Patent Publication Number: US-2021178833-A1

Title: Pneumatic tire and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Japanese Patent Application No.: 2019-225705 filed on Dec. 13 2019, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention relates to a pneumatic tire and a manufacturing method of a pneumatic tire. 
     Related Art 
     A carcass ply of a pneumatic tire disclosed in Japanese Patent No. 5629356 includes a first ply that is continuous between a pair of bead portions and a discontinuous second ply that is disposed on the outer side in the tire radial direction of the first ply. The second ply includes a pair of ply pieces extending from a tread portion to one of a pair of the bead portions. In the center of the tread portion, a region where neither of the two ply pieces exists, that is, a hollow portion is provided. The hollow portion of the second ply is intended to have two contradictory types of performance. One type of performance is rigidity (which contributes to improving steering stability) and cut resistance, and the other type of performance is weight reduction and rolling resistance reduction by the weight reduction. 
     SUMMARY 
     The structure disclosed in Japanese Patent No. 5629356 can achieve the weight reduction and rolling resistance reduction by the weight reduction while ensuring rigidity and cut resistance. However, Japanese Patent No. 5629356 does not mention uniformity in the tire circumferential direction, and there is room for improvement in the uniformity in the tire circumferential direction. 
     An object of the present invention is to provide a pneumatic tire and a manufacturing method of a pneumatic tire, which can improve the uniformity in the tire circumferential direction. 
     The present invention provides a pneumatic tire including a carcass ply stretching between a pair of bead cores disposed on both sides in a tire width direction. The carcass ply includes a pair of ply pieces disposed separately on both sides in the tire width direction, each of the pair of ply pieces has a joint portion in which both end portions in a tire circumferential direction are joined in a manner overlapping each other, and respective joint portions of the pair of ply pieces are provided at different positions in the tire circumferential direction. 
     According to the present configuration, in a case where the carcass ply includes the pair of ply pieces disposed separately on both sides in the tire width direction, the two joint portions of a pair of the ply pieces are provided at different positions in the tire circumferential direction. For this reason, as compared with the case where the two joint portions are provided at the same position in the tire circumferential direction, the joint portions are dispersed in the tire circumferential direction and uniformity in the tire circumferential direction of the pneumatic tire can be improved. 
     The joint portion of the ply piece has increased rigidity as compared with the non-joint portion of the ply piece. For this reason, the joint portion of the ply piece is less likely to bulge and deform than the non-joint portion when the tire is filled with internal pressure and bulged and deformed. Therefore, the joint portion of the ply piece may appear as a dent in the pneumatic tire. 
     By providing the two joint portions of the pair of ply pieces at different positions in the tire circumferential direction, the dents caused by the two joint portions are dispersed in the tire circumferential direction and uniformity in the tire circumferential direction can be improved as compared with the case where the two joint portions are provided at the same position in the tire circumferential direction. 
     The carcass ply includes the first ply including the central portion positioned on the inner side in the tire radial direction of the tread portion and a pair of the side portions extending to the inner side in the tire radial direction from both ends of the central portion, and the second ply having the pair of ply pieces including an inner end portion disposed on an outer side in the tire radial direction with respect to the first ply and positioned in the tread portion and a side portion extending to the inner side in the tire radial direction from the inner end portion. 
     The second ply includes the pair of ply pieces and is discontinuous. That is, between the inner end portions of the pair of ply pieces, there is a hollow portion in which no ply exists. By employing the second ply having the hollow portion, the weight can be reduced as compared with the case where the second ply is one continuous ply. Further, roiling resistance can be reduced by weight reduction. 
     In the sidewall portion, two layers of plies, that is, the side portion of the first ply and the side portion of the ply piece of the second ply are disposed. By providing two layers of plies in the sidewall portion in this way, necessary cut resistance is ensured. Further, since plies are provided in two layers, necessary rigidity in the sidewall portion is ensured. 
     Therefore, it is possible to achieve weight reduction and reduction in rolling resistance due to the weight reduction while ensuring the rigidity and the steering stability due to the rigidity and the cut resistance, and, in addition, to achieve improvement in uniformity in the tire circumferential direction. 
     The first ply has a joint portion in which both end portions in the tire circumferential direction are joined in a manner overlapping each other, and the joint portion of the first ply and the respective joint portions of the pair of ply pieces of the second ply are provided at different positions in the tire circumferential direction. 
     By the present configuration, the dents caused by the three joint portions are dispersed in the tire circumferential direction and uniformity in the tire circumferential direction can be improved as compared with the case where the joint portion of the first ply and the respective joint portions of the pair of ply pieces of the second ply are provided at the same position in the tire circumferential direction. 
     Respective joint portions of the pair of ply pieces of the second ply are preferably provided within an angle range of ±90 degrees with respect to an angular position of 180⋅ degrees in the tire circumferential direction with respect to the joint portion of the first ply. 
