JP6245701B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire. In particular, the present invention relates to improvements in tire treads.

  In recent years, the demand for lower fuel consumption of vehicles has become particularly strong due to environmental considerations. Since tires affect the fuel efficiency of a vehicle, the development of “low fuel consumption tires” that contribute to the reduction of fuel consumption is underway.

  In order to achieve low fuel consumption by using a tire, it is important to reduce the rolling resistance of the tire. The tire repeats deformation and restoration as it rolls. The energy loss resulting from this deformation and restoration is the main cause of tire rolling resistance. It is the tread that has the greatest loss at the tire site. Reducing this loss in the tread greatly contributes to a reduction in rolling resistance.

  An example of a study for reducing energy loss in a tread is disclosed in JP-A-2005-96747. In this tire, the tread cap layer is made of rubber having a small loss tangent to suppress energy loss in the tread.

JP 2005-96747 A

  As disclosed in JP-A-2005-96747, the use of rubber having a low loss tangent as a tread material can suppress tire rolling resistance. However, a tread using rubber having a low loss tangent for the cap layer is inferior in gripping force. This leads to a decrease in the braking performance of the vehicle. In the tire disclosed in Japanese Patent Laid-Open No. 2005-96747, it may happen that sufficient braking performance cannot be obtained.

  An object of the present invention is to provide a pneumatic tire in which a low rolling resistance is achieved while suppressing a decrease in grip force.

  The pneumatic tire according to the present invention includes a tread whose outer surface forms a tread surface. The tread includes a center portion, a front shoulder portion Sf, and a back shoulder portion Sb. The center portion is located at the center of the tread. The front shoulder portion Sf is located in the outer direction of the vehicle when the tire is mounted on the vehicle with respect to the center portion. In the axial direction, when the width from the equator plane to the boundary Bf between the center portion and the front shoulder portion Sf is Wf, the ratio (Wf / Wt) of the width Wf to the width Wt of the tread is 0.25 or more. 0.35 or less. The front shoulder portion Sf includes a front principal muscle that extends in the circumferential direction and forms a part of the tread surface, and a front auxiliary muscle that extends in the circumferential direction and forms a part of the tread surface. In the front shoulder portion Sf, the front accessory muscle is disposed at the inner end in the axial direction, and the front principal muscle and the front accessory muscle are alternately disposed toward the outer side. The back shoulder portion Sb is located in the vehicle inner direction with respect to the center portion when the tire is mounted on the vehicle. In the axial direction, when the width from the equator plane to the boundary Bb between the center portion and the back shoulder portion Sb is Wb, the ratio (Wb / Wt) of the width Wb to the width Wt is not less than 0.25. 35 or less. The back shoulder portion Sb includes a back main bar that extends in the circumferential direction and forms a part of the tread surface, and a back auxiliary bar that extends in the circumferential direction and forms a part of the tread surface. In the back shoulder portion Sb, the back accessory muscle is arranged at the inner end in the axial direction, and the back principal muscle and the back accessory muscle are alternately arranged toward the outside. The back accessory muscle width TSb is larger than the front accessory muscle width TSf. The total width of the back accessory muscles is larger than the total width of the front accessory muscles. The front main bar and the back main bar are made of a first rubber. The front accessory muscle and the back accessory muscle are made of a second rubber. The loss tangent LT2 of the second rubber is lower than the loss tangent LT1 of the first rubber.

  Preferably, the ratio of the width TSb to the width TSf (TSb / TSf) is 1.5 or more and 2.5 or less.

  Preferably, the width TSf is not less than 1.5 mm and not more than 3.0 mm.

  Preferably, the number of back accessory muscles is 3 or more, and the number of front accessory muscles is 3 or more.

  Preferably, when the ground contact end located in the vehicle outer direction is set to Ef when the tire is mounted on the vehicle, the sum of the widths of the front and rear auxiliary muscles located in the vehicle outward direction from the ground contact end Ef is It is larger than the sum of the widths of the sphincter muscles positioned inward of the vehicle from Ef.

  Preferably, when this tire is attached to the vehicle, when the ground contact end located in the vehicle inner direction is Eb, the total width of the back accessory muscles located in the vehicle inner direction from the ground contact end Eb is the ground contact end. It is larger than the sum of the widths of the back accessory muscles located in the vehicle outer direction from Eb.

  Preferably, the tread includes a main groove extending in a substantially circumferential direction. In the vehicle outer direction, the boundary Bf is located outside the outer end of the main groove located on the outermost side. The distance between the boundary Bf and the outer end is 7 mm or more. In the inner direction of the vehicle, the boundary Bb is located on the inner side of the inner end of the innermost main groove. The distance between the boundary Bb and the inner end is 7 mm or more.

  When the vehicle turns, a large load is applied to the shoulder portion of the outer ring tread surface when the vehicle is mounted on the outer side (referred to as the front side) of the vehicle. When turning, the grip strength of the outer shoulder portion of the outer ring is important. On the other hand, during turning, the load applied to the shoulder portion in the inner side direction of the vehicle (referred to as the back side) when mounted on the vehicle is small. The impact of the back shoulder on the grip during turning is small.

  When the vehicle travels straight, it is mainly the center portion of the tread surface that comes into contact with the ground. Many vehicles use negative camber. For this reason, the area of the center portion to be grounded is particularly large. During straight running, the area where the back and front shoulders are in contact with the ground is smaller than the center. The influence of the back and front shoulders on the grip force when going straight is small.

