JP2020023219A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire attaining reduction in rolling resistance.SOLUTION: A ratio of a width Wb in a shaft direction of a grounding surface 46 obtained by applying a normal load to a tire produced by compressing and heating a green tire in a mold, which is mounted on a normal rim and has inner pressure adjusted to normal inner pressure and causing a tread surface of the tire to contact a road surface relative to a width Wa in the shaft direction of the grounding surface 46 obtained by applying 80% of the normal load to the tire and causing the tread surface to contact the road surface is 1.05 or more.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire.

  From the viewpoint of consideration for the environment, improvement of fuel efficiency of vehicles is being promoted. In tires, reduction of rolling resistance is required.

Techniques to be considered to reduce rolling resistance include:
(1) thinning of members such as treads and sidewalls; (2) adoption of a rubber composition in which heat generation due to deformation is suppressed; and (3) reduction in the number of parts. However, when such a method is employed, for example, there is a concern that performances such as durability, abrasion resistance, and steering stability may be reduced. For this reason, the rolling resistance is reduced while suppressing the performance degradation (for example, Patent Document 1).

JP 2013-224111 A

  It is required to further reduce the rolling resistance. It is difficult to meet the required level only by the above-described method. Under such circumstances, establishment of a new technique capable of reducing the rolling resistance is required.

  The present invention has been made in view of such circumstances, and has as its object to provide a pneumatic tire with reduced rolling resistance.

  The present inventors have conducted intensive studies in order to reduce the rolling resistance, and found that the change in the axial width of the contact surface with the load (that is, the contact width) affects the degree of distortion at the contact edge, and It has been found that suppressing the distortion contributes to the reduction of the rolling resistance, and the present invention has been completed.

A preferred pneumatic tire according to the present invention is a tire obtained by pressing and heating a raw tire in a mold,
A tread that contacts a road surface at a tread surface extending in a circumferential direction,
A pair of sidewalls that are continuous with the tread, and whose outer surfaces form part of side surfaces,
A pair of beads located radially inward from the sidewall,
A carcass extending from one bead to the other bead inside the tread and the sidewall;
Is provided. The axial width Wb of the ground contact surface obtained by applying the normal load to the tire and bringing the tread surface into contact with the road surface, and incorporating 80% of the normal load to the tire, is incorporated into the normal rim and the internal pressure is adjusted to the normal internal pressure. The ratio of the tread surface to the axial width Wa obtained by applying the load and bringing the tread surface into contact with the road surface is 1.05 or more.

  Preferably, in the pneumatic tire, the contour of the tread surface is represented by a plurality of arcs arranged in the axial direction. The plurality of arcs are, in the axial direction, a center arc located at the center, a pair of middle arcs extending outward from an end of the center arc, and a pair of side arcs extending further outward from the outer end of the middle arc. And The radius TR2 of the middle arc is smaller than the radius TR1 of the center arc, and the radius TR3 of the side arc is smaller than the radius TR2 of the middle arc.

  Preferably, in the pneumatic tire, the ratio of the radius TR2 of the middle arc to the radius TR1 of the center arc is 40% or more and 50% or less. The ratio of the radius TR3 of the side arc to the radius TR1 of the center arc is 30% or more and 45% or less.

  Preferably, in the pneumatic tire, a ratio of an axial distance from an equatorial plane to a boundary between the center arc and the middle arc to a half of a width of the tread is 7% or more and 9% or less. A ratio of an axial distance from the equatorial plane to a boundary between the middle arc and the side arc with respect to a half of a width of the tread is 25% or more and 42% or less.

  Preferably, in this pneumatic tire, the ratio of the radial distance from the bead baseline to the tire maximum width position to the tire cross-sectional height is 48% or less.

  Preferably, in the pneumatic tire, a ratio of a clip width of the mold to a tire cross-sectional width is 100% or less.

  Preferably, in this pneumatic tire, a shoulder surface is located between the tread surface and the side surface. The contour of the shoulder surface is represented by a circular arc, and the radius of the circular arc is 15% or more and 25% or less of the tire section height.

  Preferably, the pneumatic tire includes a belt laminated with the carcass on a radially inner side of the tread. In this tire, the length of the carcass from the axial outer end of the contact surface between the carcass and the belt to the radial outer end of the bead is 83% or more of the tire section height.

