Pneumatic tire

Abstract

To provide a pneumatic tire that has a specific tire size and is used under high load environment which exhibits excellent abrasion resistance.SOLUTION: There is provided a pneumatic tire. The rim diameter RD of a rim R is 10 to 15 inches. The cross-sectional width SW of the tire is less than 192 mm. A ratio SH / SW is 0.20 to 0.40. A ratio RW / SW is 0.78 to 0.99. On a contact surface 2s of a tread part 2, a plurality of grooves 13 are provided. A land ratio La which is a ratio of an actual contact area of the contact surface 2s, to a virtual contact area of the contact surface 2s is 0.80 to 0.95.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire. [Background technology]

[0002] In recent years, various minibuses have been proposed for the purpose of transporting people and goods in urban areas. Such vehicles are required to efficiently utilize the interior space while taking into consideration ease of boarding and disembarking for passengers (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-029132 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the introduction of electric vehicles, known as green slow mobility, has been under consideration. These vehicles are intended to provide transportation for the elderly in areas where traditional public transportation services such as trains and buses are inadequate. Therefore, these vehicles are designed to carry many passengers and travel short distances at speeds of less than 20 km / h, placing strict demands on the vehicle interior space, ease of boarding and disembarking, and low floors. Therefore, the tires mounted on these vehicles must also be smaller in diameter and width.

[0005] Furthermore, although the vehicle travels at a low speed, it is heavy due to the battery it is equipped with, and because it travels at a low speed, it is often driven at a large steering angle. Therefore, tires mounted on such vehicles are required to have high wear resistance.

[0006] The present invention was devised in consideration of the above-described circumstances, and its main objective is to provide excellent wear resistance in a pneumatic tire having a specific tire size and used under high-load environments. [Means for solving the problem]

[0007] The present invention is a pneumatic tire that is mounted on a rim for use, wherein the rim diameter RD of the rim is 10 to 15 inches, the tire section width SW is less than 192 mm, the ratio SH / SW of the tire section height SH to the tire section width SW is 0.20 to 0.40, and the ratio RW / SW of the rim width RW to the tire section width SW is 0.78 to 0.99, the pneumatic tire has a tread portion, the contact surface of the tread portion is provided with a plurality of grooves, and the land ratio La, which is the ratio of the actual contact area of ​​the contact surface to the virtual contact area of ​​the contact surface when all of the plurality of grooves are filled, is 0.80 to 0.95. [Effects of the Invention]

[0008] The pneumatic tire of the present invention employs the above-described configuration, and is therefore able to exhibit excellent wear resistance. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a pneumatic tire according to one embodiment of the present invention. [Figure 2] 1 is a perspective view of a vehicle on which a tire according to the present embodiment is mounted. [Figure 3] FIG. 2 is an enlarged cross-sectional view of the tread portion of FIG. 1. [Figure 4] 10 is a graph showing a desirable relationship between the land ratio La and the rubber hardness H of the cap rubber. [Figure 5] FIG. 4 is a development view showing the cord arrangement of the belt layer of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings are intended to illustrate the features of the present invention, but may include exaggerated representations and representations that differ from the dimensional ratios of the actual structure to facilitate understanding of the present invention. Furthermore, identical or common elements are designated by the same reference numerals throughout the embodiments, and redundant explanations will be omitted. Furthermore, well-known configurations may 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") illustrating one embodiment of the present invention. FIG. 2 is a perspective view conceptually showing a vehicle Ve on which the tire 1 of the present invention is mounted. As shown in FIGS. 1 and 2, the tire 1 of this embodiment is mounted on a rim R and is used under high load conditions. In particular, the tire of this embodiment is suitably mounted on low-speed electric vehicles with a maximum speed of less than 20 km / h, which have recently become known as green slow mobility.

[0012] Green slow mobility is used, for example, to provide a means of transportation for the elderly in areas where conventional public transportation services such as trains and buses are inadequate. For this reason, green slow mobility is intended to carry many people and travel short distances at speeds of less than 20 km / h, and strict requirements are placed on the vehicle interior space, ease of boarding and disembarking, and low floor.

