PNEUMATIC TIRE

Abstract

A pneumatic tire comprising a belt formed of two inclined belt layers formed of a rubberized layer of cords extending in a manner inclined with respect to a tire circumferential direction, the cords crossing each other between the layers, wherein: the two inclined belt layers have different tire widthwise widths W1 (mm) and W2 (mm); a ratio W2/W1 satisfies a relation expression 0.25≦(W2/W1)≦0.8; a tire radial outer side of the belt further includes a reinforcing belt formed of one or more circumferential belt layers formed of a rubberized layer of cords extending along the tire circumferential direction; and a circumferential rigidity of the reinforcing belt in a tire widthwise region between an end of the one inclined belt layer and an end of the other inclined belt layer is higher than a circumferential rigidity of the reinforcing belt in a tire widthwise inner side of the region.

Claims

1. A pneumatic tire, comprising a belt formed of two inclined belt layers formed of a rubberized layer of cords extending in a manner inclined with respect to a tire circumferential direction, the cords crossing each other between the layers, wherein: at an unloaded condition, when the pneumatic tire is mounted to an applicable rim and is applied with a prescribed internal pressure, the two inclined belt layers have different tire widthwise widths; among the two inclined belt layers, when W1 (mm) is a tire widthwise width of an inclined belt layer having a larger tire widthwise width, W2 (mm) is a tire widthwise width of the other inclined belt layer, a ratio W2/W1 satisfies a relation expression
0.25≦(W2/W1)≦0.8; a tire radial outer side of the belt further includes a reinforcing belt formed of one or more circumferential belt layers formed of a rubberized layer of cords extending along the tire circumferential direction; and a circumferential rigidity of the reinforcing belt in a tire widthwise region between an end of the one inclined belt layer and an end of the other inclined belt layer is higher than a circumferential rigidity of the reinforcing belt in a tire widthwise inner side of the region.

2. The pneumatic tire according to claim 1, wherein: the ratio W2/W1 further satisfies a relation expression
0.6≦(W2/W1)≦0.8.

3. The pneumatic tire according to claim 1, wherein: a number of circumferential belt layers disposed within the region is larger than a number of circumferential belt layers disposed on a tire widthwise side inner than the region.

4. The pneumatic tire according to claim 3, wherein: two circumferential belt layers are disposed within the region, and one circumferential belt layer is disposed on a tire widthwise side inner than the region.

5. The pneumatic tire according to claim 1, wherein: an inclination angle θ of the cords of the inclined belt layers with respect to the tire circumferential direction is 10°≦θ≦30°.

6. The pneumatic tire according to claim 2, wherein: a number of circumferential belt layers disposed within the region is larger than a number of circumferential belt layers disposed on a tire widthwise side inner than the region.

7. The pneumatic tire according to claim 2, wherein: two circumferential belt layers are disposed within the region, and one circumferential belt layer is disposed on a tire widthwise side inner than the region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 illustrates a tire widthwise schematic cross-sectional view of a pneumatic tire according to the first embodiment of this disclosure; and

[0019] FIG. 2 illustrates a schematic view of a belt structure of the tire of FIG. 1.

DETAILED DESCRIPTION

[0020] Having intensively studied the aforementioned problems, we discovered that in a pneumatic tire including a belt formed of two inclined belt layers, by forming the belt with two inclined belt layers with different tire widthwise widths, and reinforcing a region where merely one inclined belt layer exist by using a reinforcing belt formed of circumferential belts, in some cases the load dependence of cornering force were reduced.

[0021] By reducing the width of one inclined belt layer among the two inclined belt layers, the belt rigidity is deteriorated and the belt becomes likely to be displaced in the tire width direction, which reduces the obtained cornering force. Here, at low load, the displacement amount of the belt during cornering is small. Therefore, at low load, the reduction amount of the cornering force due to the reduction of the rigidity of the belt is small.

[0022] On the other hand, at high load, the displacement of the belt becomes large. Here, at high load, the displacement amount of the belt during cornering is large. Therefore, the degree of cornering force reduction due to belt displacement is large.

