Automobile Engineering

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Engine - Components and Functions
and Materials, Emission

Automobile Engineering – 05ME72
Dr. A. S. Krishnan
Department of Mechanical Engineering
Coimbatore Institute of Technology

Working of a 4-s engine

Main body of the engine
1. Cylinder block - Comprises
1.
2.
3.

Cylinders in which the pistons slide up and down
Ports or openings for valves
Passages for cooling water

2. Cylinder head – comprises
1.
2.
3.
4.

Combustion chamber
Spark plug or fuel injector
Valves (in case of I-head and F-head)
Coolant water passages

3. Crank case
1.
2.
3.
4.
5.

Attached to bottom face of cylinder block
Acts as base of engine
Supports crankshaft and camshaft in suitable bearings
Provides arms for supporting the engine on to the frame
Contains the oil sump

Cylinder block

Separate cylinder block and crankcase
•restricted to stationary & marine engines
•Separate aluminium crankcase will help
in weight reduction, cheaper and quicker
replacement

Integral cylinder block and crankcase
•Most modern engines
•Rigid structure, sometimes ribs are cast
in the crankcase to enhance strenght

Engine components
1.
2.
3.
4.
5.
6.
7.

Cylinder block
Cylinder head
Crank case
Piston
Piston rings
Piston pin
Connecting rod

8. Crank shaft
9. Flywheel
10.Valves and valve
actuating mechanisms
11.Rocker arm
12.Cam shaft
13.Air induction system
14.Fuel system
15.Exhaust system

Materials [1]
S No.

Component

Material

1

Cylinder block

1. Gray Cast Iron with addition of nickel and chromium
2. Aluminium with cast-iron or steel sleeves

2

Cylinder Head

1. Aluminium alloy
2. Gray iron

3

Piston

1. Aluminium alloy
2. Cast iron

4

Piston rings

Fine-grained alloy cast iron

5

Connecting rod

1. Forged steel
2. Alumnium alloy

6

Crank shaft

Casting or forging of heat treated alloy steel

7

Flywheel

Steel

8

Valves

Austenitic stainless steel

Engine Emission Control

• 3 way catalytic controller
• Emission measuring instruments for CO, HC
and NOx

Catalytic Convertor

[2]

• Most effective after-treatment for reducing engine
emission
• Used in most automobiles and other modern engines of
medium or large size
• CO and HC can be oxidized to CO2 and H2O in exhaust and
thermal system if 600C T  700C.
• Use of catalysts reduces oxidation temperature to 250C
T  300C.
• Catalyst – substance that accelerates a chemical reaction
without being consumed
• Catalytic convertor
– mounted in the flow system in the passage of exhaust gases
– Generally 3 way convertors: reduce concentrations of CO, HC
and NOx

Catalytic convertor [2]
Convertor - a stainless steel container housing a porous ceramic structure;
mounted in the path of exhaust gases

Loose Granular Ceramic with Gas passing
through the packed spheres
Ceramic honeycomb structure
(Unit) with many flow passages

•Volume of the ceramic structure  half the engine displacement volume
•5 to 30 changeovers of gas each second through the convertor
•Catalytic convertors for CI engines require larger flow passages owing to solid
soot in the exhaust gases
•Catalytic particles (which promote oxidation reaction) are embedded in the
ceramic passages

Catalytic convertors for SI engines

Catalysts
Catalyst

Reactants / Reaction

Aluminium Oxide
(Alumina)

•Base material for most catalytic convertors
•Withstand high temperatures, chemically inert
•Does not thermally degrade with age

Platinum &
Palladium

Oxidation of CO and HC

1
CO  O2  CO2
2
C x H y  zO2  xCO2  yH 2O
z  x  0.25 y

Rhodium

Reaction of NOx

1
N 2  CO2
2
2 NO  5CO  3H 2O  3 NH 3  5CO2
NO  CO 

2 NO  CO  N 2O  CO2
1
N 2  H 2O
2
2 NO  5 H 2  2 NH 3  2 H 2O
NO  H 2 

2 NO  H 2  N 2O  H 2O

Cerium Oxide

Water-gas shift

CO  H 2O  CO2  H 2

Conversion efficiency of catalytic
convertors

Catalytic convertor efficiency

Degradation Of Catalytic Activity
• Effective life time  2,00,000km
• Loss of efficiency – due to thermal degradation (500C
- 900 C), poisoning of active catalyst material
• Source of impurities
– Fuel: lead and sulphur
– Lubricating oil: zinc, phosphorous, antimony, calcium, and
magnesium from oil additives
– Air

• Cold start up
– Contributes from 70 to 90 % emission
– Artificial heating:





locating convertor close to engine
Electric preheating
Incorporating thermal batteries
Using flame heating

Poisoning
Lead Poisoning

Sulphur poisoning
* Some catalyst promote
conversion of SO2 to SO3
* Eventually converted to
sulphuric
acid
degradation of catalytic
convertor ; acid rain
* Development of new
catalyst, which produce
no SO3 if Tcat<400C

References
1. Gupta, R. B., “Automobile Engineering”, Tech
India Publications, 7th edition, New Delhi,
2011.
2. Ganesan, V., “Internal Combustion Engines”,
2nd edition, Tata McGraw Hill, New Delhi,
2004.

