In automobile engineering, Vehicle Structure and Engines focus on the design, strength, and performance of a vehicle’s framework and power unit. The vehicle structure includes the chassis and body, designed for safety, aerodynamics, and durability. The engine is the heart of the vehicle, converting fuel energy into mechanical power using internal combustion or electric propulsion. Various engine types include petrol, diesel, hybrid, and electric systems. A well-engineered structure and engine ensure efficiency, safety, and overall vehicle performance. 🚗🔧

1. 20ME603PE-
Automobile Engineering
UNIT I - VEHICLE STRUCTURE AND ENGINES
Prepared By
Chandra kumar S
Assistant professor
Kongunadu college of
engineering and technology

2. UNIT I VEHICLE STRUCTURE AND
ENGINES
Types of automobiles – vehicle construction
and different layouts – chassis, frame and
body – resistances to vehicle aerodynamics
(various resistances and moments involved) –
IC engines - components, functions and
materials – Variable Valve Timing (VVT).

3. Requirements of an Automobile
1. It should develop power by itself.
2. The rate of power development must be easily controlled.
3. There should be an arrangement to transmit developed power to wheels.
4. An arrangement must exist to continue and discontinue power flow to wheels.
5. It should be possible to control or vary the torque.
6. The driving thrust should successfully be carried in the vehicle.
7. It must have a directional control.

4. Essential features of an Automobile

5. Types of Automobiles
 With respect to the purpose:
(a) Passenger vehicles. Examples: Car, bus, jeep, scooter, mopeds and motor
cycle.
(b) Goods carriers. Examples: Trucks and Lorries.
 Weight of the vehicle:
(a) Heavy weight vehicle such as buses, trucks and trailers.
(b) Light weight vehicles such as cars, jeeps etc.
(c) Medium weight vehicles such as minibus and station wagon.
 With respect to the fuel used:
(a) Petrol vehicles Examples: Scooters, cars, motors cycles etc.
(b) Diesel vehicles Exemples: Buses, trucks etc.
(c) Gas vehicles Examples: Coal gas, LPG, CNG vehicles.
(d) Electric vehicle Examples: Heavy cranes, battery truck, cars and forklifts.
(e) Solar vehicle.

6. Types of an Automobile
 With respect to the number of wheels:
(a) Two wheelers. Examples: Scooters, mopeds.
(b) Four wheelers. Examples: Car, jeep, buses, trucks.
(c) Three wheelers. Examples: Auto, tempos.
(d) Six wheelers. Example: Heavy trucks.
 With respect to the drive of the vehicle:
(a) Single wheel drive vehicles
(b) Two-wheel drive vehicles
(c) Four-wheel drive vehicles
(d) Six-wheel drive vehicles.
 With respect to the side of driver seat:
(a) Left hand drive. Example: Most of the American, European and UAE
vehicles.
(b) Right hand drive. Example: Most of the Indian vehicles

7.  With respect to the side of power drive:
(a) Front wheel drive. Example: Most of the light weight cars.
(b) Rear wheel drive. Example: Trucks and buses.
(c) Four-wheel drive. Example: Jeep, military trucks and off-road vehicles.
 With respect to transmission:
(a) Conventional type: In this type, ordinary gear box is fitted. Example: Most of Indian vehicles.
(b) Semi-automatic type: A combination of manual plus some automatic gear box is fitted.
Example: Most of British vehicles.
(c) Fully automatic type: In this type, vehicles are equipped with full automatic transmission system
by using epicyclic gears and torque convertors. Example: American and European vehicles.
 With respect to their construction:
(a) Single unit vehicles
(b) Articulated vehicles
(c) Heavy tractor vehicle

8.  With respect to motion:
(a) Reciprocating Piston engines
(b) Rotary - Wankel engine
(c) Gas turbine.
 With respect to the suspension:
(a) Conventional type. Example: Leaf spring
(b) Independent. Example: Coil, torsion bar, pneumatic.
 With respect to engine capacity:
The capacity of an engine is expressed in swept volume of the cylinder which is normally expressed in
cubic centimetre (CC).