  In the pneumatic tire of the present invention, the axial width of the ground contact surface increases as the load applied to the tire increases. In particular, in the conventional tire, the axial width of the ground contact surface obtained by applying the normal load to the tire in the normal state is compared with the axial width of the contact surface obtained by applying a load of 80% of the normal load to the normal tire. This ratio is not less than 1.05 in this tire, while the ratio does not exceed 1.05. In this tire, the change in the axial width of the ground contact surface when the load is increased is larger than that of the conventional tire. In this tire, the concentration of strain on the edge of the ground contact surface is suppressed as compared with the conventional tire. Since the degree of distortion is small, heat generation due to deformation is suppressed. This tire has a lower rolling resistance than a conventional tire. ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire which reduced rolling resistance was achieved is obtained.

FIG. 1 is a sectional view showing a part of a pneumatic tire according to one embodiment of the present invention. FIG. 2 is a diagram illustrating a mold used in manufacturing the tire of FIG. FIG. 3 is a diagram illustrating the shape of the ground contact surface of the tire of FIG. 1. FIG. 4 is a diagram illustrating the shape of the tread surface of the tire of FIG.

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

  FIG. 1 shows a part of a pneumatic tire 2 (hereinafter, may be simply referred to as “tire 2”) according to an embodiment of the present invention. The tire 2 is mounted on a passenger car.

  FIG. 1 shows a part of a cross section of the tire 2 along a plane including a rotation axis of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, a chain line CL represents an equatorial plane of the tire 2.

  In FIG. 1, the tire 2 is incorporated in a rim R. This rim R is a regular rim. The inside of the tire 2 is filled with air, and the internal pressure of the tire 2 is adjusted to a normal internal pressure. No load is applied to the tire 2.

  In the present invention, a state in which the tire 2 is incorporated into the rim R (regular rim), the internal pressure of the tire 2 is adjusted to the normal internal pressure, and no load is applied to the tire 2 is referred to as a normal state. In the present invention, unless otherwise specified, the dimensions and angles of the tire 2 and each part of the tire 2 are measured in a normal state.

  In this specification, the regular rim means a rim defined in a standard on which the tire 2 depends. The “standard rim” in the JATMA standard, the “Design Rim” in the TRA standard, and the “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 2 depends. The “maximum value” described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the JATMA standard, “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “INFLATION PRESSURE” in the ETRTO standard are normal internal pressures.

  In the present specification, the normal load means a load determined in a standard on which the tire 2 depends. The “maximum load capacity” in the JATMA standard, the “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and the “LOAD CAPACITY” in the ETRTO standard are normal loads.

  In FIG. 1, a solid line BBL extending in the axial direction is a bead base line. The bead base line is a line that defines the rim diameter (see JATMA or the like) of the rim R (regular rim).

  The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a pair of chafers 12, a carcass 14, a belt 16, a band 18, and an inner liner 20.

  The tread 4 contacts the road surface at its outer surface 22. The outer surface 22 of the tread 4 is a tread surface. The tread surface 22 extends in the circumferential direction. A groove 24 is formed in the tread 4.

  In the tire 2, the tread 4 includes a base portion 26 and a cap portion 28 located radially outside the base portion 26. The base 26 is made of a crosslinked rubber in consideration of adhesiveness. The cap portion 28 is made of a crosslinked rubber in consideration of wear resistance and grip performance.

  In FIG. 1, the symbol PE is the equator of the tire 2. This equator PE is the intersection of the virtual tread surface and the equatorial surface obtained assuming that there is no groove 24. The double arrow H is the radial distance from the bead baseline to the equator PE. The radial distance H is a sectional height of the tire 2 (see JATMA or the like).

  Each sidewall 6 continues to the end of the tread 4. The sidewall 6 extends radially inward from the end of the tread 4 along the carcass 14. The sidewall 6 is made of a crosslinked rubber. The sidewall 6 protects the carcass 14. The outer surface 30 s of the sidewall 6 forms a part of the side surface 30 of the tire 2.

  Each clinch 8 is located inside the sidewall 6 in the radial direction. As shown in FIG. 1, a part of the clinch 8 comes into contact with the flange RF of the rim R. The clinch 8 is made of a crosslinked rubber in consideration of wear resistance. The outer surface 30c of the clinch 8 forms a part of the side surface 30 of the tire 2.

  In FIG. 1, reference symbol PW indicates an axially outer end of the tire 2. The outer end PW is specified based on the outer surface 30s of the sidewall 6 and the outer surface 30c of the clinch 8, that is, a virtual side surface obtained assuming that the side surface 30 of the tire 2 has no decoration such as a pattern or character. You. The axial distance from one outer end PW to the other outer end PW is the maximum width of the tire 2, that is, the cross-sectional width of the tire 2 (see JATMA or the like). The outer end PW is a position where the tire 2 has a maximum width (hereinafter, also referred to as a maximum width position of the tire 2).

