JP2008024105A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve heating durability and uneven wear resistance by making radial growth amount of a pneumatic radial tire uniform in the tire width direction and suppressing deterioration of a grounding shape when traveling. <P>SOLUTION: The first to fourth belt layers 11-14 are arranged from an inner peripheral side toward an outer peripheral side in a tread part 5. The second to third belt layers 12 and 13 are made crossing layers having small belt angles with the tire peripheral direction and opposite directions with each other. A hollow part 11C is provided in a center part of the first belt layer 11 to lower peripheral direction rigidity of the center part. The fourth belt layer 14 is divided into three of a center part 14C and outside parts 14D. Peripheral direction rigidity of a shoulder part is increased by making a belt angle of the outside part 14D closer to the tire peripheral direction as compared with a belt angle of the third belt layer 13 and inclining the belt angle in the opposite direction of the tire peripheral direction. As a result, the radial growth amount suppressing effect of the shoulder part is relatively enhanced to make the radial growth amount uniform in the tire width direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic radial tire provided with a belt layer having a multi-layer structure in a tread portion, and more particularly, a pneumatic radial tire in which the tire diameter growth is more uniform in the tire width direction during internal pressure filling and running. About.

  In a pneumatic radial tire, for example, a pneumatic radial tire for heavy loads such as a truck or a bus, generally, a large load is applied when the vehicle travels. Therefore, three or more belt layers are provided on the outer peripheral side of the carcass layer in the tread portion. To ensure sufficient tread rigidity and to achieve a high tagging effect.

3 and 4 are views showing examples of such a conventional pneumatic radial tire, and FIG. 3 is a sectional view in the tire width direction schematically showing a tread portion of the pneumatic radial tire. 4 is a developed plan view schematically showing the structure of the tread portion by breaking it.
As shown in the figure, this conventional pneumatic radial tire 80 is disposed on the tread portion 5 on the outer circumferential side of the carcass layer 6 having a radial structure having a skeleton element 6B in the radial direction such as a steel cord, for example. Further, at least three (four in the figure) belt layers 11 to 14 and a tread rubber 7 constituting a tire outer peripheral surface disposed on the outer peripheral side of the belt layers 11 to 14 are provided.

  The belt layers 11 to 14 include a first belt layer 11, a second belt layer 12, a third belt layer 13, and a fourth belt layer 14 that are sequentially arranged adjacent to each other from the inner side to the outer side in the tire radial direction. In each, a plurality of parallel reinforcing elements 11B to 14B such as a metal cord such as steel or an organic fiber cord are provided. The reinforcing elements 11B to 14B of the belt layers 11 to 14 are arranged at a predetermined angle with respect to the tire equatorial plane CL (tire circumferential direction). In the present invention, such belt layers The inclination angle of the inner reinforcing element (the extending angle of the reinforcing element) is called the belt angle of the belt layer.

  In the pneumatic radial tire 80, the belt angle of the second and third belt layers 12 and 13 with respect to the tire circumferential direction is relatively small (for example, 10 ° or more and 30 ° or less) and opposite to each other with respect to the tire circumferential direction. Forming. That is, the second and third belt layers 12 and 13 are crossing layers in which the reinforcing elements 12B and 13B cross (cross) each other in opposite directions (see FIG. 4) with respect to the tire circumferential direction. The rigidity against deformation (hereinafter referred to as circumferential rigidity) is high, and it has a function of mainly suppressing the growth of the outer diameter of the tire by mainly bearing the tension in the same direction. Further, in the tire 80, the belt angle of the first belt layer 11 is set in the same direction as the belt angle of the second belt layer 12 adjacent to the outer peripheral side with respect to the tire circumferential direction, and a larger angle (for example, 45 The belt angle of the fourth belt layer 14 in the same direction as the belt angle of the third belt layer 13 adjacent to the inner circumferential side with respect to the tire circumferential direction, and substantially the same angle. Is formed.

  Here, in general, in the pneumatic tire, when the amount of growth of the outer diameter of the tire at the time of internal pressure filling or running becomes uneven in the tire width direction, the contact shape at the time of rolling on the road surface deteriorates, or the contact pressure increases. Uneven wear in the tire width direction or the like tends to cause uneven wear in the tread portion. At the same time, at locations where the diameter growth is large, the amount of heat generation increases as the ground pressure increases, and the heat generation durability may decrease. Therefore, it is desirable that the diameter growth is uniform from the center portion (center portion in the tire width direction) to the shoulder portion (both end portions in the tire width direction).

