Pneumatic tire, manufacturing method of pneumatic tire, and groove molding material

Abstract

To provide a technology that enables improvement of snow performance of pneumatic tires.SOLUTION: A pneumatic tire has a tread T. The tread T has lands (1, 2, 3) having a tread surface T1, and axial grooves 5 extending in an axial direction AD of a tire on a land and opening on the tread surface T1. The axial grooves 5 include a first part 5A disposed on a tire radially inner side RD2 of the tread surface T1, and a second part 5B disposed from the first part 5A to the tread surface T1 and having a groove width larger than that of the first part 5A. The second part 5B includes a spreading surface 57 extending from an end P1 on a tire radially outer side RD1 of a groove wall 55 constituting the first part 5A to the tread surface T1. The spreading surface 57 has a convex line 6 protruding from the spreading surface 57 and extending linearly.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a pneumatic tire, a method for manufacturing a pneumatic tire, and a groove molding material. [Background technology]

[0002] Pneumatic tires are manufactured by vulcanizing raw tires in a vulcanization mold. A groove molding material is used to form sipes, which are a type of groove, on the tread surface. For example, Patent Document 1 discloses an example of a groove molding material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-58458 Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, there is a demand for improved snow performance in pneumatic tires.

[0005] The present disclosure provides techniques that enable improved snow performance of pneumatic tires. [Means for solving the problem]

[0006] The pneumatic tire of the present disclosure includes a tread, the tread having a land having a tread surface, and an axial groove extending in the land in the tire axial direction and opening on the tread surface, The axial groove includes a first portion located radially inward of the tread surface, and a second portion located from the first portion to the tread surface and having a larger groove width than the first portion, the second portion including an expansion surface extending from a radially outer end of a groove wall constituting the first portion to the tread surface, and the expansion surface has a convex line protruding from the expansion surface and extending linearly. [Brief description of the drawings]

[0007] [Figure 1] 1 is a development view of a tread surface T1 of a tread T of a pneumatic tire of a first embodiment when the tire is new. [Diagram 2] 1 is an enlarged development showing an axial groove 5 (slit 51) of a shoulder land 1. FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. [Figure 4] FIG. 2 is an enlarged development showing the axial grooves 5 (slits 51 having sipes 50) of the second center land 2. [Diagram 5] FIG. 5 is a cross-sectional view of the VV portion in FIG. [Figure 6] 1 is a cross-sectional view showing a tire vulcanizing mold 7 according to a first embodiment. [Figure 7] FIG. 2 is a cross-sectional view of a tire vulcanizing mold 7. [Figure 8] 6 is a diagram showing an example of a groove forming material 77 for forming the axial groove 5 shown in FIG. 4 and FIG. 5. FIG. [Figure 9] FIG. 11 is a development view of a tread surface T1 of a tread T of a pneumatic tire of a second embodiment when the tire is new. [Figure 10] 1 is an enlarged development view showing an axial groove 5 (slit 51) of a second center land 2. FIG. [Figure 11] 11 is a cross-sectional view of the area XI-XI in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [First embodiment] Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings.

[0009] FIG. 1 is a development view of a tread surface T1 of a tread T of a pneumatic tire of a first embodiment when the tire is new.

[0010] As shown in Fig. 1, a tread surface T1 (contact surface that comes into contact with the road surface) of a tread T of a pneumatic tire is provided with a plurality of main grooves (40, 41) that extend continuously in the tire circumferential direction CD. In the first embodiment, there are four main grooves (40, 41), but the number of main grooves (40, 41) can be changed. In the first embodiment, the plurality of main grooves (40, 41) includes a shoulder main groove 40 that is located on the outermost side in the tire axial direction AD.

[0011] The main grooves (40, 41) are not particularly limited, but may be continuous in the tire circumferential direction CD and have the deepest groove depth on the tread surface. The main grooves (40, 41) may be partially provided with a TWI (treadwear indicator) in order to indicate the limit of use due to wear.

