阅读说明：本技术 充气轮胎 (Pneumatic tire ) 是由 竹森谅平 长安政明 笹谷雄贵 丹野笃 甲田啓 松田淳 于 2018-11-19 设计创作，主要内容包括：本发明提供一种在侧壁部具备胎侧增强层的充气轮胎,其改善胎圈部的结构,减轻轮胎重量,同时使嵌合压和耐轮辋脱离性良好。在将由子午线剖面中的胎圈钢丝5A的多个环绕部分的共同切线形成的多边形作为胎圈芯5的外廓形状时,外廓形状在轮胎径向外侧具有单一的顶点51,使夹住该顶点51的两边所成内角θ1为锐角,使外廓形状的底边52相对于轮胎宽度方向在2°～9°的范围内倾斜,将胎体层4在各胎圈部3中沿胎圈芯5的周缘弯曲并折回,使胎体层4的折回部4B从胎圈芯5的轮胎径向外侧端的位置与主体部4A接触并朝向各侧壁部2侧延伸。(The invention provides a pneumatic tire with a side reinforcing layer on a side wall part, which improves the structure of a bead part, reduces the weight of the tire and has good embedding pressure and rim separation resistance. When a polygon formed by common tangents to a plurality of circumferential portions of a bead wire 5A in a meridian cross section is used as the outer shape of the bead core 5, the outer shape has a single apex 51 on the outer side in the tire radial direction, an inner angle θ 1 formed by two sides sandwiching the apex 51 is an acute angle, a base 52 of the outer shape is inclined in a range of 2 ° to 9 ° with respect to the tire width direction, the carcass layer 4 is bent and folded back along the circumferential edge of the bead core 5 in each bead portion 3, and a folded back portion 4B of the carcass layer 4 is brought into contact with the main body portion 4A from the position of the outer end in the tire radial direction of the bead core 5 and extends toward each sidewall portion 2 side.)

1. A pneumatic tire is provided with: a tread portion extending in a tire circumferential direction and having a ring shape; a pair of side wall portions disposed on both sides of the tread portion; and a pair of bead portions disposed on the inner side of the sidewall portion in the tire radial direction, the pneumatic tire including: a bead core provided in each bead portion; a carcass layer mounted between the pair of bead portions; a side wall reinforcing layer having a crescent-shaped cross section and provided on the inner side in the tire width direction of the carcass layer in the side wall portion, the pneumatic tire being characterized in that,

the bead core includes at least one bead wire wound in a tire circumferential direction, a plurality of wrapped portions of the bead wire forming at least one row aligned in a tire width direction and a plurality of layers overlapping in a tire radial direction in a meridian section,

when a polygon formed by common tangents of a plurality of circumferential portions of the bead wire in a meridian section is used as an outline shape of the bead core, the outline shape has a single vertex on the outer side in the tire radial direction, an inner angle formed by two sides sandwiching the vertex is an acute angle, the outline shape has a base extending obliquely with respect to the tire width direction on the inner side in the tire radial direction, the angle formed by the base with respect to the tire width direction is 2-9 DEG,

the carcass layer comprises: a main body portion that reaches each bead portion from the tread portion through each sidewall portion; and a folded-back portion that is bent and folded back along a peripheral edge of the bead core in each bead portion, that is in contact with the main body portion from a position of an outer end of the bead core in the tire radial direction, and that extends toward each sidewall portion side.

2. A pneumatic tire according to claim 1,

when a rubber layer located more inward in the tire radial direction than a portion of the carcass layer in contact with the bottom side of the outline is used as the under-core material, the under-core material compression ratio Cm calculated from the thickness H of the under-core material before rim assembly measured on a perpendicular line L2 that hangs from the apex of the outline toward the bottom side and the thickness H' of the under-core material after rim assembly measured on the perpendicular line L2 is 10% to 60% by the following equation (1),

Cm＝(H-H')/H×100 (1)。

3. a pneumatic tire according to claim 1 or 2,

when a portion between a toe and a heel in the bead portion is defined as a bead base, an outline of the bead base in a meridian cross section is curved to have two kinds of taper angles.

4. A pneumatic tire according to claim 3,

a length α in the tire radial direction from an intersection point P2 of a perpendicular line L2 that hangs from the apex to the base of the outer contour and the outer surface of the carcass layer that is located on the inner side of the bead core in the tire radial direction to the bending point of the contour line of the bead base and a length β in the tire radial direction from the intersection point P2 to the bead toe satisfy a relationship of 0.3 ≦ α/β ≦ 0.8.

