pneumatic tires

Abstract

Pneumatic tires (1), comprising: two circumferential grooves (3) in a tread surface (2A) of a tread section (2) which are arranged in a tire transverse direction and extend in a tire circumferential direction; a plurality of transverse grooves (4) in the tread surface (2A) which are arranged in the direction of the tire circumference and extend to cross the direction of the tire circumference, wherein the plurality of transverse grooves (4) are connected at both ends to both circumferential grooves (3) and each define a block-shaped rib section (5) between the circumferential grooves (3); two narrow grooves (6) in the tread surface (2A) of the rib section (5), which are arranged in the transverse direction of the tire and extend in the circumferential direction of the tire, wherein the narrow grooves (6) each communicate at both ends with a respective transverse groove (4) of the plurality of transverse grooves (4) and divide the rib section (5), which is defined by each of the circumferential grooves (3) and each of the transverse grooves (4), into a plurality of small rib sections (5A, 5B); wherein the two narrow grooves (6) in the web section (5) are formed such that they have a smaller groove width than the circumferential grooves (3) and each comprise a curved section (6A) in a central section, wherein the curved section (6A) is arranged inwards in the transverse direction of the tire in a direction in which the narrow grooves (6) are opposite each other by an imaginary straight connecting line (A) which connects the ends of the respective narrow grooves (6), wherein bending points (6Aa) of the curved sections (6A) are arranged at positions offset from each other in the circumferential direction of the tire, and wherein the narrow grooves (6) do not cross the imaginary straight connecting line (A).

Description

Technical field

[0001] The present invention relates to a pneumatic tire. State of the art

[0002] In a typical tire, uneven wear is caused by high pressure exerted on the tire when it comes into contact with the ground. Therefore, the ground contact pressure must be appropriately reduced.

[0003] A known pneumatic tire, for example, the pneumatic tire described in JP 2003-182315A, is designed to improve steering stability on snow in a worn condition without reducing dry steering stability. This pneumatic tire incorporates, in a road contact patch section of a tread, a plurality of main grooves extending circumferentially and a block defined by transverse grooves intersecting the main grooves. The block includes sipes and a pair of acute-angled block corner sections on opposite sides circumferentially. The blocks further include a pair of small blocks defined by the pair of acute-angled block corner sections and two of the sipes, and a central block positioned between the small blocks, the central block being larger than the small blocks.

[0004] The pneumatic tire described in JP 2008 - 260 343 A, for example, includes in a belt layer a small-angle belt including cord threads inclined at an angle of 5° to 30° with respect to a tire circumference direction, and a large-angle belt including cord threads inclined at an angle of 45° to 90° with respect to the tire circumference direction.

[0005] The pneumatic tire described in JP 2015 - 174 469 A includes, in another example, a belt layer with a multilayered structure, comprising a pair of cross-belt layers and a circumferential belt.

[0006] JP 2007 153 104 A describes a pneumatic radial tire capable of adequately achieving the edge effect while maintaining the required stiffness. According to one example, the tire consists of several circumferential grooves and several lateral grooves. Some of the blocks between the grooves consist of zigzag-shaped axial sipes oriented in the width direction of the tire and zigzag-shaped axial sipes oriented in the circumferential direction of the tire.

[0007] EP 1 459 908 A1 describes a tread pattern for a winter tire. According to an example, the tire consists of several circumferential grooves and several lateral grooves. Each of the blocks to the left and right of the center line M consists of a curved groove, which is not described further.

[0008] DE 696 04 427 T2 describes a tire with improved wet-ground performance. According to one example, the tire consists of several circumferential grooves and several lateral grooves. Some blocks consist of support rods running along the tire's width. The lateral grooves are S-shaped and converge at the equatorial plane. Thus, the angles of inclination of the lateral grooves are greatest near the equatorial plane and smallest further away from it.

[0009] DE 11 2008 001 558 B4 describes a pneumatic tire in general, which can be advantageously applied to a pneumatic tire with a block-based tread pattern and which combines performance on snow with resistance to uneven wear. Summary of the invention: Technical problem

[0010] The stiffness of blocks and ribs is reduced by the formation of narrow grooves and slots, such as lamellae. This can lead to splitting and spalling.

[0011] In light of the foregoing, it is an object of the present invention to provide an air tire which can provide improved resistance to uneven wear while maintaining durability performance by reducing ground contact pressure without reducing block stiffness.

[0012] A heavy-duty pneumatic tire for mounting on a truck or bus, in particular a low aspect ratio pneumatic tire, may include a small-angle belt as in JP 2008 - 260 343 A or a circumferential belt as in JP 2015 - 174 469 A (hereinafter collectively referred to as the ‘circumferential belt’) to maintain the shape of the tread section.

[0013] In the area of ​​the tire's equatorial plane where the circumferential belt is located, the belt provides high circumferential stiffness, thus suppressing radial expansion when the tire is new and thereafter. However, areas outside the circumferential belt in the tire's transverse direction experience high radial expansion due to circumferential stiffness that is relatively low compared to that of the area at or near the tire's equatorial plane. This results in uneven wear.

[0014] In light of the foregoing, it is an object of the present invention to provide an air tire which, even in a configuration with a circumferential belt, can provide improved resistance to uneven wear. Solution to the problem

[0015] To solve the problems described above and to achieve the objective as described above, a pneumatic tire according to one aspect of the present invention includes i) two circumferential grooves in a tread surface of a tread section, which are arranged in a transverse direction of the tire and extend in a circumferential direction of the tire, ii) a plurality of transverse grooves in the tread surface, arranged in the direction of the tire circumference and extending to cross the direction of the tire circumference, wherein the plurality of transverse grooves are connected at both ends to both circumferential grooves and each define a block-shaped rib section between the circumferential grooves, iii) two narrow grooves in the tread surface of the rib section, arranged in the transverse direction of the tire and extending in the circumferential direction of the tire, wherein the narrow grooves each communicate at both ends with a respective transverse groove of the plurality of transverse grooves and divide the rib section defined by each of the circumferential grooves and each of the transverse grooves into a plurality of small rib sections, iv) wherein the two narrow grooves in the web section are formed such that they have a smaller groove width than the circumferential grooves and each comprise a curved section in a central section, (v) wherein the curved section is arranged inwards in the transverse direction of the tire in a direction in which the narrow grooves are opposite each other from an imaginary straight connecting line which connects the ends of the respective narrow grooves, wherein bending points of the curved sections are arranged at positions offset from each other in the circumferential direction of the tire, and wherein the narrow grooves do not cross the imaginary straight connecting line.

[0016] In the pneumatic tire design, each of the rib sections defined by the circumferential and transverse grooves is divided by two narrow grooves to form smaller rib segments. This results in reduced stiffness, which helps to lower ground contact pressure when the tread section comes into contact with the ground. Additionally, the length of the narrow grooves is increased by the curved sections formed within them. This further reduces stiffness, thus mitigating ground contact pressure even more. Therefore, resistance to uneven wear can be improved. Furthermore, in the pneumatic tire design, the curved section is oriented inwards in the tire's transverse direction, in the direction where the two narrow grooves face each other, relative to the imaginary straight line connecting the ends of the narrow groove.As a result, a reduction in the area of ​​the small lateral rib sections on the tread surface is suppressed, and a decrease in stiffness is prevented. Furthermore, the bending points of the two narrow grooves are offset from each other in the tire's circumferential direction, thus suppressing local narrowing of the central small rib section and preventing a reduction in stiffness. This prevents separation and spalling of the rib section. Consequently, the pneumatic tire's resistance to uneven wear is improved, while maintaining overall durability by suppressing separation and spalling.

[0017] In the pneumatic tire according to one aspect of the present invention, the curved section of the narrow groove preferably has a bending angle in the range between 90° and 160°.

[0018] According to pneumatic tire specifications, if the bending angle of the bent section is 90° or greater, the bend becomes less sharp. As a result, separation and spalling are less likely to occur, and the effect on maintaining durability is significant. If the bending angle of the bent section is 160° or less, the length of the narrow grooves increases, and the effect on stiffness decreases significantly.

[0019] In the pneumatic tire according to one aspect of the present invention, a relative displacement width Lc in the tire circumferential direction of each bending point of the two narrow grooves and a tire circumferential direction dimension L of the rib section in which the narrow grooves are formed preferably meet 0.1 ≤ Lc / L.

[0020] According to the pneumatic tire specifications, achieving a coefficient of friction of 0.1 ≤ Lc / L further suppresses localized narrowing of the central small rib section between the two narrow grooves, and a reduction in stiffness can be further prevented. As a result, the effect on maintaining durability is significant.

