Automobile module iv

CHASSIS, BRAKES AND TYRES

Anoop P

Asst. Professor

Dept. of Mechanical Engg.

MITS, Puthencruz

Department of Mechanical Engineering, MITS Puthencruz 1

CHASSIS AND FRAMES


CHASSIS Chassis is a French term which is now denotes the whole vehicle

except body.

“Chassis consists of engine, power train, brakes, steering system

and wheels mounted on a frame”.


REQUIREMENTS OF FRAMES


FRAME

A frame is the main structure of the chassis of a motor vehicle. All

other components fasten to it.


CONSTRUCTION OF A FRAME


CLASSIFICATION OF FRAMES

1. Conventional frame

2. Integral frame

3. Semi-integral frame


CONVENTIONAL FRAME


INTEGRAL/UNITIZED FRAME


SEMI-INTEGRAL FRAME


TYPES OF FRAMES 1. Ladder Frame

2. Backbone Frame

3. X-frame

4. Perimeter Frame

5. Platform Frame

6. Unibody (or) Unit body

7. Sub Frame


LADDER FRAME

The ladder frame is the simplest and oldest of all designs.

It consists of two symmetrical rails, or beams, and cross member

connecting them.

Originally seen on almost all vehicles, the ladder frame was gradually

phased out on cars around the 1940s and is now seen mainly on trucks.

This design offers good beam resistance because of its continuous rails

from front to rear, but poor resistance to torsion.

Also, the vehicle's overall height will be higher due to the floor pan sitting

above the frame instead of inside it


BACKBONE FRAME Backbone frame is a type of an automobile construction frame that is

similar to the body-on-frame design.

Instead of a two-dimensional ladder type structure, it consists of a

strong tubular back bone (usually rectangular in cross section) that

connects the front and rear suspension attachment areas.

A body is then placed on this structure.


X-FRAME

This is the design used for the full-size American models of General Motors.

In which the rails from alongside the engine seemed to cross in the passenger

compartment, each continuing to the opposite end of the cross member at the

extreme rear of the vehicle.

It was specifically chosen to decrease the overall height of the vehicles, and

to increase in the space for transmission.

The X-frame was claimed to improve on previous designs, but it lacked side

rails and thus did not provide adequate side-impact and collision protection.

So This design was replaced by perimeter frames.


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PERIMETER FRAME

Similar to a ladder frame, but the middle sections of the frame rails sit

outboard of the front and rear rails.

This was done to allow for a lower floor pan, and therefore lower overall

vehicle in passenger cars.

In addition to the perimeter frame allows lower seating positions when that

is desirable, and offers better safety in the event of a side impact.

However, the design lacks stiffness, because the transition areas from front

to center and center to rear reduce beam and torsional resistance.


PLATFORM FRAME

This is a modification of the perimeter frame in which the passenger

compartment floor and often the luggage compartment floor were

permanently attached to the frame, for extra strength.

Neither floor pieces were sheet metal straight off the roll, but had been

stamped with ridges and hollows for extra strength.

This was used by the Germans on the Volkswagen Beetle and the

Mercedes-Benz "Ponton" cars of the 1950s and 1960s, where it was called

in English-language advertisements as the "frame floor".


UNI-BODY

In an unibody (also unit body, unitary construction, or unitized

construction) design.

the frame and body are constructed as a single unit.

This became the preferred construction for mass market automobiles and

crossovers especially in the wake of the two energy crises of the 1970s

and the mid-2000s oil price increases.


SUB FRAME

A subframe is a structural component of a vehicle.

Such as an automobile or an aircraft, that uses a separate structure within

a larger body-on-frame or unit body to carry certain components, such as

the engine, drivetrain, or suspension.

The sub frame is bolted and/or welded to the vehicle.

When bolted, it is sometimes equipped with rubber bushings or springs to

dampen vibration.


The principal purposes of using a subframe are, to spread high chassis

loads over a wide area of relatively thin sheet metal of a monocoque body

shell, and to isolate vibration and harshness from the rest of the body.

For example, in an automobile with its power train contained in a subframe,

forces generated by the engine and transmission can be damped enough

that they will not disturb passengers.

As a natural development from a car with a full chassis, separate front and

rear subframes are used in modern vehicles to reduce the overall weight

and cost.


