JP2016203779A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire which achieves both of riding comfort and uneven wear resistant performance even when used as a thin gauge side wall tire or a tire with a small rim width.SOLUTION: A pneumatic tire is provided in which a value RW/TW obtained by dividing a rim width RW (mm) by a nominal cross sectional width TW (mm) is less than 0.78. When a height of a radial direction outer end of a carcass 5 from an innermost end B of the carcass is h in a rim assembly state with an internal pressure 0, a height CWh of a width direction outermost end CW of the carcass from the innermost end is within a virtual region L satisfying 0.47h<CWh<0.67h in the rim assembly state; an acute angle θ between an inclined linear AL made by connecting the width direction outermost end and the innermost end and an axis line satisfies θ≥63° in the rim assembly state; and a portion of the carcass between the width direction outermost end and the innermost end is within a virtual region in which a distance from the inclined linear is 0.045h in the rim assembly state.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire.

  Conventionally, by regulating the shape of the tread surface such as the tread pattern and the radius of curvature of the outer surface of the tread, a tire in which the distribution of the contact pressure is made uniform and the uneven wear of the tread shoulder portion is suppressed is known (for example, Patent Document 1).

JP-A-6-199105

  In recent years, as a means for coping with the reduction in fuel consumption of a tire that is particularly desired from the viewpoint of reducing the environmental load, development of a tire with a thinner sidewall rubber has been progressing in order to reduce the weight of the tire. In tires with thin gauges of sidewall rubber and tires for light vehicles, the tire gauge measured along the normal of the carcass in the sidewall in the cross section along the tire width direction is thin, so that the rigidity in that part Decreases, and hence the lateral spring constant decreases. Then, as shown in FIG. 3, when the side force SF acts on the tire in the tire width direction when the vehicle turns, the side portion on the side force acting side sinks into the ground and is opposite to the side force acting side. The side portion on the side is greatly deformed so as to float up from the ground, with the portion F ′ where the gauge is thinned as a bending node position (fulcrum). At this time, the contact length of the shoulder portion sinking into the ground increases, and the force borne by the shoulder portion increases, thereby promoting the wear of the shoulder portion sinking into the ground.

  Especially in tires with thin gauge rubber, the rigidity of the sidewall is reduced and the bead area is easily deformed when turning, and in the case of light vehicle tires, the ratio of the rim width to the tread width is small. In addition, the periphery of the bead portion is easily deformed during turning, and in any case, the contact length of the shoulder portion is remarkably increased, and uneven wear becomes more prominent. For this reason, tires with thin sidewall rubber and light vehicle tires require higher uneven wear resistance than the uneven wear resistance obtained by regulating the tread surface shape of conventional passenger car tires. Has been.

  As a technique for suppressing large deformation around the bead part during turning, there is a technique of increasing the rigidity of the bead part periphery by increasing the thickness of the bead part or by making the bead part material harder. However, in these methods, the weight of the tire increases, and the weight reduction of the tire is impaired, and the ride performance may be impaired.

  Therefore, the present invention provides a tire that can obtain high uneven wear resistance while maintaining riding comfort even in a tire with a thin gauge of sidewall rubber and a tire with a relatively small rim width for a light vehicle. The purpose is to do.

The pneumatic tire of the present invention includes a carcass composed of at least one carcass ply straddling a pair of bead cores in a toroidal shape, and a value RW obtained by dividing a rim width RW (mm) by a nominal TW (mm) of a tire cross-sectional width. / TW is a pneumatic tire smaller than 0.78, and in a rim assembled state in which the tire is assembled to an applicable rim and is not loaded with substantially no internal pressure, in a cross section along the tire width direction When the carcass height, which is the height of the tire in the tire radial direction from the innermost end in the tire radial direction of the carcass, is h, the tire rim assembly state extends along the tire width direction. In the cross-section, the outermost end in the tire width direction of the carcass has a tire radial direction height CWh from the innermost end in the tire radial direction of the carcass satisfying 0.47h <CWh <0.67h. An inclined straight line in the tire radial direction virtual region and connecting the outermost end in the tire width direction of the carcass and the innermost end in the tire radial direction of the carcass in a cross section along the tire width direction in the rim assembled state And an acute angle θ formed by a straight line parallel to the tire rotation axis is θ ≧ 63 °, and in the rim assembly state, in the cross section along the tire width direction, the carcass is the outermost end in the tire width direction. A portion between the innermost end in the tire radial direction exists in a virtual region sandwiched between two parallel straight lines having a distance from the inclined straight line of 0.045h.
According to the present invention, a pneumatic tire capable of obtaining high uneven wear resistance while maintaining riding comfort performance even in a tire having a thin gauge of sidewall rubber and a tire having a relatively small rim width for a light vehicle. Can be provided.

