Automobile module iii

Steering and Suspension
Systems
Anoop P
Department of Mechanical Engineering
DepartmentofMechanical
Engineering,MITSPuthencruz
1

FUNCTIONAND PRINCIPLE
• The purpose of the steering system is to allow the driver to
control the direction of the vehicle by turning the front wheels.
• This is done by means of steering wheel, a steering column
which transmits the rotation of the steering wheel to the
steering gears, the steering gears which increase the rotational
force of the steering wheel in order to transmit greater torque
to the steering linkage, and the steering linkage which
transmits the steering gear movement to the front wheels.
• The steering system configuration depends on vehicle design
(the drive train and suspension system used, whether it is a
passenger car or a commercial vehicle, etc.).
• At present, the rack-and-pinion type and the recirculation-ball
types are in use.
2

Requirementsof Steering system
• Excellent maneuverability
• Proper steering effort
• Smooth recovery
• Minimum transmission of shock from road surface
3

Principle
• The relative motion between the wheels of a vehicle at the
road surface should be of a pure rolling type so that wear of
the tires is minimum and uniform.
• When the vehicle is moving on a curved path, the steering
gear must be so designed that the paths of the points of
contact of each wheel with the ground are concentric circular
arcs.
• For proper steering the axis of rotation of all the wheels
should meet at G i.e. the instantaneous centre of rotation of
the vehicle
• To satisfy this inner wheels should be turned through a greater
angle
4

To satisfy this inner wheels should be turned through a greater angle
5

6

STEERINGGEARMECHANISMS
There are two types of steering gear mechanisms
• Davis steering gear
• Ackermann steering gear
The main difference between the two steering gear mechanisms
is that the Davis steering gear has sliding pairs, whereas the
Ackermann steering gear has only turning pairs.
7

TYPESOF STEERINGGEARS
• The steering gear converts the turning motion of the steering
wheel into the to-and-fro motion of the link rod of the
steering linkage.
• Moreover, it also provides the necessary leverage so that the
driver is able to steer the vehicle without fatigue.
• There are many types and makes of steering gears in use for
automobiles.
8

• The steering gear changes the rotary motion of the
wheel into linear motion of the steering linkage.
9

Worm and wheel steeringgear
10

• The movement of the steering wheel turns the worm, which
in turn drives the worm wheel.
• Attached to the wheel spindle rigidly is drop arm, so that the
rotation of the steering wheel corresponds to a linear motion
of the drop arm end, which is connected to the link rod.
11

Worm and nut steering gear
12

• The steering wheel rotation rotates the worm which in turn
moves the nut along its length.
• This causes the drop arm end to move linearly, further moving
the link rod and thus steering the wheels.
13

RecirculatingBall TypeSteering Gear
14

• It consists of a worm at the end of steering rod .
• A nut is mounted on the worm with two sets of balls in the
grooves of the worm, in between the nut and the worm.
• The balls reduce the friction during the movement of the nut
on the worm.
• The nut has a number of teeth on the outside, which mesh
with the teeth on a worm wheel sector, on which is further
mounted the drop arm, which steers the road wheels through
the link rod and the steering arms.
15

Rackand pinionsteeringgear
16

• This type of steering gear is used on light vehicles like cars and
in power steering.
• It is simple light and responsive.
• It occupies very small space and uses lesser number of linkage
components compared to the worm and wheel type of gear.
• The rotary motion of the steering wheel is transmitted to the
pinion of the steering gear through universal joints
• The pinion is in mesh with a rack.
• The circular motion of the pinion is transferred into the linear
rack movement, which is further relayed through the ball joints
and tie rods to the stub axles for the wheels to be steered.
17

Cam and Double Roller Steering gear
• Similar to worm and wheel type steering gear
18

Power steering (ECPS)
19

• The main objective of power steering is to reduce the driver’s
effort in steering.
• This system may employ electrical devices, pneumatic and
hydraulic pressure.
• Power steering is basically power assisted steering in which an
arrangement to boost the steering wheel turning is provided.
20

Principlesof PowerSteering
• It is type of hydraulic device for utilizing engine power as
steering effort
• Engine is used to drive a pump to develop fluid pressure
• Pressure acts on the piston within the power cylinder so that
the piston assists the rack effort
• The amount of this assistance depends upon the extent of
pressure acting on the piston
• If more steering force is required the pressure must be raised
21

22

Electricalpowersteering
• In this kind of power steering employs electric power instead
of hydraulic power
• The electric power is imparted to the rack which then drives
the pinion
Advantages
• Vehicle can be steered even when the engine is inoperative
• Energy is consumed only when the vehicle is being steered
• The arrangement is neat and clean since the problem of
leakage is out of question
• Steering assembly is in the form of a compact unit
23

