JP2021091332A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire making both on-dry steering stability and on-ice braking performance compatible.SOLUTION: In a tire planar view, when an ellipse whose areas are smallest of ellipses passing on at least three points of an outer edge of a land part (30) and surrounding the whole regions of the land part is defined as a circumscribed ellipse (O1) and when a region passing on a position which is away by a distance corresponding to 20% of a major diameter of the circumscribed ellipse and on a position which is away by a distance corresponding to 20% of a minor diameter of the circumscribed ellipse respectively from a center of the circumscribed ellipse and is surrounded by an ellipse (O2) concentric with the circumscribed ellipse is defined as a center part (31) of the land part, the land part has a top part (35) whose height in a tire radial direction is maximum at the center part.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a pneumatic tire that has both dry maneuverability and ice braking performance.

Conventionally, it has been attempted to improve the ground contact property, drainage performance, braking performance, turning performance, etc. by forming a land portion having a specific shape on the tire tread portion.

For example, in Patent Document 1, the shape of the land portion is composed of a plurality of blocks divided by a plurality of widthwise grooves, and each of the blocks is raised from all sides toward the central portion, and further. It is disclosed that the groove in the width direction can be designed to include a sipe to improve the ground contact property of the block and improve the drainage performance, the braking performance and the turning performance.

Japanese Unexamined Patent Publication No. 2017-222208

However, when a plurality of performances are improved at the same time as in the pneumatic tire of Patent Document 1, these performances may not be sufficiently compatible with each other. For example, steering stability on a dry road surface (hereinafter, "dry maneuverability") If one of the braking performance on a snowy road surface (hereinafter, may be referred to as “ice braking performance”) is improved, the performance of the other may usually deteriorate.

The present invention has been made in view of the above findings, and an object of the present invention is to provide a pneumatic tire having both dry maneuverability and ice braking performance.

The Discloser has found that the above tasks can be achieved by the following means:
(Aspect 1)
At least one land portion is partitioned by at least two circumferential grooves extending in the tire circumferential direction and at least two widthwise grooves extending in the tire width direction.
In the plan view of the tire, the ellipse that passes through at least three points of the outer edge of the land portion and has the smallest area among the ellipses surrounding the entire area of the land portion is defined as the circumscribing ellipse, and from the center of the circumscribing ellipse. When the region surrounded by the ellipse that passes through each of the 20% of the major axis and the minor axis of the circumscribing ellipse and is concentric with the circumscribing ellipse is the central portion of the land portion. ,
The land portion is a pneumatic tire having a top portion having a maximum height in the radial direction of the tire in the central portion.
(Aspect 2)
The pneumatic tire according to aspect 1, wherein the tire radial height of the land portion is gradually decreased radially at least outside the central portion.
(Aspect 3)
The pneumatic tire according to aspect 2, wherein the tire radial height of the land portion is gradually reduced in a curved shape at least outside the central portion in a cross-sectional view perpendicular to the tire rotation axis.
(Aspect 4)
The pneumatic tire according to aspect 2 or 3, wherein the tire radial height of the land portion is gradually decreased in a curved shape at least outside the central portion in a cross-sectional view of the tire meridian.
(Aspect 5)
In the tire plan view, the center of the circumscribed ellipse is set as the origin, and the dimension from the origin to the end of the land portion in the tire circumferential direction is a.
In a cross-sectional view perpendicular to the tire rotation axis, the tire circumferential direction is the X-axis, the tire radial direction is the Y-axis, the amount of variation in the tire radial height of the land portion is b, and the tire near the outer edge of the central portion. When the radial variation coefficient is _Pab and the tire radial variation coefficient near the tire circumferential edge is _Qab ,
The air according to aspect 3, wherein when the rim is assembled and 5% of the normal internal pressure is applied, the profile of the land portion that gradually decreases in a curved shape in a cross-sectional view perpendicular to the tire rotation axis satisfies the following equation (1). Tires with rims.
(X / a) ^Pab + (y / b) ^Qab = 1 (1)
However, y ≧ 0, b> 1, 5 ≦ a / b ≦ 100, -10 ≦ P _ab −Q _ab ≦ 10
(Aspect 6)
In the tire plan view, the center of the circumscribed ellipse is set as the origin, and the dimension from the origin to the end of the land portion in the tire width direction is c.
In the tire meridional cross-sectional view, the tire width direction is the X-axis, the tire radial direction is the Y-axis, the amount of fluctuation in the tire radial height of the land portion is d, and the tire radial direction fluctuation coefficient in the vicinity of the outer edge of the central portion. _Is P cd, and the tire radial fluctuation coefficient in the vicinity of the tire width direction edge is Q _cd .
The pneumatic tire according to aspect 4, wherein the profile of the land portion that gradually decreases in a curved shape in the tire meridional cross-sectional view satisfies the following equation (2) when the rim is assembled and 5% of the normal internal pressure is applied.
(X / c) ^Pcd + (y / d) ^Qcd = 1 (2)
However, y ≧ 0, d> 1, 1 ≦ c / d ≦ 50, -10 ≦ P _cd −Q _cd ≦ 10
(Aspect 7)
The ratio b / d of the fluctuation amount b of the tire radial height of the land portion in the cross-sectional view perpendicular to the tire rotation axis and the fluctuation amount d of the tire radial height of the land portion in the tire meridional cross-sectional view. The pneumatic tire according to any one of aspects 1 to 6, wherein the tire is 0.1 or more and 10 or less.
(Aspect 8)
The pneumatic tire according to any one of aspects 1 to 7, wherein the profile of the land portion is asymmetric on both sides of the tire circumferential position at the center of the circumscribed ellipse in a cross-sectional view perpendicular to the tire rotation axis.
(Aspect 9)
The pneumatic tire according to any one of aspects 1 to 8, wherein the profile of the land portion is asymmetrical on both sides of the position in the tire width direction at the center of the circumscribed ellipse in a cross-sectional view of the tire meridian.