  The tire according to the present invention includes a center portion, a front shoulder portion located on the front side of the center portion, and a back shoulder portion located on the back side of the center portion. In the front shoulder portion, the front major muscle and the front minor muscle are arranged. The back main muscle and the back auxiliary muscle are arranged in the back shoulder portion. The front and back main bars are made of the first rubber. The front and back accessory muscles are composed of the second rubber. The loss tangent LT2 of the second rubber is smaller than the loss tangent LT2 of the first rubber. Front and back sub-bars having a small loss tangent can reduce tire rolling resistance. This tire contributes to improving the fuel efficiency of the vehicle.

  In this tire, the total width of the front accessory muscles arranged in the front shoulder portion is smaller than the total width of the back accessory muscles arranged in the rear shoulder portion. When turning, a load is mainly applied to the front shoulder portion. The effect of this small width accessory muscle on the grip force of the tire is small. The effect of the splint with a small loss tangent on the grip force during turning is suppressed. In this tire, a good grip force at the time of turning is maintained.

  In this tire, the total width of the back accessory muscles arranged in the back shoulder portion is larger than the total width of the front accessory muscles arranged in the front shoulder portion. A large back accessory muscle further reduces rolling resistance more effectively. As described above, the influence of the back shoulder portion on the grip force of the tire during turning and straight traveling is small. In this tire, rolling resistance is effectively suppressed while maintaining a good gripping force during turning and straight traveling.

FIG. 1 is a cross-sectional view showing a part of a tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire of FIG. FIG. 3 is an enlarged cross-sectional view showing a part of the tire of FIG.

  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. 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 symmetrical with respect to the equator plane except for the tread pattern.

  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 edge band 18, an inner liner 20, and a chafer 22. 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 24 that contacts the road surface. As shown in the figure, the tread 4 includes a main groove 26 extending in the circumferential direction. The main groove 26 contributes to drainage of the tire 2. Although not shown, the tread 4 further includes a plurality of sub grooves. A tread pattern is formed by the main groove 26 and the sub-groove. In the illustrated tire 2, the number of main grooves 26 is four. The number of main grooves 26 is not limited to four. The tread 4 may include three or less main grooves 26. The tread 4 may include five or more main grooves 26. The tread 4 may not include the main groove 26. The tread 4 may not include the auxiliary groove.

  The tread 4 has a base layer 28 and a cap layer 30. The cap layer 30 is located on the radially outer side of the base layer 28. The cap layer 30 is laminated on the base layer 28. The base layer 28 is made of a crosslinked rubber having excellent adhesiveness. A typical base rubber of the base layer 28 is natural rubber.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. This sidewall 6 is made of a crosslinked rubber having excellent cut resistance and weather resistance. This sidewall 6 prevents the carcass 12 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 contacts the flange of the rim.

  The bead 10 is located inside the clinch 8 in the axial direction. The bead 10 includes a core 32 and an apex 34 that extends radially outward from the core 32. The core 32 has a ring shape and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 34 is tapered outward in the radial direction. The apex 34 is made of a highly hard crosslinked rubber.

  The carcass 12 includes a carcass ply 36. The carcass ply 36 is bridged between the beads 10 on both sides, and extends along the inside of the tread 4 and the sidewall 6. The carcass ply 36 is folded around the core 32 from the inner side to the outer side in the axial direction. By this folding, the carcass ply 36 has a main portion and a folded portion.

  Although not shown, the carcass ply 36 includes a plurality 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 12 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 36.

  The belt 14 is located on the inner side in the radial direction of the tread 4. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes an inner layer 14a and an outer layer 14b. Although not shown, each of the inner layer 14a and the outer layer 14b 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. The absolute value of the tilt angle is usually 10 ° to 35 °. The inclination direction of the cord of the inner layer 14a with respect to the equator plane is opposite to the inclination direction of the cord of the outer layer 14b with respect to the equator plane. A preferred material for the cord is steel. An organic fiber may be used for the cord. The belt 14 may include three or more layers.

  The band 16 is located on the inner side in the radial direction of the tread 4. The band 16 is located on the radially outer side of the belt 14. The band 16 is laminated on the belt 14. The band 16 is made of a cord and a topping rubber. The cord is wound in a spiral. The band 16 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. The band 16 can contribute to the radial rigidity of the tire 2. The band 16 can suppress the influence of centrifugal force that acts during traveling. The tire 2 is excellent in high speed stability. A preferred material for the cord is steel. An organic fiber may be used for the cord. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The belt 14 and the band 16 constitute a reinforcing layer. The reinforcing layer may be formed only from the belt 14. A reinforcing layer may be formed only from the band 16.

  The edge band 18 is located radially outside the belt 14 and in the vicinity of the end of the belt 14. Although not shown, the edge band 18 is made of a cord and a topping rubber. The cord is wound in a spiral. The edge band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the end of the belt 14 is restrained by this cord, the lifting of the belt 14 is suppressed. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The inner liner 20 is located inside the carcass 12. The inner liner 20 is joined to the inner surface of the carcass 12. The inner liner 20 is made of a crosslinked rubber. The inner liner 20 is made of rubber having excellent air shielding properties. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 holds the internal pressure of the tire 2.

