Pneumatic tire

Abstract

To provide a pneumatic tire improved in rim assembling work in a specific tire size.SOLUTION: This pneumatic tire is fitted to a rim R to be used. The rim diameter RD of the rim R is 10-18 inches. The ratio SH / SW of a tire sectional height SH to a tire sectional width SW is 0.30-0.45. The ratio RW / SW of the rim R to the tire sectional width SW is 0.78-0.99. The pneumatic tire comprises a pair of beads 4 in each of which a bead core 5 is embedded. The sectional width Wb (mm) of at least one of the bead cores 5 in a tire width direction satisfies the following expression (1). Wb≤21×(SH / SW) (1).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] In recent years, small shuttle buses for the purpose of transporting people and goods in urban areas have been proposed (see, for example, Patent Document 1 below). Such small shuttle buses are required to secure a large passenger compartment space. In addition, in-wheel motors may be employed in the small shuttle buses.

[0003] Patent Document 2 below proposes a pneumatic tire used for the small shuttle bus. In order to secure the passenger compartment space and a wide rim space capable of accommodating the in-wheel motor, the rim diameter, the ratio of the tire cross-sectional height to the tire cross-sectional width, and the ratio of the rim width of the rim to the tire cross-sectional width are defined for this tire.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The above-mentioned tire has a problem that the workability when mounting on a rim (hereinafter referred to as rim mounting workability) is poor.

[0006] The present invention has been devised in view of the above problems, and the main object thereof is to provide a pneumatic tire with improved rim mounting workability in a specific tire size.

Means for Solving the Problems

[0007] The present invention relates to a pneumatic tire to be mounted on a rim, wherein the rim diameter RD of the rim is 10 to 18 inches, the ratio SH / SW of the section height SH of the tire to the section width SW of the tire is 0.30 to 0.45, the ratio RW / SW of the rim width RW of the rim to the section width SW of the tire is 0.78 to 0.99, the pneumatic tire includes a pair of bead portions each embedded with a bead core, and at least one of the bead cores has an axial section width Wb (mm) of the tire satisfying the following formula (1). Wb≦21×(SH / SW)…(1)

Advantages of the Invention

[0008] By adopting the above configuration, the pneumatic tire of the present invention can improve the rim assembly workability.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Although the drawings include the features of the present invention, in order to assist the understanding of the present invention, there may be included exaggerated expressions or expressions different from the actual structural dimensional ratios. Also, throughout each embodiment, the same or common elements are denoted by the same reference numerals, and duplicate explanations are omitted. In addition, well-known configurations can be appropriately adopted for configurations not described in this specification.

[0011] FIG. 1 shows a cross-sectional view of a pneumatic tire 1 (hereinafter sometimes simply referred to as "tire 1") showing an embodiment of the present invention. FIG. 2 is a perspective view conceptually showing a vehicle Ve to which the tire 1 of the present invention is mounted. As shown in FIGS. 1 and 2, the tire 1 of the present embodiment is mounted on a rim R and used, and is preferably used as a pneumatic tire for a vehicle Ve such as a minibus or a small shuttle bus.

[0012] As shown in FIG. 2, the above-described vehicle Ve is a four-wheeled vehicle. Note that the vehicle Ve is not limited to four wheels and may have a six-wheel configuration or an eight-wheel configuration. Also, a predetermined number of tires 1 are mounted on the vehicle Ve according to the wheel configuration.

[0013] The vehicle Ve belongs to, for example, a small shuttle bus used for transporting people and goods in the city. The small shuttle bus is assumed to be a vehicle having an overall length of 4 m to 7 m, an overall width of about 2 m, and a gross vehicle weight of about 3 t. However, the tire 1 of the present invention is not adopted only for vehicles within the above range and can be adopted for various vehicles.

[0014] Also, the vehicle Ve is not necessarily limited to transporting people, and may be used as a means for transporting goods, a mobile store, a mobile office, etc. The vehicle Ve is preferably, for example, an electric vehicle equipped with an autonomous driving function. Also, since the vehicle Ve is mainly focused on transporting people and goods in the city, a relatively low driving speed range (average speed of about 50 km / h) is assumed. However, the vehicle Ve is not limited to such a mode.

