JP2012111269A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of reducing the heating of a tread part while maintaining chipping-resistant performance.SOLUTION: In a pneumatic tire 1 in which relationship of loss tangent tanδA of cap tread rubber 2a to loss tangent tanδB of under tread rubber 2b measured at 60 [°C] is tanδB<tanδA, the under tread rubber 2b is provided at the nearest part to the tread face 21 of a shoulder region 20 outside tire width direction of the tread part 2 on the basis of tire width direction end 73a of a belt 73 outside in the tire radial direction of cross belts 72, 73 in the cross-sectional view of the tire meridian direction. In addition, the maximum dimension H thereof closest to the tread face 21 from a groove bottom reference line B1 passing along the groove bottom of a circumferential main groove 22 nearest to the shoulder region 20 and parallel to the tread face 21 is set to 0.3≤H/D to the groove depth D of the circumferential main groove 22.

Description

  The present invention relates to a pneumatic tire in which rubber in a tread portion is formed in a laminated structure of at least two layers.

  For example, in the pneumatic tire described in Patent Document 1, in order to prevent a situation (belt edge separation) in which the belt layer disposed in the tread portion is peeled off due to heat generated by the rubber in the tread portion, the tread portion rubber is attached to the tread surface. The cap tread rubber is formed with a laminated structure of an under tread rubber disposed inside the tire tread rubber in the tire radial direction, and a low heat-generating rubber is used as the under tread rubber.

  However, since the under-tread rubber with reduced heat generation is accompanied by a decrease in elongation at break, chipping (chipping) is likely to occur at the center portion (center portion) in the tire width direction at the end of wear. Thus, the chipping resistance and the low heat generation of the tread portion are contradictory properties, and it is eagerly desired to achieve both.

  Further, the pneumatic tire described in Patent Document 2 has a low rolling resistance performance by increasing the ratio of the low heat-generating undertread rubber in the shoulder portion where the heat generation is large and the energy loss is large in the tread portion. We are trying to improve.

JP 63-149202 A JP 2007-137411 A

  By the way, in the shoulder portion, the portion where the distortion is large and the heat generation is large is the shoulder region in the tire width direction outside the tire width direction end of the belt on the outer side in the tire radial direction in the cross belt, and passes through the end in the tire width direction of the belt. It has been discovered by the inventors' research that the region is located outside the tire radial direction from the reference line parallel to the tread surface.

  The pneumatic tire described in Patent Document 2 has a large distortion and a large amount of heat generation, and no low heat-generating undertread rubber is disposed. For this reason, low heat generation in the tread portion is not sufficient.

  This invention is made | formed in view of the above, Comprising: It aims at providing the pneumatic tire which can reduce the heat_generation | fever of a tread part, maintaining a chipping-proof performance.

  In order to solve the above-described problems and achieve the object, the pneumatic tire of the present invention has a pair of cross belts arranged on the outer side in the tire radial direction of the carcass layer, and the outer side in the tire radial direction of the cross belt. In addition, a tread in which a cap tread rubber and an under tread rubber provided on the inner side in the tire radial direction of the cap tread rubber are stacked, and a plurality of circumferential main grooves extending in the tire circumferential direction are formed on the tread surface. And a relationship between a loss tangent tan δA of the cap tread rubber measured at 60 [° C.] and a loss tangent tan δB of the under tread rubber is tan δB <tan δA, the under tread rubber is a tire The tire width direction of the belt on the outer side in the tire radial direction of the intersecting belts in a cross-sectional view in the meridian direction The tread portion is provided closest to the tread surface in the shoulder region on the outer side in the tire width direction of the tread portion with reference to the tread surface and passes through the groove bottom of the circumferential main groove closest to the shoulder region. The maximum dimension H closest to the tread surface from the groove bottom reference line parallel to the groove depth D is 0.3 ≦ H / D with respect to the groove depth D of the circumferential main groove.

  According to this pneumatic tire, the heat generation in the tread portion can be reduced because the low-heat-generating under-tread rubber is disposed in the shoulder region, which is a portion with large distortion and large heat generation. In addition, the low heat generation under tread rubber in the shoulder area can reduce the heat generation of the entire tread, so the amount of under tread rubber near the tire equator can be reduced. The situation in which the rubber contacts the road surface can be suppressed and the chipping performance can be maintained.