  The chafer 22 is located in the vicinity of the bead 10. When the tire 2 is incorporated into the rim, the chafer 22 comes into contact with the rim. By this contact, the vicinity of the bead 10 is protected. The chafer 22 is made of cloth and rubber impregnated in the cloth. The chafer 22 may be configured integrally with the clinch 8.

  In FIG. 1, the symbol X represents the outer side direction (referred to as the front side) of the vehicle when the tire 2 is mounted on the vehicle, and the symbol Y represents the inner side direction (back side) of the vehicle when the tire 2 is mounted on the vehicle. It is called). The cap layer 30 of the tread 4 includes a center portion, a front shoulder portion, and a back shoulder portion. In FIG. 1, the symbol C represents the center portion, the symbol Sf represents the front shoulder portion, and the symbol Sb represents the back shoulder portion.

  The center portion C is located at the center of the tread 4. The center portion C is laminated on the outer side in the radial direction of the base layer 28. The center part C forms a part of the tread surface 24.

  The front shoulder portion Sf is located on the front side of the center portion C. In FIG. 1, a point Bf is a boundary between the center portion C and the front shoulder portion Sf. A double-headed arrow Wf is an axial width from the equator plane CL to the boundary Bf. A double-headed arrow Wt represents the axial width of the tread 4 of the tire 2. In the tire 2, the ratio of the width Wf to the width Wt (Wf / Wt) is 0.25 or more and 0.35 or less.

  FIG. 2 is an enlarged cross-sectional view of the tire 2 of FIG. 1 showing the vicinity of the front shoulder portion Sf. In FIG. 2, the vertical direction is the radial direction, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. The front shoulder portion Sf includes a front main muscle 38 and a front sub muscle 40. In the front shoulder portion Sf, the front accessory muscle 40 is disposed at the inner end in the axial direction, and the front principal muscle 38 and the front accessory muscle 40 are alternately disposed toward the outer side.

  Each front accessory muscle 40 is formed in a ring shape along the circumferential direction. In the cross section obtained by cutting the tire 2 along a plane perpendicular to the circumferential direction, the front and secondary reinforcing bars 40 extend in the radial direction from the surface of the base layer 28 to the tread surface 24. The front accessory muscle 40 forms a part of the tread surface 24. The front accessory muscle 40 is laminated on the outer side in the radial direction of the base layer 28.

  As shown in FIG. 2, each front accessory muscle 40 includes a pair of side surfaces 42. The pair of side surfaces 42 are substantially parallel to each other. In FIG. 2, a point Pf <b> 0 is an intersection of the inner side surface 42 of the front accessory muscle 40 and the tread surface 24, and a point Pf <b> 1 is an intersection of the outer side surface 42 of the front accessory muscle 40 and the tread surface 24. In FIG. 2, the double arrow TSf is the width of the front accessory muscle 40. Specifically, the width TSf is a distance in the axial direction between the point Pf0 and the point Pf1. As shown in FIG. 2, in the tire 2, the widths of all the front accessory muscles 40 are the same. The widths of all the front accessory muscles 40 may not be the same. In this case, the width TSf represents the average of the widths of all the sphincter muscles 40.

  Each of the front principal bars 38 is formed in a ring shape along the circumferential direction. In a cross section obtained by cutting the tire 2 along a plane perpendicular to the circumferential direction, the front main reinforcement 38 extends in the radial direction from the surface of the base layer 28 to the tread surface 24. The front principal muscle 38 forms a part of the tread surface 24. The front main bar 38 is laminated on the outer side in the radial direction of the base layer 28.

  The back shoulder portion Sb is located on the back side of the center portion C. In FIG. 1, a point Bb is a boundary between the center portion C and the back shoulder portion Sb. A double-headed arrow Wb is an axial width from the equator plane CL to the boundary Bb. In the tire 2, the ratio of the width Wb to the width Wt (Wb / Wt) is 0.25 or more and 0.35 or less.

  FIG. 3 is an enlarged cross-sectional view of the tire 2 of FIG. 1 showing the vicinity of the back shoulder portion Sb. In FIG. 3, the vertical direction is the radial direction, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. The back shoulder portion Sb includes a back main muscle 44 and a back auxiliary muscle 46. In the back shoulder portion Sb, the back accessory muscles 46 are arranged at the inner end in the axial direction, and the back principal muscles 44 and the back accessory muscles 46 are alternately arranged toward the outside.

  Each back accessory muscle 46 is formed in a ring shape along the circumferential direction. In the cross section obtained by cutting the tire 2 along a plane perpendicular to the circumferential direction, the back accessory muscles 46 extend in the radial direction from the surface of the base layer 28 to the tread surface 24. The back accessory muscle 46 forms a part of the tread surface 24. The back accessory muscle 46 is laminated on the outer side in the radial direction of the base layer 28.

  As shown in FIG. 3, each back accessory muscle 46 includes a pair of side surfaces 48. The pair of side surfaces 48 are substantially parallel to each other. In FIG. 3, a point Pb <b> 0 is an intersection of the inner side surface 48 of the back accessory muscle 46 and the tread surface 24, and a point Pb <b> 1 is an intersection of the outer side surface 48 of the back accessory muscle 46 and the tread surface 24. In FIG. 3, a double arrow TSb is the width of the back accessory muscle 46. Specifically, the width TSb is an axial distance between the point Pb0 and the point Pb1. As shown in FIG. 3, in the tire 2, the widths of all back accessory muscles 46 are the same. The widths of all back accessory muscles 46 may not be the same. In this case, the width TSb represents the average of the widths of all the back accessory muscles 46.

