JP7530774B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire.

A pneumatic tire is known that has a tread, a pair of sidewalls extending from both sides of the tread inward in the width direction, and a pair of bead portions each continuing to the inner diameter side of the sidewalls, and in which the pair of bead portions are formed wider than the normal rim width when not assembled to the rim. In addition, in the non-rim-assembled state, the outer surface of the bead portion on the outer side in the tire width direction extends at an incline outward in the tire width direction toward the outer side in the tire radial direction.

When this pneumatic tire is mounted on a corresponding standard rim, the pair of bead portions must be close to the standard rim width. Furthermore, since pneumatic tires are inclined outward in the tire width direction, particularly from the bead portions toward the sidewalls, when mounted on the rim, the bead portions tend to incline outward in the tire width direction toward the tire radial direction.

As a result, as shown in FIG. 8, the bead portion 130 tends to come into contact with the rim seat portion 51 of the regular rim 50 at two points, and a space S is created between the bead portion 130 and the rim flange 53. In particular, the bead portion 130 tends to come into strong local contact with the rim flange 53 at its outer surface in the width direction due to the inclination of the outer surface in the width direction.

Patent Document 1 also discloses a pneumatic tire in which a recess is formed on the back surface of the bead, recessed toward the inside in the tire width direction. When assembled to the rim, this pneumatic tire is locally and strongly abutted against the rim flange at two points, the outer portion of the recess in the tire radial direction and the inner portion of the recess in the tire radial direction, which is intended to strengthen the fixation of the bead portion to the rim flange and improve steering stability.

JP 2015-212112 A

When the pneumatic tire is assembled to the rim, the bead back surface is in strong local contact with the rim flange, and is therefore strongly compressed at this contact area. For example, when a load acts in the tire radial direction and/or tire width direction during cornering, the contact area is not likely to be compressed further because it is already strongly compressed, so the sidewall is less likely to deform in the area close to the bead, and deformation is likely to be biased toward the area close to the tread. In other words, the sidewall is not able to support the load efficiently, making it difficult to improve steering stability.

The present invention aims to provide a pneumatic tire that can improve driving stability by making the sidewall more efficient in supporting the load.

The present invention relates to
The tire has a tread, a pair of tire side portions extending radially inward from both ends of the tread in the tire width direction, and a pair of bead portions each continuing to the radially inward side of the pair of tire side portions and spaced apart wider than a normal rim width when not assembled to the rim,
The bead portion is
a bead base portion extending in a tire width direction at an inner end portion in a tire radial direction;
a bead heel portion that curves outward in the tire radial direction from an outer end portion in the tire width direction of the bead base portion toward the outer side in the tire width direction and further curves inward in the tire width direction toward the outer side in the tire radial direction;
a bead back surface portion extending from an outer end portion in the tire radial direction of the bead heel portion toward the outside in the tire radial direction,
In the non-rim assembled state, a recess is formed in the bead back surface portion, the recess being recessed inward in the tire width direction from an outer end portion in the tire width direction of the bead heel portion,
The bead back surface portion is
An arc-shaped recess R portion having a center of curvature on the outer side in the tire width direction and at least a portion of which constitutes the deepest portion of the recess;
a straight portion provided between the bead heel portion and the recessed R portion,
In the non-rim mounted state, the angle formed between the bead base portion and the straight portion is 95° or greater.

According to the present invention, a recess is formed in the bead back surface, so that in the non-rim-assembled state, the inner diameter side portion of the bead back surface located on the inner diameter side from the deepest part of the recess is inclined toward the inner side in the tire radial direction and outward in the tire width direction. In the rim-assembled state where the pair of bead portions are close to the rim width of the regular rim, the inner diameter side portion is likely to bend toward the inner side in the tire width direction starting from the periphery of the deepest part of the recess and generally follow the tire radial direction. In other words, in the rim-assembled state, the bead back surface is likely to be in close contact with almost the entire radial portion of the rim flange while eliminating the recess, and the contact area can be expanded.

In this way, when the tire is assembled to the rim and in an unloaded state, surface pressure acts over almost the entire surface of the bead back surface that is in close contact with the radial portion of the rim flange, so the load borne by the entire bead back surface is distributed compared to when surface pressure acts only on a portion of the bead back surface. In other words, compared to when high surface pressure acts locally on the bead back surface, there is more room for compression to allow the bead back surface to elastically deform.

Therefore, when a load or lateral force is input, the bead back surface can be further compressed by the amount of the available compression. In this case, the sidewall can deform in the area close to the bead as a result of further compression of the bead back surface, so the sidewall can be deformed so that it flexes overall from the bead side to the tread side. This improves the efficiency of load support in the sidewall, improving handling stability.

In particular, when a pair of bead portions are assembled to a standard rim width, if the inner end of the bead base portion, which is inclined radially inward toward the inner side of the tire width direction when not assembled to the rim, comes into contact with the rim seat portion of the standard rim, the bead base portion rotates around the inner end of the bead base portion in the tire radial direction so that the inclination angle of the bead base portion with respect to the tire axial direction becomes smaller (toward the inner side of the tire radial direction so that the bead base portion extends along the tire axial direction). As the bead base portion rotates, the bead back surface portion rotates so that the inclination angle of the straight portion with respect to the tire radial direction becomes zero (toward the outer side of the tire width direction so that the straight portion extends along the tire radial direction).

In this case, when not assembled to the rim, the angle between the straight section and the bead base section is greater than 95°, so even if the rotation angle of the bead base section is reduced by the compression allowance when the bead base section is compressed by the rim seat section and elastically deformed when assembled to a regular rim in which the angle between the radial portion of the rim flange and the rim seat section is approximately 95°, the straight section can be tightly attached to the rim flange.

Furthermore, as the base part rotates, the straight part rotates so that it extends along the tire radial direction (so that the inclination angle of the straight part with respect to the tire radial direction becomes zero), so the straight part easily follows the radial part of the rim flange, and the recess disappears when assembled to the rim.

In the non-rim mounted state, the angle between the straight portion and the tire radial direction may be 10° or less.

