JP7565168B2 - Pneumatic tires - Google Patents

Description

The present invention relates to pneumatic tires.

The tread portion of the pneumatic tire disclosed in Patent Document 1 has a shoulder land portion in which a secondary groove that is shallower and narrower than the main groove and extends in the tire circumferential direction is formed. The secondary groove improves the drainage of the shoulder land portion, contributing to improved vehicle handling stability on wet road surfaces. The secondary groove also contributes to uniform ground contact pressure in the tire width direction in the shoulder land portion.

JP 2017-94765 A

Patent Document 1 only considers the equalization of ground pressure in the shoulder land portion under the limited condition that the secondary groove is provided closer to the center of the tread portion than the center of the shoulder land portion in the tire width direction. Conventional pneumatic tires, including those disclosed in Patent Document 1, have room for further improvement in the equalization of ground pressure distribution in the tire width direction in land portions where secondary grooves are formed.

The objective of the present invention is to improve the uniformity of the ground contact pressure distribution in the tire width direction in the land areas where the secondary grooves are formed.

One aspect of the invention provides a pneumatic tire having a tread portion including land portions defined by main grooves extending in a tire circumferential direction and ground contact edges , and a sub- groove extending in the tire circumferential direction and consisting of a groove that is shallower and narrower than the main groove is formed in the land portion on the tire width direction center side of the tread portion or the ground contact edge side of the tire width direction center of the land portion, the land portion being partitioned in the tire width direction by the sub-groove into a first portion having a first length along a tire profile reference line that passes between both ends of the main groove in the tire width direction and the ground contact edges , and a second portion having a second length along the tire profile reference line that is shorter than the first length, and a second protrusion amount that is the maximum protrusion amount of the second portion from the tire profile reference line is greater than a first protrusion amount that is the maximum protrusion amount of the first portion from the tire profile reference line.

The ground pressure tends to be higher at the end of the first portion in the tire width direction. Similarly, the ground pressure tends to be higher at the end of the second portion in the tire width direction. By making the first portion protrude from the tire profile reference line, the difference in ground pressure between the end of the first portion in the tire width direction and the other portions of the first portion is reduced. Similarly, by making the second portion protrude from the tire profile reference line, the difference in ground pressure between the end of the second portion in the tire width direction and the other portions of the second portion is reduced. Therefore, by making the first and second portions protrude from the tire profile reference line, it is possible to uniformize the ground pressure distribution in the tire width direction in the land portion where the secondary groove is formed.

The second length of the second portion along the tire profile reference line is shorter than the first length of the first portion along the tire profile reference line. In other words, the second portion is relatively narrower than the first portion, and the first portion is relatively wider than the second portion. The narrow second portion has a more pronounced tendency for the ground pressure to be high at the ends in the tire width direction compared to the wide first portion. By setting the second protrusion amount, which is the maximum protrusion amount of the narrow second portion from the tire profile reference line, to be larger than the first protrusion amount, which is the maximum protrusion amount of the wide first portion from the tire profile reference line, the tendency for the ground pressure to be high at the ends in the tire width direction in the second portion can be further alleviated. As a result, the ground pressure distribution in the tire width direction can be made more uniform in the land portion where the secondary groove is formed.

The secondary groove may be located closer to the center of the tread portion in the tire width direction than the center of the land portion in the tire width direction, and the second portion may be located closer to the center of the tread portion in the tire width direction than the first portion.

The secondary groove may be located closer to the ground edge than the center of the land portion in the tire width direction, and the second portion may be located closer to the ground edge than the first portion.

When the first length is 1.5 times or more and less than 2 times the second length, the second protrusion amount may be 1.05 times or more and 1.25 times or less the first protrusion amount.

A first maximum protrusion of the first portion having the first protrusion amount may be located on the sub-groove side of the center of the first portion in the tire width direction, and a second maximum protrusion of the second portion having the second protrusion amount may be located on the sub-groove side of the center of the second portion in the tire width direction.

The first maximum protrusion, which has the greatest protrusion amount in the first portion, is located closer to the secondary groove than the center of the first portion in the tire width direction. Also, the second maximum protrusion, which has the greatest protrusion amount in the second portion, is located closer to the secondary groove than the center of the second portion in the tire width direction. These configurations mitigate deformation that causes the first portion and the second portion to collapse overall toward the secondary groove. As a result, closure of the secondary groove can be suppressed or prevented.

