FRONT AXLE AND STEERING
The
Steering System — controls the position of the front wheels and allows
the driver to change vehicle direction.
INTRODUCTION
In any motor cars and other four and six-wheeled vehicles,
steering is main component. Properly designed steering, works well and guides
the vehicle to move in correct direction. Mainly steering is linked to the
front axle with gear train mechanism. On the front axle, wheels are mounted,
and with the help of steering wheel, the driver can turn the vehicle in right,
left or straight directions.
FRONT AXLE
(a) It supports the weight of front part of the vehicle.
(b) It facilitates steering.
(c) It absorbs shocks which are transmitted due to road
surface irregularities.
(d) It absorbs torque applied on it due to braking of
vehicle.
TYPES OF FRONT AXLES
There is two types of front axles :
(a) Dead front axle, and
(b) Line front axle.
DEAD FRONT AXLE
Dead axles are those axles, which donet rotate. These axles have
sufficient rigidity and strength to take the weight. The ends of front axle are
suitably designed to accommodate stub axles.
LINE FRONT AXLE
Line axles are used to transmit power from gear box to front
wheels. Line front axles although, front wheels. Line front axles although
resemble rear axles but they are different at the ends where wheels are
mounted. Maruti-800 has line front axle.
STUB AXLE
Stub axles are connected to the front axle by king pins.
Front wheels are mounted on stub axles arrangement for steering is connected to
stub axles. Stub axle turns on kind pins. Kingpins is fitted in the front axle
beam eye and is located and locked there by a taper cotter pin.
STUB AXLES ARE
OF FOUR TYPES:
(a) Elliot
(b) Reversed elliot
FRONT AXLE AND STEERING
(c) Lamoine
(d) Reversed lamoine
STEERING
The front wheels are
mounted on front axles to allow their left and right swing for steering the
vehicle. Steering is done by providing a suitable gearing and linkage between
front wheels and steering wheel.
Introduction: This system provides the directional change in the movement of
an Automobile and maintain in a position as
per the driver’s decision without
much strain on him.
REQUIREMENTS OF STEERING SYSTEM:
a. It must keep the wheel at all times in
to rolling motion with out
rubbing on the road.
b. This system should associate to control
the speed.
c. It must light and stable.
d. It should also absorb the road shocks.
e. It must easily be operated with less
maintenance.
f. It should
have self-centering action to some extent.
Functions of Steering System:
1. It helps in swinging the wheels to the
left or right.
2. It helps in turning the vehicle at the
will of the driver.
3. It provides directional stability.
4. It is used to minimize the tyre wear and
tear.
5. It helps in achieving self-centering efforts.
6. It absorbs major part of the road
shocks.
MAIN
COMPONENTS OF STEERING SYSTEM:
The following are the main components of steering system are
1. Steering Wheel
2. Steering column or shaft
3. Steering Gear
4. Drop Arm or Pitman Arm
5. Drag Link
6. Steering Arm
7. Track-Arms
8. Track Rod or Tie-Rod
9. Adjusting Screws
Types of Steering Gear Boxes:
1. Worm and Wheel Steering Gear.
2. Worm and Roller Steering Gear.
3. Re-circulating Ball type Steering Gear.
4. Rack and Pinion type Steering Gear.
5. Cam and Roller Gear type Steering Gear.
6. Cam and Peg Steering Gear.
7. Cam and Double lever Steering Gear.
8. Worm and Sector Type Steering Gear.
Functions of
Steering Gear Box:
1. It converts the Rotary movement of the
steering wheel in to the
angular turning of the front wheels.
2. It also multiplies drivers’ efforts and
give MEHANICAL ADVANTAGE.
1.Worm and Wheel Type: This type of steering gear has a square cut screw
threads at the end of the steering column;
which forms a worm, at the end of
it a worm wheel is fitted and works rigidly
with it. Generally covered shaft is
used for the worm wheel. The worm wheel can
be turned to a new position
the drop arm can be readjusted to the
correct working position.
2. Re-circulating Ball Type: In this type of gear box the endless chain of balls
are provided between the worm and nut
members. The nut forms a ring of
rack having an axial movement. So that the
sector on the rocker shaft racks,
the balls roll continuously between the
worm and nut. Being provided with
return chambers at the ends of the worm.
This method reduces friction
between worm and nut members. This type of
steering gear is used for heavy
vehicles.
3. Rack and Pinion Type: This is common manual type of steering gear box
is used in most of the vehicles. In this
type of steering a pinion is provided the
bottom end of the steering column. The
teeth of the pinion wheel in mesh
with
corresponding teeth provided on the rack, the end of which are
connected to the stub axle through the rod.
The rotating motion of the
pinion operates the rack in FORE and AFT
direction which in turn operates the
stub axle.
4. Cam and Lever Type: The cam and lever steering use one or two lever
studs fitted in taper roller bearing. When
the worm in the form of helical
groove rotates the stub axle and it also
rotates along with it. This imports a
turning motion
to the drop arm shaft.
5. Worm and Sector Type: In this type the worm on the end of the steering
shaft meshes with a sector mounted on a
sector shaft. When the worm is
rotated by rotation of the steering wheel,
the sector also turns rotating the
sector shaft. Its motion is transmitted to
the wheel through the linkage. The
sector shaft is attached to the drop arm or
pitmen arm.
Power Steering: Power steering reduces much
strain on the part of the driver
while
negotiating sharp curves. It makes easy to turn sharp corners. It is usually
arranged to be operative when the effort of
steering wheel exceeds a predetermined
value. It is fitted on heavy commercial
vehicles and medium
cars.