  However, in the conventional pneumatic radial tire 80 provided with such belt layers 11 to 14, especially in the case of a flat tire (for example, a flat ratio of 70% or less), the circumferential rigidity and the radial growth suppressing effect of the belt layers 11 to 14 are achieved. However, there is a tendency that the diameter growth of the shoulder portion becomes relatively large and the diameter growth amount becomes non-uniform in the tire width direction as compared with the shoulder portion. As a result, in this pneumatic radial tire 80, the diameter growth of the shoulder portion during driving is promoted, the contact area on both shoulder portions of the tire 80 is increased, the contact shape is deteriorated, and the contact pressure of the portion is increased. The amount of heat generation increases and the uneven wear resistance and heat generation durability may decrease.

  In order to deal with such problems, conventionally, a pneumatic radial tire has been proposed in which a narrow belt layer is added in addition to the plurality of belt layers described above to achieve uniform diameter growth (patent) Reference 1).

FIG. 5 is a developed plan view schematically showing the structure of the tread portion of this conventional pneumatic radial tire, broken away.
As shown in the figure, the pneumatic radial tire 100 includes a first belt layer 101 between a carcass layer 109 of a tread portion 108 and a tread rubber (not shown) in order from the inner side to the outer side in the tire radial direction. A second belt layer 102, a third belt layer 103, a fourth belt layer 104, and a narrow belt layer 105 are provided. The second and third belt layers 102 and 103 are crossing layers in which the belt angle crosses in the opposite direction to the tire circumferential direction and at the same angle. On the other hand, the first belt layer 101 is formed in the same direction as the belt angle of the adjacent second belt layer 102 with respect to the tire circumferential direction, and the fourth belt layer 104 has a belt angle with respect to the tire circumferential direction. It is formed in the same direction and in the same direction as the belt angle of the adjacent third belt layer 103.

  In addition to the above, in the tire 100, the narrow belt layer 105 is provided on both sides of the narrowest fourth belt layer 104 in the tire width direction, and both side portions of the third belt layer 103 adjacent to the inner side in the tire radial direction are provided. It is arranged so as to cover it. Further, the belt angle with respect to the tire circumferential direction of both narrow belt layers 105 is formed in the same direction as the belt angle of the adjacent third belt layer 103 and closer to the tire circumferential direction to increase the circumferential rigidity. ing. Thereby, the rigidity in the vicinity of both side portions (shoulder portions) of the third belt layer 103 is strengthened to suppress the diameter growth of the shoulder portions, and the diameter growth amount in the tire width direction is made uniform.

  However, in the conventional pneumatic radial tire 100, the radial growth amount in the tire width direction can be made uniform to some extent as compared with the pneumatic radial tire 80 shown in FIGS. It is difficult to effectively improve the balance of the radial growth suppression effect in the entire tire width direction, for example, it remains unchanged and remains high. Therefore, in this tire 100, it cannot be said that the effect of making the diameter growth uniform is still sufficient, and there is a possibility that the diameter growth amount becomes excessive and insufficient in the tire width direction and becomes non-uniform. In particular, tires tend to be flattened in recent years. In such flattened tires, as the width of the tire and belt layer increases, the difference in circumferential rigidity from the center portion to the shoulder portion also increases. . As a result, the promotion of diameter growth in the vicinity of the shoulder portion also appears more conspicuously, so the degree of diameter growth becoming uneven in the tire width direction also increases, and the contact shape deteriorates and the heat generation durability and uneven wear resistance decrease. Such problems are likely to occur. Therefore, in such a flat tire, it is necessary to make the diameter growth suppression effect more uniform in the tire width direction and to further uniform the diameter growth amount.

JP-A-5-131808

  The present invention has been made in view of the above-described conventional problems, and its purpose is to uniformize the radial growth amount of the pneumatic radial tire in the tire width direction, suppress deterioration of the ground contact shape during traveling, and generate heat. It is to improve durability and uneven wear resistance.

