Unit IV: Automobiles and Power

Transmission, Gear Drives, Belt

Drives & Fasteners

Objective: To understand elements of Power transmission

systems used in automobiles and fasteners
 Content

• Automobiles and Power Transmission: Different types of

automobiles, types of power units in automobiles; brief
description of major components and their functions.

• Gear Drives: Types - spur, helical, bevel, worm and rack and
pinion.

• Belt Drives: Types of belt drives, Flat-Belt Drive, V-Belt

Drives.

• Fasteners: Definition, Classification, brief description of

permanent, temporary, threaded and non-threaded fasteners.
 Different Types of Automobiles
• “A self-propelled passenger vehicle, used for land transport and generally has four to eight
tires, and is powered by an internal combustion engine or an electric motor”
• The branch of Engineering which deals with the manufacturing and technology of
automotive vehicles is known as Automobile engineering.
• Today automobiles play a major role in our lives, without them luxuries of modern world
cannot be imagined.
• Automobiles are used for both passenger and goods transport, hence performing as a
lifeline to humans.
• In our day to day life we come across different types of automobiles but we exactly don’t
know how many types of automobiles are present in the world.
 Classification of Automobiles
1. Based on Purpose :
• Passenger vehicles: These vehicles carry passengers. e.g: Buses, Cars, passenger trains.
• Goods vehicles: These vehicles carry goods from one place to another place. e.g: Goods
lorry, Goods carrier.
• Special Purpose: These vehicles include Ambulance, Fire engines, Army Vehicles.

2. Based on Load Capacity:

• Light duty vehicle: Small motor vehicles. eg: Car, jeep, Scooter, motorcycle
• Heavy duty vehicle: large and bulky motor vehicles. e.g: Bus, Truck, Tractor

3. Based on fuel used:

• Petrol engine vehicles : Automobiles powered by a petrol engine. e.g: scooters, cars,
motorcycles.
• Diesel engine vehicles : Automobiles powered by diesel engine. e.g: Trucks, Buses,
Tractors.
• Gas vehicles : Vehicles that use gas turbine as a power source. e.g: Turbine powered cars.
• Electric vehicles : Automobiles that use electricity as a power source. e.g: Electric cars,
electric buses.
• Steam Engine vehicles : Automobiles powered by steam engine. e.g: Steamboat, steam
locomotive, steam wagon.
 Classification of Automobiles
4. Based on Drive of the vehicles:
• Left-Hand drive : Steering wheel fitted on the left-hand side.
• Right-Hand drive : Steering wheel fitted on the right-hand side.
• Fluid drive : Vehicles employing torque converter, fluid flywheel or hydramatic transmission.
5. Based on number of wheels and axles:
• Two wheeler : motorcycles, scooters
• Three-wheelers : Tempo, auto-rickshaws
• Four wheeler : car, Jeep, Bus, truck
• Six-wheelers : Buses and trucks have six tires out of which four are carried on the rear
wheels for additional reaction.
• Six axle wheeler : Dodge(10 tire) vehicle
6. Based on type of transmission:
• Automatic transmission vehicles: Automobiles that are capable of changing gear ratios
automatically as they move. e.g: Automatic Transmission Cars.
• Manual transmission vehicles: Automobiles whose gear ratios have to be changed
manually.
• Semi-automatic transmission vehicles: Vehicles that facilitate manual gear changing with a
clutch pedal.
7. Based on Suspension system used:
• Convectional – Leaf Spring
• Independent – Coil spring, Torsion bar, Pneumatic.
Classification of Automobiles
Components of the Automobile and their Functions
Five basic components :
(a) The Engine : It is source of power.
(b) The Body and Chasis : It supports the engine,
wheels, body, braking system, steering, etc.
(c) The transmission which transmits power from
the engine to the car wheels. It consists of
clutch, transmission, shaft, axles and
differential.
(d) The body.
(e) Accessories including light, air
conditioner/heater, stereo, wiper, etc.
 Engine

• Spark ignition engine (SI engine) An engine in which the combustion process in
each cycle is started by use of an external spark.

• Compression ignition engine (CI engine) An engine in which the combustion

process starts when the air-fuel mixture self ignites due to high temperature in the
combustion chamber caused by high compression.

