pneumatic tires

Abstract

To decrease CFmax according to means that is different from a groove outside a ground contact end, and to secure excellent wear performance of a block and excellent maneuverability during steady travel.SOLUTION: A tire 1 includes a tread 10 which has: a center block 40; a mediate block 45 provided on a tire axial direction one side of the center block; and a shoulder block 51 provided on a tire axial direction outer side of the mediate block. The mediate block has: a circumferential direction width groove 46 extending in a tire circumferential direction; and a plurality of outer small blocks 48 and a plurality of inner large blocks 62 provided on a tire axial direction outer side and a tire axial direction inner side of the circumferential direction width groove. Each inner large block has a ground contact area which is larger than in each outer small block. A total ground contact area of the plurality of outer small blocks is 30-50% of a ground contact area of the mediate block.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire provided with a tread including a plurality of blocks.

Background Art

[0002] Patent Document 1 describes a configuration in which a groove extending in a direction forming an angle of 0 to 35 degrees with respect to the tire circumferential direction is formed outside the ground contact end of a pneumatic tire. According to this configuration, CFmax, which is the maximum value of cornering force, can be reduced when the vehicle turns at a large steering angle. Therefore, even for a vehicle with a high center of gravity position, it is possible to prevent the tire from gripping too much during turning, and prevent the vehicle from significantly losing balance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As in the pneumatic tire of Patent Document 1, reducing CFmax by means of forming a wide groove extending in the tire circumferential direction or at an angle close to this circumferential direction outside the ground contact end may cause a sudden change in the rigidity of the ground contact portion of the tire during turning, which may lead to unstable vehicle behavior. For this reason, it is desired to reduce CFmax by means different from the groove outside the ground contact end. It is also desired to ensure good wear performance of the blocks formed on the tire tread, and to ensure good motion performance during steady running.

[0005] An object of the present invention is to provide a pneumatic tire that can reduce CFmax by means different from the groove outside the ground contact end, and can ensure good wear performance of blocks and good motion performance during steady running. [Means for solving the problem]

[0006] The pneumatic tire according to the present invention comprises a tread including a center block, a mediate block provided on one side of the center block in the tire axial direction via a center main groove which is a main groove in the tire circumferential direction, and a shoulder block provided on the outer side of the mediate block in the tire axial direction via a shoulder main groove which is a main groove in the tire circumferential direction, wherein the mediate block includes a circumferential sub-groove smaller than the width of the center main groove and the shoulder main groove, a plurality of outer small blocks provided outward from the circumferential sub-groove in the tire axial direction and divided in the tire circumferential direction by the plurality of outer grooves, and a plurality of inner large blocks provided inward from the circumferential sub-groove in the tire axial direction and divided in the tire circumferential direction by the plurality of inner grooves, wherein each of the plurality of inner large blocks has a larger contact area than each of the plurality of outer small blocks, and the total contact area of ​​the plurality of outer small blocks is 30-50% of the contact area of ​​the mediate block. [Effects of the Invention]

[0007] According to the pneumatic tire of the present invention, the mediate block is provided with circumferential sub-grooves. In addition, a plurality of outer small blocks are provided axially outward from the circumferential sub-grooves of the mediate block, and a plurality of inner large blocks, which have a larger contact area than the outer small blocks, are provided axially inward. This makes it possible to improve the handling performance and braking performance during steady-state driving with no steering angle or a small steering angle, and also to increase the contact pressure of the outer small blocks, thereby reducing the coefficient of friction on the outer side of the tire's contact surface. As a result, the maximum cornering force (CFmax) can be reduced. Furthermore, since the total contact area of ​​the plurality of outer small blocks is 30-50% of the contact area of ​​the mediate block, good wear performance of the outer small blocks and good handling performance during steady-state driving can be ensured. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view of a pneumatic tire, which is an example of an embodiment. [Figure 2] Figure 1 is a plan view of a portion of the tread in the circumferential direction. [Figure 3] This is an enlarged view of section A in Figure 2. [Figure 4] This figure shows the contact pressure distribution of the tread during a large steering angle turn, in a configuration where the tread has multiple blocks, similar to the pneumatic tire in Figure 1. [Modes for carrying out the invention]

[0009] 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, selectively combining the various components of the multiple embodiments and modifications described below is included in the present invention.

[0010] Figure 1 is a cross-sectional view of a pneumatic tire 1, which is an example of an embodiment. Figure 2 is a plan view of a circumferential portion of the tread 10 shown in Figure 1. Figure 3 is an enlarged view of portion A in Figure 2. As shown in Figures 1 and 2, the pneumatic tire 1 includes a tread 10, which is the portion that contacts the road surface. Hereinafter, "pneumatic tire 1" will be referred to as "tire 1". The tread 10 has a tread pattern that includes a plurality of blocks spaced apart in the tire axial direction and is formed in an annular shape along the tire circumferential direction (vertical direction in Figures 2 and 3). In Figures 1 to 3, the OUT side and IN side refer to the outside and inside of the vehicle, respectively, when the tire 1 is mounted on the vehicle.