[0023] In this way, the degree of cornering force reduction due to belt displacement is larger at high load, and thus by reducing the width of one inclined belt layer among the two inclined belt layers, it is possible to lower the load dependence of cornering force. However, if the width of either inclined belt layer is reduced, a region with reduced number of inclined belt layers is generated. In this region, since the inclined belt layers are few, due to, e.g., easiness of tire diameter growth, the durability of the tire is deteriorated.

[0024] Then, we have studied means for compensating the durability of this region without reenlarging the reduced dependence of cornering force. As a result, it was discovered that even if a circumferential cord layer for compensating the rigidity is disposed in the region in which the number of inclined belt layers is reduced due to reduction of the width of the inclined belt layers, the cornering force at high load is not increased. The reason is considered as that a locally disposed circumferential cord layer contributes little to the rigidity of the tire width direction, and does not suppress the displacement of the inclined belt layers.

[0025] Based on such knowledge, we accomplished this disclosure as a result of further study on the dimensional ratio of the two inclined belt layers.

[0026] Hereinafter, an embodiment of this disclosure is exemplified in details by referring to the drawings.

[0027] FIG. 1 illustrates a schematic cross-sectional view in the tire width direction of the pneumatic tire (hereinafter referred to as merely “the tire”) according to the first embodiment of this disclosure. Moreover, in FIG. 1, the tire widthwise cross section of the tire at a condition when the tire is mounted to an applicable rim, applied with a prescribed internal pressure and set to an unloaded condition (hereinafter referred to as “the reference state” as well), is illustrated.

[0028] As illustrated in FIG. 1, the tire (pneumatic tire) 1 of the present embodiment includes a carcass 3 toroidally extending between bead cores 2a between a pair of bead portions 2, a belt 4 arranged on a tire radial outer side of a crown portion of the carcass 3, and a tread 5 arranged on a tire radial outer side of the belt 4. The material of the cords of the carcass ply of the carcass 3 may be, e.g., steel cord, etc. without limited thereto.

[0029] The belt 4 of the tire 1 according to the first embodiment as illustrated in FIG. 1 is formed of an inclined belt layer 4a having a tire widthwise width W1, and an inclined belt layer 4b having a tire widthwise width W2 smaller than the inclined belt layer 4a. The two inclined belt layers 4a, 4b are belt layers having belt cords extending in a manner inclined with respect to the tire circumferential direction, where the belt cords cross each other between the inclined belt layers. The material of the belt cords is preferably steel cord, without limited thereto. The one inclined belt layer 4a arranged on the tire radial inner side has a tire widthwise width W1 larger than the tire widthwise width W2 of the other inclined belt layer 4b arranged on the tire radial outer side. In this disclosure, the inclined belt layer 4a and the inclined belt layer 4b are formed in a manner such that the ratio W2/W1 of the width W1 of the inclined belt layer 4a to the width W2 of the inclined belt layer 4b satisfies the relation expression 0.25≦(W2/W1)≦0.8. In particular, in the present embodiment, the inclined belt layer 4a and the inclined belt layer 4b are formed in a manner such that the ratio W2/W1 of the width W1 of the inclined belt layer 4a to the width W2 of the inclined belt layer 4b satisfies the relation expression 0.6≦(W2/W1)≦0.8. Further, the inclined belt layer 4b with a smaller tire widthwise width may be arranged on the tire radial inner side, and the inclined belt layer 4a with a larger tire widthwise width may be arranged on the tire radial outer side.

[0030] FIG. 2 illustrates a schematic view of the structure of the belt 4 of the tire of FIG. 1. In the present embodiment, the inclined belt layer 4a is disposed in a manner such that an inclination angle θ1 of the cords of the inclined belt layer 4a with a larger tire widthwise width with respect to the tire circumferential direction is 10°≦θ1≦30°. Moreover, in the present embodiment, the inclined belt layer 4b is disposed in a manner such that an inclination angle θ2 of the cords of the inclined belt layer 4b with a smaller tire widthwise width with respect to the tire circumferential direction is 10°≦θ2≦30°. Further, the inclined belt layer 4a and the inclined belt layer 4b of the present embodiment are disposed in a manner such that tire widthwise centers of the inclined belt layer 4a and the inclined belt layer 4b are in accordance on the tire equatorial plain CL.