(x) With respect to combination of number of wheels and axles:
The digital figures like 4-2, 4-4, 6-4 etc. are commonly used in the classification of vehicles. By
increasing the number of axles, the load per axle can be reduced which protects the tyres from
overloading and road surface from damage.

9. LAYOUT OF A CAR

10. VEHICLE CONSTRUCTION
• bullock cart:
A bullock cart consists of the following main parts.
i) Frame.
ii) Wheels and axle.
iii) Yoke.
iv) Body or superstructure and platform.
• These parts can be divided into the following two main portions
(i) Machine portion.
(ii) Carriage portion.

11. VEHICLE CONSTRUCTION
• Construction of automobiles :
– The basic construction of automobile is similar to a cart.
– The speed of the cart is slow as compared to automobiles
– Due to this fact, the automobile is subjected to more shocks which
in turn put more strains on the frame
– the automobile is needed robust frame and shock absorbers to bear
all stresses and strains.

12. DIFFERENT LAYOUTS OF A CAR
 Layout for the Light Passenger Vehicle (Car):
– Front Engine:
– Rear engine
– Central or Mid-Engine
 Front Engine Front Wheel Drive
 Front Engine Rear Wheel Drive
 Rear Engine Rear Wheel Drive
 Four-Wheel Drive

13. Layout for the Light Passenger Vehicle (Car):
– Front Engine
• Engine cooling is simple
• Better weight in front
– Rear Engine
• Single unit to incorporate the clutch,
gearbox and final drive assembly.
– Central/ Mid engine
• sports cars

14. Layout for the Light Passenger Vehicle (Car):
Front Engine Front Wheel Drive
Front Engine Rear Wheel Drive

15. Layout for the Light Passenger Vehicle (Car):
Rear Engine Rear Wheel Drive
Four-Wheel Drive

17. Main Components of Chassis
1. Frame.
2. Front suspension.
3. Steering mechanism.
4. Engine, clutch and gear box.
5. Radiator.
6. Propeller shaft.
7. Wheels.
8. Rear and front springs and shock absorber.
9. Differential unit.
10. Universal joint.
11. Brakes and braking systems.
12. Storage battery.
13. Fuel tank.
14. Electrical systems.
15. Silencer.
16. Shock absorbers, fuel tank, petrol and hydraulics pipe cables and
some means of mounting these components.

18. Classification of Chassis
1. According to the fitting of engine:
(a) Full-forward (fitted outside the driver cabin - Car)
(b) Semi-forward (half portion of the engine is exactly in the driver's
cabin )
(c) Bus chassis (total engine is fitted in the driver cabin)
(d) Engine at back (Volkswagen cars)
(e) Engine at centre. (Royal tiger world master buses of Delhi transport)
2. According to the number of wheels fitted in the vehicles and the
number of driving wheels:
(a) 4x2 drive chassis-It has four wheels out of which 2 are driving wheels
(b) 4x4 drive chassis-It has four wheels and all of them are driving wheels
(c) 6x2 drive chassis-It has six wheels out of which 2 are driving wheels
(d) 6x4 drive chassis-It has six wheels out of which 4 are driving wheels

19. Layout of Chassis

20. Components and Drive Systems in Chassis
1. Frame. (Foundation of Components)
2. Suspension. ( Smooth ride)
3. Steering system. (driver to accurately control the direction taken by the
vehicle )
4. Braking system (moving motor vehicle to rest or slow down)
5. Internal combustion engines (the combustion takes place within the
engine , the air is supplied along with a measured quantity of fuel )
6. Clutch (The main function of the clutch is to take up the drive smoothly
from the engine and to release or disengage whenever desired)
7. Gear box (to provide the necessary variation to the torque applied by the
engine to the road wheel according to the operating conditions)
8. Propeller shaft (transmit power from the rear end of the gear-box to the
final reduction gear in the axle)
9. Universal joint (fitted to the rear axle and To permit the turning of the
propeller shaft)

21. Components and Drive Systems in Chassis
10.Differential (It helps two rear wheels to turn at different speeds when
rounding a curve.)
11.Springs: (Springs are fitted between frame and wheel to prevent the
upward movement of the frame along with up and down movement of the
wheel)
12.Front axle: (. Steering arms and track rod link, two stub axles are
together used for swivelling them)
13.Rear axle: (It is enlarged at the centre for enclosing the final drive gears
used for providing main speed reduction between engine and driving
wheels)
14. Battery: (battery is the heart of the electrical system of a motor vehicle
and supplies current to the cranking motor and ignition system)
15. Wheels: (fitted below the chassis to support the load of the vehicle and
The shocks caused by road irregularities are absorbed by them.)