[0011] The tread 10 comprises blocks 40, 44, 45, 50, and 51, which are demarcated by, for example, four circumferential main grooves of the tire: two center main grooves 20 and two shoulder main grooves 21. Blocks 40, 44, 45, 50, and 51 are protrusions that project outward in the tire radial direction from the reference surface of the tread 10. The "reference surface" is a virtual surface along the bottom surface of the deepest center main grooves 20 and shoulder main grooves 21, and represents the outer circumferential surface of the tread 10 when no blocks are present. The depth of each center main groove 20 and each shoulder main groove 21 in the tire radial direction is approximately the same. The tread 10 has two center main grooves 20 and two shoulder main grooves 21, and as blocks, it has a center block 40 including the axial center CL of the tire, two mediate blocks 44 and 45 provided on both sides of the center block 40 via the center main grooves 20 in the axial direction, and two shoulder blocks 50 and 51 provided on the outer sides of the two mediate blocks 44 and 45 in the axial direction via the shoulder main grooves 21. As a result, the two shoulder blocks 50 and 51 are provided on both sides in the axial direction of the tire (left and right direction in Figures 2 and 3), and the ends on the axial center CL side of the tire are defined by the shoulder main grooves 21. The axial ends of the center block 40, mediate blocks 44 and 45, and shoulder blocks 50 and 51 are positioned substantially symmetrically with respect to the axial center CL of the tire.

[0012] Each of the center block 40, the two mediate blocks 44 and 45, and the two shoulder blocks 50 and 51 is rib-shaped and continuous around the entire circumference of the tire.

[0013] The tire 1 is provided on the axial side of the tread 10 and comprises a sidewall 12 that bulges outward most in the axial direction and a bead 14 that is fixed to the rim of the wheel. The sidewall 12 and bead 14 are formed in an annular shape along the circumferential direction of the tire and constitute the tire sidewall 13. The sidewall 12 extends radially inward from both axial ends of the tread 10.

[0014] Tire 1 is a pneumatic tire filled with air at a predetermined pressure. The tread 10 and sidewall 12 are made of different types of rubber, for example.

[0015] The shoulder blocks 50 and 51, positioned at both axial ends of the tread 10, include a contact end T (Figure 2), which is the outer end of the contact surface in the tire axial direction. Thus, the tread 10 includes a shoulder block 51, provided at the outer end in the tire axial direction and having a contact end T, on one half of the tread 10 (right side in Figures 1 to 3). The shoulder block 51 is defined by a shoulder main groove 21, which is the main groove in the tire circumferential direction, at its central end in the tire axial direction. The tread 10 also includes a shoulder block 50, provided at the outer end in the tire axial direction and having a contact end T, on the other half of the tread 10 (left side in Figures 1 to 3). The shoulder block 50 is defined by a shoulder main groove 21, which is the main groove in the tire circumferential direction, at its central end in the tire axial direction.

[0016] The axial ends of the shoulder blocks 50 and 51 extend outward in the axial direction of the tire from the contact end T, and are gently curved inward in the radial direction of the tire so that their outer surface is convex outward. The portion of the shoulder block 50 that extends outward in the axial direction of the tire from the contact end T is called a buttress.

[0017] "Contact point T" refers to the axial ends of the tire's contact area with a flat road surface when an unused tire 1 is mounted on a standard rim, inflated to the standard internal pressure, and subjected to a load of 70% of the standard load at the standard internal pressure.

[0018] Here, "standard rim" refers to the rim defined by the tire standard, which is "standard rim" for JATMA, "Design Rim" for TRA, and "Measuring Rim" for 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. "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.

[0019] The tire 1 comprises a carcass 15, a belt 16, and an inner liner 17. The carcass 15 is a cord layer covered with rubber, forming the skeleton of the tire 1 that can withstand loads, impacts, air pressure, etc. The belt 16 is a reinforcing band placed between the rubber that makes up the tread 10 and the carcass 15. The belt 16 tightens the carcass 15 tightly, increasing the rigidity of the tire 1. The inner liner 17 is a rubber layer provided on the inner circumferential surface of the carcass 15, and maintains the air pressure of the tire 1. The bead 14 also has a bead core 14a and a bead filler 14b.