     By the present configuration, the joint portion of the first ply and the two joint portions of the second ply are effectively dispersed and disposed in the tire circumferential direction, so that improvement in uniformity in the tire circumferential direction can be effectively achieved. 
     The tread rubber constituting the tread portion preferably has a joint portion in which both end portions in the tire circumferential direction are joined, and the joint portion of the tread rubber is preferably provided at the same position in the tire circumferential direction as the joint portion of the first ply. 
     Since the tread rubber constituting the tread portion is molded in a manner that both end portions overlap each other when the joint is formed, the rubber thickness of the joint portion tends to be thicker than that of the non-joint portion. Therefore, the joint portion of the tread rubber, which is thicker than the non-joint portion of the tread rubber, may appear as a convex portion in the pneumatic tire. 
     By providing the joint portion of the tread rubber and the joint portion of the first ply at the same position in the tire circumferential direction, the convex portion caused by the joint portion of the tread rubber and the dents caused by the joint portion of the first ply can be combined to improve the uniformity in the tire circumferential direction, as compared with the case where the two joint portions are provided at different positions in the tire circumferential direction. 
     The joint portion of the sidewall rubber disposed on one side in the tire width direction of a pair of the sidewall rubbers constituting a pair of the sidewall portions is preferably provided at the same position in the tire circumferential direction as the joint portion of the ply piece of the second ply disposed on the one side in the tire width direction. 
     Since the sidewall rubber constituting the sidewall portion is molded in a manner that both end portions overlap each other when the joint is formed, the rubber thickness of the joint portion tends to be thicker than that of the non-joint portion. Therefore, the joint portion of the sidewall rubber, which is thicker than the non-joint portion of the sidewall rubber, may appear as a convex portion in the pneumatic tire. 
     By providing the joint portion of the sidewall rubber disposed on one side in the tire width direction and the joint portion of the ply piece of the second ply at the same position in the tire circumferential direction, the convex portion caused by the joint portion of the sidewall rubber and the dent caused by the joint portion of the ply piece of the second ply can be combined to improve the uniformity in the tire circumferential direction, as compared with the case where the two joint portions are provided at different positions in the tire circumferential direction. 
     The present invention further provides a manufacturing method of a pneumatic tire, the manufacturing method including preparing a carcass ply including a pair of ply pieces disposed separately on both sides in a tire width direction and stretching between a pair of bead cores disposed on both sides in the tire width direction, forming a joint portion obtained by winding one ply piece of the pair of ply pieces in a cylindrical shape and joining both end portions in a circumferential direction of the one ply piece in a manner overlapping each other, forming a joint portion obtained by winding the other ply piece of the pair of ply pieces in a cylindrical shape and joining both end portions in the circumferential direction of the other ply piece in a manner overlapping each other, and providing the joint portion of the other ply piece at a different position in a tire circumferential direction from the joint portion of the one ply piece. 
     According to the present configuration, in a case where the carcass ply includes a pair of the ply pieces disposed separately on both sides in the tire width direction, the joint portion of the other one of the ply pieces is provided at a different position in the tire circumferential direction from the joint portion of the one of the ply pieces. For this reason, uniformity in the tire circumferential direction can be improved as compared with the case where the two joint portions of a pair of the ply pieces are provided at the same position in the tire circumferential direction, and improvement in uniformity in the tire circumferential direction of the pneumatic tire can be achieved. 
     According to the pneumatic tire and the manufacturing method of the pneumatic tire according to the present invention, it is possible to achieve improvement in uniformity in the tire circumferential direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and the other features of the present invention will become apparent from the following description and drawings of an illustrative embodiment of the invention in which: 
         FIG. 1  is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention; 
         FIG. 2  is a meridian cross-sectional view of a tread portion of the pneumatic tire according to the embodiment of the present invention and its surroundings; 
         FIG. 3  is an enlarged view of Part III of  FIG. 1 ; 
         FIG. 4  is an enlarged view of Part IV of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view of a carcass ply along Line V-V of  FIG. 2 ; and 
         FIG. 6  is a schematic side view of a pneumatic tire for explaining a joint portion of the carcass ply. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIGS. 1 to 4  show a pneumatic tire  1  made from rubber according to an embodiment of the present invention. 
     The pneumatic tire  1  includes a tread portion  2 , a pair of sidewall portions  3 , and a pair of ring-shaped bead portions  4 . 
     The tread portion  2  extends in the tire width direction (indicated by the reference numeral TW in  FIG. 1 ). A groove  2   a  is provided on the surface, that is, the tread surface of the tread portion  2 . 
     Each of a pair of the sidewall portions  3  extends from both ends in the tire width direction of the tread portion  2  to the inner side in the tire radial direction (reference numeral TR in  FIG. 1 ). 
