tire

Abstract

To provide a tire which can reduce air columnar resonance sound when a vehicle is travelling.SOLUTION: A tire is a tire having a plurality of circumferential main grooves 2 on a tread 1, wherein, when a pair of circumferential main grooves that are arranged so as to be closest to each of tread ends on both sides in a tire width direction out of the plurality of circumferential main grooves 2 are represented by shoulder main grooves 21a and 21b, at least the one shoulder main groove is a normal main groove configured so that the maximum groove width position in a groove depth direction is only a tread, and at least the one circumferential main groove other than at least the one shoulder main groove is a wide main groove configured so that at least the one maximum groove width position in the groove depth direction is closer to a groove bottom side than the tread position.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Conventionally, in the noise generated by a moving automobile, the contribution of noise caused by the rolling load of the tire has increased along with the quieting of the vehicle, and there has been a demand for reducing the noise. In particular, noise caused by air column resonance is the main cause of external noise generated by tires. Air column resonance is noise generated by resonance of air in a tube surrounded by the road surface and the circumferential grooves that extend continuously in the circumferential direction of the tread surface.

[0003] Here, as an example of a tire intended to reduce air column resonance noise, there is a tire that is provided with a Helmholtz-type resonator in a land portion separated by a plurality of circumferential main grooves, the Helmholtz-type resonator being composed of a cavity that is substantially sealed inside the land portion and whose both longitudinal ends are terminated inside the land portion, and communication holes and sipes that connect the cavity with the circumferential main grooves (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-116195 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is a demand for reducing air column resonance noise with a simpler configuration or the like.

[0006] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a tire capable of reducing air column resonance noise generated when a vehicle is running. [Means for solving the problem]

[0007] The gist of the present invention is as follows. A tire having a plurality of circumferential main grooves on a tread surface, the groove width being such that both side walls do not contact each other when the tire is in contact with the ground, Among the plurality of circumferential main grooves, a pair of circumferential main grooves disposed closest to the tread ends on both sides in the tire width direction are referred to as shoulder main grooves. At least one of the shoulder main grooves is a normal main groove configured such that a maximum groove width position in a groove depth direction is only at a tread surface position, At least one of the circumferential main grooves other than the at least one shoulder main groove is a widening main groove configured such that at least one maximum groove width position in the groove depth direction is located closer to the groove bottom than the tread surface position. According to the tire of the present invention, it is possible to reduce air column resonance noise during vehicle running.

[0008] In the tire of the present invention, When the circumferential main groove other than the shoulder main groove is referred to as a center main groove, The circumferential main groove includes the pair of shoulder main grooves and at least one of the center main grooves, It is preferable that the pair of shoulder main grooves are the normal main grooves, and the center main groove is the widened main groove. This allows the frequencies of air column resonance noise generated when the vehicle is running to be dispersed in a well-balanced manner, making it possible to more effectively reduce air column resonance noise generated when the vehicle is running.

[0009] In the tire of the present invention, The ratio of the number of the widening main grooves to the number of the normal main grooves is preferably 1 / 1 to 3 / 2. This allows the frequencies of air column resonance noise generated when the vehicle is running to be dispersed in a well-balanced manner, making it possible to more effectively reduce air column resonance noise generated when the vehicle is running.

[0010] In the tire of the present invention, It is preferable that the widened main groove has a portion in which the groove width gradually increases from the tread surface side toward the groove bottom side. This makes it possible to suppress, over the long term, the deterioration of drainage performance that occurs as wear progresses.

[0011] In the tire of the present invention, It is preferable that the minimum groove width of the circumferential main groove is 1.5 mm or more. This makes it possible to effectively reduce air column resonance noise while the vehicle is running, and also ensures sufficient drainage both when new and when the tire has become worn.

[0012] In the tire of the present invention, It is preferable that the tire has a width direction groove that communicates with the shoulder main groove, which is the normal main groove, extends in the tire width direction, and opens at a tread end. This makes it possible to more efficiently reduce air column resonance noise while the vehicle is running.