“Applicable rim” is an industrial standard effective in the area where tires are produced and used. In Japan, JATMA (Japan Automobile Tire Association) JATMA YEAR BOOK, and in Europe, ETRTO (The European Tire and Rim). STANDARDDS MANUAL of Technical Organization, TRA (The Tire and Rim Association, Inc.) YEAR BOOK, etc. in the United States, etc. Rim).
The “specified internal pressure” refers to the air pressure corresponding to the maximum load capacity in the applicable size / ply rating described in the above JATMA YEAR BOOK and the like.

“Rim width” refers to the nominal dimension of the rim width of the applicable rim.
“Nominal width of tire cross section” is, for example, the nominal width of the cross section of a tire for each tire size specified in JATMA Year Book. For example, when the tire size is “195 / 65R15”, The width obtained by adding unit millimeters to “195”. In addition, when the area where a tire is produced or used is an area other than Japan, the nominal width refers to a tire that conforms to an industrial standard applied to the area.

  “Substantially not filled with internal pressure” means that the internal pressure of the tire is, for example, 30 to 50 kpa, a very low internal pressure that is the minimum required for the tire to support its own load and maintain the shape when the rim is assembled. This is the case.

The “outermost end in the tire width direction of the carcass” is the outermost end in the tire width direction of the ply on the outermost side in the tire radial direction when the carcass is composed of a plurality of plies. Further, when the carcass has a main body portion and a folded portion, it is the outermost end in the tire width direction of the main body portion. Furthermore, when the outermost end in the tire width direction of the carcass extends in the tire radial direction, it indicates the center.
“The innermost end in the tire radial direction of the carcass” is the innermost end in the tire radial direction of the ply on the innermost side in the tire radial direction when the carcass is composed of a plurality of plies. When the carcass extends in the tire width direction at the innermost end in the tire radial direction, it indicates the center thereof.
Further, in the case where the carcass has a main body portion and a turn-back portion, the regulations by the carcass are based on the outer surface in the tire width direction of the main body portion of the carcass unless otherwise specified.

In the pneumatic tire of the present invention, the carcass has two or more belts in a cross section along the tire width direction in a rim assembled state in which the tire is assembled to an applied rim and is not loaded with an internal pressure substantially. The portion between the overlapping end position on the radial straight line passing through the tire width direction outer end of the overlapping virtual region where the layers overlap in the tire radial direction and parallel to the tire equator plane and the outermost end in the tire width direction is the diameter. A first arc connecting a directional straight line and an axial straight line passing through the outermost end in the tire width direction and parallel to the tire rotation axis; a radius of curvature of 0.36 h; the radial straight line and the axial straight line; It is preferable to exist in an arcuate virtual region sandwiched between a second arc having a radius of curvature of 0.42h in parallel with the first arc.
Thereby, the ground contact shape change when the side force is applied to the tire is reduced, and uneven wear of the shoulder portion can be further suppressed.

  According to the present invention, a pneumatic tire capable of obtaining high uneven wear resistance while maintaining riding comfort performance even in a tire having a thin gauge of sidewall rubber and a tire having a relatively small rim width for a light vehicle. Can be provided.

1 is a tire width direction cross-sectional view showing an embodiment of a pneumatic tire of the present invention. It is a figure which shows typically the specific example of the some belt layer which comprises a belt. It is a tire width direction sectional view for explaining modification at the time of side force action of a pneumatic tire.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of the pneumatic tire of the present invention (hereinafter sometimes simply referred to as “tire”). In the example of FIG. 1, the tire structure is symmetric with respect to the tire equator plane C, but may be asymmetric with respect to the tire equator plane C.

