Automotive Suspension system

SRI KRISHNA COLLEGE OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF MECHATRONICS ENGINEERING
Session: Vehicle Suspension System
11/24/2020 16MT407 - Theory of Automobile Engineering 1
MODULE 1

SESSION OBJECTIVES
 On the completion of this session, the students might
be able to understand,
 Proper selection of suspension system for your
vehicle.
 Good chosen of shock absorber for comfort ride

Topics
 Introduction
 Types of suspension system
 Basic suspension movements
 Suspension springs
 Shock absorber

INTRODUCTION
Where suspension system is located in
vehicle?
 It’s located b/n wheels & Body of the
vehicle
Purpose of suspension system:
 Connects the vehicle body & the wheels & thus supports
the weight of the vehicle
 Absorb the vibration & shocks from the road surface.
 Improve the driving comfort and protect the passenger from the road shocks.
 It ensures that the wheels always contact with road surface.
 And maintain the inclination of body in order to improve the stability of the
vehicle in any possible driving condition including acceleration, braking and
cornering.

TYPES OF SUSPENSION SYSTEM
Types of Suspension System
Rigid Axle Suspension System
Independent Suspension
System

Rigid Axle Suspension system :
 Also called non independent suspension system.
 Here right & Left wheel attached to the same solid axle.
 When one wheel expose to bump on road, causes a slight tilt on other wheel.

Independent Suspension system :
 No axle beam connecting the left & Right wheels
 Load directed to the wheel is supported by the suspension arm.
 Each wheel moves independently in response to its specific road condition.
 Provides driving comfort & stability

Rigid Axle Suspension Independent Suspension
Irregularities encountered wheel axle tilts
and wheel no longer remains vertical
Irregularities encountered wheel axle does
not tilts and wheel remains vertical
The riding comfort is reduced The riding comfort is increased
Road adhesion is decreased Road adhesion is increased
Chances of wobbling of wheels No wobbling of wheels
Leaf spring are used in this type Coil spring or Torsion bar are generally used
Generally used in large vehicles like trucks &
Buses
Generally used in cars & Light commercial
vehicle

Suspension arrangement in vehicle :
 It differs in vehicle at each case.
 Some time front & Rear suspension are not same.
Different suspension arrangement:
 Conventional Rigid axle suspension at both front &
Rear.
 Conventional rigid axle suspension at rear &
independent suspension at front.
 Independent suspension at both Front & Rear

Types of Front wheel suspension system:
 Independent suspension universally chosen for front
axle, due its simplicity.
 Wishbone type or parallel link type (Double
Wishbone system)
 Macpherson strut type
 Vertical guide type
 Trailing Link type
 Swing half – axle type

Double Wishbone suspension:
 Consists of two wishbone shaped arms, a coil
spring, a shock absorber assembly.
 Each arm is connected to steering knuckle via
bushes
 The two arm are like the two legs of chicken
wishbone or letter V
 Upper wishbone arms are shorter in length
than the lower ones
 This helps to keep the wheel track constant.
 There by avoid the tyre scrub & thus
minimizing the tyre wear.
Legs of
Chicken
Wishbone or
Letter V

Double Wishbone suspension: On
Front Axle
 The upper Positioned in the region
above the top of the wheel.
 Side force experienced during
cornering do not cause the wheel
alignment to be disturbed.

Double Wishbone suspension: On
Rear Axle
 The upper arm generally Positioned
inside the radius of the wheel in order
to have large cabin space.
 This is known as “In wheel – Type –
Double – Wishbone suspension”
 This system consists of upper arm,
lower arm, shock absorber assembly.
 Regards of external force, the lower
arm can move in a small amount in
lateral & transverse direction.
 It improves driving comfort & ensure
no disturbance in Wheel alignment.

