JP4212617B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire in which a ridge is provided on the groove bottom of a groove portion of a tread surface.

  The tread surface of a pneumatic tire is usually provided with groove portions such as circumferential grooves and lateral grooves and land portions divided by the groove portions, and various tread patterns according to required tire performance and use conditions are provided. It is formed. When running on a gravel road that is not leveled, the groove on the road may get caught on the road, and when the tire rolls in such a state, the force that pushes and widens the groove is repeated. There was a problem that the stones that acted or the sandwiched stones entered the groove bottom and caused damage such as cracks at the groove bottom.

  For this problem, as described in Patent Documents 1 to 3 below, it has been proposed to provide protrusions as shown in FIG. 14 at the groove bottom of the groove, thereby preventing stone biting. However, if the pebbles S are sandwiched between the ridges 60 and the groove walls 9b as shown in the drawing, the side surfaces of the ridges 60 may be locally deformed and held so as to wrap the pebbles S. It could not be said that the stone biting property was sufficient.

  In addition, since the volume on the groove bottom 9a side is reduced by providing the protrusion 60, the drainage performance may deteriorate in a state where wear has progressed, and the WET performance (wet road running performance) may be deteriorated. Thus, if the groove wall angle θ3 is reduced to secure the volume on the groove bottom 9a side, there is a problem that stone biting is likely to occur. Furthermore, there is a concern about a groove bottom crack starting from the root of the ridge 60.

  Conventionally, the rigidity of the ridge tends to be increased in order to increase the resistance against the invasion of stones, and in Patent Document 3 below, a ridge having a trapezoidal cross section with a width gradually reduced from the groove bottom toward the upper surface is disclosed. Are listed. However, when pebbles are sandwiched between the ridge and the groove wall as described above, the pebbles are strongly held because of their high rigidity, making it difficult to discharge out of the grooves. I understood.

The following Patent Document 4 also describes a pneumatic tire in which a ridge is provided on the groove bottom of the groove portion. However, the ridge has a height of 1 mm or less, and a plurality of juxtapositions are provided in the groove bottom. It is a fine protrusion that can be done, and cannot prevent the above-mentioned stone biting.
Japanese Patent Laid-Open No. 10-35224 JP 2000-185525 A JP 2002-29218 A JP-A-10-226206

  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 that can effectively enhance stone-biting resistance and suppress damage such as groove bottom cracks.

The above object can be achieved by the present invention as described below. That is, the pneumatic tire of the present invention is a pneumatic tire in which a groove portion and a land portion divided by the groove portion are provided on a tread surface, and the groove bottom of the groove portion extends along the extending direction of the groove portion. A ridge that extends toward the outer periphery of the tire, and a base that is narrower than the top and connects the top and the groove bottom , The base has a side surface with an arc-shaped cross section, and the side surface is smoothly connected to the side surface of the top portion and the groove bottom, and the top portion has a substantially rectangular cross section, and the ridge line portion on the tire outer peripheral side Are formed with a curved surface having a circular arc cross section, the top surface is flat, and the ratio H / D of the height H of the ridge to the groove depth D of the groove is 0.2 <H / D <0.5. It is characterized by satisfying .

  In the present invention, by providing the ridge as described above, when a pebble is sandwiched between the ridge and the groove wall, the top of the head easily tilts around the base, and the ridge is entirely formed. Deforms and deforms. Therefore, based on the deformation restoring force of the ridges, a reaction force that pushes up the pebbles on the side surfaces of the ridges is effectively generated, and the ridges function to discharge the pebbles out of the grooves. As a result, stone biting resistance can be improved and damage such as groove bottom cracks can be suppressed.

  In short, the present invention utilizes the deformation restoring force generated by positively deflecting and deforming the ridge as a reaction force for discharging pebbles. On the other hand, in the ridge 60 shown in FIG. 14, the reaction force as described above hardly occurs, and the pebbles S sandwiched between the ridge 60 and the groove wall 9b cannot easily come out.

Moreover, in this invention, damages, such as a groove bottom crack, are suppressed also in the point of following ac.
a: Since the top of the head easily tilts, the holding force of the pebbles is smaller than in the past, and the pebbles are easily discharged by the centrifugal force at the time of rolling of the tire, so that the stone biting resistance is improved.
b: In a state where the top of the head is tilted with pebbles sandwiched between them, the gap between the groove wall on the falling side and the top of the head is narrowed. improves.
c: Since the base of the ridge is narrower than the top of the head, the boundary between the groove bottom and the base can be easily formed at an obtuse angle or an arc of a large diameter in the comparative example. The occurrence of cracks as a starting point can be suppressed.