In the pneumatic tire according to the present invention, the existing region of the top where the height in the tire radial direction of the land portion is maximized is improved. As a result, according to the pneumatic tire according to the present invention, both dry maneuverability and ice braking property can be achieved at the same time.

FIG. 1 is a plan view of the pneumatic tire 100 according to the first embodiment of the present invention. FIG. 2 is a plan view of the land portion 30 of the pneumatic tire 100 according to the first embodiment shown in FIG. FIG. 3 is a plan view of the land portion 30 of the pneumatic tire 100 according to the second embodiment of the present invention. FIG. 4 is a plan view of the land portion 30 of the pneumatic tire 100 according to the third embodiment of the present invention. FIG. 5 is a perspective view of the land portion 30 of the pneumatic tire 100 according to the fourth embodiment of the present invention. FIG. 6 is a cross-sectional view of the land portion 30 of the pneumatic tire 100 according to the fourth embodiment of the present invention, which is perpendicular to the tire rotation axis. FIG. 7 is a cross-sectional view of the tire meridian of the land portion 30 of the pneumatic tire 100 according to the fourth embodiment of the present invention. FIG. 8 is a graph showing an example of a plurality of curves satisfying the equations (1) and (2). FIG. 9 is a cross-sectional view of the land portion 30 of the pneumatic tire 100 according to the fifth embodiment of the present invention, which is perpendicular to the tire rotation axis. FIG. 10 is a tire meridional cross-sectional view of the land portion 30 of the pneumatic tire 100 according to the sixth embodiment of the present invention.

Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments, and can be variously modified within the scope of the main purpose of the disclosure.

In the following description, the tire radial direction means a direction orthogonal to the rotation axis of the pneumatic tire, the inner side in the tire radial direction is the side toward the rotation axis in the tire radial direction, and the outer side in the tire radial direction is the tire radial direction. The side away from the axis of rotation. The tire circumferential direction refers to a circumferential direction centered on the rotation axis. Further, the tire width direction means a direction parallel to the rotation axis, the inside in the tire width direction is the side toward the tire equatorial plane (tire equatorial line) in the tire width direction, and the outside in the tire width direction is in the tire width direction. The side of the tire away from the equatorial plane. The tire equatorial plane is a plane that is orthogonal to the rotation axis of the pneumatic tire and passes through the center of the tire width of the pneumatic tire.

(principle)
The principle that the pneumatic tire of the present embodiment can achieve both dry maneuverability and ice braking performance is as follows.

In a conventional pneumatic tire having at least one land portion formed by a plurality of circumferential grooves extending in the tire circumferential direction and a plurality of width direction grooves extending in the tire width direction, the land portion The ground contact pressure tends to be high at the ends (particularly, the end in the tire circumferential direction and / or the end in the tire width direction). That is, when a load is applied to the tire, a force is applied in the compression direction from the outside to the inside in the tire width direction in the land portion, so that the contact pressure tends to increase at the end of the land portion. Therefore, it has been difficult to achieve both dry maneuverability and ice braking performance.

Therefore, as a result of diligent studies, the present inventor has made that if a top portion having the maximum tire radial height is formed in the central portion of the land portion in a tire plan view, the contact pressure at the central portion (particularly the top portion) is formed. Therefore, the ground pressure on the outside of the central part can be relatively lowered, and the ground pressure on the entire land including the central part can be made uniform, and therefore the dry operation can be performed. It was found that both the property and the ice braking property can be achieved at the same time. The following embodiments are based on such findings.