With this configuration, when the tire is assembled to the rim, the bead back surface can be easily brought into contact with almost the entire radial surface of the rim flange while eliminating any recesses, improving steering stability.

When the angle between the straight portion and the tire radial direction is greater than 10° in a non-rim mounted state, the straight portion is inclined too much relative to the tire radial direction, making it difficult to eliminate the inclination even when the tire is mounted to the rim. In this case, the recess is unlikely to disappear in the rim mounted state, and it is difficult to abut the back surface of the bead over almost the entire radial portion of the rim flange.

In the non-rim mounted state, the angle between the bead base portion and the straight portion may be 105° or less.

With this configuration, when the tire is assembled to the rim, the bead back surface can be easily brought into contact with almost the entire radial surface of the rim flange while eliminating any recesses, improving steering stability.

When the bead base and straight section are not in a rim-assembled state, if the angle between them is greater than 105°, the recess in the back surface of the bead may be indented against the rim flange even when the tire is assembled to the rim. In this case, the recess is unlikely to disappear when the tire is assembled to the rim, and it is difficult to bring the back surface of the bead into contact with almost the entire radial portion of the rim flange.

The recess may have a depth in the tire width direction of less than 1.0 mm.

According to this configuration, the inner diameter side portion is moderately inclined outward in the tire width direction when not assembled to the rim, so when it is folded inward in the tire width direction when assembled to the rim, the outward inclination in the tire width direction is easily eliminated, and it is easy to fit exactly to the radial portion of the rim flange. If the depth of the recess is 1.0 mm or more, the inner diameter side portion is likely to be excessively inclined outward in the tire width direction when not assembled to the rim, so even if it is folded inward in the tire width direction when assembled to the rim, the outward inclination in the tire width direction is difficult to eliminate. In this case, when assembled to the rim, the recess is unlikely to disappear, and the bead back portion is unlikely to abut almost the entire radial portion of the rim flange.

The present invention improves the steering stability by making the sidewall more efficient in supporting the load.

1 is a meridian cross-sectional view of a pneumatic tire according to one embodiment of the present invention. 1 is a meridian cross-section of a pneumatic tire around a bead portion before it is mounted on a rim. 1 is a meridian cross-sectional view of the vicinity of a bead portion of a pneumatic tire mounted on a rim. 5 is a graph showing fitting pressure on the outer surface of a bead portion 30 during inflation. 5 is a graph showing fitting pressure on the outer surface of the bead portion 30 when a radial load is applied. 6 is a meridian cross-sectional view showing deformation of the pneumatic tire of FIG. 5 . 1 is a meridian cross-sectional view showing deformation of a pneumatic tire when a lateral load is applied; FIG. 11 is a meridian cross-sectional view of the periphery of a bead portion of a conventional pneumatic tire assembled to a rim.

Embodiments of the present invention will now be described with reference to the accompanying drawings. Note that the following description is essentially merely illustrative and is not intended to limit the present invention, its applications, or its uses. The drawings are schematic, and the ratios of dimensions, etc., differ from the actual ones.

Figure 1 is a cross-sectional view in the meridian direction of a pneumatic tire 1 according to one embodiment of the present invention, showing only one side relative to the tire equator line CL. The pneumatic tire 1 has a tread 10, a pair of sidewalls 20 extending radially inward from both ends of the tread 10 in the tire width direction, and a pair of bead portions 30 each continuing to the radially inward side of the pair of sidewalls 20.

A bead core 31 and a bead filler 32 connected to the outer side in the tire radial direction are embedded in the bead portion 30. The bead core 31 is formed by covering an annular bundle of bead wires made of steel wires wound multiple times with rubber. The cross-sectional shape of the bead core 31 is formed into a polygonal shape so that the outer end of the bead core 31a extends in the tire width direction. In this embodiment, the height Hb of the bead core outer end surface 31a in the tire radial direction based on the nominal rim diameter (specified in JIS4102) NR (also called the reference rim diameter) is 6.7 mm.

The bead filler 32 is made of hard rubber that extends in an annular shape along the outer end surface 31a of the bead core, and its cross-sectional shape in the meridian direction is triangular, narrowing in the tire width direction toward the tire radial outside.

A carcass ply 2 is laid across the tread 10 and sidewall 20 between a pair of bead cores 31. The carcass ply 2 is folded back around the bead cores 31 from the inner side of the tire to the outer side of the tire. An inner liner 3 is provided on the inner side of the carcass ply 2 to maintain air pressure.

In the tread 10, a belt layer 11 and a belt reinforcing layer 12 are laminated in this order on the tire radial outer side of the carcass ply 2. In this embodiment, the belt layer 11 is composed of two layers. A tread rubber 13 is laminated on the tire radial outer side of the belt reinforcing layer 12. The tread rubber 13 forms the outer surface of the pneumatic tire 1 in the tire radial direction.

A tire side rubber 21 is arranged on the outer side of the carcass ply 2 in the tire width direction, spanning the sidewall 20 and the bead portion 30. The tire side rubber 21 has a sidewall rubber 21a that extends from the tire width direction end of the tread rubber 13 to the tire radial direction inward, and a rim strip rubber 21b that is connected to the inner diameter side end and extends further to the tire radial direction inward. The tire side rubber 21 forms the outer surface of the pneumatic tire 1 in the tire width direction.

The sidewall rubber 21a constitutes the majority of the sidewall 20. The rim strip rubber 21b is provided to correspond to at least the portion of the tire side rubber 21 that abuts against the rim flange 53 when the tire is assembled to the corresponding regular rim 50 (see FIG. 2) (referred to as the rim assembled state). The rim strip rubber 21b is made of a rubber that has superior abrasion resistance compared to the sidewall rubber 21a.

The tire side rubber 21 is formed with a rim protector 4 that protrudes outward in the tire width direction. The rim protector 4 is located radially inward of the tire maximum width position Z. The maximum width position Z is the position where the profile line of the outer surface of the sidewall 20 is furthest from the tire equator line CL in the tire width direction. In other words, the tire side rubber 21 gradually increases in thickness from the maximum width position Z toward the rim protector 4, and gradually decreases in thickness from the rim protector 4 toward the tire radially inward.