[0015] When the vehicle Ve is an electric vehicle, it is desirable that the motor be arranged inside the rim. Also, in this case, the vehicle Ve preferably has an independent steering function in which each wheel can be independently steered. Thereby, turning on the spot and the like become easy, and the passenger compartment space of the vehicle Ve can be increased.

[0016] The tire 1 of the present embodiment that acts on such a vehicle Ve is required to have high space efficiency. For this reason, the tire 1 is required to have a small rim diameter and a small cross-sectional height of the tire.

[0017] FIG. 1 is a cross-sectional view including the rotation axis of the tire 1 in a normal state. The "normal state" means that in the case of a pneumatic tire with various specifications defined, the tire is rim-mounted on a normal rim and filled with a normal internal pressure, and moreover, it is in a no-load state. In the case of a tire without various defined specifications, the normal state means a standard use state according to the purpose of use of the tire, which means a state where the tire is not mounted on a vehicle and is in a no-load state. In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are values measured in the normal state. Also, the dimensions of a configuration that cannot be measured in the normal state (for example, an internal member of the tire) are values measured in a state where the tire is approximated to the normal state as much as possible.

[0018] The "normal rim" is the rim defined for each tire in a standard system including the standards on which the tire is based. For example, in JATMA, it is the "standard rim", in TRA, it is the "Design Rim", and in ETRTO, it is the "Measuring Rim".

[0019] The "normal internal pressure" is the air pressure defined for each tire in a standard system including the standards on which the tire is based. In JATMA, it is the "maximum air pressure", in TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in ETRTO, it is the "INFLATION PRESSURE".

[0020] The tire 1 includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The sidewall portion 3 is continuous with the outside of the tread portion 2 in the tire axial direction and extends in the tire radial direction. The bead portion 4 is continuous with the inside of the sidewall portion 3 in the tire radial direction. Further, a bead core 5 for fixing the bead portion 4 to the rim R is embedded in the bead portion 4.

[0021] Further, the tire 1 includes a carcass 6. The carcass 6 extends between the pair of bead portions 4. In other words, the carcass 6 extends from one bead portion 4 through one sidewall portion 3, the tread portion 2, and the other sidewall portion 3 to the other bead portion 4.

[0022] The carcass 6 is composed of, for example, two carcass plies 6A and 6B. These carcass plies include, for example, a body portion 6a and a turned-up portion 6b. The body portion 6a extends between the pair of bead portions 4, for example. The turned-up portion 6b is continuous with the body portion 6a and is turned up from the inside to the outside in the tire axial direction around the bead core 5.

[0023] The carcass plies 6A and 6B include a plurality of carcass cords and a topping rubber covering them (not shown). As the carcass cords, for example, organic fiber cords such as aramid and rayon are employed. The carcass cords are preferably arranged at an angle of 70 to 90° with respect to the tire equator C, for example. However, the tire 1 of the present invention is not limited to such a mode.

[0024] In the tread portion 2 of the present embodiment, a belt layer 7 is disposed. The belt layer 7 is composed of, for example, a first belt ply 7A and a second belt ply 7B. These belt plies include, for example, a plurality of belt cords arranged at an angle of 15 to 45° with respect to the tire circumferential direction. Further, the belt cords included in the first belt ply 7A and the belt cords included in the second belt ply 7B are inclined in opposite directions with respect to the tire circumferential direction. Thereby, the tread portion 2 is effectively reinforced.

[0025] In the present invention, the rim diameter RD of the rim R is 10 to 18 inches. Further, the ratio SH / SW of the section height SH of the tire 1 to the section width SW of the tire is 0.30 to 0.45. The ratio RW / SW of the rim width RW of the rim R to the section width SW of the tire 1 is 0.78 to 0.99. The section width SW is, for example, 150 to 250 mm. As the tire size, for example, 205 / 40R15, 205 / 30R15, 215 / 40R15, 225 / 40R15, etc. are assumed. However, the present invention is not limited to such tire sizes.

