JP2015120428A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving straight running performance without excessively increasing a ply steer residual cornering force even in the final stage of abrasion.SOLUTION: Inclined grooves 22 are disposed to communicate adjacent lug grooves 20a and 20a with each other in a tire circumferential direction. In at least 50% of the lug grooves 20a, a bottom-up part 24a is formed in at least a portion of a tire circumferential region between adjacent inclined grooves 22a and 22a. A relation between an angle α formed in the tire circumferential direction of the lug groove 20a and an angle β formed in the tire circumferential direction of a line segment connecting an opening end to one circumferential groove of the adjacent lug grooves 20a and 20a with the other ground contact end is α<β<90°.

Description

  The present invention relates to a pneumatic tire having improved straight running performance without excessively increasing the price tear residual cornering force even at the end of wear.

  A residual cornering force (hereinafter sometimes referred to as “RCF”) is known as an index representing the non-straightness of a pneumatic tire. The RCF is a cornering force at a slip angle at which the self-aligning torque is 0. Generally, a price tear residual cornering force (hereinafter sometimes referred to as “PRCF”), a conicity residual cornering force (CRCF), It is expressed as the sum of

  PRCF as an element of RCF is a residual cornering force resulting from a tread pattern, a belt angle, and the like.

  In recent years, there has been known a pneumatic tire that has improved straight running performance without excessively increasing the PRCF by improving the groove wall angle of the groove formed in the tread (see, for example, Patent Document 1). The technique disclosed in Patent Document 1 is a technique for controlling the PRCF particularly when a tire is new.

Japanese Patent Laid-Open No. 05-178026

  In general, when tread wear progresses, block rigidity increases due to a decrease in groove depth, and therefore PRCF tends to increase. In recent years, in consideration of the environment, it is desired to extend the life of a tire, and there is a demand for the development of a pneumatic tire excellent in straight running performance without excessively increasing the PRCF even at the end of wear.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pneumatic tire with improved straight running performance without excessively increasing the price tear residual cornering force even at the end of wear.

  The pneumatic tire according to the present invention has a circumferential groove, at least one end in the tire width direction of the tread portion, and a plurality of lug grooves extending obliquely from the circumferential groove with respect to the tire width direction, Is a pneumatic tire in which is disposed. An inclined groove that communicates the lug grooves adjacent to each other in the tire circumferential direction is provided. In at least 50% of the lug grooves, a bottom raised portion is formed in at least a part of the tire circumferential direction region between adjacent inclined grooves. An angle α formed by the tire circumferential direction of the lug groove, a tire circumferential direction of a line segment connecting an opening end to the circumferential groove of one of the adjacent lug grooves and the other grounding end; The relationship between the angle β and the angle is α <β <90 °.

  In the pneumatic tire according to the present invention, the configuration of the inclined groove, the formation of the bottom raised portion, the extending direction of the lug groove, and the composite groove composed of the two adjacent lug grooves and the inclined grooves sandwiched between them. The extension direction is improved. As a result, according to the pneumatic tire of the present invention, straight running performance can be improved without excessively increasing the price tear residual cornering force even at the end of wear.

FIG. 1 is a plan view showing a tread portion when a pneumatic tire according to an embodiment of the present invention is new. FIG. 2 is a plan view showing a tread portion in the middle stage of wear of the pneumatic tire according to the embodiment of the present invention. FIG. 3 is a graph showing the relationship between the price tear residual cornering force and the wear rate for the pneumatic tire according to the embodiment of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a pneumatic tire according to the present invention (basic forms and additional forms 1 to 6 shown below) will be described in detail with reference to the drawings. Note that these embodiments do not limit the present invention. In addition, the constituent elements of the above embodiment include those that can be easily replaced by those skilled in the art, or those that are substantially the same. Furthermore, various forms included in the above-described embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

[Basic form]
Below, the basic form is demonstrated about the pneumatic tire which concerns on this invention. In the following description, the tire radial direction means a direction orthogonal to the rotational axis of the pneumatic tire, the tire radial inner side is the side toward the rotational axis in the tire radial direction, and the tire radial outer side is in the tire radial direction. The side away from the rotation axis. The tire circumferential direction refers to a circumferential direction with the rotation axis as a central axis. Further, the tire width direction means a direction parallel to the rotation axis, the inner side in the tire width direction is the side toward the tire equator plane (tire equator line) in the tire width direction, and the outer side in the tire width direction is in the tire width direction. The side away from the tire equator. The tire equator plane is a plane that is orthogonal to the rotational axis of the pneumatic tire and passes through the center of the tire width of the pneumatic tire.