  The bead 10 is located inside the clinch 8 in the axial direction. The bead 10 is located radially inward of the sidewall 6. The bead 10 includes a core 32 and an apex 34. The core 32 extends in the circumferential direction. As shown in FIG. 1, the core 32 has a rectangular cross-sectional shape. The core 32 includes a steel wire. The apex 34 is located radially outside the core 32. In the cross section of the tire 2 shown in FIG. 1, the apex 34 is tapered radially outward. In this tire 2, the apex 34 is made of a crosslinked rubber having high rigidity.

  Each chafer 12 is located radially inside the bead 10. As shown in FIG. 1, at least a portion of the chafer 12 contacts the sheet RS of the rim R. In this tire 22, the chafer 12 is made of cloth and rubber impregnated in the cloth.

  The carcass 14 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 14 extends from one bead 10 to the other bead 10. The carcass 14 includes at least one carcass ply 36. In the tire 2, the carcass 14 is composed of one carcass ply 36.

  Although not shown, the carcass ply 36 includes a number of carcass cords arranged in parallel. These carcass cords are covered with topping rubber. Each carcass cord intersects the equatorial plane. In the tire 2, the angle formed by the carcass cord with respect to the equatorial plane is 70 ° or more and 90 ° or less. The carcass 14 of the tire 2 has a radial structure. In the tire 2, a cord made of an organic fiber is used as a carcass cord. The organic fibers include nylon fibers, polyester fibers, rayon fibers and aramid fibers.

  In the tire 2, the carcass ply 36 is folded around each core 32. The carcass ply 36 includes a main body 38 that bridges the one core 32 and the other core 32, and a pair of main bodies 38 that are connected to the main body 38 and that are folded around the respective cores 32 from the inside in the axial direction to the outside. And a folded portion 40. In the tire 2, the end 40a of the folded portion 40 is located outside the maximum width position PW in the radial direction.

  The belt 16 is laminated on the carcass 14 inside the tread 4 in the radial direction. In the axial direction, the width of the belt 16 is set in a range of 0.85 to 1.05 times a width TW of the tread 4 described later.

  In FIG. 1, reference symbol CV is an axially outer end of a contact surface between the belt 16 and the carcass 14. In the axial direction, the outer end CV is located inside the end 42 of the belt 16.

  In the tire 2, the belt 16 is composed of two belt plies 44. The inner belt ply 44 is also referred to as an inner layer 44a. The outer belt ply 44 is also called an outer layer 44b. As shown in FIG. 1, the width of the inner layer 44a is smaller than the width of the outer layer 44b in the axial direction.

  Although not shown, each belt ply 44 includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The angle formed by the belt cord with respect to the equatorial plane is 10 ° or more and 35 ° or less. In this tire 2, the material of the belt cord is steel.

  The band 18 is located between the tread 4 and the belt 16 in the radial direction. The band 18 covers the entire belt 16. This band 18 is also called a full band. In the case of a full band, the width of the band 18 is set in a range of 0.9 to 1.1 times the width of the belt 16 in the axial direction. This band 18 has a jointless structure. Although not shown, the band 18 includes a spirally wound band cord. A cord made of organic fibers is used as a band cord.

  The inner liner 20 is located inside the carcass 14. The inner liner 20 forms an inner surface of the tire 2. The inner liner 20 is made of a crosslinked rubber having excellent air shielding properties. The inner liner 20 holds the internal pressure of the tire 2.

  The tire 2 described above is manufactured as follows. In the manufacture of the tire 2, an uncrosslinked tire 2, that is, a raw tire, is formed by combining members such as the tread 4 and the sidewall 6 in a forming machine (not shown). In the manufacture of the tire 2, a raw tire is put into a mold.

  As shown in FIG. 2, the outer surface of the raw tire 2 r put into the mold M comes into contact with the cavity surface C of the mold M. The inner surface of the raw tire 2r contacts the bladder B. When a rigid core (not shown) is used instead of the bladder B, the inner surface of the raw tire 2r contacts the rigid core. The green tire 2r is pressurized and heated in the mold M. Thereby, the tire 2 shown in FIG. 1 is obtained.

  FIG. 3 shows a transfer diagram of the ground contact surface 46 obtained by bringing the tire 2 shown in FIG. 1 into contact with a flat road surface. 3, the left-right direction is the axial direction of the tire 2, and the up-down direction is the circumferential direction of the tire 2. The direction perpendicular to the paper is the radial direction of the tire 2.