  The tire shown in FIG. 1 is continuous from the tread portion 1, a pair of sidewall portions 2 extending inward in the tire radial direction from both ends in the tire width direction of the tread portion 1, and from the sidewall portions 2 to the inside in the tire radial direction. It consists of a pair of bead parts 3. This tire includes a bead core 4a and a bead filler 4b respectively embedded in the bead portion 3, and a carcass 5 including at least one layer (one layer in the example) of a carcass ply extending between the bead cores 4a. Have. The carcass ply is a radial carcass formed by rubber covering a cord made of steel or organic fiber. In the example of the figure, the carcass 5 extends from the both ends of the main body 5a in a toroidal manner between the bead cores 4a, and extends from both ends of the main body 5a toward the outer side in the tire width direction around the bead core 4a. It includes a pair of folded portions 5b that are folded back.

  In the tire according to an embodiment of the present invention shown in FIG. 1, a belt 6 and a tread rubber 7 composed of a plurality of belt layers are sequentially arranged outside the crown area of the carcass 5 in the tread portion 1 in the tire radial direction. A tread pattern including a plurality of (three in FIG. 1) circumferential grooves 1a extending in the tire circumferential direction, for example, is formed on the tire outer surface of the tread rubber 7.

  A tire according to an embodiment of the present invention is a pneumatic tire having a value RW / TW obtained by dividing a rim width RW (mm) by a nominal section width TW (mm) of the tire and smaller than 0.78. In such a tire, since the ratio of the rim width to the tread width is generally smaller than that of other tires, deformation around the bead portion 3 during turning is generally larger than that of other tires. Therefore, the configuration of an embodiment of the present invention that suppresses deformation around the bead portion 3 is a pneumatic tire in which the deformation around the bead portion 3 during turning is large, and the RW / TW value is less than 0.78. In, there is a remarkable effect.

  Hereinafter, the dimensions and the shape of the tire in a cross section along the tire width direction will be described in a state where the tire is assembled to the applied rim and the internal pressure is not substantially filled and no load is applied.

The tire according to one embodiment of the present invention is assembled in the tire width direction in the tire width direction shown in FIG. 1 in the rim assembly state in which the tire is assembled to the applied rim and is not substantially filled with internal pressure and is unloaded. In the cross section, when the carcass height, which is the height in the tire radial direction from the innermost end in the tire radial direction of the carcass 5 at the outer end in the tire radial direction of the carcass 5, is h, the outermost side in the tire width direction of the carcass 5 It is necessary that the end CW is in the tire radial virtual region where the tire radial height CWh from the tire radial innermost end B of the carcass 5 satisfies 0.47h <CWh <0.67h.
If the tire radial direction height CWh of the carcass 5 outermost end CW in the tire width direction from the innermost end B in the tire radial direction of the carcass 5 is 0.47h or less, the side force during turning is added to the tire. In addition, the carcass 5 tends to have a shape in which the main body 5a portion of the carcass 5 in the vicinity of the bead portion 3 falls into the ground, and deformation around the bead portion 3 during turning cannot be sufficiently suppressed.
Further, when the tire radial direction height CWh from the tire radial direction innermost end B of the carcass 5 in the tire width direction outermost end CW of the carcass 5 is 0.67 h or more, the increase in the carcass tension increases, and the bead is increased. There may be concerns about deterioration of durability.
On the other hand, the outermost end CW in the tire width direction of the carcass 5 is in the tire radial direction virtual region where the tire radial height CWh from the innermost end B in the tire radial direction of the carcass 5 satisfies 0.47h <CWh <0.67h. In this case, the curvature of the portion of the main body portion 5a of the carcass 5 in the sidewall portion 2 is increased as a whole, so that a local decrease in tension is suppressed in the portion, and therefore the side force is reduced. The deformation of the tire during operation can be suppressed.

  In the tire according to an embodiment of the present invention, in the above-described rim assembly state, an inclined straight line AL connecting the tire width direction outermost end CW of the carcass 5 and the tire radial direction innermost end B of the carcass 5 and tire rotation The acute angle θ formed by a straight line parallel to the axis (in FIG. 1, indicated by a straight line connecting the innermost ends B in the tire radial direction of the carcass 5) needs to satisfy θ ≧ 63 °.