Engine – Auxiliary Systems

Automobile Engineering – 05ME72
Dr. A. S. Krishnan
Department of Mechanical Engineering
Coimbatore Institute of Technology

Topics for discussion
• Carburettor – Working Principle
• Electronic Fuel Injection – Mono Point Injection
systems – Construction
• Operation and Maintenance of Lead Acid Battery
• Electrical Systems
– Battery Generator
– Starting Motor and Drives
– Lighting and Ignition (Battery, Magneto – coil and
electronic type)
– Regulators
– Cut outs
7/10/2012

05ME72 Automotive Engineering

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Carburetor
• Introduction
• Construction & defects in Simple Carburetor
• Classification
• Typical Carburetors
• Disadvantages
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05ME72 Automotive Engineering

19

Introduction
• SI engine
– Use volatile fuel; Mixture preparation outside cylinder
– Formation of homogenous mixture not completed in
inlet manifold
– Fuel droplets continue to evaporate during suction
and compression

• Carburetion
– Definition: process of formation of a combustible fuelair mixture by mixing proper amount of fuel with air
before admission to engine cylinder
– Purpose: provide combustible mixture of required
quality and quantity for efficient operation of the
engine under all conditions
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05ME72 Automotive Engineering

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Air fuel mixtures
Types
o
o
o

Chemically
correct
(stoichiometric) ~15:1
Rich mixture (limited to > 9:1)
Lean Mixture (limited to < 19:1)

Anticipated Carburetor Performance
At full open throttle
and constant speed
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Ranges of throttling operation
1. Idling
o

o

No load and with nearly closed throttle
Exhaust gas dilution of fresh charge - prominent

2. Cruising
o
o

Maximum fuel economy – prime objective
Exhaust gas dilution of fresh charge – relatively insignificant

3. Power
o
o

7/10/2012

To provide best power
To prevent overheating of exhaust valve and area near it –
enriched mixture results in lower flame temperature

05ME72 Automotive Engineering

22

Factors affecting Carburetion
1. Engine speed
o

o

Modern engines are of high speed
Little time for mixture formation: 10ms for 3000rpm and
5ms for 6000rpm

2. Vaporization characteristic of the fuel
o

presence of highly volatile components ensure high
quality carburetion

3. Temperature of incoming air
o
o

Higher atmospheric air temperature aids fuel
vaporization
However  reduced o/p due to reduced vol due to
reduced mass flow rate

4. Design of the carburetor
o

7/10/2012

Proper design alone ensures supply of desired
composition of mixture for different operating conditions
of the engine
05ME72 Automotive Engineering

23

The Simple Carburetor
•Float – vented to atmosphere
or upstream side of venturi
•Carburetor
depression

pressure difference between
the float chamber and throat
of the venturi
•Throat Pressure @ fully open
throttle ~ 5 cm Hg below atm
•Liquid level in float < tip of
discharge jet
•SI engine – quantity governed
i.e., power o/p at constant
speed is varied by varying the
amount of charge to the
cylinder

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05ME72 Automotive Engineering

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The Simple Carburetor
• Main components of a Carburetor
• Fuel Strainer – prevent entry of dust particles and consequently
blockage of nozzle; serviceable
• Float Chamber – supply fuel to nozzle at constant pressure
• Main Fuel metering System
• Idling System
• Choke and throttle – cold starting; speed and power output of engine
• Compensating devices
• Air-bleed jet
• compensating jet
• emulsion tube
•Back suction & control mechanism
• auxiliary air valve and air port
• Simple Carburetor provides the necessary AFR only at one throttle
position
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05ME72 Automotive Engineering
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Carburetor - Classification
• Based on flow direction
• Up-draught
• Down draught
• Cross draught
• Constant choke
• Constant vacuum
•emulsion tube
•Back suction & control mechanism
• auxiliary air valve and air port
• Multiple Venturi
• Multi-jet
• Multi-barrel Venturi
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05ME72 Automotive Engineering

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Solex Carburetor
1 – float
2 – main metering jet
3- venturi
4 – emulsion tube with lateral
holes
5 – air correction jet
6 – spraying orifice / nozzles
7 – throttle valve
8 – bi-starter valve (disc)
9 – starter gasoline jet
10 – starter air jet
11 – starter lever
12 – dashboard control
13 – pilot jet
14 – small pilot air bleed orifice
15 – idling volume control screw
16 – idle port; 17 – by-pass
orifice
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Carter Carburetor

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Lead Acid Battery





Introduction
Construction
Operation
Maintenance

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Introduction - Battery

• Need for Battery –
four main circuits
1.
2.
3.
4.

