JP2014091336A - Pneumatic tire and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving durability while suppressing the increase of tire weight and reducing a ply-steer force, and a manufacturing method thereof.SOLUTION: A carcass 6 includes a carcass ply 6A having an inner layer part 10, an outer layer part 11, one side edge 12, and the other side edge 13. The carcass ply 6A includes a first carcass cord group 20 which repeats a first spiral movement to incline and extend in a tire peripheral circumferential direction on the inner layer part 10 from the other side edge 13 to one side edge 12, to be folded at one side edge 12 to incline and extend in a tire peripheral circumferential direction toward the other edge side 13 on the outer layer part 11, and to be folded at the other side edge 13 to reach the inner layer part 10, and a second carcass cord group 21 which repeats second spiral movement in a direction reverse to that of the first carcass cord group.

Description

  The present invention relates to a pneumatic tire with improved carcass and a method for manufacturing the same.

  In recent years, with the increase in output of vehicles, pneumatic tires are required to improve the durability of tread portions and sidewall portions. Therefore, for example, as shown in FIG. 13, a pneumatic tire a including a carcass E having a high turn-up structure in which the outer end of the folded portion f of the carcass ply e is extended to the sidewall portion c or the shoulder portion d. (See Patent Document 1 below).

  Such a pneumatic tire a improves the rigidity and durability of the tread part b and the sidewall part c. However, in such a pneumatic tire a, the outer end of the turned-up portion f of the carcass ply e is approaching the shoulder portion d that generates a large amount of heat. For this reason, there is a problem that separation of the folded portion f due to heat is likely to occur. In addition, the amount of cord material for the carcass ply is increased due to the high turn-up structure, and the tire weight is increased.

  On the other hand, in the pneumatic tire a, a belt layer G is provided inside the tread portion b and outside the carcass E in order to increase the rigidity of the tread portion b. The belt layer G is usually composed of a plurality of belt plies g, and is overlapped so that the belt cords of the belt plies g and g intersect each other.

  However, in such a belt layer G, the belt cord of the outermost belt ply in the tire radial direction is inclined and arranged in the same direction over the entire surface, so that the price tear force becomes large and the vehicle flow is increased. In particular, there is a problem that the steering stability at a high speed is lowered.

  In order to reduce such price tear force, for example, as shown in FIG. 14, a pneumatic tire using a belt layer h in which a belt cord is knitted in a net shape (see Patent Document 2) has been proposed. Yes. However, even such a belt layer h is affected by the inclination direction of the carcass cord of the carcass ply disposed on the inner side of the belt layer h, and the reduction of the price tear force is not sufficient. Further, in such a belt layer h, since the cut end i of each belt cord appears at the end in the tire axial direction, the binding force of the belt layer h in the vicinity of the shoulder portion is reduced, and consequently high-speed durability is reduced. There was a problem.

JP 2004-352174 A JP-A-5-139113

  The present invention has been devised in view of the above-described problems, and is arranged on a carcass ply having an inner layer portion and an outer layer portion whose both end portions are connected in opposite directions and at the same angle with respect to the tire equator. A pneumatic tire capable of improving durability while reducing an increase in tire weight and reducing price tear force based on the first carcass cord and the second carcass cord being spirally moved. The main purpose is to provide a manufacturing method.

