Automobile Steering system

SRI KRISHNA COLLEGE OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF MECHATRONICS ENGINEERING
Session: Vehicle Steering 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 steering mechanism for vehicle
 Good chosen of steering gear box for easy steering
 Important of wheel alignment factors for good
Steerability & stability of vehicle.

Topics
 Introduction
 Steering Mechanism
 Steering Ratio
 Steering Lock
 Steering Gear Box
 Power Steering
 Steering Geometry

Introduction
Simple steering system:
 Change the direction of motion of a
vehicle.
 Simply converted the Rotary motion
of steering wheel into angular turn
of front wheels.
 The motion of steering shaft is
transferred to the steering gear
box.
 Gear box convert the rotary motion
into lateral motion
 And it will transferred it to steering
linkage. Components of steering system

Introduction
Simple steering system:
 The left & Right linkages are
connected to the steering knuckle
on the left & right wheels
respectively.
 Each knuckle is pivoted on the
suspension’s upper & lower arms
and rotate about the axis.
 This cause the wheel to move left
or right, allowing the direction of
the vehicle to be changed.
Components of steering system

Introduction
Important terms used in Steering:
Steerability:
 Measure of the vehicle’s
responsiveness to the steering
operation of the driver.
Stability:
 Dynamic Meaning of vehicle
 Capability of a vehicle to restore
original motion by itself without
intervention of driver.
 When there is some external
disturbance during steady driving.

Introduction
Principle of Correct Steering:
 When the vehicle take a turn,
the front wheel along with the
respective axles turn about
the respected pivot points
 The rear wheel remains
straight and do not turn.
 The steering is done by means
of front wheels.

Introduction
 For avoid skidding, the two
front wheels must turn about
the same instantaneous center
I,
 Which lies on the axis of the
back wheels
 If “I” for two front wheels do
not coincide with the “I” of the
rear wheels, skidding of the
front wheel takes place
 This will leads to more wear &
tear of the tyres

Introduction
Let,
a = Wheel Track
B = Wheel Base
C = Distance b/n the pivot
points of wheel
From Triangle IBP,
cot 𝜃 =
𝐵𝑃
𝐼𝑃
From Triangle IAP,
cot ∅ =
𝐴𝑃
𝐼𝑃
=
𝐴𝐵 + 𝐵𝑃
𝐼𝑃
=
𝐴𝐵
𝐼𝑃
+
𝐵𝑃
𝐼𝑃
=
𝑐
𝑏
+ cot 𝜃
B A
C D

Introduction
cot ∅ − cot 𝜃 =
𝑐
𝑏
This is the fundamental equation
of correct steering, If this
condition is satisfied, then there
will be no skidding of the wheels,
when the wheel take a turn.
B A
C D

STEERING MECHANISM
Steering Mechanism:
 Good turning means, all the
four wheels must rotate about
the common “I”.
 In order to achieve this two
types of mechanism is
followed by automakers.
 Davis Steering Mechanism
 Ackerman Steering
Mechanism

STEERING MECHANISM
Davis Steering Mechanism:
 Located in front of front axle.
 It has sliding pairs
 It’s fulfills the fundamental
equation of correct steering in
all directions.
Drawback:
 Due to more friction, leads to
easy wearing.
 It becomes inaccurate after
sometimes
 So Davis steering is not
common in use
A,B – Pivot points of front wheels
AM,BH – Slotted link
α – Angle of inclination of the links AC
and BD, to the vertical
α α

STEERING MECHANISM
 The slotted link AM and BH are
attached to the front wheel
axle at the pivots A & B to
turn its on.
 The rod C & D is constrained
by the sliding members P & Q
to move along it’s length
direction.
 These constraints are
connected to the slotted link
AM & BH by a Sliding &
Turning pair at each end
α
αϴ
Φ
a – Vertical distance b/n AB and CD
b – Wheel Base
C – Distance b/n the pivots A and B of
the front Axle

STEERING MECHANISM
 The steering is affected by
moving CD to the right or left
of its normal position.
 C’D’ shows the position of CD
for turning to the left.
α
αϴ
Φ
d – Horizontal distance b/n AC and BD
x – Distance moved by AC to AC’ = CC’
= DD’
α – Angle of inclination of the links AC and BD,
to the vertical