5. A pneumatic tire according to any one of claims 1 to 4,

at least one of the corner portions located at both ends of the bottom side of the outline has an internal angle of 90 ° or more.

6. A pneumatic tire according to any one of claims 1 to 5,

in a meridian cross section, when an intersection point of a straight line L3, which is tangent to the tire axial direction inner side of the most tire axial direction-inner one of the plurality of circumferential portions of the bead wire and extends in the tire radial direction, and the outer surface of the carcass layer is P4, and an intersection point of the straight line L3 and the contour line of the bead base is P5, a distance T between the intersection points P4 and P5 is 3.1mm to 4.0 mm.

7. A pneumatic tire according to any one of claims 1 to 6,

in a meridian section, when an auxiliary line A1 and an auxiliary line A2 are drawn, a tire section width T1 on the auxiliary line A1 and a tire section width T2 on the auxiliary line A2 satisfy a relationship of 0.7. ltoreq.T 1/T2. ltoreq.1.5, the auxiliary line A1 passes through an intersection point P1 of a straight line L1 separated by 20mm from a bead toe toward the tire radial direction outer side and extending in parallel to the tire radial direction and a contour line of the outer surface of the side wall portion and is perpendicular to the carcass layer, and the auxiliary line A2 passes through the center of gravity of the bead core and extends in an inclined direction of the bottom side of the contour shape.

8. A pneumatic tire according to any one of claims 1 to 7,

only one of said carcass layers is provided.

Technical Field

The present invention relates to a pneumatic tire having a side reinforcing layer on a sidewall portion, and more particularly, to a pneumatic tire having an improved bead structure, reduced tire weight, and balanced compatibility between excellent rim separation resistance and low fitting pressure.

Background

In general, a bead core and a bead filler are embedded in a bead portion of a pneumatic tire. In a pneumatic tire (so-called run flat tire) capable of safely traveling a fixed distance even if a puncture occurs, a sidewall reinforcement layer (a layer made of hard rubber having a crescent-shaped cross section) for supporting a load of a vehicle at the time of the puncture is provided on a sidewall portion. In such a tire, the tire radial direction inner end portion of the side reinforcing layer may reach the vicinity of the bead portion, and the vicinity of the bead portion tends to be thick, so that the tire weight tends to increase. In recent years, there has been a strong demand for reduction in the weight of tires, and weight reduction has also been studied in runflat tires such as those described above. For example, patent document 1 proposes: in a pneumatic tire having a side reinforcing layer with a crescent-shaped cross section, the bead core is eliminated by designing the shape of the bead core, thereby reducing the weight of the tire.

On the other hand, in the run-flat tire, since the side reinforcing layer is present and the vicinity of the portion where the rim flange abuts is highly rigid, a force is generated that rotates the bead portion toward the tire inner side direction with the portion where the rim flange abuts as a fulcrum during run-flat running, and the rim is liable to be easily detached by the rotation force. In addition, in the case of the rim drop, the improvement of the rim drop resistance tends to increase the fitting pressure, which may result in a reduction in the rim assembling performance. In the tire of the above cited document 1, although a certain degree of rim drop resistance is obtained, the rim drop due to the above-mentioned rotational force with the portion where the rim flange abuts as a fulcrum is not considered, and such rim drop cannot be sufficiently prevented. Further, the fitting pressure is not sufficiently reduced. As described above, in the run-flat tire, a further measure for reducing the weight of the tire while achieving both excellent rim drop resistance and low fitting pressure in a balanced manner is required.

Disclosure of Invention

Problems to be solved by the invention

The invention aims to provide a pneumatic tire, in which a side wall part is provided with a side reinforcing layer, the structure of a bead part is improved, the weight of the tire is reduced, and simultaneously, the excellent rim separation prevention performance and the low embedding pressure are balanced and simultaneously achieved.