• [Spark ignition and Compression Ignition engine operate on either a four stroke cycle
or a two stroke cycle]
 Basic Parts of IC Engine
• Cylinder Block • Connecting Rod
• Cylinder • Crank Shaft
• Piston • Piston Rings
• Combustion Chamber • Gudgeon Pin
• Inlet Manifold • Cam Shaft
• Exhaust Manifold • Cams
• Inlet & Exhaust Valves • Fly Wheel
• Spark Plug
Cylinder Block
• The main supporting structure for the various components.
• This Cylinder block with the Cylinder head will be tightened
with the number of bolts and studs. (A gasket will be placed
between the Cylinder block and the head).
• Cylinder Block is provided with the cooling fins If the
engine cooling system is an air cooling system
• If it is a water cooling system the water jackets will be provided
on the walls of the Cylinder blocks
 Basic Parts of IC Engine
Cylinder
• Inside the Cylinder Block, there will be a cylindrical shape which is
machined accurately to accommodate the piston to reciprocate. It is
called a cylinder.
• This cylinder filled with the working fluid and undergoes the different
thermodynamic processes to produce work output.
Piston
• A cylindrical component fitted into the cylinder is called as the piston.
• Plays a crucial role in producing the work output.
• It forms the moving boundary of the combustion system by creating a
gas-tight space with the help of piston rings and the lubricant.
Piston rings
• Fitted into the slots available in the piston itself to provide a tight seal
between the piston and the cylinder.
Combustion Chamber
• The space between the upper part of the cylinder and the piston top as
shown in fig called the combustion chamber.
• The combustion of the fuel takes place in the combustion chamber.
• Combustion of the fuel release the thermal energy results in building the
pressure in the cylinder.
 Basic Parts of IC Engine
Inlet Manifold
• The pipe which connects the intake system to the Inlet valve of
the engine is called Inlet manifold.
• Thru the Inlet manifold, the air and the fuel mixture and
directly drawn into the cylinder.
Exhaust Manifold
• The pipe which connects the Exhaust system to the exhaust
valve of the engine is called Exhaust manifold.
• Thru the Exhaust manifold, the combustion products will be
escaped into the atmosphere.
Inlet & Exhaust Valves
• Value is a device to operate the fluid in one direction only.
• Inlet and the Exhaust valves are provided on the cylinder head
or the side of the cylinder for regulating the charge coming into
the cylinder(Inlet Valve) or for discharging the combustion
products from the cylinder(Exhaust Valve).
• Valves will be available if it is a 4 stroke engine only. In 2 stroke
engines , there are ports available for the regulating the charge
coming into the cylinder(Transfer port) or for discharging the
combustion products from the cylinder(Exhaust port).
 Basic Parts of IC Engine
Connecting Rod
• Connects the piston and the crankshaft
• One end of the connecting rod is called a small end which is
connected on the piston side by gudgeon pin.
• The other end of the connecting rod is called the big end which is
connected to the crankshaft by crank pin.
Crank Shaft
• Cranks shaft converts the reciprocating motion of the piston
into the rotary motion to an output shaft.
• There are some balance weights are provided on the
crankshafts for dynamic balancing of the rotating system.
Cams & Cam Shaft
• To operate the Inlet and outlet valves at the correct timing, cams are
provided on the camshaft. And also drives the ignition system
• The camshaft is driven by the crankshaft through timing gears.
• The associated parts in the cams and the camshaft are the pushrods
rocker arms, valve springs, and tappets
Fly Wheel
• To achieve a uniform torque generation an inertia mass in the form
of a wheel is provided on the crankshaft called as the flywheel.
 Basic Parts of IC Engine
Spark Plug
• The component used to initiate the combustion process in the spark
ignition system.
• Spark plug will be located in the Cylinder Head.
• Spark plug will be only available in the Spark Ignition engines only.

Fuel injector
• A pressurized nozzle that sprays fuel into the incoming air
(SI engines )or into the cylinder (CI engines).

