pneumatic tires

Abstract

To provide a pneumatic tire which is excellent in brake performance.SOLUTION: In a pneumatic tire 1, a tread 10 has a center rib 30. In the center rib 30, a plurality of sipes 31 are formed at an interval in a tire circumferential direction. The sipe 31 is a sipe crossing the center rib 30, and has a bent part 31c which is bent so as to project to a side closer to one side in the tire circumferential direction than both ends (first end 31d and second end 31e) in the length of the sipe in plan view of the center rib 30.SELECTED DRAWING: Figure 2

Description

Technical Field

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[0001] The present invention relates to a pneumatic tire, and more particularly to a tire in which the mounting direction with respect to a vehicle is specified.

Background Art

[0002] Conventionally, a pneumatic tire having a plurality of main grooves extending in the tire circumferential direction and ribs partitioned by the main grooves, and in which the mounting direction with respect to a vehicle is specified, is widely known. Tires in which the mounting direction with respect to a vehicle is specified generally have an asymmetric tread pattern. For example, Patent Document 1 discloses a pneumatic tire having three main grooves extending in the tire circumferential direction and two center ribs partitioned by the three main grooves, and in which sipes are formed in different patterns on each center rib.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] <G Tires in which the mounting direction with respect to a vehicle is specified can achieve functional distribution between the inner region and the outer region of the vehicle, and thus are superior to tires without a specified mounting direction in, for example, grip performance and drainage performance. In such tires, it is an important problem to improve the braking performance without impairing the handling stability during vehicle turning. Incidentally, the tire disclosed in Patent Document 1 has much room for improvement in terms of braking performance.

Means for Solving the Problems

[0005] The pneumatic tire according to the present invention is a pneumatic tire having a tread and a specified mounting direction for a vehicle, wherein the tread has a first main groove extending in the circumferential direction of the tire, a second main groove positioned on the vehicle side of the first main groove, and a center rib partitioned by the first main groove and the second main groove, wherein a plurality of sipes are formed on the center rib at intervals in the circumferential direction of the tire, and the sipes are sipes that cross the center rib and have bent portions that, in a plan view of the center rib, protrude to one side in the circumferential direction of the tire from both ends in the longitudinal direction of the sipe. [Effects of the Invention]

[0006] The pneumatic tire according to the present invention can improve braking performance. The pneumatic tire according to the present invention provides excellent braking performance while ensuring good handling stability during vehicle turns, thanks to the function of the sipes formed on the center rib on the inside of the vehicle. [Brief explanation of the drawing]

[0007] [Figure 1] This is a perspective view of a pneumatic tire, which is an example of an embodiment, and also shows the internal structure of the tire. [Figure 2] This is a plan view of a pneumatic tire, which is an example of an embodiment. [Figure 3] This is a plan view showing an enlarged view of the first center block. [Figure 4] This is a plan view showing an enlarged view of the second center block. [Figure 5] This diagram shows a modified example of a pneumatic tire. [Modes for carrying out the invention]

[0008] Hereinafter, an example of an embodiment of the pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining each component of the embodiments described below are included in the present invention.

[0009] Figure 1 is a perspective view of a pneumatic tire 1, which is an example of an embodiment. Figure 1 also shows the internal structure of the pneumatic tire 1. As shown in Figure 1, the pneumatic tire 1 includes a tread 10, which is the part that contacts the road surface. The tread 10 has at least two main grooves 20, 21 and a center rib 30 partitioned by the main grooves 20, 21, and is formed in an annular shape along the circumferential direction of the tire. In this embodiment, three main grooves 20, 21, and 22 extending in the circumferential direction of the tire are formed. The three main grooves are formed straight along the circumferential direction of the tire without curving in the axial direction of the tire.

[0010] The pneumatic tire 1 is a tire with a specified mounting direction on the vehicle, where the mounting direction is opposite on the right and left sides of the vehicle. The tread 10 has an asymmetrical tread pattern with respect to the tire equator CL (see Figure 2). The equator CL is a virtual line along the tire circumferential direction that passes exactly through the center of the tread 10 in the tire axial direction. In this specification, for the sake of explanation, the terms "left and right" are used, and these "left and right" refer to the left and right sides in the direction of travel of the vehicle when the pneumatic tire 1 is mounted on the vehicle.

[0011] In this embodiment, the central main groove 20, located in the middle of the three main grooves 20, 21, and 22, is positioned on the equator CL. The main groove 20 is formed straight in the circumferential direction of the tire along the equator CL, and the widthwise center of the main groove 20 is located on the equator CL. The three main grooves 20, 21, and 22 are formed parallel to each other and may have the same width and depth, or they may have different widths and depths. The distance between the main grooves 20 and 21 in the tire axial direction, and the distance between the main grooves 20 and 22 in the tire axial direction, are substantially the same.

[0012] The tread 10 has center ribs 30, 40 and shoulder blocks 50, 60. The ribs and blocks are raised portions extending radially outward from a position corresponding to the bottom of the main groove, and are also called land. Generally, the ribs of the tread refer to narrow land sections sandwiched between the main grooves, formed in a continuous, annular shape in the circumferential direction of the tire. Blocks refer to land sections that are wider than the ribs, or land sections formed intermittently in the circumferential direction of the tire.