VARIOUS LOADS ACTING ON THE FRAME

1. Short duration Load – While crossing a broken patch.

2. Momentary duration Load – While taking a curve.

3. Impact Loads – Due to the collision of the vehicle.

4. Inertia Load – While applying brakes.

5. Static Loads – Loads due to chassis parts.

6. Over Loads – Beyond Design capacity.


MATERIALS FOR FRAME


CRUMPLE ZONE

Crumple zones were first introduced in cars by Mercedes-Benz in

1953.

The introduction saw a complete shift in the design of cars.

Where previously cars were designed with extremely rigid bodies

that were intended to be very resistant during an accident they

were now built so that they would crumple or deform in the event

of a crash


Crumple zones are areas at the front and back of a car that are

designed to deform in a controlled manner in the event of an accident.

They are intended to increase the stopping time of a collision so

therefore decrease the force acting on the occupants.

Crumple Zones are designed to absorb the kinetic energy from impact

during an accident by controlled deformation.

The purpose of crumple zones is to reduce the force experienced by

the occupant of a car during a crash.

This is achieved by the controlled deformation of the crumple zones

during a collision.

The crumpling increases the stopping time and prevents the car from

rebounding.

This has the effect of minimizing the momentum change and the

impulse and so the forces experienced by the occupants is minimized.


IMPACT BEAMS/ ANTI -INTRUSION BAR An anti-intrusion bar or beam is a passive safety device,

installed in most cars and other ground vehicles, which must

protect passengers from side impacts.

Side impacts are particularly dangerous for two reasons:

a) the location of impact is very close to the passenger, who can

be immediately reached by the impacting vehicle

b) in many side-impact accidents, the impacting vehicle may be

larger, taller, heavier, or structurally stiffer than the struck

vehicle.

The role of an anti-intrusion bar is to absorb the kinetic energy of

the colliding vehicles that is partially converted into internal work

of the members involved in the crash.


SEATBELTS Seatbelts limit the forward motion of an occupant, stretch to

absorb energy, to lengthen the time of the occupant's negative

acceleration in a crash, reducing the loading on the occupants

body.

They prevent occupants being ejected from the vehicle and

ensure that they are in the correct position for the operation of the

airbags.


AIR BAGS Airbags inflate to cushion the impact of a vehicle occupant with

various parts of the vehicle's interior.

The most important being the prevention of direct impact of the

driver's head with the steering wheel and door pillar.



An airbag is an automotive safety restrain system for an occupant as well

as passengers. The system consists of a flexible fabric envelope or

cushion, designed to inflate rapidly during an automobile collision.

A safety device used in the four wheelers to avoid the Head and Chest

injuries from collision by providing the cushion between the occupants.

AIR BAG INFLATION SYSTEM The sensor sends the electric signal to burn the propellant kept

here to generate the gas

Monitors the readiness of the airbag system

A device that stores enough electrical energy to deploy the airbag

if the vehicle’s battery destroyed in it


BRAKING SYSTEM


INTRODUCTION Brakes are one of the most important control components of the

vehicle.

They contribute very much in the running and control of the

vehicle.

The efficiency of the brakes depends on the lives and comfort not

only of driver and passengers but other persons moving on the

road.

Furthermore it is a fact that owing to recent improvements in the

braking mechanism may be chiefly attributed the increased

speeds of the modern cars on the road.


FUNCTION To stop the moving vehicle in the shortest possible distance.

To help in controlling the speed of the vehicle and to reduce the

speed at turning and other crowded places.

To control the speed of vehicle at turns and also at the time of

driving down on a hill slope.


PRINCIPLE

Braking of a vehicle depends upon the static function that acts between

tyres and road surface.

Brakes work on the following principle to stop the vehicle :

“The kinetic energy due to motion of the vehicle is dissipated in the form

of heat energy due to friction between moving parts (wheel or wheel

drum) and stationary parts of vehicle (brake shoes)”.

The heat energy so generated due to application of brakes is dissipated

into air.

Brakes operate most effectively when they are applied in a manner so

that wheels do not lock completely but continue to roll without slipping on

the surface of road.


CLASSIFICATION On the Basis of Method of Actuation

• Foot brake (also called service brake) operated by foot pedal.

• Hand brake – it is also called parking brake operated by hand.

On the Basis of Mode of Operation

• Mechanical brakes

• Hydraulic brakes

• Air brakes

• Vacuum brakes

• Electric brakes.

On the Basis of Action on Front or Rear Wheels

• Front-wheel brakes

• Rear-wheel brakes.

On the Basis of Method of Application of Braking Contact

• Internally – expanding brakes

• Externally – contracting brakes.