  The ground contact surface 46a shown in FIG. 3A is obtained by applying a load of 80% of the normal load to the tire 2 in a normal state and bringing the tire 2 into contact with the road surface at a camber angle of 0 °. In FIG. 3A, the double-headed arrow Wa indicates the axial width of the ground plane 46a.

  The contact surface 46b shown in FIG. 3B is obtained by applying a normal load to the tire 2 in a normal state and bringing the tire 2 into contact with a road surface at a camber angle of 0 °. In FIG. 3B, the double-headed arrow Wb is the axial width of the ground plane 46b.

The tire 2 is a tire 2 obtained by pressing and heating a raw tire 2r in a mold M. And this tire 2
A tread 4 that contacts a road surface at a tread surface 22 extending continuously in a circumferential direction;
A pair of sidewalls 6 connected to the tread 4 and having an outer surface forming part of the side surface 30;
A pair of beads 10 located radially inward of the sidewalls 6,
A carcass 14 extending from one bead 10 toward the other bead 10 inside the tread 4 and the sidewall 6;
Is provided. Then, a normal load is applied to the tire 2 in the normal state, and a load of 80% of the normal load is applied to the tire 2 in the normal state having the axial width Wb of the tread surface 46b obtained by bringing the tread surface 22 into contact with the road surface. The ratio of the ground contact surface 46a obtained by bringing the tread surface 22 into contact with the road surface to the axial width Wa is 1.05 or more.

  In the tire 2, the axial width of the ground contact surface 46 increases as the load applied to the tire 2 increases. In the conventional tire, the ratio of the axial width of the tread obtained by applying the normal load to the tire in the normal state to the axial width of the tread obtained by applying a load of 80% of the normal load to the tire in the normal state Does not exceed 1.05, whereas in the tire 2, this ratio is 1.05 or more. In the tire 2, a change in the axial width of the ground contact surface 46 when the load is increased is larger than that of the conventional tire. In the tire 2, the concentration of strain on the end of the ground contact surface 46, that is, on the axially outer portion of the ground contact surface 46 is suppressed as compared with the conventional tire. Since the degree of distortion is small, heat generation due to deformation is suppressed. The tire 2 has a lower rolling resistance than a conventional tire. In the tire 2, a reduction in rolling resistance is achieved.

  As shown in FIG. 3, as the axial width of the ground plane 46 increases, the ground area increases. If the ground area is too large, there is a possibility that the rolling resistance will increase. From this viewpoint, in this tire 2, the ratio of the axial width Wb of the ground contact surface 46b to the axial width Wa of the ground contact surface 46a is preferably 1.4 or less, more preferably 1.35 or less, and 1.25 or less. More preferred.

  FIG. 4 shows the outline of the tire 2. The contour is specified in a cross section of the tire 2 along a plane including the rotation axis of the tire 2. 4, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2.

  The outline shown in FIG. 4 shows a state in which the tire 2 is incorporated into the rim R (regular rim), the internal pressure of the tire 2 is adjusted to 10% of the normal internal pressure, and no load is applied to the tire 2. It is a contour. This contour corresponds to the shape of the cavity surface C of the mold M.

  The outer surface of the tire 2 includes a tread surface 22, a pair of shoulder surfaces 48 connected to the tread surface 22, and a pair of side surfaces 30 further connected to the shoulder surface 48.

  In the tire 2, the contour of the tread surface 22 shown in FIG. 4 is represented by a plurality of arcs 50 arranged in the axial direction. These arcs 50 are, in the axial direction, a center arc 50c positioned at the center, a pair of middle arcs 50m extending outward from an end of the center arc 50c, and a pair of middle arcs 50m extending further outward from the outer end of the middle arc 50m. And a side arc 50s.

  In FIG. 4, the arrow TR1 is the radius of the center arc 50c. Arrow TR2 is the radius of the middle arc 50m. The arrow TR3 is the radius of the side arc 50s. The symbol P1 is a boundary between the center arc 50c and the middle arc 50m. In the tire 2, the center arc 50c and the middle arc 50m contact at this boundary P1. This boundary P1 is a contact point between the center arc 50c and the middle arc 50m. The symbol P2 is a boundary between the middle arc 50m and the side arc 50s. In the tire 2, the middle arc 50m and the side arc 50s contact at this boundary P2. This boundary P2 is a contact point between the middle arc 50m and the side arc 50s.