Generating
Starting
Ignition
Light

• Types of Battery
1. Lead Acid
2. Alkaline
a.
b.

Nickel – Iron
Nickel - Cadmium

Branch Circuits – Special Purpose
Lights, Radio, Gasoline Gauge, Heater,
3. Zinc - Air
Cigar Lighter, Windshield wiper,
defogger, etc
Ignition, lighting and Branch Circuits – receive current from the generator
when it is operating; energy supplied from battery during excess load
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Construction – Lead Acid Battery
1.
2.
3.
4.
5.
6.
7.
8.
9.
1.
2.

3.
4.
5.

Container
Plates
Separators Chemicals used
Cell covers 1. Sponge Lead (solid)
Electrolyte 2. Lead Oxide (paste)
3. Sulfuric Acid
Grids
Cell connectors (liquid)
Tapered
terminals
Sealing
Positive
Plate: Lead Peroxide
compounds
(PbO2)
Negative Plate: Lead (porous
spongy lead)
Electrolyte: Sulfuric Acid (40%)
Separators
Sealing compounds

PbO2  2H 2 SO4  Pb  PbSO4  2H 2O  PbSO4  Q(energy)

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Construction – Lead Acid Battery [3]

7/10/2012

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Lead
Acid
Construction


Battery

Container

– Houses individual cells
– rubber, plastic etc., resistant to
electrolyte and mechanical shock,
withstand high temperatures



Vent plugs
– allows the gases from within the
cells to escape



Plates
– Anode (positive plate group)
– Cathode (negative plate group)
– Interlaced with a terminal attached
to each plate group



Cells
– Connected in series



Terminals
– Individual cell terminals connected by link connectors
– +ive terminal of one end cell becomes +ive terminal of the
battery
– -ive terminal of opposite end cell becomes +ive terminal of
the battery
Source: http:// www.tpub.com/neets/book1/chapter2/1e.htm

http://pvcdrom.pveducation.org/BATT
ERY/operlead.htm
Overall reaction

Negative terminal reaction

Positive terminal reaction

Factors Affecting Battery Life
• Overcharging
– Decomposition of electrolyte into H2 & O2 gas
– Decomposition results in acid concentration, harmful to separators
and –ive electrode
– Softening and distortion of container

• Undercharging
– Liable to freeze in severe winter
– Development of lead sulphate over the plates – dense, hard &
crystalline, cannot be electrochemically converted to normal active
material again, leads to shorting, distortion of plates

• Lack of water
– Lead to high concentrations of acid which may charge and
disintegrate the separators, permanently sulphate the plates and
impair the performance
– [Sulfuric acid must never be added to a cell unless it has been lost
due to spillage]

Factors Affecting Battery Life
• Loose hold-downs
• Excessive Loads
– Never use battery to propel car – by using starting motor with
clutch engaged
– Produce extremely high internal battery temperature and
damage the starting motor

• Freezing of Electrolyte
– Crack the container and damage the positive plates

Battery testing





Specific Gravity test
Open volt test
High Discharge test
Cadmium test

Battery troubles
1.
2.
3.
4.
5.
6.
7.
8.

Self discharging
Sulphation
Internal short circuiting
Deterioration
Cracking of container
Corrosion of battery terminals and clamps
Loss of water
Variation in specific gravity of electrolyte

Maintenance of Batteries












Electrolyte
Sulphation
Battery size and Design
Performance
Shock and vibration
Charging System
A.C/ D.C system
Charger output
Fast charging
Maintenance of Acid level
Laying up of batteries

Charging System - Generator [4]

1. Restores to the battery the charge
removed to crank the engines
2. Handles the load of the ignition, lights,
radio and other electrical and electronic
components while the engine is running
Regulator – prevents the alternator from
producing excess current
Rectifier – converts ac to dc

7/10/2012

05ME72 Automotive Engineering

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Position of the Generator /
Alternator

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05ME72 Automotive Engineering

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Alternator
Principle

The current in the loop
can be increased by
increasing
i. magnetic field
strength
ii. speed of rotation
iii. number of loops

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05ME72 Automotive Engineering

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Alternator stator and rotor

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05ME72 Automotive Engineering

[4]

44

Alternator – rectifier [4]

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Rectification of alternator current

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References
1. Gupta, R. B., “Automobile Engineering”, Tech
India Publications, 7th edition, New Delhi, 2011.
2. Ganesan, V., “Internal Combustion Engines”, 2nd
edition, Tata McGraw Hill, New Delhi, 2004.
3. Rajput, R. K., “A text book of Automotive
Engineering”, Laxmi Publications, New Delhi,
2007.
4. William H. Crouse and Donald L. Anglin,
“Automotive Mechanics”, 10th edition, Tata
McGraw Hill, New Delhi, 2004.
7/10/2012

05ME72 Automotive Engineering

47

Transmission Systems

Automobile Engineering – 05ME72
Dr. A. S. Krishnan
Department of Mechanical Engineering
Coimbatore Institute of Technology

Topics
1.
2.
3.
4.
5.
6.
7.