[0013] When the pneumatic tire 1 is mounted on the vehicle, the shoulder block 50 (first shoulder block) is positioned on the inside of the vehicle, and the shoulder block 60 (second shoulder block) is positioned on the outside of the vehicle. In other words, the pneumatic tire 1 is mounted on the vehicle such that the shoulder block 50 is positioned on the inside of the vehicle and the shoulder block 60 is positioned on the outside of the vehicle. The center rib 30 is positioned between the shoulder block 50 and the equator CL, and the center rib 40 is positioned between the shoulder block 60 and the equator CL.

[0014] The pneumatic tire 1 comprises a pair of sidewalls 11 that bulge outward in the tire axial direction and a pair of beads 12. The bead 12 is the portion that is fixed to the rim of the wheel and has a bead core 17 and a bead filler 18. The sidewalls 11 and bead 12 are formed in an annular shape along the tire circumferential direction and constitute the side surface of the pneumatic tire 1. The sidewalls 11 extend radially from both ends of the tread 10 in the tire axial direction.

[0015] In a pneumatic tire 1, side ribs 13 may be formed between the contact edges E1 and E2 of the tread 10 and the portion of the sidewall 11 that protrudes most outward in the tire axial direction. The contact edge E1 is the contact edge on the inside of the vehicle, and the contact edge E2 is the contact edge on the outside of the vehicle, and are located on the shoulder blocks 50 and 60, respectively. The side ribs 13 protrude outward in the tire axial direction and are formed in an annular shape along the circumferential direction of the tire. The portion of the pneumatic tire 1 from the contact edges E1 and E2, or their vicinity, to the left and right side ribs 13 is also called the shoulder or buttress region.

[0016] The tread 10 and sidewall 11 are generally made of different types of rubber. The shoulder may be made of the same rubber as the tread 10 or of a different rubber. In this specification, the contact points E1 and E2 are defined as the axial ends of the area (contact surface) that contacts a flat road surface when a predetermined load is applied to an unused pneumatic tire 1 mounted on a normal rim and inflated to the normal internal pressure. For passenger car tires, the predetermined load is equivalent to 88% of the normal load.

[0017] Here, "standard rim" refers to the rim defined by the tire standard, which is "standard rim" for JATMA and "Measuring Rim" for TRA and ETRTO. "Standard internal pressure" is "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. The standard internal pressure is usually 180kPa for passenger car tires, but it is 220kPa for tires marked as Extra Load or Reinforced. "Standard load" is "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO.

[0018] The pneumatic tire 1 includes a carcass 14, a belt 15, and an inner liner 16. The carcass 14 is a cord layer coated with rubber and forms the framework of the pneumatic tire 1 that can withstand loads, impacts, air pressure, etc. The belt 15 is a reinforcing band disposed between the rubber constituting the tread 10 and the carcass 14. The belt 15 strongly tightens the carcass 14 to increase the rigidity of the pneumatic tire 1. The inner liner 16 is a rubber layer provided on the inner peripheral surface of the carcass 14 and holds the air pressure of the pneumatic tire 1.

[0019] Since the pneumatic tire 1 is used as a tire with a specified mounting direction for a vehicle, it is preferable that the pneumatic tire 1 has a display for indicating the mounting direction for the vehicle. The display indicating the mounting direction may be characters, symbols, illustrations, etc. indicating the inside or outside of the vehicle, and its configuration is not particularly limited. Generally, a symbol called a serial is provided on the side surface of the pneumatic tire 1, but the serial may be used as the display indicating the mounting direction.

[0020] The serial includes information such as, for example, a size code, a manufacturing time (manufacturing year and week), a manufacturing location (manufacturing plant code), etc. By providing the serial only on the side surface (sidewall 11) of the pneumatic tire 1 facing the outside of the vehicle, or by providing different serials on the side surface facing the outside of the vehicle and the side surface facing the inside of the vehicle, the mounting direction of the pneumatic tire 1 for the vehicle may be specified. As a specific example, a manufacturing plant code and a size code are provided on both side surfaces of the pneumatic tire 1, and the manufacturing year and week are provided only on the side surface facing the outside of the vehicle.

[0021] Hereinafter, the tread pattern of the pneumatic tire 1 will be described in detail while referring to FIG. 2. FIG. 2 is a plan view of the pneumatic tire 1 (tread 10).

[0022] As shown in Figure 2, the tread 10 has an asymmetrical tread pattern with respect to the equator CL. Hereafter, the region on the side of the equator CL towards the contact end E1 will be referred to as the first region 10A, and the region on the side of the equator CL towards the contact end E2 will be referred to as the second region 10B. As will be described in more detail later, the tread pattern of the pneumatic tire 1 exhibits excellent braking performance and handling stability during cornering when the tire is mounted on the vehicle such that the first region 10A is located on the inside of the vehicle and the second region 10B is located on the outside of the vehicle.

[0023] The tread 10 has a main groove 20 (center main groove) formed on the equator CL, a main groove 21 formed between the equator CL and the vehicle inner contact end E1, a main groove 22 formed between the equator CL and the vehicle outer contact end E2, and a plurality of ribs and blocks partitioned by these three main grooves. The width of the three main grooves is, for example, 9 to 13 mm. In this specification, unless otherwise specified, the width of the groove means the width of the profile surface along the contact surface of the tread 10.

