TYRE

Abstract

A tyre includes a tread portion including first and second land portions. The first middle land portion is provided with first middle lateral grooves traversing the first middle land portion completely. The second middle land portion is provided with second middle lateral grooves traversing the second middle land portion completely. One of the first middle lateral grooves includes a raised portion in which a groove bottom thereof is raised, the raised portion traversing an axial center location of the first middle land portion. One of the second middle lateral grooves includes a raised portion in which a groove bottom thereof is raised, the raised portion traversing an axial center location of the second middle land portion. An axial length of the raised portion of the first middle lateral groove is greater than an axial length of the raised portion of the second middle lateral groove.

Description

BACKGOUND ART

Field of the disclosure

The present disclosure relates to a tyre, more particularly to a tyre including a tread portion having a designated mounting direction to a vehicle.

Description of the Related Art

Recently, tyres having tread portions with a. designated mounting direction to a vehicle have been proposed. For example, the following Patent document 1 discloses a pneumatic tyre including a tread center land portion which is provided with a plurality of center sipes having a width of less than 2 mm, but is not provided with any grooves that have groove widths more than 2 mm and that traverse the land portion completely in the tyre axial direction. The above-mentioned pneumatic tyre enhances stiffness of the tread center land portion, thus expecting to improve steering stability on dry road conditions.

• [Patent document 1] Japanese Unexamined Patent Application Publication 2015-140047

SUMMARY OF THE DISCLOSURE

Since the tread center land portion has high stiffness, the above-mentioned pneumatic tyre tends to deteriorate noise performance due to large impact noise generated by the tread center land portion upon grounding. The inventors have found out that steering stability and noise performance of tyre can be improved by improving an arrangement of the lateral grooves in tyres having a tread portion with a designated mounting direction.

The present disclosure has been made in view of the above problem and has a major object to provide a tyre capable of improving steering stability and noise performance.

In one aspect of the disclosure, a tyre includes a tread portion having a designated mounting direction to a vehicle, the tread portion including a first tread edge and a second tread edge to be located outwardly and inwardly of a vehicle, respectively, when being mounted to the vehicle, two or more main grooves extending continuously in a tyre circumferential direction between the first tread edge and the second tread edge, and two or more land portions divided by the main grooves, wherein the main grooves include a first shoulder main groove disposed between the first tread edge and a tyre equator, a second shoulder main groove disposed between the second tread edge and the tyre equator, and a crown main groove disposed between the first shoulder main groove and the second shoulder main groove, the land portions include a first middle land portion defined between the first shoulder main groove and the crown main groove, and a second middle land portion defined between the second shoulder main groove and the crown main groove, the first middle land portion is provided with two or more first middle lateral grooves traversing the first middle land portion completely in a tyre axial direction, the second middle land portion is provided with two or more second middle lateral grooves traversing the second middle land portion completely in the tyre axial direction, at least one of the first middle lateral grooves includes a raised portion in which a groove bottom thereof is raised, the raised portion of the at least one of the first middle lateral grooves traversing a center location in the tyre axial direction of the first middle land portion, at least one of the second middle lateral grooves includes a raised portion in which a groove bottom thereof is raised, the raised portion of the at least one of the second middle lateral grooves traversing a center location in the tyre axial direction of the second middle land portion, and a length in the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves is greater than a length in the tyre axial direction of the raised portion of the at least one of the second middle lateral grooves.

In another aspect of the disclosure, the length in the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves may be in a range of from 1.05 to 1.25 times the length in the tyre axial direction of the raised portion the at least one of the second middle lateral grooves.

In another aspect of the disclosure, a depth of the raised portion of the at least one of the first middle lateral grooves and a depth of the raised portion of the at least one of the second middle lateral grooves may be in a range of from 0.10 to 0.60 times a depth of the crown main groove.

In another aspect of the disclosure, in a plan view of the tread portion, each of the first middle lateral grooves and the second middle lateral grooves may be provided with the raised portion which is inclined at an angle with respect to the tyre axial direction, a first outer portion extending from a first end of the raised portion and having a smaller angle with respect to the tyre axial direction than the angle of the raised portion, and a second outer portion extending from a second end of the raised portion and having a smaller angle with respect to the tyre axial direction than the angle of the raised portion, so as to form a curved groove.

In another aspect of the disclosure, the curved groove may have an S-shaped manner.

In another aspect of the disclosure, in each of the first middle lateral grooves and the second middle lateral grooves, a length in the tyre axial direction of the raised portion may be greater than those in the tyre axial direction of the first outer portion and the second outer portion.

In another aspect of the disclosure, in each of the second middle lateral grooves, a length in the tyre axial direction of the second outer portion may be greater than a length in the tyre axial direction of the first outer portion.

In another aspect of the disclosure, in each of the second middle lateral grooves, a length in the tyre axial direction of the second outer portion may be in a range of from 1.10 to 2.00 times a length in the tyre axial direction of the first outer portion.

In another aspect of the disclosure, in each of the second middle lateral grooves, the second outer portion may be arranged on the second tread edge side with respect to the raised portion.

In another aspect of the disclosure, in each first middle lateral groove, a length in the tyre axial direction of the first outer portion may be same as a length in the tyre axial direction of the second outer portion.

In another aspect of the disclosure, in a. plan view of the tread portion, each of the first middle lateral grooves and the second middle lateral grooves may be a curved groove which includes a first convex portion located on a first side with respect to groove-reference-straight-line that connects both ends of a groove centerline thereof and a second convex portion located on a second side with respect to the groove-reference-straight-line of the curved groove.

In another aspect of the disclosure, in a plan view of the tread portion, the raised portion of the at least one of the first middle lateral grooves may be inclined in a first direction with respect to the tyre axial direction, and the raised portion of the at least one of the second middle lateral grooves may be inclined in a second direction which is opposite to the first direction with respect to the tyre axial direction.

In another aspect of the disclosure, an angle θ1 with respect to the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves may be smaller than an angle θ2 with respect to the tyre axial direction of the raised portion of the at least one of the second middle lateral grooves.

In another aspect of the disclosure, the first middle lateral grooves and the second middle lateral grooves, at both ends thereof in the tyre axial direction, may have a depth in a range of from 0.30 to 0.80 times a depth of the crown main groove.

