JP5851871B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that can discharge static electricity generated in a vehicle body or a tire to a road surface.

  In recent years, pneumatic tires with high silica content in tread rubber have been proposed for the purpose of reducing rolling resistance, which is closely related to lower fuel consumption of vehicles, and improving braking performance (wet braking performance) on wet road surfaces. Yes. However, such tread rubber has a higher electrical resistance than those with a high carbon black content, and since it inhibits the discharge of static electricity generated in the car body and tires to the road surface, it has a problem of easily causing problems such as radio noise. there were.

  Therefore, a pneumatic tire has been developed in which a conductive portion made of a conductive rubber compounded with carbon black or the like is provided on a tread rubber made of non-conductive rubber compounded with silica or the like so as to exhibit a current-carrying performance. . For example, Patent Documents 1 and 2 disclose that a tread rubber formed of non-conductive rubber extends inward in the tire radial direction from the ground surface, and extends in the tire width direction between the cap portion and the base portion, and sidewall rubber. Or the pneumatic tire which provided the electroconductive part connected to the topping rubber of a carcass layer is described.

  By the way, in the state where the tire is grounded, a force toward the center portion, that is, a so-called in-plane contraction force acts on the ground contact surface as shown in FIG. 8, resulting in deformation of the land portion called wiping. In the central region of the tread rubber 20, in-plane contraction force acts from both sides in the tire width direction. Therefore, when the exposed portion 23E of the conductive portion 23 is set in the central region, the cap portion 22, the base portion 21, and the conductive portion In combination with the difference in rubber hardness in No. 23, it was found that the contact pressure becomes non-uniform due to the effect of wiping, which adversely affects the steering stability performance and wear performance.

  However, depending on the number of circumferential main grooves, such as when three circumferential main grooves are provided on the surface of the tread portion, it may be difficult to keep the exposed portion of the conductive portion away from the central region of the tread rubber. . Even if the exposed portion of the conductive portion is away from the central region of the tread rubber, the conductive portion is closely arranged around one of the circumferential main grooves, so that one side in the tire width direction There is a great difference in the rigidity of the periphery of the circumferential main groove between the other side and the other side, which causes uneven contact pressure and tends to cause a decrease in steering stability performance and wear performance.

JP 2009-126291 A Japanese Patent No. 4611451

  The present invention has been made in view of the above circumstances, and the purpose of the present invention is to reduce the steering stability performance and wear performance by suppressing the non-uniformity of the contact pressure due to the influence of wiping while being able to demonstrate the energization performance. The object is to provide a pneumatic tire that can be prevented.

  The above object can be achieved by the present invention as described below. That is, the pneumatic tire according to the present invention includes a pair of shoulder main grooves positioned on the outermost side in the tire width direction on the surface of the tread portion, and a pair of center main grooves positioned between them and sandwiching the tire equator. Four circumferential main grooves are provided, and a tread rubber disposed in the tread portion is formed of non-conductive rubber and forms a ground plane; and a cap portion formed of non-conductive rubber and the cap portion In the pneumatic tire provided with a base portion disposed on the inner side in the tire radial direction and a conductive portion formed of conductive rubber and extending from a ground contact surface to a side surface or a bottom surface of the tread rubber, the conductive portions are the pair of tires. A first conductive portion extending inward in the tire radial direction from a position in the ground contact surface excluding the center land portion located between the center main grooves, and the cap portion and the front A second conductive portion extending in the tire width direction between the base portion and the starting point of the conductive portion rising from the second conductive portion toward the ground plane is one of the four circumferential main grooves. The rubber hardness Hc of the cap portion, the rubber hardness Hb of the base portion, and the rubber hardness He of the conductive portion are Hb> He> Hc, He> Hb> Hc, Hc> Hb> He. Or the groove bottom of the circumferential main groove that satisfies the relationship of Hc> He> Hb and is divided in the tire width direction on the groove bottom side of the circumferential main groove on which the starting point is disposed, and forms a pair with the base portion. On the side, the base portion continuously extends without being divided, or satisfies the relationship of Hb> Hc> He or He> Hc> Hb, and on the groove bottom side of the circumferential main groove where the starting point is arranged The base portion extends continuously without being divided, In Les paired groove bottom of the circumferential main grooves forming said base portion is divided in the tire width direction, in which the recess of the divide portion of the base portion is filled with a rubber of the cap portion.

  In this tire, when the tread rubber includes the conductive portion as described above, the energization performance can be exhibited. Moreover, the 1st electroconductive part of the electroconductive part is extended in the tire radial inside from the position in the ground-contact plane except a center land part, and the exposed location of an electroconductive part is kept away from the center area | region of a tread rubber. Nevertheless, the base part is divided at one groove bottom side of the paired circumferential main grooves, and the recesses in the divided parts are filled with the rubber of the cap part. It is possible to suppress the non-uniformity of the contact pressure due to being disposed on the surface, and to prevent deterioration of steering stability performance and wear performance.