Steering Linkages: Steering Linkage is a connection of various links between
the steering gear box and the front wheels.
The motion of the pitman arm
and steering gear box is transferred so the
steering knuckles of the front
wheels through the steering linkages. The
swinging movement of the pitman
arm from one side to the other side gives
angular movement to the front
wheel through
the steering linkages.
Types of steering Linkages:
1. Conventional steering Linkage.
2. Direct cross type steering linkage
3. Three-piece steering linkage
4. centre arm steering linkage
5. Relay type steering linkage.
Slip Angle: The angle between direction of the motion of the vehicle and the
centre plane of the tyre is known as Slip
Angle. It ranges from 8º to 10º.
Under steer: When the front slip angle is greater than that of rear, the
vehicle
tends to steer in the direction of side
force. Then it is known as under steer. This
provides greater driving stability,
especially when there is a side wind.
Over Steer: When the rear slip angle is greater than that of front slip
angle,
the vehicle tends to move away from the
direction of centre path. This is
known as over stear. This is advantageous
when the vehicle moving on the
road having many bends curves.
Steering Gear Ratio or Reduction Ratio: It has been defined as the “number
of turns on the steering wheel required to
produce on turn of steering gear
cross shaft to which the pitman arm is
attached. Generally, it varies between
14'.1 and 24'.1.
Turning Radius: It is the radius of the circle on which the outside front wheels
moves when the front wheels are turned to
their extreme outer position. This
radius is 5 to
7.5 m for buses and trucks.
Wheel Alignment: It returns to the positioning of the front wheels and steering
mechanism that gives the vehicle
directional stability, reduce the tyre wear
to a minimum.
Factors effects the wheel alignment:
1.
Factors
pertaining to wheel: -
2.
a. Balance of wheels (Static and Dynamic)
b. Inflation of tyre.
c. Brake adjustments.
2. Steering Linkages.
3. Suspension System
4. Steering Geometry –
a. caster
b.
camber
c.
king pin inclination
d. toe-in and toe-out etc.,
Steering Geometry: It refers to the angular relationship between the front
wheels and parts attached to it and car
frame.
The steering Geometry includes
1. Caster angle
2. Camber angle
3. King-pin inclination
4. toe-in
5. toe-out etc.,
Caster Angle: This is the angle between backward or forward tilting of the
king pin from the vertical axis at the top.
This is about 2º to 4º. The backward
tilt is called
as positive caster. The forward tilt is called negative caster.
CAMBER ANGLE: Camber angle is the angle between the
vertical line and centre line of the tyre when viewed from the front of the
vehicle.
The angle between wheel axis to the
vertical line at the top is
called camber angle. It is approximately ½º
to 2º.
King-pin inclination: It is the angle between vertical line to the king pin axis.
The inclination tends to keep wheels
straight ahead and make the wheels to
get return to the straight position after
completion of a turn. The inclination is
normally kept 7º
to 8º.
Toe-in: It is the amount in minimum at the front part of the wheel
points
inwards approximately 3 to 5 mm. It
prevents side slipping excessive tyre
wear, proper
rolling of front wheels and steering stability.
Toe-out: It is the difference in angles between two front wheels and
vehicle
frame during turning. It is used to prevent
dragging of tyre during turn.
Reversible steering: When the deflection of
road wheels is transmitted
through the steering wheel to road surface,
the system is called Reversible.
If every imperfection of road surface
causes the steering to rotate, it
causes much strain on the part of the
driver to control the vehicle. It causes
much strain on the part of the driver to
control the vehicle. There fore such of
the reversibility is not desired. But, some
degree of reversibility desired, so that
the wheel becomes straight after taking a
curve.
Irreversible steering: If the front road wheels does not transfer any deflection
to the steering which is called
irreversible steering. After negotiating a curve
and the steering wheel not returned easily, there causes the
production of
un due stresses on the steering mechanism,
therefore some degree of
irreversible also desired.
Steering Mechanism: There are two types of steering gear mechanisms
1. Davis Steering gear 2. Ackermann
Steering gear]
1. Davis Steering Gear: The Davis Steering gear has sliding pair, it has more
friction than the turning pair, therefore
the Davis Steering Gear wear out
earlier and become inaccurate after certain
time. This type is mathematically
Accurate.
2. Ackermann
Steering System: It has only turned pair. It is not
mathematically accurate except in three
positions. The track arms are made
inclined so that if the axles are extended,
they will meet on the longitudinal
axis of the car
near rear axle. This system is called Ackermann steering.
FRONT AXLE AND STEERING
Excessive camber is not good because it prevents proper
wheel contact with the road. Unequal camber causes the vehicle in that
direction in which camber is more. This disturbs the directional stability.
STEERING GEAR BOX
Steering gears are used to reduce the steering effort and
convert rotary motion of steering wheel into straight line motion of linkage
(a) Worm and sector type,
(b) Worm and worm wheel type,
(c) Worm and roller type,
(d) Rack and pinion type,
(e) Cam and roller type.
STEERING LINKAGE FOR INDEPENDENT FRONT SUSPENSION
If automobile is fitted with independent front suspensions,
then different type of steering linkages is used. In these linkages, the ball
joints are fitted between steering linkage and steering arm which facilitates
independent movement of the wheels.
Electric power steering system
1.Odometer- It is an instrument (usually on the
instrument panel of a car) that records distance travelled by the car.
2.Speedometer- A speedometer or a speed meter
is a gauge that measures and displays the instantaneous speed of a
land vehicle.
3.Radios -Signal processing is one of the most important mathematical fields that supports the design and effective operation of radio in cars.