The invention of claim 1 is a pneumatic radial tire comprising at least four belt layers disposed on the outer peripheral side of the carcass layer of the tread portion, and tread rubber disposed on the outer peripheral side of the belt layer. In the belt layer, a hollow belt layer with a hollow structure provided on the innermost side in the tire radial direction and divided in the tire width direction across the tire equatorial plane, adjacent to the tire radial direction, And an intersection layer composed of belt layers whose belt angles intersect with each other in the opposite direction with respect to the tire circumferential direction, and adjacent to the outer side in the tire radial direction of the intersection layer, and a center portion in the tire width direction and the center portion. And a divided belt layer arranged by being divided into three at both outer side portions sandwiched therebetween.
According to a second aspect of the present invention, in the pneumatic radial tire according to the first aspect, an outermost end portion in the tire width direction of the divided belt layer is an inner side in the tire width direction than an outer end portion in the tire width direction of the crossing layer. And the dividing position of the dividing belt layer and the groove bottom position of the main groove formed in the tread rubber extending in the tire circumferential direction are arranged apart from each other in the tire width direction. .
According to a third aspect of the present invention, in the pneumatic radial tire according to the first or second aspect, the belt of the belt layer in the crossing layer adjacent to the inner side in the tire radial direction is a belt angle of the outer portion of the divided belt layer. The angle is opposite to the tire circumferential direction.
According to a fourth aspect of the present invention, in the pneumatic radial tire according to any one of the first to third aspects, the intersection of the outer circumferential portion of the divided belt layer with respect to the tire circumferential direction is adjacent to the inner side in the tire radial direction. The belt angle in the layer is smaller than the belt angle with respect to the tire circumferential direction.
According to a fifth aspect of the present invention, in the pneumatic radial tire according to any one of the first to fourth aspects, a belt in the crossing layer in which the belt angle at the center of the divided belt layer is adjacent to the inner side in the tire radial direction. The belt angle of the layer is opposite to the tire circumferential direction.
According to a sixth aspect of the present invention, in the pneumatic radial tire according to any one of the first to fifth aspects, a belt angle with respect to a tire circumferential direction of the divided belt layer and / or the belt layer in the crossing layer is 10 °. The angle is 25 ° or less.
The invention according to claim 7 is the pneumatic radial tire according to any one of claims 1 to 6, wherein a belt angle of the hollow belt layer with respect to a tire circumferential direction is not less than 45 ° and not more than 90 °. And

  ADVANTAGE OF THE INVENTION According to this invention, the diameter growth amount of a pneumatic radial tire can be equalize | homogenized in a tire width direction, deterioration of the contact shape at the time of driving | running | working can be suppressed, and heat_generation | fever durability and uneven wear resistance can be improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The pneumatic radial tire of the present embodiment is a heavy-duty pneumatic radial tire used for buses, trucks, etc., for example, and includes a pair of bead cores and at least one carcass ply extending between them in a toroidal shape. It has the structure of a known pneumatic radial tire, such as having a carcass layer.

1 and 2 are views showing the pneumatic radial tire of the present embodiment, FIG. 1 is a cross-sectional view in the tire width direction schematically showing a tread portion of the pneumatic radial tire, and FIG. FIG. 3 is a plan development view schematically showing the structure of a tread portion in a fractured manner.
As shown in the figure, this pneumatic radial tire 1 includes a radial structure carcass layer 6 having a radial skeleton element 6B such as a steel cord in the tread portion 5, and at least an outer circumferential side of the carcass layer 6. Four layers (four layers in the figure) of belt layers 11 to 14 and a tread rubber 7 constituting a tire outer peripheral surface disposed on the outer peripheral side of the belt layers 11 to 14 are provided. A plurality of (four in the figure) main grooves 8 extending in the tire circumferential direction are formed on the surface (grounding surface) of the tread rubber 7.

  The belt layers 11 to 14 are adjacent to each other in the tire radial direction from the inner side to the outer side, and are arranged so as to overlap with each other in the tire radial direction. 2 belt layer 12, third belt layer 13, and fourth belt layer 14 on the outermost side in the tire radial direction, and as shown in FIG. And a plurality of parallel reinforcing elements 11B to 14B.