[0012] The dimensions of each part of a pneumatic tire are values ​​measured when the pneumatic tire is mounted on a standard rim, inflated to a standard internal pressure, and in an unloaded state.

[0013] A genuine rim is a rim that is defined for each tire by a standard system that includes the standard on which the tire is based, for example, a standard rim for JATMA, and a "Measuring Rim" for TRA and ETRTO.

[0014] The normal internal pressure is the air pressure set for each tire by each standard in the standard system including the standard on which the tire is based. For truck and bus tires and light truck tires, it is the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. For passenger car tires, it is usually 180kPa, but for tires marked "Extra Load" or "Reinforced", it is 220kPa.

[0015] The tread T has a plurality of lands (1, 2, 3) having a tread surface T1. The plurality of lands (1, 2, 3) include a shoulder land 1 and a center land (2, 3). The shoulder land 1 is disposed outside the shoulder main groove 40 in the tire axial direction AD, and is the land disposed on the outermost side in the tire axial direction AD. The center land (2, 3) is disposed inside the shoulder land 1 in the tire axial direction AD. In the first embodiment, the center land (2, 3) includes a first center land 3 closest to the tire equatorial plane CL, and a second center land 2 (sometimes called a quarter land) disposed between the first center land 3 and the shoulder land 1.

[0016] At least one of the lands (1, 2, 3) has an axial groove 5 that extends in the tire axial direction AD and opens on the tread surface T1. Examples of the axial groove 5 include a groove that terminates within the land and does not open to the main groove, a groove that opens to the main groove at one end and terminates within the land at the other end, and a groove that opens to the main groove at both ends. The axial groove 5 may include a sipe 50, a slit 51, and a slit 51 having a sipe 50 at its bottom. The sipe 50 means a groove having a groove width of 0.3 mm or more and 1.5 mm or less. The slit 51 means a groove having a groove width of more than 1.5 mm and 10.0 mm or less. The groove width means a dimension measured parallel to a straight line connecting the opening end P2 of the groove (the end where the tread surface T1 and the groove wall intersect) in a cross section perpendicular to the extension direction SD1 (see FIG. 2) of the axial groove 5 in the development view of the tread T. The extension direction SD1 of the axial grooves 5 may be represented by a line connecting the centers of the axial grooves 5 (the centers between the opening ends P2 of the grooves) in the developed view.

[0017] As shown in FIG. 1, in the first embodiment, all the lands (1, 2, 3) each have one or more axial grooves 5. In the first embodiment, the multiple axial grooves 5 of the tread T include grooves having a convex line 6 described later and grooves not having a convex line 6 described later. In FIG. 1, the axial grooves having a convex line 6 described later are marked with a reference symbol 5, and the axial grooves not having a convex line 6 described later are not marked with a reference symbol 5 and are indicated as sipes 50 or slits 51. The pneumatic tire of the first embodiment is a tire for which a mounting direction relative to a vehicle is specified, and is indicated in FIG. 1 as an inner side IN of the vehicle and an outer side OUT of the vehicle. The mounting direction on the vehicle is indicated on the outer surface of the tire.

[0018] <Axial groove 5 (slit 51) of shoulder land 1> As shown in FIG. 1, the shoulder land 1 on the vehicle outer side OUT has an axial groove 5 (slit 51). FIG. 2 is an enlarged development view showing the axial groove 5 (slit 51) of the shoulder land 1. FIG. 3 is a cross-sectional view of the III-III portion in FIG. 2 (a cross-sectional view perpendicular to the extending direction SD1 of the axial groove 5). As shown in FIG. 2 and FIG. 3, the axial groove 5 has a first portion 5A and a second portion 5B. The first portion 5A is disposed on the tire radially inner side RD2 of the tread surface T1. The second portion 5B is disposed from the first portion 5A to the tread surface T1, and has a groove width larger than that of the first portion 5A. The first portion 5A has a pair of groove walls 55 facing each other. The ends of the pair of groove walls 55 on the tire radially inner side RD2 are connected to the groove bottom surface 56. The first portion 5A shown in FIG. 3 is a slit 51, and the groove width of the slit 51 is as described above. The second region 5B includes a spreading surface 57 extending from an end P1 on the tire radial outer side RD1 of the groove wall 55 constituting the first region 5A to the tread surface T1. The angle of the spreading surface 57 with respect to the tire radial direction RD (an angle greater than 0 degrees and smaller than 45 degrees in the example of FIG. 3) is greater than the angle of the groove wall 55 constituting the first region 5A with respect to the tire radial direction RD (0 degree in the example of FIG. 3). Due to this angular relationship, the second region 5B has a larger groove width than the first region 5A. In the first embodiment, the spreading surface 57 is a flat surface.