[0026] The rim diameter RD is the outer diameter of the rim body portion fitted by the bead core 5 of the bead portion 4. Further, the section width SW of the tire 1 corresponds to the width excluding convex portions (not shown) indicating patterns or characters on the sidewall of the tire 1. The section height SH of the tire 1 corresponds to 1 / 2 of the difference between the outer diameter of the tire and the rim diameter RD. In other words, the section height SH corresponds to the distance in the tire radial direction from the bead base line BL to the outer end in the tire radial direction of the tire 1. The bead base line BL means a tire axial line passing through the rim diameter position.

[0027] The rim width RW of the rim R corresponds to the distance in the tire axial direction from the inner surface of one rim flange Rf to the inner surface of the other rim flange Rf. When the inner surface is inclined, it is assumed that the distance is measured at the center position in the tire radial direction of the bead core 5 when the tire 1 is mounted on the rim R.

[0028] As described above, the tire 1 of the present invention has a relatively small rim diameter RD and section height SH, and a relatively large rim width RW with respect to the section width SW of the tire. Such a tire 1, for example, improves the space efficiency in the vehicle space when mounted on the vehicle Ve (shown in FIG. 2), and can sufficiently secure the accommodation space in a vehicle in which a motor is arranged inside the rim. Further, such a tire 1 can hold a sufficient air volume to support the total vehicle weight. However, such a tire 1 tends to have poor rim assembly workability due to its shape.

[0029] Figure 3 shows an enlarged cross-sectional view of one bead portion 4 in Figure 1. In Figure 3, the carcass 6 and the rim R shown in Figure 1 are omitted. As shown in Figure 3, in the present invention, the cross-sectional width Wb (mm) of the bead core 5 in the tire axial direction satisfies the following formula (1). In the present invention, at least one of the two bead cores 5 included in the tire 1 only needs to satisfy the formula (1). As a desirable aspect, in the present embodiment, each of the two bead cores 5 satisfies the formula (1). Wb ≦ 21×(SH / SW)…(1)

[0030] In the present invention, from the viewpoint of allowing variations in the above-described respective parameters (the cross-sectional width SW and the cross-sectional height SH of the tire 1 and the cross-sectional width Wb of the bead core 5), it is desirable that the average value of each parameter be applied to the formula (1). For this reason, for example, as the cross-sectional width Wb of the bead core 5, the average value of the cross-sectional widths Wb measured at a plurality of positions different in the tire circumferential direction is applied. The same applies to other parameters (including those described below).

[0031] In the tire of a specific size specified in the present invention, since the aspect ratio is small, the cross-sectional height of the tire is small, and the rim assembly workability tends to be poor. The inventors have found that in this type of tire, in order to improve the rim assembly workability, it is effective to reduce the cross-sectional width Wb of the bead core 5 to promote the deformation of the bead portion 4, and to specify the upper limit value of the cross-sectional width Wb of the bead core 5 in relation to the aspect ratio (SH / SW). Further, as a result of investigating the relationship between the aspect ratio (SH / SW) of the tire 1 and the cross-sectional width Wb of the bead core and the rim assembly workability from various viewpoints, the above formula (1) was derived. In the tire 1 of the present invention, by making the cross-sectional width Wb satisfy the formula (1), the rim assembly workability can be improved.

[0032] The following describes the more detailed configuration of the present embodiment. Note that each configuration described below shows a specific aspect of the present embodiment. Therefore, it goes without saying that the present invention can exhibit the above-described effects even if it does not have the configurations described below. Further, even if any one of the configurations described below is applied alone to the tire of the present invention having the above-described features, an improvement in performance corresponding to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, a combined improvement in performance corresponding to each configuration can be expected.