Here, the height in the tire radial direction at a certain position on the land portion means the length in the tire radial direction from the rotation axis of the tire to the relevant position on the land portion. In the present invention, the maximum value of the tire radial height of the land portion, that is, the tire radial height at the outermost position of the tire radial direction of the land portion and the minimum value of the tire radial height of the land portion, that is, the land portion. The difference from the tire radial height at the innermost position in the tire radial direction can be appropriately selected according to the tire size. This difference can be, for example, 0.1 mm to 10 mm. Here, normally, the innermost position in the tire radial direction is any position on the peripheral edge of the land portion.

(First Embodiment)
FIG. 1 is a plan view of the pneumatic tire 100 according to the first embodiment of the present invention. As shown in the figure, the pneumatic tire 100 has at least two (four in the figure) circumferential grooves 10 extending in the tire circumferential direction and at least two (the same) extending in the tire width direction. In the figure, the land portion 30 of 20 is formed by the width direction grooves 20 (three).

The circumferential groove is a groove extending in the circumferential direction of the tire. However, the circumferential groove also includes a zigzag groove, a V-shaped groove, and the like. The circumferential grooves may or may not be parallel to each other.

The number of circumferential grooves is not particularly limited as long as it is two or more. The depth and groove width of the circumferential groove are not particularly limited, and the depth and groove width can be appropriately selected according to the tire size. For example, the depth of the circumferential groove can be 3 mm to 15 mm, and the width of the circumferential groove can be 1 mm to 15 mm. In addition, the circumferential groove can be chamfered. Here, the depth, width, and chamfer shape of the circumferential groove may be uniform or non-uniform in the tire circumferential direction, and may or may not be equal in each circumferential groove. ..

The width direction groove is a groove extending in the tire width direction. However, the widthwise groove also includes a zigzag groove, a groove including a bent portion and a curved portion, and the like. The widthwise grooves may or may not be parallel to each other.

The width direction groove is not particularly limited as long as it is two or more. The depth and groove width of the groove in the width direction are not particularly limited, and the depth and groove width can be appropriately selected according to the tire size. For example, the depth of the widthwise groove can be 3 mm to 15 mm, and the width of the widthwise groove can be 1 mm to 15 mm. Further, the width direction groove can be chamfered. Here, the depth, width, and chamfer shape of the groove in the width direction may be uniform or non-uniform in the width direction of the tire, and may or may not be equal in each groove in the width direction.

In the example shown in FIG. 1, the circumferential groove 10 is parallel to the circumferential direction of the tire, and the width direction groove 20 is parallel to the tire width direction. Therefore, the land portion 30 shown in the figure is rectangular in the tire plan view.

In the present embodiment, the shape of the land portion is not particularly limited as long as the central portion has a top portion having the maximum height in the tire radial direction. The land portion can have any shape (for example, a polygon such as a triangle, a quadrangle, or a pentagon, or a shape surrounded by a curve such as a circle or an ellipse) in the plan view of the tire, and further, a rectangle. It is also possible to form a shape or the like in which a part of the above is missing and is intricate inside. In addition, fine cuts such as sipes can be formed in the land area.

FIG. 2 is a plan view of the land portion 30 of the pneumatic tire 100 according to the first embodiment shown in FIG. As shown in FIG. 2, the circumscribed ellipse O is an ellipse that passes through the four vertices of the outer edge of the rectangular land portion 30 and has the smallest area among the ellipses surrounding the entire area of the land portion 30 in the tire plan view. _Let it be 1. Also, as each of the 20% position 20% of the positions and the minor axis of the major axis of the circumscribing ellipse O ₁ from the center of the circumscribed ellipse O _1, and is surrounded by an ellipse O ₂ is circumscribed ellipse O ₁ concentrically The area is defined as the central portion 31 of the land portion 30. In this case, the land portion 30 has a top portion 35 having the maximum tire radial height in the central portion 31. In the example shown in FIG. 2, the top 35 is located in the center of a circumscribed ellipse O _1. Further, the land portion 30 has a central portion 31 including a top portion 35 and an outer portion 33 located outside the central portion 31.

(Second embodiment)
FIG. 3 is a plan view of the land portion 30 of the pneumatic tire 100 according to the second embodiment of the present invention. As shown in the figure, in the pneumatic tire of the present embodiment, in a plan view, most of the outer shape of the land portion 30 coincides with the outer shape portion of the parallelogram, and the other outer shapes form the notch 37. It is an outer part. The notch 37 is formed from the outer portion 33 toward the central portion 31, and is terminated in the central portion 31 so as not to include the top portion 35.

(Third Embodiment)
FIG. 4 is a plan view of the land portion 30 of the pneumatic tire 100 according to the third embodiment of the present invention. As shown in the figure, in the pneumatic tire of the present embodiment, in a plan view, the land portion 30 exhibits an octagon having two intricate vertices inside the land portion, that is, on the top 35 side. There is.