  Further, in the pneumatic tire of the present invention, the under tread rubber is the cross-sectional view in the tire meridian direction, and the most tread surface is within the range in the tire width direction outer side than the normal line of the tread surface passing through the tread grounding end. It is provided near.

  The portion with the largest distortion and the largest amount of heat generation is the outer region in the tire width direction than the normal line of the tread surface passing through the tread contact edge in the shoulder region. According to this pneumatic tire, since the low-heat-generating under tread rubber is arranged in the portion where the distortion is the largest and the heat generation is large, the effect of reducing the heat generation in the tread portion while maintaining the chipping performance is remarkable. Can get to.

  The pneumatic tire according to the present invention includes a straight line connecting a tire width direction end and a tread grounding end of a belt on the outer side in the tire radial direction of the intersecting belts, and a tire radial direction outer side in a cross-sectional view in the tire meridian direction. In the range surrounded by the belt reference line passing through the tire width direction end of the belt and parallel to the tread surface, and the surface outside the tread grounding end in the tire width direction, the total area S of the range On the other hand, the area Su of the undertread rubber is 0.2 ≦ Su / S ≦ 0.8.

  If Su / S is 0.2 or more, an under tread rubber that reduces heat generation in the tread portion can be disposed in a shoulder region that is a portion having a large distortion and large heat generation. On the other hand, if Su / S is 0.8 or less, the amount of undertread rubber appearing on the tread during wear can be reduced. Therefore, according to this pneumatic tire, the situation in which the under tread rubber is exposed to the tread surface can be suppressed, and the heat generation in the tread portion can be reduced.

  In the pneumatic tire of the present invention, the relationship between the storage elastic modulus E′A of the cap tread rubber measured at 60 [° C.] and the storage elastic modulus E′B of the undertread rubber is E′B < E′A, and 5.0 [MPa] ≦ E′A ≦ 15.0 [MPa], 4.0 [MPa] ≦ E′B ≦ 10.0 [MPa].

  According to this pneumatic tire, since E′B <E′A, the undertread rubber has a smaller ability (elastic component) to retain the stress stored therein than the cap tread rubber. The effect of low heat generation by the tread rubber can be obtained. Moreover, low heat generation by the undertread rubber is achieved by setting the range to 5.0 [MPa] ≦ E′A ≦ 15.0 [MPa], 4.0 [MPa] ≦ E′B ≦ 10.0 [MPa]. A remarkable effect can be obtained.

  In the pneumatic tire of the present invention, in the tire meridian cross-sectional view, a region outside the tire width direction with respect to the normal line of the tread surface passing through the tread ground end is formed of another under tread rubber. The storage elastic modulus E′C of the other undertread rubber measured at 60 ° C., the storage elastic modulus E′A of the cap tread rubber, and the storage elastic modulus E′B of the undertread rubber. The relationship is characterized in that E′B <E′C ≦ E′A and 8.0 [MPa] ≦ E′C.

  According to this pneumatic tire, in the shoulder region, the elastic component is an under tread in a region on the outer side in the tire width direction from the normal line of the tread surface passing through the tread grounding end, which is a portion having the largest distortion and large heat generation. By providing another under tread rubber larger than the rubber and below the cap tread rubber, and by setting 8.0 [MPa] ≦ E'C, the rigidity of the tread portion can be appropriately maintained, so that the handling stability and low rolling are achieved. Resistance performance can be improved.

  Further, in the pneumatic tire of the present invention, in the tire meridian cross-sectional view, the under tread rubber in the outer side in the tire width direction than the normal line of the tread surface passing through the tread ground end is natural rubber, or 2. 0.2 parts by weight or more in which stearic acid is mainly blended with para-aramid fibers as a main component with respect to 100 parts by mass of vulcanizable rubber composed of at least two combinations of natural rubber, synthetic polyisoprene rubber and synthetic polybutadiene. A master batch of 0 part by weight or less is formed of at least a blended rubber composition.

  According to this pneumatic tire, since the rigidity of the tread portion can be appropriately maintained, the low rolling resistance can be improved without deteriorating the wear resistance.

  The pneumatic tire of the present invention is characterized by being applied to a heavy duty pneumatic tire.

  Heavy duty pneumatic tires tend to cause belt edge separation due to heat generated by the rubber in the tread. The tread is formed of a laminated structure of cap tread rubber and under tread rubber, and the under tread rubber generates low heat. Sex rubber is used. For this reason, a heavy-duty pneumatic tire is desired to achieve both chipping resistance and low heat generation in the tread portion. Therefore, by applying to a heavy duty pneumatic tire, the effect of reducing the heat generation in the tread portion can be obtained while maintaining the chipping resistance.