  It is determined according to the magnitude relationship among the rubber hardness Hc of the cap portion, the rubber hardness Hb of the base portion, and the rubber hardness He of the conductive portion, at which bottom side of the paired circumferential main grooves the base portion is divided. By filling the dent of the parted portion with the rubber of the cap part, it can be adjusted so that the difference in rigidity around the circumferential main groove on one side and the other side in the tire width direction can be reduced. It is possible to prevent the deterioration of steering stability performance and wear performance by suppressing uneven contact pressure. Specifically, it is as follows.

  That is, when Hb> He> Hc or He> Hb> Hc, in the periphery of the circumferential main groove where the conductive portion is harder than the cap portion and the starting point is arranged, the circumferential main groove which forms a pair with it Since the rigidity is higher than the periphery of the base, the base part is divided in the tire width direction on the groove bottom side of the circumferential main groove where the starting point is arranged, and on the groove bottom side of the circumferential main groove that makes a pair with it The base part is not divided, and the recess in the part to be cut is filled with the rubber of the cap part, which is softer than the base part, thereby reducing the difference in rigidity around the circumferential main groove on one side and the other side in the tire width direction. Can be adjusted.

  Further, when Hc> Hb> He or Hc> He> Hb, the circumferential main groove that is paired with the circumferential main groove where the conductive portion is softer than the cap portion and the starting point is arranged Because the rigidity is lower than the periphery of the base, the base part is divided in the tire width direction on the groove bottom side of the circumferential main groove where the starting point is arranged, and on the groove bottom side of the circumferential main groove that makes a pair with it By not filling the base part and filling the hollow of the part to be cut with the rubber of the cap part harder than the base part, the difference in rigidity around the circumferential main groove between the one side and the other side in the tire width direction is small. Can be adjusted.

  Further, when Hb> Hc> He, the conductive portion is softer than the cap portion, and the periphery of the circumferential main groove where the starting point is arranged is more rigid than the periphery of the circumferential main groove that is paired therewith. Therefore, the base part is not divided at the groove bottom side of the circumferential main groove where the starting point is arranged, but the base part is divided in the tire width direction at the groove bottom side of the circumferential main groove that makes a pair with it. In addition, by filling the depressions at the parting portions with the rubber of the cap part that is softer than the base part, it is possible to adjust the rigidity difference around the circumferential main groove on one side and the other side in the tire width direction to be small. .

  When He> Hc> Hb, the conductive portion is harder than the cap portion, and the periphery of the circumferential main groove where the starting point is arranged is more rigid than the periphery of the circumferential main groove that is paired therewith. Because it becomes higher, the base part is not divided at the groove bottom side of the circumferential main groove where the starting point is arranged, but the base part is divided in the tire width direction at the groove bottom side of the circumferential main groove that makes a pair with it. In addition, by filling the depressions at the parting portions with rubber of the cap part that is harder than the base part, it is possible to adjust the rigidity difference around the circumferential main groove on one side and the other side in the tire width direction to be small. .

  Further, another pneumatic tire according to the present invention includes three tires including a pair of shoulder main grooves positioned on the outermost side in the tire width direction and one center main groove positioned therebetween on the surface of the tread portion. The tread rubber disposed in the tread portion is formed of non-conductive rubber and forms a grounding surface, and the tire of the cap portion is formed of non-conductive rubber. In a pneumatic tire including a base portion disposed radially inside and a conductive portion formed of a conductive rubber and extending from a ground contact surface to a side surface or a bottom surface of the tread rubber, the conductive portion is the center main groove. A first conductive portion extending inward in the tire radial direction from a position in the ground contact surface between the first main portion and the shoulder main groove, and is provided continuously to the first conductive portion, and between the cap portion and the base portion. tire A second conductive portion extending in a direction, and a starting point of the conductive portion rising from the second conductive portion toward the ground plane is disposed on a groove bottom side of a pair of shoulder main grooves, and the cap The rubber hardness Hc of the portion, the rubber hardness Hb of the base portion, and the rubber hardness He of the conductive portion satisfy the relationship of Hb> He> Hc, He> Hb> Hc, Hc> Hb> He or Hc> He> Hb. In addition, the base portion is divided in the tire width direction on the groove bottom side of the shoulder main groove where the starting point is arranged, and the base portion is continuous without being divided on the groove bottom side of the shoulder main groove that is paired with the base portion. Or satisfying the relationship of Hb> Hc> He or He> Hc> Hb, and the base portion continuously extends without being divided on the groove bottom side of the shoulder main groove in which the location point is arranged, Versus it Nasu the groove bottom side of the shoulder main groove said base portion is divided in the tire width direction, in which the recess of the divide portion of the base portion is filled with a rubber of the cap portion.

