pneumatic tires

Abstract

In pneumatic tires, specifically those with a V-shaped tread pattern, the aim is to improve handling and braking performance. [Solution] The pneumatic tire includes a tread and has a designated main rotation direction. The tread includes a plurality of blocks 34 demarcated by a plurality of grooves. The plurality of grooves have a plurality of main grooves 20 that extend from the equator towards the contact end and have a greater inclination with respect to the tire axis on the equator side than on the contact end side, and a plurality of sub-grooves 22 that connect adjacent main grooves 20 in the tire circumferential direction or in an inclined direction with respect to the tire circumferential direction. The plurality of blocks 34 are elongated along the extending direction of adjacent main grooves 20. The tread surface 43 of at least some of the blocks 34 is a curved projection having a ridge Tm along the longitudinal direction of the block 34.

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] In the tread of a pneumatic tire, there may be provided a plurality of blocks partitioned by a plurality of grooves. Also, in some cases, the main rotation direction of the tire is specified, and the tire has a so-called V-shaped pattern in which the inclination of the main groove of the tread with respect to the tire axis direction is larger on the equator side than on the ground contact end side.

[0003] Patent Document 1 describes that in a pneumatic tire, each of a plurality of lands extending in the tire circumferential direction of the tread and separated in the tire axis direction has a protruding portion that protrudes in a substantially arc shape from a profile line to the outside in the tire radial direction in the tire meridian cross section, and the apex of the protruding portion is disposed outside the vehicle width direction from the center in the tire axis direction of the land.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a tire having the above V-shaped pattern of the tread, it is required to further improve the motion performance and braking performance regardless of changes in the road surface and the collapse of the blocks.

[0006] In a tire having the above V-shaped pattern, when a protruding portion with an apex disposed outside the vehicle width direction is provided on the block as in the configuration described in Patent Document 1, depending on the position of the block, the protruding portion does not have an appropriate shape corresponding to the collapse of the block, and there is room for improvement in terms of improving the motion performance and braking performance.

Means for Solving the Problems

[0007] The pneumatic tire according to the present invention is a pneumatic tire having a tread, wherein the main direction of rotation of the tire is specified, and the tread includes a plurality of blocks partitioned by a plurality of grooves, the plurality of grooves extending from the equator side toward the contact end side, having a plurality of main grooves whose inclination with respect to the tire axis is greater on the equator side than on the contact end side, and sub-grooves connecting adjacent main grooves in the tire circumferential direction or in an inclined direction toward the tire circumferential direction, the plurality of blocks being elongated along the extending direction of adjacent main grooves, and the tread surface of at least some of the blocks being a curved projection having a ridge line along the longitudinal direction of the block. [Effects of the Invention]

[0008] According to the pneumatic tire of the present invention, the handling performance and braking performance can be improved in a tire having a V-shaped tread pattern. [Brief explanation of the drawing]

[0009] [Figure 1] This is a view from below of a pneumatic tire of the first embodiment, which is an example of an embodiment. [Figure 2] This is an enlarged view of section A in Figure 1. [Figure 3] Figure 1 is a schematic diagram showing the shoulder block, mediate block, and center block as viewed from the rear side in the main rotation direction α of the tire. [Figure 4] Figure 3 is an enlarged perspective view of the mediate block. [Figure 5] Figure 2 is a cross-sectional view of BB. [Figure 6] This is a cross-sectional view of a pneumatic tire in another embodiment, taken along the width direction of the shoulder block. [Figure 7] Figure 6 is a cross-sectional perspective view of the shoulder block as seen from the outer side in the radial direction of the tire. [Figure 8]In the shoulder block of the first embodiment of a pneumatic tire without sipes, (a) is a schematic diagram showing the state in which the shoulder block is in contact with the ground when the tire is stopped, and (b) is a schematic diagram showing the state in which the shoulder block is tilted when the vehicle is braking. [Figure 9] This figure corresponds to the enlarged view of the area near the contact point in Figure 8(b) of a pneumatic tire, which is another embodiment of the present invention. [Figure 10] This figure shows the results of a test conducted to determine the degree of deviation of the tread ridge line from the center in the block width direction in another embodiment, and shows the results of measuring the portion of the contact area of ​​the comparative example pneumatic tire where the contact pressure exceeds a predetermined value at the initial braking stage (a) and the final braking stage (b). [Figure 11] In another embodiment, this figure shows the results of a test to determine the degree of deviation of the tread ridge lines from the center in the block width direction, and is a figure showing the measurement results of the time change in the ratio of the contact area relative to the initial braking state for the contact area of ​​the pneumatic tire of the comparative example where the contact pressure of the contact area is above a predetermined value. [Figure 12] This figure shows a cross-section of a pneumatic tire in another embodiment, with the center block, mediate block, and shoulder block aligned along the width direction of the blocks, with the positions of both ends in the width direction of the blocks coinciding. [Figure 13] This is a cross-sectional perspective view of a pneumatic tire according to another embodiment, including a cross-section taken along the width direction of the shoulder block. [Figure 14] This figure corresponds to Figure 9 of the shoulder block shown in Figure 13. [Figure 15] This is a cross-sectional perspective view of a pneumatic tire according to another embodiment, including a cross-section taken along the width direction of the shoulder block. [Figure 16] This figure corresponds to Figure 9 of the shoulder block shown in Figure 15. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiments described below are merely examples, and the present invention is not limited to the following embodiments. Also, forms formed by selectively combining the components of the embodiments described below are included in the present invention.

