JP6089641B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire having a plurality of carcass layers. More specifically, while maintaining good steering stability, the tire can be reduced in weight and rolling resistance can be reduced, and separation resistance can be improved. The present invention relates to a pneumatic tire that can be improved.

  In a pneumatic tire, a reinforcing structure in which a plurality of carcass layers are mounted between a pair of bead portions is employed in order to maintain a high internal pressure. For example, a three-layer carcass layer is mounted between a pair of bead portions, and both end portions of two inner-circumference-side carcass layers are folded around the bead cores from the inside of the tire to the outside, while one outer-circular-side carcass layer is folded. There has been proposed a pneumatic tire having a structure in which both end portions of the layer are disposed on the outer side in the tire width direction of the folded portion of the inner circumferential side carcass layer (see, for example, Patent Document 1).

  FIG. 7 schematically shows a conventional pneumatic tire having three carcass layers. As shown in FIG. 7, both end portions of the inner circumferential carcass layers 41, 42 are folded back from the inside of the tire around the bead core 5, and both end portions of the outer circumferential carcass layer 43 are formed on the inner circumferential carcass layers 41, 42. It is arrange | positioned outside the folding | returning part. In the pneumatic tire having such a structure, since the three carcass layers 41, 42, and 43 are present in the sidewall portion, good steering stability can be exhibited.

  However, since pneumatic tires are often exposed to harsh usage environments such as high load conditions caused by overloading and high internal pressure conditions to ensure load capacity, bending occurs in the bead part or sidewall part. If many terminals of the carcass layer are arranged at easy sites, separation failure starting from these terminals tends to occur. In addition, when three carcass layers are used, there is a problem that the tire weight increases, resulting in an increase in tire rolling resistance.

  Although the above-mentioned problem can be overcome by reducing the number of carcass layers, in this case, the rigidity of the entire tire is lowered, and steering stability is lowered.

Japanese Patent Laid-Open No. 11-32217

  An object of the present invention is to provide a pneumatic tire capable of reducing the tire weight and rolling resistance while improving steering stability while maintaining good steering stability. is there.

In order to achieve the above object, the pneumatic tire of the present invention has two carcass layers including a plurality of carcass cords mounted between a pair of bead portions, and a bead core and a bead filler are disposed on each bead portion, In the pneumatic tire in which at least two belt layers are arranged on the outer peripheral side of the carcass layer, the two carcass layers are located on the inner side in the tire radial direction in the tread portion and the tire diameter in the tread portion. and a periphery-side carcass layer positioned outwardly, both end portions of the outer peripheral side carcass layer folded back to the outside from the inside of the tire around the respective bead cores, the inner peripheral side belt layer terminal of the folded portion of the outer circumferential side carcass layer extending a while disposed between the main body portion of the outer peripheral side carcass layer, to a position that overlaps at least the bead filler both end portions of the inner peripheral-side carcass layer It was, and is characterized in that both end portions of the inner peripheral side carcass layer is terminated at each bead portion without folding around each bead core.

  In the present invention, both ends of the outer circumferential side carcass layer are folded back from the inside of the tire around each bead core to extend the folded portion of the outer circumferential side carcass layer to a position overlapping with the inner circumferential side belt layer. By terminating both ends of the side carcass layer around each bead core without being folded around each bead core, the sidewall portion has a three-layer carcass layer structure to ensure sufficient pneumatic tire rigidity and good steering stability. Can demonstrate its sexuality. On the other hand, since only the two carcass layers are used as the skeleton structure of the tire and the surplus portion of the carcass layer is eliminated as much as possible, a pneumatic tire provided with three carcass layers as in the past In comparison with the above, the weight of the tire can be reduced, and the rolling resistance of the tire can be reduced.

  Further, according to the configuration of the present invention described above, there are two ends of the carcass layer on one side of the tire, and one of them is a portion where there is little distortion between the inner peripheral belt layer and the outer peripheral carcass layer. Therefore, it is possible to suppress a separation failure starting from the terminal of the carcass layer and to improve the separation resistance.