  In this tire, when the tread rubber includes the conductive portion as described above, the energization performance can be exhibited. Further, the first conductive portion of the conductive portion extends inward in the tire radial direction from a position in the ground contact surface between the center main groove and the shoulder main groove, but the origin of the conductive portion is the groove bottom of the shoulder main groove. Arranged on the side. Nevertheless, the base part is divided at one groove bottom side of the pair of shoulder main grooves, and the depressions at the divided parts are filled with the rubber of the cap part, so that the conductive parts are densely arranged around the shoulder main grooves. This can prevent the contact pressure from becoming uneven and prevent deterioration of steering stability performance and wear performance.

  Which base side of the pair of shoulder main grooves divides the base portion is determined according to the magnitude relationship among the rubber hardness Hc of the cap portion, the rubber hardness Hb of the base portion, and the rubber hardness He of the conductive portion. By filling the depressions at the parting portions with the rubber of the cap portion, the difference in rigidity around the circumferential main groove (specifically, the shoulder main groove) on one side and the other side in the tire width direction is reduced. In other words, it is possible to prevent the deterioration of the steering stability performance and the wear performance by suppressing the unevenness of the contact pressure. Specifically, the case is as described above.

  In the pneumatic tire described above in which three circumferential main grooves are provided on the surface of the tread portion, the first conductive portion is located within a ground plane at a distance of 10% or more of the groove width from the groove edge of the center main groove. Is preferably extended inward in the tire radial direction. According to such a configuration, the exposed portion of the conductive portion is set at a position away from the center main groove by a predetermined distance, and non-uniform ground pressure due to the influence of wiping can be reduced.

  In the present invention, it is preferable that the base portion is divided only at one location in the tire width direction. In this case, the base part is divided at the groove bottom side of the specific circumferential main groove, and the base part continuously extends without being divided at the groove bottom side of all other circumferential main grooves. It is possible to effectively equalize the ground pressure without forming unnecessary portions.

  In the present invention, it is preferable that the division width of the base portion divided on the groove bottom side of the circumferential main groove is not more than four times the groove width of the circumferential main groove. As a result, the dividing width does not become larger than necessary, which is beneficial for making the ground pressure uniform.

  In the present invention, it is preferable that the ratio of the area of the pair of shoulder land portions located on the outer side in the tire width direction from the shoulder main groove to the area of the ground contact surface is within a range of 30 to 60%. Thereby, it is possible to prevent the contact pressure between the shoulder land portion and the other land portions from becoming unbalanced, and to effectively equalize the contact pressure.

Tire meridian cross-sectional view showing an example of a pneumatic tire according to the present invention Enlarged view showing the main part of FIG. Sectional drawing which shows the tread part which concerns on another embodiment of this invention. Sectional drawing which shows the tread part which concerns on another embodiment of this invention. Sectional drawing which shows the tread part which concerns on another embodiment of this invention. Sectional drawing which shows an example of the tread part of the pneumatic tire which concerns on this invention Sectional drawing which shows the tread part which concerns on another embodiment of this invention. Cross-sectional view of the tread for explaining in-plane contraction force

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
A pneumatic tire T shown in FIG. 1 includes a pair of bead portions 1, sidewall portions 2 extending outward in the tire radial direction from each of the bead portions 1, and tire radial direction outer ends of the sidewall portions 2. And a tread portion 3 connected to the front. The bead portion 1 is provided with an annular bead core 1a formed by covering a converging body such as a steel wire with rubber and a bead filler 1b made of hard rubber.

  The carcass layer 7 reaches from the tread portion 3 through the sidewall portion 2 to the bead portion 1 and is locked in a state where its end is wound up via the bead core 1a. The carcass layer 7 is composed of at least one (two in this embodiment) carcass ply, and the carcass ply is formed by covering a cord that extends at an angle of approximately 90 ° with respect to the tire circumferential direction with a topping rubber. Has been.

  In the bead portion 1, a rim strip rubber 8 is disposed outside the carcass layer 7. The rim strip rubber 8 constitutes the outer surface of the tire in the bead portion 1 and contacts a rim (not shown). In the sidewall portion 2, sidewall rubber 9 is disposed outside the carcass layer 7. The sidewall rubber 9 constitutes the tire outer surface in the sidewall portion 2. In the present embodiment, the rim strip rubber 8 and the side wall rubber 9 are each formed of conductive rubber.

  In the tread portion 3, a belt layer 6 constituted by a plurality of (two in the present embodiment) belt plies is disposed outside the carcass layer 7. Each belt ply is formed by covering a cord extending obliquely with respect to the tire equator C with a topping rubber, and the cords are laminated so that the cords cross each other in opposite directions. A belt reinforcing layer formed by covering a cord extending substantially in the tire circumferential direction with a topping rubber is disposed on the outer side of the belt layer 6, but may be omitted if necessary.

