JP2015081010A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that reduces air column resonance sound while maintaining drainage performance and steering stability performance.SOLUTION: A pneumatic tire 2 includes a tread 4 whose outer surface forms a tread surface 22, a pair of sidewalls 6, a pair of beads 10, a carcass 12 that is bridged between one bead 10 and the other bead 10 along the insides of the tread 4 and the sidewalls 6, a belt 14 that is laminated on the carcass 12 on the radially inside of the tread 4, and a reinforcing member 20 that is located on the radially outside of the belt 14. The tread surface 22 is formed with main grooves 24 extending in the circumferential direction. Each main groove 24 has a bottom surface 24a facing radially outward. The reinforcing member 20 extends in the circumferential direction along the bottom surface 24a of the main groove 24. The opening width Wa in the axial direction of the main groove is made larger than the bottom surface width Wb in the axial direction of the main groove.

Description

  The present invention relates to a pneumatic tire.

  As the vehicle travels, the tires roll on the road surface. The ground contact surface of the tire moves in the circumferential direction. The tire tread is repeatedly deformed in the circumferential direction. In a tire including a main groove extending continuously in the circumferential direction, air column resonance is generated in the main groove. This air column resonance sound is a sound having a frequency of 800 Hz to 1000 Hz, and is also called a shear sound. This air column resonance is a major cause of outside noise when the vehicle passes.

  Various tires with reduced air column resonance noise in the main groove have been proposed. By reducing the groove volume of the main groove, the air column resonance can be reduced. Also, by reducing the rigidity of the tread, air column resonance can be reduced.

JP 2010-201973 A JP 2002-240510 A

  However, reducing the groove volume of the main groove hinders drainage performance. This tire tends to be inferior in hydroplaning performance. Further, in a tire having a small tread rigidity, the cornering power tends to decrease. This tire tends to be inferior in steering stability performance. It is not easy to reduce the air column resonance noise of the main groove while maintaining the drainage performance and steering stability performance of the tire.

  An object of the present invention is to provide a tire that maintains drainage performance and steering stability performance and reduces air column resonance noise of a main groove.

A tire according to the present invention includes a tread whose outer surface forms a tread surface, a pair of sidewalls that extend substantially inward in the radial direction from the end of the tread, and a pair of beads that are positioned radially inward of the sidewalls. A carcass spanned between one bead and the other bead along the inside of the tread and the sidewall, a belt laminated with the carcass on the inner side in the radial direction of the tread, and positioned on the outer side in the radial direction of the belt And a reinforcing member.
A main groove extending in the circumferential direction is formed on the tread surface. The main groove has a bottom surface facing radially outward. The reinforcing member extends in the circumferential direction along the bottom surface of the main groove. The opening width Wa in the axial direction of the main groove is larger than the bottom width Wb in the axial direction of the main groove.

  Preferably, the axial width Wc of the reinforcing member is not less than the bottom width Wb of the main groove and not more than the opening width Wa.

  Preferably, the ratio Wb / Wa of the bottom width Wb of the main groove to the opening width Wa of the main groove is 0.1 or more.

  Preferably, a ratio T / D between the thickness T of the tread and the tire outer diameter D is set to 0.015 or more and 0.020 or less. The ratio Hg / T between the depth Hg and the thickness T of the main groove is set to 0.725 or more and 0.85 or less.

  Preferably, the rigidity of the reinforcing member is reduced from the axial center of the reinforcing member toward the axial end.

  Preferably, the ratio Ws / Wb between the axial displacement Ws between the reinforcing member and the main groove and the bottom width Wb of the main groove is 0.2 or less.

  Preferably, the reinforcing member is a reinforcing rubber member made of a crosslinked rubber harder than the tread. The hardness of the reinforcing rubber member is 70 or more and 90 or less.

  Preferably, the maximum thickness of the reinforcing rubber member is not less than 0.5 mm and not more than 1.5 mm.

  Preferably, the cross-sectional shape of the reinforcing rubber member is formed such that the axial width is gradually reduced from the radially inner side to the outer side.

  Preferably, the cross-sectional shape of the reinforcing rubber member is triangular.

  Preferably, the tire includes a band that is positioned between the belt and the tread and covers the belt. This band consists of a cord extending in the circumferential direction and a topping rubber. The cross-sectional area Sc of the cord per unit width of the band is larger on the radially inner side of the main groove than on the radially inner side of the tread surface. The reinforcing member is a portion of the band in which the cross-sectional area Sc of the cord per unit width is increased.

