JP7610093B2 - tire - Google Patents

Description

The present invention relates to a tire that has a wide shoulder land portion in the shoulder region that is located on the outside of the vehicle when mounted on the vehicle.

A technology has been known that improves handling stability by making each land portion extending in the circumferential direction of the tread portion curved to be convex radially outward, thereby improving ground contact (see, for example, Patent Document 1).

Patent No. 6186147

However, in a tire with a wide shoulder land portion in the shoulder region located on the outside of the vehicle when mounted on the vehicle, the ground contact pressure near the widthwise center of the shoulder land portion is extremely reduced, and the contact length is shortened, which may deteriorate the ground contact performance and therefore the steering stability performance. In addition, there is a problem that the ground contact pressure at both ends of the shoulder land portion in the tire width direction is relatively high, which induces uneven wear. For this reason, there is ample room for further improvement in steering stability performance and uneven wear resistance in a configuration with a wide shoulder land portion on the outside of the vehicle.

The present invention was made in consideration of the above circumstances, and aims to improve the steering stability and uneven wear resistance of tires with wide shoulder land portions on the outer side of the vehicle.

In order to solve the above problems and achieve the object, the present invention provides a tire in which the mounting direction relative to the vehicle is specified, the tire has a plurality of circumferential main grooves extending in the tire circumferential direction in the tread portion, and a plurality of land portions partitioned by these circumferential main grooves, the width W1 of the ground contact area of the shoulder land portion on the outer side of the vehicle, which is located on the outer side of the vehicle when mounted on the vehicle, has a relationship of 0.25≦W1/WT≦0.35 with respect to the width WT of the tire ground contact area, at least the shoulder land portion on the outer side of the vehicle has a ground contact surface that protrudes radially outward from the reference profile line, and an intermediate land portion adjacent to the shoulder land portion across the circumferential main groove has a ground contact surface that has the same shape as the reference profile line or that protrudes radially outward from the reference profile line by a smaller amount than the protrusion of the shoulder land portion.

In the above tire, it is preferable that the width Wd of the ground contact area of the intermediate land portion has a relationship of 0.10≦Wd/WT≦0.20 with respect to the width WT of the tire ground contact area.

In addition, in the above-mentioned tire, it is preferable that the intermediate land portion is located on the tire equatorial plane or on the vehicle outer side of the tire equatorial plane.

In addition, in the above-mentioned tire, the shoulder land portion on the vehicle outer side has a first lug groove that extends in the tire width direction, opens into the circumferential main groove and terminates within the shoulder land portion, and a second lug groove that opens into the ground contact edge on the vehicle outer side and terminates within the shoulder land portion, and it is preferable that a maximum protruding position where the protruding amount of the shoulder land portion is maximum is provided in the region between the first lug groove and the second lug groove in the tire width direction.

In addition, in the above tire, it is preferable that the region between the first lug groove and the second lug groove has a plurality of circular dimples arranged in a staggered pattern, and that some of the dimples are aligned in the same straight line as the maximum protruding position.

In addition, in the above tire, it is preferable that the maximum protrusion amount H1 of the shoulder land portion on the outer side of the vehicle from the reference profile line is 0.1 mm or more and 0.3 mm or less, and the maximum protrusion amount of the intermediate land portion from the reference profile line is 0 mm or more and 0.1 mm or less.

In addition, in the above-mentioned tire, the width Wa of the ground contact area of the shoulder land portion on the vehicle inner side and the width Wb of the ground contact area of the second land portion on the vehicle inner side adjacent to the shoulder land portion across the circumferential main groove have a relationship with the width WT of the tire ground contact area such that 0.10≦Wa/Wt≦0.20 and 0.10≦Wb/Wt≦0.20, respectively, and the shoulder land portion and the second land portion each have a ground contact surface that protrudes radially outward from the reference profile line, and it is preferable that the amount of protrusion is greater than the amount of protrusion when the intermediate land portion protrudes radially outward from the reference profile line.

In addition, in the above-mentioned tire, it is preferable that the tread portion has at least one circumferential main groove on the outer side of the vehicle and at least two on the inner side of the vehicle, with the tire equatorial plane in between, and has four or five rows of land portions partitioned in the tire circumferential direction by these circumferential main grooves.

The tire according to the present invention has a wide shoulder land portion on the outer side of the vehicle that has a contact surface that protrudes radially outward from the reference profile line, and an intermediate land portion adjacent to the shoulder land portion across the circumferential main groove has a contact surface that is the same shape as the reference profile line or that protrudes radially outward from the reference profile line by a smaller amount than the shoulder land portion, thereby improving the steering stability and uneven wear resistance of a tire with a wide shoulder land portion on the outer side of the vehicle.

FIG. 1 is a plan view showing a tread surface of a pneumatic tire according to this embodiment. FIG. 2 is a meridian cross-sectional view of the tire shown in FIG. 1 , showing a tread portion of the tire. FIG. 3 is a plan view showing the shape of the ground contact surface of a conventional pneumatic tire. FIG. 4 is a plan view showing the shape of the contact patch of the pneumatic tire of this embodiment. FIG. 5 is a plan view showing a tread surface of a pneumatic tire according to another embodiment. FIG. 6 is a plan view showing the shape of the ground contact surface of a conventional pneumatic tire. FIG. 7 is a plan view showing the shape of the ground contact surface of a pneumatic tire according to another embodiment. FIG. 8 is a table showing the results of a performance test of the pneumatic tire according to this embodiment.

