JP5612413B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly to a heavy duty pneumatic tire suitable for use in heavy-duty vehicles such as trucks and buses, and in particular, suppresses a decrease in tire fuel consumption caused by an increase in rolling resistance. In addition, the separation of the belt reinforcing layer at the outer end in the width direction and the deterioration of the fatigue resistance of the cord located at the outer end of the belt reinforcing layer in the width direction are prevented, thereby improving the durability of the tire. It is what we propose.

  A belt made of a cord extending substantially in the tread circumferential direction by extending the cord at an angle of, for example, 5 ° or less with respect to the tread circumferential direction on the outer circumferential side of the crown region of the carcass that can have a radial structure. As conventional tires in which at least one reinforcing layer is provided and the diameter of the tire is suppressed by the belt reinforcing layer, there are those disclosed in Patent Documents 1 to 3.

Here, the cord forming the belt reinforcing layer can be extended in the form of a straight line, a zigzag shape, a wave shape, etc. in the circumferential direction of the tread, and the elongation rate reaches about 2%. While it stretches greatly with a small tensile force, if it exceeds the stretch rate, the stretch rate decreases even with a large input, so it can be formed with a so-called large initial stretch, such as Lang twist cord, high elongation cord, etc. it can.
By the way, when securing the initial elongation of the cord by making the cord of the belt reinforcement layer bend in a zigzag shape, corrugated shape, etc., standards such as JATMA, TRA, ETRTO, etc. It is preferable that the detouring shape disappears in a state where the maximum air pressure defined by YEAR BOOK and others is filled, in order for the belt reinforcing layer to sufficiently exhibit the diameter growth suppressing function.

  In the pneumatic tires disclosed in Patent Documents 1 to 3, in order to improve the steering stability, the belt layer in which the cords extend so as to cross each other is widened to increase the in-plane shear rigidity, thereby generating a lateral tire. The belt reinforcement layer is a belt reinforcement layer that suppresses the separation from the belt layer at the side edge of the belt reinforcement layer and exerts a high function in the shoulder area. This also tends to be widened for the purpose of preventing the occurrence of uneven wear in the shoulder side land portion of the tread contact surface due to the absence of the layer.

  Under such circumstances, in particular, when the belt layer adjacent to the outer peripheral side of the belt reinforcing layer is made wider than the belt reinforcing layer or other belt layers, the outer side in the width direction of the wide belt layer. In order to prevent the end of the tire from falling inward in the radial direction of the tire and to ensure the desired shape of the product tire, the belt reinforcing layer Cushion rubber is disposed in a region adjacent to the side portion. In this case, the cushion rubber is made of a rubber material in which the loss tangent is reduced by reducing the blending ratio of carbon black, sulfur, and cobalt. There has been proposed a tire that is formed to thereby reduce rolling resistance and improve fuel efficiency.

JP 2000-62411 A JP 2009-184371 A JP 2009-126363 A

  However, the rubber material having a low compounding ratio of sulfur and cobalt, such as the rubber material forming the cushion rubber, is not only low in adhesion to other members, but in the tire described above, Sulfur, cobalt, etc. contained in the coating rubber covering the cord on the side of the reinforcing layer move to the cushion rubber adjacent to the side, and the adhesion of the coating rubber on the side of the belt reinforcing layer to the cord Therefore, there is a high possibility that the coating rubber peels from the belt reinforcing layer cord at the side of the belt reinforcing layer.

  In addition, since the elastic modulus of such a cushion rubber also decreases, and the elastic deformation of the cushion rubber during the load rolling of the tire greatly occurs, the cord located on the side of the belt reinforcing layer is in contact with the tire. When moving, the cushion rubber adjacent to the belt reinforcing layer cord is repeatedly subjected to tensile and compressive forces due to large elastic deformation in the tread circumferential direction, leading to a reduction in fatigue resistance of the belt reinforcing layer cord. There is also a problem.