22. Characteristics of a Good Chassis
• Fast pickup
• Strength
• Safety
• Durability
• Dependability
• Ease of control
• Quietness
• Speed
• Power accessibility
• Economy of operation
• Low centre of gravity
• Stability
• Load clearance
• Braking ability
• Good springing
• Simplicity of lubrication.

23. Frame
• It is the backbone of the vehicle
• It is a rigid structure which forms a skeleton to hold all major parts together.
• The frame is supported by wheel and tyre assembly
Functions or Importance of Frame:
 To form a base for mounting engine and transmission systems.
 To withstand the engine and transmission thrust and torque stresses as
well as accelerating and braking torque.
 To carry the load of passengers and goods in the body.
 To accommodate a suspension system.
 To carry other parts of the vehicle.
 To resist the effect of centrifugal forces when cornering a curve.
 To withstand bending and twisting stresses due to the fluctuating or rear
and front axles.
 To support the load of the body, engine, gear box, battery, fuel tank etc.

24. Car frame

25. Frame sections

26. 1.Types of Frame
There are three types of chassis frame construction as follows.
1. Conventional frame construction
– non-load carrying frame
– The frame supports engine,power transmission elements and car
body.
– For commercial vehicles with relatively low volume production,
– It has advantages of strong chassis of less weight which is sufficient
to carry considerable pay loads and localized accident damage.

27. Conventional frame

28. 2. Semi-integral frame construction:
– Rubber body mountings
– Frame is mainly used in European cars and American cars
– Construction is heavy in nature as compared to the conventional type.
3. Integral or Frameless construction:
– chassis-less, unitary or monocoque construction
– stiff light construction,
– particularly suitable for mass-produced vehicles
– The body of the vehicle gives a mounting for
engine, transmission, suspension and other
mechanical units and components

29. Materials for Frame
• The various steels used for conventional pressed frame are as follows.
1. Aluminium alloy (ALPAX)
2. Mild steel sheet
3. Carbon steel sheet
4. Nickel alloy steel sheet.
• The composition of sheet nickel alloy steel is given as follows.
• Carbon - 0.25 to 0.35%
• Magnanese - 0.35 to 0.75%
• Silicon - 0.30% (Maximum)
• Nickel - 3%
• Phosphorus - 0.05% (max)
• Sulphur- 0.5% (max.).

30. ARTICULATED VEHICLES
• An articulated vehicle is a large vehicle made in two separate units i.e., a
tractor
• connected by means of a pivoted bar or fifth wheel coupling
• a smaller turning radius than the rigid truck
• trailer is detachable- the tractor can move anywhere

31. VEHICLE BODY
• Body is the super-structure for all vehicles
• Both the chassis and the body make the complete vehicle.
• A body consists of windows and doors, engine cover, roof,
luggage cover etc.
Importance of Vehicle Body Design
• Weight of the body is 40% of total weight of the car
• The reduction in body weight is important.
• Body weight inversely proportional to Fuel mileage
• aerodynamic characteristics. Better aerodynamic structure leads
to fuel economy at high speed and stability in cross winds.
• aesthetic and ergonomics consideration

32. Requirements of Vehicle Body

Stresses induced in the body should be distributed evenly
to all portions.

Weight of the body should be as minimum as possible.

It should be able to cope with impact loads of reasonable
magnitude

It should have reasonable fatigue life.

It must provide adequate space for both passengers and
the luggage.

It should have minimum number of components.

It must ensure a quite ride, easy entry and exit.

It should create minimum vibration during runnin

It should give appeal finish in shape and colour.