  In the tire according to the present invention, the rigidity of the bottom of the main groove is improved by the reinforcing member. Due to this improvement in rigidity, vibrations at the bottom of the main groove are suppressed. Thereby, generation | occurrence | production of the air column resonance sound of a main groove is suppressed. Since it extends along the bottom of the main groove, the influence on the rigidity of the wall surface and tread surface of the main groove is suppressed. Thereby, generation | occurrence | production of the air column resonance sound of a main groove is suppressed, maintaining drainage performance and steering stability performance.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a partially enlarged view indicated by an arrow II in FIG. FIG. 3 is a partially enlarged cross-sectional view of a tire according to another embodiment of the present invention. FIG. 4 is a partially enlarged cross-sectional view of a tire according to still another embodiment of the present invention. FIG. 5 is a partially enlarged cross-sectional view of a tire according to still another embodiment of the present invention. FIG. 6 is a partially enlarged sectional view of a tire according to still another embodiment of the present invention. FIG. 7 is a partially enlarged cross-sectional view of a tire according to still another embodiment of the present invention. FIG. 8 is a partially enlarged cross-sectional view of a tire according to still another embodiment of the present invention. FIG. 9 is a partially enlarged cross-sectional view of a tire according to still another embodiment of the present invention.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 shows a pneumatic tire 2. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire 2. The shape of the tire 2 is symmetric with respect to the equator plane CL except for the tread pattern. A double arrow D in FIG. 1 indicates the outer diameter of the tire 2. The outer diameter D is measured as the diameter of the tire 2 on the equator plane CL.

  The tire 2 includes a tread 4, a sidewall 6, a clinch 8, a bead 10, a carcass 12, a belt 14, a band 16, an inner liner 18 and a reinforcing rubber member 20. In the tire 2, the reinforcing rubber member 20 functions as a reinforcing member. The tire 2 is a tubeless type. The tire 2 is mounted on a passenger car.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 22 that contacts the road surface. A main groove 24 is carved in the tread 4. The main groove 24 extends in the circumferential direction of the tire 2. The main groove 24 goes around the tread surface 22 in the circumferential direction. The main groove 24 includes a bottom surface 24a facing outward in the radial direction and a pair of wall surfaces 24b extending from the bottom surface 24a to the tread surface 22 so as to face each other. Although not shown, the tread 4 is further formed with other grooves. A plurality of blocks 25 are formed in the tread 4 by the main groove 24 and other grooves. The outer peripheral surfaces of the plurality of blocks form a tread surface 22. The main groove 24 and other grooves form a tread pattern.

  Although not shown, the tread 4 has a base layer and a cap layer. The cap layer is located on the radially outer side of the base layer. The cap layer is laminated on the base layer. The base layer is made of a crosslinked rubber having excellent adhesiveness. A typical base rubber for the base layer is natural rubber. The cap layer is made of a crosslinked rubber having excellent wear resistance, heat resistance and grip properties.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. A radially outer end of the sidewall 6 is joined to the tread 4. The radially inner end of the sidewall 6 is joined to the clinch 8. This sidewall 6 is made of a crosslinked rubber having excellent cut resistance and weather resistance. This sidewall 6 prevents the carcass from being damaged.

  The clinch 8 is located substantially inside the sidewall 6 in the radial direction. The clinch 8 is located outside the beads 10 and the carcass 12 in the axial direction. The clinch 8 is made of a crosslinked rubber having excellent wear resistance. The clinch 8 comes into contact with the flange of the rim when the tire 2 is assembled to a rim (not shown).

  The bead 10 is located inside the clinch 8 in the axial direction. The bead 10 includes a core 26 and an apex 28 that extends radially outward from the core 26. The core 26 has a ring shape and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 28 is tapered outward in the radial direction. The apex 28 is made of a highly hard crosslinked rubber.

  The carcass 12 includes a carcass ply 30. The carcass ply 30 is stretched between the beads 10 on both sides, and extends along the tread 4 and the sidewall 6. The carcass ply 30 is folded around the core 26 from the inner side toward the outer side in the axial direction. As a result of the folding, a main portion 30a and a folded portion 30b are formed in the carcass ply 30.

  The carcass ply 30 includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 75 ° to 90 °. In other words, the carcass 30 has a radial structure. The cord is made of organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. The carcass 12 may be formed from two or more carcass plies.

  The belt 14 is located on the inner side in the radial direction of the tread 4. The belt 14 is laminated on the outer side in the radial direction of the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes an inner layer 32 and an outer layer 34. As apparent from FIG. 1, the width of the inner layer 32 is slightly larger than the width of the outer layer 34 in the axial direction. Although not shown, each of the inner layer 32 and the outer layer 34 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane CL. The general absolute value of the tilt angle is 10 ° or more and 35 ° or less. The inclination direction of the cord of the inner layer 32 with respect to the equator plane CL is opposite to the inclination direction of the cord of the outer layer 34 with respect to the equator plane CL. A preferred material for the cord is steel. An organic fiber may be used for the cord. The axial width of the belt 14 is preferably 0.7 times or more the maximum width of the tire 2. The belt 14 may include three or more layers.

  The band 16 is located on the radially outer side of the belt 14. In the axial direction, the width of the band 16 is larger than the width of the belt 14. The belt 14 and the band 16 constitute a reinforcing layer 36. The reinforcing layer 36 may be configured only from the belt 14.

  The inner liner 18 is located inside the carcass 12. In the vicinity of the equator plane CL, the inner liner 18 is joined to the inner surface of the carcass 12. The inner liner 18 is made of a crosslinked rubber. For the inner liner 18, rubber having excellent air shielding properties is used. A typical base rubber of the inner liner 18 is butyl rubber or halogenated butyl rubber. The inner liner 18 maintains the internal pressure of the tire 2.