  The tread rubber 10 disposed in the tread portion 3 is formed of non-conductive rubber and forms a ground contact surface, and the tread rubber 10 is formed of non-conductive rubber and disposed inside the cap portion 12 in the tire radial direction. A base portion 11 and a conductive portion 13 made of conductive rubber and extending from the ground surface to the bottom surface of the tread rubber 10 are provided. In this embodiment, a so-called side-on-tread structure in which the end portions of the sidewall rubber 9 are placed on both end portions of the tread rubber 10 is employed, but the present invention is not limited to this.

Here, the conductive rubber refers to a rubber having a volume resistivity of less than 10 ⁸ Ω · cm at room temperature (20 ° C.). For example, the conductive rubber is produced by blending carbon black as a reinforcing agent in a high ratio with a raw material rubber. The For example, the carbon black is blended in an amount of 30 to 100 parts by weight with respect to 100 parts by weight of the rubber component. In addition to carbon black, the conductive rubber can be blended with carbon fiber, graphite or other carbon-based materials, and metal-based known conductivity imparting materials such as metal powders, metal oxides, metal flakes, and metal fibers. can get.

Non-conductive rubber refers to rubber having a volume resistivity of 10 ⁸ Ω · cm or more at room temperature (20 ° C.). For example, non-conductive rubber is produced by blending silica as a reinforcing agent in a high ratio with raw material rubber. The silica is blended at 30 to 100 parts by weight with respect to 100 parts by weight of the rubber component, for example. As silica, wet silica can be preferably used, but those commonly used as reinforcing materials can be used without limitation. The nonconductive rubber may be prepared by blending calcined clay, hard clay, calcium carbonate, or the like, in addition to silicas such as precipitated silica and anhydrous silicic acid.

  Examples of the raw rubber include natural rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), and butyl rubber (IIR). These may be used alone or in combination of two or more. Used. A vulcanizing agent, a vulcanization accelerator, a plasticizer, an anti-aging agent and the like are appropriately blended with the raw rubber.

  In the present embodiment, on the surface of the tread portion 3, a pair of shoulder main grooves 4a, 4d located on the outermost side in the tire width direction, and a pair of center main grooves 4b, 4c located between them and sandwiching the tire equator C, Four circumferential main grooves 4 are formed. These circumferential main grooves 4 extending along the tire circumferential direction define five land portions including a pair of shoulder land portions 5s, a pair of mediate land portions 5m, and a center land portion 5c. .

  The conductive portion 13 is a tire from a position within the ground contact surface excluding the center land portion 5c located between the pair of center main grooves 4b, 4c, that is, a position within the ground contact surface at the mediate land portion 5m or the shoulder land portion 5s. A first conductive portion 13a extending inward in the radial direction and a second conductive portion 13b provided continuously from the first conductive portion 13a and extending in the tire width direction between the cap portion 12 and the base portion 11 are provided.

  The conductive portion 13 has an L-shaped cross section, one end thereof is exposed to the ground surface, the other end is connected to a rim or a rubber that can be energized from the rim, and constitutes a conductive path for discharging static electricity to the road surface. . In the present embodiment, the second conductive portion 13 b reaches the end of the bottom surface of the tread rubber 10 and is connected to the sidewall rubber 9. Static electricity generated in the vehicle body and tires is discharged from the rim to the road surface through a conductive path through the rim strip rubber 8, the sidewall rubber 9, and the conductive portion 13. The conductive portion 13 may extend from the ground surface to the side surface of the tread rubber 10.

  In the tire T, at least one of the rim strip rubber 8 and the side wall rubber 9 can be formed of a non-conductive rubber. For example, the conductive path can also be configured by forming the sidewall rubber 9 with non-conductive rubber and forming the topping rubber of the carcass layer 7 with conductive rubber. When the rim strip rubber 8 is formed of non-conductive rubber, the conductive path is configured by extending the conductive portion 13 to the outer surface of the rim strip rubber 8 that contacts the rim.

  As shown in an enlarged view in FIG. 2, a starting point 13 </ b> R of the conductive portion 13 that rises from the second conductive portion 13 b toward the ground surface is disposed on the bottom side of any of the four circumferential main grooves 4. The In the present embodiment, an example is shown in which a starting point 13R is arranged on the groove bottom side of the shoulder main groove 4d and the exposed portion of the conductive portion 13 is in the mediate land portion 5m. The conductive portion 13 may be exposed at the shoulder land portion 5s. However, in order to increase the contact frequency of the conductive portion 13 with respect to the road surface, the conductive portion 13 is exposed at the inner side in the tire width direction than the shoulder main grooves 4a and 4d. Is desirable.

  As described above, in the tread structure including the four circumferential main grooves 4, the in-plane contraction force acts on the center land portion 5c from both sides in the tire width direction (see FIG. 8). Therefore, if the exposed portion of the conductive portion 13 is set in the center land portion 5c, the ground pressure becomes non-uniform due to the influence of wiping, coupled with the difference in rubber hardness in the base portion 11, the cap portion 12, and the conductive portion 13. Although there is a tendency that the steering stability performance and the wear performance are adversely affected, in the tire T, since the exposed portion of the conductive portion 13 is set to the mediate land portion 5m, such a problem does not occur.