33. TYPES OF VEHICLE BODY
1. Car
2. Truck-Straight truck or Punjab body
3. Truck-half body type
4. Truck-platform type
5. Tractor
6. Tractor with articulated trailer
7. Tanker
8. Dumper truck
9. Delivery van
10. Pick-up
11. Jeep
12. Buses and Mini-buses
13. Three-wheeler (i.e., Auto rickshaw)

34. Different types of bodies for different
vehicles

35. Vechile Body Construction and its
Components
• Main purpose of Body construction - protection of the engine
and accessories as well as the passenger.
– Structure: All load carrying
– Finish: This group includes all unstressed units such as bonnet, boot, lid,
bumper etc.
– Equipment: This group includes various parts such as rim, seats, doors,
window etc.
COMPONENTS OF CAR BODY

36. Materials for Body Construction
• The materials used for construction of various parts of the body are
– steel,
– wood,
– plastics,
– toughened glass and
– Aluminium
• Wooden bodies require a separate steel chassis frame to carry the load
• Sheet metal is widely used for body construction
– initial cost is also less
• Aluminium has also been used
– light in weight and
– more resistance to corrosion qualities
• Wind screen and window panels are made by toughened glass
– it has a special property when broken
– not form sharp edges
– form of rounded granules which do not cause injury

37. VEHICLE AERODYNAMICS
• Aerodynamics is the behaviour of air in motion relative to the vehicle body
1. Drag force (Fx):
– Force of air drag is acting in the direction of vehicle motion
– wind acting along the longitudinal direction axis.
– This force is also called air resistance
• The various factors such as profile drag (57% of total vehicle), induced drag (8%), skin
friction (10%), interference drag (15%) and cooling and ventilation system drag (10%)
affect the total drag.
• FX = CX ρv2
A/2
where
• CX -Drag coefficient
• ρ-Density of air
• V = Velocity of air
• A-Projected area of the vehicle viewed from front.

38. VEHICLE AERODYNAMICS
2. Lift force (Fz):
•Aerodynamic lift force is the vertical component of the resultant force caused by the
pressure distribution on the body.
Fz = Cz ρv2
A/2
Where
•Cz =Lift coefficient
•ρ = Density of air.
3. Cross wind force (Fy):
•Cross wind force is acting in the lateral direction on the side of the vehicle.
(a) Pitching moment (My) is caused by the drag force F, or lift force F, about Y axis.
(b) Yawing moment (Mz) is caused by the cross wind force F, about Z axis.
(c) Rolling moment (Mx) is caused by the cross wind force F, about X axis.

39. VEHICLE AERODYNAMICS
Various Resistances and its Effects
•Air resistance or aerodynamic drag ( Air Resists the motion)
•Gradient resistance ( vehicle moving in Hills)
•Rolling resistance ( Tyre and Road with friction)
•Inertia force.
– inertia forces also occur during acceleration and braking
– The total mass of the vehicle and the inertia mass of those rotating parts of the
drive accelerated or braked are the factors influencing the resistance to acceleration.

40. INTERNAL COMBUSTION ENGINES
• The burning of a fuel occurs in a confined space of the engine called a combustion
chamber.
• This exothermic reaction (release energy) of a fuel with an oxidizer (usually air)
transforms chemical energy of fuel into thermal energy.
• This thermal energy is converted into mechanical work through the mechanical
mechanism of the engine.
• IC engines are reciprocating engines having pistons that reciprocate back and forth
inside a cylinder internally within the engine

41. IC ENGINE CONSTRUCTION
• Below Figure shows the construction details of an IC engine (Four stroke petrol engine).
• The main components of a four-stroke cycle engine are
– cylinder,
– piston,
– connecting rod,
– piston rings,
– camshaft,
– crankshaft,
– crankcase,
– inlet and outlet valves,
– spark plug,
– cylinder head,
– pushrod,
– gudgeon or piston pin,
– rocker arm,
– cam follower,
– valve spring,
– big end bearing,
– inlet port,
– exhaust port etc.

