Pneumatic tire

Abstract

To provide a pneumatic tire that can effectively reduce air resistance and make irregularities appearing on side wall parts unnoticeable so as to improve outer appearance.SOLUTION: A pneumatic tire comprises a tread part 1, a pair of side wall parts 2 and a pair of bead parts 3, in which serration regions 10, which include a plurality of groove parts 11 extended in a tire circumferential direction and arranged in a tire radial direction and a plurality of ridge parts 12 formed between the groove parts 11, are formed at sites closer to the outside in the tire radial direction than a tire maximum width position Pmax on outer surfaces of the side wall parts 2. Groove depths D of the groove parts 11 are in a range of 0.1 mm to 1.0 mm, and the groove depth D of the groove part 11 positioned closer to the outside in the tire radial direction becomes larger.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic tire having a serration region including a plurality of grooves and a plurality of ridges on the outer surface of the sidewall portion, and more specifically to a pneumatic tire that effectively reduces air resistance and improves appearance by making unevenness appearing on the sidewall portion less noticeable. [Background technology]

[0002] As pneumatic tires become lighter, the rubber thickness of the sidewall portion has become thinner, which can result in unevenness on the surface of the sidewall portion at areas corresponding to splices of the carcass layer, etc. In order to make such unevenness on the sidewall portion less noticeable, it has been proposed to provide a serration region on the outer surface of the sidewall portion, which includes a plurality of grooves extending in the tire radial direction and aligned in the tire circumferential direction, and a plurality of ridges formed between these grooves (see, for example, Patent Documents 1 to 3).

[0003] However, the serration region, which includes a plurality of radially arranged grooves and ridges extending in the tire radial direction, is not necessarily effective in making the irregularities that appear on the sidewall less noticeable. Therefore, there is a need to improve the appearance by improving the effect of making the irregularities that appear on the sidewall less noticeable. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-33983 [Patent Document 2] Japanese Patent Application Publication No. 2018-2113 [Patent Document 3] Japanese Patent Application Publication No. 2019-94008 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a pneumatic tire that effectively reduces air resistance and makes unevenness appearing on the sidewall less noticeable, thereby improving the appearance. [Means for solving the problem]

[0006] In order to achieve the above object, a pneumatic tire of the present invention includes a tread portion extending in a circumferential direction of the tire to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the radially inner side of the sidewall portions, The tire has a serration region on the outer surface of the sidewall portion, located radially outward of the maximum tire width position, which region includes a plurality of grooves extending circumferentially and aligned radially, and a plurality of ridges formed between these grooves, and the groove depth D of the grooves is in the range of 0.1 mm to 1.0 mm, and the groove depth D is greater for grooves located radially outward. [Effects of the Invention]

[0007] In the present invention, a serration region including a plurality of grooves extending circumferentially and aligned radially on the outer surface of the sidewall portion, and a plurality of ridges formed between these grooves, is provided in a region radially outward of the maximum tire width position on the outer surface of the sidewall portion, thereby making unevenness appearing on the sidewall portion less noticeable. In particular, the unevenness of the sidewall portion is more noticeable in the radially outer portion of the sidewall portion. By increasing the groove depth D of grooves located radially outward, light reflection can be effectively suppressed, enhancing the effect of making unevenness appearing on the sidewall portion less noticeable, thereby improving the tire appearance. Furthermore, because the ridges formed between the grooves extend circumferentially, the contact area with the air layer that stagnates along the sidewall portion during tire rotation can be reduced, effectively reducing air resistance.

[0008] In the present invention, when the groove depth of the groove portion arranged radially innermost among the plurality of groove portions is defined as D1 and the groove depth of the groove portion arranged radially outermost among the plurality of groove portions is defined as D2, it is preferable to satisfy the relationship D2 / D1 ≥ 1.5. This effectively suppresses light reflection on the radially outer portion of the sidewall portion, making irregularities that appear on the sidewall portion less noticeable.

[0009] The groove opening width W is preferably in the range of 0.6 mm to 2.0 mm, and the grooves located radially outward preferably have smaller opening widths W. This effectively suppresses light reflection at the radially outer portions of the sidewalls, making irregularities that appear on the sidewalls less noticeable.