[0021] In the pneumatic tire according to one aspect of the present invention, the transverse groove is preferably designed such that it extends inclined with respect to the tire transverse direction, with an angle with respect to the tire transverse direction in the range of 5° to 50°.

[0022] According to the pneumatic tire design, if the angle of the lateral groove relative to the tire's transverse direction is greater than 5°, the groove length is increased, resulting in a significant reduction in stiffness. Conversely, if the lateral groove angle is 50° or less, it is prevented from becoming acute. Consequently, separation and spalling are less likely, and the tire's durability is significantly improved.

[0023] In the pneumatic tire according to one aspect of the present invention, the relationships Ha > Hb and Ha > Hc are preferably satisfied, where Ha is a groove depth of the circumferential grooves, Hb is a groove depth of the transverse grooves and Hc is a groove depth of the narrow grooves.

[0024] According to the pneumatic tire design, the groove depth Hb of the transverse grooves and the groove depth Hc of the narrow grooves are smaller than the groove depth Ha of the circumferential grooves, thus suppressing a reduction in the stiffness of the rib section in the tire's circumferential direction. This significantly improves durability.

[0025] In the pneumatic tire according to one aspect of the present invention, Hb is preferably between 1 mm and 5 mm and Hc is between 1 mm and 5 mm, wherein Hb is a groove depth of the transverse grooves and Hc is a groove depth of the narrow grooves.

[0026] According to the pneumatic tire specifications, the groove depth Hb of the transverse grooves and the groove depth Hc of the narrow grooves are between 1 mm and 5 mm to suppress a decrease in the stiffness of the rib sections. As a result, the effect on maintaining durability is significant.

[0027] In the pneumatic tire according to one aspect of the present invention, the transverse grooves are preferably designed such that they extend inclined with respect to the tire transverse direction; and a chamfer is formed in a corner section of the rib section at an acute angle with respect to the tire circumferential direction.

[0028] According to the pneumatic tire, by providing the chamfer, separation and chipping are less likely to occur, and the effect of maintaining durability is significant.

[0029] The pneumatic tire according to one aspect of the present invention preferably further comprises a sipe in the tread surface which communicates at one end with one of the circumferential grooves and terminates at the other end within the rib section; and preferably the relationships 0.3 mm ≤ Wd ≤ 2.0 mm, 0.3 ≤ Hd / Ha ≤ 1.0 and 0.03 ≤ Ld / We ≤ 0.2 are satisfied, wherein Wd is a groove width of the sipe, Hd is a groove depth of the sipe, Ld is a groove length of the sipe, We is a transverse dimension of the rib section, and Ha is a groove depth of the circumferential grooves.

[0030] According to the pneumatic tire design, the sipe reduces the stiffness of the tread section, thus mitigating ground contact pressure. As a result, the tire's resistance to uneven wear is significantly improved.

[0031] Thanks to this configuration of the angles of inclination of the lateral grooves relative to the tire's circumference, the stiffness of the rib section closest to the tire's equatorial plane is reduced, while the stiffness of the rib section increases progressively outwards in the tire's transverse direction. This suppresses the stiffness difference caused by the circumferential belt between the tire's equatorial surface area and the outer area in the tire's transverse direction, while simultaneously suppressing radial expansion when the tire is new and subsequently by increasing the circumferential stiffness through the use of the circumferential belt.As a result, the circumferential stiffness of the tread section can be uniformly formed across the tire's transverse direction, and uneven wear can be suppressed, thus ensuring resistance to uneven wear even in a configuration with a circumferential belt.

[0032] In the pneumatic tire according to one aspect of the present invention, the transverse grooves between the two adjacent rib sections in the tire transverse direction preferably have a difference in the angle of inclination, which is larger when it is closer to the tire equatorial plane and smaller when it is closer to the outside of the tire transverse direction.

[0033] According to the pneumatic tire, the difference between the angles of inclination of the acute angles of the lateral grooves with respect to the tire's circumference in two adjacent rib sections corresponds to the difference in stiffness between the two adjacent rib sections. Because the difference between the angles of inclination of the acute angles of the lateral grooves with respect to the tire's circumference is greater the closer it is to the tire's equatorial plane and smaller the closer it is to the outside of the tire's lateral direction, the stiffness difference between the adjacent rib sections with respect to the tire's equatorial plane increases. This helps to suppress excessive circumferential stiffness in the region of the tire's equatorial plane caused by the circumferential belt.As a result, the circumferential stiffness of the tread section can be made even more uniform across the tire's transverse direction, and uneven wear can be suppressed, thus providing the effect of a significant improvement in resistance performance to uneven wear even in a configuration with a circumferential belt.

[0034] In the pneumatic tire according to one aspect of the present invention, in which preferably a central region is a region defined between the outer circumferential grooves, a tire transverse dimension Wf of the central region and a tire transverse dimension Wg of the circumferential belt satisfy a relationship Wg / Wf ≥ 1.03.

[0035] In the area extending outwards from the circumferential belt in the tire's transverse direction, the circumferential stiffness is not high, so it is not necessary to make the stiffness uniform in this area by using the angles of inclination of the acute angles of the transverse grooves with respect to the tire's circumferential direction. Therefore, the central area is preferably located within the area of ​​the circumferential belt.

[0036] In the pneumatic tire according to one aspect of the present invention, preferably when the pneumatic tire is mounted on a normal rim and inflated to normal internal pressure, and is in an unloaded state, the difference in the tire transverse dimension between the two ends of the rib sections in the tire transverse direction is smaller the closer it is to the equatorial plane of the tire and larger the closer it is to the outside of the tire in the tire transverse direction, and the difference in the tire radial dimension Do of the rib section located furthest outside in the tire transverse direction and the difference in the tire radial dimension Dm of the rib section located adjacent to it inwards in the tire transverse direction satisfy the relationship Do / Dm ≥ 1.5.

[0037] According to the pneumatic tire, the circumferential stiffness is lower the smaller the difference in the tire's radial dimension between the two ends in the transverse direction of the rib section, and conversely, the greater the difference, the greater the circumferential stiffness. Similarly, with respect to the difference in the tire's radial dimension Do of the outermost rib section in the transverse direction and the difference in the tire's radial dimension Dm of the rib section adjacent to it transversely, the difference in stiffness is greater the greater the difference in the tire's radial dimension Do is located outwards in the transverse direction.Since the circumferential stiffness in the rib sections is reduced compared to the increase in circumferential stiffness in the region of the equatorial plane of the tire due to the circumferential belt, the circumferential stiffness in the rib sections is correspondingly increased compared to the decrease in circumferential stiffness in the region from the circumferential belt outwards, and since the difference in the stiffness of the rib sections in the outer regions in the tire transverse direction is specified by the relationship Do / Dm, a difference in the circumferential stiffness in the tire transverse direction in the rib sections caused by the circumferential belt can be suppressed.As a result, the circumferential stiffness of the tread section can be made even more uniform across the tire's transverse direction, and uneven wear can be suppressed, thus providing the effect of a significant improvement in resistance performance to uneven wear even in a configuration with a circumferential belt.

[0038] In the pneumatic tire according to one aspect of the present invention, the rib section is preferably designed to have several blocks defined by the two circumferential grooves adjacent in the tire's transverse direction and the two transverse grooves adjacent in the tire's circumferential direction, wherein the blocks are subdivided in the tire's transverse direction to form small blocks by means of a narrow groove that opens at both ends to two of the transverse grooves adjacent in the tire's circumferential direction, and in the majority of blocks, a surface area S Iof the small block which is closest to the equatorial plane of the tire and has a surface area S O of the small block which is closest to the outside of the tire's transverse direction, a relationship S O / S I ≥ 1.01.

[0039] According to the pneumatic tire, the surface area S can be configured in the blocks. O of the small block that is closest to the outside of the tire's transverse direction, as larger than the surface area S IThe stiffness of the small block closest to the tire's equatorial plane is increased on the side closer to the outside of the tire's transverse direction. As a result, the circumferential stiffness of the tread section across the tire's transverse direction can be made even more uniform, and uneven wear can be suppressed, thus providing a significant improvement in resistance to uneven wear, even in a configuration with a circumferential belt.

[0040] In the pneumatic tire according to one aspect of the present invention, the rib is preferably formed in such a way that it has a plurality of blocks which are defined by the two circumferential grooves adjacent in the tire transverse direction and the two transverse grooves adjacent in the tire circumferential direction, and which satisfy an aspect ratio of a tire circumferential direction dimension L and a tire transverse direction dimension We of each of the blocks 1.2 ≤ L / We ≤ 2.0.

[0041] According to the pneumatic tire, the aspect ratio of the tire's circumferential dimension L and the tire's lateral dimension We is configured to be within the range described above to make it easier, as the block has a difference in stiffness.

