JP4598553B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic system provided with two circumferential grooves extending on the tread surface in the tire circumferential direction and located on both sides of the tire equator line, and a central land portion defined by the circumferential grooves. Regarding tires.

  In general, in a pneumatic tire aimed at achieving both drainage performance and steering stability, two straight main grooves (circumferential grooves) that extend in the tire circumferential direction and are located on both sides of the tire equator line A directional tread pattern in which a plurality of inclined grooves that are located closer to the tread end portion than the straight main groove and extend in the tread width direction are formed is often employed.

  In such a directional tread pattern, the hydroplaning performance and drainage performance are secured by the two straight main grooves. Furthermore, the sloping groove located on the tread end side of the straight main groove allows the water on the road surface to escape outward in the tread width direction to ensure drainage performance.

In addition, a straight sub-groove extending in the tire circumferential direction is further formed in the central land section defined by the straight main groove, so that stable driving performance is ensured by continuous smooth contact and pattern noise is reduced. Noise performance is ensured (see, for example, Patent Document 1).
JP-A-10-278511

  Incidentally, in recent years, with the increase in speed and performance of vehicles, further improvement in drainage performance and steering stability performance is desired even in the pneumatic tire having the above-described directional tread pattern. In particular, it is important to improve the drainage performance of the central land portion in order to improve the hydroplaning resistance during high-speed traveling on a wet road surface.

  In general, as a method for improving the drainage performance of a pneumatic tire, a method of increasing the negative ratio and increasing the efficiency of water inflow into the groove is adopted, but in the directional tread pattern described above, the straight main groove If you try to improve the drainage performance of the central land part by widening the groove width of the straight sub-groove or the straight sub-groove, the rigidity of the central land part will be reduced contrary to that, the grip power when cornering etc. is insufficient, Steering stability performance sometimes deteriorated.

  The present invention has been made in view of such problems, and is a pneumatic tire having a directional tread pattern that greatly improves drainage performance, particularly drainage performance in the central land, and also improves steering stability performance. The purpose is to provide.

  In order to achieve the above-described object, the present invention has the following features. First, the present invention is characterized by two circumferential grooves (circumferential grooves 2) extending in the tire circumferential direction on the tread surface (tread surface 10) and positioned on both sides of the tire equator line (tire equator line CL). , 4) and a central land portion (central land portion 3) partitioned by a circumferential groove, wherein the central land portion includes a central region ( A plurality of transverse grooves (transverse grooves 20) extending to the central region CT) are formed in the tire circumferential direction without alternately joining the tire equator line, and the transverse grooves are stepped from the circumferential groove to the central region. A first inclined groove (long-side inclined groove 21) extending obliquely toward the side (that is, the rotation direction) and an end portion (end portion 21E) located in a central region of the first inclined groove toward the stepping side, the tire A straight groove (straight groove 22) extending substantially parallel to the equator line, The gist of the invention is that the second inclined groove (short-side inclined groove 23) extends from the end portion (end portion 22E) located on the stepping side of the groove so as to incline toward the kick-out side toward the circumferential groove. .

  Here, “substantially parallel to the tire equator line” means that the inclination angle of the straight groove with respect to the tire equator line is 20 degrees or less.

  According to the pneumatic tire according to the features of the present invention, the two circumferential grooves ensure drainage performance equivalent to that of the conventional pneumatic tire, and the transverse grooves extend from the circumferential groove to the central region of the central land portion. Drainage performance is improved.

  Specifically, the crossing groove is composed of the first inclined groove, the straight groove, and the second inclined groove, so that the water on the road surface can be discharged outward in the tread width direction, and the central land portion, that is, the drainage of the central region. Performance is improved.

  In addition, since the plurality of transverse grooves are formed in the tire circumferential direction without alternately joining the tire equator line, the central land portion is not divided in the tire circumferential direction, and the tire circumferential direction is not divided. A continuous land portion (for example, land portions 6 and 7) can be secured. Therefore, when traveling, the continuous land portion is always in contact with the road surface, and the steering stability performance is improved.

  Accordingly, it is possible to provide a pneumatic tire having a directional tread pattern in which drainage performance, particularly drainage performance in the central land portion is greatly improved and steering stability performance is also improved.

  Furthermore, in the pneumatic tire according to the feature of the present invention, the inner groove wall (inner groove wall 22a) located on the tire equator line side among the groove walls facing each other of the linear grooves is 25 degrees or more with respect to the tire normal line. It may be inclined at 45 degrees or less.

  According to such a pneumatic tire, since the inner groove wall is inclined at 25 degrees or more and 45 degrees or less with respect to the tire normal, the inflow efficiency of water into the transverse groove is enhanced and the drainage of the central land portion is performed. The performance is further improved, and the rigidity of the land portion continuous in the tire circumferential direction secured in the central land portion is increased, and the steering stability performance is further improved.

