Patent Description:
Hitherto, various pneumatic tires focusing on drainage performance, wear resistance, and noise performance have been proposed. For example, the pneumatic tire of <CIT> has been proposed to improve wear resistance and noise performance while maintaining drainage performance, by providing a narrow portion having a small width in each axial groove and increasing an angle of each axial groove with respect to the tire axial direction.

However, in the pneumatic tire of <CIT>, decreasing the groove width of each axial groove decreases the groove volume thereof, which causes a decrease in drainage performance, and increasing the angle of each axial groove causes a decrease in wear resistance. Therefore, further improvement of drainage performance, wear resistance, and noise performance is desired.

A tire having the features of the preamble of claim <NUM> is known from <CIT>. Related tires are described in <CIT>, <CIT> and <CIT>.

The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a pneumatic tire that can have improved noise performance while maintaining good drainage performance and wear resistance.

The object is solved by a tire having the features of claim <NUM>. Sub-claims are directed to embodiments of the invention. The present invention is directed to a pneumatic tire including a tread portion, wherein: the tread portion includes a plurality of circumferential grooves continuously extending in a tire circumferential direction, and a plurality of land portions demarcated by the plurality of circumferential grooves; the plurality of land portions include at least one pattern land portion on which axial grooves are arranged in a number of N pitches in the tire circumferential direction so as to extend in a tire axial direction; in a load-applied state where a load that is <NUM>% of a standardized load is applied in a state where the pneumatic tire is fitted on a standardized rim and adjusted to a standardized internal pressure, a ground-contact surface shape of the tread portion has a first tread end, a second tread end, and a first ground-contact end edge extending from the first tread end to the second tread end on one side in the tire circumferential direction; the number of pitches N is not less than <NUM>; and a first straight line connecting both ends in the tire axial direction of a portion, of the first ground-contact end edge, traversing the pattern land portion satisfies the following formula (<NUM>). <NUM>] <MAT> where.

By having the above-described configuration, the pneumatic tire of the present invention can have improved noise performance while maintaining good drainage performance and wear resistance.

According to an embodiment of the invention, in the load-applied state, the ground-contact surface shape of the tread portion has a second ground-contact end edge extending from the first tread end to the second tread end on another side in the tire circumferential direction, and
a second straight line connecting both ends in the tire axial direction of a portion, of the second ground-contact end edge, traversing the pattern land portion satisfies the following formula (<NUM>),
[Math. <NUM>] <MAT> where.

According to an embodiment of the invention, the angle θ1 of the first straight line is equal to the angle θ2 of the second straight line.

According to an embodiment of the invention, a tire rotation direction is predetermined for the tread portion, and the first ground-contact end edge is a ground-contact end edge on a leading edge side in the tire rotation direction.

According to an embodiment of the invention, an angle θ3 of each of the axial grooves with respect to the tire axial direction is in a range of <NUM> to <NUM>°.

According to an embodiment of the invention, the plurality of circumferential grooves include a first shoulder circumferential groove provided between the tire equator and the first tread end, and a first middle circumferential groove provided between the first shoulder circumferential groove and the tire equator, and the pattern land portion includes a first shoulder land portion demarcated between the first shoulder circumferential groove and the first tread end.

According to an embodiment of the invention, the pattern land portion includes a first middle land portion demarcated between the first shoulder circumferential groove and the first middle circumferential groove.

<FIG> is a schematic diagram showing a ground-contact surface shape 2a of a pneumatic tire <NUM> of an embodiment of the invention. As shown in <FIG>, the pneumatic tire <NUM> of the present embodiment of the invention includes a tread portion <NUM>. The tread portion <NUM> of the present embodiment of the invention includes a plurality of circumferential grooves <NUM> continuously extending in the tire circumferential direction, and a plurality of land portions <NUM> demarcated by the plurality of circumferential grooves <NUM>.

The plurality of land portions <NUM> of the present embodiment of the invention include at least one pattern land portion <NUM> on which axial grooves <NUM> are arranged in the tire circumferential direction with the number of pitches N so as to extend in the tire axial direction. Such a tread portion <NUM> can suppress occurrence of a hydroplaning phenomenon, in which a steering wheel and brakes become uncontrollable, even during running at a high speed on a wet road surface, and serves to improve the drainage performance of the pneumatic tire <NUM>.