Next, in the pneumatic tire of the present invention (from the first embodiment to the third embodiment), the tire radial height of the central portion is larger than the tire radial height of the other portion of the land portion. Compared to conventional pneumatic tires, the ground pressure increases in the central part. On the premise of such a fact, in the first to third embodiments, in at least one of the cross-sectional view perpendicular to the tire rotation axis and the tire meridional cross-sectional view, the tire on the land outside the central portion. It is preferable to gradually reduce the radial height radially. As a result, the ground pressure is gradually reduced from the central portion of the land portion toward the outside. Therefore, according to the land portion having such a shape, the ground contact pressure can be dispersed more uniformly, and by extension, the dry maneuverability and the ice braking property can be compatible at a higher level.

In at least one of the cross-sectional view perpendicular to the tire rotation axis and the tire meridional cross-sectional view, when the height in the tire radial direction of the land portion is gradually reduced radially, it is more preferable to gradually reduce the height in a curved shape. According to the curved gradual reduction mode, the ground contact pressure can be dispersed even more uniformly, and thus both dry maneuverability and ice braking property can be achieved at an extremely high level.

Here, as a specific mode of gradual reduction of the curved shape, the curved line is a circle, an ellipse, or a plurality of circles having different diameters, for example, from the viewpoint of ease of making a tire mold. It can be a combination of.

Next, FIGS. 5 to 7 show specific embodiments of the gradual decrease in the tire radial height of the land portion of the pneumatic tire in the present embodiment.

(Fourth Embodiment)
FIG. 5 is a perspective view of the land portion 30 of the pneumatic tire 100 according to the fourth embodiment of the present invention. As shown in the figure, in the present embodiment, the height in the tire radial direction gradually decreases radially in both the tire circumferential direction and the tire width direction in the outer portion 33 existing outside the central portion 31. .. As a result, in the example shown in FIG. 5, the ground pressure of the central portion 31 can be increased, and the ground pressure can be reduced at the outer portion 33 including the peripheral portion of the land portion where the ground pressure was conventionally the highest. .. Therefore, in the pneumatic tire 100 according to the fourth embodiment of the present invention, the contact pressure of the land portion 30 can be made even more uniform, and by extension, both dry maneuverability and ice braking performance can be achieved at a higher level. Can be made to.

FIG. 6 is a cross-sectional view of the land portion 30 of the pneumatic tire 100 according to the fourth embodiment of the present invention, which is perpendicular to the tire rotation axis. As shown in the figure, in the present embodiment, in a cross-sectional view perpendicular to the tire rotation axis, the height of the land portion 30 in the tire radial direction is the peripheral edge portion of the outer portion 33 from the top 35 to both sides in the tire circumferential direction. It gradually decreases in a curved shape. Since the land portion 30 has such a shape, the contact pressure of the land portion 30 in the tire circumferential direction can be more uniformly dispersed, and by extension, both dry maneuverability and ice braking performance can be achieved at a higher level. be able to.

FIG. 7 is a cross-sectional view of the tire meridian of the land portion 30 of the pneumatic tire 100 according to the fourth embodiment of the present invention. As shown in the figure, in the present embodiment, in the tire meridional cross-sectional view, the height of the land portion 30 in the tire radial direction is curved from the top 35 to both sides in the tire width direction to the peripheral edge of the outer portion 33. It is gradually decreasing. Since the land portion 30 has such a shape, the contact pressure of the land portion 30 in the tire width direction can be more uniformly dispersed, and by extension, both dry maneuverability and ice braking performance can be achieved at a higher level. be able to.

Hereinafter, in the fourth embodiment, the profile of the land portion 30 (cross-sectional view perpendicular to the tire rotation axis (FIG. 6) and tire meridional cross-sectional view (FIG. 7)) will be described. The profile is based on the surface portion of the land part in a cross-sectional view perpendicular to the tire rotation axis or a tire meridional cross-sectional view in a no-load state in which a pneumatic tire is assembled on a regular rim and an internal pressure of 5% of the regular internal pressure is applied. The profile that is formed.

Here, the regular rim is a "standard rim" specified by JATTA, a "Design Rim" specified by TRA, or a "Measuring Rim" specified by ETRTO. The normal internal pressure is the "maximum air pressure" specified by JATTA, the maximum value described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "INFLATION PRESSURES" specified by ETRTO.