  In the present invention, the tire radial height PH from the innermost end in the tire radial direction of the bead core to the end of the inner circumferential carcass layer is relative to the tire radial height BH of the bead core and the tire radial height FH of the bead filler. Therefore, it is preferable that the relationship of 0.05 × (BH + FH) ≦ PH ≦ 0.7 × (BH + FH) is satisfied. Thereby, the position of the terminal of the inner circumference side carcass layer can be optimized and the separation resistance can be improved.

  A first buffer rubber layer having a breaking strength of 15 MPa to 25 MPa and a loss tangent at 60 ° C. of 0.10 to 0.25 between each end of the inner peripheral carcass layer and the main body of the outer peripheral carcass layer Is preferably arranged. Thereby, the shear deformation between an inner peripheral side carcass layer and an outer peripheral side carcass layer can be suppressed, and a separation-proof performance can be improved.

  The first shock-absorbing rubber layer has a width of 10 mm to 30 mm and a thickness of 0.5 mm to 2 mm. The inner end of the first shock-absorbing rubber layer in the tire radial direction is the same position as or the inner end of the inner circumferential carcass layer. It is preferable to arrange in the tire radial direction inner side than the end of the circumferential carcass layer. As a result, the terminal of the inner peripheral carcass layer is separated from the main body of the outer peripheral carcass layer only with a necessary minimum weight increase, and shear strain between the inner peripheral carcass layer and the outer peripheral carcass layer is reduced. Can be effectively mitigated.

  The tire radial height FH of the bead filler preferably satisfies the relationship of 0.05SH ≦ FH ≦ 0.5SH with respect to the tire cross-section height SH. Thereby, since high bending rigidity is ensured in a bead part and the bending deformation of the bead filler at the time of grounding is controlled, the tension applied to the end of the inner circumference side carcass layer located inside the bead filler can be reduced. This improves the separation resistance and suppresses heat generation and fatigue fracture of the bead filler.

  The overlap amount W between the folded portion of the outer peripheral side carcass layer and the inner peripheral side belt layer is preferably 5 mm to 40 mm. Thereby, a good separation resistance can be ensured.

  A second buffer rubber layer having a thickness of 0.5 mm to 2 mm and a breaking strength of 20 MPa or more is preferably disposed between the folded portion of the outer peripheral side carcass layer and the inner peripheral side belt layer. Thereby, the shear distortion of the said location can be relieve | moderated and a separation-proof performance can be improved.

  The outer end in the tire width direction of the second shock absorbing rubber layer is disposed on the outer side in the tire width direction of the end of the inner belt layer, and the inner end in the tire width direction of the second shock absorbing rubber layer is the folded portion of the outer carcass layer. It is preferable to arrange in the tire width direction inner side than the terminal. Thereby, the shear distortion of the said location can be relieve | moderated effectively.

  It is preferable to provide an auxiliary filler having a JIS hardness lower by 3 points or more than the bead filler on the outer side in the tire width direction than the folded portion of the outer peripheral side carcass layer in the bead portion. By adding such an auxiliary filler, it is possible to suppress the bending deformation of the bead filler and reduce the tension applied to the terminal of the inner circumferential carcass layer. This improves the separation resistance and suppresses heat generation and fracture fatigue of the bead filler.

  The outer end in the tire radial direction of the auxiliary filler is arranged outside the outer end in the tire radial direction of the bead filler, and the inner end of the auxiliary filler in the tire radial direction is arranged within the range of the tire radial height FH of the bead filler. It is preferable to do. Thereby, the bending deformation of the bead filler can be effectively suppressed.

  The tire radial height SFH of the auxiliary filler satisfies the relationship of 0.5FH ≦ SFH ≦ 1.5FH with respect to the tire radial height FH of the bead filler, and the auxiliary filler gradually increases toward both sides of the tire radial direction. It is preferable that the portion that has a thinned shape and the maximum thickness of the auxiliary filler is disposed within the range of the height FH of the bead filler in the tire radial direction. Thereby, the bending deformation of the bead filler can be effectively suppressed without increasing the weight excessively, and the durability can be improved.

  In the present invention, JIS hardness is durometer hardness measured at a temperature of 20 ° C. using an A type durometer in accordance with JIS K-6253. The breaking strength is a tensile strength measured at a temperature of 20 ° C. using a dumbbell-shaped test piece in accordance with JIS K-6251. Loss tangent (tan δ) is measured in accordance with JIS-K6394 using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho) under the conditions of frequency 20 Hz, initial strain 10%, dynamic strain ± 2%, temperature 60 ° C. It is what is done.