[0024] A wear indicator (not shown) is generally provided in at least one of the three main grooves 20, 21, and 22. The wear indicator is a projection located at the bottom of the groove and serves as an indicator for checking the wear level of the tread rubber. The sipes and lateral grooves, described later, are generally formed deeper than the upper surface of the wear indicator. The walls of the main grooves are sloped so that the groove width gradually narrows towards the bottom of the groove. Since the walls of the main grooves constitute the side walls of the ribs and blocks, in other words, the side walls of the ribs and blocks are sloped so that they become wider as they move away from the contact surface.

[0025] As described above, the tread 10 has center ribs 30 and 40 and shoulder blocks 50 and 60. As will be explained in more detail later, the center ribs 30 and 40 have multiple thin, linear sipes with a width of 2 mm or less, but no grooves with a width exceeding 2 mm are formed. The shoulder blocks 60 have lateral grooves 61 and 62 with a width exceeding 2 mm, but the ends of the lateral grooves 61 and 62 on the equator side CL terminate within the block, and no grooves are formed that cross the contact surface of the block. On the other hand, the contact surface of the shoulder block 50 is divided in the circumferential direction of the tire by the lateral groove 51.

[0026] The center ribs 30 and 40 are separated by the center main groove 20. Furthermore, the center rib 30 is separated from the shoulder block 50 by the main groove 21, and the center rib 40 is separated from the shoulder block 60 by the main groove 22. In this embodiment, the main grooves 21 and 22 are formed at positions equidistant from the equator CL (main groove 20), and the center ribs 30 and 40 have the same width. The shoulder blocks 50 and 60 are formed wider than the center ribs 30 and 40 and have the same width.

[0027] Furthermore, when tires have wide grooves, a noise called air pumping noise is generated when the tires roll (when the vehicle is in motion). Air pumping noise is a resonant sound that occurs within the groove cavity due to the air pumping action. When the groove is compressed and deformed by contact with the road surface, some of the air inside the groove is released through the groove opening, causing resonant vibration of the air column. Also, when the groove leaves the road surface, the groove returns to its original shape, causing air to flow into the groove cavity and generating air vibration. This is the air pumping action, and it is one of the causes of noise generated from tires when a vehicle is in motion.

[0028] In the pneumatic tire 1, wide grooves are not formed on the center ribs 30 and 40, which suppresses the generation of air pumping noise and effectively reduces noise caused by the tread pattern. As will be described in more detail later, in the pneumatic tire 1, by devising the formation pattern of sipes on the center ribs 30 and 40 and lateral grooves on the shoulder blocks 50 and 60, noise can be effectively reduced while achieving excellent braking performance and handling stability. The pneumatic tire 1 performs well not only on dry roads but also on wet roads and snowy / icy roads, making it suitable as an all-season tire.

[0029] Below, we will provide a more detailed explanation of the center ribs 30, 40 and shoulder blocks 50, 60 that constitute the tread pattern, referring to Figures 3 and 4 as appropriate, in addition to Figure 2. Figure 3 is an enlarged view of the center rib 30, and Figure 4 is an enlarged view of the center rib 40. Note that in Figures 3 and 4, dot hatching is applied to the contact surface of each center rib.

[0030] [Center Rib 30] As shown in Figures 2 and 3, the center rib 30 is formed straight along the circumferential direction of the tire and has a constant width along its entire length. The width of the contact surface of the center rib 30 corresponds to, for example, 12 to 25% of the length along the tire axial direction from contact end E1 to contact end E2 (hereinafter referred to as "tire contact width"). If the width of the center rib 30 is within this range, the improvement in braking performance becomes more pronounced. An example of the width of the center rib 30 is 15 to 35 mm.

[0031] Multiple sipes 31 are formed on the center rib 30 at intervals in the circumferential direction of the tire. In this specification, a sipe is defined as a narrow groove with a groove width of 2.0 mm or less, preferably 1.5 mm or less. The width of the sipes is, for example, 0.5 to 1.5 mm, or 0.5 to 1.0 mm. The sipes 31 contribute significantly to improving braking performance and also to improving handling stability during cornering. Other sipes with different shapes from the sipes 31 may be formed on the center rib 30, but in this embodiment only the sipes 31 are formed. Each sipe 31 has substantially the same shape. As will be described in detail later, the number of sipes crossing the center rib 30 is greater than the number of sipes crossing the center rib 40.

[0032] The sipes 31 may be formed in a variable pitch, for example, with a predetermined number of sipes spaced slightly apart in the circumferential direction of the tire, or they may be formed at the same spacing. The number of sipes 31 is not particularly limited, but as an example, there may be 2 to 6 sipes in one pitch (a predetermined number of sipes). The spacing between adjacent sipes 31 in the circumferential direction of the tire is, for example, smaller than the width of the main groove 20, and is 5 to 30 mm. Also, the spacing between the sipes 31 is smaller than the spacing between sipes formed on the center rib 40.