  In addition, in the present invention, since the base is narrower than the top, it is possible to secure a large volume on the groove bottom side, maintain drainage even when wear progresses, and have excellent WET performance. Can be demonstrated.

In the pneumatic tire of the present invention, the ridge line portion on the tire outer periphery side of the top portion is formed with a curved surface having an arcuate cross section . In the present invention, since the base of the ridge is narrower than the top of the head, there is a concern that unvulcanized rubber is difficult to be supplied to the tip of the top during the tread pattern molding. By forming the ridge portion with a curved surface having an arcuate cross section, the shape of the crown can be easily and appropriately formed. As a result, it is possible to sufficiently exhibit the excellent stone biting resistance as described above. “Arc cross section” means an arc shape in the tire meridian cross section.

The pneumatic tire of the present invention, the base portion has constricted with a circular arc cross sectional shape of the side surface, the side surface is smoothly continuous to the side surface and the groove bottom of the top section. According to such a configuration, since the top of the head can be easily tilted around the constricted portion of the base, the above-described effects of the present invention can be expressed easily and reliably. In addition, the flexibility of the deformation of the ridges is increased, the reaction force for discharging pebbles is more effectively obtained, and there is no place where distortion tends to concentrate, and the groove bottom cracks starting from the base of the ridges Can be suppressed.

Another pneumatic tire of the present invention is a pneumatic tire in which a groove portion and a land portion divided by the groove portion are provided on a tread surface, and the groove bottom of the groove portion extends along the extending direction of the groove portion. A ridge that extends toward the outer periphery of the tire, and a base that is narrower than the top and connects the top and the groove bottom, The base has a side surface with an arc-shaped cross section, and the side surface is smoothly connected to the side surface of the top of the head and the groove bottom, and the top of the head has a substantially circular cross section . According to such a configuration, since it is formed by a curved surface that is convex toward the groove wall side from the tip to the side surface of the crown, it is difficult for pebbles to be sandwiched between the crown and the groove wall, and even if pebbles are sandwiched Since the contact area between the side surface of the crown and the pebbles is relatively small, a reaction force is easily generated, and the stone biting resistance is effectively improved. The “substantially circular cross section” means a substantially circular cross section in the tire meridian.

  In the above, it is preferable that the ratio of the minimum width of the base to the maximum width of the top of the head is 0.5 to 0.9, and thereby the above-described effects of the present invention are suitably expressed. That is, if this ratio is less than 0.5, the base becomes too narrow, so that at the time of forming the tread pattern, it becomes difficult to supply unvulcanized rubber to the top of the head, or the vulcanization is finished and the tire is molded. There is a concern that the resistance at the time of releasing from the mold increases and the base portion is easily broken. On the other hand, if the above ratio exceeds 0.9, the ridges will bend flexibly and be less likely to be deformed, and the cost for improving the stone biting resistance will tend to be small.

  In the above, the communication rubber portion formed by the communication hole for communicating the groove forming portion and the groove wall forming portion of the groove forming bone provided in the tire mold includes the side surface of the protrusion and the groove wall of the groove portion. Those provided on at least one of these are preferable. Thereby, at the time of tread pattern molding, since the supply of unvulcanized rubber to the ridge forming portion is performed not only from the groove bottom side but also through the communication hole, the shape of the top portion is appropriately formed, The excellent stone biting resistance as described above can be sufficiently exhibited.

  In the above, the protrusion is provided on the groove bottom of a circumferential groove continuous along the tire circumferential direction, and the land portion has ribs separated by the circumferential groove, The groove wall angle of the directional groove is 10 ° or less, and one-side open sipes extending from the surface of the rib to the tire inner peripheral side with respect to the top of the rib are spaced apart at intervals of 3 to 6 mm at the edge of the rib. What is provided is preferable.