[0010] When the opening width of the groove portion located on the innermost side in the tire radial direction among the plurality of groove portions is defined as W1 and the opening width of the groove portion located on the outermost side in the tire radial direction among the plurality of groove portions is defined as W2, it is preferable to satisfy the relationship W2 / W1≦0.7, which effectively suppresses light reflection on the outer sidewall portion in the tire radial direction and makes irregularities that appear on the sidewall portion less noticeable.

[0011] When the groove bottom width of the groove portion located at the innermost side in the tire direction among the plurality of groove portions is B1 and the groove bottom width of the groove portion located at the outermost side in the tire direction among the plurality of groove portions is B2, it is preferable to satisfy the relationship B2 / B1≦0.7, which effectively suppresses light reflection on the outer sidewall portion in the tire radial direction and makes irregularities that appear on the sidewall portion less noticeable. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. [Figure 2] 2 is a side view showing a serration region formed in a sidewall portion of the pneumatic tire of FIG. 1. FIG. [Figure 3] FIG. 3 is a meridian cross-sectional view showing an enlarged view of a serration region formed in a sidewall portion. [Figure 4] FIG. 10 is a meridian cross-sectional view showing an enlarged view of a modified example of a serration region formed in a sidewall portion. [Figure 5] FIG. 10 is an enlarged meridian cross-sectional view showing another modified example of the serration region formed in the sidewall portion. [Figure 6] FIG. 10 is an enlarged meridian cross-sectional view showing another modified example of the serration region formed in the sidewall portion. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 shows a pneumatic tire according to an embodiment of the present invention;

[0014] As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially in a ring shape, a pair of sidewall portions 2, 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3, 3 arranged radially inward of the sidewall portions 2.

[0015] A carcass layer 4 is mounted between a pair of bead portions 3, 3. This carcass layer 4 includes a plurality of carcass cords extending in the tire radial direction, and is folded back from the inside to the outside of the tire around a bead core 5 disposed in each bead portion 3. Organic fiber cords such as polyester are preferably used as the carcass cords of the carcass layer 4. A bead filler 6 made of a rubber composition and having a triangular cross section is disposed on the outer periphery of the bead core 5.

[0016] On the other hand, multiple belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include multiple belt cords that are inclined with respect to the tire circumferential direction, and are arranged so that the belt cords cross each other between the layers. In the belt layers 7, the inclination angle of the belt cords with respect to the tire circumferential direction is set in the range of 10° to 40°, for example. Steel cords are preferably used as the belt cords of the belt layers 7.

[0017] A belt cover layer 8 is disposed on the outer periphery of the belt layer 7, with the aim of improving high-speed durability. The belt cover layer 8 may be a full cover layer that covers the entire width of the belt layer 7, or a pair of edge cover layers that locally cover both ends of the belt layer 7 in the tire width direction, either alone or in combination. The belt cover layer 8 may be formed, for example, by spirally winding a strip material in the tire circumferential direction, in which at least one reinforcing cord is aligned and covered with a coating rubber. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon is preferably used.

[0018] The tire internal structure described above is a typical example of a pneumatic tire, but is not limited to this. In the pneumatic tire, the tire maximum width position Pmax is the position where the cross-sectional width of the pneumatic tire is greatest.

[0019] In the pneumatic tire described above, as shown in FIGS. 1 to 3, a serration region 10 is formed in an annular shape in a region on the outer surface of the sidewall portion 2 radially outward of the tire's maximum width position Pmax. The serration region 10 includes a plurality of groove portions 11 extending in the tire circumferential direction and aligned in the tire radial direction, and a plurality of ridge portions 12 formed between these groove portions 11. That is, the plurality of groove portions 11 extending in the tire circumferential direction and the plurality of ridge portions 12 extending in the tire circumferential direction are alternately arranged along the tire radial direction. While both the groove portions 11 and the ridge portions 12 are preferably annular, it is also possible for the groove portions 11 and the ridge portions 12 to each be configured in a spiral shape, for example.