[0033] The sipe 31 is a sipe that crosses the center rib 30 and has a bent portion 31c that, in a plan view of the center rib 30, protrudes to one side in the tire circumferential direction from both ends of the sipe in the longitudinal direction (first end 31d and second end 31e). In Figure 3, the end of the sipe 31 in the longitudinal direction on the contact surface of the center rib 30 is the first end 31d, which is on the vehicle's outer side (main groove 21 side), and the end on the equator CL side (main groove 20 side) is the second end 31e. The sipe 31 opens into the walls (side walls of the rib) of the main grooves 20 and 21, which are inclined so that the groove width gradually narrows towards the bottom of the groove.

[0034] The sipe 31 crosses the center rib 30 and communicates with the main grooves 20 and 21, which increases the number of airflow channels in the axial center of the tread 10, thus avoiding a match in the air column resonance frequencies and suppressing the generation of air column resonance noise in the main grooves 20 and 21.

[0035] The sipe 31 is sharply bent at the bend 31c and includes a first portion 31a, which is the part from the first end 31d to the bend 31c, and a second portion 31b, which is the part from the second end 31e to the bend 31c. The pneumatic tire 1 exhibits excellent braking performance due to the edge effect of the sipe 31. When the vehicle is braking, the contact area increases in the first region 10A on the inside of the vehicle, so forming many sipes 31 on the center rib 30 enhances the edge effect and greatly improves braking performance on snowy and icy roads. In addition, the sharply bent sipe 31 increases the lateral edge component, improving handling stability when the vehicle is turning.

[0036] The depth of the sipe 31 is, for example, 60-90% of the depth of the main groove 20 at its deepest point. The sipe 31 may be shallower than other parts in a predetermined length range from both ends in the longitudinal direction. In this case, the reduction in rigidity of the center rib 30 due to the formation of the sipe 31 can be suppressed, and the improvement in braking performance becomes more pronounced. The predetermined length range is, for example, a length range corresponding to 3-10% of the width of the center rib 30. The second part 31b may be formed shallower than the deepest part along its entire length.

[0037] It is preferable that the sipe 31 bends at approximately a right angle at the bent portion 31c. Here, the angle at which the sipe 31 bends at the bent portion 31c refers to the angle θ (see Figure 3) formed by the first portion 31a and the second portion 31b in a plan view of the center rib 30. Approximately a right angle means an angle that is considered substantially right, and a suitable example of an angle θ is 90°±10° or 90°±5°. It is preferable that the bent portion 31c is gently curved without sharp edges so as not to become the starting point for cracks in the rib.

[0038] Because the sipe 31 is sharply bent at the bent portion 31c, the first portion 31a and the second portion 31b are inclined at a predetermined angle with respect to the tire circumferential direction and the tire axial direction. The first portion 31a and the second portion 31b extend in directions perpendicular to each other. In this embodiment, the inclination angle with respect to the tire axial direction is such that the inclination angle of the first portion 31a > the inclination angle of the second portion 31b. The inclination angles of the first portion 31a and the second portion 31b with respect to the tire axial direction are, for example, 30 to 60° or 35 to 55°. In this case, the improvement in braking performance becomes more pronounced while improving handling stability during vehicle turns.

[0039] The bent portion 31c is formed on the equator CL side (second end 31e side) in the width direction of the center rib 30. When the vehicle turns, a large load is applied to the second region 10B located on the outside of the vehicle, so forming the bent portion 31c closer to the equator CL, which is closer to the second region 10B, greatly improves handling stability. The bent portion 31c is formed, for example, within a length range corresponding to 10-30% of the rib width from the second end 31e of the center rib 30. In addition, the bent portions 31c of each sipe 31 are formed in a single line in the circumferential direction of the tire. In this case, more reliable tire performance can be achieved.

[0040] The sipe 31 has a shape in which the first portion 31a extends longer than the second portion 31b because the bent portion 31c is formed on the second end 31e side of the center rib 30 in the width direction. The length of the first portion 31a is, for example, 3 to 10 times, or 4 to 8 times, the length of the second portion 31b. The first portion 31a extends in approximately the same direction as the second sipe 42, third sipe 43, and fourth sipe 44 of the center rib 40, which will be described later. The second portion 31b extends in a direction approximately perpendicular to the direction in which the second sipe 42, etc., extend.

[0041] As shown in Figure 3, in this embodiment, when adjacent sipes 31 in the circumferential direction of the tire are defined as sipe A and sipe B, the first end 31d of sipe A on the contact end E1 side is located on the other side in the circumferential direction of the tire than the bent portion 31c of sipe B. Furthermore, the first end 31d of sipe A is located on the other side in the circumferential direction of the tire than the second end 31e of sipe B on the equator CL side. In this way, by forming many sipes 31 in the circumferential direction of the tire while parts of each sipe 31 overlap in the axial direction of the tire, it is possible to effectively achieve both good braking performance and handling stability.

[0042] Furthermore, if we define adjacent sipes 31 in the circumferential direction of the tire as sipe A, sipe B, and sipe C, starting from one side in the circumferential direction of the tire where the bent portion 31c protrudes, then the first end 31d of sipe A is aligned with the bent portion 31c of sipe C in the axial direction of the tire. That is, the first portion 31a of sipe A extends to a position where it overlaps with sipe C in the axial direction of the tire. On the other hand, the second end 31e of sipe A is located on one side in the circumferential direction of the tire than the bent portion 31c of sipe B, and the second portion 31b of sipe A does not extend to a position where it overlaps with sipe B in the axial direction of the tire.