Double Wishbone suspension:
Advantage Disadvantage
Ride Quality is Good Initial cost is more
Improved Steerability Maintenance cost is more
Ground Clearance increase
Required frequent wheel alignment,
Otherwise increase tyre wear

Macpherson Strut suspension:
 More popular & Efficient form of
suspension
 It has one control arm & Strut Assembly
 A coil spring and shock absorber will
normally forms the part of the strut
assembly.
 On rear Axle, The coil spring mounted on
the control arm instead of being around
the strut.
 On this type shock absorber connects the
knuckle to the frame.
For Front Axle
For Rear Axle

Macpherson Strut suspension: For Front Axle
 The top of the strut is bolted to a reinforced
section of the frame structure.
 The lower end of the strut is attached to a
steering Knuckle.
 The control arm is also attached to the steering
Knuckle
 An anti roll bar links the two control arms
together to reduce the sway (Body Roll)
Working :
 The movement of wheel is controlled by
swinging of the lower arms and the
compression or extension of the shock absorber

Macpherson Strut suspension:
Advantages Disadvantages
Light in Weight Not suitable for Heavy Motor vehicle
Camber do not change, due to up & Down
movement of wheels
Load carrying capacity is less
Maintenance cost is less
Initial cost is less
Ride comfort is more
Improve road safety

Vertical Guide suspension:
 King pin is directly attached to the
cross member of the frame
 It can slide up & Down as shown
corresponding to the motion of the
wheel and there by compressing or
elongating the springs.
 In this type, wheel track, Wheel
base, and wheel altitude remain
unchanged.
 But the system is having the
disadvange of less stability

Trailing link type independent
suspension:
 Here helical coil spring is arranged
in horizontal position rather than
vertical position.
 One end of spring fixed with cross
member of frame & Other end with
trailing Link.
 The other end of trailing is
attached to the shaft, which carries
wheel hub.
Frame
Side Member
wheel hub

Trailing link type independent
suspension:
 When the wheel moves up &
Down, it winds & Unwinds the
helical spring to absorb the wheel
vibration due to road irregularities.
 To check the vibration of the spring
a multi plate shock absorber is also
provided at the end of the cross
member.
 In some design case, helical spring
replaced by torsion bar.
Frame
Side Member
wheel hub

Swinging Half axle suspension:
 Wheels are mounted rigidly on the
half axles.
 Half axles are pivoted on either
ends of the chassis member at the
middle of the car.
 Considered as Good concept.
 But up & Down movement of the
wheel causes major changes in the
camber angle causing rapid wear.

Air suspension:
 Very popular.
 Compact & fits well in
all automobile
 Constant height can be
maintained with help of
leveling valves, even at
varying loads act on the
vehicle.

Air suspension:
 Four conventional spring replaced by four air spring units.
 It consists Barrel or dome shaped air chamber called below/Diaphragm is placed
 It is compressed by specially shaped plunger.
 Lower end attached to axles & Air chamber is fastened to car frame.
 Each unit is filled with compressed air, which supports the weight of the vehicle.

Air suspension:
 Leveling valve control the air from & to the spring.
 This way maintain the car body height parallel to ground.
 Each leveling valve contains two valves in one unit.
 One allow the air into dome & Other relieve the air to atmosphere through
return line & Lift valve.

Air suspension:
 The compressed air is supplied by an air compressor, Air tank, a pressure
regulator, solenoid valve.
 The compressed air pressure is 200 Mpa & thus maintained by air tank.
 The air compressor is driven by a belt from the crankshaft pulley.

Air suspension:
 The pressure regulator reduced the pressure up to 120 Mpa.
 This pressurized air is send by leveling valve to air spring unit.
 Insufficient air side cause low ride.
 Now levelling valve send air to the spring unit & adjust the level of vehicle by
admitting more air.

Air suspension: Advantage
 High quality ride is achieved.
Disadvantage:
 Cost of the system is high
 Compressed air supply system is complex
 Greater maintenance is required.