  FIG. 1 is a plan view showing a tread portion of a pneumatic tire according to an embodiment of the present invention when it is new (a view of a grounded tire viewed from directly above). In addition, the codes | symbols E and E 'shown in FIG. 1 have each shown the earthing | grounding end.

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

  As shown in FIG. 1, the tread surface 12 is provided with four circumferential grooves 14a, 14b, 14c, 14d extending in the tire circumferential direction at predetermined intervals in the tire width direction. With the surface CL as a boundary, the circumferential grooves 14a and 14c are provided on one side in the tire width direction, and the circumferential grooves 14b and 14d are provided on the other side in the tire width direction.

  Further, as shown in FIG. 1, the tread surface 12 extends inward in the tire width direction from one of the two circumferential grooves 14 a and 14 b close to the tire equatorial plane CL so as to be inclined with respect to the tire circumferential direction. The two first inclined grooves 16a and 16b that terminate in the land portion are provided at a constant pitch in the tire circumferential direction.

  Further, as shown in FIG. 1, the tread surface 12 is inclined with respect to the tire circumferential direction from one of the two circumferential grooves 14c and 14d separated from the tire equatorial plane CL and extends inward in the tire width direction. There are two second inclined grooves 18a and 18b that terminate in the land and are provided at a constant pitch in the tire circumferential direction.

  In the present embodiment, the circumferential grooves 14a to 14d are not limited to grooves extending linearly in the tire circumferential direction as shown in FIG. 1, but have an amplitude in the tire width direction, and are wavy or zigzag-shaped. And a groove extending in the tire circumferential direction. In the present embodiment, instead of the circumferential grooves 14a to 14d, an inclined groove group composed of a plurality of grooves that are inclined with respect to the tire circumferential direction and both ends terminate in the land portion may be provided. it can.

  Further, in the present embodiment, the first inclined grooves 16a, 16b and the second inclined grooves 18a, 18b are not limited to the grooves inclined with respect to the tire width direction as shown in FIG. Also includes an extending groove. Further, instead of these inclined grooves 16a, 16b, 18a, and 18b, grooves that allow adjacent circumferential grooves (for example, circumferential grooves 14a and 14b) to communicate with each other can be provided.

  Next, in the present embodiment, as shown in FIG. 1, each of the two circumferential grooves 14 c and 14 d separated from the tire equatorial plane CL is inclined with respect to the tire circumferential direction and outward in the tire width direction. A plurality of lug grooves 20a, 20b extending beyond the ground contact ends E, E ′ are provided at a constant pitch in the tire circumferential direction.

  Under the premise as described above, in the present embodiment, at least one of the regions on the outer side in the tire width direction from the two circumferential grooves 14c and 14d apart from the tire equatorial plane CL has the following configuration. Have. In the following, description will be made by taking as an example the outer region in the tire width direction of the circumferential groove 14c (the region on the left side of the paper surface shown in FIG. 1, hereinafter may be referred to as the “left outer region”).

  That is, in the present embodiment, as shown in FIG. 1, an inclined groove 22 a that connects the lug grooves 20 a and 20 a adjacent to each other in the tire circumferential direction is disposed in the left outer region. In the example shown in the figure, the inclined groove 22a extends substantially in the tire width direction.

  In the present embodiment, at least 50% (100% in the example shown in FIG. 1) of the left outer region of the lug groove 20a, at least a part of the tire circumferential region between the adjacent inclined grooves 22a, 22a ( In the example shown in the figure, a bottom raised portion 24a is formed in all).