  In the tire 2, the reinforcing rubber member 20 is not disposed on the inner side in the radial direction of the tread surface 22. The reinforcing rubber member 20 is disposed on the radially inner side of the main groove 24. In other words, the reinforcing rubber member 20 extends in the circumferential direction along the bottom surface 24 a of the main groove 24. In the tire 2, the reinforcing rubber member 20 is disposed radially inward from the bottom surface 24a. The reinforcing rubber member 20 is arranged on the outer side in the radial direction from the belt 14. In other words, the reinforcing rubber member 20 is disposed between the bottom surface 24a of the main groove 24 and the belt 14 in the radial direction. The reinforcing rubber member 20 is disposed on the outer side in the radial direction from the band 16. The reinforcing rubber member 20 is made of a highly hard crosslinked rubber. The hardness of the crosslinked rubber of the reinforcing rubber member 20 is larger than that of the crosslinked rubber of the base layer and the cap layer of the tread 4.

  As shown in FIG. 2, the band 16 includes a cord 38 and a topping rubber 40. The cord 38 is spirally wound in the circumferential direction. The band 16 has a so-called jointless structure. The cord 38 extends substantially in the circumferential direction. The angle of the cord 38 with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the belt 14 is restrained by the cord 38, the lifting of the belt 14 is suppressed. The cord 38 is made of an organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  A double arrow T in FIG. 2 indicates the thickness of the tread 4. A double arrow Hg indicates the depth of the main groove 24. The depth Hg is measured as a radial distance from the bottom surface 24a to the tread surface 22. A double-headed arrow Ht indicates the thickness from the bottom surface 24a to the radially inner circumferential surface of the tread 4, that is, the thickness of the tread 4 on the bottom surface 24a. A double arrow Hr indicates the thickness of the reinforcing rubber member 20. This thickness Hr is the maximum thickness measured in the radial direction of the reinforcing rubber member 20. A double-headed arrow Hu indicates the thickness from the radially outer end of the reinforcing rubber member 20 to the bottom surface 24a. A double-headed arrow Hb indicates the thickness from the bottom surface 20 c of the reinforcing rubber member 20 to the inner circumferential surface in the radial direction of the tread 4. The thickness T, depth Hg, thickness Ht, thickness Hr, thickness Hu, and thickness Hb are measured as linear distances in the radial direction. The thickness T, the depth Hg, the thickness Ht, the thickness Hr, the thickness Hu, and the thickness Hb are measured in a cross section cut out from the tire 2 as shown in FIGS.

  A double arrow Wa in FIG. 2 indicates the opening width of the main groove 24. The opening width Wa is measured as the distance between the intersection points of the extension line of the tread surface 22 and the extension line of the wall surface 24b. A double-headed arrow Wb indicates the bottom width of the main groove 24. The bottom surface width Wb is measured as the distance between the intersections of the extension line of the bottom surface 24a and the extension line of the wall surface 24b. A double arrow Wc indicates the width of the reinforcing rubber member 20. The opening width Wa, the bottom surface width Wb, and the width Wc are measured as linear distances. The opening width Wa, the bottom surface width Wb, and the width Wc are measured in a cross section cut out from the tire 2 as shown in FIGS. 1 and 2.

  A one-dot chain line Lr in FIG. 2 indicates the center line of the reinforcing rubber member 20. The center line Lr is a straight line extending in the radial direction through the center in the axial direction of the reinforcing rubber member 20. The reinforcing rubber member 20 has a symmetrical shape with respect to the center line Lr. An alternate long and short dash line Lg indicates the center line of the main groove 24. The center line Lg is a straight line extending in the radial direction through the center of the main groove 24 in the axial direction. The bottom surface 24a of the main groove 24 is formed symmetrically with respect to the center line Lg. In the tire 2, the main groove 24 is formed symmetrically with respect to the center line Lg. A double-headed arrow Ws indicates a positional deviation in the axial direction between the center line Lr and the center line Lg. This positional shift Ws indicates a positional shift in the axial direction between the reinforcing rubber member 20 and the main groove 24. This positional deviation Ws is measured in a cross section cut out from the tire 2 as shown in FIGS.

  The tire 2 is attached to the vehicle. When the vehicle travels, the tire 2 rolls. The ground contact surface of the tread surface 22 moves in the circumferential direction. In the tread 4, one rotation of the tire 2 is taken as one cycle, and a portion where the tire is compressed and deformed due to contact moves in the circumferential direction. The tread 4 repeats this periodic deformation.

  When the tread surface 22 is grounded, vibration is input to the belt 14 via the tread 4. Since the bottom surface 24a of the main groove 24 is not grounded, the bottom surface 24a is not restrained by the ground. The bottom surface 24 a is easily vibrated by the vibration of the belt 14. In the tire 2, the bottom surface 24a faces in the radial direction. Compared with both axial ends of the bottom surface 24a, the center in the axial direction is greatly vibrated. This vibration of the bottom surface 24a causes the generation of air column resonance.