  In the tread rubber 10, the base portion 11 is divided in the tire width direction on the bottom side of the shoulder main groove 4d where the starting point 13R is disposed, and the base portion 11 is separated on the groove bottom side of the shoulder main groove 4a that is paired with the base portion 11. It extends continuously without being divided, and the depression 14 at the dividing portion of the base portion 11 is filled with the rubber of the cap portion 12. In this structure, the rubber hardness Hc of the cap portion 12, the rubber hardness Hb of the base portion 11, and the rubber hardness He of the conductive portion 13 are Hb> He> Hc, He> Hb> Hc, Hc> Hb> He or Hc> He. It is adopted when satisfying the relationship of> Hb.

  On the other hand, when the relationship of Hb> Hc> He or He> Hc> Hb is satisfied, as shown in FIG. 3, the base portion 11 is divided on the groove bottom side of the shoulder main groove 4d where the starting point 13R is arranged. The base portion 11 is divided in the tire width direction at the groove bottom side of the shoulder main groove 4a that extends continuously and forms a pair with the shoulder main groove 4a, and the depression 14 at the divided portion of the base portion 11 is filled with the rubber of the cap portion 12. The

  As described above, it is determined according to the magnitude relationship of the rubber hardness Hc, Hb, and He of each part which base part 11 is divided at which groove bottom side of the paired circumferential main grooves 4 and the base. By filling the depression 14 at the parting portion of the portion 11 with the rubber of the cap portion 12, it can be adjusted so that the difference in rigidity around the circumferential main groove 4 on one side and the other side in the tire width direction is reduced. As a result, uneven contact pressure can be suppressed and deterioration of steering stability performance and wear performance can be prevented.

  The rubber hardness Hc of the cap part 12 is exemplified by 45 to 80 °. The rubber hardness Hb of the base part 11 is exemplified by 55 to 75 °. As for the rubber hardness He of the electroconductive part 13, 45-80 degrees is illustrated. The numerical value of rubber hardness is a value measured at room temperature (20 ° C.) according to the durometer hardness test (type A) of JISK6253. The magnitude relationship of these rubber hardnesses is determined by comparing integers of measured values (the first decimal place is rounded off).

  As shown in FIGS. 1 and 3, the part of the base portion 11 is formed only at one place in the tire width direction. Accordingly, the base portion 11 is divided on the groove bottom side of all the circumferential main grooves 4 except the circumferential main groove 4 (the shoulder main groove 4d or the shoulder main groove 4a) in which the starting point 13R is arranged on the groove bottom side. Without extending continuously. Thereby, it is possible to effectively equalize the ground pressure without forming unnecessary parting portions in the base portion 11.

  The dividing width W14 of the base portion 11 divided on the groove bottom side of the circumferential main groove 4 is preferably not more than four times the groove width W4 of the circumferential main groove 4. As a result, the dividing width W14 is not increased more than necessary, which is beneficial in making the ground pressure uniform. The dividing width W14 is preferably not less than 0.5 times the groove width W4 so that the effectiveness of uniformizing the contact pressure by filling the recess 14 with the rubber of the cap portion 12 can be enhanced. More preferably, the dividing width W14 is set within a range of 1 to 3 times the groove width W4.

  In FIG. 2, the starting point 13R is set within the range of the dividing width W14. In this connection, the distance from the center of the shoulder main groove 4d to the starting point 13R is preferably not more than twice the width W4 of the shoulder main groove 4d, which means that the starting point 13R is disposed in the circumferential direction. The same applies to a structure in which the base portion 11 is not divided on the groove bottom side of the main groove 4 (see FIG. 3). In the present embodiment, the starting point 13R is arranged within the range of the groove width W4 of the circumferential main groove 4.

  The first conductive portion 13a extends while being inclined with respect to the tire radial direction, and the inclination width W13 is set to be, for example, four times or less the groove width W4. The inclination width W13 is measured in a section from the starting point 13R to the ground contact surface. The conductive portion 13 of the present embodiment has an inclined width W13 in the first conductive portion 13a while appropriately extending the tip portion in the tire width direction so as to increase the exposure frequency on the ground contact surface. .

  The first conductive portion 13a is located on the tire equator C side with respect to the shoulder main groove 4d where the starting point 13R is disposed on the groove bottom side, and the second conductive portion 13b moves away from the tire equator C with the starting point 13R as a starting point. Extending in the direction. From the viewpoint of suppressing the length of the conductive path in the tread portion 3, the conductive portion 13 is preferably in the form shown in FIGS. 1 and 3 rather than in the form shown in FIGS.