  An object of the present invention is to solve the above-mentioned problems, and the object of the present invention is to widen the belt reinforcing layer and the belt layer on the outer peripheral side of the belt as required. In the tire in which a cushion rubber for reducing rolling resistance is disposed in a region adjacent to the side portion of the belt reinforcing layer, without reducing fuel consumption, It is an object of the present invention to provide a tire with improved durability performance by preventing the separation of the outer end portion in the width direction of the belt reinforcing layer and the deterioration of the fatigue resistance of the side cord of the belt reinforcing layer.

A pneumatic tire according to the present invention is disposed on the outer peripheral side of a carcass crown region extending in a toroidal shape from a pair of bead portions and a crown region of the carcass, and the cord extends in the tread circumferential direction. And at least one belt reinforcing layer formed by rubber-covering the cord, and disposed on the outer peripheral side of the belt reinforcing layer, and the cord is made to extend in a straight line inclined with respect to the tread circumferential direction. Comprising two or more belt layers and a tread rubber disposed on the outer peripheral side of the belt layer to form a tread ground surface,
Each side edge of the belt reinforcing layer and the belt layer is positioned on the outer side in the tire width direction from the position where each shoulder circumferential groove located closest to the tread shoulder side of the tread ground surface is formed. The belt layer adjacent to the outer peripheral side is the widest belt layer having the widest width compared to the belt reinforcing layer and other belt layers,
A pneumatic tire comprising cushion rubber disposed on the inner side in the tire radial direction of the outer end portion in the width direction of the wide belt layer and on the outer side in the width direction of the outer end portion in the width direction of the belt reinforcing layer,
The cushion rubber is composed of two or more types of rubber members having different elastic moduli, and any rubber that forms the remainder of the rubber member in the contact area with at least the widthwise outer end of the belt reinforcing layer of the cushion rubber. A high-hardness rubber member having a higher elastic modulus than that of the member is used, and the rubber member forming the remaining portion is a rubber member having a smaller loss tangent tan δ than the high-hardness rubber member.

Here, “extending the cord in the tread circumferential direction” includes a case where the cord is inclined and inclined at an angle of 5 ° or less with respect to the tread circumferential direction.
Further, here, the “belt reinforcing layer width direction outer side end” refers to a belt from the intersection of the belt reinforcing layer with a straight line passing through the center of the shoulder circumferential groove and perpendicular to the tire center axis in the tread width direction. The area to the outermost edge of the reinforcing layer shall be said. The “width direction outer end of the wide belt layer” also refers to the same region.

Also here, the cord forming the belt reinforcing layer can extend in a spiral shape in the tire width direction in a linear shape, a zigzag shape, a wave shape or the like, and the cord elongation rate is 2 %, It stretches greatly with a small tensile force, and after exceeding the elongation rate, the elongation rate decreases even with a large tensile force. can do.
In addition, when securing the initial elongation of the cord by extending the cord of the belt reinforcement layer in a zigzag or other detour shape, the YEAR BOOK of the standards such as JATMA, TRA, ETRTO, etc. It is preferable that the detour shape disappears in a state in which the maximum air pressure defined by others is filled, in order to sufficiently exert the diameter growth suppressing function in the use state of the pneumatic tire on the belt reinforcing layer.

Here, preferably, the cushion rubber is composed of two types of rubber members, the loss tangent tan δ of the rubber member forming the remaining portion is set to 0.01 to 0.2, and the elastic modulus E of the rubber member is set to 1. ˜4 MPa.
Here, the “loss tangent” is measured by a viscoelasticity tester at a specified frequency, strain, and temperature condition (for example, frequency 52 Hz, strain 1%, room temperature).
The “elastic modulus” here is a method according to JIS K6251, that is, measurement of dynamic stress when dynamic strain is applied under a predetermined temperature, for example, 25 ° C., frequency and strain conditions. This means the 100% modulus calculated by doing so.

  And preferably, the elastic modulus of the high hardness rubber member is larger than the elastic modulus of the coating rubber which covers the cord of the belt reinforcing layer and can be, for example, 3 to 9 MPa.