BASIC SUSPENSION MOVEMENTS
Basic suspension movements:
 The vehicle move over many irregulaties, Bumps, potholes, as well as different
types of roads like bend roads, zigzag roads, resulting in below following
movement.
 Bouncing
 Pitching
 Rolling – Centrifugal force act at Center of gravity & Force acting at tyre road
contact.
 Combination of Roll & Pitch is called as Diagonal pitch

SUSPENSION SPRINGS
Basic Requirements of a suspension system:
 It should have minimum deflection consistent with the vehicle stability in order
to provide good cushioning ability along with better ride qualities.
 It should have minimum unsprung weight.
 The total weight of the suspension system should be minimum
 It should minimize the tyre wear.
 It should have low initial cost, operation cost and maintenance cost

SUSPENSION SPRINGS
Sprung weight :
 It refers, weight which is supported by
suspension springs.
 Weight of the vehicle body,frame,engine
transmission, interior, Fuel & Passenger,
constitute the sprung weight.

SUSPENSION SPRINGS
Unsprung weight :
 It refers, weight which is not supported
by suspension springs.
 It includes the weight of the wheels,
Rear Axles, steering linkage, and
suspension components.
 Greater weight – greater absorption of
energy.
 But difficult to restore its original
position.
 Cause tyre deflection & reduce vertical
velocity on a road bump.
 A good suspension system must have
less unsprung weight.

SUSPENSION SPRINGS
Springs:
 The springs in suspension system are
used to absorb the up & Down motion of
the wheels.
 During the wheel passes through Bumps
& Pot holes.
 Protects the passengers from getting
shocks & Vibration
 Placed b/n Chassis frame & Axle
Torsion Bar
Leaf Spring
Coil Spring

SUSPENSION SPRINGS
Springs: Leaf Spring
 Made up of several flat long strips made from spring steel of rectangular cross
section.
 Each strip is called leaf.
 Here several strips are placed one after another & held together by means of
Bolt & Clamps.
 The assembly contains of a main leaf which extends to the full length of the
spring.
 The ends of main leaf are formed with loops known as eyes.

SUSPENSION SPRINGS
 The other leaves in the spring are attached to the main leaf by means of
center bolt and clamps.
 The length of each succeeding leaf is shorter than preceding one & the
complete assembly acts as flexible leaves.
 When the vehicle is goes over Bump, the spring flattens up and increase in
length and during rebound, the spring return back to it shape thereby
decreasing in length.
 Bronze bushes are fitted in the eye for reducing wear.
 Some times rubber bushes
are used, which never
required lubrication

SUSPENSION SPRINGS
Advantage :
 Commonly seen in automobile from mid of 1970’s
 Now days cars used Coil spring,
 Heavier vehicle only used leaf spring, for its wide load spreading character
 Coil spring transfer to a point, can’t used in Heavy vehicle.

SUSPENSION SPRINGS
Disadvantage :
 Leaf gets broken, while the vehicle travel over rough road & Carry heavy load.
 The broken leaf must need to be replaced by new one for using it again.
 Graphite grease should be applied b/n leaves before assembling it.
 Sometimes continuous use, spring get sagged or get straightened.
 In this case particular spring leaf taken out for hammering to retain its same
shape.
 This is known as Cambering of spring

SUSPENSION SPRINGS
Springs: Types of Leaf Spring
a.) Full Elliptical leaf spring:
 This type of leaf spring refers to two semi-elliptical springs connected at their
ends, to form a shape of an ellipse

SUSPENSION SPRINGS
b.) Three quarter Elliptical leaf spring:
 This type of leaf spring refers to one semi-elliptical spring connected over a
quarter elliptical spring.
Chassis Frame

SUSPENSION SPRINGS
c.) Semi Elliptical leaf spring:
 This type of leaf spring refers to forming the shape of half ellipse.