Embodiments of the present invention will be described in detail below with reference to the drawings. In the following description of each embodiment, components that are the same as or equivalent to those in other embodiments will be given the same reference numerals, and their description will be simplified or omitted. The present invention is not limited to each embodiment. Furthermore, the components of each embodiment include those that are replaceable and easy for a person skilled in the art, or those that are substantially the same.

The pneumatic tire according to this embodiment will be described. In the following description, the tire radial direction refers to the direction perpendicular to the rotation axis of the tire, the tire radial inner side refers to the side toward the rotation axis in the tire radial direction, and the tire radial outer side refers to the side away from the rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the rotation axis as the central axis. Furthermore, the tire width direction refers to the direction parallel to the rotation axis, the tire width inner side refers to the side toward the tire equatorial plane (tire equator line) in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane in the tire width direction. The tire equatorial plane is a plane perpendicular to the rotation axis of the pneumatic tire and passing through the center of the tire width.

Figure 1 is a plan view showing the tread surface of a pneumatic tire according to this embodiment. In Figure 1, the symbol CL indicates the tire equatorial plane, and the symbol E indicates both ground contact ends of the tire. The mounting direction of the pneumatic tire 1 according to this embodiment (hereinafter sometimes simply referred to as tire 1) on a vehicle is specified, and the tread pattern shown in Figure 1 is an asymmetric pattern between both sides of the tire equatorial plane CL in the tire width direction. In Figure 1, the area shown on the outer side of the ground contact ends E in the tire width direction is the so-called sidewall portion.

The tread portion 10 of the tire 1 is made of a rubber material (tread rubber) and is exposed at the outermost part in the tire radial direction of the tire 1, and its surface forms the outline of the tire 1. The surface of the tread portion 10 is formed as a tread surface 12 that is the surface that comes into contact with the road surface when a vehicle (not shown) on which the tire 1 is mounted is traveling.

On the tread surface 12, three circumferential main grooves 14 extending in the tire circumferential direction are provided at a predetermined interval in the tire width direction. Specifically, as shown in FIG. 1, two circumferential main grooves 14a, 14b are provided on the vehicle inner side, and one circumferential main groove 14d is provided on the vehicle outer side, with the tire equatorial plane CL as the boundary. Here, the vehicle inner side and the vehicle outer side refer to the directions when the tire 1 is mounted on the vehicle. The circumferential main grooves 14a, 14d on the outermost side in the tire width direction may be referred to as shoulder main grooves, and the circumferential main groove 14b on the inner side in the tire width direction may be referred to as a second main groove. When there is no particular distinction between these circumferential main grooves 14a, 14b, and 14d, they are simply referred to as circumferential main grooves 14.

In this embodiment, the circumferential main groove 14 is not limited to a groove extending linearly in the tire circumferential direction as shown in FIG. 1, but may be a groove extending in the tire circumferential direction with amplitude in the tire width direction and a wavy or zigzag shape. In addition, the circumferential main groove 14 may be four or more grooves, as long as there is at least one groove on the vehicle outer side and at least two grooves on the vehicle inner side across the tire equatorial plane.

Furthermore, on the tread surface 12, four land portions 20 extending in the tire circumferential direction are defined by three circumferential main grooves 14. Specifically, the vehicle inner shoulder land portion 20a is defined on the tire width direction outer side of the vehicle inner shoulder main groove 14a, and the vehicle inner second land portion 20b is defined by the vehicle inner shoulder main groove 14a and the second main groove 14b. In addition, the second main groove 14b and the vehicle outer shoulder main groove 14d define a center land portion (middle land portion) 20d, and the vehicle outer shoulder land portion 20-1 is defined on the tire width direction outer side of the vehicle outer shoulder main groove 14d. In this embodiment, the center land portion 20d is provided extending on the tire equatorial plane CL with the tire width direction centerline of the center land portion 20d being located on the vehicle outer side of the tire equatorial plane CL.

The width W1 of the ground contact area of the shoulder land portion 20-1 on the outer side of the vehicle is the widest (largest) of all the land portions 20, and has a relationship of 0.25≦W1/WT≦0.35 with respect to the width WT of the tire ground contact area. In this case, the width Wa of the ground contact area of the shoulder land portion 20a on the inner side of the vehicle, the width Wb of the ground contact area of the second land portion 20b on the inner side of the vehicle, and the width Wd of the ground contact area of the center land portion 20d each have a relationship of 0.10 or more and 0.20 or less with respect to the width WT of the tire ground contact area (0.10≦Wd/WT≦0.20; similarly for Wa/WT and Wb/WT).

Here, the ground contact area of the shoulder land portion 20-1 on the outer side of the vehicle is the area defined by the shoulder main groove 14d on the outer side of the vehicle and the ground contact edge E on the outer side of the vehicle, and the ground contact area of the shoulder land portion 20a on the inner side of the vehicle is the area defined by the shoulder main groove 14a on the inner side of the vehicle and the ground contact edge E on the inner side of the vehicle. The tire ground contact area is the area defined by the ground contact edges E located at both ends in the tire width direction. Each of these areas is set as the area where the tread surface 12 of the tread portion 10 of the tire comes into contact with a dry, flat road surface when the tire is mounted on a specified rim, inflated to a specified internal pressure, and subjected to 70% of the specified load. The specified rim is the "standard rim" defined by JATMA, the "Design Rim" defined by TRA, or the "Measuring Rim" defined by ETRTO. The specified internal pressure is the "maximum air pressure" specified by JATMA, the maximum value specified in the "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Inflation Pressures" specified by ETRTO. The specified load is the "maximum load capacity" specified by JATMA, the maximum value specified in the "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Load Capacity" specified by ETRTO.