  Of the present invention, the invention according to claim 1 is a pneumatic tire including a carcass extending in a toroidal manner between bead cores respectively disposed in a pair of bead portions, and in a tire meridian section including a tire rotation axis, The carcass has an inner layer portion straddling between the pair of bead cores on the tire lumen side, an outer layer portion straddling the pair of bead cores on the tire outer surface side of the inner layer portion, and the inner layer portion and the outer layer portion on one side. A carcass ply having a one-side edge connecting the bead cores on the inner side in the tire radial direction, and an other side edge connecting the inner layer part and the outer layer part on the other side in the tire radial direction of the bead core. Includes a first carcass cord group composed of a plurality of first carcass cords arranged at an angle θ with respect to the tire equator, and the first carcass cord with respect to the tire equator. A second carcass cord group composed of a plurality of second carcass cords arranged in a direction opposite to the cascode group and inclined at the same angle θ, wherein the first carcass cord group includes the inner layer portion on the other side edge Extending from the one side edge toward the tire circumferential direction, and folded back at the one side edge to tilt the outer layer portion toward the other side edge toward the tire circumferential direction, In addition, the first spiral movement which is folded back at the other side edge and reaches the inner layer portion is repeated, and the second carcass cord group is arranged in the tire circumferential direction from the one side edge toward the other side edge. And the inner layer is folded at the other side edge and the outer layer portion is inclined toward the one side edge with respect to the tire circumferential direction, and is folded at the one side edge. To the club And repeating the moving second spiral.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein each of the first carcass cord and the second carcass cord has an endless shape in which both ends are bonded.

  The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein the carcass ply is a jointless ply that is continuous in the tire circumferential direction without having a seam.

  The invention according to claim 4 is the pneumatic tire according to any one of claims 1 to 3, wherein the first carcass cord and the second carcass cord are arranged symmetrically with respect to the tire equator.

  The invention according to claim 5 is the carcass according to any one of claims 1 to 4, wherein the first carcass cord group and the second carcass cord group are knitted in the inner layer portion and the outer layer portion, respectively. The pneumatic tire described.

  The invention according to claim 6 is a method of manufacturing a pneumatic tire having a carcass extending in a toroidal shape between bead cores respectively disposed in a pair of bead portions, and spirals at an inclination angle β with respect to the central axis. A first carcass cord group consisting of a plurality of carcass cords wound, and a second carcass cord group consisting of a plurality of carcass cords spirally wound at the same inclination angle β opposite to the first carcass cord group. A net body forming step of forming a net body having a circular cross-section by knitting each other, and a flat annular body forming step of forming a flat annular body having a long and flat cross-section by folding the net body, And a carcass forming step of forming a carcass by forming the flat annular body into a toroidal cross section.

  The invention according to claim 7 is the method for producing a pneumatic tire according to claim 6, wherein the net body has a donut shape in which a central axis of the spiral winding is continuous in an annular shape.

  In the pneumatic tire of the present invention, the carcass straddles between the pair of bead cores on the tire lumen side, the outer layer portion straddling between the pair of bead cores on the tire outer surface side of the inner layer portion, and the inner layer portion and the outer layer portion. Is formed of a carcass ply having a first side edge and a second side edge that are connected to the inner side in the tire radial direction of the bead core on the first side and the second side.

  In the pneumatic tire of the present invention, the carcass ply includes a first carcass cord group including a plurality of first carcass cords arranged at an angle θ with respect to the tire equator and a first carcass cord with respect to the tire equator. A second carcass cord group composed of a plurality of second carcass cords arranged opposite to the carcass cord group and inclined at the same angle θ. The first carcass cord group extends the inner layer portion from the other side edge toward the one side edge with respect to the tire circumferential direction and is folded back at the one side edge so that the outer layer portion faces the other side edge. The first spiral movement that repeats the inclination with respect to the direction and is folded back at the other side edge to reach the inner layer portion is repeated. Furthermore, the second carcass cord group extends the inner layer portion from the one side edge toward the other side edge with respect to the tire circumferential direction, and is folded back at the other side edge to move the outer layer portion toward the one side edge. Inclining with respect to the tire circumferential direction, folded back at one side edge, and repeated second spiral movement to the inner layer portion.

  In such a pneumatic tire, since the inner layer portion and the outer layer portion of the carcass ply are continuous on the inner side in the tire radial direction of the bead core, the end portion of the conventional folded portion does not appear in the sidewall portion and the tread portion. For this reason, the movement of the carcass cord can be suppressed with a small amount of cord material, and the separation starting from the end portion of the carcass ply is suppressed. For this reason, durability improves, suppressing the increase in a tire weight.

