# Patent

## Title
Pneumatic tire with monofilament metallic belt cords

## Abstract

A pneumatic tire containing a belt disposed radially outside a carcass in a tread portion, the belt including two cross plies of monofilament metallic cords laid at angles of from 15 to 30 degrees with respect to the circumferential direction of the tire, each monofilament cord composed of a waved single filament, the filament having a circular sectional shape having a diameter in the range of from 0.40 to 0.50 mm, or alternatively a non-circular sectional shape having an aspect ratio in the range of from 0.65 to 0.95 and a cross-sectional area in the range of 0.09 to 0.20 sq.mm.

## Background
This application is a divisional of application Ser. No. 09/612,377, filed on Jul. 7, 2000, now U.S. Pat. No. 6,520,232, the entire contents of which are hereby incorporated by reference and for which priority is claimed under 35 U.S.C. § 120.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire with an improved belt structure being capable of reducing the tire weight without sacrificing the steering stability, ride comfort, durability and the like.
2. Description of Related Art
In pneumatic tires especially radial tires, a tread reinforcing belt, which is composed of cords each made of twisted steel filaments, is widely used.
In recent years, on the other hand, there is a great demand for a lightweight tire to save energy.
In order to reduce the amount of steel in a tread reinforcing belt, a trial has been made using a relatively thick steel filament as a cord because such a monofilament cord has a less amount of steel than a multifilament cord when the bending rigidity of the monofilament cord is set at the same degree as the multifilament cord. However, the elongation of such a monofilament cord when loaded is very small and liable to break. Thus, the durability of the belt is not good, and the cornering force becomes insufficient and the steering stability is lowered. If the thickness is increased in order to avoid breaking, the bending rigidity suddenly increases, and ride comfort is greatly decreased. Thus, it is very difficult to use a monofilament cord in a tread reinforcing belt.
SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to provide a pneumatic tire, in which a filament having a specific size which is waved in a specific manner is used as a belt cord to achieve a weight reduction without sacrificing the durability, ride comfort, steering stability and the like.
According to the present invention, the pneumatic tire includes a belt disposed radially outside a carcass in a tread portion, the belt containing two cross plies of monofilament metallic cords laid at angles of from 15 to 30 degrees with respect to the circumferential direction of the tire, each monofilament cord composed of a waved, single filament, the filament having a circular sectional shape with a diameter in the range of from 0.40 to 0.50 mm, or alternatively a non-circular sectional shape having an aspect ratio in a range of from 0.65 to 0.95 and a cross-sectional area in a range of 0.09 to 0.20 sq.mm.



DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings, wherein:
FIG. 1 is a cross sectional view of a pneumatic tire according to the present invention;
FIG. 2 is a cross sectional view of a pneumatic tire according to the present invention;
FIG. 3 is a cross sectional view of an example of the breaker;
FIG. 4 is a diagram for explaining the spiral waving nature of the cord thereof;
FIG. 5 is a cross sectional view of another example of the breaker;
FIG. 6 is a diagram for explaining the two-dimensional waving nature of the cord thereof;
FIG. 7 is a cross sectional view of still another example of the breaker;
FIG. 8 is a perspective view of the cord thereof showing its two-dimensional waving nature;
FIG. 9 is a cross sectional view thereof;
FIG. 10 is a cross sectional view of still another example of the breaker;
FIG. 11 is a diagram for explaining the orthogonal waving of the cord thereof; and
FIG. 12 is a diagram for explaining a method of waving the cord shown in FIG. 11.