[0042] Advantageous effects of the invention: The present invention can provide improved resistance performance to uneven wear while maintaining durability.

[0043] The present invention can provide improved resistance to uneven wear, even in a configuration with a circumferential belt. Brief description of the drawings Fig. Figure 1 is a top view of a tread section of a pneumatic tire according to a first embodiment of the present invention. Fig. Figure 2 is an enlarged view of a tread section of a pneumatic tire according to a first embodiment of the present invention. Fig. Figure 3 is an enlarged view of another tread section of a pneumatic tire according to a first embodiment of the present invention. Fig. Figure 4 is an enlarged view of another tread section of a pneumatic tire according to a first embodiment of the present invention. Fig. Figure 5 is an enlarged cross-sectional view of the tread section of the pneumatic tire according to a first embodiment of the present invention. Fig. Figure 6 is an enlarged cross-sectional view of the tread section of the pneumatic tire according to a first embodiment of the present invention. Fig. Figure 7 is a table which lists the results of performance tests of pneumatic tires according to examples of the present invention. Fig. Figure 8 is a table which lists the results of performance tests of pneumatic tires according to examples of the present invention. Fig. Figure 9 is a meridian cross-sectional view of a section of an air tire according to a second embodiment of the present invention. Fig. Figure 10 is a top view of a tread section of the pneumatic tire according to a second embodiment of the present invention. Fig. Figure 11 is an enlarged top view of a tread section of a pneumatic tire according to a second embodiment of the present invention. Fig. Figure 12 is an enlarged cross-sectional view of the tread section of the pneumatic tire according to a second embodiment of the present invention. Fig. Figure 13 is an enlarged cross-sectional view of the tread section of the pneumatic tire according to a second embodiment of the present invention. Fig. Figure 14 is an enlarged top view of a tread section of a pneumatic tire according to a second embodiment of the present invention. Fig. Figure 15 is an enlarged meridian cross-sectional view of the pneumatic tire according to a second embodiment of the present invention. Fig. Figure 16 is an enlarged top view of a tread section of a pneumatic tire according to a second embodiment of the present invention. Fig. Figure 17 is an enlarged top view of a tread section of a pneumatic tire according to a second embodiment of the present invention. Fig. Figure 18 is an enlarged top view of a tread section of a pneumatic tire according to a second embodiment of the present invention. Fig. Figure 19 is a table which lists the results of performance tests on pneumatic tires according to the second example of the present invention. Fig. Figure 20 is a table which lists the results of performance tests on pneumatic tires according to the second example of the present invention. Description of embodiments: First embodiment

[0044] A first embodiment of the present invention is described in detail below with reference to the drawings. However, the present invention is not limited to the first embodiment. Components of the first embodiment include elements that are essentially identical or that can be exchanged or easily devised by a person skilled in the art. Furthermore, the modified examples described in the first embodiment can be combined as required within the scope of protection obvious to a person skilled in the art.

[0045] Fig. Figure 1 is a top view of a tread section of a pneumatic tire according to the first embodiment. Fig. Figure 2 is an enlarged view of a tread section of the pneumatic tire according to the first embodiment. Fig. Figure 3 is an enlarged view of another tread section of the pneumatic tire according to the first embodiment. Fig. Figure 4 is an enlarged view of another tread section of the pneumatic tire according to the first embodiment. Fig. Figure 5 is an enlarged cross-sectional view of a tread section of the pneumatic tire according to the first embodiment. Fig. Figure 6 is an enlarged cross-sectional view of a tread section of the pneumatic tire according to the first embodiment.

[0046] In the following, "tire circumferential direction" refers to the circumferential direction, where the axis of rotation (not shown) of a pneumatic tire 1 is the central axis. "Tire lateral direction" also refers to the direction parallel to the axis of rotation. "Inward in tire lateral direction" refers to the direction toward an equatorial plane of the tire (not shown) in the tire lateral direction. "Outward in tire lateral direction" refers to the direction away from the equatorial plane of the tire in the tire lateral direction. "Tire radial direction" also refers to a direction perpendicular to the axis of rotation. "Inward in tire radial direction" refers to the direction toward the axis of rotation in the tire radial direction. "Outward in tire radial direction" refers to the direction away from the axis of rotation in the tire radial direction.An “equatorial plane of the tire” is the plane perpendicular to the axis of rotation that passes through the center of the tire width of the pneumatic tire 1.

[0047] As in Fig. As shown in Figure 1, the pneumatic tire 1 of the present embodiment includes a first tread section 2. The tread section 2 is made of a rubber material which is exposed on the outermost side of the pneumatic tire 1 in the tire radial direction, its surface, i.e. a tread surface 2A, forming the profile of the pneumatic tire 1.

[0048] The tread surface 2A of the tread section 2 includes a plurality of circumferential grooves 3 (seven in the first embodiment illustrated in Fig. 1), which extend in the circumferential direction of the tire and are arranged in a transverse direction. The circumferential groove 3 refers to a groove with, for example, a groove width (Wa in Fig. 2 and Fig. 5) of 8 mm to 15 mm and a groove depth (dimension from the opening position on the running surface 2A to the groove bottom, Ha in Fig. 5 and Fig. 6) from 10 mm to 28 mm.

[0049] Additionally, tread section 2 in the tread surface 2A includes ribs extending in the tire's circumferential direction, which is defined by adjacent circumferential grooves 3. Tread section 2 also includes several transverse grooves 4 in the tread surface 2A, which are aligned in the tire's circumferential direction, extend in the tire's transverse direction, and intersect the tire's circumferential direction. The transverse grooves 4 are connected to the circumferential grooves 3 at both ends. Accordingly, each rib defined by the circumferential grooves 3 is divided by the transverse grooves 4 to form block-shaped rib sections 5 defined between the circumferential grooves 3. The transverse groove 4 refers to a groove with, for example, a groove width (Wb in Fig. 2) from 1 mm to 4 mm and a groove depth (dimension from the opening position on the running surface 2A to the groove bottom, Hb in Fig. 6) from 1 mm to 5 mm.

[0050] Additionally, in each tread section 5 of the tread surface 2A, defined by the circumferential grooves 3 and the lateral grooves 4, the tread section 2 includes two independent narrow grooves 6 extending circumferentially without intersecting laterally. These narrow grooves 6 are connected to the lateral grooves 4 at both ends. Accordingly, each tread section 5, defined by the circumferential grooves 3 and the lateral grooves 4, is subdivided multiple times in the lateral direction by the narrow grooves 6. Thus, each tread section 5 contains a central small tread section 5A and two lateral small tread sections 5B. The central small tread section 5A is defined by the lateral grooves 4 and the narrow grooves 6, and the lateral small tread sections 5B are defined by the circumferential groove 3, the lateral grooves 4, and the narrow groove 6.The narrow groove 6 refers to a groove with, for example, a groove width (Wc in . Fig. 2 and Fig. 5) from 1 mm to 4 mm and a groove depth (dimension from the opening position on the running surface 2A to the groove bottom, Hc in Fig. 5) from 1 mm to 5 mm.

[0051] The groove width Wc of the two narrow grooves 6 in each of the web sections 5 is smaller than the groove width Wa of the circumferential grooves 3. A curved section 6A is formed in a central section of the narrow grooves 6. The curved section 6A is arranged inwards in the transverse direction of the tire in the direction in which the two narrow grooves 6 are opposite each other in the transverse direction of the tire, from an imaginary straight line connecting the ends of the narrow groove 6. Furthermore, the narrow grooves 6 are arranged with bending points 6Aa of the curved sections 6A, which are offset from each other in the circumferential direction of the tire.

[0052] As in Fig. As shown in Figure 2, in a configuration where each narrow groove 6 is formed with the curved section 6A and bends once, the bending points 6Aa are the only bending point that is located inwards in the tire transverse direction in the direction in which the two narrow grooves 6 are opposite each other in the tire transverse direction.

[0053] As in Fig. Figure 3 shows that in a configuration in which each narrow groove 6 is formed with a plurality of curved sections 6A and bends a plurality of times, the bending point 6Aa is the innermost bending point in the tire transverse direction in the direction in which the two narrow grooves 6 are opposite each other in the tire transverse direction (inwards from a reference line B in the direction in which the two narrow grooves 6 are opposite each other).

[0054] As in Fig. Figure 4 shows a configuration in which each narrow groove 6 is formed with several of the curved sections 6A and bends multiple times, and a plurality of bending points are arranged furthest inwards in the tire transverse direction, in the direction in which the two narrow grooves 6 are opposite each other in the tire transverse direction. The bending point 6Aa is the midpoint of a reference line C which connects the furthest inwards bending points at each end in the tire circumferential direction. In such a configuration, as shown in Fig. As shown in Figure 4, bending point 6Aa may not correspond to a bending point.