[0013] In the tire of the present invention, It is preferable that the widthwise groove has a groove width on the tread surface that is larger on the tread end side than on the side communicating with the shoulder main groove, which is the normal main groove. This makes it possible to further reduce air column resonance noise while the vehicle is running, while also ensuring sufficient drainage. Effect of the Invention

[0014] According to the present invention, it is possible to provide a tire capable of reducing air column resonance noise during vehicle travel. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a partial development view that illustrates a tread surface of a tire according to a first embodiment of the present invention. [Diagram 2] 2 is a tire widthwise cross-sectional view showing a part of the tire of FIG. 1 in a cross section taken along line AA of FIG. [Figure 3A] 3 is a partial cross-sectional view in the tire width direction, showing an enlarged schematic view of a part of the tire shown in FIG. 2. [Figure 3B] 3 is a partial cross-sectional view in the tire width direction, showing an enlarged schematic view of a part of the tire shown in FIG. 2. [Figure 4] FIG. 11 is a diagram for explaining the frequency of air column resonance sound. [Diagram 5] 11A and 11B are diagrams for explaining another example of a widened main groove. [Figure 6] FIG. 4 is a partial development view that illustrates a tread surface of a tire according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a diagram for explaining the frequency of air column resonance sound. [Figure 8] FIG. 7 is a partially expanded schematic view of a portion of the tread surface shown in FIG. 6. [Figure 9] 13A and 13B are diagrams for explaining other examples of width direction grooves. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The tire according to the present invention may be used for any type of tire, but is preferably used for passenger vehicle tires. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a tire according to the present invention will be described with reference to the drawings. In each drawing, the same components are designated by the same reference numerals.

[0017] The tire of each embodiment described in this specification may have any internal configuration. The tire of each embodiment described in this specification may have, for example, a pair of bead cores (not shown) provided in a pair of bead portions, a pair of bead fillers (not shown) located on the tire radial direction outer side of the bead cores, a carcass 70 (FIG. 2), a belt 60 (FIG. 2), and a tread rubber 80 (FIG. 2). The carcass 70 extends in a toroidal shape between the pair of bead cores. The carcass 70 includes at least one carcass ply (one layer in the illustrated example). The carcass ply of the carcass 70 may have a configuration in which, for example, a cord made of steel or organic fiber is covered with rubber. The carcass 70 may include, for example, a main body portion extending in a toroidal shape between the pair of bead cores, and a pair of folded-up portions folded back from the tire radial direction innermost end of the main body portion around the bead core toward the tire width direction outer side on each side of the tire equatorial plane CL. The belt 60 is disposed on the tread portion 90, radially outward of the crown region of the carcass 70 (FIG. 2). The belt 60 is made of at least one belt layer (two layers in the illustrated example). The belt layer may have a configuration in which a cord made of steel or organic fiber is covered with rubber. The tread rubber 80 is disposed on the radially outward of the belt 60.

[0018] In this specification, the term "tread surface (1)" refers to the outer peripheral surface of the tire that comes into contact with the road surface when the tire is mounted on a rim, inflated to a predetermined internal pressure, and rolls under a maximum load. In this specification, the term "tread edge (TE)" means an end of the tread surface (1) in the tire width direction. In addition, in this specification, "contact length" refers to the length along the circumferential direction of the tire at the contact surface between the tire and the road surface, and "contact surface" refers to the outer peripheral surface of the tire that comes into contact with the road surface when the tire, which has been mounted on a rim and inflated to a predetermined internal pressure, is placed in contact with the road surface under a maximum load. Here, "rim" refers to the standard rim (Measuring Rim in the ETRTO STANDARDS MANUAL, Design Rim in the TRA YEAR BOOK) for the applicable size that is described or will be described in the future in the industrial standards valid in the region where the tire is produced and used, such as the JATMA YEAR BOOK of the Japan Automobile Tire Manufacturers Association (JATMA) in Japan, the STANDARDS MANUAL of the ETRTO (The European Tyre and Rim Technical Organisation) in Europe, and the YEAR BOOK of the TRA (The Tire and Rim Association, Inc.) in the United States (in other words, the above "rim" includes not only current sizes, but also sizes that may be included in the above industrial standards in the future. An example of "sizes that will be described in the future" is the size described as "FUTURE DEVELOPMENTS" in the 2013 edition of the ETRTO STANDARDS MANUAL.), however, in the case of a size not described in the above industrial standards, it refers to a rim with a width that corresponds to the bead width of the tire. In addition, "specified internal pressure" refers to the air pressure (maximum air pressure) that corresponds to the maximum load capacity of a single wheel for the applicable size and ply rating, as listed in the above-mentioned JATMA YEAR BOOK, etc., and in the case of sizes not listed in the above-mentioned industrial standards, it refers to the air pressure (maximum air pressure) that corresponds to the maximum load capacity specified for each vehicle on which the tire is mounted. "Maximum load" refers to the load corresponding to the maximum load capacity. The air referred to here can be replaced with an inert gas such as nitrogen gas or the like.

