Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-05-24
2002-03-19
Knable, Geoffrey L. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S456000, C152S342100, C152S511000, C152S540000, C152S541000, C152S544000, C152S548000, C152S550000, C152SDIG006
Reexamination Certificate
active
06357502
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a tire wheel for vehicles, i.e. to the assembly comprising a mounting rim designed for connection to a hub of the vehicle itself, a tire mounted on said mounting rim and an inner tube inserted inside said tire, designed to be inflated with a fluid under pressure via a special inflating device.
More particularly, the invention relates, albeit not exclusively, to a tire wheel for use on motor vehicles with very high performance features, i.e. vehicles which are able to produce a high driving torque and reach high speeds both along straight road sections and around bends.
The tire wheels of the type described must be able to satisfy fully various requirements—also partly conflicting with one another—which are associated with the performance features required by the market today.
In particular they must be able to provide the vehicle with an excellent handling performance—particularly as regards the directional and transverse stability—, road-holding power and traction on any type of ground, resistance to aquaplaning, comfort, as well as the capacity to continue travelling over a reasonable distance also in the case of partial or total loss of air (run-flat conditions), without the risk of “unseating”, i.e. the condition where one or both of the tire beads comes out of the associated seat formed on the rim.
The Applicants have noticed that, hitherto, these requirements have generally been satisfied individually by a single component from among those which make up the wheel: thus the handling has been attributed to the performance features of the tire, while the resistance to “unseating” has been sought after by means of suitable shaping of the bead seats. As regards the so-called “run-flat capacity”, according to a first method, this has been obtained by modifying the carcass structure, strengthening the sidewalls of the tire so as to provide it with a self-supporting capacity; by way of an alternative, in tubeless tires this capacity has been provided by suitable supports mounted on the rim and inserted inside the tire, while in tires with inner tubes an air chamber, or inner tube, divided up into a plurality of circumferential or transverse compartments independent of one another has been used.
The presence of several independent compartments allows the tire to be provided with a sufficient inflation pressure, and hence capacity for emergency travel, even when one of said compartments has suffered a puncture.
It has been found that all these solutions, compared with the advantages offered, also have various disadvantages, such that the overall result obtained is penalized.
In particular, the Applicants have noticed that:
the increase in the structural rigidity of the sidewalls results in a greater weight of the tire and a greater rigidity thereof in all directions—longitudinal, transverse and vertical—which has a negative effect on the driving performance under normal conditions, and on the comfort;
the use of a support inside the tire increases the weight of the tire and does not provide any guarantee as to long resistance during run-flat conditions, when the weight of the car is transmitted onto the support with frictional contact between the radially internal surface of the tire and the radially external surface of the support; and
the solution with inner tube is not practical with so-called low-profile tires, i.e. those tires which have an elliptical cross-section elongated along the axis of rotation, in which difficulties both as regards insertion and use are encountered.
The Applicants have been able to establish, in fact, that the insertion of the inner tube between tire and rim is all the more difficult the lower the cross-section of the tire. In addition to this, traditional inner tubes, during inflation, assume a profile which is substantially circular in cross-section and does not combine properly with the elliptical profile of the low-profile tire, resulting in folds which form on top of one another and prevent correct and complete extension of the walls of the inner tube onto the internal surface of the toroidal cavity, in particular along the sidewalls of the tire. In this way the toroidal cavity is not filled properly and a damaging state of internal tensions in the wall of the inner tube arises, adversely affecting the duration thereof.
Furthermore, as perceived by the Applicants, further problems are associated with the fact that traditional inner tubes are provided with an inflating valve comprising a stem which passes through the rim for connection to the external environment outside the wheel. In particular travel conditions of the tire, this fact represents a risk which at present has not yet been eliminated: it has been found that, in the case of sudden accelerations or decelerations of the vehicle, such as those which are produced by high-performance vehicles which transmit to the ground very high torque values, slipping of the tire with respect to the rim may occur, with consequent tearing of the inner tube at the base of the valve or shearing of the valve stem. When this occurs, there is an immediate deflation of the tire and associated loss of stability of the vehicle, with serious danger for the lives of the driver and passengers of the vehicle itself.
Even the most recent proposition to improve the behaviour of the abovementioned tire wheels as regards the run-flat capacity, and resistance to unseating has not diverged from the known art, envisaging a solid insert inside the cavity defined by the rim and tire assembly.
For the sake of convenience of the description, it is pointed out here that this assembly has a mounting rim which is provided with conical bead seats whose axially external end has a diameter less than that of the axially internal end and is associated with a radial carcass tire, the beads of which match the corresponding seats on the rim while the carcass has a meridian profile, in cross-section, with a constant direction of curvature, the tangent of which, in the vicinity of the bead cores, is substantially parallel to the equatorial plane.
In the embodiment proposed, the rim has bead seats of different diameter and the bead seat of larger diameter is delimited in an axially internal position by a shoulder which is of considerable height so as to prevent unseating on that side, but is difficult to pass over. The wheel is completed with a tread support ring radially extending over about half the cross-section height of the tire: the ring is fitted onto the rim, in the vicinity of the bead seat of smaller diameter and, in the event of deflation of the tire, locks in position the adjacent bead, preventing unseating of the tire on the corresponding side. This wheel is described in detail for example in U.S. Pat. No. 5,634,993, to which reference should be made for further information.
The Applicants have realized that this solution is also not completely satisfactory in relation to the high standards of quality and performance which are nowadays required by the market, i.e. by vehicle manufacturers, by tire retailers and by the users themselves. In particular they have perceived that the version without tread support results in the return to tires with reinforced self-supporting sidewalls, while the internal solid support ring reduces the volume of inflating air which is already small in low-profile tires, thereby reducing the comfort, limits the vertical deformability of the tire, adversely affecting the driving performance, increases the thermal mass forming a harmful barrier against the dissipation of the heat produced during use, and requires a particular constructional form of the rim, which results in the need for a different diameter of the bead seats of the rim, making assembly and disassembly of the ring in particular, and the wheel assembly in its entirety, difficult.
All this having been stated, the Applicants have now discovered that the performance characteristics of a vehicle tire wheel may be further improved by using an assembly of partly known and partly new e
Knable Geoffrey L.
Pirelli Pneumatici S.p.A.
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