TYRE TEST RIGS

architectgeorgeMechanics

Oct 31, 2013 (3 years and 1 month ago)

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TYRE
TEST RIGS

Test rigs are used

by
automotive and tyre industri
al companies,
universities and institutes

in
order to

observe

tyre

properties such as

force
and moment generation
.

Outdoor and indoor test
rigs are available. A truck or trailer is generally used for outdoor test rigs. These trucks or
trailers are equipped with a
special wheel suspension and guidance sys
tem to which a
measuring hub is
attached.

The measuring hub inclu
des sensors such as; strain gauge and
piezoelectric force sensors.

Sometimes passenger vehicles with special equipment (i.e. sensor
s

and force measurement

platforms) can also be used for outdoor tests.
Outdoor test rigs are
also called the
over the road
testing equipment
. Typically,
moderate

speeds up to ca. 120 kp
h
can be reached

with
these test rigs
.

The frequencies with which the steer

angle c
an be varied
is relatively low. Different camber angles can be achieved by a hydraulic cylinder or
mechanically
. The vertical load can be adjusted at a required mean value thus,
the load
variat
ions due to road irregularities can

be can
celed

out.

Commonly, the longitudinal slip
results from the controlled

application of the
brake pressure.

Rarely a hydraulic motor w
hich
runs relative to the wheel speed of the vehicle is used in order to control the wheel speed.
This allows the variation of the test wheel drive and bra
ke slip in a controlled manner. Also,
water can be sprayed in front of the test wheels in order to c
reate wet road conditions. Tests
are usually performed at
quasi steady
-
state conditions

with outdoor test rigs.


Figure1 The Delft Tyre Test Trailer


Figure 2 An area dedicated to the development and testing of agricultural tires

Indoor test rigs are
based on the simulation of the road surface via a drum or a flat track
(endless belt).

A

measuring to
wer or a special wheel guidance
system with a force
measurement p
latform or hub can be installed on the drum test rig
.

By the use of indoor test
rigs highe
r frequencies of different
vertical axle

position and yaw angle can be achieved (up
to ca. 2 to
8Hz).

Drum test stands can have diameters approximately from 2m up to 5m. The
tire can be run on both the inner and the outer surfaces of the large drums. This
allow to
simulate different road conditions on the inner and the outer surface of the drum, i.e. a layer
of water or ice/snow on the inner surface.
Also, flat bed and flat plank test rigs are
available
.
Typically,

but not always, these rigs

operate at very

low speed of

travel of either the plank or
the wheel axle. Also turn table or swing arm devices

are available in order to investigate

turn
slip properties.

V
ery stiff rigs

or
very soft

seismic systems

are required for dynamic higher frequency ti
re
tests
.

Special equipment is used that is often limited to a specific

application to allow the
system to become light and sufficiently rigid, that is:

high first
natural frequency.
Some t
est
rigs which are

used for specific applications are listed below.



axle fix
ed (but adjustable in hei
ght)
: observing

tyre non
-
uniformity,

cleat response or
respons
e to brake pressure variations



axle forced to perform

only ver
tical axle oscillations
: observing

the vertical dynamic
stiffness and the

resp
onse of the longitudinal
force



axle to perform only yaw angle variations
:

observing

the tyre dynamic steer response.

Figure 3 shows

the flat tr
ack machine constructed by MTS. Camber angle can be changed (at
zero steering angle) with the upper part of the machine which can be tilte
d. This part of the
machine simulates the steering axis. The belt which simulates the road surface and it is
supported by two drums. There is a flat air or water bearing surface underneath the tyre.
The

lateral
stabilization

of the belt is achieved

by cont
rolling the yaw or the tilt

angle of one of the
drums. The test wheel can be driven and braked in a slip controlled manner.


Figure 3 The MTS flat test machine

Figures 4 and 5 indicate
two internal drum test stands.