  According to the above configuration, since the rigidity of the groove wall facing the top of the head is reduced, the holding force of the pebbles sandwiched between the groove wall and the ridge is reduced, and the reaction force generated on the ridge and the tire rolling force are reduced. Pebbles can be easily discharged out of the groove by the centrifugal force during movement. In addition, it is possible to reduce the rigidity of the edge portion of the rib to suppress local wear, to prevent the occurrence of river wear, and to improve the uneven wear resistance.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a tire meridian half sectional view showing an example of a pneumatic tire according to the present invention. FIG. 2 is a development view of the tread surface of the pneumatic tire. FIG. 3 is an enlarged perspective view of a part of FIG.

  In the present embodiment, as shown in FIGS. 1 and 2, circumferential grooves 9 as groove portions are continuously provided in the tire circumferential direction on the tread surface which is the outer circumferential side surface of the tread portion 7, and the circumferential direction thereof. Land portions divided by the grooves 9 are provided as rib patterns based on the ribs 5. Of the four circumferential grooves 9, the ridges 10 extend along the tire circumferential direction, which is the extending direction of the circumferential grooves 9, on the groove bottom 9 a of the circumferential groove 9 located on the outermost side in the tire width direction. It is installed.

  As shown in FIG. 3 in an enlarged manner, the ridge 10 includes a top portion 11 that constitutes a central portion and an upper portion in the height direction, and a base portion 12 that constitutes a lower portion in the height direction. The top portion 11 protrudes toward the tire outer peripheral side, and in the present embodiment, has a vertically long cross-sectional substantially rectangular shape. The base part 12 is narrower than the top part 11, and is interposed between the top part 11 and the groove bottom 9a so as to connect them together.

  FIG. 4 is a cross-sectional view of a main part showing a state in which the pebbles S are sandwiched between the groove wall 9 b of the circumferential groove 9 and the protrusion 10. In the present invention, when the pebbles S are sandwiched, the crown portion 11 easily tilts around the narrow base portion 12, and the protrusion 10 is bent and deformed as a whole as shown in FIG. For this reason, based on the deformation restoring force of the ridge 10, a reaction force that pushes up the pebbles S on the side surface of the ridge 10 is likely to occur, and the ridges 10 function to discharge the pebbles S out of the grooves. Further, since the pebbles S cannot be held strongly, the pebbles S are easily discharged out of the groove by the centrifugal force at the time of tire rolling. In addition, in the state where the pebbles S are sandwiched, the interval between the groove wall 9b on the left side of the example and the top 11 is narrow, and the intrusion of pebbles into this gap is suppressed.

  In the present embodiment, the side surface of the base portion 12 is formed in a shape constricted by a curved surface having an arcuate cross section, and the radius of the arc is preferably 0.5 to 2.0 mm. When the pebbles S are sandwiched, the parietal portion 11 can be easily and reliably tilted around the constricted portion of the base portion 12. In addition, since the base 12 is narrower than the top 11, the arc can be formed with a relatively large diameter, and a groove bottom crack starting from the root of the protrusion 10 can be effectively suppressed. .

  The side surface of the base portion 12 is smoothly connected to the side surface of the top portion 11 and the groove bottom 9a. From this, the flexibility of the bending deformation of the ridge 10 is increased, and a reaction force for discharging the pebbles S is easily obtained, and there is no portion where the distortion is easily concentrated, and the root of the ridge 10 is the starting point. Groove bottom cracks can be suppressed.

In the present invention, the side surface of the base portion 12 is not formed as a flat surface . In that case, however, the boundary between the side surface of the base portion 12 and the groove bottom 9a is a curved surface having an arcuate cross section from the viewpoint of suppressing groove bottom cracks. The radius of the arc is preferably 1.0 to 3.0 mm. In the present embodiment, the boundary between the groove bottom 9a and the groove wall 9b is formed by a curved surface having an arcuate cross section. The radius of the arc is, for example, 2.0 to 3.0 mm. The radius of curvature of the arc is preferably larger than the radius of curvature of the side surface of the base 12, thereby suppressing the groove bottom crack on the rib 5 side. The top 10 can be easily tilted.

  Here, as shown in FIG. 3, when the groove depth of the circumferential groove 9 is D and the height of the protrusion 10 is H, the ratio H / D of the height H to the groove depth D is 0.2. <H / D <0.5 is preferably satisfied, and 0.3 <H / D <0.4 is more preferable. When this H / D is 0.2 or less, the improvement margin for stone biting resistance tends to be small, and when H / D is 0.5 or more, drainage performance is lowered and WET performance is impaired. There is a fear.