In addition, on the tread surface 12, various lug grooves extending in the tire width direction are repeatedly formed at a predetermined pitch (interval) in the tire circumferential direction. Specifically, in the shoulder land portion 20a on the vehicle inner side, one end opens into the shoulder main groove 14a on the vehicle inner side, and a plurality of shoulder lug grooves 15a on the vehicle inner side are provided, which extend from the shoulder main groove 14a across the ground contact end E toward the vehicle inner side. In addition, in the shoulder land portion 20a on the vehicle inner side, a plurality of side lug grooves 15b on the vehicle inner side are provided, which one end terminates on the vehicle inner side (outside in the tire width direction) of the ground contact end E and extend toward the vehicle inner side. These shoulder lug grooves 15a and side lug grooves 15b are formed approximately parallel to each other and are alternately provided in the tire circumferential direction. In addition, the other ends of the shoulder lug grooves 15a and side lug grooves 15b are each connected to a plurality of arc grooves 16 formed in the sidewall portion of the tire 1. These arc grooves 16 are each formed in an arc shape and are arranged in an annular shape around the rotation axis of the tire 1.

The second land portion 20b on the vehicle inner side is provided with a plurality of lug grooves 17a, one end of which opens into the shoulder main groove 14a on the vehicle inner side, extending from the shoulder main groove 14a toward the tire equatorial plane CL side and the other end of which terminates within the second land portion 20b, and a plurality of lug grooves 17b, one end of which opens into the second main groove 14b, extending from the second main groove 14b toward the vehicle inner side and the other end of which terminates within the second land portion 20b on the vehicle inner side. These lug grooves 17a, 17b are spaced apart in the tire width direction and are arranged in a staggered pattern (alternately) in the tire circumferential direction.

The center land portion 20d is provided with a number of through lug grooves 18 that connect the second main groove 14b to the shoulder main groove 14d on the outer side of the vehicle. These through lug grooves 18 are bent, for example, twice to form a roughly Z-shape.

The shoulder land portion 20-1 on the outer side of the vehicle is provided with a plurality of lug grooves (first lug grooves) 19a, one end of which opens into the shoulder main groove 14d on the outer side of the vehicle, and the other end of which terminates within the shoulder land portion 20-1. The shoulder land portion 20-1 on the outer side of the vehicle is also provided with a plurality of shoulder lug grooves (second lug grooves) 19b on the outer side of the vehicle, one end of which terminates on the tire equatorial plane CL side of the ground contact end E and extends toward the outer side of the vehicle across the ground contact end E, and a plurality of side lug grooves 19c on the outer side of the vehicle, one end of which terminates on the outer side of the vehicle (outside in the tire width direction) of the ground contact end E and extends toward the outer side of the vehicle. These shoulder lug grooves 19b and side lug grooves 19c are formed approximately parallel to each other and are alternately provided in the tire circumferential direction. Additionally, the other ends of the shoulder lug grooves 19b and the side lug grooves 19c each communicate with a plurality of arc grooves 16 formed in the sidewall portion of the tire 1.

In addition, an area A is formed between the opposing lug grooves 19a and shoulder lug grooves 19b, and a plurality of dimples 25 are arranged in a staggered pattern in this area A. Specifically, the dimples 25 include two dimples 25A and 25B arranged side by side in the tire width direction, and one dimple 25C that is displaced in the tire circumferential direction from the dimples 25A and 25B and arranged in the center of the dimples 25A and 25B in the tire width direction, and these three rows of dimples 25A, 25B, and 25C are repeatedly arranged in the tire circumferential direction. These dimples 25 are recesses formed in a circular shape, and in this embodiment, the center is further recessed to have a stepped recess shape. The multiple dimples 25A located on the outer side in the tire width direction are arranged on a line A1 connecting one end of each shoulder lug groove 19b, and the multiple dimples 25B located on the inner side in the tire width direction are arranged on a line A2 connecting one end of each lug groove 19a. Additionally, multiple dimples 25C located in the center of each of the dimples 25A and 25B are arranged on the maximum protruding position P1 (described later) of the ground contact surface 30-1 of the shoulder land portion 20-1.

As described above, the tire 1 of this embodiment has a shoulder land portion 20-1 with a wide ground contact area formed on the outer side of the vehicle. In this type of tire 1, the ground contact pressure near the center of the width of the shoulder land portion 20-1 drops drastically, shortening the ground contact length, which may deteriorate the ground contact performance and therefore the steering stability. In addition, the ground contact pressure at both ends of the shoulder land portion 20-1 in the tire width direction becomes relatively high, which may induce uneven wear. For this reason, the tire of this embodiment is configured with a ground contact surface shape that aims to improve steering stability and uneven wear resistance. Next, the ground contact surface shape of the tread portion 10 will be described.

