Measuring and testing – Tire – tread or roadway
Reexamination Certificate
1999-04-06
2002-01-15
Oen, William (Department: 2855)
Measuring and testing
Tire, tread or roadway
Reexamination Certificate
active
06338270
ABSTRACT:
This invention relates to a method for determining the road handling of a tyre of a wheel for a vehicle.
BACKGROUND OF THE INVENTION
At the present time, to determine the road handling performance of a tyre, the manufacturers of pneumatic tyres are obliged to produce numerous physical prototypes in order to experimentally evaluate the effects of the various design parameters on the drift behaviour of the tyre, under steady state and transient state conditions. The experimental tests are conducted according to iterative procedures, that are largely empirical and based on experience and are also extremely demanding in terms of time and cost.
Furthermore, automobile manufacturing companies are insisting more and more frequently that the makers of pneumatic tyres come up with tyres with extremely precise technical characteristics as early as the initial stages of vehicle study and dynamic behaviour forecasting.
In such a position, the tyre manufacturers are finding it very difficult to respond satisfactorily and with the necessary flexibility to the various market demands.
The object of this invention is to provide a scientific methodology with which to identify the performance characteristics of a tyre in relation to road handling, on the basis of previously defined design specifications.
SUMMARY OF THE INVENTION
The above object is achieved according to this invention by a method for determining the road handling of a tyre of a wheel for a vehicle, said tyre being made from selected mixes of rubber and reinforcing materials, said method comprising:
a) a first description of said tyre by means of a first, concentrated-parameter, physical model, said first physical model comprising a rigid ring which represents the tread band provided with inserts, a belting structure and corresponding carcass portion of said tyre, a disk which represents a hub of said wheel and beading of said tyre, principal springs and dampers connecting said rigid ring to said hub and representing sidewalls of said tyre and air under pressure inside said tyre, supplementary springs and dampers representing deformation phenomena of said belting structure through the effect of a specified vertical load, and a brush model simulating physical phenomena in an area of contact between said tyre and a road, said area of contact having a dynamic length
2
a,
b) a definition of selected degrees of freedom of said first physical model, and
c) an identification of equations of motion suitable for describing the motion of said first physical model under selected dynamic conditions, characterized in that it comprises
d) the definition of said concentrated parameters, said concentrated parameters consisting of the mass M
c
and a diametral moment of inertia J
c
of said rigid ring, the mass M
m
and a diametral moment of inertia J
m
of said disk, structural stiffnesses K
c
and structural dampings R
c
respectively of said principal springs and dampers, and residual stiffnesses K
r
and residual dampings R
r
respectively of said supplementary springs and dampers, wherein
said structural stiffnesses K
c
consist of lateral stiffness K
cy
between said hub and said belt, camber torsional stiffness K
c&thgr;x
between said hub and said belt and yawing torsional stiffness K
c&thgr;z
between said hub and said belt,
said structural dampings R
c
consist of lateral damping R
cy
between said hub and said belt, camber torsional damping R
c&thgr;x
between said hub and said belt and yawing torsional damping R
c&thgr;z
between said hub and said belt,
said residual stiffnesses K
r
consist of residual lateral stiffness K
ry
, residual camber torsional stiffness K
r&thgr;x
and residual yawing torsional stiffness K
r&thgr;z
, and
said residual dampings R
r
consist of residual lateral damping R
ry
, residual camber torsional damping R
r&thgr;x
and residual yawing torsional damping R
r&thgr;z
,
e) a description of said tyre by means of a second, finite-element model comprising first elements with a selected number of nodes, suitable for describing said mixes, and second elements suitable for describing said reinforcing materials, each first finite element being associated with a first stiffness matrix which is determined by means of a selected characterization of said mixes and each second element being associated with a second supplementary stiffness matrix which is determined by means of a selected characterization of said reinforcing materials,
f) a simulation on said second, finite-element model of a selected series of virtual dynamic tests for exciting said second model according to selected procedures and obtaining transfer functions and first frequency responses of selected quantities, measured at selected points of said second model,
g) a description of the behaviour of said first physical model by means of equations of motion suitable for representing the above dynamic tests for obtaining second frequency responses of said selected quantities, measured at selected points of said first physical model,
h) a comparison between said first and said second frequency responses of said selected quantities to determine errors that are a function of said concentrated parameters of said first physical model, and
i) the identification of values for said concentrated parameters that minimize said errors so that said concentrated parameters describe the dynamic behaviour of said tyre,
j) the determination of selected physical quantities suitable for indicating the drift behaviour of said tyre, and
k) the evaluation of the drift behaviour of said tyre by means of said physical quantities.
To advantage, said selected physical quantities are the total drift stiffness K
d
of said tyre, in turn comprising the structural stiffness K
c
and the tread stiffness K
b
, and the total camber stiffness K
y
of said tyre.
According to a preferred embodiment, said method also comprises
l) a definition of said brush model, said brush model having a stiffness per unit of length c
py
and comprising at least one rigid plate, at least one deformable beam having a length equal to the length
2
a
of said area of contact and at least one microinsert associated with said beam, said microinsert consisting of at least one set of springs distributed over the entire length of said beam, said springs reproducing the uniformly distributed, lateral and torsional stiffness of said area of contact.
Preferably, said degrees of freedom referred to at previous point b) are composed of:
absolute lateral displacement y
m
of said hub, absolute yaw rotation &sgr;
m
of said hub and absolute rolling rotation &rgr;
m
of said hub,
relative lateral displacement y
c
of said belt with respect to said hub, relative yaw rotation &sgr;
c
of said belt with respect to said hub and relative rolling rotation &rgr;
c
of said belt with respect to said hub,
absolute lateral displacement y
b
of said plate, absolute yaw rotation &sgr;
b
of said plate and absolute rolling rotation &rgr;
b
of said plate, and
absolute lateral displacement y
s
of the bottom ends of said at least one microinsert.
According to another embodiment, said selected series of virtual dynamic tests referred to at previous point f) comprises a first and a second test with said tyre blown up and not pressed to the ground, said first test consisting in imposing a translation in the transverse direction y on the hub and in measuring the lateral displacement y
c
of at least one selected cardinal point of said belt and the force created between said hub and said belt in order to identify said mass M
c
, said lateral stiffness K
cy
, and said lateral damping R
cy
, said second test consisting in imposing a camber rotation &thgr;
x
on said hub and in measuring the lateral displacement of at least one selected cardinal point of said belt y
c
and the torque transmitted between said hub and said belt in order to identify said diametral moment of inertia J
c
, said camber torsional stiffness K
c&thgr;x
, said camber torsional damping R
c&thgr;x
, said yawing torsional stiffness K
c&thgr;z
and said yawing torsional dam
Mancosu Federico
Sangalli Roberto
Oen William
Pirelli Pneumatici S.p.A.
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