It is meridian sectional drawing which shows the pneumatic tire which consists of embodiment of this invention. FIG. 2 is a meridian half sectional view schematically showing the pneumatic tire of FIG. 1. It is sectional drawing which expands and shows the bead part of the pneumatic tire of FIG. It is sectional drawing which shows roughly the modification of the bead part of the pneumatic tire of FIG. It is a meridian half sectional view schematically showing a pneumatic tire according to another embodiment of the present invention. It is sectional drawing which expands and shows the bead part of the pneumatic tire of FIG. It is a meridian cross-sectional view schematically showing a conventional pneumatic tire having three carcass layers.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 to 4 show a pneumatic tire according to an embodiment of the present invention.

  As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 that extends in the tire circumferential direction and has an annular shape, a pair of sidewall portions 2 that are disposed on both sides of the tread portion 1, And a pair of bead portions 3 disposed inside the wall portion 2 in the tire radial direction.

  A pair of carcass layers 4 including a plurality of carcass cords extending in the tire radial direction is mounted between the pair of bead portions 3 and 3. The carcass layer 4 includes an inner circumferential carcass layer 4A located on the inner side in the tire radial direction in the tread portion 1 and an outer circumferential side carcass layer 4B located on the outer side in the tire radial direction in the tread portion 1. As the carcass cords constituting these carcass layers 4, organic fiber cords such as nylon and polyester are preferably used. An annular bead core 5 is embedded in each bead portion 3, and a bead filler 6 made of a rubber composition having a triangular cross section is disposed on the outer periphery of the bead core 5.

  On the other hand, at least two belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. The belt layer 7 includes an inner circumferential belt layer 7A located on the inner side in the tire radial direction and an outer circumferential side belt layer 7B located on the outer side in the tire radial direction. These belt layers 7 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layer 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. A steel cord is preferably used as the reinforcing cord of the belt layer 7.

  On the outer peripheral side of the belt layer 7, at least one belt cover layer 8 in which reinforcing cords are arranged at an angle of 5 ° or less with respect to the tire circumferential direction is disposed for the purpose of improving high-speed durability. . It is desirable that the belt cover layer 8 has a jointless structure in which a strip material formed by aligning at least one reinforcing cord and covering with rubber is continuously wound in the tire circumferential direction. Further, the belt cover layer 8 may be disposed so as to cover the entire width direction of the belt layer 7, or may be disposed so as to cover only the outer edge portion of the belt layer 7 in the width direction. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon or aramid is preferably used.

  In the pneumatic tire, both end portions of the outer peripheral side carcass layer 4B are folded around the respective bead cores 5 from the inner side to the outer side so as to wrap the bead cores 5 and the bead fillers 6. This outer peripheral side carcass layer 4B has a main body portion 4Bx inside the tire and a folded portion 4By outside the tire with the bead core 5 as a boundary. And the terminal 4Be of the folding | returning part 4By of the outer peripheral side carcass layer 4B is arrange | positioned between the inner peripheral side belt layer 7A and the main-body part 4Bx of the outer peripheral side carcass layer 4B. On the other hand, both end portions of the inner peripheral side carcass layer 4A extend at least to a position overlapping with the bead filler 6 in the tire radial direction, and both end portions of the inner peripheral side carcass layer 4A are not folded around the respective bead cores 5. Terminate at the bead portion 3. That is, the terminal 4 </ b> Ae of the inner circumferential carcass layer 4 </ b> A is disposed in the vicinity of the bead core 5. Here, the inner circumferential side carcass layer 4 </ b> A may extend to the lower side of the bead core 5, but does not extend from the radially innermost end position of the bead core 5 toward the outer side in the tire radial direction.

  In the pneumatic tire, both end portions of the outer peripheral side carcass layer 4B are folded back from the inner side to the outer side around each bead core 5, and the folded portion 4By of the outer peripheral side carcass layer 4B is extended to a position overlapping the inner peripheral side belt layer 7A. On the other hand, since both end portions of the inner circumferential side carcass layer 4A are terminated at each bead portion 3 without being folded back around each bead core 5, the carcass layer 4 is formed into a three-layer structure in the sidewall portion 2 and is a pneumatic tire. Can be sufficiently secured, and good steering stability can be exhibited.