In another aspect of the disclosure, a length in the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves may be in a range of from 0.30 to 0.80 times a width in the tyre axial direction of the first middle land portion.

In another aspect of the disclosure, a length in the tyre axial direction of the raised portion of the least one of the second middle lateral grooves may be in a range of from 0.30 to 0.80 times a width in the tyre axial direction of the second middle land portion.

In another aspect of the disclosure, the first middle land portion may include two or more first middle blocks divided by the first middle lateral grooves, the second middle land portion may include two or more second middle blocks divided by the second middle lateral grooves, each first middle lateral groove may have a groove-reference-straight-line that connects both ends of a groove centerline thereof being inclined in a first direction with respect to the tyre axial direction, and each second middle lateral groove may have a groove-reference-straight-line that connects both ends of a groove centerline thereof being inclined in a second direction which is opposite to the first direction with respect to the tyre axial direction.

In another aspect of the disclosure, each first middle block may be a smooth block having a ground contacting face which is not provided with any grooves nor sipes, and each second middle block may be provided with at least one second middle sipe extending from the second shoulder main groove and terminating within the second middle block.

In another aspect of the disclosure, in a plan view of the tread portion, the raised portion of the at least one of the second middle lateral grooves may overlap with the at least one second middle sipe in the tyre axial direction

In another aspect of the disclosure, a length in the tyre circumferential direction of the groove-reference-straight-line of each first middle lateral groove may he smaller than a length in the tyre circumferential direction of the groove-reference-straight-line of each second middle lateral groove.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a development view of a tread portion of a tyre in accordance with an embodiment of the present disclosure;

FIG. 2 is an enlarged view of a first middle land portion and a second middle land portion of FIG. 1;

FIG. 3 is a cross-sectional view taken along line A-A of FIG. 2;

FIG. 4 is an enlarged view of a first shoulder land portion of FIG. 1;

FIG. 5 is a cross-sectional view taken along line B-B of FIG. 4;

FIG. 6 is an enlarged view of a second shoulder land portion of FIG. 1;

FIG. 7 is a cross-sectional view taken along line C-C of FIG. 6;

FIG. 8 is a cross-sectional view taken along line D-D of FIG. 6; and

FIG. 9 is an enlarged view of the first middle land portion and the second middle land portion of a tyre according to a comparative example 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present disclosure will be explained below with reference to the accompanying drawings. FIG. 1 illustrates a development view of a tread portion 2 of a tyre 1 in accordance with an embodiment of the present disclosure. The tyre 1 according to the present embodiment is preferably embodied as a pneumatic tyre for passenger car. Note that the tyre 1 is not limited to such an aspect but can be embodied as a heavy-duty tyre and a non-pneumatic tyre which can structurally support the tyre load without being inflated with a compressed air, for example.

As illustrated in FIG. 1, the tyre 1 according to the present disclosure includes the tread portion 2 having a designated mounting direction to a vehicle. The tread portion 2 includes a first tread edge Te1 to be located outwardly of a vehicle when being mounted to the vehicle, and a second tread edge Te2 to be located inwardly of the vehicle when being mounted to the vehicle. The mounting direction to a vehicle may be indicated on a sidewall portion (not illustrated) using a letter or mark.

The first tread edge Te1 and the second tread edge Te2, when the tyre 1 is a pneumatic tyre, are the axial outermost edges of the ground contacting patch of the tyre 1 which occurs under a normal condition with a standard tyre load when the camber angle of the tyre is zero. As used herein, the “normal condition” is such that the tyre 1 is mounted onto a standard wheel rim with a standard pressure but loaded with no tyre load. Unless otherwise noted, dimensions of respective portions of the tyre 1 are values measured under the normal condition.

The “standard wheel rim” is a wheel rim officially approved for each tyre by standards organizations on which the tyre is based, wherein the standard wheel rim is the “standard rim” specified in JATMA, the “Design Rim” in TRA, and the “Measuring Rim” in ETRTO, for example.

The “standard pressure” is a standard pressure officially approved for each tyre by standards organizations on which the tyre is based, wherein the standard pressure is the “maximum air pressure” in JATMA, the maximum pressure given in the “Tire Load. Limits at Various Cold inflation Pressures” table in TRA, and the “Inflation Pressure” in ETRTO, for example.

The standard tyre load is a tyre load officially approved for each tyre by standards organizations in which the tyre is based, wherein the standard tyre load is the “maximum load capacity” in JATMA, the maximum value given in the above-mentioned table in TRA, the “Load Capacity” in ETRTO, for example.

The tread portion 2 includes two or more main grooves 3 extending continuously in the tyre circumferential direction between the first tread edge Te1 and the second tread edge Te2, and two or more land portions 4 divided by the main grooves 3.

The main grooves 3 include a first shoulder main groove 5 disposed between the first tread edge Te1 and the tyre equator C, a second shoulder main groove 6 disposed between the second tread edge Te2 and the tyre equator C, and a crown main groove 7 disposed between the first shoulder main groove 5 and the second shoulder main groove 6.

It is preferable that a length La in the tyre axial direction from the tyre equator C to a groove centerline of either one of the first shoulder main groove 5 or the second shoulder main groove 6, for example, is in a range of from 0.15 to 0.30 times the tread width TW. The tread width TW is a distance in the tyre axial direction from the first tread edge Te1 to the second tread edge Te2 under the normal condition.

As the crown main groove 7 according to the present embodiment, a single crown groove is provided on the tyre equator C, for example. In another aspect, two crown main groove 7 may be provided such that the tyre equator C is located therebetween, for example.

Each main groove 3 according to the present embodiment, for example, extends in a straight shape parallel with the tyre circumferential direction, i.e., having a pair of groove edges extending straight shape parallel with the tyre circumferential direction. Alternatively, the main grooves 3, for example, may extend in a zigzag or wavy manner.

It is preferable that a groove width Wa of the main grooves 3, for example, is in a range of from 4.0% to 7.0% of the tread width TW. It is preferable that a depth of the main grooves 3, for example, is in a range of from 5 to 10 mm for a pneumatic passenger car tyre.

The land portions 4 include a first middle land portion 11, a second middle land portion 12, a first shoulder land portion 13, and a second shoulder land portion 14. The tread portion 2 according to the present embodiment has a four-rib pattern which is configured by three main grooves 3 and four land portions 4. In another aspect of the present disclosure, the tread portion 2 may have a five-rib pattern which is configured by five land portions 4 divided by four main grooves including two crown main grooves 7, for example.