A first distance, which is the distance along the tire profile reference line from the first maximum protrusion to the secondary groove, may be 0.2 to 0.4 times the first length.

If the first maximum protrusion is too close to the secondary groove, local deformation of the portion of the first portion close to the secondary groove can actually make the secondary groove more likely to close. By setting the first distance, which is the distance from the first maximum protrusion to the secondary groove, to the length of the first portion in the tire width direction, i.e., 0.2 to 0.4 times the first length, the effect of local deformation of the portion of the first portion close to the secondary groove can be reduced, and closure of the secondary groove can be more reliably suppressed or prevented.

A second distance, which is the distance along the tire profile reference line from the second maximum protrusion to the secondary groove, may be 0.2 to 0.4 times the second length.

If the second maximum protrusion is too close to the secondary groove, local deformation of the portion of the second portion close to the secondary groove can actually make the secondary groove more likely to close. By setting the second distance, which is the distance from the second maximum protrusion to the secondary groove, to the length of the second portion in the tire width direction, i.e., 0.2 to 0.4 times the first length, the effect of local deformation of the portion of the second portion close to the secondary groove can be reduced, and closure of the secondary groove can be more reliably suppressed or prevented.

When the first length is greater than or equal to 2 times and less than or equal to 2.5 times the second length, the first protrusion amount may be zero.

The present invention can improve the uniformity of the ground contact pressure distribution in the tire width direction in the land areas where the secondary grooves are formed.

FIG. 2 is a partial development view of a tread portion of the pneumatic tire according to the first embodiment. FIG. 2 is a perspective view of a portion of a tread portion in the first embodiment. FIG. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 11 is a perspective view similar to FIG. 2 in a second embodiment. FIG. 7 is a cross-sectional view similar to FIG. 3 in a second embodiment. FIG. 10 is a perspective view similar to FIG. 2 in a third embodiment. FIG. 10 is a cross-sectional view similar to FIG. 3 in a third embodiment. FIG. 10 is a perspective view similar to FIG. 2 in a fourth embodiment. FIG. 10 is a cross-sectional view similar to FIG. 3 in a fourth embodiment. FIG. 13 is a perspective view similar to FIG. 2 in a fifth embodiment. FIG. 13 is a cross-sectional view similar to FIG. 3 in a fifth embodiment. FIG. 13 is a perspective view similar to FIG. 2 in a sixth embodiment. FIG. 13 is a cross-sectional view similar to FIG. 3 in a sixth embodiment.

The embodiment of the present invention will be described with reference to the attached drawings. In the following description, the dimensions of each part of a pneumatic tire are values measured when the pneumatic tire is mounted on a standard rim, inflated to the standard internal pressure, and under no load, not under the standard load.

"Genuine rim" means a rim that is specified for each tire by the standard system that includes the standard on which the tire is based. For example, for JATMA, it is a standard rim, and for TRA and ETRO, it is a "Measuring Rim."

"Normal internal pressure" refers to the air pressure set for each tire by the standards on which the tire is based, including the standards on which the tire is based. For truck and bus tires and light truck tires, it is the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and ""INFLATION PRESSURE"" for ETRTO. For passenger car tires, it is usually 180 kPa, but for tires labeled "EXTRA Load" or "Reinforced", it is 220 kPa.

"Normal load" is the load specified for each tire by each standard in the standard system on which the tire is based. For JATMA, it is "maximum load capacity." For TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." For ETRO, it is "LOAD CAPACITY." If the tire is for passenger cars, it is a load equivalent to 88% of the above load.

First Embodiment
Fig. 1 shows a pneumatic tire 1 (hereinafter, simply referred to as a tire) according to a first embodiment of the present invention. In the figure, the symbol CD indicates the tire circumferential direction, and the symbol WD indicates the tire width direction. Also, in the figure, the symbol TC indicates the center in the tire width direction of a tread portion 2 of the tire 1 (referred to as a tread center). Also, the symbols GEa and GEb indicate the ground contact ends of the tread portion 2.

Three main grooves 3A, 3B, and 3C are formed in the tread portion 2, each extending in the tire circumferential direction. In this embodiment, the main grooves 3A to 3C are all linear grooves with a constant groove width. The main grooves 3A to 3C may have a distribution in groove width in the tire circumferential direction, or may be serpentine or zigzag grooves.