[0055] According to the pneumatic tire 1 of the first embodiment with such a configuration, each of the rib sections 5, defined by the circumferential grooves 3 and the transverse grooves 4, is divided by the two narrow grooves 6 to form the central small rib section 5A and the two lateral small rib sections 5B. This results in lower stiffness, which makes it possible to reduce the ground contact pressure when the tread section 2 comes into contact with the ground. Additionally, the length of each of the narrow grooves 6 is increased by forming the curved sections 6A within the narrow grooves 6. This further reduces stiffness, thereby mitigating the ground contact pressure even more. Therefore, the resistance to uneven wear can be improved.

[0056] Furthermore, according to the pneumatic tire 1 of the first embodiment, the curved section 6A is arranged inwards in the transverse direction of the tire, in the direction in which the two narrow grooves 6 are opposite each other from the imaginary straight line A that connects the ends of the narrow groove 6. As a result, a reduction in the area of ​​the lateral small rib sections 5B on the tread surface 2A is suppressed, and a decrease in stiffness is prevented. In addition, the bending points 6Aa of the two narrow grooves 6 are arranged offset from each other in the circumferential direction of the tire, so that a local narrowing of the central small rib section 5A is suppressed and thus a decrease in stiffness is prevented. Thus, separation and spalling of the rib section 5 can be suppressed.

[0057] As a result, according to the pneumatic tire 1 of the first embodiment, resistance to uneven wear can be improved, while the resistance performance is maintained by suppressing splitting and chipping.

[0058] In the pneumatic tire 1 of the first embodiment, the bent section 6A of the narrow groove 6 has a bending angle α preferably in the range of 90° to 160°. As in the Fig. 2, Fig. 3 to Fig. As shown in Figure 4, the bending angle α is the smaller angle of the bend at the bent section 6A.

[0059] According to the pneumatic tire 1, if the bending angle α of the bent section 6A is 90° or greater, the bend becomes less sharp. As a result, separation and spalling are less likely to occur, and the effect on maintaining durability is significant. If the bending angle α of the bent section 6A is 160° or less, the length of the narrow grooves 6 is increased, and the effect on reducing stiffness is significant.

[0060] As in Fig. As illustrated in Figure 2, in the pneumatic tire 1 of the first embodiment, preferably 0.1 ≤ Lc / L is satisfied, where Lc is the displacement width of the bending points 6Aa of the two narrow grooves 6 in the tire's circumferential direction and L is the tire's circumferential dimension of the rib section 5 in which the narrow grooves 6 are formed. The maximum value of the displacement width Lc lies within a region of the imaginary line A or less.

[0061] According to the pneumatic tire 1, by achieving 0.1 ≤ Lc / L, a localized narrowing of the central small rib section 5A between the two narrow grooves 6 is further suppressed, and a reduction in stiffness can be further prevented. As a result, the effect on maintaining durability is significant.

[0062] In addition, according to the pneumatic tire 1 of the first embodiment, the transverse grooves 4 are designed such that they extend at an angle with respect to the tire's transverse direction. An angle β with respect to the tire's transverse direction is preferably in the range of 5° to 50°.

[0063] According to the pneumatic tire 1, if the angle β of the lateral grooves 4 with respect to the tire's transverse direction is greater than 5°, the length of the lateral grooves 4 is increased, resulting in a significant reduction in stiffness. If the angle β of the lateral grooves 4 with respect to the tire's transverse direction is 50° or less, the angle is prevented from becoming acute. As a result, separation and spalling are less likely to occur, and the effect on maintaining durability is significant.

[0064] It should be noted that in the pneumatic tire 1 of the first embodiment, the transverse grooves 4 in a rib defined by adjacent circumferential grooves 3 are inclined in the same direction with respect to the tire's transverse direction. Additionally, in the pneumatic tire 1 of the first embodiment, the transverse grooves 4 in adjacent ribs are also inclined in the same direction with respect to the tire's transverse direction. In such a configuration, each of the rib sections 5 has a uniform shape, which contributes to improved resistance to uneven wear.

[0065] In the pneumatic tire 1 of the first embodiment, the relationships Ha > Hb and Ha > Hc are preferably satisfied, where Ha is the groove depth of the circumferential grooves 3, Hb is the groove depth of the transverse grooves 4 and Hc is the groove depth of the narrow grooves 6.

[0066] According to the pneumatic tire 1, the groove depth Hb of the transverse grooves 4 and the groove depth Hc of the narrow grooves 6 are smaller than the groove depth Ha of the circumferential grooves 3, thus suppressing a reduction in the stiffness of the rib section 5 in the circumferential direction of the tire. Therefore, the effect on maintaining durability is significant.

[0067] In the pneumatic tire 1 of the first embodiment, Hb preferably is 1 mm to 5 mm and Hc preferably is 1 mm to 5 mm, where Hb is the groove depth of the transverse grooves 4 and Hc is the groove depth of the narrow grooves 6.

[0068] According to the pneumatic tire 1, the groove depth Hb of the transverse grooves 4 and the groove depth Hc of the narrow grooves 6 are configured to be between 1 mm and 5 mm in order to suppress a decrease in the stiffness of the rib sections 5. As a result, the effect of maintaining durability is significant.

[0069] In the pneumatic tire 1 of the first embodiment, the transverse grooves 4 extend at an inclination with respect to the tire transverse direction, and a chamfer 4A is preferably formed in the corner section of the rib section 5, where an acute angle is formed with respect to the tire circumferential direction.

[0070] According to the pneumatic tire 1, by providing the chamfer 4A, separation and chipping are less likely to occur, and the effect of maintaining durability is significant.

[0071] As in the Fig. 2, Fig. 3, Fig. 4 to Fig. As shown in Figure 5, the pneumatic tire 1 of the first embodiment preferably further includes a sipe 7 in the tread surface 2A. The sipe 7 is connected to the circumferential groove 3 at one end and terminates within the rib section 5 at the other end, without intersecting the narrow groove 6. The following relationships are preferably satisfied for the sipe 7: 0.3 mm ≤ Wd ≤ 2.0 mm, 0.3 ≤ Hd / Ha ≤ 1.0, and 0.03 ≤ Ld / We ≤ 0.2, where Wd is the groove width, Hd is the groove depth, Ld is the groove length, We is the transverse dimension of the rib section 5, and Ha is the groove depth of the circumferential groove 3.

[0072] According to the pneumatic tire 1, the sipe 7 reduces the stiffness of the rib section 5, thus mitigating the ground contact pressure. As a result, the effect of improved resistance to uneven wear is significant. First examples

[0073] For the first examples, performance tests for resistance to uneven wear and durability were carried out under different conditions on a plurality of types of test tires (see Fig. 7 and Fig. 8).

[0074] In the performance tests, pneumatic tires (heavy-duty pneumatic tires) with a tire size of 445 / 50R22.5 were mounted on normal rims, inflated to normal internal pressure and fitted to the trailer axle of a test vehicle (2-D•D vehicle).

[0075] Here, "normal rim" refers to a "standard rim" as defined by the Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a "design rim" as defined by the Tire and Rim Association, Inc. (TRA), or a "measuring rim" as defined by the European Tyre and Rim Technical Organisation (ETRTO). "Normal inflation pressure" refers to a "maximum air pressure" as defined by JATMA, the maximum value in "tire load limits at various cold inflation pressures" as defined by the TRA, or "inflation pressures" as defined by the ETRTO.

[0076] In the performance test for resistance to uneven wear, the test vehicle was driven 100,000 miles (approximately 160,000 km), after which the area and depth of uneven wear occurring in the rib sections were measured. The measurement results are expressed as index values ​​and evaluated using the state of the art as a reference value (100). In this evaluation, higher values ​​are preferred, as they indicate excellent resistance to uneven wear.

[0077] In the durability performance test, the test vehicle was driven 100,000 miles (approximately 160,000 km), after which the number of separations and chips occurring in the rib sections was measured. The measurement results are expressed as index values ​​and evaluated using the state of the art as a reference value (100). In this evaluation, higher values ​​are preferred, as they indicate a lower number of separations and chips and excellent durability performance.

[0078] The pneumatic tire of the in Fig. The conventional example shown in Figure 7 does not contain narrow grooves. The pneumatic tires of each of the comparison examples shown in Figure 7 do not contain narrow grooves. Fig. The tires shown in section 7 include narrow grooves, but the configuration of the narrow grooves differs from the specifications of the examples. In contrast, the pneumatic tires shown in the examples include narrow grooves. Fig. 7 and Fig. The 8 examples shown are narrow grooves with a configuration within the specifications.