The tread portion <NUM> has, for example, the ground-contact surface shape 2a shown in <FIG>, in a load-applied state where a load that is <NUM>% of a standardized load is applied in a standardized state. Here, the "standardized state" is a state where the pneumatic tire <NUM> is fitted on a standardized rim and adjusted to a standardized internal pressure, and no load is applied to the pneumatic tire <NUM>. Hereinafter, unless otherwise specified, dimensions and the like of components of the pneumatic tire <NUM> are values measured in the standardized state.

If there is a standard system including a standard on which the pneumatic tire <NUM> is based, the "standardized rim" is a rim that is defined for each tire by the standard, and is, for example, the "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, or the "Measuring Rim" in the ETRTO standard. If there is no standard system including a standard on which the pneumatic tire <NUM> is based, the "standardized rim" is a rim having the smallest rim diameter and having the smallest rim width, among rims onto which the pneumatic tire <NUM> can be fitted and which do not cause air leakage.

If there is a standard system including a standard on which the pneumatic tire <NUM> is based, the "standardized internal pressure" is an air pressure that is defined for each tire by the standard, and is the "maximum air pressure" in the JATMA standard, the maximum value indicated in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "INFLATION PRESSURE" in the ETRTO standard. If there is no standard system including a standard on which the pneumatic tire <NUM> is based, the "standardized internal pressure" is an air pressure that is defined for each tire by the manufacturer or the like.

If there is a standard system including a standard on which the pneumatic tire <NUM> is based, the "standardized load" is a load that is defined for each tire by the standard, and is the "maximum load capacity" in the JATMA standard, the maximum value indicated in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "LOAD CAPACITY" in the ETRTO standard. If there is no standard system including a standard on which the pneumatic tire <NUM> is based, the "standardized load" is a load that is defined for each tire by the manufacturer or the like.

In the load-applied state, the ground-contact surface shape 2a of the tread portion <NUM> of the present embodiment of the invention has a first tread end Te1, a second tread end Te2, and a first ground-contact end edge <NUM> extending from the first tread end Te1 to the second tread end Te2 on one side in the tire circumferential direction. Here, the center in the tire axial direction between the first tread end Te1 and the second tread end Te2 is a tire equator C.

A first straight line 7a connecting both ends in the tire axial direction of a portion, of the first ground-contact end edge <NUM>, traversing the pattern land portion <NUM> of the present embodiment of the invention satisfies the following formula (<NUM>). <NUM>] <MAT> where.

In such a tread portion <NUM>, the portion, of the first ground-contact end edge <NUM>, traversing the pattern land portion <NUM> and the axial grooves <NUM> are continuous during running, so that the fluctuations of the groove cross-sectional areas of the axial grooves <NUM> are reduced, and pitch noise can be suppressed. Accordingly, the tread portion <NUM> can reduce pitch noise even in the case where the groove volume of each axial groove <NUM> is large and an angle θ3 of each axial groove <NUM> with respect to the tire axial direction is small. Therefore, the pneumatic tire <NUM> of the present embodiment of the invention can have improved noise performance while maintaining good drainage performance and wear resistance.

In a more preferable mode, a tire rotation direction R is predetermined for the tread portion <NUM>. The first ground-contact end edge <NUM> is, for example, a ground-contact end edge on the leading edge side in the tire rotation direction R. Such a tread portion <NUM> can reduce pitch noise caused due to contact with the ground during running.

In the load-applied state, the ground-contact surface shape 2a of the tread portion <NUM> of the present embodiment of the invention has a second ground-contact end edge <NUM> extending from the first tread end Te1 to the second tread end Te2 on the other side in the tire circumferential direction. A second straight line 8a connecting both ends in the tire axial direction of a portion, of the second ground-contact end edge <NUM>, traversing the pattern land portion <NUM> of the present embodiment of the invention satisfies the following formula (<NUM>). <NUM>] <MAT> where.

In such a tread portion <NUM>, the portion, of the second ground-contact end edge <NUM>, traversing the pattern land portion <NUM> and the axial grooves <NUM> are continuous during running, so that the fluctuations of the groove cross-sectional areas of the axial grooves <NUM> are reduced, and pitch noise can be suppressed. Accordingly, the tread portion <NUM> can reduce pitch noise even in the case where the groove volume of each axial groove <NUM> is large and the angle θ3 of each axial groove <NUM> with respect to the tire axial direction is small. Therefore, the pneumatic tire <NUM> of the present embodiment of the invention can have improved noise performance while maintaining good drainage performance and wear resistance.

