tire

Abstract

Provided is a tire having improved noise performance while maintaining wet performance. When a portion inward, in the tire width direction, of groove width center lines of circumferential main grooves 14c, 14d on the outermost side in the tire width direction is defined as a center region CR, at least one bent groove 26 (28) having at least one end in the tire width direction in communication with a circumferential main groove and having at least two bent parts is provided in at least one land part 16 formed in the center region. The groove width W1 (W2) of a first portion 26a (28a) from one end of the bent groove to just before a bent part that appears first and the groove width W3 (W4) of a second portion 26b (28b) from the other end of the bent groove to just before a bent part that appears first are substantially the same over the entire circumference of the tire, and satisfy P2 (%)>P1 (%) and P2 (%)>P3 (%).

Description

tire

[0001] The present invention relates to a tire that maintains wet performance while improving noise performance.

[0002] For the purpose of improving snow performance without degrading noise and vibration performance, a tire is known in which at least one of a plurality of center sipes includes a chamfered portion on at least one of the edges in the tire circumferential direction, and these chamfered portions are arranged alternately on each side of the tire equatorial plane in the tire circumferential direction (see Patent Document 1).

[0003] JP 2022-088310 A

[0004] However, in the tire disclosed in Patent Document 1, there is a possibility that the timing of fluctuations in the opening and closing of the grooves (chamfers and sipes) may overlap between circumferentially adjacent chamfers and / or center sipes during tire rotation. In such cases, the sound generated when the tire comes into contact with the road surface is emphasized by a horn effect, increasing so-called pass-by noise (PBN), and there is a risk of deteriorating noise performance.

[0005] To address this issue, reducing the groove area ratio could be considered to improve noise performance, but reducing the groove area ratio could lead to a deterioration in drainage performance and ultimately to a deterioration in wet performance. For this reason, there has been a demand in recent years for the development of technology that improves noise performance while maintaining wet performance without reducing the groove area ratio.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a tire that has improved noise performance while maintaining wet performance without reducing the groove area ratio.

[0007] In the tire of the present invention, at least three land portions are defined by at least two circumferential main grooves, and on each side of the tire width direction of the tire equatorial plane, with the groove width centerline of the outermost circumferential main groove in the tire width direction as the boundary, a center region is defined as the area inward in the tire width direction of the groove width centerline, and shoulder regions are defined as areas outward in the tire width direction of the groove width centerline, at least one land portion formed in the center region is provided with at least one bent groove, at least one end in the tire width direction of which is connected to the circumferential main groove and which has at least two bent portions, and a groove width of a first portion from one end of the bent groove to just before the first bent portion and a groove width of a second portion from the other end of the bent groove to just before the first bent portion are each substantially the same around the entire tire circumference, The number of bent grooves present within the same land portion is defined as N, and the lengths of the first interval between the first portion and the second portion and the second interval, which is the shortest distance between two bent grooves adjacent in the tire circumferential direction, measured around the entire tire circumference are defined as Li (1≦i≦2N), respectively; The tire circumference is defined as J (mm), the range of attention length due to transfer characteristics is defined as S1 (mm), and the ranges of attention length due to sound source are defined as S2 (mm) and S3 (mm); 12.4≦S1(mm)≦19.5; and, Within the ranges of S1 (mm) and S2 (mm) that satisfy J / (N×1.25×1)≦S2(mm)≦J / (N×0.75×1), the larger of the lower limit values ​​of the two inequalities is defined as LFL1 and the smaller of the upper limit values ​​of the two inequalities is defined as HFL1; 12.4≦S1(mm)≦19.5; and In the range of S1 (mm) and S3 (mm) that satisfies J / (N x 1.25 x 2) ≦ S3 (mm) ≦ J / (N x 0.75 x 2), the larger of the lower limit values ​​of the two inequalities is defined as LFL2, and the smaller of the upper limit values ​​of the two inequalities is defined as HFL2; Condition C1 is defined by LFL1 x 1 < Li (mm) < HFL1 x 1, or LFL2 x 1 < Li (mm) < HFL2 x 1; Conditions other than Condition C1, and are defined by LFL1 x 0.5 < Li (mm) < HFL1 x 0.5, LFL1 x 1.5 < Li (mm) < HFL1 x 1.5, LFL2 x 0.5 < Li (mm) < HFL2 x 0.5, orCondition C2 is defined as LFL2×1.5<Li (mm)<HFL2×1.5, and condition C3 is defined as a condition other than condition C1 and other than condition C2. When the proportion of intervals Li that satisfy condition C1 among a maximum of 2N intervals Li is defined as P1 (%), the proportion of intervals Li that satisfy condition C2 is defined as P2 (%), and the proportion of intervals Li that satisfy condition C3 is defined as P3 (%), the following relationships are satisfied: P2 (%) > P1 (%) and P2 (%) > P3 (%).

[0008] In the tire according to the present invention, instead of reducing the groove area ratio, overlapping of fluctuation timings of groove opening and closing between circumferentially adjacent groove portions during tire rotation is reduced in the tire widthwise central region of the tread, where the sound generated when the tire contacts the road surface is likely to be emphasized due to the horn effect. Specifically, for bent grooves provided in land portions in the tire widthwise central region, among a maximum of 2N intervals Li, the proportion of intervals Li satisfying condition C1 (the proportion of undesired intervals) is P1 (%), the proportion of intervals Li satisfying condition C2 (the proportion of desired intervals) is P2 (%), and the proportion of intervals Li satisfying condition C3 (the proportion of neither undesired nor undesired intervals) is P3 (%). This allows intentional staggering of fluctuation timings of groove opening and closing between circumferentially adjacent groove portions during tire rotation without degrading drainage performance, thereby reducing pass-by noise between these groove portions. Therefore, according to the present invention, it is possible to improve noise performance while maintaining wet performance.

[0009] Fig. 1 is a plan view showing the tread surface of a tire of this embodiment. Fig. 2 is a plan view showing the groove width of the bent groove shown in Fig. 1. Fig. 3 is a plan view showing the interval between groove portions of the bent groove shown in Fig. 1. Fig. 4 is a plan view showing a modified example of the tread surface shown in Fig. 1. Fig. 5 is a plan view showing two types of circumferential lengths of the bent groove shown in Fig. 1 or Fig. 4.

