JP2021041763A - Pneumatic tire - Google Patents

Abstract

To restrain groove bottom cracks.SOLUTION: In a tire meridian cross section, assuming that a straight line connecting an outer open end 30B and a groove bottom midpoint 30A1 of a center main groove 30 is L1, a straight line connecting an inner open end 28B and a groove bottom midpoint 28A1 of a shoulder main groove 28 is L2, a straight line connecting an intersection of the straight line L1 and the straight line L2 and the tire center is L3, and a distance in tire width direction between the groove bottom midpoint 30A1 of the center main groove and the groove bottom midpoint 28A1 of the shoulder main groove is A, a terminal 44E of an outermost belt 44 falls within a range of 15% of the distance A on the inner side and the outer side in the tire width direction with the straight line L3 as the center, respectively. Assuming that a straight line connecting an outer open end 28C and a groove bottom midpoint 28A1 of the shoulder main groove is L4, a straight line vertical to a tire rotary shaft through a grounding end 12E of a tread part is L5, a straight line connecting an intersection of the straight line L4 and the straight line L5 and the tire center is L6, a terminal 42E of a second outside belt 42 lies on the outer side in the tire width direction with respect to the straight line L6.SELECTED DRAWING: Figure 2

Description

Embodiments of the present invention relate to pneumatic tires.

Pneumatic tires generally include a tread rubber provided on the tread portion and a belt layer provided on the inner side of the tread rubber in the tire radial direction. The tread rubber is provided with a plurality of main grooves extending in the tire circumferential direction, whereby a plurality of land portions are formed on the surface of the tread portion. For example, as a main groove, there is one provided with at least one center main groove and a pair of shoulder main grooves located on both outer sides of the center main groove.

In Patent Document 1, in a pneumatic tire provided with a pair of center main grooves and a pair of shoulder main grooves, the terminal of the outermost belt located on the outermost side in the tire radial direction is located between the center main groove and the shoulder main groove. The terminal of the second outer belt, which is arranged on the inner side in the tire radial direction of the outermost belt, is arranged on the outer side in the tire width direction with respect to the shoulder main groove.

In such a pneumatic tire, cracks may occur at the bottom of the center main groove and the shoulder main groove.

In Patent Document 2, in order to suppress the occurrence of cracks at the groove bottom of the shoulder main groove, the distance from the terminal position of the belt reinforcing layer extending outward in the tire width direction from the shoulder main groove to the shoulder main groove. Is disclosed to be 50% or more of the opening width of the shoulder main groove. However, the relationship between the belt reinforcing layer and the shoulder main groove is defined, and the relationship between the belt layer and the center main groove and the shoulder main groove is not disclosed.

Japanese Unexamined Patent Publication No. 2017-071278 JP-A-2018-0437334

In view of the above points, it is an object of the present invention to provide a pneumatic tire capable of suppressing groove bottom cracks in the center main groove and the shoulder main groove.

The pneumatic tire according to the embodiment of the present invention is a pneumatic tire including a tread rubber provided on the tread portion and a belt layer provided on the inner side of the tread rubber in the tire radial direction.
The tread rubber includes a shoulder main groove extending in the tire circumferential direction and a center main groove located inside the shoulder main groove in the tire width direction and extending in the tire circumferential direction.
The belt layer includes an outermost belt located on the outermost side in the tire radial direction and a second outer belt in contact with the inner side of the outermost belt in the tire radial direction.
The terminal of the outermost belt is located between the groove bottom of the center main groove and the groove bottom of the shoulder main groove in the tire width direction, and the terminal of the second outer belt is closer to the groove bottom of the shoulder main groove. Located on the outside in the tire width direction,
In the tire meridian cross section
The straight line connecting the opening end on the outer side of the center main groove in the tire width direction and the midpoint of the groove bottom of the center main groove is defined as L1, and the opening end on the inner side in the tire width direction of the shoulder main groove and the groove of the shoulder main groove. The straight line connecting the midpoint of the bottom is L2, the straight line connecting the intersection of the straight line L1 and the straight line L2 and the center of the tire is L3, and the midpoint of the groove bottom of the center main groove and the groove of the shoulder main groove. Let A be the distance from the midpoint of the bottom in the tire width direction, and the terminal of the outermost belt is within a range of 15% of the distance A from the center to the inside and outside in the tire width direction with the straight line L3 as the center. Yes and
The straight line connecting the opening end on the outer side of the shoulder main groove in the tire width direction and the groove bottom midpoint of the shoulder main groove is defined as L4, and the straight line passing through the ground contact end of the tread portion and perpendicular to the tire rotation axis is defined as L5. The straight line connecting the intersection of the straight line L4 and the straight line L5 and the center of the tire is defined as L6, and the terminal of the second outer belt is located outside the straight line L6 in the tire width direction.

