METHOD OF MANUFACTURING PNEUMATIC TIRE AND PNEUMATIC TIRE

Abstract

A method of manufacturing a pneumatic tire comprising a belt which is wound with a belt-under diameter D outside a carcass ply in a tire-radial direction, includes preparing a strip-like rubber-coated cord member where a plurality of belt cords which are arranged approximately parallel are coated with rubber and a width of the cord member in a lateral direction is D sin . The cord member is cut at the cord angle with respect to a longitudinal direction to cut out a belt forming member having a parallelogram which includes circumferential direction sides extending in a tire circumferential direction in a wound state and formed as cut portions and inclined sides extending parallel to the belt cord and defined as both side portions of the cord member. The belt forming member is wound into a circular cylindrical shape and joined the inclined sides which face each other to each other.

Claims

1. A method of manufacturing a pneumatic tire comprising a belt which includes a belt cord extending in a direction inclined with respect to a tire circumferential direction at a cord angle and which is wound with a belt-under diameter D and disposed outside a carcass ply in a tire radial direction, the method comprising: preparing a strip-like rubber-coated cord member where a plurality of belt cords which are arranged approximately parallel to each other in a longitudinal direction are coated with rubber and a width of the strip-like rubber-coated cord member in a lateral direction is D sin ; cutting the strip-like rubber-coated cord member at the cord angle with respect to a longitudinal direction to cut out a belt forming member having a parallelogram, such that the belt forming member includes: circumferential direction sides which extend in a tire circumferential direction in a wound state and are formed as cut portions; and inclined sides which extend parallel to the belt cord and are defined as both side portions of the strip-like rubber-coated cord. member in a lateral direction; winding the belt forming member into a circular cylindrical shape; and joining the inclined sides which face each other to each other to form the belt.

9.

1. The method of manufacturing a pneumatic tire according to claim 1, wherein the cord angle is not smaller than 6 degrees and not larger than 9 degrees. The method of manufacturing a pneumatic tire according to claim 1, wherein the belt-under diameter D is not smaller than 940 mm and not larger than 960 mm.

4. A pneumatic tire comprising a belt which includes a belt cord extending in a direction inclined with respect to a tire circumferential direction at a cord angle and which is wound with a belt-under diameter D and disposed outside a carcass ply in a tire radial direction, wherein the belt is formed of a belt forming member, the belt forming member is formed by being cut out from a strip-like rubber-coated cord member where a plurality of belt cords which are arranged approximately parallel to each other in a longitudinal direction and coated with rubber and has a lateral width of D sin , and in a state where being cut out from the strip-like rubber-coated cord member with respect to the longitudinal direction at the cord angle , the belt faulting member has a parallelogram in a shape including circumferential direction sides which are formed as cut portions; and inclined sides which are defined as both side portions of the strip-like rubber-coated cord member in a lateral direction and extend parallel to the belt cord, and the belt includes joint portions where the facing inclined sides are brought into contact with each other in a state where the belt forming member is wound into a circular cylindrical shape such that the circumferential direction sides extend along a tire circumferential direction.

5. The pneumatic tire according to claim 4, wherein the pneumatic tire has an aspect ratio of not larger than 70% and a nominal section width of not smaller than 365.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The foregoing and the other features of the present invent ion will become apparent from the following description and drawing of an illustrative embodiment of the invention in which:

[0025] FIG. 1 is a meridian sectional view of a pneumatic tire according to an embodiment of the present invention;

[0026] FIG. 2 is a development view of a belt layer;

[0027] FIG. 3A and FIG. 3B are views for schematically describing a method of cutting out the belt forming member from a raw fabric;

[0028] FIG. 4A and FIG. 4B are views for schematically describing a method of forming a belt by winding the belt forming member;

[0029] FIG. 5 is a schematic partial sectional view of the pneumatic tire when a load is applied to the tire;

[0030] FIGS. 6A-6E are views for describing a conventional belt forming method.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, an embodiment of the present invention is described with reference to attached drawings.