[0079] As can be seen from the results of the Fig. 7 and Fig. As can be seen from Figure 8, the pneumatic tires of Examples 1 to 12 exhibit improved resistance to uneven wear while maintaining durability. Second embodiment

[0080] A second embodiment of the present invention is described in detail below with reference to the drawings. However, the present invention is not limited to this second embodiment. Components of the second embodiment include elements that are essentially identical or that can be exchanged or easily devised by a person skilled in the art. Furthermore, the modified examples described in the second embodiment can be combined as required within the scope of protection obvious to a person skilled in the art.

[0081] Fig. Figure 9 is a meridian cross-sectional view of a section of the pneumatic tire according to the second embodiment. Fig. Figure 10 is a top view of a tread section of the pneumatic tire according to the second embodiment. Fig. Figure 11 is an enlarged top view of a tread section of the pneumatic tire according to the second embodiment. Fig. 12 and Fig. Figure 13 shows enlarged cross-sectional views of a tread section of the pneumatic tire according to the second embodiment.

[0082] Herein, "tire radial direction" refers to the direction perpendicular to the axis of rotation (not illustrated) of a pneumatic tire 101. "Inward in tire radial direction" refers to the direction towards the axis of rotation in the tire radial direction. "Outward in tire radial direction" refers to the direction away from the axis of rotation in the tire radial direction. "Circular direction" refers to the circumferential direction, with the central axis being the axis of rotation. "Transverse direction" also refers to the direction parallel to the axis of rotation. "Inward in tire transverse direction" refers to the direction towards an equatorial plane CL of the tire (tire equator line) in the tire transverse direction. "Outward in tire transverse direction" refers to the direction away from the equatorial plane CL of the tire in the tire transverse direction.“Tire equatorial plane CL” refers to the plane perpendicular to the axis of rotation of the pneumatic tire 101, which passes through the center of the tire width of the pneumatic tire 101. “Tire equator line” refers to the line in the circumferential direction of the pneumatic tire 101 that lies on the equatorial plane of the tire CL. In the second embodiment, the tire equator line and the equatorial plane of the tire are designated by the same reference numeral CL.

[0083] A pneumatic tire 101 according to the second embodiment is a heavy-duty pneumatic tire used on a truck, bus, or the like. As in Fig. As shown in Figure 9, the pneumatic tire 101 comprises a tread section 121, shoulder sections 122 arranged on both outer sides of the same in the transverse direction of the tire, and a sidewall section and a bead section extending from each of the shoulder sections 122 in that order. It should be noted that in Fig. The sidewall section and the bead section are omitted. The pneumatic tire 101 also includes a carcass layer 124 and a belt layer 125.

[0084] The tread section 121 is made of rubber material (tread rubber) and is exposed on the outermost side of the pneumatic tire 101 in the tire radial direction, and its surface forms the profile of the pneumatic tire 101. A tread surface 121A is formed on the outer circumferential surface of the tread section 121, or in other words, on the road contact surface that comes into contact with the road surface when driving.

[0085] The shoulder sections 122 are sections of the tread section 121 that are arranged outwards on both sides in the transverse direction of the tire. Furthermore, the sidewall sections, although not shown in the drawings, are exposed at the outermost sides of the pneumatic tire 101 in the transverse direction. Additionally, the bead section, although not shown in the drawings, includes a tire bead core and a bead filler. The tire bead core is formed by winding a tire bead wire, which is a steel wire, into a ring shape. The bead filler is a rubber material arranged in the space formed by folding over one end of the carcass layer 124 in the transverse direction of the tire at the position of the bead core.

[0086] Each of the end sections of the carcass layer 124 in the tire transverse direction is folded over from the inside to the outside at the pair of bead cores, and the carcass layer 124 is stretched in a toroidal shape in the tire circumferential direction to form the tire skeleton. The carcass layer 124 is made of a plurality of carcass cord threads (not shown) arranged at an angle to the tire circumferential direction along the tire meridian direction at a predetermined angle to the tire circumferential direction and coated with coating rubber. The carcass cord threads are made of steel or organic fibers (polyester, rayon, nylon, or the like).

[0087] The belt layer 125 has a multilayered structure, in which, in the second embodiment, four layered belts 125A, 125B, 125C, 125D are arranged in the tire radial direction. In the tread section 121, the belt layer 125 is arranged outside the carcass layer 124 in the tire radial direction, i.e., on its outer circumference, and covers the carcass layer 124 in the tire circumferential direction. The belts 125A, 125B, 125C, 125D consist of cord threads (not shown) arranged at a predetermined angle with respect to the tire circumferential direction (for example, from 45° to 90° with respect to the tire circumferential direction) and coated with coating rubber. The cord threads are made of steel or organic fibers (polyester, rayon, nylon, or the like). Each of the belts 125A, 125B, 125C, 125D is arranged so that the cord threads of the different layers are arranged crosswise in the tire radial direction.It should be noted that for the belt layer 125 it is sufficient if the cord threads of at least two belts layered in the radial direction of the tire are arranged crosswise.

[0088] The belt layer 125 includes a circumferential belt 126. The circumferential belt 126 consists of cord threads (not shown) oriented in the transverse direction of the tire at an angle of 0° (including ±5°) with respect to the tire's circumferential direction and coated with coating rubber. The cord threads are made of steel or organic fibers (polyester, rayon, nylon, or the like). The circumferential belt 126 is arranged between the belts of the belt layer 125 at a position in the transverse direction of the tire that surrounds the tire's equatorial plane CL. In the second embodiment, the circumferential belt 126 is arranged between belts 125B and 125C. In other words, the circumferential belt 126 is arranged below or above the two belts of the belt layer 125 with respect to the tire's radial direction, with cord threads arranged in a crisscross pattern.

[0089] As in the Fig. 10, Fig. 11, Fig. 12 to Fig. As shown in Figure 13, the tread surface 121 is provided with an odd number of circumferential grooves 103 in the tread surface 121A, equal to or greater than seven (seven in the second embodiment). The circumferential grooves 103 are straight grooves extending in the tire circumferential direction parallel to the tire equator line CL. The circumferential grooves 103 are grooves with a groove width (Wa in Fig. 11 and Fig. 13) of 8 mm to 15 mm and a groove depth (dimension from the opening position on the running surface 121a to the groove bottom, Ha in Fig. 12 and Fig. 13) from 10 mm to 28 mm. The tread surface 121A is provided with an even number of equal to or greater than eight (eight in the second embodiment) rib-like web sections 105 aligned with each other, which are defined by the circumferential grooves 103. The web sections 105 extend in the circumferential direction of the tire.

[0090] The circumferential grooves 103 comprise a central circumferential groove 103A, whose center is located on the tire equatorial plane CL, outer circumferential grooves 103C, which are located furthest outwards in the tire's transverse direction, and intermediate circumferential grooves 103B, which are located between the central circumferential groove 103A and the outer circumferential grooves 103C. The rib sections 105 comprise inner rib sections 105A, which are located inwards from the two outer circumferential grooves 103C in the tire's transverse direction, and outer rib sections 105B, which are located outwards from the two outer circumferential grooves 103C in the tire's transverse direction. Additionally, the area inwards from the two outer circumferential grooves 103C in the tire's transverse direction, in which the inner rib sections 105A are located, is referred to as the central area Ce. That is to say, the inner rib sections 105A are located in the central area Ce.

[0091] As in the Fig. 10, Fig. 11, Fig. 12 to Fig. As shown in Figure 13, each inner rib section 105A in the central region Ce of the tread section 121A is provided with transverse grooves (which can also be referred to as transverse grooves) 104 in the tread surface 121. The transverse grooves 104 are connected at both ends to two circumferential grooves 103, which are adjacent in the transverse direction of the tire. The transverse groove 104 refers to a groove with a groove width (Wb in Fig. 11) from 1 mm to 4 mm and a groove depth (dimension from the opening position on the running surface 121A to the groove bottom, Hb in Fig. 12) from 1 mm to 5 mm. In the inner web sections 105A, each of the web sections 105, which are defined by adjacent circumferential grooves 103, is subdivided into blocks 151 by the transverse groove 104. It should be noted that, as in Fig. Figure 10 shows that the opening sections of the transverse grooves 104 facing the circumferential grooves 103 are oriented towards each other across the groove walls of the circumferential grooves 103 in the transverse direction of the tire, so that the transverse grooves 104 are arranged continuously in the transverse direction of the tire. However, no such restriction is intended, and the transverse grooves 104 cannot be continuous in the transverse direction of the tire.