     A pair of the bead portions  4  are disposed on both sides in the tire width direction and disposed in end portions on the inner side in the tire radial direction of a pair of the sidewall portions  3 . Each of the bead portions  4  includes a bead core  5  and a bead filler  6 . The bead core  5  includes a large number of steel wires bundled in a ring shape. The bead filler  6  has a ring shape and is made from rubber that is harder than rubber that constitutes the tread portion  2  and the sidewall portion  3 . The bead filler  6  includes a base end  6   a  disposed adjacent to the outer side in the tire radial direction of the bead core  5  and a tip end  6   b  on the side opposite to the base end  6   a,  and extends in a tapered shape from the base end  6   a  to the outer side in the tire radial direction toward the tip end  6   b.  Each of the bead portions  4  includes strip rubber  7  provided to wrap the bead core  5  and the bead filler  6 . 
     The pneumatic tire includes a carcass ply  10  stretching in a toroidal shape between the bead portions  4 . In the present embodiment, the carcass ply  10  includes a first carcass ply (hereinafter, referred to as “first ply”)  11  and a second carcass ply (hereinafter, referred to as “second ply”)  12 . The second ply  12  is a ply having a hollow portion  13   c,  while the first ply  11  is a normal ply having no hollow portion. The first and second plies  11  and  12  will be described in detail later. An inner liner  8  is provided on the inner side of the carcass ply  10 , that is, on the innermost peripheral surface of the pneumatic tire. 
     With reference to  FIGS. 2 and 3 , an endless belt layer  20  is provided on the tread portion  2 , more specifically, between the carcass ply  10  and the tread portion  2 . In the present embodiment, the belt layer  20  includes two belts  21  and  22 . The belt  21  is disposed adjacent to the outer side in the tire radial direction of the carcass ply  10 , and the belt  22  is disposed adjacent to the outer side in the tire radial direction of the belt  21 . Further, in the present embodiment, the dimension in the tire width direction of the belt  21  in the lower layer is larger than the dimension in the tire width direction of the belt  22  in the upper layer, and an end portion  21   a  of the belt  21  is positioned closer to the outer side in the tire width direction than an end portion  22   a  of the belt  22 . The belts  21  and  22  are formed by covering a belt cord made from steel or organic fiber with rubber. The belt layer  20  may be composed of one belt, or may include three or more belts. 
     An endless cap layer  30  is provided adjacent to the outer side in the tire radial direction of the belt layer  20 . The cap layer  30  of the present embodiment includes a pair of narrow edge plies  31  that directly cover either of the end portions  21   a  and  22   a  of the belts  21  and  22 . Further, the cap layer  30  of the present embodiment includes a wide cap ply  32 , which is disposed adjacent to the outer side in the tire radial direction of the edge ply  31 , as a single sheet that covers the entire belts  21  and  22  including the end portions  21   a  and  22   a.  The cap layer  30  may include one ply or three or more plies. Further, the cap layer  30  may be eliminated. 
     A pair of endless pads  40  made from rubber are disposed between both end portions on the outer side in the tire width direction of the belt layer  20  and the carcass ply  10 . The cross-sectional shape of the pad  40  is a flat triangular shape. The positions in the tire width direction of the end portions  21   a  and  22   a  of the belts  21  and  22 , the end portion  31   a  on the outer side in the tire width direction of the edge ply  31 , and an end portion  32   a  of the cap ply  32  are set in a region between an end portion  40   a  on the outer side in the tire width direction of the pad  40  and an end portion  40   b  on the inner side, that is, a region where the pad  40  exists. The pad  40  may be eliminated. 
     The first and second plies  11  and  12  constituting the carcass ply  10  will be described. 
     The first ply  11  is a single ply, whereas the second ply  12  is a discontinuous ply having the hollow portion  13   c  as described above, and is composed of a pair of ply pieces  13 . As will be described later, the first ply  11  and a pair of the ply pieces  13  are joined by a joining tape (joining member)  14 . All of the first ply  11  and the ply pieces  13  of the second ply  12  are a strip-shaped sheet in which a plurality of cords arranged in parallel at intervals are covered with rubber. 
     The first ply  11  and the ply pieces  13  of the second ply  12  may have the same modulus (stress generated when a constant strain is applied) or may have different moduli. Further, the first ply  11  and the ply pieces  13  of the second ply  12  may have the same breaking strength (tensile load at which breaking occurs) or may have different breaking strengths. 
     The first ply  11  includes a central portion  11   a  positioned on the inner side in the tire radial direction of the tread portion  2 , and a pair of side portions  11   b  extending from both ends in the tire width direction of the central portion  11   a  to the inner side in the tire radial direction. A pair of the side portions  11   b  are similarly configured. The side portion  11   b  is disposed in the sidewall portion  3 . The individual side portions  11   b  of the first ply  11  include an end portion  11   c  that terminates on the outer side in the tire radial direction of the bead core  5 . In other words, the first ply  11  is not wound up with respect to the bead core  5 . 