  Each back main muscle 44 is formed in a ring shape along the circumferential direction. In the cross section obtained by cutting the tire 2 along a plane perpendicular to the circumferential direction, the back main bars 44 extend in the radial direction from the surface of the base layer 28 to the tread surface 24. The back main bar 44 forms a part of the tread surface 24. The back main bars 44 are laminated on the outer side in the radial direction of the base layer 28.

  In the tire 2, the width TSb of the back accessory muscle 46 is larger than the width TSf of the front accessory muscle 40. The total width SSb of all the back accessory muscles 46 is larger than the total width SSf of all the front accessory muscles 40. In the tire 2 of FIG. 1, the total value SSf is four times the width TSf. The total value SSb is four times the width TSb.

  In the tire 2, the center portion C, the front main bar 38, and the back main bar 44 are made of the first rubber. The front accessory muscle 40 and the back accessory muscle 46 are made of a second rubber. The first rubber and the second rubber are each a crosslinked rubber composition (crosslinked rubber). The loss tangent LT2 of the second rubber is smaller than the loss tangent LT1 of the first rubber. That is, the front accessory muscle 40 and the back accessory muscle 46 are made of rubber that generates less heat than the center portion C, the front principal muscle 38, and the back principal muscle 44.

In the present invention, the loss tangents LT1 and LT2 and the complex elastic moduli E1 ^* and E2 ^{* to be} described later are viscoelastic spectrometers (“VESF-3” manufactured by Iwamoto Seisakusho) in accordance with the provisions of “JIS K 6394”. Is measured under the conditions shown below.
Initial strain: 10%
Amplitude: ± 2.0%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 30 ° C

  The front shoulder portion Sf further includes a front end portion 50. The front end portion 50 is disposed on the front side end of the front shoulder portion Sf. The outer end of the front end portion 50 coincides with the end of the tread 4. In the tire 2 of FIG. 1, the front end portion 50 is located further on the front side of the front accessory muscle 40 located on the most front side. In the tire 2, the front end portion 50 is made of a first rubber. The front end portion 50 may be made of a second rubber. In addition, the front end part 50 may be comprised other than 1st rubber | gum and 2nd rubber | gum.

  The back shoulder portion Sb further includes a back end portion 52. The back end portion 52 is disposed at the back side end of the back shoulder portion Sb. The outer end of the back end portion 52 coincides with the tread 4 end. In the tire 2 of FIG. 1, the back end portion 52 is located further on the back side of the back accessory muscle 46 located on the most back side. In the tire 2, the back end portion 52 is made of a first rubber. This back end part 52 may be comprised from the 2nd rubber | gum. In addition, the back end part 52 may be comprised other than 1st rubber | gum and 2nd rubber | gum.

  As shown in the figure, in the tire 2, the tread 4 has a base layer 28. The tread 4 may not have the base layer 28. In this case, the center portion C, the front accessory muscle 40, the front principal muscle 38, the back accessory muscle 46, and the rear principal muscle 44 are stacked on the radially outer side of the band 16 or the edge band 18.

  Below, the effect of this invention is demonstrated.

  When the vehicle turns, a large load is applied to the front side of the tread surface of the outer ring. A two-dot chain line Gf in FIG. 1 represents a road surface on the outer wheel when the vehicle is turning. When turning, the grip strength of the outer shoulder portion of the outer ring is important. On the other hand, when the vehicle turns, the back side of the outer tread surface hardly touches the ground. The back side of the tread surface of the inner ring is grounded, but the load applied to this back side is small. The back shoulder has little effect on grip when turning.

  When the vehicle travels straight, it is mainly the center that contacts the ground. A two-dot chain line Gb in FIG. 1 represents a road surface when traveling straight. Many vehicles use negative camber. For this reason, as shown in the figure, the area of the back side portion of the center portion to be grounded is particularly large. During straight running, the area where the back and front shoulders are in contact with the ground is smaller than the center. The influence of the back and front shoulders on the grip force when going straight is small.

  In the tire 2 according to the present invention, the tread 4 includes a center portion C, a front shoulder portion Sf, and a back shoulder portion Sb. The front shoulder portion Sf is located on the front side of the center portion C. The back shoulder portion Sb is located on the back side of the center portion C. The front major muscle 38 and the front minor muscle 40 are arranged in the front shoulder portion Sf. The back main muscle 44 and the back accessory muscle 46 are arranged in the back shoulder portion Sb. The front main bar 38 and the back main bar 44 are made of the first rubber. The front accessory muscle 40 and the back accessory muscle 46 are made of the second rubber. The loss tangent LT2 of the second rubber is smaller than the loss tangent LT2 of the first rubber. The front accessory muscle 40 and the rear accessory muscle 46 having a small loss tangent can reduce the rolling resistance of the tire 2. The tire 2 contributes to improving the fuel efficiency of the vehicle.

  In the tire 2, the total width SSf of the front accessory muscles 40 arranged in the front shoulder portion Sf is smaller than the total width SSb of the back accessory muscles 46 arranged in the back shoulder portion Sb. During turning, a load is mainly applied to the front shoulder portion Sf. The effect of the small accessory vice muscle 40 on the grip force of the tire 2 is small. The influence of the splint muscle 40 having a small loss tangent on the grip force during turning is suppressed. In the tire 2, a good grip force during turning is maintained.