[0092] As in the Fig. 10, Fig. 11, Fig. 12 to Fig. As shown in Figure 13, the blocks 151, which are defined in the tread section 121 by the circumferential grooves 103 and the transverse grooves 104, are provided with a narrow groove 106 that opens at both ends to form two transverse grooves 104 adjacent in the tire's circumferential direction. The narrow groove 106 refers to a groove with a groove width (Wc in the Fig. 11 and Fig. 13) from 1 mm to 4 mm and a groove depth (dimension from the opening position on the running surface 121A to the groove bottom, Hc in Fig. 13) from 1 mm to 5 mm. The blocks 151 are divided by the narrow groove 106 in the tire transverse direction to form small blocks 151A. As in the Fig. 10, Fig. 11, Fig. 12 to Fig. As shown in Figure 13, a block 151 is provided with two narrow grooves 106, which are arranged in the transverse direction of the tire. Thus, the small blocks 151A include a small central block 151Aa, which is arranged in the middle of the small block 151A in the transverse direction of the tire, and two outer small blocks 151Ab, which are arranged on each side of the small central block 151Aa in the transverse direction of the tire. In addition, a curved section 106A is formed in an intermediate section of the narrow groove 106, which is located in Fig. 11 is shown. However, the curved section 106A may not be formed, and the narrow groove 106 may extend in a linear manner (see Fig. 17). It is sufficient that at least one narrow groove 106 is provided in each block 151 (see Fig. 18). In such a configuration, the small block 151A includes two outer small blocks 151Ab arranged on each side in the transverse direction of the tire, and there is no small center block 151Aa.

[0093] As in the Fig. 10, Fig. 11, Fig. 12 to Fig. As shown in Figure 13, the tread section 121 in the tread surface 121A includes a lamella 107 which connects to the circumferential groove 103 at one end and terminates within the web section 105 (small block 151A (outer small block 151Ab)) at the other end, without intersecting the narrow groove 106. The lamella 107 reduces the stiffness of the web section 105 (small block 151A (outer small block 151Ab)) and thus reduces the ground contact pressure. Therefore, the resistance to uneven wear can be improved. The same number of lamellae 107 are provided in each block 151, and all lamellae 107 have the same groove width Wd, groove depth Hd, and groove length Ld. Accordingly, the lamellae 107 do not cause any change in stiffness across the web sections 105.The lamella 107 is a groove with groove width Wd, groove depth Hd and groove length Ld, which satisfies the following relationships with the tire transverse dimension We of the rib section 105 and the groove depth Ha of the circumferential groove 103: 0.3 mm ≤ Wd ≤ 2.0 mm, 0.3 ≤ Hd / Ha ≤ 1.0, and 0.03 ≤ Ld / We ≤ 0.2.

[0094] As in the Fig. 11 and Fig. As illustrated in Figure 12, a chamfer 104A can be formed in the corner section of the web section 105 (block 151) of the tread section 121, with the transverse groove 104 opening at an inclination towards the circumferential groove 103 and forming an acute angle. By providing the chamfer 104A, separation and chipping in the web section 105 (block 151) are less likely to occur, and durability can be maintained.

[0095] Fig. Figure 14 is an enlarged top view illustrating a section of the tread section of the pneumatic tire according to the present embodiment. Fig. Figure 15 is an enlarged meridional cross-sectional view of the pneumatic tire according to the second embodiment. Fig. 16, Fig. 17 to Fig. Figure 18 shows enlarged top views of the tread section of the pneumatic tire according to the second embodiment.

[0096] As in the Fig. 11 and Fig. As illustrated in Figure 14, in the pneumatic tire 101 according to the second embodiment, the inclination angle θ of the acute angle of the transverse groove 104 with respect to the tire's circumferential direction is smallest in the rib section 105 (inner rib section 105A) where it is closest to the tire's equatorial plane CL, and it increases the closer the rib section 105 (inner rib section 105A) is to the outside of the tire's transverse direction. As shown in Fig. As illustrated in Figure 14, in the second embodiment three web sections 105 (inner web sections 105A) are provided on a side that is located outwards from the equatorial plane CL of the tire (middle circumferential groove 103A) as a boundary in the transverse direction of the tire. The three rib sections 105 (inner rib sections 105A) have: the acute angle of the transverse groove 104 with respect to the tire circumferential direction in the rib section 105 (inner rib section 105A) closest to the equatorial plane of the tire CL with an inclination angle θ1, the acute angle of the transverse groove 104 with respect to the tire circumferential direction in the rib section 105 (inner rib section 105A) in a central position of the tire in the tire transverse direction with an inclination angle θ2, and the acute angle of the transverse groove 104 with respect to the tire circumferential direction in the rib section 105 (inner rib section 105A) at the outermost in the tire transverse direction with an inclination angle θ3.The angles of inclination θ1, θ2, θ3 satisfy the relationship θ1 < θ2 < θ3.

[0097] According to the pneumatic tire 101, thanks to such a configuration of the inclination angles θ1, θ2, θ3 of the acute angles of the transverse grooves 104 with respect to the tire's circumferential direction, the stiffness of the rib section 105 (inner rib section 105A), which is closest to the tire's equatorial plane CL, is reduced, and the stiffness of the rib sections 105 (inner rib sections 105A) increases progressively outwards in the tire's transverse direction. Thus, the stiffness difference caused by the circumferential belt 126 between the tire's equatorial surface area CL and the outer area in the tire's transverse direction is suppressed, while the effect of suppressing radial expansion is achieved when the tire is new and thereafter, by increasing the circumferential stiffness using the circumferential belt 126.As a result, the circumferential stiffness of the tread section 121 can be made uniform across the tire transverse direction and uneven wear can be suppressed, so that resistance to uneven wear can be provided even in a configuration with the circumferential belt 126.

[0098] It should be noted that the inclination angle θ of the acute angle of the transverse groove 104 with respect to the tire circumference is preferably 50° to 80°. If the inclination angle θ of the acute angle of the transverse groove 104 with respect to the tire circumference reaches 0°, the stiffness of the acute angle region is weakened, which can cause separation and spalling. If the inclination angle θ of the acute angle of the transverse groove 104 with respect to the tire circumference reaches 90°, the stiffness is excessively high and the stiffness difference between the blocks 151 closer to the tire equatorial plane CL and the blocks 151 located laterally outwards is difficult to vary. Thus, the resistance to uneven wear is reduced.Therefore, the inclination angle θ of the acute angle of the transverse groove 104 with respect to the tire circumference direction should preferably be 50° to 80° in order to maintain the stiffness in the blocks 151 appropriately. As in . Fig. As shown in Figure 10, the opening sections of the transverse grooves 104 facing the circumferential grooves 103 are oriented towards each other on each of the groove walls of the circumferential grooves 103 in the tire's transverse direction. The angles of inclination θ (θ1, θ2, θ3) starting from the equatorial plane of the tire CL and progressing outwards in the tire's transverse direction exhibit the relationship described above. Thus, the transverse grooves 104 are arranged in an approximately S-shape throughout the entire central area Ce from end to end in the tire's transverse direction. Furthermore, the blocks 151, similar to the transverse grooves 104, are also arranged in an approximately S-shape throughout the entire central area Ce from end to end in the tire's transverse direction. By arranging the transverse grooves 104 and the blocks 151 continuously in an approximately S-shape in the tire's transverse direction, a uniform circumferential stiffness of the tread section 121 transverse to the tire's transverse direction can easily be achieved.It should be noted that a uniform circumferential stiffness over the tire transverse direction can still be achieved if the transverse grooves 104 and the blocks 151 are not continuous in the tire transverse direction.

[0099] In the pneumatic tire 101 of the second embodiment, the difference in the inclination angle θ of the acute angle of the transverse groove 104 with respect to the tire's circumferential direction of two rib sections 105 (inner rib sections 105A) that adjoin each other in the tire's transverse direction is preferably greater the closer it is to the equatorial plane CL of the tire and smaller the closer it is to the outside of the tire's transverse direction. As in Fig. As illustrated in Figure 14, in the second embodiment three web sections 105 (inner web sections 105A) are provided on a side that is located outwards from the equatorial plane CL of the tire (middle circumferential groove 103A) as a boundary in the transverse direction of the tire. The three rib sections 105 (inner rib sections 105A) have: the acute angle of the transverse groove 104 with respect to the tire circumferential direction in the rib section 105 (inner rib section 105A) closest to the equatorial plane of the tire CL with an inclination angle θ1, the acute angle of the transverse groove 104 with respect to the tire circumferential direction in the rib section 105 (inner rib section 105A) in a central position of the tire in the tire transverse direction with an inclination angle θ2, and the acute angle of the transverse groove 104 with respect to the tire circumferential direction in the rib section 105 (inner rib section 105A) at the outermost in the tire transverse direction with an inclination angle θ3.Additionally, the differences between the inclination angles θ of the acute angles of the transverse grooves 104 with respect to the tire circumferential direction in the two rib sections 105 (inner rib sections 105A) that are adjacent in the tire transverse direction are θ2 - θ1 and θ3 - θ2. Here, θ2 - θ1 and θ3 - θ2 satisfy the relationship θ2 - θ1 > θ3 - θ2.