From this viewpoint, the first straight line 7a and the second straight line 8a more preferably satisfy the following formula (<NUM>) and the following formula (<NUM>), respectively. <NUM>] <MAT>
[Math. <NUM>] <MAT> where.

The angle θ1 of the first straight line 7a is preferably equal to the angle θ2 of the second straight line 8a. In such a tread portion <NUM>, a length L1 in the tire circumferential direction of the portion, of the first ground-contact end edge <NUM>, traversing the pattern land portion <NUM> and a length L2 in the tire circumferential direction of the portion, of the second ground-contact end edge <NUM>, traversing the pattern land portion <NUM> are equal to each other, so that the tread portion <NUM> serves to further reduce pitch noise.

The angle θ3 of each axial groove <NUM> with respect to the tire axial direction is preferably in the range of <NUM> to <NUM>°. Such an axial groove <NUM> inhibits a sharp corner from being formed in the land portion <NUM>, and serves to improve the wear resistance of the pneumatic tire <NUM>. From this viewpoint, the angle θ3 of each axial groove <NUM> is more preferably in the range of <NUM> to <NUM>°.

The number of pitches N of the axial grooves <NUM> is not less than <NUM>. When the number of pitches N is not less than <NUM>, overlap of the frequency of pitch noise with the frequency of air column resonance sound can be suppressed. From this viewpoint, the number of pitches N of the axial grooves <NUM> is more preferably not less than <NUM> and further preferably not less than <NUM>.

The plurality of circumferential grooves <NUM> of the present embodiment of the invention extend between the first tread end Te1 and the second tread end Te2 of the tread portion <NUM>. The plurality of circumferential grooves <NUM> preferably include a first shoulder circumferential groove 3A provided between the tire equator C and the first tread end Te1, and a second shoulder circumferential groove 3B provided between the tire equator C and the second tread end Te2.

The plurality of circumferential grooves <NUM> of the present embodiment of the invention include a first middle circumferential groove 3C provided between the first shoulder circumferential groove 3A and the tire equator C, and a second middle circumferential groove 3D provided between the second shoulder circumferential groove 3B and the tire equator C. Such a tread portion <NUM> can improve the drainage performance of the pneumatic tire <NUM> by the plurality of circumferential grooves <NUM>.

The plurality of land portions <NUM> preferably include a first shoulder land portion 4A demarcated between the first shoulder circumferential groove 3A and the first tread end Te1, and a second shoulder land portion 4B demarcated between the second shoulder circumferential groove 3B and the second tread end Te2. The plurality of land portions <NUM> of the present embodiment of the invention include a first middle land portion 4C demarcated between the first shoulder circumferential groove 3A and the first middle circumferential groove 3C, and a second middle land portion 4D demarcated between the second shoulder circumferential groove 3B and the second middle circumferential groove 3D. The plurality of land portions <NUM> include, for example, a crown land portion 4E demarcated between the first middle circumferential groove 3C and the second middle circumferential groove 3D.

<FIG> is a schematic diagram showing a ground-contact surface shape 12a of a pneumatic tire <NUM> of a second embodiment of the invention. As shown in <FIG>, the pneumatic tire <NUM> of the second embodiment of the invention includes a tread portion <NUM> as in the above-described pneumatic tire <NUM>. As in the above-described tread portion <NUM>, the tread portion <NUM> of the second embodiment of the invention includes a plurality of circumferential grooves <NUM> continuously extending in the tire circumferential direction, and a plurality of land portions <NUM> demarcated by the plurality of circumferential grooves <NUM>. As in the above-described ground-contact surface shape 2a, the ground-contact surface shape 12a in <FIG> is a ground-contact surface shape of the tread portion <NUM> in a load-applied state where a load that is <NUM>% of a standardized load is applied in a standardized state.

As in the above-described circumferential grooves <NUM>, the plurality of circumferential grooves <NUM> of the second embodiment of the invention include a first shoulder circumferential groove 13A, a second shoulder circumferential groove 13B, a first middle circumferential groove 13C, and a second middle circumferential groove 13D. As in the above-described land portions <NUM>, the plurality of land portions <NUM> of the second embodiment of the invention include a first shoulder land portion 14A, a second shoulder land portion 14B, a first middle land portion 14C, a second middle land portion 14D, and a crown land portion 14E.