Fuel pump
• Electrically or mechanically driven pump to supply fuel from the fuel tank
(reservoir) to the engine.
Carburettor
• The major function of the carburetor is to supply carburised fuel as
per speed and the engine load.
• In petrol engines the carburettor is mounted on the induction pipe
or on the induction manifold.
• The quantity of fuel air mixture in appropriate ratio is controlled by
the throttle valve and the movements of the throttle valve are
connected to the accelerator.
Chassis and Body
Chassis and Body
Lubrication System
Cooling System
Fuel Supply System
Transmission System
Gear Box and Propeller Shaft
Front Axle and Rear Axle
Steering System
Suspension System
Wheel and Rim
Tyre
Brakes
Electrical or Electronic and Air Conditioning Systems
 Gear Drives
A gear is a toothed wheel that engages another toothed mechanism to change speed or the
direction of transmitted motion.
Gears are generally used for one of four different reasons:
1. To increase or decrease the speed of rotation
2. To change the amount of force or torque
3. To move rotational motion to a different axis (i.e. parallel, right angles, rotating, linear)
4. To reverse the direction of rotation

• Gears are compact, positive-engagement, power

transmission elements capable of changing the amount of
force or torque.
• Sports cars go fast (have speed) but cannot pull any weight.
• Big trucks can pull heavy loads (have power) but cannot go
fast. Gears cause this.
Where You Can See Gears in Your Daily Life?
 Gear Types
The gears can be classified according to:
1. the position of shaft axes
2. the peripheral velocity
3. the type of gears
4. the teeth position
According to the Position of Shaft Axes
 According to the Peripheral Velocity

According to Type of Gears

External Internal Rack & Pinion

According to Teeth Position
Types of Gears
 Spur Gears
Spur gears are used to transmit power between two parallel shafts. The teeth on
these gears are cut straight and are parallel to the shafts to which they are attached.
 Helical Gears
• Helical gears resemble spur gears, but the teeth are cut at an angle rather than parallel
to the shaft axis like on spur gears.
• The angle that the helical gear tooth is on is referred to as the helix angle. The angle of helix
depends upon the condition of the shaft design and relative position of the shafts.
• To ensure that the gears run smoothly, the helix angle should be such that one end of the
gear tooth remains in contact until the opposite end of the following gear tooth has found a
contact.
• For parallel shafts, the helix angle should not exceed 20 degrees to avoid excessive end
thrust.
 Bevel Gears
• A bevel gear is shaped like a section of a cone and primarily used to transfer power
between intersecting shafts at right angles.
• The teeth of a bevel gear may be straight or spiral.
• Straight gear is preferred for peripheral speeds up to 1000 feet per minute; above that they
tend to be noisy.

Some of the disadvantages of bevel a gear is

they are difficult to assemble due to the
changeable operating angle. The shafts also
experience a large force, so like helical gears, it
is important to ensure the bearing can
withstand the force.
 Worm Gears
• Worm gears are used to transmit power between two shafts that are at right angles to each
other and are non-intersecting.
• Worm gears are special gears that resemble screws, and can be used to drive spur gears or
helical gears.
• Worm gearing is essentially a special form of helical gearing in which the teeth have line
contact and the axes of the driving and driven shafts are usually at right angles and do not
intersect.
Worm Gears
 Rack and Pinion
The rack is a bar with a profile of the gear of infinite diameter, and when used with a
meshing pinion, enables the rotary to linear movement or vice versa.
Types and Applications of Gears
Difference Between Gears
 Gears Fundamentals & Terminology

1. Pitch circle 13.Module

2. Pitch circle diameter 14.Clearance
3. Pressure angle 15.Total Depth
4. Pitch point 16.Working Depth
5. Pitch surface 17.Tooth thickness
6. Addendum 18.Tooth space
7. Dedendum 19.The face of the tooth
8. Addendum circle 20.The flank of the tooth
9. Dedendum circle 21.Top land
10.Base circle 22.Face width
11.Circular pitch 23.Profile
12.Diameter pitch 24.Backlash
 Gears Fundamentals & Terminology
1. Pitch circle
Pich circle is the imaginary circle that rolls without slipping with a pitch circle of a mating gear.
2. Pitch Circle Diameter
The pitch circle diameter is the diameter of the pitch circle. It is also known as pitch diameter.
3. Pressure angle
Pressure angle is the angle between the common normal at the point of tooth contact and the
common tangent to the pitch circle. The usual pressure angles are 14½° and 20°.