DETAILED DESCRIPTION OF THE INVENTION
Pneumatic tire 1 according to the present invention includes a tread portion 2, a pair of axially spaced bead portions 4 each with a bead core 5 therein, a pair of sidewall portions 3 extending therebetween, a carcass 6 extending between the bead portions 4, and a belt 7 disposed radially outside the carcass 6 in the tread portion 2. In FIG. 1, the pneumatic tire 1 according to the present invention is a radial tire for passenger cars, in which the aspect ratio (tire section height TH/section width TW) is 0.7. In FIG. 2, the pneumatic tire 1 according to the present invention is also a radial tire for passenger cars with an aspect ratio of 0.65.
The carcass 6 includes at least one ply of cords arranged radially at an angle of from 75 to 90 degrees with respect to the circumferential direction of the tire and extending between the bead portions 4 through the tread portion 2 and sidewall portions 3 and turned up around the bead core 5 in each bead portion 4 to form a pair of turned up portions 6B and a main portion 6A therebetween. In the embodiments shown in FIGS. 1 and 2, the carcass 6 is composed of two plies 6a and 6b both turned up around the bead cores 5.
For the carcass cords, organic fiber cords made of twisted organic fibers and multifilament steel cords made of twisted steel filaments can be used. For the material of the organic fibers, aliphatic polyamide such as Nylon, rayon, aromatic polyamides, polyvinylalcohol (for example, VINYLON), polyesters, such as polyethylene terephthalate, polyethylene naphthalate, e.g., polyethylene 2-6 naphthalate and the like can be used. The bead portions 4 are each provided between the carcass turned up portion 6B and main portion 6A with a bead apex 8. The bead apex 8 is made of hard rubber tapering radially outward and extending radially outward from the bead core 5.
** Belt **
The belt includes a breaker 7 and optionally a band 9. In FIG. 1, the band 9 is not provided, but it is possible to provide a band 9. In FIG. 2, the band 9 is provided, but it is possible not to provide the band 9.
** Band **
The band 9 is disposed radially outside the breaker 7 and made of parallel cords or alternatively windings of at least one cord, wherein the cord angle is a small value of less than 10 degrees, usually less than 5 degrees with respect to the circumferential direction of the tire.
The band 9 can be formed as a so called edge band, namely, a band composed of a pair of axially spaced pieces disposed on the axial edges of the breaker, or a so called full band disposed over the breaker, or a combination of the full band and edge band.
For the band cord 11, an aliphatic polyamide (such as nylon) fiber cord, aromatic polyamide fiber cord, polyvinylalcohol (for example VINYLON) fiber cord, polyethylene terephthalate (such as polyester) fiber cord, polyethylene naphthalate (such as polyethylene 2-6 naphthalate) fiber cord, and a hybrid cord of aliphatic polyamide fiber and aromatic polyamide fiber can be used.
In order to increase the production efficiency, the band 9 can be formed by spirally winding a tape of rubberized parallel band cords 11. Preferably, the tape 12 has a width of from 6 to 15 mm, and several cords 11 are embedded along the length thereof.
** Breaker **
The breaker 7 comprises at least two cross breaker plies 7a and 7b of parallel cords 10 laid at angles of from 15 to 30 degrees with respect to the circumferential direction of the tire.
According to the present invention, the breaker cords 10 are monofilament metallic cords, that is, each cord 10 is compose of a single steel filament, and the filament is waved two dimensionally or three-dimensionally.
** First Breaker Example **
FIG. 3 shows a first example of the breaker 7. FIG. 4 shows a first example of the breaker cord 10 which is composed of a filament 10A having a circular sectional shape whose diameter D is in the range of from 0.40 to 0.50 mm. In this example, the filament 10A is waved spirally along the length thereof. The wave pitch P or spiral pitch is in the range of not less than 14.0 mm. The wave height H is in the range of from 0.002 to 0.02 times the pitch P.
The rupture strength of the cord 10 is set in the range of not less than 3300 N/sq. mm.
Each breaker ply 7a, 7b has a rigidity index BM set in the range of from 100 to 300.
Here, the rigidity index BM is defined as the product M×N×L of the bending rigidity M (g cm) of a cord 10, the cord count N per 5 cm width of the ply and the distance L (cm) between the cord center J of the ply 7a and that of the ply 7b. 
** Second Breaker Example **
FIG. 5 shows a second example of the breaker 7. FIG. 6 show a second example of the breaker cord 10 which is composed of a filament 10B having a circular sectional shape whose diameter D is in the range of from 0.40 to 0.50 mm. In this example, the filament 10B is waved substantially on a surface parallel with the face of the ply like a sine curve. The wave pitch P or one cycle of the wave is in the range of not less than 14.0 mm. The wave height H is in the range of from 0.002 to 0.02 times the pitch P.
Each breaker ply 7a, 7b has a rigidity index BM set in the range of from 100 to 300.
* Comparison Test
Test tires of size 175/70R13 (standard rim: 5JX13) having the structure shown in FIG. 1 and specifications shown in Table 1 were made and tested for the tire weight, durability, steering stability, ride comfort and tire strength. The test results are shown in Table 1.
(I) Tire Weight
The weight of a tire is indicated by an index based on Prior art tire (Pr.) being 100. The smaller the index, the lighter the weight.
(2) Durability
A 2000 cc passenger car provided on all the wheels with test tires was run 500 laps in a figure-8 test course having diameters of 14 meters, and then the tires were cut-open inspected to count breakages of the cords. (Tire pressure 200 kPa) The number of breakages is indicated by an index based on Prior art tire (Pr.) being 100. The smaller the index, the better the durability.
(3) Steering Stability
During running the passenger car on a dry asphalt road in a tire test course, the test driver evaluated the steering response, rigidity and road grip into ten ranks. The higher the value, the better the steering stability.
(4) Ride Comfort
During running the passenger car on dry rough roads including washboard asphalt road, stone paved road and gravel road, harshness, thrust and damping were evaluated into ten ranks by the test driver. The larger the value, the better the ride comfort.
(5) Tire Strength
According to the Japanese Industrial Standard JIS-D4230, a plunger test was made and the breaking energy was measured under a standard pressure of 200 kPa. The result is indicated by an index based on Prior art tire (Pr.) being 100. The larger the index, the better the strength.


