  On the other hand, since only the two carcass layers 4A and 4B are used as the skeleton structure of the tire and the surplus portion of the carcass layer 4 is eliminated as much as possible, the conventional carcass layer has three carcass layers. In comparison with a pneumatic tire, the weight of the tire can be reduced. In particular, since the folded portion 4By of the outer peripheral side carcass layer 4B extends to a position overlapping the inner peripheral belt layer 7A, the side wall portion 2 has a three-layer structure of the carcass layer 4, while the tread portion 1 In the lower region of the belt layer 7, the carcass layer 4 can have a two-layer structure. Further, since both end portions of the inner circumferential side carcass layer 4A are not folded around the bead cores 5, the weight around the bead portions 3 can be reduced. Thereby, a tire can be reduced in weight and rolling resistance of a tire can be reduced in connection with it.

  Furthermore, according to the pneumatic tire, there are two ends (4Ae, 4Be) of the carcass layer 4 on one side of the tire, and one of the ends is between the inner peripheral belt layer 7A and the outer peripheral carcass layer 4B. Therefore, the separation failure starting from the end of the carcass layer 4 can be suppressed, and the separation resistance can be improved.

  In the pneumatic tire, as shown in FIG. 3, the tire radial height PH from the innermost end in the tire radial direction of the bead core 5 to the terminal 4Ae of the inner circumferential carcass layer 4A is the height in the tire radial direction of the bead core 5. It is preferable that the relationship of 0.05 × (BH + FH) ≦ PH ≦ 0.7 × (BH + FH) is satisfied with respect to the height FH in the tire radial direction of BH and bead filler 6. Thereby, the position of terminal 4Ae of inner circumference side carcass layer 4A can be optimized, and separation-proof performance can be improved. If PH <0.05 × (BH + FH), the end 4Ae of the inner circumferential carcass layer 4A may be disposed below the bead core 5 due to manufacturing errors, and tire performance may become unstable. Further, when PH> 0.7 × (BH + FH), the effect of improving the separation resistance decreases because the terminal 4Ae of the inner circumferential side carcass layer 4A and the apex of the bead filler 6 are close to each other.

  The tire radial height BH of the bead core 5 is the height in the tire radial direction from the radially innermost end to the outermost end of the bead core 5. As the bead core 5, for example, a cross-sectional shape that is a quadrangle or a hexagon can be used, but the shape is not particularly limited. In any case, the height BH of the bead core 5 in the tire radial direction is specified based on the above definition.

  Further, the tire radial height FH of the bead filler 6 is a height in the tire radial direction from the radially innermost end to the outermost end of the bead filler 6.

  As shown in FIG. 4, between each end of the inner peripheral carcass layer 4A and the main body 4Bx of the outer peripheral carcass layer 4B, the breaking strength is 15 MPa to 25 MPa and the loss tangent at 60 ° C. is 0.10 to 0. A buffer rubber layer 11 (first buffer rubber layer) that is .25 can be disposed. Thereby, the shear deformation between the inner circumferential side carcass layer 4A and the outer circumferential side carcass layer 4B can be suppressed, and the separation resistance can be improved. Here, if the breaking strength of the buffer rubber layer 11 is less than 15 MPa, the effect of improving the separation resistance is reduced, and conversely, if it exceeds 25 MPa, fatigue fracture tends to occur. If the loss tangent at 60 ° C. of the buffer rubber layer 11 exceeds 0.25, heat generation due to deformation is likely to occur, which causes an increase in rolling resistance. Further, in order to ensure adhesion between the buffer rubber layer 11 and the carcass layers 4A and 4B, the rubber composition constituting the buffer rubber layer 11 and the rubber composition used for the coat rubber of the carcass layers 4A and 4B are mutually connected. It is desirable to match.