SUSPENSION SPRINGS
d.) Quarter Elliptical leaf spring:
 This type of leaf spring refers to forming the shape of half of semi – elliptical
spring.
 This type of system is also called as cantilever spring system.

SUSPENSION SPRINGS
e.) Transverse leaf spring:
 This type of leaf spring refers to a semi elliptical spring mounted in a inverted
manner.

SUSPENSION SPRINGS
f.) Platform type leaf spring:
 This type of leaf spring refers to a quarter elliptical leaf spring with extensive
platform supported by shackle.

SUSPENSION SPRINGS
Springs: Helper Springs
 Mounted directly on the main springs.
 Used in commercial vehicles such as trucks
and buses to provide additional support for
heavy loads at rear end only.
 Fixed on the top of the rear main spring.
 With the help of center bolt and then
clamped with U-Bolt to the rear axle.
 During light load on vehicle, main spring
are in active.
 In case of heavy loads, the helpers springs
rest against the brackets on the frame.
 Now both the spring share the load
Helper Springs
Brackets on Frame

SUSPENSION SPRINGS
Springs: Tapered Leaf Springs
 Consists of 1 to 4 leaves.
 Designed with reducing thickness from
the center to end.
 Leaf is thick in center & Taper out to the
end.
 All the leaves are approximately of the
same length
Advantage :
 Reducing Spring Stresses :
 Load or stress is spread out evenly along
the entire length of the leaf.

SUSPENSION SPRINGS
Springs: Tapered Leaf Springs
 Reducing Spring Weight:
 Due to the even stress distribution, allows for maximum use of the
material properties and reducing the thickness
 This minimize the Weight of the spring 60% to the convention spring.
 Improved ride quality by reducing interleaf friction:
 Friction b/n Spring during deflection
 Tapered spring can contact at center & Tips – Suits for small loads or
Bumps.
 Increase spring life:
 By reducing weight.
 Zinc rich painting of each leaf greatly
extends spring life by postponing the
start of corrosion, it cause cracking

SUSPENSION SPRINGS
Springs: Coil Springs – Standard Type
 Extensive use in commercial vehicle.
 Made from a length of special spring steel
 Round in cross section
 Wound in the shape of coil.
 Ends of coil springs are kept flat, so that they seat
properly.
 During load, it is more elastic & Compresses
 By compressing & Expanding the spring, it can absorb
the shock, during vehicle moves over Bump & Pot hole.

SUSPENSION SPRINGS
Springs: Coil Springs – Progressive Type
 It has progressively increase pitch of wire wound.
 Larger pitch section absorb shocks or Impacts with
smaller pitch section of the spring completely
compressed, when vehicle moves over Bump.
 Mostly used in Independent suspension system.
 Can be assembled in Compact space.
 Capable of storing twice the energy that than of a leaf
spring.

SUSPENSION SPRINGS
Springs: Torsion Bar
 Made from spring steel bar which function by
twisting.
 One end is fixed with frame, so that it may not
turn
 Other end is attached to the lower control arm.
 When the vehicle goes over a Bump or Pot hole, It
gets twisting effect.
 This elasticity of the rod is utilized to bring back
the wheel to its normal position in the same
manner as a spring arrangement

SUSPENSION SPRINGS
Springs: Torsion Bar
Advantage:
 More durability
 Easy adjustability of ride height.
 Small space required to mounting.
Disadvantage:
 Cannot provide a progressive spring rate.

SUSPENSION SPRINGS
Springs: Rubber Torsion Unit
 Design is similar to the steel
torsion bar type.
 The twisting member,
consists of two tubes of
different sizes vulcanized to a
rubber core.
 The outer tube is fixed with
chassis frame.
 While inner tube serves as a
shaft for suspension arm
over which the wheel is
fitted.

SUSPENSION SPRINGS
 As the wheel moves up &
Down, the suspension arm
swings, which twists and
untwists the inner tube.
 Since the inner tube is
vulcanized with outer tube,
 That medium of rubber
provides springing action.

