JP4487570B2 - Pneumatic radial tire - Google Patents

Description

The present invention relates to a pneumatic radial tire, and more particularly to a pneumatic radial tire that low lessen the entire frequency band of the road noise from low frequencies to high frequencies without decreasing the steering stability.

  In recent years, flattening of passenger car tires is spreading rapidly, and this flattening increases the rigidity of the tire side part, which has the advantage of improving steering stability. In particular, there is a problem that the sound pressure level of low-frequency road noise in the vicinity of 80 to 160 Hz increases.

  Road noise refers to noise generated when the vibration of a tire caused by road surface unevenness is transmitted to the vehicle body via the axle when the vehicle travels, and each part in the vehicle body resonates due to the vibration. . Depending on the frequency band, such road noise includes low-frequency “humming noise” around 40 Hz, low-frequency road noise around 80 to 160 Hz, medium-frequency road noise around 250 to 315 Hz, and around 800 to 1000 Hz. It has been found that there is high frequency road noise (so-called “shear noise”) and the like.

  Of these road noises, low-frequency road noise in the vicinity of 80 to 160 Hz can be reduced by lowering the primary natural frequency f1 in the radial direction of the tire. There are known methods for reducing the rigidity. However, since there is a problem that the steering stability is lowered as the rigidity of the tire side portion is lowered, as a countermeasure, Patent Document 1 uses a reinforcing rubber layer (auxiliary filler) having a rubber hardness lower than that of the bead filler. Proposed to be placed on the tire side to be 50-60% of the tire cross-section height, thereby improving the tire circumferential rigidity and reducing the “boom noise” around 40 Hz. ing. However, this measure cannot solve the medium frequency road noise of 250 to 315 Hz and the high frequency road noise of 800 to 1000 Hz.

On the other hand, since medium-frequency road noise in the vicinity of 250 to 315 Hz can be reduced by increasing the secondary natural frequency f2 in the tire cross-sectional direction, Patent Document 2 discloses that the belt cover layer provided on the outer periphery of the belt layer is the uppermost. It has been proposed to improve the shoulder rigidity by extending the outer belt layer from the end of the outer belt layer to the shoulder side by 15 to 40 mm. However, this countermeasure, the protruding width of the belt cover layer is not only difficult to tire manufacturing because it is too large, there is a problem that the cornering power balance reduces the steering stability deteriorates.
JP-A-5-131815 Japanese Patent Laid-Open No. 11-34610

  An object of the present invention is to provide a pneumatic radial tire that eliminates the above-described conventional problems and reduces road noise in the entire frequency band from a low frequency to a high frequency without deteriorating steering stability.

In the pneumatic radial tire of the present invention that achieves the above object, bead fillers are arranged on the outer circumferences of a pair of left and right bead cores, and both bead cores are engaged with both ends of the carcass layer so as to wrap the bead filler, A pneumatic radial having a flatness ratio of 40 to 65%, arranged on the outer periphery of the carcass layer so as to cover the belt cover layer around which the reinforcing cord is wound in the tire circumferential direction on at least both ends of the belt layer. In the tire,
The belt cover layer is made into a plurality of layers at both end regions of the belt layer so as to be more rigid than the center region, and the plurality of layer portions are extended outward from the maximum width end of the belt layer by 5 to 10 mm, together with the JIS-a hardness 75 to 100, the cross-sectional height H1 from the bead base to 20-30% of the tire section height SH, the engagement so as to wrap a bead filler sealed allowed tire width of the carcass layer place the reinforcing rubber layer extending to the sidewall portion while overlapping in the tire radial direction against the bead filler in the outward direction, lower than the bead filler hardness of the reinforcing rubber layer, the tan [delta 0.20-0 .30 and higher than the bead filler, and the sectional height H2 from the bead base is 45 to 80% of the tire sectional height SH. It is an butterfly.

As described above, by reducing the bead filler cross-sectional height H1 to 20-30% of the tire cross-sectional height SH, the low-frequency road noise of 80-160 Hz is reduced, and the bead filler is wrapped so as to wrap. The reinforcing rubber layer having a lower hardness than the bead filler, tan δ higher than the bead filler, and 0.20 to 0.30 is disposed outside the carcass layer , thereby increasing the hysteresis of the tire side portion. In addition to supplementing the steering stability that has been lowered with the downsizing of the bead filler, the tire circumferential rigidity can be increased to reduce the 40-Hz booming noise. Furthermore, since the increase in hysteresis at the tire side portion increases the rigidity of the shoulder portion, it can also contribute to the reduction of medium frequency road noise at 250 to 315 Hz.