The first middle land portion 11 is defined between the first shoulder main groove 5 and the crown main groove 7. The second middle land portion 12 is defined between the second shoulder main groove 6 and the crown main groove 7. The first shoulder land portion 13 is defined between the first shoulder main groove 5 and the first tread edge Te1. The second shoulder land portion 14 is defined between the second shoulder main groove 6 and the second tread edge Te2.

FIG. 2 illustrates an enlarged view of the first middle land portion 11 and the second middle land portion 12. As illustrated in FIG. 2, it is preferable that widths W1 and W2 in the tyre axial direction of the first middle land portion 11 and the second middle land portion 12, respectively, are preferably in a range of from 0.10 to 0.25 times the tread width TW, for example.

The first middle land portion 11 is provided with two or more first middle lateral grooves 16. The first middle lateral grooves 16 traverse the first middle land portion 11 completely in the tyre axial direction. The second middle land portion 12 is provided with two or more second middle lateral grooves 17. The second middle lateral grooves 17 traverse the second middle land portion 12 completely in the tyre axial direction. A groove width of the first middle lateral grooves 16 and the second middle lateral grooves 17, for example, is in a range of from 0.10 to 0.20 times a groove width of the crown main groove 7.

FIG. 3 illustrates a cross-sectional view of one of the first middle lateral grooves 16 and one of the second middle lateral grooves 17 taken along line A-A of FIG. 2. As illustrated in FIG. 3, in the present disclosure, at least one of the first middle lateral grooves 16 includes a raised portion 18 in which a groove bottom thereof is raised. In addition, at least one of the second middle lateral grooves 17 includes a raised portion 19 in which a groove bottom thereof is raised.

To help understand the raised portions 18 and 19, they are colored on one of the first middle lateral grooves 16 and one of the second middle lateral grooves 17 in FIG. 2. As illustrated in FIG. 2, the raised portions 18 and 19 traverse the respective center locations in the tyre axial direction of the first middle land portion 11 and the second middle land portion 12, respectively. The first middle lateral groove 16 and the second middle lateral groove 17 which include the above-mentioned raised portions can prevent deformation of the first middle land portion 11 and the second middle land portion 12 effectively, and thus superior steering stability can be exerted. As a preferred embodiment, in the present embodiment, each of the first middle lateral grooves 16 and the second middle lateral grooves 17 includes a respective raised portion which has the above-mentioned structure.

Further, the first middle lateral grooves 16 and the second middle lateral grooves 17 can reduce pumping noise by the raised portions which disturb air flow through the grooves. In addition, the first middle lateral grooves 16 and the second middle lateral grooves 17 with the raised portions can ensure sufficient stiffness of the respective middle land portions, thus improving steering stability.

As illustrated in FIG. 3, a length L3 in the tyre axial direction of the raised portions 18 of the first middle lateral grooves 16 is greater than a length L4 in the tyre axial direction of the raised portions 19 of the second middle lateral grooves 17. Such a structure of the grooves can enhance stiffness of the first middle land portion 11 relatively. Thus, upon cornering where the center of the ground contact area moves to the first tread edge Te1 side, steering feeling can be linear, resulting in superior steering stability.

In some preferred embodiments, the length L3 of the raised portions 18 of the first middle lateral grooves 16 is in a range of from 1.05 to 1.25 times the length L4 of the raised portions 19 of the second middle lateral grooves 17. Such a configuration of the raised portions can help to improve steering stability and ride comfort in a well-balanced manner.

The length L3 in the tyre axial direction of the raised portions 18 of the first middle lateral grooves 16 is in a range of from 0.30 to 0.80 times the width W1 (shown in FIG. 2) in the tyre axial direction of the first middle land portion 11, for example. The length L4 in the tyre axial direction of the raised portions 19 of the second middle lateral grooves 17 is in a range of from 0.30 to 0.80 times the width W2 (shown in FIG. 2) in the tyre axial direction of the second middle land portion 12, for example.

A depth d2 of the raised portions 18 and 19, for example, is preferably equal to or more than 0.10 times, more preferably equal to or more than 0.20 times a depth d1 of the crown main groove 7, but preferably equal to or less than 0.60 times, more preferably equal to or less than 0.50 times the depth d1. In addition, the first middle lateral grooves 16 and the second middle lateral grooves 17, at both ends thereof in the tyre axial direction, have a depth in a range of from 0.30 to 0.80 times the depth d1 of the crown main groove 7. The first middle lateral grooves 16 and the second middle lateral grooves 17 configured as such can improve steering stability and ride comfort in a well-balanced manner.

As illustrated in FIG. 2, in a plan view of the tread portion, each of the first middle lateral grooves 16 is a curved groove which includes a first convex portion 16a located on a first side with respect to a groove-reference-straight-line 16c that connects both ends of a groove centerline thereof and a second convex portion 16b located on a second side with respect to the groove-reference-straight-line 16c. Similarly, each of the second middle lateral grooves 17 is a curved groove which includes a first convex portion 17a located on the first side with respect to a groove-reference-straight-line 17c that connects both ends of a groove centerline thereof and a second convex portion 17b located on the second side with respect to the groove-reference-straight-line 17c. In some preferred embodiments, the curved grooves have an S-shaped manner.

Since the first middle lateral grooves 16 and the second middle lateral grooves 17 can mitigate stiffness of the respective middle land portions, impact noise generated by the respective middle land portions can be reduced. In particular, the S-shaped first and second middle lateral grooves 16 and 17 can facilitate deformation along the respective groove-reference-straight-lines so that impact noise can be reduced. In addition, the above-mentioned curved grooves can help to reduce pumping noise upon grounding since the curved grooves enable to make the air flowing in the grooves slow down.

In the present embodiment, each first middle lateral groove 16 is configured such that an entire center portion 16d in the tyre axial direction thereof is the above-mentioned raised portion 18. Specifically, each first middle lateral groove 16 includes the center portion 16d (the raised portion 18) traversing the center location in the tyre axial direction of the first middle land portion 11 obliquely, a first outer portion 16e, and a second outer portion 16f. The first outer portion 16e extends from one end side of the center portion 16d at a smaller angle with respect to the tyre axial direction than that of the center portion 16d. The second outer portion 16f extends from the other end side of the center portion 16d at a smaller angle with respect to the tyre axial direction than that of the center portion 16d. In the present embodiment, the first outer portion 16e is arranged on the first tread edge Te1 side with respect to the center portion 16d, and the second outer portion 16f is arranged on the second tread edge Te2 side with respect to the center portion 16d.