The main grooves 3A and 3B define a center rib 4 that extends continuously in the tire circumferential direction on the tread center TC. The main grooves 3B and 3C define an intermediate rib 5 that extends continuously in the tire circumferential direction at a position adjacent to the center rib 4 on the ground contact end Gb side in the tire width direction. The main groove 3A and the ground contact end Ga define a shoulder rib 6 that extends continuously in the tire circumferential direction at a position adjacent to the center rib 4 on the ground contact end Ga side in the tire width direction. The main groove 3C and the ground contact end Gb define a shoulder rib 7 that extends continuously in the tire circumferential direction at a position adjacent to the intermediate rib 5 on the ground contact end Gb side in the tire width direction.

Referring to both Figures 2 and 3, the shoulder rib 6 is provided with a secondary groove 10 that extends continuously in the tire circumferential direction. The secondary groove 10 is shallower and narrower than the main grooves 3A to 3C. Specifically, the depth Dm of the main grooves 3A to 3C is 7.5 mm to 8.5 mm, and the groove width Wgm of the main grooves 3A to 3C is 7.5 mm to 9.5 mm. In contrast, the depth Ds of the secondary groove 10 is 0.75 to 0.95 times (6.5 mm to 7.0 mm) the depth Dm of the main grooves 3A to 3C, and the groove width Wgs of the secondary groove 10 is 0.1 to 0.2 times (1.0 mm to 1.5 mm) the groove width Wgm of the main grooves 3A to 3C.

The intermediate rib 5 and the shoulder rib 7 are also provided with sub-grooves 11 and 12, respectively, similar to the sub-groove 10.

The shoulder rib 6 will be described in detail below. Unless otherwise specified, the following description relates to the shape, dimensions, etc. of the shoulder rib 6 in a cross section in the tire width direction or a tire meridian cross section. In particular, the tire profile reference line L shown in FIG. 3 is an arc that passes through the tire width direction ends 3a, 3b of the main groove 3A and the ground contact edge GEa in a cross section in the tire width direction or a tire meridian cross section.

2 and 3, the shoulder rib 6 is divided into two parts in the tire width direction by the sub-groove 10. Specifically, the shoulder rib 6 is divided into an inner part 20 defined by the sub-groove 10 and the main groove 3A, and an outer part 21 defined by the sub-groove 10 and the ground edge Ga. The inner part 20 is located on the tread center TC (see FIG. 1) side with respect to the outer part 21 (the outer part 21 is located on the ground edge GEa side with respect to the inner part 20). The inner part 20 has a length Lin along the tire profile reference line L, and the outer part 21 has a length Lout along the tire profile reference line L. The total length of the shoulder rib 6 along the tire profile reference line L, that is, the sum of the groove width Wgs of the sub-groove 10, the length Lin of the inner part 20, and the length Lout of the outer part 21, is, for example, 20 mm or more and 35 mm or less.

The secondary groove 10 is provided closer to the tread center TC (see FIG. 1) than the center Csh of the shoulder rib 6 in the tire width direction. More specifically, the center Cgs of the secondary groove 10 in the tire width direction is located closer to the tread center TC than the center Csh of the shoulder rib 6 in the tire width direction. Therefore, the length Lin of the inner portion 20 is shorter than the length Lout of the outer portion 21. In this embodiment, the length Lout of the outer portion 21 is set to be 1.5 times or more and less than 2 times the length Lin of the inner portion 20.

The inner portion 20 and the outer portion 21 both protrude in a crown shape relative to the tire profile reference line L. The ground contact surface of the inner portion 20 is a partial arc having a radius of curvature Rin, and the ground contact surface of the outer portion 21 is a partial arc having a radius of curvature Rout larger than the radius of curvature Rin. The ground contact surfaces of the inner portion 20 and the outer portion 21 may be convex curves other than partial arcs.

In the inner portion 20, the portion having the maximum protrusion amount PAin relative to the tire profile reference line L, i.e., the maximum protrusion 20a, is located at the center 20b in the tire width direction of the inner portion 20. Therefore, the distance DSin along the tire profile reference line L from the maximum protrusion 20a to the end 20c on the ground edge GEa side of the inner portion 20, i.e., to the secondary groove 10, is 1/2 the length Lin of the inner portion 20.