[0010] In the following description, the tire radial direction refers to the direction perpendicular to the tire's rotational axis, the tire radially inner side refers to the side toward the rotational axis in the tire radial direction, and the tire radially outer side refers to the side away from the rotational axis in the tire radial direction. The tire circumferential direction refers to the direction around the rotational axis as the central axis. The tire width direction refers to the direction parallel to the rotational axis, the tire widthwise inner side refers to the side toward the tire equatorial plane (tire equator line) in the tire width direction, and the tire widthwise outer side refers to the side away from the tire equatorial plane in the tire width direction. The tire equatorial plane is a plane perpendicular to the tire's rotational axis and passing through the center of the tire width.

[0011] Similarly, in the following description, a regular rim refers to an "application rim" defined by JATMA, a "design rim" defined by TRA, or a "measuring rim" defined by ETRTO.

[0012] Similarly, in the following description, "normal internal pressure" refers to the "maximum air pressure" specified by JATMA, the maximum value specified in "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Inflation Pressures" specified by ETRTO. Also, "normal load" refers to the "maximum load capacity" specified by JATMA, the maximum value specified in "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Load Capacity" specified by ETRTO.

[0013] FIG. 1 is a plan view showing the tread surface of a tire of this embodiment, in an unloaded state (non-contact state) with the tire mounted on a standard rim and given a standard internal pressure. In FIG. 1, only one of several identical components is designated by a reference numeral. The tread portion of the tire 10 shown in the figure is made of a rubber material (tread rubber). The surface of the tread portion (tread surface 12) located at the outermost part in the tire's radial direction comes into contact with the road surface when the vehicle is traveling. As shown in FIG. 1, a predetermined tread pattern is formed on the tread surface. In the tread pattern shown in FIG. 1, the left side is the inside of the tire mounted on the vehicle.

[0014] In the example shown in FIG. 1 , four circumferential main grooves 14 (14a, 14b, 14c, 14d) are provided on the tread surface 12, symmetrically arranged in the tire width direction across the tire equatorial plane CL. The circumferential main grooves 14 have a groove width of 6 mm or more and 14 mm or less. Here, groove width refers to the groove dimension (maximum value) measured in a direction perpendicular to the groove extension direction (the same applies hereinafter to other grooves). The circumferential main grooves 14 also have a groove depth of 5 mm or more and 10 mm or less. Here, groove depth refers to the groove dimension (maximum value) measured in the tire radial direction from a profile line in the absence of the groove (the same applies hereinafter to other grooves).

[0015] In the example shown in Fig. 1, five land portions 16, 18, 20, 22, and 24 are defined and formed by these circumferential main grooves 14. The center land portion 16 includes the tire equatorial plane CL, and second land portions 18 and 20 are defined and formed on each side of the center land portion 16 in the tire width direction, and shoulder land portions 22 and 24 are defined and formed on the outer sides of those in the tire width direction. In this embodiment, the land portions defined and formed by the circumferential main grooves 14a to 14d include not only ribs as shown in Fig. 1 but also block rows.

[0016] In the example shown in FIG. 1 , on each side of the tire equatorial plane CL in the tire width direction, the groove width center lines (not shown) of the circumferential main grooves 14 c, 14 d that are outermost in the tire width direction are used as the boundary, and the area inside these groove width center lines in the tire width direction is defined as a center region CR, and the areas outside the groove width center lines in the tire width direction are defined as shoulder regions SR, SR.

[0017] The center land portion 16 formed in the center region CR is provided with a plurality of bent grooves 26, each of which has two bent portions and whose both ends in the tire width direction communicate with the circumferential main grooves 14a, 14b.

[0018] The bent grooves 26 have a groove width of 0.5 mm to 1.5 mm, and a groove depth of 40% to 90% of the groove depth of the circumferential main groove.

[0019] 1, the second land portion 18 formed in the center region CR on the outer side fitted to the vehicle is provided with first lug grooves 30 that communicate with both of the circumferential main grooves 14a, 14c on both sides in the tire width direction and whose inclination direction with respect to the tire width direction reverses midway as they extend from the inner side to the outer side in the tire width direction. The first lug grooves 30 are provided on the outer side fitted to the vehicle to improve wet performance, and by reversing the inclination direction with respect to the tire width direction midway as they extend, pass-by noise can be reduced compared to grooves whose inclination direction is not reversed.

[0020] In the second land portion 18, sipes 32 are formed between adjacent first lug grooves 30 in the tire circumferential direction, extending substantially parallel to the first lug grooves 30. In this specification, a sipe means a groove having a groove width of 1.5 mm or less and a groove depth of 2.0 mm or more.

[0021] To improve wet performance, the second land portion 20 on the vehicle mounting inner side formed in the center region CR is provided with second lug grooves 34 extending inward in the tire width direction from the circumferential main groove 14d on the outer side in the tire width direction and terminating within the land portion 20. The second land portion 20 also has sipes 36 formed therein that extend from the inner end of the second lug groove 34 in the tire width direction and communicate with the circumferential main groove 14b on the inner side in the tire width direction. Furthermore, the second land portion 20 also has sipes 38 formed between the second lug grooves 34, 34 adjacent in the tire circumferential direction, that extend approximately parallel to the second lug grooves 34 and communicate with both of the circumferential main grooves 14b, 14d on both sides in the tire width direction.

[0022] The shoulder land portion 22 formed in the shoulder region SR on the vehicle-mounted outer side is provided with third lug grooves 40 that extend inward in the tire width direction across a ground contact edge (not shown) and terminate within the land portion 22. Also, the shoulder land portion 22 is provided with sipes 42 extending outward in the tire width direction from the circumferential main groove 14c between adjacent third lug grooves 40, 40 in the tire circumferential direction, and the sipes 42 communicate with small grooves 44 near the ground contact edge. Furthermore, triangular grooves 46 are provided at a constant pitch in the tire circumferential direction on the tire width outer side of the ground contact edge. The small grooves 44 have a groove width of 0.5 mm or more and 3.0 mm or less and a groove depth of 0.3 mm or more and 2.0 mm or less, and the triangular grooves 46 also have a groove depth of 0.3 mm or more and 2.0 mm or less.