[0020] As shown in FIG. 3, in the tire meridian cross section, the groove portion 11 has a groove depth D, an opening width W, and a groove bottom width B. The groove depth D is the depth from a reference profile line of the sidewall portion 2 (i.e., a profile line passing through the apex of the ridge portion 12) to the groove bottom of the groove portion 11, the opening width W is the width of the groove portion 11 at the apex position of the ridge portion 12, and the groove bottom width B is the width of the groove bottom of the groove portion 11. The reference profile line is generally a curve, but is depicted as a straight line in FIG. 3 for ease of understanding. In FIG. 3, "OUT" indicates the outer side in the tire radial direction, and "IN" indicates the inner side in the tire radial direction. The groove depth D of the groove portion 11 is in the range of 0.1 mm to 1.0 mm, and is set so that the groove depth D increases as the groove portion 11 is located radially outward in the tire.

[0021] The pneumatic tire described above includes a serration region 10 including a plurality of grooves 11 extending circumferentially and aligned radially on the outer surface of the sidewall portion 2 radially outward of the tire's maximum width position Pmax. The serration region 10 includes a plurality of grooves 11 extending circumferentially and aligned radially, and a plurality of ridges 12 formed between the grooves 11. This makes it possible to reduce the visibility of irregularities on the surface of the sidewall portion 2 at splices of the carcass layer 4 or the like. In particular, the irregularities on the sidewall portion 2 are more noticeable on the radially outer side of the sidewall portion 2. By increasing the groove depth D of the grooves 11 located radially outward, light reflection can be effectively reduced, enhancing the effect of reducing the visibility of irregularities on the sidewall portion 2 and improving the appearance. Furthermore, because the ridges 12 formed between the grooves 11 extend circumferentially, the contact area with the air layer that stagnates along the sidewall portion 2 during tire rotation can be reduced, effectively reducing air resistance.

[0022] Here, if the groove depth D of the groove portion 11 is less than 0.1 mm, the effect of making the unevenness appearing in the sidewall portion 2 less noticeable will be insufficient, and conversely, if it exceeds 1.0 mm, the distance between the groove bottom of the groove portion 11 and the carcass layer 4, which is a reinforcing material, will become small, raising concerns about reduced durability.

[0023] In the pneumatic tire, as shown in FIG. 4 , when the groove depth of the groove 11 located at the innermost side in the tire radial direction among the plurality of grooves 11 is D1 and the groove depth of the groove 11 located at the outermost side in the tire radial direction among the plurality of grooves 11 is D2, it is preferable to satisfy the relationship D2 / D1 ≥ 1.5. This effectively suppresses light reflection at the tire radially outer portion of the sidewall portion 2, making irregularities that appear in the sidewall portion 2 less noticeable. Here, if D2 / D1 is less than 1.5, the effect of making irregularities in the sidewall portion 2 less noticeable is reduced. Furthermore, if D2 / D1 is too large, the distance between the groove bottom of the groove 11 and the carcass layer 4, which serves as a reinforcing material, becomes small at the tire radially outer portion of the sidewall portion 2, raising concerns about reduced durability. Therefore, it is preferable to satisfy the relationship 1.5 ≤ D2 / D1 ≤ 10.0.

[0024] In the pneumatic tire described above, as shown in Fig. 4, the opening width W of the groove portions 11 is preferably set to be in the range of 0.6 mm to 2.0 mm, with the opening width W of the groove portions 11 being smaller as they are positioned radially outward in the tire. This effectively suppresses light reflection at the radially outer portions of the sidewall portions 2, making irregularities that appear in the sidewall portions 2 less noticeable. If the opening width W of the groove portions 11 is less than 0.6 mm, there are concerns about mold processing, and conversely, if it exceeds 2.0 mm, the effect of making irregularities that appear in the sidewall portions 2 less noticeable is reduced.

[0025] In the pneumatic tire, as shown in FIG. 4, when the opening width of the groove portion 11 located at the innermost position in the tire radial direction among the plurality of groove portions 11 is W1 and the opening width of the groove portion 11 located at the outermost position in the tire radial direction among the plurality of groove portions 11 is W2, it is preferable to satisfy the relationship W2 / W1≦0.7. This effectively suppresses light reflection at the outer portion of the sidewall portion 2 in the tire radial direction, making irregularities that appear in the sidewall portion 2 less noticeable. Here, if W2 / W1 exceeds 0.7, the effect of making irregularities in the sidewall portion 2 less noticeable is reduced. Furthermore, if W2 / W1 is too small, there are concerns about mold processing, so it is preferable to satisfy the relationship 0.5≦W2 / W1≦0.7.