In the pneumatic tire according to the present embodiment, a recess is provided on the side surface of the tread portion, and the belt layer is provided with a maximum width belt having the largest dimension in the tire width direction inside the second outer belt in the tire radial direction. The shortest distance between the end of the maximum width belt and the recess may be 10 mm or more.

In the pneumatic tire according to the present embodiment, the tread rubber is a pair of the center main grooves arranged on both sides of the tire equator and a pair of the said tread rubbers arranged outside the pair of center main grooves in the tire width direction. A shoulder main groove and four circumferential main grooves including the shoulder main groove may be provided.

In the pneumatic tire according to the present embodiment, the tread rubber includes one center main groove arranged on the equator of the tire and a pair of shoulder mains arranged outside the center main groove in the tire width direction. A groove and three circumferential main grooves including the groove may be provided.

In the present specification, unless otherwise specified, the dimensions and the like of each part of the pneumatic tire are values measured in a no-load state in which the pneumatic tire is mounted on a regular rim and filled with a regular internal pressure. A regular rim is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, JATMA is a standard rim, TRA is "Design Rim", and ETRTO is "". Measuring Rim ". The regular internal pressure is the air pressure defined for each tire in the standard system including the standard on which the tire is based. For JATTA, the maximum air pressure, and for TRA, the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION". The maximum value described in "PRESSURES", or "INFLATION PRESSURE" for ETRTO.

According to this embodiment, it is possible to suppress groove bottom cracks in the center main groove and the shoulder main groove.

A cross-sectional view of the meridian in the tread portion of the pneumatic tire according to the embodiment. Enlarged view of a part of FIG. 1 (semi-cross-sectional view of the tread portion) Enlarged view of the vicinity of the terminal of the outermost belt in the cross section of FIG. A semi-cross-sectional view showing a meridian cross section of a tread portion of a pneumatic tire according to another embodiment.

Hereinafter, embodiments will be described with reference to the drawings.

The pneumatic tire 10 according to the embodiment shown in FIG. 1 has a tread portion 12 forming a contact patch, a pair of left and right bead portions, and a pair of left and right sidewall portions 14 interposed between the tread portion 12 and the bead portion. , 14 and so on. The pneumatic tire 10 according to the present embodiment is a heavy-duty pneumatic tire mounted on a truck, a bus, or the like.

In the figure, reference numeral CL indicates a tire equatorial plane corresponding to the center in the tire width direction. In this example, the pneumatic tire 10 is symmetrical with respect to the tire equatorial plane CL. The line where the tire equator surface CL and the surface of the tread portion 12 intersect is called the tire equator.

Here, the tire width direction is a direction parallel to the tire rotation axis, is also referred to as a tire axis direction, and is indicated by reference numeral WD in the figure. The inside of the WD in the tire width direction is a direction approaching the tire equatorial plane CL, and the outside of the WD in the tire width direction is a direction away from the tire equatorial plane CL. The tire radial direction is a direction perpendicular to the tire rotation axis, and is indicated by reference numeral RD in the figure. The inside of the tire radial direction RD is a direction approaching the tire rotation axis, and the tire radial direction RD outside is a direction away from the tire rotation axis. The tire circumferential direction is a direction on the circumference centered on the tire rotation axis.