     In the present embodiment, the end portion  11   c  of the side portion  11   b  of the first ply  11  is positioned closer to the inner side in the tire radial direction than the tip end  6   b  of the bead filler  6  and closer to the outer side in the tire radial direction than the base end  6   a  of the bead filler  6 . That is, the side portion  11   b  of the first ply  11  overlaps the bead filler  6 . 
     The second ply  12  is disposed adjacent to the outer side in the tire radial direction of the first ply  11 , and is a discontinuous ply composed of a pair of the ply pieces  13  disposed separately on both sides in the tire width direction. A pair of the ply pieces  13  are configured similarly except for the positions of joint portions J 2  and J 3 , which will be described later. The ply piece  13  has the inner end portion  13   a  disposed between the belt layer  20  and the central portion  11   a  of the first ply  11 . The pad  40  is interposed between the inner end portion  13   a  and the belt layer  20 . The position in the tire width direction of the inner end portion  13   a  of the ply piece  13  is set in the region on the outer side in the tire width direction of the tread portion  2 , more specifically, in the region closer to the inner side in the tire width direction than both the end portions  21   a  and  22   a  of the belts  21  and  22  constituting the belt layer  20 . The hollow portion  13   c  is provided in the region at the center in the tire width direction of the tread portion  2 , more specifically, in the region between the inner end portions  13   a  of a pair of the ply pieces  13 . In the hollow portion  13   c,  the second ply  12  does not exist, and only the central portion  11   a  of the first ply  11  exists. 
     The ply piece  13  includes a side portion  13   b  extending to the inner side in the tire radial direction from the inner end portion  13   a.  The side portion  13   b  is disposed adjacent to the outer side in the tire width direction of the side portion  11   b  of the first ply  11 . 
     The ply piece  13  includes a wind-up portion  13   d  provided continuously with the side portion  13   b  and wound up from the inner side to the outer side in the tire width direction with respect to the bead core  5 . The wind-up portion  13   d  is terminated in the sidewall portion  3 . 
     The wind-up portion  13   d  of the ply piece  13  includes an inner portion  13   e  disposed closer to the inner side in the tire width direction than the bead portion  4 , that is, the bead core  5  and the bead filler  6 . Further, the wind-up portion  13   d  includes a winding portion  13   f  which is provided continuously with the inner portion  13   e  and is wound around the bead core  5 . Further, the wind-up portion  13   d  includes an outer portion  13   g  which is provided continuously with the winding portion  13   f  and is disposed closer to the outer side in the tire width direction than the bead portion  4 . The outer portion  13   g  is disposed so as to overlap the outer side in the tire radial direction of the side portion  13   b.  An end portion of the outer portion  13   g  constitutes an outer end portion  13   h  of the ply piece  13 . The outer end portion  13   h  is positioned closer to the outer side in the tire radial direction than the tip end  6   b  of the bead filler  6  and is positioned closer to the inner side in the tire radial direction than the tread portion  2 . 
     The pneumatic tire  1  includes a pair of joining tapes  14  that join either one of a pair of the side portions  11   b  of the first ply  11  to the wind-up portion  13   d  of either one of a pair of the ply pieces  13 , more specifically, the inner portion  13   e.  As most clearly shown in  FIG. 4 , the joining tape  14  joins a portion including the end portion  11   c  of the side portion  11   b  of the first ply  11  to the inner portion  13   e  of the wind-up portion  13   d  of the ply piece  13 . 
     The joining tape  14  is made from rubber and preferably has an adhesive strength of 500 gf or more in order to secure the joining strength of the first ply  11  to the second ply  12 . 
     An end portion  14   a  on the outer side in the tire radial direction of the joining tape  14  is positioned closer to the outer side in the tire radial direction than the tip end  6   b  of the bead filler  6 . The position in the tire radial direction of an end portion  14   b  on the inner side in the tire radial direction of the joining tape  14  is set between the base end  6   a  and the tip end  6   b  of the bead filler  6 . 
     The end portion  11   c  of the first ply  11  is positioned between the end portion  14   b  on the inner side and the end portion  14   b  on the outer side in the tire width direction of the joining tape  14 . 
     The pneumatic tire  1  according to the present embodiment will be further described with reference to  FIGS. 5 and 6 . 
       FIG. 5  shows a cross section of the first ply  11  of the carcass ply  10 . As shown in  FIG. 5 , the first ply  11  of the carcass ply  10  is wound in a cylindrical shape, and one end portion  11   d  and the other end portion  11   e  are joined in a manner overlapping each other. A joint portion J 1  in which the one end portion  11   d  and the other end portion  11   e,  which are both end portions in the circumferential direction of the first ply  11 , are joined in a manner overlapping each other, is formed to be thicker than a non-joint portion  11   f  excluding the joint portion J 1  of the first ply  11 . 
