Transcript INTRODUCTION TO PROFESSIONAL WHEEL ALIGNMENT

INTRODUCTION TO
PROFESSIONAL
WHEEL ALIGNMENT
GENERAL
•
‘’VEHICLE ATTITUDE’’ is taken to mean the geometric
condition of all the parts which contribute to the
determination of the position of the wheels when moving on
the ground, either in a straight line or on bends.
• This geometric attitude can be checked only in a static
state, i.e. when the vehicle is stationary, with the wheels in
the straight travel position and in the turning position.
VEHICLE GEOMETRY BASIC CONDITION
The vehicle must satisfy certain set conditions of symmetry and
perpendicularity in the axes
BEFORE STARTING TO CHECK THE
GEOMETRIC ATTITUDE OF THE VEHICLE
1.
Locate and eliminate any play on the suspension and
steering rods
2.
Position the vehicle on a level surface
3.
Carefully check the tyre pressures
4.
Respect and take into account the specified load
conditions
5.
Respect and take into account the load distribution
6.
Check to see if there is any irregular give on the elastic
parts of the suspension or stiffening of the joints.
SUSPENSION SYSTEMS
THE WORD SUSPENSION IS USED TO DESCRIBE THE TOTALITY
OF ELASTIC PARTS THAT CONNECT THE WHEELS TO THE
CHASSIS OR UNITIZED BODY
SUSPENSION SYSTEMS HAVE THE FOLLOWING FUNCTIONS:
•
To absorb the bumps, more
confort for passengers.
•
to avoid subjecting the
mechanical parts to
excessive wear.
•
To ensure that the tires are
in constant contact with
the ground to achieve good
road-holding and more
safety.
CHARACTERISTIC ANGLES
•
•
WHEEL ANGLES
KINGPIN ANGLES
1.
Wheel toe-in
2.
Wheel camber angle
3.
Wheel toe-out on
turns (only in front)
4.
Longitudinal caster
angle or, in brief form
"caster angle“
5.
Transverse king pin
inclination or, in brief
form "king pin
inclination
WHEEL TOE-IN AND TOE-OUT
•
Wheel toe-in is the
angle formed by the
center line of the
wheel and the
longitudinal axis of
the vehicle, looking
at the vehicle from
above.
•
The sum of the toe-in
values for each
single wheel (α+β)
gives the total toe-in
value
•
Parallel Wheels = 0
toe
POSITIVE
NEGATIVE
• EFFECT OF LOAD ON
•
DYNAMIC EFFECTS
ON TOE-IN/OUT
1. When measuring the toe-in/out,
it is advised to refer to the
manufacturers' specifications
and check whether the toein/out tendency is positive or
negative by moving the vehicle
up and down in a vertical
direction; after this, apply the
specified data and tolerances
according to the average use
and load conditions.
1.
The front wheels or rear nondrive wheels have a TOE-IN
position when the vehicle is
stationary
2.
The front wheels or rear drive
wheels have a TOE-OUT
position when the vehicle is
stationary
TOE-IN/OUT
BOZZA
IRREGULAR TYRE WEAR TOE
The wear caused on a tyre with excessive toe-in or toeout, has certain typical characteristics:
•
A wheel with
excessive toe-in tends
to consume the
outside of the wheel
•
A wheel with
excessive toe-out
tends to consume the
inside of the wheel
CAMBER ANGLE
The wheel camber angle is the
angle, measured in degrees,
between the center line of the
wheel and the perpendicular to
the ground, looking at the
vehicle from the front.
POSITIVE
NEGATIVE
EFFECTS
• With the introduction of independent-arm suspension, the
wheel camber angle tends towards a value very close to
zero under the most common use, the camber angles of
the wheels will tend to change as the vehicle is jolted
about.
•
The independent-arm suspension being preferred to rigidaxle suspension. The benefits of this effect are most
apparent on bends, where the compression of the
suspension on the outer wheel on the bend, caused by
centrifugal force, produces a negative camber on the
wheel and more stability
TOE-IN ON BENDS
•
The steering geometry is defined as the toe-out position taken by the
during a turn; it is expressed by the two values, in degrees, through
which the wheels turn (considering one fixed value on the turn of 20
grade, set by convention).
EXAMPLE : The outer
wheel on the turn turns
through 20 and the inner
wheel through 23 or, vice
versa, the inner wheel on
the turn turns through 20
and the outer wheel
through 17. In the
example it can be seen
that the toe-in on the
basis of 20 is 3, taken
from the difference (2017), or from the difference
(23-20)
TOE-IN ON BENDS
•
The ideal condition is the following:
The wheels, when travelling in a straight line, must have a
toe-out value near to 0 degrees, and as soon as they start
to turn the toe-out value must increase progressively,
becoming more accentuated with the increase in the angle
of the turn.
CASTER ANGLE
•
•
The CASTER
ANGLE is the angle,
measured in
degrees, formed
between the
steering axis and
the perpendicular
to the ground,
looking at the
vehicle from the
side
1. Steering axis
longitudinal
inclination
2. Vertical
3. Steering axis
4. Projection of the
steering axis
5. Contact point
between wheel
and ground
POSITIVE
The caster angle is
zero when the
steering axis is
perfectly vertical
1. Direction of travel
NEGATIVE
EFFECTS
The CASTER ANGLE given to the steering axis creates two
very important phenomena for the ride of the vehicle:
•
The first is related to stability, in maintaining the straight
line travel of the vehicle, with the relative return of the
steering after steering round a bend.
•
The second is the tilt of wheel which occurs during steering,
and which is observed by the inclination of the wheel when
being turned
KINGPIN INCLINATION
• The KINGPIN
INCLINATION is the
angle, measured in
degrees, that forms the
line passing through
the steering axis and
the perpendicular to
the ground, looking at
the vehicle from the
front
1. Kingpin inclination
2. Steering axis (Kingpin axis)
KINGPIN INCLINATION
The Kingpin inclination is defined
positive when the projection of
the kingpin axis goes near to the
wheel at its point of contact with
the ground (inclined in the
opposite way to the wheel
camber) ; it is difficult, if not
impossible, to have a negative
kingpin inclination
POSITIVE
V. Kingpin Inclination
B. Nearly null
EFFECTS
The king pin inclination angle, amongst other things, creates
the phenomenon of the return of wheels to the straight
position after a steering operation
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ATTENTION
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