The pneumatic tire 10 includes a carcass layer 16 that extends toroidally across a pair of bead portions. The carcass layer 16 reaches the bead portion from the tread portion 12 through the sidewall portions 14 on both sides, and is locked at the bead portion. The carcass layer 16 is composed of at least one carcass ply formed by arranging carcass cords such as steel cords so as to be substantially perpendicular to the tire circumferential direction and coating them with rubber.

The tread portion 12 is provided with a tread rubber 18 forming a ground contact surface and a belt layer 20 provided inside the tire radial RD of the tread rubber 18.

The tread rubber 18 is laminated on the outer side of the RD in the tire radial direction of the belt layer 20, and includes a tread surface 22 that comes into contact with the road surface. Although not shown, the tread rubber 18 may have a two-layer structure including a cap rubber layer forming a ground contact surface and a base rubber layer arranged inside the cap rubber layer in the tire radial direction.

The tread surface 22 is an outer peripheral surface of the tread portion 12 forming a ground contact surface. The tread portion 12 has a tread surface 22 and a pair of left and right side surfaces 24, so that the tread portion 12 has a shape convex outward in the tire radial direction RD. The outer surface of the tread portion 12 (specifically, the tread rubber 18) in the tire radial direction is the tread surface 22, and the outer surface of the tread surface 22 in the tire width direction extends inward in the tire radial direction from the outer end in the tire width direction. Is the side surface 24. The outer end of the tread surface 22 in the tire width direction is the ground contact end 12E of the tread portion 12.

Here, the ground contact end 12E of the tread portion 12 is the outermost position of the WD in the tire width direction on the ground contact surface. The ground contact surface refers to the surface of the tread portion 12 that is in contact with the road surface when a pneumatic tire is mounted on a regular rim, the tire is placed vertically on a flat road surface and a regular load is applied, and the tire is placed vertically on a flat road surface. The normal rim and the normal internal pressure are as described above. The normal load is the load defined for each tire in the standard system including the standard on which the tire is based. For JATTA, the maximum load capacity, and for TRA, the maximum value described in the above table. If it is ETRTO, it is "LOAD CAPACITY".

The tread rubber 18 is located inside the shoulder main groove 28 extending in the tire circumferential direction and inside the tire width direction WD of the shoulder main groove 28 to partition the shoulder land portion 26 and the land portion inside the tire width direction. A center main groove 30 extending in the tire circumferential direction is provided on the tread surface 22. In this example, the tread rubber 18 has a pair of left and right center main grooves 30 and 30 arranged on both sides of the tire equator and a pair of left and right center main grooves 30 and 30 arranged outside the WD in the tire width direction. It is provided with four shoulder main grooves 28 and 28 and four circumferential main grooves. The shoulder main groove 28 and the center main groove 30 are substantially parallel to the equator of the tire, and in this example, extend linearly in the tire circumferential direction. The groove width (opening width) of the circumferential main groove, that is, the center main groove 30 and the shoulder main groove 28 is not particularly limited, and may be, for example, 6 mm or more, or 8 mm or more.

A plurality of land portions are formed on the surface of the tread portion 12 by these circumferential main grooves. In this example, the center land portion 32 between the pair of center main grooves 30 and 30, the mediate land portion 34 between the center main groove 30 and the shoulder main groove 28, and the tire width direction from the shoulder main groove 28. An outer shoulder land portion 26 is provided.

The center land portion 32 is a land portion at the center in the tire width direction, including the tire equatorial plane CL. The mediate land portion 34 is a pair of left and right land portions provided on both sides of the center land portion 32 in the tire width direction WD. The shoulder land portion 26 is a pair of left and right land portions provided on the outer sides of the pair of left and right mediate land portions 34, 34 in the tire width direction WD, respectively, and is a land portion including the ground contact end 12E.

The center land portion 32, the mediate land portion 34, and the shoulder land portion 26 may be ribs that are continuous land portions in the tire circumferential direction that are not divided by the lateral grooves, and may be spaced apart in the tire circumferential direction. It may be a block row which is an intermittent land portion divided by a lateral groove arranged in a row.