Also preferably, the cushion rubber has a substantially triangular contour shape in a cross section in the tire width direction, and the high-hardness rubber member in the contact area with the outer end in the width direction of the belt reinforcing layer is the cushion rubber. The outer peripheral side region opposite to the inner peripheral side region close to the carcass extends over the entire region.
Note that the “substantially triangular” means that even if the sides are bent or the corners are rounded, the whole may be triangular.

  Preferably, the side edge of the belt reinforcing layer is positioned between the side edge position of the wide belt layer and a position spaced 30 mm inward in the tire width direction from the position in a posture in which it is assembled to the adaptive rim and filled with the specified internal pressure. And each of the side edge of another belt layer is arrange | positioned.

Here, “adaptive rim” refers to a rim defined in the following standards according to tire size, and “specified internal pressure” refers to an air pressure defined in accordance with the maximum load capacity in the following standards. “Maximum load capacity” means the maximum mass allowed to be loaded on a tire according to the following standards.
The standard is determined by an industrial standard effective in the region where tires are produced or used. For example, in the United States, “THE TIRE AND RIM ASSOCIATION INC. YEAR BOOK” is used in Europe. "The European Tire and Rim Technical Organization's STANDARDDS MANUAL", and in Japan, the Japan Automobile Tire Association's "JATMA YEAR BOOK".

  According to the pneumatic tire of the present invention, two or more types of cushion rubber are disposed on the outer side in the width direction of the belt reinforcing layer on the outer side in the width direction on the outer side in the tire radial direction of the outer end in the width direction of the wide belt layer. The rubber member is composed of a rubber member, and at least a rubber member in a contact region with the outer end in the width direction of the belt reinforcing layer of the cushion rubber is a high-hardness rubber member having a larger elastic modulus than any of the rubber members forming the remaining part. As a result, the high-hardness rubber member between the low-loss rubber member with a small loss tangent of the cushion rubber and the outer end in the width direction of the belt reinforcing layer is made of sulfur or cobalt contained in the coating rubber of the belt reinforcing layer. Because it functions to block the transition to a low-loss rubber member, the adhesion of the coating rubber on the outer edge of the belt reinforcement layer in the width direction to the cord is ensured. Te, in the width direction outer end portion of the belt reinforcing layer, the coating rubber can be effectively prevented from delamination from the code.

Further, the cord positioned at the outer end in the width direction of the belt reinforcing layer is protected by a high-hardness rubber member having a large elastic modulus disposed in the contact area with the outer end in the width direction. The tensile force and compressive force acting on the outer end cord in the width direction of the belt reinforcing layer due to the large elastic deformation of the low loss rubber member during load rolling is alleviated. As a result, the width direction of the belt reinforcing layer is reduced. A decrease in fatigue resistance of the outer end cord can be prevented.
In addition, since the low loss rubber member that has reduced the loss tangent by reducing the blending ratio of carbon black, sulfur, and cobalt, etc. is provided as the remaining part of the cushion rubber other than the high hardness rubber member. A reduction in resistance and, in turn, an improvement in tire fuel efficiency is ensured.

Here, two types of rubber members constituting the cushion rubber are used, and the loss tangent tan δ of the low-loss rubber member that forms the remainder other than the high-hardness rubber member as described above is set to 0.01 to 0.2. When the elastic modulus E of the low-loss rubber member is set to 1 to 4 MPa, the separation of the outer end portion in the width direction of the belt reinforcing layer and the deterioration of the fatigue resistance of the outer end cord in the width direction of the belt reinforcing layer are prevented more effectively. However, the increase in rolling resistance due to the provision of the high-hardness rubber member that forms a part of the cushion rubber can be suppressed sufficiently small, and the fuel consumption of the tire can be further increased.
That is, when the loss tangent tan δ of the rubber member forming the remainder is less than 0.01, there is a possibility that peeling due to poor adhesion may occur at the interface with the peripheral rubber. When it exceeds 2, loss energy is large and the effect of suppressing rolling resistance is small.
Also, if the elastic modulus E of the rubber member forming the remainder is less than 1 MPa, the cushion itself may be distorted and may be self-destructed. On the other hand, if the elastic modulus E exceeds 4 MPa May increase the concentration of strain on the surrounding rubber, and the surrounding rubber may self-destruct.