Similarly, each second middle lateral grooves 17 is configured such that an entire center portion 17d in the tyre axial direction thereof is the above-mentioned raised portion 19. Specifically, each second middle lateral groove 17 includes the center portion 17d (the raised portion 19) traversing the center location in the tyre axial direction of the second middle land portion 12 obliquely, a first outer portion 17e, and a second outer portion 17f. The first outer portion 17e extends from one end side of the center portion 17d at a smaller angle with respect to the tyre axial direction than that of the center portion 17d. The second outer portion 17f extends from the other end side of the center portion 17d at a smaller angle with respect to the tyre axial direction than that of the center portion 17d. In the present embodiment, the first outer portion 17e is arranged on the first tread edge Te1 side with respect to the center portion 17d, and the second outer portion 17f is arranged on the second tread edge Te2 side with respect to the center portion 17d.

In the present embodiment, the groove-reference-straight-line 16c of each first middle lateral groove 16, for example, is inclined in a first direction (e.g. downward to the right) with respect to the tyre axial direction. In addition, it is preferable that each first middle lateral groove 16 has the raised portion 18 which is inclined in the first direction with respect to the tyre axial direction. In each first middle lateral groove 16, an angle θ1 of the raised portion 18 with respect to the tyre axial direction is greater than an angle of the groove-reference-straight-line 16c with respect to the tyre axial direction. Specifically, the angle θ1 of the raised portion 18 of each first middle lateral groove 16 with respect to the tyre axial direction is preferably in a range of from 5 to 40 degrees, more preferably from 15 to 30 degrees.

In the present embodiment, the groove-reference-straight-line 17c of each second middle lateral groove 17, for example, is inclined with respect to the tyre axial direction in a second direction (e.g., upward to the right) opposite to the first direction.

The first middle lateral grooves 16 and the second middle lateral grooves 17 configured as such can suppress “tyre pull” in which unequal forces cause a vehicle to pull to the side due to the tread pattern even when it is steered straight ahead, thus improving steering stability. in addition, the first middle lateral grooves 16 and the second middle lateral grooves 17 help to disperse frequency ranges of the respective pumping noise, thus improving noise performance.

In each second middle lateral groove 17, it is preferable that the raised portion 19 is inclined in the second direction with respect to the tyre axial direction. In each second middle lateral groove 17, an angle θ2 of the raised portion 19 with respect to the tyre axial direction is greater than an angle of the groove-reference-straight-line 17c with respect to the tyre axial direction. Specifically, the angle θ2 of the raised portion 19 of each second middle lateral groove 17 with respect to the tyre axial direction is preferably in a range of from 20 to 60 degrees, more preferably in a range of from 40 to 55 degrees.

In the present embodiment, the angle θ1 of the raised portion 18 of each first middle lateral groove 16 with respect to the tyre axial direction is smaller than the angle θ2 of the raised portion 19 of each second middle lateral groove 17 with respect to the tyre axial direction. Thus, stiffness of the first middle land portion 11 in the tyre axial direction can be enhanced relatively, improving steering stability further.

As illustrated in FIG. 3, in each first middle lateral groove 16, a length L3 in the tyre axial direction of the raised portion 18 is greater than a length L5 in the tyre axial direction of the first outer portion 16e and a length L6 in the tyre axial direction of the second outer portion 16f. Similarly, in each second middle lateral groove 17, a length L4 in the tyre axial direction of the raised portion 19 is greater than a length L7 in the tyre axial direction of the first outer portion 17e and a length L8 in the tyre axial direction of the second outer portion 17f. The first middle lateral grooves 16 and the second middle lateral grooves 17 configured as such can enhance stiffness of the first middle land portion 11 and the second middle land portion 12 sufficiently, exerting superior steering stability.

In each first middle lateral groove 16, the length L6 in the tyre axial direction of the second outer portion 16f is preferably in a range of from 0.90 to 1.10 times the length L5 in the tyre axial direction of the first outer portion 16e. In the present embodiment, in each first middle lateral groove 16, the length L6 of the second outer portion 16f is the same as the length L5 of the first outer portion 16e.

In each second middle lateral groove 17, it is preferable that the length L8 in the tyre axial direction of the second outer portion 17f is greater than the length L7 in the tyre axial direction of the first outer portion 17e. Specifically, the length L8 of the second outer portion 17f, for example, is preferably in a range of from 1.10 to 2.00 times the length L7 of the first outer portion 17e. Thus, stiffness of the second middle lateral grooves 17 on the first tread edge Te1 side can be enhanced, enabling to provide a linear steering response upon cornering.

Further, by configuring the raised portions 18 and 19 as described above, the respective ranges of frequency of pumping noise generated by the first middle lateral grooves 16 and the second middle lateral grooves 17 can be deviated, generating white noise.

As illustrated in FIG. 2, it is preferable that a length L1 in the tyre circumferential direction of the groove-reference-straight-line 16c of each first middle lateral groove 16 is smaller than a length L2 in the tyre circumferential direction of the groove-reference-straight-line 17c of each second middle lateral groove 17. Such a groove arrangement enables to enhance stiffness in the tyre axial direction of the first middle land portion 11 relatively. Thus, upon cornering where the center of the ground contacting surface moves toward the first tread edge Te1, a linear steering response can be obtained which provides better steering stability.

It is preferable that the length in the tyre circumferential direction of the groove-reference-straight-line 16c of each first middle lateral groove 16 is in a range of from 0.20 to 0.40 times the length in the tyre circumferential direction of the groove-reference-straight-line 17c of each second middle lateral groove 17. Such a groove arrangement can improve a linear steering response upon cornering further.

It is preferable that the length L1 in the tyre circumferential direction of the groove-reference-straight-line 16c of each first middle lateral groove 16, for example, is smaller than pitch lengths P1 in the tyre circumferential direction of the first middle lateral grooves 16. Specifically, the length L1 in the tyre circumferential direction of the groove-reference-straight-line 16c of each first middle lateral groove 16 is preferably in a range of from 0.05 to 0.20 times the pitch lengths P1 in the tyre circumferential direction of the first middle lateral grooves 16, for example. An arrangement of the first middle lateral grooves 16 as such helps to prevent uneven wear of the first middle land portion 11.