  The first belt layer 11 is a hollow belt layer with a hollow structure that is divided and arranged in the tire width direction across the tire equatorial plane CL, and in the center portion (on the tire equatorial plane CL) at the center in the tire width direction. It has a hollow portion 11C. That is, the first belt layer 11 includes a pair of side portions (divided belts) 11D that are spaced apart in the tire width direction with the hollow portion 11C interposed therebetween, and these both side portions 11D are on both sides of the tire equatorial plane CL. It is arranged on the (shoulder part side) with a predetermined distance (centering width). Further, the first belt layer 11 has a belt angle with respect to the tire circumferential direction that is larger than that of the other belt layers 12 to 14 (close to the tire width direction), and is formed at 45 ° or more and 90 ° or less here. .

  The second and third belt layers 12 and 13 are crossing layers adjacent to each other in the tire radial direction and intersecting (crossing) in opposite directions with respect to the tire circumferential direction. The angle is formed in the same direction as the belt angle of the first belt layer 11 adjacent to the inner side in the tire radial direction and the tire circumferential direction. Further, the second and third belt layers 12 and 13 have a relatively small belt angle with respect to the tire circumferential direction (close to the tire circumferential direction), and are formed at 10 ° or more and 25 ° or less here.

  The fourth belt layer 14 is a protective layer for protecting the crossing layer provided adjacent to the outer side in the tire radial direction of the crossing layer, and both the outer side part sandwiching the central part 14C and the central part 14C in the tire width direction. 14D is a divided belt layer that is divided into three parts. That is, the fourth belt layer 14 is composed of three narrow belts divided in the tire width direction, a central portion 14C disposed in the center portion and an outer portion 14D disposed on both shoulder portions. In addition, the divided end portions are arranged with a predetermined distance therebetween, or the divided end portions are overlapped with each other by a predetermined width. In addition, the belt angle of both the outer portion 14D and the central portion 14C is such that the belt angle of the third belt layer 13 in the crossing layer adjacent to the inner side in the tire radial direction and the tire circumferential direction of the fourth belt layer 14 are both. And in the opposite direction and at the same angle (here, 10 ° to 25 °).

  Further, in the present embodiment, the belt angles of the respective portions 14C and 14D are made different in the fourth belt layer 14, and at least the belt angle of the outer portion 14D with respect to the tire circumferential direction is set in the crossing layer adjacent to the inner side in the tire radial direction. The belt angle of the third belt layer 13 with respect to the tire circumferential direction is made smaller and closer to the tire circumferential direction. Further, the dividing position of the fourth belt layer 14 and the groove bottom position of the main groove 8 (see FIG. 1) formed in the tread rubber 7 extending in the tire circumferential direction are arranged to be spaced apart from each other in the tire width direction. The divided end portions of the respective portions 14C and 14D of the fourth belt layer 14 are prevented from being positioned near the bottom of the main groove 8 (in the tire radial direction).

  Within each of these belt layers 11 to 14, the second belt layer 12 constituting the crossing layer is the widest belt layer having the widest width in the tire width direction (hereinafter simply referred to as width), and is also the crossing layer. The width of the third belt layer 13 and the width of the first belt layer 11 that is the innermost belt layer (the width between the outer ends in the tire width direction of both side portions 11D) are substantially the same, and the second belt layer 12 It is formed with a narrower width. Further, the outermost fourth belt layer 14 has a width (a width between outer end portions in the tire width direction of both outer side portions 14D) larger than a width of the crossing layer (third belt layer 13) adjacent to the inner side in the tire radial direction. Is also the narrowest and the narrowest. Accordingly, the outermost end portion in the tire width direction of the fourth belt layer 14 (the shoulder portion side end portion of the outer portion 14D) is disposed on the inner side in the tire width direction with respect to the outer end portion in the tire width direction of the crossing layer.

  In the pneumatic radial tire 1 of the present embodiment described above, each of the belt layers 11 to 14 includes four belt layers 11 to 14, the second belt layer 12 and the third belt layer 13 are cross layers, and the belt layer has a circumference. Various functions such as the rigidity of the direction, the diameter growth suppression effect, and the tagging effect are effectively exhibited. In addition, the innermost first belt layer 11 has a hollow structure, and a hollow portion 11C is provided at the center of the tire, and both side portions 11D are arranged on the shoulder portion side, so that the circumferential rigidity of the shoulder portion is reduced. Only the circumferential rigidity of the center portion and the effect of suppressing the radial growth can be made lower than before. As a result, the diameter growth of the center part can be slightly increased while suppressing the diameter growth of the shoulder part during internal pressure filling and traveling, and the difference in the diameter growth amount between them can be reduced to reduce the tire width direction. The diameter growth balance can be improved. At the same time, the number of belt layers in the center portion is reduced and rigidity is lowered, and the center portion is easily deformed.Therefore, the center portion is deformed so as to wrap them when riding on a protrusion on the road surface during traveling. Thus, the flexibility of the center portion can be increased, for example, the occurrence of cut scratches can be suppressed, and the tire performance on rough roads can also be improved.