  In the tire 2, the total width SSb of the back accessory muscles 46 arranged in the back shoulder portion Sb is larger than the total width SSf of the front accessory muscles 40 arranged in the front shoulder portion Sf. The back accessory muscle 46 having a large width further effectively reduces rolling resistance. As described above, the influence of the back shoulder Sb on the grip force of the tire 2 during turning and straight traveling is small. In the tire 2, rolling resistance is effectively suppressed while maintaining a good gripping force during turning and straight traveling.

  As described above, in the tire 2, the front main muscle 38 and the front auxiliary muscle 40 are alternately arranged in the front shoulder portion Sf in the axial direction. In the back shoulder portion Sb, the back main bars 44 and the back auxiliary bars 46 are alternately arranged in the axial direction. With this structure, when the ground contact surface of the tread 4 transitions from the front shoulder portion Sf or the back shoulder portion Sb to the center portion C, or the ground contact surface of the tread 4 changes from the center portion C to the front shoulder portion Sf or the back shoulder portion. When shifting to Sb, the driver is less likely to feel uncomfortable due to the difference in grip force between the first rubber and the second rubber. The tire 2 is excellent in ride comfort. Furthermore, this structure prevents the step wear of the tread 4 due to the difference in wear resistance between the first rubber and the second rubber. In the tire 2, appearance defects due to step wear are prevented. In the tire 2, a decrease in grip force due to the wear step is prevented.

  As described above, in the tire 2, the ratio (Wf / Wt) is 0.25 or more and 0.35 or less. The tire 2 having a ratio (Wf / Wt) of 0.25 or more has a sufficient grip force when going straight. In this respect, the ratio (Wf / Wt) is more preferably equal to or greater than 0.28. In the tire 2 having a ratio (Wf / Wt) of 0.35 or less, the rolling resistance is effectively reduced. In this respect, the ratio (Wf / Wt) is more preferably equal to or less than 0.33.

  As described above, in the tire 2, the ratio (Wb / Wt) is 0.25 or more and 0.35 or less. The tire 2 having a ratio (Wb / Wt) of 0.25 or more has a sufficient grip force when traveling straight. In this respect, the ratio (Wb / Wt) is more preferably equal to or greater than 0.28. In the tire 2 having the ratio (Wb / Wt) of 0.35 or less, the rolling resistance is effectively reduced. In this respect, the ratio (Wb / Wt) is more preferably equal to or less than 0.33.

  The ratio (TSb / TSf) of the width TSb of the back accessory muscle 46 to the width TSf of the front accessory muscle 40 is preferably 1.5 or more and 2.5 or less. By setting the ratio (TSb / TSf) to 1.5 or more and 2.5 or less, the rolling resistance can be more effectively reduced while preventing a decrease in grip force. In this respect, the ratio (TSb / TSf) is more preferably equal to or greater than 1.7 and equal to or less than 2.3.

  The ratio (SSb / SSf) of the total width SSb of all back accessory muscles 46 to the total value SSf of all front accessory muscles 40 is preferably 1.5 or more and 2.5 or less. When the ratio (SSb / SSf) is 1.5 or more and 2.5 or less, the rolling resistance can be more effectively reduced while preventing the grip force from being lowered. From this viewpoint, the ratio (SSb / SSf) is more preferably 1.7 or more and 2.3 or less.

  The width TSf of the front accessory muscle 40 is preferably 1.5 mm or more. When the width TSf is 1.5 mm or more, the rolling resistance is effectively reduced. In this respect, the width TSf is more preferably 2.0 mm or more. Further, the width TSf is preferably 3.0 mm or less. By setting the width TSf to be equal to or less than 3.0 mm, the tire 2 has a good grip force when turning. From this viewpoint, the width TSf is more preferably 2.5 mm or less.

  In FIG. 2, the double arrow TMf is the width of the front principal muscle 38. The width TMf of the front major muscle 38 is the distance between the two front minor muscles 40 located on both sides thereof. The width TMf of the inner principal muscle 38 located on the innermost side is the distance in the axial direction between the point Pf1 and the point Pf2. In the tire 2 of FIG. 2, all the front principal bars 38 have the same width.

  In the tire 2, the width TSf of the front accessory muscle 40 is preferably smaller than the width TMf of the front principal muscle 38. By making the width TSf smaller than the width TMf, a good gripping force during turning is maintained.

  The width TMf of the front main bar 38 is preferably 4.0 mm or more. By setting the width TMf to 4.0 mm or more, a good grip force during turning can be maintained. Further, by setting the width TMf to 4.0 mm or more, the wear step can be reduced. From this viewpoint, the width TMf is more preferably 5.0 mm or more. The width TMf is preferably 8.0 mm or less. By setting the width TMf to 8.0 mm or less, the rolling resistance is effectively reduced. In this respect, the width TMf is more preferably equal to or less than 7.0 mm.

  The width TSb of the back accessory muscle 46 is preferably 2.0 mm or more. By setting the width TSb to 2.0 mm or more, the rolling resistance is effectively reduced. In this respect, the width TSb is more preferably equal to or greater than 3.0 mm. The width TSb is preferably 6.0 mm or less. By setting the width TSb to 6.0 mm or less, the tire 2 has a good grip force when traveling straight. In this respect, the width TSb is more preferably equal to or less than 5.0 mm.