[0031] As illustrated in FIG. 1, the tire 1 of this disclosure further includes a reinforcing belt 6 on the tire radial outer side of the belt 4. The reinforcing belt 6 of the present embodiment is formed of two circumferential belt layers 6a and 6b. The circumferential belt layer 6a is formed in a manner covering the entire belt 4 in the tire width direction. The circumferential belt layer 6b is disposed in a manner separated from a tire radial outer side of the circumferential belt layer 6a, in merely a tire widthwise region between an end of the inclined belt layer 4a and an end of the inclined belt layer 4b. The circumferential belt layers 6a and 6b preferably use cords formed of organic fibers, and may use cords formed of organic fibers such as aramid and the like, hybrid cords of aramid and nylon, etc., without limited thereto. In the present embodiment, the circumferential belt layer 6b is disposed on the tire radial outer side of the circumferential belt layer 6a, while the circumferential belt layer 6b may be disposed on a tire radial inner side of the circumferential belt layer 6a as well.

[0032] The effect of the tire according to present embodiment is described in the following.

[0033] According to the tire of the present embodiment, first, in the aforementioned reference state, among the two inclined belt layers for forming the belt 4, when W1 is the tire widthwise width of the inclined belt layer 4a with a larger tire widthwise width, and W2 is the tire widthwise width of the inclined belt layer 4b, the ratio W2/W1 satisfies the relation expression 0.25≦(W2/W1)≦0.8. The tire of the present embodiment further includes the reinforcing belt 6 formed of the circumferential belt layers 6a and 6b, and the circumferential rigidity of the reinforcing belt 6 is higher in the tire widthwise region between the end of the inclined belt layer 4a and the end of the inclined belt layer 4b than on the tire widthwise side inner than this region.

[0034] As mentioned above, at low load, the displacement amount of the belt during cornering is small. Therefore, at low load, the reduction amount of the cornering force due to the reduction of the rigidity of the belt is small. On the other hand, at high load, the displacement of the belt becomes large. Here, at high load, the displacement amount of the belt during cornering is large. Therefore, the degree of cornering force reduction due to belt displacement is large. In this way, the degree of cornering force reduction due to belt displacement is larger at high load, and thus by reducing the width of one inclined belt layer among the two inclined belt layers, the load dependence of cornering force is reduced. Moreover, in a part where the number of inclined belt layers is reduced due to the reduction of the width of the inclined belt layer, by disposing circumferential cord layers for compensating the rigidity, the width of the inclined belt layers is reduced without increasing the degree of cornering force at high load, and thus the diameter growth of the tire in the region in which the number of the inclined belt layers is reduced is suppressed and the durability is compensated.

[0035] According to the above, the tire of the present embodiment is capable of reducing the load dependence of cornering force and simultaneously ensuring the durability.

[0036] Here, if 0.25>(W2/W1), there are cases that the belt rigidity is excessively small and a sufficient cornering force cannot be obtained. Moreover, if (W2/W1)>0.8, there are cases that the reduction of the belt rigidity is insufficient, and the load dependence of cornering force cannot be reduced.

[0037] In particular, regarding the circumferential rigidity according to the aforementioned definition, the circumferential rigidity of the reinforcing belt 6 in the region between the end of the inclined belt layer 4a and the end of the inclined belt layer 4b is preferably 1.5 to 2.5 times to the circumferential rigidity of the reinforcing belt 6 on the tire widthwise side inner than this region.

[0038] Here, in this disclosure, the ratio W2/W1 preferably satisfies the relation expression 0.6≦(W2/W1)≦0.8. By forming the belt layers 4a and 4b in such manner, it is possible to maintain a high rigidity of the tire, and to suppress excessive increase of the rigidity of the tire. Therefore, it is possible to obtain a sufficient cornering force, and to simultaneously increase the cornering force at high load.