Means for solving the problems

A pneumatic tire according to the present invention for achieving the above object includes: a tread portion extending in a tire circumferential direction and having a ring shape; a pair of side wall portions disposed on both sides of the tread portion; and a pair of bead portions disposed on the inner side of the sidewall portion in the tire radial direction, the pneumatic tire including: a bead core provided in each bead portion; a carcass layer mounted between the pair of bead portions; and a side reinforcing layer having a crescent-shaped cross section provided on the inner side in the tire width direction of the carcass layer in the side wall portion, the bead core including at least one bead wire wound in the tire circumferential direction, the bead wire having a plurality of circumferential portions formed in at least one row arranged in the tire width direction and a plurality of layers overlapping in the tire radial direction in a meridian cross section, the outer profile having a single apex on the outer side in the tire radial direction, an inner angle formed by two sides sandwiching the apex being an acute angle, and a base inclined and extending with respect to the tire width direction and having an angle of 2 to 9 ° with respect to the tire width direction on the inner side in the tire radial direction, when a polygon formed by common tangents of the plurality of circumferential portions of the bead wire in the meridian cross section is taken as the outer profile of the bead core, the carcass layer comprises: a main body portion that reaches each bead portion from the tread portion through each sidewall portion; and a folded portion that is bent and folded along a peripheral edge of the bead core in each bead portion, contacts the main body from a position of an outer end of the bead core in the tire radial direction, and extends toward each sidewall portion side.

Effects of the invention

In the present invention, since the bead core has the above-described structure, the number of turns of the bead wire is reduced on the apex side of the outline shape, while the number of turns of the bead wire is sufficiently secured on the base side of the outline shape, it is possible to reduce the amount of bead wire used to reduce the weight of the tire while maintaining sufficient performance as the bead core to secure the durability of the tire. Further, since the bead core carcass having such a shape is bent and folded back, only the bead core is substantially present in the closed region surrounded by the main body portion and the folded-back portion of the carcass layer, and therefore, the tire weight can be reduced as compared with a tire having a conventional bead filler. Further, since no bead core is present, the rigidity can be appropriately suppressed, and the rim can be prevented from coming off due to a rotational force with a portion where the rim flange abuts as a fulcrum. In this case, when the carcass layer is folded back while being flexed, the bead core has the aforementioned shape having a single apex, and therefore, the carcass layer can be prevented from being sharply bent. Further, since the folded-back portion of the carcass layer is in contact with the main body portion, failure due to stress concentration at the terminal end of the folded-back portion can be prevented. In addition, the bottom side of the outline shape is moderately inclined, so that the fitting pressure can be reduced and the rim assembling performance can be improved.

In the present invention, when the rubber layer located more inward in the tire radial direction than the portion of the carcass layer contacting the bottom side of the outline shape is used as the under-core material, the under-core material compression ratio Cm calculated from the thickness H of the under-core material before the rim assembly measured on the perpendicular line L2 that is drawn from the apex of the outline shape toward the bottom side and the thickness H' of the under-core material after the rim assembly measured on the perpendicular line L2 is preferably 10% to 60% by the following equation (1).

Cm＝(H-H')/H×100 (1)

In the present invention, it is preferable that, when a portion between the toe and the heel in the bead portion is a bead base portion, an outline of the bead base portion in the meridian cross section is curved to have two kinds of taper angles. This improves the shape of the bead base portion that abuts the rim, and is advantageous in that the fitting pressure is reduced while exhibiting excellent rim separation resistance.

In the present invention, it is preferable that a length α in the tire radial direction from an intersection point P2 of a perpendicular line L2 that hangs down from the apex to the base of the outer shape and the outer surface of the carcass layer located on the inner side in the tire radial direction of the bead core to the bending point of the contour line of the bead base and a length β in the tire radial direction from the intersection point P2 to the bead toe satisfy a relationship of 0.3. ltoreq. α/β. ltoreq.0.8.

In the present invention, it is preferable that at least one of the corner portions located at both ends of the bottom side of the outline shape has an internal angle of 90 ° or more. This prevents disturbance of the arrangement of the bead wires during vulcanization, and improves the shape of the bead core after vulcanization, which contributes to securing excellent rigidity and reducing the weight of the tire.

In the present invention, it is preferable that, in a meridian cross section, when an intersection point of a straight line L3 extending in the tire radial direction and being tangent to the tire axial direction inner side of the most inner circumferential portion in the tire axial direction among the plurality of circumferential portions of the bead wire is P4 and an intersection point of a straight line L3 and the outer surface of the carcass layer is P5, a distance T between the intersection points P4 and P5 is 3.1mm or more and 4.0mm or less, whereby a positional relationship among the respective elements constituting the bead portion becomes good, and excellent rim drop resistance is exhibited, and the fitting pressure is reduced.