[0026] In the pneumatic tire, as shown in Fig. 4, it is preferable that the groove bottom width B of the groove portion 11 is in the range of 0.4 mm to 1.3 mm, and that the groove bottom width B is smaller for groove portions 11 located radially outward in the tire. This effectively suppresses light reflection at the radially outer portions of the sidewall portion 2, making irregularities that appear in the sidewall portion 2 less noticeable. If the groove bottom width B of the groove portion 11 is less than 0.4 mm, there are concerns about mold processing, and conversely, if it exceeds 1.3 mm, the effect of making irregularities that appear in the sidewall portion 2 less noticeable is reduced.

[0027] In the pneumatic tire, as shown in FIG. 4, when the groove bottom width of the groove 11 located at the innermost position in the tire radial direction among the plurality of grooves 11 is B1 and the groove bottom width of the groove 11 located at the outermost position in the tire radial direction among the plurality of grooves 11 is B2, it is preferable to satisfy the relationship B2 / B1≦0.7. This effectively suppresses light reflection at the outer portion of the sidewall portion 2 in the tire radial direction, making irregularities that appear in the sidewall portion 2 less noticeable. Here, if B2 / B1 exceeds 0.7, the effect of making irregularities in the sidewall portion 2 less noticeable is reduced. Furthermore, if B2 / B1 is too small, there are concerns about mold processing, so it is preferable to satisfy the relationship 0.5≦B2 / B1≦0.7.

[0028] 5 and 6 each show another modified example of the serration region formed in the sidewall portion. In FIG. 5, the groove bottoms of the groove portions 11 converge to form a corner, and the groove bottom width B is substantially 0 mm. In FIG. 6, the top portions of the ridge portions 12 are flat. Even when the serration region has the above-described structure, by increasing the groove depth D of the groove portions 11 located radially outward, it is possible to effectively suppress light reflection and enhance the effect of making irregularities appearing in the sidewall portion 2 less noticeable. [Example]

[0029] Tires of Comparative Examples 1 to 3 and Examples 1 to 8 were manufactured in which the tire size was 155 / 65R14 and the pneumatic tire had a tread portion, a pair of sidewall portions, and a pair of bead portions, and the tire had a serration region including multiple grooves and multiple ridge portions in a portion of the outer surface of the sidewall portion that was radially outward of the maximum tire width position, and the orientation direction of the grooves, the direction in which the groove depth D of the grooves increased, the range of the groove depth D, D2 / D1, the direction in which the groove opening width W of the grooves decreased, the range of the opening width W, W2 / W1, the direction in which the groove bottom width B of the grooves decreased, the range of the groove bottom width B, B2 / B1 were set as shown in Table 1.

[0030] In Table 1, for the direction in which the groove depth D of the groove portion increases, the direction in which the opening width W of the groove portion decreases, and the direction in which the groove bottom width B of the groove portion decreases, "inner" means the inner side in the tire radial direction, "outer" means the outer side in the tire radial direction, and "constant" means that the dimensions are constant.

[0031] The test tires were evaluated for air resistance and appearance using the following evaluation methods, and the results are shown in Table 1.

[0032] Tire air resistance: Each test tire was mounted on a wheel with a rim size of 14 x 4.5J, and the tire was mounted on a FR passenger car with an engine displacement of 660cc at an air pressure of 240 kPa, and the tire's air resistance was measured while the vehicle was running. The air resistance was calculated based on the fuel efficiency when the vehicle was run a predetermined distance. The evaluation results were expressed as an index value, with Comparative Example 1 being set at 100. The higher the index value, the lower the tire's air resistance.

[0033] exterior: For each test tire, 20 panelists evaluated the visibility of unevenness occurring in the sidewall portion on a scale of 1 to 5. In this evaluation, a 5-point scale was used, with 1 point being assigned when the unevenness was clearly visible and 5 points being assigned when the unevenness was completely invisible. The sum of the evaluation scores from the 20 panelists was then calculated. The evaluation results were expressed as an index value, with the comparative example being assigned an index value of 100. The higher the index value, the better the tire's appearance.