  In addition, when the maximum width of the top 11 of the ridge 10 is W1 and the minimum width of the base 12 is W2, the ratio W2 / minimum of the minimum width W2 with respect to the maximum width W1 from the viewpoint of suitably expressing the effects of the present invention. W1 preferably satisfies 0.5 ≦ W2 / W1 ≦ 0.9, and more preferably satisfies 0.7 ≦ W2 / W1 ≦ 0.8. In addition, it is preferable that the height h of the minimum width position of the base 12 is 1/2 or less of the height H of the protrusion 10 from a viewpoint of appropriately bending and deforming the protrusion 10. Specifically, the height h is preferably 0.7 to 2.0 mm, and more preferably 1.0 to 1.5 mm.

  Further, when the groove bottom width of the circumferential groove 9 is W3, the ratio W1 / W3 of the maximum width W1 to the groove bottom width W3 preferably satisfies 0.2 ≦ W1 / W3 ≦ 0.6, and 0.3 More preferably, ≦ W1 / W3 ≦ 0.5 is satisfied. When W1 / W3 is less than 0.2, the reaction force generated on the protrusion 10 tends to be small, and when W1 / W3 exceeds 0.6, the protrusion 10 tends to bend and be difficult to deform. .

  In the present invention, since the base portion 12 is narrower than the top portion 11, a large volume on the groove bottom 9a side of the circumferential groove 9 can be secured, and drainage is maintained even in a state where wear has progressed. Excellent WET performance can be exhibited.

  The pneumatic tire of the present invention is the same as the conventional pneumatic tire except that the above-described protrusions are provided in the groove portion of the tread surface, and any known materials, shapes, structures, manufacturing methods, etc. Can be adopted. However, because it can demonstrate excellent resistance to rock biting, it is very useful as a heavy-duty pneumatic tire to be installed on gravel roads where pebbles are scattered and trucks and construction vehicles that have many opportunities to move on leveling sites. is there.

  In the present embodiment, an example of a heavy duty pneumatic tire is shown. In this tire, as shown in FIG. 1, the carcass ply 1 is wound around the bead core 3 and the rubber filler 4 arranged in the bead portion 2 from the inside to the outside, and the winding end is rubber. The filler 4 is disposed in the middle of the oblique side. The pad 6 is provided so as to sandwich the winding end of the carcass ply 1 together with the rubber filler 4.

  The carcass ply 1 is composed of one or a plurality of plies in which steel cords, high-strength organic fiber cords, and the like are arranged in the tire radial direction. The bead core 3 is made of a laminate of a bead wire and a covering rubber, and the rubber filler 4 is made of a hard rubber having a substantially triangular cross section whose bottom is an arc.

  A belt layer 8 is disposed on the tire outer periphery side of the carcass ply 1 of the tread portion 7, and a belt reinforcing layer is disposed on the outer periphery as necessary. The rubber hardness of the tread rubber is not particularly limited as long as it is normally used, and the tread pattern as described above is formed on the tread surface. Inner liner rubber for maintaining air pressure is provided on the inner peripheral side of the carcass ply 1, and side wall rubber is provided on the outer peripheral side of the carcass ply 1 between the tread portion 7 and the bead portion 2.

  In the tread pattern illustrated in FIG. 2, the central rib 5 near the tire equator line CL and the ribs 5 on both sides thereof are provided with closed sipes for the purpose of improving the WET performance. The shape of the rib 5 is not particularly limited. For example, the rib 5 may be divided by a circumferential groove extending zigzag. In such a case, a protrusion extending in a zigzag shape or a wave shape is provided along the extending direction of the circumferential groove.

  In the heavy load pneumatic tire, the groove bottom width W3 of the circumferential groove 9 is 7 to 16 mm or 10 to 12 mm, the groove depth D of the circumferential groove 9 is 10 to 20 mm or 14 to 16 mm, and the circumferential groove 9 In which the groove wall angle θ1 is 0 to 20 °. At this time, as an example of the dimensions of the protrusion 10, the height H is 5 to 7 mm, the maximum width W1 of the top 11 is 3 to 5 mm, and the minimum width W2 of the base 12 is 2.5 to 3.0 mm. Can be mentioned.