  In this tire 2, the radius TR2 of the middle arc 50m is smaller than the radius TR1 of the center arc 50c, and the radius TR3 of the side arc 50s is smaller than the radius TR2 of the middle arc 50m. In the tire 2, when the load applied to the tire 2 is increased, the axial width of the ground contact surface 46 does not converge to a constant value, but increases. In the tire 2, the change in the axial width of the ground contact surface 46 when the load is increased is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced. From this viewpoint, in the tire 2, it is preferable that the radius TR2 of the middle arc 50m is smaller than the radius TR1 of the center arc 50c, and the radius TR3 of the side arc 50s is smaller than the radius TR2 of the middle arc 50m. In the tire 2, the radius TR1 of the center arc 50c is usually set in the range of 500 mm to 1000 mm.

  In this tire 2, the ratio of the radius TR2 of the middle arc 50m to the radius TR1 of the center arc 50c is preferably 40% or more, and more preferably 50% or less. Thereby, the tire 2 is configured such that when the load applied to the tire 2 is increased, the axial width of the ground contact surface 46 is increased. In the tire 2, since the concentration of the strain on the end of the ground contact surface 46 is suppressed, the rolling resistance can be reduced.

  In the tire 2, the ratio of the radius TR3 of the side arc 50s to the radius TR1 of the center arc 50c is preferably 30% or more, and more preferably 45% or less. In the tire 2, the tread surface 22 is configured such that the side arc 50s has a larger radius TR3 than the side arc in the conventional tire. In the tire 2, when the load applied to the tire 2 is increased, the change in the axial width of the ground contact surface 46 is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced. In this respect, the ratio is more preferably equal to or greater than 32% and more preferably equal to or less than 41%.

  From the viewpoint of effectively reducing the rolling resistance, in the tire 2, the ratio of the radius TR2 of the middle arc 50m to the radius TR1 of the center arc 50c is 40% or more and 50% or less, and the radius TR3 of the side arc 50s is not more than 50%. The ratio of the center arc 50c to the radius TR1 is more preferably 30% or more and 45% or less.

  As described above, in the tire 2, the radius TR3 of the side arc 50s is smaller than the radius TR2 of the middle arc 50m. From the viewpoint of reducing the rolling resistance, in the tire 2, the ratio of the radius TR3 of the side arc 50s to the radius TR2 of the middle arc 50m is preferably equal to or greater than 60%, and more preferably equal to or less than 90%.

  In this tire 2, the shoulder surface 48 is located between the tread surface 22 and the side surface 30. In FIG. 4, reference symbol Pt is a boundary between the tread surface 22 and the shoulder surface 48. This boundary Pt is the end of the tread surface 22 and the inner end of the shoulder surface 48. The symbol Ps is a boundary between the shoulder surface 48 and the side surface 30. This boundary Ps is the outer end of the shoulder surface 48 and the outer end of the side surface 30. The shoulder surface 48 connects the tread surface 22 and the side surface 30.

  In the tire 2, the contour of the shoulder surface 48 shown in FIG. In the tire 2, the arc 52 representing the shoulder surface 48, that is, the shoulder arc 52 contacts the side arc 50s at the boundary Pt. Although not described in detail, a portion of the contour of the side surface 30 on the shoulder surface 48 side is represented by an arc or a straight line. In the tire 2, the shoulder arc 52 is in contact with a straight line or an arc representing the contour of the side surface 30 at the boundary Ps. In FIG. 4, the arrow SR indicates the radius of the shoulder arc 52.

  In FIG. 4, reference symbol TE is a reference point that defines the width TW of the tread 4 of the tire 2. The reference point TE is specified by the intersection of the tangent to the shoulder arc 52 at the inner end Pt and the tangent to the shoulder arc 52 at the outer end Ps. In the tire 2, the width TW of the tread 4 is represented by the axial distance from one reference point TE to the other reference point TE.

  In FIG. 4, the double-headed arrow WP1 is the axial distance from the equatorial plane to the boundary P1 between the center arc 50c and the middle arc 50m. The double arrow WP2 is the axial distance from the equatorial plane to the boundary P2 between the middle arc 50m and the side arc 50s.

  In the tire 2, the ratio of the axial distance WP1 from the equatorial plane to the boundary P1 between the center arc 50c and the middle arc 50m to half the width TW of the tread 4 is preferably 7% or more, and more preferably 9% or less. Thereby, the tire 2 is configured such that when the load applied to the tire 2 is increased, the axial width of the ground contact surface 46 is increased. In the tire 2, since the concentration of the strain on the end of the ground contact surface 46 is suppressed, the rolling resistance can be reduced.