     Each of a pair of the ply pieces  13  of the second ply  12  of the carcass ply  10  is also wound in a cylindrical shape in a similar manner to the first ply  11 , and one end portion and the other end portion are joined in a manner overlapping each other. A joint portion in which the one end portion and the other end portion, which are both end portions in the circumferential direction of the ply piece  13 , are joined in a manner overlapping each other, is formed to be thicker than a non-joint portion excluding the joint portion of the ply piece  13 . 
     In  FIG. 6 , the joint portion of the first ply  11  is indicated by a broken line as J 1 , the joint portion of one of the ply pieces  13  of the second ply  12  is indicated by a broken line as J 2 , and the joint portion of the other one of the ply pieces  13  of the second ply  12  is shown by a broken line as J 3 . As shown in  FIG. 6 , in the pneumatic tire  1 , the respective joint portions J 2  and J 3  of a pair of the ply pieces  13  of the second ply  12  are provided at different positions in the tire circumferential direction TC. 
     The two joint portions J 2  and J 3  of the second ply  12  are provided at different positions in the tire circumferential direction from the joint portion J 1  of the first ply  11 . The two joint portions J 2  and J 3  of the second ply  12  are preferably provided within an angle range of ±90 degrees with respect to the joint portion J 1  of the first ply  11  with respect to an angular position of 180 degrees in the tire circumferential direction. 
     As shown in  FIG. 6 , assuming that the position in the tire circumferential direction of the joint portion J 1  of the first ply  11  around the axial direction of the pneumatic tire  1  is an angular position of 0 degrees, the joint portion J 2  of one of the ply pieces  13  of the second ply  12  is preferably provided so that a position θ 1  in the tire circumferential direction is between 90 degrees and 270 degrees, and provided within an angle range of ±90 degrees with respect to an angular position of 180 degrees in the tire circumferential direction. 
     The joint portion J 3  of the other of the ply pieces  13  of the second ply  12  is also preferably provided so that a position θ 2  in the tire circumferential direction is between 90 degrees and 270 degrees, and provided within an angle range of ±90 degrees with respect to an angular position of 180 degrees in the tire circumferential direction at a different position in the tire circumferential direction TC from the joint portion J 2  of the one of the ply pieces  13  of the second ply  12 . 
     In the present embodiment, the joint portion J 1  of the first ply  11  is provided so that the position in the tire circumferential direction is an angular position of 0 degrees, the joint portion J 2  of one of the ply pieces  13  of the second ply  12  is provided so that the position θ 1  in the circumferential direction is an angular position of 120 degrees, and the joint portion J 3  of the other one of the ply pieces  13  of the second ply  12  is provided so that the position θ 2  in the tire circumferential direction is an angular position of 240 degrees. The first ply  11  and a pair of the ply pieces  13  of the second ply  12  are provided with the joint portions J 1 , J 2 , and J 3  dispersed in the tire circumferential direction. 
     As shown in  FIG. 5 , the position in the tire circumferential direction of the joint portion J 1  of the first ply  11  refers to an angular position of a center line L 1  extending in the tire radial direction of the joint portion J 1 , and the center line L 1  is a straight line that passes through the center of the tire and divides the joint portion J 1  into two equal parts in the tire circumferential direction. The positions in the tire circumferential direction of the two joint portions J 2  and J 3  of a pair of the ply pieces  13  of the second ply  12  are also set in a similar manner to the first ply  11 . 
     The joint portion J 1  of the first ply  11  is preferably at a predetermined angle θ 3 , for example, within an angle within 2 degrees, in the tire circumferential direction with respect to the center line L 1 . However, the configuration is not limited to this. The joint portions J 2  and J 3  of the second ply  12  is also preferably at a predetermined angle, for example, within an angle within 2 degrees, in the tire circumferential direction with respect to the center line of the joint portions J 2  and J 3 . However, the configuration is not limited to this. 
     In the pneumatic tire  1 , tread rubber  2   b  constituting the tread portion  2  is disposed on the outer side in the tire radial direction of the carcass ply  10 , and the tread rubber  2   b  constitutes the outer surface of the tire. The tread rubber  2   b  is a strip-shaped sheet, and is formed to be relatively thicker than the carcass ply  10 . 
     The tread rubber  2   b  is also wound in a cylindrical shape, and one end portion in the circumferential direction and the other end portion in the circumferential direction are joined in a manner overlapping each other. A joint portion in which the one end portion and the other end portion, which are both end portions in the circumferential direction of the tread rubber  2   b,  are joined in a manner overlapping each other, is formed to be thicker than a non-joint portion excluding the joint portion of the tread rubber  2   b.    