STEERING MECHANISM
From triangle AA’C’,
tan(𝛼 + ∅) =
𝐴′ 𝐶′
𝐴𝐴′
=
𝑑 + 𝑥
𝑎
From triangle AA’C
tan 𝛼 =
𝐴′
𝐶
𝐴𝐴′
=
𝑑
𝑎
From triangle BB’D’
tan 𝛼 − 𝜃 =
𝐵′
𝐷′
𝐵𝐵′
=
𝑑 − 𝑥
𝑎
We know that,
tan 𝛼 + ∅ =
tan 𝛼 + tan ∅
1 − tan 𝛼 . tan ∅
α
αϴ
Φ

STEERING MECHANISM
𝑑 + 𝑥
𝑎
=
𝑑
𝑎
+ tan ∅
𝑎 − 𝑑/𝑎 tan ∅
=
(𝑑 + 𝑎 tan ∅)
𝑎
(𝑎 − 𝑑 tan ∅)
𝑎
=
(𝑑 + 𝑎 tan ∅)
(𝑎 − 𝑑 tan ∅)
𝑑 + 𝑥 (𝑎 − 𝑑 tan ∅) = 𝑎 ( 𝑑 + 𝑎 tan ∅)
α
αϴ
Φ

STEERING MECHANISM
𝑎𝑑 − 𝑑2
tan ∅ + 𝑎. 𝑥 − 𝑑𝑥 tan ∅ = 𝑎𝑑 + 𝑎2
tan ∅
𝑎𝑥 = 𝑑2 tan ∅ + 𝑎2 tan ∅ + 𝑑𝑥 tan ∅
𝑎𝑥 = tan ∅ ( 𝑑2
+ 𝑎2
+ 𝑑𝑥)
tan ∅ =
𝑎𝑥
𝑎2 + 𝑑2 − 𝑑𝑥
Similarly, from
tan 𝛼 − 𝜃 =
𝑑 − 𝑥
𝑎
tan 𝜃 =
𝑎𝑥
𝑎2 + 𝑑2 − 𝑑𝑥
We know that for correct steering,
cot ∅ − cot 𝜃 =
𝑐
𝑏
𝑜𝑟
1
tan ∅
−
1
tan 𝜃
=
𝑐
𝑏
α
αϴ
Φ

STEERING MECHANISM
𝑎2 + 𝑑2 + 𝑑. 𝑥
𝑎. 𝑥
−
𝑎2 + 𝑑2 − 𝑑𝑥
𝑎. 𝑥
=
𝑐
𝑏
2𝑑. 𝑥
𝑎𝑥
=
𝑐
𝑏
𝑜𝑟
2𝑑
𝑎
=
𝑐
𝑏
2 tan 𝛼 =
𝑐
𝑏
tan 𝛼 =
𝑐
2𝑏
 The range of c/b is 0.4 to 0.5.
 Thus, the value of α lies b/n 11.3o to 14.10
α
αϴ
Φ

STEERING MECHANISM
Ackerman Steering Mechanism:
 Invented by German carriage builder
Mr. Georg Lankensperger.
 Patent by Anglo – German, Mr. Rudolph
Ackermann.
 The mechanism is placed inside the
Front Axle.
 It has only turning pair.
Drawback:
 Fulfills the fundamental equation of
correct steering at the middle and at
the two extreme position
 But not for remaining positions.
Georg
Lankensperger
Rudolph
Ackermann

STEERING MECHANISM
 Four Link Mechanism ABCD.
 The shorter Link BC and AD are of
equal length
 And are connected with stub Axles
BF & AE respectively.
 The longer link AB & CD are of
unequal length.
 CD link< AB link
 During Straight motion of vehicle,
the links BC and AD are parallel and
subtend equal angles with the
center line of the vehicle.
𝜽
𝜽
∅
∅

STEERING MECHANISM
 During vehicle turn, The stub Axle
AE & BF make an different angles,
in respect to their previous
positions.
 The stub axle BF will turn through a
greater angle ϴ,
 The stub axle AE, which will turn
through a greater angle Ф
 At this moment, the lines from the
front wheels axle intersect on the
rear wheels axle at the
instantaneous center I.
𝜽
𝜽
∅
∅
 This arrangement is known as Ackerman Steering Mechanism