[0039] As illustrated in the embodiment of FIG. 1, in the pneumatic tire of this disclosure, the number of the circumferential belt layers disposed within the region between the end of the inclined belt layer 4a and the end of the inclined belt layer 4b is preferably more than the number of the circumferential belt layers disposed on the tire widthwise side inner than this region. Such relation of the number of the circumferential belt layers is capable of improving the rigidity of the tire widthwise region between the end of the inclined belt layer 4a and the end of the inclined belt layer 4b with a simple configuration. Here, the rigidity within this region may be improved with a method other than setting the number of the circumferential belt layers disposed in this region larger than the number of the circumferential belt layers disposed on the tire widthwise side inner than this region. For example, the rigidity between the end of the inclined belt layer 4a and the end of the inclined belt layer 4b may be improved by using cords with a Young's modulus higher than the cords used in the circumferential belt layers on a tire widthwise side inner than this region as the cords used in the circumferential belt layers within this region. Here the “Young's modulus” is determined according to JIS L1017 8.8(2002) by performing tests according to JIS L1017 8.5 a) (2002). Further, a filament number per unit length in the tire width direction in a tire widthwise cross section may be varied, a filament number within the aforementioned tire widthwise region may be set larger than the filament number on the side inner than the aforementioned tire widthwise region.

[0040] In particular, in the case where the configuration of the cords other than Young's modulus, such as the layer number, the filament number per unit length and the like, is the same, the Young's modulus in the region between the end of the belt layer 4a and the end of the belt layer 4b is preferably 1.5 to 2.5 times to the Young's modulus of the cords on the side inner than the aforementioned tire widthwise region. Similarly, in the case where the configuration of the cords other than the filament number per unit length in the tire width direction, such as the layer number, the Young's modulus and the like, is the same, the filament number per unit length in the tire width direction in the region between the end of the belt layer 4a and the end of the belt layer 4b is preferably 1.5 to 2.5 times to the filament number per unit length in the tire width direction of the cords on the side inner than the aforementioned tire widthwise region.

[0041] Moreover, as illustrated in the embodiment of FIG. 1, in the pneumatic tire of this disclosure, it is preferable to dispose two circumferential belt layers 6a and 6b within the tire width direction region between the end of the belt layer 4a and the end of the belt layer 4b, and dispose one circumferential belt layer 6a on the tire widthwise side inner than this region. According to such configuration, it is possible to improve the rigidity of the region between the end of the belt layer 4a and the end of the belt layer 4b with a small number of members. Further, the number of the circumferential belt layers in this region and the tire widthwise side inner than this region are not limited to respectively two and one. For example, it is possible to dispose circumferential belt layers merely in this region, without disposing circumferential belt layers in the tire widthwise side inner than this region. Further, for example, three or more circumferential belt layers may be disposed within this region, and in this case, the difference between the number of the circumferential belt layers within this region and within the tire widthwise side inner than this region may be one, two or more.

[0042] As illustrated in FIG. 2, in the pneumatic tire of this disclosure, it is preferable that the inclination angle θ1 of the cords of the inclined belt layer 4a with respect to the tire circumferential direction is 10°≦θ1≦30°, and the inclination angle θ2 of the cords of the inclined belt layer 4b with respect to the tire circumferential direction is 10°≦θ2≦30°. In this way, it is possible to suppress excessive deterioration of widthwise rigidity, and to suppress excessive reduction of the cornering force at high load.

[0043] Hereinafter, examples for this disclosure are described, while this disclosure is not limited to these examples.

EXAMPLES

[0044] In order to certify the effect of this disclosure, the tires of Examples 1 to 3 and Comparative Examples 1 to 3 were produced experimentally. The dimensions of each tire are as shown in the following Table 1. The tire size of each is 225/50R17. Each tire was subjected to tests for evaluating the load dependence of cornering force and the durability of tire.