[0011] FIG. 1 is a view seen from below of a pneumatic tire 1 according to a first embodiment which is an example of an embodiment. As shown in FIG. 1, the pneumatic tire 1 includes a tread 10 which is a portion that contacts the road surface. The tread 10 has a so-called V-shaped pattern having a plurality of main grooves 20, 21 that extend from the equator CL side toward the grounding ends E1, E2 sides and have a larger inclination angle with respect to the tire axial direction (the left-right direction in FIG. 1) on the equator CL side than on the grounding ends E1, E2 sides. Further, the tread 10 has a plurality of sub-grooves 22 that connect adjacent main grooves 20, 21 in the tire circumferential direction or in a direction inclined with respect to the tire circumferential direction, and a plurality of blocks 28 partitioned by the plurality of main grooves 20, 21 and the plurality of sub-grooves 22, 23 and separated in both the tire circumferential direction and the tire axial direction. Hereinafter, the pneumatic tire 1 will be referred to as the tire 1.

[0012] The plurality of blocks 28 are formed along the main grooves 20, 21 and have blocks 30 on the vehicle outer side with respect to the tire equator and blocks 31 on the vehicle inner side with respect to the tire equator. The main groove 20 and the block 30 extend from the equator CL side toward the grounding end E1 side, and the main groove 21 and the block 31 extend from the equator CL side toward the grounding end E2 side.

[0013] The equator CL means a line along the tire circumferential direction passing through the center in the tire axial direction of the tread 10 (a position equidistant from the grounding ends E1, E2). In this specification, the grounding ends E1, E2 are defined as both ends in the tire axial direction of the region that contacts the flat road surface when a predetermined load is applied in a state where an unused pneumatic tire 1 is mounted on a regular rim and filled with air to a regular internal pressure. In the case of a passenger car tire, the predetermined load is a load corresponding to 88% of the regular load.

[0014] Here, the "regular rim" is the rim defined by the tire standard. In the case of JATMA, it is the "standard rim"; in the case of TRA and ETRTO, it is the "Measuring Rim". The "regular internal pressure" is the "maximum air pressure" in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO. The regular internal pressure is usually 180 kPa for passenger car tires, but 220 kPa for tires marked as Extra Load or Reinforced. The "regular load" is the "maximum load capacity" in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "LOAD CAPACITY" in the case of ETRTO. In the case of tires for racing carts, the regular load is 392 N.

[0015] Tire 1 is a directional tire with a specified main rotation direction. In FIG. 1, an arrow α indicating the main rotation direction of Tire 1 is illustrated. In this specification, the "main rotation direction" of a tire means the rotation direction when the vehicle on which Tire 1 is mounted moves forward. Since FIG. 1 is a view of Tire 1 seen from below, the tire main rotation direction α and the vehicle traveling direction β are in opposite directions. The inflated Tire 1 preferably has a display for indicating the mounting direction with respect to the vehicle. On the side surface of the inflated Tire 1, for example, at least one of a character and an arrow indicating the main rotation direction is provided.

[0016] The tread 10 has a tread pattern in which the blocks 30, 31 are arranged in a staggered manner along the tire circumferential direction. Most of the blocks 30, 31 are arranged separately on the left and right of the tread 10 with the equator CL in between.

[0017] The blocks 30 are formed along the main grooves 20 and are arranged alternately with the main grooves 20 in the circumferential direction of the tire. The blocks 30 include a center block 32 located on the equator CL side, a shoulder block 34 located on the contact end E1 side, and a mediate block 33 sandwiched between the center block 32 and the shoulder block 34. Thus, the blocks 30 have the center block 32, the mediate block 33, and the shoulder block 34 arranged in order from the equator CL side toward the tire axial outward toward the contact end E1 side. Between the center block 32 and the mediate block 33, and between the mediate block 33 and the shoulder block 34, sub-grooves 22 are formed, connecting two main grooves 20 in the circumferential direction of the tire or in an inclined direction toward the circumferential direction of the tire. The sub-grooves 22 divide the blocks 30 into three blocks.

[0018] The blocks 31 are formed along the main grooves 21 and are arranged alternately with the main grooves 21 in the circumferential direction of the tire. The blocks 31 include a center block 35 located on the equator CL side, a shoulder block 37 located on the contact end E2 side, and a mediate block 36 sandwiched between the center block 35 and the shoulder block 37. Thus, the blocks 31 have the center block 35, the mediate block 36, and the shoulder block 37 arranged in order from the equator CL side toward the tire axial outward toward the contact end E2 side. Between the center block 35 and the mediate block 36, and between the mediate block 36 and the shoulder block 37, sub-grooves 23 are formed, connecting two main grooves 21 in the circumferential direction of the tire or in an inclined direction toward the circumferential direction of the tire. The sub-grooves 23 divide the blocks 31 into three blocks.

[0019] As described above, the multiple blocks 30, 31 are separated in both the tire circumferential direction and the tire axial direction by being partitioned by multiple main grooves 20, 21 and multiple sub-grooves 22, 23. The multiple blocks 30, 31 are elongated along the direction of extension of adjacent main grooves 20, 21. Therefore, the direction along adjacent main grooves 20, 21 is the block longitudinal direction for each block 30, 31, and the direction perpendicular to the block longitudinal direction is the block width direction.