[0019] The spreading surface 57 has a convex line 6 that protrudes from the spreading surface 57 and extends linearly. In the first embodiment, a plurality of convex lines 6 are formed on one spreading surface 57. When the tread T contacts a snowy road, the convex lines 6 have the effect of scraping the snow that enters the axial grooves 5, thereby improving snow performance (any of snow driving performance, snow braking performance, and snow cornering performance). In the first embodiment, the spreading surface 57 is formed on both sides of the axial groove 5 in the groove width direction SD2 across the first portion 5A, and a plurality of convex lines 6 are formed on each spreading surface 57. By forming the convex lines 6 on each of the two spreading surfaces 57 that sandwich the first portion 5A, it is possible to improve snow performance both during driving and braking.

[0020] In the cross section perpendicular to the extending direction SD1 of the axial groove 5 shown in FIG. 3, the width D2 of the convex line 6 is preferably 10% or more and 90% or less of the width D1 of the spreading surface 57. The protruding height D3 of the convex line 6 in the direction perpendicular to the spreading surface 57 is preferably 6% or more and 20% or less of the width D1 of the spreading surface 57. If the width D2 or the protruding height D3 of the convex line 6 is smaller than the above numerical range, it is difficult to obtain an improvement effect on snow performance. If the width D2 or the protruding height D3 of the convex line 6 is larger than the above numerical range, the effect of the convex line 6 to scratch the snow is weakened, and it is difficult to obtain an improvement effect on snow performance. The width D1 of the spreading surface 57 and the width D2 of the convex line 6 are dimensions along a virtual line connecting the end P1 of the spreading surface 57 on the inner side RD2 in the tire radial direction and the end P2 of the spreading surface 57 on the outer side RD1 in the tire radial direction.

[0021] The convex lines 6 extend parallel to the extension direction SD1 of the axial grooves 5 in the plan view (developed view) shown in Fig. 2. The convex lines 6 extend from one end to the other of the spreading surface 57 in the plan view (developed view), but are not limited thereto. If the convex lines 6 extend from one end to the other of the spreading surface 57 in the plan view (developed view), it becomes easier to obtain an improved effect on snow performance. Moreover, the convex lines 6 are preferably provided within a range Ar1 of 2.0 mm or less from the tread surface T1 toward the tire radially inner side RD2 as shown in Fig. 3. This is to facilitate obtaining an improved effect on snow performance.

[0022] <Axial groove 5 of second center land 2 (slit 51 having sipe 50)> As shown in FIG. 1, the second center land 2 adjacent to the shoulder land 1 among the center land (2, 3) on the vehicle outer side OUT has an axial groove 5 (slit 51 having a sipe 50). FIG. 4 is an enlarged development view showing the axial groove 5 (slit 51 having a sipe 50) of the second center land 2. FIG. 5 is a cross-sectional view of the VV portion in FIG. 4 (a cross-sectional view perpendicular to the extending direction SD1 of the axial groove 5). The axial groove 5 shown in FIG. 4 and FIG. 5 has a first portion 5A and a second portion 5B, similar to the axial groove 5 shown in FIG. 2 and FIG. 3. The first portion 5A has a pair of groove walls 55, and the second portion 5B has an expanding surface 57, as in the example shown in FIG. 2 and FIG. 3, so the description will be omitted. The first portion 5A shown in FIG. 5 is a sipe 50, and the groove width of the sipe 50 is as described above. The second portion 5B shown in FIG. 5 is a slit 51, and the groove width of the slit 51 is as described above. As shown in Figures 4 and 5, spreading surfaces 57 are formed on both sides of the first portion 5A in the groove width direction SD2 of the axial groove 5, and a plurality of convex lines 6 are formed on each spreading surface 57, as in the example shown in Figures 2 and 3. The width D2 of the convex lines 6 and the protruding height D3 of the convex lines 6 are the same as in the example shown in Figures 2 and 3. The other numerical values ​​are also similar.