The outer surface of the drum of Figure
4

can also

be used with a maximum speed of 250 kph.
The arrangement of the

wheel loading,
ti
lting and steering system allow
s centre point steering and tilting

about a line that touches the
inner drum surface and lie
s in the wheel centre

plane. The sequence

of changing

the wheel
angles: first steering about the

vertical axis and then tilting about the new

x
-
axis,

ensures that
each o
f the angles, defined
with respect to the vertical,

remains constant when the other is
changed. The wheel slip ratio can be controlled via a hydraulic motor in the test rig shown in
Figure 5. Here, the measuring hub

rotates together

with the wheel. This prevents the
constructional measure to

suppress parasitic forces and cross
-
talk such as t
he brake torque
interaction with

aligning torque that arises due to slight misalignment.

One of the
disadvantage
s of rotating measuring

systems is the fact that the sensitivity about the vertical
axis (for the small

aligning torque) can
not be chosen larger

than the sensitivity about the
horizontal

longitudinal axis about which the moment may become relatively large.


Figure 4 Internal drum test stand originally possessed and operated by Porsche


Figure 5

The Karlsruhe University internal drum test stand

A

doub
le Cardan coupling drive shaft
including a length change

compensation element

can be
used with a
stationary

measuring hub
. This type of construction ensures that
only the
drive/brake torque is transmitted to the wheel
. Other devices can also be used
(i.e. a set of two
membranes such as thin flexible discs) instead of double Cardan coupling. Accurate
alignment is necessary for all type of test rigs with a stationary measuring hub. However, w
ith

the UMTRI configuration (University of Michigan) cross
-
tal
k has been

prevented by
positioning the brake s
ystem between the
stationary

measuring system and the wheel.

The f
lat plank tyre test rig

(Figure 6
) can be used to observe tyre characteristics at low speed

of 2.3cm/s
.

A flat steel track moves horizontally.

Forces and moments are generated in the
wheel centre if the track rolls over the tyre.

The following parameters

can be adjusted:



s
ide slip angle



inclination

(camber)

angle

by tiltin
g the plank with respect to the
longitudinal

centre
line on the test
surface



vertical axle position and tire load



t
rack angle

and track speed



b
raking


Figure 6

Schematic of the flat plank tyre test rig

Cleats can be mounted on the plank surface. Typically,

tyre static stiffness tests (vertical,
longitudinal, lateral, yaw
and camber),

transient (step) side slip and camber tests (relaxation
lengths and non
-
lagging

part), impulse turning and low speed cleat test
s are performed on this
machine.


Figure 7

Dynamic brake and cleat test facility in side and front view

The

drum test rig shown in Figure 7

is designed in order to measure in plane tyre dynamics.
The rig should be sufficiently rigid for this purpose.
This resulted in a lowest natural
frequency of

just over 100Hz which allows the use of test data up to ca. 70Hz.

F
orce and
moment cross
-
talk

is prevented via
two flexible couplings

which connect the brake shaft
with
the wheel

shaft through an intermediate shaft
. These couplings

are flexible in all directions
except about the axis of rotation. If properly

aligned, th
is ensures that only the brake torque is
transmitted to the wheel and

that other parasiti
c forces and moments are sufficiently

suppressed.
S
train gauges

are positioned

to the intermediate coupling shaft

in order to
measure

t
he brake torque.
T
he

fluctuations in brake pressure is controlled via a
hydraulic
servo system
. The forces and
moments that act on the wheel (except the brake torque) can be
derived

from the signals produced by the piezoelectric force sensors positioned
on top of the
bearings

of the wheel shaft
.

D
ynamic brake tests

and cleat tests

can be performed via this test
rig. The rig can also be used for response
measurements to vertical axle oscillations (<20Hz)

in a different set
-
up.

The

drum test rig shown in Figure 8

is used for
out
-
of
-
plane tyre dynamic experiments
. It is
the
trailing arm ‘pendulum’

test rig
with at one end a vert
ical hinge and at the other the
steering head (for adjusting the average slip angle
) with piezoelectric measuring
hub
.

A
hydraulic actuator is used to exci
te the arm laterally up to ca. 25Hz.

The arm length is 1.65m
and the tyre is subjected to an

almost purely lateral slip variation.