SUSPENSION SPRINGS
Advantage:
 Excellent vibration damping.
 Rubber spring system is
more compact.
 Can store greater energy per
unit weight than steel.
 No abnormal squeaking
Noise

SHOCK ABSORBER
Shock Absorber: Purpose
 Vehicle experience impact force while it
moves over road irregularities.
 Here the spring flexes to absorb the
impact force.
 But spring oscillate in vertical direction
for a finite time period & can return to
its original position.
 In order to damp down the oscillating
motion of springs for ensure the driving
comfort & Steerability a shock absorber
is used
 Shock absorber act as a damper.

SHOCK ABSORBER
Shock Absorber: Types
Shock Absorber
Mechanical Shock Absorber Hydraulic Shock Absorber

SHOCK ABSORBER
Shock Absorber: Mechanical
 Consists of two links
 Connected with each other by means of
pins
 One link is connected to the frame of
the vehicle.
 Whereas other link is fixed with axle.
 A number of friction disc of different
metals are placed in between links
 This will control the spring action due to
its frictional effect.
 This will help to absorb the road shock
 But obsolete now days due to its non
predictable damping characteristics

SHOCK ABSORBER
Shock Absorber: Hydraulic
 It uses a fluid
 Which passes through an orifice
 It resisting the fluid movement
 The resistance force that is created at
this time which is used to suppress the
motion of the spring.
Telescopic Shock Absorber
Cam Actuated piston type shock absorber
Rotary Vane Type Shock Absorber

SHOCK ABSORER
Principle of Hydraulic Shock absorber:
 Simplified Version of a shock absorber.
 In this set up , a piston having orifices moves up & Down
inside an oil filled cylinder.
 As it moves the oil passes through an orifices in the piston
 This creates a resistance force (Damping force), which is
used to suppress the motion of spring.
 Effective capacity of the cylinder is reduced, when the
piston is introduced into the cylinder in mono tube type.
 This problem is over come by twin tube type shock
absorber.
 Piston movement allows the oil escape to a reservoir in-
between the inner and outer tube.
Mono - Tube
Twin - Tube

SHOCK ABSORER
Mono Tube Hydraulic Shock absorber: Construction
 It has Single Tube Only.
 It has two chamber.
 Working Chamber
 Expansion chamber
 Expansion chamber charged with
Nitrogen gas b/n 25 to 30 Bar.
 It ensure the rebound effect
 Keeps the working chamber
constantly filled with Oil.

SHOCK ABSORER
Mono Tube Hydraulic Shock absorber: Principle
 Here the oil is forces to flow through the
orifices in the piston valve.
 It is heated.
 It is the mechanism which allows the shock
absorber to dissipate energy stored by the
suspension spring.
 “Road shock is absorbed by converting
Kinetic Energy (Energy of Motion) into heat
which is absorbed by the oil in the shock
absorber”.

SHOCK ABSORER
Mono Tube Hydraulic Shock absorber: Working
Compression:
 When bumps on roads.
 Oil compress the Gas &
Reducing its volume.
Rebound:
 By contrast, the shock
absorber is extending.
 Rod leaves the working
chamber.
 Floating piston moves up.
 Ensure the pressurized oil
in the working chamber

SHOCK ABSORER
Twin Tube Hydraulic Shock absorber: Construction
 Also called as Direct Double acting
Telescopic type Hydraulic Shock absorber.
 Because shock absorber acts on both the
compression (Downward movement of
the body) & Rebound stroke(Upward
Movement of the body).
 There are two chamber
 Outer chamber – Reservoir
 Inner chamber
 Piston splits the inner chamber into two.
 Rebound chamber
 Compression chamber

SHOCK ABSORER
Twin Tube Hydraulic Shock absorber: Working
 When the wheels goes over a Bump.
 The suspension system moves, relative
motion b/n the sprung & Unsprung
masses force the piston and rod assemble
to move or telescope.
 Piston & valve assembly pushed into the
lower chamber of the cylinder.
 Causing, compressing the oil in the
chamber.
 Since the oil is incompressible, so via the
valve orifice it moves to the upper
chamber & Reservoir.