  The shock absorbing rubber layer 11 has a width Wr of 10 mm to 30 mm and a thickness of 0.5 mm to 2 mm. It is good to arrange | position inside the tire radial direction rather than the terminal 4Ae of 4 A of carcass layers. As a result, the terminal 4Ae of the inner peripheral carcass layer 4A is separated from the main body 4Bx of the outer peripheral carcass layer 4B with only a necessary minimum weight increase, and the inner peripheral carcass layer 4A and the outer peripheral carcass layer 4B are separated from each other. The shear strain can be effectively relieved. Here, when the width Wr or the thickness of the buffer rubber layer 11 exceeds the upper limit value, the weight increase becomes remarkable, and conversely, when the buffer rubber layer 11 falls below the lower limit value, the effect of reducing the shear strain is reduced.

  The tire radial height FH of the bead filler 6 may satisfy the relationship of 0.05SH ≦ FH ≦ 0.5SH, more preferably 0.1SH ≦ FH ≦ 0.4SH, with respect to the tire cross-section height SH. . When the tire radial height FH of the bead filler 6 is set in the above range, a high bending rigidity is ensured in the bead portion 3 by a so-called sandwich effect sandwiched between the main body portion 4Bx and the turned-up portion 4By of the outer carcass layer 4B. And since the bending deformation of the bead filler 6 at the time of grounding is suppressed, the tension applied to the terminal 4Ae of the inner peripheral side carcass layer 4A located inside the bead filler 6 can be reduced. This improves the separation resistance and suppresses heat generation and fatigue fracture of the bead filler 6.

  As shown in FIG. 2, the overlap amount W between the folded portion 4By of the outer peripheral side carcass layer 4B and the inner peripheral side belt layer 7A is preferably 5 mm to 40 mm. Thereby, a good separation resistance can be ensured. When the overlap amount W is less than 5 mm, the terminal 4Be of the outer peripheral side carcass layer 4B and the end of the inner peripheral side belt layer 7A are close to each other, so that the effect of improving the separation resistance is reduced. Since the usage-amount of 4 increases, the reduction effect of rolling resistance falls.

  The overlap amount W is outside the reference line of the inner peripheral belt layer 7A when a reference line passing through the terminal 4Be of the outer peripheral carcass layer 4B and orthogonal to the inner peripheral belt layer 7A is obtained. The width of the part.

  5 to 6 show a pneumatic tire according to another embodiment of the present invention. 5 to 6, the same components as those in FIGS. 1 to 3 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 5, a buffer rubber layer 12 (second buffer rubber layer) is disposed between the folded portion 4By of the outer peripheral side carcass layer 4B and the inner peripheral belt layer 7A. The buffer rubber layer 12 has a thickness of 0.5 mm to 2 mm and a breaking strength of 20 MPa or more. By adding such a buffer rubber layer 12, the shear strain of the said location can be relieved and a separation-proof performance can be improved. When the thickness of the buffer rubber layer 12 is less than 0.5 mm, the effect of improving the separation resistance is reduced. Conversely, when the thickness exceeds 2 mm, the effect of reducing the rolling resistance is reduced due to an increase in weight. Further, if the breaking strength of the buffer rubber layer 12 is less than 20 MPa, the effect of improving the separation resistance is lowered.

  The outer end in the tire width direction of the cushioning rubber layer 12 is disposed on the outer side in the tire width direction than the end of the inner peripheral belt layer 7A, and the inner end in the tire width direction of the cushioning rubber layer 12 It is good to arrange | position inside the tire width direction rather than the terminal 4Be. Thereby, the shear distortion of the said location can be relieve | moderated effectively.

  On the other hand, an auxiliary filler 13 is disposed on the outer side in the tire width direction than the folded portion 4By of the outer peripheral side carcass layer 4B in the bead portion 3. The auxiliary filler 13 is embedded between a sidewall rubber layer or a rim cushion rubber layer (not shown) disposed on the outer surface of the tire and the folded portion 4By of the inner circumferential carcass layer 4B. The JIS hardness of the auxiliary filler 13 is set lower by 3 points or more than the JIS hardness of the bead filler 6. By adding such an auxiliary filler 13, bending deformation of the bead filler 6 can be suppressed, and tension applied to the terminal 4Ae of the inner circumferential carcass layer 4A can be reduced. This improves the separation resistance and suppresses heat generation and fatigue fracture of the bead filler 6. Here, when the difference between the JIS hardness of the auxiliary filler 13 and the JIS hardness of the bead filler 6 is less than 3 points, the above-described effects cannot be expected. The JIS hardness of the bead filler 6 is preferably set in the range of 75 to 97, and the JIS hardness of the auxiliary filler 13 is preferably set in the range of 72 to 94.

