Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1996-06-05
2001-07-10
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S539000, C152S540000, C264S326000, C425S036000, C425S054000, C425S058000
Reexamination Certificate
active
06257292
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to tires and more precisely to the beads of tires.
The role of the beads of tires is known. It is to assure the “clamping” of the tire on the rim on which it is mounted. For this purpose, the shape of the bead of the tire is adapted to the shape of the rim for which it is designed; in other words, the outer side face of the bead as well as its seat (that is to say, its radially inner face) have a shape which corresponds substantially to the shape of the corresponding rim, if one neglects the slight differences for the purpose of assuring good clamping of the bead on the rim.
As to the shape of the inner side face, it corresponds more or less to the shape of the outer side face until encountering the seat of the bead in a zone which in the present description will be referred to as the inner edge of the bead, where there is generally present a rather sharp edge known as the “bead toe”. The rubber which appears there is known as the “bead point”.
Tires for passenger cars are mounted, as a rule, on single-piece rims having flanges which are substantially perpendicular to the axis of the rim and having seats which receive the bead. The seats have a frustoconical surface slightly inclined with respect to the axis of the rim (by an angle of about 5°) and are bordered by a protuberance known as a “hump” having a central groove which is radially lower than the seats. The bead toe cooperates with this protuberance which is arranged on the rim in order to impart to the tire the ability to remain mounted on the rim even when its inflation pressure is very insufficient.
The role of the inner edge of the bead is therefor important for the proper holding of the tire mounted on its rim.
When the tire is to be mounted on its rim or removed from it, tools are used which come into engagement with the rim substantially at the level of the lower edge of bead. These tools apply deformations very locally on the bead of the tire, which deformations may be very substantial to the extent of damaging the bead.
This leads to the need to reinforce the point of the bead of the tire in order that it can withstand without damage the stresses which the bead must undergo during its use. For this, textile strips are used, which increases the cost price of the tire.
It is also known that the mounting and removal of the tire cause a swinging of the bead by rotation around its center, that is to say, approximately around the bead wire that it contains. The stresses resulting therefrom are greater the greater the stiffness in rotation of the bead. The stiffness will be greater when using bead wires of a shape which is further from a circular cross section or when the anchoring of the carcass of the tire comprises numerous reinforcements intended to increase the strength thereof.
The present invention relates, in particular, to tires which include a bead on each side of the tire equational plane, each bead being defined by a substantially frustoconical seat which is inclined slightly with respect to the axis of the tire when the bead is in mounted position, an inner edge, an inner side face and an outer side face, the bead being intended to be applied radially from above on the seat of a rim, the inner side wall being directed towards the inner cavity of the tire, the inner edge forming a transition between said seat and the said inner side wall, and having a stiffness of the bead in rotation which is greater than 5 mN/radian. This covers the very great majority of ordinary tires, and it is intended to exclude tires which are especially developed so that the bead is easy to swing, such as, for instance, collapsible tires (see, for instance, U.S. Pat. No. 4,057,091) or tires designed to be mounted on special rims without central mounting grooves (see, for instance, U.S. Pat. No. 4,768,573).
SUMMARY OF THE INVENTION
The object of the present invention is to propose a new design of the bead of these tires which makes it capable of being subjected to the mounting and removal operations without damage and without impairing its ability to cooperate with the humps provided on the rim in order to avoid bead unseating and without the necessity of using textile reinforcements, such as those present in the bead points.
The inner edge of the tire of the invention is rounded; it therefore does not have the sharp edge forming an angle of less than 90° which usually separates the inner side face of the bead from its seat, from which edge there results the customary name of bead point. The angle in question is the angle which can be measured on a radial section of the bead between the tangent to the seat and the tangent to the inner side face, passing from one tangent to the other along the tire.
In another aspect, the tire in accordance with the invention is characterized by the fact that the inner edge has a transition surface the inclination of which, measured by the tangent along the contour seen in radial section, passes through an intermediate value between the inclination of the seat and that of the inner side wall.
By way of example of such a transition surface, the inner edge has at least one conical surface the inclination of which is intermediate between the inclination of the seat and the inclination of the inner side wall. This arrangement constitutes an alternative for the inner edge of a rounded shape.
In order to facilitate the molding of such a tire, the invention also proposes the use of a molding apparatus which makes it possible very precisely to control the shape of the bead at its inner edge. Instead of using a very flexible membrane, similar to an inner tube, a rigid mold is preferably used in order to assure the molding of the inner side face, at least in the portion thereof close to the inner edge.
It is well known that the ability of a tire to prevent loosening from the rim depends to a very great extent on the inner edge of the bead. The tires for passenger cars which are designed at the present time are subjected to tests in order to verify that, even upon a very sudden turn with reduced pressure, the beads remain in place on their seat.
It is known that the greater the seat pressure of the tire the less the tendency of the tire to leave its rim. Furthermore, the greater the rigidity in rotation of the bead, the less the tendency of the tire to come loose from its rim. It may be recalled that the seat pressure depends on the amount of rubber to be compressed between the bead wire and the radially outer surface of the seat of the corresponding rim. A certain level of seat pressure is necessary in order to be able to transmit a braking or driving torque between the rim and the tire. However, the greater the seat pressure, the greater the difficulties in mounting and/or removing the tire, particularly removal with portable tools. The designer of the tire therefore seeks to achieve a good compromise between safety (little sensitivity to loosening from the rim), obtained by controlling the clamping and the rigidity in rotation of the tire, and the ease of mounting/removal.
The tire in accordance with the present invention, with rounded inner edge and without bead point retains as good performance as the tire with bead point with respect to its very low propensity to loosen from the rim when mounted on its rim, since it permits an increase both of the seat pressure and of the rigidity in rotation on the rim while retaining the same ease of mounting it on its rim or removing it from its rim.
The following description, read with reference to the accompanying drawing, will make it possible fully to understand the invention.
REFERENCES:
patent: 1408678 (1922-03-01), Ayres
patent: 1432004 (1922-10-01), Wheatley
patent: 2563787 (1951-08-01), Keefe
patent: 4051292 (1977-09-01), Kresta et al.
patent: 4057091 (1977-11-01), Gardner et al.
patent: 4088168 (1978-05-01), Boileau et al.
patent: 4269251 (1981-05-01), Harrington et al.
patent: 4345634 (1982-08-01), Giron
patent: 4406317 (1983-09-01), Merten
patent: 4434831 (1984-03-01), Uemura
patent: 4580610 (1986
Baker & Botts L.L.P.
Johnstone Adrienne C.
Sedepro
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