  Further, in the present embodiment, as shown in FIG. 1, the angle α formed between the lug groove 20a and the tire circumferential direction, and the open end to one circumferential groove 14c of the adjacent lug grooves 20a, 20a. The angle β formed by a line segment connecting the other ground contact end and the tire circumferential direction is α <β <90 °.

  Here, the opening end to one circumferential groove 14c of the adjacent lug grooves 20a, 20a is an opening portion of one lug groove 20a to the circumferential groove 14c (shown by a line segment in FIG. 1). The center position in the tire circumferential direction. Similarly, the other ground contact end of the adjacent lug grooves 20a and 20a refers to the center position in the tire circumferential direction of the overlapping portion (shown by a line segment in FIG. 1) with the ground contact end of the other lug groove 20a. . Further, the angle α and the angle β formed are the angles on the same side in the tire circumferential direction (in the example shown in FIG. 1, the lower side of the page).

  Further, in the example shown in FIG. 1, the outer region in the tire width direction of the circumferential groove 14 d (the region on the right side of the paper surface shown in FIG. 1, hereinafter sometimes referred to as “right outer region”) is also referred to as the left outer region. It has the same configuration. In FIG. 1, members indicated by reference numerals 20b, 22b, and 24b in the right outer area correspond to members indicated by reference numerals 20a, 22a, and 24a in the left outer area, respectively.

(Action etc.)
Generally, the price tear residual cornering force (PRCF) when the tire is new (wear rate 0%) is inversely proportional to the angle formed by the lug groove with respect to the tire circumferential direction, and the value of PRCF increases as the angle formed decreases. In addition, PRCF tends to gradually increase as the tire wears due to an increase in shear rigidity of the tread pattern, regardless of the angle formed above. Here, the wear rate is an index indicating the degree of wear of the tread rubber in the tire radial direction when the new tire is 0% and the wear indicator exposed to the tire surface is 100%.

  Since PRCF has such properties, it is necessary to keep the PRCF value from the ideal value as much as possible from the time when the tire is new to the end of wear (wear rate: 100%). It is important to demonstrate at a high level. Based on such knowledge, the inventor hypothesized the temporal change of PRCF shown below, and realized this temporal change by improving the tread pattern.

  FIG. 3 is a graph showing the relationship between PRCF and wear rate for the pneumatic tire according to the embodiment of the present invention. First, as shown in the figure, the inventor hypothesized a value X1 close to the ideal PRCF value (ideal value X0) when the tire is new (point P1). Next, the inventor intentionally increases the PRCF to the value X3 (point P3) when the PRCF gradually increases as the tire wears and reaches a value X2 (point P2) considerably away from the ideal value X0. It was hypothesized that the PRCF was sufficiently set to the value X4 (point P4) sufficiently close to the ideal value X0 even at 100% wear when the PRCF increased with further wear of the tire.

  Specifically, the inventor arranges the imaginary behavior of the PRCF in the left outer region shown in FIG. 1 by providing the inclined grooves 22a that connect the lug grooves 20a, 20a, and at least 50% of the left outer region. In the lug groove 20a, a bottom-up portion is formed in at least a part of the tire circumferential direction region between the adjacent inclined grooves 22a, 22a, and the relationship between the angle α and the angle β formed is α <β <90 °. That was realized.

  That is, when the tire is new, the angle α formed by the lug groove 20a shown in FIG. 1 is set to a predetermined range, and the PRCF is set to a value X1 close to the ideal value X0 (corresponding to the point P1 in FIG. 3). Here, the angle α formed can be 20 ° or more and 70 ° or less.

  Next, wear progresses, and the raised portion 24a shown in FIG. 1 gradually approaches the tire surface (corresponding to point P2 in FIG. 3). When the raised portion 24a is completely exposed on the tire surface 12, as shown in FIG. 2 (a plan view showing the tread portion in the middle stage of wear of the pneumatic tire according to the embodiment of the present invention), the lugs excluding the raised portion are removed. A composite groove composed of two portions of the groove 20a and an inclined groove 22a sandwiched between them newly appears, and the tread pattern in the left outer region is different from that when the tire is new (corresponding to point P3 in FIG. 3). .