[0020] The tire 1 comprises a pair of sidewalls that bulge outward in the tire axial direction and a pair of beads. The beads are the portion that is fixed to the rim of the wheel and have a bead core and a bead filler. The sidewalls and beads are formed in an annular shape along the tire circumferential direction and form the side surface of the pneumatic tire 1. The sidewalls extend radially from both ends of the tread 10 in the tire axial direction.

[0021] The tread pattern of tire 1 will be described in detail below. The main grooves 20 are formed at arbitrary intervals in the circumferential direction of the tire. Similarly, the main grooves 21 are formed at arbitrary intervals in the circumferential direction of the tire. The tread 10 has a tread pattern in which most of the main grooves 20 and blocks 30 are located on the side of the equator CL towards the contact edge E1 (the left side of the tread 10), and most of the main grooves 21 and blocks 31 are located on the side of the equator CL towards the contact edge E2 (the right side of the tread 10). Blocks are portions that protrude outward in the radial direction of the tire.

[0022] In the tread 10, center blocks 32 and 35 are arranged alternately along the tire's circumferential direction, centered in the axial center of the tire. Furthermore, center blocks 32 and 35 are arranged in a staggered pattern along the equator CL.

[0023] The tread pattern of this embodiment is a pattern in which, in a plan view, blocks 30 and 31 are arranged symmetrically on the left and right sides, offset by a predetermined pitch in the tire circumferential direction with respect to the equator CL. The shape of block 30 is the same as the shape of block 31 when it is inverted with respect to the equator CL (the same applies to the main grooves 20 and 21). If block 31, which has been inverted at the equator CL, is slid in the tire circumferential direction, it will coincide with block 30. The tread pattern of this embodiment has good left-right balance and is effective in improving handling stability.

[0024] The main groove 20 and block 30 have a plan view shape that is curved so as to be convex toward the rear in the main rotation direction α of the tire. Similarly, the main groove 21 and block 31 also have a plan view shape that is curved so as to be convex toward the rear in the main rotation direction α of the tire. The main grooves 20, 21 and blocks 30, 31 are inclined with respect to the tire axis direction so that they are gradually located toward the rear in the main rotation direction α of the tire, starting from the axial center side of the pneumatic tire 1 toward both sides in the axis direction.

[0025] As described above, the main grooves 20 and 21 have a greater angle of inclination with respect to the tire axis on the equator CL side than on the contact end E1 and E2 side. In other words, the main grooves 20 and 21 gradually become more aligned with the tire axis as they move from the equator CL side toward the contact end E1 and E2, and the angle of inclination with respect to the tire axis becomes gentler. The angle of inclination of the main grooves 20 and 21 with respect to the tire axis is, for example, 20° to 50° or 25° to 40° on the equator CL side.

[0026] The main groove 20 connects to the main groove 21 near the equator CL. The main groove 20 extends from the intersection with the main groove 21 toward the contact end E1 and extends beyond the contact end E1 to the left annular side rib (not shown). The main groove 21 extends from the intersection with the main groove 20 near the equator CL toward the contact end E2 and extends beyond the contact end E2 to the right annular side rib (not shown). Each side rib is formed at its respective end in the tire axial direction between the contact ends E1, E2 of the tread 10 and the part of the sidewall 11 that protrudes most outward in the tire axial direction. The side ribs protrude outward in the tire axial direction and are formed in an annular shape along the tire circumferential direction. The side ribs may be omitted.

[0027] The width of the main grooves 20 and 21 may be constant along their entire length, but in this embodiment, it gradually increases from the equator CL side toward the ground contact ends E1 and E2. The width of the main grooves 20 and 21 may be maximum, for example, at or near the ground contact ends E1 and E2, or at or near the intersection with the secondary grooves 22 and 23. In this case, drainage performance is improved, and the snow column shear force that grips and compacts the snow is also improved, resulting in good snow performance. The main grooves 20 and 21 are formed to the same depth, for example.

[0028] The sub-grooves 22 and 23 are narrower in width (maximum width) than the main grooves 20 and 21. The sub-groove 22 extends in the circumferential direction of the tire or in a direction inclined with respect to the circumferential direction of the tire, dividing the block 30 and connecting adjacent main grooves 20. In the example shown in Figure 1, the sub-groove 22 is inclined with respect to the circumferential direction of the tire so as it moves gradually away from the contact edge E1 from the front to the rear in the main rotation direction α of the tire. Similarly, the sub-groove 23 divides the block 31 and connects adjacent main grooves 21, and is inclined with respect to the circumferential direction of the tire so as it moves gradually away from the contact edge E2 from the front to the rear in the main rotation direction α of the tire. The sub-grooves 22 and 23 may be shallower or deeper than the main grooves 20 and 21, but it is preferable that they be formed to the same depth as the main grooves 20 and 21. In this case, compared to when the groove depth changes, the water flow for drainage is not disturbed, thus improving drainage performance.

[0029] Each block 32, 33, 34, 35, 36, 37 may have a slit formed along the main grooves 20, 21. The slit may terminate within each block 32, 33, 34, 35, 36, 37 without dividing the block. This increases the edge area and improves the snow performance of tire 1. The slit may also penetrate each block 30, 31. In this case, it is possible to improve the snow performance and drainage performance of tire 1.