[0023] An auxiliary groove 48 is provided in the shoulder land portion 22 in the inner region in the tire width direction, parallel to the circumferential main groove 14c. Generally, the shoulder land portion 22 on the outer side of the vehicle contributes significantly to wet performance, particularly cornering performance. Therefore, by providing the auxiliary groove 48 in the shoulder land portion 22, the rigidity of the shoulder land portion 22 can be suitably adjusted, and cornering performance can be efficiently improved. The groove depth of the auxiliary groove 48 can be 0.3 to 0.8 times the groove depth of the circumferential main groove 14c.

[0024] The shoulder land portion 24 formed in the shoulder region SR on the vehicle-mounted inner side is provided with a fourth lug groove 50 that extends inward in the tire width direction across a ground contact edge (not shown) and terminates within the land portion 24. The shoulder land portion 24 also has a sipe 52 formed between adjacent fourth lug grooves 50 in the tire circumferential direction, extending from the circumferential main groove 14d outward in the tire width direction, and the sipe 52 communicates with a small groove 54 near the ground contact edge. Furthermore, an auxiliary groove 56 is provided in the inner region in the tire width direction within the shoulder land portion 24, extending parallel to the circumferential main groove 14d. The groove depth of the auxiliary groove 56 may be 0.3 to 0.8 times the groove depth of the circumferential main groove 14d.

[0025] Fig. 2 is a plan view showing the groove width of the bent groove shown in Fig. 1. Of the multiple bent grooves provided in the tire circumferential direction, only two bent grooves 26, 28 that are adjacent in the tire circumferential direction will be described below. For the two types of bent grooves 26 (28) shown in Fig. 1, the groove width W1 (W2) of the first portion 26a (28a) from one end to just before the first bend shown in Fig. 2 and the groove width W3 (W4) of the second portion 26b (28b) from the other end of the bent groove 26 (28) to just before the first bend are each approximately the same over the entire circumference of the tire.

[0026] The groove width W1 (W2) of the first portion 26a (28a) is determined by dividing the first portion 26a (28a) into five equal sections in the extension direction, calculating the dimension of the center of each section in the extension direction in the direction perpendicular to the extension direction, and averaging the calculated values ​​for the five sections. The same applies to the groove width W3 (W4) of the second portion 26b (28b).

[0027] The first portion 26a (28a) and the second portion 26b (28b) may be linear or curved in the extension direction. The bent portion refers to a portion connected to the first portion 26a (28a) and / or the second portion 26b (28b), extending from a point where the curvature of the groove width center line changes relative to the first portion 26a (28a) or the second portion 26b (28b) to a point where the curvature changes again.

[0028] The phrase "groove width W1 and groove width W2 are approximately the same" means that, for portions 26a and 28a, the ratio of the standard deviation calculated from each portion to the average value calculated from each portion (standard deviation / average value) is in the range of 0 to 0.1. Similarly, the phrase "groove width W3 and groove width W4 are approximately the same" means that, for portions 26b and 28b, the ratio of the standard deviation calculated from each portion to the average value calculated from each portion (standard deviation / average value) is in the range of 0 to 0.1.

[0029] The groove widths W1 and W3 of the groove portions included in the bent groove 26 may be the same or different. Similarly, the groove widths W2 and W4 of the groove portions included in the bent groove 28 may be the same or different. In the example shown in FIG. 2 , the groove widths W1 to W4 are all the same. However, if the groove widths W1 and W3 (or the groove widths W2 and W4) are different, the difference in groove width between these groove portions (e.g., between the first portion 26 a and the second portion 26 b) is likely to cause different fluctuation times regarding the opening and closing of the groove portions. For this reason, it is more preferable for the groove widths W1 and W3 (or the groove widths W2 and W4) to be different than if they were the same, because this increases the pass-by noise reduction effect.

[0030] Figure 3 is a plan view showing the distance between groove portions of the bent grooves shown in Figure 1. Regarding Figure 3, of the multiple bent grooves provided in the tire circumferential direction, only two bent grooves 26, 28 that are adjacent in the tire circumferential direction will be described. The number of bent grooves present in the central land portion 16 shown in Figure 1 is N, and the lengths of the first distance D1 (D2) between the first portion 26a (28a) and the second portion 26b (28b) and the second distance D3, which is the shortest distance between the two bent grooves 26, 28 that are adjacent in the tire circumferential direction, measured over the entire tire circumference are respectively Li (1 ≦ i ≦ 2N).

[0031] For example, if only one bent groove is provided in the center land portion 16 (if only the bent groove 26 is provided), the first interval D1 shown in Fig. 3 can be defined, but the first interval D2 and the second interval D3 cannot be defined, so the number of i is only 1. In contrast, if 30 bent grooves are provided in the center land portion 16, there is one first interval D1, D2 shown in Fig. 3 for each bent groove, and there are the same number of second intervals D3 as the number of bent grooves, so the maximum number of i is N × 2 = 60.

[0032] When the groove portions of one bent groove (e.g., the first portion 26a and the second portion 26b) are parallel to each other, the first distance D1 for the bent groove 26 is determined as the shortest distance between a virtual line drawn based on the center points (not shown) of the groove widths of each of the five equal sections used to determine the groove width W1 shown in FIG. 2 and a virtual line drawn based on the center points (not shown) of the groove widths of each of the five equal sections used to determine the groove width W3 shown in FIG. 2. Each virtual line is set so that the five groove width center points are as close as possible to each virtual line. The first distance D2 for the bent groove 28 shown in FIG. 3 is determined in the same manner as the first distance D1 (based on the groove widths W2 and W4).

[0033] In contrast, when the groove portions of one bent groove (e.g., the first portion 26a and the second portion 26b) are not parallel to each other, the first distance D1 for the bent groove 26 is determined as follows: First, the groove width center points (not shown) of the five equal sections used when determining the groove width W1 shown in FIG. 2 are designated as points a1, b1, c1, d1, and e1, respectively, from one vehicle mounting side; and the groove width center points (not shown) of the five equal sections used when determining the groove width W3 shown in FIG. 2 are designated as points a3, b3, c3, d3, and e3, respectively, from one vehicle mounting side. Next, the distance between points a1 and a3 is designated as sa, the distance between points b1 and b3 as sb, the distance between points c1 and c3 as sc, the distance between points d1 and d3 as sd, and the distance between points e1 and e3 as se. The average value of the distances sa and se is calculated as the first distance D1. The first distance D2 for the bent groove 28 shown in FIG. 3 is also determined in the same manner as the first distance D1 (based on the groove widths W2 and W4).