  If the acute angle θ formed by the inclined straight line AL connecting the outermost end CW in the tire width direction of the carcass 5 and the innermost end B in the tire radial direction of the carcass 5 and a straight line parallel to the tire rotation axis is smaller than 63 °. The carcass 5 tends to have a shape in which the main body portion 5a of the carcass 5 near the bead portion 3 falls into the ground, and the deformation around the bead portion 3 during turning cannot be sufficiently suppressed.

On the other hand, in one embodiment of the present invention, an acute angle formed by an inclined straight line AL connecting the outermost end CW in the tire width direction of the carcass 5 and the innermost end B in the tire radial direction of the carcass 5 and a straight line parallel to the tire rotation axis. Since θ is set to θ ≧ 63 °, the portion of the main body portion 5a of the carcass 5 between the outermost end CW in the tire width direction of the carcass 5 and the innermost end B in the tire radial direction of the carcass 5 is shown in FIG. With respect to the straight line connecting the innermost ends B in the tire radial direction of the carcass 5, the carcass 5 exists in a more standing state.
Therefore, the deformation of the bead part 3 when side force is applied to the bead part 3 at the time of turning can be a deformation approximate to a rigid body centered on the bead part 3. Therefore, the main body 5a of the carcass 5 is less likely to fall into the ground, and the moment applied to the bead 3 can be reduced, so that the rigidity of the entire bead 3 can be secured and the periphery of the bead 3 when turning. Can be sufficiently suppressed.

  In the tire according to the embodiment of the present invention, in the rim assembly state described above, the main body portion 5a of the carcass 5 has an inclined portion between the tire width direction outermost end CW and the tire radial direction innermost end B. It is necessary to exist in a virtual region L surrounded by two parallel straight lines IL1 and IL2 whose distance from the straight line AL is 0.045h.

  When a portion existing outside the virtual region L exists between the outermost end CW in the tire width direction and the innermost end B in the tire radial direction of the carcass 5 in the main body portion 5a of the carcass 5, The body portion 5a of the carcass 5 between the innermost end B in the tire radial direction cannot be shaped so as to extend substantially along the inclined straight line AL, the tension is reduced, and the bead at the time of side force action The deformation of the portion 3 cannot be sufficiently suppressed. Further, when the portion of the main body portion 5a of the carcass 5 between the outermost end CW in the tire width direction and the innermost end B in the tire radial direction exists outside the virtual region L, particularly outside the virtual region L in the tire width direction. Therefore, the body portion 5a of the carcass 5 in the vicinity of the bead portion 3 is likely to fall into the ground, and deformation around the bead portion 3 during turning cannot be sufficiently suppressed.

  On the other hand, in one embodiment of the present invention, the distance between the main body portion 5a of the carcass 5 between the tire width direction outermost end CW and the tire radial direction innermost end B is 0.045h from the inclined straight line AL. Since it exists in the virtual region L surrounded by the two parallel parallel lines IL1 and IL2, the carcass 5 in the bead portion 3 is not greatly curved, and has a shape closer to a straight line substantially along the inclined straight line AL. Therefore, the tension of the main body portion 5a of the carcass 5 in the bead portion 3 can be maintained, and deformation of the bead portion 3 during the side force action can be sufficiently suppressed.

  As described above, according to the tire of the present embodiment, high uneven wear resistance while maintaining riding comfort performance even in a tire with a thin sidewall rubber or a tire with a relatively small rim width for a light vehicle. Can be obtained.