The first shoulder land portion 14A of the second embodiment of the invention is a pattern land portion <NUM> on which axial grooves <NUM> are arranged in the tire circumferential direction with a number of pitches N so as to extend in the tire axial direction. <FIG> illustrates that the axial grooves <NUM> of the first shoulder land portion 14A extend along the tire axial direction. Such axial grooves <NUM> serve to improve the wear resistance of the pneumatic tire <NUM>.

In the pattern land portion <NUM> of the second embodiment of the invention, a length L1 in the tire circumferential direction of a portion, of a first ground-contact end edge <NUM>, traversing the first shoulder land portion 14A approximates each pitch P in the tire circumferential direction of the axial grooves <NUM> of the first shoulder land portion 14A. In such a pattern land portion <NUM>, the axial grooves <NUM> sequentially come into contact with the ground when the pneumatic tire <NUM> contacts the ground, so that the pattern land portion <NUM> can further reduce pitch noise.

In the pattern land portion <NUM> of the second embodiment of the invention, a length L2 in the tire circumferential direction of a portion, of a second ground-contact end edge <NUM>, traversing the first shoulder land portion 14A approximates each pitch P in the tire circumferential direction of the axial grooves <NUM> of the first shoulder land portion 14A. In such a pattern land portion <NUM>, the axial grooves <NUM> sequentially become separated from the ground when the pneumatic tire <NUM> is separated from the ground, so that the pattern land portion <NUM> can further reduce pitch noise.

<FIG> is a schematic diagram showing a ground-contact surface shape 22a of a pneumatic tire <NUM> of a third embodiment of the invention. As shown in <FIG>, the pneumatic tire <NUM> of the third embodiment of the invention includes a tread portion <NUM> as in the above-described pneumatic tire <NUM>. As in the above-described tread portion <NUM>, the tread portion <NUM> of the third embodiment of the invention includes a plurality of circumferential grooves <NUM> continuously extending in the tire circumferential direction, and a plurality of land portions <NUM> demarcated by the plurality of circumferential grooves <NUM>. As in the above-described ground-contact surface shape 2a, the ground-contact surface shape 22a in <FIG> is a ground-contact surface shape of the tread portion <NUM> in a load-applied state where a load that is <NUM>% of a standardized load is applied in a standardized state.

As in the above-described circumferential grooves <NUM>, the plurality of circumferential grooves <NUM> of the third embodiment of the invention include a first shoulder circumferential groove 23A, a second shoulder circumferential groove 23B, a first middle circumferential groove 23C, and a second middle circumferential groove 23D. As in the above-described land portions <NUM>, the plurality of land portions <NUM> of the third embodiment of the invention include a first shoulder land portion 24A, a second shoulder land portion 24B, a first middle land portion 24C, a second middle land portion 24D, and a crown land portion 24E.

The first shoulder land portion 24A and the first middle land portion 24C of the third embodiment of the invention are each a pattern land portion <NUM> on which axial grooves <NUM> are arranged in the tire circumferential direction with a number of pitches N so as to extend in the tire axial direction. <FIG> illustrates that the axial grooves <NUM> of the first shoulder land portion 24A and the first middle land portion 24C extend along the tire axial direction. Such axial grooves <NUM> serve to improve the wear resistance of the pneumatic tire <NUM>.

In the pattern land portion <NUM> of the third embodiment of the invention, a length L1 in the tire circumferential direction of a portion, of a first ground-contact end edge <NUM>, traversing the first middle land portion 24C approximates each pitch P in the tire circumferential direction of the axial grooves <NUM> of the first middle land portion 24C. In such a pattern land portion <NUM>, the axial grooves <NUM> sequentially come into contact with the ground when the pneumatic tire <NUM> contacts the ground, so that the pattern land portion <NUM> can further reduce pitch noise.

In the pattern land portion <NUM> of the third embodiment of the invention, a length L2 in the tire circumferential direction of a portion, of a second ground-contact end edge <NUM>, traversing the first middle land portion 24C approximates each pitch P in the tire circumferential direction of the axial grooves <NUM> of the first middle land portion 24C. In such a pattern land portion <NUM>, the axial grooves <NUM> sequentially become separated from the ground when the pneumatic tire <NUM> is separated from the ground, so that the pattern land portion <NUM> can further reduce pitch noise.