[0030] Furthermore, within the tread surface of each block 32, 33, 34, 35, 36, 37, a sipe 40 is formed that passes through the middle of the tire's circumferential direction and has a maximum depth shallower than the maximum depth of the multiple main grooves 20, 21 and sub-grooves 22, 23. The maximum depth of each sipe 40 is, for example, 40% to 95% of the maximum depth of the main grooves 20, 21. The sipes 40 formed on the center blocks 32, 35 and mediate blocks 33, 36 are aligned along the longitudinal direction of each block so as to reach two adjacent sub-grooves 22, 23 at both ends of the tire axial direction of the respective block. The sipes 40 formed on the shoulder blocks 34, 37 are aligned along the longitudinal direction of the shoulder blocks 34, 37 so that one end reaches an adjacent sub-groove 22, 23 on the inner side of the shoulder block 34, 37 in the tire axial direction, while the other end terminates within the shoulder block 34, 37.

[0031] The tread surface, which is the outer surface of each block in the radial direction of the tire, is a projection that protrudes outward in the radial direction of the tire and has a ridge line along the longitudinal direction of each block.

[0032] The treads of the blocks will be described in detail below using Figures 2 to 5. Below, the treads 43 of the center block 32, mediate block 33, and shoulder block 34 of the multiple blocks 30 will be mainly described, but the treads of the center block 35, mediate block 36, and shoulder block 37 of the multiple blocks 31 are similar except that they have a shape that is symmetrical with respect to the equator CL with respect to blocks 32, 33, and 34. As shown in Figure 3, the treads 43, which are the outer surfaces in the tire radial direction of each block 32, 33, and 34, are projections that protrude outward in the tire radial direction and have a ridge line Tm along the longitudinal direction of each block 32, 33, and 34.

[0033] In the following, we will mainly describe the tread surface of the mediate block 33 of block 30, among the multiple blocks 30 and 31, but the same applies to the mediate block 36 of block 31, and the tread surfaces of the center blocks 32 and 35 and shoulder blocks 34 and 37 of each block 30 and 31.

[0034] As shown in Figure 2, each mediate block 33 is separated from the other blocks 32, 33, and 34 by two main grooves 20 spaced apart in the circumferential direction of the tire, and two spaced secondary grooves 22 that intersect each of the main grooves 20. The distance between the two secondary grooves 22 is longer than the distance between the two main grooves 20.

[0035] Furthermore, as shown in Figures 3 to 6, the tread surface 43 of each mediate block 33 is a protruding surface that extends outward in the radial direction of the tire, and the protrusion is larger in the middle of the tire circumferential direction than at both ends in the circumferential direction of the tire.

[0036] As shown in Figure 5, the tread surface 43 of each mediate block 33 protrudes radially outward from the profile surface Sp of the tread 10. The profile surface Sp is a hypothetical surface along the tread near the contact ends E1, E2 of the shoulder blocks 34, 37 on both sides of the tire axial direction, assuming that the main grooves 20, 21 and the secondary grooves 22, 23 do not exist. It is a hypothetical surface formed by the continuous profile line, which is a hypothetical contour in the tire meridian cross-section where multiple arcs of curvature are smoothly continuous, extending around the entire circumference of the tire. The profile surface Sp does not include the protruding surfaces of the tread surfaces of each block 32, 33, 34, 35, 36, 37 that protrude radially outward from the tread.

[0037] As shown in Figure 5, the tread surface 43 of each mediate block 33 has a curved shape with a roughly circular arc in cross-section, increasing in height towards the center C1, so as to be symmetrical with respect to the center C1 in the block width direction on both sides of the block width direction. In this example, a sipe 40 is provided at the center C1 in the block width direction. Therefore, both ends of the opening of the sipe 40 in the width direction are the edges Tm of the tread surface 43.

[0038] As a result, as shown in Figures 3 and 4, the tread surface 43 of the mediate block 33 is a curved projection on the radially outward side of the convex portion having a ridge Tm that extends in the longitudinal direction of the block along the main groove 20. The ridge Tm is located at the maximum height position of the tread surface 43.

[0039] In this example, the upper end of the sipe 40 is located at the center C1 in the block width direction of each block 32, 33, 34, 35, 36, 37, including the mediate block 33. However, the sipe 40 may be formed at a position different from the center C1. Also, the sipe 40 may be omitted. If the sipe 40 is omitted, as shown in Figure 8 below, the tread surface of the shoulder block 34 has a ridge line Tm1 at the center in the block width direction.

[0040] According to the tire 1 described above, in a tire 1 having a V-shaped pattern on the tread 10, the tread surface of the block is a curved projection that protrudes outward in the radial direction of the tire and has a ridge Tm extending in the longitudinal direction of the block. Therefore, regardless of the position of the block in the tire axis direction, which differs from the inclination of the block with respect to the circumferential direction of the tire, the tread surface of the block becomes a shape that can deform more appropriately in response to the tilting of the block. As a result, regardless of the deformation of the block during rolling and braking, the block can more easily make contact with the road surface in accordance with the shape of the road surface, and the contact performance when the block tilts can be improved, thereby improving handling performance and braking performance.

[0041] In particular, the center blocks 32 and 35 are more susceptible to load when the vehicle is moving straight compared to the mediate blocks 33 and 36 and the shoulder blocks 34 and 37, thus improving ground contact and significantly enhancing rolling performance. Similarly, the shoulder blocks 34 and 37 are more susceptible to load when the vehicle is braking or turning compared to the center blocks 32 and 35 and the mediate blocks 33 and 36, thus improving ground contact and significantly enhancing braking and turning performance.