In the same view point, it is preferable that the length L2 in the tyre circumferential direction of the groove-reference-straight-line 17c of each second middle lateral groove 17, for example, is smaller than pitch lengths P2 in the tyre circumferential direction of the second middle lateral grooves 17. Specifically, the length L2 in the tyre circumferential direction of the groove-reference-straight-line 17c of each second middle lateral groove 17 is preferably in a range of from 0.35 to 0.50 times the pitch lengths P2 in the tyre circumferential direction of the second middle lateral grooves 17, for example. Note that the pitch lengths P2 of the second middle lateral grooves 17 are the same as the pitch lengths P1 of the first middle lateral grooves 16.

A maximum distance L9 of each first middle lateral groove 16 between a groove edge thereof and the groove-reference-straight-line 16c thereof is smaller than a maximum distance L10 of each second middle lateral groove 17 between a groove edge thereof and the groove-reference-straight-line 17c thereof. Thus, stiffness of the first middle land portion 11 can be enhanced relatively, and the above-mentioned effects can further be improved.

It is preferable that the first middle lateral grooves 16 are arranged so as to be continuous to the respective second middle lateral grooves 17 smoothly through the crown main groove 7. As used herein, “one lateral groove is continuous to another lateral groove smoothly through a main groove” shall mean that respective regions in which the lateral grooves are elongated along the respective groove longitudinal directions, in the tyre circumferential direction, overlap with one another within the main groove, or that the respective regions, in the tyre circumferential direction, are located away from one another within a distance of less than 1.0 mm within the main groove. If a lateral groove is curved, the above-mentioned region is defined such that the lateral groove is elongated while keeping the radius of curvature of an axial end thereof on the main groove side.

The first middle land portion 11 includes a plurality of first middle blocks 21 divided by the first middle lateral grooves 16. The second middle land portion 12 includes a plurality of second middle blocks 22 divided by the second middle lateral grooves 17.

In the present embodiment, each first middle blocks 21, for example, is a smooth block having a ground contacting face which is not provided with any grooves nor sipes. As used herein, “sipe” shall mean a narrow cut having a width of less than 1.5 mm.

Each second middle block 22 is provided with a second middle sipe 23 which extends from the second shoulder main groove 6 and which terminates within the second middle block 22. In the present embodiment, the second middle sipe 23, for example, has a width of from 0.5 to 1.0 mm. Such first middle blocks 21 and second middle blocks 22 can enhance stiffness of the first middle land portion 11 relatively, providing a linear steering response so that steering stability can be improved.

It is preferable that a length L11 in the tyre axial direction of each second middle sipe 23, for example, is in a range of from 0.20 to 0.80 times the width W2 in the tyre axial direction of the second middle land portion 12. Such a second middle sipe 23 can help to improve steering stability and ride comfort in a well-balanced manner.

It is preferable that the raised portion 19 of each second middle lateral groove 17 overlaps with the respective second middle sipes 23 in the tyre axial direction. Thus, the second middle sipes 23 can help to reduce impact noise generated when the second middle land portion 12 grounds, improving noise performance,

For example, a maximum depth of the second middle sipes 23 is in a range of from 0.90 to 1.10 times the depths of the raised portions 19 of the second middle lateral grooves 17. In the present embodiment, the maximum depth of the second middle sipes 23 is the same as the depths of the raised portions 19 of the second middle lateral grooves 17. The second middle sipes 23 can help to prevent uneven wear of the second middle land portion 12.

FIG. 4 illustrates an enlarged view of the first shoulder land portion 13. As illustrated in FIG. 4, the first shoulder land portion 13 is provided with a plurality of first shoulder lateral grooves 25 traversing the first shoulder land portion 13 completely in the tyre axial direction. A groove width of the plurality of first shoulder lateral grooves 25, for example, is in a range of from 0.35 to 0.50 times the groove width of the first shoulder main groove 5.

Each first shoulder lateral groove 25, for example, is inclined in the second direction. An angle θ3 of the first shoulder lateral grooves 25, for example, is in a range of from 5 to 15 degrees with respect to the tyre axial direction.

It is preferable that an inner end in the tire axial direction of at least one of the first shoulder lateral grooves 25 is located in a different position in the tyre circumferential direction from the axially outer ends of the respective first middle lateral grooves 16. In addition, it is preferable that a minimum distance L12 in the tyre circumferential direction between the inner end of the at least one of the first shoulder lateral grooves 25 and the outer ends of the respective first middle lateral grooves 16, for example, is equal to or less than 0.35 times pitch lengths P3 in the tyre circumferential direction of the first shoulder lateral grooves 25. Note that the minimum distance L12 is measured between groove centerlines of the inner end and the respective first shoulder lateral grooves 25. Thus, pumping noise generated when regions of intersections of the first shoulder lateral grooves 25 and the first shoulder main groove 5 come into contact with the ground can be reduced.

FIG. 5 illustrates a cross-sectional view of one of the first shoulder lateral grooves 25 taken along line B-B of FIG. 4. As illustrated in FIG. 5, one or more first shoulder lateral grooves 25 include a shallow bottom portion 26 having a raised bottom face in an end region on the first shoulder main groove 5 side thereof. Such first shoulder lateral grooves 25 can enhance stiffness of the first shoulder land portion 13, improving steering stability.

Preferably, a length L13 in the tyre axial direction of the shallow bottom portion 26 of the first shoulder lateral grooves 25, for example, is in a range of from 0.20 to 0.30 times the width W3 (shown in FIG. 4) in the tyre axial direction of the first shoulder land portion 13. In some preferred embodiments, the length L13 in the tyre axial direction of the shallow bottom portion 26 of the first shoulder lateral grooves 25, for example, is smaller than lengths L3 and L4 of the raised portions 18 (shown in FIG. 3) and 19 (shown in FIG. 4) of the first middle lateral grooves 16 and the second middle lateral grooves 17, respectively. The first shoulder lateral groove 25 configured as such can prevent excessive increase of stiffness of the first shoulder land portion 13, helping to improve steering stability and ride comfort in a well-balanced manner.