2 is a tire meridian cross-sectional view showing the tread portion of the tire shown in FIG. 1. Among the reference symbols in FIG. 2, the same symbols as those in FIG. 1 indicate the same members as those shown in FIG. 1. In FIG. 2, the two end points (edges) in the tire width direction of the center land portion 20d are B1 and B2, respectively, and the points on both ground contact ends E and E of the tread portion 10 aligned in the tire width direction with these end points B1 and B2 are E1 and E2, respectively. A curve including at least one of the end points B1 and B2 in the tire width direction of the center land portion 20d and both points E1 and E2 on the ground contact ends is defined as a reference profile line PL0 of the tread surface 12. This reference profile line PL0 may include both end points B1 and B2 in the tire width direction of the center land portion 20d. In addition, the reference profile line PL0 may be a circular arc, an elliptical arc, or any other curve.

Under these assumptions, in this embodiment, as shown in Figure 2, the shoulder land portion 20-1 on the vehicle outer side, which has a wide contact area, has a contact surface 30-1 that protrudes radially outward from the reference profile line PL0. In contrast, the center land portion 20d adjacent to the shoulder land portion 20-1 on the vehicle outer side is configured to protrude less from the reference profile line PL0 than the contact surface 30-1, and in the example of Figure 2, has a contact surface 30d that is the same shape as the reference profile line PL0.

The maximum protruding position P1 where the ground contact surface 30-1 of the shoulder land portion 20-1 on the outer side of the vehicle protrudes most outward in the tire radial direction is located at a position displaced by a predetermined distance Wh outward in the tire width direction from the shoulder main groove 14d on the outer side of the vehicle, as shown in FIG. 1, and the distance Wh to the width W1 of the ground contact area of the shoulder land portion 20-1 is 0.40≦Wh/W1≦0.60. In other words, the maximum protruding position P1 of the ground contact surface 30-1 is located in the center of the shoulder land portion 20-1 in the tire width direction, and is preferably located in the range of 0.45≦Wh/W1≦0.55. As a result, the shoulder land portion 20-1 on the outer side of the vehicle can be configured to have a ground contact surface 30-1 with a protruding center in the tire width direction. This ensures the ground contact length of the center in the tire width direction of the shoulder land portion 20-1 on the outer side of the vehicle, improves steering stability, uniforms the ground contact pressure, and suppresses uneven wear of the tire 1. In addition, the ground contact surface 30d of the center land portion 20d has the same shape as the reference profile line PL0, so that the ground contact surface 30d (profile line) of the center land portion 20d, where the ground pressure is sufficiently uniform, does not protrude, thereby preventing excessive wear on the center land portion 20d.

The maximum protrusion amount H1 of the contact surface 30-1 from the reference profile line PL0 is 0.1 mm≦H1≦0.3 mm. By making the contact surface 30d of the center land portion 20d equivalent to the reference profile line PL0 and making the maximum protrusion amount H1 0.1 mm or more, the contact pressure near the center position in the tire width direction for the shoulder land portion 20-1 on the outer side of the vehicle can be made closer to the contact pressure at both outer positions in the tire width direction, and the contact length can be smoothly and gradually decreased toward both outer sides in the tire width direction. This increases the grip force with the road surface, improves steering performance, especially when the vehicle is traveling straight, and further improves straight-line performance (steering stability).

In addition, by setting the maximum protrusion amount H1 to 0.3 mm or less, it is possible to suppress excessive ground pressure distribution within the contact surface 30-1 of the shoulder land portion 20-1 on the vehicle outer side, ensure the contact width, and suppress the amount of protrusion in the tire radial direction near the center position in the tire width direction. This prevents the amount of wear near the center position from being excessively large compared to the amount of wear at other positions, and thus further improves uneven wear resistance. It also makes it possible to prevent users from feeling uncomfortable in appearance due to the change from the conventional profile shape (the above-mentioned reference profile line shape).

In this embodiment, the contact surface 30d of the center land portion 20d has the same shape as the reference profile line PL0, i.e., the maximum protrusion amount of the contact surface 30d from the reference profile line PL0 is set to 0 mm, but this is not limited to this and it may be set to a range (0 mm or more and 0.1 mm or less) smaller than the maximum protrusion amount H1 of the contact surface 30-1 of the shoulder land portion 20-1 on the outer side of the vehicle.

In addition, in the tire 1 described above, it is preferable that the shoulder land portion 20a and the second land portion 20b on the vehicle inner side have contact surfaces 30a, 30b that protrude radially outward from the reference profile line PL0 described above. In this case, the maximum protruding position Pa at which the contact surface 30a of the shoulder land portion 20a on the vehicle inner side protrudes most radially outward is provided at a position displaced toward the shoulder main groove 14a on the vehicle inner side from the tire width direction center position of the shoulder land portion 20a, as shown in FIG. 2. Similarly, the maximum protruding position Pb at which the contact surface 30b of the second land portion 20b on the vehicle inner side protrudes most radially outward is provided at a position displaced toward the shoulder main groove 14a on the vehicle inner side from the tire width direction center position of the second land portion 20b. That is, in the shoulder land portion 20a and the second land portion 20b on the vehicle inner side, which are provided on either side of the shoulder main groove 14a on the vehicle inner side, the maximum protruding positions Pa and Pb of the contact surfaces 30a and 30b are provided on the shoulder main groove 14a side. Therefore, the ground pressure on the shoulder main groove 14a side of the shoulder land portion 20a and the second land portion 20b can be made closer to the ground pressure on the side away from the shoulder main groove 14a (the ground edge E side in the shoulder land portion 20a, and the second main groove 14b side in the second land portion 20b). This can increase the grip force with the road surface, improve the steering performance, especially when the vehicle is traveling straight, and further improve the straight-line performance (steering stability).