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MECHANICAL BRAKES


INTERNAL EXPANDING BRAKE


EXTERNAL CONTRACTING BRAKE


HYDRAULIC BRAKES


Hydraulics is the use of a liquid under pressure to transfer force or motion, or to

increase an applied force.

The pressure on a liquid is called HYRAULIC PRESSURE.

And the brakes which are operated by means of hydraulic pressure are called

HYDRAULIC BRAKES.

These brakes are based on the principle of Pascal’s law.


A TYPICAL HYDRAULIC BRAKE


PASCAL’S LAW

The pressure exerted anywhere in a mass of confined liquid is transmitted

undiminished in all directions throughout the liquid.

Applied in hydraulic lifts, hydraulic brakes etc.


MASTER CYLINDER IN ACTION

When we press the brake pedal, it pushes on primary piston through a linkage.

Pressure is built in the cylinder and the lines as the brake pedal is depressed

further.

The pressure between the primary and secondary piston forces the secondary

piston to compress the fluid in its circuit.

If the brakes are operating properly, the pressure will be same in both the circuits.

If there is a leak in one of the circuits, that circuit will not be able to maintain

pressure.


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TANDEM MASTER CYLINDER


WORKING


WHEEL CYLINDER/SLAVE CYLINDER


BLEEDING OF BRAKES When air enters, into the brake system and any brake line is

disconnected, bleeding of brakes has to be done.

Since air is compressible so any presence of air inside brake

lining does not allow to transmit brake force to apply brakes.

Therefore, the system must be free from presence of air.

“ Bleeding is the process of removal of air from the braking

system”.


BLEEDING PROCEDURE

Remove all dirt from the master cylinder filler plug. Then fill the master cylinder

up to lower edge of the filler neck by removing the filler plug.

Clean all the bleeding connections provided on all wheel cylinders.

After this bleeder hose and fixture is connected to that wheel cylinder which has

longest brake line. The other rend of bleeder hose is placed in a glass jar, and

submerge this end in the brake fluid.

How bleeder valve is opened by half to three quarter turn.

Then press the foot pedal and allow it to return back slowly.

This pumping action must be continued till all the air along with some brake fluid

comes out through bleeding hose.

After this bleeding operation is carried out on all wheel cylinders. This completes

the bleeding operation. At the end master cylinder is filled with brake fluid to

required level


ADVANTAGES OF HYDRAULIC BRAKES


Equal braking effort to all the four wheels

Less rate of wear (due to absence of joints compared to mechanical

brakes)

Force multiplication (or divisions) is very easy by changing the size of one

piston and cylinder relative to other.

DIS-ADVANTAGES OF HYDRAULIC BRAKES

Even slight leakage of air into the breaking system makes it useless.

The brake shoes are liable to get ruined if the brake fluid leaks out.

VACUUM BRAKE


DRUM BRAKES

Drum brakes work on the same principle as the disc brakes. Shoes

press against a rotating surface.

In this system that surface is called a drum.

Drum brake also has an adjuster mechanism, an emergency brake

mechanism and lots of springs.

The shoes are pulled away from the drum by the springs when the

brakes are released.


DISC BRAKES


In a disc brake, the fluid from the master cylinder is forced into a caliper

where it presses against a piston.

The piston in turn squeezes two

brake pads against the disc

(rotor), which is attached to

wheel, forcing it to slow down

or stop.

EMERGENCY BRAKES

In cars with disc brakes on all four wheels, an emergency brake has to be

actuated by a separate mechanism than the primary brakes in case of a total

primary break failure.

Most cars use a cable to actuate the emergency brake.

Some cars with four wheel disc breaks have a separate drum brake integrated

into the hub of the rear wheels.

This drum brake is only for emergency brake system and is actuated only by

the cable.

It has no hydraulics.


APPLICATIONS OF BRAKES Disc brake

used in aircraft brakes; preferred for front axles of vehicles, motorcycles, scooters, bicycles, Still-

larger discs are used for railroad cars and some airplanes. Passenger rail cars and light rail

vehicles, in racing and very-high-performance road cars.

Hydraulic brakes

Used in automobiles, cranes and lifts or elevators, airplanes, mining vehicles etc.

Air Brakes

used in large heavy vehicles, such as trucks, buses, trailers etc.

Vacuum Brakes

In railways ( India and South Africa) in the mid-1880s.

Electric brakes

Brake controlled by an electric current and are seen on medium duty trailers like caravans,

Recreational vehicle and Consumer-Grade Car Trailers.