24

Front axle
• The constructional features of front axle is quite different
compared to a rear axle
• Rear axles transmit power to rear wheels in rear wheel drive
vehicles and front axles do not take part in power transfer.
• They just obey the commands of steering linkages for
swiveling the road wheels
• Also known as dead axle
25

Front axle arrangements
• Stub axle with rigid axle beam type
• Used earlier on all types of vehicles, but now it is limited to
medium and heavy commercial vehicles
• Eg: trucks, buses etc.
• Stub axle without rigid axle beam type
• These are widely employed in cars and light commercial vehicles
26

RigidAxle Beam
• It is a stationary structural member used to take up bending
and torsional loads
• Used to connect the stub axles
• Bending is induced in the central region due to vehicle’s
weight
• Torsion occurs at its ends due to braking of wheels
• Axle is made of I-section at the centre and circular portion at
the ends so as to resist the loads efficiently.
27

28

Stub Axle
• An inter--mediatory small link between the road wheels and
the front axle.
• It gets connected with the front axle by means of king pin or a
ball joint
• The ends of which are connected to the road wheels
29

Stub Axle- Types
• Depending on the shape and style of connection stub axles
can be of the following types:
• Elliot type
• Reversed Elliot type
• Lamoine type
• Reversed Lamoine type
• Ball joint type
30

31

Centre point steering
32

Wheel Alignment
• It refers to the setting of front wheels and the steering
mechanism that provides
• an easier directional control of the vehicle
• Minimum tyre wear
• Stability to vehicle while negotiating a curve
• Parallel rolling of front wheels in straight ahead position
33

Steering Geometry
• It is the group of design variables outside the steering
mechanism that affect the behavior
Camber
King pin inclination
Caster
Scrub Radius
Included angle
34

Toe-in Toe-out
• It is the initial setting of front wheels carried out in a garage
• Here the front wheels are set closer at the front than at the
rear – toe in
• If the front of front wheels are are far off than rears – toe out
35

The purpose of providing toe in is to offset the tendency of wheel
rolling:
• On curves due to limitation of correct steering
• Due to possible play in steering linkages
• Due to camber effects
The toe out is provided to counter the tendency of inward rolling
of the wheels
• Due to soil condition on agricultural land
• On account of side thrusts and cross wind effects
36

37
• The amount of toe in varies from 0-6mm on different
vehicles
• 2-4mm for Maruti 800 car

Camber/ Wheel Rake
• The front wheels are tilted outwards at the top and inwards at
the bottom when viewed from the front of the vehicle
• The centre line of the tyre forms an angle with the vertical.
• This is known as camber angle
38

• Some vehicles are provided with positive camber while others
have negative camber
• Most vehicles are provided with positive camber
Camber is used to prevent inward titling at the top of the wheels
caused due to
• Excessive load
• Play in king pins
• Play in wheel bearings
• Camber on both wheels must be equal
• The amount of camber is generally kept between 0-1.50
39

King pininclination/Steering axisinclination
• King pin is mounted in such a way that it remains inclined with
respect to the vertical axis
• The angle thus formed between the centre line of king pin and
the vertical axis is called king pin angle (king pin rake)
• In case of modern cars which employ ball joints instead of king
pin, steering axis inclination is referred instead of king pin
inclination
• It is kept around 7-8 degrees
40

This inclination
• Helps in a straight ahead recovery and provides directional
stability
• Reduces the wear and tear of the tyres
• Tends to reduce the effect of road shock on the steering system
Incorrect steering inclination leads to
• Hard steering
• Pulling of vehicle to a side
• Wheel doesn’t return to straight ahead position
41

Caster
42
• It is the tilt of king pin centre line or steering axis towards the front
or rear of the vehicle
• It lies in the range of 2-8degrees
• 3 degree is optimum
• With positive caster the steering axis is ahead of road resistance to
the tyre which aids in directional stability

• Excessive positive castor leads to
• Increased road shocks on steering wheel
• Requirement of greater steering effort
• Wheel wobbling at low speed
43

IncludedAngle/Combinedangle
• The angle formed in the vertical plane between the king pin
center line and the wheel center line.
• A correct measure of included angle contribute to steering
ease.
• Include angle is around 9-100
44

ScrubRadius
• The tractive force of the vehicle acts at a point where the
steering axis meets the road at a point on the ground
• The distance between the extended centre line of the steering
axis and centre line of the tyre where the tread contacts the
road is called scrub radius
45