[0043] The first portion 31a may have a bent portion 31f that is bent less than the bent portion 31c. The bent portion 31f of sipe A is bent slightly so as to protrude to the other side in the circumferential direction of the tire at a position corresponding to the bent portion 31c of sipe B and the bent portion 31c of sipe C.

[0044] [Center Rib 40] As described above, the center rib 40 is positioned opposite the center rib 30 in the tire axial direction, with the main groove 20 in between, and is formed straight along the tire circumferential direction. The width of the contact surface of the center rib 40 is, for example, 12 to 25% of the tire contact width. If the width of the center rib 40 is within this range, the effect of improving steering stability during cornering becomes more pronounced. In this embodiment, the center rib 40 has the same width as the center rib 30 and is formed with a constant width along its entire length.

[0045] Multiple first sipes 41 are formed on the center rib 40 at intervals in the circumferential direction of the tire. The first sipes 41 have a substantially S-shape in plan view and greatly contribute to improving handling stability when the vehicle turns. The multiple first sipes 41 may be formed with a variable pitch, for example, by slightly changing the spacing between sipes in units of a predetermined number in the circumferential direction of the tire, or they may be formed at the same interval. Only the first sipes 41 may be formed on the center rib 40, but in this embodiment, in addition to the first sipes 41, three types of sipes (second sipes 42, third sipes 43, and fourth sipes 44) are formed.

[0046] The first sipe 41 is a sipe that crosses the center rib 40 and connects to the main grooves 20, 21. The first sipe 41 includes a first portion 41a that extends inclined in the circumferential and axial directions from the main groove 20, a second portion 41b that is positioned away from the first portion 41a in the circumferential direction of the tire and extends inclined in the circumferential and axial directions from the main groove 21, and a third portion 41c that connects the first portion 41a and the second portion 41b. The third portion 41c may be formed straight along the circumferential direction of the tire, but preferably has a predetermined inclination angle with respect to the circumferential direction of the tire. In this case, the steering stability during cornering can be improved while maintaining the high durability of the center rib 40.

[0047] In this embodiment, the bent portion 41f is the boundary between the first portion 41a and the third portion 41c, and the bent portion 41i is the boundary between the second portion 41b and the third portion 41c. The lengths of each portion of the first sipe 41 along the tire circumferential direction are third portion 41c > first portion 41a and second portion 41b. Also, the lengths of each portion along the tire axial direction are first portion 41a and second portion 41b > third portion 41c. The first sipe 41 extending from the first end 41d, which is the intersection with the main groove 20, bends at the bent portion 41f either along the tire circumferential direction or inclined toward the main groove 20 towards the bent portion 41i. Also, the portion extending from the second end 41e, which is the intersection with the main groove 22, bends at the bent portion 41i either along the tire circumferential direction or inclined toward the main groove 22 towards the bent portion 41f.

[0048] The first sipe 41 preferably has a substantially S-shape in a plan view of the center rib 40. In this case, the effect of improving steering stability during vehicle turning becomes more pronounced. The first portion 41a and the second portion 41b of the first sipe 41 extend in the same direction, for example, and are inclined at an angle of 30 to 60° with respect to the tire axis. Furthermore, the first portion 41a and the second portion 41b have substantially the same length, and a portion of each is formed to overlap in the circumferential direction of the tire. The third portion 41c is inclined in the opposite direction to the direction in which the first portion 41a and the second portion 41b are inclined with respect to the circumferential direction of the tire.

[0049] The third portion 41c may have multiple bends. In this embodiment, the third portion 41c is formed such that the vicinity of the first portion 41a protrudes in the direction of the main groove 22, and the vicinity of the second portion 41b protrudes in the direction of the main groove 21. The third portion 41c extends straight along the tire circumferential direction from both ends in the longitudinal direction (bends 41f, 41i), and bends toward the center in the width direction of the center rib 40 at positions equidistant from both ends. Bends 41g and 41h are formed at positions equidistant from both ends in the longitudinal direction of the third portion 41c, respectively. Each bend of the first sipe 41 is gently curved, similar to the bend 31c of the sipe 31.

[0050] In this embodiment, the third portion 41c, which is the connection between the bent portion 41f and the bent portion 41i, is formed by a plurality of bent portions and a plurality of straight portions. Specifically, the third portion 41c includes bent portions 41g and 41h, a straight portion 41j formed between the bent portion 41f and the bent portion 41g, a straight portion 41k formed between the bent portion 41g and the bent portion 41h, and a straight portion 41m formed between the bent portion 41h and the bent portion 41i. The straight portions 41j and 41m are, for example, of the same length as each other, shorter than the straight portion 41k, and formed along the circumferential direction of the tire. The straight portion 41k extends in a direction substantially perpendicular to the direction in which the straight portions 41j and 41m extend. The angle between the direction in which the straight portion 41k extends and the direction in which the straight portions 41j and 41m extend is, for example, 90° ± 5°.