Clutch – Construction & Types
Gear Box – Manual & Automatic
Simple Floor Mounted Shift
Overdrives – Transfer box and Fluid Flywheel
Propeller shaft, U-Joint & Slip Joint
Hotchkiss and Torque Tube Drive
Differential & Rear Axle

Clutch

[3]

• Location - Between engine flywheel and Transmission or
Transaxle
• Functions
– While disengaged
• Allow engine cranking, permits engine to run freely without delivering
power to transmission
• Permit shifting transmission to various gears

– While engaging
• Slip momentarily, for smooth engagement and lessens shock on gears,
shafts and other drive-train parts

– While engaged
• Transmit engine power to transmission

• Construction - Flywheel + Pressure Plates + Friction disc
• Operation – Pressing / releasing of Pressure plate against
friction disc
• Types – Coil Spring, Diaphragm Spring, Double disc

Clutch - Location

Clutch - Location

Clutch parts

Clutch linkage

Clutch operation

http://www.tpub.com/basae/89.htm

Clutch

http://www.tpub.com/basae/89.htm

Friction Plate
•Cushion Springs & Dampening
Springs
•Cushion Springs – slightly
waved springs attached to plate
(compresses slightly to take up
shock of engagement)
• dampening springs – torsional
springs – drives the hub and
reduces torsional vibrations
caused by engine power
impulses
• Facings provided with grooves
to prevent sticking of facings by
breaking vacuum
•Facings – cotton & asbestos,
woven or moulded, saturated
with resins or binders

Cover assembly

Types of Clutches





Single Plate
Multi Plate
Coil spring
Diaphragm Spring

Single Plate Clutch

Multi Plate Clutch

Diaphragm Spring Clutch

Coil Spring Clutch

http://www.tpub.com/basae/89.htm

Gears[5]





Power transmission
Change angular velocity and torque
Teeth provide a positive driving action, no slippage
Many types of gears – almost every type used in
automobile






Straight tooth spur: transmit high torque – 1st & reverse
Helical spur: progressive meshing – axial load transmission
Straight tooth bevel: noisy as type1 - differential
Spiral Bevel: final drives to connect interconnecting shafts
Hypoid: final drives to connect shafts which are neither
parallel nor intersecting

• The table below shows some example gear
ratios for a 5-speed manual gearbox (in this
case a Subaru Impreza) Read more:
http://www.carbibles.com/transmission_bible
RPM of gearbox
.html#ixzz1S3dsajeA
Gear

Ratio

1st
2nd
3rd
4th
5th

3.166:1
1.882:1
1.296:1
0.972:1
0.738:1

output shaft
when the engine is
at 3000rpm
947
1594
2314
3086
4065

http://www.mekanizmalar.com/menu
_gear.html

Types of Gears [5]
Straight spur gears:
•straight teeth parallel to the axis of rotation
•engagement - instantaneously along the tooth face; sudden meshing
- results in high impact stresses and noise; replaced with helical gears
in most transmissions.
•do not generate axial (or thrust) loads along the shaft axis.
•easier to manufacture; transmit high torque loads; many
transmissions use spur gears for first and reverse gears - This accounts
for the distinctive "whine" when a car is reversed rapidly.

Helical gears:
•teeth cut in the form of helix on a cylindrical
surface
•engagement – contact begins at leading edge,
progresses along tooth face
• greatly reduced impact load and noise, but
generates a thrust load that must be absorbed at
the end of shaft with suitable bearing

Types of Gears [5]
Straight –tooth bevel gears:
• Straight teeth cut on conical surface
• Power transmission between intersecting non-parallel
shafts
• Noisy; In differential, they rotate only when axles are
rotating at different speeds

Spiral bevel gears:
• Helix teeth cut on conical surface
• Final drives to connect intersecting shafts

Hypoid gears:
• Helical teeth cut on hyperbolic surface
• Final drives to connect non-intersecting, non-parallel
shafts; high tooth loads & greater sliding - specially
lubricated
• less efficient than spiral bevel; however allow driveshaft to
be lowered; hence smaller transmission tunnel in body

Power transmission
Gears – a review [5]

through

Summing moments about the centre,

Tangential force at the point of meshing
must be equal and opposite, so:

Pitch diameter proportional to number of teeth (N), angular velocity
inversely related to diameter  leads to the gear law

Extension of gear law
Where, n – number of meshing

[5]

A gear train

For gaining torque ratio, a compound gear train needs to be used:

A compound gear train

Types of Transmissions [1]





Manually operated
Overdrive
Chrysler semi-automatic
Automatic

Sliding Mesh Gear Box [1]

Sliding Mesh – 1st and Reverse Gears

Sliding Mesh – 2nd and Top Gears

Constant Mesh Gear Box

Dog Clutch

Gear Boxes[5]

Power transmission through various gears

Power transmission through various gears

http://www.carbibles.com/transmissio
n_bible.html

Read more: http://www.carbibles.com/transmission_bible.html#ixzz1S3dktg3u

http://auto.howstuffworks.com/seque
ntial-gearbox1.htm

Manual Gear Box[6]

Cross-section of a front-wheel
drive manual gear box







Simple floor mounted shift mechanism
Overdrives
Transfer box, Fluid Flywheel, Torque convertor
Propeller shaft, Slip Joint, Universal Joint
Hotchkiss and Torque Tube Drive

Overdrives[4]
• Top gear position (generally) – direct drive between
clutch shaft and main shaft; gear ratio 1:1
• Overdrive
– main shaft of gear box revolves faster than clutch shaft
– Fitted to rear of the gear box, between gear box and
propeller shaft

• Advantages of Overdrive
– Permits an engine to run at lower speed while the car is
running at high speed
– Engine runs at slower speed, producing less power,
consequently lesser fuel consumption, lesser wear and
tear on the engine and accessories

Construction & Operation
of an Overdrive[4]

•Two shafts – input and output
shafts
• Input shaft – Main shaft of
gear box
• Output shaft – connected to
propeller shaft
• Epicyclic train - sun + planet
gear
• Sun gear – free to rotate on
input shaft
• Carrier – moves on splines of
the input shaft
• Free wheel clutch – attached
to splines
• Ring gear – connected to
output shaft

• Sun gear locked to casing – becomes stationary, overdrive engaged, o/p shaft speed
increases
• Sun gear locked to carrier – solid drive through gear train achieved, normal drive
obtained
• Sun gear locked to ring – same as the previous

http://www.buckeyetriumphs.org/techni
cal/jod/JOD1/JOD1.htm





A: Sun gear
B: Planet gears
C: Outer ring gear or annulus
D Planet gear carrier

1. Input rotary power is applied to the planet gear carrier (D).
2. Output rotary power is taken from the annulus (C).
3. For direct drive (no speed change) the sun gear (A) is locked to the
annulus (C).
4. For an output that is a higher speed than the input (overdriven) the sun
gear (A) is locked stationary.

Mekanizmalar.com

• Deceleration
Power input: ring gear
Power output: planetary carrier
Stationary: sun gear
When the sun gear is held stationary, only the pinion
gear rotates and revolves. Therefore, the output shaft
decelerates in proportion to the input shaft only by
the rotation of the pinion gear.

• Direct
Power
Power

Coupling
input:
sun
output:

gear,
ring
gear
planetary
carrier

Ring gear rotates with the locked planetary
carrier, the input and output shafts rotate at the
same rate.

• Reverse Rotation
Power input: sun gear
Power output: ring gear
Stationary: Planetary carrier
When the planetary carrier is fixed in position
and
the sun gear turns, the ring gear turn on its axis
and the rotational direction is reversed.

http://www.servocity.com/html/plane
tary_gearbox.html

Fluid couplings and Torque Convertors

Fluid flow path in a fluid coupling

Propeller shaft, Slip Joint and Universal
Joint

Hotchkiss Drive and Torque Tube Drive
– Types of Drive
• Rear End Torque
– Torque transmission: transmission box  propeller shaft 
differential  rear wheels; causes wheels to rotate, attempts to
rotate differential housing in opposite direction
– Propeller shaft turns pinion, forces (side thrust of pinion) ring
gear & wheels to rotate
– Side thrust causes pinion to push against shaft bearing, push
opposite to side thrust
– Pinion bearings held in differential housing, housing tries to
rotate in a direction opposite to ring gear and wheel

• Methods of bracing the housing – to prevent excessive
movement of differential housing
– Hotchkiss Drive
– Torque Tube Drive

Torque Tube Drive [1]
•Propeller shaft enclosed in a hollow tube
• Hollow tube
• rigidly bolted to differential housing
at one end
• fastened to transmission through a
marginally flexible joint
• incorporates bearing to support
propeller shaft
• Sliding joint not required for propeller
shaft
• Pair of truss rods attached between rear
axle housing and transmission end of
torque tube
• Torque tube + truss rods  brace
differential housing to prevent excessive
differential housing movement
• Springs - take side thrusts and weight of
the body

Hotchkiss Drive [1]
• Propeller shaft (not enclosed), 2
universal joints and a slip joint
•Springs
• front end rigidly fixed to
frame, rear supported on a
shackle
• absorbs rear end torque
• Forward movement of car
• front
half
of
springs
compressed, rear expanded
• Two universal joint unlike the
torque tube drive
• Used in most cars

References
1.
2.
3.
4.
5.
6.