4. Pitch point
It is a common point of contact between two pitch circles.
5. Pitch surface
It is the surface of the imaginary rolling cylinder that the toothed gear may be considered to
replace.
6. Addendum
The addendum is the radial distance of a tooth from the pitch circle to the top of the tooth.
7. Dedendum
Dedendum is the circle drawn through the bottom of the teeth. It is also called “root circle”.
 Gears Fundamentals & Terminology
8. Addendum circle
It is the circle drawn through the top of the teeth and it is concentric with the pitch circle.
9. Dedendum circle
It is the circle drawn through the bottom of the tooth. It is also called “root circle”.
10. Base Circle
The base circle of involute gear is the circle from which involute tooth profiles are determined.
11. Circular pitch
The circular pitch is the distance measured on the circumference of the pitch circle from a point
of one tooth to the corresponding point on the next tooth. It is denoted by Pc. Pc = πd/T
12. Diametral Pitch
It is the ratio of a number of teeth to the pitch circle diameter. It is indicated by Pd. Pd = T/d

13. Module
A module is the ratio of pitch circle diameter by m. m= d/T
14. Clearance
Clearance is the difference between the dedendum of one gear and the addendum of the
mating gear.
15. Total Depth
Total depth is the radial distance between the addendum and the dedendum of a gear. It is
equal to the sum of addendum and dedendum.
 Gears Fundamentals & Terminology
16. Working Depth
It is the radial distance from the addendum circle to the clearance circle. It is equal to the sum of
the addendum of the two meshing gears.
17. Tooth thickness
Tooth thickness is the width of the tooth measured along the pitch circle.
18. Tooth space
Tooth space is the width of space between the two adjacent teeth measured along the pitch
circle.
19. Face of the tooth
It is the surface of the tooth above the pitch surface.
20. Flank of the tooth
The flank of the tooth is the surface of the tooth below the pitch surface.

21. Top land

The top land is the surface of the top of the tooth.
22. Face width
Face width is the width of the gear tooth measured parallel to its axis.
23. Profile
It is the curve formed by the face and flank of the tooth.
24. Backlash
Backlash is the difference between the thickness of a tooth and the width of a tooth space on
which it meshes.
 Belt Drives
• Belt Drives are used to transfer power from one shaft to another.
• One of the easiest and cheapest ways to transfer power in a machine.
• In a belt drive system, there are two or more pulleys connected with a belt in
tension.
• The pulley that transfers the power is called the driver pulley, and the pulley that
receives the power is called the driven pulley.
• Belt drive is used in automobiles, home appliances like washing machine, toys, and
other similar products.
 Working Principle of Belt Drives
• When the driver’s pulley rotates, it causes pulling action to the belt due to friction.
The driven pulley absorbs that pulling action and rotates in the same direction as
the driver pulley. If the belt is attached in the reverse direction, then the driven
pulley will also rotate in the reverse direction.
• The pulling action is generated due to the friction between belts and pulleys.
More the friction, better the power transmission and less chance of slippage.
• Power transmission capacity of belt drive depends on the co-efficiant of friction
between the belt and pulley, belt velocity, angle of wrap and the unit mass of the
belt.
• If the distance between two pulleys is more, then one side of the belt will be under
tension, and it is called the tight side. The other side of the belt will be loose, and it
is called the slack side.
 Types of Belt Drive
Based on how pulleys are arranged and how power is transmitted, belt drives
are categorised into following types.
Selection of Belt Drive
• Open belt drive The following factors are considered in the
• Crossed belt drive selection of belt drives.
• The speed of the driver and driven pulleys
• Stepped cone pulley drive
• Speed reduction ratio
• Jockey pulley drive
• Power to be transmitted
• Fast and loose pulley drive
• Center distance between the shaft
• Shaft layout
• Positive drive requirements
 Open Belt Drive
• In these types of belt drive, the belt is employing when the two parallel shafts have to rotate
in the same direction.
• When the shafts are far apart, the lower side of the belt should be the tight side and the
upper side must be the slack side.
• This is because, when the upper side becomes the slack side, it will sag due to its own weight
and thus increase the arc of contact.

