles to each other • Worm gearing consists of worm and worm wheel • Worm is a threaded screw and is used as the driver

• Worm wheel is a toothed wheel • Teeth of the worm wheel remain engaged with the threads of the worm

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6.RACK AND PINION

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Rack and pinion gears are used to convert rotation(pinion) into linear motion(rack) or vice versa

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Advantages of gear drive • Smooth and reliable • Transmits more power Disadvantages • Not suitable for large distances • Needs lubrication • Maintenance cost is high • Power loss due to friction • Production cost is high

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LAW OF GEARING

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• A gear is a toothed wheel • One gear is mounted on the driving shaft and another one on the driven shaft, their teeth meshing with each other • It is a positive drive(no slip) • The axes of the shafts may be parallel or non-parallel • When two gears of different sizes mesh, the smaller one is called pinion and the larger one is called gear • When pinion(smaller gear) is the driver, output speed decreases and torque increases • When the gear(larger gear) is the driver, output speed increases and torque decreases

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GEAR RATIO • Ratio of the number of teeth on the driven gear to that of the driver gear • Z1 = number of teeth on the driver gear • Z2 = number of teeth on the driven gear

Gear Ratio, G

= Z2/ Z1

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G increases • Driven shaft speed decreases • Driven shaft torque increases

G decreases • Driven shaft speed increases • Driven shaft torque decreases

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PLANETARY GEAR TRAINS SIMPLE GEAR TRAINS

COMPOUND GEAR TRAINS

GEAR TRAINS ARUN JOSE TOM, MLMCE, BME

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GEAR TRAINS

Combination of gears by means of which motion and power are transmitted from one shaft to another

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1) Simple Gear Train

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• Series of gear wheels in which each gear is mounted on a separate shaft • Gears in between Driver and Driven gear called idler gears

Fig. A ARUN JOSE TOM, MLMCE, BME

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Fig. A shows one driver, one follower and 2 idler gears

Speed ratio = Nfollower/Ndriver = Zdriver/Zfollower Nfollower = speed of the follower(rpm) Ndriver = speed of the driver(rpm) Zfollower = number of teeth on the follower Zdriver = number of teeth on the driver

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2) Compound Gear Train

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Fig.B

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• From Fig.B, gear 1 and gear 4 mounted on separate shafts • Gear 2 and gear 3 on same shaft, so gear 2 and gear 3 rotate with equal speed • Gear 1 is the driver and gear 4 is the follower

Speed ratio = Nfollower/Ndriver = (Zdriver/Z2) X (Z3/Zfollower)

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Nfollower = speed of the follower(rpm) Ndriver = speed of the driver(rpm) Zfollower = number of teeth on the follower Zdriver = number of teeth on the driver Z2 = number of teeth on gear 2 Z3 = number of teeth on gear 3

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3. Planetary Gear Train

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Sun gear or ring gear(DRIVER)

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• Planetary gear trains are having one or more gears orbiting about the central axis of the train

• From the above animation central small gear is called Sun gear • Gears over the sun gear called Planet gear • Outer larger gear called Ring gear

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GEAR TERMINOLOGY

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• Pitch Circle: Theoretical or imaginary circle upon which all the calculations are made • Pitch Circle Diameter: Diameter of the pitch circle or it is the mean diameter of the gear wheel. Normally, the size of the gear is specified by pitch circle diameter • Pitch Point: Point of contact of two pitch circles • Addendum Circle: Circle passing through the tips of teeth • Addendum: Radial distance between pitch circle and addendum circle • Dedendum Circle(Root Circle): Circle passing through the roots of the teeth

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• Dedendum: Radial distance between pitch circle and dedendum circle • Full Depth(Whole Depth) of Teeth: Full Depth = Addendum+Dedendum • Top Land: Surface at the top of tooth • Bottom Land: Surface at the root of the tooth, in between two adjacent teeth • Tooth Thickness: Width of the tooth measured along the pitch circle • Tooth Space: Width of space between the two adjacent teeth measured along the pitch circle ARUN JOSE TOM, MLMCE, BME

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• Face: Tooth surface between the pitch circle and the top land • Flank: Tooth surface between the pitch circle and the bottom land

• Face Width: Length of tooth measured parallel to the axis of gear • Profile: Curve formed by the face and flank of the tooth

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• Backlash: Amount by which the width of a tooth space(mating gear) exceeds the thickness of the engaging gear tooth in order to prevent tooth binding under operating conditions also backlash is the difference between the tooth space of the mating gear and the tooth thickness of gear, measured along the pitch circle ARUN JOSE TOM, MLMCE, BME

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• Working Depth: Radial distance between the addendum circle of a gear and the addendum circle of its mate

• Clearance: Clearance = Whole depth - Working depth Also clearance is the radial distance between the addendum circle of a gear and the root circle of its mate ARUN JOSE TOM, MLMCE, BME

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• Circular Pitch(Pc): Distance measured along the circumference of pitch circle from a point from one tooth to the corresponding point on the adjacent tooth

Pc = (лd)/Z • Diametral Pitch(P): Number of teeth per unit length of pitch circle diameter P = Z/d • Module(m): Ratio of pitch circle diameter in mm to the number of teeth m = d/Z d=Pitch circle diameter, Z= Number of teeth ARUN JOSE TOM, MLMCE, BME

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