First, in the profile (FIG. 6) in the cross-sectional view perpendicular to the tire rotation axis, the center of the above-mentioned circumscribing ellipse is the origin in the tire plan view, and the dimension from the origin to the end of the tire in the circumferential direction of the land is a. (Fig. 2), in a cross-sectional view perpendicular to the tire rotation axis, the tire circumferential direction is the X axis, the tire radial direction is the Y axis, and the tire radial direction from the origin to the end of the land portion in the tire width direction. the variation of the height b (FIG. 6), the tire radial direction coefficient of variation near the outer edge of the central portion when P _ab, the tire radial direction variation coefficient in the vicinity tire circumferential direction edge Q _ab, and, following ( It is preferable to satisfy the formula 1).
(X / a) ^Pab + (y / b) ^Qab = 1 (1)
However, y ≧ 0, b> 1, 5 ≦ a / b ≦ 100, -10 ≦ P _ab −Q _ab ≦ 10

_{Here, the significance of setting the coefficient of variation P ab} and Q _ab , the dimension a, and the amount of variation b defined in the above equation (1) will be described in detail below.

That is, the above equation (1) is, for example, _{a linear function if P ab} = 1 and Qab = 1, a quadratic function if P _ab = 2 and Q _ab = 1, and P _ab = 2 and Q _ab. If = 2, it becomes a circle or an ellipse, and if P _ab > 2 and Q _ab > 2, it becomes a superellipse or the like.

FIG. 8 is a graph showing an example of a plurality of curves satisfying the equation (1). In FIG. 8, the S ellipse means a so-called superellipse. Further, in FIG. 8, the dimensions shown on the vertical axis and the horizontal axis are not actual dimensions but numerical values used to indicate the aspect ratio. In the present embodiment, the profiles of the central portion 31 and the outer portion 33 in FIG. 6 can be appropriately set by providing such various variations of the coefficient of variation P _ab and Q _ab.

Further, in a normal pneumatic tire, the length of the land portion in the tire circumferential direction is larger than the length in the tire width direction, so a / b is set to 5 or more and 100 or less. By setting a / b to 5 or more, the tire radial dimensional difference between the innermost position (peripheral portion) in the tire radial direction (peripheral portion) and the outermost position (top) in the land portion (hereinafter, may be referred to as "bulging amount"). (There is) is not excessive (more specifically, the contact pressure at the central portion 31 in FIG. 6 becomes too high), and by extension, the contact pressure at the land portion is made more uniform as a whole in the tire circumferential direction. Can be done.

On the other hand, by setting a / b to 100 or less, the amount of swelling is not excessive (more specifically, the contact pressure at the central portion 31 in FIG. 6 cannot be sufficiently increased). As a result, the ground contact pressure on the land can be made more uniform in the tire circumferential direction as a whole.

When the ratio a / b is 20 or more and 90 or less, each of the above effects is produced at a higher level, which is preferable, and when it is 30 or more and 80 or less, each of the above effects is even higher. It is more preferable because it is played at the level.

Further, P _ab −Q _ab is -10 or more and 10 or less. By _{setting P ab} −Q _ab to -10 or more, the amount of swelling does not become excessive (more specifically, the contact pressure at the central portion 31 in FIG. 6 becomes too high), and by extension, land. The ground contact pressure of the portion can be made more uniform in the entire tire circumferential direction.

On the other hand, by _{setting P ab} −Q _ab to 10 or less, the amount of swelling becomes too small (more specifically, the contact pressure at the central portion 31 in FIG. 6 cannot be sufficiently increased). As a result, the ground contact pressure on the land can be made more uniform in the tire circumferential direction as a whole.

When the difference P _ab −Q _ab is -8 or more and 8 or less, each of the above effects is produced at a higher level, which is preferable. When the difference is -6 or more and 6 or less, each of the above effects is achieved. It is even more preferable because each is played at an even higher level.

Next, the profile in the tire meridional cross-sectional view (FIG. 7) has the center of the circumscribing ellipse as the origin in the tire plan view, and the dimension from the origin to the end of the land portion in the tire width direction is c (FIG. 7). 2), the tire width direction is the X-axis, the tire radial direction is the Y-axis, and the amount of change in the tire radial height from the origin to the end of the land portion in the tire width direction is determined in the tire meridional cross-sectional view. d (FIG. 7), the following equation (2) is satisfied when the tire radial fluctuation coefficient in the vicinity of the outer edge of the central portion is P _cd and the tire radial fluctuation coefficient in the vicinity of the tire width direction edge is Q _cd. Is preferable.
(X / c) ^Pcd + (y / d) ^Qcd = 1 (2)
However, y ≧ 0, d> 1, 1 ≦ c / d ≦ 50, -10 ≦ P _cd −Q _cd ≦ 10

_{Here, the significance of setting the coefficient of variation P cd} and Q _cd , the dimension c, and the amount of variation d defined in the above equation (2) will be described in detail below.

That is, the above equation (2) is, for example, _{a linear function if P cd} = 1 and Q _cd = 1, a quadratic function if P _cd = 2 and Q _cd = 1, and P _cd = 2 and Q. _{If cd} = 2, it becomes a circle or an ellipse, and if P _cd > 2 and Q _cd > 2, it becomes a super ellipse or the like.