In the outer portion 21, the portion having the maximum protrusion amount PAout relative to the tire profile reference line L, i.e., the maximum protrusion 21a, is located at the center 21b in the tire width direction of the outer portion 21. Therefore, the distance DSout along the tire profile reference line L from the maximum protrusion 21a to the end 21c on the tread center TC side of the outer portion 21, i.e., to the secondary groove 10, is 1/2 the length Lout of the outer portion 21.

As described above, the length Lin of the inner portion 20 is shorter than the length Lout of the outer portion 21. In other words, the inner portion 20 is relatively narrower than the outer portion 21, and the outer portion 21 is relatively wider than the inner portion 20. The maximum protrusion amount PAin of the narrow inner portion 20 is set to be greater than the maximum protrusion amount PAout of the wide outer portion 21. Specifically, the maximum protrusion amount PAin of the narrow inner portion 20 is set to be 1.05 to 1.25 times the maximum protrusion amount PAout of the wide outer portion 21.

The ground pressure tends to be higher at the ends of the outer portion 21 in the tire width direction, that is, the end 21c on the tread center TC side and the end 21d on the ground edge Ga side. Similarly, the ground pressure tends to be higher at the ends of the inner portion 20 in the tire width direction, that is, the end 20c on the ground edge Ga side and the end 20d on the tread center TC side. By making the outer portion 21 protrude in a crown shape with respect to the tire profile reference line L, the difference in ground pressure between the ends 21c, 21d in the tire width direction of the outer portion 21 and the other parts of the outer portion 21 is reduced. Similarly, by making the inner portion 20 protrude in a crown shape with respect to the tire profile reference line L, the difference in ground pressure between the ends 20c, 20d in the tire width direction of the inner portion 20 and the other parts of the inner portion 20 is reduced. Therefore, by making the outer portion 21 and the inner portion 20 protrude with respect to the tire profile reference line L, the ground pressure distribution in the tire width direction can be made uniform in the shoulder rib 6 in which the secondary groove 10 is formed.

The length Lin of the inner portion 20 along the tire profile reference line L is shorter than the length Lout of the outer portion 20 along the tire profile reference line L. In other words, the inner portion 20 is relatively narrower than the outer portion 21, and the outer portion 21 is relatively wider than the inner portion 20. The narrow inner portion 20 has a more pronounced tendency for the ground pressure to be high at the ends in the tire width direction compared to the wide outer portion 21. By setting the maximum protrusion amount PAin of the narrow inner portion 20 from the tire profile reference line L to be larger than the maximum protrusion amount PAout of the wide outer portion 21 from the tire profile reference line L, the tendency for the ground pressure to be high at the ends 20c, 20d in the tire width direction in the inner portion 20 can be further alleviated. As a result, the ground pressure distribution in the tire width direction can be made more uniform in the shoulder rib 6 in which the secondary groove 10 is formed.

The second to fifth embodiments of the present invention will be described below. In the description of these embodiments, matters that are not specifically mentioned are the same as those in the first embodiment. In addition, in the drawings of these embodiments, elements that are the same as those in the first embodiment are given the same reference numerals.

Second Embodiment
In the second embodiment of the present invention shown in Figures 4 and 5, the length Lout of the outer portion 21 is set to be 2 times or more and 2.5 times or less than the length Lin of the inner portion 20. That is, the length Lout of the outer portion 21 is set to be sufficiently longer than the length Lin of the inner portion 20. In this case, the difference in ground pressure between the other portions of the ends 21c, 21d in the tire width direction of the outer portion 21 is significantly smaller than the case in which the length Lout of the outer portion 21 is 1.5 times or more and less than 2 times the length Lin of the inner portion 20 as in the first embodiment, that is, the length Lout of the outer portion 21 is relatively short. Therefore, even if the outer portion 21 is not protruded from the tire profile reference line L as in this embodiment and the maximum protrusion amount PAout of the outer portion 21 is set to zero, the ground pressure distribution in the tire width direction in the shoulder rib 6 in which the auxiliary groove 10 is formed can be made uniform.