[0020] The tread 10 of the tire 1 according to the embodiment has a substantially line-symmetric configuration with respect to the tire axial center CL in the two axially opposite halves, excluding the sipes and slits of each block. Further, in the two axially opposite halves of the tread 10, the circumferential sipes 53 to be described later provided in the shoulder blocks 50, 51, the axial sipes 55, the slits 60, and the outer grooves 47 and inner sipes 49 to be described later provided in the mediate blocks 44, 45 differ in position in the tire circumferential direction, but have the same basic configuration in the two axially opposite halves. Therefore, in the following, regarding the shoulder blocks 50, 51, the mediate blocks 44, 45, the center main groove 20, and the shoulder main groove 21, the description will focus on the configurations of the shoulder block 51, the mediate block 45, the center main groove 20, and the shoulder main groove 21 in the half on one side in the tire axial direction (the right side in FIGS. 1 to 3).

[0021] In the embodiment, in the half on one side in the tire axial direction, a plurality of circumferential sipes 53 extending in the tire circumferential direction are formed at predetermined positions in the tire axial direction of the shoulder block 51. The plurality of circumferential sipes 53 are formed spaced apart from each other in the tire circumferential direction. The position of each circumferential sipe 53 in the tire axial direction is at a position that is 50% or more and 90% or less of the length from the shoulder main groove 21 with respect to the length L2 (FIG. 3) from the shoulder main groove 21 to the ground contact end T. Thereby, the tire axial length L1 from the shoulder main groove 21 to the circumferential sipe 53 satisfies L2×(50 / 100) to L2×(90 / 100). The width of each circumferential sipe 53 is, for example, 1 mm or less. By forming such circumferential sipes 53, CFmax can be reduced by a means different from the grooves outside the ground contact end.

[0022] Furthermore, in the embodiment, a plurality of slits 60 extending substantially in the tire axial direction are formed at a plurality of positions in the tire circumferential direction of the shoulder block 51 on one half side in the tire axial direction. The slits 60 correspond to shoulder-side slits. The tire axially inner end of each slit 60 terminates within the shoulder block 51 and does not open to the wall surface of the shoulder block 51. The width of each slit 60 is greater than the widths of the circumferential sipes 53 and the axial sipes 55 described later. By forming such slits 60, the drainage performance toward the tire axially outer side can be improved.

[0023] Furthermore, each circumferential sipe 53 is formed between two slits 60 adjacent to each other in the circumferential direction in the shoulder block 51. The length La (length in the tire circumferential direction) of each circumferential sipe 53 is 50% or more and 90% or less of the length Lb at the same position as the circumferential sipe 53 in the tire axial direction (left-right direction in Fig. 3) between the two slits 60 where the circumferential sipe 53 is interposed. If the length La of the circumferential sipe 53 is less than 50% of the length Lb between the slits 60, the effect of reducing CFmax by providing the circumferential sipe 53 becomes small. On the other hand, if the length La of the circumferential sipe 53 is greater than 90% of the length Lb between the slits 60, the rigidity of the central portion of the corresponding shoulder block 51 decreases, making it impossible to ensure satisfactory steering stability.

[0024] Furthermore, the end of each slit 60 on the shoulder main groove 21 side is spaced apart from the shoulder main groove 21. The end of each slit 60 on the shoulder main groove 21 side is located at a tire axial position that is 15% or more and 50% or less of the length L2 from the shoulder main groove 21 to the ground contact end T, measured from the shoulder main groove. Thereby, the tire axial length L3 from the shoulder main groove 21 to the end of the slit 60 on the shoulder main groove 21 side satisfies L2×(15 / 100) to L2×(50 / 100). For this reason, the slits 60 do not reach the shoulder main groove 21, that is, do not communicate with the shoulder main groove 21.

[0025] By forming such slits 60 in the shoulder block 51, the rigidity near the shoulder main groove 21 in the shoulder block 51 can be increased while ensuring good drainage. This promotes buckling that occurs near the shoulder main groove 21 in the shoulder block 51. As a result, the coefficient of friction in the shoulder block 51 decreases, and consequently, a further reduction in CFmax can be achieved. This will be explained in more detail later.

[0026] If the axial length L3 of the tire from the shoulder main groove 21 to the shoulder main groove 21 side end of the slit 60 is less than 15% of the length L2 from the shoulder main groove 21 to the contact end T, the effect of increasing the rigidity of the shoulder block 51 near the shoulder main groove 21 will be eliminated or negligible. If the axial length L3 of the tire from the shoulder main groove 21 to the shoulder main groove 21 side end of the slit 60 is greater than 50% of the length L2, good drainage cannot be ensured.

[0027] The shoulder block 51 includes an axial sipe 55 that extends from the shoulder main groove 21 in the tire axial direction, between two adjacent slits 60 in the circumferential direction of the tire, and is narrower than the slits 60, intersecting the circumferential sipe 53 in a roughly cross shape. The length L4 of the axial sipe 55 is 110% or more of the length L2 from the shoulder main groove 21 to the contact point T. This ensures that the length L4 satisfies L2 × (110 / 100) or more. Therefore, as described later, it is possible to further reduce CFmax while ensuring good drainage. If the length L4 is less than L2 × (110 / 100), the axial sipe 55 may or may not touch the contact point T depending on the steering angle, resulting in unstable vehicle behavior.

