PNEUMATIC RADIAL TYRE

Abstract: A radial pneumatic tire having excellent run-flat durability. The tire is equipped with a belt layer (4), which includes a plurality of metal cord layers, and a tread (5) successively at a periphery of a crown portion (3) of a toroidal radial carcass (2), and is equipped with, at an inner peripheral surface of the side portion (6) of the carcass, a rubber reinforcing layer (7) having a crescent moon shaped cross-section and bearing and supporting load. The tire has an auxiliary layer (8) disposed between the carcass and the belt layer and including organic fiber cords which are oriented so as to intersect the cords of the carcass and the cords of the belt layer with a central equatorial plane between, on the one hand, the cords of the auxiliary layer, and on the other hand, the cords of the carcass and the cords of the belt layer.

Description: The present invention relates to a pneumatic radial tire, and more specifically, to a pneumatic radial tire which is strengthened by providing, at the sidewall of the tire, a rubber reinforcing layer having a crescent moon shaped cross-section, such that when the pneumatic tire installed on a vehicle is punctured during running, the tire can run for a considerable distance in the punctured state. Conventionally, various measures have been devised for safely continuing running, without damaging the tire further and without disadvantages such as poor steering, over a distance from the place where the tire was punctured to a place desired by the driver, e.g. a service station where the tire can be changed, at the time when the internal pressure decreases or becomes zero (hereinafter, "punctured") for some reason, and in many cases due to a foreign object such as a nail or a metal piece piercing the tire, during traveling of the pneumatic tire installed on a vehicle. Among these measures, as a simple and effective measure for radial tires for passenger vehicles in particular, Japanese Patent Application Publication No. 52-41521 discloses art relating to a so-called side reinforced run-flat tire in which a rubber reinforcing layer having a crescent moon shaped cross-section is made to line the carcass inner peripheral surface of the sidewall which is the region in the tire having the lowest rigidity, so that the entire sidewall has approximately the same thickness and so as to provide rigidity. In this side reinforced run-flat tire, in an ordinary state, the load is mainly supported by the internal pressure. When the tire is punctured, the supporting of the load is taken over by the rigidity inherent in the reinforced sidewall. However, in this side reinforced run-flat tire, as illustrated in Fig. 2 of the accompanying drawings, when the tire is punctured, buckling of a sidewall S is avoided, but a crown portion 21 exhibits the phenomenon known as buckling, and a tread 22 is thereby lifted up from a road surface R. As a result, a portion 23 of the sidewall separated from the tread 22 contacts the ground. In this ground-contacting state, obviously, stress concentrates and defects arise at an early stage at portions at which there is much bending deformation. As a result, in order to increase the durability of the run-flat tire, buckling of the crown portion 21 must be suppressed, and tire deformation must, as much as possible, be maintained the same as before the puncture. Japanese Patent Application Laid-Open No. 6-191243 and Japanese Patent Application Laid-Open No. 6-191244 disclose techniques in which at least one organic fiber cord layer, which is effective for weight reduction, is disposed at the outer periphery of the belt layer, so as to increase the rigidity of the tread base portion. However, these disclosed techniques do not exhibit sufficient effects for suppressing buckling, and the current situation is that, even if the rigidity of the tread base portion is increased even more by winding a plurality of layers, the effects are small in proportion to the increase in cost and in weight. Attention is also drawn to the disclosure of FR-A-2425334, which forms the preamble of claim 1, according to which a pneumatic radial tire comprises: a toroidal radial carcass 21, a pair of sidewalls 14, a belt layer 23 which includes a plurality of metal cord layers, and a tread 11 successively placed on a periphery of a crown portion of said toroidal radial carcass, and, at an inner peripheral surface of each side portion of the carcass, a rubber reinforcing layer 20 having a crescent moon shaped cross-section, and an auxiliary layer (reinforcing ply) 31 disposed between the toroidal radial carcass 21 and the belt layer 23 and including cords which are oriented with respect to a central equatorial plane so as to intersect both the cords of the carcass and the belt layer, and the cords of the auxiliary layer intersecting the central equatorial plane. The present invention has taken into considering the above-described problems, and an object thereof is to provide a pneumatic tire in which, when the tire is punctured, buckling of the crown portion is suppressed, and durability is increased. The present invention provides a pneumatic radial tire comprising a toroidal radial carcass, a pair of sidewalls, a belt layer which includes a plurality of metal cord layers, and a tread successively placed on a periphery of a crown portion of said toroidal radial carcass, and, at an inner peripheral surface of each side portion of the carcass, a rubber reinforcing layer having a crescent moon shaped cross-section, and an auxiliary layer disposed