[0019] In this specification, unless otherwise specified, the dimensions of each element such as a groove or land portion, the contact width (TW), etc. are measured in the "reference state" described below. In this specification, the "reference condition" refers to a state in which a tire is mounted on a rim, inflated to the above-mentioned specified internal pressure, and no load is applied.

[0020] In this specification, the "groove width of the circumferential main groove" refers to the length of the circumferential main groove measured in the above-mentioned reference state in a direction perpendicular to the extension direction of the circumferential main groove. Similarly, the "groove width of the width direction groove" refers to the length of the width direction groove measured in the reference state in a direction perpendicular to the extension direction of the width direction groove.

[0021] [First embodiment] Hereinafter, a tire according to a first embodiment of the present invention will be described with reference to Figs. 1, 2, 3A and 3B. Fig. 1 is a partial development view showing a tread surface 1 of a tire 10 according to a first embodiment of the present invention. Fig. 2 is a tire width direction cross-sectional view showing a part of the tire 10 in Fig. 1 as a cross section taken along line AA in Fig. 1. Fig. 3A is a tire width direction partial cross-sectional view showing an enlarged schematic view of a part of the tire shown in Fig. 2, and Fig. 3B is a tire width direction partial cross-sectional view showing an enlarged schematic view of a part of the tire shown in Fig. 2.

[0022] As shown in FIG. 1, the tire 10 of the first embodiment has a plurality of circumferential main grooves 2 on the tread surface 1. Each circumferential main groove 2 extends in the tire circumferential direction. As shown in FIG. 1, each circumferential main groove 2 may extend linearly along the circumferential direction, or may extend in a zigzag or wavy manner. Of these multiple circumferential main grooves 2, a pair of circumferential main grooves arranged closest to the tread ends TE on both sides in the tire width direction are referred to as a pair of shoulder main grooves 21a and 21b. Furthermore, a circumferential main groove located on the inner side in the tire width direction from the pair of shoulder main grooves 21a and 21b is referred to as a center main groove 22. In addition, it is preferable from the viewpoint of drainage performance that the number of circumferential main grooves 2 is three or more as in this embodiment (three in this embodiment), but it may be two.

[0023] Each circumferential main groove 2 has a groove width that prevents both side walls from contacting each other when the tire is in contact with the ground. That is, when the tire is mounted on a rim, inflated to a predetermined internal pressure, and subjected to a maximum load, a pair of opposing groove walls are configured not to contact each other at a position directly under the load.

[0024] In addition, in the tread surface 1 of the tire 10 of the first embodiment, four land portions 31a, 31b, 32a, and 32b are defined by the shoulder main grooves 21a and 21b, the center main groove 22, and the tread edge TE. The shoulder land portions 31a and 31b are defined on the outer side in the tire width direction by the tread edge TE and the shoulder main grooves 21a and 21b, and the center land portions 32a and 32b are defined on the inner side in the tire width direction from the land portions 31a and 31a by the center main groove 22 and the shoulder main grooves 21a and 22b.

[0025] As shown in Fig. 2 and Fig. 3A, at least one of the shoulder main grooves, both of the pair of shoulder main grooves 21a and 21b in the first embodiment, is a normal main groove configured such that the maximum groove width position in the groove depth direction is only at the tread surface position. That is, in the standard state, the shoulder main grooves 21a and 21b have a maximum groove width w1 at the tread surface 1 position, and have a groove width smaller than the groove width w1 at any position on the tire radial direction inner side than the tread surface 1, i.e., on the groove bottom side. In the tire 10 of this embodiment, the groove width gradually decreases from the groove width w1 side on the tread surface 1 toward the tire radial direction inner side, and the groove width w2 at the groove bottom is the minimum groove width. Note that the "normal main groove" only needs to have a maximum groove width position at the tread surface position, and the minimum groove width position may be at a position other than the groove bottom. Here, "gradually decreasing" means that the groove width is constantly decreasing.

