Pneumatic tire with band cord modulus higher in side portion than in center portion of band

A band (14) of a tire covers a belt (12). The band (14) is formed by a band ply (36). The band ply (36) includes a side portion (38) and a center portion (40). A band cord having a high modulus (Ms) is used for the side portion (38). Typically, a band cord to be a composite of a nylon fiber and an aramid fiber is used for the side portion (38). A band cord having a low modulus (Mc) is used for the center portion (40). Typically, a nylon fiber is used for the band cord of the center portion (40). A ratio (Ms/Mc) is 2.0 to 4.0. A ratio of a width (Ws) of the side portion (38) to a width (Wb) of the band (14) is 5.0% to 20.0%.

This application claims priority on Patent Application No. 2004-081803 filed in JAPAN on Mar. 22, 2004, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pneumatic tire which is mainly attached to a passenger car.

2. Description of the Related Art

A radial tire for high speed running comprises a band between a tread and a belt. The band includes a band cord wound in a circumferential direction. The band cord binds the belt. The lifting of the belt which is caused by a centrifugal force in the high speed straight running is suppressed by the band cord. Japanese Laid-Open Patent Publication No. 2002-137606 has disclosed a band obtained by combining a band cord having a high modulus and a band cord having a low modulus.

A band covering the whole area of the belt sufficiently binds the vicinity of a center in the axial direction of the belt. On the other hand, the band has an insufficient binding force in the vicinity of the edge of the belt. The band does not sufficiently suppress the lifting in the vicinity of the edge. In addition, the insufficient binding force causes a great road noise.

If a cord having a high modulus is used in the band, the vicinity of the edge of the belt is also bound sufficiently. By this band, however, the stiffness of a tire is increased excessively. The excessive stiffness impedes the ride comfort of the tire. The band also causes a great exterior noise. If the modulus of the cord is excessively high, a handling stability is also deteriorated.

It is an object of the present invention to provide a pneumatic tire having an excellent silence and ride comfort.

SUMMARY OF THE INVENTION

A pneumatic tire according to the present invention comprises a tread having an external surface forming a tread surface, a pair of sidewalls extended almost inward in a radial direction from both ends of the tread, a pair of beads extended almost inward in the radial direction from the sidewalls, a carcass laid between both of the beads along insides of the tread and the sidewalls, a belt provided on the carcass at an inside in the radial direction of the tread, and a band positioned between the belt and the tread and covering the belt. A band ply constituting the band is formed by a band cord and a topping rubber. The band ply includes a side portion positioned in the vicinity of an edge of the belt and a center portion positioned in the vicinity of a center in an axial direction. A modulus of the band cord of the side portion is higher than that of the band cord of the center portion. A width Ws of the side portion is 5.0% to 20.0% of a width Wb of the band.

It is preferable that a ratio of the modulus of the band cord of the side portion to that of the band cord of the center portion should be 2.0 to 4.0. It is more preferable that the ratio should be 2.6 to 3.7.

It is preferable that the width Ws of the side portion should be 12.0% to 18.0% of the width Wb of the band.

It is preferable that the modulus of the band cord of the side portion should be 3000 N/mm2to 8000 N/mm2. It is suitable that a composite of a nylon fiber and an aramid fiber should be used for the band cord of the side portion.

In the tire, the vicinity of the edge of the belt is bound sufficiently. The tire makes a small road noise. In the tire, a stiffness in the vicinity of the center in the axial direction is not excessively great. The tire also has an excellent ride comfort.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below in detail based on preferred embodiments with reference to the drawings.

InFIG. 1, a vertical direction is set to be a radial direction of a tire2, a transverse direction is set to be an axial direction of the tire2, and a perpendicular direction to a paper is set to be a circumferential direction of the tire2. The tire2takes an almost symmetrical shape about a one-dotted chain line CL inFIG. 1. The tire2comprises a tread4, a sidewall6, a bead8, a carcass10, a belt12, a band14, an inner liner16and a chafer18.