[0051] In the center rib 40, a second sipe group consisting of a plurality of second sipes 42 and a third sipe group consisting of a plurality of third sipes 43 are formed in the region that overlaps each of the first sipes 41 in the tire axial direction. The second sipes 42 extend from the main groove 20 and terminate within the rib, and the third sipes 43 extend from the main groove 22 and terminate within the rib. The second sipes 42 and the third sipes 43 are short sipes formed at a predetermined distance from the first sipes 41. Furthermore, each of these sipes is inclined with respect to the tire axial direction and the circumferential direction, and extends in the same direction as, for example, the first portion 41a and the second portion 41b of the first sipe 41.

[0052] In this embodiment, the second group of sipes that overlaps with the first sipe 41 in the axial direction of the tire is composed of three second sipes 42. These three second sipes 42 are formed, for example, parallel to each other and at equal intervals. Similarly, the third group of sipes is composed of three third sipes 43 that are formed parallel to each other and at equal intervals. The multiple second sipes 42 constituting each second group of sipes have different lengths, becoming longer as they approach the first portion 41a of the first sipe 41. The multiple third sipes 43 constituting each third group of sipes have different lengths, becoming longer as they approach the second portion 41b of the first sipe 41.

[0053] Specifically, each second sipe 42 extending from the main groove 20 is longer in the region where the first sipe 41 protrudes toward the main groove 22, and shorter in the region where it protrudes toward the main groove 20. Similarly, the third sipe 43 extending from the main groove 22 is longer in the region where the first sipe 41 protrudes toward the main groove 20, and shorter in the region where it protrudes toward the main groove 22. In this case, the rigidity balance of the center rib 40 is improved, resulting in more reliable tire performance.

[0054] The shortest of the three second sipes 42 is positioned on the extension of the second portion 41b of the first sipe 41, and the shortest of the three third sipes 43 is positioned on the extension of the first portion 41a. The remaining two second sipes 42 are aligned in the same line as the remaining two third sipes 43. More specifically, the longest second sipe 42 is aligned in the same line as the second longest third sipe 43, and the longest third sipe 43 is aligned in the same line as the second longest second sipe 42.

[0055] In the region between each of the first sipes 41 of the center rib 40, a substantially straight fourth sipe 44 is formed that crosses the center rib 40. That is, the first sipes 41 and the fourth sipes 44 are arranged alternately in the circumferential direction of the tire on the center rib 40. The fourth sipe 44 is formed parallel to the first portion 41a and the second portion 41b of the first sipe 41 and extends straight without bending along the way. The fourth sipe 44 plays an important role in noise reduction. Specifically, the fourth sipe 44 communicates with the main grooves 20 and 22, increasing the number of airflow channels, avoiding a match in the air column resonance frequency, and effectively suppressing the generation of air column resonance noise in the main grooves 20 and 22.

[0056] The depth of each sipe formed in the center rib 40 may be the same as that of the others. The depth of each sipe is, for example, 60-90% of the depth of the main groove 20 at its deepest point. In this embodiment, the shorter second sipe 42 and third sipe 43 have a constant depth along their entire length. On the other hand, the first sipe 41 and fourth sipe 44 are shallower than the other parts in a predetermined length range from both ends in the longitudinal direction. In this case, the reduction in rigidity of the center rib 40 due to the formation of the sipes can be suppressed, and the improvement in steering stability becomes more pronounced. The predetermined length range is, for example, a length range corresponding to 3-10% of the width of the center rib 40.

[0057] The first sipe 41 may be formed shallower than the deepest part in the middle section of the third section 41c, specifically in the straight section 41k. In this case, steering stability can be improved while maintaining the high durability of the center rib 40. The straight section 41k formed shallower than the deepest part may be formed to substantially the same depth as both ends of the first sipe 41 in the longitudinal direction, for example.

[0058] It is preferable that the number of sipes crossing the center rib 40 is less than the number of sipes crossing the center rib 30. In the center rib 30, all sipes cross the rib, but in the center rib 40, the second sipe 42 and the third sipe 43 terminate within the rib, while the first sipe 41 and the fourth sipe 44 cross the rib. In addition, the spacing between sipes formed on each rib in the tire circumferential direction is larger in the center rib 40 than in the center rib 30. For this reason, when comparing the center ribs 30 and 40, the number of sipes crossing the rib is significantly less in the center rib 40.

[0059] Furthermore, when the second sipe 42 and the third sipe 43, which are located on the same straight line, are counted as one sipe, the number of sipes on the center rib 30 may be greater than the number of sipes on the center rib 40. In this case, the number of sipes on the center rib 30 is, for example, 1.1 to 1.5 times the number of sipes on the center rib 40. Alternatively, when the second sipe 42 and the third sipe 43 are each counted as one sipe, the number of sipes on the center rib 30 may be greater than the number of sipes on the center rib 40.

[0060] By making the number of sipes on the center rib 30 greater than the number of sipes on the center rib 40, the frequency of pitch noise generated by the sipes can be shifted, thus avoiding resonance and resulting in a more pronounced noise reduction effect. Furthermore, it becomes easier to achieve a higher level of balance between braking performance and handling stability.