Furthermore, the tire according to the embodiment of the present invention is, as in the embodiment shown in FIG. 1, in the tire width direction in the rim assembly state in which the tire is assembled to the applied rim and the internal pressure is not substantially filled and no load is applied. In the cross section, the carcass 5 has an overlapping end on a radial straight line SL passing through the tire width direction outer end ME of the overlapping virtual region M where two or more belt layers overlap in the tire radial direction and parallel to the tire equatorial plane C. A portion between the part position CE and the outermost end CW in the tire width direction connects the radial straight line SL and an axial straight line HL that passes through the outermost end CW in the tire width direction and is parallel to the tire rotation axis. A first arc R1 having a radius of curvature of 0.36h and a second radius having a radius of curvature of 0.42h are connected between the radial straight line SL and the axial straight line HL in parallel with the first arc R1. Circle between the arc R2 Present in Jo virtual area T, in the conventional tire is the presence of the carcass 5 outward from the preferred virtual area T, by filling the internal pressure, the deformation of the tire inner occurs in the carcass 5. Further, since the shoulder portion grows in diameter by the internal pressure, the belt tension of the shoulder portion increases. Therefore, in the conventional tire, the bending rigidity due to the carcass 5 of the shoulder portion is reduced, so that bending deformation due to side force is likely to occur, and the shoulder ground contact length is likely to be increased.
In the present embodiment, by disposing the main body 5a of the carcass 5 in the virtual region T, the carcass 5 is not deformed at the time of internal pressure filling, or is deformed to the tire outer side at the time of internal pressure. In the shoulder portion, diameter growth due to internal pressure is suppressed, so the belt tension of the shoulder portion does not increase, and the tension of the carcass 5 increases. Therefore, in one embodiment of the present invention, the bending rigidity due to the carcass of the shoulder portion is increased, and the buttress portion mainly bears the bending deformation due to the side force. Therefore, the shoulder ground contact length is difficult to increase.
Therefore, even if deformation occurs due to side force during turning, the buttress part can bear most of the bending deformation due to side force and the shoulder part does not deform following the deformation of the buttress part. It is possible to suppress changes in the ground contact shape such that the shoulder portion is sometimes pushed inward in the tire width direction. Therefore, it can suppress that the contact length of the shoulder part at the time of turning becomes long, and can suppress the uneven wear of a shoulder part.

  In order to further increase the difference in tension between the portion of the carcass 5 in the arcuate virtual region T and the portion of the carcass 5 on the inner side in the tire width direction from the overlapping end position CE, the belt includes a plurality of belt layers. The tension of the belt 6 may be weakened. By reducing the tension of the belt 6 composed of a plurality of belt layers, the tension of the carcass 5 portion in the virtual region where the belt 6 exists is increased, and the tension difference between the buttress portion and the carcass 5 portion is further increased. It becomes possible.

The specific configuration of the plurality of belt layers of the belt 6 includes, for example, cords that are inclined with respect to the tire circumferential direction as shown in FIGS. 1 and 2A, and the cords cross each other between the layers. In the structure composed of two inclined belt layers having different dimensions in the tire width direction, since at least the shoulder portion is not covered with the circumferential cord layer, in the conventional tire having the belt of these structures, the shoulder portion The contact length tends to extend in the circumferential direction, and uneven wear of the shoulder portion is likely to deteriorate. However, according to one embodiment of the present invention, even in a tire where the shoulder portion is not covered with the circumferential cord layer, the uneven wear of the shoulder portion is sufficiently maintained while maintaining the light weight and riding comfort performance of the tire. Can be suppressed.
Further, as shown in FIG. 2B, a belt reinforcing layer (layer layer) comprising two inclined belt layers in which cords cross each other between layers and a circumferential cord covering only the end of the inclined belt layer. It can be set as the structure which consists of these. In the structure as shown in FIG. 2B, the number of circumferential members bearing the tension increases, so the carcass tension of the shoulder portion decreases. In addition, since the diameter growth of the shoulder portion due to internal pressure is suppressed by the layer layer, the contact length of the shoulder portion is difficult to increase in a ground contact shape at the time of flat pressing or in a vehicle straight traveling state without side force input. However, as described above, since the carcass tension is reduced, when the side force is input, the bending rigidity due to the carcass of the shoulder portion is reduced, so that bending deformation is likely to occur, and the shoulder ground contact length is likely to be increased. Uneven wear tends to worsen. However, according to one embodiment of the present invention, uneven wear of the shoulder portion can be sufficiently suppressed while maintaining the lightness and riding comfort performance of the tire.
In addition, it is generally used for tires for passenger cars, and includes two inclined belt layers in which cords intersect each other between layers, and a circumferential cord layer that covers most of the inclined belt layers across the tire equatorial plane. Needless to say, the belt reinforcing layer (FIG. 2C) can be provided.