Internally – expanding brakes

This type of brake is commonly used in motor cars and light trucks.

Externally – contracting brakes

This type of brake is used on the wheel brakes of cars and. trucks because it permits a more

compact and economical construction.

Department of Mechanical Engineering, MITS Puthencruz

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AIR BRAKES


COMPONENTS

The main components of air brake system are :

Air compressor with air filter to compress atmosphere air.

Un-loader valve to maintain a set pressure.

Air reservoir to store compressed air at specified pressure.

Brake valve to control the intensity of braking.

Brake chambers are installed at each wheel to convert air pressure into useful mechanical energy.


ADVANTAGES Air brakes are more powerful than mechanical or hydraulic brakes,

are exclusively used in heavy vehicles.

The air brake simplifies the chassis design. The components of the

system can be located on the chassis any where and are

interconnected by a pipe line.

Apart from braking, the compressed air from the reservoir can be

used for tyre inflation, windscreen wipers, horns and many other

accessories.


DIS-ADVANTAGES Air brakes involve more parts.

Air compressor uses engine power.

ELECTRIC BRAKES This type of brakes are not very popular, as service brakes.

These are commonly used on trailers.

The current from the battery is utilized to energize an electromagnet within

the brake drum.

This actuates a cam to expand the brake shoes.

When current stops, the cam and brake shoes are returned to the release

position by retractor springs.

The severity of braking is controlled by means of a rheostat, which is

operated by the driver through the foot pedal.

Hydraulic pressure has also been used to apply electric brakes. As pedal is

pressed more, hydraulic pressure actuates the rheostat to increase current to

the electromagnet.


ADVANTAGES OF ELECTRIC BRAKES

The operating linkage is simplified in electric brakes. The require only one

cable for each drum.

There is less time-lag between the pressing of the brake pedal and application

of brakes at the wheels.

For trailer brakes, this type offers much simplified connection; simply on cable

has to be carried to the trailer side.


ENGINE EXHAUST BRAKES


This type of brake is used on Tata vehicles as a auxiliary brake.

It is meant for use while travelling on a lengthy downhill gradient and

in heavy traffic.

It becomes necessary to slow down continuously over a large

distance.

The brake comes into operation when the foot control valve is

pressed and remains engaged as long as this valve is kept pressed.

The moment the foot is taken off the valve, the brake gets released.

When the foot control valve is pressed, the compressed air from the

air tank enters the air cylinder, where it operates a linkage to close

the butterfly valve at the exhaust manifold.

This brake is used to sow down the vehicle speed to 40 kmph or

less.


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HAND BRAKE/ PARKING BRAKE


Hand brakes are usually the mechanical brakes.

On most of the vehicles hand brake applied only the

rear brakes.

WHEELS AND TYRES


INTRODUCTION The importance of wheels and tyres in the automobile is obvious.

Without the engine the car may be towed, but even that is not

possible without the wheels.

The wheel, along with the tyre has to take the vehicle load, provide a

cushioning effect and cope with the steering control.


REQUIREMENTS

The various requirements of an automobile wheel are:

1. It must be strong enough to perform the above said functions.

2. It should be balanced both statically as well as dynamically.

3. It should be lightest possible so that the un-sprung weight is least.

4. It should be possible to remove or mount the wheel easily

5. It material should not deteriorate with weathering and age. In case the

material is susceptible to corrosion, it must be given suitable protective

treatment


WHEEL - BASICS


TYPES OF WHEELS

Disc Wheel

Wire Wheel

Alloy Wheel


DISC WHEEL


OUTSET, ZERO SET, IN SET


WIRE WHEEL


ALLOY WHEEL


TYRE -FUNCTIONS

• Act as the primary suspension, cushioning the vehicle from

effects of rough surface.

• Provide frictional contact with the road surface which allows

the driving wheels to move the vehicle

• Front tyres allows the wheels to steer

• Tyres allow braking to slow or stop the vehicle


PROPERTIES OF TYRES

•Non-skidding

•Uniform wear

•Load-carrying capacity

•Speed Capacity

•Cushioning

•Power consumption

•Noise

•Balance


TERMINOLOGIES • Steel Wheels – Most popular design. Very strong and cheap to produce.

• Alloy Wheels – Attractive and light weight, but expensive and difficult to clean.

• Spoked Wheels – Used on older vehicles. Cannot be fitted with tubeless tyres.