The tread4is formed by a crosslinked rubber and takes the shape of an outward convex in the radial direction. The tread4forms a tread surface20to come in contact with a road surface. A groove22is provided on the tread surface20. A tread pattern is formed by the grooves22.

The sidewall6is extended almost inward in the radial direction from the end of the tread4. The sidewall6is formed by a crosslinked rubber. The sidewall6absorbs a shock from the road surface by a flexure. Moreover, the sidewall6prevents the external damage of the carcass10.

The bead8is extended almost inward in the radial direction from the inside end of the sidewall6. The bead8is constituted by a core24and an apex26extended outward in the radial direction from the core24. The core24is ring-shaped and includes a plurality of non-extensible wires (typically, wires formed of steel). The apex26is outward tapered in the radial direction and is formed by a crosslinked rubber having a high hardness.

The carcass10is constituted by a first carcass ply28and a second carcass ply30. The first carcass ply28and the second carcass ply30are laid between the beads8on both sides along the insides of the tread4and the sidewall6. The first carcass ply28and the second carcass ply30are wound from an inside toward an outside in the axial direction around the core24.

The first carcass ply28and the second carcass ply30are constituted by a carcass cord and a topping rubber, which is not shown. The absolute value of an angle formed by the carcass cord in the circumferential direction is usually 75 to 90 degrees. In other words, the tire2is a radial tire. An organic fiber is usually used for the carcass cord. Examples of a preferable organic fiber include a polyester fiber, a nylon fiber, a rayon fiber, a polyethylene naphthalate fiber (PEN) and an aramid fiber.

The belt12is positioned on an outside in the radial direction of the carcass10. The belt12is provided on the carcass10. The belt12reinforces the carcass10. The belt12is constituted by an inner belt ply32and an outer belt ply34. Each of the inner belt ply32and the outer belt ply34is constituted by a belt cord and a topping rubber, which is not shown. The belt cord is inclined to the circumferential direction. The direction of inclination to the circumferential direction of the belt cord of the inner belt ply32is reverse to the direction of inclination to the circumferential direction of the belt cord of the outer belt ply34. The preferable material of the belt cord is steel. An organic fiber may be used for the belt cord.

The inner liner16is bonded to the inner peripheral surface of the carcass10. The inner liner16is formed by a crosslinked rubber. A rubber having a small air transmittance is used for the inner liner16. The inner liner16plays a part in holding the internal pressure of the tire2.

The chafer18is positioned in the vicinity of the bead8. When the tire2is incorporated in a rim, the chafer18abuts on the rim. By the abutment, the vicinity of the bead8is protected. The chafer18is usually constituted by a cloth and a rubber impregnated into the cloth. It is also possible to use the chafer18formed by a single rubber.

FIG. 2is an enlarged sectional view showing a part of the belt12and the band14of the tire2inFIG. 1. The band14is constituted by a band ply36. The band ply36covers the whole belt12. The band ply36is a so-called full ply. The band ply36includes a side portion38and a center portion40. The side portion38is positioned in the vicinity of the edge of the belt12. The center portion40is positioned in the vicinity of a center in the axial direction of the tire2.

FIG. 3is an enlarged exploded perspective view showing the side portion38and the center portion40of the band ply36inFIG. 2. InFIG. 3, an X direction indicates the axial direction, a Y direction indicates the circumferential direction, and a Z direction indicates the radial direction.

The side portion38is constituted by a band cord42S and a topping rubber44S. The band cord42S is wound spirally. The band cord42S is exactly jointless. The band cord42S is extended substantially in the circumferential direction. As described above, the band cord42S is wound spirally. Therefore, the band cord42S is strictly inclined slightly to the circumferential direction. The absolute value of an angle formed by the band cord42S in the circumferential direction is smaller than 2.0 degrees. In the present invention, a direction in which the absolute value of an angle in the circumferential direction is smaller than 2.0 degrees is set to be a “substantial circumferential direction”.