  In addition, since the fourth belt layer 14 is divided into three parts and the outer portions 14D are arranged on both shoulder portions, the circumferential rigidity of the shoulder portion where the diameter growth is increased can be increased, and the diameter growth in the vicinity thereof is further suppressed. can do. Further, the central portion 14C disposed on the center portion side of the fourth belt layer 14 mainly functions as a protective layer, and both outer side portions 14D function as a diameter growth suppression layer of a shoulder portion having high circumferential rigidity. Thus, it is possible to effectively improve the functions required for each part, such as to exhibit each.

  Therefore, according to the pneumatic radial tire 1 of the present embodiment, the tire diameter growth amount can be made uniform in the tire width direction, and deterioration of the ground contact shape during traveling can be suppressed. As a result, it is possible to prevent a local contact pressure and increase in the amount of heat generated, and to improve heat generation durability and uneven wear resistance. In particular, in flat tires with a flatness ratio of 80% or less, the diameter growth of the shoulder portion and the difference in the amount of radial growth in the tire width direction may be larger, leading to failure at an early stage. By providing, each effect mentioned above is exhibited and an early failure etc. can be prevented effectively.

  Here, the belt angle of the outer portion 14D of the divided fourth belt layer 14 is equal to the belt angle of the crossing layer (third belt layer 13) adjacent to the inner side in the tire radial direction and the tire circumferential direction as in this embodiment. It is desirable to reverse the direction. In this case, in addition to the crossing layers, the belt angle also crosses (crosses) between the third belt layer 13 and the outer portion 14D, so that the circumferential rigidity of the shoulder portion can be further increased, and the diameter of the shoulder portion can be increased. It is possible to suppress and make the diameter growth amount more uniform in the tire width direction. Similarly, the belt angle of the central portion 14C of the fourth belt layer 14 may be formed in the same direction as the belt angle of the third belt layer 13 with respect to the tire circumferential direction. It is more desirable because it can cross the third belt layer 13 to suppress the diameter growth over the entire tire width direction.

  The belt angle of the outer portion 14D with respect to the tire circumferential direction is desirably smaller than the belt angle of the third belt layer 13 with respect to the tire circumferential direction. In this case, the circumferential rigidity of the outer portion 14D can be further increased, the effect of suppressing the radial growth of the shoulder portion can be effectively improved, and the radial growth amount can be made more uniform in the tire width direction.

  Furthermore, the belt angle with respect to the tire circumferential direction of the fourth belt layer 14 (the center portion 14C and the outer portion 14D) and the crossing layers (the second belt layer 12 and the third belt layer 13) is 10 ° or more and 25 ° or less. Is desirable. When these angles are smaller than 10 °, there is a risk that the tire will break down, such as a large distortion generated at the belt end in the tire width direction and separation occurring near the end. On the other hand, when the angle is larger than 25 °, the effect of suppressing the diameter growth becomes too small, and the entire tire grows in diameter, which may cause the tire to break down. In particular, when the belt angle is smaller than 10 °, the outer portion 14D of the fourth belt layer 14 may cause early interlayer separation with the third belt layer 13, and is larger than 25 °. In some cases, the required circumferential rigidity cannot be obtained, and the diameter growth of the shoulder portion may increase. Further, in the central portion 14D of the fourth belt layer 14, when the belt angle is smaller than 10 °, the diameter growth of the center portion is excessively suppressed and the difference in the diameter growth amount from the shoulder portion becomes large. When it is larger than 25 °, there is a possibility that it cannot serve as a protective layer. However, the belt angles of the fourth belt layer 14 and the crossing layer may both be formed in the above range, but may be only one of them.