[0042] Furthermore, in another embodiment, each shoulder block 34, 37 may have a curved projection, which is a tread surface, that protrudes outward in the radial direction of the tire and has a ridge Tm extending in the longitudinal direction of the block. This tread surface may be positioned in a portion that is axially outward from the contact edges E1, E2 of the tread 10, for example, including positions P1 and P2 in Figure 1. This configuration improves the contact performance in the portion of the tread 10 axially outward from the contact edges E1, E2, which is the region where pressure is concentrated on the tire when the vehicle turns, thereby further enhancing turning performance.

[0043] Figure 6 is a cross-sectional view of a tire 1a of another embodiment, taken along the block width direction of the shoulder block 34. Figure 7 is a cross-sectional perspective view of the shoulder block 34 shown in Figure 6, viewed from the outside in the tire radial direction.

[0044] In this example, the ridge line Tm of the tread surface of each shoulder block 34 and each shoulder block 37 (see Figure 1) is offset to the front side of the tire's main rotation direction α with respect to the center C1 between the two ends in the block width direction in a cross-section along the block width direction. In this example, the shapes of each center block 32, 35 and each mediate block 33, 36 are the same as those shown in Figures 1 to 5. The shape of the shoulder block 37 is the same as that of the shoulder block 34, except that it is symmetrical with respect to the equator CL. For this reason, the shoulder block 34 will be described in more detail below.

[0045] As shown in Figure 6, the tread surface 43a of each shoulder block 34 is a projection surface that protrudes with a maximum projection height H2 from the profile surface Sp, with respect to the center C1 between the two ends of each shoulder block 34 in the block width direction, and is located on the front side of the tire's main rotation direction α. ​​In Figure 7, the front surface of the shoulder block 34 in the plane of the paper is the cross-section shown in Figure 6. The ridge line Tm is at the maximum height position of the tread surface 43a. As shown in Figure 6, when the shoulder block 34 is cut in a cross-section along the block width direction, perpendicular to the block length direction, the ridge line Tm is located on the front side of the tire's main rotation direction α (right side in Figure 6) with respect to the center C1 between the two main grooves 20 adjacent to each other on both sides of the shoulder block 34 in the block width direction. In Figure 7, the position of the ridge line Tm in the block width direction is shown by a dashed line.

[0046] Furthermore, in this example, the ridge line Tm of the tread surface 43a is shifted to the front side of the tire's main rotation direction α by more than 7 / 10 of the distance between the two ends of the cross section in the block width direction of the shoulder block 34. Therefore, when a1 is the length in the block width direction from the main groove 20 to the ridge line Tm on one side of the tire's circumferential direction (left side in Figures 6 and 7), and a2 is the length in the block width direction from the main groove 20 to the ridge line Tm on the other side of the tire's circumferential direction (right side in Figures 6 and 7), a1 and a2 satisfy the relationship a1 / (a1+a2)≧0.7.

[0047] Furthermore, as shown in Figure 6, the cross-sectional shape of the tread surface 43a along the block width direction has a curve formed by two connected arcs R1 and R2 in the region 44 behind the ridge line Tm in the main tire rotation direction α, where the radius of curvature increases from the rear end wall surface 20a toward the front. In addition, the cross-sectional shape of the tread surface 43a along the block width direction has a curve formed by a single arc R3 in the region 45 in front of the ridge line Tm in the main tire rotation direction α. ​​The radius of curvature of arc R3 in region 45 is intermediate in size between the radii of curvature of the smallest arc R1 and the largest arc R2 in region 44. In this example, region 44 is formed by a shape formed by two connected arcs R1 and R2, but region 44 may also be a shape formed by three or more connected arcs where the radius of curvature increases from the rear end wall surface 20a toward the front.

[0048] In the tire 1a of this example, the ridge line Tm of the tread surface 43 of each shoulder block 34 is offset to the front side of the tire's main rotation direction α with respect to the center C1 in the block width direction. Also, when the tread has a V-shaped pattern, the inclination of each shoulder block 34 with respect to the tire axis is small. Furthermore, during braking, a larger load is applied to the contact surface of each shoulder block 34 compared to the center block and mediate block. As a result, even though the contact surface of the shoulder block 34 is inclined with respect to the road surface during braking, the contact area can be increased over a wide range from the front to the rear in the vehicle's direction of travel β. This improves braking performance.

[0049] To explain this effect, we will first describe the tilting state of the shoulder block 34 of the tire 1b in the first embodiment shown in Figures 1 to 5, in which sipes are omitted from the tread surface of each block. Figure 8 shows the first embodiment tire 1b without sipes, where (a) is a schematic diagram showing the contact state of the shoulder block 34 when the tire 1b is stopped, and (b) is a schematic diagram showing the state in which the shoulder block 34 tilts when the vehicle is braking. Hereinafter, the first embodiment tire 1b without sipes will be simply referred to as the first embodiment tire 1b.

[0050] As shown in Figure 8(a), in the tire 1b of the first embodiment, the entire tread surface 48 of the shoulder block 34 protrudes outward in the radial direction of the tire. The tread surface 48 is a convex surface having a ridge line Tm1 at its center in the block width direction. In this case, as shown in Figure 8(a), the contact portion of the shoulder block 34 with the road surface 80 makes contact most of the area near the center in the circumferential direction of the tire where the ridge line Tm1 is located.

