Front Axle & Steering System

1. UNIT I
FRONT AXLE AND STEERING SYSTEM
SECTION I: FRONT AXLE
Definition:
 An axle is a central shaft for a rotating wheel or gear.
 On wheeled vehicles, the axle may be fixed to the wheels, rotating with
them, or fixed to the vehicle, with the wheels rotating around the axle.
 Bearings or bushings are provided at the mounting points where the axle
is supported.
 Front wheels of the vehicle are mounted on front axles. It supports the
weight of front part of the vehicle
REAR
AXLE
• Full Floating
• Semi Floating
• Three Quarter
Floating
FRONT
AXLE
• Dead Front Axle
• Line Front Axle
• Elliot
• Reversed Elliot
• Lamoine
• Reversed Lamoine
 Stub Axle
Type of Stub
Axle

2. FRONT AXLE
 It facilitates steering.
 It absorbs shocks, which are transmitted due to road surface
irregularities.
 It absorbs torque applied on it due to braking of vehicle.
A) 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 axle.
Stub
Axle
Main Beam
King
Pin
Track Rod

3. B) Line Front Axle :
Line axles are used to transmit power from gearbox 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.
C) Stub Axle :
A stub axle, which is provided in the ends of the axle beam of a front 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. King pins 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
(c) Lamoine
(d) Reversed Lamoine
All are differ from each other in the manner in which they are connected to
the front axle.

4. (a) Elliot
 Elliot is a type of Stub-Axle, they are connected to the
front axle by king pins.
 Kingpins is fitted in the front axle beam eye and is located and
locked there by a taper cotter pin.
(b) Reversed Elliot
 The Stub axle forms the fork end.
 The Front axle end forms eye .
 The thrust washer is placed at the bottom of the front axle beam.
 The cotter pin in the joint locks locks the movement of king pin in
the front axle beam.
(c) Lamoine
 The Front axle beam end forms eye to take supports the Stub axle.
 The Stub axle and King pin are integrated to form L- shape assembly
to receive the front axle.
 The thrust washer is placed at the bottom.
 The cotter pin in the joint is used to lock the front axle in position .
 The king pin is free to move (swing or oscillate) in the Phosphor
bronze bushes placed in the eye of the front axle .
 The thrust washer takes the vertical load in the joint .
 The use of thrust washer increases the life of both the stub axle and
front axle

5. (d) Reversed Lamoine
 The Front axle beam end forms eye to take supports the Stub axle.
 The Stub axle and King pin are integrated to form Inverted L- shape
assembly to receive the front axle.
 The thrust washer is placed at the bottom as shown in the figure.
 The cotter pin in the joint is used to lock the front axle in position .
 The king pin is free to move (swing or oscillate) in the Phosphor bronze
bushes placed in the eye of the front axle .
 The thrust washer takes the vertical load in the joint .
 The use of thrust washer increases the life of both the stub axle and front
axle.
SECTION II: STEERING SYSTEM
STEERING GEOMETRY
The term "steering geometry" (also known as "front-end geometry") refers to
the angular Relationship between suspension and steering parts, front wheels,
and the road surface. Because alignment deals with angles and affects
steering, the method of describing alignment measurements is called steering
geometry.
There are five steering geometry angles :
1) Camber
2) Caster
3) king pin inclination
4) Toe in & Toe-out on turns

6. 1) Camber:
 Camber angle is the angle between the vertical line and centre line of
the tyre when viewed from the front of the vehicle.
 Camber angle is positive when this is outward. This happens when
wheels are further apart at top than at bottom. On the contrary, camber
angle is negative when angle is inward. This happens when wheels are
further apart at bottom than at top.
 The camber, should not be more than 2 degree, because this causes
uneven or more tyre wear on one side than on other side.

7. 2) Caster:
 Caster angle is the tilt of king pin centre line towards front of back
from the vertical line.
 It is the angle between the vertical line and king pin centre line
in the wheel plane when looked from side.
3) King pin inclination
 It is the angle between king pin centre line and vertical line when
seen from the front of the vehicle.
 It is also called steering axle inclination.
 King pin inclination and caster are used to improve directional
stability in cars.
 This is also used to reduce steering effort when steering a stationary
 It reduces tyre wear.
 This inclination varies from 4 to 8 degree in modern cars.

8. 4) Toe In & Toe Out
 In automotive engineering, toe also known as tracking.
 This can be contrasted with steer, which is the anti symmetric
angle, i.e. both wheels point to the left or right, in parallel (roughly).
 Positive toe, or toe in, is the front of the wheel pointing in towards
the centreline of the vehicle
 Negative toe, or toe out, is the front of the wheel pointing away
from the centreline of the vehicle.