STEERING MECHANISM
Let
r = Length of the shorter links BC and
AD
L = Length of the track rod, i.e link
CD
Now, from the geometry of fig,
sin ∝ + 𝜃 =
(𝑥 + 𝑦)
𝑟
sin 𝛼 − ∅ =
(𝑦 − 𝑥)
𝑟
- i
- ii

STEERING MECHANISM
Let
Adding equations (i) and (ii), we have
sin 𝛼 + 𝜃 + sin 𝛼 − ∅ =
(𝑥 + 𝑦)
𝑟
+
(𝑦 − 𝑥)
𝑟
=
2𝑦
𝑟
sin 𝛼 + 𝜃 + sin 𝛼 − ∅ = 2 sin 𝛼
∴ Sin α =
𝑦
𝑟
 This mechanism has three value of ϴ
for correct steering
 While turning right, While turning left,
While running straight ahead. (ϴ = 0)
 However, for other angles also, it gives
a close approximation to the ideal
condition.

STEERING RATIO
Steering Gear Ratio:
 Ratio of angle turned by the steering wheel to the corresponding angles of
stub axle (Steering Knuckle or front wheels)
 Now a days, for cars steering gear ratio 12:1, for heavy vehicles 35:1,
 Larger steering gear ratio will reduce the amount of steering effort required
 But the steering wheel needs to be turned through a larger angle.
 It says steering will not very responsive.
 On the other hand smaller steering ratio will improve the steering response.
 But increasing the steering effort

STEERING LOCK
Steering Lock:
 To ensure the vehicle safety from theft.
 The put the lock for steering, also
switch off the ignition.
 It will lock the gear shift lever of the
transmission.

STEERING GEAR BOX
Steering Gear Box:
 Consists of two gear enclosed in
a housing
 One of them is attached to the
steering shaft & the other is
attached to the steering linkages
Function of steering box:
 Converts the rotary motion of
steering wheel into straight line
motion to move steering
linkage.
 Provides mechanical advantages
gear reduction for easy vehicle
steer.

STEERING GEAR BOX
Steering Gear Box: Worm Gears
 It used worm gears
 A worm drive is a gear arrangement in which a
worm meshes with a worm gear
 Major advantages of worm gear drive units are can
transfer motion in 90o
 Like other gear arrangement, a worm drive reduce
rotational speed or transmit high torque.
Worm
Screw
Worm
Wheel

STEERING GEAR BOX
Steering Gear Box: Types
 Worm & Worm wheel (Sector
Steering).
 Worm & Nut steering gear
 Worm & Roller steering gear
 Recirculating ball type
 Cam and lever type steering
gear
 Rack & Pinion

STEERING GEAR BOX
Steering Gear Box: Worm & Worm wheel
(Sector Steering)
 Worm is placed at the end of the steering
shaft
 And it is constant mesh with worm wheel
 Worm wheel mounted on a shaft, which is
attached to the pitman arm (Drop arm)
 Worm shaft is supported in the housing
with the help of two bearings by placed
above & below the worm
 It helps the worm rotate easily

STEERING GEAR BOX
(Sector Steering)
 When driver rotates the steering wheel,
drop arm moves forward & backward
resulting in motion of stub axle.
 The arc movement of the drop arm
usually from 60o to 90o
 Commonly seen in tractors

STEERING GEAR BOX
(Sector Steering)
 This is similar to worm & worm wheel
type.
 Here instead of worm wheel, a sector
gear is placed

STEERING GEAR BOX
Steering Gear Box: Worm & Nut Steering
Gear
 Steering rod end have worm.
 Worm is connected with nut arrangement
 When the worm rotates, the nut is able to
move.
 Movement is along the axis of the column
either up or down.
 This move cross shaft in arc, which also
moves drop arm.
 This can be commonly seen in all steering

STEERING GEAR BOX
Steering Gear Box: Worm & Roller
Steering Gear
 Worm and roller gear have two teethed
roller which are fastened to the cross
shaft called roller shaft or sector shaft.
 The threads of the worm gear are meshed
with roller shaft at the end of the steering
tube
 Diameter of worm is greater at end and
reduced at center
 When the worm shaft is turned by the
steering tube, the roller will also be
moved in an arc for rotating the roller
shaft

STEERING GEAR BOX
Steering Gear Box: Worm & Roller
Steering Gear
 The bearings are designed to resist both
radial and end thrust.
 Used in Leyland & American Passenger
car

STEERING GEAR BOX
Steering Gear Box: Recirculating
Ball type Steering
 Consist of worm at the end of
steering rod.
 Nut is mounted on the worm with
two sets of balls in the groves of
the worm.
 Ball reduce the friction b/n Nut &
Worm
 The teeth of nut is meshed with
teeth of worm wheel sector to
which drop arm is mounted.