  In FIG. 3, the double arrow TMb is the width of the back main bar 44. The width TMb of the back major bar 44 is the distance between the two back minor bars 46 located on both sides thereof. The width TMb of the back main bar 44 located on the innermost side is the distance in the axial direction between the point Pb1 and the point Pb2. In the tire 2 of FIG. 3, all the back main bars 44 have the same width.

  In the tire 2, the width TSb of the back accessory bar 46 is preferably smaller than the width TMb of the back main bar 44. By making the width TSb smaller than the width TMb, a good grip force during straight traveling is maintained.

  The width TMb of the back main bar 44 is preferably 4.0 mm or more. By setting the width TMb to 4.0 mm or more, it is possible to maintain a good grip force when going straight. In addition, the wear step can be reduced by setting the width TMb to 4.0 mm or more. In this respect, the width TMb is more preferably equal to or greater than 5.0 mm. The width TMb is preferably 8.0 mm or less. By setting the width TMb to 8.0 mm or less, the rolling resistance is effectively reduced. In this respect, the width TMb is more preferably equal to or less than 7.0 mm.

  The number of front accessory muscles 40 and back accessory muscles 46 is preferably 3 or more. By making the number of the front accessory muscle 40 and the back accessory muscle 46 three or more, the sense of incongruity caused by the difference in grip force between the first rubber and the second rubber is effectively suppressed. The tire 2 is excellent in ride comfort. Furthermore, this effectively prevents step wear of the tread 4 due to the difference in wear resistance between the first rubber and the second rubber. In this respect, the number of front accessory muscles 40 and back accessory muscles 46 is more preferably 4 or more.

  The number of front main bars 38 and back main bars 44 is preferably 2 or more. By setting the number of the front main bars 38 and the back main bars 44 to 2 or more, the uncomfortable feeling caused by the difference in grip force between the first rubber and the second rubber is effectively suppressed. The tire 2 is excellent in ride comfort. Furthermore, this effectively prevents step wear of the tread 4 due to the difference in wear resistance between the first rubber and the second rubber. In this respect, the number of front main bars 38 and back main bars 44 is more preferably 3 or more.

  In FIG. 2, a point Ef is a front side grounding end. The ground contact end is an end located on the outermost side in the axial direction in a portion where the tire 2 is in contact with the road surface when a normal load is applied to the tire 2 in a state of normal internal pressure. The ground contact end is measured with the tire 2 mounted on the vehicle. In the tire 2, it is preferable that the total width of the front accessory muscles 40 located on the front side from the ground contact end Ef is larger than the total width of the front accessory muscles 40 located on the back side from the ground contact end Ef. Thereby, grip force can be maintained. The tire 2 is excellent in brake performance. In the tire 2 of FIG. 2, all the front accessory muscles 40 are located on the front side with respect to the ground contact end Ef.

  In FIG. 3, the point Eb is the grounding end on the back side. In the tire 2, it is preferable that the total width of the back accessory muscles 46 located on the back side of the ground contact edge Eb is larger than the total width of the back accessory muscles 46 located on the front side of the contact edge Eb. Thereby, a high grip force can be maintained. The tire 2 is excellent in brake performance. In the tire 2 of FIG. 3, the three back accessory bars 46 are located on the back side from the ground contact Eb from the back side. Further, with respect to the back auxiliary muscle 46 located on the most front side, the point from the ground contact Eb to the point Pb1 is located behind the ground contact Eb. With respect to the back accessory muscle 46, the point from the ground contact Eb to the point Pb0 is located on the front side from the ground contact Eb.

  As shown in FIG. 1, the boundary Bf between the center portion C and the front shoulder portion Sf is preferably located on the front side of the front end of the main groove 26 located on the most front side. In FIG. 1, a double-headed arrow Cf is the axial distance from the front-side end of the main groove 26 located on the most front side to the boundary Bf. The distance Cf is preferably 7 mm or more. Thereby, a high grip force can be maintained in the tire 2. The tire 2 is excellent in brake performance.

  As shown in FIG. 1, the boundary Bb between the center portion C and the back shoulder portion Sb is preferably located on the back side rather than the back side end of the main groove 26 located on the most back side. In FIG. 1, a double-headed arrow Cb is an axial distance from the end on the back side of the main groove 26 located on the most back side to the boundary Bb. The distance Cb is preferably 7 mm or more. Thereby, a high grip force can be maintained in the tire 2. The tire 2 is excellent in brake performance.

  The ratio (LT2 / LT1) of the loss tangent LT2 to the loss tangent LT1 is preferably 0.6 or less. In the tire 2 including the first rubber and the second rubber having a ratio (LT2 / LT1) of 0.6 or less, a low rolling resistance can be realized. In this respect, the ratio (LT2 / LT1) is more preferably equal to or less than 0.5.

  The ratio (LT2 / LT1) is preferably 0.3 or more. In the tire 2 having the ratio (LT2 / LT1) of 0.3 or more, it is possible to prevent the occurrence of a wear step due to the difference in wear resistance between the first rubber and the second rubber. In the tire 2, a good appearance and grip force can be maintained. In this respect, the ratio (LT2 / LT1) is more preferably equal to or greater than 0.4.