The wheel load is adjusted
by tilting the vertical

hinge slightly forward. The rig is useful to observe

the overall

relaxation
length and the gyroscopic couple parameter.


Figure 8

The trailing arm pendulum test rig


Figure 9

Yaw oscillation test rig

Yaw oscillation tes
t rig (Figure 9
)
can be used for tests around an average steer angle that can
be set

at a value ranging between
-
5 and +5 degrees. The test rig

is light and very stiff. The
two

guiding members with flexible hinges intersect in the vertical virtual steering axis

that is
positioned in the wheel centre plane (centre point steering).
T
he yaw
vibration (typically
random with a

bandwidth of 65Hz)

is generated by a

hydraulic

actuator. The whee
l axle is
provided with a piezo
electric measuring

hub. The tyre is loaded
mechanically adjusting the
axle height above the drum

surface.


Figure 10

The dy
namic tyre test rig available at ika/fka

The dynamic tyre test rig

available at ika/fka

(Institute für Kraftfahrzeuge)

is shown in Figure
10
. It is designed to observe
ste
ady
-
state and dynamic characteristics of both

vehicle
and
motorcycle tyres, at a
maximum wheel load of 10 kN.

Any tire with a rim diameter between
13“ and 19“ can be

tested. As the tyres are fixed to the test rig

with
their original rims, the
effect of new rim

designs on the tyre characteristics can be investigated
.

The large drum of t
he
test rig

is driven

by an electric DC motor and is capable of a maximum

speed of 150 kph. S
lip
angle, camber angle, wheel load and tyre inflation

press
ure can be adjusted separately. The
k
inematic design

of the test rig ensures

that a change in

slip or

c
amber angle does not result in

any lateral or longitudinal

displacement of the tyre contact patch as this might

cause

a
distortion of measurement results.

Adjustment

of slip

angle

and camber angle

is being
performed by
hydraulic units and digital controll
ers
. Wheel load is being applied via

an

air
-
spring to provide smooth force application.

Force and moments characteristics of the tire are
measured

with a 6 components measuring hub (strain
-
gage

type).

H
ighest quality of
measuring

is ensured via
well
-
tuned
digital amplifiers and low
-
pass

filters
. Several additional
sensors are available in the test rig such as
infrared temperature

sensors to observe the tyre
temperature during testing
. The adjustments

of wheel load, tire inflation pressure and slip

and
cam
be
r angle can either be performed

manually by the

operator or generated in the course of
time by an integrated

computer system. Therefore even customer
-
dependant

testing
p
rocedures can be easily performed
.

Figure 11

shows a

test stand of Continental. It is a

6 position e
ndurance

test s
tand for

passenger car t
ires
.
It enables the simultaneous testing of up to 6 tires.
This test stand is used
to test the durability of

tires w
ith a combination of parameters such as;

internal

ti
re pressure,
loading force, and speed of rotation.

The impact on the tire is

significantly

higher than
real
conditions to reduce the time

required

until the tir
e shows malfunctions such as buc
kling.

The
test rig

provides the option of testing all combinations

of the three main parameters and
influences

on a tire according to ETRTO (European Tire and Rim

Technical Organization)
guidelines and standards.

The main purpose

is to detect the evolving defect early

enoug
h to
remove the tire from the machine before

the tire is seriously damaged. Quality management

thus has the opportunity to document this specific

defect and attribute it to either faulty design
or normal

abrasion
. E
arly detection

is ensured via

a bulge ind
icator.


Figure 11

6
-
position endurance test stand of Continental



References

1.

Hans B. Pacejka,

Tyre and Vehicle Dynamics

,
Butterworth
-
Heinemann, Elsevier,
Second
edition, 2006

2.

Leon Merkx,
Overturning moment analysis

using the

f
lat plank tyre tester
,
The University
of Eindhoven, 2004

3.

6 Position Endurance Test Stand for Passenger Car Tires,

Continental

Catalogue

4.

Dynamic Tire Test Facility
,
Forschungsgesellschaft Kraftfahrwesen mbH Aachen (fka)
,
gb1
-
06e_tire_test_facitity.doc, 02.04.07