[0033] It is desirable that the sectional width Wb (mm) satisfies the following formula (2). Thereby, the durability of the bead portion 4 can be ensured. Wb≧15×(SH / SW)…(2)

[0034] It is desirable that the sectional height Hb (mm) in the tire radial direction of the bead core 5 and the sectional width Wb satisfy the following formula (3). Thereby, the aspect ratio of the bead core 5 is optimized, and the rim assembly workability and the durability of the bead portion 4 are improved in a well-balanced manner. 0.8≦Wb / Hb≦1.4…(3)

[0035] The width Wa (mm) of the bead portion 4 in the tire axial direction is, for example, 3.0 times or less the sectional width Wb of the bead core 5. Thereby, the rigidity of the bead portion 4 is relaxed, and the rim assembly workability is further improved. From this viewpoint, the width Wa is desirably 2.8 times or less the sectional width Wb, more desirably 2.6 times or less. Further, it is desirable that the width Wa is 18 mm or less. Note that the width Wa means the width of the bead portion 4 in the tire axial direction at the position of the bead core 5, and more specifically, the width of the bead portion 4 in the tire axial direction passing through the centroid 5c of the cross section of the bead core 5.

[0036] In order to ensure the durability of the bead portion 4, the width Wa of the bead portion 4 is, for example, 2.0 times or more the sectional width Wb, desirably 2.2 times or more, more desirably 2.4 times or more. Further, it is desirable that the width Wa is 12 mm or less.

[0037] Figure 4 shows an enlarged cross-sectional view that shows the bead core 5 in more detail. As shown in Figure 4, the bead core 5 includes a plurality of bead wires 10 in its cross-section. The bead core 5 may be such that one bead wire 10 is wound around a plurality of times in the tire circumferential direction, or it may be such that a plurality of annular bead wires 10 are bundled together. In addition, in Figures 1 and 3, the cross-section of the bead core 5 is shown in a state where the bead wire 10 shown in Figure 4 is omitted.

[0038] It is desirable that the cross-sectional width Wb of the bead core 5 and the wire diameter D1 of one bead wire 10 (the unit is "mm") satisfy the following formula (4). Similarly, it is desirable that the cross-sectional height Hb of the bead core 5 and the wire diameter D1 of one bead wire satisfy the following formula (5). Thereby, the rim assembly workability and the durability of the bead portion 4 are improved in a well-balanced manner. 4 ≦ Wb / D1 ≦ 7…(4) 4 ≦ Hb / D1 ≦ 7…(5)

[0039] As described above, the pneumatic tire according to one embodiment of the present invention has been described in detail. However, the present invention is not limited to the above specific embodiments and can be implemented in various modes.

Example

[0040] A pneumatic tire having the basic structure shown in Figure 1 and a rim diameter of 15 inches was prototyped based on the specifications in Table 1. In addition, as a comparative example, a tire that does not satisfy the above formula (1) was prototyped. The tire of the comparative example is substantially the same as the tire of the example except for the above matters. The rim assembly workability and the durability of the bead portion of each test tire were tested. The common specifications and test methods of each test tire are as follows. Mounting rim: 15 × 7.0J Tire internal pressure: 350 kPa

[0041] <Rim assembly workability> The workability when mounting the test tire on the rim was evaluated by the operator's senses. The evaluation results indicate that the higher the numerical value, the better the rim mounting workability.

[0042] <Durability of the bead portion> After assembling the rim, the test tire was further filled with air, and the internal pressure when damage occurred in the bead portion was measured. The results are the internal pressure indexed, and the higher the numerical value, the better the durability of the bead portion. The test results are shown in Table 1.

[0043]

Table 1

[0044]

Table 2

[0045] All of the above evaluation items (rim mounting workability and durability of the bead portion) are such that 80 points or more satisfy the market requirements (hereinafter referred to as "having marketability"). As shown in Tables 1 and 2, Comparative Example 1 has a rim mounting workability of 80 points, and Comparative Examples 2 to 4 have a rim mounting workability of 70 to 75 points. That is, Comparative Examples 1 to 4 are at a level where improvement in rim mounting workability is desired. On the other hand, it can be understood that in Examples 1 to 10, the rim mounting workability has been greatly improved to 100 to 115 points. That is, it was confirmed that the tire of the present invention has excellent rim mounting workability. Also, in Examples 1 to 10, regarding the durability of the bead portion, the worst is 90 points, which has marketability. That is, it was confirmed that the tire of the present invention can also maintain the durability of the bead portion.