  The pneumatic tire according to the present invention can reduce heat generation in the tread portion while maintaining chipping resistance.

FIG. 1 is a partially cut meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a partially cut meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 3 is a partially cut meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 4 is a partially cut meridian cross-sectional view of the pneumatic tire according to the embodiment of the present invention. FIG. 5 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention.

  Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  1 to 4 are partially cut meridian cross-sectional views of a pneumatic tire according to the present embodiment. In the following description, the tire radial direction refers to a direction orthogonal to the rotation axis (not shown) of the pneumatic tire 1, and the tire radial direction inner side refers to the side toward the rotation axis in the tire radial direction, the tire radial direction outer side. Means the side away from the rotation axis in the tire radial direction. Further, the tire circumferential direction refers to a direction around the rotation axis as a central axis. Further, the tire width direction means a direction parallel to the rotation axis, the inner side in the tire width direction means the side toward the tire equator plane (tire equator line) in the tire width direction, and the outer side in the tire width direction means in the tire width direction. The side away from the tire equator. The tire equator plane is a plane orthogonal to the rotation axis of the pneumatic tire and passing through the center of the tire width of the pneumatic tire 1. The tire width is the width in the tire width direction between the portions located outside in the tire width direction, that is, the distance between the portions farthest from the tire equatorial plane in the tire width direction. The tire equator line is a line along the circumferential direction of the pneumatic tire 1 on the tire equator plane. In addition, since the pneumatic tire 1 described below is configured to be substantially symmetric with respect to the tire equatorial plane, the pneumatic tire 1 is cut along a plane passing through the rotation axis of the pneumatic tire 1. In the meridional sectional views (FIGS. 1 to 4), only one side of the tire equatorial plane (right side in FIGS. 1 to 4) is illustrated and only one side is described, and the other side (FIGS. 1 to 4). The description on the left side in FIG.

  The pneumatic tire 1 of the present embodiment has a tread portion 2 as shown in FIG. The tread portion 2 is made of a rubber material (tread rubber), is exposed at the outermost side in the tire radial direction of the pneumatic tire 1, and the surface thereof is the contour of the pneumatic tire 1. The surface of the tread portion 2 is formed as a tread surface 21 that is a contact surface that comes into contact with the road surface when a vehicle (not shown) on which the pneumatic tire 1 is mounted travels.

  As shown in FIGS. 1 and 2, the tread surface 21 is provided with a plurality of circumferential main grooves 22 extending along the tire circumferential direction. The tread surface 21 extends along the tire circumferential direction by a plurality of circumferential main grooves 22, and a plurality of rib-like land portions 23 parallel to the tire equator line are formed. Although not clearly shown in the drawing, the tread surface 21 may be provided with lug grooves that intersect the tire circumferential direction for each land portion 23. Further, although not shown in the figure, the tread surface 21 may be provided with sipes for each land portion 23.

  The tread portion 2 is mainly composed of a cap tread rubber 2a that forms the tread surface 21 and an under tread rubber 2b provided on the inner side in the tire radial direction of the cap tread rubber 2a. 1-4, the under-tread rubber 2b is hatched. The relationship between the loss tangent tan δA of the cap tread rubber 2a measured at 60 [° C.] and the loss tangent tan δB of the undertread rubber 2b is tan δB <tan δA.

  The pneumatic tire 1 according to the present embodiment includes a carcass layer 6 and a belt layer 7.

  The carcass layer 6 is configured such that each tire width direction end portion is folded back from the tire width direction inner side to the tire width direction outer side by a pair of bead cores (not shown), and is wound around in a toroidal shape in the tire circumferential direction. It constitutes. The carcass layer 6 is composed of at least one layer, and a carcass cord (not shown) arranged in parallel in the tire circumferential direction along the tire meridian direction at an angle of 90 degrees (± 5 degrees) with respect to the tire circumferential direction. ) Is coated with a coat rubber. The carcass cord is made of steel or organic fiber (polyester, rayon, nylon, etc.).