  Furthermore, the first carcass cord group and the second carcass cord group arranged in the opposite direction and inclined at the same angle with respect to the tire equator are arranged in the inner layer portion and the outer layer portion. As a result, the carcass cords having the orientations in two directions are inclined and arranged over the entire surface of the carcass ply. For this reason, the price tear force is reduced, the vehicle flow is reduced, and the steering stability at high speed is improved.

It is sectional drawing which shows one Embodiment of the pneumatic tire of this invention. It is a perspective view of the carcass of FIG. It is a fragmentary perspective view of the carcass of FIG. FIG. 3 is a plan development view of the carcass of FIG. 2. It is an enlarged view of the knitted carcass cord group. It is a perspective view of a net body. It is a fragmentary perspective view of the net body of other embodiments. It is a perspective view of a flat annular body. It is a perspective view of the flat annular body by which edge parts were joined. It is the side view and sectional drawing of a doughnut-shaped net body. It is the side view and sectional drawing of the flat annular body shape | molded by the net body of FIG. It is explanatory drawing of a carcass shaping | molding process. It is sectional drawing of the pneumatic tire of other embodiment. It is sectional drawing which shows an example of the conventional pneumatic tire. It is a perspective view which shows an example of the conventional belt layer.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a tire meridian cross-sectional view including a tire shaft in a normal state of the pneumatic tire 1 of the present embodiment.

  Here, the normal state is a no-load state in which the tire is assembled on a normal rim (not shown) and filled with a normal internal pressure. Hereinafter, unless otherwise specified, dimensions and the like of each part of the tire are values measured in the normal state.

  “Regular rim” is a rim determined by each tire in the standard system including the standard on which the tire is based. For example, JAMMA is a standard rim, TRA is “Design Rim”, and ETRTO. For example, “Measuring Rim”. Furthermore, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA and the table “TIRE LOAD LIMITS AT” is TRA. Maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, but 180 kPa for tires for passenger cars.

  As shown in FIG. 1, a pneumatic tire 1 according to the present embodiment includes a carcass 6 extending in a toroidal manner between bead cores 5A and 5B arranged in a pair of bead portions 4A and 4B, and a tire radius of the carcass 6. A belt layer 7 disposed on the outer side in the direction and inside the tread portion 2 and a bead apex rubber 8 extending in a tapered shape from the bead core 5 toward the outer side in the radial direction of the tire are provided. A pneumatic tire is shown.

  The bead apex rubber 8 has a substantially triangular cross section extending in a tapered manner from the bead core 5 toward the outer side in the tire radial direction along the carcass 6, and reinforces the bead portion 4.

  The belt layer 7 includes two belt plies 7A and 7B in the tire radial direction in which the belt cord is inclined with respect to the tire equator C at a small angle of 10 to 40 °, for example. The belt layer 7 is configured, for example, such that the belt cords of the belt plies 7A and 7B are overlapped with each other so as to cross each other.

  The carcass 6 forms a toroid from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4. The carcass 6 includes, in the tire meridian cross section including the tire rotation axis, an inner layer portion 10 straddling between the pair of bead cores 5A and 5B on the tire lumen side, and a pair of bead cores 5A and 5B on the tire outer surface side of the inner layer portion 10. It consists of a carcass ply 6A having an outer layer part 11 straddling it. Further, the carcass ply 6A includes a tire 12 of a bead core 5B on one side, and a side edge 12 connecting the inner layer portion 10 and the outer layer portion 11 inside the bead core 5A on one side in the tire radial direction, and the inner layer portion 10 and the outer layer portion 11 on the other side. It has the other side edge 13 which continues in a radial direction inside.