  The outer end in the tire radial direction of the auxiliary filler 13 is disposed on the outer side in the tire radial direction of the outer end in the tire radial direction of the bead filler 6, and the inner end of the auxiliary filler 13 in the tire radial direction is the height FH of the bead filler 6 in the tire radial direction. It is good to arrange within the range. Thereby, the bending deformation of the bead filler 6 can be effectively suppressed. That is, by arranging the auxiliary filler 13 at a position shifted to the outer side in the tire radial direction with respect to the bead filler 6, the bending deformation of the bead portion 3 with the rim flange as a fulcrum can be effectively suppressed.

  The tire radial height SFH of the auxiliary filler 13 satisfies the relationship of 0.5 FH ≦ SFH ≦ 1.5 FH with respect to the tire radial height FH of the bead filler 6, and the auxiliary filler 13 is on both sides of the tire radial direction. A portion having a crescent-shaped cross-sectional shape that gradually decreases toward the maximum thickness of the auxiliary filler 13 may be disposed within the range of the height FH of the bead filler 6 in the tire radial direction. Thereby, the bending deformation of the bead filler 6 can be effectively suppressed without increasing the weight excessively, and the durability can be improved. If SFH <0.5FH, the above effect cannot be expected. Conversely, if SFH> 1.5FH, excessive weight increase causes an increase in rolling resistance. In addition, when the cross-sectional shape of the auxiliary filler 13 is not a crescent shape and the thickness of the auxiliary filler 13 is constant along the tire radial direction, an excessive weight increase causes an increase in rolling resistance. For the same reason, the maximum thickness of the auxiliary filler 13 is preferably set to 6 mm or less.

  In the embodiment described above, the buffer rubber layer 12 is disposed on the tread portion 1 and the auxiliary filler 13 is disposed on the bead portion 3. However, it is not necessary to provide both at the same time, and only one of them is provided. It is also possible.

  In tire size 225 / 70R16, a plurality of carcass layers including a plurality of carcass cords are mounted between a pair of bead portions, a bead core and a bead filler are disposed in each bead portion, and two layers are provided on the outer peripheral side of the carcass layer. Conventional tires, comparative examples 1 and 2 and examples 1 to 8 in which the structure of the carcass layer was varied in the pneumatic tire in which the belt layer was arranged were manufactured.

  The conventional tire has a structure using three carcass layers (see FIG. 7), and both end portions of the inner circumferential carcass layer (first ply and second ply) are folded around each bead core. The both ends of the outer peripheral side carcass layer (third ply) are terminated at each bead portion without being folded around each bead core.

  The tire of Comparative Example 1 has a structure using two carcass layers, and ends both ends of the inner peripheral carcass layer (first ply) without being folded around each bead core. Both ends of the layer (second ply) are folded around each bead core, and the terminal of the folded portion of the outer circumferential carcass layer is disposed between the inner circumferential belt layer and the main body of the outer circumferential carcass layer. In Comparative Example 1, both end portions of the inner circumferential carcass layer do not reach the bead filler.

  The tire of Comparative Example 2 has a structure using two carcass layers, and both end portions of the inner peripheral carcass layer (first ply) are extended to at least a position overlapping with the bead filler. Both end portions of the outer peripheral side carcass layer (second ply) are folded back around each bead core while the both end portions are terminated at each bead portion without being folded back around each bead core. In Comparative Example 2, the end of the folded portion of the outer peripheral side carcass layer does not reach the position overlapping the inner peripheral side belt layer.

  The tires of Examples 1 to 8 have a structure using two carcass layers (see FIGS. 1 to 6), and positions where both end portions of the inner circumferential carcass layer (first ply) overlap at least the bead filler. And both ends of the inner circumferential carcass layer are terminated at each bead without being folded around each bead core, while both ends of the outer circumferential carcass layer (second ply) are folded around each bead core. The terminal of the folded portion of the outer circumferential side carcass layer is disposed between the inner circumferential belt layer and the main body portion of the outer circumferential side carcass layer.