The band cord42S having a high modulus Ms is used in the side portion38. Accordingly, the binding force of the side portion38to the vicinity of the edge of the belt12is great. By the great binding force, a road noise is suppressed. In particular, a noise having a frequency in a middle range is suppressed. The tire2has an excellent silence.

The center portion40is constituted by a band cord42C and a topping rubber44C. The band cord42C is wound spirally. The band cord42C is exactly Pointless. The band cord42C is also extended substantially in the circumferential direction in the same manner as the band cord42S of the side portion38.

The band cord42C having a low modulus Mc is used in the center portion40. Accordingly, the binding force of the center portion40to the vicinity of the center of the belt12is comparatively small. The stiffness of the vicinity of the center of the tire2including the center portion40is comparatively small. The tire2has an excellent ride comfort. The band cord42C having the low modulus Mc also contributes to a reduction in an exterior noise and a decrease in a rolling resistance.

In respect of the compatibility of the silence obtained by the side portion38with the ride comfort obtained by the center portion40, it is preferable that a ratio (Ms/Mc) of the modulus Ms of the band cord42S to the modulus Mc of the band cord42C should be 2.0 to 4.0. The ratio (Ms/Mc) is more preferably 2.3 and is particularly preferably equal to or higher than 2.6. The ratio (Ms/Mc) is more preferably equal to or lower than 3.8 and is particularly preferably equal to or lower than 3.7. In the present invention, the ratio (Ms/Mc) is calculated based on the moduli Ms and Mc obtained when an elongation percentage is 2%. The moduli Ms and Mc are measured in accordance with the rules of “JIS L 1017”.

In respect of a reduction in the road noise, the modulus Ms of the band cord42S of the side portion38is preferably equal to or higher than 3000 N/mm2and is more preferably equal to or higher than 5000 N/mm2. If the modulus Ms is excessively high, a handling stability is impeded, and furthermore, a rolling resistance is increased. From this viewpoint, the modulus Ms is preferably equal to or lower than 8000 N/mm2, is more preferably equal to or lower than 7500 N/mm2, and is particularly preferably equal to or lower than 7000 N/mm2.

An organic fiber can be suitably used for the band cord42S. Examples of the preferable material of the band cord42S include a polyethylene naphthalate (PEN) fiber and an aramid fiber. The composite of a nylon fiber and the aramid fiber may be used for the band cord42S. The composite contributes to a reduction in a road noise, an enhancement in a handling stability and a decrease in a rolling resistance. The ratio of the weights of the nylon fiber and the aramid fiber in the composite is preferably 1/4 to 4/1 and more preferably 2/3 to 3/2.

In respect of an enhancement in a ride comfort, a reduction in an exterior noise and a decrease in a rolling resistance, the modulus Mc of the band cord42C in the center portion40is preferably equal to or lower than 2500 N/mm2and is more preferably equal to or lower than 2200 N/mm2. If the modulus Mc is excessively low, the durability of the tire2becomes insufficient. From this viewpoint, the modulus Mc is preferably equal to or higher than 1000 N/mm2and is more preferably equal to or higher than 1500 N/mm2.

An organic fiber can be suitably used for the band cord42C. Typically, a nylon fiber is used for the band cord42C. A polyester fiber or a vinylon fiber may be used for the band cord42C.

It is preferable that the densities of the band cords42S and42C in the band ply36should be 5 ends/cm to 20 ends/cm. It is preferable that the sectional areas of the band cords42S and42C in the band ply36should be 0.10 mm2to 1.6 mm2.