As a cord for the belt layer, a metal cord, particularly a steel cord is most commonly used, but an organic fiber cord can also be used. The steel cord is mainly composed of steel and can contain various trace contents such as carbon, manganese, silicon, phosphorus, sulfur, copper, and chromium.
As the cord, a monofilament cord or a cord obtained by twisting a plurality of filaments can be used. Various designs can be adopted for the twist structure, and various cross-sectional structures, twist pitches, twist directions, and distances between adjacent filaments can be used. Furthermore, a cord in which filaments of different materials are twisted can be adopted, and the cross-sectional structure is not particularly limited, and various twisted structures such as single twist, layer twist, and double twist can be adopted.
The inclination angle of the cord is preferably 10 ° or more and particularly preferably 30 ° or less with respect to the tire circumferential direction.
The number of cords to be driven is generally in the range of 15 to 60 pieces / 50 mm, but is not limited to this range.

In addition, the belt 6 composed of a plurality of belt layers is assembled to the applicable rim and is not filled with the specified internal pressure, and is in an unloaded state, the width of the maximum width inclined belt layer (the outer end in the tire width direction of the inclined belt layer). ) Is preferably 90% to 115% of the tread width, and more preferably 100% to 105%.
Moreover, it is preferable that the tire width direction dimension MW (mm) of the overlapping virtual region M is 80% to 100% of the tread width.

Further, in one embodiment of the present invention, in addition to the above-mentioned definition of the tire size, when the tire is assembled to the applicable rim and is filled with the specified internal pressure and is in an unloaded state, the nominal width TW ( mm) is divided by the tire outer diameter TR (mm), and a remarkable effect is exerted on the uneven wear resistance performance of the shoulder portion in a pneumatic tire having a value TW / TR smaller than 0.31.
Here, the tire outer diameter TR can be obtained by “(side height of tire) × 2 + rim width”. The “side height of the tire” is a value obtained by multiplying the nominal width TW of the tire by the nominal width ratio of the tire and dividing it by 100.
The “nominal ratio of tire” is, for example, the nominal width of the flatness ratio for each tire size specified in JATMA Year Book. For example, when the tire size is expressed as “195 / 65R15”, “65 ".
For pneumatic tires with the tire width TW (mm) divided by the tire outer diameter TR (mm) smaller than 0.31, the diameter difference between the center and shoulder tends to be small when going straight, and the shoulder is grounded. Since the length tends to increase, uneven wear of the shoulder portion tends to deteriorate. Therefore, by applying the present invention to a tire having a value obtained by dividing the tire width TW (mm) by the tire outer diameter TR (mm) smaller than 0.31, uneven wear during both turning and straight traveling can be sufficiently achieved. It becomes possible to suppress.
In addition, as such a tire, the pneumatic radial tire for passenger cars is assumed, and especially the tire for light vehicles is assumed. Specific tire sizes include 165 / 50R15, 165 / 50R16, 155 / 55R14, 165 / 55R14, 185 / 55R14, 165 / 55R15, 175 / 55R15, 185 / 55R15, 185 / 55R16, 175 / 60R13, 185 / 60R13, 165 / 60R14, 175 / 60R14, 185 / 60R14, 155 / 60R15, 165 / 60R15, 175 / 60R15, 185 / 60R15, 175 / 60R16, 185 / 60R16, 155 / 65R12, 145 / 65R13, 155 / 65R13, 165 / 65R13, 145 / 65R14, 155 / 65R14, 165 / 65R14, 175 / 65R14, 185 / 65R14, 145 / 65R15, 165 / 65R15, 175 / 65R15, 185 / 65R15, 145 / 70R12, 155 / 70R12, 165 / 70R12, 175 / 70R12, 145 / 70R13, 155 / 70R13, 165 / 70R13, 175 / 70R13, 185 / 70R13, 165 / 70R14, 175 / 70R14, 185 / 70R14, 135 / 80R12, 145 / 80R12, 155 / 80R12, Examples of sizes include 135 / 80R13, 145 / 80R13, 155 / 80R13, 165 / 80R13, 175 / 80R13, 165 / 80R14, 175 / 80R14, 185 / 80R14, 175 / 80R15, and 175 / 80R16.