[0026] As shown in FIG. 2 and FIG. 3B, at least one circumferential main groove other than at least one shoulder main groove, which is the center main groove 22 in this embodiment, is a widening main groove configured such that at least one maximum groove width position in the groove depth direction is located at a position closer to the groove bottom than the tread surface position. In this embodiment, the center main groove 22 has a maximum groove width w4 at the groove bottom in the reference state, and has a groove width smaller than the groove width w4 at any position on the tire radial direction outer side than the groove bottom, i.e., on the tread surface 1 side. In this embodiment, the groove width gradually decreases from the groove width w4 side at the groove bottom toward the tire radial direction outer side, and the groove width w3 at the tread surface 1 is the minimum groove width. Note that the "widening main groove" is sufficient as long as at least one of the maximum groove width positions in the groove depth direction is located closer to the groove bottom than the tread surface position, and the "widening main groove" also includes a configuration in which there are multiple maximum groove width positions in the groove depth direction and a configuration in which the groove width is constant in the groove depth direction. However, from the viewpoint of more effectively obtaining the air column resonance sound reduction effect described below, it is preferable that the "widened main groove" does not have a constant groove width in the groove depth direction, and further, that all maximum groove width positions in the groove depth direction are located closer to the groove bottom than the tread surface.

[0027] Hereinafter, the effects of the tire configuration of the first embodiment will be described with reference to FIG.

[0028] 4 is a diagram for explaining the frequency of air column resonance in the circumferential main groove, which shows the relationship between sound pressure and frequency of air column resonance in the normal main groove and air column resonance in the widened main groove. In the normal main groove, the maximum groove width position is only at the tread surface position, so that the opening of the groove that comes into contact with the road surface and air has a shape that is, so to speak, open. In contrast, in the widened main groove, the maximum groove width position is located closer to the bottom side of the tread surface position than the tread surface position, so that the opening of the groove that comes into contact with the road surface and air has a shape that is, so to speak, closed compared to the normal main groove. In this case, the widened main groove behaves as a relatively "longer" pipe than the normal main groove of the same cross-sectional area due to the open end correction. In this way, when the pipe behaves as if it is relatively long, the frequency of the air column resonance sound generated in the circumferential main groove during vehicle running becomes relatively lower. Therefore, in the widened main groove, the peak of the sound pressure level can be shifted to the lower frequency side compared to the normal main groove. In this way, by shifting the frequency at the peak of the air column resonance sound generated in the circumferential main groove while the vehicle is traveling between the normal main groove and the widened main groove, the peak value of the sum of these sound pressures can be lowered, thereby reducing the air column resonance sound and mitigating the noise of the entire tire (making it less harsh to the ear).

[0029] In addition, according to the tire of this embodiment, the maximum groove width position of the center main groove 22 is configured to be at the groove bottom rather than at the tread surface position, so that when the tire wears, the wide groove width portion is exposed to the tread surface 1, and drainage can be improved as wear progresses compared to when the maximum groove width position of the center main groove 22 is at the tread surface position, and drainage can be suppressed even when wear progresses. Since the center main groove 22 is located on the inner side in the tire width direction than the shoulder main grooves 21a and 21b, the ground contact pressure in the tire width direction when the tire travels straight tends to be relatively higher than that on the shoulder main groove side, which is particularly effective in ensuring sufficient drainage when the tire travels straight when wear progresses.

[0030] Hereinafter, preferred configurations and modified examples of the tire of the first embodiment will be described.

[0031] In the tire 10 of the first embodiment, the number of normal main grooves and widening main grooves is not particularly limited as long as there is at least one of each, but it is preferable that the circumferential main grooves 2 include a pair of shoulder main grooves 21a and 21b and at least one center main groove 22, with the pair of shoulder main grooves 21a and 21b being normal main grooves and the center main groove 22 being a widening main groove. Generally, the contact length of a tire is longer on the tire equatorial plane CL side than on the tread edge TE side, and therefore the contact length of the circumferential main groove is generally longer on the tire equatorial plane CL side than on the tread edge TE side. On the other hand, when comparing circumferential main grooves with the same cross-sectional shape and dimensions, the frequency of the sound pressure peak of the air column resonance sound is lower in the circumferential main groove with a longer contact length than in the circumferential main groove with a shorter contact length, and therefore, in general, the frequency of the sound pressure peak of the air column resonance sound is lower in the circumferential main groove on the tire equatorial plane CL side than in the circumferential main groove on the tread edge TE side. Therefore, by making the circumferential main groove on the tread end TE side a normal main groove and making the circumferential main groove on the tire equatorial plane CL side a widened main groove in which the frequency of the sound pressure peak is lower than that of the normal main groove as described above, the difference in frequency of the sound pressure peak between the circumferential main groove on the tread end TE side and the circumferential main groove on the tire equatorial plane CL side can be further increased, and ultimately the peak value of the sum of these sound pressures can be further lowered. In other words, with the above-described configuration, the frequencies of air column resonance noise generated when the vehicle is running can be distributed in a well-balanced manner, thereby more effectively reducing the air column resonance noise and mitigating noise generated throughout the tire (making it less harsh to the ear).