9. ACKERMANN STEERING GEOMETRY
 Ackermann steering geometry is a geometric arrangement of linkages in
the steering of a car or other vehicle designed to solve the problem of
wheels on the inside and outside of a turn needing to trace out circles of
different radii.
 Modern cars do not use pure Ackermann steering partly because it ignores
important dynamic and compliant effects.
 The use of such geometry helps reduce tyre temperatures during high-
speed cornering but compromises performance in low speed maneuvers.
 The intention of Ackermann geometry is to avoid the need for tyre to slip
sideways when following the path around a curve.
 As the rear wheels are fixed, this centre point must be on a line extended
from the rear axle.
 Intersecting the axes of the front wheels on this line as well requires that
the inside front wheel is turned, when steering, through a greater angle
than the outside wheels.

10. Mechanism :
Ackermann steering geometry is a geometric arrangement of linkages in the
steering of a car or other vehicle designed to solve the problem of wheels on
the inside and outside of a turn needing to trace out circles of different radius.
When the vehicle moves along straight path, the longer links AB and CD are
parallel and the shorter links BC and AD are equally inclined to the
longitudinal axis of the vehicle. When the vehicle moves left, the position of
the gear is shown by dotted lines in figure.
Derivation :

12. DAVIS STEERING

13. This is an exact steering gear mechanism. This mechanism fulfils the above
steering condition. But due to presence of more sliding members, the wear will
be increased and this eliminates the accuracy.

14. Difference between Ackermann and Davis Mechanism

15. LAYOUT OF A STEERING SYSTEM
A typical steering system consists of
 Steering wheel
 Steering shaft
 Steering gear box
 Pitman arm
 Drag link
 Steering knuckle arm
 Tie rod
 Track rod arm
STEERING GEAR BOXES :
Steering gears are used to reduce the steering effort and convert rotary motion
of steering wheel into straight line motion of linkage. Thus, steering gear
provides mechanical advantage also to make steering easy. Steering gears are
put inside the steering gear box. Steering gear box connects steering shaft and
steering linkages. Various types of steering gears used in different
automobiles are listed below :
1) Worm and sector type.
2) Worm and worm wheel type.
3) Worm and roller type.
4) Rack and pinion type.
5) Cam and roller type.

16. 1. Worm and Sector Type Steering Gear :
In a worm and sector type steering gear a worm is provided at the end of
steering shaft which meshes with a sector provided on a sector shaft. When
the worm is rotated, the sector turns which moves the linkages for steering
the vehicle. The sector shaft is also called pitman arm shaft, roller shaft or
cross shaft.
 Worm and sector are based on the principle of transmitting the motion
from the steering tube to the Pitman arm.
 The worm is attached with the inner column of the bearing block.
 The box is connected to the level of the plug with normal gear oil for
lubrication of the steering gear.
 The worm at the end of the steering shaft meshes with a sector mounted
on a sector shaft.
 When the steering wheel is rotates, then the worm will rotates.

17. 2. Worm and Worm Wheel Type Steering Gear :
 There are square threads or worms on the steering rod end which
engages in a worm wheel.
 Worm wheel is connected to a drop arm.
 When driver rotates the steering wheel, drop arm moves forward or
backward resulting in motion of stub axle.
 The arc movement of the drop arm is usually from 60 to 90 deg.
 This system is commonly used in tractors.
 A square shaft is generally used on which worm wheel is mounted.

18. 3. Worm and Roller Type Steering Gear :
In the worm and roller steering gear, a roller with two teeth is meshes with
the teeth on roller. This type of system was popular in American passenger
cars.
 Worm and roller gear have two-toothed roller which are fastened to the
cross shaft called as roller shaft or sector shaft.
 The threads of the worm gear are meshed with roller shaft at the end
of the steering tube.
 When the worm shaft is turned by the steering tube, the roller will also
be moved in an arc for rotating the roller shaft.
 The bearings are designed to resist both radial and end thrust.

19. 4. Rack and Pinion Steering Gear
A pinion is attached at the end of the steering shaft. A rack mashes with the
pinion. The rotary movement of the steering moves the pinion which gives
motion to the rack. The movement of the rack is responsible for turning the
wheels through steering linkages.
Construction:
 This type of steering gear is mainly used in cars having independent
front suspension.
 The pinion is mounted at the end of the steering shaft.
 A universal joint is connected at the bottom end of the steering shaft to
mount the steering box centrally.
 A rack is engaged with the pinion. The rack reciprocates sideways to
give lateral movement to the front wheels.
 Spring pads connected with the rack reduce the backlash between gears
to a minimum.

20. 5. Cam and Roller
Construction
The cam and roller steering boxes are very efficient.
 The cam is carried by the steering shaft connected with rollers.
 The drop arm spindle carries the vee shaped roller.
 This spindle is carried by ball bearings in the casing.
 The meshing member contains the spiral grooves. The centre position
of the pin supports the roller.

21. Working :
 By moving the steering wheel and steering shaft, the cam is rotated.
 Due to this rotation, the roller is constrained to follow the helix of the
groove.
 When the cam rotates, the roller is followed the cam and made the
rocker shaft to rotate.
 The contour of the cam is properly designed to match with
 our aim.