  The contact surface on which the conductive portion 13 is exposed is the surface of the tread portion 3 that is rim-assembled on a regular rim, is placed on a flat road surface with a normal internal pressure filled, and contacts the road surface when a normal load is applied. Point to. The ground contact CE indicates the outermost position of the ground contact surface in the tire axial direction. The regular rim is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim is used for JATMA, “Design Rim” is used for TRA, and “Measuring” is used for ETRTO. Rim ".

  The normal internal pressure is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. "INFLATION PRESSURE" for the maximum value described in "ETRTO", but 200 kPa for tires for passenger cars. In addition, the normal load is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. If it is JATMA, it is the maximum load capacity, and if it is TRA, the maximum load described in the above table. If the value is ETRTO, it is "LOAD CAPACITY", but if the tire is for a passenger car, it will be 80% of the maximum load capacity.

  The ratio of the area of the pair of shoulder land portions 5s located on the outer side in the tire width direction from the shoulder main grooves 4a and 4d to the area of the ground contact surface is preferably in the range of 30 to 60%. When this area ratio is 30% or more, the contact pressure of the shoulder land portion 5s is prevented from becoming too high, and when it is 60% or less, the contact pressure of other land portions is prevented from becoming too high. Therefore, the above-described uniform ground pressure can be made more effective. The area of the shoulder land portion 5s is based on the ground contact end CE, and the area of the ground contact surface corresponds to the sum of the areas of the land portions.

  FIG. 4 is an example in which a starting point 13R is arranged on the groove bottom side of the center main groove 4b and the conductive portion 13 is exposed at the mediate land portion 5m. (A) is a structure when the relationship of Hb> He> Hc, He> Hb> Hc, Hc> Hb> He or Hc> He> Hb is satisfied, and the base portion 11 is formed on the groove bottom side of the center main groove 4b. The base portion 11 extends continuously without being divided on the groove bottom side of the center main groove 4c that is paired with the center main groove 4c. (B) is a structure when the relationship of Hb> Hc> He or He> Hc> Hb is satisfied, and the base portion 11 extends continuously without being divided on the groove bottom side of the center main groove 4b. The base portion 11 is divided at the groove bottom side of the groove 4c.

  FIG. 5 is an example in which the starting point 13R is arranged on the groove bottom side of the shoulder main groove 4a and the conductive portion 13 is exposed at the shoulder land portion 5s. (A) is a structure when the relationship of Hb> He> Hc, He> Hb> Hc, Hc> Hb> He or Hc> He> Hb is satisfied, and the base portion 11 is formed on the bottom side of the shoulder main groove 4a. The base portion 11 extends continuously without being divided on the groove bottom side of the shoulder main groove 4d. (B) is a structure when the relationship of Hb> Hc> He or He> Hc> Hb is satisfied, and the base 11 extends continuously without being divided on the groove bottom side of the shoulder main groove 4a, and the shoulder main The base portion 11 is divided at the groove bottom side of the groove 4d.

[Second Embodiment]
Since the second embodiment has the same configuration and operation as the first embodiment except for the configuration described below, common points will be omitted and differences will be mainly described. In addition, the same code | symbol is attached | subjected to the member and site | part same as the member and site | part demonstrated in 1st Embodiment, and the overlapping description is abbreviate | omitted.

  The pneumatic tire T shown in FIG. 6 includes a pair of shoulder main grooves 4e and 4g positioned on the outermost side in the tire width direction on the surface of the tread portion 3, and a single center main groove 4f positioned therebetween. Three circumferential main grooves 4 are provided. These circumferential main grooves 4 extending along the tire circumferential direction divide four land portions including a pair of shoulder land portions 5s and a pair of center land portions 5c.

  The conductive portion 13 is a first conductive portion 13a extending inward in the tire radial direction from a position in the ground contact surface between the center main groove 4f and the shoulder main grooves 4e and 4g, that is, a position in the ground contact surface in the center land portion 5c. And a second conductive portion 13b provided continuously with the first conductive portion 13a and extending between the cap portion 12 and the base portion 11 in the tire width direction. On the bottom side of either of the pair of shoulder main grooves 4e, 4g, a starting point 13R of the conductive portion 13 is disposed. In the present embodiment, an example in which the starting point 13R is arranged on the groove bottom side of the shoulder main groove 4g is shown.

  As described above, in the tread structure including the three circumferential main grooves 4, when the conductive portion 13 is exposed to avoid the shoulder land portion 5s, the exposed portion of the conductive portion 13 is set to the center land portion 5c, and the wiping is performed. Since there is a concern that the contact pressure becomes uneven due to the influence, in this tire T, the starting point 13R of the conductive portion 13 is arranged on the groove bottom side of the shoulder main groove 4g. The first conductive portion 13a is positioned closer to the tire equator C than the shoulder main groove 4g where the starting point 13R is disposed, and the second conductive portion 13b extends in a direction away from the tire equator C with the starting point 13R as a starting point. Yes.