  In the tire 2, the reinforcing rubber member 20 extends in the circumferential direction along the bottom surface 24 a of the main groove 24. The reinforcing rubber member 20 is located between the bottom surface 24a of the main groove 24 and the belt 14 in the radial direction. By arranging the reinforcing rubber member 20, the vibration of the belt 14 is suppressed. The reinforcing rubber member 20 suppresses transmission of vibration to the bottom surface 24a. Thereby, generation | occurrence | production of air column resonance is suppressed. From this viewpoint, it is preferable that the axial width Wc of the reinforcing rubber member 20 is equal to or larger than the bottom surface width Wb.

  In the tire 2, a block 25 in which a tread surface 22 is formed sandwiches a main groove 24 in the axial direction. The reinforcing rubber member 20 is located radially inward from the bottom surface 24a. The reinforcing rubber member 20 is not exposed on the bottom surface 24 a and the wall surface 24 b of the main groove 24. The reinforcing rubber member 20 does not hinder the deformation of the block 25. In addition, cracks may occur on the bottom surface 24 a and the wall surface 24 b of the main groove 24 due to repeated deformation of the tread 4. In the tire 2, since the reinforcing rubber member 20 is not exposed on the bottom surface 24a, generation of cracks is suppressed. In the tire 2, a decrease in durability is suppressed. From this viewpoint, the thickness Hu is preferably greater than 0, and more preferably 0.3 mm or more.

  In the tire 2, the opening width Wa of the main groove 24 is made larger than the bottom surface width Wb. Thereby, it is suppressed that the reinforcing rubber member 20 is located inside the tread surface 22 in the radial direction. By this reinforcing member 20, the deterioration of the riding comfort of the tire 2 is suppressed. Further, in the tire 2, the width Wc of the reinforcing rubber member 20 is larger than the bottom surface width Wb and smaller than the opening width Wa. Thereby, the vibration of the bottom surface 24a of the main groove 24 can be effectively suppressed. On the other hand, since the width Wc is equal to or smaller than the opening width Wa, the reinforcing rubber member 20 is not positioned on the inner side in the radial direction of the tread surface 22. By this reinforcing member 20, the deterioration of the riding comfort of the tire 2 is suppressed.

  In the tire 2, the reinforcing rubber member 20 is disposed along the bottom surface 24a. By making the opening width Wa of the main groove 24 larger than the bottom surface width Wb, the influence of the reinforcing rubber member 20 on the radially inner portion of the tread surface 22 is reduced. By increasing the opening width Wa, deterioration in ride comfort can be suppressed. From this viewpoint, the ratio Wb / Wa of the bottom surface width Wb to the opening width Wa of the main groove 24 is preferably 0.9 or less, and particularly preferably 0.8 or less.

  The tire 2 having a large bottom width Wb of the main groove 24 can increase the groove volume of the main groove 24. The tire 2 having a large groove volume of the main groove 24 is excellent in drainage performance. Since the tire 2 includes the reinforcing rubber member 20, even if the bottom surface width Wb is increased, generation of air column resonance noise is suppressed. From the viewpoint of drainage performance, this ratio Wb / Wa is preferably 0.1 or more, more preferably 0.3 or more, and particularly preferably 0.5 or more.

  In the tire 2, by providing the reinforcing rubber member 20, generation of air column resonance noise is suppressed. Since the generation of air column resonance is suppressed, the thickness T of the tread 4 can be increased and the depth Hg of the main groove 24 can be increased. The depth Hg of the main groove 24 can be increased to improve drainage performance. From this viewpoint, the ratio T / D between the thickness T of the tread 4 and the tire outer diameter D is preferably 0.015 or more, more preferably 0.016 or more, and particularly preferably 0.017 or more. is there. The ratio Hg / T between the depth Hg and the thickness T of the main groove 24 is preferably 0.725 or more, more preferably 0.730 or more, and particularly preferably 0.735 or more. On the other hand, from the viewpoint of suppressing the generation of the air column resonance, the ratio T / D is preferably 0.020 or less, more preferably 0.019 or less, and particularly preferably 0.018 or less. . The ratio Hg / T is preferably 0.850 or less, more preferably 0.845 or less, and particularly preferably 0.840 or less.

  The reinforcing rubber member 20 has a triangular cross section perpendicular to the circumferential direction. Here, the cross-sectional shape is an isosceles triangle. The central portion 20a of the reinforcing member 20 is thicker than the axial end portion 20b. The rigidity of the reinforcing rubber member 20 is reduced from the axial center to the axial end. Vibration at the center of the bottom surface 24a of the main groove 24 can be suppressed. The reinforcing rubber member 20 can more effectively suppress the generation of air column resonance sound. In addition, since the cross-sectional shape is triangular, air column resonance can be suppressed with a small cross-sectional area. The reinforcing rubber member 20 can suppress an increase in weight of the tire 2.

  The cross-sectional shape of the reinforcing rubber member 20 is one form of a preferable shape. The cross-sectional shape of the reinforcing rubber member 20 is not limited to a triangle. The cross-sectional shape is not particularly limited, but it is preferable that the axial width be gradually reduced from the radially inner side to the outer side.

  From the viewpoint of suppressing the vibration of the bottom surface 24 a of the main groove 24, it is preferable that the axial positional deviation Ws between the reinforcing rubber member 20 and the main groove 24 is small. From this viewpoint, the ratio Ws / Wb between the positional deviation Ws and the bottom surface width Wb is preferably 0.2 or less, and more preferably 0.1 or less.