  In the tire 2, the ratio of the axial distance WP2 from the equatorial plane to the boundary P2 between the middle arc 50m and the side arc 50s to half the width TW of the tread 4 is preferably 25% or more, and more preferably 42% or less. In the tire 2, the tread surface 22 is configured such that the side arc 50s has a larger radius TR3 than the side arc in the conventional tire. In the tire 2, when the load applied to the tire 2 is increased, the change in the axial width of the ground contact surface 46 is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced. In this respect, the ratio is more preferably equal to or greater than 27% and more preferably equal to or less than 34%.

  From the viewpoint of effectively reducing the rolling resistance, in the tire 2, the ratio of the axial distance WP1 from the equatorial plane to the boundary P1 between the center arc 50c and the middle arc 50m with respect to half the width TW of the tread 4 is 7%. % To 9%, and the ratio of the axial distance WP2 from the equatorial plane to the boundary P2 between the middle arc 50m and the side arc 50s to half the width TW of the tread 4 is 25% to 42%. More preferred.

  In FIG. 4, the double-headed arrow Wt is an axial distance from an end Pt of one tread surface 22 to an end Pt of the other tread surface 22. The axial distance Wt is the width of the tread surface 22.

  In the tire 2, the ratio of the width TW of the tread 4 to the width Wt of the tread surface 22 is preferably 80% or more, and more preferably 90% or less. Thereby, the tread surface 22 is configured such that the side arc 50s has a larger radius TR3 than the side arc in the conventional tire. In the tire 2, when the load applied to the tire 2 is increased, the change in the axial width of the ground contact surface 46 is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced.

  As described above, by configuring the tread surface 22 with an unconventional contour, the tire 2 having a large change in the axial width of the ground contact surface 46 when the load applied to the tire 2 is increased is obtained. In the present invention, even when the load applied to the tire 2 is increased by a method other than forming the tread surface 22 with an unconventional contour, the tire 2 having a large change in the axial width of the ground contact surface 46 can be obtained. can get. Hereinafter, this method will be described.

  In FIG. 1, the double arrow LP indicates the length of the main body 38 of the carcass 14 from the axial outer end CV of the contact surface between the belt 16 and the carcass 14 to the outer end 54 of the apex 34. This length LP is also called a code path. The double-headed arrow HW is a radial distance from the bead base line to the maximum width position PW.

  In this tire 2, the cord path LP is preferably 83% or more of the sectional height H of the tire 2. In the tire 2, a long code path LP is formed. In the tire 2, the contact surface 46 easily spreads in the axial direction by the action of the load. In other words, in the tire 2, when the load applied to the tire 2 is increased, the change in the axial width of the ground contact surface 46 is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced. In this respect, the ratio of the code path LP to the cross-sectional height H is more preferably equal to or greater than 84%, and still more preferably equal to or greater than 86%. If this ratio is too large, the rigidity of the tire 2 may be insufficient. In light of maintaining good steering stability and durability, this ratio is preferably equal to or less than 97%, and more preferably equal to or less than 96%.

  In this tire 2, the ratio of the radial distance HW from the bead base line to the maximum width position PW to the sectional height H is preferably 48% or less. By setting this ratio to 48% or less, a long code path LP is formed in the tire 2. In the tire 2, the contact surface 46 easily spreads in the axial direction by the action of the load. In other words, in the tire 2, when the load applied to the tire 2 is increased, the change in the axial width of the ground contact surface 46 is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced. In this respect, the ratio is more preferably equal to or less than 40%. If the ratio is too small, the rigidity of the tire 2 may be insufficient. From the viewpoint of maintaining good steering stability and durability, this ratio is preferably 30% or more.

  In FIG. 2, the double arrow CW is the clip width of the mold M. The mold M has a bead outer surface forming surface BF that forms a contact surface 58 of the bead portion 56 of the tire 2 with the flange RF. The clip width CW is represented by an axial distance from one bead outer surface forming surface BF to the other bead outer surface forming surface BF.

  In the tire 2, the ratio of the clip width CW of the mold M to the sectional width W of the tire 2 is preferably 100% or less. By setting this ratio to 100% or less, a long code path LP is formed in the tire 2. In the tire 2, the contact surface 46 easily spreads in the axial direction by the action of the load. In other words, in the tire 2, when the load applied to the tire 2 is increased, the change in the axial width of the ground contact surface 46 is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced. In this respect, the ratio is more preferably equal to or less than 91%. If the ratio is too small, the rigidity of the tire 2 may be insufficient. From the viewpoint of maintaining good steering stability and durability, this ratio is preferably 86% or more.