TABLE 1





Tire
Pr. A1
Ref. A1
Ref. A2
Ref. A3
Ref. A4
Ex. A1
Ex. A2
Ex. A3
Ex. A4
Ex. A5
Ex. A6







Breaker cord
multi
multi
multi
multi
multi
mono
mono
mono
mono
mono
mono


Number of filament
5
5
5
5
5
1
1
1
1
1
1


Filament Dia. D (mm)
0.25
0.38
0.53
0.42
0.42
0.4
0.42
0.42
0.42
0.45
0.5


Waving
—
spiral
spiral
spiral
spiral
spiral
2-D wave
spiral
spiral
spiral
spiral


Wave pitch P (mm)
—
18
25
8
20
19
20
20
20
21
24


Wave height H (mm)
—
0.16
0.22
0.18
0.45
0.17
0.18
0.18
0.18
0.19
0.21


Bending rigidity M (g cm)
28
29
89
42
42
35
42
42
42
56
84


Cord strength (N)
601
375
684
432
418
408
438
444
499
501
608


Strength/section area (N/sq. mm)
2450
3300
3100
3117
3016
3250
3160
3200
3600
3150
3100


Cord count N/5 cm ply width
30
42
32
42
42
46
42
42
42
38
32


Distance L (cm)
0.12
0.095
0.115
0.1
0.1
0.097
0.1
0.1
0.1
0.105
0.11


Rigidity index BM
101
115
328
176
176
156
176
176
176
223
296


Tire weight
100
89
97
92
92
92
92
92
92
93
93


Durability
100
160
104
220
200
80
60
40
40
52
92


Steering stability
7
4
9
8
8
8
8
8
7
9
9


Ride comfort
7
8
4
8
8
8
8
8
9
7
6


Tire strength
100
87
121
101
97
104
102
103
116
106
108









In the first and second examples of the breaker:
If the diameter D is less than 0.40 mm, as the rigidity of the cord 10 decreases, it becomes difficult for the belt to provide an essential cornering power and steering stability. If the diameter D is more than 0.50 mm, the residual stress of the cord increases, and the cord durability decreases. In addition, if the diameter D is more than 0.50 mm, as the rigidity of the filament becomes very high for the belt cord, it is necessary to magnify the wave to decrease the rigidity. If the wave is magnified, however, the durability, strength and resistance to fatigue are decreased. Further, as the cords approach each other partially and non-uniformly, a rubber separation failure is liable to occur. If the wave pitch P is less than 14 mm, the cord durability is easily decreased by cord deformation during running.
If the wave height H is more than 0.02 times the pitch P, the cord strength and fatigue resistance are liable to decrease as the filament is thick. In case of FIG. 3, as the rubber thickness (t) between the cords decreases accordingly, a ply separation failure is be liable to occur.
If the wave height H is less than 0.002 times the pitch P and/or the pitch P is more than 50 mm, the effects of the waving can not be obtained.
If the breaker rigidity index BM is less than 100, the belt rigidity becomes insufficient. If the breaker rigidity index BM is more than 300, the belt rigidity becomes excessively high and ride comfort is deteriorated.