  In particular, in the tires of Examples 3 to 8, the first buffer rubber layer was disposed between each end portion of the inner peripheral side carcass layer and the main body portion of the outer peripheral side carcass layer. In the tire of Example 7, the second buffer rubber layer was disposed between the folded portion of the outer peripheral side carcass layer and the inner peripheral side belt layer. In the tire of Example 8, the second buffer rubber layer is disposed between the folded portion of the outer peripheral side carcass layer and the inner peripheral belt layer, and the tire width direction is greater than the folded portion of the outer peripheral side carcass layer in the bead portion. An auxiliary filler was placed on the outside.

In the above-described conventional examples, comparative examples 1 and 2, and examples 1 to 8, the end position of the carcass layer (first to third plies) (distance from the innermost end in the tire radial direction of the bead core to the outer side in the tire radial direction) The ratio of the tire radial height FH of the bead filler to the tire cross-section height SH (FH / SH), the tire radial height BH of the bead core and the tire radial height FH of the bead filler Ratio of height PH in the tire radial direction [PH / (BH + FH)], breaking strength and loss tangent of the first buffer rubber layer, width and thickness of the first buffer rubber layer, terminal of the inner circumferential carcass layer The distance in the tire radial direction from the first cushioning rubber layer to the inner terminal in the tire radial direction (denoted as “inner terminal position”) was set as shown in Table 1. The inner terminal position of the first shock-absorbing rubber layer is indicated by a positive value when the inner terminal is positioned on the outer side in the tire radial direction than the terminal of the inner circumferential carcass layer, and the inner terminal is positioned on the inner circumferential carcass layer. The case where it is located on the inner side in the tire radial direction from the terminal is indicated by a negative value.

  In Examples 1 to 8 and Comparative Example 1, the overlap amount W between the folded portion of the outer peripheral side carcass layer and the inner peripheral side belt layer was 30 mm. In Examples 7 and 8, the thickness of the second buffer rubber layer was 1.0 mm, and the breaking strength was 10 MPa. In Example 8, the auxiliary filler had a JIS hardness of 85, and the bead filler had a JIS hardness of 90 in all tires.

  These test tires were evaluated for separation resistance, tire weight, rolling resistance, and steering stability by the following evaluation methods, and the results are also shown in Table 1.

Separation resistance:
Each test tire is assembled to a wheel with a rim size of 16 × 6 1 / 2JJ and mounted on a drum durability tester. A running test is performed under the conditions of air pressure 400 kPa, load 11.8 kN, speed 80 km / h, and separation of the carcass layer. The mileage until failure was measured. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the separation resistance.

Tire weight:
The weight of each test tire was measured. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. A larger index value means lighter weight.

Rolling resistance:
Each test tire is assembled to a wheel of rim size 16 × 6 1/2 JJ and mounted on a rolling resistance tester equipped with a drum having a radius of 854 mm, and the pressure is 210 kPa, the load is 6.47 kN, and the speed is 80 km / h for 30 minutes. After the preliminary running, the rolling resistance was measured under the same conditions. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. It means that rolling resistance is so small that this index value is large.

Steering stability:
Each test tire was assembled on a wheel with a rim size of 16 × 6 1/2 JJ and mounted on a test vehicle, and sensory evaluation was performed on a test course by a test driver under the condition of an air pressure of 210 kPa. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the steering stability.

  As can be seen from Table 1, the tires of Examples 1 to 8 can reduce the weight of the tire and reduce the rolling resistance while maintaining good steering stability in comparison with the conventional example, and also have anti-separation performance. Was able to improve.