STEERING GEAR BOX
Steering Gear Box: Recirculating
Ball type Steering
 By turning steering wheel , the
balls in worm roll in the grooves
and cause nut to move along the
length of worm, balls recirculates
through the guide.
 Movement of nut causes the wheel
sector to turn and actuate the link
rod through the drop arm resulting
in desired steering of wheels.
 Teeth on the nut are tapered to
minimize the wear
 Used in TATA motors, etc..

STEERING GEAR BOX
Steering Gear Box: Cam & Lever
steering gear.
 The worm is cut in the form of a
cylindrical cam at the steering shaft
lower end.
 The cam is held in housing by
thrust bearing.
 The inner end of drop arm (pitman
arm) has a lever that contains a
tapered stud.
 Stud engages in the cam, so the
lever is moved up & Down when
the cam is turned.
Lever
Cam
Thrust bearing
Stud

STEERING GEAR BOX
Steering Gear Box: Rack & Pinion steering gear (End Take off type)
 Rotary Motion of the steering wheel is transmitted to the pinion of the steering
gear through universal joint.
 Now circular motion is transferred as linear motion.
 That lateral movement transferred to the stub axle through Tie rod & Ball joint
arrangement.

STEERING GEAR BOX
Steering Gear Box: Rack & Pinion steering
gear (Center Take off type)
 Here Tie rods are connected at the center of
the rack instead of at the ends.
 It is called of center take off rack & pinion
steering gear.
 Large boot covers center part of rack &
pinion housing.
 A slot in the housing permits the inner tie
rod end to move with the rack

STEERING GEAR BOX
Steering Gear Box: Rack & Pinion steering
gear (Center Take off type)
Advantage :
 Save spacing
 Shortening the length of the steering
column.
 During vehicle moves over road bump
(Bump Steer) steering gets affected in end
take type is reduced in Center take off.
 Bump Steer : tendency of wheels to steer
themselves without driver input.
 When the toe of wheels changes as they go
over a bump or through a depression on the
rod.

STEERING GEAR BOX
Steering Gear Box: Rack & Pinion
steering gear: Geometry
 Tooth profiles of both the pinion as well
as rack are of the Involute form.
 Side profile of teeth is curved.
 Side profile of rack teeth is straight line.
 Rack pitch circle being straight line
 Helical teeth ensure the quiet & Smooth
operation
 It enable the steering to withstand
higher loads compared to spur gears.
 It uses larger gear ratio can be used for
rack travel.

STEERING GEAR BOX
 Helical teeth & Inclination of pinion axis,
causes the sliding action b/n the teeth
which increases friction and hence teeth
wear.
 But it provides damping to the road
shocks & Ensure not to transmitted to
the steering wheel.

STEERING GEAR BOX
Let,
rs = Radius of the steering wheel
rp = Radius of the pinion pitch – circle
T = Number of teeth on pinion
P = Circular pitch of the pinion
= Linear pitch of the rack
For one revolution of steering wheel,
Input - 𝑥𝑖 = 2𝜋𝑟𝑠
Output moment of the rack,
Output - 𝑥 𝑜 = 2𝜋𝑟𝑝 = 𝑇 × 𝑃

STEERING GEAR BOX
Steering Gear Box: Rack & Pinion steering gear:
Geometry
Movement Ratio MR =
𝑥 𝑖
𝑥0
=
2𝜋𝑟𝑠
2𝜋𝑟 𝑝
=
𝑟𝑠
𝑟 𝑝
Also,
MR =
2𝜋𝑟𝑠
𝑇 𝑃
If there is no friction in the gears,
Movement ratio =
𝑂𝑢𝑡𝑝𝑢𝑡 𝑙𝑜𝑎𝑑 𝑎𝑡 𝑡ℎ𝑒 𝑟𝑎𝑐𝑘
𝑖𝑛𝑝𝑢𝑡 𝑒𝑓𝑓𝑜𝑟𝑡 𝑎𝑡 𝑡ℎ𝑒 𝑠𝑡𝑒𝑒𝑟𝑖𝑛𝑔 𝑤ℎ𝑒𝑒𝑙
MR =
𝑊
𝐸