Gupta, R. B., “Automobile Engineering”, Tech India Publications,
7th edition, New Delhi, 2011.
Rajput, R. K., “A text book of Automotive Engineering”, Laxmi
Publications, New Delhi, 2007.
William H. Crouse and Donald L. Anglin, “Automotive Mechanics”,
10th edition, Tata McGraw Hill, New Delhi, 2004.
Srinivasan, S., “Automotive Mechanics”, 2nd Edition, Tata McGraw
Hill, New Delhi, 2003.
Richard Stone and Jeffery, K. Ball, “Automotive Engineering
Fundamentals”, ISBN 0-7680-0987-1, SAE International,
Warrendale, 2004.
David, A. Crolla (Editor), “Automotive Engineering – Power Train,
Chassis and Body”, Butterworth – Heinemann, Oxford, 2009.

7/10/2012

05ME72 Automotive Engineering

105

Steering, Brakes and Suspension
Systems
Automobile Engineering – 05ME72
Dr. A. S. Krishnan
Department of Mechanical Engineering
Coimbatore Institute of Technology

Topics
1. Wheels
1. Types
2. Alignment Parameters

2. Steering
1. Geometry
2. Types of Steering Gear Box
3. Power Steering

3. Types of Front Axle
4. Suspension
5. Brakes
1. Hydraulic
2. Vacuum Assisted Servo Brakes

• Types of wheels
i.

Wheels [4]

Pressed Steel Disc Wheel
» mostly used in LMVs
» some rims are attached using bolt & nut or rivets;
» tyres rest on rim;
» wheels fit to axle by bolting to flange attached to axle

ii.

Wire Wheel
» Comprises hub, spoke and rim – made of iron
» Spokes connected between hub and rim
» Tyre-tube rests on rim
» Mostly used in motor-cycles

iii. Alloy Wheel
» Light wheels, less bouncing, faster cooling, better braking
» Made from aluminium or magnesium alloys
» Magnesium alloy wheel half the mass of steel wheel, 70% mass of
aluminium alloy wheel for the same strength

• Cast wheels – for cars
• Forged wheels – for heavy vehicles

Wheels – requirements [1]






Strong enough to withstand weight of the vehicle
Flexible to absorb road shocks
Able to grip the road surface
Static and dynamic balance
Light and easy to replace

Pressed Steel Disc Wheel [4,3]

Wire Wheel[4]

Alloy Wheel[4]

Wheels - Attachment & Covers
• Attached to brake drum
or disc by 5 or 3 wheel
nuts or lug nuts
• Lug nuts – tapered at
wheel that matches its
seat in wheels; helps
tightening lug nuts to
centre the wheel
• Hub caps / wheel covers
– attached by clips;
locks to protect theft,
removed by key wrench
• Aluminium wheels –
have locking lug nut as
anti-theft device

[4]

Wheel Alignment Parameters [5]
Steering system – to allow for
• Turning of the vehicle
• To track straight ahead without steering effort from the
driver

Wheel Alignment Parameters
• Wheel alignment – positioning of front wheels
and steering mechanism that gives directional
stability, reduces tire wear to minimum [1]
• Camber
• Steering Axis Inclination
• Toe
• Caster

Camber[5]
• Angle made by the tire/wheel
with respect to the vertical in
the front view of the vehicle
• Approximately 1
• Types
– Positive – top of wheel tilted
away from vehicle; used in
most vehicles
– Negative – top of wheel tilted
towards the vehicle; used in
off-road vehicles and race
vehicles (which sometimes use
zero camber also)

Steering Axis Inclination[5]
• Angle from the vertical defined by the centerline
passing through the upper and lower ball joints (as
viewed from front of the vehicle)
• Upper ball joint is closer (usually) to the vehicle
Vertical Steering
centerline than the lower
Axis

SAI + Positive Camber
 Reduced - Scrub Radius during turning, Tire wear &
Steering Effort
 Wheel arc no longer parallel to the ground turning
of wheel causes it to arc toward the ground
ground immovable, causing the front of the
vehicle to be raised  not the position of minimum
potential energy  weight of vehicle tends to turn
the wheel back to straight ahead position
Inclined Steering Axis with
Positive Camber

Toe[5]
• Defined as the difference of the
distance between the leading edge
of the wheels and the distance
between the trailing edge of the
wheels when viewed from above
• Toe-in  front of the wheels are
closer than the rear
• Toe-out  rear of the wheels are
closer than the front
• Rear wheel drive: front wheels
have slight amount of toe-in
• Front wheel drive: require slight
toe-out