  In addition, the width of the fourth belt layer 14 is made narrower than the width of the crossing layer, and the outermost end portion in the tire width direction of the fourth belt layer 14 (the outer end portion in the tire width direction of the outer portion 14D) is the tire of the crossing layer. When arranged in the tire width direction inner side than the width direction outer side end, it is possible to prevent a failure at the end of the belt, such as preventing distortion at the end of the fourth belt layer 14 from being increased. desirable. Further, when the divided end portion of the fourth belt layer 14 is positioned near the groove bottom of the main groove 8 of the tread rubber 7 (inner side in the tire radial direction of the groove bottom), shear strain is applied to the groove bottom due to the rigidity step. Such a load force is generated and stress concentration occurs, which may cause the groove bottom portion to crack and generate a groove crack. Therefore, it is desirable that the dividing position of the fourth belt layer 14 and the groove bottom position of the main groove 8 of the tread rubber 7 are separated from each other in the tire width direction.

  On the other hand, when the belt angle with respect to the tire circumferential direction is smaller than 45 °, the first belt layer 11 has a lower restraining force in the tire width direction, and the second belt layer 12 and the crossing layer tend to shrink in the tire width direction. Since there is a possibility that the force cannot be suppressed, it is desirable to form the belt angle at 45 ° or more and 90 ° or less with respect to the tire circumferential direction. The upper limit of 90 ° is the maximum angle at which the belt angle can be inclined.

  In this embodiment, a belt layer having a four-layer structure is provided on the tread portion 5 of the pneumatic radial tire 1. However, if the belt layers 11 to 14 described above are included in the belt layer, the belt layer 5 You may provide the belt layer more than a layer. That is, for example, a belt layer is added between the first belt layer 11 and the second belt layer 12, or a belt layer is added to the outer peripheral side of the fourth belt layer 14. May be disposed on the outer peripheral side of the carcass layer 6 of the tread portion 5. Similarly, the belt layer to be added may be continuous in the tire width direction or may be divided.

  Further, the outer portion 14D of the fourth belt layer 14 of the present embodiment has an outer side in the tire width direction when the width of the adjacent third belt layer 13 is L2 (see FIG. 1) and the width of the central portion 14C is L3. The end portion is arranged in a range where the distance from the tire equatorial plane CL is 0.30 × L2 to 0.49 × L2, and the inner end portion in the tire width direction is 0.45 distance from the tire equatorial plane CL. It is desirable to arrange within a range of × L3 to 0.55 × L3.

  This is because if the distance between the outer end portion of the outer portion 14D in the tire width direction and the tire equatorial plane CL is shorter than 0.30 × L2, the end portion approaches the center portion side and the width of the outer portion 14D becomes narrower. This is because the range in which the outer portion 14D covers the shoulder portion may be reduced, and as a result, the circumferential rigidity of the shoulder portion is lowered and the crossing effect when crossing with the crossing layer is reduced. Further, if it is longer than 0.49 × L2, the position of the end of the outer portion 14D and the end of the crossing layer are too close, or the end of the outer portion 14D is positioned outside the crossing layer in the tire width direction. This is because there is a possibility that separation between layers may occur at an early stage due to an increase in distortion during the process.

  On the other hand, the inner end of the outer portion 14D in the tire width direction is closer to the tire equatorial plane CL than the end of the central portion 14C when the distance from the tire equatorial plane CL is 0.45 × L3 or more and less than 0.50 × L3. Will be located. In this case, since the split end portions of the outer portion 14D and the central portion 14C overlap each other in the fourth belt layer 14, each end portion suppresses deformation from each other and distortion is reduced. It is more desirable because it can suppress the occurrence of cracks. However, if the distance between the tire width direction inner end portion of the outer portion 14D and the tire equatorial plane CL is shorter than 0.45 × L3, the end portion of the outer portion 14D approaches the center portion side and the center portion side with respect to the shoulder portion. , The radial growth on the center portion side (particularly the overlapping portion between the end portions) is suppressed more than necessary, and the amount of radial growth in the shoulder portion may be relatively increased. Moreover, when longer than 0.55 * L3, the edge part approaches the shoulder part side, the width | variety of outer side part 14D becomes narrow, and there exists a possibility that the range which outer side part 14D covers a shoulder part may decrease. As a result, the circumferential rigidity of the shoulder portion is reduced, and the crossing effect when crossing with the crossing layer is reduced.