  The belt layer 7 has a multilayer structure in which a plurality of belts are laminated, and is disposed inside the tread portion 2 on the outer side in the tire radial direction, which is the outer periphery of the carcass layer 6, and covers the carcass layer 6 in the tire circumferential direction. The belt layer 7 of the present embodiment is formed by laminating four belts 71, 72, 73, 74 from the inner side in the tire radial direction toward the outer side in the tire radial direction. In the belt layer 7, the belt 71 disposed on the innermost side in the tire radial direction is a reinforcing belt, and a plurality of cords (parallel to each other at a predetermined angle (for example, 15 degrees to 30 degrees) with respect to the tire circumferential direction) (Not shown) is coated with a coat rubber. The belts 72 and 73 disposed on the outer side in the tire radial direction of the belt 71 are a pair of cross belts, and a plurality of cords arranged in parallel at a predetermined angle (for example, 15 degrees to 30 degrees) with respect to the tire circumferential direction. (Not shown) is coated with a coat rubber. The belts 72 and 73 are provided so that the cords are inclined and crossed in opposite directions. The belt 74 disposed on the outer side in the tire radial direction of the belt 73 is a protective belt, and a plurality of cords (not shown) arranged in parallel at a predetermined angle (for example, 15 degrees to 30 degrees) with respect to the tire circumferential direction. Is coated with a coated rubber. The belt 74 is provided such that the belt 73 on the inner side in the tire radial direction and the cord are inclined in the same direction. The cords of the belts 71, 72, 73, 74 are made of steel or organic fibers (polyester, rayon, nylon, etc.). The belt layer 7 may have at least belts 72 and 73 that are a pair of cross belts.

  In the pneumatic tire 1 having such a configuration, as shown in FIGS. 1 to 4, in a cross-sectional view in a tire meridian direction in a no-load state, which is incorporated in a normal rim and filled with 5% of a normal internal pressure, The width of the tire is greater than the normal A1 of the tread surface 21 passing through the tire width direction end 73a of the belt 73 with reference to the tire width direction end of the belt 73 on the outer side in the tire radial direction of the belts 72 and 73 forming the cross belt. The tread portion 2 on the outer side in the direction is referred to as a shoulder region 20. The end 73a of the belt 73 in the tire width direction is a cord located at the outermost end of the belt 73 in the tire width direction.

  Here, 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, “standard rim” for JATMA, “Design Rim” for TRA, ETRTO means “Measuring Rim”. In addition, the normal internal pressure is an air pressure determined by the standard for each tire, for example, “maximum air pressure” for JATMA, maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” for TRA, If it is ETRTO, it means “INFLATION PRESSURES”.

  The under tread rubber 2 b constituting the tread portion 2 is provided closest to the tread surface 21 in the shoulder region 20. That is, the under tread rubber 2 b is formed so as to protrude most outward in the tire radial direction in the shoulder region 20. The under tread rubber 2b shown in FIG. 1 is formed so as to protrude most outward in the tire radial direction at the position of the buttress portion 3 in the shoulder region 20. Further, the under tread rubber 2b shown in FIG. 2 is the tire radial direction most in the tire radial direction inner side of the tapered surface 4 in the pneumatic tire 1 in which the tapered surface 4 is formed from the tread grounding end T to the buttress portion 3. It is formed to protrude outward. The position where the undertread rubber 2b protrudes most outward in the tire radial direction may be in the shoulder region 20. Further, the form in which the under tread rubber 2b protrudes most outward in the tire radial direction is not limited to the form in which the under tread rubber 2b gradually protrudes outward in the tire radial direction from the normal A1 toward the outer side in the tire width direction as shown in FIG. Instead, it may be recessed inward in the tire radial direction from the normal A1 toward the outer side in the tire width direction.

  Here, the buttress portion 3 is a portion inclined outward in the tire radial direction on the outer side in the tire width direction of the tread surface 21 of the tread portion 2. Further, the tread contact end T is the outermost end in the tire width direction of the tread surface 21 that is a contact surface. The ground contact surface is a surface that contacts the road surface when the pneumatic tire 1 is assembled on a regular rim, filled with a regular internal pressure, and 70% of the regular load is applied. The normal load means the “maximum load capacity” defined in JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined in TRA, or “LOAD CAPACITY” defined in ETRTO.