[0051] On the other hand, as shown in Figure 8(b), in the tire 1b of the first embodiment, when the vehicle is braked, the area of ​​the shoulder block 34 near the contact point with the road surface 80 tilts downward so as to face the rear side of the vehicle's direction of travel β. As a result, in the area of ​​the shoulder block 34 near the contact point, which is in front of the direction of travel β and behind the main rotation direction α of the tire, the contact point of the tread surface 48 moves to the front side of the direction of travel β.

[0052] On the other hand, in the tire 1b of the first embodiment, the ridge line Tm1 of the tread surface 48 of the shoulder block 34 is located near the center of the tread surface 48 in the circumferential direction of the tire. Therefore, in the area near the contact point, in the region on the front side of the main rotation direction α of the tire, which is on the rear side of the direction of travel β, the curved surface with a circular arc cross-section is farther away from the road surface 80, and the contact area tends to be smaller. As a result, the tire 1b of the first embodiment has room for improvement in terms of improving braking performance.

[0053] Figure 9 is a diagram of another embodiment of tire 1a, corresponding to the enlarged view of the area near the contact patch in Figure 8(b). According to tire 1a shown in Figure 9, the ridge line Tm of the tread surface 43a of the shoulder block 34 is easily shifted to the front side of the main rotation direction α of the tire, i.e., to the rear side of the direction of travel β when the vehicle is moving forward, relative to the sipe 40 located in the center of the block width direction of the tread surface 43a. This makes it easier for the tread surface 43a to make contact with the road surface 80 over a wide area in the longitudinal direction of the vehicle. Therefore, the contact area of ​​the tread surface 43a can be increased during braking, thereby improving braking performance.

[0054] In particular, in another embodiment, the ridge line Tm of the tread surface 43a is shifted to the front side of the main rotation direction α of the tire for more than 7 / 10 of the distance between the ends of the cross section in the block width direction. This makes it easier for the tread surface 43a to make contact with the road surface 80 over a wider area of ​​the tread surface 43a in the vehicle longitudinal direction. As a result, the contact area of ​​the tread surface 43a can be increased during braking, further improving braking performance.

[0055] Furthermore, as shown in Figure 9, in another embodiment, near the contact portion of the shoulder block 34, a curved surface 90 having a small radius of curvature is provided near the wall surface 20a of the region 44 rear of the ridge line Tm of the tread surface 43a in the main rotation direction α, corresponding to a circular arc R1 (Figure 6) with a small radius of curvature in its cross-sectional shape. This makes it easier for the front end of the tread surface 43a in the direction of vehicle travel β to deform flexibly in accordance with the irregularities of the road surface 80, thereby increasing the contact area with the road surface 80. In addition, this front end is more likely to catch on the rear side of the protrusions 81 made of stone or the like on the road surface 80 in the direction of vehicle travel, further improving braking performance.

[0056] Using Figures 10 and 11, we will explain the tests conducted in another embodiment to determine the degree of deviation of the ridge line Tm of the tread surface 43a from the center in the block width direction, which is 7 / 10 or greater.

[0057] The test was conducted using a comparative example tire. The comparative example tire has a tread with a basic shape similar to that of the embodiment, but the tread surface, which is the outer surface of each block in the radial direction of the tire, does not have a protruding surface that extends radially outward, and is a smooth surface along the profile of the tread. In addition, a sipe 40 extending along the longitudinal direction of the main groove is formed in the middle of the circumferential direction of the tread surface of each block, similar to the configuration in Figures 1 to 5.

[0058] Figure 10 shows the results of measuring the contact pressure of the tire of the comparative example at the initial braking stage (a) and the final braking stage (b), where the contact pressure exceeds a predetermined value. In Figure 10, the right side is the front side in the direction of vehicle travel β. In Figure 10, the black areas indicate the portions of the tread where the contact pressure of the center block 35, mediate block 36, and shoulder block 37 on one side of the tire axial direction exceeds a predetermined value. These black areas are essentially the contact surface during braking.

[0059] From the measurement results shown in Figure 10, in the comparative example tire, the effective contact area decreases by approximately 70% at the end of braking compared to the initial braking stage in both the front and rear regions of the vehicle direction β separated by the sipes 40 of each block. From this, it can be considered that, averaging the reduction in contact area of ​​each block during braking along the length direction of the main groove, approximately 70% of the main groove 21 or sipes 40 on the front side of the vehicle direction β is in effective contact with the rear side of the vehicle direction β in each region separated by the sipes 40 of each block. Furthermore, unlike the embodiment, in the comparative example the tread surface of the block does not protrude outward in the radial direction of the tire in a curved shape, so the contact performance at the rear end of the front region of the vehicle direction β separated by the sipes 40 is also worse, and consequently the contact area at the front end of the rear region of the vehicle direction β separated by the sipes 40 is increased. On the other hand, in the tire 1b of the first embodiment shown in Figure 8, the tread surface 48 of the shoulder block 34 protrudes outward in the radial direction of the tire in a curved shape. Therefore, as the shoulder block 34 collapses during braking, it continuously contacts the front to rear of the vehicle in the direction of travel β, and in this case, it is thought that only about 70% of the area contacts the front to rear of the vehicle in the direction of travel β. This shows that it is effective to make approximately 70% of the area of ​​each block near the contact point during braking contact the front to rear of the vehicle in the direction of travel β more efficiently.