[0028] Furthermore, in this embodiment, the mediate block 45 includes a circumferential sub-groove 46 on one half of the tire axial side. The circumferential sub-groove 46 is formed to extend in the circumferential direction of the tire at a predetermined position in the tire axial direction of the mediate block 45. For example, the circumferential sub-groove 46 is formed to extend in the circumferential direction of the tire at a position slightly off-center in the tire axial direction from the center of the mediate block 45 in the tire axial direction. The width of the circumferential sub-groove 46 is smaller than the width of the center main groove 20 and the shoulder main groove 21.

[0029] Multiple small outer blocks 48 are provided on the tire axial side, which is the first side in the tire axial direction, from the circumferential sub-grooves 46 of the mediate block 45. The multiple small outer blocks 48 are divided in the tire circumferential direction by multiple outer grooves 47 that extend in a direction inclined with respect to the tire axial direction. The outer grooves 47 correspond to the mediate side slits.

[0030] Furthermore, multiple large inner blocks 62 are provided on the axial side of the tire, which is the second side in the tire axial direction, from the circumferential sub-grooves 46 of the mediate block 45. The multiple large inner blocks 62 are divided in the circumferential direction of the tire by multiple thin, linear inner sipes 49, which are inner grooves that extend in a direction inclined with respect to the tire axial direction. Each large inner block 62 has a larger contact area than each small outer block 48. Moreover, the total contact area of ​​the multiple small outer blocks 48 is 30-50% of the contact area of ​​the mediate block 45.

[0031] As a result, during steady-state driving with little to no steering angle, the rigidity of the inner large block 62 of the mediate block 45 can be made higher than that of the outer small block 48, thereby increasing the rigidity of the tire's contact patch center and improving handling performance during steady-state driving. In addition, with the mediate block 45, buckling at large steering angles during cornering is less likely to occur than with the shoulder block 51. On the other hand, since each inner large block 62 has a larger contact area than each outer small block 48, the contact area of ​​the outer small block 48 can be reduced, increasing the contact pressure and thus lowering the coefficient of friction at the tire's contact edge. In particular, since the total contact area of ​​the multiple outer small blocks 48 is 50% or less of the contact area of ​​each mediate block 44, 45, it is easier to increase the contact pressure of the outer small blocks 48. This makes it easier to further reduce the coefficient of friction on the outer side of the tire's contact surface. As a result, CFmax can be reduced.

[0032] Furthermore, since the total contact area of ​​the multiple outer small blocks 48 is 30-50% of the contact area of ​​the mediate block 45, good wear performance of the outer small blocks 48 and good motion performance during steady-state driving can be ensured. If the total contact area of ​​the multiple outer small blocks 48 is less than 30% of the contact area of ​​the mediate block 45, the contact pressure of the outer small blocks 48 becomes excessively high, and the coefficient of friction at the contact point decreases excessively, making it difficult to ensure good wear performance. On the other hand, if the total contact area of ​​the multiple outer small blocks 48 is greater than 50% of the contact area of ​​the mediate block 45, the rigidity of the center of the contact point decreases due to the inner large block 62, making it difficult to ensure good motion performance during steady-state driving.

[0033] Furthermore, the width of the inner sipe 49 of the mediate block 45 is smaller than that of the outer groove 47. The width of the inner sipe 49 is 1 mm or less. As a result, the opening of the inner sipe 49 is easily closed when the tire makes contact with the ground. Therefore, it is easier to make the rigidity of the mediate block 45 on the inner side of the tire axial direction (towards the inner large block 62) higher than that of the circumferential sub-groove 46, and even higher than the rigidity on the outer side of the tire axial direction (towards the outer small block 48) higher than that of the circumferential sub-groove 46. This makes it possible to further improve the handling performance during steady-state driving.

[0034] Furthermore, the center block 40 is provided with a plurality of small center blocks 42. The plurality of small center blocks 42 are divided in the circumferential direction of the tire by a plurality of thin, linear center sipes 41 that extend in a direction inclined with respect to the tire axis in the center block 40. The center sipes 41 correspond to the center groove. The contact area of ​​each large inner block 62 is 100-120% of the contact area of ​​each small center block 42.