  Further, the under tread rubber 2b has a maximum dimension H closest to the tread surface 21 from a groove bottom reference line B1 passing through the groove bottom of the circumferential main groove 22 closest to the shoulder region 20 and parallel to the tread surface 21. , 0.3 ≦ H / D with respect to the groove depth D of the circumferential main groove. The position where the under tread rubber 2b is closest to the tread surface 21 in the shoulder region 20 may be a position where the under tread rubber 2b appears on the tread surface 21 (0.3 ≦ H / D ≦ 1). It is preferable that the under-tread rubber 2b is located at a position where the under-tread rubber 2b does not appear on the tread surface 21 (0.3 ≦ H / D <1). The maximum dimension H of the undertread rubber 2b is the shortest distance between the maximum dimension line B2 passing through the position closest to the tread surface 21 of the undertread rubber 2b and parallel to the tread surface 21 and the groove bottom reference line B1. It is. Then, 0.3 ≦ H / D is larger than the minimum reference line B3 parallel to the tread surface 21 through a position of a distance of 0.3 × D from the groove bottom reference line B1 to the outer side in the tire radial direction. It shows that the dimension line B2 exists in the tire radial direction outer side.

  As described above, in the pneumatic tire 1 according to the present embodiment, the pair of cross belts 72 and 73 are disposed outside the carcass layer 6 in the tire radial direction, and the cross belts 72 and 73 are outside in the tire radial direction. Further, a cap tread rubber 2a and an under tread rubber 2b provided on the inner side in the tire radial direction of the cap tread rubber 2a are laminated, and a circumferential main groove 22 extending in the tire circumferential direction is formed on the tread surface 21. The relationship between the loss tangent tan δA of the cap tread rubber 2a and the loss tangent tan δB of the undertread rubber 2b, which is provided with a plurality of tread portions 2 and measured at 60 ° C., is tan δB <tan δA. In this pneumatic tire 1, the under tread rubber 2 b is a tread based on the tire width direction end 73 a of the belt 73 on the outer side in the tire radial direction of the cross belts 72 and 73 in a cross-sectional view in the tire meridian direction. The shoulder region 20 on the outer side in the tire width direction of the portion 2 is provided closest to the tread surface 21. Moreover, the under tread rubber 2b has a maximum dimension H that passes through the groove bottom of the circumferential main groove 22 closest to the shoulder region 20 and is closest to the tread surface 21 from the groove bottom reference line B1 parallel to the tread surface 21. 0.3 ≦ H / D with respect to the groove depth D of the circumferential main groove 22.

  According to this pneumatic tire 1, since the low-heat-generating under-tread rubber 2b is disposed in the shoulder region 20 which is a portion having a large distortion and a large amount of heat generation, it is possible to reduce the heat generation of the tread portion 2. Become. Moreover, since the heat generation of the entire tread portion 2 can be reduced by arranging the low heat-generating under-tread rubber 2b in the shoulder region 20, the amount of the under-tread rubber 2b in the vicinity of the tire equator surface can be reduced, and the wear is caused accordingly. It becomes possible to maintain the chipping resistance performance by suppressing the situation where the under-tread rubber 2b comes into contact with the road surface at the end.

  Further, in the pneumatic tire 1 of the present embodiment, the under tread rubber 2b is in a range outside the tire width direction from the normal line A2 of the tread surface 21 passing through the tread grounding end T in a cross-sectional view in the tire meridian direction. It is preferable to be provided closest to the tread surface.

  The portion with the largest distortion and the largest amount of heat generation is a region on the outer side in the tire width direction from the normal line A2 of the tread surface 21 passing through the tread ground contact end T in the shoulder region 20. According to this pneumatic tire 1, since the low-heat-generating under-tread rubber 2b is disposed in a portion where the distortion is greatest and the heat generation is large, heat generation of the tread portion 2 is reduced while maintaining chipping resistance. The effect can be obtained remarkably.

  Further, the pneumatic tire 1 of the present embodiment has a tire width direction end 73a and a tread grounding end T of the belt 73 on the outer side in the tire radial direction of the intersecting belts 72 and 73 in a cross-sectional view in the tire meridian direction. A straight line L to be connected, a belt reference line B4 passing through the tire width direction end 73a of the belt 73 on the outer side in the tire radial direction and parallel to the tread surface 21, and a surface (buttress portion 3) on the outer side in the tire width direction from the tread grounding end T Or the outer surface of the buttress portion 3 including the tapered surface 4), the area Su of the undertread rubber 2b is 0.2 ≦ Su / S ≦ 0. 8 is preferable.