  Further, in the pneumatic tire according to the feature of the present invention, the first inclination angle (inclination angle θ1) of the first inclined groove with respect to the tire equator line is the second inclination angle (inclination angle θ2) of the second inclined groove with respect to the tire equator line. ) May be smaller.

  According to such a pneumatic tire, when the first inclination angle is smaller than the second inclination angle, flowing water in the first inclined groove is promoted, and the drainage performance in the central region is further improved.

  Further, in the pneumatic tire according to the feature of the present invention, on the tread surface, the groove width (groove width W2) of the linear groove is the groove width of the first inclined groove (groove width W1) and the groove width of the second inclined groove ( It may be wider than the groove width W3).

  According to such a pneumatic tire, since the groove width of the straight groove is wider than the groove width of the first inclined groove and the groove width of the second inclined groove, the groove width of the straight groove is sufficiently secured and the transverse groove is formed. Water inflow efficiency is increased, and drainage performance in the central area is further improved.

  Furthermore, the pneumatic tire according to the feature of the present invention includes an inner groove wall length (inner groove) which is a length in the tire circumferential direction of an inner groove wall located on the tire equator line side among groove walls facing each other of the linear grooves. The wall length SW) may be ½ or less of the adjacent distance (adjacent distance LW) that is the distance between the inner groove wall and the inner groove wall adjacent to the inner groove wall in the tire circumferential direction.

  According to such a pneumatic tire, when the inner groove wall length is 1/2 or less of the adjacent distance, the rigidity of the land portion continuous in the tire circumferential direction secured in the central land portion is further enhanced, Steering stability is further improved.

  Further, in the pneumatic tire according to the feature of the present invention, the second outer end portion (second outer end portion 25a) which is an end portion of the second inclined groove located on the circumferential groove side is a bottom for raising the groove bottom. You may have an upper groove bottom (bottom upper groove bottom 26).

  According to such a pneumatic tire, since the second outer end portion has the bottom groove top, the rigidity of the land portion sandwiched between the first inclined groove and the second inclined groove adjacent to each other in the tire circumferential direction is increased. It can be ensured, and uneven wear (such as heel and toe wear) that tends to occur in the land portion can be suppressed.

  Further, in the pneumatic tire according to the feature of the present invention, the groove width (groove width W3a) of the second outer end portion having the bottom groove top is the end portion of the second inclined groove located on the tire equator line side. 2 is wider than the groove width (groove width W3b) of the inner end portion (second inner end portion 25b), and the shape of the bottom groove top is on the groove edge (groove edge 27) with one side positioned on the stepping side of the second inclined groove. ) And a substantially triangular shape with one apex (vertex 28) directed toward the kicking side, and may descend from the stepping side toward the kicking side.

  According to such a pneumatic tire, the second outer end portion has the substantially triangular bottom upper groove bottom that descends from the stepping side toward the kicking side, whereby the second inclined groove and the circumferential groove The turbulence of the drainage at the confluence is suppressed, and the drainage performance of the central land is further improved.

  Further, the pneumatic tire according to the feature of the present invention is provided with a second outer end portion (end portion of the second inclined groove (short-side inclined groove 123) positioned on the circumferential groove side (circumferential grooves 102, 104) ( The outer end 125a) may extend to the front of the circumferential groove without opening in the circumferential groove.

  According to such a pneumatic tire, the rigidity of the land portion sandwiched between the first inclined groove and the second inclined groove adjacent to each other in the tire circumferential direction because the second outer end portion does not open in the circumferential main groove. As a result, the steering stability performance is greatly improved, and the impact of the block edge is suppressed to improve the noise performance.

  Furthermore, in the pneumatic tire according to the feature of the present invention, on the tread surface, one linear groove and the other linear groove are formed on the tire equator line without overlapping on the tire equator line. The separation distance (separation distance wp) between one linear groove and the other linear groove with respect to the equator line may be ½ or less of the groove width of the linear groove.

  According to such a pneumatic tire, the distance between one straight groove and the other straight groove with respect to the tire equator line is ½ or less of the groove width of the straight groove, so that the drainage of the central land portion is performed. While ensuring the performance, the rigidity of the central land is improved and the handling stability is further improved.

  Further, in the pneumatic tire according to the features of the present invention, one linear groove and the other linear groove overlap with each other on the tire equator line on the tread surface, and the tire equator line on the tread surface. The overlapping distance between one linear groove and the other linear groove may be not more than ½ of the groove width of the linear groove.

