The present invention relates to a tire intended to be mounted on a rim having at least a first frustoconical seat, the generatrix of which has an axially outer end closer to the axis of rotation than the axially inner end.
Such a tire is described in international application WO 94/13498. It comprises at least a first bead, intended to be mounted on a first seat inclined towards the outside, the said first bead, having a seat the generatrix of which has its axially outer end closer to the axis of rotation than its axially inner end, and the said generatrix being extended axially towards to the outside by an outer face delimiting the bead toe, the said face forming with the axis of rotation an angle .gamma., open radially and axially towards the outside and of less than 90.degree.. The radial carcass reinforcement of the said tire, anchored in each bead to at least an inextensible annular bead ring, has a meridian profile, when the tire is mounted on its service rim and inflated to its service pressure, with a constant direction of curvature in the sidewall and bead terminated by the toe and which is such that, in said bead, the tangent to the point of tangency of said profile with the inextensible bead ring forms with the axis of rotation an angle .o slashed. open towards the outside of at least 70.degree..
The bead of such a tire and more particularly the structure of the anchoring of carcass reinforcement may be variable. In the application WO 95/23073, the radial carcass reinforcement is anchored to the inextensible bead wire by winding around the said wire passing from the heel to the toe of the bead to form an upturn extending in a rubber section, made of rubber mix in the form of a wedge defined by two sides coming from an apex A located beneath the meridian section of the coated bead wire, the radially outer side forming, with a line parallel to the axis of rotation passing through said apex A, an acute angle .o slashed..sub.1, open radially towards the outside and between 20.degree. and 70.degree., and the radially inner side forming with said parallel line an acute angle .o slashed..sub.2, open radially towards the inside, the rubber mix forming the rubber section axially adjacent to the bead wire having a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes located axially and radially above the wire and the rubber section.
The combination of the carcass reinforcement meridian profile such as described in the first cited application with a structure of hooking such as described in the second cited application makes possible to obtain a very good compromise between the handling properties of the tire inflated to its recommended pressure and the said properties when the tire is inflated to a reduced pressure or even zero. Whether the initial clamping on the rim be zero or of a given value, the axial displacement of the anchoring bead wire of the carcass reinforcement, which may result from the tension of said reinforcement, which tension is due, for instance, to the inflation pressure of the tire, makes possible, in combination with the axial disposition of the rubber section reinforced by the upturn, to obtain clamping of the toe of the bead on the rim seat. The value of this clamping increases as a function of the tension force to which the carcass reinforcement is subjected, and may become great in the case of high tension, for instance when one of the side walls of the tire is placed under great tension by a transverse force.
The preferential solution described in the application WO 95/23073 is such that the carcass reinforcement upturn has a length such that it is in contact with the total perimeter of the rubber section or wedge; it thus forms the two radially outer and inner sides of the rubber section and the side opposite the apex or center of said rubber section, and its end is located axially beyond the point of intersection of the two outer and inner sides. The part of the upturn immediately adjacent to the part of said upturn which is wound around the bead wire may, in the first instance, form the radially outer edge of the rubber section or wedge and then finally the radially inner side of said rubber section, ending beyond the junction point of the two outer and inner sides. It may also form firstly the radially inner side of the rubber section or wedge, then the side opposite the apex of said wedge, and then finally the radially outer side of said rubber section, ending in the same manner as previously described.
The above two structures are complicated and difficult to use industrially, and as a consequence, expensive. Furthermore, in severe conditions of load, the contact pressure exerted by the bead toe upon the axially outer hump of the rim and the great temperature that may be reached in the said bead are such that fissures of rubber may occur in the external protecting layer of the bead, fissures which are propagated along the upturn of the carcass reinforcement and reach the radially inner face of the anchoring bead wire with destruction of the bead.
The invention has for object to remedy these drawbacks while keeping the excellent properties of unseating of tire beads.