FIG. 6 illustrates an enlarged view of the second shoulder land portion 14. As illustrated in FIG. 6, the second shoulder land portion 14, for example, is provided with a plurality of second shoulder lateral grooves 31, a plurality of connecting sipes 32, and a plurality of non-traversing narrow grooves 33.

Each second shoulder lateral groove 31, for example, extends from the second tread edge Te2 inwardly in the tyre axial direction and terminates so as to have a terminating end 31a within the second shoulder land portion 14. A length L14 in the tyre axial direction of the second shoulder lateral grooves 31, for example, is in a range of from 0.50 to 0.70 times the width W4 in the tyre axial direction of the second shoulder land portion 14. A groove width of the second shoulder lateral grooves 31, for example, is in a range of from 0.30 to 0.50 times the groove width of the second shoulder main groove 6.

Each connecting sipe 32 extends from the terminating end 31a of a respective one of the second shoulder lateral grooves 31 to the second shoulder main groove 6. A length L15 in the tyre axial direction of the connecting sipes 32, for example, is in a range of from 0.30 to 0.50 times the width W4 in the tyre axial direction of the second shoulder land portion 14. The second shoulder lateral grooves 31 and the connecting sipes 32 can help to ensure stiffness of the second shoulder land portion 14, exerting superior steering stability. In addition, the second shoulder lateral grooves 31 and the connecting sipes 32 can generate less pumping noise, improving noise performance.

FIG. 7 illustrates a cross-sectional view of one of the second shoulder lateral grooves 31 and one of the connecting sipes 32 taken along line C-C of FIG. 6. As illustrated in FIG. 7, each second shoulder lateral groove 31, for example, in an end on the second shoulder main groove 6 side, includes an inclined bottom face 31b inclined at an angle with respect to the tyre axial direction. Thus, it helps to prevent the second shoulder land portion 14 from being formed a portion in which stiffness thereof is abruptly changed.

Each connecting sipe for example, includes a first portion 32a, a second portion 32b and a third portion 32c which have different depths from one another. The first portion 32a is connected to the second shoulder lateral groove 31. The second portion 32b is connected to the first portion 32a on the second shoulder main groove 6 side and has a depth greater than that of the first portion 32a. The third portion 32c is connected to the second portion 32b on the second shoulder main groove 6 side and has a depth smaller than those of the first portion 32a and the second portion 32b, Such a connecting sipe 32 can mitigate stiffness of the second shoulder land portion 14 moderately, improving steering stability and ride comfort in a well-balanced manner.

In each connecting sipe 32, depths of the first portion 32a and the second portion 32b, for example, are greater than that of the raised portions 19 of the second middle lateral grooves 17. A depth of the third portion 32c of each connecting sipe 32 is preferably smaller than that of the raised portions 19 of the second middle lateral grooves 17. Such a connecting sipe 32 can help to prevent uneven wear of the second shoulder land portion 14.

As illustrated in FIG. 6, the connecting sipes 32 are arranged so as to be continuous to the respective second middle sipes 23 smoothly through the second shoulder main groove 6.

Each non-traversing narrow groove 33, for example, extends from the second shoulder main groove 6 and terminates within the second shoulder land portion14. A length L16 in the tyre axial direction of each non-traversing narrow groove 33. for example, is in a range of from 0.50 to 0.65 times the width W4 in the tyre axial direction of the second shoulder land portion 14. The non-traversing narrow grooves 33 configured as such can improve noise performance while ensuring steering stability.

In some preferred embodiments, it is preferable that the length L16 in the tyre axial direction of each non-traversing narrow groove 33 is greater than the length L15 in the tyre axial direction of each connecting sipe 32. Such a non-traversing narrow groove 33 can mitigate stiffness of the second shoulder land portion 14 moderately, improving ride comfort.

It is preferable that the non-traversing narrow grooves 33, for example, are arranged so as to be continuous to the respective second middle lateral grooves 17 smoothly through the second shoulder main groove 6. Such a groove arrangement can help to reduce impact noise since the non-traversing narrow grooves 33 as well as the second middle lateral grooves 17 are easy to open when the second shoulder land portion 14 grounds.

FIG. 8 illustrates a cross-sectional view of one of the non-traversing narrow grooves 33 taken along line D-D of FIG. 6. As illustrated in FIG. 8, each non-traversing narrow groove 33, for example, includes an opening portion 33a on a ground contacting surface side and a narrow width portion 33b located inwardly in the tyre radial direction of the opening portion 33a and having a width smaller than that of the opening portion 33a. A width W5 of the narrow width portion 33b, for example, is in a range of from 0.5 to 1.0 mm. The non-traversing narrow grooves 33 can improve the above-mentioned effects without excessive reduction of stiffness of the second shoulder land portion 14.

As illustrated in FIG. 1, the above-mentioned structure can enhance stiffness of the first middle land portion 11 and the first shoulder land portion 13 relative to the land portions 12 and 14. Thus, the tyre 1 can generate large self-aligning torque (SAT). For example, a passenger car with four wheels equipped with the tyres 1 can generate the front cornering power approximate to the rear cornering power since the front cornering power is reduced by large SAT by the front tyres. Hence, a passenger car equipped with the tyres as its front and rear wheels according to the present embodiment, given a slip angle on the front wheels, tends to transit a neutral cornering state where the front cornering force substantially balances with the rear cornering force, exerting superior steering stability.

While the particularly preferable embodiments in accordance with the present disclosure have been described in detail, the present disclosure is not limited to the illustrated embodiments, but can be modified and carried out in various aspects.

EXAMPLE-1

Tyres (205/55R16) having the basic tread pattern shown in FIG. 1 with the first middle lateral grooves and the second middle lateral grooves provided with the raised portions shown in FIG. 3 were manufactured by way of trial based on the detail shown in Table 1. As a comparative example 1 (Ref. 1), tyres having the basic tread pattern shown in FIG. 1 with the first middle lateral grooves and the second middle lateral grooves were also manufactured by way of trial, wherein a length in the tyre axial direction of the raised portions of the first middle lateral grooves is the same as a length in the tyre axial direction of the raised portions of the second middle lateral grooves. Note that the length in the tyre axial direction of the raised portion of the first middle lateral grooves is the same as the length in the tyre axial direction of the raised portion of the tyre axial direction shown in FIG. 3. Then, steering stability and noise performance of each test tyre was tested. The common specification and the test method are as follows:

rim size: 16×6.5J;

tyre inner pressure: front 200 kPa and rear 200 kPa;

test vehicle: FF vehicle having displacement of 1600 cc; and

tyre location: all wheels.