  In the tire 2, the radius SR of the shoulder arc 52 is preferably 15% or more of the sectional height H of the tire 2, and more preferably 25% or less. Thereby, a long code path LP is formed in the tire 2. In the tire 2, the contact surface 46 easily spreads in the axial direction by the action of the load. In other words, in the tire 2, when the load applied to the tire 2 is increased, the change in the axial width of the ground contact surface 46 is large. Since the concentration of strain on the end of the ground contact surface 46 is suppressed, the rolling resistance of the tire 2 is reduced.

  As described above, even when the long cord path LP is formed, similarly to the case where the tread surface 22 is formed with an unconventional contour, the axial direction of the ground contact surface 46 when the load applied to the tire 2 is increased. The tire 2 having a large width change margin can be obtained. In the present invention, a method of forming a long code path LP and a method of forming the tread surface 22 with an unconventional contour can be used in combination. In this case, it is possible to more effectively obtain the tire 2 having a large margin of change in the axial width of the ground contact surface 46 when the load applied to the tire 2 is increased.

  As is apparent from the above description, according to the present invention, the pneumatic tire 2 in which the rolling resistance has been reduced can be obtained.

  The embodiment disclosed this time is an example in all respects and is not restrictive. The technical scope of the present invention is not limited to the above-described embodiment, and includes all modifications within a scope equivalent to the configuration described in the claims.

  Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited to only such Examples.

[Example 1]
A pneumatic tire (tire size = 185 / 60R15) for a passenger car having the basic configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained.

  In the first embodiment, the ratio (TR2 / TR1) of the radius TR2 of the middle arc to the radius TR1 of the center arc is set to 50%. The ratio (TR3 / TR1) of the radius TR3 of the side arc to the radius TR1 of the center arc was set to 37%. The ratio (2 · WP1 / TW) of the axial distance WP1 from the equatorial plane to the boundary P1 between the center arc and the middle arc with respect to half the tread width TW was set to 8%. The ratio (2 · WP2 / TW) of the axial distance WP2 from the equatorial plane to the boundary P2 between the middle arc and the side arc with respect to half the width TW of the tread was set to 34%.

  In the first embodiment, the ratio (HW / H) of the radial distance HW from the bead base line to the tire maximum width position PW to the sectional height H was set to 48%. The ratio (CW / W) of the clip width CW of the mold to the cross-sectional width W was set to 91%. The ratio (SR / H) of the radius SR of the shoulder arc to the section height H was set to 27%. The ratio (LP / H) of the length LP of the carcass to the cross-sectional height H from the axial outer end CV of the contact surface between the carcass and the belt to the radial outer end of the bead was set to 84%.

[Comparative Example 1]
Same as Example 1 except that the ratio (TR2 / TR1), ratio (TR3 / TR1), ratio (2 · WP1 / TW) and ratio (2 · WP2 / TW) were as shown in Table 1 below. Thus, a tire of Comparative Example 1 was obtained. Comparative Example 1 is a conventional tire.

[Example 2]
A tire of Example 2 was obtained in the same manner as Example 1 except that the ratio (TR2 / TR1) was as shown in Table 1 below.

[Example 3-5 and Comparative Example 2-4]
Tires of Example 3-5 and Comparative Example 2-4 were obtained in the same manner as in Example 1 except that the ratio (TR3 / TR1) was as shown in Tables 1 and 2 below.

[Example 6-8 and Comparative Example 5]
Tires of Examples 6-8 and Comparative Example 5 were obtained in the same manner as in Example 1 except that the ratio (2 · WP2 / TW) was as shown in Table 2 below.

[Example 9-11]
Tires of Examples 9 to 11 were obtained in the same manner as in Example 1 except that the ratio (HW / H) and the ratio (LP / H) were as shown in Table 3 below.

[Examples 12 and 15]
Tires of Examples 12 and 15 in the same manner as Example 1 except that the ratio (CW / W), the ratio (HW / H) and the ratio (LP / H) were as shown in Tables 3 and 4 below. I got

[Example 13-14]
The same as Example 1 except that the ratio (2 · WP2 / TW), ratio (CW / W), ratio (HW / H) and ratio (LP / H) were as shown in Tables 3 and 4 below. Thus, tires of Examples 12 to 13 were obtained.

[Example 16]
Example 1 was repeated in the same manner as in Example 1 except that the ratio (SR / H), the ratio (CW / W), the ratio (HW / H), and the ratio (LP / H) were as shown in Table 4 below. 15 tires were obtained.

[Example 17]
Except that the ratio (2 · WP2 / TW), ratio (CW / W), ratio (HW / H) and ratio (LP / H) were as shown in Table 4 below, the same as in Example 1, The tire of Example 15 was obtained.