FIG. 8 is a graph showing an example of a plurality of curves satisfying the equation (2). In FIG. 8, the S ellipse means a so-called superellipse. Further, in FIG. 8, the dimensions shown on the vertical axis and the horizontal axis are not actual dimensions but numerical values used to indicate the aspect ratio. In the present embodiment, by providing such various variations of the coefficient of variation P _cd and Q _cd , the profile of the central portion 31 and the outer portion 33 in FIG. 7 can be appropriately set.

Further, in a normal pneumatic tire, the length in the tire width direction of the land portion is smaller than the length in the tire circumferential direction, so the c / d is set to 1 or more and 50 or less. By setting c / d to 1 or more, the amount of swelling does not become excessive (more specifically, the ground contact pressure at the central portion 31 in FIG. 7 does not become too high), and as a result, the ground contact is made. The pressure can be made more uniform throughout the tire width direction.

On the other hand, by setting c / d to 50 or less, the amount of swelling is not excessive (more specifically, the contact pressure at the central portion 31 in FIG. 7 cannot be sufficiently increased). As a result, the ground contact pressure on the land can be made more uniform as a whole in the tire width direction.

When the ratio c / d is 10 or more and 45 or less, each of the above effects is produced at a higher level, which is preferable, and when it is 20 or more and 40 or less, each of the above effects is even higher. It is more preferable because it is played at the level.

Further, P _cd −Q _cd is -10 or more and 10 or less. By _{setting P cd} −Q _cd to -10 or more, the amount of swelling does not become excessive (more specifically, the contact pressure at the central portion 31 in FIG. 7 does not become too high), and by extension, land. The ground contact pressure of the portion can be made more uniform as a whole in the tire width direction, and in particular, the ice braking property can be further improved.

On the other hand, by _{setting P cd} −Q _cd to 10 or less, the amount of swelling becomes too small (more specifically, the contact pressure at the central portion 31 in FIG. 6 cannot be sufficiently increased). As a result, the ground contact pressure in the land area can be made more uniform as a whole in the tire width direction, and in particular, the ice braking property can be further improved.

When the difference P _cd −Q _cd is -8 or more and 8 or less, each of the above effects is produced at a higher level, which is preferable. When the difference is -6 or more and 6 or less, each of the above effects is achieved. It is even more preferable because each is played at an even higher level.

Next, in the present embodiment, the amount of variation b in the tire radial height of the land portion in the cross-sectional view perpendicular to the tire rotation axis and the variation in the tire radial height of the land portion in the tire meridional cross-sectional view. The ratio b / d to the amount d is preferably 0.1 or more and 10 or less.

The ratio b / d is set in order to balance the bulging amount in the tire circumferential direction and the tire width direction. By setting the ratio b / d to 0.1 or more, the amount of bulge in the cross-sectional view (FIG. 6) perpendicular to the tire rotation axis becomes smaller than the amount of bulge in the tire meridional cross-sectional view (FIG. 7). Is suppressed. As a result, a sufficient amount of bulge is obtained in a cross-sectional view (FIG. 6) perpendicular to the tire rotation axis, and it is possible to prevent uneven contact of each edge portion between the stepping side and the kicking side in the tire circumferential direction. As a result, dry maneuverability and ice braking performance can be further improved.

On the other hand, by setting the ratio b / d to 10 or less, the amount of bulge in the tire meridional cross-sectional view (FIG. 7) is smaller than the amount of bulge in the cross-sectional view perpendicular to the tire rotation axis (FIG. 6). Is suppressed. As a result, a sufficient amount of bulge in the tire meridional cross-sectional view (FIG. 7) is obtained, and it is suppressed that each edge portion at both edge portions in the tire width direction touches unevenly, which in turn results in dry maneuverability. Ice braking performance can be further improved.

When the ratio b / d is 0.3 or more and 8 or less, each of the above effects is produced at a higher level, which is preferable. It is even more preferable because each is played at an even higher level.

(Fifth Embodiment)
Next, it is preferable that the above profile is asymmetrical on both sides of the tire circumferential position at the center of the circumscribed ellipse in a cross-sectional view perpendicular to the tire rotation axis.

FIG. 9 is a cross-sectional view of the land portion 30 of the pneumatic tire 100 according to the fifth embodiment of the present invention, which is perpendicular to the tire rotation axis. In the figure, reference numeral 30a indicates the kicking side, and reference numeral 30b indicates the stepping side.

As shown in the figure, the mode of bulging on the stepping side 30b in the tire circumferential direction with the position of the center of the circumscribed ellipse in the tire circumferential direction is gentler than the mode of bulging on the kicking side 30a. It is preferable to have. According to such a configuration, when the vehicle is traveling (especially when traveling straight) in which the ground contact surface of the land portion changes sequentially, the ground contact pressure in the tire circumferential direction of the land portion can always be made uniform, whereby on a dry road surface. It is possible to improve straightness and ride comfort.