  According to such a pneumatic tire, since the overlap distance between one straight groove and the other straight groove with respect to the tire equator line is 1/2 or less of the groove width of the straight groove, the rigidity of the central land portion is reduced. The drainage performance of the central land area is further improved while securing the above.

  Furthermore, in the pneumatic tire according to the features of the present invention, the circumferential groove may be formed at a position that divides one tread surface and the other tread surface into approximately two equal parts with respect to the tire equator line. .

  According to such a pneumatic tire, the circumferential groove is formed at a position that bisects one tread surface and the other tread surface with respect to the tire equator line. The rigidity balance between the region and the side land portion partitioned on the tread end side by the circumferential groove is appropriately maintained, and better steering stability is obtained.

  Further, in the pneumatic tire according to the feature of the present invention, among the groove walls facing each other in the linear groove, the outer groove wall (outer groove wall 22b) positioned on the circumferential groove side is the inner groove positioned on the tire equator line side. The inclination angle with respect to the tire normal line may be smaller than the wall.

  According to such a pneumatic tire, the outer groove wall has a smaller inclination angle with respect to the tire normal than the inner groove wall, so that the groove width in the groove depth direction of the straight groove can be appropriately maintained. Even when the land portion in the land portion is worn, the drainage performance can be ensured by suppressing the decrease in the groove width (decrease in the groove volume) of the straight groove.

  Further, in the pneumatic tire according to the feature of the present invention, a plurality of lug grooves (lug grooves 35) are formed in a side land portion (shoulder land portion 8) partitioned on the tread end side by a circumferential groove. May be.

  According to such a pneumatic tire, a plurality of lug grooves are formed in the side land portion, thereby ensuring the drainage performance from the circumferential groove to the tread end portion, as well as the lateral rigidity of the tread surface and the tread end portion. The uneven wear can be suppressed.

  Further, in the pneumatic tire according to the feature of the present invention, the lug groove is formed in an arc shape as a groove communicating with the first inclined groove with the circumferential groove interposed therebetween, and opens to the circumferential groove and the tread end portion, respectively. In the side land portion, a secondary lug groove (sub lug groove 36) that opens to the circumferential groove and the tread end portion and is substantially parallel to the lug groove is provided between the lug grooves adjacent to each other in the tire circumferential direction. The sub lug inner end portion (sub lug inner end portion 36a) of the sub lug groove that is provided and located on the circumferential groove side is a bottom upper sub lug groove bottom (bottom upper sub lug groove bottom 30) that raises the groove bottom. The shape of the bottom upper sub-lag groove bottom is such that one side is on the groove edge (groove edge 31) located on the side of the auxiliary lug groove and one apex (vertex 32) faces the step-in side. It is substantially triangular and may descend from the kicking side toward the stepping side.

  According to such a pneumatic tire, the lug groove that opens at the circumferential groove and the tread end portion is formed in an arc shape as a groove that communicates with the first inclined groove with the circumferential groove interposed therebetween. Water can be efficiently released to the outside in the tread width direction, and the drainage performance is further improved. Moreover, the drainage performance of the side land portion is further improved by forming the sub lug groove between the lug grooves adjacent to each other in the tire circumferential direction.

  Furthermore, by forming the bottom sub-lag groove bottom at the sub-lag inner end, turbulence of drainage at the junction of the sub-lag inner end and the circumferential groove is suppressed, and drainage in the side land portion is suppressed. The performance is further improved.

  It is possible to provide a pneumatic tire having a directional tread pattern that greatly improves drainage performance, particularly drainage performance in a central land portion, and also improves steering stability performance.

  Next, an example of an embodiment of a pneumatic tire according to the present invention will be described with reference to the drawings. In addition, it should be noted that the drawings described in the following description are schematic and ratios of dimensions and the like are different from actual ones. Accordingly, specific dimensions and the like should be determined in consideration of the following description.

(First embodiment)
FIG. 1 is a partial development view of a tread surface 10 of a pneumatic tire according to a first embodiment of the present invention. As shown in the figure, the tread surface 10 extends in the tire circumferential direction and is located on both sides of the tire equator line CL, and a center defined by the circumferential grooves 2 and 4. A land portion 3 is provided.

  The circumferential grooves 2 and 4 are formed at positions that divide the one tread surface 10 and the other tread surface 10 into approximately two equal parts with respect to the tire equator line CL. That is, the circumferential grooves 2 and 4 are formed on the circumferential lines L1 and L2 that bisect one side of the tire equator line CL.

  In the central land portion 3, a plurality of transverse grooves 20 extending from the circumferential grooves 2, 4 to the central region CT of the central land portion 3 are formed in the tire circumferential direction without alternately joining the tire equator line CT. ing.