[0061] [Shoulder Block 50] As shown in Figure 2, the shoulder block 50 is positioned opposite the center rib 30 in the tire axial direction, with the main groove 21 in between, and is formed straight along the tire circumferential direction. The width of the contact surface of the shoulder block 50 is, for example, 15-35% of the tire contact width, and is larger than the width of the contact surface of the center rib 30. In this embodiment, the shoulder block 50 has the same width as the shoulder block 60 and is formed with a constant width along its entire length.

[0062] The shoulder block 50 has two types of lateral grooves 51 and 52 of different lengths formed thereon, which extend in the axial direction of the tire and connect to the main groove 21. Both lateral grooves have a length that extends beyond the contact edge E1 from the main groove 21 and traverse the contact surface of the shoulder block 50. The lateral grooves 51 and 52 have a width of more than 2 mm and are distinguished from sipes, which are thin, linear grooves. As described above, the contact surface of the shoulder block 50 is divided in the circumferential direction of the tire by the lateral grooves 51 and 52.

[0063] In this specification, when a lateral groove is described as "extending in the direction of the tire axis," it refers to both a configuration in which the lateral groove extends along the tire axis and a configuration in which it extends at an inclination angle of 45° or less, preferably 30° or less, with respect to the tire axis. The same applies to main grooves extending in the circumferential direction of the tire; the main grooves may be formed in a zigzag pattern, curving at an inclination angle of 45° or less with respect to the circumferential direction of the tire.

[0064] The lateral grooves 51 and 52 have a constant width, for example, from the main groove 21 to the contact edge E1. By forming lateral grooves 51 and 52 connected to the main groove 21, drainage is improved, and braking performance on wet surfaces can be significantly improved. If the lateral grooves 51 and 52 are connected to the main groove 21, air will flow from the main groove 21 to the lateral grooves 51 and 52, which is expected to increase noise and air resistance. However, since the shoulder block 50 is located on the inside of the vehicle, the effect of the lateral grooves 51 and 52 is small. The lateral groove 52 is formed in a straight line along its entire length. The lateral groove 51 is formed in a straight line up to a position beyond the contact edge E1, and curves to one side in the circumferential direction of the tire at or near the boundary with the side rib 13.

[0065] In the shoulder block 50, two types of sipes (first sipe 53 and second sipe 54) of different lengths are formed in the region located between the lateral grooves 51 and 52. Both sipes have a length extending from the main groove 21 beyond the contact edge E1 and are connected to each other on the shoulder of the pneumatic tire 1. The second sipe 54 is longer than the first sipe 53 and has the same length as the lateral groove 52. In the shoulder block 50, grooves and sipes are repeatedly formed in the circumferential direction of the tire in the order of lateral groove 51, first sipe 53, second sipe 54, and lateral groove 52. The multiple grooves and sipes are formed, for example, with a variable pitch.

[0066] The lateral grooves 51, 52, the first sipe 53, and the second sipe 54 are formed parallel to each other and inclined with respect to the tire axis. The inclination angle of these lateral grooves and sipes is smaller than, for example, the sipes of the center ribs 30, 40. The lateral grooves and sipes of the shoulder block 50 are inclined with respect to the tire axis in the opposite direction to the first portion 31a of the sipe 31.

[0067] [Shoulder Block 60] As shown in Figure 2, the shoulder block 60 is positioned opposite the center rib 40 in the tire axial direction, with the main groove 22 in between, and is formed straight along the tire circumferential direction. The width of the contact surface of the shoulder block 60 is, for example, 20-35% of the tire contact width, which is larger than that of the center rib 40. As described above, the shoulder block 60 does not have grooves formed across the contact surface of the block, and is continuous in the tire circumferential direction.

[0068] The shoulder block 60 is similar to the shoulder block 50 in that it has lateral grooves 61 and 62, a first sipe 63, and a second sipe 64 that extend in the axial direction of the tire. The longer groove, the lateral groove 61, curves in the opposite direction to the lateral groove 51 of the shoulder block 50 at or near the boundary with the side rib 13. The shoulder block 50 has grooves and sipes repeatedly formed in the circumferential direction of the tire in the order of lateral groove 61, second sipe 64, first sipe 63, and lateral groove 62. On the other hand, the shoulder block 60 differs from the shoulder block 50 in that the lateral grooves 61 and 62 are not directly connected to the main groove 22.

[0069] In this embodiment, the lateral grooves 61 and 62 are connected to the main groove 22 via third sipes 65. In this case, the flow of air from the main groove 22 into the lateral grooves 61 and 62 and its discharge to the outside of the vehicle can be suppressed, thus making the noise suppression effect more pronounced. The air resistance of the pneumatic tire 1 is also effectively reduced. Noise and air resistance are more greatly influenced by the groove configuration of the shoulder block 60, which is located on the outside of the vehicle, than by the shoulder block 50, which is located on the inside of the vehicle. The length of the third sipes 65 is not particularly limited, but a preferred example is 5 to 40% or 10 to 30% of the width of the contact surface of the shoulder block 60. Each third sipe 65 has, for example, the same length as one another.