[0023] The convex line 6 extends from one end to the other end of the extension direction SD1 of the spreading surface 57 in a plan view (developed view), but is not limited thereto. The convex line 6 is inclined with respect to the extension direction SD1 of the axial groove 5 in a plan view (developed view) shown in FIG. 4. As shown in FIG. 4, the width D1 (see FIG. 5) of the spreading surface 57 in the groove width direction SD2 spreads from the inside of the second center land 2 toward the land end (main groove 41) of the second center land 2. In the plan view (developed view) shown in FIG. 4, the convex line 6 is inclined in a direction facing outward in the groove width direction SD2 of the spreading surface 57 as the width D1 (see FIG. 5) of the spreading surface 57 in the groove width direction SD2 spreads.

[0024] As shown in Figures 2 and 4, in a plan view of the tread T, the inclination angle of the convex line 6 at the second center land 2 with respect to the tire axial direction AD is different from the inclination angle of the convex line 6 at the shoulder land 1 with respect to the tire axial direction AD. The inclination angle of the convex line 6 at the shoulder land 1 with respect to the tire axial direction AD is smaller than the inclination angle of the convex line 6 at the second center land 2 with respect to the tire axial direction AD. Depending on the inclination angle of the convex line 6 with respect to the tire axial direction AD, the ease with which the effect of improving snow driving performance and braking performance is exhibited and the ease with which the effect of improving snow cornering performance is exhibited differ. By making the inclination angles of the convex lines 6 provided on the different lands (1, 2) different from each other, it is possible to provide both lands that are likely to exhibit the effect of improving snow driving performance and braking performance and lands that are likely to exhibit the effect of improving snow cornering performance.

[0025] When the vehicle turns, the contact area on the outer side of the vehicle (OUT) increases and the contact area on the inner side of the vehicle (IN) decreases. As shown in Fig. 1, the land axial groove 5 on the outer side of the vehicle (OUT) has a spreading surface 57, and the spreading surface 57 has a convex line 6, so that the convex line 6 of the spreading surface 57 has an increased effect of grabbing snow on the contact area on the outer side of the vehicle (OUT), thereby improving snow cornering performance.

[0026] <Tire curing mold 7> The pneumatic tire of the first embodiment is manufactured by a tire vulcanizing mold 7 shown in Fig. 6 and Fig. 7. Fig. 6 is a cross-sectional view showing the tire vulcanizing mold 7 according to the first embodiment. Fig. 7 is a cross-sectional view of the tire vulcanizing mold 7.

[0027] As shown in FIG. 6, the tire vulcanizing mold 7 molds the outer surface of a pneumatic tire. The tire vulcanizing mold 7 has an upper side mold 71 and a lower side mold 73 that are paired vertically, an upper bead ring 72 and a lower bead ring 74 that are paired vertically, and a plurality of sectors 75 arranged in the tire circumferential direction. The sectors 75 are molds for molding the tread surface T1 of the tread T of the pneumatic tire. The plurality of sectors 75 are displaceable in the tire radial direction RD, and move to the tire radial outer side RD1 when the mold opens. The upper side mold 71 and the upper bead ring 72 are configured to be movable in the up-down direction (AD) relative to the lower side mold 73 and the lower bead ring 74, and move upward (AD1) when the mold opens. The up-down direction (AD) coincides with the tire axial direction AD. One side in the tire axial direction AD is the upper side (AD1), and the other side in the tire axial direction AD is the lower side (AD2).