between the carcass and the belt layer and including organic fiber cords which are oriented with respect to a central equatorial plane so as to intersect the cords of the carcass and the cords of the belt layer, and the cords of the auxiliary layer intersecting the central equatorial plane. As is known, a belt layer for improving the rigidity of the base portion of the tread is provided at the crown portion of a radial tire. The belt layer is usually formed by a plurality of steel cord layers. It is known that when, due to a puncture, the tread receives bending deformation so as to rise up, the steel cord layer becomes a neutral axis, and compressive force is applied to the tread and tension is applied to the carcass. Accordingly, in a conventional reinforcing method in which the outer periphery of the belt layer is additionally reinforced, the compression side is reinforced, and the intrinsic tensile direction high elasticity of the reinforcing cord is not generated. The tire of the present invention is provided with an auxiliary layer at the side of the crown portion of the tire to which side tension is applied at the time of a puncture. Accordingly, even if the cords are reinforced by flexible organic fibers, the crown portion is effectively provided with flexural rigidity, and rising up of the tread at the time of a puncture can be effectively suppressed. As a result, local concentration of stress can be avoided, and the run-flat running can be greatly improved. In this case, it is preferable that the cords of the auxiliary layer intersect the central equatorial plane at an angle of greater than or equal to 30°, because at angles of less than 30° with respect to the central equatorial plane, sufficient tire radial direction rigidity may not be obtained and buckling may not be suppressed. It is even more preferable that the cords of the auxiliary layer are in a range of 45 to 75° with respect to the central equatorial plane. It has been confirmed that, in order to sufficiently and effectively suppress buckling, there must be sufficient tire radial direction rigidity, and circumferential direction rigidity must be maintained, and the angle with respect to the equatorial plane is optimally in a range of 45 to 75°. Other than aramid, polyester, rayon, and the like can be optimally used for the organic fiber cords. Further, the number of organic fiber cord layers is not limited to one, and plural layers may be superposed such that the cords thereof intersect each other. The invention will be further described with reference to the accompanying drawings, in which: Fig. 1 is a tire cross-sectional view of an embodiment to which the present invention is applied; and Fig. 2 is a cross-sectional contour view illustrating deformation at the time a conventional tire is punctured. In order to confirm the effects of a tire to which the present invention was applied, run-flat durability due to actual running on a vehicle was evaluated for 205/ 65R15 size Example tires and Conventional Example tires. As the test method, each test tire was assembled to a 15 × 5 1/2J rim. After filling wich internal pressure to fit the bead on the rim, the valve core was removed, and test tires having an internal pressure of substantially zero were respectively installed on the front right wheel of a passenger vehicle. The tires were run on a test track at a constant speed of 20 km/h. The driver sensed the generation of abnormal vibrations caused by a defect of the test tire (the limit of durability), and the running distance until the defect was generated was measured. Hereinafter, description will be given on the basis of the accompanying drawing, wherein Fig. 1 is a cross-sectional view of a tire illustrating an embodiment of the present invention. Fig. 1 (designated as Example 1) is an example of a 205/65R15 size passenger vehicle tire 1. A carcass 2 is formed from two plies 6 in which 1000d/2 polyester cords are disposed so as to be oriented substantially orthogonally to an equatorial plane O. Both end portions of the carcass 2 are wound up around bead rings 9 so as to form wound-up end portions 2'. A hard rubber bead filler 10 is embedded taperingly between the carcass 2 above the bead ring and the ply wound-up end portion 2' thereof. The tire tread is provided on the periphery of a crown portion 3 of the carcass 2. At an inner peripheral surface of a side portion 5 of the carcass 2, a rubber reinforcing layer 7 (shore A hardness 84°, maximum width 10 mm) having a crescent moon shaped cross-section is disposed such that the entire sidewall S has a substantially uniform thickness from the position where the rubber reinforcing layer 7 is superposed on the bead filler via the carcass. Reference numeral 11 is an air-impermeable inner liner. A belt layer 4 comprises two layers, each layer being a twisted structure in which 1 × 5 steel cords are disposed so as to be inclined at an angle of 26° with respect to the equatorial plane O, and the two layers are superposed such that the cords intersect one another. An auxiliary layer 8 which is more narrow than the belt layer is disposed between the belt layer 4 and the carcass 2. In Example 1, the auxiliary layer 8 is disposed between the carcass 2 and the belt layer 4 and comprises organic fiber cords which are oriented with respect to the central equatorial plane O so as to intersect the cords of the carcass and the cords of the belt layer, the cords of the auxiliary layer intersecting the central equatorial plane. The auxiliary layer 8 is formed by one rubber-coated layer