POWER STEERING
Power steering:
 Reduce the effort required to
operate the steering wheel.
 Most of the front engine mount
vehicle requires power steering
because of more weight on front
side.
 It also has fail safe design, which
allows manual steering to be done.
If the system develops some
problem

POWER STEERING
Power steering:
Advantage:
 Reduce the number of turns of the
steering wheel.
 Easy steering at parking, at low
speeds or tight turns.
Disadvantages:
 Little cost than conventional
steering system

POWER STEERING
Power steering: Types
 Hydraulic Power steering
 Electrical assisted, Electronic power
steering system.

POWER STEERING
Power steering: Hydraulic Power
Steering
 Hydraulic booster that reduces the
forces required to operate the steering
wheel.
Pump : It generates hydraulic pressure
Control Valve :It switches the oil passage
to the power cylinder according to the
rotational direction of the steering wheel.
Power Cylinder :It moves the piston in the
cylinder to tight right or left with hydraulic
forces and there by assists the steering
wheel operation.

POWER STEERING
Steering
Fluid Reservoir :Stores the fluid & Cleans it
using a built in filter.
Working :When steer wheel rotates
CCW/CW the hydraulic pressure from the
pump is shifted by the control valve &
Drawn into the power cylinder left (or
Right) Chamber.
The power cylinder piston is moved by
the hydraulic pressure to the left
This will assist the steering wheel
operation & There by steering wheel can
operated with light force.

POWER STEERING
Steering – Types
 Linkage Type – Has separate
hydraulic cylinder controlled by a
valve & it is attached to the drop
arm to assist in steering.

POWER STEERING
Steering – Types
 Integral Type – Power steering has
the power cylinder & the control
valve as the integral part of the
steering system.

POWER STEERING
Power steering: Linkage Hydraulic Power
Steering :
 It includes Fluid Reservoir, and pump, a control
valve (Spool Type), a power cylinder,
Connecting Fluid lines and the necessary
steering Linkage.
 Hydraulic pump is drive by Engine mechanical
means
 Pressure relief valve with the pump controls the
pressure in the system as per the load
 The control Valve is operated by the movement
of the steering wheel and supplies the fluid to
the power cylinder by switching the oil passage
according to the rotation of the cylinder
Valve in Central (Neutral)
Position
i.)Steering wheel is not operated condition

POWER STEERING
Power steering: Linkage Hydraulic Power Steering :
During Steering wheel is
operated
ii.) Steering wheel is operated condition:
 Steering wheel rotates in CW direction.
 The fluid passage is open by Spool valve &
Filled the Chamber B.
 This will assist the steering action in Right
turn
 Similar operation is reversed for steering
Wheel CCW for Left turn .
 If no force on steering wheel means, spring
force make the spool valve in neutral
position.
 Now the vehicle in Straight ahead position.

POWER STEERING
Power steering: Integral Type Hydraulic Power Steering :
 It includes fluid reservoir & Pump
 Pump is connected to the power cylinder with
flexible hydraulic lines through control valves
 Here the control valve is an integral part of a
gear box.
 Control valve is rotary spool type & is located
above gear box.
 Control valve simple in construction & Compact
size
 It consists of Input shaft, Torsion bar and a
valve.
 All of these are mounted in co-axial manner.

POWER STEERING
 Valve consists the below two section.
 Steering wheel & input shaft
 Pinion shaft & valve
 Input shaft & the pinion shaft are each
connected to an opposing end of the torsion bar.
 Valve is mounted over the input shaft and is
connected with pinion shaft through a pin.
 During steering wheel rotation, the torsion bar
twist & cause the input shaft and valve to rotate
with steering wheel.
 Relative position of the valve & the input shaft is
changed in response to twisting

POWER STEERING
 Now the flow of fluid and pressure is controlled in
accordance with this motion and is directed to
the proper side of power cylinder to assist the
turning action

POWER STEERING
i.) When the steering wheel is not operated
condition:
 No force applied on steering wheel
 Input shaft in neutral position and fluid from the
pump returns to the reservoir through the rotary
valve
 No flow of oil to either side of cylinder, but each
side kept the equal pressure of oil.so it doesn’t
move.
 Now the fluid act as a cushion to absorb the
shocks, so they are not transferred to the
steering wheel.