[0034] When the groove portions of two circumferentially adjacent bent grooves (for example, the second portion 26b and the first portion 28a) are parallel to each other, the second distance D3 between the bent grooves 26, 28 is determined as the shortest distance between an imaginary line drawn based on the groove width center points (not shown) of each of the five equal sections used when determining the groove width W3 shown in Fig. 2, and an imaginary line drawn based on the groove width center points (not shown) of each of the five equal sections used when determining the groove width W2 shown in Fig. 2. Each imaginary line is set so that the five groove width center points are as close as possible to each other.

[0035] In contrast, when the groove portions of two circumferentially adjacent bent grooves (for example, the second portion 26b and the first portion 26a) are not parallel to each other, the second distance D3 between the bent grooves 26, 28 is determined as follows. Specifically, the groove width center points (not shown) of the five equal sections used to determine the groove width W3 shown in FIG. 2 are designated as points a3, b3, c3, d3, and e3, respectively, from one vehicle mounting side. The groove width center points (not shown) of the five equal sections used to determine the groove width W2 shown in FIG. 2 are designated as points a2, b2, c2, d2, and e2, respectively, from one vehicle mounting side. Next, the distance between points a3 and a2 is designated as Sa, the distance between points b3 and b2 as Sb, the distance between points c3 and c2 as Sc, the distance between points d3 and d2 as Sd, and the distance between points e3 and e2 as Se. Then, the average value from the distance Sa to the distance Se is calculated and set as the second distance D3.

[0036] Next, the tire circumference is defined as J (mm), the attention length due to the transfer characteristics is defined as S1 (mm), and the attention lengths due to the sound source are defined as S2 (mm) and S3 (mm).

[0037] Here, the attention length S1 (mm) due to the transfer characteristics means the range sandwiched between the lower limit value and the upper limit value calculated by dividing the representative speed of the pass-by noise by the upper limit and the lower limit, respectively, of the frequency range that is emphasized in the center region due to the horn effect when the acoustic characteristics of the space around the tire are measured.

[0038] In addition, the range of attention length S2 (mm) due to the sound source means a range of ±25% of the first order of the pitch order that occurs when the block formed by the curved groove comes into contact with the road surface, and the range of attention length S3 (mm) due to the sound source means a range of ±25% of the second order of the pitch order that occurs when the block formed by the curved groove comes into contact with the road surface.

[0039] Next, the range of the length S1 (mm) due to the transfer characteristics, in which the sound generated from the curved groove 26 provided in the center land portion 16 is emphasized by the horn effect, is as follows: 12.4<S1 (mm)<19.5

[0040] The ranges of the caution lengths S2 (mm) and S3 (mm) due to the sound source, in which the bent grooves provided in the center land portion 16 cause pass-by noise, are as follows: J / (N×1.25×1)<S2(mm)<J / (N×0.75×1) J / (N×1.25×2)<S3(mm)<J / (N×0.75×2)

[0041] Based on the above ranges of S1 (mm), S2 (mm), and S3 (mm), in the range of S1 (mm) and S2 (mm) that satisfies S1 (mm) ≦ 19.5 and J / (N × 1.25 × 1) ≦ S2 (mm) ≦ J / (N × 0.75 × 1), the larger of the lower limit values ​​of these two inequalities is defined as LFL1, and the smaller of the upper limit values ​​of the two inequalities is defined as HFL1.

[0042] Similarly, in the range of S1 (mm) and S3 (mm) that satisfies 12.4≦S1 (mm)≦19.5 and J / (N×1.25×2)≦S3 (mm)≦J / (N×0.75×2), the larger of the lower limit values ​​of these two inequalities is defined as LFL2, and the smaller of the upper limit values ​​of the two inequalities is defined as HFL2.

[0043] Furthermore, based on the above findings, the condition defined by LFL1×1<Li (mm)<HFL1×1 or LFL2×1<Li (mm)<HFL2×1 is defined as condition C1.

[0044] A condition other than condition C1 that is specified by LFL1 x 0.5 < Li (mm) < HFL1 x 0.5, LFL1 x 1.5 < Li (mm) < HFL1 x 1.5, LFL2 x 0.5 < Li (mm) < HFL2 x 0.5, or LFL2 x 1.5 < Li (mm) < HFL2 x 1.5 is defined as condition C2.

[0045] A condition other than the condition C1 and other than the condition C2 is defined as a condition C3.

[0046] Then, among the maximum 2N intervals Li, the proportion of intervals Li that satisfy condition C1 is P1 (%), the proportion of intervals Li that satisfy condition C2 is P2 (%), and the proportion of intervals Li that satisfy condition C3 is P3 (%).

[0047] When condition C1 is satisfied, it means that there is a high possibility that the timing of fluctuations in the opening and closing of groove portions will overlap between adjacent groove portions in the tire circumferential direction during tire rotation, resulting in large, undesirable pass-by noise.

[0048] The case where condition C2 is satisfied means that the timing of fluctuations in the opening and closing of groove portions is unlikely to overlap between adjacent groove portions in the tire circumferential direction when the tire is rolling, and therefore pass-by noise is small and desirable.

[0049] The case where condition C3 is satisfied (the case where neither condition C1 nor condition C2 is satisfied) means that there is a moderate possibility that the timing of fluctuations in the opening and closing of groove portions will overlap between adjacent groove portions in the tire circumferential direction when the tire is rolling, and therefore pass-by noise is moderate and neither undesirable nor desirable.

[0050] The above inequalities used to derive any of conditions C1 to C3 were obtained by the inventors through extensive research and numerous experiments. Although the inventors have not found a clear technical basis for these inequalities, they have found that they are supported by a large amount of experimental data and are ultimately useful inequalities for improving noise performance.

[0051] Under the above assumptions, this embodiment satisfies P2 (%) > P1 (%) and P2 (%) > P3 (%). That is, these rules compare the desired case rate P2, the undesired case rate P1, and the undesired and neither desired case rate P3, and indicate that of these three rates, the desired case rate P2 is higher than either the other case rates P1 or P3.

[0052] In the tire 10 of the present embodiment described above, the groove area ratio is not reduced compared to conventional tires, but the shape and arrangement of the curved grooves 26 provided in specific land portions (specifically, the center land portion 16 included in the central region in the tire width direction, etc.) are changed, so that wet performance (a combination of drainage performance, steering stability performance, cornering performance, traction performance, etc.; the same applies hereinafter) can be maintained at a conventional level.