  As shown in FIG. 5, the pneumatic tire of the present invention is modified to the extent that a ridge forming portion 16 for forming the ridge 10 is provided on the groove forming bone 15 provided in the tire mold. Can be manufactured in the same manner as the conventional tire manufacturing process. The groove-forming bone 15 is pressed against the tread surface of the green tire to form the circumferential groove 9, and at this time, unvulcanized rubber is supplied from the groove bottom side to the ridge forming part 16. The protrusion 10 is provided in a protruding manner. The groove wall 9 b of the circumferential groove 9 is formed by the groove wall forming portion 17.

  In the present invention, since the base portion 12 of the ridge 10 is narrower than the top portion 11, there is a concern whether unvulcanized rubber is filled in the tip of the ridge forming portion 16, but in this embodiment, As shown in FIG. 3, the ridge line portion 11 a on the tire outer periphery side of the crown portion 11 is formed with a curved surface having an arc-shaped cross section, so that the unvulcanized rubber is easily filled into the ridge forming portion 16, and the shape of the crown portion 11 is formed. Formation can be performed appropriately.

[Second Embodiment]
The second embodiment has the same configuration as that of the first embodiment except that the grooves and the protrusions are configured as follows, and therefore, the differences will be mainly described with the common points omitted. In addition, the same code | symbol is attached | subjected to the member same as the member demonstrated in 1st Embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 6, the ridge 20 includes a top portion 21 that constitutes the upper half body and a base portion 22 that constitutes the lower half body. The top portion 21 has a substantially circular cross section and protrudes toward the outer periphery of the tire, and is formed by a curved surface that protrudes toward the groove wall 9b from the tip to the side surface. The base portion 22 has substantially the same shape as the base portion 12 of the first embodiment, and connects the top portion 21 and the groove bottom 9a integrally.

  In the present embodiment, since the ridge 20 has the shape as described above, the pebbles S are not easily sandwiched between the crown portion 21 and the groove wall 9b, and even if the pebbles S are sandwiched, Since the contact area between the side surface and the pebbles S is relatively small, a reaction force is easily generated, and the stone biting resistance is effectively improved.

  In the cross section of the tire meridian, the arc constituting the contour of the top portion 21 is smoothly connected to the arc constituting the side surface of the base portion 22, and the arc constituting the side surface of the base portion 22 is also continuously connected to the groove bottom 9a. Yes. As a result, the flexibility of the bending deformation of the ridge 20 is effectively increased, and the portion where the distortion is easily concentrated is eliminated, and the groove bottom crack starting from the root of the ridge 20 can be suppressed.

[Third Embodiment]
The third embodiment has the same configuration as that of the first embodiment except that the groove portions and the protrusions are configured as follows, and therefore, the common points will be omitted and differences will be mainly described. In addition, the same code | symbol is attached | subjected to the member same as the member demonstrated in 1st Embodiment, and the overlapping description is abbreviate | omitted. Note that the third embodiment is not included in the present invention.

  As shown in FIG. 7, the ridge 30 includes a top 31 that constitutes the upper half of the ridge 30 and a base 32 that constitutes the lower half of the ridge 30. The parietal portion 31 has a substantially rectangular cross section and projects toward the tire outer peripheral side, and the projection height is smaller than the parietal portion 11 of the first embodiment. The base portion 32 has substantially the same shape as the base portion 12 of the first embodiment, and connects the top portion 31 and the groove bottom 9a integrally.

  In the present embodiment, the groove wall angle θ2 of the circumferential groove 9 is set to 10 ° or less, and a one-side open sipe 35 that opens at the groove wall 9b is provided at the edge portion of the rib 5. The sipe 35 extends in the groove depth direction from the surface of the rib 5 and terminates at a position on the tire inner peripheral side with respect to the top surface of the crown portion 31, and extends along the extending direction of the circumferential groove 9. They are spaced at predetermined intervals.

  As a result, the rigidity of the groove wall 9b is reduced, and the holding force of the pebbles sandwiched between the groove wall 9b and the protrusion 30 is reduced. Therefore, pebbles can be easily discharged out of the groove by the centrifugal force at the time of tire rolling in addition to the reaction force generated on the protrusion 30. In addition, by setting the groove wall angle θ2 to 10 ° or less, the circumferential groove 9 can easily pinch pebbles, but in the present invention, it can exhibit excellent stone biting resistance as described above. While suppressing, increasing the volume on the groove bottom 9a side can improve the WET performance during the progress of wear. In addition, since the local wear can be suppressed by reducing the rigidity of the edge portion of the rib 5, the occurrence of river wear can be prevented and the uneven wear resistance can be enhanced.