  As shown in FIGS. 1 and 2, the extending direction of the newly emerged composite groove is as follows. One of the adjacent lug grooves 20 a, 20 a has an opening end to one circumferential groove 14 c and the other grounding end. Can be approximated as the direction of the line segment connecting In the present embodiment, the angle β formed by the line segment and the tire circumferential direction is made larger than the angle α formed by the above.

  Thus, by setting the angle β to be larger than the angle α, the PRCF value can be intentionally lowered from the value X2 (point P2) to the value X3 (point P3). Then, with further wear of the tire thereafter, the PRCF gradually increases, and reaches a value X4 when it reaches 100% wear (corresponding to the point P4 in FIG. 3).

  Note that the angle α and the angle β formed above are regions surrounded by the line segment L0 indicating the ideal value of PRCF shown in FIG. 3 and the line segments L1, L2, and L3 indicating temporal changes in PRCF. It is preferable to set (Aspect 1) so that the area of (the hatched portion shown in the figure) is as small as possible. Further, the formed angle α and the formed angle β are set so that the difference between the minimum value and the maximum value of PRCF and the ideal value X0 between 0% wear and 100% wear shown in FIG. 3 is as small as possible. (Mode 2) is preferable. According to the aspect 1, the PRCF can be brought close to the ideal value as a whole from the time when the tire is new to the end of wear. Further, according to the aspect, it is possible to avoid a local occurrence of the time when the PRCF is excessively separated from the ideal value from when the tire is new to the end of wear.

  As described above, the pneumatic tire according to the present embodiment is sandwiched between the inclined groove arrangement mode, the bottom-up portion forming mode, the lug groove extending direction, and the two adjacent lug grooves. By improving the extending direction of the composite groove including the inclined groove, the PRCF can be set to a substantially ideal value from the time when the tire is new to the end of wear. As a result, according to the pneumatic tire of the present invention, the price tear residual cornering force is not excessively increased even at the end of wear, and the straight running performance can be improved.

  In addition, although not shown in figure, the pneumatic tire which concerns on this Embodiment shown above has the same meridional cross-sectional shape as the conventional pneumatic tire. Here, the meridional cross-sectional shape of the pneumatic tire refers to a cross-sectional shape of the pneumatic tire that appears on a plane perpendicular to the tire equatorial plane. The pneumatic tire according to the present embodiment has a bead portion, a sidewall portion, a shoulder portion, and a tread portion from the inner side in the tire radial direction toward the outer side in a tire meridian cross-sectional view. The pneumatic tire includes, for example, a carcass layer extending from a tread portion to bead portions on both sides and wound around a pair of bead cores in a tire meridional section, and a tire radial outside of the carcass layer. The belt layer and the belt reinforcing layer are sequentially formed.

  In addition, the pneumatic tire of the present embodiment includes normal manufacturing processes, that is, a tire material mixing process, a tire material processing process, a green tire molding process, a vulcanization process, and an inspection process after vulcanization. It is obtained through the process. When manufacturing the pneumatic tire of the present embodiment, in particular, a concave portion and a convex portion corresponding to the convex portion formed in the tread portion shown in FIG. 1 are formed on the inner wall of the vulcanizing mold. Then, vulcanization is performed using this mold.

[Additional form]
Next, additional modes 1 to 6 that can be optionally implemented with respect to the basic mode of the pneumatic tire according to the present invention will be described.

(Additional form 1)
In the basic configuration, it is preferable that the raised portion 24a (24b) shown in FIG. 1 is formed in at least one lug groove 20a (20b) in the tire width direction (additional configuration 1). .

  By forming the raised portion 24a (24b) in all the lug grooves 20a (20b) on at least one side in the tire width direction, the virtual behavior of the PRCF shown in FIG. Can be realized everywhere in the direction. As a result, according to the present embodiment, the effect of preventing the PRCF from being excessively separated from the ideal value from when the tire is new to the end of wear, which has been described in detail in the basic embodiment, can be realized at a higher level.