[0100] According to the pneumatic tire 101, the difference between the inclination angles θ of the acute angles of the transverse grooves 104 with respect to the tire's circumferential direction in the two adjacent rib sections 105 (inner rib sections 105A) corresponds to the difference in stiffness between the two adjacent rib sections 105 (inner rib sections 105A). Accordingly, since the difference between the inclination angles θ of the acute angles of the transverse grooves 104 with respect to the tire's circumferential direction is greater the closer it is to the equatorial plane CL of the tire, and smaller the closer it is to the outside of the tire's transverse direction, the stiffness difference between the adjacent rib sections 105 (inner rib sections 105A) with respect to the equatorial plane of the tire increases.This makes it possible to suppress excessive circumferential stiffness in the region of the equatorial plane CL of the tire, which is caused by the circumferential belt 126. As a result, the circumferential stiffness of the tread section 121 can be made even more uniform across the tire's transverse direction, and uneven wear can be suppressed, thus providing a significant improvement in resistance to uneven wear performance even in a configuration with the circumferential belt 126.

[0101] It should be noted that θ2 - θ1 and θ3 - θ2 preferably satisfy the relationship 1° ≤ (θ2 - θ1) - (θ3 - θ2) ≤ 5°, so that the circumferential stiffness of the tread section 121 over the tire transverse direction can be made further uniform by the transverse grooves 104.

[0102] As in Fig. As shown in Figure 9, in the pneumatic tire 101 of the second embodiment, the area from the two outer circumferential grooves 103C, 103C inwards in the tire transverse direction, where the inner web sections 105A are arranged, is designated as the central area Ce, and a tire transverse dimension Wf of the central area Ce and a tire transverse dimension Wg of the circumferential belt 126 preferably satisfy the relationship Wg / Wf ≥ 1.03.

[0103] In the region extending outwards from the circumferential belt 126 in the transverse direction of the tire, the circumferential stiffness is not high, so it is not necessary in this region to make the stiffness uniform by using the angles of inclination θ of the acute angles of the transverse grooves 104 with respect to the tire circumferential direction. Accordingly, the central region Ce is preferably arranged within the region of the circumferential belt 126.

[0104] It should be noted that the tire transverse dimensions Wf, Wg preferably satisfy the relationship Wg / Wf ≥ 1.05, so that the area in which the stiffness is made uniform using the inclination angles θ of the acute angles of the transverse grooves 104 with respect to the tire circumferential direction is sufficiently located within the area of ​​the circumferential belt 126.

[0105] In the pneumatic tire 101 according to the second embodiment, when the pneumatic tire 101 is mounted on a normal rim and inflated to normal internal pressure, and is in an unloaded state, the difference in the tire's transverse dimension between the two ends of the rib sections 105 (inner rib sections 105A) is preferably smaller in the tire's transverse direction the closer it is to the equatorial plane CL of the tire and larger the closer it is to the outer side of the tire in the tire's transverse direction, and a difference in the tire's radial dimension Do of the rib section 105 (inner rib section 105A) located furthest out in the tire's transverse direction, and a difference in the tire's radial dimension Dm of the rib section 105 (inner rib section 105A) located adjacent to it inwards in the tire's transverse direction, preferably satisfy the relationship Do / Dm ≥ 1.5. As in Fig. As illustrated in Figure 15, in the second embodiment three web sections 105 (inner web sections 105A) are provided on a side that is located outwards from the equatorial plane CL of the tire (middle circumferential groove 103A) as a boundary in the tire transverse direction. There is a difference in the tire radial dimension between both ends in the tire transverse direction of the rib section 105 (inner rib section 105A), which is closest to the tire equatorial plane CL, D1; a difference in the tire radial dimension between both ends in the tire transverse direction of the rib section 105 (inner rib section 105A) in an intermediate position in the tire transverse direction, D2; and a difference in the tire radial dimension between both ends in the tire transverse direction of the rib section 105 (inner rib section 105A), which is located furthest outside in the tire transverse direction, D3, in the three rib sections 105 (inner rib sections 105A).The differences in the tire lateral dimension D1, D2, D3 satisfy the relationship D1 < D2 < D3, and the difference in the tire lateral dimension Do (D3) of the rib section 105 (inner rib section 105A), which is located furthest outside in the tire lateral direction, and the difference in the tire lateral dimension Dm (D2) of the rib section 105 (inner rib section 105A), which is adjacent to it inwards in the tire lateral direction, satisfy the relationship D3 / D2 ≥ 1.5.

[0106] Here, "normal rim" refers to a "standard rim" as defined by the Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a "design rim" as defined by the Tire and Rim Association, Inc. (TRA), or a "measuring rim" as defined by the European Tyre and Rim Technical Organisation (ETRTO). "Normal inflation pressure" refers to a "maximum air pressure" as defined by JATMA, the maximum value in "tire load limits at various cold inflation pressures" as defined by the TRA, or "inflation pressures" as defined by the ETRTO.

[0107] According to pneumatic tire 101, the circumferential stiffness is lower when the difference in the tire radial dimension between the two ends in the tire transverse direction of the rib section 105 (inner rib section 105A) is smaller, and the circumferential stiffness is greater when the difference is larger. Similarly, with respect to the difference in the tire radial dimension Do of the outermost rib section 105 (inner rib section 105A) in the tire transverse direction and the difference in the tire radial dimension Dm of the rib section 105 (inner rib section 105A) adjacent to it transversely, the difference in stiffness is greater when the difference in the tire radial dimension Do is greater for the outermost rib section in the tire transverse direction.Since the circumferential stiffness in the rib sections 105 (inner rib sections 105A) is reduced compared to the increase in circumferential stiffness in the region of the equatorial plane CL of the tire due to the circumferential belt 126, the circumferential stiffness in the rib sections 105 (inner rib sections 105A) is correspondingly increased compared to the decrease in circumferential stiffness in the region from the circumferential belt 126 outwards, and the difference in the stiffness of the rib sections 105 in the outer regions in the tire transverse direction is specified by the relationship Do / Dm, a difference in the circumferential stiffness in the tire transverse direction in the rib sections 105 (inner rib sections 105A) caused by the circumferential belt 126 can be suppressed.As a result, the circumferential stiffness of the tread section 121 can be made even more uniform across the tire transverse direction and uneven wear can be suppressed, so that the effect of a significant improvement in resistance performance to uneven wear can be provided even in a configuration with the circumferential belt 126.

[0108] It should be noted that the differences in the tire radial dimension Do, Dm preferably satisfy the relationship Do / Dm ≥ 2.0. This allows the difference in stiffness of the rib sections 105 (inner rib sections 105A) in the outer end regions of the circumferential belt 126 in the tire transverse direction, where the difference in circumferential stiffness is large, to be increased, thereby enabling the circumferential stiffness of the tread section 121 in the tire transverse direction to be made more uniform.

[0109] As in Fig. As illustrated in Figure 11, in the pneumatic tire 101 of the second embodiment, the rib section 105 (inner rib section 105A) is formed in the block 151, which is defined by two circumferential grooves 103 adjacent in the tire's transverse direction and two transverse grooves 104 adjacent in the tire's circumferential direction, and the block 151 is divided in the tire's transverse direction by the narrow grooves 106, which open at both ends to the two transverse grooves 104 adjacent in the tire's circumferential direction in order to form the small blocks 151A. As shown in Fig. 16, Fig. 17 to Fig. As illustrated in 18, blocks 151 have a surface area S I of the outer small block 151Ab, which is closest to the tire equatorial plane CL, and a surface area S O of the outer small block 151Ab, which is closest to the outside of the tire transverse direction, preferably the relationship S O / S I ≥ 1.01.

[0110] According to the pneumatic tire 101, in the blocks 151, the fact that the surface area S O of the outer small block 151Ab, which is closest to the outside of the tire's transverse direction, larger than the surface area S I The stiffness of the outer small block 151Ab, which is closest to the tire equatorial plane CL, is increased on the side closer to the outside of the tire's transverse direction within block 151. As a result, the circumferential stiffness of the tread section 121 across the tire's transverse direction can be made even more uniform, and uneven wear can be suppressed, thus providing a significant improvement in resistance to uneven wear performance, even in a configuration with the circumferential belt 126.