  When the outer end portion in the tire width direction of the outer portion 14D of the fourth belt layer 14 is within the above-described desirable range, and the distance from the tire equatorial plane CL is 0.45 × L2 to 0.49 × L2. Since the distance between the end portion of the outer portion 14D and the end portion of the adjacent third belt layer 13 is reduced, it is desirable to place an interlayer rubber between both end portions and between the belt layers. In such a case, the thickness of the rubber in the tire radial direction in the vicinity of the end portion between the outer portion 14D and the third belt layer 13 becomes thicker than the other portions on the center portion side. Strain generated between the layers can be reduced, and separation between the layers can be suppressed in the vicinity thereof.

(Tire test)
In order to confirm the effects of the present invention, five types of tires (hereinafter referred to as “Examples 1 to 5”) including the belt layer having the structure described above and conventional tires (hereinafter referred to as “conventional products”) are used. The tire growth test and the drum running test were performed under the following conditions. All of these tires are pneumatic radial tires for trucks and buses having a tire size of 385 / 65R22.5 as defined by ETRTO (The European Tire and Rim Technical Organization, 2006).

First, the structure of the belt layer of each tire will be described.
The conventional product is a tire including the belt layers 11 to 14 having the configuration shown in FIGS. 3 and 4 described above, and is formed in a conventional belt layer structure in which the belt layer is not divided. In this conventional product, the width of the third belt layer 13 in the crossing layer is 290 mm, the width of the adjacent fourth belt layer 14 is 260 mm, and the belt angles are formed in the same direction with respect to the tire circumferential direction. .

  The implementation products 1 to 5 are tires including the belt layers 11 to 14 having the above-described configuration illustrated in FIGS. 1 and 2, and the fourth belt layer 14 has a width of the third belt layer 13 of 290 mm. The width of the central portion 14C was 120 mm, and the belt angles were formed in the same direction with respect to the tire circumferential direction. On the other hand, the outer portion 14D of the fourth belt layer 14 was formed to have a width of 70 mm, but was formed by changing the belt angle and the belt direction in each embodiment.

  That is, in the embodiment 1, the outer portion 14D of the fourth belt layer 14 has a belt angle of 5 ° with respect to the tire circumferential direction, and is in the same direction as the belt angle of the adjacent third belt layer 13 and the tire circumferential direction. Formed. In the same manner, in the product 2, the belt angle was set to 10 ° and the belt was formed in the same direction as the third belt layer 13. In the product 3, the belt angle was set to 25 ° and the belt was formed in the same direction as the third belt layer 13. In the product 4, the belt angle was set to 25 ° and the third belt layer 13 was formed in the opposite direction. In the product 5, the belt angle was 30 °, and the belt was formed in the same direction as the third belt layer 13.

  In the tire growth test, each of the above tires is mounted on an 11.75 × 22.5 rim and the internal pressure is set to 900 kPa, and the difference in the diameter growth amount between the center portion and the shoulder portion (hereinafter referred to as the diameter growth difference). Was measured to evaluate the uniformity in the tire width direction of the diameter growth amount of each tire. Also, in the drum running test, each tire mounted on the test rim and filled with the internal pressure under the same conditions as above was pressed against the outer periphery of the test drum, loaded with a constant load of 44.1 kN, and on the drum at a speed of 57 km / h. The distance traveled until the vehicle was rolled and a failure occurred was measured.

Table 1 shows the belt layer structure and test results of the tires described above.
The belt angle in the table is an angle with respect to the tire circumferential direction, and the direction of the fourth belt layer outer portion with the third belt layer is the direction of the belt angle between the outer portion and the third belt layer with respect to the tire circumferential direction. Indicate the same or opposite.

  In Table 1, the difference in diameter growth of each tire is represented by an index with 0.93 mm of the conventional product as 100, and the smaller the diameter growth uniformity index, the higher the uniformity of the diameter growth in the tire width direction. Yes. In addition, the travel distance on the drum of each tire is represented by an index with 3200 km of the conventional product as 100, and the greater the drum travel distance index, the longer the travel distance and the less likely that a failure or the like occurs. The diameter growth uniformity index is 95 or less to satisfy the required performance, and the drum mileage index is 120 or more to satisfy the required performance.