  FIG. 2 is a perspective view of the carcass of the present embodiment. FIG. 3A shows a partial perspective view of the carcass ply 6A. FIG. 3B shows a plan development view of the carcass ply 6A. FIG. 3 (b) shows a tread where the carcass ply 6A extending in the tire circumferential direction A is cut in the tire axial direction B at an arbitrary position in the tire circumferential direction A, and the cut one end is 0 ° and the other end is 360 °. FIG. 3 is a plan development view in which the part 2 is developed on a plane and the one side edge 12 and the other side edge 13 are developed on both outer sides of the plane. That is, in FIG. 3B, the tread portion, the sidewall portion, and the bead portion are developed in a substantially straight section, and the vertical direction of FIG. 3B is the tire circumferential direction A, and the horizontal direction is the tire axial direction. B. FIG. 3B is a view as seen from the outer layer part 11 side. When the carcass cord passes through the inner layer part 10, it is indicated by a broken line, and when the carcass cord passes through the outer layer part 11, it is indicated by a solid line.

  As shown in FIG. 3A, the carcass ply 6A includes a first carcass cord group 20 including a plurality of first carcass cords 22 arranged at an angle θ with respect to the tire equator C, and a tire equator. And a second carcass cord group 21 composed of a plurality of second carcass cords 23 arranged in a direction opposite to the first carcass cord group 20 and inclined at the same angle θ. Accordingly, the first carcass cord 22 of the first carcass cord group 20 and the second carcass cord 23 of the second carcass cord group 21 intersect each other.

  As shown in FIG. 3B, each carcass cord 22 of the first carcass cord group 20 extends, for example, from the position of 0 ° toward the one side edge 12 in the tire circumferential direction starting from the position of 0 °, The first spiral movement is repeated at the one side edge 12 to extend the outer layer portion toward the other side edge 13 in the tire circumferential direction, and at the other side edge 13 to the inner layer portion 10.

  Similarly, each carcass cord 23 of the second carcass cord group 21 starts from the position of 0 °, extends the inner layer portion toward the other side edge 13 in the tire circumferential direction, and is folded back at the other side edge 13 to be the outer layer. The second spiral movement is repeated in the direction opposite to the first spiral movement extending in the tire circumferential direction toward the one side edge 12 and folded back at the one side edge 12 to reach the inner layer part 10.

  In the pneumatic tire 1 having such a carcass ply 6A, since the inner layer portion 10 and the outer layer portion 11 are continuous at the one side edge 12 and the other side edge 13, the end portion of the carcass ply is the sidewall portion 3. And does not appear in the tread portion 2. Therefore, the movement of the carcass cords 22 and 23 can be suppressed with a small amount of cord material, and the tread portion 2 can be suppressed while suppressing an increase in the tire weight as compared with the conventional pneumatic tire as shown in FIG. And the side wall part 3 can be reinforced. Moreover, in such a carcass ply 6A, separation starting from the end of the carcass ply is effectively suppressed, and durability is improved. Furthermore, since such a carcass ply 6A fixes the position of the carcass cord at the time of tire molding, the uniformity is improved and the variation in quality is reduced.

  The carcass ply 6A includes an outer layer portion 11 in which a first carcass cord group 20 and a second carcass cord group 21 arranged in a direction opposite to the tire equator C and inclined at the same angle are arranged on the tire outer surface side. Pass through. For this reason, the carcass cords having two directions are inclined and arranged over the entire outer layer portion 11, the price tear force is reduced, the vehicle flow is reduced, and the driving stability at high speed is improved.

  The carcass ply 6A is preferably made of a jointless ply that is continuous in the tire circumferential direction without having a seam. Thereby, tire damage is effectively suppressed.

  The first carcass cord group 20 and the second carcass cord group 21 may be formed by arranging a plurality of carcass cords wound only once in the tire circumferential direction, and one carcass cord is formed in the tire circumferential direction. It may be formed by winding a plurality of times.