  The loss tangent LT1 of the first rubber is preferably 0.16 or more. In the tire 2 including the first rubber having the loss tangent LT1 of 0.16 or more, high grip performance is maintained. In this respect, the loss tangent LT1 is more preferably equal to or greater than 0.17. The loss tangent LT1 is preferably 0.22 or less. In the tire 2 including the first rubber having the loss tangent LT1 of 0.22 or less, an appropriate rolling resistance can be realized. In this respect, the loss tangent LT1 is more preferably equal to or less than 0.21.

  The glass transition temperature Tg2 of the second rubber is preferably −20 ° C. or higher. The second rubber having a glass transition temperature Tg2 of −20 ° C. or higher can suppress a decrease in grip force. In this respect, the glass transition temperature Tg2 is more preferably equal to or higher than −22 ° C. The glass transition temperature Tg2 is preferably −40 ° C. or lower. The second rubber having a glass transition temperature Tg2 of −40 ° C. or less contributes to reduction of rolling resistance and improvement of wear resistance. In this respect, the glass transition temperature Tg2 is more preferably −30 ° or less.

  The glass transition temperature Tg1 of the first rubber is preferably −10 ° C. or higher. The first rubber having a glass transition temperature Tg1 of −10 ° C. or higher contributes to good grip. In this respect, the glass transition temperature Tg1 is more preferably −12 ° C. or higher. The glass transition temperature Tg1 is preferably −25 ° C. or lower. The first rubber having a glass transition temperature Tg1 of −25 ° C. or lower contributes to reduction of rolling resistance and improvement of wear resistance. In this respect, the glass transition temperature Tg1 is more preferably −20 ° C. or lower.

  In the present invention, the glass transition temperatures Tg1 and Tg2 are based on the standard of “JIS K 7121” using a differential scanning calorimeter (“Q200” manufactured by TA Instruments Japan), It is measured at a temperature rising rate of 10 ° C./min.

The ratio (E2 ^* / E1 ^* ) of the complex elastic modulus E2 ^* of the second rubber to the complex elastic modulus E1 ^* of the first rubber is preferably 0.8 or more and 1.2 or less. In the tire 2 having the ratio (E2 ^* / E1 ^* ) of 0.8 or more and 1.2, the rigidity of the tread 4 can be kept uniform. In the tire 2, it is difficult to feel a sense of incongruity caused by using rubbers of different materials for the tread 4 during driving. From this viewpoint, the ratio (E2 ^* / E1 ^* ) is more preferably 0.9 or more and 1.0 or less.

The complex elastic modulus E1 ^* of the first rubber is preferably 5.0 MPa or more and 8.0 MPa or less. The tire 2 having a complex elastic modulus E1 ^* of 5.0 MPa or more and 8.0 MPa or less can achieve both grip force and wear resistance. From this viewpoint, the complex elastic modulus E1 ^* is more preferably 6.0 MPa or more and 7.1 MPa or less.

  In the present invention, the dimensions and angles of the tire 2 and each member of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “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. In the case of the passenger car tire 2, the dimensions and angles are measured in a state where the internal pressure is 180 kPa.

  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 tire of Example 1 having the structure shown in FIG. 1 was obtained. The tire size was 195 / 65R15 91H. Table 1 shows the specifications of the tire. The width of the front principal muscle was the same for all front principal muscles. This width is shown in the column of “main bar width TMf” on the front side. The width of the vice versa was the same for all the vice versa. This width is shown in the column of “sub-bar width TSf” on the front side. The width of the back main bars was the same for all back main bars. This width is shown in the column of “main bar width TMb” on the back side. The width of the back accessory muscle was the same for all back accessory muscles. This width is shown in the column of “sub-bar width TSb” on the back side.

[Comparative Example 1]
A tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the front and back shoulders were not formed and the front shoulder part and the back shoulder part were composed of only the first rubber. Comparative Example 1 is a conventional tire.

[Comparative Example 2]
As shown in Table 1, a tire of Comparative Example 2 was obtained in the same manner as in Example 1 except that the width of the front accessory muscle was made larger than that of the back accessory muscle.

[Comparative Example 3-4]
As shown in Table 1, a tire of Comparative Example 3-4 was obtained in the same manner as in Example 1 except that the width of the front accessory muscle was the same as that of the back accessory muscle.

[Rolling resistance]
Using a rolling resistance tester, rolling resistance was measured under the following measurement conditions.
Rim used: 15 x 6 JJ (aluminum alloy)
Internal pressure: 230 kPa
Load: 3.43kN
Speed: 80km / h
The results are shown in Table 1 below as index values with Comparative Example 1 taken as 100. The smaller the value, the smaller the rolling resistance and the better the fuel efficiency. A smaller numerical value is preferable.

[Brake performance]
The prototype tire was assembled into a standard rim (size = 15 × 6J) and mounted on the front wheel of a commercial passenger car. The internal pressure of this tire was 230 kPa. A commercially available tire (size = 195 / 65R15) was attached to the rear wheel and filled with air so that the internal pressure was 230 kPa. On the test course, braking was performed while the vehicle was traveling at a speed of 80 km / h, and the traveling distance (braking distance) from when the brake was applied to when the vehicle stopped was measured. The braking distance was measured both when the road surface was dry and wet. The results are shown in Table 1 below, which is the reciprocal of the index with Comparative Example 1 taken as 100. In the table, the “brake (DRY)” column is an evaluation result when the road surface is dry, and the “brake (WET)” column is an evaluation result when the road surface is wet. The larger this value, the shorter the braking distance. Larger values are preferred.