[0035] This makes it possible to make the contact pressure at the center of the tire's contact patch more uniform, and by suppressing the unevenness of the friction coefficient at the center of the contact patch, unevenness of braking force can be suppressed. As a result, braking performance during steady-state driving can be improved. At this time, the circumferential contact length of the tire's axial center CL where the small center block 42 is located is approximately 110% of the contact length at the tire's axial position where the large inner block 62 is located, and is longer than the contact length at the location of the large inner block 62. Furthermore, during steady-state driving, the contact load on the entire contact area of ​​the tire's axial center CL and the entire contact area at the tire's axial position where the large inner block 62 is located are almost the same. Therefore, in the case of the large inner block 62, by increasing the contact area of ​​each large inner block to compensate for the shorter contact length of the entire contact area at the tire's axial position where the large inner block 62 is located, the difference in contact pressure between each small center block 42 can be reduced or eliminated. From the perspective of making the ground pressure of each center small block 42 and the ground pressure of each inner large block 62 as close to uniform as possible, it is more preferable to make the ground area of ​​each inner large block 62 approximately 110% of the ground area of ​​each center small block 42.

[0036] As described above, the contact surfaces of the center block 40, mediate block 45, and shoulder block 51 are formed with a plurality of thin, linear sipes 41, 49, 53, and 55 that extend approximately in the direction of the tire axis or inclined with respect to the tire axis. Each sipe 41, 49, 53, and 55 enhances the edge effect for scratching snow and ice, and has the effect of achieving good braking and driving performance and handling stability on snowy and icy road surfaces.

[0037] Furthermore, in this embodiment, the ratio of the volume of the shoulder main groove 21 to the volume of the center main groove 20 is 90-100%. This allows for improved noise performance while maintaining the drainage performance of the center main groove 20.

[0038] Furthermore, when the sum of the widths of the two center main grooves 20 and the widths of the two shoulder main grooves 21 is defined as the total main groove width Wz, the ratio of the total main groove width Wz to the grounding width Lt between the two grounding ends T is 20% to 25%. If the ratio of the total main groove width Wz to the grounding width Lt is less than 20%, drainage performance deteriorates. On the other hand, if the ratio of the total main groove width Wz to the grounding width Lt is greater than 50%, the effect of suppressing the deterioration of noise performance becomes smaller.

[0039] Furthermore, since the shoulder main groove 21 side end of the slit 60 formed in each shoulder block 51 is separated from the shoulder main groove 21, it is possible to prevent the transmission of sound from the shoulder main groove 21 to the slit 60 and to improve the drainage performance of the tire's contact edge.

[0040] Furthermore, the outer groove 47 described above is formed on the tire axial side of the mediate block 45. The inner sipe 49 described above is formed on the tire axial side of the mediate block 45. The groove width of the inner sipe 49 is 1 mm or less, which is smaller than the groove width of the outer groove 47. In addition, the length L6 of each inner sipe 49 is 50% or more of the tire axial length L5 of the mediate block 45.

[0041] As described above, an inner sipe 49 with a narrow groove width is formed on the inner side of the mediate block 45 in the tire axial direction. As a result, the inner sipe 49 is closed when the formed portion of the mediate block 44, 45 makes contact with the ground, thereby suppressing sound propagation between the center main groove 20 and the shoulder main groove 21. In addition, one end of the inner sipe 49 communicates with only one of the main grooves on both sides of the mediate block 44, 45, which are the center main groove 20 and the shoulder main groove 21. The other end of the inner sipe 49 is positioned to abut against the outer groove 47 on the outer side of the mediate block 44, 45 in the tire axial direction. This improves noise performance by suppressing sound propagation between the main grooves 20 and 21 while increasing drainage towards the shoulder main groove.

[0042] If the length L6 of the inner sipe 49 is less than 50% of the axial length L5 of the mediate block 45, the rigidity of the inner large block 62 decreases. The inner sipe 49 is more likely to close up as the rubber deforms when the tire contacts the road surface. On the other hand, if the rigidity of the inner large block 62 is low, the rubber is more likely to deform excessively when external forces are applied to the tire during cornering, etc., causing the inner sipe 49 to spread more easily, resulting in sound propagation through the inner sipe 49 and reducing the effectiveness of suppressing the deterioration of noise performance. On the other hand, if the groove width of the inner sipe 49 is greater than 1 mm, the effect of suppressing sound propagation between the center main groove 20 and the shoulder main groove 21 decreases.

[0043] Furthermore, the outer grooves 47 formed in each mediate block 45 are formed on the shoulder main groove 21 side, which is axially outward of the tire, and the inner sipes 49 are formed on the center main groove 20 side, which is axially inward of the tire. As a result, the outer grooves 47, which have a wider groove width, are positioned on the shoulder main groove 21 side, making it easier to drain water from the center main groove 20 side of the mediate block 45 to the shoulder main groove 21 side. This improves drainage performance. In particular, if the volume of the center main groove 20 is greater than or equal to the volume of the shoulder main groove 21, the drainage performance of the center main groove 20 tends to decrease. Therefore, forming the outer grooves 47 on the shoulder main groove 21 side and the inner sipes 49 on the center main groove 20 side significantly improves drainage performance. It should be noted that, although drainage performance will decrease, the mediate block 45 may also be configured in which a wide mediate-side slit is formed on the center main groove 20 side, which is axially inward of the tire, and a narrow sipe is formed on the shoulder main groove 21 side, which is axially outward of the tire. This also improves noise performance. In this case, the inner side of the tire axial direction becomes the first side in the tire axial direction, and the outer side of the tire axial direction becomes the second side in the tire axial direction.