In addition, when the elastic modulus of the high hardness rubber member is larger than the elastic modulus of the coating rubber covering the belt reinforcing layer cord, the high hardness rubber member located between the coating rubber and the remaining rubber member has high elasticity. It is possible to block the transmission of the strain generated in the remaining rubber member having a low elastic modulus to the coating rubber.
In other words, if the elastic modulus of the high-hardness rubber member is equal to or lower than the elastic modulus of the coating rubber that covers the cord of the belt reinforcing layer, the high-hardness rubber member itself is likely to be distorted. The coating rubber existing next to the member is easily affected by the distortion of the high-hardness rubber member, and the coating rubber may be distorted.

By the way, from the viewpoint of increasing the tire production efficiency, when manufacturing a tire, a cushion rubber material composed of two or more kinds of rubber materials is integrally extruded with one extruder such as a dual extruder. However, at the time of manufacturing the tire, a high hardness rubber material is provided only in a required area corresponding to the contact area of the cushion rubber material with the outer end in the width direction of the belt reinforcing layer, and these rubber members are used. When the extrusion molding is performed integrally, depending on the variation in the extrusion molding accuracy, the manufactured tire does not have a high-hardness rubber member over the entire contact area with the widthwise outer end of the belt reinforcing layer. There is a possibility that a location where the loss rubber member contacts the outer end portion in the width direction of the belt reinforcing layer may occur.
In this case, sulfur or cobalt contained in the coating rubber at the outer end in the width direction of the belt reinforcing layer is contacted with the outer end in the width direction of the belt reinforcing layer at the low loss rubber member. As a result, the adhesiveness of the coating rubber of the portion to the cord decreases.

  On the other hand, the overall shape of the cushion rubber has a substantially triangular contour shape in the cross section of the tire width direction, and the high hardness rubber member in the contact area with the outer end in the width direction of the belt reinforcing layer is cushioned. When extending over the entire outer peripheral area of the rubber, even if there is a variation in the integral extrusion of the cushion rubber material during tire manufacture, in the manufactured tire, the high-hardness rubber member is made of a cushion rubber belt. Since it can be reliably positioned over the entire contact area with the width direction outer end of the reinforcing layer, and the low loss rubber member can be prevented from contacting the width direction outer end of the belt reinforcing layer, as described above, The separation of the outer end portion in the width direction of the belt reinforcing layer and the deterioration of the fatigue resistance of the cord at the outer end portion in the width direction of the belt reinforcing layer can be more reliably prevented.

  By the way, when the side edge of the belt reinforcing layer and the side edge of the other belt layer are disposed between the side edge position of the wide belt layer and the position 30 mm away from the position inward in the tire width direction. Can suppress the breakage of the cord at the end of the belt reinforcing layer, and can suppress an increase in distortion at the end of the belt layer, thereby preventing belt end separation.

It is a partial cross-section half figure of the tread width direction which shows embodiment of this invention. It is sectional drawing similar to FIG. 1 which shows the modification of cushion rubber.

In FIG. 1, reference numeral 1 denotes a carcass extending in a toroidal shape between a pair of unshown bead parts, for example, a carcass ply which can be a radial structure, and 2 is a carcass 1 For example, a ribbon-like strip having a width of 3 to 20 mm, in which a plurality of cords arranged in parallel and covered with rubber, are spirally wound around a tire axis, disposed on the outer peripheral side of the crown region, A belt reinforcing layer that can be formed by a cord extending at an angle of 5 ° or less with respect to the tread circumferential direction (here, referred to as “cord extending in the tread circumferential direction”) is shown.
Two or more belt reinforcing layers 2 can be provided.