  It is desirable that the first carcass cord group 20 and the second carcass cord group 21 are knitted at the inner layer portion 10 and the outer layer portion 11, respectively. That is, as shown in FIG. 4, it is desirable that the intersection points 24a where the first carcass cords 22 are outside and the intersection points 24b where the second carcass cords 23 are outside are alternately arranged. In the first carcass cord group 20 and the second carcass cord group 21, the occurrence of the price tear force due to the one carcass cord group being arranged in an inclined manner, and the other carcass cord group being arranged in an inclined manner. Can be counteracted by the price tear force. For this reason, the vehicle flow can be further reduced, and excellent straight running stability can be exhibited.

  The first carcass cord 22 and the second carcass cord 23 are preferably endless in which both ends are bonded. The first carcass cord 22 and the second carcass cord 23 can reliably prevent the end portion of the carcass cord from becoming a starting point of tire damage.

  It is desirable that the first carcass cord 22 and the second carcass cord 23 are arranged symmetrically with respect to the tire equator C. That is, it is desirable that not only the angle θ but also the end of each carcass cord is the same. Furthermore, it is more desirable that the positions of the start and end portions of the first carcass cord 22 and the positions of the start and end portions of the second carcass cord 23 are line-symmetric. As a result, the effect of canceling the price tear force is further improved, excellent straight running stability is exhibited, and tire uniformity can be improved.

  When the angle θ (shown in FIG. 3 (a)) of the first carcass cord 22 and the second carcass cord 23 with respect to the tire equator C decreases, the rigidity of the tread portion 2 in the tire axial direction decreases and the cornering force decreases. If it becomes large, the amount of winding of the carcass cord becomes large and the tire weight may increase. For this reason, angle (theta) becomes like this. Preferably it is 70 degrees or more, More preferably, it is 75 degrees or more, Preferably it is 85 degrees or less, More preferably, it is 80 degrees or less.

  As the carcass cords 22 and 23, organic fiber cords are used in the present embodiment. Examples of the organic fiber cord include nylon, polyester, aramid, rayon and the like. These organic fiber cords are useful for improving ride comfort, reducing weight, and reducing rolling resistance.

  When the total fineness f of the carcass cords 22 and 23 decreases, the rigidity of the tread portion 2 may decrease. When the total fineness f increases, the tire weight increases and the fuel efficiency may decrease. For this reason, the total fineness f of the carcass cords 22 and 23 is preferably 1200 dtex or more, more preferably 1300 dtex or more, and preferably 1600 dtex or less, more preferably 1500 dtex or less.

  The pneumatic tire 1 of the present invention reduces price tear force, reduces vehicle flow, and improves steering stability particularly at high speeds. In order to further exhibit this effect, as shown in FIG. 14, the belt layer 7 preferably has a belt cord knitted in a net shape.

  Also, as shown in FIG. 12, the belt layer 7 is preferably a flat annular body in which two end portions in the tire axial direction of the belt ply formed in two layers in the tire radial direction are continuous. Further, it is desirable that the belt layer 7 is disposed in the tire circumferential direction while the first belt cord and the second belt cord disposed in opposite directions and at the same angle with respect to the tire equator are moved in a flat spiral manner. In such a belt layer 7, the belt cord is knitted in a net shape by both the inner layer belt ply 7i and the outer layer belt ply 7o, and the price tear force can be further reduced.

Next, an example of a method for manufacturing a pneumatic tire as described above will be described with reference to the drawings.
FIG. 5 is a perspective view showing a net body 25 for molding the carcass ply 6A. In the present embodiment, first, the first carcass cord group 20 composed of a plurality of first carcass cords 22 spirally wound at the spiral angle β with respect to the central axis CA, and the first carcass cord group 20 are opposite to each other. A net body forming step of forming a net body 25 having a circular cross section by knitting together a second carcass cord group 21 composed of a plurality of second carcass cords 23 spirally wound at the same inclination angle β. Done. The net body 25 of the present embodiment has a cylindrical shape in which a spiral winding central axis CA extends linearly.