Toe-in &

[5]
Toe-out

• Rear wheel drive
– Front wheels have slight toe in
– As vehicle begins to roll, rolling
resistance produces a force
through the tire contact patch
 rolling axis
– Existence of scrub radius causes
this force to produce a torque
about the steering axis causing
wheels to toe-out

• Front wheel drive
– Tractive force on wheels
produces a moment about the
steering axis
– This moment tends to toe the
wheel inward

Caster

• Caster is the angle of the
steering axis from the
vertical as viewed from
the side
• Positive caster is defined
as the steering axis
inclined toward the rear
of the Vehicle.
 Positive caster
 Tire contact patch after the intersection of steering axis and ground

 During turn, cornering force acts  to wheel axis through contact patch
 Creates torque about the steering axis tending to centre the wheel

 Example – shopping cart, wheels free to turn around the axis, self-align

to move in straight-ahead position when cart is pushed straight

Factors aiding in self-straightening[5]

Steering

Horse carriage steering [5]

• High forces required by the driver
• Unstable at high speeds

Ackerman Steering System[5]
• Developed by German engineer
Lankensperger (1817); patented in the
name of British lawyer Rudolph
Ackerman

•Each end of axle has a spindle that pivots around a kingpin
•Linkages connecting spindle form a trapezoid
•Base of trapezoid – rack and tie rods

Parallelogram steering linkages [5]

Steering System (Simplified diagram)[1]

References
1.
2.
3.
4.
5.
6.

Gupta, R. B., “Automobile Engineering”, Tech India Publications,
7th edition, New Delhi, 2011.
Rajput, R. K., “A text book of Automotive Engineering”, Laxmi
Publications, New Delhi, 2007.
William H. Crouse and Donald L. Anglin, “Automotive Mechanics”,
10th edition, Tata McGraw Hill, New Delhi, 2004.
Srinivasan, S., “Automotive Mechanics”, 2nd Edition, Tata McGraw
Hill, New Delhi, 2003.
Richard Stone and Jeffery, K. Ball, “Automotive Engineering
Fundamentals”, ISBN 0-7680-0987-1, SAE International,
Warrendale, 2004.
David, A. Crolla (Editor), “Automotive Engineering – Power Train,
Chassis and Body”, Butterworth – Heinemann, Oxford, 2009.

7/10/2012

05ME72 Automotive Engineering

129

ALTERNATIVE ENERGY SOURCES
Use of Natural Gas, LPG, Biodiesel,
Gasohol and Hydrogen in
Automobiles – Electric and Hybrid
Vehicles, Fuel Cells
(9)

Automobile Engineering – 05ME72
Dr. A. S. Krishnan
Department of Mechanical Engineering
Coimbatore Institute of Technology

Topics
1. Use of the following fuels in automobiles
1.
2.
3.
4.
5.

Natural Gas
LPG
Bio-diesel
Gasohol
Hydrogen

2. Electrical and Hybrid Vehicles
3. Fuel Cells

Natural Gas
• Constituents – 80 to 90% methane; rest higher HCs, primarily
ethane
• Advantages
– Clean, non-toxic and non-corrosive, safer
• produces lesser CO2, CO and volatile than any other fossil fuel
• combustion produces no significant aldehydes or other air toxins as petrol
• CNG tanks suffer less damage, high self-ignition temperature (540C)

– Economical – cheaper than diesel and much cheaper than petrol

• Performance
– More efficient than SI engine
– Low energy density, compressed to a pressure of 200 to 250 ksc
– On energy basis, 1 kg of natural gas is equivalent to
• 1.349 liters of Petrol
• 1.18 liters of Diesel

Layout of CNG system

[1]

CNG System [5]

LPG
• Primarily Propane and Butane (more in winter
and more in summer respectively) [6]
• Heavier than air

LPG system[1]

LPG System [5]

Fuel properties[1]

Optimization points
CNG System

LPG System

Emission

Compression ratio

Mixer flow diameter

Valve and Valve seat

Air-Fuel ratio

ECU

Location of the mixer

Air-Gas valve

Vehicle drivability

Ignition timing

Vehicle performance

Gasohol[4]

WHY HYDROGEN ?
• Potentially an inexhaustible supply of energy
• Can be produced from several primary energy sources
• Reduced dependence on petroleum imports if produced
from coal or renewables
• Potential environmental benefits
• High energy conversion efficiency by use of H2 in Fuel
Cells(UPTO 90%) in place of I.C. engines (30-35%)

HYDROGEN GENERATION
PROCESSES
 Steam reforming of Natural Gas/Naphtha
 Partial oxidation of hydrocarbons
 Thermal cracking of Natural Gas
 Coal/Bio mass Gasification
 Electrolysis – Electricity from renewable sources like
solar, wind, hydel etc.

HYDROGEN PRODUCTION
World wide production
 From Natural gas (mostly steam reforming) - 48%
 Oil (mostly consumed in refineries) – 30%
 Coal – 18%
 Electrolysis –4%
Nearly all H2 production is based on fossil fuels at present.