Third Embodiment
6 and 7, the sub groove 10 is provided closer to the ground contact edge GEa than the center Csh of the shoulder rib 6 in the tire width direction. More specifically, the center Cgs of the sub groove 10 in the tire width direction is located closer to the ground contact edge GEa than the center Csh of the shoulder rib 6 in the tire width direction. Therefore, the length Lout of the outer portion 21 is shorter than the length Lin of the inner portion 20. In this embodiment, the length Lin of the inner portion 20 is set to be 1.5 times or more and less than 2 times the length Lout of the outer portion 21.

The maximum protrusion amount PAout of the outer portion 21 is set to be greater than the maximum protrusion amount PAin of the inner portion 20. Specifically, the maximum protrusion amount PAout of the outer portion 21 is set to be 1.05 to 1.25 times the maximum protrusion amount PAin of the inner portion 20.

The length Lout of the outer portion 21 along the tire profile reference line L is shorter than the length Lin of the inner portion 21 along the tire profile reference line L. In other words, the outer portion 21 is relatively narrower than the inner portion 20, and the inner portion 20 is relatively wider than the outer portion 21. The narrow outer portion 21 has a more pronounced tendency for the contact pressure to be high at the ends in the tire width direction compared to the wide inner portion 20. By setting the maximum protrusion amount PAout of the narrow outer portion 21 from the tire profile reference line L to be larger than the maximum protrusion amount PAin of the wide inner portion 20 from the tire profile reference line L, the tendency for the contact pressure to be high at the ends 21c, 21d in the tire width direction in the outer portion 21 can be further alleviated. As a result, the contact pressure distribution in the tire width direction can be made more uniform in the shoulder rib 6 in which the secondary groove 10 is formed.

Fourth Embodiment
The fourth embodiment of the present invention shown in Figures 8 and 9 differs from the third embodiment in that the length Lin of the inner portion 20 is set to be 2 times or more and 2.5 times or less than the length Lout of the outer portion 21. That is, the length Lin of the inner portion 20 is set to be sufficiently longer than the length Lout of the outer portion 21. In this case, the difference in ground pressure between the ends 20c, 20d in the tire width direction of the inner portion 20 and other parts of the inner portion 20 becomes significantly smaller than when the length Lin of the inner portion 20 is 1.5 times or more and less than 2 times the length Lout of the outer portion 21 as in the third embodiment, that is, when the length Lin of the inner portion 20 is relatively short. Therefore, in this embodiment, the inner portion 20 is not protruded from the tire profile reference line L, and the maximum protrusion amount PAin of the inner portion 20 is set to zero, but the ground pressure distribution in the tire width direction in the shoulder rib 6 in which the auxiliary groove 10 is formed can be made uniform.

Fifth Embodiment
10 and 11, in the same manner as in the first embodiment, the sub groove 10 is provided closer to the tread center TC (see FIG. 1) than the center Csh of the shoulder rib 6 in the tire width direction. Therefore, the length Lin of the inner portion 20 is shorter than the length Lout of the outer portion 21. Specifically, the length Lout of the outer portion 21 is set to be 1.5 times or more and less than 2 times the length Lin of the inner portion 20.

The maximum protrusion amount PAin of the narrow inner portion 20 is set to be greater than the maximum protrusion amount PAout of the wide outer portion 21. Specifically, the maximum protrusion amount PAin of the narrow inner portion 20 is set to be 1.05 to 1.25 times the maximum protrusion amount PAout of the wide outer portion 21.

The maximum protrusion 21a of the outer portion 21 is located closer to the secondary groove 10 than the center 21b of the outer portion 21 in the tire width direction. Specifically, the distance DSout, which is the distance along the tire profile reference line L from the maximum protrusion 21a to the secondary groove 10, is set to be 0.2 to 0.4 times the length Lout of the outer portion 21 along the tire profile reference line L.

Similarly, the maximum protrusion 20a of the inner portion 20 is located closer to the secondary groove 10 than the center 20b of the inner portion 20 in the tire width direction. Specifically, the distance DSin, which is the distance along the tire profile reference line L from the maximum protrusion 20a to the secondary groove 10, is set to be 0.2 to 0.4 times the length Lin of the inner portion 20 along the tire profile reference line L.

The radius of curvature Rout1 of the ground contact surface of the outer portion 21 in the region from the maximum protrusion 21a to the secondary groove 10 is smaller than the radius of curvature Rout2 of the ground contact surface of the outer portion in the region from the maximum protrusion 21a to the secondary groove 10. Also, the radius of curvature Rin1 of the ground contact surface of the inner portion 20 in the region from the maximum protrusion 20a to the secondary groove 10 is smaller than the radius of curvature Rin2 of the ground contact surface of the inner portion 20 in the region from the maximum protrusion 20a to the secondary groove 10.