  The distance between the sipe 35 is 3 to 6 mm, and if it is less than 3 mm, the thickness of the rubber piece between the sipe 35 tends to be thin and easily deformed. . On the other hand, if it exceeds 6 mm, the effect of lowering the rigidity of the groove wall 9b is poor, and the cost for improving the stone biting resistance becomes small. In addition, from the viewpoint of rigidity reduction of the groove wall 9b and durability of the rib 5, the groove width of the sipe 35 is preferably 0.5 to 1.0 mm, and the length of the sipe 35 on the tread surface is preferably 3 to 5 mm.

[Fourth Embodiment]
The fourth embodiment has the same configuration as that of the first embodiment except that the groove portions and the protrusions are configured as follows, and thus the differences will be mainly described with the common points omitted. In addition, the same code | symbol is attached | subjected to the member same as the member demonstrated in 1st Embodiment, and the overlapping description is abbreviate | omitted.

  The ridge 40 includes a top 41 and a base 42 as shown in FIG. 8, and the cross-sectional shape is substantially the same as the ridge 10 of the first embodiment. In the present embodiment, a plate-like communication rubber portion 45 extending so as to connect the side surface of the protrusion 40 and the groove wall 9b is provided. The communication rubber portion 45 is integrally connected to the lower portion of the top portion 41 and the side surface of the base portion 42, the groove wall 9 b, and the groove bottom 9 a, with a predetermined interval along the extending direction of the circumferential groove 9. Separated.

  The protrusion 40 is formed by a groove forming bone 15 as shown in FIG. The groove forming bone 15 is provided with a communication hole 18 that allows the protrusion forming part 16 and the groove wall forming part 17 to communicate with each other, and when pressed against the tread surface of the green tire, the protrusion forming part. Since the unvulcanized rubber is supplied to 16 not only from the groove bottom 9a side but also through the communication hole 18, the shape of the top 41 is smoothly formed.

  Such a configuration is useful when the shape of the top portion 41 is vertically long as shown in the figure, and together with this, the ridge line portion 41a on the tire outer periphery side of the top portion 41 is formed with a curved surface having an arcuate cross section. Thus, the shape formation becomes better. In addition, you may provide the communication rubber part 45 in the groove wall 9b of both sides.

  In addition, as shown in FIG. 10, the side surface of the top portion 41 and the groove wall 9b facing the head portion 41 may be connected by a columnar communication rubber portion 46. It is supplied directly to the top of the head 41, and its shape formation becomes better. The communication rubber portion 46 is formed by the communication hole 19 of the groove forming bone 15 as shown in FIG. 11, and is cut when the vulcanization is finished and released from the tire mold, and the side surface and the groove of the top portion 41 are formed. It will be in the state provided in at least one of the walls 9b.

[Other Embodiments]
(1) In the above-described embodiment, an example in which the tread pattern is a rib pattern is shown. However, the present invention is not limited to this, and the pattern may include a part or all of blocks as land portions. The groove part provided with the protrusion may be a lateral groove or an inclined groove. However, since the occurrence of stone biting is remarkable in the circumferential groove, it is preferable that the protrusion is provided at the groove bottom of at least one circumferential groove.

  (2) In the above-described embodiment, the example in which the protrusion is provided only in the circumferential groove located on the outermost side in the tire width direction is shown, but the present invention is not limited to this, for example, the groove portion located on the center side in the tire width direction. A protrusion may be provided only on the groove, or a protrusion may be provided on all the grooves on the tread surface.

  (3) In the above-described embodiment, the example in which the protrusions extend continuously has been described. However, the present invention is not limited to this, and the protrusions may extend intermittently as in the protrusion 60 shown in FIG. Thereby, drainage can be improved and the WET performance especially at the time of wear progress can be improved. However, by interrupting the ridge 60, it becomes easy to pinch pebbles at the intermittence portion 65. Therefore, in the present invention, whether the ridges are continuous or intermittent, and the interval between the intermittence portions is the stone biting performance and WET resistance. An appropriate selection may be made in consideration of a balance with performance.

  The ridge 70 shown in FIG. 13 extends intermittently in the same manner as the ridge 60, but in the intermittent portion 75, the end portions of the crown portions 71 facing each other are formed in a hemispherical shape. According to such a configuration, a reaction force is generated by bending the end of the crown portion 71 with respect to the pebbles that are about to enter the interrupting portion 75, and the stone biting at the interrupting portion 75 can be effectively suppressed. The stone biting performance can be improved while improving the WET performance.