(Additional form 2)
In the basic form and the form in which the additional form 1 is added to the basic form, as shown in FIG. 1, the bottom raised portions 24a and 24b are provided at both ends of the tread portion 10 in the tire width direction (the left outer region and the right side in FIG. It is preferable that it is formed in both the outer region (additional form 2).

  By forming the bottom raised portions 24a and 24b at both ends in the tire width direction of the tread portion 10, the behavior of the PRCF shown in FIG. 3 can be realized at both ends in the tire width direction. As a result, according to the present embodiment, the effect of preventing the PRCF from being excessively separated from the ideal value from when the tire is new to the end of wear, which has been described in detail in the basic embodiment, can be realized at a higher level.

(Additional form 3)
In the basic form and the form obtained by adding at least one of the additional forms 1 and 2 to the basic form, the relationship between the angle α and the angle β is β−α ≧ 20 ° (additional form 3) Is preferred.

  By setting β−α ≧ 20 ° as the relationship between the formed angle α and the formed angle β, it is possible to sufficiently secure the amount of decrease in the PRCF (X2−X3) from the point P2 to the point P3 shown in FIG. it can. As a result, even if the PRCF value X2 at the point P2 shown in FIG. 3 is considerably different from the ideal value X0, the PRCF value X3 at the point P3 is taken into account for the behavior of the PRCF up to the subsequent 100% wear. Thus, it can be suitably set. As a result, according to the present embodiment, the effect of preventing the PRCF from being excessively separated from the ideal value from when the tire is new to the end of wear, which has been described in detail in the basic embodiment, can be realized at a higher level.

(Additional form 4)
In the basic form and the form obtained by adding at least one of the additional forms 1 to 3 to the basic form, the tire between the adjacent inclined grooves 22a, 22a (22b, 22b) of the lug groove 20a (20b) shown in FIG. It is preferable that the raised portion 24a (24b) is formed in at least 50% of the circumferential region (100% in the example shown in the figure) (additional form 4).

  By forming the bottom raised portion 24a (24b) in at least 50% of the region in the tire circumferential direction between the adjacent inclined grooves 22a, 22a (22b, 22b) of the lug groove 20a (20b), the bottom raised portion 24a ( 24b) appears when the tire surface 12 is completely exposed, and the inclined groove occupies a composite groove composed of two portions of the lug groove 20a (20b) excluding the raised bottom portion and the inclined groove 22a (22b) sandwiched between them. The ratio of 22a (22b) can be increased. Thus, the tread pattern of the left outer region (right outer region) when the bottom raised portion 22a (22b) is exposed is not a pattern composed of the lug groove 20a (20b) and the inclined groove 22a (22b), but the composite It can be reliably regarded as a pattern composed only of grooves. That is, the angle β formed by the angle α formed by the groove extending direction and the tire circumferential direction in the tread pattern of the left outer region (right outer region) when the bottom raised portion 22a (22b) is exposed enters. Rather than grasping as a mixture, it is possible to reliably grasp only the angle β formed. For this reason, the extending direction of the groove in the left outer region (right outer region) before and after the bottom raised portion 24a (24b) is completely exposed to the tire surface 12 can be clearly changed. As a result, it is possible to reliably reduce the PRCF (value X3 in FIG. 3) when the bottom raised portion 24a (24b) is completely exposed to the tire surface 12 with respect to the PRCF (value X1 in FIG. 3) when the tire is new. It is possible to achieve the effect of preventing the PRCF from being excessively separated from the ideal value from the time when the tire is new to the end of wear, as described in detail in the basic embodiment.

(Additional form 5)
In the basic form and the form in which at least one of the additional forms 1 to 4 is added to the basic form, as shown in FIG. 1, the adjacent inclined grooves 22a and 22a (22b and 22b) of the lug groove 20a (20b) are provided. It is preferable that the bottom raised portion 24a (24b) is formed at least in the innermost region in the tire width direction among the regions in the tire circumferential direction (additional form 5).