[0053] In the tire 10 of this embodiment, the timing of changes in the opening and closing of groove portions 26 a, 26 b adjacent in the tire circumferential direction within the same groove (see FIGS. 2 and 3 ) and groove portions 26 b, 28 a adjacent in the tire circumferential direction across other grooves (see FIGS. 2 and 3 ) can be intentionally shifted during tire rotation so as to reduce noise generated from the center land portion 16, etc., where noise generated when the tire comes into contact with the road surface is likely to be emphasized by the horn effect, thereby reducing pass-by noise caused by these groove portions. In the example shown in FIG. 1 , in particular, by providing four circumferential main grooves, the width of the center land portion 16, which contributes most to pass-by noise reduction, can be made relatively small, thereby reducing the rigidity of the land portion 16, thereby efficiently reducing pass-by noise.

[0054] Therefore, according to the tire 10 of this embodiment, it is possible to improve noise performance while maintaining wet performance.

[0055] 1, only the above-mentioned bent groove 26 is provided in the center land portion 16, but this embodiment is not limited to this example, and other grooves may be provided in the center land portion 16. However, if grooves other than the bent grooves are provided in the center land portion 16, the effect of providing the bent grooves (which allows the timing of fluctuations regarding the opening and closing of the groove portions during tire rotation to be intentionally shifted, thereby reducing pass-by noise between these groove portions) may be weakened by the presence of the other grooves, and therefore, from the perspective of reducing pass-by noise, it is not preferable to provide grooves other than the bent grooves in the center land portion 16.

[0056] In the example shown in FIG. 1, the curved grooves 26 are provided only in the center land portion 16, but this embodiment is not limited to this case. The curved grooves can be provided in any of the land portions (land portions 16, 18, 20) defined and formed in the center region CR, and the same effect as that achieved by the tread pattern shown in FIG. 1 can be obtained.

[0057] Figure 4 is a plan view showing a modified example of the tread surface shown in Figure 1. Note that for components not assigned with a reference numeral in Figure 4, the reference numerals assigned to the corresponding components in Figure 1 are omitted. In the example shown in Figure 4, unlike the example shown in Figure 1, curved grooves 26, 58 are provided in two land portions (a center land portion 16 and a second land portion 20) defined and formed in the center region CR. In this way, when curved grooves are provided in two or more land portions, the groove widths W1 to W4 shown in Figure 2 and the intervals D1 to D3 shown in Figure 3 are calculated for each land portion, but the above-mentioned proportions P1 to P3 are calculated for the entire tire.

[0058] 1 or 4, it is preferable that the difference between the percentage P2 and the percentage P1 be 20% or more, and that the difference between the percentage P2 and the percentage P3 be 10% or more. When these conditions are met, the percentage P1 of undesired cases described above is lower than the percentage P3 of undesired and undesired cases, so that the percentage P1 of undesired cases as a whole can be further reduced. As a result, the timing of fluctuations in the opening and closing of circumferentially adjacent groove portions during tire rotation can be intentionally shifted by a larger amount, thereby further reducing pass-by noise between these groove portions.

[0059] In the examples shown in Fig. 1 or 4, it is preferable that the proportion P1 is 30% or less. When this condition is satisfied, the proportion P1 of undesirable cases as a whole can be further reduced. As a result, the timing of fluctuations in the opening and closing of circumferentially adjacent groove portions during tire rotation can be intentionally shifted by a larger degree, thereby further reducing pass-by noise between these groove portions.

[0060] When the ratio P1 is 30% or less and ratio P2 > ratio P3 > ratio P1 is satisfied, the timing of fluctuations in the opening and closing of the groove portions during tire rotation can be intentionally shifted to an even greater extent, thereby further reducing pass-by noise between these groove portions.

[0061] In the examples shown in Figures 1 and 4, the average number of grooves having a tire width direction component (hereinafter sometimes referred to as "width direction grooves") provided in the shoulder land portions 22, 24 defined in the shoulder region SR is preferably greater than the average number of width direction grooves provided in the land portions 16, 18, 20 defined in the center region CR. Here, grooves having a tire width direction component (width direction grooves) refer to all grooves other than grooves extending in the tire circumferential direction. For example, in Figures 1 and 4, the width direction grooves include grooves (including sipes) 26, 30, 32, 34, 36, 38, 40, 42, 44, 46, 50, 52, 54, and 58.

[0062] In this way, by controlling the average number of widthwise grooves formed between the shoulder regions SR and the center region CR, it is possible to reduce the number of widthwise grooves provided in the center region CR, where the sound generated upon contact with the road surface is less likely to be emphasized by the horn effect, without changing (increasing) the groove area ratio of the entire tire, thereby reducing pass-by noise and improving drainage performance and, ultimately, wet performance.

[0063] 1 and 4, auxiliary grooves 48, 56 are provided on each side of the vehicle. The groove width of the auxiliary grooves 48, 56 relative to the groove width of each of the outermost circumferential main grooves 14c, 14d in the tire width direction (groove width ratio of the auxiliary groove) is preferably 5% to 40%. Note that the groove width ratio of the auxiliary groove is calculated relative to a predetermined circumferential main groove (i.e., the circumferential main groove closest to the target auxiliary groove among the outermost circumferential main grooves of the tire).

[0064] By making the groove width ratio of the auxiliary grooves 48, 56 5% or more, the block rigidity of the shoulder land portions 22, 24 can be reduced, and the timing of fluctuations regarding the opening and closing of adjacent grooves (including sipes) in the tire circumferential direction in the shoulder land portions 22, 24 can be efficiently shifted, thereby further reducing pass-by noise.

[0065] In contrast, by setting the groove width ratio of the auxiliary grooves 48, 56 to 40% or less, it is possible to ensure a high level of wet performance, particularly steering stability, without excessively reducing the block rigidity of the shoulder land portions 22, 24.

[0066] The groove width ratio of the auxiliary grooves 48, 56 is more preferably 8% or more and 37% or less, and most preferably 10% or more and 35% or less.

[0067] Fig. 5 is a plan view showing two types of circumferential lengths of the bent groove shown in Fig. 1 or 4. As shown in Fig. 5, it is preferable that the tire circumferential length DG1 (DG2) between one end and the other end of the bent groove 26 (28) is equal to or greater than the tire circumferential length DB1 (DB2) of the third portion 26c (28c) of the bent groove 26 (28) (a portion other than the first portion and the second portion in each bent groove).