     The joint portion of the tread rubber  2   b  is provided at the same position in the tire circumferential direction as the joint portion J 1  of the first ply  11 . The position in the tire circumferential direction of the joint portion of the tread rubber  2   b  is also set in a similar manner to the joint portion J 1  of the first ply  11 . 
     Further, in the pneumatic tire  1 , a pair of sidewall rubbers  3   b  constituting a pair of the sidewall portions  3  are disposed on the outer side in the tire width direction of the carcass ply  10 , and a pair of the sidewall rubbers  3   b  constitute the outer surface of the tire. The sidewall rubber  3   b  is a strip-shaped sheet, and is formed to be relatively thicker than the carcass ply  10 . 
     Each of a pair of the sidewall rubbers  3   b  is also wound in a cylindrical shape, and one end portion in the circumferential direction and the other end portion in the circumferential direction are joined in a manner overlapping each other. A joint portion in which the one end portion and the other end portion, which are both end portions in the circumferential direction of the sidewall rubber  3   b,  are joined in a manner overlapping each other, is formed to be thicker than a non-joint portion excluding the joint portion of the sidewall rubber  3   b.    
     The joint portion of the sidewall rubber  3   b  disposed on one side in the tire width direction of a pair of the sidewall rubbers  3   b  is provided at the same position in the tire circumferential direction as the joint portion of the ply pieces  13  of the second ply  12  disposed on one side in the tire width direction of a pair of the ply pieces  13  of the second ply  12 . 
     The joint portion of the sidewall rubber  3   b  disposed on the other side in the tire width direction of a pair of the sidewall rubbers  3   b  is provided at the same position in the tire circumferential direction as the joint portion of the ply piece  13  of the second ply  12  disposed on the, other side in the tire width direction of a pair of the ply pieces  13  of the second ply  12 . 
     In the pneumatic tire  1 , the joint portion J 2  of one of the ply pieces  13  of the second ply  12  of the carcass ply  10  and the joint portion of the sidewall rubber  3   b  disposed on the outer side in the tire width direction of the ply piece  13  are provided at the same position in the tire circumferential direction. Further, the joint portion J 3  of the other one of the ply pieces  13  of the second ply  12  of the carcass ply  10  and the joint portion of the sidewall rubber  3   b  disposed on the outer side in the tire width direction of the ply piece  13  are provided at the same position in the tire circumferential direction. 
     Next, a manufacturing method of the pneumatic tire  1  configured in this way will be described. 
     When manufacturing the pneumatic tire  1 , first, tire components for molding a cylindrical tread band, such as the tread rubber  2   b  constituting the tread portion  2  and the belts  21  and  22 , are prepared. On the other hand, tire components for molding a cylindrical carcass band, such as the carcass ply  10  that includes the first ply  11  and the second ply  12  and is stretched between a pair of the bead cores  5  and the inner liner  8 , are prepared. 
     Then, tire components such as the inner liner  8  and the carcass ply  10  are wound around a molding drum to mold a cylindrical carcass band. In the molding of the carcass band, the first ply  11  is wound in a cylindrical shape, and the joint portion J 1  in which both the end portions  11   d  and  11   e  in the circumferential direction of the first ply  11  are joined in a manner overlapping each other is formed. 
     Next, one of the ply pieces  13  of the second ply  12  is wound in a cylindrical shape and the joint portion J 2  in which both end portions in the circumferential direction of the one of the ply pieces  13  are joined in a manner overlapping each other is formed, and the other one of the ply pieces  13  of the second ply  12  is wound in a cylindrical shape and the joint portion J 3  in which both end portions in the circumferential direction of the other one of the ply pieces  13  are joined in a manner overlapping each other is formed. A pair of the ply pieces  13  may be wound simultaneously or separately. 
     The carcass band is transferred to another molding drum, and, after that, the bead core  5  and bead filler  6  are assembled on both side portions of the carcass band, and the carcass band is folded back on both sides in the drum width direction around the bead core  5 , so that a cylindrical green case is molded. 
     On the other hand, tire components such as a belt and tread rubber are further wound around another molding drum to mold a cylindrical tread band. Then, after the tread band is transported to the outer side in the radial direction of the green case, the green case is bulged in a toroidal shape to the outer side in the radial direction, the outer surface of the green case is bonded to the inner surface of the tread band, and a carcass tread bond body is molded. 
     Next, a pair of sidewall rubbers  9  are wound around the carcass tread bond body to mold a green tire. The molded green tire is vulcanized and molded vulcanization molding machine (not shown) including a tire vulcanization mold, and the pneumatic tire  1  is manufactured. 
     A pair of the sidewall rubbers  9  are wound and molded after the carcass tread bond body is molded. However, it is also possible to wind and mold the sidewall rubber  9  when the carcass band is molded. 