Steering Stability Test:

A test driver drove the above-mentioned test vehicle on a dry road, and evaluated steering stability by the driver's sense when driving in low speed ranges (40 to 80 km/h) and high-speed ranges (100 to 120 km/h). The test results are shown in Table 1 using a score based on Ref. 1 being 100. The larger value indicates better steering stability.

Noise Performance Test:

Car interior noise was measured when the above-mentioned test vehicle was traveling on a dry road having bumps at speed ranges between 40 to 100 km/h in order to evaluate the maximum level of sound pressure of frequency ranges between 100 to 350 Hz. The test results are shown in Table 1 using an index based on Ref. 1 being 100. The smaller value indicates better noise performance.

Table 1 shows the test results.

	TABLE 1
	Ref. 1	Ex. 1	Ex. 2	Ex. 3	Ex. 4	Ex. 5	Ex. 6	Ex. 7	Ex. 8	Ex. 9
Length L3 of raised portions	1.00	1.16	1.05	1.10	1.20	1.25	1.16	1.16	1.16	1.16
of first middle lateral grooves/
length L4 of raised portions of
second middle lateral grooves
Depth d2 of raised portions/	0.37	0.37	0.37	0.37	0.37	0.37	0.10	0.20	0.50	0.60
depth d1 of crown main groove
Steering stability (score)	100	105	103	105	105	104	106	105	105	104
Noise performance (index)	100	97	98	98	97	96	99	98	97	97

From the test results, it is confirmed that the tyres (Ex. 1 to Ex. 9) improve steering stability and noise performance.

EXAMPLE-2

Tyres (205/55R16) having the basic tread pattern shown in FIG. 1 with the first middle lateral grooves and the second middle lateral grooves provided with the raised portions shown in FIG. 3 were manufactured by way of trial based on the detail shown in Table 2. As a comparative example 2 (Ref. 2), tyres having the basic tread pattern shown in FIG. 1 were also manufactured by way of trial, wherein no raised portions are provided on the first middle lateral grooves and the second middle lateral grooves, Note that the tyres of Ref. 2 have substantially the same configuration as that of FIG. 1 except the raised portions. Then, steering stability and noise performance of each test tyre was tested. The common specification and the test method are the same as mentioned above. As to the test results, the score as well as the index is indicated based on Ref. 2 being 100.

Table 2 shows the test results.

TABLE 2
	Ref. 2	Ex. 10	Ex. 11	Ex. 12	Ex. 13	Ex. 14	Ex. 15
Raised portions	none	presence	presence	presence	presence	presence	presence
Angle θ1 of raised portions of	20	20	5	15	30	40	20
first middle lateral grooves
(deg.)
Angle θ2 of raised portions of	50	50	20	30	55	60	50
second middle lateral grooves
(deg.)
Length L3 of raised portions of	—	0.54	0.54	0.54	0.54	0.54	0.30
first middle lateral grooves/
width W1 of first middle land
portion
Length L4 of raised portions of	—	0.47	0.47	0.47	0.47	0.47	0.30
second middle lateral grooves/
width W2 of second middle land
portion
Depth d2 of raised portions/	—	0.37	0.37	0.37	0.37	0.37	0.37
depth d1 of crown main groove
Steering stability (score)	100	110	108	110	109	107	107
Noise performance (index)	100	94	96	95	94	94	95
	Ex. 16	Ex. 17	Ex. 18	Ex. 19	Ex. 20	Ex. 21	Ex. 22
Raised portions	presence	presence	presence	presence	presence	presence	presence
Angle θ1 of raised portions of	20	20	20	20	20	20	20
first middle lateral grooves
(deg.)
Angle θ2 of raised portions of	50	50	50	50	50	50	50
second middle lateral grooves
(deg.)
Length L3 of raised portions of	0.40	0.60	0.80	0.54	0.54	0.54	0.54
first middle lateral grooves/
width W1 of first middle land
portion
Length L4 of raised portions of	0.40	0.60	0.80	0.47	0.47	0.47	0.47
second middle lateral grooves/
width W2 of second middle land
portion
Depth d2 of raised portions/	0.37	0.37	0.37	0.1	0.25	0.50	0.60
depth d1 of crown main groove
Steering stability (score)	108	110	110	109	110	108	106
Noise performance (index)	94	95	96	96	95	95	96

From the test results, it is confirmed that the tyres (Ex. 10 to Ex. prove steering stability and noise performance.

EXAMPLE-3

Tyres (205/55R16) having the basic tread pattern shown in FIG. 1 were manufactured by way of trial based on the detail shown in Table 3. As a comparative example 3 (Ref. 3), as illustrated in FIG. 9, the groove-reference-straight-lines d of the first middle lateral grooves c provided on the first middle land portion (a) are inclined with respect to the tyre axial direction in the same direction as the groove-reference-straight-lines f of the second middle lateral grooves (e) provided on the second middle land portion b. Note that the second middle land portion b of the tyres of Ref. 3 is not provided with the second middle sipe. The tread pattern of the tyre of Ref. 3, except the above-mentioned structure, is substantially the same as that of FIG. 1. Then, steering stability and noise performance of each test tyre was tested. The common specification and the test method are the same as mentioned above. As to the test results, the score as well as the index is indicated based on Ref. 3 being 100.

Table 3 shows the test results.

	TABLE 3
	Ref 3	Ex. 23	Ex. 24	Ex. 25	Ex. 26	Ex. 27	Ex. 28	Ex. 29
Figure showing first and second	FIG. 9	FIG. 2	FIG. 2	FIG. 2	FIG. 2	FIG. 2	FIG. 2	FIG. 2
middle land portions
Angle θ1 of raised portions of	20	20	20	20	20	20	50	50
first middle lateral grooves
Angle θ2 of raised portions of	50	50	50	50	50	50	50	20
second middle lateral grooves
Length L11 of second middle	—	0.35	0.20	0.30	0.50	0.80	0.35	0.35
sipes/width W2 of second middle
land portion
Steering stability (score)	100	107	106	106	105	104	103	101
Noise performance (index)	100	95	97	96	95	95	95	96

From the test results, it is confirmed that the tyres (Ex. 23 to Ex. 29) improve steering stability and noise performance.