Few examples are Flour Mills, Cam Shaft,

Alternator, belt conveyor etc.
How To Calculate Belt Length Of Open Belt Drive?
 Cross Belt Drive
• In crossed belt drive, the driver pulley and the driven pulley rotates in the opposite direction.
When you need to transfer more power, then crossed belt drive is good.
• But the speed in a crossed belt drive is slow. This is because there will be more wear and tear
at the junction ( where the tight side and slack side meet) if the speed is more.

• The angle of contact is more in a crossed

belt drive. The belt length is usually less,
and there is less chance of slippage in
cross belt drive.
• Few examples are lathe machine,
treadmill, paper machine drives etc.

How To Calculate Belt Length of Crossed Belt Drive?

 Stepped Cone Pulley Drive
• This types of belt drives are used when the speed of the driven shaft is to be changed very
frequently as in the case of machine tools such as lathe, drilling machine, etc.
• A stepped cone pulley is an integral casting having three or number of pulleys of different
sizes one adjacent to the other as shown in fig.
• One set of stepped cone pulley is mounted in reverse on the driven shaft. An endless belt
will be wrapped around one pair of pulleys.
• By shifting the belt from one pair of pulleys to the other, the speed of the driven shaft can
be varied.
• The diameter of the driving and driven pulleys is such that the same belt will operate when
shifted on different pairs of pulleys.
 Fast and Loose Pulley Drive
• This types of belt drives are used when the driven or machine shaft is to be started or
stopped whenever desired without interfering with the driving shaft.
• A pulley which is keyed to the machine shaft is called a fast pulley and run at the same
speed as that of the machine shaft.
• A loose pulley runs freely over the machine shaft and is incapable of transmitting any
power.
• When the driven shaft is required to be stopped, the belt is pushed on to the loose pulley
by means of a sliding bar having belt forks.
 Jockey Pulley Drive
• In an open belt drive arrangement, if the center distance is small, or if the driven pulleys are
very small, then the arc of contact of the belt with the driven pulley will be very small,
which reduces the tensions in the belt, or if the required tension of the belt cannot be
obtained by other means, an idler pulley, called jockey pulley is placed on the slack side of
the belt.
• Which increases the arc of contact and thus the tension which results in increased power
transmission.
• Jockey Pulley is used to taking up the slack and sometimes changing the direction of driven
pulley rotation. The idle pulley or jockey pulley does not transmit power to any shaft.
 Types of Belts
Flat Belt V Belt Circular Belt Timing Belt
Flat Belt
• Flat Belt is the simplest belt type having a rectangular cross-section. This type of belt
transmits low power between long-distance(5-10 miters ) pulleys.
• The friction between belt and pulley creates the pull force that drives the driven
pulley.
 Types of Belts
V Belt Circular Belt
• V Belt has a trapezoidal cross-section. It • Circular Belt or round belt has a
is used to transfer a high amount of circular cross-section and is used in
power between short distances. grooved pulleys.
• This type of belt is used with grooved • Widely used to transmit power
pulleys. between long distances.
 Types of Belts
Timing Belt
• The timing belt has teeth similar to gears, and those are used with teethed pulleys.
• The timing belt drive is often called Positive Drive, as there is almost no slippage.
• This is because once the timing belt is engaged with teethed pulleys, there is
absolutely no room to slip.
 Things To Consider While Choosing
Materials For Belts
• The material should have a high coefficient of friction
• Low weight per unit length
• Can able to withstand temperature
• Capable of resisting high tensile stress
• Should be flexible as well as durable
• Self-lubricated
• Resistance to wear and tear
• Food grade compatible if the belt is in contact with any food items.
• It should be odor-free
• Should not be toxic
 Belt Materials
Although there are many materials that can be used in belts, the following materials
are widely used in industries for belts.
• Leather
• Fabric
• Balata
• Rubber