A plurality of recesses 36 are provided on the side surface of the shoulder land portion 26 (that is, the side surface 24 of the tread portion 12) at intervals in the tire circumferential direction. The recess 36 is a lug groove that extends in the tire radial direction RD on the side surface 24, opens to the tread surface 22 at the ground contact end 12E, and does not divide the shoulder land portion 26. The recess 36 may be provided by terminating it in the side surface 24 without opening it in the tread surface 22.

The belt layer 20 is a strength member that is arranged on the outer side of the RD in the tire radial direction of the carcass layer 16 and tightens the carcass layer 16. The belt layer 20 has a plurality of belts arranged in the tire radial direction RD, and in this example, it is composed of four belts 38, 40, 42, 44. The belts 38, 40, 42, 44 are formed by arranging belt cords such as steel cords at an inclined angle of, for example, 10 ° to 60 ° with respect to the tire circumferential direction and covering them with rubber.

The belt layer 20 has a four-layer structure having four belts, the first belt 38, the second belt 40, the third belt 42, and the fourth belt 44, in this order from the inside of the tire radial direction RD.

The first belt 38 is the innermost belt (hereinafter, referred to as “innermost belt 38”) located on the innermost side in the tire radial direction RD. The fourth belt 44 is the outermost belt (hereinafter, referred to as “outermost belt 44”) located on the outermost side in the tire radial direction RD. The third belt 42 is a second outer belt (hereinafter, referred to as “second outer belt 42”) that is in contact with the inner side of the tire radial RD of the outermost belt 44 (that is, adjacent to the outermost belt 44). The second belt 40 is the maximum width belt (hereinafter, referred to as “maximum width belt 40”) having the largest belt width (that is, the dimension in the tire width direction WD) among the four belts, and the second outer belt 42. It is provided inside the tire radial RD of the tire.

As shown in FIG. 2, the terminal 44E of the outermost belt 44 is located between the groove bottom 30A of the center main groove 30 and the groove bottom 28A of the shoulder main groove 28 in the tire width direction WD. The terminal 44E of the outermost belt 44 is the outer end of the outermost belt 44 in the tire width direction WD. Further, the terminal 42E of the second outer belt 42 is located outside the WD in the tire width direction with respect to the groove bottom 28A of the shoulder main groove 28. The terminal 42E of the second outer belt 42 is the outer end of the second outer belt 42 in the tire width direction WD.

The terminal 40E of the maximum width belt 40 is located outside the WD in the tire width direction with respect to the terminal 42E of the second outer belt 42. The terminal 40E of the maximum width belt 40 is the outer end of the maximum width belt 40 in the tire width direction WD. Further, the terminal 38E of the innermost belt 38 is located outside the WD in the tire width direction from the groove bottom 28A of the shoulder land portion 26, and is located inside the WD in the tire width direction from the terminal 42E of the second outer belt 42. There is. The terminal 38E of the innermost belt 38 is the outer end of the innermost belt 38 in the tire width direction WD.

The belt layer 20 is provided with a belt cushion rubber 46 having a triangular cross section inside the tire radial RD at both ends so that both ends thereof are gradually separated from the carcass layer 16. Further, a rubber 48 between belt edges having a triangular cross section is also provided between the maximum width belt 40 and the second outer belt 42 so that the ends thereof are gradually separated from each other toward the outside of the WD in the tire width direction. There is.

Reference numeral 50 indicates an inner liner which is an air-resistant permeable layer provided on the entire inner surface of the tire. Reference numeral 52 indicates a sidewall rubber constituting the outer surface of the sidewall portion 14.

This embodiment is characterized by the configuration of the tread portion 12, which will be described later, and a known configuration can be adopted for the sidewall portion 14 and the bead portion, and is not particularly limited.

In the pneumatic tire 10 according to the present embodiment, in the tire meridian cross section in a no-load state mounted on a regular rim and filled with a regular internal pressure as shown in FIGS. 1 and 2, each part of the tread portion 12 is as follows. Arrangement, dimensions, etc. are set. The normal rim and the normal internal pressure are as described above. The tire meridian cross section is a cross section obtained by cutting a tire on a plane including a tire rotation axis, and is also referred to as a tire width direction cross section.