The rim protector 4 is bent inward in the tire width direction from the end that extends from the maximum width position Z toward the tire radially inward, and has an apex 4a that is the thickest. The apex 4a is located at a height H6 outward in the tire radial direction from the nominal rim diameter NR. The height H6 of the apex 4a is located radially outward in the tire radial direction than the rim flange 53 of the corresponding regular rim 50 when assembled to the rim.

In this specification, the portion located on the outer diameter side of the tip portion 32a of the bead filler 32 in the tire radial direction is referred to as the sidewall 20, and the portion located on the inner diameter side is referred to as the bead portion 30. The rim protector 4 is located in the bead portion 30. In this specification, the thickness of the tire side rubber 21 is defined as the direction perpendicular to the outer surface of the carcass ply 2.

2 shows an enlarged view of the bead portion 30 and its periphery when not assembled to a genuine rim 50 (referred to as a non-rim assembled state), along with the periphery of the corresponding rim flange 53 of the genuine rim 50. The genuine rim 50 has a rim seat portion 51 that extends outward in the tire width direction, a rim heel portion 52 that curves in an arc from the outer end in the tire width direction outward in the tire radial direction, and a rim flange 53 that extends outward in the tire radial direction from the outer end in the tire radial direction.

The rim seat portion 51 is inclined radially inward toward the inner side in the tire width direction, and the inclination angle with respect to a line parallel to the tire axis is A0. The rim flange 53 has a flange radial portion 53a that extends from the rim heel portion 52 to the outer side in the tire radial direction parallel to the tire radial direction, and a flange curved portion 53b that is continuous with the outer end in the tire radial direction and curves in an arc shape toward the outer side in the tire width direction.

The outer surface of the rim heel portion 52 located on the side where the pneumatic tire 1 is fitted extends in an arc shape with a radius of curvature R11 centered on the center of curvature O11 located on the pneumatic tire 1 side of the outer surface. A pair of flange radial portions 53a are arranged in the tire width direction with a rim width W0 between them. The flange radial portions 53a extend from the nominal rim diameter NR to a height H11 outward in the tire radial direction. The flange curved portion 53b extends in an arc shape with a radius of curvature R12 centered on the center of curvature O12 located on the tire outer surface side.

The regular rim 50 is a rim that is determined for each tire by the standard system that includes the standard on which the tire is based. For example, it is called a "standard rim" in the case of JATMA, and a "Measuring Rim" in the cases of TRA and ETRTO.

The regular rim 50 according to this embodiment conforms to the flange symbol J of a 5° deep bottom rim as defined by JATMA, with the inclination angle A0 of the rim seat portion 51 being 5°, the radius of curvature R11 of the rim heel portion 52 being 6.5 mm, the height H11 of the flange radial portion 53a being 8 mm, and the radius of curvature R12 of the flange curved portion 53b being 9.5 mm. In addition, the angle between the rim seat portion 51 and the radial portion 53a of the regular rim 50 according to this embodiment is 95°.

The bead portion 30 has a bead base portion 34 that extends in the tire width direction at the tire radial inner end, a bead heel portion 35 that curves outward in the tire radial direction from the tire width outer end of the bead base portion 34 toward the tire width outer side, and a bead back surface portion 36 that extends outward in the tire radial direction from the tire radial outer end of the bead heel portion 35 and continues to the rim protector 4.

In a non-rim mounted state, the bead base portion 34 is inclined linearly radially inward toward the tire width direction, and the inclination angle with respect to a line parallel to the tire axis is A1. That is, the bead base portion 34 is composed of a single straight portion. Specifically, the inclination angle A1 is larger than the inclination angle A0 of the rim seat portion 51. Preferably, the difference between the inclination angle A1 and the inclination angle A0 is 8° or less. In this embodiment, the inclination angle A1 is 12°, which is 7° larger than the inclination angle A0. Note that the bead base portion 34 may have multiple base surfaces that incline radially inward in a stepwise manner toward the tire width direction. In this case, the inclination angle parallel to the tire axis of the base surface that is located on the outermost side in the tire width direction (i.e., continuous with the bead heel portion 35) among the multiple base surfaces is defined as the inclination angle A1 according to this embodiment.

The bead heel portion 35 is located on the inner side in the tire radial direction and on the outer side in the tire width direction with respect to the bead core 31. The outer surface of the bead heel portion 35 is composed of a first curved portion 61 (heel R portion). The first curved portion 61 extends from a first point P1 located at the outer end of the bead base portion 34 in the tire width direction, curving outward in the tire radial direction toward the outer side in the tire width direction, to a second point P2 located at the outermost position in the tire width direction of the inner part of the tire radial direction of the bead portion 30 in the non-rim assembled state, and further extends from the second point P2 toward the outer side in the tire radial direction, curving inward in the tire width direction, to a third point P3.

The first curved portion 61 is formed of an arc-shaped portion with a radius of curvature R1 centered on a center of curvature O1 located closer to the inner surface of the tire than the outer surface of the bead portion 30. The center of curvature O1 and the radius of curvature R1 are set to be approximately the same as the center of curvature O11 and the radius of curvature R11 of the rim heel portion 52, respectively. In this embodiment, the radius of curvature R11 of the rim heel portion 52 is 6.5 mm, so the radius of curvature R1 of the first curved portion 61 is set to be 5.5 mm or more and 7.5 mm or less.

The bead back surface 36 has at least a second curved portion 62 (recess R portion) located on the inside in the tire radial direction and constituting at least a part of the recess 70 described below, and a third curved portion 63 (outer diameter side R portion) located on the outside in the tire radial direction and reaching the top 4a of the rim protector 4.