InFIG. 2, an arrow Ws indicates the width of the side portion38and an arrow Wb/2 indicates a half of the width of the band14. It is preferable that a ratio of the width Ws of the side portion38to the width Wb of the band14should be 5.0% to 20.0%. In some cases in which the ratio is lower than the range, the road noise cannot be suppressed sufficiently. From this viewpoint, the ratio is more preferably equal to or higher than 12% and is particularly preferably equal to or higher than 15%. In some cases in which the ratio exceeds the range, the ride comfort becomes insufficient and the rolling resistance is increased, and furthermore, the exterior noise is increased. From this viewpoint, the ratio is more preferably equal to or lower than 19% and is particularly preferably equal to or lower than 18%.

The tire may comprise two full plies or more. In this case, a side portion and a center portion are provided in at least one full ply.

In the present invention, the dimension of each portion of the tire2is measured in a state in which the tire2is incorporated in a normal rim and air is filled to obtain a normal internal pressure. In this specification, the normal rim implies a rim determined in rules on which the tire2depends. A “standard rim” in the JATMA rules, a “Design Rim” in the TRA rules and a “Measuring Rim” in the ETRTO rules are included in the normal rim. In this specification, the normal internal pressure implies an internal pressure determined in the rules on which the tire2depends. A “maximum air pressure” in the JATMA rules, a “maximum value” described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA rules and an “INFLATION PRESSURE” in the ETRTO rules are included in the normal internal pressure. The normal internal pressure of a tire for a car in accordance with the JATMA rules is 180 kPa.

FIG. 4is a sectional view showing a part of a pneumatic tire45according to another embodiment of the present invention.FIG. 4shows a belt46and a band48. The belt46is formed by an inner belt ply50and an outer belt ply52. The tire45comprises the same tread, sidewall, bead, carcass, inner liner and chafer as those in the tire2ofFIG. 1, which is not shown.

As shown inFIG. 4, the band48is formed by an edge ply54and a full ply56. In the tire45, the edge ply54constitutes a side portion58. A portion of the full ply56which does not overlap with the side portion58constitutes a center portion60. The side portion58is positioned in the vicinity of the edge of the belt46. The center portion60is positioned in the vicinity of a center in the axial direction of the tire45.

The side portion58and the center portion60are formed by a band cord and a topping rubber, which is not shown. The band cord is wound spirally. The band cord is exactly jointless. The band cord is extended substantially in a circumferential direction.

A band cord having a high modulus Ms is used in the side portion58. Accordingly, the binding force of the side portion58to the vicinity of the edge of the belt46is great. By the great binding force, a road noise is suppressed. In particular, a noise having a frequency in a middle range is suppressed. The tire45has an excellent silence.

A band cord having a low modulus Mc is used in the center portion60. Accordingly, the binding force of the center portion60to the vicinity of the center of the belt46is comparatively small. The stiffness of the vicinity of the center of the tire45including the center portion60is comparatively small. The tire45has an excellent ride comfort. The band cord having the low modulus Mc also contributes to a reduction in an exterior noise and a decrease in a rolling resistance.

In respect of the compatibility of the silence obtained by the side portion58with the ride comfort obtained by the center portion60, it is preferable that a ratio (Ms/Mc) of the modulus Ms to the modulus Mc should be 2.0 to 4.0. The ratio (Ms/Mc) is more preferably 2.3 and is particularly preferably equal to or greater than 2.6. The ratio (Ms/Mc) is more preferably equal to or lower than 3.8 and is particularly preferably equal to or lower than 3.7.

In respect of a reduction in the road noise, the modulus Ms of the band cord of the side portion58is preferably equal to or higher than 3000 N/mm2and is more preferably equal to or higher than 5000 N/mm2. If the modulus Ms is excessively high, a handling stability is impeded, and furthermore, a rolling resistance is increased. From this viewpoint, the modulus Ms is preferably equal to or lower than 8000 N/mm2, is more preferably equal to or lower than 7500 N/mm2, and is particularly preferably equal to or lower than 7000 N/mm2.