  The reinforcing rubber member 20 is made of a crosslinked rubber that is harder than the tread 4. The hard reinforcing rubber member 20 suppresses vibration of the bottom surface 24 a of the main groove 24. From this viewpoint, the hardness of the reinforcing rubber member 20 is preferably 70 or more, and more preferably 75 or more. On the other hand, in a tire having a small hardness of the reinforced rubber member 20, an increase in rolling resistance is suppressed. From this viewpoint, the hardness of the reinforcing rubber member 20 is preferably 90 or less, and more preferably 85 or less.

  The reinforcing rubber member 20 having a large thickness Hr suppresses vibration of the bottom surface 24a of the main groove 24. From this viewpoint, the thickness Hr is preferably 0.5 mm or more, more preferably 0.7 mm or more, and particularly preferably 1.0 mm or more. On the other hand, the reinforcing rubber member 20 having a small thickness Hr contributes to reduction of the rolling resistance of the tire 2. From this viewpoint, the thickness Hr is preferably 1.5 mm or less, more preferably 1.3 mm or less, and particularly preferably 1.0 mm or less.

  FIG. 3 shows a part of another tire 42 according to the present invention. The tire 42 includes a reinforcing rubber member 43 instead of the reinforcing rubber member 20 of the tire 2. FIG. 4 shows a part of still another tire 44 according to the present invention. The tire 44 includes a reinforcing rubber member 45 instead of the reinforcing rubber member 20 of the tire 2. FIG. 5 shows a part of still another tire 46 according to the present invention. The tire 46 includes a reinforcing rubber member 47 instead of the reinforcing rubber member 20 of the tire 2. Other configurations of the tire 42, the tire 44, and the tire 46 are the same as those of the tire 2, and the description thereof is omitted. Here, the same configuration as the tire 2 will be described using the same reference numerals.

  In the tire 42 of FIG. 3, the reinforcing rubber member 43 has a trapezoidal cross-sectional shape perpendicular to the circumferential direction. The reinforcing rubber member 43 includes a central portion 43a located at the axial center and a pair of end portions 43b sandwiching the central portion 43a in the axial direction. The reinforcing rubber member 43 has a symmetrical shape with respect to the center line Lr. The reinforcing rubber member 43 has a lower base 43c that is longer than an upper base 43d. The lower bottom 43c is located on the radially inner side. The upper base 43d is located radially outward. The tire 42 can obtain the same effects as the tire 2.

  In the tire 44 of FIG. 4, the reinforcing rubber member 45 has a rectangular cross section perpendicular to the circumferential direction. The reinforcing rubber member 45 has a symmetrical shape with respect to the center line Lr. The tire 44 can also obtain the same effect as the tire 2.

  In the tire 46 of FIG. 5, the reinforcing rubber member 47 has a pentagonal cross-sectional shape perpendicular to the circumferential direction. The reinforcing rubber member 47 has a symmetrical shape with respect to the center line Lr. The tire 46 can also obtain the same effect as the tire 2.

  FIG. 6 shows a part of still another tire 50 according to the present invention. The tire 50 includes a band 52 instead of the band 16 of the tire 2. The tire 50 does not include the reinforcing rubber member 20. The tire 50 may include the reinforcing rubber member 20. The other configuration of the tire 50 is the same as that of the tire 2, and the description thereof is omitted. Here, the same configuration as the tire 2 will be described using the same reference numerals. The band 52 is located on the radially outer side of the belt 14. The band 52 includes a cord 38 and a topping rubber 40.

  Double arrows P1 and P2 in FIG. 6 indicate the axial pitch of the cord 38. The pitch P <b> 1 indicates the pitch inside the tread surface 22 in the radial direction. The pitch P <b> 2 indicates the pitch inside the main groove 24 in the radial direction. The pitch P2 is smaller than the pitch P1. A double-headed arrow Wc indicates a width in which the cord 38 is set to the pitch P2. The tire 50 has a width Wc that is greater than the bottom surface width Wb. The width Wc is smaller than the opening width Wa.

  Here, Sc is the cross-sectional area of the cord 38 per unit width in the axial direction. The cross-sectional area Sc at the pitch P1 is Sc1, and the cross-sectional area Sc at the pitch P2 is Sc2. The cross-sectional area Sc1 indicates the cross-sectional area on the inner side in the radial direction of the tread surface 22. The cross-sectional area Sc2 indicates the cross-sectional area inside the main groove 24 in the radial direction. In the tire 50, the sectional area Sc2 is larger than the sectional area Sc1.

  In the band 52, the cord 38 extends substantially in the circumferential direction, so that vibration transmitted in the axial direction is reduced. Since the cord 38 has the pitch P2 within the range indicated by the width Wc, the vibration of the bottom surface 24a of the main groove 24 is suppressed. The portion indicated by the width Wc of the band 52 functions as a reinforcing member in the same manner as the reinforcing rubber member 20. When the cord 38 is set to the pitch P2 in the entire axial direction of the band 52, the weight of the tire 50 increases. In the tire 50, the cord 38 on the inner side in the radial direction of the tread surface 22 has a pitch P1, which contributes to weight reduction of the tire 50.