46

Reversible,IrreversibleandSemi-reversibleSteering
• When an effort (i/p) is applied on the steering wheel which
causes the road wheels to swivel(o/p).
• If this action is reversed by swiveling the road wheels (i/p), the
steering wheel can be turned(o/p) then the system is known
as reversible steering.
• In an irreversible steering it is not possible to turn the steering
wheel by swiveling the road wheels.
• A compromise made between the short coming of the two
systems results in semi reversible steering
47

Description Reversible Irreversible Semi irreversible
Transmission of
road shocks to
steering
Yes, fully No, nil no
Control of steering Difficult Less difficult Better
Fatigue to driver Greater Lesser Intermediate
Feeling of road
conditions
Yes, fully No, nil Yes
Load on joints Less More Fair
48

Slip angle, corneringforce &
Self righting torque
49Cornering force produced per unit slip angle is defined as cornering
power

• Various factors affecting cornering force and self righting torque
50

Oversteer and Understeer
• It is evident from the names that the vehicle gets steered either
more or less than the normal desired steering.
• While negotiating a curve the vehicle should follow a well defined
path under normal steering condition
• When the vehicle exhibits a tendency to take either a more sharp
turn than intended by the driver or a lesser turning.
• The former situation is known as over steering and the latter under
steering
• Several factors contribute to this kind of steering to vehicle such as
load, slip angle, cornering force and suspension systems etc.
51

Comparison
Factor Under steer Over steer
Stability of vehicle Increased Decreased
Desirability More Less
Path of travel Wider Narrower
Driver’s effort More Less
For correct turning of
wheels
Steering has to be
rotated more
Steering wheel has to be
unwound
Effect at higher speeds Increased un-stability Chances of accidents are
high
Means to minimise By increasing inflation
pressure in front wheels
By increasing inflation
pressure in rear wheels
52

Steering Gear Ratioand overall steeringRatio
SGR
• The ratio of angle turned by steering wheel to the
corresponding angle turned by the steering gear cross shaft.
• Drop arm/pitman arm is attached to the cross shaft
OSR
• The ratio of angle turned by the steering wheel to the
corresponding angle turned by the front road wheels.
53

Suspension Systems
54
The suspension system is made up of springs, shock absorbers and linkage so as
to allow the wheels and tyres to follow the road roughness without excessively
raising the frame and transmitting shock.

Objectives
• To safe guard passengers and goods against road shocks
• To preserve the stability of vehicles while in motion
• To provide the wheels always in contact with road while
driving cornering and braking
• To maintain proper steering geometry
• To provide suitable riding and cushioning properties
55
The suspension system connects the body of vehicle with the wheels and restricts the
direct impact of wheels to the chassis and body.

Components
• Springs, which neutralize the shocks from the road surface
• Dampers (shock absorbers), which act to improve comfort by
limiting the free oscillation of the springs.
• Stabilizer (sway bar or anti-roll bar), which prevents lateral
swaying of the car.
• A linkage system, which acts to hold the above components in
place and the control the longitudinal and lateral movements
of the wheels.
56

Types of Suspension System
57
Non-independent/Rigid suspension has both right and left wheel attached to the
same solid axle. When one wheel hits a bump in the road, its upward movement
causes a slight tilt of the other wheel.
Independent suspension allows one wheel to move up and down with minimal
effect to the other.

Independent
58
Non-Independent

59
Coil Spring used in cars and even in modern vehicles
Leaf spring is seldom used in rear part of the cars

Suspension springs
• Metallic springs
• Leaf springs
• Coil Springs
• Torsion bar
• Non- metallic springs
• Pneumatic(air) springs
• Rubber springs
60

Leaf Springs
• It is a stock of spring steel strips/ laminations called leaves
61
These are also known as semi-elliptical leaf
springs since they are in bent form

• Leaves/ laminations are comprised of leaf springs that are curved and are
bound together to act as a single unit.
• Stack of leaves is fastened together at the center with a central bolt/rivet
• The longest leaf in the assembly is called master leaf. The assembly acts as a
flexible beam due to different lengths of each spring.
• The curvature of leaf spring is called nip. The overall curvature of leaf spring is
called camber
• Inter leaf friction reduces riding comfort, so to reduce this silencer pads are
inserted in between the leaf springs, also leaves are lubricated with special
graphite rich oil,
• Helper springs is a special type of leaf spring with no eye at ends. It is placed
above the master leaf spring. When the load exceeds a prescribed value both
the main and helper springs comes into operation
62

Types of Leaf Springs
63
• Quarter elliptic was used in earlier models
• Transverse leaf spring increases the tendency
of vehicle to roll while negotiating sharp turns