In the present invention, it is preferable that, in the meridian cross section, when the auxiliary line a1 and the auxiliary line a2 are drawn, the tire section width T1 on the auxiliary line a1 and the tire section width T2 on the auxiliary line a2 satisfy a relationship of 0.7 ≦ T1/T2 ≦ 1.5, the auxiliary line a1 passes through an intersection point P1 of a straight line L1 separated by 20mm from the bead toe toward the tire radial direction outer side and extending parallel to the tire radial direction and the contour line of the outer surface of the side wall portion and is perpendicular to the carcass layer, and the auxiliary line a2 passes through the center of gravity of the bead core and extends in the inclination direction of the bottom side of the outline shape.

In the present invention, it is preferable that the carcass layer has only one layer. This can suppress the amount of use of the carcass layer, and is advantageous for reducing the weight of the tire.

In the present invention, "normal Rim" measured in a state where a TIRE Rim is assembled to a normal Rim and filled with normal internal pressure means that in a specification system including the specification based on the TIRE, the specification is defined for each TIRE, and for example, JATMA is used as a standard Rim and TRA is used as a "Design Rim" (Design Rim), or ETRTO is used as a "Measuring Rim" (measurement Rim), "normal internal pressure" means that in the specification system including the specification based on the TIRE, the air pressure defined for each TIRE by each specification is the maximum air pressure in the case of JATMA and TRA is used as an "TIRE ROAD limit under VARIOUS cold inflation PRESSURES (TIRE ROAD L IMITS AT v vehicles CO L DINF L requirements)" and if ETRTO is used as ETRTO be "inflation pressure (inflation pressure L) in the case of a car passenger", but 180kPa is used for a TIRE.

Drawings

Fig. 1 is a radial half-sectional view of a pneumatic tire constructed by an embodiment of the present invention.

Fig. 2 is an enlarged explanatory view showing the vicinity of the bead portion of fig. 1.

Fig. 3 is an explanatory view showing an enlargement of the bead core of fig. 2.

Figure 4 is a schematic view of a bead core constructed from another embodiment of the present invention.

Fig. 5 is an enlarged explanatory view showing the vicinity of the bead portion of fig. 1.

Fig. 6 is an enlarged explanatory view showing the vicinity of the bead portion of fig. 1.

Fig. 7 is an explanatory view schematically showing bead structures of a conventional example and a comparative example.

Detailed Description

Hereinafter, the configuration of the present invention will be described in detail with reference to the drawings.

As shown in fig. 1, the pneumatic tire of the present invention includes a tread portion 1 extending in a tire circumferential direction and having a ring shape, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3 disposed on the inner side of the sidewall portions 2 in the tire radial direction, and in fig. 1, C L represents a tire equator.

A carcass layer 4 is mounted between a pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the vehicle inner side to the vehicle outer side around bead cores 5 disposed in the respective bead portions 3. In the following description, a portion reaching each bead portion 3 from the tread portion 1 through each sidewall portion 2 is referred to as a body portion 4A, and a portion folded around a bead core 5 in each bead portion 3 and extending toward each sidewall portion 2 side is referred to as 4B. In the present invention, since basic performances such as rim drop resistance can be ensured by the structure of the bead portion 3 described later, it is not necessary to obtain these basic performances by providing a plurality of carcass layers 4, and the number of layers of the carcass layers 4 can be reduced. It is particularly preferred that only one carcass layer 4 is provided, as shown in the figures.

As shown in fig. 2 and 3 in an enlarged manner, the bead core 5 includes at least one bead wire 5A wound in the tire circumferential direction, and a plurality of circumferential portions of the bead wire 5A form at least one row aligned in the tire width direction and a plurality of layers overlapping in the tire radial direction. In the present invention, in the meridian cross section, when the plurality of circumferential portions of the bead wire 5A are formed in rows and layers as described above, a so-called single winding structure in which a single bead wire 5A is continuously wound may be employed, or a so-called layer winding structure in which a plurality of bead wires 5A are wound in a state of being aligned may be employed. In the illustrated example, there are stacked: a structure of a total of five layers including three rows of the surrounding portions, four rows of the surrounding portions, three rows of the surrounding portions, two rows of the surrounding portions, and one row of the surrounding portions in this order from the innermost side in the radial direction of the tire. In the following description, this structure is referred to as a "3 +4+3+2+1 structure". Similarly, in the following description, the layered structure of the bead wires 5A is represented in the same manner as the number of rows included in each layer is connected by "+" in order from the innermost layer in the tire radial direction. Also, in the bead core 5 of the illustrated example, the bead cores 5A are stacked in a stacked shape. The term "stacked" refers to a stacked structure in which the centers of three surrounding portions which are in contact with each other form a substantially regular triangle, and the stacked structure has a high packing ratio and is also referred to as a hexagonal packing arrangement.