  If Su / S is 0.2 or more, the under-tread rubber 2b that reduces the heat generation of the tread portion 2 can be disposed in the shoulder region 20 which is a portion with large distortion and large heat generation. On the other hand, if Su / S is 0.8 or less, the amount of undertread rubber 2b appearing on the tread surface during wear can be reduced. Therefore, according to this pneumatic tire 1, it is possible to suppress the situation where the under tread rubber 2b is exposed to the tread surface and to reduce the heat generation of the tread portion 2.

  Further, in the pneumatic tire 1 of the present embodiment, the relationship between the storage elastic modulus E′A of the cap tread rubber 2a measured at 60 [° C.] and the storage elastic modulus E′B of the undertread rubber 2b is E 'B <E'A and 5.0 [MPa] ≦ E′A ≦ 15.0 [MPa], 4.0 [MPa] ≦ E′B ≦ 10.0 [MPa] Is preferred.

  According to this pneumatic tire 1, by setting E′B <E′A, the ability of the undertread rubber 2b to retain the stress accumulated therein (elastic component) is small with respect to the cap tread rubber 2a. Therefore, the effect of reducing heat generation by the undertread rubber 2b can be obtained. In addition, by setting the range to 5.0 [MPa] ≦ E′A ≦ 15.0 [MPa], 4.0 [MPa] ≦ E′B ≦ 10.0 [MPa], the low due to the under tread rubber 2b It is possible to obtain a remarkable effect of heat generation. In order to suppress the situation where the cap tread rubber 2a is too soft and easily worn, it is preferable to satisfy 8.0 [MPa] ≦ E′A ≦ 15.0 [MPa].

  In addition, as shown in FIGS. 3 and 4, the pneumatic tire 1 of the present embodiment has a tire width that is larger than the normal A2 of the tread surface 21 that passes through the tread ground contact edge T in a cross-sectional view in the tire meridian direction. The area outside in the direction is formed of another under tread rubber 2c. And the storage elastic modulus E′C of the other undertread rubber 2c measured at 60 [° C.], the storage elastic modulus E′A of the cap tread rubber 2a, and the storage elastic modulus E′B of the undertread rubber 2b It is preferable that E′B <E′C ≦ E′A and 8.0 [MPa] ≦ E′C.

  According to this pneumatic tire 1, in the range outside the tire width direction from the normal line A2 of the tread surface 21 that passes through the tread ground contact end T, which is the portion of the shoulder region 20 that is the most distorted and generates a large amount of heat. By providing another under tread rubber 2c having an elastic component larger than that of the under tread rubber 2b and not more than the cap tread rubber 2a and satisfying 8.0 [MPa] ≦ E′C, the rigidity of the tread portion 2 is appropriately maintained. Therefore, it is possible to improve the handling stability and the low rolling resistance performance. The loss tangent tan δC of another undertread rubber 2c measured at 60 [° C.] is preferably tan δC ≦ 0.15, and the effect of improving the steering stability and the low rolling resistance performance can be obtained remarkably. Is possible.

  Further, the pneumatic tire 1 of the present embodiment has an under-tread rubber 2b in a range on the outer side in the tire width direction from the normal line A2 of the tread surface 21 passing through the tread ground end T in a cross-sectional view in the tire meridian direction. Another under tread rubber 2c is a master comprising natural rubber or a vulcanizable rubber composed of at least two of natural rubber, synthetic polyisoprene rubber and synthetic polybutadiene, and para-aramid fiber as a main component and stearic acid. It is preferable to form a batch (for example, Teijin Limited: Sulfuron (registered trademark) 3001) at least with a rubber composition blended. In the rubber composition, the master batch is preferably 0.2 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the vulcanizable rubber. By using this rubber composition for the part, the rigidity of the tread portion 2 can be appropriately maintained in a range outside the normal line A2 of the tread surface 21 in the tire width direction, so that steering stability and low rolling resistance performance are achieved. It is effective to improve. Further, since the loss tangent tan δC (60 ° C.) of the undertread rubber 2c is effective to make tan δC ≦ 0.15, it is possible to obtain an improvement effect of more remarkable steering stability and low rolling resistance performance. become.

  According to this pneumatic tire 1, since the rigidity of the tread portion 2 can be appropriately maintained, it is possible to improve the low rolling resistance without deteriorating the wear resistance.

  Moreover, it is preferable that the pneumatic tire 1 of this Embodiment is applied to the heavy load pneumatic tire.