** Third Breaker Example **
FIG. 7 shows a third example of the breaker 7. FIGS. 8 and 9 show a third example of the breaker cord 10 which is composed of a filament 10C having a rectangular sectional shape whose minor axis and major axis lie along the tire radial direction and a normal direction thereto, respectively. Here, the “rectangular shape” means a rounded rectangle whose corners are chamfered rather than a rectangle having angled corners, and thus includes a shape resembling an oval. The cross-sectional area S of the filament 10C is in the range of 0.09 to 0.20 sq.mm. The aspect ratio H/W of the filament 10C is in the range of from 0.65 to 0.95.
In this example, the filament 10C is waved by bending zigzag on a surface normal to the major axis, that is, normal to the face of the ply. Thus, the waving is two-dimensional. The wave pitch P1 is in the range of not less than 5.0 mm, preferably from 10.0 to 50 mm. The wave height h1 is in the range of from 0.002 to 0.02 times the wave pitch P1.
Each ply 7a, 7b is formed such that the product S×N of the cross-sectional area S (sq.mm) of a filament 10C or a cord and the cord count N per 5 cm width of the ply is in the range of from 4.0 to 6.5.
* Comparison Test
Test tires of size 175/70R13 having the structure shown in FIG. 1 and specifications shown in Table 2 were made and tested for the tire weight (1), durability (2), steering stability (3) and ride comfort (4) as explained as above. The test results are shown in Table 2.















TABLE 2







Tire
Pr. B1
Ref. B1
Ref. B2
Ref. B3
Ref. B4
Ref. B5
Ex. B1
Ex. B2





Breaker cord
multi
mono
mono
mono
mono
mono
mono
mono


Number of filament
5
1
1
1
1
1
1
1


Filament


Sectional shape
circle
circle
circle
rect.
rect.
rect.
rect.
rect.


H (mm)
0.25
0.38
0.42
0.41
0.3
0.37
0.34
0.37


W (mm)
0.25
0.38
0.42
0.42
0.5
0.44
0.4
0.44


H/W
1
1
1
0.98
0.6
0.84
0.85
0.84


Waving
—
spiral
spiral
2-D wave
2-D wave
2-D wave
2-D wave
2-D wave


P1 (mm)
—
18
20
8
20
20
19
5


h1 (mm)
—
0.16
0.18
0.18
0.18
0.45
0.18
0.05


P1/h1
—
0.009
0.009
0.023
0.009
0.023
0.009
0.01


Sectional area S (sq. mm)
0.2454
0.1134
0.1385
0.1385
0.1385
0.1385
0.1134
0.1385


Cord strength (N)
638
352
416
415
388
390
346
410


Strength/section area
2600
3100
3000
2995
2800
2816
3050
2960


(N/sq. mm)


Cord count/5 cm ply width
35
40
40
40
40
40
40
40


Tire weight
100
91
93
93
93
93
91
93


Durability
100
160
40
43
200
220
96
91


Steering stability
7
4
8
8
9
9
8
9


Ride comfort
7
8
8
8
9
8
10
10



















Tire
Ex. B3
Ex. B4
Ex. B5
Ex. B6
Ex. B7
Ex. B8
Ex. B9







Breaker cord
mono
mono
mono
mono
mono
mono
mono



Number of filament
1
1
1
1
1
1
1



Filament



Sectional shape
rect.
rect.
rect.
rect.
rect.
rect.
rect.