At this time, if a polygon formed by common tangents to a plurality of circumferential portions of the bead wire 5A in a meridian cross section is taken as an outline shape (broken line in the drawing) of the bead core 5 for each bead core 5, the outline shape has a single apex 51 on the outer side in the tire radial direction and has a base 52 on the inner side in the tire radial direction so as to face the apex 51. In particular, the bead core 5 of the illustrated example has the 3+4+3+2+1 structure described above, and therefore has the outline shape of a pentagon. In the present invention, the inner angle θ 1 between the two sides of the apex 51 is always an acute angle, and the bead core 5 as a whole has a tapered shape in which the width gradually decreases from a portion having the maximum width toward the tire radial direction outer side (hereinafter, this shape may be referred to as "outer diameter side wedge shape"). Further, in the present invention, the bottom side 52 extends while being inclined with respect to the tire width direction, and the bead core 5 is formed in an inclined structure as a whole. More specifically, the bottom side 52 is inclined outward in the tire radial direction with respect to the tire width direction from the tire width direction inner side toward the tire width direction outer side. At this time, the angle θ 2 of the bottom side 52 with respect to the tire width direction is set to 2 ° to 9 °.

The carcass layer 4 is folded back around the bead core 5 as described above, but the bead core 5 of the present invention has a special shape (outer diameter side wedge shape) as described above, and therefore the carcass layer 4 is curved along the periphery of the bead core 5. For example, in the illustrated example, the bead core 5 satisfies the above-described setting, and as a result, the cross-sectional shape is substantially pentagonal, and therefore the carcass layer 4 extending along the periphery thereof is also bent into a substantially pentagonal shape. Further, the portion of the folded portion 4B of the carcass layer 4 that is located further toward the tire radial direction outer side than the tire radial direction outer end of the bead core 5 is in contact with the main body portion 4A of the carcass layer 4, and extends toward each sidewall portion 2 side along the main body portion 4A of the carcass layer 4. As a result, a closed region surrounding the bead core 5 is formed by the main portion 4A and the folded portion 4B of the carcass layer 4.

A plurality of (two in the illustrated example) belt layers 6 are embedded in the outer circumferential side of the carcass layer 4 in the tread portion 1. Each belt layer 6 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction. The reinforcing cords are arranged between the layers such that the reinforcing cords cross each other. In these belt layers 6, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range of, for example, 10 ° to 40 °. Further, a belt reinforcing layer 7 is provided on the outer peripheral side of the belt layer 6. In particular, in the illustrated example, two layers of a full cover layer covering the entire width of the belt layer 6 and an edge cover layer covering only both end portions of the belt reinforcing layer 7 are provided. The belt reinforcing layer 7 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 7, the angle of the organic fiber cord with respect to the tire circumferential direction is set to, for example, 0 ° to 5 °.

A side reinforcing layer 8 having a crescent-shaped cross section is disposed on the inner side of the carcass layer 4 in the tire width direction in the sidewall portion 2. The side reinforcing layer 8 is made of rubber harder than the other rubbers constituting the side wall portion 2. Specifically, the rubber constituting the side reinforcing layer 8 has A JIS-A hardness of, for example, 70 to 80 and A modulus at 100% elongation of, for example, 9.0 to 10.0 MPA. The sidewall reinforcing layer 8 having such physical properties can support a load at the time of air leakage based on its rigidity to perform run-flat running.

