Resilient tires and wheels – Tires – resilient – With electrical conducting means
Reexamination Certificate
2000-08-24
2004-12-28
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
With electrical conducting means
C152S209500, C152SDIG002, C156S244110, C156S501000, C264S167000, C264S173100, C264S173170, C264S174110, C425S131100, C425S380000, C425S462000, C425S465000
Reexamination Certificate
active
06834693
ABSTRACT:
BACKGROUND OF THE INVENTION
The object of the present invention is a tire made from several mixes comprising as the principal charge a non-reinforcing charge such as silica, or mixes with low carbon black contents, at least one of these mixes forming the tread. More particularly, it concerns a tire whose internal temperature may increase not inconsiderably when rolling, such as a tire designed, for example, to support heavy loads. It also concerns a process designed to produce such a tire and equipment for carrying out such a process.
Since environmental problems are becoming increasingly crucial and fuel economy and the suppression of pollution produced by motor vehicles have become a priority, one of the tire manufacturers' objectives is to produce a tire which combines the properties of very low rolling resistance, excellent adhesion to both dry and wet or snow-covered or icy ground, very good wear resistance, and finally low rolling noise.
To achieve that objective, a tire was proposed in European Patent EP A 501 227, which has a tread comprising silica as its main reinforcing charge. Though this solution provides the best compromise between the aforementioned group of very contradictory properties, it has been found that during the operation of the vehicle, tires with a tread whose main reinforcing charge is silica have the disadvantage that they accumulate more or less high levels of static electricity, which is produced by friction between the tire and the road when the vehicle is rolling, because silica is an electrically non-conductive material.
When certain particular conditions co-exist, the static electricity so accumulated in a tire can give rise to a disagreeable shock to the occupant of a vehicle when the occupant touches the vehicle body. It can also hasten the ageing of the tire because of the ozone generated by the electrical discharge. Depending on the nature of the ground and the vehicle, it can in addition cause the radio fitted in the vehicle to function poorly because of the interferences it produces.
This problem of static electricity accumulation in a tire and most of the disadvantages associated therewith is a very old one and already existed when the reinforcing charge used was carbon black.
Patent application EP 0 658 452 A1 describes the adaptation of principles known for a long time, to a so-termed modem tire. This adaptation provides a solution of the main problems associated with the solutions proposed in various older documents, and in particular the harmful heterogeneities introduced in tire structures. The solution proposed is to insert a strip of conductive rubber mix or ‘insert’, preferably extending all around the circumference of the tire and connecting the surface of the tread either to one of the crown plies, or to the carcass reinforcement, or to any other part of the tire that conducts electricity sufficiently well, the necessary electrical conductivity being conferred by the presence of a suitable form of carbon black.
Though such a solution is perfectly viable for a tire having a tread which consists of just one and the same non-conductive mix, for example the tread of a touring vehicle, this does not apply in the case of a tire comprising several layers of rubber mixes above the crown reinforcement and the carcass reinforcement, as is the case with any tire that can roll with a stable and high operating temperature, such as those fitted to heavy or high-speed vehicles.
In fact, if for any reason it is wished to produce such a tire with a layer or internal portion of the tread (the portion not in contact with the ground), which is non-conductive, between the crown reinforcement and the outer portion of the tread (the portion in contact with the ground) which has been made conductive by the presence of a circumferential insert or striation, the said internal portion must be made conductive. Similarly, a layer between the carcass reinforcement and the crown reinforcement, one which has the familiar excess thickness in the area of the edges of the crown plies, must also be made conductive if it is not already so. A first solution for obtaining a conductive tread is to co-extrude the inside and outside portions of the tread and to provide the combination so formed with a conductive circumferential insert. This solution is unsatisfactory for several reasons, two of which are worth mentioning: in the type of tire considered, the total thickness of the tread is too large; besides, it may be advantageous for the conductive inserts, respectively of the inside and outside layers of the tread not to be made using the same quality of rubber mix.
As described in French Patent Application FR 97/02276, another solution is to provide electrical connection between two conductive layers, or layers rendered conductive, separated by a non-conductive layer, by means of at least one strip of rubber mix with small thickness, width and length, positioned between the two weld faces of the non-conductive layers and in contact with the means used to make the two layers joined by the connection conductive. Though industrially satisfactory, this method entails positioning a supplementary product and therefore involves additional manufacturing costs.
A third solution consists in providing each non-conductive portion with a circumferential insert having a rectilinear circular path, or circular striation, after extrusion of the said portion by the usual extrusion methods, and then joining the two products together before they are positioned on the crown reinforcement. In that the striations are generally very thin so as not to affect the physical properties of the compositions constituting the two portions of the tread, the thickness of these inserts in the tire viewed in cross-section being of the order of 0.01 to 2.0 mm, such a solution entails that the path of the striation in the outside portion of the tread on the contact surface between the two portions should be perfectly aligned with or centered on the path on the said contact surface of the striation in the inside portion of the same tread.
However, the mechanical properties of rubber compositions before vulcanization are very poor, since the raw rubber mix may be in the form of a very soft paste or conversely a very hard agglomerate. Whatever the means used to work such mixtures, it is difficult to achieve perfect control of the geometry of the semi-finished product consisting of the combination of the two unvulcanized portions of the tread: coincidence or alignment between the respective paths of the two striations on the contact surface between the two portions is very difficult to achieve, so the solution involving two circular striations cannot be considered structurally optimized and industrially viable, from the standpoint either of cost or of the performance obtained. The manufacture of a tire designed in this way would be more akin to precision engineering than to an industrial process.
SUMMARY OF THE INVENTION
One of the invention's aims is to dissipate electrostatic charges induced by the rolling of a tire comprising several electrically non-conductive mixes without significantly affecting the properties of the tire. Another aim is to obtain a tire as simple and cheap as possible to produce in terms of the material costs and/or manufacturing costs involved.
The present invention proposes a tire comprising at least two radially adjacent layers of electrically non-conductive rubber mixes the said two layers sharing a common contact surface, characterized in that each layer contains a circumferential insert of electrically conductive mix whose footprint on the said contact interface is circumferential, the insert of the first of these layers having on the said contact surface a circumferential footprint of circular path of width e, the insert of the second layer having on the contact surface a circumferential footprint with a path of width e′ which crosses and presents crests on either side of the circular path of the first layer insert, such that around the circumference there ar
Bardy Daniel
Calvar Didier
Nicolas Serge
Baker & Botts
Compagnie Generle des Etablissements Michelin-Michelin & Cie
Maki Steven D.
LandOfFree
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