     As described above, the joint portion J 3  of the other one of the ply pieces  13  of the second ply  12  is provided at a position different in the tire circumferential direction from the joint portion J 2  of one of the ply pieces  13 . The two joint portions J 2  and J 3  of a pair of the ply pieces  13  of the second ply  12  are provided at different positions in the tire circumferential direction from the joint portion J 1  of the first ply  11 . 
     The joint portion of the tread rubber  2   b  is provided at the same position in the tire circumferential direction as the joint portion J 1  of the first ply  11 . Joint portions of sidewall rubber  3   b  disposed on one side and the other side in the tire width direction are provided at the same positions in the tire circumferential direction as the joint, portions of the ply pieces  13  of the second ply  12  disposed on one side and the ether side in the tire width direction. 
     In the present embodiment, the second ply  12  includes the wind-up portion  13   d  wound up with respect to the bead core  5 , and, although the first ply  11  is not wound up with respect to the bead core  5 , the first ply  11  can include a wind-up portion that is wound up with respect to the bead core  5 . Further, both the first ply  11  and the second ply  12  may include a wind-up portion wound up with respect to the bead core  5 . 
     As described above, the pneumatic tire  1  according to the present embodiment includes the carcass ply  10  stretching between a pair of the bead cores  5  disposed on both sides in the tire width direction, and the carcass ply  10  includes a pair of the ply pieces  13  disposed separately on both sides in the tire width direction. Each of a pair of the ply pieces  13  has the joint portions J 2  and J 3  in which both end portions in the tire circumferential direction are joined in a manner overlapping each other, and the two joint portions J 2  an J 3  of a pair of the ply pieces  13  are provided at different positions in the tire circumferential direction. 
     In this manner, in a case where the carcass ply  10  includes pair of the ply pieces  13  disposed separately on both sides in the tire width direction, the two joint portions J 2  and J 3  of a pair of the ply pieces  13  are provided at different positions in the tire circumferential direction. For this reason, as compared with the case where the two joint portions J 2  and J 3  are provided at the same position in the tire circumferential direction, the joint portions J 2  and J 3  are dispersed in the tire circumferential direction and uniformity in the tire circumferential direction of the pneumatic tire  1  can be improved. 
     The joint portions J 2  and J 3  of the ply piece  13  have increased rigidity as compared with the non-joint portion of the ply piece  13 . For this reason, the joint portions J 2  and J 3  of the ply piece  13  are less likely to bulge and deform than the non-joint portion when the tire is filled with internal pressure and bulged and deformed. Therefore, the joint portions J 2  and J 3  of the ply piece  13  may appear as dents in the pneumatic tire. 
     By providing the two joint portions J 2  and J 3  of a pair of the ply pieces  13  at different positions in the tire circumferential direction, the dents caused by the two joint portions J 2  and J 3  are dispersed in the tire circumferential direction and uniformity in the tire circumferential direction of the pneumatic tire  1  can be improved as compared with the case where the two joint portions J 2  and J 3  are provided at the same position in the tire circumferential direction. 
     Further, the carcass ply  10  includes the first ply  11  including the central portion  11   a  positioned on the inner side in the tire radial direction of the tread portion  2  and a pair of the side portions  11   b  extending to the inner side in the tire radial direction from both ends of the central portion  11   a,  and the second ply  12  having a pair of the ply pieces  13  including the inner end portion  13   a  disposed on the outer side in the tire radial direction with respect to the first ply  11  and positioned in the tread portion  2  and the side portion  13   b  extending to the inner side in the tire radial direction from the inner end portion  13   a.    
     The second ply  12  includes a pair of the ply pieces  13  and is discontinuous. That is, between the inner end portions  13   a  of a pair of the ply pieces  13 , there is the hollow portion  13   c  in which no ply exists. By employing the second ply  12  having the hollow portion  13   c , the weight can be reduced as compared with the case where the second ply  12  is one continuous ply. Further, rolling resistance can be reduced by weight reduction. 
     In the sidewall portion  3 , two layers of plies, that is, the side portion  11   b  of the first ply  11  and the side portion  13   b  of the ply piece  13  of the second ply  12  are disposed. By providing two layers of plies in the sidewall portion  3  in this way, necessary cut resistance is ensured. Further, since plies are provided in two layers, necessary rigidity in the sidewall portion  3  is ensured. 
     Therefore, it is possible to achieve weight reduction and reduction in rolling resistance due to the weight reduction while ensuring the rigidity and the steering stability due to the rigidity and the cut resistance, and, in addition, to achieve improvement in uniformity in the tire circumferential direction. 