In the present invention, since the bead core 5 has a special shape (outer diameter side wedge shape) as described above, the number of turns of the bead wire 5A is reduced on the side of the apex 51 of the outline shape, while the number of turns of the bead wire is sufficiently ensured on the side of the bottom 52 of the outline shape, so that the tire can be made lightweight while maintaining sufficient performance as the bead core 5 and ensuring durability of the tire, and the amount of the bead wire 5A used is reduced. Further, since the carcass layer 4 is folded back while being curved along the bead core 5 of this shape, substantially only the bead core 5 is present in the closed region surrounded by the main body portion 4A and the folded-back portion 4B of the carcass layer 4, and therefore, the tire weight can be reduced as compared with a tire having a conventional bead filler. Further, since the bead core is not present, the rigidity is appropriately suppressed, and the rim can be prevented from coming off due to the rotational force with the portion where the rim flange abuts as the fulcrum. At this time, when the carcass layer 4 is bent and folded back, the bead core 5 has the shape having the single apex 51 as described above, and therefore, the carcass layer 4 can be prevented from being sharply bent. Further, since the folded-back portion 4B of the carcass layer 4 is in contact with the main body portion 4A, failure due to stress concentration at the terminal end of the folded-back portion 4B can be prevented. In addition, the bottom side 52 of the outline shape is moderately inclined, so that the fitting pressure can be reduced and the rim assembling performance can be improved.

In the above-described structure, if the inner angle θ 1 is an obtuse angle, the bead filler needs to be disposed on the outer side of the bead core 5 in the tire radial direction in order to properly fold the carcass layer 4 around the bead core 5, and thus it is difficult to effectively reduce the tire weight. If the angle θ 2 of the bottom side 52 is smaller than 2 °, the fitting pressure cannot be sufficiently reduced. If the angle θ 2 of the bottom side 52 exceeds 9 °, the rim drop resistance cannot be improved.

In each bead core 5, as shown in fig. 3, when the maximum width of the bead core 5 is W0, the width of the innermost layer in the tire radial direction is W1, and the width of the outermost layer in the tire radial direction is W2, it is preferable that these widths satisfy the relationship of W1> W2 and W2 ≦ 0.5 × W0, further, it is preferable that the layer having the maximum width W0 among the plurality of layers constituting the bead core 5 is located on the inner side in the tire radial direction than the tire radial direction center position of the bead core 5, it is necessary to describe that the widths W0 to W2 are the lengths in the tire width direction between the ends on the outer side in the tire width direction of each layer in both outer sides in the tire width direction, as shown in the drawing, if the widths W0, W1, W2 fail to satisfy the above relationship, the shape of the bead core 5 becomes inappropriate, the shape of the bead portion 3 cannot be stabilized, and particularly, if the relationship of W1 ≦ W2, W2>0. 0.5 × W0, the rim contact portion is difficult to suppress the increase of the rim flange, and the rim contact resistance of the rim contact portion is increased, and the rim contact resistance of the rim.

The specific shape of the bead core 5 is not particularly limited as long as the above relationship is satisfied. For example, the shape shown in fig. 4 may be adopted. The example of fig. 4 satisfies the above-described relationship, and thus conforms to the "outer diameter wedge shape" of the present invention. Specifically, fig. 4 (a) has a stacked 5+4+3+2+1 structure, fig. 4 (b) has a stacked 4+4+3+2+1 structure, and fig. 4 (c) has a 4+4+3+2+1 structure in which the innermost layer in the tire radial direction and the adjacent layer on the inner side in the tire radial direction are stacked not in series (a stacking manner in which the circumferential portions adjacent to each other in the tire radial direction are vertically stacked in the tire width direction).

In the bead core 5 having such various shapes, the inner angle θ 3 of the corner portion located at both ends of the bottom side 52 of the outline shape is preferably 90 ° or more, and more preferably 100 ° or more and 150 ° or less. That is, in the example of fig. 4, the structures of fig. 4 (b) and 4 (c) are preferable. By setting the inner angle θ 3 in this manner, it is possible to prevent the bead wires 5A from being arranged in disorder during vulcanization and to improve the shape of the bead core 5 after vulcanization, which is advantageous in that excellent rigidity can be secured and the weight of the tire can be reduced. If the inner angle θ 3 is smaller than 90 °, the number of turns of the bead wire 5A cannot be sufficiently reduced, and the effect of reducing the tire weight is reduced. Further, if the inner angle θ 3 is smaller than 90 °, the bead wires 5A located at both ends of the bottom side 52 of the outer shape are easily affected by the rubber flow during vulcanization, and it is difficult to maintain the shape of the bead core 5 after vulcanization satisfactorily.