[0028] 6, the bladder 76 is shown by a dashed line. The bladder 76 is configured to include a toroidal shaped expandable and contractible rubber elastic body, is disposed on the inner surface side of the pneumatic tire, and pressurizes the pneumatic tire from the inside by inflating when pressurized gas is supplied.

[0029] Next, a sector 75, which is a mold for molding the tread surface T1 of the tread T of a pneumatic tire, will be described. As shown in FIG. 7, the sector 75 has a mold body 750 for forming the tread surface T1, and a groove molding material 77 for forming axial grooves 5 such as sipes 50 or slits 51 (see FIGS. 1 to 5) on the tread surface T1. A plurality of groove molding materials 77 are cast-into the mold body 750. Cast-in generally refers to pouring molten metal around a different material to obtain a casting integrated with the main body, and here refers to obtaining a sector 75 in which the groove molding material 77 is integrated with the mold body 750 by pouring molten metal using the groove molding material 77 as an insert.

[0030] The mold body 750 is made of a soft metal such as aluminum (including aluminum alloy). The mold body 750 has a tread molding surface 750A for molding the tread surface T1. The tread molding surface 750A is provided with ribs 751 for molding main grooves (40, 41, see FIG. 1) on the tread surface T1. The ribs 751 are convex stripes that protrude from the tread molding surface 750A and extend in the tire circumferential direction, and are formed integrally with the mold body 750. The ribs 751 partition the tread T, forming lands (1, 2, 3) (see FIG. 1).

[0031] The groove molding material 77 is made of a material different from the die body 750, and is preferably made of an iron-based metal from the viewpoint of strength and the like. The groove molding material 77 is preferably made of stainless steel. The groove molding material 77 is used in particular to form the axial groove 5 having the spreading surface 57 on which the convex line 6 is formed. In the first embodiment, the axial groove 5 having the convex line 6 is formed by the groove molding material 77, and the axial groove not having the convex line 6 is formed by the die body 750.

[0032] FIG. 8 is a diagram showing an example of a groove molding material 77 for forming the axial groove 5 shown in FIG. 4 and FIG. 5. As shown in FIG. 8, the groove molding material 77 has a molding portion 77A that protrudes from the mold body 750 and molds the axial groove 5 (see FIG. 4 and FIG. 5), and an embedded portion 77B that is embedded in the mold body 750. To facilitate distinction between these in the drawing, the embedded portion 77B is hatched in FIG. 8. As shown in FIG. 8, the groove molding material 77 (its molding portion 77A) has a thick portion 77C disposed on the shallow side of the axial groove 5, and a thin portion 77D disposed on the deep side of the axial groove 5. The thick portion 77C is a portion that is thicker (has a larger dimension (width) in the groove width direction SD2) than the thin portion 77D. The thick portion 77C forms the second portion 5B of the axial groove 5 shown in FIG. 5. The thin portion 77D forms the first portion 5A of the axial groove 5 shown in FIG. 5. Therefore, thick portion 77C has a surface that forms spreading surface 57 and linear recessed lines 77E that correspond to protruding lines 6.

[0033] In the first embodiment, since the recessed lines 77E are minute, it is preferable that the groove molding material 77 is produced by metal molding (also called metal additive manufacturing) using a 3D printer. Metal molding refers to a technique for fusing and stacking metal powder layer by layer to produce a three-dimensional shape. Examples of metal molding include SLS (Selective laser sintering) and SLM (Selective laser melting), in which metal powder is selectively sintered or melted on a support plate by irradiation with a laser beam, thereby forming a layer by layer according to the shape of the object to be molded.

[0034] <Manufacturing method of pneumatic tires> A raw tire is manufactured, and the raw tire is placed in the tire vulcanization mold and heated and pressurized to perform a vulcanization process, thereby manufacturing a vulcanized pneumatic tire. In the vulcanization process, a tire vulcanization mold 7 having a mold body 750 for forming a tread surface T1 and a groove molding material 77 protruding from the mold body 750 is used, and the tread surface T1 is formed by the mold body 750, and the axial grooves 5, the expansion surface 57, and the convex lines 6 are formed by the groove molding material 77.