  Specifically, the transverse groove 20 includes a long-side inclined groove 21 (first inclined groove) extending from the circumferential grooves 2 and 4 to the center region CT so as to incline toward the stepping side (that is, the rotation direction), and a long-side inclination. A straight groove 22 extending substantially parallel to the tire equator line CL from the end 21E located in the central region CT of the groove 21 toward the stepping side, and a circumferential direction from the end 22E located on the stepping side of the straight groove 22 It is comprised by the short side inclination groove | channel 23 (2nd inclination groove | channel) inclined and extended toward a kicking side toward a groove | channel.

  The inclination angle θ1 (first inclination angle) of the long side inclined groove 21 with respect to the tire equator line CL is smaller than the inclination angle θ2 (second inclination angle) of the short side inclined groove 23 with respect to the tire equator line CL. Further, the groove width W2 of the linear groove 22 is wider than the groove width W1 of the long side inclined groove 21 and the groove width W3 of the short side inclined groove 23.

  Here, as shown in FIG. 2, in the AA ′ cross section, among the groove walls facing each other of the linear grooves 22, the inner groove wall 22 a located on the tire equator line CL side is 25 with respect to the tire normal NL. It is inclined at not less than 45 degrees and not more than 45 degrees (α1). When the inner groove wall 22a is smaller than 25 degrees with respect to the tire normal line NL, the rigidity of the central land portion 3 is insufficient and the steering stability performance is deteriorated. Is likely to occur, and the hydroplaning resistance deteriorates. Further, if the inner groove wall 22a is larger than 45 degrees with respect to the tire normal line NL, the groove volume of the linear groove 22 is reduced, the amount of drainage is insufficient, and the hydroplaning performance is deteriorated.

  Of the groove walls facing each other in the linear groove 22, the outer groove wall 22b located on the circumferential groove 2, 4 side has a smaller inclination angle (α2) with respect to the tire normal NL than the inner groove wall 22a. (Α2 <α1). If the angle α2 of the outer groove wall 22b with respect to the tire normal NL is larger than the angle α1 of the outer groove wall 22a with respect to the tire normal NL, the groove volume of the linear groove 22 decreases, the amount of drainage becomes insufficient, and the hydroplaning performance is improved. May get worse.

  The inner groove wall length SW, which is the length of the inner groove wall 22a in the tire circumferential direction, is the distance between the inner groove wall 22a and the inner groove wall 22a adjacent to the inner groove wall 22a and the tire equator line CL. It is 1/2 or less of the distance LW.

  Moreover, as shown to Fig.9 (a), the one linear groove | channel 22 and the other linear groove | channel 22 are formed without overlapping on the tire equator line CL with respect to the tire equator line CL. At this time, the separation distance wp between one linear groove 22 and the other linear groove 22 with respect to the tire equator line CL is equal to or less than ½ of the groove width W2 of the linear groove 22.

  An outer end 25a (second outer end) that is an end of the short-side inclined groove 23 located on the circumferential grooves 2 and 4 side has a bottom upper groove bottom 26 that raises the groove bottom. The groove width W3a of the outer end 25a having the bottom upper groove bottom 26 is the groove width W3b of the inner end 25b (second inner end) which is the end of the short-side inclined groove 23 located on the tire equator line CL side. Is wider than.

  The shape of the bottom upper groove bottom 26 is a substantially triangular shape with one side on the groove edge 27 located on the stepping side of the short side inclined groove 23 and one vertex 28 facing the kicking side. Here, as shown in FIG. 3, in the B-B ′ cross section, the shape of the bottom upper groove bottom 26 is lowered from the stepping side toward the kicking side.

  A plurality of lug grooves 35 are formed in the side land portions 1 and 5 partitioned on the tread end portion TE side by the circumferential grooves 2 and 4. The lug groove 35 is formed in an arc shape as a groove communicating with the long side inclined groove 21 with the circumferential grooves 2 and 4 interposed therebetween. Furthermore, the lug groove 35 is opened to each of the circumferential grooves 2 and 4 and the tread end TE.

  In addition, the side surface portions 1 and 5 are respectively opened to the circumferential grooves 2 and 4 and the tread end portion TE, and the auxiliary lug grooves 36 substantially parallel to the lug grooves 35 are adjacent to each other in the tire circumferential direction. Each is provided in between.

  The auxiliary lug inner end 36a, which is the end of the auxiliary lug groove 36 located on the circumferential grooves 2 and 4 side, has a bottom upper auxiliary lug groove bottom 30 that raises the groove bottom.

  The shape of the bottom upper sub lug groove bottom 30 is a substantially triangular shape with one side on the groove edge 31 positioned on the kicking side of the sub lug groove 36 and one apex 28 facing the stepping side. Here, as shown in FIG. 4, in the C-C ′ cross section, the shape of the bottom upper groove bottom 30 is lowered from the kicking side toward the stepping side.