As shown in FIG. 2, a straight line (virtual line) connecting the opening end 30B outside the tire width direction WD of the center main groove 30 and the groove bottom midpoint 30A1 of the center main groove 30 is L1 (hereinafter, "first straight line"). It is called "L1"). Here, the open end 30B is a boundary between the center main groove 30 and the tread surface 22, and is an outer end in the tire width direction WD. The groove bottom midpoint 30A1 is the center position of the center main groove 30 in the groove bottom 30A in the tire width direction.

As shown in FIG. 2, a straight line (virtual line) connecting the opening end 28B inside the tire width direction WD of the shoulder main groove 28 and the groove bottom midpoint 28A1 of the shoulder main groove 28 is L2 (hereinafter, “second”. It is called "straight line L2"). Here, the open end 28B is a boundary between the shoulder main groove 28 and the tread surface 22, and is an inner end in the tire width direction WD. The groove bottom midpoint 28A1 is the center position of the WD in the tire width direction at the groove bottom 28A of the shoulder main groove 28.

Then, the straight line (virtual line) connecting the intersection P1 of the first straight line L1 and the second straight line L2 and the tire center is referred to as L3 (hereinafter, referred to as “third straight line L3”). Here, the tire center is the intersection of the tire equatorial plane CL and the tire rotation axis, and is the center position of the pneumatic tire 10 in the width direction WD and the radial direction RD. The third straight line L3 passes between the center main groove 30 and the shoulder main groove 28 at a position away from both the center main groove 30 and the shoulder main groove 28.

Further, as shown in FIG. 2, the distance between the groove bottom midpoint 30A1 of the center main groove 30 and the groove bottom midpoint 28A1 of the shoulder main groove 28 in the tire width direction WD is A (hereinafter, “groove bottom distance A””. ).

As shown in FIG. 2, a straight line (virtual line) connecting the opening end 28C outside the tire width direction WD of the shoulder main groove 28 and the groove bottom midpoint 28A1 of the shoulder main groove 28 is L4 (hereinafter, “fourth straight line”). It is called "L4"). Here, the open end 28C is a boundary between the shoulder main groove 28 and the tread surface 22, and is an outer end in the tire width direction WD.

As shown in FIG. 2, a straight line (virtual line) that passes through the ground contact end 12E of the tread portion 12 and is perpendicular to the tire rotation axis is referred to as L5 (hereinafter, referred to as “fifth straight line L5”). The fifth straight line L5 is a line including the ground contact end 12E and parallel to the line indicating the tire equatorial plane CL in the tire meridional cross section, that is, a line parallel to the tire radial direction RD.

Then, the straight line (virtual line) connecting the intersection P2 of the fourth straight line L4 and the fifth straight line L5 and the tire center is referred to as L6 (hereinafter, referred to as "sixth straight line L6"). The sixth straight line L6 passes outside the shoulder main groove 28 in the tire width direction WD.

Under the above definition, the tread portion 12 satisfies the following conditions in the tire meridian cross section.

(1) The terminal 44E of the outermost belt 44 is within a range of 15% of the groove bottom distance A from the center to the inside and outside of the tire width direction WD with the third straight line L3 as the center. Here, the terminal 44E of the outermost belt 44 is the outer end of the outermost belt 44 in the tire width direction WD, and more specifically, at the end of the belt cord 44F excluding the covering rubber as shown in FIG. is there.

In other words, as shown in an enlarged view in FIG. 3, the condition (1) is defined as an intersection P3 at the point where the thickness center line 44X of the outermost belt 44 or its extension line 44Y intersects with the third straight line L3. When the position separated from P3 by 15% of the groove bottom distance A inside the tire width direction WD is P4, and the position separated from the intersection P3 outside the tire width direction WD by 15% of the groove bottom distance A is P5. It means that 44E is located within the range from position P4 to position P5. Here, the thickness center line 44X is a line that bisects the outermost belt 44 in the thickness direction thereof, and the extension line 44Y is a virtual extension of the thickness center line 44X along the second outer belt 42. It is a line.