in which 1670d/2 aramid cords are disposed at an angle of 20° with respect to the equatorial plane O. The belt layer 4 may be a structure strengthened by a cap layer which is formed by arranging a plurality of heat shrinking cords such as nylon or the like and winding the cords spirally in the peripheral direction of a rubber coated strip, at the entire periphery or a predetermined region of the belt layer. Although the details of the half at the right side of the equatorial plane O are omitted from Fig. 1, there is symmetry to the left and the right. In an Example 2, the reinforcing layer 8 of Example 1 is formed from one rubber-coated layer in which aramid cords are disposed at an angle of 30° with respect to the equatorial plane O. Example 2 is substantially similar to Example 1 in all other respects. In an Example 3, the reinforcing layer 8 of Example 1 is formed from one rubber-coated layer in which aramid cords are disposed at an angle of 45° with respect to the equatorial plane O. Example 3 is substantially similar to Example 1 in all other respects. In an Example 4, the reinforcing layer 8 of Example 1 is formed from one rubber-coated layer in which aramid cords are disposed at an angle of 60° with respect to the equatorial plane O. Example 4 is substantially similar to Example 1 in all other respects. In an Example 5, the reinforcing layer 8 of Example 1 is formed from one rubber-coated layer in which aramid cords are disposed at an angle of 75° with respect to the equatorial plane O. Example 5 is substantially similar to Example 1 in all other respects. In an Example 6, the reinforcing layer 8 of Example 1 is formed from one rubber-coated layer in which aramid cords are disposed at an angle of 90° with respect to the equatorial plane O. Example 6 is substantially similar to Example 1 in all other respects. In a Comparative Example 1, one layer of the same structure as the auxiliary layer 8 is disposed between the belt layer 4 and the tread. The reinforcing layer 8 is formed from one rubber-coated layer in which aramid cords are disposed at an angle of 60° with respect to the equatorial plane O. Comparative Example 1 is substantially similar to Example 1 in all other respects. A comparative Example 2 is substantially similar to Example 1 except that no additional cord layer such as the auxiliary layer 8 is used. The results of measurement of the running distances until defects occurred are listed in the following table. In this way, run-flat durability can be advantageously improved by placing between the carcass and the belt layer an auxiliary layer including organic fiber cords which are oriented with respect to the central equatorial plane so as to intersect the cords of the carcass and the cords of the belt layer, the cords of the auxiliary layer, intersecting the central equatorial plane, as compared with a tire having, at the side portion inner peripheral surface of the radial carcass, a rubber reinforcing layer which has a crescent moon shaped cross-section and bears and supports the load. As described above, the pneumatic radial tire relating to the present invention can run for a long distance even if punctured and is therefore extremely useful to the automotive industry in today's vehicle-oriented society.

Claims: A pneumatic radial tire (1) comprising: a toroidal radial carcass (2), a pair of sidewalls, a belt layer (4) which includes a plurality of metal cord layers, and a tread successively placed on a periphery of a crown portion (3) of said toroidal radial carcass, and, at an inner peripheral surface of each side portion (5) of the carcass, a rubber reinforcing layer (7) having a crescent moon shaped cross-section, and an auxiliary layer (8) disposed between the toroidal radial carcass and the belt layer and including cords which are oriented with respect to a central equatorial plane (O) so as to intersect both the cords of the carcass and the cords of the belt layer, and the cords of the auxiliary layer intersecting the central equatorial plane, characterized in that the cords of the auxiliary layer (8) are organic fiber cords. A pneumatic radial tire as claimed in claim 1, characterized in that the cords of said auxiliary layer (8) intersect the central equatorial plane (O) at an angle of greater than or equal to 30°. A pneumatic radial tire as claimed in claim 1 or 2, characterized in that said rubber reinforcing layers (7) each have a cross-sectional shape such that both sidewalls of said tire have a substantially uniform thickness. A pneumatic radial tire as claimed in any of claims 1 to 3, characterized in that said auxiliary layer (8) is a single layer of rubber coated aramid cords. A pneumatic radial tire as claimed in any of claims 1 to 4, further characterized by a cap layer positioned radially outside said belt layer (4). A pneumatic radial tire as claimed in claim 5, characterized in that said cap layer is formed by winding a plurality of heat shrinking cords in a rubber coated strip spirally in the peripheral direction at the entire periphery or a predetermined region of the periphery of the belt layer (4). A pneumatic radial tire as claimed in any of claims 1 to 6, characterized in that said auxiliary layer (8) has a width narrower than that of said belt layer (4). A pneumatic radial tire as claimed in any of claims 1 to 7, characterized in that the auxiliary layer (8) is disposed adjacent the belt layer (4).

Inventors: TSUDA TORU, TSUDA, TORU
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1996
Main classification: B60C17
IPC codes: B60C17, B60C9