The second curved portion 62 extends from a fourth point P4, which is located radially outward and widthwise inward of the third point P3, toward the radially outward direction of the tire, in a direction inclined inward in the tire width direction, and curves outward in the tire width direction to a fifth point P5. The fifth point P5 is located outward in the tire width direction of the second point P2. The second curved portion 62 is formed by an arc-shaped portion with a curvature radius R2 centered on a curvature center O2 located on the tire outer surface side of the outer surface of the bead portion 30.

The height H2 of the center of curvature O2 in the tire radial direction based on the nominal rim diameter NR is equal to or greater than the height H11 of the flange radial portion 53a of the corresponding regular rim 50. Preferably, the height H2 of the center of curvature O2 is equal to or less than 1.5 times the height H11 of the flange radial portion 53a. In this embodiment, the height H11 of the flange radial portion 53a is 8 mm, so the height H2 of the center of curvature O2 is set to 8 mm or more and 12 mm or less. Preferably, the height H2 of the center of curvature O2 in the tire radial direction based on the nominal rim diameter NR is equal to or greater than 0.2 times and equal to or less than 0.6 times the height H6 of the top 4a of the rim protector 4 in the tire radial direction based on the nominal rim diameter NR.

The center of curvature O2 is located in a radial range W between a radial position X1 that is 2 mm radially inward from the bead core outer end surface 31a and a radial position X2 that is 9 mm radially outward from the bead core outer end surface 31a.

Furthermore, the height H2 of the center of curvature O2 is set to be less than 0.25 times the tire cross-sectional height H0 (see FIG. 1). The tire cross-sectional height H0 is calculated by subtracting the nominal rim diameter from the outer diameter of the pneumatic tire 1 and dividing the result by 2.

The radius of curvature R2 is greater than the radius of curvature R12 of the corresponding flange curved portion 53b of the regular rim 50. Preferably, the radius of curvature R2 is 1.4 times or more the radius of curvature R12, and more preferably, is 1.6 times or more and 2.4 times or less the radius of curvature R12. In this embodiment, since the radius of curvature R12 of the flange curved portion 53b is 9.5 mm, the radius of curvature R2 is set to 14 mm or more, and more preferably, 16 mm or more and 22 mm or less.

The radius of curvature R2 is set to be 1.0 to 4.5 times the radius of curvature R1 of the first curved portion 61.

The third curved portion 63 extends from a sixth point P6 located at the apex 4a of the rim protector 4, curving inward in the tire radial direction toward the inner side in the tire width direction to a seventh point P7. The third curved portion 63 is composed of an arc-shaped portion having a radius of curvature R3 centered on a center of curvature O3 located on the tire outer surface side of the outer surface of the bead portion 30. The radius of curvature R3 is set to be equal to or larger than the radius of curvature R2 of the second curved portion 62. Preferably, the radius of curvature R3 is equal to or larger than 1.2 times the radius of curvature R2.

As shown in the enlarged view of FIG. 2, a virtual curve 62a extending the second curved portion 62 radially outward and a virtual curve 63a extending the third curved portion 63 radially inward intersect at a virtual intersection point P8 so as to be convex toward the inner surface of the tire.

The height H8 of the virtual intersection point P8 in the tire radial direction based on the nominal rim diameter NR is greater than 1.5 times and less than 3.0 times the height H2 of the center of curvature O2 of the second curved portion 62. More preferably, the height H8 of the virtual intersection point P8 is greater than 2 times and less than 2.5 times the height H2 of the center of curvature O2. In addition, the height H8 of the virtual intersection point P8 is 0.7 times or more the height H6 of the top 4a of the rim protector 4. The height H8 of the virtual intersection point P8 is, for example, 15 mm or more and 25 mm or less, and preferably 20 mm or more and 24 mm or less.

The height H8 of the virtual intersection P8 is smaller than the height H9 of the tip 32a of the bead filler 32 based on the nominal rim diameter NR. Specifically, the height H9 of the tip 32a of the bead filler 32 is preferably 1.1 times or more, and more preferably 1.3 times or more, of the height H8 of the virtual intersection P8.

The crossing angle A3 between the virtual curves 62a and 63a, i.e., the angle between the tangent 62b to the second curved portion 62 (virtual curve 62a) extending from the virtual intersection point P8 and the tangent 63b to the third curved portion 63 (virtual curve 63a) extending from the virtual intersection point P8, is greater than 0° and less than or equal to 45°. If the crossing angle A3 exceeds 45°, distortion tends to concentrate between the second curved portion 62 and the third curved portion 63, and bead durability tends to deteriorate. Preferably, the crossing angle A3 is less than or equal to 30°. The crossing angle A3 is defined as the angle between the tangent 62b and the tangent 63b extending from the virtual intersection point P8 to the outside in the tire width direction.

The bead back surface 36 also has a straight section 69 on its outer surface that connects the third point P3 and the fourth point P4 in a straight line, and a fourth curved section 64 (connection R section) that connects the fifth point P5 and the seventh point P7 in an arc shape.

The straight portion 69 connects the first curved portion 61 and the second curved portion 62 in a tangent manner. In other words, the third point P3 constitutes a tangent point of the first curved portion 61 to the straight portion 69, and the fourth point P4 constitutes a tangent point of the second curved portion 62 to the straight portion 69. The straight portion 69 is inclined toward the tire width direction inward toward the tire radial direction outward, and the inclination angle with respect to a straight line parallel to the tire radial direction is A2. The inclination angle A2 is set to be smaller than the inclination angle A1 of the bead base portion 34. In this embodiment, the inclination angle A2 is 10° or less. Furthermore, the inclination angle A2 is set so that the angle A4 between the straight portion 69 and the bead base portion 34 is 95° or more and 105° or less. The inclination angle A2 is set to be smaller than the value obtained by subtracting the inclination angle A0 of the seat portion 51 of the rim from the inclination angle A1 of the bead base portion 34 (A2<A1-A0).

The fourth curved portion 64 connects the second curved portion 62 and the third curved portion 63 in a tangentially continuous manner, and is formed of an arc-shaped portion with a curvature radius of R4 centered on a curvature center O4 located on the tire outer surface side of the bead portion 30. In other words, the fifth point P5 forms a contact point between the second curved portion 62 and the fourth curved portion 64, and the seventh point P7 forms a contact point between the third curved portion 63 and the fourth curved portion 64.