[0060] Figure 11 shows the measurement results of the change in the ratio of the contact area of ​​the tire in the comparative example, where the contact pressure of the tire contact patch is above a predetermined value, relative to the initial braking state. From the measurement results shown in Figure 11, it can be seen that at the initial stage of braking, the tire's contact load becomes excessively high due to the sinking of the front of the vehicle, causing the contact area to increase from the standard value of 100%. Subsequently, as the sinking subsides and the blocks of the contact patch collapse, the contact area decreases, and it was confirmed that the ratio of this contact area becomes approximately 70% of the standard value. From this, it can be seen that, during braking, it is effective to make approximately 70% of the area from the front to the rear in the direction of vehicle travel β of each block near the contact patch more efficiently in contact with the road surface.

[0061] As in another embodiment, by configuring the degree of the bias towards the front in the main rotation direction α of the tire, corresponding to the bias towards the rear in the direction of vehicle travel of the contact area with respect to the center C1 in the block width direction of the ridge line Tm of the tread surface 43a, to be 7 / 10 or more of the bias between the two ends in the block width direction, the contact area can be increased more efficiently regardless of the collapse of the block near the contact area during braking.

[0062] Figure 12 shows a cross-section of the center block 32, mediate block 33, and shoulder block 34 along the block width direction in another embodiment of tire 1c, with the positions of both ends in the width direction of the blocks aligned.

[0063] The following describes blocks 32, 33, and 34 of block 30, but blocks 35, 36, and 37 of block 31 are similar, except that they are symmetrical to block 30 with respect to the equator CL.

[0064] The center block 32, mediate block 33, and shoulder block 34 each have tread surfaces 43b, 43c, and 43d, respectively. The cross-sectional shape of the tread surface 43d of the shoulder block 34 along the block width direction is the same as the cross-sectional shape of the mediate block 33 along the block width direction shown in Figures 1 to 5.

[0065] Furthermore, the maximum protrusion height of the tread surfaces 43b, 43c, and 43d of each block 32, 33, and 34 from the profile surface Sp outward in the tire radial direction increases in the order of center block 32, mediate block 33, and shoulder block 34, with the tread surfaces 43b, 43c, and 43d being the largest.

[0066] According to the configuration in this example, the maximum protrusion height of the tread surface 43b of the center block 32, which is subjected to a larger load during straight-line movement, can be increased. This improves ground contact and, consequently, significantly enhances the rolling performance.

[0067] In Figure 12, the overall height of the center block 32, mediate block 33, and shoulder block 34 is shown to increase in that order. However, it is sufficient that the height from the profile surface Sp increases, and the overall block height may be the same in some parts. For example, the overall height of the center block 32 and mediate block 33 may be approximately the same. In this example, the other configurations and functions are the same as those in Figures 1 to 5.

[0068] Figure 13 is a cross-sectional perspective view of tire 1e, an alternative embodiment, including a cross-section of the shoulder block 34 cut along the block width direction. Figure 14 is a diagram of the shoulder block 34 shown in Figure 13, corresponding to Figure 9.

[0069] In this example, the shoulder blocks 34 and 37 (see Figure 1) have a cross-sectional shape along the block width direction of the tread surface 43e that is formed by a first circular arc R4 in the region 44b behind the ridge line Tm in the main tire rotation direction α. ​​Furthermore, the cross-sectional shape along the block width direction of the tread surface 43e has a curve formed by a second circular arc R5 in the region 45b in front of the ridge line Tm in the main tire rotation direction α. ​​The radius of curvature of the first circular arc R4 is greater than the radius of curvature of the second circular arc R5. In this example, sipes are omitted in the shoulder block 34, but a configuration with sipes is also possible.

[0070] According to the configuration of this example, as shown in Figure 14, during braking, the radius of curvature of the front side of the tread surface 43e in the vehicle direction of travel β relative to the ridge line Tm at the contact point of the shoulder block can be made larger overall, thereby increasing the contact area with the road surface 80 and further improving braking performance. In addition, unlike the configuration shown in Figure 9, the radius of curvature of the curve at the front end of the tread surface 43e in the vehicle direction of travel β can be made larger in this configuration, so that the tilting of the block toward the rear side of the vehicle direction of travel β can be suppressed. As a result, the part of the tread surface 43e that is toward the rear side of the vehicle direction of travel β relative to the ridge line Tm can be brought closer to the road surface 80, thereby increasing the effective contact area. This further improves braking performance. Furthermore, by making the radius of curvature of the second arc R5 of the part of the tread surface 43e that is toward the rear side of the vehicle direction of travel β relative to the ridge line Tm larger than the radius of curvature of the third arc R3 in the configuration of Figure 6, the effective contact area can be increased further, and braking performance can be further improved. In this example, the other configurations and functions are the same as those in Figures 1 to 5, or in Figures 6, 7, and 9.