  A pair of bead members 26 are inserted into the net body 25. The bead member 26 includes, for example, a bead core 5 and a bead apex rubber 8. The bead member 26 extends parallel to the central axis CA in the length direction of the net body. As shown in FIG. 6, the net body 25 may be formed by spirally winding the carcass cords 22 and 23 around the bead member 26.

Next, as shown in FIG. 7, a flat annular body forming step for forming a flat annular body 27 having a long and flat cross section is performed by folding the net body 25 flatly along the central axis CA. The flat annular body 27 is formed in a sheet shape overlapping two layers, and both ends in the width direction become the one side edge 12 and the other side edge 13. The pair of bead members 26 arranged inside the net body 25 are arranged on both sides of the flat annular body 15 in the width direction. In the bead member 26, for example, the bead core 5 is disposed on the inner side in the width direction of the one side edge 12 or the other side edge 13, and the bead apex rubber 8 is further disposed on the inner side in the width direction.

As shown in FIG. 8, the flat annular body 27 has a cylindrical shape in which end portions 27 s and 27 e in the length direction are jointed. This seam 28 tends to be a starting point of tire damage. For this reason, as shown in FIG. 9, the net body 25 may be formed into a donut shape in which the central axis CA of the spiral winding is continuous in an annular shape. As shown in FIG. 10, such a donut-shaped net body 25 is folded along a central axis CA to form a cylindrical flat annular body 27 that is seamless in the circumferential direction. For this reason, a jointless ply continuous in the tire circumferential direction can be formed without having a seam.

  Next, a carcass forming step of forming the carcass 6 by forming the flat annular body 27 into a toroidal cross section is performed. The carcass forming step is performed by, for example, a cylindrical former 30 disposed inside the cylindrical flat annular body 27. As shown in FIG. 11, the former 30 has the bead gripping portions 31A and 31B that grip the one side edge 12 and the other side edge 13 approach each other toward the inner side C in the axial direction of the former 30, and By expanding the central portion 32c of the main body 32 toward the radially outward direction D of the former 30, the flat annular body 27 is formed into a toroidal cross section. Thereby, the carcass 6 shown in FIG. 2 is formed.

  As mentioned above, although the pneumatic tire of this invention and its manufacturing method were demonstrated in detail, it cannot be overemphasized that this invention can be changed into a various aspect, without being limited to said specific embodiment. Absent.

  A passenger car pneumatic tire (185 / 60R14) having the basic structure shown in FIG. 1 was prototyped. As a comparative example, a pneumatic tire having a carcass ply having a high turn-up structure shown in FIG. 13 was prototyped. Each sample tire was evaluated for tire weight, uniformity and durability. Each sample tire was mounted on a test vehicle, and straight running stability, steering stability and steering response were evaluated in actual vehicle running. Each test method is as follows.

<Tire weight>
The weight per tire was measured. A result is an index which sets comparative example 1 as 100, and shows that tire weight is so small that a numerical value is small.

<Uniformity>
For each sample tire, the radial force variation RFV, which is a fluctuation component of the force in the tire radial direction at the time of rotation, is determined according to JASO C607: 2000 “Uniformity test method for automobile tires” using a tire uniformity tester. Measured. A result is an index | exponent which sets the comparative example 1 to 100, and shows that uniformity is so favorable that a numerical value is small.