[0044] Furthermore, in this embodiment, the tire circumferential positions of the slits 60 and axial sipes 55 of the shoulder blocks 50 and 51 are different for the two shoulder blocks 50 and 51. Also, the slit 60 of one shoulder block 50 and the axial sipe 55 of the other shoulder block 51 are in approximately the same position in the tire circumferential direction, and the axial sipe 55 of one shoulder block 50 and the slit 60 of the other shoulder block 51 are in approximately the same position in the tire circumferential direction.

[0045] Furthermore, each outer groove 47 and each inner sipe 49 of each mediate block 44, 45, and each center sipe 41 of the center block 40 are inclined toward one side in the tire axial direction (right side in Figures 2 and 3) toward the same side in the tire circumferential direction, and at approximately the same angle.

[0046] Furthermore, in each mediate block 44, 45, the number of outer grooves 47 is twice the number of inner sipes 49. Every other outer groove 47 and inner sipe 49 are arranged on the same straight line in the circumferential direction of the tire. This improves drainage between the shoulder main groove 21 and the center main groove 20. In addition, the circumferential positions of the outer grooves 47 and inner sipes 49 of the mediate blocks 44, 45 are different in the two mediate blocks 44, 45.

[0047] According to tire 1 described above, circumferential sub-grooves are formed in the mediate block. In addition, multiple outer small blocks are provided outward in the tire axial direction from the circumferential sub-grooves of the mediate block. Multiple inner large blocks, which have a larger contact area than the outer small blocks, are provided inward in the tire axial direction from the circumferential sub-grooves of the mediate block. This makes it possible to improve the handling performance and braking performance during steady-state driving with no steering angle or a small steering angle, and also to increase the contact pressure of the outer small blocks, thereby reducing the coefficient of friction on the outside of the tire's contact surface. In particular, since the total contact area of ​​the multiple outer small blocks 48 is 50% or less of the contact area of ​​each mediate block 44, 45, it is easier to increase the contact pressure of the outer small blocks 48, which makes it easier to further reduce the coefficient of friction on the outside of the tire's contact surface. This makes it possible to reduce CFmax.

[0048] As a result, even in vehicles with a high center of gravity, excessive grip from tire 1 during cornering can be prevented, thus preventing the vehicle from losing balance significantly. Furthermore, since CFmax can be reduced by a means different from grooves outside the contact patch, the groove does not engage with the contact patch in accordance with the steering angle, thereby stabilizing the vehicle's behavior.

[0049] Using Figure 4, we will explain, with reference to the ground pressure distribution, that the ground pressure can be increased by reducing the contact area of ​​the outer small block on the outer side of the tire axis in the mediate block. Figure 4 shows the ground pressure distribution of the tread during a large steering angle turn in a configuration in which the tread has multiple blocks 40, 44, 45, 50, and 51, similar to tire 1 in Figure 1. In Figure 4, the areas where the contact pressure of multiple blocks 40, 44, 45, 50, and 51 is high at the contact point of the tire, and the contact area increases from the shoulder block 50 on the inside of the turn to the shoulder block 51 on the outside of the turn. The direction the tire is facing during straight-line driving is shown in the vertical direction, and the direction of the tire axis at that time is shown in the horizontal direction. The area with the highest ground pressure is shown as a black-filled area, and the ground pressure decreases in the order of high concentration areas in sandy areas, medium concentration areas, and low concentration areas, with the uncolored area showing the area with the lowest ground pressure. In Figure 4, the ground pressure distribution is calculated assuming that there are no sipes, circumferential sub-grooves, or slits in each block 40, 44, 45, 50, and 51.

[0050] As can be seen from the ground pressure distribution diagram in Figure 4, during turning, the area with the highest ground pressure is widened on the outer shoulder block 51. Furthermore, on the outer shoulder block 51, the line indicating the contact area at the shoulder main groove 21 side end is curved inward towards the shoulder block 51. The reason for this phenomenon is thought to be that buckling occurs near the shoulder main groove 21 of the shoulder block 51, compressing the inside of the belt 16, which worsens the ground contact performance.

[0051] On the other hand, in the mediate block, the load applied by the vehicle is smaller than that of the shoulder block, so buckling is less likely to occur even near the shoulder main groove 21, as can be seen from the contact pressure distribution in Figure 4. As a result, in the mediate block, the contact area of ​​the outer small block on the outer side of the tire axial direction is made smaller than the contact area of ​​the inner large block on the inner side of the tire axial direction, thereby increasing the contact pressure on the outer side of the tire's contact surface. This reduces the coefficient of friction on the outer side of the tire's contact surface, thus reducing CFmax.