(Operation and effect in the first embodiment)
According to the pneumatic tire according to the first embodiment, the drainage performance equivalent to that of the conventional pneumatic tire is ensured by the circumferential grooves 2 and 4, and then the central region of the central land portion 3 from the circumferential grooves 2 and 4. Drainage performance is improved by the transverse groove 20 extending to CT.

  Specifically, when the transverse groove 20 is constituted by the long side inclined groove 21, the straight groove 22, and the short side inclined groove 23, the water on the road surface can be released to the outside in the tread width direction, the central land portion 3, That is, the drainage performance of the central region CT is improved.

  Further, since the plurality of transverse grooves 20 are formed in the tire circumferential direction without alternately joining the tire equator line CT, the central land portion 3 is not divided in the tire circumferential direction, and the tire Land portions 6 and 7 that are continuous in the circumferential direction can be secured. Therefore, during running, the continuous land portions 6 and 7 are always in contact with the road surface, and the steering stability performance is improved.

  Furthermore, since the inner groove wall 22a is inclined at 25 degrees or more and 45 degrees or less with respect to the tire normal line NL, the inflow efficiency of water into the transverse groove 20 is enhanced, and the drainage performance of the central land portion 3 is further increased. In addition to the improvement, the rigidity of the land portions 6 and 7 continuous in the tire circumferential direction secured in the central land portion 3 is enhanced, and the steering stability performance is further improved.

  Further, since the inclination angle θ1 of the long side inclined groove 21 with respect to the tire equator line CL is smaller than the inclination angle θ2 of the short side inclined groove 23 with respect to the tire equator line CL, flowing water in the long side inclined groove 21 is promoted. The drainage performance of the central region 3 is further improved.

  Further, since the groove width W2 of the straight groove 22 is wider than the groove width W1 of the long side inclined groove 21 and the groove width W3 of the short side inclined groove 23, the groove width W2 of the straight groove 22 is sufficiently secured and the transverse groove 20 is obtained. The inflow efficiency of water into the water is increased, and the drainage performance of the central region 3 is further improved.

  In addition, since the inner groove wall length SW is ½ or less of the adjacent distance LW, the rigidity of the land portions 6 and 7 continuous in the tire circumferential direction secured in the central land portion 3 is further increased, and the steering is Stability performance is further improved.

  Further, since the outer end portion 25a of the short side inclined groove 23 has the bottom upper groove bottom 26, the land portion 6 sandwiched between the long side inclined groove 21 and the short side inclined groove 23 adjacent to each other in the tire circumferential direction is provided. 7 can be secured, and uneven wear (such as heel and toe wear) that tends to occur in the land portions 6 and 7 can be suppressed.

  Further, the outer end 25a of the short side inclined groove 23 has a substantially triangular bottom upper groove bottom 26 that descends from the stepping side toward the kicking side, whereby the short side inclined groove 23 and the circumferential groove 2 are provided. , 4 is prevented from turbulent drainage, and the drainage performance of the central land 3 is further improved.

  Further, the distance wp between the one straight groove 22 and the other straight groove 22 with respect to the tire equator line CL is equal to or less than ½ of the groove width W2 of the straight groove 22, thereby draining the central land portion 3. While ensuring the performance, the rigidity of the central land portion 3 is improved and the steering stability is further improved.

  Further, the circumferential grooves 2 and 4 are formed at positions that divide the one tread surface 10 and the other tread surface 10 into approximately two equal parts with respect to the tire equator line CL, so that the center of the central land portion 3 is formed. The rigidity balance between the region CT and the side land portions 1 and 5 partitioned on the tread end TE side by the circumferential grooves 2 and 4 is appropriately maintained, and better steering stability is obtained.

  In addition, since the outer groove wall 22b has a smaller inclination angle with respect to the tire normal NL than the inner groove wall 22a (α2 <α1), the groove width in the groove depth direction of the linear groove 22 can be kept moderate. Even when the land portions 6 and 7 in the central land portion 3 are worn, the drainage performance can be ensured by suppressing the decrease in the groove width (decrease in the groove volume) of the linear groove 22.

  Further, by forming the plurality of lug grooves 35 in the side land portions 1 and 5, the drainage performance from the circumferential grooves 2 and 4 to the tread end portion TE is ensured, and the lateral rigidity and tread of the tread surface 10 are secured. Uneven wear of the end TE can be suppressed.

  In addition, the lug grooves 35 that open at the circumferential grooves 2 and 4 and the tread end TE are formed in an arc shape as grooves that communicate with the long-side inclined groove 21 with the circumferential groove interposed therebetween. Water can be efficiently released to the outside in the tread width direction, and drainage performance is further improved. Moreover, the drainage performance of the side land portion is further improved by forming the sub lug groove 26 between the lug grooves 35 adjacent to each other in the tire circumferential direction.