[0032] In the tire 10 of the first embodiment, the number of center main grooves 22, which are widening main grooves, is one, and the number of shoulder main grooves 21a and 21b, which are normal main grooves, is two, so that the ratio of the number of widening main grooves to the number of normal main grooves (number of widening main grooves / number of normal main grooves) is 1 / 2, but the ratio of the number of widening main grooves to the number of normal main grooves is not particularly limited. In the tire 10 of the first embodiment, the ratio of the number of widened main grooves to the number of normal main grooves is preferably 1 / 1 to 3 / 2. With such a configuration, the frequency of air column resonance sound generated during vehicle travel can be dispersed in a well-balanced manner, and the air column resonance sound can be reduced more effectively, thereby mitigating noise throughout the tire (making it less harsh to the ear).

[0033] In the tire 10 of the first embodiment, the center main groove 22, which is a widening main groove, preferably has a portion in which the groove width gradually increases from the tread surface 1 side toward the groove bottom side. With this configuration, it is possible to suppress the deterioration of drainage performance during wear progression over a long period of time. More preferably, the groove width gradually increases from the tread surface 1 to the groove bottom. With this configuration, it is possible to more effectively suppress the deterioration of drainage performance during wear progression over a long period of time.

[0034] In the tire of the first embodiment, each circumferential main groove 2 may have a groove width such that both side walls do not contact each other when the tire is in contact with the ground, but it is preferable that the minimum groove width (groove width w2 and groove width w3 in the examples of Figs. 3A and 3B) is 1.5 mm or more. With such a configuration, it is possible to reliably reduce air column resonance sound while the vehicle is running, and to ensure sufficient drainage both when new and when worn.

[0035] The groove depth of each circumferential main groove 2 (groove depths d1 and d2 in the examples of FIGS. 3A and 3B) is preferably 3.0 mm or more. This ensures sufficient drainage. From the viewpoint of the rigidity of the tire 10, the groove depth of each circumferential main groove 2 (groove depths d1 and d2 in the examples of FIGS. 3A and 3B) is preferably 20 mm or less. More preferably, the groove depth of each circumferential main groove 2 is 3.0 mm or more from the viewpoint of ensuring sufficient drainage, and is 15 mm or less from the viewpoint of the rigidity of the tire 10.

[0036] In the tire of the first embodiment 1, the inclination angles θ1 and θ2 of the side walls 211 and 222 constituting the shoulder main grooves 21a and 21b, which are normal main grooves, are preferably 91° or more in terms of ensuring rigidity. Also, the inclination angles θ1 and θ2 are preferably 150° or less in terms of ensuring sufficient drainage. More preferably, the inclination angles θ1 and θ2 are 100° or more in terms of ensuring rigidity, and 130° or less in terms of ensuring sufficient drainage. In this case, "the inclination angle of the side walls 211 and 222 constituting the shoulder main grooves 21a and 21b, which are normal main grooves" refers to the angle between the tread surface 1 and the side wall 211, and between the tread surface 1 and the side wall 222, respectively, at the opening ends of the shoulder main grooves 21a and 21b in a cross-sectional view in the tire width direction.

[0037] In the tire of the first embodiment, the inclination angles θ3 and θ4 of the side walls 221 and 222 constituting the center main groove 22, which is the widening main groove, are preferably 30° or more to prevent the opening ends of the tread surface 1 from peeling off when the tire touches the ground. Also, the inclination angles θ3 and θ4 are preferably 89° or less to suppress the deterioration of drainage performance as wear progresses over the long term. More preferably, the inclination angles θ3 and θ4 are 50° or more from the viewpoint of effectively preventing the opening ends of the tread surface 1 from peeling off when the tire touches the ground, and are 85° or less from the viewpoint of more effectively suppressing the deterioration of drainage performance as wear progresses over the long term. Here, "the inclination angle of the side walls 221 and 222 constituting the center main groove 22, which is a widening main groove" refers to the angle formed by the tread surface 1 and the side wall 221, and the angle formed by the tread surface 1 and the side wall 222 at the opening end of the center main groove 22.