In addition, in the above-mentioned shoulder land portion 20a and second land portion 20b on the vehicle inner side, the maximum protrusion amounts Ha, Hb of each ground contact surface 30a, 30b relative to the reference profile line PL0 are set to be greater than the protrusion amount when the above-mentioned center land portion 20d protrudes radially outward from the reference profile line PL0, and it is preferable to set them to be equal to the maximum protrusion amount H1 of the ground contact surface 30-1 in the shoulder land portion 20-1 on the vehicle outer side, for example.

The pneumatic tire 1 according to the present embodiment has a meridian cross-sectional shape similar to that of a conventional pneumatic tire. Here, the meridian cross-sectional shape of a pneumatic tire refers to the cross-sectional shape of the pneumatic tire that appears on a plane perpendicular to the tire equatorial plane CL. Although not shown, the tire 1 according to the present embodiment has a bead portion, a sidewall portion, a shoulder portion, and a tread portion from the inner side to the outer side in the tire radial direction in the tire meridian cross-sectional view. The tire 1 includes, for example, a carcass layer that extends from the tread portion to the bead portions on both sides in the tire meridian cross-sectional view and is wound around a pair of bead cores, and a belt layer and a belt reinforcing layer that are sequentially formed on the outer side in the tire radial direction of the carcass layer.

In this embodiment, as shown in Figures 1 and 2, the following effects are achieved by protruding the contact surfaces 30-1, 30a, and 30b of the shoulder land portion 20-1 on the outer side of the vehicle, the shoulder land portion 20a on the inner side of the vehicle, and the second land portion 20b radially outward from the reference profile line PL0.

Figure 3 is a plan view showing the ground contact surface shape of a conventional pneumatic tire. Figure 4 is a plan view showing the ground contact surface shape of a pneumatic tire of this embodiment. Note that the conventional tread pattern shown in Figure 3 is the same as the tread pattern shown in Figure 1, but is an example in which the ground contact surfaces of all land portions coincide with the reference profile line PL0.

In conventional pneumatic tires, the contact surface of each land portion 20 coincides with the reference profile line PL0 and does not protrude in the tire radial direction. Therefore, due to the low ground contact pressure near the tire width direction center position of the shoulder land portion 20-1 on the vehicle outer side, which is formed wide, and near the shoulder main groove 14a that divides the shoulder land portion 20a and the second land portion 20b on the vehicle inner side, as shown by arrows Y1 and Y2 in Figure 3, both ends of the tire circumferential direction near the width direction center position of the shoulder land portion 20-1 and near the shoulder main groove 14a deform toward the inside of each land portion, and the outer peripheral line of the contact area when it touches the ground becomes uneven. Due to the influence of the uneven shape of the outer peripheral line, there are parts where the contact length is short near the tire width direction center position of the shoulder land portion 20-1 on the vehicle outer side and near the shoulder main groove 14a located between the shoulder land portion 20a and the second land portion 20b on the vehicle inner side, which may deteriorate the ground contact performance and therefore the steering stability performance.

In contrast, in the pneumatic tire 1 of this embodiment, as shown in FIG. 2, the center of the shoulder land portion 20-1 on the outer side of the vehicle in the tire width direction, the shoulder main groove 14a side of the shoulder land portion 20a on the inner side of the vehicle, and the shoulder main groove 14a side of the second land portion 20b all have maximum protruding positions P1, Pa, and Pb that protrude in the tire radial direction relative to the reference profile line PL0. The ground contact surface 30d of the center land portion 20d coincides with the reference profile line PL0. Therefore, the ground contact pressure near the center position in the tire width direction of the shoulder land portion 20-1 on the outer side of the vehicle is made equal to the ground contact pressure at both outer positions in the tire width direction, and the ground contact pressure near each shoulder main groove 14a of the shoulder land portion 20a and the second land portion 20b on the inner side of the vehicle can be made almost equal to the ground contact pressure on the side away from the shoulder main groove 14a. This makes it possible to suppress deformation of both ends in the tire circumferential direction near the center position in the width direction of the shoulder land portion 20-1 and near the shoulder main groove 14a toward the inside of each land portion. As a result, as shown in Figure 4, both ends of the ground contact area of each land portion in the tire circumferential direction are located on a single smooth curve. Therefore, the ground contact length of each land portion 20 in the tire circumferential direction can be made more uniform than in the example of Figure 3, and thus the ground contact can be improved.

In addition, in this embodiment, as shown in FIG. 2, the center land portion 20d adjacent to the shoulder land portion 20-1 on the outer side of the vehicle has the same shape as the reference profile line PL0. Therefore, the center land portion 20d, which has a sufficiently uniform ground pressure, does not protrude the ground contact surface 30d, thereby preventing excessive wear in the center land portion 20d.