  Further, the bottom upper sub lug groove bottom 30 is formed in the sub lug inner end 36a, so that the turbulent flow of drainage at the junction of the sub lug inner end 36a and the circumferential grooves 2, 4 is suppressed. The drainage performance in the side land portions 1 and 5 is further improved.

(Second Embodiment)
Next, the present invention is not limited to the tread surface 10 described in the first embodiment. Hereinafter, the tread surface 100 according to the second embodiment will be described with reference to the drawings.

  That is, the tread surface 100 according to the second embodiment is different from the tread surface 10 according to the first embodiment in the shape of the outer end of the transverse groove and the shape of the inner end of the sub lug groove. Except for the point, it has almost the same configuration. In the following, only differences from the first embodiment described above will be described.

  FIG. 5 is a partial development view of the tread surface 100 of the pneumatic tire according to the second embodiment of the present invention. As shown in the figure, the transverse groove 120 provided in the central land portion 103 defined by the circumferential grooves 102 and 104 is constituted by a long side inclined groove 121, a straight groove 122, and a short side inclined groove 123. Yes.

  Here, as shown in FIG. 6, among the groove walls facing each other of the linear grooves 122 in the DD ′ cross section, the inner groove wall 122 a located on the tire equator line CL side is 25 with respect to the tire normal NL. It is inclined at not less than 45 degrees and not more than 45 degrees (α1).

  Of the groove walls of the linear groove 22 facing each other, the outer groove wall 122b located on the circumferential groove 102, 104 side has a smaller inclination angle (α2) with respect to the tire normal NL than the inner groove wall 122a. (Α4 <α3).

  The outer end 125a, which is the end of the short-side inclined groove 123, extends to the front of the circumferential groove without opening in the circumferential groove. The outer end 12a of the short side inclined groove 123 has a bottom upper groove bottom 126 that raises the groove bottom.

  Specifically, as shown in FIG. 7, in the EE ′ cross section, the bottom upper groove bottom 126 extends from the groove edge 127 located on the circumferential grooves 102 and 104 side of the short-side inclined groove 123 to the tire equator line CL. It is going down. More specifically, the bottom upper groove low 126 is configured by two surfaces (a bottom surface 126a and a bottom surface 126b) having different angles (α5 and α6) with respect to the tire normal NL.

  A plurality of lug grooves 135 are formed in the side land portions 101 and 105 partitioned on the tread end TE side by the circumferential grooves 102 and 104. Further, between the lug grooves 135 adjacent to each other in the tire circumferential direction, there are provided auxiliary lug grooves 136 that open to the circumferential grooves 102 and 104 and the tread end portion TE and are substantially parallel to the lug groove 135. The outer end portion 136a of the sub lug groove 136 has a bottom upper groove bottom 130 that raises the groove bottom.

  Specifically, as shown in FIG. 8, in the FF ′ cross section, the bottom upper groove bottom 130 is directed from the groove edge 131 located on the circumferential grooves 102 and 104 side of the auxiliary lug groove 136 toward the tread end TE. Is going down. More specifically, the bottom upper groove low 130 is configured by two surfaces (a bottom surface 130a and a bottom surface 130b) having different angles (α7 and α8) with respect to the tire normal NL.

(Operations and effects in the second embodiment)
According to the pneumatic tire according to the second embodiment, in addition to the operations and effects of the first embodiment, the outer end 125a of the short-side inclined groove 123 is not opened in the circumferential main grooves 102 and 104. Further, the rigidity of the land portions 6 and 7 sandwiched between the long-side inclined groove 121 and the short-side inclined groove 123 adjacent to each other in the tire circumferential direction is further improved, the driving stability performance is greatly improved, and the impact of the block edge is suppressed. Noise performance is improved.

(Modification)
Next, with reference to FIG.9 (b), the example of a change in each embodiment mentioned above is demonstrated. In addition, although the modified example demonstrated below demonstrates as what is applied to 1st Embodiment mentioned above, of course, you may apply to 2nd Embodiment.

  As shown in FIG. 9B, the one straight groove 22 and the other straight groove 22 may overlap with the tire equator line CL with respect to the tire equator line CL. At this time, on the tread surface 10, the overlap distance Wq between the one straight groove 22 and the other straight groove 22 with respect to the tire equator line CL is ½ or less of the groove width W <b> 2 of the straight groove 22. This further improves the drainage performance of the central land portion 3 while ensuring the rigidity of the central land portion 3.

(Comparison evaluation)
In order to confirm the effect of the present invention, the inventors evaluated one type of pneumatic tire according to a conventional example and two types of pneumatic tires according to examples to which the present invention was applied as evaluation tires. The test was conducted.