[0038] In addition, in the example shown in FIG. 3B of the first embodiment of tire 10, the sidewall 221 and groove bottom 223, and the sidewall 222 and groove bottom 223 constituting the center main groove 22, which is a widening main groove, are each configured in a straight line in a cross section perpendicular to the extension direction of the groove, but as shown in FIG. 5, the boundary between the sidewall 221 and groove bottom 223 and the boundary between the sidewall 222 and groove bottom 223 may be an arc-shaped sidewall and groove bottom having radii of curvature R1 and R2. With this configuration, the durability of the center main groove 22, which is a widened main groove, can be improved.

[0039] In the tire 10 of the first embodiment, the values ​​of the radii of curvature R1 and R2 are not particularly limited, but the radii of curvature R1 and R2 are preferably 0.5 mm or more. With such a configuration, cracks at the boundary between the sidewall 221 or 222 and the groove bottom 223 can be effectively prevented, and the durability of the center main groove 22 can be further improved. In addition, from the viewpoint of drainage, the radii of curvature R1 and R2 are preferably 5.0 mm or less. More preferably, from the viewpoint of further improving the durability of the center main groove 22, the radii of curvature R1 and R2 are 1 mm or more, and from the viewpoint of drainage, they are 3.0 mm or less.

[0040] In this embodiment, it is preferable that the entire center main groove 22 is located in the center region C, and the entire shoulder main grooves 21a and 21b are located in the shoulder region S. Here, the center region C refers to a region of the tread surface 1 that is centered on the tire equatorial plane CL and has a width in the tire width direction that is 50 percent of the contact width TW. On the other hand, the shoulder region S refers to a pair of regions of the tread surface 1 that are located on the outer side of the center region C in the tire width direction. With this configuration, it is possible to more effectively reduce air column resonance noise and ensure sufficient drainage.

[0041] In the tire 10 of the first embodiment, the contact length of the tire 10 is preferably longer on the tire equatorial plane CL side than on the tread edge TE side. In the tire 10 of the first embodiment, the contact length of the circumferential main groove 2 is preferably longer in the center main groove 22 than in the shoulder main grooves 21a and 21b. As described above, with this configuration, the frequency at the peak of the air column resonance sound generated in the circumferential main groove while the vehicle is traveling can be reliably shifted between the normal main groove and the widened main groove, thereby reducing the air column resonance sound and mitigating the noise of the entire tire (making it less harsh to the ear).

[0042] [Second embodiment] Next, a tire according to another embodiment (second embodiment) of the present invention will be described with reference to Fig. 6. A tire 11 of the second embodiment has a similar configuration to the tire 10 of the first embodiment, except that the tire 11 has widthwise grooves that communicate with the normal main grooves. Therefore, the same components as those of the first embodiment are denoted by the same reference numerals and the description thereof will be omitted.

[0043] FIG. 6 is a partial development view that illustrates a tread surface of a tire 11 according to a second embodiment of the present invention.

[0044] The tire 11 of the second embodiment has a widthwise groove 4 that communicates with the shoulder main grooves 21a and 21b, which are normal main grooves, extends in the tire width direction (in this embodiment, at a predetermined angle exceeding 0° with respect to the tire width direction), and opens to the tread end TE.

[0045] In the tire 11 of the second embodiment, the widthwise grooves 4 are arranged in the shoulder land portions 31a and 31b, communicate with the shoulder main grooves 21a and 21b, respectively, extend in the tire width direction, and open at the tread edge TE.

[0046] The widthwise grooves 4 may be either line-symmetric or point-symmetric with respect to the tire equatorial plane CL, and may not be line-symmetric or point-symmetric with respect to the tire equatorial plane CL. In the example of Fig. 6, the widthwise grooves 4 arranged in the shoulder land portion 31a and the widthwise grooves 4 arranged in the shoulder land portion 31b are arranged in a position shifted in the tire circumferential direction from a point-symmetric state with respect to the tire equatorial plane CL.

[0047] The effects of the configuration of the tire 11 of the second embodiment will be described with reference to FIG.

[0048] 7 is a diagram for explaining the frequency of the air column resonance sound of the circumferential main groove. Fig. 7 shows the relationship between the sound pressure and the frequency of the air column resonance sound in the normal main groove (with width direction grooves), the normal main groove (without width direction grooves), and the widened main groove. Here, "normal main groove (with widthwise groove)" refers to a normal main groove having a widthwise groove that communicates with the normal main groove, extends in the tire width direction, and opens to the tread edge TE, and "normal main groove (without widthwise groove)" refers to a normal main groove that does not have a widthwise groove.