  In addition, by extending the belt cover layer in the belt layer end area multiple layers from the belt layer maximum width end to the outside by 5 to 10 mm, medium frequency road noise of 250 to 315 Hz can be achieved without deteriorating the cornering power balance. To reduce. In addition, since the belt cover layer has a plurality of layers at both end regions of the belt layer and has higher rigidity than the center region, high frequency road noise (shear noise) of 800 to 1000 Hz can also be reduced.

  Therefore, according to the present invention, road noise in the entire frequency band from a low frequency to a high frequency can be reduced without lowering the steering stability.

  FIG. 1 is a half sectional view of a meridian section of a pneumatic radial tire for passenger cars according to an embodiment of the present invention, and FIG. 2 is an enlarged half sectional view of a tread portion in particular.

  1 and 2, the pneumatic radial tire is a flat tire having a flatness ratio of 40 to 65%, where 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A plurality of main grooves 10 are provided on the surface of the tread portion 1 so as to extend in the tire circumferential direction, and a recess 11 is formed in the buttress portion on the side wall of the tread portion 1 so as to be continuous in the tire circumferential direction. Yes.

  A two-ply carcass layer 4 is provided inside the tire. The inner carcass layer 4 of the two plies is folded back so as to wrap the bead filler 6 around the bead core 5 from the inside to the outside of the tire. Further, the outer carcass layer 4 passes through the outer side of the folded portion 4 a of the inner carcass layer and is bent toward the inner side of the bead core 5. A reinforcing rubber layer 7 is provided outside the tire of the outer carcass layer 4, and the reinforcing rubber layer 7 extends from the region overlapping the height of the bead filler 6 to the sidewall portion 2. That is, the sectional height of the bead filler 6 from the bead base is H1, while the sectional height of the reinforcing rubber layer 7 from the bead base is H2 higher than that.

  A two-ply belt layer 8 made of a steel cord is disposed on the outer peripheral side of the carcass layer 4. The steel cord of each belt layer 8 has a cord angle of 10 ° to 30 ° with respect to the tire circumferential direction, and intersects with each other between the layers. A belt cover layer 9 is provided outside the belt layer 8. The belt cover layer 9 is formed by continuously winding reinforcing cords (organic fiber cords or the like) in a spiral shape at an angle of 0 ° to 10 ° with respect to the tire circumferential direction. Two layers 9a are formed, and the rigidity at both end regions of the belt layer is larger than that of the center portion. The portions of the plurality of layers 9a extend outward from the maximum width end of the belt layer 8 to form a protruding length L. The shoulder portion rigidity is increased by the protruding length L of the plurality of layers 9a.

  In the above pneumatic tire, the belt layer is composed of high strength and high modulus organic fiber cords such as steel cords or aramid fibers, but the outermost belt layer width W1 is adopted for ordinary passenger car tires. In general, 97 to 106% of the tread ground contact width GCW is adopted.

  Here, the tread contact width GCW means that the tire is mounted on the standard rim described in the 2003 edition of the JATMA Yearbook, grounded perpendicular to the plane at an air pressure of 230 kPa, and the load capacity described in the JATMA-specified air pressure-load capacity correspondence table. Of the contact surface center in the radial direction of the tire when a load equivalent to 70% is applied to the tire.

  Moreover, the bead filler is comprised with the rubber composition whose JIS-A hardness is 75-100. More preferably, the rubber composition has a tan δ of 0.20 to 0.22. This bead filler has a sectional height H1 from the bead base of 20 to 30% of the tire sectional height SH, and is formed relatively short. Since the bead filler having a high hardness is formed in such a short length, the rigidity of the side portion is lowered, and the primary natural frequency f1 in the radial direction of the tire is lowered. As the radial primary natural frequency f1 decreases in this way, low-frequency road noise in the vicinity of 80 to 160 Hz is reduced.

  The reinforcing rubber layer disposed on the outside of the bead filler with the carcass layer interposed therebetween is composed of a rubber composition having a hardness lower than that of the bead filler and tan δ higher than that of the bead filler, and 0.20 to 0.30. Yes. More preferably, the rubber composition has a JIS-A hardness of 75 to 80. This reinforcing rubber layer is formed so that the cross-sectional height H2 from the bead base is 45 to 80% of the tire cross-sectional height SH.

  The thus-inserted reinforcing rubber layer is composed of a rubber composition having a hardness lower than that of the bead filler and tan δ being higher than that of the bead filler and being 0.20 to 0.30. Therefore, the decrease in steering stability due to the downsizing of the bead filler as described above is suppressed, and the steering stability is improved without inhibiting the reduction effect of low-frequency road noise. Moreover, since the circumferential rigidity of the tire is increased by the arrangement of the reinforcing rubber layer, it is possible to reduce a booming noise in the vicinity of 40 Hz. Furthermore, since the increase in the hysteresis of the side portion also increases the rigidity of the shoulder portion, it can contribute to the reduction of the medium frequency road noise of 250 to 315 Hz.