In addition, the tread pattern of the pneumatic tire which concerns on a prior art example is shown in FIG. As shown in the figure, the tread surface of the conventional pneumatic tire has two circumferential main grooves 202 extending in the tire circumferential direction and two tire ribs that also extend in the tire circumferential direction and define a center rib 206. A circumferential groove 205 is formed. The central land portion 203 has a plurality of inclined grooves 220 and the side land portion 201 has a plurality of lug grooves 235. Table 1 shows the dimensions of each part of a pneumatic tire according to a conventional example that was prototyped for this evaluation.

Further, the pneumatic tire according to Example 1 applies the first embodiment of the present invention, and the pneumatic tire according to Example 2 applies the second embodiment of the present invention. Table 2 and Table 3 show the dimensions of each part of the pneumatic tires according to Example 1 and Example 2 that were prototyped for this evaluation.

  The test conditions are as follows for both the conventional example and the pneumatic tires according to Example 1 and Example 2.

・ Tire size: PSR225 / 45R17
・ Tread width: 180mm (at JATMA standard internal pressure and load)
・ Tire pressure: 2.3kg / cm
-Load load: Equivalent to two actual vehicles In this evaluation test, the following four items were evaluated for the above-described conventional example and the pneumatic tires according to Example 1 and Example 2, respectively.

  1) Wet high pre (straight line): Feeling evaluation by a test driver at a critical speed at which hydroplaning occurs when a wet road surface having a water depth of 5 mm is passed.

  2) Pattern noise: Feeling evaluation of low noise performance by a test driver for in-vehicle sound when coasting from 100 km / h on a straight smooth road.

  3) Uneven wear resistance: In mode running assuming highways, urban roads, and mountain slopes, visual evaluation of the tire tread surface after running 5000 km and measurement of remaining grooves.

  4) Steering stability performance (dry road surface): Feeling evaluation by a test driver when driving on a dry circuit course in various driving modes.

Table 4 shows the evaluation results of the prototyped conventional example and the pneumatic tire according to the example. In addition, the evaluation score of the pneumatic tire which concerns on a prior art example was made into 100 points, and it was set as the evaluation score of the pneumatic tire which concerns on an Example on the basis of this. (The higher the value, the better the evaluation score.)

(result)
As is clear from Table 4, the pneumatic tires according to Example 1 and Example 2 to which the present invention is applied are equivalent or equivalent in any of the four evaluation items as compared with the pneumatic tire according to the conventional example. It is the above evaluation.

  The pneumatic tires according to Example 1 and Example 2 have improved steering stability performance compared to the pneumatic tires according to the conventional example, and the wet high-pre performance is excellent when new, and the same even when worn at 50%. It was found that the steering stability performance and drainage performance were improved.

  Furthermore, the pneumatic tires according to Example 1 and Example 2 are also highly evaluated in terms of pattern noise and uneven wear resistance, compared to the pneumatic tire according to the conventional example, and low noise performance, and It was found that the wear resistance performance was improved.

1 is a partial development view of a tread surface 10 of a pneumatic tire according to a first embodiment of the present invention. It is A-A 'sectional drawing in the linear groove | channel 22 shown in FIG. It is B-B 'sectional drawing in the bottom upper groove bottom 26 shown in FIG. It is C-C 'sectional drawing in the sub lug groove | channel 36 shown in FIG. FIG. 4 is a partial development view of a tread surface 100 of a pneumatic tire according to a second embodiment of the present invention. FIG. 6 is a cross-sectional view taken along line D-D ′ in the straight groove 122 shown in FIG. 5. FIG. 6 is a cross-sectional view taken along line E-E ′ at a bottom upper groove bottom 126 shown in FIG. 5. FIG. 6 is a cross-sectional view taken along the line F-F ′ in the auxiliary lug groove 136 shown in FIG. 5. It is a figure which shows the modification in each embodiment. It is a figure which shows the tread pattern of the pneumatic tire of a prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,5 ... Side land part, 2, 4 ... Circumferential groove | channel, 3 ... Central land part, 6,7 ... Land part, 10 ... Tread surface, 20 ... Transverse groove, 21 ... Long side inclined groove, 21E ... End part 22 ... straight groove, 22a ... inner groove wall, 22b ... outer groove wall, 22E ... end, 23 ... short side inclined groove, 25a, 25b ... end, 26 ... bottom top groove bottom, 27 ... groove edge, 28 ... Apex, 30 ... Bottom upper sub lug groove bottom, 31 ... Groove edge, 32 ... Vertex, 35 ... Lug groove, 36 ... Sub lug groove, 36a ... End, 100 ... Tread surface, 102 circumferential groove, 103 ... Central land Part 106 106 land part 120 transversal groove 121 long inclined groove 122 linear groove 122 a inner groove wall 122 b outer groove wall 123 short inclined groove 125 a end 126 Bottom bottom surface, 127 ... groove edge, 130 ... bottom sub-lag groove bottom, 130a, 130b ... bottom surface, 131 ... groove edge, 135 ... lug groove 136 ... Vice lug grooves