Here, the cord of the belt reinforcing layer 2 can be a long twist steel cord, a high elongation steel cord, an organic fiber cord, or the like having a large initial extension as described above, and also in the tread circumferential direction. A steel cord extending in a detour shape such as a zigzag shape, a crank shape, or a wave shape may be used.
Here, when the cord of the belt reinforcing layer 2 is a cord having a large initial elongation, the tire that has been assembled to the rim is filled with the maximum air pressure defined by YEAR BOOK or other standards such as JATMA, TRA, ETRTO, etc. Therefore, it is preferable that the elongation rate exceeds the range showing the low elastic modulus, and when the cord extends in a detoured shape such as a zigzag shape, the detoured shape is filled with the above-mentioned maximum air pressure. It is preferable that the form disappears in order to cause the belt reinforcing layer 2 to sufficiently exhibit the diameter growth suppressing function.

Further, on the outer peripheral side of the belt reinforcing layer 2, two or more belt layers made of cords extending in a straight line inclined at an angle of, for example, 40 ° to 50 ° with respect to the tread circumferential direction, in the figure, two-layer belts The layers 3 and 4 are disposed, and here, the cords forming the belt layers 3 and 4 extend in directions opposite to each other with respect to the tread circumferential direction.
Further, a tread rubber 5 that forms a tread grounding surface is disposed on the outer peripheral side of the belt layers 3 and 4, and the four tread grooves 6 to 9 are formed in the tread rubber 5, for example, in the tread half. Form.

  Here, in this pneumatic tire, in-plane shear rigidity is increased, the lateral force generated by the tire is increased, and the belt is reinforced for the purpose of preventing uneven wear on the shoulder side land portion of the tread contact surface. The side edges of the layer 2 and the belt layers 3 and 4 are positioned on the outer side in the tire width direction of the tread ground surface from the position where the shoulder circumferential groove 6 positioned closest to the tread shoulder is formed, and the outer periphery of the belt reinforcing layer 2 The belt layer 3 adjacent to the side is the widest belt layer having the widest width as compared with the belt reinforcing layer 2 and the other belt layers 4.

Further, here, the cushion rubber 10 is arranged on the inner side in the tire radial direction of the width direction outer end portion 3a of the belt layer 3 thus widely disposed on the width direction outer side of the width direction outer end portion 2a of the belt reinforcing layer 2. This cushion rubber 10 prevents the widthwise outer end 3a of the wide belt layer 3 having a width wider than that of the belt reinforcing layer 2 from dropping in the tire radial direction, and the desired shape of the product tire. Further, the cushion rubber 10 is subjected to a difference between the amount of elastic deformation of the belt layers 3 and 4 in the tread circumferential direction and the amount of elastic deformation in the circumferential direction of the belt reinforcing layer 2 when the tire rolls. The circumferential shear stress on the side edge of the belt reinforcing layer 2 is relaxed by contributing to absorption.
As illustrated in FIG. 1, the cushion rubber 10 may be disposed along the carcass 1 so as to be inclined radially inward at the width direction outer end 2 a of the belt reinforcing layer 2. it can.

  By the way, this cushion rubber 10 is preferably formed from a rubber member having a reduced loss tangent from the viewpoint of reducing rolling resistance and improving tire fuel efficiency. In this case, the belt reinforcing layer 2 is used. The cushion rubber 10 disposed adjacent to the width direction outer end 2a of the belt reinforcing layer 2 is transferred with sulfur, cobalt, etc. contained in the coating rubber of the belt reinforcing layer 2 to cause peeling of the coating rubber of the belt reinforcing layer, Further, since the elastic modulus of the cushion rubber 10 is reduced by reducing the loss tangent, the belt reinforcing layer 2 has a widthwise outer end 2a based on the large elastic deformation of the cushion rubber 10 when the tire rolls. There is a possibility that the fatigue resistance of the cords extending in the tire circumferential direction is lowered.