  In addition, JIS-A hardness used in this invention means the measured value in temperature 20 degreeC. Tan δ is a value measured using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho) at a temperature of 20 ° C. under conditions of an initial strain of 10%, a dynamic strain of ± 2%, and a vibration frequency of 20 Hz. .

  If the tan δ of the reinforcing rubber layer is higher than 0.30, or the cross-sectional height H2 of the reinforcing rubber layer is lower than 45% of the tire cross-sectional height SH, it is difficult to obtain an effect of improving steering stability. . On the other hand, if tan δ of the reinforcing rubber layer is lower than 0.20, the effect of reducing low-frequency road noise is reduced. Further, if the cross-sectional height H2 of the reinforcing rubber layer is higher than 80% of the tire cross-sectional height SH, the fuel efficiency deteriorates, which is not preferable.

  Furthermore, in order to make the above-described effect of the present invention more remarkable, the difference in tan δ between the bead filler and the reinforcing rubber layer is set to 0.02 to 0.1 and / or the difference in JIS-A hardness is set. It is good to set it as the range of 13-17. Further, the cross-sectional area Sr of the reinforcing rubber layer is preferably in the range of 0.9 to 1.2 in terms of the cross-sectional area ratio Sr / Sb with respect to the cross-sectional area Sb of the bead filler.

  On the other hand, the belt cover layer is formed into a plurality of layers in the belt layer end region, and the portions of the plurality of layers extend so that the protruding length L is 5 to 10 mm from the belt layer maximum width end to the shoulder side. . Thus, the protrusion length L of the plurality of layers is relatively short 5 to 10 mm, so that the rigidity of the shoulder portion is increased without disturbing the cornering power balance, and the secondary natural frequency f2 in the tire cross-section direction is shifted higher. To do. By shifting the secondary natural frequency f2 in the tire cross-sectional direction to the higher side, the medium frequency road noise of 250 to 315 Hz can be reduced.

  In this way, the reduction effect of the medium frequency road noise brought about by the increased rigidity of the shoulder portion is also added by the above-described reduction effect by the reinforcing rubber layer having a high tan δ. There is an effect. In addition, since the rigidity of the belt cover layer is higher than the center region at both end regions of the belt layer, high frequency road noise (shear noise) of 800 to 1000 Hz can also be reduced.

  The effect of reducing the medium frequency road noise and the high frequency road noise can be further increased by forming the shallow recess 11 in the buttress portion of the tread portion side wall as in the embodiment of FIGS. it can. When the recess 11 is formed in the buttress portion, when the tire is filled with air and inflated, the recess portion having a relatively thin rubber wall swells, so that the belt cover composite layer 9a protrudes. This is because the tension of the portion of the length L is increased, and the shoulder portion rigidity is further increased. The shape of the recess 11 is not limited to a trapezoid as shown in the figure, and may be a V shape or other shapes.

  The belt cover layer 9 is not limited to the one that covers the entire width of the belt layer as in the illustrated example, but may be one that is disposed only at both ends. Further, the belt cover layer 9 is formed in a plurality of layers 9a in both end regions of the belt layer, but the number of plies is not limited to two layers as shown in FIGS. 1 and 2, and the embodiment of FIG. 3 layers may be sufficient, or more. Further, as a form of forming the plurality of layers 9a, as shown in the embodiment shown in FIG. 4, a tape having a predetermined width formed by aligning a plurality of reinforcing cords is wound while partially overlapping the width direction. It may be formed as described above. In any case, it suffices if the end layer of the belt layer 8 has a higher rigidity than the center region by being formed in the plurality of layers 9a.

  The reinforcement cord constituting the belt cover layer should have an intermediate elongation of 3 to 9% at a load of 44 N, and the number of ends of the reinforcement cord per layer is 40 to 70 in a portion formed in a plurality of layers. / 50mm is recommended. By using such a middle-strength reinforcing cord and setting the number of ends (density) within the above range, the effect of increasing the rigidity by the belt cover layer can be further improved.

  The type of reinforcing cord having the intermediate elongation is not particularly limited, and examples thereof include nylon 6 fiber, nylon 66 fiber, polyethylene terephthalate fiber, polyethylene naphthalate fiber, and aromatic polyamide fiber. These fibers may be used alone or in combination of two or more.

  The present invention can be preferably applied particularly to a pneumatic tire for passenger cars. Further, the number of plies in the carcass layer is not limited to two plies as in the illustrated example, and may be only one ply. In the case of a two-ply carcass layer, the method for locking the bead core is to fold one ply of the inner layer from the inner side to the outer side of the tire as shown in the example shown in the figure, and to place the one ply of the outer layer along the outer side of the folded portion of the inner layer The two plies may be folded around the bead core from the inside of the tire to the outside.