[0034] [Table 1]

[0035] As can be seen from Table 1, the pneumatic tires of Examples 1 to 8 were able to effectively reduce air resistance and improve appearance by making irregularities appearing on the sidewall less noticeable, compared to Comparative Example 1. On the other hand, the tire of Comparative Example 2 had a constant groove depth D, which made the effect of making irregularities appearing on the sidewall less noticeable. Similarly, the tire of Comparative Example 3 had a groove depth D that was smaller in the grooves located radially outward, which reduced the effect of making irregularities appearing on the sidewall less noticeable.

[0036] The present disclosure includes the following inventions [1] to [5]. Invention [1] is a pneumatic tire having a tread portion extending in the tire circumferential direction and forming an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the tire radially inner side of the sidewall portions, The pneumatic tire is characterized in that it has a serration region on the outer surface of the sidewall portion radially outward of the maximum tire width position, the serration region including a plurality of grooves extending circumferentially of the tire and aligned radially of the tire, and a plurality of ridges formed between these grooves, the groove depth D of the grooves being in the range of 0.1 mm to 1.0 mm, and the groove depth D is greater for grooves located radially outward. Invention [2] is the pneumatic tire according to invention [1], characterized in that, when the groove depth of the groove portion arranged radially innermost of the plurality of groove portions is D1 and the groove depth of the groove portion arranged radially outermost of the plurality of groove portions is D2, the relationship D2 / D1≧1.5 is satisfied. Invention [3] is a pneumatic tire according to invention [1] or [2], characterized in that the opening width W of the groove portion is in the range of 0.6 mm to 2.0 mm, and the opening width W of the groove portion located radially outward in the tire is smaller. Invention [4] is the pneumatic tire according to invention [3], characterized in that, when the opening width of the groove portion arranged radially innermost among the plurality of groove portions is defined as W1 and the opening width of the groove portion arranged radially outermost among the plurality of groove portions is defined as W2, the relationship W2 / W1≦0.7 is satisfied. Invention [5] is a pneumatic tire according to any one of inventions [1] to [4], characterized in that, when the groove bottom width of the groove portion arranged radially innermost among the plurality of groove portions is B1 and the groove bottom width of the groove portion arranged radially outermost among the plurality of groove portions is B2, the relationship B2 / B1≦0.7 is satisfied. [Explanation of symbols]

[0037] 1 Tread section 2 Sidewall 3 Bead section 4 carcass layers 5 bead core 6 Bead filler 7 Belt Layer 8 Belt cover layer 10 Serration Area 11 Groove 12 Ridge Pmax Tire maximum width position

Claims

1. A pneumatic tire having a tread portion extending in a tire circumferential direction to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the tire radially inner side of the sidewall portions, A pneumatic tire comprising: a serration region including a plurality of grooves extending in the tire circumferential direction and aligned in the tire radial direction, and a plurality of ridges formed between these grooves, in a region on the outer surface of the sidewall portion radially outward of a maximum tire width position; a groove depth D of the grooves ranging from 0.1 mm to 1.0 mm; and a groove depth D greater for grooves positioned radially outward.

2. 2. The pneumatic tire according to claim 1, wherein when a groove depth of the groove portion arranged at the innermost side in the tire radial direction among the plurality of groove portions is defined as D1 and a groove depth of the groove portion arranged at the outermost side in the tire radial direction among the plurality of groove portions is defined as D2, the relationship D2 / D1 ≧ 1.5 is satisfied.

3. 3. The pneumatic tire according to claim 1, wherein the opening width W of the groove portion is in the range of 0.6 mm to 2.0 mm, and the opening width W of the groove portion is smaller as it is positioned radially outward.

4. 4. The pneumatic tire according to claim 3, wherein when an opening width of the groove portion arranged at the innermost side in the tire radial direction among the plurality of groove portions is defined as W1 and an opening width of the groove portion arranged at the outermost side in the tire radial direction among the plurality of groove portions is defined as W2, the relationship W2 / W1≦0.7 is satisfied.

5. 3. The pneumatic tire according to claim 1, wherein when a groove bottom width of the groove portion arranged at the innermost side in the tire radial direction among the plurality of groove portions is defined as B1 and a groove bottom width of the groove portion arranged at the outermost side in the tire radial direction among the plurality of groove portions is defined as B2, the relationship B2 / B1≦0.7 is satisfied.

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