In any of the configurations shown in fig. 4, since at least a part of the bead wires are stacked in a stacked state, the bead wires 5A can be arranged closer to each other to increase the filling ratio of the bead wires 5A as compared with the bead wires having a configuration in which the entire structure is stacked in series. As a result, the rigidity and the pressure resistance of the bead portion 3 can be ensured well while maintaining the running performance, and the weight of the tire can be reduced to exhibit these performances in a balanced manner. When the filling rate of the bead wires 5A is focused, it is preferable to stack all the bead wires 5A in a stacked state as shown in fig. 4 (a) and 4 (b).

Further, regarding the shape of the bead core 5, in order to improve stability of the shape of the entire bead core 5, it is preferable that the shape of the entire bead core 5 is line-symmetrical with respect to the center of the bead core 5 in the tire width direction. From this viewpoint, the shapes as shown in fig. 4 (a) and 4 (c) are preferable.

The shape of each of these bead cores 5 can be appropriately selected in consideration of the entire structure of the pneumatic tire, important characteristics, and the like from the various viewpoints described above.

The structure of the bead wire 5A itself is not particularly limited, but in view of satisfying both reduction in tire weight and improvement in rim drop resistance, the average diameter is preferably 0.8mm to 1.8mm, more preferably 1.0mm to 1.6mm, and further preferably 1.1mm to 1.5 mm. Further, the total cross-sectional area of the bead wires 5A (the sum of the cross-sectional areas of the surrounding portions of the bead wires 5A included in the meridian section of each bead core 5) is preferably 10mm²～50mm²More preferably 15mm²～48mm²More preferably 20mm²～45mm²It is preferable. If the average diameter of the bead wire 5A is less than 0.8mm, the effect of improving the rim drop resistance is limited, and if the average diameter of the bead wire 5A is more than 1.8, the effect of reducing the weight of the tire is limited. If the total cross-sectional area of the bead wire 5A is less than 10mm²The effect of improving the rim drop resistance is limited, and if the total cross-sectional area of the bead wire 5A is larger than 50mm²The effect of reducing the weight of the tire becomes limited.

As described above, in the present invention, in the closed region formed by the main body portion 4A and the folded-back portion 4B of the carcass layer 4, substantially only the bead core 5 is present, and the bead filler or the tire constituent member similar thereto (the member which is disposed outside the bead core 5 in the tire radial direction, and is enclosed by the main body portion 4A and the folded-back portion 4B of the carcass layer 4 to improve the rigidity from the bead portion 3 to the sidewall portion 2) as used in the conventional pneumatic tire is not disposed, that is, even if there is an insulating rubber covering the bead wire 5A, or a rubber filling a minute gap formed between the bead core 5 and the carcass layer 4, a bead core having a large volume as used in the conventional pneumatic tire is not used, the tire weight can be effectively reduced by such a substantially no bead core structure, and at this time, if the ratio of the total area a of the rubber present in the closed region to the area a of the closed region in the radial cross section (a/a × 100%) is set as the rubber occupancy ratio of the closed region, the rubber occupancy is preferably 0.1% to 15%, and therefore, the rubber occupancy of the closed region is not more preferably 0.1% as the rubber occupancy of the closed region.

In the case where only the bead core 5 is substantially present in the closed region as described above, a filler layer (not shown) may be provided on the outer side in the tire width direction of the carcass layer 4 (the main body portion 4A and the folded-back portion 4B) in the sidewall portion 2 in accordance with the tire size and the desired performance, the filler layer may be provided in cooperation with the sidewall reinforcing layer 8 to ensure the rigidity of the sidewall portion 2, unlike the bead core provided between the main body portion 4A and the folded-back portion 4B of the carcass layer 4 in the conventional pneumatic tire, and the filler layer may be provided merely in place of the conventional bead core layer, so that the tire weight does not increase as compared with the tire having the conventional bead core layer even if the filler layer is provided, it is desirable to associate the structure of the filler layer and the like with the sidewall reinforcing layer 8 in order to more effectively reduce the tire weight, and for example, the relationship between the cross-sectional area S2 and the hardness H2 of the sidewall reinforcing layer with respect to the cross-sectional area S1 and the H1 of the sidewall reinforcing layer 8 satisfies 0.15 (S2 × H3875H) and the weight of the filler layer 60, and the filler layer may be appropriately used to suppress the weight of the filler layer, thereby achieving the effect of the tire.