[0070] As illustrated in Figure 5, the lateral grooves 51 and 52 formed in the shoulder block 50 may be connected to the main groove 21 via sipes 55, similar to the lateral grooves 61 and 62 of the shoulder block 60. That is, in the tread pattern illustrated in Figure 2, the connection configuration between the lateral grooves and the main grooves differs in the left and right shoulder blocks 50 and 60, but in the tread pattern illustrated in Figure 5, the connection configuration between the lateral grooves and the main grooves is the same in the shoulder blocks 50 and 60. The length, width, depth, etc. of the sipes 55 may be substantially the same as those of the third sipe 65 of the shoulder block 60.

[0071] Here, we present the evaluation results for the wet braking performance and noise level of a pneumatic tire 1 having the tread pattern exemplified in Figure 2 (hereinafter referred to as "Tire X") and a pneumatic tire 1 having the tread pattern exemplified in Figure 5 (hereinafter referred to as "Tire Y"). The evaluation was performed by mounting tires X and Y, with size 195 / 60R17 90H and air pressure of 240kPa, on an actual vehicle.

[0072] When the sound pressure level was measured while driving on a dry road surface at 100 km / h and the noise level was evaluated (with two occupants), the noise levels of tires X and Y were similar in the frequency range of 250 Hz to 2 kHz. In fact, the noise level of tire X was lower. This indicates that directly connecting the lateral grooves 51 and 52 of the shoulder block 50 located on the inside of the vehicle to the main groove 21 does not affect the noise level.

[0073] When braking force was applied and the ABS activated while driving on a wet road surface at 100 km / h, the braking distance was measured and the wet braking performance was evaluated (with one person on board). It was confirmed that the braking distance of tire X was approximately 3% shorter than that of tire Y. In other words, when the lateral grooves 51 and 52 of the shoulder block 50 are directly connected to the main groove 21, the drainage performance is improved and the improvement in wet braking performance becomes more pronounced.

[0074] As described above, the pneumatic tire 1, in particular due to the function of the sipes 31 formed on the center rib 30, ensures good handling stability during vehicle turns while achieving excellent braking performance. In addition, it effectively reduces noise and achieves a high degree of balance between excellent braking performance and handling stability on wet roads and snowy / icy roads.

[0075] The above embodiments can be modified as appropriate without impairing the objectives of the present invention. The tread pattern including the center ribs 30, 40 and shoulder blocks 50, 60 effectively achieves both excellent braking performance and handling stability, making it suitable for all-season tires. However, it is possible to achieve the objectives of the present invention by changing the components other than the center rib 30 to other configurations. For example, sipes similar to those of sipe 31 may be formed on the center rib located on the outer-inside side of the vehicle, without impairing the objectives of this disclosure. [Explanation of symbols]

[0076] 1 pneumatic tire, 10 tread, 10A first area, 10B second area, 11 sidewall, 12 bead, 13 side rib, 14 carcass, 15 belt, 16 inner liner, 17 bead core, 18 bead filler, 20, 21, 22 main groove, 30, 40 center rib, 31 sipe, 31a, 41a first section, 31b, 41b second section, 31c, 31f, 41f, 41g, 41h, 41i curved section, 41j, 41k, 41m straight section, 31d, 41d first end, 31e, 41e second end, 41, 53, 63 first sipe, 41c third section, 42, 54, 64 second sipe, 43, 65 third sipe, 44 fourth sipe, 50, 60 Shoulder blocks, 51, 52, 61, 62; Transverse grooves, CL; Equator, E1, E2; Grounding ends

Claims

1. A pneumatic tire having a tread and a specified mounting direction for the vehicle, The aforementioned tread is A first main groove extending in the circumferential direction of the tire, A second main groove is located on the vehicle side of the first main groove, The center rib is partitioned by the first main groove and the second main groove, It has, Multiple sipes are formed on the aforementioned center rib at intervals in the circumferential direction of the tire. The sipe is a sipe that crosses the center rib and has a bent portion that, in a plan view of the center rib, protrudes from both ends of the sipe in the longitudinal direction toward one side in the circumferential direction of the tire. A pneumatic tire in which, when adjacent sipes in the circumferential direction of the tire are defined as sipe A and sipe B, the end of sipe A on the contact end side is located on the other side in the circumferential direction of the tire than the bent portion of sipe B.

2. The pneumatic tire according to claim 1, wherein the sipe is bent at approximately a right angle at the bending portion.

3. The pneumatic tire according to claim 2, wherein the bent portion is formed on the tire equator side in the width direction of the center rib.

4. The tread has three main grooves extending in the circumferential direction of the tire. The pneumatic tire according to any one of claims 1 to 3, wherein the central main groove among the three main grooves is positioned on the tire equator.

5. The aforementioned tread is The first shoulder block is positioned inside the vehicle, relative to the tire equator, The second shoulder block is positioned outside the tire equator of the vehicle, It further possesses, The first shoulder block has a first transverse groove that extends in the tire axial direction and is connected to the main groove. The pneumatic tire according to claim 4, wherein the second shoulder block has a second transverse groove that extends in the tire axial direction and is connected to the main groove via a sipe.

6. The aforementioned tread is A third main groove is located on the vehicle side of the first main groove, A second center rib is separated by the first main groove and the third main groove, It further possesses, The pneumatic tire according to any one of claims 1 to 3, wherein the number of sipes crossing the second center rib is less than the number of sipes crossing the center rib.

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