[0035] [Second embodiment] A pneumatic tire according to a second embodiment will be described with reference to Fig. 9. Fig. 9 is a development view of a tread surface T1 of a tread T of a pneumatic tire according to a second embodiment when the tire is new. In the first embodiment shown in Fig. 1, the axial groove 5 having the convex line 6 is arranged on the land on the outer side OUT of the tire equator CL of the vehicle, and is not arranged on the land on the inner side IN of the vehicle of the tire equator CL. In contrast, in the second embodiment shown in Fig. 9, the axial groove 5 having the convex line 6 is not arranged on the land on the outer side OUT of the tire equator CL of the vehicle, and is arranged on the land on the inner side IN of the vehicle of the tire equator CL.

[0036] The axial grooves 5 (slits 51) arranged on the shoulder land 1 on the vehicle inner side IN of the tire equator CL shown in FIG. 9 have the same shape as the axial grooves 5 shown in FIGS. 1 to 3, and therefore a description thereof will be omitted.

[0037] As shown in FIG. 9, the second center land 2 adjacent to the shoulder land 1 among the center land (2, 3) on the vehicle inner side IN has an axial groove 5 (slit 51). FIG. 10 is an enlarged development view showing the axial groove 5 (slit 51) of the second center land 2. FIG. 11 is a cross-sectional view of the XI-XI portion in FIG. 10 (a cross-sectional view perpendicular to the extending direction SD1 of the axial groove 5). The axial groove 5 shown in FIG. 10 and FIG. 11 has a first portion 5A and a second portion 5B, similar to the axial groove 5 shown in FIG. 2 and FIG. 3. The first portion 5A has a pair of groove walls 55, and the second portion 5B has an expanding surface 57, as in the example shown in FIG. 2 and FIG. 3, so the description will be omitted. The first portion 5A and the second portion 5B shown in FIG. 11 are slits 51, and the groove width of the slit 51 is as described above. 10 and 11, spreading surfaces 57 are formed on both sides of the axial groove 5 in the groove width direction SD2 across the first portion 5A, and a plurality of convex lines 6 are formed on each spreading surface 57, as in the example shown in Figures 2 and 3. The width D2 of the convex lines 6 and the protruding height D3 of the convex lines 6 are the same as in the example shown in Figures 2 and 3.

[0038] 10, the convex line 6 extends parallel to the extension direction SD1 of the axial groove 5. The convex line 6 extends from one end to the other end of the expanding surface 57 in the extension direction SD1 in the plan view (developed view), but is not limited thereto.

[0039] As shown in Fig. 9, in a plan view of the tread T, the inclination angle of the convex line 6 at the second center land 2 with respect to the tire axial direction AD is different from the inclination angle of the convex line 6 at the shoulder land 1 with respect to the tire axial direction AD. The inclination angle of the convex line 6 at the shoulder land 1 with respect to the tire axial direction AD is smaller than the inclination angle of the convex line 6 at the second center land 2 with respect to the tire axial direction AD. This makes it possible to provide both a land that is likely to exhibit the effect of improving snow driving performance and braking performance, and a land that is likely to exhibit the effect of improving snow cornering performance.

[0040] In a straight-ahead state, the camber angle reduces the contact area on the outer side of the vehicle (OUT) and increases the contact area on the inner side of the vehicle (IN). As shown in Fig. 9, the land axial groove 5 on the inner side of the vehicle (IN) has a spreading surface 57, and the spreading surface 57 has a convex line 6, so that the convex line 6 of the spreading surface 57 has an increased effect of grabbing snow on the contact area on the inner side of the vehicle (IN), thereby improving driving performance on snow and cornering performance on snow.

[0041] [Variations] (A) The pneumatic tires in the above embodiments are tires for which the mounting direction relative to a vehicle is specified, but the present disclosure is applicable to tires for which the mounting direction relative to a vehicle is not specified.

[0042] (B) In the above embodiment, the expanding surface 57 is a flat surface in a cross section of the groove width direction SD2 of the axial groove 5, but is not limited to this. For example, the expanding surface 57 may be a curved surface.