The maximum protrusion 21a of the outer portion 21 is located closer to the secondary groove 10 than the center 21b of the outer portion 21 in the tire width direction. The maximum protrusion 20a of the inner portion 20 is located closer to the secondary groove 10 than the center 21b of the inner portion 20 in the tire width direction. These configurations mitigate deformation of the outer portion 21 and the inner portion 20 that causes the outer portion 21 and the inner portion 20 to collapse toward the secondary groove 10 as a whole. As a result, closing of the secondary groove 10 can be suppressed or prevented.

If the maximum protrusion 21a of the outer portion 21 is too close to the sub-groove 10, the sub-groove 10 is more likely to be closed due to local deformation of the portion of the outer portion 21 close to the sub-groove 10. By setting the distance DSout from the maximum protrusion 21a to the sub-groove 10 to 0.2 to 0.4 times the length Lout of the outer portion 21, the influence of local deformation of the portion of the outer portion 21 close to the sub-groove 10 can be reduced, and the closure of the sub-groove 10 can be more reliably suppressed or prevented. For the same reason, for the inner portion 20, by setting the distance DSin from the maximum protrusion 20a to the sub-groove 10 to 0.2 to 0.4 times the length Lin of the inner portion 20, the influence of local deformation of the portion of the inner portion 20 close to the sub-groove 10 can be reduced, and the closure of the sub-groove 10 can be more reliably suppressed or prevented.

Sixth Embodiment
12 and 13, similarly to the third embodiment, the sub groove 10 is provided closer to the ground edge GEa than the center Csh of the shoulder rib 6 in the tire width direction. Therefore, the length Lout of the outer portion 21 is shorter than the length Lin of the inner portion 20. Specifically, the length Lin of the inner portion 20 is set to be 1.5 times or more and less than 2 times the length Lout of the outer portion 21.

The maximum protrusion amount PAout of the narrow outer portion 21 is set to be greater than the maximum protrusion amount PAin of the wide inner portion 20. Specifically, the maximum protrusion amount PAout of the narrow outer portion 21 is set to be 1.05 to 1.25 times the maximum protrusion amount PAin of the wide inner portion 20.

The maximum protrusion 21a of the outer portion 21 is located closer to the secondary groove 10 than the center 21b of the outer portion 21 in the tire width direction. Specifically, the distance DSout, which is the distance along the tire profile reference line L from the maximum protrusion 21a to the secondary groove 10, is set to be 0.2 to 0.4 times the length Lout of the outer portion 21 along the tire profile reference line L.

Similarly, the maximum protrusion 20a of the inner portion 20 is located closer to the secondary groove 10 than the center 20b of the inner portion 20 in the tire width direction. Specifically, the distance DSin, which is the distance along the tire profile reference line L from the maximum protrusion 20a to the secondary groove 10, is set to be 0.2 to 0.4 times the length Lin of the inner portion 20 along the tire profile reference line L.

The radius of curvature Rout1 of the ground contact surface of the outer portion 21 in the region from the maximum protrusion 21a to the secondary groove 10 is smaller than the radius of curvature Rout2 of the ground contact surface of the outer portion in the region from the maximum protrusion 21a to the secondary groove 10. Also, the radius of curvature Rin1 of the ground contact surface of the inner portion 20 in the region from the maximum protrusion 20a to the secondary groove 10 is smaller than the radius of curvature Rin2 of the ground contact surface of the inner portion 20 in the region from the maximum protrusion 20a to the secondary groove 10.

By positioning the maximum protrusion 21a of the outer portion 21 and the maximum protrusion 20a of the inner portion 20 on the minor groove 10 side, the deformation of the outer portion 21 and the inner portion 20 that causes them to collapse toward the minor groove 10 as a whole is mitigated. As a result, the closure of the minor groove 10 can be suppressed or prevented.