  In the present embodiment, the base portion 11 is divided in the tire width direction on the groove bottom side of the shoulder main groove 4g where the starting point 13R is arranged, and the base portion 11 is divided on the groove bottom side of the shoulder main groove 4e that makes a pair with the base portion 11. The recesses 14 extend continuously without being filled, and the recesses 14 of the base part 11 are filled with the rubber of the cap part 12. In this structure, the rubber hardness Hc of the cap portion 12, the rubber hardness Hb of the base portion 11, and the rubber hardness He of the conductive portion 13 are Hb> He> Hc, He> Hb> Hc, Hc> Hb> He or Hc> He. It is adopted when satisfying the relationship of> Hb.

  On the other hand, when the relationship of Hb> Hc> He or He> Hc> Hb is satisfied, as shown in FIG. 7, the base portion 11 is divided on the groove bottom side of the shoulder main groove 4g where the starting point 13R is arranged. The base portion 11 is divided in the tire width direction on the groove bottom side of the shoulder main groove 4e that extends continuously and forms a pair with it, and the depression 14 at the division portion of the base portion 11 is filled with the rubber of the cap portion 12. The

  As described above, which of the shoulder main grooves 4e, 4g making a pair is to be divided at the bottom of the base 11 depending on the magnitude relationship of the rubber hardness Hc, Hb, He of each part, By filling the recess 14 at the part where the base portion 11 is divided with the rubber of the cap portion 12, the circumferential main groove 4 (of the shoulder main grooves 4e and 4g) around the one side and the other side in the tire width direction Adjustment can be made so that the difference in rigidity is reduced. As a result, nonuniform contact pressure due to the dense arrangement of the conductive portions 13 around the shoulder main groove 4e or the shoulder main groove 4g can be prevented, and deterioration of steering stability performance and wear performance can be prevented.

  The first conductive portion 13a preferably extends inward in the tire radial direction from a position in the ground contact surface that is separated from the groove edge of the center main groove 4f by 10% or more of the groove width. As a result, the exposed portion of the conductive portion 13 is set at a position away from the center main groove 4f by a predetermined distance, and non-uniform ground pressure due to the influence of wiping can be reduced. The distance from the groove edge of the center main groove 4f to the exposed portion of the conductive portion 13 is more preferably 30% or more, and further preferably 50% or more of the groove width of the center main groove 4f.

  The pneumatic tire of the present invention is the same as a normal pneumatic tire except that it has the tread structure as described above, and any conventionally known material, shape, structure, manufacturing method, etc. can be adopted in the present invention. it can.

  The present invention is not limited to the embodiment described above, and various improvements and modifications can be made without departing from the spirit of the present invention.

  Examples that specifically show the structure and effects of the present invention will be described below. Each performance evaluation of the tire was performed as follows.

(1) Ground pressure dispersion A predetermined load was applied to the tire mounted on the rim, and the ground pressure in the surface of the tread portion that touches the road surface was measured to determine the dispersion of the ground pressure. The index evaluation is made with the result of Comparative Example 1 being 100, and the larger the value, the better the contact pressure dispersion.

(2) Steering stability performance Driving on the road with tires attached to an actual vehicle, it was evaluated by a driver's sensory test. The index evaluation is made with the result of Comparative Example 1 being 100, and the larger the value, the better the steering stability performance.

(3) Wear performance A tire was mounted on a passenger car, and the vehicle traveled a predetermined distance on a dry road. The wear amount of the tread portion was measured, and the reciprocal thereof was obtained. Index evaluation is made with the result of Comparative Example 1 being 100, and the larger the value, the smaller the amount of wear and the better the wear performance.

(4) Energizing performance A predetermined load was applied to the tire mounted on the rim, and an electric resistance value was measured by applying an applied voltage (variable: upper limit 1000 V) from the shaft supporting the rim to the metal plate where the tire contacts the ground.

  The tire (size: P245 / 55R19 103S) used for evaluation includes four circumferential main grooves as shown in FIG. 1 on the surface of the tread portion. The tread structure in each example is as shown in Table 1, and other tire structures are common. Table 2 is referred to for the rubber hardness relationship in Table 1. The conductive portion provided in other than Comparative Example 1 is located at the bottom of the shoulder main groove as shown in FIGS. 1 to 3 and is exposed at the mediate land portion (only the land portion of Example 9 is the center land portion). is there. In Comparative Example 2, the base portion is divided at the groove bottom sides of the shoulder main grooves on both sides. Table 3 shows the evaluation results.

  In Comparative Example 2, since the base portion is divided at the groove bottom side of the shoulder main grooves on both sides, the difference in rigidity around the shoulder main grooves on the left and right sides of the tread rubber is not reduced, and the contact pressure becomes uneven. Steering stability and wear performance are degraded. In Comparative Examples 3 to 16, since the base portion is divided on the side opposite to the present invention, the ground pressure is uneven. On the other hand, in Examples 1-9, according to the magnitude relationship of rubber hardness Hc, Hb, and He, a base part is parted on the groove bottom side of a predetermined circumferential main groove, thereby making the ground pressure uniform. This prevents the deterioration of steering stability and wear performance. Although Examples 7 and 8 are inferior to other Examples, the shoulder area ratio is improved as compared with Comparative Examples 5 and 11.