Claims

1. A tyre comprising: a tread portion having a designated mounting direction to a vehicle, the tread portion comprisinga first tread edge and a second tread edge to be located outwardly and inwardly of a vehicle, respectively, when being mounted to the vehicle,two or more main grooves extending continuously in a tyre circumferential direction between the first tread edge and the second tread edge, andtwo or more land portions divided by the main grooves, whereinthe main grooves comprise a first shoulder main groove disposed between the first tread edge and a tyre equator, a second shoulder main groove disposed between the second tread edge and the tyre equator, and a crown main groove disposed between the first shoulder main groove and the second shoulder main groove,the land portions comprise a first middle land portion defined between the first shoulder main groove and the crown main groove, and a second middle land portion defined between the second shoulder main groove and the crown main groove,the first middle land portion is provided with two or more first middle lateral grooves traversing the first middle land portion completely in a tyre axial direction,the second middle land portion is provided with two or more second middle lateral grooves traversing the second middle land portion completely in the tyre axial direction,at least one of the first middle lateral grooves comprises a raised portion in which a groove bottom thereof is raised, the raised portion of the at least one of the first middle lateral grooves traversing a center location in the tyre axial direction of the first middle land portion,at least one of the second middle lateral grooves comprises a raised portion in which a groove bottom thereof is raised, the raised portion of the at least one of the second middle lateral grooves traversing a center location in the tyre axial direction of the second middle land portion, anda length in the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves is greater than a length in the tyre axial direction of the raised portion of the at least one of the second middle lateral grooves.

2. The tyre according to claim 1, wherein the length in the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves is in a range of from 1.05 to 1.25 times the length in the tyre axial direction of the raised portion the at least one of the second middle lateral grooves.

3. The tyre according to claim 1, wherein a depth of the raised portion of the at least one of the first middle lateral grooves and a depth of the raised portion of the at least one of the second middle lateral grooves are in a range of from 0.10 to 0.60 times a depth of the crown main groove.

4. The tyre according to claim 1, wherein in a plan view of the tread portion, each of the first middle lateral grooves and the second middle lateral grooves is provided with the raised portion which is inclined at an angle with respect to the tyre axial direction, a first outer portion extending from a first end of the raised portion and having a smaller angle with respect to the tyre axial direction than the angle of the raised portion, and a second outer portion extending from a second end of the raised portion and having a smaller angle with respect to the tyre axial direction than the angle of the raised portion, so as to form a curved groove.

5. The tyre according to claim 4, wherein the curved groove has an S-shaped manner.

6. The tyre according to claim 4, wherein in each of the first middle lateral grooves and the second middle lateral grooves, a length in the tyre axial direction of the raised portion is greater than those in the tyre axial direction of the first outer portion and the second outer portion.

7. The tyre according to claim 4, wherein in each of the second middle lateral grooves,a length in the tyre axial direction of the second outer portion is greater than a length in the tyre axial direction of the first outer portion.

8. The tyre according to claim 4, wherein in each of the second middle lateral grooves, a length in the tyre axial direction of the second outer portion is in a range of from 1.10 to 2.00 times a length in the tyre axial direction of the first outer portion.

9. The tyre according to claim 8, wherein in each of the second middle lateral grooves, the second outer portion is arranged on the second tread edge side with respect to the raised portion.

10. The tyre according to claim 4, wherein in each first middle lateral groove, a length in the tyre axial direction of the first outer portion is same as a length in the tyre axial direction of the second outer portion.

11. The tyre according to claim 1, wherein in a plan view of the tread portion, each of the first middle lateral grooves and the second middle lateral grooves is a curved groove which comprises a first convex portion located on a first side with respect to a groove-reference-straight-line that connects both ends of a groove centerline thereof and a second convex portion located on a second side with respect to the groove-reference-straight-line of the curved groove.

12. The tyre according to claim 11, wherein in a plan view of the tread portion,the raised portion of the at least one of the first middle lateral grooves is inclined in a first direction with respect to the tyre axial direction, andthe raised portion of the at least one of the second middle lateral grooves is inclined in a second direction which is opposite to the first direction with respect to the tyre axial direction.

13. The tyre according to claim 12, wherein an angle θ1 with respect to the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves is smaller than an angle θ2 with respect to the tyre axial direction of the raised portion of the at least one of the second middle lateral grooves.

14. The tyre according to claim 11, wherein the first middle lateral grooves and the second middle lateral grooves, at both ends thereof in the tyre axial direction, have a depth in a range of from 0.30 to 0.80 times a depth of the crown main groove.

15. The tyre according to claim 11, wherein a length in the tyre axial direction of the raised portion of the at least one of the first middle lateral grooves is in a range of from 0.30 to 0.80 times a width in the tyre axial direction of the first middle land portion.

16. The tyre according to claim 11, wherein a length in the tyre axial direction of the raised portion of the least one of the second middle lateral grooves is in a range of from 0.30 to 0.80 times a width in the tyre axial direction of the second middle land portion.

17. The tyre according to claim 1, wherein the first middle land portion comprises two or more first middle blocks divided by the first middle lateral grooves,the second middle land portion comprises two or more second middle blocks divided by the second middle lateral grooves,each first middle lateral groove has a groove-reference-straight-line that connects both ends of a groove centerline thereof being inclined in a first direction with respect to the tyre axial direction, andeach second middle lateral groove has a groove-reference-straight-line that connects both ends of a groove centerline thereof being inclined in a second direction which is opposite to the first direction with respect to the tyre axial direction.

18. The tyre according to claim 17, wherein each first middle block is a smooth block having a ground contacting face which is not provided with any grooves nor sipes, andeach second middle block is provided with at least one second middle sipe extending from the second shoulder main groove and terminating within the second middle block.

19. The tyre according to claim 18, wherein in a plan view of the tread portion, the raised portion of the at least one of the second middle lateral grooves overlaps with the at least one second middle sipe in the tyre axial direction,

20. The tyre according to claim 18, wherein a length in the tyre circumferential direction of the groove-reference-straight-line of each first middle lateral groove is smaller than a length in the tyre circumferential direction of the groove-reference-straight-line of each second middle lateral groove.