  The common condition is that the tire size is 215 / 60R16, the belt layer width W1 in the tire structure of FIG. 1 is 100% of the tread ground contact width GCW, and the carcass layer is a two-ply structure, belt cover layer, bead filler, Eleven types of pneumatic radial tires (Examples 1 to 3, Comparative Examples 1 to 6, Conventional Examples 1 and 2) in which the conditions of the reinforcing rubber layer were made different as shown in Table 1 were manufactured.

  For these 11 types of pneumatic radial tires, road noise and steering stability were measured by the test methods described below, and the results shown in Table 1 were obtained.

[Road noise]
The test tire is mounted on a wheel with a rim size of 16 x 7 JJ, filled with air pressure of 220 kPa and mounted on a passenger car with a displacement of 3000 cc. The sound pressure levels of sound, low frequency road noise around 80 to 160 Hz, medium frequency road noise around 250 to 315 Hz, and high frequency road noise (shear sound) around 800 to 1000 Hz were recorded and measured on the microphone.

  The evaluation was performed using the reciprocal of the sound pressure level, and the index was represented by an index with the reciprocal of the measured value of the tire of Conventional Example 1 being 100. The larger the index, the better the road noise reduction effect.

[Maneuvering stability]
The test tire is assembled on a wheel with a rim size of 16 × 7 JJ, filled with air pressure of 220 kPa and mounted on a passenger car with a displacement of 3000 cc. Sensory evaluation of stability and stability when going straight.

  The evaluation was expressed as an index with the reciprocal of the measured value of the tire of Conventional Example 1 being 100. The larger the index, the better the steering stability.

1 is a half sectional view of a meridional section of a pneumatic radial tire according to an embodiment of the present invention. FIG. 2 is an enlarged half sectional view of a tread portion of the pneumatic radial tire of FIG. 1. It is the schematic diagram which showed the half cross section of the belt layer and belt cover layer of the tire which consist of other embodiment of this invention. It is the schematic diagram which showed the half cross section of the belt layer and belt cover layer of the tire which consists of further another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Reinforcement rubber layer 8 Belt layer 9 Belt cover layer 9a (belt cover layer) multiple layers 10 Main groove 11 Recess

Claims (7)

A bead filler is disposed on the outer periphery of each of the pair of left and right bead cores, both ends of the carcass layer are engaged with both bead cores so as to wrap the bead filler, and a belt layer is disposed on the outer periphery of the carcass layer. In a pneumatic radial tire having a flatness ratio of 40 to 65%, disposed so as to cover a belt cover layer around which a reinforcing cord is wound in at least both ends of the tire,
The belt cover layer is made into a plurality of layers at both end regions of the belt layer so as to be more rigid than the center region, and the plurality of layer portions are extended outward from the maximum width end of the belt layer by 5 to 10 mm, together with the JIS-a hardness 75 to 100, the cross-sectional height H1 from the bead base to 20-30% of the tire section height SH, the engagement so as to wrap a bead filler sealed allowed tire width of the carcass layer place the reinforcing rubber layer extending to the sidewall portion while overlapping in the tire radial direction against the bead filler in the outward direction, lower than the bead filler hardness of the reinforcing rubber layer, the tan [delta 0.20-0 .30, and higher than the bead filler, and the sectional height H2 from the bead base is 45 to 80% of the tire sectional height SH. Radial tire.   The pneumatic radial tire according to claim 1, wherein the reinforced rubber layer has a JIS-A hardness of 75 to 80.   The pneumatic radial tire according to claim 1 or 2, wherein a sectional area ratio Sr / Sb of a sectional area Sr of the reinforcing rubber layer to a sectional area Sb of the bead filler is 0.9 to 1.2.   The intermediate elongation at 44 N load of the reinforcing cord of the belt cover layer is 3 to 9%, and the number of ends of the reinforcing cord per layer in the plurality of layers is 40 to 70/50 mm. Or a pneumatic radial tire according to 3;   The pneumatic radial tire according to claim 4, wherein the reinforcing cord is made of nylon 6 fiber, nylon 66 fiber, polyethylene terephthalate fiber, polyethylene naphthalate fiber, or aromatic polyamide fiber.   The pneumatic radial tire according to any one of claims 1 to 5, wherein a concave portion continuous in a tire circumferential direction is formed in a buttress portion on a side wall of the tread portion. The pneumatic radial tire according to any one of claims 1 to 6, wherein a belt width W1 of the outermost layer in the belt layer is 97% to 106% of a tread ground contact width GCW.

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