As shown in Table 1, the diameter growth uniformity index is 100 for the conventional product, the highest value is 85 for the implementation product 1 and 94 for the implementation product 5 for the implementation products 1 to 5, It can be seen that the diameter growth amount was uniform in the tire width direction and the above required performance (95 or less) was satisfied.
Also, the drum mileage index is 100 for the conventional product, while the highest value for the products 1 to 5 is 140 for the product 4 and the lowest value is 123 for the product 1. It can be seen that failure and the like are less likely to occur for a long time, and the required performance (120 or more) is satisfied.

  From the above results, according to the present invention, the radial growth amount of the pneumatic radial tire can be made uniform in the tire width direction, deterioration of the contact shape during running can be suppressed, and heat generation durability and uneven wear resistance can be improved. Proved.

It is sectional drawing of the tire width direction which shows typically the tread part of the pneumatic radial tire of this embodiment. FIG. 2 is a plan development view schematically showing a structure of a tread portion of the pneumatic radial tire of FIG. It is sectional drawing of the tire width direction which shows typically the tread part of the conventional pneumatic radial tire. FIG. 4 is a developed plan view schematically showing a structure of a tread portion of the pneumatic radial tire of FIG. It is a plane development view which shows the structure of the tread part of the conventional pneumatic radial tire roughly fractured.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pneumatic radial tire, 5 ... Tread part, 6 ... Carcass layer, 7 ... Tread rubber, 8 ... Main groove, 11 ... 1st belt layer, 11B ... Reinforcing element, 12 ... second belt layer, 12B ... reinforcing element, 13 ... third belt layer, 13B ... reinforcing element, 14 ... fourth belt layer, 14B ... reinforcing element , 14C ... center part, 14D ... outer part, CL ... tire equatorial plane.

Claims (7)

A pneumatic radial tire comprising: at least four belt layers disposed on the outer peripheral side of the carcass layer of the tread portion; and a tread rubber disposed on the outer peripheral side of the belt layer,
In the belt layer, a hollow belt layer of a hollow structure provided on the innermost side in the tire radial direction and divided and arranged in the tire width direction across the tire equatorial plane,
An intersecting layer composed of belt layers adjacent to each other in the tire radial direction and intersecting in opposite directions with respect to the circumferential direction of the tire;
A dividing belt layer provided adjacent to the outer side in the tire radial direction of the crossing layer, and divided into three parts at the center part in the tire width direction and both outer parts sandwiching the center part;
A pneumatic radial tire characterized by comprising: In the pneumatic radial tire according to claim 1,
The outermost end portion in the tire width direction of the dividing belt layer is disposed on the inner side in the tire width direction than the outer end portion in the tire width direction of the crossing layer, and is formed in the dividing position of the dividing belt layer and the tread rubber. A pneumatic radial tire, characterized in that a groove bottom position of a main groove extending in the tire circumferential direction is spaced apart in the tire width direction. In the pneumatic radial tire according to claim 1 or 2,
A pneumatic radial tire characterized in that a belt angle of an outer portion of the divided belt layer is opposite to a belt angle of a belt layer in the crossing layer adjacent to the inner side in the tire radial direction and a tire circumferential direction. In the pneumatic radial tire according to any one of claims 1 to 3,
A pneumatic radial tire characterized in that a belt angle with respect to a tire circumferential direction of an outer portion of the divided belt layer is smaller than a belt angle with respect to the tire circumferential direction of a belt layer in the crossing layer adjacent to the inner side in the tire radial direction. In the pneumatic radial tire according to any one of claims 1 to 4,
A pneumatic radial tire characterized in that the belt angle at the center of the divided belt layer is opposite to the belt angle of the belt layer in the crossing layer adjacent to the inner side in the tire radial direction and the tire circumferential direction. In the pneumatic radial tire according to any one of claims 1 to 5,
A pneumatic radial tire, wherein a belt angle with respect to a tire circumferential direction of the divided belt layer and / or a belt layer in the crossing layer is 10 ° or more and 25 ° or less. In the pneumatic radial tire according to any one of claims 1 to 6,
A pneumatic radial tire characterized in that a belt angle of the hollow belt layer with respect to a tire circumferential direction is 45 ° or more and 90 ° or less.

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