• Divided rims – Rims are made in two halves which are bolted together, (rims must never be

separated while the tyre is inflated)

• Split rims –Tyre is held in place by a large circlip

• Plies – Layers of strong fabric which are built up to give the tyre its strength and shape

• Bead – loops of steel which are the anchor point for the plies

• Cross Ply Tyre – Main plies of the tyre run at an angle (45 degrees) from one bead to the

other

• Radial Ply Tyre – Main plies of the tyre run at 90 degrees from one bead to the other

• Tread – Rubber pattern. Provides grip with the road surface and assists in clearing water

away

• Side Wall – Connects the beads to the tread of the tyre


PARTS

•Beads: Two rings that are made of steel wire and encased in rubber. They

hold tire side walls snugly against the rim and prevent tyre from coming off

•Body Plies: Rubberized fabric and cords wrapped around beads. Form

carcass or body of the tyre.

•Tread: Outer surface of the tyre that comes in contact with the road


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•Sidewall: Outer part of the tyre that extends from the bead to the tread.

•Marking on the sidewall provides the information about the tyre.

•Liner: Thin layer of rubber that is bonded to the inside of the plies. Provides a leak proof membrane for tubeless tires.

•Belts: Used to strengthen the body plies and stiffen the tread.

•Lie between tread and plies


CUTAWAY SECTION OF A TYRE


BIAS PLY/CROSS PLY TYRE

•One of the oldest design

•Several textile plies are laid across each other, running from bead to

bead in alternate directions

•Number of plies depends on the size of the tyre and the load it has to

carry

•Same number of plies is used on the crown and the sidewalls

•Plies run at an angle from bead to bead

•Does not use belts

•Allows body of the tyre to flex easily

•Improved cushioning, hence smooth ride on rough roads

•Weakness: Reduced traction at high speeds and increase rolling

resistance


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RADIAL PLY TYRE

•Plies run straight across from bead to bead.

•Has a very flexible sidewall and a stiff tread, giving it a very stable

footprint

•Consist of a carcass ply formed by textile arcs running from one bead to

the other.

•Each ply is laid at an angle of 90 degrees to the direction the tyre rolling

•At the top of the tyre crown (under the tread), a belt made up of several

plies reinforced with metal wire is laid.

•These crown plies, laid one on top of the other, overlap at an angle

determined by the type of the tyre.


BELTED BIAS TYRE

•Bias ply tyres with belts added to increase tread stiffness.

•Belts do not run around the sidewalls, they lay under the tread area only

•Belts and plies run at different angles

•Offers some reduction in rolling resistance over a bias ply tire

•Provides smooth ride and good traction


ADVANTAGES OF RADIAL PLY TYRES

•Side walls can bend easily, its shock absorbing capacity is 25% more

than bias ply or cross ply.

•Lower rolling resistance and hysteresis loss leads to less fuel

consumption

•Longer tread life because of less heat build in tyre.

•Breaking efficiency on wet roads is better because of greater sidewall

flexibility and tread stiffness.

•Better steering characteristics.

•While taking turns it has less tendency to distort and lift off the road from

one side.

•Larger resistance to punctures ,cuts and impacts in the tread area.



Bias contact patch

Radial contact patch

Non-Directional Tyres

Uniform grooves

Can run in any direction

Unidirectional Tyres

Grooves are in one direction

Direction of rotation is clearly marked


TUBED AND TUBELESS TYRES


CROSS-SECTION OF TUBELESS TYRE


ADVANTAGES OF TUBELESS TYRES

•Lesser un-sprung weight.

•Better cooling

•Lesser rolling resistance

•Comfortable ride

•Slower leakage of air

•Simpler assembly

•Improved safety


TYRE SPECIFICATIONS


NITROGEN IN TYRES

•Makes up around 80% of the air

•Dry inert gas. It is less reactive than oxygen.

•Leaks out of the sidewall three times slower then oxygen.

•Oxygen oxidizes the rubber in the sidewall.

•Pumped into tyres in a pure form, hence it does not contain moisture found in compressed ambient air which causes rusting of steel rims.

•The result is that all materials that come into contact with the compressed gas inside the tyre are less subject to oxidation corrosion


WHEEL BALANCING


TYRE ROTATION


CAUSES OF TYRE WEAR • Over inflation

• Under-inflation

• Front-wheel-Misalignment

• Rear-wheel Misalignment

• Defective wheels

• Excessive Speeds

• Excessive Wheel Camber

• Flats on Tyres


THANK YOU!!!


Automobile module iv

Education

Transcript of Automobile module iv