The radius of curvature R4 of the fourth curved portion 64 is smaller than the radii of curvature R2, R3 of the second curved portion 62 and the third curved portion 63.

Here, in the non-rim mounted state, a recess 70 is formed on the inner side of the bead portion 30 in the tire radial direction, extending from the bead heel portion 35 to the bead back surface portion 36, and recessed inward in the tire width direction. The recess 70 refers to the portion of the bead heel portion 35 and the bead back surface portion 36 that is located on the inner side in the tire width direction with respect to the radial straight line L1 that passes through the second point P2 and extends parallel to the tire radial direction. In other words, the recess 70 is composed of the portion of the first curved portion 61 that is located between the second point P2 and the third point P3, the straight portion 69, and the portion of the second curved portion 62 that is located on the inner side in the tire radial direction.

The recess 70 has a deepest part 71 that is recessed most inward in the tire width direction. The deepest part 71 is located on the second curved part 62. The deepest part 71 is located radially outward from the straight part 69. In other words, the straight part 69 is located radially inward from the deepest part 71 in the tire radial direction. The depth D of the deepest part 71 is set to less than 1.0 mm, preferably 0.8 mm or less, and more preferably 0.3 mm or more and 0.5 mm or less, based on the radial straight line L1.

The height H10 of the deepest part 71 based on the nominal rim diameter NR is equal to or greater than the height H11 of the flange radial portion 53a of the corresponding regular rim 50. Also, preferably, the height H10 of the deepest part 71 is equal to or less than 1.5 times the height H11 of the flange radial portion 53a. In this embodiment, the height H11 of the flange radial portion 53a is 8 mm, so the height H11 of the deepest part 71 is set to be equal to or greater than 8 mm and equal to or less than 12 mm.

In this embodiment, the deepest part 71 is located on a widthwise straight line L2 that extends parallel to the tire width direction from the center of curvature O2 of the second curved part 62 that extends in an arc shape, so the height H10 of the deepest part 71 is equal to the height H2 of the center of curvature O2 of the second curved part 62.

Here, in the pneumatic tire 1, when not assembled to the rim, the pair of bead portions 30 are spaced apart at a distance wider than the rim width W0. Specifically, the outer width W1 in the tire width direction between the pair of bead heel portions 35 (i.e., the distance between the second points P2) is greater than the rim width W0. For example, the difference between the outer width W1 and the rim width W0 is 1.5 inches or less, and preferably 1 inch or less.

Figure 3 shows the periphery of the bead portion 30 when the pneumatic tire 1 is inflated to a specified internal pressure while being mounted on a corresponding regular rim 50, with the imaginary line showing the pneumatic tire 1 before mounting on the rim and the dashed line showing the pneumatic tire 1 when a load is applied. Since the outer width W1 between the pair of bead portions 30 of the pneumatic tire 1 is formed wider than the rim width W0 of the corresponding regular rim 50, when mounting the pneumatic tire 1 on the rim, it is necessary to bring the pair of bead portions 30 close to each other on the inner side in the tire width direction. At this time, the pneumatic tire 1 is deformed so that it inclines inward in the tire width direction toward the inner side in the tire radial direction across the sidewall 20 and the bead portion 30 (arrow Y1 in the figure).

Furthermore, since the inclination angle A1 of the bead base portion 34 is greater than the inclination angle A0 of the rim seat portion 51, when the bead base portion 34 is fitted to the rim seat portion 51 in the tire radial direction, the bead base portion 34 rotates clockwise in FIG. 3 (arrow Y2 in the figure) by an angle obtained by subtracting the amount by which the bead base portion 34 is compressed from the angle difference between the inclination angles A0 and A1. The bead base portion 34 rotates so that the inclination angle A1 becomes smaller, and is fitted to the rim seat portion 51 in the radial direction.

As a result, in the bead portion 30, the portion located radially inward from the deepest portion 71 of the recess 70 is inclined so as to rotate in the clockwise direction in FIG. 3 inward in the tire width direction compared to the non-rim mounted state (arrow Y3 in the figure). With the rotation of the bead base portion 34, the bead back surface portion 36 rotates inward in the tire width direction from the deepest portion 71 so that the inclination angle A2 becomes zero, that is, so that the straight portion 69 extends along the tire radial direction. In this embodiment, the inclination angle A1 is 7° larger than the inclination angle A0, so that the portion located radially inward from the deepest portion 71 rotates at an angle of 7° or less.

As a result, when the pneumatic tire 1 is assembled to the rim, the recess 70 disappears and the portion of the bead back surface 36 located radially inward of the deepest part 71 deforms so as to extend generally along the tire radial direction. Therefore, the bead base 34, the bead heel 35, and the portion of the bead back surface 36 located radially inward of the deepest part 71 of the bead portion 30 are in close contact with the rim seat 51, the rim heel 52, and the radial part 53a of the rim flange 53 over substantially the entire surface.

The bead core 31 rotates clockwise in FIG. 3 (arrow Y2 in the figure) in the same manner as the bead base portion 34 from the non-rim-assembled state to the inflated state. The rotation angle A6 of the bead core 31 is approximately equal to the inclination angle A2 with respect to a line parallel to the tire radial direction. In this embodiment, the rotation angle A6 of the bead core 31 is defined by the angle between the extension line L7 of the outer end surface 31a of the bead core 31 in the non-rim-assembled state and the extension line L8 of the outer end surface 31a of the bead core 31 in the inflated state.

In this rim-assembled state, the bead back surface 36 is formed so as to be sufficiently spaced apart in the tire radial direction from the flange curved portion 53b. Specifically, the bead back surface 36 is formed so that the distance in the tire radial direction between the apex P10 located at the outermost position in the tire radial direction of the flange curved portion 53b and the intersection point P11 between the bead back surface 36 and a radial line L3 that passes through the apex P10 and extends in the tire radial direction is 4 mm or more.