[0013] As shown in Fig. 2, the vehicle Ve described above is a four-wheeled automobile. Note that the vehicle Ve is not limited to a four-wheeled automobile, and may have six or eight wheels. Furthermore, the vehicle Ve is fitted with a predetermined number of tires 1 according to the wheel configuration.

[0014] The vehicle Ve has, for example, an overall length of 4 m to 7 m, an overall width of about 2 m, and a total vehicle weight of about 3 tons. However, the tire 1 of the present invention is not limited to being used on vehicles in the above-mentioned range.

[0015] The tire 1 of this embodiment to be mounted on such a vehicle Ve is required to have a small diameter and width. Therefore, the tire 1 is required to have a small rim diameter, a small cross-sectional height, and a small cross-sectional width. On the other hand, since the vehicle Ve has a considerable weight, the tire 1 is also required to have high wear resistance.

[0016] 1 is a cross-sectional view of a tire 1 in a normal state, including the axis of rotation. "Normal state" refers to a state in which the tire is mounted on a rim specified by the manufacturer, inflated to an air pressure specified by the manufacturer, and no load is applied. In this specification, unless otherwise specified, various dimensions refer to those measured in the normal state.

[0017] In the case of tires for which various standards are established, the rim specified for each tire by the standard may be used instead of the rim specified by the manufacturer, i.e., for example, a "standard rim" for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO.

[0018] In the case of tires for which various standards are established, the air pressure specified for each tire by each standard, i.e., the "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, or the "INFLATION PRESSURE" for ETRTO, may be applied instead of the air pressure specified by the manufacturer.

[0019] The tire 1 includes a tread portion 2, a pair of sidewall portions 3, and a pair of bead portions 4. The sidewall portions 3 are continuous with the tread portion 2 on the outer side in the tire axial direction and extend in the tire radial direction. The bead portions 4 are continuous with the sidewall portions 3 on the inner side in the tire radial direction. The tire 1 also 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.

[0020] The carcass 6 is composed of, for example, two carcass plies 6A and 6B. These carcass plies include, for example, a main body portion 6a and a turned-up portion 6b. The main body portion 6a extends, for example, between the pair of bead portions 4. The turned-up portion 6b is, for example, continuous with the main body portion 6a and is turned up around the bead core 5 from the axially inner side to the axially outer side of the tire.

[0021] The carcass plies 6A, 6B include a plurality of carcass cords and a topping rubber covering the cords (not shown). The carcass cords are made of organic fiber cords such as aramid or rayon. The carcass cords are preferably arranged at an angle of 70 to 90 degrees with respect to the tire equator C. However, the tire 1 of the present invention is not limited to this embodiment.

[0022] In the present invention, the rim diameter RD of the rim R is 10 to 15 inches. The ratio SH / SW of the tire's section height SH to its section width SW is 0.20 to 0.40. The ratio RW / SW of the rim R's rim width RW to its section width SW is 0.78 to 0.99. The tire's section width SW is, for example, less than 192 mm.

[0023] The rim diameter RD is the outer diameter of the rim body portion that is fitted by the bead core 5 of the bead portion 4. Furthermore, the cross-sectional width SW of the tire 1 corresponds to the width excluding any protrusions (not shown) that indicate patterns or letters on the sidewall of the tire 1. The cross-sectional height SH of the tire 1 corresponds to half the difference between the outer diameter of the tire and the rim diameter RD. In other words, the cross-sectional height SH corresponds to the distance in the tire radial direction from the bead base line BL to the outer edge of the tire 1 in the tire radial direction. The bead base line BL refers to the tire axial line that passes through the rim diameter position.

[0024] 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. If the inner surfaces are inclined, 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.