In addition, in this embodiment, as shown in FIG. 1, of the dimples 25 provided on the shoulder land portion 20-1 on the outer side of the vehicle, the dimples 25C in the widthwise central row of the shoulder land portion 20-1 are arranged on the maximum protruding position P1, which prevents the ground pressure at the maximum protruding position from becoming excessively high and optimizes the ground pressure distribution around the dimples, thereby suppressing uneven wear and improving steering stability.

Next, another embodiment will be described. FIG. 5 is a plan view showing the tread surface of a pneumatic tire according to another embodiment. In the above embodiment, the tire 1 is configured with three circumferential main grooves 14 extending in the tire circumferential direction on the tread surface 12. However, in this another embodiment, the pneumatic tire 1A (hereinafter sometimes simply referred to as tire 1A) is configured differently in that the tread surface 12A has four circumferential main grooves 14.

Specifically, as shown in FIG. 5, the circumferential main grooves 14 are arranged such that two circumferential main grooves 14a, 14b are provided on the vehicle inner side, one circumferential main groove 14d is provided on the vehicle outer side, and one circumferential main groove 14c is provided on the tire equatorial plane CL. As in the above embodiment, the circumferential main grooves 14a, 14d on the outermost side in the tire width direction are referred to as shoulder main grooves, the circumferential main groove 14b on the inner side in the tire width direction is referred to as a second main groove, and the circumferential main groove 14c is referred to as a center main groove. That is, in this embodiment, the center main groove 14c is provided between the shoulder main groove 14d on the vehicle outer side and the second main groove 14b on the vehicle inner side.

In this embodiment, five land portions 20 extending in the tire circumferential direction are defined on the tread surface 12A by four circumferential main grooves 14. Specifically, the vehicle inner shoulder land portion 20a is defined on the tire width direction outer side of the vehicle inner shoulder main groove 14a, and the vehicle inner second land portion 20b is defined by the vehicle inner shoulder main groove 14a and the second main groove 14b. In addition, the vehicle inner center land portion 20c is defined by the second main groove 14b and the center main groove 14c, the vehicle outer center land portion (middle land portion) 20d is defined by the center main groove 14c and the vehicle outer shoulder main groove 14d, and the vehicle outer shoulder land portion 20-1 is defined on the tire width direction outer side of the vehicle outer shoulder main groove 14d.

In this embodiment, the width W1 of the ground contact area of the shoulder land portion 20-1 on the outer side of the vehicle is the widest (largest) of all the land portions 20, and has a relationship of 0.25≦W1/WT≦0.35 with respect to the width WT of the tire ground contact area. In this case, the width Wa of the ground contact area of the shoulder land portion 20a on the inner side of the vehicle, the width Wb of the ground contact area of the second land portion 20b on the inner side of the vehicle, the width Wc of the ground contact area of the center land portion 20c on the inner side of the vehicle, and the width Wd of the ground contact area of the center land portion 20d each have a relationship of 0.10 to 0.20 (0.10≦Wd/WT≦0.20; similarly for Wa/WT, Wb/WT, and Wc/WT) with respect to the width WT of the tire ground contact area.

In this embodiment, each land portion 20 has various lug grooves extending in the tire width direction. In addition, the center land portion 20c on the vehicle inner side is provided with a plurality of lug grooves 17a, which open at one end in the second main groove 14b on the vehicle inner side, extend from the second main groove 14b toward the tire equatorial plane CL side, and terminate at the other end within the center land portion 20c, as in the second land portion 20b, and a plurality of lug grooves 17b, which open at one end in the center main groove 14c, extend from the center main groove 14c toward the vehicle inner side, and terminate at the other end within the center land portion 20c. These lug grooves 17a, 17b are spaced apart in the tire width direction and are arranged in a staggered pattern (alternately) in the tire circumferential direction.

Also in this embodiment, the shoulder land portion 20-1 on the outer side of the vehicle, the shoulder land portion 20a on the inner side of the vehicle, and the second land portion 20b, which have wide contact areas, each have contact surfaces 30-1, 30a, 30b that protrude radially outward from the reference profile line PL0 (Figure 2). These contact surfaces 30-1, 30a, 30b are formed to have the maximum protrusion amount at the maximum protrusion positions P1, Pa, Pb shown in Figure 5, respectively. In contrast, the center land portion 20d on the outer side of the vehicle adjacent to the shoulder land portion 20-1 on the outer side of the vehicle, and the center land portion 20c on the inner side of the vehicle adjacent to that, have contact surfaces 30c, 30d that are the same shape as the reference profile line PL0. Note that these contact surfaces 30c, 30d have the same shape as the reference profile line PL0, i.e., the maximum protrusion of the contact surfaces 30c, 30d from the reference profile line PL0 is set to 0 mm, but this is not limited to this and may be set to a range (0 mm or more and 0.1 mm or less) smaller than the maximum protrusion H1 of the contact surface 30-1 of the shoulder land portion 20-1 on the outer side of the vehicle.

In this embodiment, the following effects are achieved by having the ground contact surfaces 30-1, 30a, and 30b of the shoulder land portion 20-1 on the outer side of the vehicle, the shoulder land portion 20a on the inner side of the vehicle, and the second land portion 20b protrude radially outward from the reference profile line PL0.

Figure 6 is a plan view showing the ground contact surface shape of a conventional pneumatic tire. Figure 7 is a plan view showing the ground contact surface shape of a pneumatic tire of another embodiment. Note that the conventional tread pattern shown in Figure 6 is the same as the tread pattern shown in Figure 5, but is an example in which the ground contact surfaces of all land portions coincide with the reference profile line PL0.