As shown by the dashed line in Figure 3, the bead back surface 36 is formed so as to be sufficiently spaced apart in the tire radial direction from the flange curved portion 53b even in a load input state corresponding to the load index set for the pneumatic tire 1. Specifically, the bead back surface 36 is formed so that the distance in the tire radial direction between the apex P10 and the intersection point P12 between the radial line L3 and the bead back surface 36 in the load input state is 3 mm or more.

Figure 4 is a graph showing the fitting pressure at the fitting portion between the bead portion 30 and the regular rim 50 when the pneumatic tire 1 is mounted on the regular rim 50 and inflated. The fitting pressure was measured by a sheet-type pressure sensor sandwiched between the bead portion 30 and the regular rim 50. In this graph, the horizontal axis represents each position along the outer surface of the bead portion 30 from the inner end of the bead base portion 34 in the tire width direction to the bead back surface portion 36, and the vertical axis represents the fitting pressure. Figure 4 also shows the fitting pressure of the bead portion 130 in the pneumatic tire 100 according to the conventional example in Figure 8. The fitting pressure for the pneumatic tire 1 is shown by a solid line, and the fitting pressure for the pneumatic tire 100 is shown by a dashed line.

As shown in FIG. 4, in the conventional pneumatic tire 100, fitting pressure is generated locally at two points: the bead base portion 134 and the contact portion 136a located on the radially outer side of the bead back surface portion 136. The peak at the bead base portion 134 is roughly fitting pressure A, and the peak at the contact portion 136a is lower than fitting pressure A and slightly exceeds fitting pressure B, which is lower than fitting pressure A. In other words, referring also to FIG. 8, no fitting pressure is generated at the non-contact portion 136b, which is located between the bead base portion 134 and the bead back surface portion 136 and does not contact the regular rim 50.

Therefore, the pneumatic tire 100 is tightly fitted locally at two locations, the bead base portion 134 and the abutment portion 136a, and the bead portion 130 is tightly compressed at these two locations.

In contrast, in the pneumatic tire 1 according to this embodiment, fitting pressure is generated between the bead base portion 34 and the regular rim 50 from the bead heel portion 35 to the bead back surface portion 36. In other words, unlike the pneumatic tire 100, the inner diameter side portions of the bead heel portion 35 and the bead back surface portion 36 also abut against the regular rim 50.

Specifically, the fitting pressure of the pneumatic tire 1 is lower in the portion of the pneumatic tire 100 that corresponds to the portion of the pneumatic tire 100 that is locally strongly fitted than that of the pneumatic tire 100. That is, the peak in the bead base portion 34 is approximately fitting pressure B, and the peak in the bead back portion 36 is slightly lower than fitting pressure C, which is lower than fitting pressure B. On the other hand, the pneumatic tire 1 generates fitting pressure in the portion of the pneumatic tire 100 that corresponds to the unfitted portion. That is, the pneumatic tire 1 has fitting pressure from the bead base portion 34 to the bead back portion 36 and is in close contact with the regular rim 50, and local compression is suppressed.

Figure 5 shows the fitting pressure on the outer surface of the bead portion 30 when a load is applied in the tire radial direction from the state shown in Figure 4. As in Figure 4, the fitting pressure for the pneumatic tire 1 is shown by a solid line, and the fitting pressure for the pneumatic tire 100 is shown by a dashed line. As shown in Figure 5, in the conventional pneumatic tire 100, the bead base portion 134 and the abutment portion 136a of the bead back surface portion 136 are already tightly fitted in the inflated state, so that these portions are unlikely to be further compressed even when a load is applied in the tire radial direction, and the increase in fitting pressure is small.

In contrast, in the pneumatic tire 1 according to this embodiment, the fitting pressure in the inflated state is lower than that of the conventional pneumatic tire 100, so there is room for the fitting pressure to increase when a further load is applied. Therefore, compared to the state in FIG. 4, the fitting pressure increases overall, increasing from fitting pressure B to a level exceeding fitting pressure A in the bead base portion 34, and increasing from fitting pressure C to fitting pressure B in the bead back surface portion 36.

Figure 6 is a cross-sectional view in the meridian direction showing the deformation of the pneumatic tire 1,100 in the state shown in Figure 5. As shown in Figure 6, the pneumatic tire 100 according to the conventional example is deformed so that it bends at a position of the sidewall 120 biased toward the tread 110, because the bead portion 130 side is less likely to be compressed further in response to an additional load on the bead portion 130 in an inflated state.

In contrast, in the pneumatic tire 1 according to this embodiment, the bead portion 30 has a larger margin for additional load in the inflated state than the pneumatic tire 100, so there is room for deformation in the bead portion 30 even in response to additional load, and the sidewall 120 can be deformed so as to bend overall from the tread 10 side to the bead portion 30 side.

Figure 7 is a cross-sectional view in the meridian direction showing the state in which a load is applied in the tire width direction to the pneumatic tire 1,100 in an inflated state. As shown in Figure 7, similar to Figure 6, in the pneumatic tire 1, the sidewall 20 is deformed so as to bend overall from the bead portion 30 to the tread 10, while in the pneumatic tire 100, the sidewall 120 is deformed so as to bend at a position biased toward the tread 110 side. Since the pneumatic tire 1 deforms so as to bend the sidewall 20 overall, it is easier to increase the amount of load absorption compared to the pneumatic tire 100, and as a result, the handling stability is improved.

The pneumatic tire 1 according to this embodiment has the following advantages:

(1) The bead back surface portion 36 has a recess 70 formed therein, so that in the non-rim-assembled state, the inner diameter side portion of the bead back surface portion 36 located on the inner diameter side of the deepest part 71 of the recess 70 is inclined toward the inner side in the tire radial direction and toward the outer side in the tire width direction. In the rim-assembled state in which the pair of bead portions 30 are brought close to the rim width W0 of the regular rim 50, the inner diameter side portion is likely to bend toward the inner side in the tire width direction starting from the periphery of the deepest part 71 of the recess 70 and generally follow the tire radial direction. In other words, in the rim-assembled state, the bead back surface portion 36 is likely to be brought into close contact with almost the entire radial portion 53a of the rim flange 53 while eliminating the recess 70, and the contact area can be expanded.