[0025] As described above, the tire 1 of the present invention has a relatively small rim diameter RD and cross-sectional height SH, and a relatively large rim width RW relative to the tire cross-sectional width SW. When mounted on the vehicle Ve (shown in FIG. 2), for example, such tire 1 can ensure a large interior space while improving ease of ingress and egress and enabling a low floor. Furthermore, such tire 1 can retain a sufficient air volume to support the total vehicle weight.

[0026] Fig. 3 shows an enlarged cross-sectional view of the tread portion 2 of the tire 1 of Fig. 1. As shown in Fig. 3, a plurality of grooves 13 are provided in the contact surface 2s of the tread portion 2. Although Fig. 3 only shows the cross section of longitudinal grooves extending in the tire circumferential direction, lateral grooves extending in the tire axial direction may also be arranged in the contact surface 2s of the tread portion 2 of this embodiment (not shown).

[0027] In the present invention, the land ratio La, which is the ratio of the actual contact area of ​​the contact patch 2s to the virtual contact area when all of the grooves 13 of the contact patch 2s are filled, is 0.80 to 0.95. In conventional pneumatic tires, the land ratio is often set to approximately 0.60 to 0.80 from the perspective of ensuring drainage. As described above, the tire 1 of the present invention is designed to be mounted on green slow mobility vehicles, and therefore does not require the conventional drainage performance, and the land ratio La can be set high. By setting the land ratio La in the above range, the tire 1 of the present invention can exhibit excellent wear resistance.

[0028] The boundary between the contact patch 2s and the non-contact patch is the tread edge Te, which corresponds to the edge of the contact patch when the tire 1 in the normal state is placed on a flat surface with a camber angle of 0° and is subjected to the maximum load specified by the manufacturer.

[0029] The following describes the configuration of this embodiment in more detail. Note that each configuration described below represents a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-described effects even if it does not include the configurations described below. Furthermore, even if any one of the configurations described below is applied alone to the tire 1 of the present invention having the above-described characteristics, an improvement in performance corresponding to each configuration can be expected. Furthermore, when several of the configurations described below are applied in combination, an improvement in combined performance corresponding to those configurations can be expected.

[0030] From the viewpoint of maintaining various tire performance characteristics while ensuring cabin space, improving ease of ingress and egress, and achieving a low floor, as required for a vehicle Ve (shown in Fig. 2), the tire cross-sectional width SW is preferably 150 to 180 mm, as shown in Fig. 1. The ratio SH / SW is preferably 0.25 to 0.35. Furthermore, the ratio RW / SW is preferably 0.85 to 0.90.

[0031] In order to achieve the above dimensions, tire sizes such as 155 / 40R12 and 175 / 40R12 are adopted for the tire 1 of this embodiment.

[0032] As shown in Fig. 3, the tread portion 2 includes a cap rubber 15 that forms the contact surface 2s. The rubber hardness H of the cap rubber 15 is, for example, preferably 55 or more, more preferably 60 or more, and preferably 70 or less, more preferably 65 or less. This improves the tire's grip and wear resistance in a well-balanced manner.

[0033] In this specification, the rubber hardness refers to the durometer A hardness measured in an environment of 23°C using a durometer type A according to JIS-K6253.

[0034] The inventors have conducted extensive research into the relationship between the land ratio La and the rubber hardness H of the cap rubber 15 and the ride comfort performance, taking into account the driving conditions of the green slow mobility. The driving conditions include the fact that the vehicle is heavy, that it travels at a low speed, that it often travels with a large steering angle due to the low speed, and that many people ride in the vehicle.

[0035] As a result, it was found that it is desirable for the rubber hardness H of the cap rubber 15 to satisfy the following formula (1). In FIG. 4, a desirable relationship between the land ratio La and the rubber hardness H of the cap rubber 15 is shown by graph GR1. Formula (1) indicates that the rubber hardness H is in region 18 (dotted in FIG. 4) above graph GR1 shown in FIG. 4. This optimizes the rubber hardness H of the cap rubber 15 to counter the deterioration of ride comfort due to an increase in the land ratio La, and makes it possible to effectively maintain ride comfort. H≧(275-100La) / 3…(1)

[0036] As shown in Fig. 3, the tread portion 2 includes a belt layer 7. The belt layer 7 of this embodiment includes a plurality of belt plies, each of which includes a plurality of belt cords arranged at an angle with respect to the tire circumferential direction. The belt layer 7 of this embodiment is composed of a first belt ply 11 arranged on the carcass 6 side and a second belt ply 12 arranged on the outer side of the first belt ply 11 in the tire radial direction.