Leather: The leather may be oak-tanned or mineral salt tanned ex: Chrome
tanned. When the thickness of the belt required is more than, two or more
strips are cemented together. Leather belts require periodic cleaning.
Fabric: Fabric belts are made by folding canvas or cotton ducks is a layer
(depending on the required thickness) and stitching together.
Rubber: The belts are made of Fabric with a rubber layer. These are used in
sawmills, paper mills, etc.
Balata: The belts are made out of these materials are similar to rubber belts
expect that balata gum is used instead of rubber. The belts of these materials
are acid and waterproof but cannot be used where the temperature is above
45°.
 Slip in Belts
• Consider an open belt drive rotating in a clockwise direction, this rotating of the belt
over the pulleys is assumed to be due to firm frictional grip between the belt and the
pulleys.
• When this frictional grip becomes insufficient, there is a possibility of forwarding
motion of driver without pulley with it, this is known as the slip in a belt.
• Therefore slip may be defined as the relative motion between the pulley and the belt
in it. This reduces the velocity ratio and usually expressed in % and it is denoted by S.
 Creep in Belts
• Consider as an open belt drive rotating in the clockwise direction. The portion of the
belt leaving the driven and entering the driver is known as the tight side and a
portion of the belt leaving the driver and entering the is known as the slack side.
• During rotation, there is an expansion of a belt on a tight side and contraction of the
belt on the slack side.
• Due to this uneven expansion and contraction of the belt over the pulleys, there will
be a relative movement (motion) of the belt over the pulleys this phenomenon is
known as Creep in a belt.
 Fasteners
• Fasteners are the mechanical units which are used to join two or more objects together.
• Fasteners can be used to join either permanently or temporarily
• A fastener can be a bolt and nut, a screw, a rivet, or even a staple.
• The majority of fasteners used in industry are threaded fasteners.
• They are used to join individual elements in a secure and cheap way that can be assembled
and disassembled as often as required.
 Classifications of Fasteners
Permanent Fasteners, such as rivets and nails, are single-use fasteners that are
designed to permanently join two materials or parts. Removing the fastener destroys it.

Non-Permanent (Temporary) fasteners, on the other hand are designed to allow for
easy removal and re-use. Fasteners such as bolts and screws are commonly used in a
number of industries and products as they allow for parts to be dissassmbled and re-
assembled if required.
- Non-Permanent fasteners can be threaded (bolts, screws, etc.) or non-threaded
(pins, retaining rings, etc.).
 Threaded Fasteners
Threaded fasteners are among the most commonly used for assembling components due to
the ease in which they can be installed and uninstalled as needed. There are three main
types of threaded fastener; Bolts, Screws and Studs.
• Bolts have a head on one end (this is usually a hex head) and are threaded on the other.
They are generally used in conjunction with a nut (and sometimes a washer) to hold them in
place.
• Screws are similar to bolts in that they have a head on one end and a thread on the other.
They key difference is that screws are usually used to screw into an internally threaded hole.
There are many different types of screws, such as Cap Screws, Machine Screws, and
Woodscrews.
• Studs are threaded on both ends, and therefore have no head. They are used to join two
components with internally threaded holes together.
 Nomenclature of Threaded Fasteners

Threads

Thread Profiles
 Types of Threaded Fasteners - Bolts
Bolts and Set screws - Bolts and Setscrews usually feature a hexagonal head with a thread,
and can be used either in conjunction with a nut or in a threaded hole. Bolts generally have a
shank beneath the head, while Setscrews are threaded all the way up to the head.

Set/Grub Screws
 Types of Threaded Fasteners - Nuts

Hex Nuts Lock Nuts Nylon Insert Shear Nuts

Nuts

Wing Nuts
Types of Threaded Fasteners - Nuts
 Washers
• Washers are commonly used between the head of a bolt, screw or nut and the material they
are clamping.
• Their primary function is to increase the bearing area of the head whilst also protecting the
material underneath from damage. There are several different types of Washer, each with
their own uses.

Flat Washers Spring Washers Cup Washers Repair Washers

Flat Washers - These are the most common type of washer and are used to evenly distribute
the load of the bolt, screw or nut as the fastener is tightened.
Spring Washers - These locking washers are designed to stop the bolt, screw or nut from
vibrating loose.
Cup Washers - Cup Washers form a cup for the head of the fastener to fit in, creating a flush
finish with the fastener head. They are used in conjunction with a wood screw.
Repair Washers - Also commonly referred to as Penny Washers or Fender Washers, they
feature a small inside diameter hole and are design to create a greater bearing surface and
prevent pull-through.
Rivets
Rivets
Unit IV
• Automobiles and Power Transmission
• Gear Drives
• Belt Drives
• Fasteners

Thank you