POWER STEERING
ii.) When the steering wheel is operated:
 When steering wheel is turned counter-clock
wise, the input shaft will also turn in same
direction.
 The torsion bar is twisted & creates a gap b/n
the input shaft and the valve.
 Now fluid enters into chamber A & increase the
pressure on cylinder piston, forcing it to move.
 This provides assistance for steering wheel
operation
 At the same time, chamber B valves opens,
causes the fluid to move into reservoir through
the valve.

POWER STEERING
ii.) When the steering wheel is operated:
 When the turning effort is removed from the
steering wheel, the torsion bar untwists,
returning the valve to a straight ahead position.
 Now oil pressure is equal on both sides of the
power cylinder.
 No power assist is present on steering.
 Now vehicle move on straight ahead, due to the
steering geometry and wheel alignment.
 For right turn (Steering wheel – CW direction) –
same process occur in reverse manner.

POWER STEERING
Power steering: Electronic Power Steering :
 Operating principle is same as hydraulic
power steering with some changes in
system components
 The torque sensor instead of valve
body unit
 Hydraulic power cylinder is replaced
by electric motor
 EPS control unit is added

POWER STEERING
Construction:
 Consists of rack & pinion steering gear
with an electric motor(i.e DC Motor)
Installed around the rack, which
supplies the power.
 The rack shaft passes through the
motor’s armature and is held by
recirculating ball screw
 The motor transmits its power to push
the rack right or left.
 Pinion shaft contains two sensors are
torque sensor & speed sensor

POWER STEERING
Construction:
 Sensors converts the torque, speed &
direction of motion into voltage signal &
send it to EPS unit

POWER STEERING
Working:
 Vehicle speed input & Steering sensors input
are processed by microprocessor control
unit.
 The ECU unit compares the sensor input &
calculate the force requirement from the look
up table in the memory.
 Now the control unit sends the signal to the
motor to assist the steering action by DC -
motor with the proper current flow direction.
 The motor pushes the rack to the right or
left side depending on which the way the
current flow.

POWER STEERING
Fail safe design of EPS:
 Over load causes the motor to damage.
 It could be avoid by controlling the current
to the motor with help of ECU.
 Voltage surges problem due to faulty
alternator or charge problem rectified by
ECU unit.
 If any abnormal situation detects /No
possible to operate EPS means – The
steering will done by manually

POWER STEERING
Advantage:
 It is compact, light and quiet in operation.
 Precise control of steering at different speed
is achieved.
 It requires less maintenance as there no
hydraulic line to break

STEERING GEOMETRY
Wheel Alignment :
 Relative positioning of the wheel
for obtaining a true and free
rolling movement over the road.
 If the wheels were mounted
directly on the vehicle at right
angles, then that vehicle would be
actually be very difficult to
handle.
 It would steer poorly and would
be particularly dangerous at high
speeds
 Moreover, the tyre exhibit rapid
wear
Diagonal Wear

STEERING GEOMETRY
Wheel Alignment :
The important wheel alignment factors are,
 Camber
 Toe in & Toe out
 Steering Axis inclination (King pin Inclination)
 Cater

STEERING GEOMETRY
Wheel Alignment : Camber
 The camber is an inward or outward tilting of the
wheels at the top from the vertical axis
 If the wheel tilt outwards at the top, the camber is
positive.
 If the wheel tilt inwards means, the camber is
negative.
 The camber is measured in degrees.
 Positive camber is reduce the steering effort

STEERING GEOMETRY
 Race cars/Rally cars have negative camber on
Tarmac road & No camber on Gravel.
 Negative camber ensure the tyre has full
contact with road during cornering.
 As the car turns on corners, the body rolls, as
the body rolls, the suspension compresses the
tyre roll.
 This action makes the negative camber into
zero camber.
 Zero camber during body roll, ensure the
maximum tyre contact patch with road.
Tarmac road
Gravel Road

STEERING GEOMETRY
 On the gravel road grip is reduced.
 So traction is main priority for car.
 This achieved by Zero camber.
 Because gravel road are normally undulating
and rough.
 The car use large suspension to keep the tyre
contact with road surface.
Tarmac road
Gravel Road

STEERING GEOMETRY
 Vehicle weight cause the wheels
to tile inwards, here the camber
is used to compensate the tilting.
 The positive camber is used to
compensate this type of tilting.
 During vehicle motion on corner
the positive camber changes as
zero camber.
 Zero camber gives maximum
tyre life
 Here the tyre treads contact with
road equally on both side of the
tyre.