[0071] Figure 15 is a cross-sectional perspective view of a tire 1f of another embodiment, including a cross-section cut along the block width direction of the shoulder block 34. Figure 16 is a diagram of the shoulder block 34 shown in Figure 15, corresponding to Figure 9. In the configuration of this example, in the shoulder block 34 and shoulder block 37 (see Figure 1), the cross-sectional shape of the tread surface 43f along the block width direction is such that it can flexibly respond to various road surface angle movements in the region 44c behind the ridge line Tm in the main rotation direction α of the tire. Specifically, in region 44c, multiple curved surfaces S1, S2...S5 are connected via boundary lines, and one end of each boundary line is located near a point Pm on the ridge line Tm. Each curved surface S1, S2...S5 becomes lower as it moves away from the ridge line Tm. Furthermore, the curved surfaces S1 and S5, which have portions along the ridge line Tm, are gently sloping surfaces, while the other curved surfaces S2, S3, and S4, up to near the wall surface of the groove 20, slope sharply as they move away from the ridge line Tm, and then slope gently. In the region 45c, which is in front of the ridge line Tm in the main rotation direction α of the tire, the surface is similar to the region 45 of the tread surface 43a shown in Figures 6 and 7. In this example, in the cross section visible on the front side of the page in Figure 15, in region 44c, a circular arc R7 with a large radius of curvature is connected to the ridge line Tm, and a circular arc R6 with a smaller radius of curvature than arc R7 and recessed toward the inside of the shoulder block 34 is connected to the wall surface of the groove 20. In this example, sipes are omitted in the shoulder block 34, but a configuration with sipes is also possible.

[0072] According to the configuration in this example, as shown in Figure 16, during braking, the area 44c of the tread surface 43f of the shoulder block, specifically the area in front of the ridge line Tm in the direction of vehicle travel β, can flexibly respond to changes in the unevenness of the road surface 80, making it easier to increase the contact area. This allows for higher braking force on road surfaces 80 with large variations in unevenness. In this example, the other configurations and functions are the same as those in Figures 1 to 5, or in Figures 6, 7, and 9.

[0073] Although not shown in the illustrations, in each block of the tire in each of the above embodiments, the sipes may be configured to be inclined with respect to the tire's radial direction. For example, each sipe may be configured to be inclined toward the front of the tire's main rotation direction α toward the inside of the tire's radial direction.

[0074] Furthermore, the configurations shown in Figures 6, 7, and 9, Figures 13 and 14, or Figures 15 and 16 may be combined with the configuration shown in Figure 12. That is, in a configuration where the ridge of the tread surface of the shoulder block is shifted to the front side in the direction of the main rotation of the tire relative to the center between the two ends in the block width direction, the maximum protrusion height outward in the tire radial direction from the profile surface Sp of the tread surface may be increased in the order of center block, mediate block, and shoulder block. This configuration can improve braking performance and straight-line driving performance.

[0075] Furthermore, in this configuration, the ridge of the tread surface of each shoulder block may be shifted towards the front side in the main rotation direction of the tire for at least 7 / 10 of the distance between the two ends in the block width direction in a cross-section along the block width direction. This configuration can further improve braking performance.

[0076] Furthermore, in each of the above embodiments, the tread surface of only some of the blocks among the multiple blocks of the tread may be configured to be a curved protruding surface having a ridge line along the longitudinal direction of the block. [Explanation of Symbols]

[0077] 1,1a~1f Pneumatic tire (tire), 10 Tread, 11 Sidewall, 20,21 Main groove, 22,23 Secondary groove, 28,30,31 Block, 32,35 Center block, 33,36 Mediate block, 34,37 Shoulder block, 40 Sipe, 43,43a~43f Tread, 44,44b,44c,45,45b,45c Area, 48 Tread, 80 Road surface, 81 Protrusion, 90 Curved surface, CL Equator, E1,E2 Contact edge.

Claims

1. A pneumatic tire having a tread, The main rotation direction of the tire is specified, and The tread includes a plurality of blocks partitioned by a plurality of grooves, The plurality of grooves extend from the equator towards the contact end, and have a plurality of main grooves whose inclination with respect to the tire axis is greater on the equator side than on the contact end side, and sub-grooves that connect adjacent main grooves in the tire circumferential direction or in an inclined direction with respect to the tire circumferential direction. The aforementioned plurality of blocks are elongated along the direction of extension of the adjacent main grooves, At least some of the tread surfaces of the aforementioned blocks are curved protrusions having ridges along the longitudinal direction of the block. Pneumatic tires.

2. The tread surface is positioned in a portion of the tread that includes the tire axial side outward from the contact end of the tread. The pneumatic tire according to claim 1.

3. The plurality of blocks include a center block, a mediate block, and a shoulder block, arranged in order from the equator side toward the tire axial side outwards. The aforementioned tread surface is the tread surface of the shoulder block, The ridge of the tread surface, in a cross-section along the block width direction, is offset to the front side in the main rotation direction of the tire with respect to the center between the two ends in the block width direction. The pneumatic tire according to claim 1.

4. The ridge of the tread surface is shifted towards the front side in the main rotation direction of the tire for more than 7 / 10 of the distance between the ends of the cross section in the block width direction along the block width direction. The pneumatic tire according to claim 3.

5. The tread surface of each of the center block, mediate block, and shoulder block is a curved projection having the ridge line along the longitudinal direction of the block, The maximum protrusion height outward in the tire radial direction from the profile surface of the tread increases in the order of the center block, the mediate block, and the shoulder block. The pneumatic tire according to claim 3.

6. The plurality of blocks include a center block, a mediate block, and a shoulder block, arranged in order from the equator side toward the tire axial side outwards. The tread surface of each of the center block, mediate block, and shoulder block is a curved projection having the ridge line along the longitudinal direction of the block, The maximum protrusion height outward in the tire radial direction from the profile surface of the tread increases in the order of the center block, the mediate block, and the shoulder block. The pneumatic tire according to claim 1.

Images