[Measurement of axial width of contact surface]
The prototype tire was mounted on a rim (size = 15 × 5.5 J), and the inside of the tire was filled with air to adjust the internal pressure to 210 kPa. Using a tire tread surface analyzer, an axial width Wa of the tread surface obtained by applying a load of 80% of the normal load to the tire and bringing the tread surface into contact with the road surface, and making the tread surface contact the road surface by applying the regular load to the tire. Thus, the axial width Wb of the contact surface obtained as described above was obtained. The ratio (Wb / Wa) of the axial width Wb to the axial width Wa was calculated. The results are shown in Tables 1 to 4 below.

[Rolling resistance]
The prototype tire was mounted on a regular rim, and the internal pressure was adjusted to 210 kPa. The rolling resistance (RR) was measured using a rolling resistance tester. The load was set to 80% of the normal load. The speed was set at 60 km / h. The results are shown by indexes in Tables 1 to 4 below. The smaller the value, the lower the rolling resistance.

  As shown in Tables 1 to 4, the rolling resistance of the example is smaller than the rolling resistance of the comparative example. The examples have higher evaluations than the comparative examples. From the evaluation results, the superiority of the present invention is clear.

  The technology for reducing rolling resistance described above is also applied to various tires.

2 ... tire 2 r ... raw tire 4 ... tread 6 ... sidewall 8 ... clinch 10 ... bead 14 ... carcass 16 ... belt 18 ... band 22 ...・ Tread surface (outer surface)
30 ... side surface (outer surface)
30s: outer surface of sidewall 6 30c: outer surface of clinch 8 42: end of belt 16 46, 46a, 46b: ground surface 48: shoulder surface 50: arc of tread surface 22 50c: Center arc 50m: Middle arc 50s: Side arc 52: Arc on shoulder surface (shoulder arc)
56: Bead part 58: Contact surface with flange RF

Claims (8)

A tire obtained by pressing and heating a raw tire in a mold,
A tread that contacts a road surface on a tread surface extending continuously in a circumferential direction,
A pair of sidewalls that are continuous with the tread, and whose outer surfaces form part of side surfaces,
A pair of beads located radially inward from the sidewall,
A carcass extending from one bead to the other bead inside the tread and the sidewall;
With
The axial width Wb of the ground contact surface obtained by applying the normal load to the tire and bringing the tread surface into contact with the road surface, and incorporating 80% of the normal load to the tire, is incorporated into the normal rim and the internal pressure is adjusted to the normal internal pressure. A pneumatic tire, wherein a ratio of a tread surface to an axial width Wa obtained by contacting the tread surface with a road surface under a load is 1.05 or more. The contour of the tread surface is represented by a plurality of arcs juxtaposed in the axial direction,
The plurality of arcs are, in the axial direction, a center arc located at the center, a pair of middle arcs extending outward from an end of the center arc, and a pair of side arcs extending further outward from the outer end of the middle arc. And
A radius TR2 of the middle arc is smaller than a radius TR1 of the center arc;
The pneumatic tire according to claim 1, wherein a radius TR3 of the side arc is smaller than a radius TR2 of the middle arc. A ratio of the radius TR2 of the middle arc to the radius TR1 of the center arc is 40% or more and 50% or less;
The pneumatic tire according to claim 2, wherein a ratio of a radius TR3 of the side arc to a radius TR1 of the center arc is 30% or more and 45% or less. A ratio of an axial distance from an equatorial plane to a boundary between the center arc and the middle arc to a half of a width of the tread is 7% or more and 9% or less;
The pneumatic tire according to claim 2 or 3, wherein a ratio of an axial distance from the equatorial plane to a boundary between the middle arc and the side arc with respect to a half of a width of the tread is 25% or more and 42% or less. .   The pneumatic tire according to any one of claims 1 to 4, wherein a ratio of a radial distance from a bead base line to a tire maximum width position to a tire cross-sectional height is 48% or less.   The pneumatic tire according to any one of claims 1 to 5, wherein a ratio of a clip width of the mold to a tire cross-sectional width is 100% or less. A shoulder surface is located between the tread surface and the side surface,
The pneumatic tire according to any one of claims 1 to 6, wherein the contour of the shoulder surface is represented by an arc, and a radius of the arc is 15% or more and 25% or less of a tire cross-sectional height. On the radially inner side of the tread, a belt stacked with the carcass is provided,
8. The carcass according to claim 1, wherein a length of the carcass from an axial outer end of a contact surface between the carcass and the belt to a radial outer end of the bead is 83% or more of a tire sectional height. The pneumatic tire described in Crab.