[0037] Fig. 5 is a development view conceptually showing the cord arrangement of the belt layer 7. As shown in Fig. 5, in the first belt ply 11, the belt cords 7a are inclined in a first direction (downward to the right in Fig. 5) with respect to the tire circumferential direction. In addition, in the second belt ply 12, the belt cords 7b are inclined in a second direction (upward to the right in Fig. 5) with respect to the tire circumferential direction. Such a belt layer 7 can reliably reinforce the tread portion 2.

[0038] As described above, since the traveling speed of green slow mobility is low, if the belt cords are arranged at conventional angles, there is a risk of excessively constraining the tread portion 2. From this perspective, the angle θ1 of the belt cords included in the first belt ply with respect to the tire circumferential direction and the angle θ2 of the belt cords included in the second belt ply with respect to the tire circumferential direction are each preferably 40 to 70°, more preferably 50 to 60°. This optimizes the constraining force of the tread portion 2 and improves cushioning properties against unevenness in the road surface.

[0039] The angle θ2 is 90% to 110% of the angle θ1, and in a desirable embodiment, these angles are the same, which improves the conicity of the tire.

[0040] Although the pneumatic tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be modified and implemented in various aspects. [Example]

[0041] Pneumatic tires of size 155 / 40R12 having the basic structure shown in Figure 1 were prototyped based on the specifications in Table 1. Additionally, tires with a land ratio La outside the range of the present invention were prototyped as comparative examples. The comparative example tires were substantially the same as the example tires, except for the above-mentioned points. Each test tire was tested for wear resistance and ride comfort. The common specifications and test methods for each test tire are as follows: Rim: 12x4.5 Tire pressure: 230kPa Test vehicle: Green Slow Mobility

[0042] <Wear resistance> After the test vehicle was driven a certain distance, the amount of wear on the tread was measured and the distance traveled per unit amount of wear was calculated. The results were expressed as an index of the distance traveled. The larger this value, the greater the distance that can be traveled per unit amount of wear, indicating superior wear resistance.

[0043] <Ride comfort> The test vehicle fitted with the test tires was driven and the ride comfort was evaluated by the driver. The results were expressed as a score, with a higher score indicating better ride comfort. The test results are shown in Table 1.

[0044] [Table 1]

[0045] As shown in Table 1, it was confirmed that the tires of the examples exhibited excellent wear resistance performance. It was also confirmed that the tires of the examples maintained ride comfort performance.