In conventional pneumatic tires, the contact surface of each land portion 20 coincides with the reference profile line PL0 and does not protrude in the tire radial direction. Therefore, due to the low ground contact pressure near the tire width direction center position of the shoulder land portion 20-1 on the vehicle outer side, which is formed wide, and near the shoulder main groove 14a that divides the shoulder land portion 20a and the second land portion 20b on the vehicle inner side, as shown by arrows Y1 and Y2 in Figure 6, both ends of the tire circumferential direction near the width direction center position of the shoulder land portion 20-1 and near the shoulder main groove 14a deform toward the inside of each land portion, and the outer peripheral line of the contact area when it touches the ground becomes uneven. Due to the influence of the uneven shape of the outer peripheral line, there are parts where the contact length is short near the tire width direction center position of the shoulder land portion 20-1 on the vehicle outer side and near the shoulder main groove 14a located between the shoulder land portion 20a and the second land portion 20b on the vehicle inner side, which may deteriorate the ground contact performance and therefore the steering stability performance.

In contrast, in the pneumatic tire 1 of this embodiment, as shown in FIG. 7, the center of the shoulder land portion 20-1 on the outer side of the vehicle in the tire width direction, the shoulder main groove 14a side of the shoulder land portion 20a on the inner side of the vehicle, and the shoulder main groove 14a side of the second land portion 20b all have maximum protruding positions P1, Pa, Pb that protrude in the tire radial direction relative to the reference profile line PL0. In addition, the ground contact surfaces 30c, 30d of the center land portions 20c, 20d coincide with the reference profile line PL0. Therefore, the ground contact pressure near the center position in the tire width direction of the shoulder land portion 20-1 on the outer side of the vehicle is made equal to the ground contact pressure at both outer positions in the tire width direction, and the ground contact pressure near each shoulder main groove 14a of the shoulder land portion 20a and the second land portion 20b on the inner side of the vehicle can be made almost equal to the ground contact pressure on the side away from the shoulder main groove 14a. This makes it possible to prevent the circumferential ends of the tire near the widthwise center position of the shoulder land portion 20-1 and near the shoulder main groove 14a from deforming toward the inside of each land portion. As a result, as shown in FIG. 7, the circumferential ends of the tire in the ground contact region of each land portion are positioned on a single smooth curve. Therefore, the ground contact length in the circumferential direction of the tire for each land portion 20 can be made more uniform than in the example of FIG. 6, and thus the ground contact performance can be improved.

In this embodiment, the center land portion 20d on the outer side of the vehicle adjacent to the shoulder land portion 20-1 on the outer side of the vehicle and the center land portion 20c on the inner side of the vehicle have the same shape as the reference profile line PL0. Therefore, the center land portions 20c, 20d, which have sufficiently uniform ground pressure, do not protrude the contact surfaces 30c, 30d, thereby preventing excessive wear at the center land portions 20c, 20d.

Figure 8 is a table showing the results of a performance test of the pneumatic tires according to this embodiment. Pneumatic tires of Examples 1 to 8 were produced with a tire size of 185/70R13 (13 x 5.0J), a tread pattern similar to that shown in Figure 1, and contact surfaces 30-1, 30a to 30d of the tread surface 12 shown in Figure 2. The detailed conditions of the contact surfaces of the tread surface 12 of the pneumatic tires of Examples 1 to 8 are as shown in Figure 8.

In contrast, conventional pneumatic tires were produced that have the same structure as the pneumatic tire of Example 1, except that the tire size is 185/70R13 (13 x 5.0J) and the tread surface 12 shown in Figure 2 coincides with the reference profile line PL0. Comparative Examples 1 and 2 pneumatic tires were also produced that have the same structure as the pneumatic tire of Example 1, except that the tire size is 185/70R13 (13 x 5.0J) and the ground contact surface of the center land portion 20d is made to protrude to the same extent as the shoulder land portion 20-1 on the outer side of the vehicle, or the positional relationship of the maximum protruding position of the ground contact surface of the shoulder land portion 20-1 on the outer side of the vehicle is changed.

The test tires of Examples 1 to 8, Comparative Examples 1 to 2, and the conventional example were assembled on 13 x 5.0J rims, inflated to 220 kPa, and fitted to a van-type vehicle with an engine displacement of 1500 cc to evaluate steering stability and resistance to uneven wear.

Regarding the steering stability, a sensory evaluation was performed on the vehicle stability (straight running and cornering) on a dry road surface. Based on the evaluation results, an index was evaluated with the conventional example set as the standard (100). The higher the index, the higher the steering stability.
Regarding the uneven wear resistance, the tire was driven for 10,000 km in a specific driving pattern, and the wear amount of the shoulder land portion 20-1 and the center land portion 20d on the outer side of the vehicle was measured, and the wear amount ratio of the shoulder land portion 20-1 to the center land portion 20d was calculated. Then, based on the calculation results, an index evaluation was performed with Conventional Example 1 as the standard (100). In this evaluation, the higher the index, the higher the uneven wear resistance.