[0043] (C) In the above embodiment, a plurality of protruding lines 6 are formed on one spreading surface 57, but the present invention is not limited to this. The number of protruding lines 6 formed on one spreading surface 57 may be one. Although the expanding surface 57 is formed on both sides of the axial groove 5 in the groove width direction SD2 across the first portion 5A, the present invention is not limited to this. The expanding surface 57 may be formed on only one side of the axial groove 5 in the groove width direction SD2 across the first portion 5A. In the above embodiment, the convex line 6 is formed on each of the two spreading surfaces 57 that sandwich the first portion 5A, but this is not limited to this. For example, the convex line 6 may be formed on only one of the two spreading surfaces 57 that sandwich the first portion 5A.

[0044] (D) In ​​the axial groove 5 shown in Figures 4 and 5, the first portion 5A is a sipe 50 and the second portion 5B is a slit, but is not limited thereto. For example, the groove width of the axial groove 5 shown in Figures 4 and 5 may be set so that both the first portion 5A and the second portion 5B are sipes 50.

[0045] (E) In the above embodiment, the sectors 75 are given as an example of the tire vulcanizing mold 7, but the present invention is not limited to a segmented mold having sectors 75, and can also be applied to a two-piece mold not using sectors 75.

[0046] (F) In the above embodiment, the groove molding material 77 is formed by metal molding using a 3D printer, but the manufacturing method is not limited thereto. For example, the groove molding material 77 may be produced by sheet metal processing.

[0047] [1] As described above, the pneumatic tires of the first and second embodiments include a tread T, the tread T has land (1, 2, 3) having a tread surface T1, and axial grooves 5 extending in the tire axial direction AD on the land and opening to the tread surface T1, the axial grooves 5 include a first portion 5A arranged on the tire radially inner side RD2 than the tread surface T1, and a second portion 5B arranged from the first portion 5A to the tread surface T1 and having a groove width larger than that of the first portion 5A, the second portion 5B including an expansion surface 57 extending from an end P1 on the tire radially outer side RD1 of the groove wall 55 constituting the first portion 5A to the tread surface T1, and the expansion surface 57 may have a convex line 6 protruding from the expansion surface 57 and extending linearly. Since the expansion surface 57 has the convex lines 6, when the tread T comes into contact with a snowy road, the convex lines 6 have the effect of scraping off snow that enters the axial grooves 5, thereby improving snow performance.

[0048] [2] In the pneumatic tire described in [1] above, in a cross section perpendicular to the extension direction SD1 of the axial groove 5, the width D2 of the convex line 6 may be 10% or more and 90% or less of the width D1 of the expansion surface 57, and the protruding height D3 of the convex line 6 in a direction perpendicular to the expansion surface 57 may be 6% or more and 20% or less of the width D1 of the expansion surface 57. This configuration makes it easier to achieve improved snow performance.

[0049] [3] The pneumatic tire according to the above [1] or [2] may have a tread T having a shoulder land 1 located on the outermost side in the tire axial direction AD, and a center land (second center land 2) located inside the shoulder land 1 in the tire axial direction AD, and an axial groove 5 having a convex line 6 is provided in each of the center land (second center land 2) and the shoulder land 1, and in a plan view of the tread T, the inclination angle of the convex line 6 of the axial groove 5 of the center land (second center land 2) with respect to the tire axial direction AD and the inclination angle of the convex line 6 of the axial groove 5 of the shoulder land 1 with respect to the tire axial direction AD may be different. This makes it possible to provide both land where snow driving performance and braking performance are easily demonstrated, and land where the effect of improving snow turning performance is easily demonstrated, thereby making it possible to improve the three performance aspects of snow driving performance, snow braking performance, and snow turning performance.

[0050] [4] In the pneumatic tire according to any one of the above [1] to [3], the first portion 5A may be a slit 51 having a groove width greater than 1.5 mm and less than or equal to 10.0 mm.