In addition, by setting the distance DSout from the maximum protrusion 21a to the secondary groove 10 to 0.2 to 0.4 times the length Lout of the outer portion 21, and setting the distance DSin from the maximum protrusion 20a to the secondary groove 10 to 0.2 to 0.4 times the length Lin of the inner portion 20, the effect of local deformation of the portions of the outer portion 21 and the inner portion 20 close to the secondary groove 10 can be reduced, and closure of the secondary groove 10 can be more reliably suppressed or prevented.

The embodiment of the present invention has been described with respect to the shoulder rib 6. However, the present invention can also be applied to the intermediate rib 5 in which the secondary groove 11 is formed, and the shoulder rib 7 in which the secondary groove 12 is formed. Furthermore, the present invention is not limited to cases in which the secondary groove is formed in the rib, but can also be applied to cases in which the secondary groove is formed in a block defined by the main groove and the lateral groove in the shoulder region or intermediate region of the tread portion.

Reference Signs List 1 Pneumatic tire 2 Tread portion 3A, 3B, 3C Main groove 3a, 3b End of main groove in tire width direction 4 Center rib 5 Intermediate rib 6, 7 Shoulder rib 10, 11, 12 Sub groove 20 Inner portion 20a Maximum protruding portion of inner portion 20b Center of inner portion in tire width direction 20c End of inner portion on ground contact edge side 20d End of inner portion on tread center side 21 Outer portion 21a Maximum protruding portion of outer portion 21b Center of outer portion in tire width direction 21c End of outer portion on tread center side 21d End of outer portion on ground contact edge side CD Tire circumferential direction WD Tire width direction TC Tread center GEa, GEb Ground contact edge L Tire profile reference line Dm Depth of main groove Wgm Groove width of main groove Csh Center of shoulder rib in tire width direction Ds Depth of the sub groove Wgs Groove width of the sub groove Cgs Center of the sub groove in the tire width direction Lin Length of the inner part PAin Maximum protrusion amount of the inner part DSin Distance from the center of the inner part in the tire width direction to the sub groove Rin, Rin1, Rin2 Radius of curvature Lout Length of the outer part PAout Maximum protrusion amount of the outer part DSout Distance from the center of the outer part in the tire width direction to the sub groove Rout, Rout1, Rout2 Radius of curvature

Claims (8)

The tread portion has a land portion defined by a main groove extending in a circumferential direction of the tire and a ground contact edge ,
In the land portion, a sub-groove is formed on the tire width direction center side of the tread portion or on the ground contact end side of the tire width direction center of the land portion, the sub- groove being shallower and narrower than the main groove and extending in the tire circumferential direction,
The land portion is partitioned in the tire width direction by the sub groove into a first portion having a first length along a tire profile reference line passing through both ends of the main groove in the tire width direction and the ground contact edge , and a second portion having a second length along the tire profile reference line that is shorter than the first length,
a first protrusion amount that is a maximum protrusion amount of the first portion from the tire profile reference line is greater than a second protrusion amount that is a maximum protrusion amount of the second portion from the tire profile reference line. The sub groove is located closer to the center of the tread portion in the tire width direction than the center of the land portion in the tire width direction,
The pneumatic tire according to claim 1 , wherein the second portion is located closer to a center of the tread portion in the tire width direction than the first portion. The sub groove is located closer to the ground contact end than the center of the land portion in the tire width direction,
The pneumatic tire according to claim 1 , wherein the second portion is located closer to the tread end than the first portion. the first length is greater than or equal to 1.5 times and less than 2 times the second length,
The pneumatic tire according to claim 1 , wherein the second protrusion amount is equal to or greater than 1.05 times and equal to or less than 1.25 times the first protrusion amount. a first maximum protruding portion of the first portion having the first protruding amount is located on the sub-groove side relative to a center of the first portion in the tire width direction,
The pneumatic tire according to claim 4 , wherein a second maximum protruding portion of the second portion having the second protruding amount is located on the auxiliary groove side relative to a center of the second portion in the tire width direction. The pneumatic tire according to claim 5, wherein a first distance, which is a distance along the tire profile reference line from the first maximum protrusion to the secondary groove, is 0.2 to 0.4 times the first length. The pneumatic tire according to claim 5 or 6, wherein a second distance, which is a distance along the tire profile reference line from the second maximum protrusion to the secondary groove, is 0.2 to 0.4 times the second length. The first length is greater than or equal to 2 times and less than or equal to 2.5 times the second length,
The pneumatic tire according to claim 1 , wherein the first protrusion amount is zero.

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