In this way, in the unloaded state when assembled to the rim, surface pressure acts over almost the entire surface of the bead back portion 36 that is in close contact with the radial portion 53a of the rim flange 53, so the load borne by the bead back portion 36 as a whole is distributed compared to when surface pressure acts only on a portion of the bead back portion 36. In other words, compared to when high surface pressure acts locally on the bead back portion 36, there is a margin of compression for the bead back portion 36 to elastically deform.

Therefore, when a load or lateral force is input, the bead back surface 36 can be further compressed by the amount of the available compression. In this case, the sidewall 20 can be deformed in the area close to the bead portion 30 due to the further compression of the bead back surface 36, so the sidewall 20 can be deformed so that it bends overall from the bead portion 30 side to the tread 10 side. This improves the efficiency of load support in the sidewall 20, improving steering stability.

In particular, when a pair of bead portions 30 are assembled to a standard rim width, when the inner end of the bead base portion 34 in the tire width direction, which is inclined radially inward toward the inner side of the tire width direction in the unassembled state, comes into contact with the rim seat portion 51 of the standard rim 50, the bead base portion 34 rotates around the inner end of the bead base portion 34 in the tire radial direction so that the inclination angle A1 of the bead base portion 34 with respect to the tire axial direction becomes smaller (toward the inner side in the tire radial direction so that the bead base portion 34 extends along the tire axial direction). With this rotation of the bead base portion 34, the bead back surface portion 36 rotates so that the inclination angle A2 of the straight portion 69 with respect to the tire radial direction becomes zero (toward the outer side in the tire width direction so that the straight portion 69 extends along the tire radial direction).

At this time, since the angle A4 between the straight portion 69 and the bead base portion 34 is greater than 95° when not assembled to the rim, when assembling to a regular rim in which the angle between the radial portion 53a of the rim flange 53 and the rim seat portion 51 is approximately 95°, for example, a regular rim 50 with flange symbol J for a 5° deep rim as specified by JATMA, the bead base portion 34 is compressed by the rim seat portion 51 and elastically deformed, the straight portion 69 can be tightly attached to the rim flange 53 even if the rotation angle of the bead base portion 34 is reduced due to the compression allowance when the bead base portion 34 is compressed by the rim seat portion 51 and elastically deformed.

Furthermore, as the bead base portion 34 rotates, the straight portion 69 rotates so that it extends along the tire radial direction (so that the inclination angle A2 of the straight portion 69 with respect to the tire radial direction becomes zero), so that the straight portion 69 easily follows the radial portion 53a of the rim flange 53, and the recess 70 disappears when assembled to the rim.

(2) When not assembled to the rim, the angle between the straight portion and the tire radial direction is 10° or less. Therefore, when assembled to the rim, the bead back surface portion 36 can be easily brought into contact with substantially the entire radial portion 53a of the rim flange 53, improving steering stability.

When the inclination angle A2 of the straight portion 69 relative to the tire radial direction is greater than 10° in the non-rim mounted state, the straight portion 69 is excessively inclined relative to the tire radial direction, and this inclination is difficult to eliminate even in the rim mounted state. In this case, the recess 70 is difficult to disappear in the rim mounted state, and it is difficult to abut the bead back surface portion 36 over substantially the entire radial portion 53a of the rim flange 53.

(3) In the non-rim-assembled state, the angle A4 between the bead base portion 34 and the straight portion 69 is 105° or less. Therefore, in the rim-assembled state, the bead back surface portion 36 can be easily brought into contact with substantially the entire radial portion 53a of the rim flange 53, improving steering stability.

When the angle A4 between the bead base portion and the straight portion 69 is greater than 105° in a non-rim assembled state, the recess 70 of the bead back surface portion 36 may be indented against the rim flange 53 even in a rim assembled state. In this case, the recess 70 is unlikely to disappear in a rim assembled state, and it is difficult to bring the bead back surface portion 36 into contact with substantially the entire radial portion 53a of the rim flange 53.

(4) If the depth D of the recess 70 is less than 1.0 mm, the portion located on the inner side of the deepest part 71 is moderately inclined outward in the tire width direction when not assembled to the rim, so that it is easy to bend inward in the tire width direction when assembled to the rim to eliminate the outward inclination in the tire width direction and to fit exactly along the radial part 53a of the rim flange 53. If the depth of the recess is 1.0 mm or more, the portion located on the inner side of the deepest part 71 is easy to be excessively inclined outward in the tire width direction when not assembled to the rim, so that it is difficult to eliminate the outward inclination in the tire width direction even if it is bent inward in the tire width direction when assembled to the rim. In this case, the recess 70 is difficult to disappear when assembled to the rim, and it is difficult to abut the bead back surface part 36 over almost the entire surface of the radial part 53a of the rim flange 53. In addition, when the depth D of the recess 70 is 0.8 mm or less, the portion located on the inner diameter side of the deepest part 71 is moderately inclined toward the outer side in the tire width direction when not assembled to the rim, and is more likely to fit the radial part 53a of the rim flange 53 when assembled to the rim. Furthermore, when the depth D of the recess 70 is 0.3 mm or more and 0.5 mm or less, the portion located on the inner diameter side of the deepest part 71 is even more moderately inclined toward the outer side in the tire width direction when not assembled to the rim, and is more likely to fit the radial part 53a of the rim flange 53 when assembled to the rim.

The present invention is not limited to the configuration described in the above embodiment, and various modifications are possible.

In the above embodiment, the recess 70 is configured by a part of the first curved portion 61, the straight portion 69, and at least a part of the second curved portion 62, but this is not limited to the above. The first curved portion 61 and the second curved portion 62 may be directly connected without using the straight portion 69. In this case, the first curved portion 61 and the second curved portion 62 may be connected in a tangent continuous manner.