(Sixth Embodiment)
Similarly, the profile is preferably asymmetric on both sides of the tire width direction position at the center of the circumscribed ellipse in tire meridional cross-section.

FIG. 10 is a tire meridional cross-sectional view of the land portion 30 of the pneumatic tire 100 according to the sixth embodiment of the present invention. In the figure, reference numeral 30c indicates the inside of the vehicle, and reference numeral 30d indicates the outside of the vehicle.

As shown in the figure, the mode of bulging in the tire width direction at the vehicle mounting outer side 30d is gentler than the bulging mode at the vehicle mounting inner side 30c with the position of the center of the circumscribed ellipse in the tire width direction as a boundary. Is preferable. According to such a configuration, when the vehicle is traveling (especially when cornering) in which the contact patch of the land portion changes sequentially, the contact pressure in the tire width direction of the land portion can always be made uniform, whereby on a dry road surface. Steerability can be improved.

(Other structures and manufacturing methods for pneumatic tires)
Although the entire pneumatic tire according to the present invention is not shown, it has a meridional cross-sectional shape similar to that of a conventional pneumatic tire. That is, the pneumatic tire according to the present invention has a bead portion, a sidewall portion, a shoulder portion, and a tread portion from the inside to the outside in the tire radial direction in a cross-sectional view of the tire meridian. The pneumatic tire has, for example, a carcass layer extending from the tread portion to the bead portions on both sides and wound around a pair of bead cores in a cross-sectional view of the tire meridian, and has a tire diameter of the carcass layer. A belt layer as described above and, in some cases, a belt cover layer are provided on the outer side in the direction.

Further, the pneumatic tire according to the present invention shown above is a normal manufacturing process, that is, a tire material mixing process, a tire material processing process, a green tire molding process, a vulcanization process, and a post-vulcanization inspection process. It is obtained through the above. When manufacturing a pneumatic tire according to the present invention, for example, convex portions and concave portions corresponding to the tread pattern shown in FIG. 1 are formed on the inner wall of the vulcanization die, and vulcanization is performed using this die. I do.

The tire size was set to 225 / 65R17 102Q (specified by JATTA), and the pneumatic tires of Invention Examples 1 to 9 and the conventional pneumatic tires having the land portion shown in FIG. 1 were produced. The detailed conditions of these pneumatic tires are shown in Table 1 below.

In Table 1, the "existence position of the top" indicates whether the top is located in the central portion 31 or the outer portion 33 shown in FIG. The "mode of gradual reduction of the tire radial height in the outer portion" indicates whether the gradual reduction in the outer portion 33 shown in FIG. 2 is stepwise or radial. The "gradual reduction mode in a cross-sectional view perpendicular to the tire rotation axis" means the gradual reduction mode shown in FIG. The “gradual reduction mode in cross-sectional view of the tire meridian” means the gradual reduction mode shown in FIG. The “formula (1)” and the “formula (2)” mean the respective formulas described in the present specification. The "ratio b / d" is the amount of fluctuation b in the tire radial height of the land portion in the cross-sectional view perpendicular to the tire rotation axis and the fluctuation amount of the tire radial height in the land portion in the tire meridional cross-sectional view. It means the ratio with d. The “profile shape on the stepping side and the kicking side” means the shape shown in FIG. 9, and in particular, in the case of asymmetry, the mode of bulging on the stepping side 30b is bulging on the kicking side 30a. It means a case where it is more gradual than the mode of output. The "profile shape on the inside and outside of the vehicle mounting" means the shape shown in FIG. 10, and in particular, in the case of asymmetry, the mode of swelling on the outside of the vehicle mounting 30d is bulging on the inside of the vehicle mounting 30c. It means a case where it is more gradual than the mode of output.

Each of the above test tires is assembled to a regular rim of size 17 x 7J, internal pressure (front wheels 230 kPa and rear wheels 230 kPa) is applied, and it is mounted on a front engine four-wheel drive passenger car (test vehicle) with a displacement of about 2000 cc. Tests were conducted on dry maneuverability and ice braking performance.

(Dry maneuverability)
Three professional drivers evaluated the feeling of the above test vehicle when it ran three laps while changing lanes on a test course of 2 km per lap. As the evaluation result, the average value of the evaluation points of each test tire was displayed as an index when the average value of the feeling evaluation points of the conventional example was set to 100. The results are also shown in Table 1. The larger this index value is, the better the dry maneuverability is.

(Ice braking property)
The test vehicle was run on the ice road surface of the ice test site, and the braking distance from a traveling speed of 40 km / h was measured. Then, based on this measurement result, an index evaluation was performed using the conventional example as a reference 100. The results are also shown in Table 1. This evaluation indicates that the larger the value, the shorter the braking distance and the better the ice braking performance.