[0052] Furthermore, in this embodiment, the total contact area of ​​the multiple outer small blocks 48 is 30-50% of the contact area of ​​each mediate block 44, 45, thus ensuring good wear performance of the outer small blocks 48 and good motion performance during steady-state driving.

[0053] Furthermore, the center block 40 is provided with multiple small center blocks 42, which are divided in the circumferential direction of the tire by multiple center sipes 41. The contact area of ​​each large inner block 62 is 100-120% of the contact area of ​​each small center block 42. This makes it possible to make the contact pressure at the center of the tire's contact patch more uniform and suppresses unevenness in braking force at the center of the contact patch. As a result, braking performance during steady-state driving can be improved.

[0054] Next, the results of the first and second simulations conducted by the inventors to confirm the effects of the embodiments will be described. In each simulation, the effect of the ratio of the contact area of ​​the multiple outer small blocks 48 to the total contact area of ​​the mediate blocks 44 and 45 on CFmax was confirmed using the tires of the examples and comparative examples.

[0055] First, in the first simulation, Examples 1-3 and Comparative Examples 1-2 were used. Examples 1-3 have the same configuration as the embodiments shown in Figures 1-3. In Examples 1-3, the ratio of the contact area of ​​the multiple outer small blocks 48 to the contact area of ​​the mediate blocks 44, 45 was varied to 50%, 40%, and 30%, respectively.

[0056] In Comparative Example 1, the ratio of the contact area of ​​the multiple outer subblocks to the contact area of ​​the mediate block was set to 60%, while in Comparative Example 2, it was set to 20%. In Comparative Examples 1 and 2, the other configurations were the same as in Example 1.

[0057] Table 1 shows the simulation results for CFmax, wear performance, and motion performance during steady-state driving in Examples 1-3 and Comparative Examples 1-2. In Table 1, the values ​​in the "Mediate Block Medium Outer Small Block" column represent the ratio (%) of the contact area of ​​multiple outer small blocks 48 to the contact area of ​​mediate blocks 44 and 45.

[0058] [Table 1]

[0059] Table 1 shows the relative values ​​for Examples 1-3 and Comparative Example 2, with the CFmax of Comparative Example 1 set to a baseline value of 100, as a simulation result. In Table 1, the simulation results in the "Wear Performance" column show that A has the best wear performance, followed by B and C in decreasing order of wear performance, with C indicating insufficient wear performance. In Table 1, the simulation results in the "Motor Performance" column show that A has the best motor performance during steady-state driving, followed by B and C in decreasing order of motor performance, with C indicating insufficient motor performance during steady-state driving.

[0060] As can be seen from the simulation results in Table 1, in the case of Comparative Example 1, the ratio of the contact area of ​​the multiple outer subblocks to the contact area of ​​the mediate block was high at 60%, so the CFmax reduction effect could not be obtained, and furthermore, the motion performance during steady-state driving was insufficient. On the other hand, in Comparative Example 1, good wear performance was ensured.

[0061] In Comparative Example 2, the ratio of the contact area of ​​the multiple outer subblocks to the contact area of ​​the mediate block was low at 20%, thus achieving a reduction in CFmax and ensuring good dynamic performance during steady-state driving. On the other hand, Comparative Example 2 exhibited insufficient wear performance.

[0062] On the other hand, in Examples 1 to 3, the ratio of the contact area of ​​the multiple outer small blocks 48 to the contact area of ​​the mediate blocks 44 and 45 is within an appropriate range of 30 to 50%, so it was confirmed that CFmax can be reduced while ensuring good wear performance and good motion performance during steady-state driving. This confirmed the effects of the present invention.

[0063] In the second simulation, Examples 4-6 and Comparative Examples 3-4 were used. Examples 4-6 have the same configuration as the embodiments shown in Figures 1-3. In Examples 4-6, the ratio of the contact area of ​​the multiple outer small blocks 48 to the contact area of ​​the mediate blocks 44, 45 was varied to 45%, 40%, and 34%. In Examples 4-6, the contact area of ​​each inner large block 62 was varied to 100%, 110%, and 120% of the contact area of ​​each center small block 42.

[0064] In Comparative Example 3, the ratio of the contact area of ​​the multiple outer small blocks to the contact area of ​​the mediate block was set to 51%. In Comparative Example 3, the contact area of ​​each inner large block was set to 90% of the contact area of ​​each center small block.

[0065] In Comparative Example 4, the ratio of the contact area of ​​the multiple outer small blocks to the contact area of ​​the mediate block was set to 29%. In Comparative Example 4, the contact area of ​​each inner large block was set to 130% of the contact area of ​​each center small block. In Comparative Examples 3 and 4, the other configurations were the same as in Example 1.