H (mm)
0.37
0.37
0.37
0.39
0.32
0.4
0.44



W (mm)
0.44
0.44
0.44
0.42
0.48
0.47
0.52



H/W
0.84
0.84
0.84
0.93
0.67
0.85
0.85



Waving
2-D wave
2-D wave
2-D wave
2-D wave
2-D wave
2-D wave
2-D wave



P1 (mm)
20
20
35
20
20
21
24



h1 (mm)
0.18
0.38
0.3
0.18
0.18
0.19
0.21



P1/h1
0.009
0.019
0.009
0.009
0.009
0.009
0.009



Sectional area S (sq. mm)
0.1385
0.1385
0.1385
0.1385
0.1385
0.159
0.1963



Cord strength (N)
410
402
423
413
402
469
569



Strength/section area
2960
2900
3055
2980
2900
2950
2900



(N/sq. mm)



Cord count/5 cm ply width
40
40
40
40
40
36
30



Tire weight
93
93
93
93
93
94
95



Durability
38
102
35
37
110
53
82



Steering stability
10
10
10
9
10
10
10



Ride comfort
10
10
10
9
10
9
8










**Fourth Breaker Example **
FIG. 10 show a fourth example of the breaker. FIG. 11 shows a fourth example of the breaker cord 10 which is composed of a filament 10D having a rectangular sectional shape whose minor axis and major axis lie along the tire radial direction and a normal direction thereto, respectively. Here, the “rectangular shape” is used in the same sense as in the third example. The cross-sectional area S of the filament 10D is in the range of 0.09 to 0.20 sq.mm. The aspect ratio H/W of the filament 10D is in the range of from 0.65 to 0.95.
In this example, the filament 10D is waved by bending zigzag on a surface normal to the major axis, that is, normal to the face of the ply. (hereinafter, minor-axis waving X1)
Further, the filament 10D is waved by bending zigzag on a surface normal to the minor axis, that is, parallel to the face of the ply. (hereinafter, major-axis waving X2) That is, the filament 10D is waved on the two orthogonal surfaces. (hereinafter, orthogonal waving)
In the minor-axis waving X1, the wave pitch P1 is set in the range of not less than 3.0 mm, and the waving height h1 is set in the range of from 0.002 to 0.05 times the wave pitch P1.
In the major-axis waving X2, the wave pitch P2 is set in the range of not less than 5.0 mm, and the waving height h2 is set in the range of from 0.002 to 0.05 times the wave pitch P2.
The pitches P1 and P2 are substantially the same in FIG. 11, but they can be different from each other. Preferably, the pitches P1 and P2 are set in the range of from 10.0 to 50 mm.
Each ply 7a, 7b is formed such that the product S×N of the cross-sectional area S (sq.mm) of a filament 10D or a cord and the cord count N per 5 cm width of the ply is in the range of from 4.0 to 6.5.
* Comparison Test
Test tires of size 195/65R15 having the structure shown in FIG. 2 and specifications shown in Table 3 were made and tested for noise (6) in addition to the above-explained tire weight (1), durability (2), steering stability (3) and ride comfort (4). The test results are shown in Table 3.
(6) Noise
During coasting the passenger car on a smooth asphalt road at a speed of 50 km/h, the noise level in dB(A) was measured near the driver's ears. The results are indicated by an index based on Prior art tire (Pr.Cl) being 100. The smaller the index, the better the noise.

















TABLE 3







Tire
Ex. C3
Ex. C4
Ex. C5
Ex. C6
Ex. C7
Ex. C8
Ex. C9
Ex. C10
Ex. C11
Ex. C12





Breaker cord
mono
mono
mono
mono
mono
mono
mono
mono
mono
mono


Number of filament
1
1
1
1
1
1
1
1
1
1


Filament Sectional shape
rect.
rect.
rect.
rect.
rect.
rect.
rect.
rect.
rect.
rect.


H (mm)
0.37
0.37
0.37
0.37
0.37
0.37
0.39
0.32
0.4
0.44


W (mm)
0.44
0.44
0.44
0.44
0.44
0.44
0.42
0.48
0.47
0.52


H/W
0.84
0.84
0.84
0.84
0.84
0.84
0.93
0.67
0.85
0.85


Waving
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal


Minor axis waving


P1
20
20
20
20
20
35
20
20
21
24


h1
0.18
0.18
0.18
0.18
0.8
0.3
0.18
0.18
0.18
0.21


h1/P1
0.009
0.009
0.009
0.009
0.04
0.009
0.009
0.009
0.009
0.009


Major axis waving


P2
20
20
20
20
20
35
20
20
21
24


h2
0.18
0.18
0.18
0.18
0.18
0.3
0.18
0.18
0.19
0.21


h2/P2
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009


Sectional area S (sq. mm)
0.1385
0.1385
0.1385
0.1385
0.1385
0.1385
0.1385
0.1385
0.159
0.1963