  (4) A cross-sectional shape other than those described above may be employed as the cross-sectional shape of the protrusion, but from the viewpoint of easily tilting the crown, it may be locally bundled at the base as in the above-described embodiment. preferable. Moreover, you may change the height of a protrusion periodically.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.

(1) Groove bottom damage and groove bottom crack After attaching a test tire to the steering wheel of a tractor head with an axle arrangement of 2-D and running on a dry road surface of 100,000 km, the groove bottom damage (excluding cracks) In addition, the occurrence of groove bottom cracks was visually examined, and the number of occurrences was counted. About the reciprocal number of the count number, the index evaluation is made with Comparative Example 1 as 100, and the larger the value, the better the stone-resisting performance.

(2) Number of chewed stones In traveling on the above-mentioned dry road surface, the number of pebbles sandwiched in the groove at the time of traveling 10,000, 20,000, and 30,000 km was counted, and an average value was calculated.

(3) WET performance A test tire with a tread surface trimmed until the groove depth of the circumferential groove reaches 4 mm is mounted on the steering wheel of a tractor head with an axle arrangement of 2-D, and it feels by running on the WET road surface. Evaluation was performed. Index evaluation is performed with Comparative Example 1 being 100, and the larger the value, the better the WET performance.

Comparative Example 1
A pneumatic tire (size 295 / 75R22.5) having the structure shown in FIGS. 1 and 2 was prepared and evaluated as described above. The rubber hardness of the tread rubber (rubber hardness according to JISK6253 durometer hardness test (type A)) is 65 °, the groove width at the tread of the circumferential groove is 13 mm, the groove depth D is 14 mm, and the groove bottom width W3 is 9 mm. It was. Further, the protrusion has a substantially rectangular cross section as shown in FIG. 14 and has a height of 4 mm and a width of 3.5 mm.

Comparative Example 2
The same pneumatic tire as Comparative Example 1 was prepared, and the above evaluation was performed, except that the ridge was integrally formed with a groove wall on one side and formed into a shelf shape.

Example 1
A pneumatic tire (size 295 / 75R22.5) having the structure shown in FIGS. 1 and 2 was prepared and evaluated as described above. The rubber hardness of the tread rubber was 65 °, the groove width on the tread surface of the circumferential groove was 13 mm, the groove depth D was 14 mm, and the groove bottom width W3 was 9 mm. Further, the protrusion has a shape having a top and a base as shown in FIG. 3, and the maximum width W1 of the top is 3.5 mm and the minimum width W2 of the base is 1.7 mm (W2 / W1 = 0.49). ), The height h of the minimum width position of the base was 1.2 mm. This is a shape in which the side surface of the protrusion of Comparative Example 1 is scraped off by 0.9 mm on one side in a semicircular shape.

Example 2
The maximum width W1 of the top of the head is 3.5 mm, the minimum width W2 of the base is 3.1 mm (W2 / W1 = 0.89), and the height h of the minimum width of the base is 1.5 mm. The same tire as in Example 1 was prepared and the above evaluation was performed except that the side surface of the tire was cut into a semicircular arc shape by 0.2 mm on each side.

Example 3
The maximum width W1 of the top of the head is 3.5 mm, the minimum width W2 of the base is 2.5 mm (W2 / W1 = 0.71), and the height h of the minimum width position of the base is 1.7 mm. The same tire as in Example 1 was prepared and the above evaluation was performed, except that the side surface was made into a semicircular arc shape by cutting 0.5 mm on each side.

Example 4
Except for extending the ridge intermittently as shown in FIG. 12, the same tire as in Example 1 was prepared and the above evaluation was performed. In addition, the circumferential direction length of the divided protrusions was 8 mm, and the interval between the intermittent portions was 3 mm. The evaluation results of each example are shown in Table 1.

  From Table 1, in Examples 1-4, the damage of a groove bottom and generation | occurrence | production of a groove bottom crack are less than the comparative examples 1 and 2, there are few pebbles pinched | interposed into the groove part, and the above-mentioned protrusion is provided. It can be seen that the stone biting performance is improved. In Comparative Example 2, it is considered that the pebbles easily reached the groove bottom because the groove bottom was relatively wide open, leading to damage to the groove bottom. Moreover, in Examples 1-4, the volume by the side of a groove | channel is large compared with the comparative examples 1 and 2, and the outstanding WET performance is exhibited by it, and it can have both stone-proofing performance and WET performance. I understand that.