  Heavy-duty pneumatic tires tend to cause belt edge separation due to heat generated by the rubber in the tread portion 2, and the tread portion 2 is formed of a laminated structure of a cap tread rubber 2a and an under tread rubber 2b, and the under tread. A low heat-generating rubber is used for the rubber 2b. For this reason, the heavy-duty pneumatic tire is desired to achieve both chipping resistance and low heat generation of the tread portion 2. Therefore, by applying the pneumatic tire of the present embodiment to a heavy duty pneumatic tire, it is possible to significantly obtain the effect of reducing the heat generation in the tread portion while maintaining the anti-chipping performance.

  In this example, performance tests on low rolling resistance performance, chipping resistance performance, steering stability performance, and belt edge separation resistance performance were performed on multiple types of pneumatic tires with different conditions (see FIG. 5). In this example, the loss tangent tan δ and the storage elastic modulus E ′ are obtained by molding a rubber composition into a sheet, and a vulcanized rubber sheet having a thickness of 2 [mm] under a vulcanization condition of 160 [° C.] for 20 minutes. The prepared vulcanized rubber sheet was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho, measuring temperature 60 [° C.], frequency 20 [Hz], initial strain (elongation) 10 [%], amplitude ± 2 Measurement was performed under the conditions of [%].

  In this performance test, a heavy-duty pneumatic tire having a tire size of 275 / 80R22.5 was assembled to a regular rim and filled with a regular internal pressure as a test tire.

  The evaluation method is a low rolling resistance performance test. The test tire to which a load (30.89 [kN]) is applied is applied to a drum type rolling resistance tester with a drum diameter of 1707 [mm] at a speed of 80 [km. / H], the rolling resistance is measured. Then, based on this measurement result, index evaluation with the conventional (100) as the standard is performed. This evaluation shows that rolling resistance decreases as the index increases.

  In the performance test for chipping resistance, the test tire is mounted on a heavy load test vehicle having a total vehicle weight of 25 [t] (6 × 2), and a pattern running for chipping evaluation is performed on a dry road at 30,000 [km]. After execution, the degree of chipping of the tread portion was determined by visual inspection. Then, based on this determination result, index evaluation with the conventional (100) as the standard is performed. This evaluation shows that the larger the index is, the more chipping is reduced, and that the index is 98 or more indicates that the chipping resistance performance is allowed.

  The steering stability performance test was conducted by mounting the above test tire on a heavy-duty test vehicle having a total vehicle weight of 25 [t] (6 × 2), and on a dry road, steering performance during lane change and cornering, and straight traveling The stability was evaluated by sensory evaluation by a test driver and scored. Then, based on this sensory evaluation score, index evaluation with the conventional value as the reference (100) is performed. This evaluation shows that the larger the index is, the better the steering stability is, and that the index is 98 or more indicates that the steering stability is allowed.

  In the performance test of the belt edge separation resistance performance, the tire is destroyed by increasing the load by 10 [%] of the normal load every step (every 24 hours) from the normal load at a traveling speed of 45 [km / h] per hour. Measured at mileage up to.

  In the pneumatic tires of the conventional example and the example, a pair of cross belts are disposed on the outer side in the tire radial direction of the carcass layer, and the cap tread rubber and the under tread rubber are disposed on the outer side in the tire radial direction of the cross belt. The tread portion has a tread portion in which a plurality of circumferential main grooves extending in the tire circumferential direction are formed on the tread surface, and the loss tangent tan δA of the cap tread rubber measured at 60 [° C.] and the under tread rubber The relationship with the loss tangent tan δB is tan δB <tan δA.

  In the conventional pneumatic tire, the undertread rubber is not provided closest to the tread surface in the shoulder region shown in the above-described embodiment.

  On the other hand, in the pneumatic tires of Examples 1 to 6, the under-tread rubber is provided in the shoulder region shown in the above-described embodiment, closest to the tread surface, and 0.3 ≦ H / D. It is said that. In the pneumatic tires of Examples 2 to 5, Su / S is in the range of 0.2 ≦ Su / S ≦ 0.8. Further, the pneumatic tires of Example 5 and Example 6 have another under tread rubber. In the pneumatic tire of Example 6, another undertread rubber is formed of the rubber composition shown in the above-described embodiment.

  As shown in the test results of FIG. 5, the pneumatic tires of Examples 1 to 6 have improved belt edge separation performance and low rolling resistance performance related to heat generation in the tread portion while maintaining chipping resistance. You can see that. In addition, it can be seen that the pneumatic tire of Example 6 is further improved in handling stability related to the rigidity of the tread portion.