<Durability>
Each sample tire was run on a drum under the following conditions, and the running distance until damage occurred was measured. A result is an index | exponent which set the comparative example 1 to 100, and shows that durability is so high that a numerical value is large.
Wearing rim: 14 x 5.5J
Internal pressure: 180 kPa
Longitudinal load: 4.66kN
Speed: 80km / h
Drum diameter: 1.7m

<Straight running stability, steering stability, steering response>
Prototype tires were mounted on a test vehicle under the following conditions, and the straight running stability, steering stability and steering response when running on a dry asphalt road test course were evaluated by sensory evaluation of the driver. A result is displayed by the 100-point method which makes Comparative Example 1 50 points, and it is so favorable that a numerical value is large.
Wearing rim: Same as above Internal pressure: 200 kPa
Test vehicle: Front-wheel drive vehicle with a displacement of 1500 cc Tire mounting position: All wheels Table 1 shows the test results.

  As a result of the test, it can be confirmed that the durability of the tire of the example is significantly improved while the straight running stability, the steering stability, and the steering response are improved as compared with the tire of the comparative example.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 5 Bead core 6 Carcass 6A Carcass ply 10 Inner layer part 11 Outer layer part 12 One side edge 13 The other side edge 20 1st carcass cord group 21 2nd carcass cord group 22 1st carcass cord 23 2nd carcass cord 23

Claims (7)

A pneumatic tire having a carcass extending in a toroidal manner between bead cores respectively arranged in a pair of bead parts,
In the tire meridian section including the tire rotation axis, the carcass includes an inner layer portion straddling between the pair of bead cores on the tire lumen side, an outer layer portion straddling between the pair of bead cores on the tire outer surface side of the inner layer portion, One side edge connecting the inner layer part and the outer layer part on the inner side in the tire radial direction of the bead core on one side, and the other side edge connecting the inner layer part and the outer layer part on the inner side in the tire radial direction of the bead core on the other side. A carcass ply having
The carcass ply includes a first carcass cord group composed of a plurality of first carcass cords arranged at an angle θ with respect to the tire equator, and a direction opposite to the first carcass cord group with respect to the tire equator and A second carcass cord group composed of a plurality of second carcass cords arranged at the same angle θ,
The first carcass cord group extends the inner layer portion from the other side edge toward the one side edge with respect to the tire circumferential direction and is folded back at the one side edge so that the outer layer portion is turned into the other side edge. While inclining with respect to the tire circumferential direction toward the side edge, and repeating the first spiral movement that is folded back at the other side edge and reaches the inner layer part,
In the second carcass cord group, the inner layer portion is inclined with respect to the tire circumferential direction from the one side edge toward the other side edge, and is folded back at the other side edge so that the outer layer portion is turned into the one side edge. A pneumatic tire characterized in that it is inclined with respect to the tire circumferential direction toward the side edge, and is folded back at the one side edge to repeat the second spiral movement reaching the inner layer portion.   2. The pneumatic tire according to claim 1, wherein each of the first carcass cord and the second carcass cord has an endless shape in which both ends are bonded.   The pneumatic tire according to claim 1 or 2, wherein the carcass ply includes a jointless ply that is continuous in the tire circumferential direction without having a seam.   The pneumatic tire according to any one of claims 1 to 3, wherein the first carcass cord and the second carcass cord are arranged line-symmetrically with respect to the tire equator.   The pneumatic tire according to any one of claims 1 to 4, wherein the carcass includes the first carcass cord group and the second carcass cord group that are knitted in the inner layer portion and the outer layer portion, respectively. A method of manufacturing a pneumatic tire including a carcass extending in a toroidal manner between bead cores respectively arranged in a pair of bead parts,
A first carcass cord group consisting of a plurality of carcass cords spirally wound at an inclination angle β with respect to the central axis, and a plurality of carcasses spirally wound at the same inclination angle β opposite to the first carcass cord group A net body forming step of forming a net body having a continuous cross-section in a circular shape by knitting the second carcass cord group consisting of cords;
A flat annular body forming step of forming a flat annular body having a long and flat cross section by folding the net body,
And a carcass forming step of forming a carcass by forming the flat annular body into a toroidal cross section.   The method for manufacturing a pneumatic tire according to claim 6, wherein the net body has a donut shape in which a central axis of the spiral winding is annularly continuous.

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