The tire meridian half sectional view showing an example (first embodiment) of a pneumatic tire according to the present invention Development view of the tread surface of the pneumatic tire 1 is an enlarged perspective view of a part of FIG. Cross-sectional view of the main part showing a state where pebbles are sandwiched in the groove of the pneumatic tire A perspective cross-sectional view showing a groove forming bone provided in a tire mold for molding the pneumatic tire Sectional drawing of the principal part which shows an example (2nd Embodiment) of the pneumatic tire which concerns on this invention Cross-sectional perspective view showing an example (third embodiment) of a pneumatic tire not included in the present invention A perspective sectional view showing an example (fourth embodiment) of a pneumatic tire according to the present invention. A perspective cross-sectional view showing a groove forming bone provided in a tire mold for molding the pneumatic tire A perspective sectional view showing an example (fourth embodiment) of a pneumatic tire according to the present invention. A perspective cross-sectional view showing a groove forming bone provided in a tire mold for molding the pneumatic tire The perspective sectional view showing the pneumatic tire concerning another embodiment of the present invention. The perspective sectional view showing the pneumatic tire concerning another embodiment of the present invention. Cross-sectional view of main parts showing an example of a conventional pneumatic tire

Explanation of symbols

5 rib 7 tread portion 9 circumferential groove 9a groove bottom 9b groove wall 10 ridge 11 head top 11a ridge line portion 12 base 15 groove portion forming bone 16 ridge formation portion 17 groove wall formation portion 18 communication hole 19 communication hole 20 ridge 21 head top 22 base 30 ridge 31 head top 32 base 35 one side open sipe 40 ridge 41 head top 42 base 45 communication rubber portion 46 communication rubber portion 60 ridge 65 interrupted portion 70 ridge 75 interrupted portion D of circumferential groove Groove depth H Projection height S Pebble W1 Maximum width W2 at the top Minimum width W3 at the base W3 Groove bottom width θ1 in the circumferential groove Groove wall angle

Claims (5)

In a pneumatic tire provided with a groove part and a land part divided by the groove part on the tread surface,
A ridge extending along the extending direction of the groove is provided on the groove bottom of the groove,
The ridge includes a top part protruding toward the tire outer peripheral side, and a base part that is narrower than the top part and connects the top part and the groove bottom .
The base portion has a side surface with an arc-shaped cross section, and the side surface is smoothly connected to the side surface of the head top portion and the groove bottom, and the head top portion has a substantially rectangular cross section, and the ridge line on the tire outer peripheral side Only the part is formed of a curved surface with a circular arc cross section, and the top surface is flat,
The pneumatic tire according to claim 1, wherein a ratio H / D of a height H of the protrusion to a groove depth D of the groove satisfies 0.2 <H / D <0.5 . In a pneumatic tire provided with a groove part and a land part divided by the groove part on the tread surface,
A ridge extending along the extending direction of the groove is provided on the groove bottom of the groove,
The ridge includes a top part protruding toward the tire outer peripheral side, and a base part that is narrower than the top part and connects the top part and the groove bottom.
The air is characterized in that the base portion has a side surface with an arc-shaped cross section, the side surface is smoothly connected to the side surface of the top of the head and the groove bottom, and the top of the head has a substantially circular cross section. Enter tire. The pneumatic tire according to claim 1 or 2 , wherein a ratio of a minimum width of the base portion to a maximum width of the top portion is 0.5 to 0.9. A communication rubber portion formed by a communication hole that communicates the groove forming portion and the groove wall forming portion of the groove forming bone provided in the tire mold is at least one of the side surface of the protrusion and the groove wall of the groove portion. The pneumatic tire according to any one of claims 1 to 3 , wherein the pneumatic tire is provided. The ridge is provided at the groove bottom of a circumferential groove continuous along the tire circumferential direction, and the land portion has ribs separated by the circumferential groove,
The groove wall angle of the circumferential groove is 10 ° or less, and a one-side open sipe extending from the surface of the rib to the tire inner peripheral side than the top is placed at an edge of the rib by 3 to 6 mm. The pneumatic tire according to any one of claims 1 to 4 , wherein the pneumatic tire is spaced apart from each other.

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