Therefore, in the present invention, the cushion rubber 10 is composed of two or more types of rubber members, and in the figure, two types of rubber members, and at least the rubber in the contact area of the cushion rubber 10 with at least the widthwise outer end 2a of the belt reinforcing layer 2. The member 10a is a high-hardness rubber member having a larger elastic modulus than that of the rubber member 10b that forms the remainder, and this high-hardness rubber member 10a is used for peeling the coating rubber from the belt reinforcing layer 2 or the belt reinforcing layer as described above. It functions to prevent a decrease in fatigue resistance of the cord.
Further, in the drawing, one type of rubber member 10b, which forms the remaining portion of the cushion rubber 10, is reduced in loss tangent as compared with the high hardness rubber member 10a by, for example, reducing the blending ratio of carbon black, sulfur and cobalt. By using a reduced low-loss rubber member, the rolling resistance is reduced and the fuel efficiency of the tire is increased.

  That is, according to the tire of the present invention, the transition to the low-loss rubber member 10b having a small loss tangent, such as sulfur and cobalt contained in the coating rubber of the width direction outer end 2a of the belt reinforcing layer 2, is performed between them. Since it is blocked by the existing high-hardness rubber member 10a, it is possible to prevent a decrease in the adhesiveness of the coating rubber due to a decrease in sulfur, cobalt, etc., so that the outer side in the width direction of the belt reinforcing layer 2 is prevented. The peeling of the coating rubber from the reinforcing layer cord at the end 2a can be effectively prevented, and the large elastic deformation of the low-loss rubber member 10b of the cushion rubber 10 occurs when the tire rolls. The tensile force and compressive force exerted on the cord of the outer end 2a in the width direction of the reinforcing layer 2 can be relaxed by the high hardness rubber member 10a having a large elastic modulus. The remaining rubber member 10b of the cushion rubber 10 has a small loss tangent and the rolling resistance is reduced to improve the fuel efficiency of the tire, while the coating rubber is peeled off from the belt reinforcing layer 2 and the belt reinforcing layer. A decrease in the fatigue resistance of the cord can be effectively prevented.

  Here, as shown in FIG. 1, when the cushion rubber 10 is disposed so as to enter the inner side in the tire radial direction of the width direction outer end 2 a of the belt reinforcing layer 2, The rubber member disposed in this entering portion that is a part of the contact area with the widthwise outer end 2a of the reinforcing layer 2 is also a high hardness rubber member 10a having a large elastic modulus.

Here, the loss tangent tan δ of the low loss rubber member 10b having a small loss tangent of the cushion rubber 10 is in the range of 0.01 to 0.2, and the elastic modulus E of the low loss rubber member 10b is in the range of 1 to 4 MPa. It is preferable that
Here, the elastic modulus of the high hardness rubber member 10a is preferably larger than the elastic modulus of the coating rubber of the belt reinforcing layer 2 which can be set to 3 to 9 MPa.

  The thickness of the high hardness rubber member 10a in the cross section in the tire width direction, that is, the outer end 2a in the width direction of the belt reinforcing layer 2, and the remaining rubber member 10b of the cushion rubber 10 adjacent to the high hardness rubber member 10a. The thickness of the portion located between the belt reinforcing layer 2 and the high-rubber rubber member 10a is sufficiently reduced to have a rolling resistance of 1.0 to 2.0 mm. It is preferable for sufficiently exhibiting the function of preventing peeling and deterioration of fatigue resistance of the belt reinforcing layer cord.

  By the way, when manufacturing tires, in order to improve production efficiency, for example, when a cushion rubber material made of two types of rubber materials is integrally extruded with a single extruder, depending on variations in extrusion molding accuracy, In the manufactured tire, the cushion rubber 10 is displaced in the position where the high-hardness rubber member 10a is disposed in the contact area with the widthwise outer end 2a of the belt reinforcing layer 2, and the low-loss rubber member 10b is Since the belt reinforcing layer 2 may be in contact with the widthwise outer end 2a, the belt of the cushion rubber 11 having a substantially triangular contour shape in the cross section in the tire width direction as shown in FIG. A high-hardness rubber member 11 a disposed in a contact area with the width direction outer end 2 a of the reinforcing layer 2 is provided so as to extend over the entire outer peripheral side region of the cushion rubber 11.