[0066] Table 2 shows the simulation results of CFmax and braking performance for Examples 4-6 and Comparative Examples 3-4. The meaning of the values ​​in the "Mediate Block Middle Outer Small Block Ratio" column in Table 2 is the same as in Table 1. In Table 2, the values ​​in the "Center Block," "Mediate Block Inner Large Block," and "Mediate Block Outer Small Block" columns represent the relative values ​​of the contact area of ​​each center small block 42, each inner large block 62, and each outer small block 48 in Examples 4-6 and Comparative Examples 3-4, respectively, with the contact area of ​​each center small block 42 set to a baseline value of 100.

[0067] [Table 2]

[0068] Table 2 shows the relative values ​​for Examples 4-6 and Comparative Example 4, with the CFmax of Comparative Example 3 set to a baseline value of 100, as a simulation result. In Table 2, the simulation results show that in the braking performance column, A has the best braking performance during steady-state driving, while C has insufficient braking performance during steady-state driving.

[0069] As can be seen from the simulation results in Table 2, in Comparative Example 3, the ratio of the contact area of ​​the multiple outer small blocks to the contact area of ​​the mediate block was high at 51%, so the CFmax reduction effect was not obtained. Furthermore, in Comparative Example 3, the contact area of ​​each inner large block was small at 90% compared to the contact area of ​​each center small block, so uneven braking force was likely to occur in the center of the tire's contact area, resulting in insufficient braking performance during steady-state driving.

[0070] In Comparative Example 4, the ratio of the contact area of ​​the multiple outer small blocks to the contact area of ​​the mediate block was low at 29%, which allowed for a reduction in CFmax. On the other hand, in Comparative Example 4, the contact area of ​​each inner large block was 130% larger than the contact area of ​​each center small block, which made uneven braking force likely to occur in the center of the tire's contact area, resulting in insufficient braking performance during steady-state driving.

[0071] On the other hand, in Examples 4 to 6, the ratio of the contact area of ​​the multiple outer small blocks 48 to the contact area of ​​the mediate blocks 44 and 45 was within an appropriate range of 30 to 50%, thus reducing CFmax. Also, in Examples 4 to 6, the contact area of ​​each inner large block 62 was within an appropriate range of 100 to 120% of the contact area of ​​each center small block 42. As a result, the contact pressure at the center of the tire's contact patch can be made more uniform, which suppresses uneven braking force and ensures good braking performance during steady-state driving.

[0072] In the above embodiment, the case in which each outer groove 47 and each inner sipe 49 of each mediate block 44, 45 extends in a direction inclined with respect to the tire axis direction was described, but they may also be shaped to extend in the direction of the tire axis direction. In addition, in the embodiment, each center slit 60 of the center block 40 may be shaped to extend in the direction of the tire axis direction. [Explanation of Symbols]

[0073] 1 pneumatic tire (tire), 10 tread, 12 sidewall, 13 tire side, 14 bead, 14a bead core, 14b bead filler, 15 carcass, 16 belt, 17 inner liner, 20 center main groove, 21 shoulder main groove, 40 center block, 41 center sipe, 42 center small block, 44, 45 mediate block, 46 circumferential minor groove, 47 outer groove, 48 outer small block, 49 inner sipe, 50, 51 shoulder block, 53 circumferential sipe, 55 axial sipe, 60 slit, 62 inner large block.

Claims

1. The tread includes a center block, a mediate block provided on one side of the center block in the tire axial direction via a center main groove which is a main groove in the tire circumferential direction, and a shoulder block provided on the outer side of the mediate block in the tire axial direction via a shoulder main groove which is a main groove in the tire circumferential direction. The mediate block includes a circumferential sub-groove smaller than the width of the center main groove and the shoulder main groove, a plurality of outer small blocks provided outward in the tire axial direction from the circumferential sub-groove, divided in the tire circumferential direction by the plurality of outer grooves, and a plurality of inner large blocks provided inward in the tire axial direction from the circumferential sub-groove, divided in the tire circumferential direction by the plurality of inner grooves, wherein each of the plurality of inner large blocks has a larger contact area than each of the plurality of outer small blocks. The total contact area of ​​the aforementioned multiple outer subblocks is 30-50% of the contact area of ​​the mediate block. The center block includes a plurality of small center blocks that are divided in the circumferential direction of the tire by a plurality of center grooves. The contact area of ​​each of the aforementioned multiple inner large blocks is 100 to 120% of the contact area of ​​each of the aforementioned multiple center small blocks. Pneumatic tires.

2. Each of the aforementioned plurality of inner grooves is an inner sipe that is narrower in width than the aforementioned plurality of outer grooves. The pneumatic tire according to claim 1.

3. One end of the inner sipe communicates with the center main groove, The other end of the inner sipe is positioned to abut against the outer groove. The pneumatic tire according to claim 2.

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