[0032] FIG. 1 shows a rubber pneumatic tire (hereinafter referred to as tire) 1 according to an embodiment of the present invention. The tire 1 is a pneumatic radial tire for a heavy load used for a vehicle such as a truck or a bus. Further, the tire 1 is a low-profile tire having an aspect ratio of not larger than 70%. An aspect ratio is defined as a ratio of a maximum tire-section height Ht to a maximum tire-section width Wt. Specifically, a size of the tire 1 in this embodiment is 445/50R22.5 (expressed in accordance with ISO standard).

[0033] The tire 1 includes a tread portion 2, a pair of side portions 4, and a pair of bead portions 6. The bead portions 6 are respectively formed on inner edge portions of the side portions 4 in a tire-radial direction (edge portions of the side portions 4 opposite to the tread portion 2). A carcass 8 is arranged between the pair of bead portions 6. An inner liner (not shown in the drawing) is arranged in an innermost peripheral surface of the tire 1. A belt layer 10 is arranged between the carcass 8 and a tread surface of the tread portion 2. In other words, in the tread portion 2, the belt layer 10 is arranged at an outer side of the carcass 8 in the tire-radial direction. As described later in detail, in this embodiment, the belt layer 10 includes five belts 11 to 15.

[0034] The bead portion 6 includes a bead core 22, a bead filler 24, and a chafer 26. Around the bead core 22, an end portion of the carcass 8 in atire-width direction is wound up from an inner side to art outer side in a tire-width direction along the bead filler 24. The chafer 26 is arranged around the bead filler 24 so as to be arranged adjacently to an outer side of the end portion of the carcass 8.

[0035] Referring to FIGS. 1 and 2, the carcass 8 in this embodiment is formed of one carcass ply, and is formed of a plurality of carcass cords 8a arranged parallel to each other and coated by a rubber layer. Each carcass cord 8a is arranged so as to extend in the tire-radial direction, and has an angle 0 with respect to a tire-circumferential direction (cord angle) set to 90 degrees. In FIGS. 1 and 2, symbol Ce indicates a center line in the tire-width direction. The direction along which the center line Ce extends is a tire-radial direction. While the carcass cord 8a in this embodiment is made of steel, the carcass cord 8a can be made of organic fibers.

[0036] Referring to FIGS. 1 and 2, the belt layer 10 in this embodiment includes five belts arranged in an overlapping manner. These belts include a buffer belt 11, a first main working belt 12, a reinforcement belt 13, a second main working belt 14, and a protection belt 15.

[0037] The buffer belt 11 is arranged adjacently to an outer side of the carcass 8 in the tire-radial direction. The first main working belt 12 is arranged adjacently to an outer side of the buffer belt 11 in the tire-radial direction. The second main working belt 14 is arranged at an outer side of the first main working belt 12 in the tire-radial direction. The reinforcement belt 13 is arranged between the first main working belt 12 and the second main working belt 14. That is, the reinforcement belt 13 is arranged adjacently to the outer side of the first main working belt 12 in the tire-radial direction, and is also arranged adjacently to an inner side of the second main working belt 14 in the tire-radial direction. The protection belt 15 is arranged adjacently to an outer side of the second main working belt 14 in the tire-radial direction.

[0038] Main functions of the first and second main working belts 12 and 14 are to apply a binding force in the tire-radial direction to the carcass 8 (with a cord angle 0 being set to 90 degrees). A main function of the reinforcement belt 13 is to compensate for the shortage in a binding force in the tire-radial direction which is applied to the tire 1 by the first and second main working belts 12 and 14. A main function of the protection belt 15 is to enhance external damage resistance of the tire 1 by protecting the first and second main working belts 12 and 14. A main function of the buffer belt 11 is to enhance impact resistance of the tire 1.

[0039] Each of these belts 11 to 15 is formed of a plurality belt cords 11a, 12a, 13a, 14a, and 15a arranged parallel to each other with extending in a direction inclined with respect to a tire circumferential direction and coated by a rubber layer.