  In the tire 50, the width Wc is larger than the bottom surface width Wb of the main groove 24. From the viewpoint of suppressing the vibration of the bottom surface 24a, the width Wc is preferably set to be equal to or larger than the bottom surface width Wb. On the other hand, the width Wc is smaller than the opening width Wa of the main groove 24. Thereby, deterioration of riding comfort is controlled. Further, the weight Wc can be reduced by reducing the width Wc. This weight reduction suppresses deterioration of rolling resistance. From these perspectives. The width Wc is preferably set to be equal to or smaller than the opening width Wa.

  Also in the tire 50, the provision of the band 52 suppresses the generation of air column resonance noise. Since the generation of air column resonance is suppressed, the thickness T of the tread 4 can be increased and the depth Hg of the main groove 24 can be increased. As with the tire 2, the depth Hg of the main groove 24 can be increased to improve drainage performance.

  FIG. 7 shows a part of still another tire 54 according to the present invention. The tire 54 includes a band 56 instead of the band 52 of the tire 50. FIG. 8 shows a part of still another tire 58 according to the present invention. The tire 58 includes a band 60 instead of the band 52 of the tire 50. FIG. 9 shows a part of still another tire 62 according to the present invention. The tire 62 includes a band 64 instead of the band 52 of the tire 50. Other configurations of the tire 54, the tire 58, and the tire 62 are the same as those of the tire 50, and a description thereof is omitted. Here, the same configuration as the tire 50 will be described using the same reference numerals.

  In the tire 54 of FIG. 7, double-headed arrows P1, P2, and P3 indicate the axial pitch of the cord. The pitch P <b> 1 indicates the pitch inside the tread surface 22 in the radial direction. Pitches P2 and P3 indicate pitches inside the main groove 24 in the radial direction. The pitch P3 indicates the pitch in the radial direction of the bottom surface 24a, particularly in the center in the axial direction. A double-headed arrow Wc indicates the width from one end to the other end in the axial direction in which the cords 38 are set to the pitch P2. A double-headed arrow Wd indicates the width in the axial direction in which the cords 38 are set to the pitch P3.

  The band 56 of the tire 54 includes a central portion 56a and a pair of end portions 56b. The central portion 56a is a portion indicated by the width Wd. The end portion 56b is obtained by removing the central portion 56a from the portion indicated by the width Wc. The end portion 56b sandwiches the central portion 56a in the axial direction. The pitch P3 is smaller than the pitch P2. The pitch P2 is smaller than the pitch P1. In the band 56, the portion indicated by the width Wc suppresses the vibration of the bottom surface 24a of the main groove 24. The portion indicated by the width Wc of the band 56 functions as a reinforcing member. Furthermore, in this band 56, the rigidity of the center part 56a is made larger than the rigidity of the end part 56b. By providing the central portion 56a, the vibration of the bottom surface 24a is further suppressed.

  The cross-sectional area of the cord 38 per unit width in the central portion 56a is Sc3. The cross-sectional area of the cord 38 per unit width at the end portion 56b is Sc2. Since the pitch P3 is smaller than the pitch P2, the sectional area Sc3 is larger than the sectional area Sc2. The cross-sectional area Sc2 is larger than the cross-sectional area Sc1. The tire 54 can also obtain the same effect as the tire 50.

  In the tire 58 of FIG. 8, the band 60 includes an inner band 66, an intermediate band 68, and an outer band 70. Each of the inner band 66, the middle band 68 and the outer band 70 includes a cord 38 and a topping rubber 40. In each of the inner band 66, the middle band 68, and the outer band 70, the cord 38 is wound at a pitch P1. The pitch of the cord 38 in the inner band 66, the middle band 68, and the outer band 70 may be changed. The inner band 66 is laminated on the outer side in the radial direction of the belt 14. The middle band 68 is laminated outside the inner band 66 in the radial direction. The outer band 70 is laminated on the outer side in the radial direction of the middle band 68.

  In the band 60, the middle band 68 is laminated on the inner band 66 in the range indicated by the width Wc. The middle band 68 is located on the radially inner side of the main groove 24. The band 60 suppresses vibration of the bottom surface 24 a of the main groove 24. The portion indicated by the width Wc of the band 60 functions as a reinforcing member. Further, in this band 60, an outer band 70 is laminated in the range indicated by the width Wd. The band 60 includes a central portion 60a indicated by the width Wd and a pair of end portions 60b indicated by a range of the width Wc excluding the range of the width Wd. The rigidity of the center part 60a is made larger than the rigidity of the end part 60b.

  Also in the tire 58, the cross-sectional area Sc2 per unit width at the end portion 60b is larger than the cross-sectional area Sc1 on the radially inner side of the tread surface 22. The cross-sectional area Sc3 per unit width in the central portion 56a is larger than the cross-sectional area Sc2. The tire 58 can also obtain the same effects as the tire 50.

  In the tire 62 of FIG. 9, the band 64 includes an inner band 66 and an intermediate band 68. The band 64 is configured in the same manner as the tire 58 except that the outer band 70 of the band 60 is not provided. In the band 64, the middle band 68 is laminated on the inner band 66 in the range indicated by the width Wc. The middle band 68 is located on the radially inner side of the main groove 24. The band 64 suppresses vibration of the bottom surface 24 a of the main groove 24. The portion indicated by the width Wc of the band 64 functions as a reinforcing member. The tire 62 can also achieve the same effect as the tire 50.