Cord strength (N)
406
406
406
406
386
415
401
394
455
558


Strength/section area (N/sq.
2960
2960
2960
2960
2900
3055
2980
2900
2950
2900


mm)


Cord count/5 cm
40
40
40
40
40
40
40
40
36
30


Band
none
present
present
present
none
none
none
none
none
none


Band cord
—
nylon
PET
aramide
—
—
—
—
—
—


Material


Tire weight
93
93
93
93
94
94
94
93
95
96


Durability
20
20
20
20
93
18
20
98
41
65


Steering stability
10
10
10
10
9
10
9
10
10
10


Ride comfort
10
10
10
10
10
10
10
10
10
9


Noise
98.1
96.9
96.2
94.9
98.4
98
98.1
98.3
97.7
97





















Tire
Pr. C1
Ref. C1
Ref. C2
Ref. C3
Ref. C4
Ref. C5
Ref. C6
Ex. C1
Ex. C2







Breaker cord
multi
mono
mono
mono
mono
mono
mono
mono
mono



Number of filament
5
1
1
1
1
1
1
1
1



Filament Sectional shape
circle
circle
circle
rect.
rect.
rect.
rect.
rect.
rect.



H (mm)
0.25
0.38
0.42
0.41
0.3
0.37
0.37
0.34
0.37



W (mm)
0.25
0.38
0.42
0.42
0.5
0.44
0.44
0.4
0.44



H/W
1
1
1
0.98
0.6
0.84
0.84
0.85
0.84



Waving
—
spiral
spiral
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal
orthogonal



Minor axis waving



P1
—
18
20
20
20
2
2
19
3



h1
—
0.16
0.18
0.18
0.18
0.08
0.12
0.18
0.03



h1/P1
—
0.009
0.009
0.009
0.009
0.04
0.06
0.009
0.01



Major axis waving



P2
—
18
20
20
20
4
4
19
5



h2
—
0.16
0.18
0.18
0.18
0.18
0.24
0.18
0.05



h2/P2
—
0.009
0.009
0.009
0.009
0.045
0.06
0.009
0.01



Sectional area S (sq. mm)
0.2454
0.1134
0.1385
0.1385
0.1385
0.1385
0.1385
0.1134
0.1385



Cord strength (N)
638
352
416
407
376
395
361
332
398



Strength/section area (N/sq.
2600
3100
3000
2995
2800
2853
2610
3050
2874



mm)