  In this way, the high hardness rubber member 11a has a laminated structure extending over the entire outer peripheral side region of the cushion rubber 11, so that the tire manufactured can be made high regardless of the accuracy of the extrusion molding of the cushion rubber material. Since the hardness rubber member 11a can be reliably positioned in the contact area of the cushion rubber 11 with the outer end 2a in the width direction of the belt reinforcing layer 2a, peeling of the coating rubber from the belt reinforcing layer 2 or the belt reinforcing layer The effect of preventing the deterioration of the fatigue resistance of the cord is further enhanced.

Here, each of the side edge of the belt reinforcing layer 2 and the side edge of the belt layer 4 is in a posture in which the tire mounted on the adaptive rim is filled with the specified internal pressure, and from the side edge of the wide belt layer 3 to the inner side in the tire width direction. It is preferable to arrange between 30 mm apart.
Further, in order to sufficiently improve the wear resistance performance of the shoulder region of the tire, the width of the belt reinforcing layer 2 is preferably 75% or more, more preferably 80% or more of the tire width. In order to ensure exercise performance, the width of the wide belt layer 3 adjacent to the outer peripheral side of the belt reinforcing layer 2 is set to 75% or more, more preferably 80% or more of the tire width. The width of the layer 4 is 55% or more, more preferably 70% or more of the tire width.
Also preferably, in the drawing, the cord crossing width of the two belt layers 3 and 4 is 65% or more, more preferably 70% or more of the tire width.

By the way, as shown in FIGS. 1 and 2, the gap between the width direction outer end 3a of the wide belt layer 3 and the width direction outer end 2a of the belt reinforcement layer 2 is larger than the coating rubber of the belt reinforcement layer 2. A soft interstitial rubber 12 can be provided.
According to this, at the time of tire rolling, particularly the widthwise outer end 3a of the wide belt layer 3 that greatly expands and contracts in the tread circumferential direction at the outer end in the width direction is difficult to stretch and deform in the tread circumferential direction. The belt reinforcing layer 2 can be separated from the outer end 2a in the width direction and the soft rubber 12 between them can absorb the difference in expansion / contraction between the wide belt layer 3 and the belt reinforcing layer 2. Therefore, it is possible to prevent the cord constituting the belt reinforcing layer 2 from being broken and the separation of the wide belt layer 3 from the belt reinforcing layer 2.
In addition, the 100% modulus of such a rubber | gum 12 can be 1.0-4.0 Mpa, for example.

The following three types of tests were carried out under the conditions of a tire for trucks and buses with a size of 435 / 45R22.5 mounted on a rim of 14.00 x 22.5, a filling air pressure of 900 Pa, and a load load of 49 kN. Each of these test results was index evaluated using the conventional tire as a control, and the specifications are shown in Table 1.
In addition, while Example tire 1 shall have the structure shown in FIG. 2, Example tire 2 shall have the structure shown in FIG. 1, and conventional tires 1-4 are provided with a high hardness rubber member. In addition, the tire tire had the same structure as that of the example tire except that a cushion rubber made of only one kind of rubber member having a small loss tangent was disposed up to the contact area with the belt reinforcing layer.
“R50” in each cord angle item of the belt layer in Table 1 is a plan view of the belt layer, and the cord extends in an attitude of 50 ° that rises to the right with respect to the tire circumferential direction. On the other hand, "L50" means that the cord extends in a 50 [deg.] Posture that rises to the left with respect to the tire circumferential direction in the same plan view.