[0068] 5 (FIG. 1 or FIG. 4), the longitudinal portion (the tire widthwise centerline) excluding the bent portion is located on the tire equatorial plane CL, and therefore extends in the tire circumferential direction. However, when the longitudinal portion (the tire widthwise centerline) is located offset to either side in the tire width direction from the tire equatorial plane CL, it is preferable to provide the longitudinal portion so that it extends from the inner side to the outer side in the tire width direction, from the leading side to the trailing side of the tire, in consideration of drainage performance.

[0069] By making the tire circumferential length DG1 (DG2) equal to or greater than the tire circumferential length DB1 (DB2), the first portion 26a (28a) and the second portion 26b (28b) of the bent groove 26 (28) become more easily deformed when the tire 10 comes into contact with the road surface, thereby further reducing pass-by noise and further improving noise performance.

[0070] 1 and 4, three circumferential main grooves may be provided to define two land portions in the center region without changing the groove area ratio. By providing two or more circumferential main grooves, it is possible to obtain excellent noise performance while maintaining the desired drainage performance and, therefore, wet performance in this embodiment.

[0071] 1 or 4, it is preferable that the groove widths of the circumferential main grooves 14c, 14d located on the outermost sides in the tire width direction are smaller than the groove widths of the other circumferential main grooves (14a, 14b). By adopting such a configuration, the groove widths of the circumferential main grooves can be increased in the center region, which contributes greatly to drainage performance, and as a result, drainage performance and, ultimately, wet performance can be further improved.

[0072] Comparing the example shown in FIG. 1 with the example shown in FIG. 4, the second land portion 20 defined in the center region CR is provided with second lug grooves 34, sipes 36, and sipes 38 in the example shown in FIG. 1, whereas the example shown in FIG. 4 only has a bent groove 58, with no other grooves or sipes. The bent groove 58 shown in FIG. 4 achieves the same effect as the bent groove 26 shown in FIG. 1 (reducing pass-by noise due to intentionally shifting the timing of fluctuations related to the opening and closing of the groove portion during tire rotation). In contrast, the example shown in FIG. 1 does not achieve such an effect. Therefore, the example shown in FIG. 4 can further improve noise performance compared to the example shown in FIG. 1.

[0073] In the tire 10 shown in Figure 1, it is preferable that the number of grooves (widthwise grooves) having a tire width direction component provided in land portions other than the center land portion 16 (second land portions 18, 20 and shoulder land portions 22, 24) (the number of widthwise grooves in the non-center land portions) is 1.3 to 2.6 times the number of curved grooves 26 provided in the center land portion 16 (the number of curved grooves in the center land portion).

[0074] By making the number of widthwise grooves in the non-center land portion 16 1.3 times or more the number of curved grooves in the center land portion, drainage performance and therefore wet performance can be further improved, while by making it 2.6 times or less, the generation of sliding noise can be suppressed without excessively reducing the rigidity of land portions other than the center land portion 16, and therefore pass-by noise can be further reduced.

[0075] The number of widthwise grooves in the non-center land portion is more preferably 1.5 to 2.4 times, and most preferably 1.6 to 2.3 times, the number of bent grooves in the center land portion.

[0076] 1 or 4, the position where the extension direction of the first lug groove 30 becomes the tire width direction (inclination direction change position) is preferably present in the tire width direction outer region within the second land portion 18. Here, the tire width direction outer region within the second land portion 18 refers to a region from a position of 50% or more to a position less than 100% (preferably 90% or less), where the tire width direction inner end of the second land portion 18 is defined as the 0% position and the tire width direction outer end is defined as the 100% position.

[0077] By positioning the inclination direction change position in the outer region in the tire width direction within the second land portion 18, the length of the portion (inner groove portion) of the first lug groove 30 that extends from the circumferential main groove 14a on the inner side in the tire width direction to the inclination direction change position can be made longer than the length of the portion (outer groove portion) that extends from the circumferential main groove 14c on the outer side in the tire width direction to the inclination direction change position.

[0078] When a tire rolls under rainy conditions, the closer to the tire equatorial plane CL, the more likely it is to come into contact with a water film on the road surface. Therefore, even for the same groove, particularly excellent drainage performance is required in the inner groove portion in the tire width direction. For this reason, even for the first lug groove 30, drainage performance is more important in the inner groove portion than in the outer groove portion. Considering that water flows from the inner side to the outer side in the tire width direction during drainage, adopting the above-mentioned configuration (making the length of the inner groove portion longer than the length of the outer groove portion) allows for drainage in the same direction to some extent in the inner groove portion, which is more likely to come into contact with a water film, and then changes the direction of the water flow to continuously drain in the outer groove portion, thereby further improving wet performance.

[0079] 1 , the second lug grooves 34 preferably terminate in an inner region in the tire width direction within the second land portion 20. Here, the inner region in the tire width direction within the second land portion 20 refers to a region from a position of 50% or more to a position less than 100% (preferably 90% or less), where the outer end portion in the tire width direction of the second land portion 20 is defined as the 0% position and the inner end portion in the tire width direction is defined as the 100% position.

[0080] The second lug grooves 34 extend to the inner region in the tire width direction within the second land portion 20, thereby further improving drainage performance and, in turn, wet performance. On the other hand, the second lug grooves 34 terminate within the second land portion 20, thereby suppressing the generation of noise in the inner portion in the tire width direction of the second lug grooves 34 and further reducing pass-by noise.

[0081] 1 or 4, the third lug groove 40 extends from the ground contact edge on the vehicle-mounted outer side, crosses the auxiliary groove 48, and terminates within the land portion 22, and the fourth lug groove 50 extends from the ground contact edge on the vehicle-mounted inner side, crosses the auxiliary groove 56, and terminates within the land portion 24. Here, the lug groove 40 (50) crossing the auxiliary groove 48 (56) means that the tire width direction inner end of the lug groove 40 (50) is located on the tire width direction inner side of the tire width direction inner end of the auxiliary groove 48 (56), and the tire width direction outer end of the lug groove 40 (50) is located on the tire width direction outer side of the tire width direction outer end of the auxiliary groove 48 (56).