In addition, in this embodiment, the recess 70 is configured as an arc-shaped portion, but this is not limited to this. In other words, the recess 70 may be formed in a trapezoidal shape, a triangular shape, or various other configurations can be adopted. Note that, by configuring the recess 70 as a tangent-continuous arc-shaped portion as in this embodiment, the bead back surface portion 36 can be smoothly deformed to extend parallel to the tire radial direction when assembled to the rim, resulting in excellent rim fitting.

Evaluation tests were conducted on the pneumatic tires of Comparative Examples 1 and 2 and Examples 1 and 2 for the contact area between the pneumatic tire and the regular rim, bead durability, and steering stability.

Comparative Example 1 is a conventional pneumatic tire 100 that does not have a recess. In Comparative Example 2, the inclination angle A2 of the straight portion 69 with respect to the tire radial direction is 12°, which exceeds the upper limit of 10° according to the present invention. In Comparative Example 2, the angle A4 between the straight portion 69 and the bead base portion 34 is 90°, which is below the lower limit of 95° according to the present invention. The inclination angle A2 of the straight portion 69 with respect to the tire radial direction is 6° in both Examples 1 and 2. The angle A4 between the straight portion 69 and the bead base portion 34 is 96° in Example 1 and 104° in Example 2. The depth D of the recess 70 is 0.4 mm, which is common to Comparative Example 2, Examples 1, and 2. The regular rim used in the evaluation conforms to the flange symbol J of the 5° deep bottom rim specified by JATMA.

The contact area between the pneumatic tire and the standard rim was evaluated by measuring the contact area between the pneumatic tire and the standard rim when each pneumatic tire was mounted on a standard rim and the specified internal pressure was applied, and the contact areas of Comparative Example 2, Examples 1 and 2 were expressed as an index, with the contact area of Comparative Example 1 set at 100. A higher value indicates better rim fitting.

To evaluate air leakage performance, each pneumatic tire is mounted on a regular rim and given the specified internal pressure. After leaving it for one month, the internal pressure of the pneumatic tire is measured, and tires that are 95% or more of the specified internal pressure are considered to pass. In Table 1, pass is indicated by "○" and fail is indicated by "×". "○" indicates excellent air leakage performance.

The handling stability was evaluated by a sensory relative assessment by the driver when the vehicle was fitted with the device and driven on the road. The maximum score is 10 points, with 6.0 being the median value, and the higher the value, the better the handling stability.

As is clear from Table 1, comparing Comparative Examples 1 and 2 with Examples 1 and 2, when the inclination angle A2 of the straight portion 69 relative to the tire radial direction and the angle A4 between the straight portion 69 and the bead base portion 34 are set within the ranges prescribed by the present invention, the contact area between the tire and the rim increases, resulting in excellent rim fitting.

In Comparative Example 2, the angle A4 between the straight portion 69 and the bead base portion 34 is less than 95°, which is the angle between the rim seat portion 51 and the radial portion 53a of the regular rim 50. Therefore, even when assembled to the rim and inflated, the straight portion 69 does not extend along the radial portion 53a, the recess 70 does not disappear, and the contact area between the tire and the rim is smaller than in Examples 1 and 2. As a result, the air leakage performance and handling stability are also worse than in Comparative Example 1 and Examples 1 and 2.

In Example 1, the straight portion 69 extends at an appropriate angle, so that when the tire is assembled to the rim and inflated, the recess 70 disappears and the bead portion 30 is in almost full contact with the radial portion 53a of the rim flange 53 from the bead base portion 34 to the bead back surface portion 36. This results in a larger contact area between the tire and the rim than in Comparative Example 1, and as a result, the air leakage performance and handling stability are superior to those of Comparative Example 1.

As in Example 1, in Example 2, the straight portion 69 extends at an appropriate angle, so that when assembled to the rim and inflated, the recess 70 disappears and the bead portion 30 is in almost full contact with the radial portion 53a of the rim flange 53 from the bead base portion 34 to the bead back surface portion 36.

REFERENCE SIGNS LIST 1 pneumatic tire 4 rim protector 10 tread 20 sidewall 30 bead portion 31 bead core 31a bead core outer end surface 32 bead filler 32a bead filler tip portion 34 bead base portion 35 bead heel portion 36 bead back portion 50 regular rim 51 rim seat portion 52 rim heel portion 53 rim flange 53a radial portion 53b curved portion 61 first curved portion 62 second curved portion 63 third curved portion 64 fourth curved portion 69 straight portion 70 recess 71 deepest portion

Claims (4)

The tire has a tread, a pair of tire side portions extending radially inward from both ends of the tread in the tire width direction, and a pair of bead portions each continuing to the radially inward side of the pair of tire side portions and spaced apart wider than a normal rim width when not assembled to the rim,
The bead portion is
a bead base portion extending in a tire width direction at an inner end portion in a tire radial direction;
a bead heel portion that curves outward in the tire radial direction from an outer end portion in the tire width direction of the bead base portion toward the outer side in the tire width direction and further curves inward in the tire width direction toward the outer side in the tire radial direction;
a bead back surface portion extending from an outer end portion in the tire radial direction of the bead heel portion toward the outside in the tire radial direction,
In the non-rim assembled state, a recess is formed in the bead back surface portion, the recess being recessed inward in the tire width direction from an outer end portion in the tire width direction of the bead heel portion,
The bead back surface portion is
An arc-shaped recess R portion having a center of curvature on the outer side in the tire width direction and at least a portion of which constitutes the deepest portion of the recess;
a straight portion provided between the bead heel portion and the recessed R portion,
In the non-rim mounted state, the angle between the bead base portion and the straight portion is 95° or greater. The pneumatic tire according to claim 1, wherein, in the non-rim mounted state, the angle between the straight portion and the tire radial direction is 10° or less. The pneumatic tire according to claim 1 or 2, wherein, in the non-rim mounted state, the angle between the bead base portion and the straight portion is 105° or less. The pneumatic tire according to any one of claims 1 to 3, wherein the recess has a depth in the tire width direction of less than 1.0 mm.

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