[Wear appearance]
The prototype tire was assembled into a standard rim (size = 15 × 6J) and mounted on the front wheel of a commercial passenger car. The internal pressure of this tire was 230 kPa. A commercially available tire (size = 195 / 65R15) was attached to the rear wheel and filled with air so that the internal pressure was 230 kPa. This vehicle was run on the test course, and the appearance of the front shoulder portion and the back shoulder portion at the time when the travel distance was 20000 km was observed. The results are shown in Table 1 below. When the wear step is 1.0 mm or more, “NG” is indicated, and when the wear step is less than 1.0 mm, “OK” is indicated. The wear step is preferably less than 1.0 mm.

  As shown in Table 1, in the tire according to the present invention, reduction in rolling resistance is achieved while suppressing deterioration in brake performance and deterioration in wear appearance. ADVANTAGE OF THE INVENTION According to this invention, the pneumatic tire with which the fall of the grip power was suppressed and the fuel consumption performance was excellent can be provided. From this evaluation result, the superiority of the present invention is clear.

  The tire according to the present invention can be mounted on various vehicles.

2 ... Tire 4 ... Tread 6 ... Sidewall 8 ... Clinch 10 ... Bead 12 ... Carcass 14 ... Belt 14a ... Inner layer 14b ... Outer layer 16. ..Band 18 ... Edge band 20 ... Inner liner 22 ... Chafer 24 ... Tread surface 26 ... Main groove 28 ... Base layer 30 ... Cap layer 32 ... Core 34 ... Apex 36 ... Carcass ply 38 ... Front major muscle 40 ... Front accessory muscle 42, 48 ... Side 44 ... Back major muscle 46 ... Back accessory muscle 50 ... Front Edge 52 ... Back edge

Claims (7)

It has a tread whose outer surface forms a tread surface,
This tread has a center, front shoulder and back shoulder,
The center is located in the center of the tread,
The front shoulder portion is located in the outer direction of the vehicle when the tire is mounted on the vehicle with respect to the center portion,
In the axial direction, when the width from the equator plane to the boundary Bf between the center portion and the front shoulder portion is Wf, the ratio (Wf / Wt) of the width Wf to the tread width Wt is 0.25 or more and 0. .35 or less,
The front shoulder portion includes a front principal muscle that extends in the circumferential direction and forms a part of the tread surface, and a front auxiliary muscle that extends in the circumferential direction and forms a part of the tread surface,
In the front shoulder portion, the front accessory muscle is arranged at the inner end in the axial direction, and the front principal muscle and the front accessory muscle are alternately arranged toward the outside,
The back shoulder portion is located in the vehicle inner direction when the tire is mounted on the vehicle with respect to the center portion,
In the axial direction, when the width from the equator plane to the boundary Bb between the center portion and the back shoulder portion is Wb, the ratio (Wb / Wt) of the width Wb to the width Wt is 0.25 or more and 0.35. And
The back shoulder portion includes a back main muscle that extends in the circumferential direction and forms a part of the tread surface, and a back auxiliary muscle that extends in the circumferential direction and forms a part of the tread surface,
In the back shoulder, the back accessory muscle is arranged at the inner end in the axial direction, the back principal muscle and the back accessory muscle are alternately arranged toward the outside,
The width TSb of the back accessory muscle is larger than the width TSf of the front accessory muscle,
The sum of the widths of all the back accessory muscles is greater than the sum of the widths of all the front accessory muscles;
The front main bar and the back main bar are composed of the first rubber,
The front accessory muscle and the back accessory muscle are composed of the second rubber,
A pneumatic tire in which the loss tangent LT2 of the second rubber is lower than the loss tangent LT1 of the first rubber.   The tire according to claim 1, wherein a ratio (TSb / TSf) of the width TSb to the width TSf is 1.5 or more and 2.5 or less.   The tire according to claim 1 or 2, wherein the width TSf is 1.5 mm or more and 3.0 mm or less.   The tire according to any one of claims 1 to 3, wherein the number of back accessory muscles is 3 or more, and the number of front accessory muscles is 3 or more.   When the ground contact end located in the vehicle outer direction is set to Ef when this tire is mounted on the vehicle, the sum of the widths of the vice versa located in the vehicle outward direction from the ground contact end Ef is the vehicle from the ground contact end Ef. The tire according to any one of claims 1 to 4, wherein the tire is larger than the sum of the widths of the front and left accessory muscles located in the inner direction.   When the ground contact end located in the vehicle inner direction is set to Eb when the tire is mounted on the vehicle, the total width of the back accessory muscles located in the vehicle inner direction from the ground contact end Eb is the vehicle from the ground contact end Eb. The tire according to any one of claims 1 to 5, wherein the tire is larger than the sum of the widths of the back accessory muscles located in the outer direction of the tire. The tread includes a plurality of main grooves extending substantially in the circumferential direction,
In the outer direction of the vehicle, the boundary Bf is located outside the outer end of the main groove located on the outermost side of the main grooves, and the distance between the boundary Bf and the outer end is 7 mm or more,
The boundary Bb is located on the inner side of the innermost main groove among the main grooves in the inner side direction of the vehicle, and the distance between the boundary Bb and the inner end is 7 mm or more. The tire according to any one of 1 to 6.

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