  As described above, the pneumatic tire according to the present invention is suitable for reducing heat generation in the tread portion while maintaining chipping resistance.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 2a Cap tread rubber 2b Under tread rubber 2c Another under tread rubber 20 Shoulder area 21 Tread surface 22 Circumferential main groove 23 Land part 3 Buttress part 4 Tapered surface 6 Carcass layer 7 Belt layer 71 Belt ( Reinforcement belt)
72,73 belt (cross belt)
74 Belt (Protective belt)
73a Tire width direction end of the cross belt outside the tire radial direction A1 Normal line of the tread surface passing through the tire width direction end of the cross belt outside the tire radial direction A2 Normal line of the tread surface passing through the tread ground end B1 Groove bottom reference Line B2 Maximum dimension line B3 Minimum reference line B4 Belt reference line H Maximum dimension of the under tread rubber closest to the tread surface from the groove bottom reference line L A straight line connecting the tire width direction end and the tread ground contact end S L straight line and belt The area enclosed by the reference line and the outer surface in the tire width direction from the tread contact edge Su The area of the under tread rubber in the area S S T tread contact edge

Claims (7)

A pair of cross belts are disposed on the outer side in the tire radial direction of the carcass layer, and a cap tread rubber and an under tread rubber provided on the inner side in the tire radial direction of the cap tread rubber are disposed on the outer side in the tire radial direction of the cross belt. And a tread portion formed with a plurality of circumferential main grooves extending in the tire circumferential direction on the tread surface, and the loss tangent tan δA of the cap tread rubber measured at 60 [° C.] and the above In the pneumatic tire in which the relationship between the loss tangent tan δB of the under tread rubber is tan δB <tan δA,
The under-tread rubber is the shoulder region on the outer side in the tire width direction of the tread portion based on the tire width direction end of the belt on the outer side in the tire radial direction of the intersecting belts in a cross-sectional view in the tire meridian direction. The maximum dimension H which is provided near the tread surface and passes through the groove bottom of the circumferential main groove closest to the shoulder region and is closest to the tread surface from a groove bottom reference line parallel to the tread surface. However, 0.3 ≦ H / D with respect to the groove depth D of the circumferential main groove.   The under tread rubber is provided closest to the tread surface in a range outside in the tire width direction with respect to a normal line of the tread surface passing through the tread contact edge in a cross-sectional view in the tire meridian direction. The pneumatic tire according to claim 1.   In a cross-sectional view in the tire meridian direction, the straight line connecting the tire width direction end of the belt on the outer side in the tire radial direction and the tread contact end of the intersecting belt passes through the tire width direction end of the belt on the outer side in the tire radial direction. In the range surrounded by the belt reference line parallel to the tread surface and the surface outside the tread contact edge in the tire width direction, the area Su of the undertread rubber is equal to the total area S of the range. The pneumatic tire according to claim 1, wherein 0.2 ≦ Su / S ≦ 0.8.   The relationship between the storage elastic modulus E′A of the cap tread rubber measured at 60 ° C. and the storage elastic modulus E′B of the undertread rubber is E′B <E′A, and 5.0 4. [MPa] ≦ E′A ≦ 15.0 [MPa], 4.0 [MPa] ≦ E′B ≦ 10.0 [MPa] The described pneumatic tire.   In the tire meridian cross-sectional view, a region outside the tire width direction outside the normal line of the tread surface passing through the tread contact edge is formed of another undertread rubber, and measured at 60 [° C.]. The relationship between the storage elastic modulus E′C of another undertread rubber, the storage elastic modulus E′A of the cap tread rubber, and the storage elastic modulus E′B of the undertread rubber is E′B <E′C. The pneumatic tire according to claim 1, wherein ≦ E′A and 8.0 [MPa] ≦ E′C.   In the tire meridian cross-sectional view, the under tread rubber in a range outside the normal of the tread surface passing through the tread ground end in the tire width direction is natural rubber, or natural rubber, synthetic polyisoprene rubber, and synthetic polybutadiene. 100 parts by mass of a vulcanizable rubber consisting of at least two combinations with a master batch of 0.2 parts by weight or more and 3.0 parts by weight or less, in which stearic acid is blended mainly with para-aramid fibers, The pneumatic tire according to any one of claims 1 to 5, wherein the pneumatic tire is formed of a blended rubber composition.   The pneumatic tire according to claim 1, wherein the pneumatic tire is applied to a heavy duty pneumatic tire.

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