[0082] The lug grooves 40 (50) extend from the ground contact edge on the vehicle mounting outer side (vehicle mounting inner side), which reduces the rigidity of the land portions near each ground contact edge to a certain extent, thereby improving traction performance. Furthermore, the lug grooves 40 (50) cross the auxiliary grooves 48 (56) and terminate within the land portions 22 (24), which ensures a certain length of the lug grooves 40 (50) in the tire width direction, thereby further improving drainage performance. Furthermore, by not communicating the lug grooves 40 (50) with the circumferential main grooves 14 c (14 d), noise generation at the inner portions of the lug grooves 40 (50) in the tire width direction can be suppressed, thereby further reducing pass-by noise.

[0083] In the example shown in Figure 1 or Figure 4, the lug groove 40 (50) crosses the auxiliary groove 48 (56) and terminates within the land portion 22 (24), but this embodiment is not limited to such an example and also includes an example in which the lug groove crosses the auxiliary groove and terminates within the land portion only on either the outer or inner side of the vehicle mounting surface.

[0084] In the tire 10 shown in Fig. 1, the average inclination angle of the second lug grooves 34 with respect to the tire width direction (average angle of the second lug grooves) is preferably larger than the average inclination angle of the fourth lug grooves 50 with respect to the tire width direction (average angle of the fourth lug grooves). Here, the average angle of the second lug grooves refers to the angle formed with the tire width direction by a line segment connecting the innermost position and the outermost position of the second lug grooves 34 in the tire width direction. Also, the average angle of the fourth lug grooves refers to the angle formed with the tire width direction by a line segment connecting the innermost position and the ground contact edge position of the fourth lug grooves 34 in the tire width direction.

[0085] By making the average angle of the second lug grooves larger than the average angle of the fourth lug grooves, it is possible to disperse the point at the ground contact edge on the extension line of the second lug grooves 34 extending outward in the tire width direction in Figure 1 (the point at the ground contact edge of the series of curves connecting the second lug grooves 34, sipes 52, and small grooves 54 from the inner side to the outer side in the tire width direction) and the point at the ground contact edge of the fourth lug groove 50 on the ground contact edge line, thereby further reducing pass-by noise.

[0086] In the tire 10 shown in Fig. 1 , the tire width direction outer portion of the first lug groove 30 and the tire width direction inner portion of the third lug groove 40 are all inclined toward the same side in the tire width direction, and the tire width direction outer portion of the second lug groove 34 and the tire width direction inner portion of the fourth lug groove 50 are all inclined toward the same side in the tire width direction. With this configuration, a point at the ground contact end of an extension line of the first lug groove 30 extended outward in the tire width direction and a point at the ground contact end of the third lug groove 40 can be dispersed on the ground contact edge line on the outer side as mounted on the vehicle, thereby further reducing pass-by noise, and a point at the ground contact end of an extension line of the second lug groove 34 extended outward in the tire width direction and a point at the ground contact end of the fourth lug groove 50 can be dispersed on the ground contact edge line on the inner side as mounted on the vehicle, thereby further reducing pass-by noise.

[0087] Test tires (comparative tire and invention examples 1 to 14) were manufactured with a tire size of 245 / 70R18 110H (specified by JATMA), four circumferential main grooves, and meeting the conditions shown in Table 1. Note that all terms in Table 1 are equivalent to the terms explained in this embodiment. Furthermore, among the components of each test tire, components not shown in Table 1 are equivalent to the tire shown in FIG. 1.

[0088] Next, each test tire was mounted on a rim of 18x7.5J size, and the air pressure was adjusted to 230 kPa, and the vehicle was fitted with a 4WD vehicle with an engine displacement of 3500 cc. All test tires were evaluated for noise performance (related to pass-by noise) and wet performance (related to lap time when running on a wet road) according to the following procedures.

[0089] (Method of Evaluating Noise Performance) On a test course, the noise level (dB) of passing noise was measured for each test tire when the vehicle was running at a speed of 50 km / h, with the transmission in neutral and the engine stopped. The difference in noise level between each example tire and the comparative tire was determined, and this difference itself was used as a rating. The lower the rating, the better the noise performance. The results are also shown in Table 1.

[0090] (Method of Evaluating Wet Performance) The lap time of each test tire was measured on a test course when the tire was driven on a wet road surface. Next, a rating was calculated for each example tire, with the comparative example tire being set at 100. The higher the rating, the better the wet performance. The results are also shown in Table 1.

[0091]

[0092] Table 1 shows that all of the tires of Invention Example 1 to Invention Example 14, which fall within the technical scope of the present invention (i.e., satisfying P2 (%) > P1 (%) and P2 (%) > P3 (%)), have improved noise performance while maintaining wet performance compared to the comparative tire that does not fall within the technical scope of the present invention.

[0093] 10 Tire 12 Tread surface 14, 14a, 14b, 14c, 14d Circumferential main groove 16 Center land portion 18, 20 Second land portion 22, 24 Shoulder land portion 26, 28, 58 Bend groove 26a, 28a First portion 26b, 28b Second portion 26c, 28c Third portion 30 First lug groove 32, 36, 38, 42, 52 Sipe 34 Second lug groove 40 Third lug groove 44, 54 Small groove 46 Triangular groove 48, 56 Auxiliary groove 50 Fourth lug groove CL Tire equatorial plane CR Center region D1, D2 First distance D3 Second distance DB Circumferential length of third portion 26c (28c) of bent groove 26 (28) DG Circumferential length of the bent groove 26 (28) between one end and the other end of the bent groove 26 (28) SR Shoulder region W1, W2, W3, W4 Groove width