It is more preferable that the terminal 44E of the outermost belt 44 is within a range of 5% of the groove bottom distance A from the center to the inside and outside of the tire width direction WD with the third straight line L3 as the center.

By setting the terminal 44E of the outermost belt 44 on or near the straight line L3 defined by the center main groove 30 and the shoulder main groove 28 in this way, the center main groove caused by the terminal 44E of the outermost belt 44 Groove bottom cracks in 30 and the shoulder main groove 28 can be effectively suppressed.

From the viewpoint of more effectively suppressing groove bottom cracks, the distance between the terminal 44E of the outermost belt 44 and the groove bottom midpoint 30A1 of the center main groove 30 in the tire width direction WD (direction parallel to the tire width direction WD). The distance) is preferably 7.0 mm or more. Further, for the same reason, the distance between the terminal 44E of the outermost belt 44 and the groove bottom midpoint 28A1 of the shoulder main groove 28 in the tire width direction WD is preferably 7.0 mm or more.

(2) The terminal 42E of the second outer belt 42 is outside the WD in the tire width direction with respect to the sixth straight line L6. Here, the terminal 42E of the second outer belt 42 is the outer end of the second outer belt 42 in the tire width direction WD, and more specifically, the end of the belt cord excluding the covering rubber.

Satisfying the condition (2) means that the second outer belt 42 intersects the sixth straight line L6, that is, has an intersection P6, as shown in FIG. By setting the terminal 42E of the second outer belt 42 outside the straight line L6 defined by the shoulder main groove 28 and the ground contact end 12E in the tire width direction in this way, the terminal 42E of the second outer belt 42 is shouldered. By separating the main groove 28 from the groove bottom 28A, it is possible to effectively suppress the groove bottom crack of the shoulder main groove 28 caused by the terminal 42E.

From the viewpoint of more effectively suppressing groove bottom cracks, the distance between the terminal 42E of the second outer belt 42 and the groove bottom midpoint 28A1 of the shoulder main groove 28 in the tire width direction WD is 7.0 mm or more. Is preferable.

(3) The shortest distance B between the terminal 40E of the maximum width belt 40 and the recess 36 provided on the side surface 24 of the tread portion 12 is 10 mm or more. Here, the terminal 40E of the maximum width belt 40 is the outer end of the maximum width belt 40 in the tire width direction WD, and more specifically, the end of the belt cord excluding the covering rubber. The shortest distance B between the terminal 40E and the recess 36 is the shortest distance between the bottom of the recess and the terminal 40E when the recess 36 is a recess having an opening surface on the side surface 24. The shortest distance B is more preferably 12 mm or more. The upper limit is not particularly limited, but may be, for example, 30 mm or less.

By providing the terminal 40E of the maximum width belt 40 at a distance of a predetermined value or more from the recess 36 provided on the side surface 24 of the tread portion 12, the groove bottom crack in the recess 36 caused by the terminal 40E of the maximum width belt 40 is provided. Can be suppressed.

In the pneumatic tire 10 according to the present embodiment, the distance (that is, rubber thickness) from the groove bottom 30A of the center main groove 30 to the outermost belt 44 is preferably 1.2 mm or more, and more preferably 1. It is 5 mm or more. Thereby, the groove bottom crack in the center main groove 30 can be suppressed more effectively. The distance (that is, rubber thickness) from the groove bottom 28A of the shoulder main groove 28 to the second outer belt 42 is also preferably 1.2 mm or more, more preferably 1.5 mm or more, for the same reason.

FIG. 4 is a view showing a meridian cross section of the tread portion 12A of the pneumatic tire according to another embodiment. In this embodiment, the tread rubber 18 includes one center main groove 30 arranged on the equator of the tire and a pair of shoulder main grooves 28, 28 arranged outside the center main groove 30 in the tire width direction WD, respectively. It is provided with three circumferential main grooves made of, and is different from the above-described embodiment in this respect.