Coil springs
• It is a heavy duty strip of spring steel formed into shape of
helix
• These are ideal for absorbing vertical energy
and can take up bending and shear stress.
• There is no inter leaf friction as with leaf
springs.
• No control of oscillations by the spring itself
• Helper springs provide progressive stiffness
against increasing load
64

65
• Helper Spring
• Main spring

Torsion Bar
• It is a circular rod made of spring steel.
• One end is anchored to the frame and other end is attached to
the control arm of vehicle, which is subjected to torsional load
66

• The energy absorption per unit weight is high
• Suspension system gets lighter
• Provides a compact design
• Can’t take driving/braking thrust
• No friction force and no inherent damping to control the
vibrations produced due to road shocks
• These are used with independent front and rear suspensions
67

Rubber springs
• Absorbs oscillations through generation of internal friction
when they are deformed by an external force.
• More compact system
• Excellent vibration damping properties
• Absence of squeaking
• Greater reliability
• Good fatigue strength in compression
68

Air Springs
• It is based upon the elasticity of compressed air
• System employs rubber bellows which has compressed air.
• The air filled bellows
acts as suspension
• Vibration and shocks are absorbed
• Air pressure can be controlled for optimum riding comfort
• Complexity of compressed air and accessory system
69

Stabilizer
(Sway bar/Anti roll bar)
• This prevents vehicle from rolling while taking a turn
• Fastened to lower control arms
• During cornering, centrifugal force makes the outside of body
drop and inside raise.
• The bar’s resistance to twisting motion limits body lean in
corners.
70

Sprung and un-sprung weight
• Refers to the weight of those parts of the vehicle that are
supported on front and rear springs
eg: vehicle frame, body, engine, power train
Jounce and Rebound
The suspension springs gets compressed when the vehicle goes
over a bump. This state is known as jounce, which is the energy
stored in the spring that forces the spring to original state.
While returning the spring over runs the neutral position and this
action is termed as rebound
71

Dampers/ Shock Absorbers
• These are used in suspension system to check any continuous
vibration which may follow the initial force on the system
• Shock absorbers are necessary because springs do not settle
down fast enough.
• A dampening device is needed to control the spring
oscillations while bouncing, such device is called a shock
absorber
• The shock absorber absorbs the energy of shock converted
into vertical movement of axle by producing damping and
dissipating the same into heat.
• Damper is a better term technically to describe a shock
absorber
72

Principle of operation
Hydraulic Dampers
In these dampers hydraulic fluid is used as the damping agent.
“When a piston forces a fluid in a cylinder to pass through some
hole, a high resistance to the movement of the piston is
developed which provides the damping effect”
• An advantage of hydraulic damper is that damping is
proportional to the square of the speed.
73

Telescopic Dampers
74

When the shock absorber is under compression
• Fluid in the cylinder passes upwards through the restricted valves
of the piston
• At the same time the fluid passes down through a small valve of
the cylinder tube
• Due to this arrangement the piston is able to move against the
resistance of the fluid, thus the shock is absorbed.
When the shock absorber is under tension:
• Liquid from the top portion of piston is forced downward through
the piston valves
• At the same time the fluid enters through the valve at the bottom
of the cylinder tube.
• The lengthening of shock absorber is thus made very slow, since it
has to overcome the resistance of the fluid
75

Gas filled shock absorber
• Here instead of oil, a mixture of oil and gas is used for the
dampening effect
Advantages
• Provides longer life to tyres and other related suspension
components
• Can tolerate heat to a greater degree
• This can be mounted in any position
• Increases ground clearance
• Prevents the formation of bubbles
76

Independent Suspension
• It is an arrangement by which wheels are connected to the
carriage unit in a manner such that the rise and fall of one
wheel has no effect on the others. eg: passenger cars
Advantages
• Engine position can be moved forward, hence passenger
space is greatly increased
• Gyroscopic effects are reduced to minimum
• Diminished wheel wobble and steering tramp
• Reduced un-sprung weight
• Provides a greater springing movement
77

Disadvantages
• High initial cost
• Due to large no. of bearings greater maintenance is required
• More rigid sub frames are required
• Force due to unbalanced wheels are transmitted easily to
steering
• Misalignment of steering geometry due to wear of component,
hence requires more attention
78

Front wheel Independent
Suspension
• Wishbone arm system
• Trailing link system
• Sliding pillar system
79

Wishbone Arm system
80

Macpherson Strut assembly
81

Trailing link system
82

Vertical guide type
83

Sliding pillar type
84

Rear wheel Suspension system
• Leaf spring rear suspension system (rigid suspension)
• Independent rear suspension
• Swinging half axle
• Macpherson strut
• Trailing Arm Design
85

Swinging half axle
86

Trailing Arm Design
87

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