[0046] [Appendix] The present invention includes the following aspects.

[0047] [Invention 1] A pneumatic tire mounted on and used with a rim, wherein the rim diameter RD of the rim is 10 to 18 inches, the ratio SH / SW of the section height SH of the tire to the section width SW of the tire is 0.30 to 0.45, the ratio RW / SW of the rim width RW of the rim to the section width SW of the tire is 0.78 to 0.99, the pneumatic tire includes a pair of bead portions each embedded with a bead core, wherein at least one of the bead cores has a cross-sectional width Wb (mm) in the tire axial direction that satisfies the following formula (1), Pneumatic tire. Wb ≦ 21×(SH / SW)…(1) [Invention 2] The cross-sectional width Wb (mm) satisfies the following formula (2), the pneumatic tire according to Invention 1. Wb ≧ 15×(SH / SW)…(2) [Invention 3] The cross-sectional height Hb (mm) in the tire radial direction of at least one of the bead cores and the cross-sectional width Wb (mm) satisfy the following formula (3), the pneumatic tire according to Invention 1 or 2. 0.8 ≦ Wb / Hb ≦ 1.4…(3) [Invention 4] At the position of at least one of the bead cores, the axial width Wa (mm) of the bead portion is 3.0 times or less of the cross-sectional width Wb (mm), the pneumatic tire according to any one of Inventions 1 to 3. [Invention 5] The width Wa (mm) is 2.0 times or more of the cross-sectional width Wb (mm), the pneumatic tire according to Invention 4. [Invention 6] The width Wa (mm) is 18 mm or less, the pneumatic tire according to Invention 4 or 5. [Invention 7] The bead core includes a plurality of bead wires in its cross-section, The pneumatic tire according to any one of Claims 1 to 6 of the present invention, wherein the width Wb (mm) and the wire diameter D1 (mm) of one bead wire satisfy the following formula (4). 4 ≦ Wb / D1 ≦ 7…(4)

Explanation of Signs

[0048] 4 Bead part 5 Bead core R Rim RD Rim diameter RW Rim width SW Section width of tire SH Section height of tire Wb Section width of bead core

Claims

1. A pneumatic tire mounted on and used with a rim, wherein the rim diameter RD of the rim is 10 to 18 inches, the ratio SH / SW of the section height SH of the tire to the section width SW of the tire is 0.30 to 0.45, the ratio RW / SW of the rim width RW of the rim to the section width SW of the tire is 0.78 to 0.99, the pneumatic tire includes a pair of bead portions each embedded with a bead core, at least one of the bead cores has an axial cross-sectional width Wb (mm) of the tire satisfying the following formula (1), Pneumatic tire. Wb ≤ 21×(SH / SW)…(1)

2. The pneumatic tire according to claim 1, wherein the cross-sectional width Wb (mm) satisfies the following formula (2). Wb ≥ 15×(SH / SW)…(2)

3. The pneumatic tire according to claim 1 or 2, wherein at least one of the bead cores has an axial cross-sectional height Hb (mm) of the tire and the cross-sectional width Wb (mm) satisfying the following formula (3). 0.8 ≤ Wb / Hb ≤ 1.4…(3)

4. The pneumatic tire according to claim 1 or 2, wherein at the position of at least one of the bead cores, the axial width Wa (mm) of the bead portion is not more than 3.0 times the cross-sectional width Wb (mm).

5. The pneumatic tire according to claim 4, wherein the width Wa (mm) is not less than 2.0 times the cross-sectional width Wb (mm).

6. The pneumatic tire according to claim 4, wherein the width Wa (mm) is 18 mm or less.

7. The bead core includes a plurality of bead wires in its cross-section, the pneumatic tire according to claim 1 or 2, wherein the cross-sectional width Wb (mm) and the wire diameter D1 (mm) of one of the bead wires satisfy the following formula (4). 4 ≤ Wb / D1 ≤ 7…(4)

Images