[0040] Referring FIG. 2, inclination angles (cord angles) 1 to 5 of the belt cords 11a to 15a belts 11 to 15 forming the belt layer 10 will be described. In the description hereinafter, regarding the cord angles 1 to 5, a direction along which the belt cords 11a to 15a extend rightward and away from the center line Ce in the tire-width direction when an arrow A in FIG. 2 is set as a reference direction can be referred to as right upward direction. Similarly, a direction along which the belt cords lla to 15a extend leftward and away from the center line Ce in the tire-width direction when the allow A in FIG. 2 is set as the reference direction can be referred to as left upward direction.

[0041] In this embodiment, the cord angle 2 of the belt cord 12a of the first main working belt 12 is set to 17 degrees (right upward direction). The cord angle 2 can be set to any value which falls within a range of 2010 degrees, and can preferably be set to a value which falls within a range of 175 degrees.

[0042] In this embodiment, the cord angle 4 of the belt cord 14a of the second main working belt 14 is set to 17 degrees (left upward direction). The cord angle 4 can be set to a value which falls within a range of 2010 degrees, and can preferably be set to a value which falls within a range of 175 degrees.

[0043] The cord angles 2 and 4 of the first and second main working belts 12, 14 are set so that the belt cords 12a and 14a extend in different directions with respect to the center line Ce in the tire-width direction. That is, one of the cord angles 2 and 4 is set so that the belt cords extend in the right upward direction, and the other of them is set so that the belt cords extend in the left upward direction.

[0044] The cord angle 3 of the belt cord 13a of the reinforcement belt 13 is set to 7 degrees (left upward direction) in this embodiment. The cord angle 3 can be set to a value which falls within a range of not smaller than 6 degrees and not larger than 9 degrees.

[0045] The cord angle 1 of the belt cord 11a of the buffer belt 11 is set to 65 degrees in this embodiment. The cord angle 1 can be set to a value which falls within a range of 6015 degrees.

[0046] The cord angle 5 of the belt cord 15a of the protection belt 15 is set to 20 degrees in this embodiment. The cord angle 5 can be set to a value which falls within a range of 2010 degrees.

[0047] Numerical values (including upper and lower limit values of a numerical value range) of the cord angles 1 to 5 can include substantially unavoidable errors, and are not necessarily geometrically precise values as long as that functions required for the belts 11 to 15 are satisfied. This is also applied to the cord angle 0 of the carcass cords 8a.

[0048] The cord angles 1 to 5 of the belts 11 to 15 can be coordinated as shown in the following Table 1.

TABLE-US-00001 TABLE 1 Embodiment Settable range of angle Buffer belt 65 degrees 60 15 degrees (right upward (right upward direction) direction) First main working belt 17 degrees 20 10 degrees (right upward (17 5 degrees) direction) (right upward direction) Reinforcement belt 7 degrees Not smaller than 6 degrees (left upward and not larger than direction) 9 degrees Second main working belt 17 degrees 20 10 degrees (left upward (17 5 degrees) direction) (left upward direction) Protection belt 20 degrees 20 10 degrees (right upward (right upward direction) direction)

[0049] Next, a method of forming a belt is described with reference to FIG. 3 and FIG. 4 by taking the reinforcement belt 13 as an example. Firstly, referring to FIG. 3A, a raw fabric(strip-like rubber-coated cord member) 50 where a plurality of belt cords 13a which are arranged approximately parallel to each other in a longitudinal direction are coated by rubber is prepared. The raw fabric 50 is formed such that a width X3 of the raw fabric in a lateral direction becomes D sin 3 when a belt-under diameter of the reinforcement belt 13 is D.

[0050] Next, referring to FIG. 3B, in a cutting step, the raw fabric 50 is conveyed in the longitudinal direction by a predetermined feed amount F and, thereafter, the raw fabric 50 is cut in a direction inclined with respect to the longitudinal direction of the raw fabric 50 at a cord angle 3. Cutting is performed by a cutter 60 capable of moving in a direction inclined with respect to the longitudinal direction of the raw fabric 50 at the cord angle 3. Thereafter, by sequentially repeating the conveyance and the cutting of the raw fabric 50, a reinforcement belt forming member 130 having a parallelogram is cut out from the raw fabric 50.