[0111] It should be noted that the surface areas S I , S O preferably the relationship 1.03 ≤ SO / S I ≤ 1.10. This ensures that the difference in stiffness in blocks 151 in the tire's transverse direction is not excessive. Furthermore, the surface areas S include I , S O not the lamellae 107 described above. In other words, the lamellae 107 do not cause any change in stiffness. Thus, as described above, the same number of lamellae 107 are provided in each block 151, and all lamellae 107 have the same groove width Wd, groove depth Hd, and groove length Ld.

[0112] Furthermore, as in Fig. As illustrated in Figure 11, in the pneumatic tire 101 of the second embodiment, the web sections 105 (inner web sections 105A) are formed into the blocks 151, which are defined by two circumferential grooves 103 adjacent in the tire transverse direction and two transverse grooves 104 adjacent in the tire circumferential direction, and the aspect ratio of the tire circumferential dimension L and the tire transverse dimension We of each block 151 is preferably 1.2 ≤ L / We ≤ 2.0.

[0113] According to the pneumatic tire 101, the aspect ratio of the tire circumference direction dimension L and the tire lateral direction dimension We of block 151 is configured in the area described above, so that it is easier for block 151 to have a difference in stiffness.

[0114] It should be noted that the aspect ratio of the tire circumference dimension L and the tire lateral dimension We of block 151 should preferably be in the range of 1.4 ≤ L / We ≤ 1.8. This ensures that the difference in stiffness in block 151 is not excessive. Second examples

[0115] For the second examples, performance tests for resistance to uneven wear were carried out under different conditions on a plurality of types of test tires (see Fig. 19 and Fig. 20).

[0116] In the performance tests, pneumatic tires (heavy-duty pneumatic tires) with a tire size of 445 / 50R22.5 were mounted on normal TRA-specified rims (22.5”×14.00”), inflated to the normal internal pressure (830 kPa) and mounted on the trailer axle of a test vehicle (6×4 tractor trailer).

[0117] In the performance test for resistance to uneven wear, the test vehicle was driven 10 km, and the groove depth of the inner and outer circumferential grooves was then measured. This difference is measured as the value for uneven wear. The measurement results are expressed as index values ​​and evaluated using the state of the art as a reference value (100). In this evaluation, higher values ​​are preferred, as they indicate excellent resistance to uneven wear.

[0118] The pneumatic tires according to the state of the art and according to the Fig. 19 and Fig. Examples 101 to 118, given in the 20 examples, include a circumferential belt, three rib sections divided in the transverse direction of the tire by intermediate circumferential grooves arranged between a central circumferential groove and an outer circumferential groove, and a plurality of transverse grooves arranged in each of the rib sections oriented in the transverse direction of the tire, wherein the transverse grooves are inclined with respect to the circumferential direction of the tire and open at both ends towards the circumferential grooves adjacent in the transverse direction of the tire.In the pneumatic tire of the prior art example, the angle of inclination θ1 of the acute angle of the transverse groove with respect to the tire's circumferential direction in the rib section closest to the tire's equatorial plane CL, the angle of inclination θ2 of the acute angle of the transverse groove with respect to the tire's circumferential direction in the rib section at an intermediate position in the tire's transverse direction, and the angle of inclination θ3 of the acute angle of the transverse groove with respect to the tire's circumferential direction in the rib section located furthest outwards in the tire's transverse direction, exhibit the relationship θ1 = θ2 = θ3. In contrast, in the pneumatic tires of Examples 101 to 118, the condition θ1 < θ2 < θ3 is satisfied. The pneumatic tires of the prior art example and Examples 101 to 110 do not include narrow grooves. The pneumatic tires of examples 111 to 118 include narrow grooves and the relationship of the surface areas S. O , S I The small blocks are specified.

[0119] As can be seen from the results of the Fig. 19 and Fig. As can be seen from 20, the pneumatic tires of examples 101 to 118 exhibit improved resistance to uneven wear. List of reference symbols 1 pneumatic tire 2. Tread section 2A Tread surface 3 circumferential groove 4 transverse grooves 4A Bevel 5 Bridge section 5A medium small bridge section 5B lateral small bridge section 6 narrow groove 6A curved section 6Aa Bending point 7 lamella An imaginary straight line 101 pneumatic tires 121 Tread section 121A Tread surface 122 Shoulder section 124 Carcass layers 125 belt layer 125A, 125B, 125C, 125D belt 126 Circumference belts 103 Circumferential groove 103A middle circumferential groove 103B Intermediate groove 103C outer circumferential groove 104 transverse groove 104A Bevel 105 Bridge section 105A inner web section 105B outer web section Block 151 151A small block 151Aa medium small block 151Ab outer small block 106 narrow groove 106A curved section 107 lamella Central sector CL Equatorial plane of the tire (tire equator line) D1, D2, D3 Difference in tire radial direction dimension Do, Dm difference in tire radial direction dimension L Tire circumference direction dimension S I , S O Surface area of ​​the small block Tire lateral dimension Wf tire lateral dimension of the center area Regarding the tire's transverse dimension of the circumferential belt θ (θ1, θ2, θ3) Inclination angle of the acute angle of the transverse groove with respect to the tire circumferential direction

Claims

[1] Pneumatic tires (1), comprising: two circumferential grooves (3) in a tread surface (2A) of a tread section (2) which are arranged in a tire transverse direction and extend in a tire circumferential direction; a plurality of transverse grooves (4) in the tread surface (2A) which are arranged in the direction of the tire circumference and extend to cross the direction of the tire circumference, wherein the plurality of transverse grooves (4) are connected at both ends to both circumferential grooves (3) and each define a block-shaped rib section (5) between the circumferential grooves (3); two narrow grooves (6) in the tread surface (2A) of the rib section (5), which are arranged in the transverse direction of the tire and extend in the circumferential direction of the tire, wherein the narrow grooves (6) each communicate at both ends with a respective transverse groove (4) of the plurality of transverse grooves (4) and divide the rib section (5), which is defined by each of the circumferential grooves (3) and each of the transverse grooves (4), into a plurality of small rib sections (5A, 5B); wherein the two narrow grooves (6) in the web section (5) are formed such that they have a smaller groove width than the circumferential grooves (3) and each comprise a curved section (6A) in a central section, wherein the curved section (6A) is arranged inwards in the transverse direction of the tire in a direction in which the narrow grooves (6) are opposite each other by an imaginary straight connecting line (A) which connects the ends of the respective narrow grooves (6), wherein bending points (6Aa) of the curved sections (6A) are arranged at positions offset from each other in the circumferential direction of the tire, and wherein the narrow grooves (6) do not cross the imaginary straight connecting line (A). [2] Pneumatic tire (1) according to claim 1, wherein the curved section (6A) of the narrow groove (6) has a bending angle in the range of 90° to 160°. [3] Pneumatic tire (1) according to claim 1 or 2, wherein a relative displacement width (Lc) in the circumferential direction of each bending point (6Aa) of the two narrow grooves (6) and a circumferential direction dimension (L) of the web section (5) in which the narrow grooves (6) are formed, satisfy 0.1 ≤ Lc / L. [4] Pneumatic tire (1) according to one of claims 1 to 3, wherein the transverse groove (4) is designed such that it extends inclined in relation to the tire transverse direction, wherein an angle in relation to the tire transverse direction is in the range of 5° to 50°. [5] Pneumatic tires (1) according to any one of claims 1 to 4, where the relationships Ha > Hb and Ha > Hc are satisfied, where Ha is a groove depth of the circumferential grooves (3), Hb is a groove depth of the transverse grooves (4) and Hc is a groove depth of the narrow grooves (6). [6] Pneumatic tires (1) according to any one of claims 1 to 5, where Hb is in the range of 1 mm to 5 mm and Hc is in the range of 1 mm to 5 mm, where Hb is a groove depth of the transverse grooves (4) and Hc is a groove depth of the narrow grooves (6). [7] Pneumatic tire (1) according to any one of claims 1 to 6, wherein the transverse grooves (4) are designed such that they extend at an angle in relation to the transverse direction of the tire; and a chamfer is formed in a corner section of the bridge section (5) at an acute angle with respect to the tire circumferential direction. [8] Pneumatic tire (1) according to any one of claims 1 to 7, further comprising a lamella (7) in the running surface (2A) which is connected at one end to one of the circumferential grooves (3) and terminates at another end within the web section (5); and wherein the relationships 0.3 mm ≤ Wd ≤ 2.0 mm, 0.3 ≤ Hd / Ha ≤ 1.0, and 0.03 ≤ Ld / We ≤ 0.2 are satisfied, where Wd is a groove width of the sipe, Hd is a groove depth of the sipe, Ld is a groove length of the sipe, We is a tire transverse dimension of the rib section, and Ha is a groove depth of the circumferential grooves.

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