As described above, in the pneumatic tire provided with the side reinforcing layer 8, when the vicinity of the portion where the rim flange abuts is made highly rigid, there is a possibility that a force rotating the bead portion toward the tire inner side direction with the portion where the rim flange abuts as a fulcrum is generated during run-flat running to induce rim detachment, and therefore, it is effective to improve the rim detachment prevention property by optimizing the structure in the vicinity of the portion where the rim flange abuts, that is, in the meridian cross section, when the auxiliary line a1 and the auxiliary line a2 are drawn out as shown in fig. 2, it is good that the relationship between the tire section width T1 on the auxiliary line a1 and the tire section width T2 on the auxiliary line a2 satisfies preferably 0.7. T1/T2. 1.5, more preferably 0.8. T1/T2. 1.0, the auxiliary line a1 passes through the intersection point P of the straight line L separated from the bead toe toward the tire radial direction outer side and extending in parallel to the tire radial direction and is made sufficiently smaller than the tire side wall portion P L, and the tire bead portion P3, and the tire bead portion where the rim flange contacts the rim flange 583, and the tire is made less than the tire support point P3, and the tire support point P3, and the tire support point T52, and the tire support point T3, and the tire support point T52, and the tire bead edge of the tire bead portion is made to improve the tire support point T52, and the tire bead edge of the tire bead portion for suppressing rim detachment prevention property by the tire.

In the bead portion 3, it is preferable that, when a portion between the toe and the heel is a bead base portion, as shown in fig. 2, an outline of the bead base portion in a meridian cross section is curved to have two kinds of taper angles. If the taper angle in the tire width direction with respect to the toe side is θ 4 and the taper angle in the tire width direction with respect to the heel side is θ 5, it is preferable that these taper angles satisfy the relationship of θ 4> θ 5. These taper angles are not particularly limited, but θ 4 may be, for example, 15 ° to 25 °, and θ 5 may be, for example, 5 ° to 10 °. With such a configuration, the shape of the bead base portion in contact with the rim becomes favorable, and therefore, it is advantageous to reduce the fitting pressure to improve the rim assembling property and to improve the rim separation resistance.

At this time, as shown in fig. 5, assuming that α is a length in the tire radial direction from an intersection point P2 of a perpendicular line 632 that hangs down from an apex 51 of the outer shape to a bottom side 52 and an outer surface of the carcass layer 4 that is located inward in the tire radial direction of the bead core 5 to a bending point P3 of a contour line of the bead base, and α is a length in the tire radial direction from an intersection point P2 to a bead toe, it is preferable that the lengths α, α satisfy 0.3 ≦ α/β ≦ 0.8, and more preferably satisfy a relationship of 0.45 ≦ α/β ≦ 0.65.

Further, as shown in fig. 6, in the meridian cross section, it is preferable that when an intersection point of a straight line L3, which is tangent to the inside of the tire axial direction of the most inside circumferential portion in the tire axial direction among the plurality of circumferential portions of the bead wire 5A and extends in the tire radial direction, and the outer surface of the carcass layer 4 is P4, and an intersection point of a straight line L3 and the contour line of the bead base is P5, a distance T between the intersection points P4 and P5 is 3.1mm or more and 4.0mm or less, whereby the positional relationship of the respective elements constituting the bead portion 3 becomes good, which is advantageous in reducing the fitting pressure to improve the rim assembling property, and is advantageous in improving the rim separation resistance property.

In each bead portion 3, when a rubber layer located on the tire radial direction inner side of a portion of the carcass layer 4 in contact with the bottom side 52 of the outline shape of the bead core 5 is used as the under-core material by the following equation (1), the under-core material compression ratio Cm calculated from the thickness H of the under-core material before rim assembly measured on the perpendicular line L2 hanging from the apex 51 of the outline shape to the bottom side 52 and the thickness H' of the under-core material after rim assembly measured on the perpendicular line L2 hanging from the apex of the outline shape to the bottom side is preferably 10% to 60%, more preferably 15% to 50%, and still more preferably 20% to 45%.

Cm＝(H-H')/H×100 (1)

The above-described structures of the respective portions may be combined as appropriate. In any case, in the pneumatic tire having the above-described structure, the structure of the bead portion 3 is improved, and therefore, it is possible to reduce the weight of the tire while maintaining the durability of the tire, and to improve the fitting pressure and the rim drop resistance.