In this case, on the surface of the tread portion 12A, a center land portion 32 located between the center main groove 30 and the shoulder main groove 28 and a shoulder land portion 26 located outside the shoulder main groove 28 in the tire width direction are provided. Has been done. The center land portion 32 is a pair of left and right land portions provided on both sides of the tire equatorial plane CL in the tire width direction WD. The shoulder land portion 26 is a pair of left and right land portions provided on the outer sides of the pair of left and right center land portions 32, 32 in the tire width direction WD, respectively.

Regarding the embodiment shown in FIG. 4, the configuration of the belt layer 20 and other configurations and effects including the configurations (1) to (3) above are the same as those of the embodiments shown in FIGS. 1 to 3. The corresponding elements are designated by the same reference numerals, and the description thereof will be omitted.

The size of the pneumatic tire 10 according to the present embodiment is not particularly limited, and for example, the distance in the tire width direction WD from one ground contact end 12E of the tread portion 12 to the other ground contact end 12E, that is, the distance between the ground contact ends. May be 180 to 280 mm, and may be 200 to 260 mm.

Tire size: 11R22.5 14PR heavy load pneumatic radial tires were subjected to Examples and Comparative Examples. The basic configurations of the tires of the examples and the comparative examples are as described in the embodiments shown in FIGS. 1 to 3, and the tires were prototyped by setting the specifications as shown in Table 1 below.

In all the examples and comparative examples, the surface shape of the tread portion 12 (including the positions, widths and depths of the circumferential main grooves 28 and 30 and the recesses 36) was the same. Specifically, the center main groove 30 has a groove width (opening width) of 10.8 mm and a depth of 20.8 mm, and the shoulder main groove 28 has a groove width of 8.0 mm and a depth of 20.8 mm. The distance from the tire equatorial plane CL to the groove bottom midpoint 30A1 of the center main groove 30 in the tire width direction WD was set to 26 mm. The distance between the groove bottom midpoint 30A1 of the center main groove 30 and the groove bottom midpoint 28A1 of the shoulder main groove 28 in the tire width direction WD (distance between groove bottoms A) was set to 50.0 mm. The distance from the tire equatorial plane CL to the ground contact end 12E with the tire width direction WD was set to 122 mm.

For each prototype tire, the groove bottom crack resistance was evaluated for the center main groove 30, the shoulder main groove 28, and the recess 36 on the side surface 24. The evaluation method is as follows.

Groove bottom crack resistance: After assembling the prototype tire to a 22.5 x 7.50 rim, it was filled with an internal pressure of 700 kPa and mounted as a front tire on an actual vehicle (a large truck with a gross vehicle weight of 20 tons). Presence or absence of groove bottom cracks in each of the center main groove 30, shoulder main groove 28 and recess 36 after traveling on a paved road up to a predetermined mileage (about 40,000 km) under a load condition of 80% of the maximum load capacity. Was visually evaluated. In the evaluation, the case where no crack occurred was indicated by "◯", the case where a minute crack having a length of 1 mm or less occurred was indicated by "Δ", and the case where a crack having a length exceeding 1 mm occurred was indicated by "x".

結果は、表１に示す通りである。比較例１では、上記（２）の条件は満足するものの、上記（１）の条件について最外ベルト４４の端末４４Ｅが規定範囲よりもタイヤ幅方向ＷＤ内側にあるため、センター主溝３０で溝底クラックが発生した。

The results are shown in Table 1. In Comparative Example 1, although the condition (2) is satisfied, the terminal 44E of the outermost belt 44 is inside the WD in the tire width direction from the specified range with respect to the condition (1), so that the groove is formed in the center main groove 30. A bottom crack occurred.

In Comparative Example 2, although the condition (2) is satisfied, the terminal 44E of the outermost belt 44 is outside the WD in the tire width direction with respect to the condition (1), so that the shoulder main groove 28 is used as a groove. A bottom crack occurred.

In Comparative Example 3, although the condition (1) is satisfied, the condition (2) is not satisfied, and the terminal 42E of the second outer belt 42 is closer to the shoulder main groove 28 than the specified range. The effect of suppressing cracks at the bottom of the groove 28 was inferior.