  By forming the raised portion 24a (24b) at least in the innermost region in the tire width direction among the tire circumferential direction regions between the adjacent inclined grooves 22a, 22a (22b, 22b) of the lug groove 20a (20b), The deformation of the block B adjacent to the circumferential groove 14c (14d) shown in FIG. 1 can be efficiently suppressed from when the tire is new to the beginning of wear (until the raised bottom portion is exposed). As a result, according to the present embodiment, the PRCF value (absolute value) can be reduced, and the effect of preventing the PRCF from being excessively separated from the ideal value from when the tire is new, particularly at the initial stage of wear, is realized at a higher level. can do.

(Additional form 6)
In the basic form and the form obtained by adding at least one of the additional forms 1 to 5 to the basic form, the groove depth of the bottom raised portion 24a (24b) shown in FIG. 1 is not less than 30% and not more than 70% of the effective depth. Some (additional form 6) is preferred. Here, the groove depth of the bottom raised portion 24a (24b) is the tire diameter from the tire profile line to the bottom raised portion 24a (24b) when the lug groove 20a (20b) is not disposed when the tire is new. The direction dimension. The effective groove depth refers to the tire radial direction dimension from the tire profile line to the wear indicator when the lug groove 20a (20b) is not disposed when the tire is new.

  By setting the groove depth of the bottom raised portion 24a (24b) to 30% or more and 70% or less of the effective depth, the bottom raised portion 24a (24b) is completely exposed to the tire surface 12, and a new tread pattern appears. The timing, that is, the transition timing from the point P2 to the point P3 shown in FIG. 3, can be set between 30% wear and 70% wear. As a result, the area of the region (hatched portion shown in the figure) surrounded by the line segment L0 indicating the ideal PRCF value X0 shown in FIG. 3 and the line segments L1, L2, and L3 indicating changes over time of the PRCF. 3 can be further reduced, or the difference between the minimum value and / or maximum value of PRCF and the ideal value X0 between 0% wear and 100% wear shown in FIG. 3 can be further reduced. it can. As a result, according to the present embodiment, the effect of preventing the PRCF from being excessively separated from the ideal value from when the tire is new to the end of wear, which has been described in detail in the basic embodiment, can be achieved at a higher level.

  The tire size is 195 / 65R15, four circumferential grooves, and a plurality of lug grooves extending obliquely with respect to the tire width direction from both circumferential grooves on the outermost side in the tire width direction to the outer side in the tire width direction; Example 1 in which an inclined groove communicating with the lug grooves adjacent to each other in the tire circumferential direction is provided, and an angle β formed with an angle α shown in FIG. 1 satisfies a relationship of α <β <90 °. To 7 pneumatic tires were produced. In addition, various conditions of the details of each tread pattern of the pneumatic tires of Examples 1 to 7 are as shown in Table 1 below.

  On the other hand, a pneumatic tire of a conventional example having the same tread pattern as the tread pattern of Example 1 was manufactured except that the tire size was 195 / 65R15 and the bottom raised portion was not formed in the lug groove.

  Each of the test tires of Examples 1 to 7 and the conventional example manufactured as described above was assembled to a 15 × 6J rim at an air pressure of 200 kPa, and a load of 80% of the normal load was applied on a cornering tester to a speed of 10 km / A cornering test was conducted at h. Here, the normal load means “maximum load capacity” defined by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO. Say.

  Specifically, for each test tire, the price tear residual cornering force (PRCF) was measured at 0% wear (new time), 50% wear (mid wear) and 100% wear (end wear). . These measurement results are also shown in Table 1. In Table 1, the value of PRCF is good at 40N or more.

  According to Table 1, examples belonging to the technical scope of the present invention (with improvements in the arrangement of the inclined grooves, the formation of the raised bottom, the extending direction of the lug grooves, and the extending direction of the composite grooves) As for the pneumatic tires of Examples 1 to 7, none of them belong to the technical scope of the present invention. It can be seen that the tear residual cornering force (PRCF) exhibits a good value. For this reason. With respect to the pneumatic tire of each example, excellent straight running performance is realized without excessively increasing the value of PRCF from the time when the tire is new to the end of wear.