[0051] The reinforcement belt forming member 130 has first and second sides 131, 132 which are formed by cutting, and third and fourth sides 133, 134 which correspond to both side portions of the raw fabric 50 in a lateral direction, thus having a parallelogram where an angle made by the first side 131 and the fourth side 134 and an angle made by the second side 132 and the third side 133 define the cord angle 3.

[0052] Next, referring to FIG. 4A, as a forming step, the reinforcement belt forming members 130 is wound around a forming drum 70 (indicated by an imaginary line only in FIG. 4A) such that the first and second sides 131, 132 extend parallel to a tire circumferential direction (drum circumferential direction), and the third and fourth sides 133, 134 which face each other are brought into contact with each other and are joined to each other. With such processing, a circular cylindrical-shaped reinforcement belt 13 shown in FIG. 4B is formed.

[0053] That is, in a wound state, the reinforcement belt forming members 130 is configured such that the first and second sides 131, 132 form the circumferential direction sides extending in the tire circumferential direction, and a length thereof is a belt-under circumferential direction length D of the reinforcement belt 13, and the third and fourth sides 133, 134 form the inclined sides extending in a direction inclined with respect to the tire circumferential direction by a cord angle 3.

[0054] Here, a raw fabric width X3 of the raw fabric 50 is set to sin 3 and hence, a length of each of the first and second sides 131, 132 which form cut portions formed by cutting the raw fabric 50 in a direction inclined with respect to the longitudinal direction of the raw fabric 50 by a cord angle 3 becomes D. That is, by winding the first and second sides 131, 132 around the forming drum 70 by one turn, the reinforcement belt 13 haying a belt-under diameter D is formed. Further, a feed amount P of the reinforcement belt 13 is set to W/sin 3 and hence, a distance between the first side 131 and the second side 132 becomes a belt width W.

[0055] With respect to the reinforcement belt 13 formed in this manner, in the cutting step, it is unnecessary to form short members as primary members for forming the reinforcement belt forming member 130 and hence, it is unnecessary to connect the plurality of short members to each other. Therefore, cut joints which are formed in the cutting step do not exist in the reinforcement belt 13, and only the forming joints 130A in the forming step exist. Accordingly, the number of joint portions in the reinforcement belt 13 can be decreased and hence, the uniformity of the tire can be enhanced. Further, the cut joints become unnecessary and hence, the belt can be formed efficiently whereby the productivity of the tire can be enhanced.

[0056] The belt-under diameter D is preferably not smaller than 940 mm and not larger than 960 mm. By setting the belt-under diameter D to a value which falls within such a range, it is possible to suppress the excessive increase of the width of the raw fabric 50 in a lateral direction and hence, it is possible to form the belt more efficiently.

[0057] Although the description has been made by taking the reinforcement belt 13 having a relatively small cord angle as an example, other belts 11, 12, 14, 15 in the belt layer 10 can be also formed suitably by the method of the present invention. Table 2 shows main data other than cord angles of the belts 11 to 15 according to this embodiment. Table 3 shows main data of raw fabrics and belt forming members for forming these belts 11 to 15.

TABLE-US-00002 TABLE 2 Cord thickness including coating Cord rubber End Raw diameter thickness number Belt width material (mm) (mm) (EPI) W (mm) Buffer belt Steel 1.1 1.7 12 W1 = 345 First main Steel 1.4 2.6 12 W2 = 370 working belt Reinforcement Steel 1.1 1.7 12 W3 = 290 belt Second main Steel 1.4 2.6 12 W4 = 325 working belt Protection belt Steel 1.1 1.9 9 W5 = 295