An organic fiber can be suitably used for the band cord of the side portion58. Examples of the preferable organic fiber include a polyethylene naphthalate fiber and an aramid fiber. The composite of a nylon fiber and the aramid fiber may be used for the band cord of the side portion58. The composite contributes to a reduction in a road noise, an enhancement in a handling stability and a decrease in a rolling resistance. The ratio of the weights of the nylon fiber and the aramid fiber in the composite is preferably 1/4 to 4/1 and more preferably 2/3 to 3/2.

In respect of an enhancement in a ride comfort, a reduction in an exterior noise and a decrease in a rolling resistance, the modulus Mc of the band cord of the center portion60is preferably equal to or lower than 2500 N/mm2and is more preferably equal to or lower than 2200 N/mm2. If the modulus Mc is excessively low, the durability of the tire45becomes insufficient. From this viewpoint, the modulus Mc is preferably equal to or higher than 1000 N/mm2and is more preferably equal to or higher than 1500 N/mm2.

An organic fiber can be suitably used for the band cord of the center portion60. Typically, a nylon fiber is used. A polyester fiber or a vinylon fiber may be used for a band cord42C of the center portion60.

It is preferable that the densities of the band cords in the edge ply54and the full ply56should be 5 ends/cm to 20 ends/cm. It is preferable that the sectional areas of the band cords in the edge ply54and the full ply56should be 0.10 mm2to 1.6 mm2.

It is preferable that a ratio of a width Ws of the side portion58to a width Wb of the band48should be 5.0% to 20.0%. In some cases in which the ratio is lower than the range, the road noise cannot be suppressed sufficiently. From this viewpoint, the ratio is more preferably equal to or higher than 12% and is particularly preferably equal to or higher than 15%. In some cases in which the ratio exceeds the range, the ride comfort becomes insufficient and the rolling resistance is increased, and furthermore, the exterior noise is increased. From this viewpoint, it is more preferable that the ratio should be equal to or lower than 18%.

The tire may comprise two or more edge plies in each of edges on left and right sides. In this case, at least one edge ply having a higher modulus Ms than the modulus Mc of the band cord of the center portion is provided in each of the edges on the left and right sides.

EXAMPLES

A pneumatic tire for a passenger car which has a structure shown inFIGS. 1 to 3was obtained. The details of the band of the tire are shown in the following Table 1. In the tire, an angle in a circumferential direction which is formed by the belt cord of an inner belt ply is +24 degrees and an angle in the circumferential direction which is formed by the belt cord of an outer belt ply is −24 degrees. The tire has a size of “215/60R16 95H”.

Examples 2 to 8 and Comparative Examples 1 to 4

A tire according to each of examples 2 to 12 and comparative examples 1 to 4 was obtained in the same manner as in the example 1 except that the specifications of a band were set as shown in the following Tables 1 and 2.

A tire was incorporated in a rim of “16×6.5-JJ” and the internal pressure of the tire was set to be 230 kPa. The tire was attached to a passenger car with front side engine and front wheel drive which has a engine displacement of 2300 cm3. The car was caused to run at a speed of 50 km/h over an asphalt road surface having a high roughness. A volume (an overall value) in the right ear of a driver and an exterior volume in the running were measured. Based on the comparative example 1, an evaluation was carried out. Referring to the examples 1 to 12 and the comparative examples 2 to 4, a value was calculated by subtracting a volume according to the comparative example 1 from each of volumes. This result is shown in the following Tables 1 and 2.

The driver of the car was caused to evaluate a handling stability and a ride comfort at a maximum of 10 points. This result is shown in the following Tables 1 and 2.

The tire was attached to a rolling resistance testing machine. A load of 4400 N was applied to the tire and a rolling resistance was measured at a speed of 80 km/h. This result is shown in the following Tables 1 and 2 as an index in the case in which a rolling resistance according to the comparative example 1 is set to be 100.

As shown in the Tables 1 and 2, the tire according to each of the examples is excellent in all of a silence, a rolling resistance, a handling stability and a ride comfort. From the results of the evaluation, the advantages of the present invention are apparent.

The above description is only illustrative and various changes can be made without departing from the scope of the present invention.