  In the present invention, the hardness of the rubber is measured with a type A durometer in accordance with JIS K6253. As shown in FIG. 1, a durometer is pressed against the cut section, and the hardness is measured. The measurement is made at a temperature of 23 ° C.

  In the present invention, the size and angle of each member of the tire are measured in a state where the tire is incorporated in a regular rim and filled with air so as to have a regular internal pressure unless otherwise specified. During the measurement, no load is applied to the tire. In this specification, the normal rim means a rim defined in a standard on which a tire depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In this specification, the normal internal pressure means an internal pressure defined in a standard on which the tire depends. “Maximum air pressure” in JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A pneumatic tire having the basic structure shown in FIGS. 1 and 2 was obtained. The tire size was 235 / 45R18. The opening width Wa of the main groove of this tire was 12 mm. The bottom width Wb of the main groove was 7 mm.

[Comparative Example 1]
A conventional pneumatic tire was prepared. Although not shown, this tire had the same structure as that of Example 1 except that the reinforcing rubber member was not provided.

[Example 2]
A pneumatic tire having the basic structure shown in FIG. 3 was obtained. This tire had the same structure as that of Example 1 except that the reinforcing rubber member was different.

[Example 3]
A pneumatic tire having the basic structure shown in FIG. 4 was obtained. This tire had the same structure as that of Example 1 except that the reinforcing rubber member was different.

[Example 4]
A pneumatic tire having the basic structure shown in FIG. 5 was obtained. This tire had the same structure as that of Example 1 except that the reinforcing rubber member was different.

[Example 5-8]
A tire was obtained in the same manner as in Example 1 except that the ratio Ws / Wb between the positional deviation Ws between the main groove and the reinforcing rubber member and the bottom surface width Wb was set as shown in Table 2.

[Comparative Example 9-13]
A tire was obtained in the same manner as in Example 1 except that the thickness Hu was changed as shown in Table 3.

[Examples 14-17]
A tire was obtained in the same manner as in Example 1 except that the thickness Hr of the reinforced rubber member was as shown in Table 4.

[Example 18-21]
A tire was obtained in the same manner as in Example 1 except that the width Wc of the reinforced rubber member was as shown in Table 5.

  The tire of Comparative Example 1 and the tire of Example 1-21 were incorporated into a regular rim 18 × 8.0J. Air was filled so that the internal pressure of these tires was 230 kPa. These tires were evaluated for outside noise, drainage performance and steering stability performance.

[Vehicle noise]
Passage noise during actual coasting was measured. This measurement was carried out on an ISO road surface test course defined by ISO 10844 based on JASO C606. The evaluation results are shown in Tables 1 to 5. This evaluation result is obtained by comparing sound pressure values at a frequency of 800 Hz. In this evaluation result, the evaluation result of the tire of Comparative Example 1 is indicated as 100, and the evaluation results of other tires are indicated as indexes. The evaluation result is preferably as the numerical value is larger.

[Drainage performance]
An inside drum tester was prepared. Using this inside drum tester, a running test was performed on an asphalt wet road surface with a load of 5 kN and a slip angle of 1 ° and a water depth of 5 mm. The generation rate of hydroplaning was evaluated by an index with Comparative Example 1 as 100. The evaluation results are shown in Tables 1 to 5. This evaluation result is excellent in drainage performance, so that a numerical value is high.

[Steering stability]
These tires were mounted on a passenger car having a displacement of 3500 cc. The driver was allowed to drive the passenger car on the racing circuit to evaluate the steering stability performance. The results are shown in Tables 1 to 5 as indices with Comparative Example 1 as 100. The evaluation result is preferably as the numerical value is larger.

[Rolling resistance]
Further, these tires were subjected to a rolling resistance test in accordance with JIS D 4234 based on ISO 28580 using a rolling resistance tester. The rolling resistance coefficient was measured under the following measurement conditions.
Air pressure: 210kPa
Load: 5.3kN
Speed: 80km / h
The results are shown in Tables 1 to 5 as indices with Comparative Example 1 as 100. The evaluation result is preferably as the numerical value is larger.

[Example 22]
A pneumatic tire having the basic structure shown in FIG. 4 was obtained. This tire had the same structure as that of Example 1 except that the reinforcing rubber member was different.

[Comparative Example 2]
A tire having the same structure as that of Example 22 was prepared except that the reinforcing rubber member was not provided.

[Comparative Example 3]
A tire having the same structure as Example 22 was prepared except that the reinforcing rubber member covered the outer peripheral surface of the band from one end to the other end in the axial direction.

[Examples 23-25]
A tire was obtained in the same manner as in Example 22 except that the thickness Hr of the reinforcing rubber member was as shown in Table 6.

[Comparative Example 4]
A tire having the same structure as that of Comparative Example 2 was prepared except that the two-layer full band was used.

[Example 26]
A tire having the same structure as that of Example 22 was prepared except that the band structure shown in FIG. 8 was provided and the reinforcing rubber member was not provided.