3 tread portion 4 circumferential main groove 4a shoulder main groove 4b center main groove 4c center main groove 4d shoulder main groove 4e shoulder main groove 4f center main groove 4g shoulder main groove 5c center land portion 5s shoulder land portion 10 tread rubber 11 base portion 12 Cap portion 13R Origin point 13 Conductive portion 13a First conductive portion 13b Second conductive portion 14 Dimple

Claims (6)

Four circumferential main grooves including a pair of shoulder main grooves positioned on the outermost side in the tire width direction and a pair of center main grooves sandwiching the tire equator between them are provided on the surface of the tread portion,
A tread rubber disposed in the tread portion is formed of non-conductive rubber and forms a ground plane, and a base portion is formed of non-conductive rubber and is disposed on the inner side in the tire radial direction of the cap portion. And a pneumatic tire provided with a conductive portion formed of conductive rubber and extending from the ground contact surface to the side surface or bottom surface of the tread rubber,
The conductive portion is provided continuously from the first conductive portion extending inward in the tire radial direction from a position in the ground contact surface excluding the center land portion located between the pair of center main grooves, and the first conductive portion. A second conductive portion extending in the tire width direction between the cap portion and the base portion,
The starting point of the conductive part rising from the second conductive part toward the ground plane is arranged on the bottom side of any of the four circumferential main grooves,
The relationship between the rubber hardness Hc of the cap portion, the rubber hardness Hb of the base portion, and the rubber hardness He of the conductive portion is Hb>He> Hc, He>Hb> Hc, Hc>Hb> He or Hc>He> Hb. And the base portion is divided in the tire width direction on the groove bottom side of the circumferential main groove where the starting point is arranged, and the base portion is divided on the groove bottom side of the circumferential main groove that forms a pair with the base portion. The base portion is not divided at the groove bottom side of the circumferential main groove where the starting point is arranged, while extending continuously without satisfying the relationship of Hb>Hc> He or He>Hc> Hb. The base part is divided in the tire width direction on the groove bottom side of the circumferential main groove that extends continuously and pairs with it,
The pneumatic tire according to claim 1, wherein a recess in the divided part of the base part is filled with rubber of the cap part. On the surface of the tread portion, there are provided three circumferential main grooves including a pair of shoulder main grooves located on the outermost side in the tire width direction and one center main groove located between the shoulder main grooves,
A tread rubber disposed in the tread portion is formed of non-conductive rubber and forms a ground plane, and a base portion is formed of non-conductive rubber and is disposed on the inner side in the tire radial direction of the cap portion. And a pneumatic tire provided with a conductive portion formed of conductive rubber and extending from the ground contact surface to the side surface or bottom surface of the tread rubber,
A first conductive portion extending inward in a tire radial direction from a position within a ground contact surface between the center main groove and a shoulder main groove; and the cap is provided continuously to the first conductive portion. A second conductive portion extending in the tire width direction between the portion and the base portion,
The starting point of the conductive part that rises from the second conductive part toward the ground plane is arranged on the bottom side of any one of the pair of shoulder main grooves,
The relationship between the rubber hardness Hc of the cap portion, the rubber hardness Hb of the base portion, and the rubber hardness He of the conductive portion is Hb>He> Hc, He>Hb> Hc, Hc>Hb> He or Hc>He> Hb. And the base portion is divided in the tire width direction on the groove bottom side of the shoulder main groove where the starting point is arranged, and the base portion is not divided on the groove bottom side of the shoulder main groove that is paired with the base portion. Continuously extending, or satisfying the relationship of Hb>Hc> He or He>Hc> Hb, and the base portion continuously without being divided at the groove bottom side of the shoulder main groove where the starting point is arranged The base part is divided in the tire width direction on the groove bottom side of the shoulder main groove that extends and pairs with it,
The pneumatic tire according to claim 1, wherein a recess in the divided part of the base part is filled with rubber of the cap part.   3. The pneumatic tire according to claim 2, wherein the first conductive portion extends inward in the tire radial direction from a position within a ground contact surface that is separated from a groove edge of the center main groove by 10% or more of a groove width.   The pneumatic tire according to any one of claims 1 to 3, wherein a part of the base portion is formed only at one place in a tire width direction.   The pneumatic tire according to any one of claims 1 to 4, wherein a dividing width of the base portion divided on the groove bottom side of the circumferential main groove is not more than four times a groove width of the circumferential main groove. .   The ratio of the area of the pair of shoulder land portions located on the outer side in the tire width direction with respect to the shoulder main groove to the area of the ground contact surface is in a range of 30 to 60%. Pneumatic tires.

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