According to Table 1, the pneumatic tires of Invention Examples 1 to 9 belong to the technical scope of the present invention (that is, the region where the apex having the maximum tire radial height in the land portion exists is improved). It can be seen that the dry maneuverability and the ice braking property are improved in a well-balanced manner as compared with the conventional pneumatic tires, which do not belong to the technical scope of the present invention.

10 Circumferential groove 20 Width groove 30 Land part 31 Central part 33 Outer part 35 Top 37 Notch 100 Pneumatic tire a Dimension from the origin to the tire circumferential end of the land part in the tire plan view b On the tire rotation axis Amount of fluctuation in tire radial height in land in a vertical cross-sectional view c Dimensions from the origin to the end in the tire width direction in land in a tire plan view d Tires in land in a tire meridional cross-sectional view Radial height variation O ₁ Outer elliptical O ₂ Elliptical

Claims (9)

A pneumatic tire in which at least one land portion is partitioned by at least two circumferential grooves extending in the tire circumferential direction and at least two widthwise grooves extending in the tire width direction. ,
In the plan view of the tire, the ellipse that passes through at least three points of the outer edge of the land portion and has the smallest area among the ellipses surrounding the entire region of the land portion is defined as the circumscribing ellipse, and from the center of the circumscribing ellipse. When the region surrounded by the ellipse that passes through each of the 20% of the major axis and the minor axis of the circumscribing ellipse and is concentric with the circumscribing ellipse is the central portion of the land portion. ,
The land portion is a pneumatic tire, characterized in that the central portion has a top portion having a maximum height in the radial direction of the tire. The pneumatic tire according to claim 1, wherein the tire radial height of the land portion is gradually decreased radially at least outside the central portion. The pneumatic tire according to claim 2, wherein the height of the land portion in the tire radial direction is gradually reduced in a curved shape at least outside the central portion in a cross-sectional view perpendicular to the tire rotation axis. The pneumatic tire according to claim 2 or 3, wherein in a cross-sectional view of the tire meridian, the height of the land portion in the tire radial direction gradually decreases in a curved shape at least outside the central portion. In the tire plan view, the center of the circumscribed ellipse is set as the origin, and the dimension from the origin to the end of the land portion in the tire circumferential direction is a.
In a cross-sectional view perpendicular to the tire rotation axis, the tire circumferential direction is the X-axis, the tire radial direction is the Y-axis, the amount of variation in the tire radial height of the land portion is b, and the tire near the outer edge of the central portion. When the radial variation coefficient is _Pab and the tire radial variation coefficient near the tire circumferential edge is _Qab ,
The third aspect of the present invention, wherein when the rim is assembled and 5% of the normal internal pressure is applied, the profile of the land portion that gradually decreases in a curved shape in a cross-sectional view perpendicular to the tire rotation axis satisfies the following equation (1). Pneumatic tires.
(X / a) ^Pab + (y / b) ^Qab = 1 (1)
However, y ≧ 0, b> 1, 5 ≦ a / b ≦ 100, -10 ≦ P _ab −Q _ab ≦ 10 In the tire plan view, the center of the circumscribed ellipse is set as the origin, and the dimension from the origin to the end of the land portion in the tire width direction is c.
In the tire meridional cross-sectional view, the tire width direction is the X-axis, the tire radial direction is the Y-axis, the amount of variation in the tire radial height of the land portion is d, and the tire radial direction variation coefficient in the vicinity of the outer edge of the central portion. _Is P cd, and the tire radial fluctuation coefficient in the vicinity of the tire width direction edge is Q _cd .
The pneumatic tire according to claim 4, wherein the profile of the land portion that gradually decreases in a curved shape in the tire meridional cross-sectional view satisfies the following equation (2) when the rim is assembled and 5% of the normal internal pressure is applied.
(X / c) ^Pcd + (y / d) ^Qcd = 1 (2)
However, y ≧ 0, d> 1, 1 ≦ c / d ≦ 50, -10 ≦ P _cd −Q _cd ≦ 10 The ratio b / d of the fluctuation amount b of the tire radial height of the land portion in the cross-sectional view perpendicular to the tire rotation axis and the tire radial height fluctuation amount d of the land portion in the tire meridional cross-sectional view. The pneumatic tire according to any one of claims 1 to 6, wherein the tire is 0.1 or more and 10 or less. The pneumatic tire according to any one of claims 1 to 7, wherein the profile of the land portion is asymmetric on both sides of the tire circumferential position at the center of the circumscribed ellipse in a cross-sectional view perpendicular to the tire rotation axis. .. The pneumatic tire according to any one of claims 1 to 8, wherein the profile of the land portion is asymmetric on both sides of the position in the tire width direction at the center of the circumscribed ellipse in a cross-sectional view of the tire meridian.

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