[Example 27]
A tire was obtained in the same manner as in Example 22 except that the band structure shown in FIG. 9 was provided and the reinforcing rubber member was not provided.

  The tire of Comparative Example 2-4 and the tire of Examples 22-27 were incorporated into a regular rim 18 × 8.0J. Air was filled so that the internal pressure of these tires was 230 kPa. These tires were evaluated for vehicle noise, drainage performance, steering stability performance, and riding comfort. The outside noise, drainage performance and steering stability performance were measured in the same manner as the tire of Example 1 described above. Furthermore, the rolling resistance of these tires was evaluated. This rolling resistance was also measured under the same measurement conditions as the tire of Example 1 described above. These evaluation results are shown in Tables 6 and 7. This evaluation result is shown as an index with Comparative Example 2 as 100. The evaluation result is preferably as the numerical value is larger.

[Ride comfort]
Riding comfort was evaluated for these tires. These tires were mounted on a passenger car having a displacement of 3500 cc. The driver was driven on the racing circuit to evaluate the ride comfort. The results are shown in Tables 6 and 7 as indices with Comparative Example 2 as 100. The evaluation result is preferably as the numerical value is larger.

[Weight measurement]
Regarding the tire of Comparative Example 2-4 and the tire of Examples 22-27, the weight of the tire alone was measured before assembling the rim. The results are shown in Tables 6 and 7 as indices with Comparative Example 2 as 100. The evaluation result is preferably as the numerical value is larger.

  As shown in Tables 1 to 7, the tire of the example has a higher evaluation than the tire of the comparative example. The tire of Example 9 in Table 3 obtained the same effects as the tires of Examples 10 to 13 in the evaluation results, but cracks were confirmed on the bottom surface of the main groove. From these evaluation results, the superiority of the present invention is clear.

  The invention described above can be widely applied to various tires having a main groove.

2, 42, 44, 46, 50, 54, 58, 62 ... tire 4 ... tread 6 ... sidewall 8 ... clinch 10 ... bead 12 ... carcass 14 ... belt 16, 52, 56, 60, 64 ... Band 18 ... Inner liner 20, 43, 45, 47 ... Reinforcing rubber member 22 ... Tread surface 24 ... Main groove 25 ... Block 26 ... Core 28 ... Apex 30 ... Carcass ply 32 ... Inner layer 34 ... Outer layer 36 ... Reinforcing layer 38 ... Cord 40 ... Topping rubber 66 ... Inside Band 68 ... Middle band 70 ... Outer band

Claims (11)

A tread whose outer surface forms a tread surface, a pair of sidewalls each extending substantially inward in the radial direction from the end of the tread, a pair of beads each positioned radially inward of the sidewalls, and a tread and sidewalls A carcass spanned between one bead and the other bead along the inner side, a belt laminated with the carcass on the inner side in the radial direction of the tread, and a reinforcing member positioned on the outer side in the radial direction of the belt And
A main groove extending in the circumferential direction is formed on the tread surface,
The main groove has a bottom surface facing radially outward,
This reinforcing member extends in the circumferential direction along the bottom surface of the main groove,
A pneumatic tire in which the axial opening width Wa of the main groove is larger than the bottom width Wb of the main groove in the axial direction.   2. The tire according to claim 1, wherein an axial width Wc of the reinforcing member is not less than a bottom surface width Wb of the main groove and not more than an opening width Wa.   The tire according to claim 1 or 2, wherein a ratio Wb / Wa of a bottom width Wb of the main groove to an opening width Wa of the main groove is 0.1 or more. The ratio T / D between the thickness T of the tread and the tire outer diameter D is set to 0.015 or more and 0.020 or less,
The tire according to any one of claims 1 to 3, wherein a ratio Hg / T between a depth Hg and a thickness T of the main groove is 0.725 or more and 0.85 or less.   The tire according to any one of claims 1 to 4, wherein rigidity of the reinforcing member is reduced from an axial center of the reinforcing member toward an axial end.   The tire according to any one of claims 1 to 5, wherein a ratio Ws / Wb between an axial displacement Ws between the reinforcing member and the main groove and a bottom surface width Wb of the main groove is 0.2 or less. The reinforcing member is a reinforcing rubber member made of a crosslinked rubber harder than the tread,
The tire according to any one of claims 1 to 6, wherein the hardness of the reinforcing rubber member is 70 or more and 90 or less.   The tire according to claim 7, wherein the maximum thickness of the reinforcing rubber member is 0.5 mm or more and 1.5 mm or less.   The tire according to claim 7 or 8, wherein a cross-sectional shape of the reinforcing rubber member has a shape in which an axial width is gradually reduced from an inner side in a radial direction toward an outer side.   The tire according to claim 9, wherein the reinforcing rubber member has a triangular cross-sectional shape. A band is provided between the belt and the tread to cover the belt,
This band consists of a cord and topping rubber extending in the circumferential direction,
The cross-sectional area Sc of the cord per unit width of the band is larger on the radially inner side of the main groove than the radially inner side of the tread surface
The tire according to any one of claims 1 to 6, wherein the reinforcing member is a portion of a band in which a cross-sectional area Sc of the cord per unit width is increased.

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