H2 OPTIONS FOR INDIA
Hydrocarbon Liquid Fuels
Natural Gas
Solar / Wind power for electrolysis
Coal
Bio-mass
Other options like Chlor-Alkali Units & Co-generation
electricity from Bagasse at sugar mills

STORAGE OPTIONS
 Storage as gas under pressure (250 – 350 bar)
 Cryogenic storage as liquid hydrogen
(Temp. –253 0 C)
 Storage as metallic hydrides
 Carbon adsorption and glass microsphere
storage techniques (under development)

WHY FUEL CELL TECHNOLOGY IS FAVOURED ?


Batteries are the cleanest automotive energy source.



To liberate electric cars from electro-chemical battery.



Electric cars have a limit range and slow charging.



GM’s EV-1 and Honda’s EV- Plus have limited range.



Decades of research and investment on electro-chemical batteries.



Power density required for effective automotive propulsion haven’t attained.



Hybrid Electric Vehicle (HEV) approach followed to increase range of vehicle.



Toyota Prius and Honda Insight have been introduced.



HEVs are having high efficiency internal combustion engines with batteries.



Batteries supplement power to the engine during acceleration and hill climbing.



Combined electric and mechanical drives make them costly and complex.

FUEL CELL THEORY
• First demonstrated in principle by British Scientist Sir
Willliam Robert Grove in 1839.
• Grove’s invention was based on idea of reverse
electrolysis.
• In electrolysis, an electric current is introduced in to
electrolyte.
• This flow between two electrodes causes the splitting of
water.

FUEL CELL THEORY








A fuel cell consists of two electrodes - Anode and Cathode.
Hydrogen and Oxygen are fed into the cell.
Catalyst at Anode causes hydrogen atoms to give up electrons leaving positively
charged protons.
Oxygen ions at Cathode side attract the hydrogen protons.
Protons pass through electrolyte membrane.
Electrons are redirected to Cathode through external circuit.
Thus producing the current - power

FUEL CELLS FOR DIRECT ENERGY
CONVERSION

TYPES OF FUEL CELLS









Alkaline (AFC)
Phosphoric Acid
(PAFC)
Solid Polymer
(PEMFC)
Moltan Carbonate
(MCFC)
Solid Oxide
(SOFC)
Direct Methanol
(DMFC)

Temp.°C

Application

70-90
150-210

Space
Commercially available

70-90

Automotive application

550-650

Power generation

1000-1100

Power generation

70-90

Under development

FUEL CELL CARS






Start to look real
Fuel cell car - the long awaited
Prototype vehicles have been displayed
Clear personal transportation of the future
Moving from laboratory vision to technical
reality

FUEL CELL APPLICATION FOR AUTOMOTIVE USE







Proton exchange membrane (PEM) variety has emerged as the best design
GM has obtained nearly 400 patents in PEM technology
SOFC together with and on-board gasoline fuel processor or reformer would be
suited as auxiliary power units (APUs)
Replacement of low efficiency alternator in automobiles
BMW, Renault and Delphi are pursuing this approach

FUEL CELL VEHICLE CONFIGURATION
Wheels

Batteries

Fuel

Fuel
Cell

Power
conditioner

AC/DC
Drive
motor

Accessories
Wheels

FUELS FOR FUEL CELL SYSTEMS


General Motor’s and Adam Opel AG’s View (GAPC)
Long term vision :
Hydrogen
Problem
:
H2 - Storage
H2 -Infrastructure

Bridging Strategy :
conventional

Fuel Cell Systems for vehicles using
/ Pump Grade Fuels
Gasoline tank

Fuel Cell Drive System

Establishing infrastructure and storage technology for
hydrogen in between co-operation of
OEM’s with mineral oil companies
GM / Exxon / Mobil / BP

References
1.
2.

3.
4.
5.
6.
7.

Gupta, R. B., “Automobile Engineering”, Tech India Publications,
7th edition, New Delhi, 2011.
Richard Stone and Jeffery, K. Ball, “Automotive Engineering
Fundamentals”, ISBN 0-7680-0987-1, SAE International,
Warrendale, 2004.
David, A. Crolla (Editor), “Automotive Engineering – Power Train,
Chassis and Body”, Butterworth – Heinemann, Oxford, 2009.
http://upload.wikimedia.org/wikipedia/commons/c/c8/Common_
ethanol_fuel_mixtures.gif
http://www.btautomotive.com.my/VSI-CNG-s-LPG.aspx
http://en.wikipedia.org/wiki/Liquefied_petroleum_gas
HYDROGEN – ACTIVITIES IN THE OIL & GAS SECTOR, 15th April,
2004, R & D Centre, NTPC, Noida. Slides 12-29.

7/10/2012

05ME72 Automotive Engineering

159

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