[0045] Here, each tire is a tire as illustrated in FIG. 1 including a carcass fixed to bead cores embedded in a pair of bead portions, an inclined belt formed of two inclined belt layers disposed on a tire radial side outer than a crown portion of the carcass, and a tread.

[0046] <Cornering Force>

[0047] The tires of each aforementioned example and comparative example were mounted to a rim (size: 7.5J-17), applied with an internal pressure of 220 kPa, and then installed to a vehicle, and subjected to measurement on a flat belt type cornering testing machine. Here, measured was the cornering force obtained at a belt speed of 100 km/h under two different load conditions, under the load conditions respectively corresponding to 80% and 30% of a maximum load capability at applicable size and ply rating.

[0048] <Rigidity of Reinforcing Belt>

[0049] When E1 is a Young's modulus of the reinforcing belt fibers, and a is a number of cords per unit width of the belt, the rigidity of the reinforcing belt was evaluated as a×E1.

[0050] <Tire Durability>

[0051] The tires of each aforementioned examples and comparative examples were travelled on a drum testing machine in the state mounted to a rim (size: 7.5J-17) and applied with an internal pressure of 220 kPa, and the durability was evaluated by comparing the degrees of breakage amount (size of crack) generated inside and outside the tire.

[0052] The result was as shown in Table 1. The value of the cornering force is evaluated via index evaluation, with the cornering force of the tire at 30% of the load of the tire 2 of Comparative Example as 100. A larger index shows a larger cornering force. Further, by referring to the α/β (%) in the table, the load dependence of cornering force can be understood. A lower value shows a lower load dependence.

TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 1 Example 2 Example 3 Inclined belt W1 (mm) 197 197 197 197 197 197 layer 3a θ1 30 40 40 30 30 30 Inclined belt W2 (mm) 140 140 100 40 180 140 layer 3b θ2 30 40 30 30 30 30 W2/W1 0.7 0.7 0.5 0.2 0.91 0.7 Rigidity of Within region 200 200 200 200 200 100 reinforcing belt Inner than 100 100 100 100 100 100 region Number of Within region 2 2 2 2 2 1 circumferential Inner than 1 1 1 1 1 1 belt layers region Cornering force α at high load 199.68 186.03 173.23 137.26 208.00 198.90 β at low load 101.00 92.13 94.25 84.39 100.00 101.50 α/β 1.98 2.02 1.84 1.63 2.08 1.96

[0053] As shown in Table 1, each tire according to Examples 1 to 3 had improved load dependence of cornering force as compared to the tires according to Comparative Examples 1 to 3. Moreover, although not shown in Table 1, each tire according to Examples 1 to 3 had an ensured tire durability as compared to the tires according to Comparative Examples 1 to 3. On the other hand, in Comparative Example 1, although the load dependence of cornering force was improved, since the width W2 of the inclined belt layer 4b was small and the value of W2/W1 was smaller than 0.25, the durability of the tire could not be ensured. In comparative Example 2, since the width W2 of the inclined belt layer 4b was large and the value of W2/W1 was larger than 0.8, although the tire durability was not worse as compared to Examples 1 to 3, the load dependence of cornering force could not be improved. In Comparative Example 3, the numbers of the circumferential belt layer were equal within the regions and among the regions, the durability of the tire could not be ensured. Comparing Example 1 and Example 2, Example 1, of which θ1 and θ2 are 10° or more and 30° or less, has a reduced load dependence of cornering force. Comparing Example 2 and Example 3, Example 2, which satisfies 0.6≦(W2/W1)≦0.8, is capable of maintaining a high durability of the tire.

REFERENCE SIGNS LIST

[0054] 1 tire (pneumatic tire)

[0055] 2 bead portion

[0056] 3 carcass

[0057] 4 belt

[0058] 4a, 4b inclined belt layer

[0059] 5 tread

[0060] 6 reinforcing belt

[0061] 6a, 6b circumferential belt layer

[0062] CL tire equatorial plain