  Furthermore, in the present invention, the dimension of the bead filler 4b in the tire radial direction is 5% to 20%, preferably 5% to 10%, of the carcass height h. In one embodiment of the present invention, deformation of the bead portion 3 during the side force action can be sufficiently suppressed without changing the shape and material of the bead filler 4b. Therefore, if the bead filler 4b has a tire radial dimension in such a range, the tire radial dimension of the bead filler 4b is set to 5% or more of the carcass height h, and the tire radial direction is larger than the vicinity of the rim flange. By making the bead filler 4 on the outer side, the size of the bead filler 4b in the tire radial direction is 20% or less, and the bead filler 4 is not present on the tread side of the maximum width of the carcass, thereby reducing the bead filler 4b. It is possible to achieve both a reduction in tire weight. Further, in the conventional tire, when the small bead filler as described above is used, the steering stability tends to be lowered, and a reinforcing cord layer is provided in the vicinity of the bead filler in order to compensate the steering stability. However, in the present invention, without requiring an additional member such as a reinforcing cord layer, the steering stability can be compensated by the shape of the ply, and compatibility with a small bead filler is possible. .

  In the present invention, as in the embodiment shown in FIG. 1, the crown surface of the tread portion 1 in the tire width direction cross section does not have a flat crown shape that is parallel or substantially parallel to the tire rotation axis. It is possible to sufficiently suppress uneven wear of the shoulder portion. In this case, “substantially parallel” means that, for example, the dimensional difference between the tire radius at the tread edge and the tire radius at the equator plane (so-called falling width) is within 9% of the tread width dimension. It is.

  In the present invention, as in the embodiment shown in FIG. 1, the plurality of belt layers of the belt 6 are not parallel or substantially parallel to the tire rotation axis in the tire radial cross section. Since the end portion is inclined toward the inner side in the tire radial direction, the tire radial direction position of the belt at the tire width direction outer end ME of the overlapping virtual region M and the tire radial direction position of the belt at the tire equatorial plane position are Preferably they are different. In this case, the belt tension borne by the plurality of belt layers is reduced, so that the tension of the ply at the outer end ME in the tire width direction of the overlapping virtual region M is increased, and the tension difference from the carcass 5 portion of the buttress portion is increased. It can be made larger, and the steering stability can be further improved. In this case, the tire width direction dimension of the overlapping virtual region M is MW (mm), and the tire radial direction position between the tire radial direction position of the belt at the tire width direction outer end ME and the tire radial direction position of the belt at the tire equatorial plane position. ED / MW is preferably 5% or more and 10% or less, where ED (mm) is the dimensional difference (belt drop width in the tire radial direction).

  Furthermore, in the present invention, when the carcass 5 includes the folded portion 5b, the folded portion 5b is preferably in the virtual region L. In this way, the entire carcass including the turn-up portion 5b exists in a state of standing more than the straight line connecting the innermost ends B in the tire radial direction of the carcass in FIG. Uneven wear can be further suppressed.

Examples of the present invention will be described below. Example tires 1 and 2 and comparative example tires 1 to 4 were prototyped under the specifications shown in Table 1 and evaluated for uneven wear resistance and riding comfort performance. In the tires according to Examples 1-2 and Comparative Examples 2-4, the tire size is 195 / 65R15, and the rim is 6J. In the tire according to Comparative Example 1, the tire size is 155 / 65R14, and the rim is 4.5J.
As shown in FIG. 1, each tire has a carcass 5 locked to a bead core embedded in a pair of bead portions, and a two-layer inclined belt provided on the outer side in the tire radial direction of the crown portion of the carcass 5. The tire includes a belt 6 and a tread rubber 7 made of layers.

(Evaluation of uneven wear resistance)
The test was performed by applying the same load as when running on a cant road surface and performing a wear drum test to reproduce the wear state indoors. Specifically, the vehicle was driven 5000 km at a constant speed of 70 km / h on a cant road surface having an inclination angle of 0.2 ° with respect to the horizontal direction from the road surface edge toward the center of the road surface. Then, in each of the main grooves of the tire center virtual region and the shoulder virtual region, the groove depth at the time of new article and the groove depth after wear are measured, and the wear life of each groove is calculated from the result, and the tire center virtual region It was evaluated by the ratio of the wear life of the shoulder virtual region to the wear life. The value of wear resistance in Table 1 is the numerical value of the index of the ratio of wear life of each tire to the value of the ratio of wear life in Comparative Example 1 ((the ratio of the wear life in each tire / the wear in Comparative Example 1). Life ratio) × 100). The smaller this index value, the harder the shoulder uneven wear, that is, the better the uneven wear performance. The main groove in the tire center virtual region referred to here is the circumferential main groove on the tire equatorial plane C in FIG. 1, and the shoulder virtual region groove is the outermost circumferential main groove in the tire width direction. That is.