[0049] By providing the normal main groove with a widthwise groove connecting the normal main groove and the tread edge TE, the frequency of the air column resonance sound in the normal main groove becomes relatively higher than that of a normal main groove that does not have a widthwise groove. Therefore, the normal main groove with the widthwise groove can shift the sound pressure level peak to the high frequency side compared to a normal main groove that does not have a widthwise groove. Furthermore, similar to the widening main groove of tire 10 of the first embodiment, the widening main groove of tire 11 of the second embodiment can shift the peak of the sound pressure level to a lower frequency side compared to a normal main groove that does not have a widthwise groove. As a result, the normal main groove having widthwise grooves and the widened main groove can more greatly differ in frequency at the peak of the air column resonance sound generated in the circumferential main groove when the vehicle is traveling, and thus the peak value of the sum of these sound pressures can be lowered, thereby more efficiently reducing the air column resonance sound.

[0050] Hereinafter, preferred configurations and modified examples of the widthwise grooves 4 will be described with reference to Fig. 6 and Fig. 8. Fig. 8 is a partially developed view that shows a schematic enlarged view of a part of the tread surface of Fig. 6. However, for ease of explanation, Fig. 8 is drawn to a slightly different scale from Fig. 6.

[0051] The widthwise grooves 4 are arranged in the shoulder land portions 31a and 31b, respectively. As described above, in the example of FIG. 6, the widthwise grooves 4 are arranged in the same configuration except that they are shifted in the tire circumferential direction from a point-symmetric state with respect to the tire equatorial plane CL. Therefore, the widthwise groove 4 arranged in the shoulder land portion 31a will be described below as a typical example.

[0052] The widthwise groove 4 may have a shape in which the groove width on the tread surface 1 is constant, or may have a shape in which the groove width changes midway in the tire width direction. It is preferable that the groove width of the widthwise groove 4 on the tread surface 1 is larger on the side that opens to the tread edge TE side than on the side that communicates with the shoulder main groove 21a, which is a normal main groove. As shown in FIG. 8, the widthwise groove 4 includes a first widthwise groove portion 4a that communicates with the shoulder main groove 21a, and a second widthwise groove portion 4b that is adjacent to and connected to the tread edge TE side of the first widthwise groove portion 4a and opens to the tread edge TE. The groove width w6 of the second widthwise groove portion 4b on the tread surface 1 is larger than the groove width w5 of the first widthwise groove portion 4a on the tread surface 1. According to this configuration, air flow is formed from the narrow first widthwise groove portion 4a communicating with the shoulder main groove 21a to the wide second widthwise groove portion 4b, which promotes air flow outward in the tire width direction and further reduces air column resonance noise. In addition, moisture easily flows from the narrow first widthwise groove portion 4a to the wide second widthwise groove portion 4b, which promotes drainage toward the tread end TE, and ensures sufficient drainage of the tire.

[0053] In the widthwise groove 4, the groove width w5 of the first widthwise groove portion 4a communicating with the shoulder main groove 21a is preferably narrower than the groove width w6 of the second widthwise groove portion 4b by 1 mm or more. This configuration can further enhance the effect of reducing air column resonance.

[0054] In the tire 11 of the second embodiment, the groove width w5 of the first widthwise groove portion 4a on the tread surface 1 is preferably 0.3 mm or more. With such a configuration, sufficient air can be made to flow from the shoulder main groove 21a to the first widthwise groove portion 4a, and the function of reducing air column resonance can be further exhibited. More preferably, it is 0.4 mm or more.

[0055] In the widthwise groove 4, the groove width w6 in the tread surface 1 of the second widthwise groove portion 4b opening at the tread edge TE may be a groove width that does not contact both side walls with each other when the tire is in contact with the ground, but it is more preferable that the groove width is 1.5 mm or more. With such a configuration, the effect of reducing the air column resonance can be effectively achieved and sufficient drainage can be ensured.

[0056] It is preferable that the groove depth of the first widthwise groove portion 4a of the widthwise groove 4 is approximately the same as the groove depth of the second widthwise groove portion 4b. This is because, with such a configuration, even in a worn tire, the drainage performance can be maintained and air columnar resonance noise can be reduced.