Cord count/5 cm
35
40
40
40
40
40
40
40
40



Band
none
none
none
none
none
none
none
none
none



Band cord
—
—
—
—
—
—
—
—
—



Material



Tire weight
100
91
93
94
94
93
93
91
94



Durability
100
160
40
40
187
213
235
92
85



Steering stability
7
4
8
7
8
7
6
8
9



Ride comfort
7
8
8
8
9
7
8
10
10



Noise
100
98.8
98.4
98.2
98.4
98.6
98.8
98.6
98










In the third and fourth examples of the breaker, the monofilament cords 10 are arranged such that the major axes lie along the thickness center plane or surface of the ply. Accordingly, with respect to the axial direction of the tire, an effect similar to that by an increased cord count can be obtained, and the in-plane rigidity of the ply increases. Therefore, the cornering power and steering stability can be improved. On the other hand, with respect to the radial direction of the tire, the cords do not exert such effect. Thus, the out-of-plane rigidity of the ply is not increased. Therefore, the ride comfort is improved.
In contrast with the spiral waving, the orthogonally waved cord has no twist back when the cord is elongated, and the direction of the major axis remains unchanged. Thus, separation between the cord and topping rubber can be prevented.
In the third and fourth examples of the breaker:
If the aspect ratio H/W is more than 0.95, the steering stability and ride comfort deteriorate. If the aspect ratio H/W is less than 0.65, the cord strength is liable to decrease during processing.
If the cross-sectional area S is less than 0.09 sq.mm, the cord rigidity and strength become insufficient, the belt can not provide an essential cornering power and the steering stability deteriorates. If the cross-sectional area S is more than 0.20 sq.mm, the cord rigidity excessively increases, and the ride comfort deteriorate. Further, the residual stress increases, and the durability decreases.
If the wave pitch P1 is less than 5 mm, the cord durability is decreased by deformation during running.
If the wave height h1 is more than 0.02 times the pitch P1, the cord strength and fatigue resistance are decreased.
If the pitch P1 is more than 50 mm and/or the wave height hl is less than 0.002 times the pitch P1, the cord lacks its elongation.
In the fourth example of the breaker:
If the wave pitch P1 is less than 3.0 mm and the wave pitch P2 less than 5.0 mm, the cord durability is decreased by deformation during running.
If the wave pitches P1 and P2 are more than 50 mm, the advantageous effect from the waving can not be obtained.
If the wave height h1 is more than 0.05 times the pitch P1 and the waving height h2 is more than 0.05 times the pitch P2, the cord strength and fatigue resistance decrease.
** Method of Making the Orthogonally Waved Cord **
FIG. 12 shows a method of making the cord shown in FIG. 11. First, a material steel wire 22 having a circular cross sectional shape is waved by passing through between a pair of rolls 20 having a waved circumference like a cogwheel.
Then, the wire 22 is again waved by passing through between a pair of rolls 21 having a waved circumference like a cogwheel. The rolls 21 are arranged orthogonally to the rolls 21, and flaten the circular cross sectional shape into a rectangular shape.
In the present invention, all the cords in each of the ply 7a and 7b have the same cord specifications. However, between one ply 7a and the other ply 7b, the cord specifications, for example sectional shape, size, wave pitch and/or wave height may be changed, but preferably the same specifications are employed. In each ply, all the cords are the same wave pitch, but it is preferable that the phase of wave gradually shift from a cord at one end to a cord at the other end of the ply at a substantially constant rate.
As explained above, according to the present invention, as the monofilament cord is waved, the elongation of the cord under load increases. Accordingly, an excessive increase in the belt rigidity is controlled and deterioration of ride comfort can be prevented. Further, the breaking of the cord is decreased and the belt durability can be improved. Thus, it becomes possible to use a monofilament steel cord as a breaker cord, and as a result, the amount of steel can be decreased to 80% or lower while maintaining the belt rigidity and thereby maintaining the cornering power, steering stability and the like.

## Claims

1. A pneumatic tire comprising
a belt disposed radially outside a carcass in a tread portion, and
a band disposed radially outside the belt,
the belt comprising two cross plies of monofilament metallic cords laid at angles of from 15 to 30 degrees with respect to the circumferential direction of the tire,
each of said monofilament metallic cords having a waved single filament, the filament having a non-circular sectional shape having an aspect ratio in a range of from 0.65 to 0.95 and a cross-sectional area S in a range of 0.09 to 0.20 sq.mm, wherein in each of said ply, the product S×N of the cross-sectional area S and the cord count N per 5 cm width of the ply is in the range of from 4.0 to 6.5, and the non-circular sectional shape of each filament has a major axis which lies in a direction parallel to the face of the ply, and the filament is waved by bending zigzag on a surface normal to the major axis with a wave pitch of not less than 5.0 mm and a wave height of 0.002 to 0.02 times the wave pitch,
and wherein the band is composed of windings of at least one cord wound at an angle of less than 10 degrees with respect to the circumferential direction of the tire, the band cord being selected from the group consisting of an aliphatic polyamide fiber cord, an aromatic polyamide fiber cord, a polyvinylalcohol fiber cord, a polyethylene terephthalate fiber cord, a polyethylene naphthalate fiber cord, and a hybrid cord of an aliphatic polyamide fiber and an aromatic polyamide fiber.

2. The pneumatic tire according to claim 1, wherein the wave pitch is in a range of from 10.0 to 50.0 mm.

3. The pneumatic tire according to claim 1, wherein
the non-circular sectional shape has a minor axis orthogonal to the major axis, and further
the filament is waved by bending zigzag on a surface normal to the minor axis with a wave pitch P2 of not less than 5.0 mm and a wave height of 0.002 to 0.05 times the wave pitch P2.

4. The pneumatic tire according to claim 3, wherein the wave pitch P1 is in a range of from 10.0 to 50.0 mm, and the wave pitch P2 is in a range of from 10.0 to 50.0 mm.