(Evaluation of ride comfort performance)
Driving on a dry road course on five different types of pavement roughness, the test driver feels about the riding comfort of the running tire based on the vibration and sound transmitted to the passenger compartment. Evaluation was performed. The value of the ride comfort performance in Table 1 is the numerical value of the ratio of the ratio of the vibration and sound transmitted to the passenger compartment of each tire relative to the ride comfort performance value in Comparative Example 1 ((in each tire Vibration and sound volume / vibration and sound volume in Comparative Example 1) × 100). The smaller this index value, the smaller the vibration and sound, that is, the better the riding comfort performance.

  As is clear from the results shown in Table 1, each of the Example tires 1 and 2 has improved uneven wear resistance performance without lowering the riding comfort performance as compared with the comparative tires 1 to 4. Yes. From this, it was found that according to the pneumatic tire of the present invention, high uneven wear resistance performance can be obtained while maintaining riding comfort performance.

DESCRIPTION OF SYMBOLS 1: Tread part, 1a: Circumferential groove, 2: Side wall part, 3: Bead part, 3a: Bead heel, 4a: Bead core, 4b: Bead filler 5: Carcass, 5a: Main-body part, 5b: Folding part, 6: Belt 7: tread rubber, AL: straight slope, B: innermost end in the tire radial direction of the carcass, C: tire equatorial plane, CE, overlapping end position, CW: outermost end in the tire width direction of the carcass, CWh: carcass Height of outermost end in tire width direction, h: carcass height, HL: axial straight line, L: virtual region, M: overlapping virtual region, ME: outer end in tire width direction, R1: first arc, R2: Second arc, SF: side force, SL: radial straight line, T: arcuate virtual region,

Claims (2)

A value RW / TW obtained by dividing a rim width RW (mm) by a nominal TW (mm) of a tire cross-sectional width is 0.78, provided with a carcass composed of at least one carcass ply straddling a pair of bead cores in a toroidal shape. Is a small pneumatic tire,
In the rim assembly state in which the tire is assembled to the applicable rim and the internal pressure is not substantially filled and no load is applied, in the cross section along the tire width direction, the carcass tire radial direction at the outer end in the tire radial direction of the carcass When the carcass height, which is the height in the tire radial direction from the innermost end, is h,
In the rim assembly state, in the cross section along the tire width direction, the outermost end in the tire width direction of the carcass has a tire radial height CWh from the innermost end in the tire radial direction of the carcass of 0.47h <CWh < In the tire radial direction virtual region satisfying 0.67h,
In the rim assembly state, in a cross section along the tire width direction, an inclined straight line connecting the outermost end in the tire width direction of the carcass and an innermost end in the tire radial direction of the carcass, and a straight line parallel to the tire rotation axis And the acute angle θ is θ ≧ 63 °,
In the rim assembly state, in the cross section along the tire width direction, the carcass has a distance between the outermost end in the tire width direction and the innermost end in the tire radial direction at a distance of 0. A pneumatic tire characterized by existing in a virtual region sandwiched between two parallel straight lines of 045h. In the rim assembly state in which the tire is assembled to the applicable rim and the internal pressure is not substantially charged and is not loaded, in a cross section along the tire width direction,
The carcass includes an overlapping end position on a radial straight line passing through a tire width direction outer end of an overlapping virtual region where two or more belt layers overlap in the tire radial direction and parallel to the tire equator plane, and the tire width direction outermost end. Between the radial straight line and the axial straight line passing through the outermost end in the tire width direction and parallel to the tire rotation axis, the first arc having a curvature radius of 0.36h, and the diameter It exists in an arcuate virtual region that is connected between a directional straight line and the axial straight line in parallel with the first circular arc and a second circular arc having a curvature radius of 0.42h. The pneumatic tire according to claim 1.

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