Each pitch P in the tire circumferential direction of the axial grooves <NUM> of the first middle land portion 24C is preferably smaller than each pitch P in the tire circumferential direction of the axial grooves <NUM> of the first shoulder land portion 24A. As for such pattern land portions <NUM>, the first shoulder land portion 24A and the first middle land portion 24C can cooperate to reduce pitch noise.

Although not shown, the second shoulder land portion 24B and the second middle land portion 24D are also preferably pattern land portions <NUM> in which pitches P of axial grooves <NUM> are equal to those of the first shoulder land portion 24A and the first middle land portion 24C. The tread portion <NUM> can achieve the above-described effects if any one of the first shoulder land portion 24A, the second shoulder land portion 24B, the first middle land portion 24C, and the second middle land portion 24D is a pattern land portion <NUM>.

Although the particularly preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made to implement the present invention within the scope of the appended claims.

Two types of pneumatic tires (first and second tires) having the pattern land portion shown in <FIG> and having different sizes were produced as test tires such that first shoulder land portions thereof had specifications in Table <NUM> and Table <NUM>, and were tested for noise performance, drainage performance, and wear resistance. Common specifications and test methods are as follows.

Using a drum type tester installed in an anechoic room, sound pressure was measured when a test tire was caused to coast from <NUM>/h to <NUM>/h. The results are represented as indexes with the result of Comparative Example <NUM> being regarded as <NUM> for the first tires and with the result of Comparative Example <NUM> being regarded as <NUM> for the second tires. A higher value indicates that the sound pressure is lower and that the noise performance is better.

Using an inside drum type tester, a running speed at which a hydroplaning phenomenon occurred was measured for a test tire. The results are represented as indexes with the result of Comparative Example <NUM> being regarded as <NUM> for the first tires and with the result of Comparative Example <NUM> being regarded as <NUM> for the second tires. A higher value indicates that the running speed is higher and that the drainage performance is better.

Using a bench wear energy evaluation tester, the wear energy of a test tire was measured. The results are represented as indexes with the result of Comparative Example <NUM> being regarded as <NUM> for the first tires and with the result of Comparative Example <NUM> being regarded as <NUM> for the second tires. A higher value indicates that the wear energy is smaller and that the wear resistance is better.

The results of the tests are shown in Table <NUM> and Table <NUM>. Thereby, example tires Ex. <NUM> to Ex. <NUM> refer to not-claimed embodiments.

Here, a parameter α is the following formula (<NUM>). <NUM>] <MAT>.

Claim 1:
A pneumatic tire (<NUM>, <NUM>, <NUM>) comprising a tread portion (<NUM>, <NUM>, <NUM>), wherein
the tread portion (<NUM>, <NUM>, <NUM>) includes a plurality of circumferential grooves (<NUM>, <NUM>, <NUM>) continuously extending in a tire circumferential direction, and a plurality of land portions (<NUM>, <NUM>, <NUM>) demarcated by the plurality of circumferential grooves (<NUM>, <NUM>, <NUM>),
the plurality of land portions (<NUM>, <NUM>, <NUM>) include at least one pattern land portion (<NUM>, <NUM>, <NUM>) on which axial grooves (<NUM>, <NUM>, <NUM>) are arranged in a number of N pitches in the tire circumferential direction so as to extend in a tire axial direction, and
in a load-applied state where a load that is <NUM>% of a standardized load is applied in a state where the pneumatic tire (<NUM>, <NUM>, <NUM>) is fitted on a standardized rim and adjusted to a standardized internal pressure, a ground-contact surface shape (2a, 12a, 22a) of the tread portion (<NUM>, <NUM>, <NUM>) has a first tread end (Te1), a second tread end (Te2), and a first ground-contact end edge (<NUM>, <NUM>, <NUM>) extending from the first tread end (Te1) to the second tread end (Te2) on one side in the tire circumferential direction,
characterized in that
the number of pitches N is not less than <NUM>, and
a first straight line (7a) connecting both ends in the tire axial direction of a portion, of the first ground-contact end edge (<NUM>, <NUM>, <NUM>), traversing the pattern land portion (<NUM>, <NUM>, <NUM>) satisfies the following formula (<NUM>),
[Math. <NUM>] <MAT> where
N: number of pitches of the axial grooves (<NUM>, <NUM>, <NUM>)
L: tire circumferential length at a tire equator (C) (m)
w: width in the tire axial direction of the pattern land portion (<NUM>, <NUM>, <NUM>) (m)
θ1: angle of the first straight line (7a) with respect to the tire axial direction (°).