[0051] [5] In the pneumatic tire according to any one of the above items [1] to [3], the first portion 5A may be a sipe 50 having a groove width of 1.5 mm or less.

[0052] [6] The method for manufacturing a pneumatic tire according to any one of the above [1] to [5] may include a step of using a tire vulcanization mold 7 having a mold body 750 for forming a tread surface T1 and a groove molding material 77 protruding from the mold body 750 to form the tread surface T1 with the mold body 750, and forming the axial grooves 5, the expansion surface 57, and the convex line 6 with the groove molding material 77.

[0053] [7] The groove molding material 77 for forming an axial groove 5 in a pneumatic tire described in any one of [1] to [5] above may have a recessed line 77E for forming a convex line 6 on the spreading surface 57 that protrudes from the spreading surface 57 and extends linearly.

[0054] Although the embodiments of the present disclosure have been described above based on the drawings, the specific configurations should not be considered to be limited to these embodiments. The scope of the present disclosure is indicated not only by the description of the above-mentioned embodiments but also by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

[0055] The structures employed in the above-described embodiments may be employed in any other embodiment. The specific configurations of the components are not limited to the above-described embodiments, and may be modified in various ways without departing from the spirit of the present disclosure.

[0056] For example, the order of execution of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings, can be arbitrary, as long as the output of a previous process is not used in a subsequent process. Even if the flow in the claims, specifications, and drawings is described using "first," "next," and the like for convenience, this does not mean that it is essential to execute the processes in this order. [Explanation of symbols]

[0057] 1: Shoulder Land 5: Axial groove 5A: 1st part 5B: 2nd part 6: Convex line 7: Tire curing mold 50: Sipe 51: Slit 55: Groove wall 57: Spreading surface 77: Groove molding material 77E: Concave line 750: Mold body AD: Tire axial direction CD: Tire circumferential direction RD: Tire radial direction RD1: Tire radial outer side RD2: Tire radial inner side T: Tread T1: Tread surface

Claims

1. With tread, The tread has a land having a tread surface, and an axial groove extending in the land in the tire axial direction and opening on the tread surface, The axial groove includes a first portion disposed radially inward of the tread surface, and a second portion disposed from the first portion to the tread surface and having a groove width larger than that of the first portion, The second portion includes an expansion surface extending from an outer end in the tire radial direction of a groove wall constituting the first portion to the tread surface, The expanding surface has a convex line that protrudes from the expanding surface and extends linearly.

2. 2. The pneumatic tire according to claim 1, wherein in a cross section perpendicular to the extension direction of the axial groove, a width of the convex line is 10% or more and 90% or less of a width of the expansion surface, and a protruding height of the convex line in a direction perpendicular to the expansion surface is 6% or more and 20% or less of the width of the expansion surface.

3. The tread has a shoulder land disposed on the outermost side in the tire axial direction, and a center land disposed on the inner side in the tire axial direction than the shoulder land, The axial groove having the convex line is provided on each of the center land and the shoulder land, 2. The pneumatic tire according to claim 1, wherein, in a plan view of the tread, an inclination angle of the convex line of the axial groove of the center land relative to the tire axial direction is different from an inclination angle of the convex line of the axial groove of the shoulder land relative to the tire axial direction.

4. The pneumatic tire according to any one of claims 1 to 3, wherein the first portion is a slit having a groove width greater than 1.5 mm and less than or equal to 10.0 mm.

5. The pneumatic tire according to any one of claims 1 to 3, wherein the first portion is a sipe having a groove width of 1.5 mm or less.

6. A method for manufacturing a pneumatic tire according to claim 1, A method for manufacturing a pneumatic tire includes a step of using a tire vulcanizing mold having a mold body that forms the tread surface and a groove molding material protruding from the mold body to form the tread surface with the mold body, and forming the axial grooves, the expansion surface, and the convex line with the groove molding material.

7. A groove molding material for forming the axial groove in the pneumatic tire according to claim 1, A groove molding material having a recessed line for forming the convex line on the spreading surface, the convex line protruding from the spreading surface and extending linearly.

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