TABLE-US-00003 TABLE 3 Feed Cutting Belt-under Raw fabric width amount F length diameter X (mm) (mm) W/ (mm) Cord angle D (mm) Dsin sin D Buffer belt 65 degrees 941 2680 381 2957 First main working belt 17 degrees 945 868 1266 2968 Reinforcement belt 7 degrees 950 364 2380 2985 Second main working 17 degrees 953 876 1112 2995 belt Protection belt 20 degrees 959 1030 863 3012

[0058] As shown in Table 3, the belt-under diameters of the belts 11 to 15 are set to values not smaller than 940 mm and not larger than 960 mm, and cord angles 1 to 5 are made to largely differ from each other, The buffer belt 11 has a large cord angle 1 and hence, a raw fabric width X1 of the buffer belt 11 is largely increased to 2680 mm. Cord angles 2, 4 of the first and second main working belts 12, 14 are each set to 17 degrees so that the cord angles 2, 4 are smaller than the cord angle 1 of the buffer belt 11. Accordingly, raw fabric widths X2, X4 each become approximately 870 mm respectively. In the same manner, a cord angle 5 of the protection belt 15 becomes 20 degrees, and a raw fabric width X5 becomes approximately 1000 mm.

[0059] To the contrary, the cord angle 3 of the reinforcement belt 13 is set to 7 degrees. That is, the cord angle 3 is smaller than cord angles of other belts 11, 12, 14, 15 and hence, a raw fabric width X3 is also small, that is, approximately 360 mm. Accordingly, the smaller the cord angle, the smaller the raw fabric width X becomes and hence, the raw fabric 50 can be easily formed and, at the same time, the handling of the raw fabric 50 becomes easy so that the belt can be formed more efficiently.

[0060] On the other hand, a feed amount F in the forming the reinforcement belt 13 is increased compared to feed amounts P in forming the other belts 11, 12, 14, 15. In this embodiment, the feed amount F is also a length of a forming joint in the forming step. That is, the forming joint 130A of the reinforcement belt 13 extends in a direction inclined with respect to the tire circumferential direction by a cord angle 3. Accordingly, when the cord angle 3 is small, a length of the forming joint 130A is increased. Accordingly, when the cord angle is excessively small, a length of a joint portion is excessively increased and hence, it is not easy to join the inclined sides to each other with high accuracy over the length of the forming joint. Further, when the cord angle is small, in the cutting step, the raw fabric 50 is cut in an inclined manner with respect to the belt cord at an excessively acute angle and hence, it is not easy to cut the raw fabric 50.

[0061] As has been described heretofore, to carry out the present invention more efficiently, it is preferable to apply the present invention to a belt where a cord angle is set to a value of not smaller than 6 degrees and not larger than 9 degrees. In this embodiment, an advantageous effect of the present invention can be acquired more effectively with respect to the reinforcement belt 13. However, by applying the present invention also to the other belts 11, 12, 14, 15, cut joints formed in the cutting step become unnecessary and hence, the uniformity of the tire can be enhanced while the belt is formed efficiently.

[0062] As shown in Table 2, in this embodiment, a width W4 (325 mm) of the second main working belt 14 which is arranged relatively outer side in the tire-radial direction is set narrower than a width W2 (370 mm) of the first main working belt 12 which is arranged relatively inner side in the tire-radial direction.

[0063] A width W3 of the reinforcement belt 13 is set to a value equal to or wider than 50% of a maximum tire-section width Wt (W30.5 Wt). In this embodiment, the maximum tire-section width Wt is a value set under conditions where the tire 1 is mounted on a predetermined rim (a rim 31 is schematically shown in FIG. 1), the tire 1 is filled with air until an inner pressure reaches a predetermined internal pressure (830 kPa which is an internal pressure determined by the Tire and Rim Association, Inc (TRA)), and the tire 1 is in an unloaded state. The width W3 of the reinforcement belt 13 is set narrower than a width of either one of the first and second main working belts 12 and 14 having a narrower width than the other (W3<W2, W4). In this embodiment, the width W3 of the reinforcement belt 13 is set to 290 mm. Accordingly, the width W3 of the reinforcement belt 13 is equal to or wider than 50% of a maximum tire-section width Wt (440 mm) under the above-mentioned conditions, and is narrower than the width W4 (325 mm) of the second main working belt 14 having a narrower width.