Claims (14)

In the tread surface, a pneumatic tire provided with two circumferential grooves extending in the tire circumferential direction and positioned on both sides of the tire equator line, and a central land portion defined by the circumferential grooves. ,
In the central land portion, a plurality of transverse grooves extending from the circumferential groove to the central region of the central land portion are formed in the tire circumferential direction without merging alternately with the tire equator line,
The transverse groove is
A first inclined groove extending obliquely from the circumferential groove to the stepping side to the central region;
A linear groove extending substantially parallel to the tire equator line from an end portion of the first inclined groove located in the central region toward the stepping side;
A pneumatic tire comprising: a second inclined groove that extends from the end portion of the linear groove located on the stepping side toward the kicking side toward the circumferential groove.   The inner groove wall located on the tire equator line side among the groove walls facing each other of the linear grooves is inclined at 25 degrees or more and 45 degrees or less with respect to the tire normal line. The described pneumatic tire.   The first inclination angle of the first inclined groove with respect to the tire equator line is smaller than the second inclination angle of the second inclined groove with respect to the tire equator line. Pneumatic tire.   The groove width of the linear groove is wider than the groove width of the first inclined groove and the groove width of the second inclined groove on the tread surface. The described pneumatic tire.   Among the groove walls facing each other of the linear grooves, the inner groove wall length, which is the length in the tire circumferential direction of the inner groove wall located on the tire equator line side, is the inner groove wall, the inner groove wall, and the tire. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire is ½ or less of an adjacent distance that is a distance from the inner groove wall adjacent in the circumferential direction.   The second outer end portion, which is an end portion of the second inclined groove located on the circumferential groove side, has a bottom upper groove bottom for raising the groove bottom. The pneumatic tire according to any one of the above. The groove width of the second outer end portion having the bottom groove top is wider than the groove width of the second inner end portion which is an end portion of the second inclined groove located on the tire equator line side,
The shape of the bottom upper groove bottom is a substantially triangular shape with one side on the groove edge located on the stepping side of the second inclined groove and one apex toward the kicking side, and the kicking side from the stepping side The pneumatic tire according to claim 6, wherein the pneumatic tire descends toward the exit side.   The second outer end which is an end of the second inclined groove located on the circumferential groove side extends to the front of the circumferential groove without opening in the circumferential groove. The pneumatic tire according to any one of claims 1 to 5. In the tread surface, one linear groove and the other linear groove with respect to the tire equator line are formed without overlapping on the tire equator line,
2. The tread surface, wherein a separation distance between one linear groove and the other linear groove with respect to the tire equator line is equal to or less than ½ of a groove width of the linear groove. The pneumatic tire according to claim 8. In the tread surface, the one straight groove and the other straight groove overlap the tire equator line on the tire equator line,
2. The overlap distance between one linear groove and the other linear groove with respect to the tire equator line on the tread surface is ½ or less of a groove width of the linear groove. The pneumatic tire according to claim 8.   The circumferential groove is formed at a position that bisects one of the tread surface and the other tread surface with respect to the tire equator line, respectively. The pneumatic tire according to any one of 10.   Of the groove walls facing each other of the linear grooves, the outer groove wall located on the circumferential groove side has a smaller inclination angle with respect to the tire normal than the inner groove wall located on the tire equator line side. The pneumatic tire according to any one of claims 1 to 11.   The pneumatic tire according to any one of claims 1 to 12, wherein a plurality of lug grooves are formed in a side land portion defined on the tread end portion side by the circumferential groove. The lug groove is formed in an arc shape as a groove communicating with the first inclined groove across the circumferential groove, and is open to the circumferential groove and the tread end portion, respectively.
In the side land portion, the circumferential groove and the tread end portion are respectively opened, and sub-lug grooves substantially parallel to the lug groove are provided between the lug grooves adjacent to each other in the tire circumferential direction, respectively.
The auxiliary lug inner end of the auxiliary lug groove located on the circumferential groove side has a bottom upper auxiliary lug groove bottom that raises the groove bottom,
The shape of the bottom upper sub lug groove bottom is a substantially triangular shape with one side on the groove edge located on the kick side of the sub lug groove and one apex toward the stepping side, and from the kicking side to the stepping side. The pneumatic tire according to claim 13, wherein the pneumatic tire descends toward the front.

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