(Exothermic test)
A drum test was performed under the conditions of the specified internal pressure, load, and speed, and a so-called QC durability drum test was performed in which heat generation was evaluated by the time until failure occurred. The results are shown in Table 1. In addition, the index value shown in Table 1 represents that it is excellent in durability, so that a numerical value is large.
(Rolling resistance test)
Rotate the drum with the test tire in contact with the drum, raise the drum to the specified rotation speed, cut off transmission of the rotational driving force to the drum, and decrease the drum rotation speed by rolling the tire The rolling resistance was calculated from this ratio. The rolling resistance shown in Table 1 indicates that the smaller the index value, the better the fuel economy of the tire.
(Abrasion test)
The test tire was run on the drum for a certain distance at a predetermined speed, and the amount of wear of the tread rubber of each test tire after running was measured and evaluated. The wear resistance performance shown in Table 1 indicates that the larger the index value, the smaller the wear amount and the better the wear resistance performance.

  As is clear from the results shown in Table 1, both Example tires 1 and 2 are superior in QC durability and wear resistance and have low rolling resistance as compared with any of Conventional Tires 1 to 4. Accordingly, it was found that the pneumatic tire of the present invention can improve the durability and fuel consumption even when the wear resistance is improved.

DESCRIPTION OF SYMBOLS 1 Carcass 2 Belt reinforcement layer 2a Width direction outer side edge 3, 4 Belt layer 3a Width direction outer side edge 5 Tread rubber 6-9 Circumferential groove 10, 11 Cushion rubber 10a, 11a High hardness rubber member 10b, 11b Low loss rubber member 12 Rubber

Claims (5)

A carcass made of at least one carcass ply extending in a toroidal shape from a pair of bead portions, and disposed on the outer peripheral side of the crown area of the carcass, extending the cord in the tread circumferential direction, and covering the cord with rubber And at least one belt reinforcing layer, and two or more belt layers disposed on the outer peripheral side of the belt reinforcing layer and extending in a straight line with the cord inclined with respect to the tread circumferential direction, A tread rubber disposed on the outer peripheral side of the belt layer to form a tread ground surface,
Each side edge of the belt reinforcing layer and the belt layer is positioned on the outer side in the tire width direction from the position where each shoulder circumferential groove located closest to the tread shoulder side of the tread ground surface is formed. The belt layer adjacent to the outer peripheral side is the widest belt layer having the widest width compared to the belt reinforcing layer and other belt layers,
A pneumatic tire comprising cushion rubber disposed on the inner side in the tire radial direction of the outer end portion in the width direction of the wide belt layer and on the outer side in the width direction of the outer end portion in the width direction of the belt reinforcing layer,
The cushion rubber is composed of two or more types of rubber members having different elastic moduli, and any rubber that forms the remainder of the rubber member in the contact area with at least the widthwise outer end of the belt reinforcing layer of the cushion rubber. A pneumatic tire in which a high-hardness rubber member having a higher elastic modulus than that of the member is formed, and a rubber member forming the remainder is formed from a rubber member having a loss tangent tan δ smaller than that of the high-hardness rubber member.   The cushion rubber is composed of two types of rubber members, the loss tangent tan δ of the rubber member forming the remaining portion is set to 0.01 to 0.2, and the elastic modulus E of the rubber member is set to 1 to 4 MPa. Item 2. The pneumatic tire according to Item 1.   The pneumatic tire according to claim 1 or 2, wherein the elastic modulus of the high hardness rubber member is made larger than the elastic modulus of the coating rubber covering the cord of the belt reinforcing layer.   The cushion rubber has a substantially triangular contour shape in the cross section in the tire width direction, and the high-hardness rubber member in the contact area with the outer end in the width direction of the belt reinforcing layer is formed on the outer peripheral side region of the cushion rubber. The pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire extends over the entirety.   In a posture in which it is assembled to the adaptive rim and filled with the specified internal pressure, the side edge of the belt reinforcing layer and the other edge between the side edge position of the wide belt layer and the position 30 mm inward in the tire width direction from the position. The pneumatic tire according to any one of claims 1 to 4, wherein each side edge of the belt layer is disposed.