[0057] In addition, in the widthwise grooves 4, the groove depth of the second widthwise groove portion 4b is preferably approximately the same as that of the shoulder main groove 21a. More specifically, the groove depth of the second widthwise groove portion 4b is preferably 3.0 mm or more. This ensures sufficient drainage. From the viewpoint of the rigidity of the tire 11, the groove depth of the second widthwise groove portion 4b is preferably 20 mm or less. More preferably, from the viewpoint of ensuring sufficient drainage, the groove depth of the second widthwise groove portion 4b is 5.0 mm or more, and from the viewpoint of the rigidity of the tire 10, it is 15 mm or less.

[0058] 6 and 8, the width direction groove 4 has a length L1 along the extension direction of the first width direction groove portion 4a that is shorter than a length L2 along the extension direction of the second width direction groove portion 4b, but is not limited to such a configuration, and may have a length L1 along the extension direction of the first width direction groove portion 4a that is longer than a length L2 along the extension direction of the second width direction groove portion 4b, as shown in Fig. 9. However, it is preferable that the length L1 is shorter than the length L2 from the viewpoint of providing a volume difference between the first width direction groove portion 4a and the second width direction groove portion 4b and reducing air columnar resonance sound.

[0059] The widthwise grooves 4 preferably have an inclination angle θ5 of 0° to 20° with respect to the tire width direction on the tread surface 1. By setting the inclination angle to be between 0° and 20°, uneven wear at the opening ends of the widthwise grooves 4 relative to the shoulder main grooves 21a can be prevented, while reducing air column resonance and suppressing the generation of other noises. From the viewpoints of preventing uneven wear and suppressing the generation of other noises, the inclination angle θ5 is more preferably 5° to 15°.

[0060] In the second embodiment, the widthwise grooves 4 are preferably arranged at both ends of the ground contact surface of the tire 11 so that the number of grooves in the ground contact surface at both ends of the ground contact surface is 4 to 10. Here, the "number in the ground contact surface" refers to a widthwise groove 4 being located within the ground contact surface if even a part of the widthwise groove 4 is located within the ground contact surface. According to this configuration, it is possible to more effectively reduce air column resonance noise and ensure sufficient drainage.

[0061] More specifically, the widthwise grooves 4 are preferably arranged at intervals of 10 to 40 mm in the tire circumferential direction on one side of the tread edge TE, which is bounded by the tire equatorial plane CL. With such a configuration, it is possible to more effectively reduce air column resonance noise and ensure sufficient drainage. More preferably, the widthwise grooves 4 are arranged at intervals of 20 to 30 mm in the tire circumferential direction. [Industrial Applicability]

[0062] The tire according to the present invention can be used for any type of pneumatic tire, but is preferably used for a pneumatic tire for a passenger vehicle. [Explanation of symbols]

[0063] 1: tread surface, 2: circumferential main groove, 4: widthwise groove, 4a: first widthwise groove portion, 4b: second widthwise groove portion, 10, 11: tire, 21a, 21b: shoulder main groove, 22: center main groove, 31a, 31b: shoulder land portion, 32a, 32b: center land portion, 60: belt, 70: carcass, 80: tread rubber, 90: tread portion, 211, 212, 221, 222: sidewall, 213, 223: groove bottom, S: shoulder portion, C: center portion, CL: tire equatorial plane, TE: tread edge

Claims

1. A tire having a plurality of circumferential main grooves on a tread surface, the grooves extending in a tire circumferential direction and having a groove width such that both side walls do not contact each other when the tire is in contact with the ground, Among the plurality of circumferential main grooves, a pair of circumferential main grooves disposed closest to both tread ends in the tire width direction are referred to as shoulder main grooves, and the circumferential main grooves other than the shoulder main grooves are referred to as center main grooves. All of the shoulder main grooves are normal main grooves configured such that the maximum groove width position in the groove depth direction is only at the tread surface position, All of the center main grooves are widened main grooves configured such that at least one maximum groove width position in the groove depth direction is located closer to the groove bottom than the tread surface position, A tire characterized in that a ratio of the number of the widened main grooves to the number of the normal main grooves is 1 / 1 to 3 / 2.

2. The tire according to claim 1 , wherein the widened main groove has a portion in which the groove width gradually increases from a tread surface side toward a groove bottom side.

3. The tire according to claim 1 or 2, wherein the circumferential main groove has a minimum groove width of 1.5 mm or more.

4. The tire according to any one of claims 1 to 3, further comprising a width direction groove that communicates with the shoulder main groove that is the normal main groove, extends in the tire width direction, and opens at a tread end.

5. The tire according to claim 4 , wherein the widthwise grooves have a groove width on a tread surface that is larger on a tread end side than on a side communicating with the shoulder main groove, which is the normal main groove.

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