42. IC Engine Components, their Functions and Materials
1. Cylinder block:
– piston reciprocates inside the cylinder to develop power.
– accurately finished to accommodate pistons
– During combustion, high pressure and temperature will be developed inside the
cylinder
– It is made of grey cast iron or aluminium with steel sleeves
– In water-cooled engines, the cylinder block is provided with water jackets for the
circulation of cooling water

43. IC Engine Components, their Functions and Materials
2. Cylinder Head:
– It is bolted at the top of the cylinder block
– It houses the inlet and exhaust valves
– It also contains a spark plug hole or injector hole and cooling water jacket
– They are manufactured by casting or forging method.
3. Crankcase :
It supports crankshaft and camshaft with the help of bearings.
It is made of cast iron, aluminium alloys or alloy steels.
4. Oil Sump or oil pan:
bottom of crankcase by using a gasket
It is made of pressed steel sheet
5. Cylinder liners:
1.Dry liners
2.Wet Cylinders
piston constantly moves up and down
To avoid cylinder wear
liner which is in the form of the sleeve is inserted into the cylinder bore

44. IC Engine Components, their Functions and Materials
6. Piston:
– reciprocates inside the cylinder
– The top of the piston is called crown and
sides are called skirt
– T slots are provided in the skirt to allow expansion.
– The materials used for cylinder heads are cast iron,
aluminium alloy etc.
7. Connecting rod:
– It is used to connect the piston and crankshaft with the help of bearings
– small end is connected to the piston by the piston pin
– big end is connected to the crank by the crank pin.
– They are generally made of plain carbon steel, aluminium alloy and nickel alloy
steels.
8. Gudgeon pin or Piston pin
– connects the piston to the connecting rod.
– They are made of steel alloyed with
3-4% of nickel to increase toughness

45. IC Engine Components, their Functions and Materials
9. Piston rings:
– used to maintain air-tight sealing between piston and cylinder to prevent gas
leakages
– The materials used for piston rings are cast iron, alloy cast iron containing silicon
and manganese, alloy steels etc. Piston rings are generally coated with chromium or
cadmium.
Two Types:
1.Compression rings (effective seal for high-pressure gases inside the cylinder)
2.Oil rings (rings wipe off the excess oil from cylinder walls)

46. IC Engine Components, their Functions and Materials
10. Crankshaft:
– convert the reciprocating motion of the piston into rotary motion
11. Flywheel:
– Flywheel serves as an energy reservoir
– It stores energy during power stroke and releases energy during other strokes
12. Camshaft:
– It is used to convert the rotary motion of the camshaft into linear motion of the
follower or lifter.
– It has as many cams as the number of valves in an engine.
– The camshaft is usually made of chilled cast iron and billet steel; however forged
steel, grey cast iron or nickel steel may be used depending upon the application.
13. Spark plug:
– park plug is to ignite the air-fuel mixture after completing the compression stroke in
the petrol engine

47. 14. Valve Mechanism:

48. VARIABLE VALVE TIMING (VVT)
• The valves opened and closed at a fixed period in relation to crankshaft rotation at
all engine speeds and loads
• inlet and exhaust valve timing is fixed- not suitable for all engines
• So, there is increase in use of mechanisms to provide variable valve timing (VVT).
• A petrol engine has to operate at varying engine speeds
• typically 750 rpm. through to high speeds up to 7000 rpm and above
• Slow engine speeds:
• High engine speeds:
• Valve opening period:
IVC- Intake valve open
IVC- Intake valve Close
EVO- Exhaust Valve open
EVC- Exhaust Valve Close

49. TYPES VARIABLE VALVE TIMING (VVT)
1. Cam-changing VVT
2. Cam-phasing VVT
3. Combined cam-changing and cam-phasing VVT:
With cam changing, the engine control unit (ECU) selects a different cam profile based
on engine load and speed, whereas with cam phasing, an actuator rotates the camshaft,
changing the phase angle.
1. Cam-changing VVT:
– engine runs more than 5000 to 6000 rpm
– the Electronic Control Unit (ECU) activates an oil pressure-controlled pin to lock
these three rocker arms simultaneously.
During low speed During high speed

50. 2. Cam-phasing VVT:
• It is the simplest, cheapest and most commonly used mechanism in recent days.
• it varies the valve timing by shifting the phase angle of camshafts.
• Generally, the actuation is done by hydraulic valve gears.
3. Combined cam-changing and cam-phasing VVT:
– both cam changing and cam phasing VVT in terms of top end power and flexibility
throughout the whole range of speed.
– The only drawback is more complex in design,