  On the other hand, in the tire of Comparative Example 1, since both end portions of the inner circumferential side carcass layer did not reach the bead filler, the steering stability was worse than that of the conventional example, and the separation resistance was also lowered. Moreover, since the tire of Comparative Example 2 does not reach the position where the end of the folded portion of the outer circumferential side carcass layer overlaps with the inner circumferential side belt layer, the steering stability is worse than that of the conventional example, and the separation resistance is also lowered. Was.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 4A Inner circumference side carcass layer 4B Outer circumference side carcass layer 5 Bead core 6 Bead filler 7 Belt layer 7A Inner circumference side belt layer 7B Outer circumference side belt layer 8 Belt cover layer 11 Buffer rubber Layer (first buffer rubber layer)
12 Buffer rubber layer (second buffer rubber layer)
13 Auxiliary filler

Claims (11)

A two-layer carcass layer including a plurality of carcass cords is mounted between a pair of bead portions, a bead core and a bead filler are disposed on each bead portion, and at least two belt layers are disposed on the outer peripheral side of the carcass layer. the pneumatic tire includes an outer peripheral-side carcass layer carcass layer of the two layers located on the outer side in the tire radial direction in the inner peripheral side carcass layer and said tread portion located in the tire radial direction inner side in the tread portion, the outer periphery One end of the side carcass layer is folded back from the inside to the outside of the tire around each bead core, and the terminal of the folded portion of the outer circumferential carcass layer is disposed between the inner circumferential belt layer and the main body of the outer circumferential carcass layer. in the both end portions of the inner peripheral-side carcass layer is extended at least to a position overlapping the bead filler, the both end portions of the inner peripheral side carcass layer of each bead core around A pneumatic tire which is characterized in that is terminated at each bead portion without folding the.   The tire radial height PH from the tire radial innermost end of the bead core to the end of the inner circumferential carcass layer is relative to the tire radial height BH of the bead core and the tire radial height FH of the bead filler. The pneumatic tire according to claim 1, wherein a relationship of 0.05 × (BH + FH) ≦ PH ≦ 0.7 × (BH + FH) is satisfied.   A first buffer rubber having a breaking strength of 15 MPa to 25 MPa and a loss tangent at 60 ° C. of 0.10 to 0.25 between each end of the inner peripheral carcass layer and the main body of the outer peripheral carcass layer The pneumatic tire according to claim 1, wherein a layer is disposed.   The width of the first buffer rubber layer is 10 mm to 30 mm and the thickness is 0.5 mm to 2 mm, and the tire radial direction inner end of the first buffer rubber layer is located at the same position as the end of the inner circumferential carcass layer Alternatively, the pneumatic tire according to claim 3, wherein the pneumatic tire is arranged on an inner side in a tire radial direction from a terminal of the inner circumferential side carcass layer.   5. The tire radial height FH of the bead filler satisfies a relationship of 0.05SH ≦ FH ≦ 0.5SH with respect to a tire cross-section height SH. Pneumatic tires.   The pneumatic tire according to any one of claims 1 to 5, wherein an overlap amount W between the folded portion of the outer peripheral side carcass layer and the inner peripheral side belt layer is 5 mm to 40 mm.   The second buffer rubber layer having a thickness of 0.5 mm to 2 mm and a breaking strength of 20 MPa or more is disposed between the folded portion of the outer peripheral side carcass layer and the inner peripheral side belt layer. Item 7. The pneumatic tire according to any one of Items 1 to 6.   The outer end in the tire width direction of the second shock absorbing rubber layer is disposed on the outer side in the tire width direction of the end of the inner peripheral belt layer, and the inner end in the tire width direction of the second shock absorbing rubber layer is disposed on the outer carcass. The pneumatic tire according to claim 7, wherein the pneumatic tire is disposed on the inner side in the tire width direction from the end of the folded portion of the layer.   The auxiliary filler having a JIS hardness lower by 3 points or more than the bead filler is provided on the outer side in the tire width direction than the folded portion of the outer peripheral side carcass layer in the bead portion. The described pneumatic tire.   The outer end of the auxiliary filler in the tire radial direction is disposed on the outer side of the tire radial direction of the bead filler in the radial direction of the tire, and the inner end of the auxiliary filler in the radial direction of the tire has a tire radial height FH of the bead filler. The pneumatic tire according to claim 9, wherein the pneumatic tire is disposed within a range.   The tire radial height SFH of the auxiliary filler satisfies the relationship of 0.5FH ≦ SFH ≦ 1.5FH with respect to the tire radial height FH of the bead filler, and the auxiliary filler is on both sides of the tire radial direction. The shape according to claim 9 or 10, wherein the portion having a shape that gradually becomes thinner toward the maximum thickness of the auxiliary filler is disposed within the range of the radial height FH of the bead filler. Pneumatic tire.

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