As can be seen from Figure 8, the pneumatic tires of Examples 1 to 8 were able to improve steering stability and uneven wear resistance in comparison with Conventional Example 1. On the other hand, the pneumatic tires of Comparative Examples 1 and 2 did not meet the specified conditions, and therefore did not sufficiently achieve both steering stability and uneven wear resistance.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the present embodiment, a pneumatic tire is used as an example of the tire, but the present invention is not limited to this, and can of course also be applied to tires that are not filled with air, such as airless tires. Furthermore, in addition to normal air or air with an adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used as the gas filled into the pneumatic tire exemplified in this embodiment.

Reference Signs List 1, 1A Tire 10 Tread portion 12, 12A Tread surface 14 Circumferential main groove 14a Shoulder main groove on vehicle inner side 14b Second main groove on vehicle inner side 14d Shoulder main groove on vehicle outer side 20 Land portion 20-1 Shoulder land portion on vehicle outer side 20a Shoulder land portion on vehicle inner side 20b Second land portion on vehicle inner side 20d Center land portion (middle land portion)
25, 25A, 25B, 25C Dimple 30-1 Contact surface of shoulder land portion on outer side of vehicle 30a Contact surface of shoulder land portion on inner side of vehicle 30b Contact surface of second land portion on inner side of vehicle 30d Contact surface of center land portion CL Tire equatorial plane E Ground contact edge P1 Maximum protruding position of contact surface of shoulder land portion on outer side of vehicle Pa Maximum protruding position of contact surface of shoulder land portion on inner side of vehicle Pb Maximum protruding position of contact surface of second land portion on inner side of vehicle PL0 Reference profile line

Claims (8)

A tire in which the mounting direction on a vehicle is specified,
The tread portion includes a plurality of circumferential main grooves extending in a circumferential direction of the tire, and a plurality of land portions defined by the circumferential main grooves,
a width W1 of a ground contact area of a shoulder land portion on an outer side of a vehicle, which is located on the outer side of the vehicle when the tire is mounted on the vehicle, and a width WT of the ground contact area of the tire have a relationship of 0.25≦W1/WT≦0.35,
When both end points in the tire width direction of an intermediate land portion adjacent to the shoulder land portion on the vehicle outer side across the circumferential main groove are defined as end points B1, B2, respectively, and points on both ground contact ends E, E of the tread portion aligned in the tire width direction with these end points B1, B2 are defined as points E1, E2, respectively, and a circular or elliptical arc curve including at least one of the end points B1, B2 in the tire width direction of the intermediate land portion and the points E1, E2 on the ground contact ends is defined as a reference profile line,
At least the vehicle-outer shoulder land portion has a contact surface that protrudes radially outward in the tire direction with respect to the reference profile line, and a maximum protruding position at which the contact surface protrudes radially outward in the tire direction to a maximum extent is provided at a position displaced by a distance Wh outward in the tire width direction from the circumferential main groove between the vehicle-outer shoulder land portion and the intermediate land portion, and the distance Wh with respect to a width W1 of the contact area of the vehicle-outer shoulder land portion has a relationship of 0.40≦Wh/W1≦0.60,
The intermediate land portion has a contact surface that is the same shape as the reference profile line or that protrudes radially outward from the reference profile line by a smaller amount than the protrusion of the shoulder land portion on the vehicle outer side . The tire according to claim 1, wherein the width Wd of the ground contact area of the intermediate land portion has a relationship of 0.10≦Wd/WT≦0.20 with respect to the width WT of the tire ground contact area. The tire according to claim 1 or 2, wherein the intermediate land portion is disposed on the tire equatorial plane or on the vehicle outer side of the tire equatorial plane. 4. The tire according to claim 1, wherein the shoulder land portion on the vehicle outer side has a first lug groove that extends in the tire width direction, opens into the circumferential main groove and terminates within the shoulder land portion, and a second lug groove that opens into the vehicle outer side ground contact edge and terminates within the shoulder land portion, and the maximum protruding position is provided in a region between the first lug groove and the second lug groove in the tire width direction. The tire according to claim 4, which has a plurality of circular dimples arranged in a staggered pattern in the region between the first lug groove and the second lug groove, and some of the dimples are aligned in the same straight line as the maximum protruding position. The tire according to any one of claims 1 to 5, wherein the maximum protrusion amount H1 of the shoulder land portion on the outer side of the vehicle relative to the reference profile line is 0.1 mm or more and 0.3 mm or less, and the maximum protrusion amount of the intermediate land portion relative to the reference profile line is 0 mm or more and 0.1 mm or less. a width Wa of a ground contact area of a shoulder land portion on an inner side of a vehicle and a width Wb of a ground contact area of a second land portion on an inner side of a vehicle adjacent to the shoulder land portion across the circumferential main groove have a relationship with the width WT of the tire ground contact area of 0.10≦Wa/Wt≦0.20 and 0.10≦Wb/Wt≦0.20, respectively;
7. The tire according to claim 1, wherein the shoulder land portion and the second land portion each have a contact surface that protrudes radially outward from a reference profile line, and the amount of protrusion of each of the shoulder land portion and the second land portion is greater than the amount of protrusion of the intermediate land portion radially outward from the reference profile line. The tire according to any one of claims 1 to 7, wherein the tread portion has at least one circumferential main groove on the outer side of the vehicle and at least two circumferential main grooves on the inner side of the vehicle, with the tire having four or five rows of land portions partitioned in the tire circumferential direction by these circumferential main grooves.

Images