STEERING GEOMETRY
offset (Scrub Radius)
 The distance b/n the wheel
centerline and steering axis
centerline at the point where
they intersect at the road surface
called as camber offset.
 The smaller the offset is the
lower the effort required to steer
the vehicle
 Excessive camber causes the
uneven tyre wear and loss of
traction

STEERING GEOMETRY
offset (Scrub Radius)
 So modern vehicle designed with
wider tyres and power steering
 Most vehicle have only small
degree of camber angle (1o to
3o)

STEERING GEOMETRY
Wheel Alignment : Toe in & Toe out
 Toe is angle of tyre pointing inwards or
outwards.
 It should be visualize by Birds
perspective.
 Positive Toe is – Toe in = Front of the
tyre is facing each other (inwards)
 Preferred in Rear wheel drive.
 Tyre straightness with body roll
 Negative Toe is - Toe Out = Front of the
tyre is facing outwards
 Preferred in Front wheel drive
 Created moment straightness the
tyre

STEERING GEOMETRY
 The purpose of Toe – in is to ensure
parallel rolling of wheels, steering
stability, and to prevent both side of
slipping and excessive wear of tyre.
 It is set for stand still condition of
vehicle.
 During vehicle motion, the front portion
of wheel comes straight ahead position
because of road resistance.
 This will ensure the parallel Rolling.
 Toe in & Camber are properly combine
means to ensure the rolling of the wheel
in straight line

STEERING GEOMETRY
 The greater the camber angle more toe
– in is needed & Vice-versa.
 The toe-in can be adjusted by modifying
the length of the left and right tie rods.
 During adjustment that the length of
both tie rods are set equal.
 Otherwise, the vehicle may tend to pull
in either direction due to the steering
wheel being out of center.

STEERING GEOMETRY
Wheel Alignment : Steering Axis Inclination
 The steering axis inclination is the angle b/n the
steering axis and the vertical axis.
 Helps the vehicle wheels straight ahead position
after the turn has been made.
 Also called as Kingpin inclination.
 Because in older vehicle, the stub axle is fixed
with front axle with the help of Kingpin
considered as Steering axis.

STEERING GEOMETRY
Wheel Alignment : Steering Axis Inclination
 When the steering wheel is turned, the front of
the vehicle is lifted up by a small amount.
 When the driver releases the steering wheel,
the weight of the vehicle actually tries keep the
wheel straight ahead position.
 This is because of force generated by the
steering axis inclination, to move the wheels
back, is known as steering-aligning torque.
 Helps to reduce the excessive camber.
 By reducing the Camber offset, can reducing
the force required by the steering wheel.
 Allowable angle limit – 6o to 8o.

STEERING GEOMETRY
Wheel Alignment : Caster Angle
 It is an angle viewed from the side of the car.
 It’s lie b/n steering axis & Vertical axis.
 Direction control angle can be either positive or
negative.
 Positive caster angle – Steering axis is tilted
backward.
 Negative cater angle – steering axis is tilted
forward.

STEERING GEOMETRY
Wheel Alignment : Caster Angle
 This will provide the degree of self – centering
for the steering.
 This makes the car easier to drive & improves
the directional stability.
 The excessive caster angle will make the
steering heavier & less responsive.
 +ve caster – 3o to 6o.
 - ve caster – 1o-2o.

STEERING GEOMETRY
Effects of incorrect wheel alignment :
Problem Effect on Vehicle
Incorrect camber
setting
 Uneven tire wear
 Vehicle pulls to the side of the most positive or least negative
camber
Incorrect Toe - in
 Excessive tire wear
 Unstable steering
Uneven Toe - in  Vehicles tends to pull to one side
Incorrect steering axis
inclination
 Instability of vehicle
 Poor steering
 Vehicle pull to the side of lesser inclination
 Hard steering
Too much cater
 Hard steering
 Excessive road shock
 Wheel shimmy - Wobbles

STEERING GEOMETRY
Effects of incorrect wheel alignment :
Problem Effect on Vehicle
Insufficient caster  Instability at high speed
Unequal caster  Vehicle pulls to the side of the most caster

END

Automobile Steering system

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