On the other hand, in Examples 1 to 3 that satisfy both the above conditions (1) and (2), both the center main groove 30 and the shoulder main groove 28 were excellent in suppressing groove bottom cracks. Further, in Examples 1 and 2, since the condition (3) above is also satisfied, the effect of suppressing the crack at the bottom of the groove in the recess 36 provided on the side surface 24 of the tread portion 12 is also excellent.

Although some embodiments have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention.

10 ... Pneumatic tire, 12 ... Tread part, 18 ... Tread rubber, 20 ... Belt layer, 24 ... Side, 26 ... Shoulder land part, 28 ... Shoulder main groove, 28A ... Shoulder main groove groove bottom, 28A1 ... Shoulder main Groove bottom midpoint, 28B ... Shoulder main groove inner opening end in tire width direction, 28C ... Shoulder main groove outer opening end in tire width direction, 30 ... Center main groove, 30A ... Center main groove 30 groove bottom , 30A1 ... Center main groove groove bottom midpoint, 30B ... Center main groove outer opening end in tire width direction, 36 ... Recess, 40 ... Maximum width belt, 40E ... Maximum width belt terminal, 42 ... Second outer belt , 42E ... 2nd outer belt terminal, 44 ... outermost belt, 44E ... outermost belt terminal, CL ... tire equatorial plane, WD ... tire width direction, RD ... tire radial direction

Claims (4)

In a pneumatic tire provided with a tread rubber provided on a tread portion and a belt layer provided on the inner side of the tread rubber in the tire radial direction.
The tread rubber includes a shoulder main groove extending in the tire circumferential direction and a center main groove located inside the shoulder main groove in the tire width direction and extending in the tire circumferential direction.
The belt layer includes an outermost belt located on the outermost side in the tire radial direction and a second outer belt in contact with the inner side of the outermost belt in the tire radial direction.
The terminal of the outermost belt is located between the groove bottom of the center main groove and the groove bottom of the shoulder main groove in the tire width direction, and the terminal of the second outer belt is closer to the groove bottom of the shoulder main groove. Located on the outside in the tire width direction,
In the tire meridian cross section
The straight line connecting the opening end on the outer side of the center main groove in the tire width direction and the midpoint of the groove bottom of the center main groove is defined as L1, and the opening end on the inner side in the tire width direction of the shoulder main groove and the groove of the shoulder main groove. The straight line connecting the midpoint of the bottom is L2, the straight line connecting the intersection of the straight line L1 and the straight line L2 and the center of the tire is L3, and the midpoint of the groove bottom of the center main groove and the groove of the shoulder main groove. Let A be the distance from the midpoint of the bottom in the tire width direction, and the terminal of the outermost belt is within a range of 15% of the distance A from the center to the inside and outside in the tire width direction with the straight line L3 as the center. Yes and
The straight line connecting the opening end on the outer side of the shoulder main groove in the tire width direction and the groove bottom midpoint of the shoulder main groove is defined as L4, and the straight line passing through the ground contact end of the tread portion and perpendicular to the tire rotation axis is defined as L5. The straight line connecting the intersection of the straight line L4 and the straight line L5 and the center of the tire is defined as L6, and the terminal of the second outer belt is outside the straight line L6 in the tire width direction.
Pneumatic tires that feature that. A recess is provided on the side surface of the tread portion, and the belt layer includes a maximum width belt having the largest dimension in the tire width direction inside the tire radial direction of the second outer belt, and the terminal of the maximum width belt and the recess. The pneumatic tire according to claim 1, wherein the shortest distance is 10 mm or more. The tread rubber consists of four main grooves, a pair of center main grooves arranged on both sides of the tire equator and a pair of shoulder main grooves arranged on the outer sides of the pair of center main grooves in the tire width direction. The pneumatic tire according to claim 1 or 2, further comprising a circumferential main groove. The tread rubber has three circumferential directions including one center main groove arranged on the equator of the tire and a pair of shoulder main grooves arranged outside the center main groove in the tire width direction. The pneumatic tire according to claim 1 or 2, which comprises a main groove.

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