SHOCK ABSORER
Twin Tube Hydraulic Shock absorber: Working
 As the shock absorber is extended during
this stroke, oil is drawn into the cylinder
tube, equal to the piston rod volume.
 At the same time air or gas in the
reservoir tube expands to account for oil
leaving the space b/n the cylinder &
reservoir tube
 “Thus the shock is absorbed by
converting Kinetic Energy (i.e Energy of
motion) into heat which is absorbed by
the oil in the shock absorber”.
 Damping Force = ∆𝑃 (𝐴 𝑝 − 𝐴 𝑟)

SHOCK ABSORER
Twin Tube Hydraulic Shock absorber: Cavitation
 As the shock absorber operates excessively,
the air inside the reservoir mixes with oil in
the form of Bubbles.
 This phenomenon is commonly known as
cavitation.
 When the pressure is applied to these
bubbles.
 They passes through orifice without
generating any resistance force,.
 Damping force delivered by the shock
absorber is reduced.
 Using of Nitrogen gas is prevent the cavitation
problem & Ensure stable operation

SHOCK ABSORER
Cam Actuated piston type Hydraulic Shock absorber:
Single Acting cam actuated type :
 When vehicle moves over Bump.
 Frame moves downward, Lever
moves upward, Cam moves Right
side.
 Intake valve open & It has large
port.
 It offers little resistance to oil flow.

SHOCK ABSORER
Single Acting cam actuated type :
 When vehicle spring rebounds.
 The car frame moves upwards,
 Now lever moves downwards,
 So cam is moved in reverse
direction,
 & Apply the pressure on Piston.
 The intake valve gets closed.
 Relief valve send the oil to reservoir
from cylinder.
 This entire action cause damping to
the Suspension spring rebound &
Suppress it’s oscillation

SHOCK ABSORER
Double Acting cam actuated type :
 This type has two piston.
 One for regulate vehicle spring
rebound.
 Other regulate vehicle spring
compression.
 One piston is called rebound piston
 Other is called Compression piston.
 The pistons are actuated by a cam
fitted on a shaft.
 A lever actuated the cam shaft &
there by cam resulting in piston
movement.

SHOCK ABSORER
 Each piston contain one relief valve
& Intake valve.
Working :
 During vehicle moves on Bump.
 The oil flow takes place like
 Compression cylinder to
Reservoir via relief valve
 At the same time rebound
intake valve open due to partial
vacuum created in the rebound
cylinder & Filling it with oil.

SHOCK ABSORER
 Each piston contain one relief valve
& Intake valve.
Working :
 During vehicle rebounds,
 Pressure set up in the rebound
cylinder forces oil through the
rebound relief valve into
reservoir
 At the same time compression
intake valve opens, due to the
vacuum in it & fill the
compression cylinder

SHOCK ABSORER
Rotary Vane type Hydraulic Shock
absorber: Construction
 It contains Round Hollow Body, Fixed to
the chassis Frame.
 Two lobe rotor moves in viscous oil.
 The rotor divide the body into two
chambers & is provided with a valve.
 The rotor is mounted on a shaft.
 The other end of the rotor shaft is
operated by an actuating arm which is
connected with the axle by means of
link.

SHOCK ABSORER
Rotary Vane type Hydraulic Shock
absorber: Working
 When a vehicle goes over a Bump.
 The rotor is moved due to restricted
flow of the oil from the valve.
 So pressure is build up in one chamber.
 This pressure causes resistance to the
movement of the axle.
 Similarly, during rebound, the oil has to
pass through the same valve and causes
resistance to the movement of axle.

END

Automotive Suspension system

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