[0064] The cord angle 3 of the reinforcement belt 13 is not smaller than 6 degrees and not larger than 9 degrees, instead of a small angle of not smaller than 0 degrees to not more than 5 degrees (an angle which can be substantially regarded as 0 degrees or an angle close to 0 degrees). Such configuration can prevent a binding force in a tire-radial direction generated by a reinforcement belt 13 from becoming excessively large, and therefore the excessively large deformation of the tire in the tire-width direction can be suppressed. Since the excessively large deformation of the tire in the tire-width direction can be suppressed, the distortion generated in the bead portion 6 can be suppressed, and therefore bead durability (resistance against the generation of a defect such as separation in the bead portion can be enhanced.

[0065] As conceptually shown in FIG. 5, in a loaded state (a state where the tire 1 is mounted on a vehicle), belt cords 13a of the reinforcement belt 13 are bent in regions (symbols C) of a tread surface of the tread portion 2 in front of and behind a road contact surface 2a in the rotational direction of the tire indicated by an arrow B. The smaller cord angle 3, the more conspicuous the bending of the belt cords 13a becomes. By setting the cord angle 3 to a value not smaller than 6 degrees and not larger than 9 degrees, compared to a case where the cord angle 3 is set to a small angle such as an angle not smaller than 0 degrees and not larger than 5 degrees, bending of the belt cord 13a of the reinforcement belt 13 in the vicinity of the road contact surface 2a can be alleviated, and therefore cord breakage can be effectively prevented.

[0066] As described above, the width W3 of the reinforcement belt 13 is set narrower than the width W4 of the second main working belt 14 which is narrower one of the first and second main working belts 12, 14. Such configuration can also effectively prevent cord breakage of the belt cord 13a of the reinforcement belt.

[0067] As described above, the reinforcement belt 13 is arranged between the first main working belt 12 and the second main working belt 14. Due to such an arrangement, the reinforcement belt 13 is protected by the first and second main working belts 14, and therefore cord breakage of the belt cord 13a of the reinforcement belt 13 caused due to bending of the cord in the vicinity of the road contact surface 2a (symbols C in FIG. 3) can be effectively prevented.

[0068] Due to these reasons, cord breakage of the reinforcement belt 13 can be effectively prevented.

[0069] By setting the cord angle 3 of the reinforcement belt 13 to a value not smaller than 6 degrees and not larger than 9 degrees, an effect of suppressing a growth of the tire 1 in the radial direction is reduced compared to the case where the cord angle 3 is set to a value not smaller than 0 degrees and not larger than 5 degrees. However, the cord angle 3 of the reinforcement belt 13 is 9 degrees at maximum, and therefore there is no possibility that a binding force in the tire-radial direction is excessively reduced. Further, as described above, the width W3 of the reinforcement belt 13 is equal to or wider than 50% of a maximum tire-section width Wt. That is, a width of the reinforcement belt 13 is not narrow but is sufficiently wide. Due to these reasons, the tire 1 can ensure a required effect of suppressing a growth of the tire 1 in the radial direction. Further, the tire can acquire a sufficient force for holding a shape of the tread portion 2 so that distortion at the end portion of the belt can be reduced whereby the tire can ensure required belt durability. The width W3 of the reinforcement belt 13 is narrower than a width of the narrower one of the first and second main working belts 12 and 14 (widths W2, W4), Accordingly, the distortion generated in the reinforcement belt 13 can be reduced.

[0070] As described above, according to the tire 1 of the present embodiment, bead durability can be enhanced while an effect of suppressing a growth of the tire 1 in the radial direction and belt durability are also ensured,

[0071] The tire according the present invention is favorably applicable to a pneumatic tire so-called super single tire) having an aspect ratio of not larger than 70% and a nominal section width of not smaller than 365. The tire according to the present invention is also applicable to a pneumatic tire having a small aspect ratio and falling outer side a range of a pneumatic radial tire for heavy load.