Claims

1. At least three land portions are defined by at least two circumferential main grooves, and on each side of the tire width direction of the tire equatorial plane, the groove width centerline of the circumferential main groove that is the outermost in the tire width direction is defined as a center region, and the groove width centerline is defined as a shoulder region, the center region being a region inside the tire width direction of the groove width centerline, and at least one land portion formed in the center region is provided with at least one bent groove, at least one end of which in the tire width direction is connected to the circumferential main groove and which has at least two bent portions, and the groove width of a first portion from one end of the bent groove to just before the first bent portion and the groove width of a second portion from the other end of the bent groove to just before the first bent portion are each approximately the same around the entire tire, The number of bent grooves present within the same land portion is N, and the lengths of a first interval between the first portion and the second portion and a second interval which is the shortest distance between two bent grooves adjacent in the tire circumferential direction, measured around the entire circumference of the tire, are Li (1≦i≦2N), respectively; the tire circumference is J (mm), the attention length due to the transfer characteristics is S1 (mm), and the attention lengths due to the sound source are S2 (mm) and S3 (mm); 12.4≦S1(mm)≦19.5, and, Within the range of S1 (mm) and S2 (mm) which satisfies J / (N×1.25×1)≦S2(mm)≦J / (N×0.75×1), the larger of the lower limit values ​​of the two inequalities is LFL1 and the smaller of the upper limit values ​​of the two inequalities is HFL1; 12.4≦S1(mm)≦19.5, and, In the range of S1 (mm) and S3 (mm) which satisfies J / (N x 1.25 x 2) ≦ S3 (mm) ≦ J / (N x 0.75 x 2), the larger of the lower limit values ​​of the two inequalities is defined as LFL2 and the smaller of the upper limit values ​​of the two inequalities is defined as HFL2; Condition C1 is defined by LFL1 x 1 < Li (mm) < HFL1 x 1, or LFL2 x 1 < Li (mm) < HFL2 x 1; Conditions other than Condition C1 and which are defined by LFL1 x 0.5 < Li (mm) < HFL1 x 0.5, LFL1 x 1.5 < Li (mm) < HFL1 x 1.5, LFL2 x 0.5 < Li (mm) < HFL2 x 0.5, or Condition C2 is defined as LFL2×1.5<Li(mm)<HFL2×1.5, andA tire characterized in that: a condition C3 is set to conditions other than C1 and other than C2; and, among a maximum of 2N intervals Li, an existence ratio of intervals Li that satisfy the condition C1 is P1(%), an existence ratio of intervals Li that satisfy the condition C2 is P2(%), and an existence ratio of intervals Li that satisfy the condition C3 is P3(%), wherein P2(%)>P1(%) and P2(%)>P3(%) are satisfied.

2. The tire according to claim 1, wherein said P1(%) is 30% or less.

3. A tire as described in claim 1 or 2, wherein the average number of grooves having a tire width direction component of the land portion in the shoulder region is greater than the average number of grooves having a tire width direction component of the land portion in the center region.

4. The tire according to claim 1 or 2, wherein an auxiliary groove is provided in the shoulder region, extending in the tire circumferential direction and having a groove width of 5% to 40% of the groove width of the circumferential main groove on the outermost side in the tire width direction.

5. A tire as described in claim 1 or 2, wherein a tire circumferential length DG between one end and the other end of the bent groove is equal to or greater than a tire circumferential length DB of a third portion of the bent groove other than the first portion and the second portion.

6. A tire according to claim 1 or 2, wherein at least four land portions are defined by at least three circumferential main grooves.

7. A tire as described in claim 1 or 2, wherein five land portions are defined and formed by four circumferential main grooves, and the groove width of the circumferential main groove located on the outermost side in the tire width direction is smaller than the groove width of the other circumferential main grooves.

8. The tire according to claim 1 or 2, wherein only the bent grooves are provided in the land portion in the center region.

9. A tire as claimed in claim 1 or 2, wherein five land portions are defined and formed by four circumferential main grooves, the bent groove is provided only in a center land portion which is the third of the five land portions, counting from the outermost side in the tire width direction on each side on which the tire is mounted, and the number of grooves having a tire width direction component provided in the land portions other than the center land portion is 1.3 to 2.6 times the number of the bent grooves provided in the center land portion.

10. A tire as described in claim 1 or 2, wherein, among the second land portions adjacent to each side in the tire width direction of the center land portion including the tire equatorial plane, the second land portion on the vehicle-mounted outer side is provided with a first lug groove that is connected to both of the circumferential main grooves on both sides in the tire width direction and whose inclination direction with respect to the tire width direction is reversed midway as it extends from the inner side to the outer side in the tire width direction, and the position where the extension direction of the first lug groove becomes the tire width direction is present in the outer region in the tire width direction of the second land portion.

11. A tire as described in claim 1 or 2, wherein, of the second land portions adjacent to each other in the tire width direction on each side of the center land portion including the tire equatorial plane, the second land portion on the vehicle-mounted inner side is provided with a second lug groove that communicates with the circumferential main groove on the outer side in the tire width direction, extends from the outer side in the tire width direction to the inner side, and terminates in an inner region in the tire width direction of the second land portion.

12. A tire as set forth in claim 4, wherein a third lug groove is provided on an outer side mounted on a vehicle, extending from the ground contact edge toward the circumferential main groove, the third lug groove crossing the auxiliary groove, and / or a fourth lug groove is provided on an inner side mounted on a vehicle, extending from the ground contact edge toward the circumferential main groove, the fourth lug groove crossing the auxiliary groove.

13. A tire as described in claim 11, wherein a fourth lug groove is provided on an inner side mounted on a vehicle, extending from a ground contact edge toward the circumferential main groove, the fourth lug groove traversing the auxiliary groove, and an average inclination angle of the second lug groove with respect to the tire width direction is greater than an average inclination angle of the fourth lug groove with respect to the tire width direction.

14. Among the second land portions adjacent to each side in the tire width direction of the center land portion including the tire equatorial plane, the second land portion on the vehicle-mounted outer side is provided with a first lug groove that is connected to both of the circumferential main grooves on both sides in the tire width direction and whose inclination direction with respect to the tire width direction is reversed midway as it extends from the inner side to the outer side in the tire width direction, and the point at which the extension direction of the first lug groove becomes the tire width direction is present in the tire width direction outer region of the second land portion; Among the second land portions adjacent to each side in the tire width direction of the center land portion including the tire equatorial plane, the second land portion on the vehicle-mounted inner side is provided with a second lug groove that is connected to the circumferential main groove on the outer side in the tire width direction, extends from the outer side in the tire width direction to the inner side, and terminates in the tire width direction inner region of the second land portion; On the vehicle-mounted outer side, a third lug groove is provided extending from the ground contact edge toward the circumferential main groove, and the third lug groove crosses the auxiliary groove, and / or 3. The tire according to claim 1 or 2, wherein a fourth lug groove is provided on an inner side mounted on a vehicle, extending from a ground contact edge toward the circumferential main groove, and the fourth lug groove crosses the auxiliary groove, and an outer portion of the first lug groove and an inner portion of the third lug groove in the tire width direction are both inclined toward the same side with respect to the tire width direction, and an outer portion of the second lug groove and an inner portion of the fourth lug groove in the tire width direction are both inclined toward the same side with respect to the tire width direction.

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