     Further, the first ply  11  has the joint portion J 1  in which both end portions in the tire circumferential direction are joined in a manner overlapping each ether, and the joint portion J 1  of the first ply  11  and the two joint portions J 2  and J 3  of a pair of the ply pieces  13  of the second ply  12  are provided at different positions in the tire circumferential direction. In this manner, the dents caused by the three joint portions J 1 , J 2 , and J 3  are dispersed in the tire circumferential direction and uniformity in the tire circumferential direction can be improved as compared with the case where the joint portion J 1  of the first ply  11  and the two joint portions J 2  and J 3  of a pair of the ply pieces  13  of the second ply  12  are provided at the same position in the tire circumferential direction. 
     Further, the two joint portions J 2  and J 3  of a pair of the ply pieces  13  of the second ply  12  are provided within an angle range of ±90 degrees with respect to the angular position of 180 degrees in the tire circumferential direction with respect to the joint portion J 1  of the first ply  11 . In this manner, the joint portion J 1  of the first ply  11  and the two joint portions J 2  and J 3  of the second ply  12  are effectively dispersed and disposed in the tire circumferential direction, so that improvement in uniformity in the tire circumferential direction can be effectively achieved. 
     Further, the tread rubber  2   b  constituting the tread portion  2  has a joint portion in which both end portions in the tire circumferential direction are joined, and the joint portion of the tread rubber  2   b  is provided at the same position in the tire circumferential direction as the joint portion J 1  of the first ply  11 . 
     Since the tread rubber  2   b  constituting the tread portion  2  is molded in a manner that both end portions overlap each other when the joint is formed, the rubber thickness of the joint portion tends to be thicker than that of the non-joint portion. Therefore, the joint portion of the tread rubber  2   b,  which is thicker than the non-joint portion of the tread rubber  2   b,  may appear as a convex portion in the pneumatic tire  1 . 
     By providing the joint portion of the tread rubber  2   b  and the joint portion J 1  of the first ply  11  at the same position in the tire circumferential direction, the convex portion caused by the joint portion of the tread rubber  2   b  and the dents caused by the joint portion J 1  of the first ply  11  can be combined to improve the uniformity in the tire circumferential direction, as compared with the case where the two joint portions J 1  are provided at different positions in the tire circumferential direction. 
     Further, the joint portion of the sidewall rubber  3   b  disposed on one side in the tire width direction of a pair of the sidewall rubbers  3   b  constituting a pair of the sidewall portions  3  is provided at the same position in the tire circumferential direction as the joint portion of the ply pieces  13  of the second ply  12  disposed on one side in the tire width direction. 
     Since the sidewall rubber  3   b  constituting the sidewall portion  3  is molded in a manner that both end portions overlap each other when the joint is formed, the rubber thickness of the joint portion tends to be thicker than that of the non-joint portion. Therefore, the joint portion of the sidewall rubber  3   b,  which is thicker than the non-joint portion of the sidewall rubber  3   b,  may appear as a convex portion in the pneumatic tire  1 . 
     By providing the joint portion of the sidewall rubber  3   b  disposed on one side in the tire width direction and the joint portion of the ply pieces  13  of the second ply  12  at the same position in the tire circumferential direction, the convex portion caused by the joint portion of the sidewall rubber  3   b  and the dents caused by the joint portion of the ply pieces  13  of the second ply  12  can be combined to improve the uniformity in the tire circumferential direction, as compared with the case where the two joint portions are provided at different positions in the tire circumferential direction. 
     Further, in the manufacturing method of the pneumatic tire  1  according to the present embodiment, the carcass ply  10  that includes a pair of the ply pieces  13  disposed separately on both sides in the tire width direction and is stretched between a pair of the bead cores  5  disposed on both sides in the tire width direction is prepared. Then, one of the ply pieces  13  is wound in a cylindrical shape and both end portions in the circumferential direction are joined in a manner overlapping each other to form the joint portion J 2 , and the other one of the ply pieces  13  is wound in a cylindrical shape and both end portions in the circumferential direction of the other one of the ply pieces  13  are joined in a manner overlapping each other to form the joint portion J 3 . The joint portion J 3  of the other one of the ply pieces  13  is provided at a different position in the tire circumferential direction from the joint portion J 2  of the one of the ply pieces  13 . 
     In this manner, in a case where the carcass ply  10  includes a pair of the ply pieces  13  disposed separately on both sides in the tire width direction, the joint portion J 3  of the other one of the ply pieces  13  is provided at a different position in the tire circumferential direction from the joint portion J 2  of the one of the ply pieces  13 . For this reason, uniformity in the tire circumferential direction can be improved as compared with the case where the two joint portions J 2  and J 3  of a pair of the ply pieces  13  are provided at the same position in the tire circumferential direction, and improvement in uniformity in the tire circumferential direction of the pneumatic tire  1  can be achieved. 
     The present invention is not limited to the illustrated embodiment, and various improvements and design changes can be made without departing from the gist of the present invention.