  The present invention includes the following aspects.

(1) Air in which a circumferential groove and a plurality of lug grooves extending obliquely with respect to the tire width direction from the circumferential groove are disposed at least at one end in the tire width direction of the tread portion. In the entering tire, an inclined groove that connects the lug grooves adjacent to each other in the tire circumferential direction is disposed,
In at least 50% of the lug grooves, a bottom raised portion is formed in at least a part of a tire circumferential direction region between adjacent inclined grooves, and an angle α formed by the tire circumferential direction of the lug grooves and the adjacent lug grooves The relationship between the angle β formed by the tire circumferential direction of the line segment connecting the opening end to one of the circumferential grooves and the other grounding end is α <β <90 °. Pneumatic tire.

(2) The pneumatic tire according to (1), wherein the bottom raised portion is formed in all lug grooves on at least one side in the tire width direction.

(3) The pneumatic tire according to (1) or (2), wherein the bottom raised portion is formed at both ends of the tread portion in the tire width direction.

(4) The pneumatic tire according to any one of (1) to (3), wherein a relationship between the formed angle α and the formed angle β is β−α ≧ 20 °.

(5) The raised portion is formed in at least 50% of a region in the tire circumferential direction between adjacent inclined grooves of the lug groove, according to any one of (1) to (4) above. Pneumatic tire.

(6) Any one of the above (1) to (5), wherein a bottom-up portion is formed at least in the innermost region in the tire width direction in the tire circumferential region between adjacent inclined grooves of the lug groove. Pneumatic tire described in one.

(7) The pneumatic tire according to any one of (1) to (6), wherein a groove depth of the raised bottom portion is 30% or more and 70% or less of an effective depth.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 10 Tread part 12 Tread surface 14a, 14b, 14c, 14d Circumferential groove | channel 16a, 16b 1st inclination groove 18a, 18b 2nd inclination groove 20a, 20b Lug groove 22a, 22b Inclination groove 24a, 24b Bottom raising part CL Tire Equatorial Plane E, E 'Grounding End Lines L0, Lines Showing Ideal Values of PRCF L1, L2, L3 Constituent Lines Showing Graphs of PRCF over Time P1, P2, P3, P4 Graphs showing the time course of PRCF Each point above X0 PRCF ideal value X1, X2, X3, X4 PRCF value

Claims (7)

In a pneumatic tire in which a circumferential groove and a plurality of lug grooves extending obliquely with respect to the tire width direction from the circumferential groove are disposed at least at one end portion in the tire width direction of the tread portion. ,
Inclined grooves communicating the lug grooves adjacent in the tire circumferential direction are disposed,
In at least 50% of the lug grooves, a bottom-up portion is formed in at least a part of a tire circumferential direction region between adjacent inclined grooves,
An angle α formed by the tire circumferential direction of the lug groove, a tire circumferential direction of a line segment connecting the opening end to the circumferential groove of one of the adjacent lug grooves and the other ground contact end. The angle β with which α <β <90 °,
A pneumatic tire characterized by that.   The pneumatic tire according to claim 1, wherein the bottom raised portion is formed in all lug grooves on at least one side in the tire width direction.   The pneumatic tire according to claim 1 or 2, wherein the bottom raised portion is formed at both ends of the tread portion in the tire width direction.   The pneumatic tire according to any one of claims 1 to 3, wherein a relationship between the formed angle α and the formed angle β is β-α ≧ 20 °.   The pneumatic tire according to any one of claims 1 to 4, wherein a bottom raised portion is formed in a region of at least 50% of a region in the tire circumferential direction between adjacent inclined grooves of the lug groove.   The pneumatic according to any one of claims 1 to 5, wherein a bottom-up portion is formed at least in an innermost region in the tire width direction among tire circumferential direction regions between adjacent inclined grooves of the lug grooves. tire.   The pneumatic tire according to any one of claims 1 to 6, wherein a groove depth of the raised bottom portion is 30% or more and 70% or less of an effective depth.

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