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

[0047] [Invention 1] A pneumatic tire that is mounted on a rim and used, The rim diameter RD of the rim is 10 to 15 inches, The tire's cross-sectional width SW is less than 192 mm, a ratio SH / SW of a tire's section height SH to a tire's section width SW is 0.20 to 0.40; a ratio RW / SW of a rim width RW of the rim to a cross-sectional width SW of the tire is 0.78 to 0.99; The pneumatic tire has a tread portion, A plurality of grooves are provided on the ground contact surface of the tread portion, a land ratio La, which is the ratio of the actual ground contact area of ​​the ground contact surface to the virtual ground contact area in a state where all of the grooves of the ground contact surface are filled, is 0.80 to 0.95; Pneumatic tires. [Invention 2] the tread portion includes a cap rubber that forms the ground contact surface, The pneumatic tire according to invention 1, wherein the rubber hardness H of the cap rubber satisfies the following formula (1): H≧(275-100La) / 3…(1) [Invention 3] 3. The pneumatic tire according to claim 2, wherein the rubber hardness H is 70 or less. [Invention 4] The tread portion includes a belt layer, the belt layer includes a plurality of belt plies each including a plurality of belt cords arranged obliquely with respect to the tire circumferential direction, The pneumatic tire according to any one of claims 1 to 3, wherein the belt plies include a first belt ply in which the belt cords are inclined in a first direction with respect to the tire circumferential direction, and a second belt ply in which the belt cords are inclined in a second direction opposite to the first direction with respect to the tire circumferential direction. [Invention 5] The pneumatic tire according to invention 4, wherein an angle θ1 of the belt cord included in the first belt ply with respect to the tire circumferential direction and an angle θ2 of the belt cord included in the second belt ply with respect to the tire circumferential direction are each 40 to 70 degrees. [Invention 6] 6. The pneumatic tire according to claim 5, wherein the angle θ2 is 90% to 110% of the angle θ1. [Invention 7] 7. The pneumatic tire according to any one of claims 1 to 6, wherein the tire has a cross-sectional width SW of 150 to 180 mm. [Invention 8] 8. The pneumatic tire according to any one of claims 1 to 7, wherein the ratio SH / SW is 0.25 to 0.35. [Invention 9] 9. The pneumatic tire according to any one of claims 1 to 8, wherein the ratio RW / SW is 0.85 to 0.90. [Invention 10] 10. The pneumatic tire according to any one of claims 1 to 9, which is for a low-speed electric vehicle having a maximum speed of less than 20 km / h. [Explanation of symbols]

[0048] 2 Tread section 2s ground plane 13 Groove La Land Ratio R rim RD rim diameter SW tire section width SH Tire section height RW rim width

Claims

1. A pneumatic tire that is mounted on a rim and used, The rim diameter RD of the rim is 10 to 15 inches, The tire's section width SW is less than 192 mm, a ratio SH / SW of a tire section height SH to a tire section width SW is 0.20 to 0.40; a ratio RW / SW of a rim width RW of the rim to a cross-sectional width SW of the tire is 0.78 to 0.99; The pneumatic tire has a tread portion, A plurality of grooves are provided on the ground contact surface of the tread portion, a land ratio La, which is a ratio of an actual ground contact area of ​​the ground contact surface to a virtual ground contact area in a state where all of the grooves of the ground contact surface are filled, is 0.80 to 0.95; Pneumatic tires.

2. the tread portion includes a cap rubber that forms the ground contact surface, The pneumatic tire according to claim 1 , wherein the rubber hardness H of the cap rubber satisfies the following formula (1): H≧(275-100La) / 3...(1)

3. The pneumatic tire according to claim 2 , wherein the rubber hardness H is 70 or less.

4. The tread portion includes a belt layer, the belt layer includes a plurality of belt plies each including a plurality of belt cords arranged obliquely with respect to the tire circumferential direction, 4. The pneumatic tire according to claim 1, wherein the belt plies include a first belt ply in which the belt cords are inclined in a first direction with respect to the tire circumferential direction, and a second belt ply in which the belt cords are inclined in a second direction opposite to the first direction with respect to the tire circumferential direction.

5. 5. The pneumatic tire according to claim 4, wherein an angle θ1 of the belt cord included in the first belt ply with respect to the tire circumferential direction and an angle θ2 of the belt cord included in the second belt ply with respect to the tire circumferential direction are each 40 to 70 degrees.

6. The pneumatic tire according to claim 5, wherein the angle θ2 is 90% to 110% of the angle θ1.

7. 4. The pneumatic tire according to claim 1, wherein the tire has a cross-sectional width SW of 150 to 180 mm.

8. 4. The pneumatic tire according to claim 1, wherein the ratio SH / SW is 0.25 to 0.

35.

9. 4. The pneumatic tire according to claim 1, wherein the ratio RW / SW is 0.85 to 0.

90.

10. The pneumatic tire according to any one of claims 1 to 3, which is for a low-speed electric vehicle having a maximum speed of less than 20 km / h.

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