JP2019142370A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire of which the stone-biting prevention performance and travel performance on an unpaved road are improved.SOLUTION: A tread portion 1 is formed with: a pair of main grooves 10 extending in a zigzag shape along the tire circumferential direction on both sides of a tire equator CL; a shoulder lug groove 20; and a center lug groove 30, and the groove depth d3 of at least the center lug groove 30 is made smaller than the groove depth d1 of the main grooves 10, and a groove bottom of each of the grooves is formed with a projection part 40 extending along the groove by protruding from the groove bottom of the groove, and a projection part 41 formed in the main groove 10 is constituted of a plurality of divided pieces 41a and 41b arranged at an interval in the longitudinal direction of the main grooves 10, and the respective divided pieces 41a and 41b are bent by extending while straddling a bending part bending in a zigzag shape in the main grooves 10.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire suitable as a tire for traveling on an unpaved road, and more particularly to a pneumatic tire having improved stone biting prevention performance and traveling performance on an unpaved road.

  Pneumatic tires intended for running on unpaved roads such as rough terrain, muddy ground, snowy roads, sandy terrain, and rocky terrain are generally tread patterns mainly composed of lug grooves and blocks with many edge components. A thing with a large area is adopted. In such tires, mud, snow, sand, stones, rocks, etc. on the road surface (hereinafter collectively referred to as “mud etc.”) get traction performance, and mud etc. The clogging is prevented and the running performance on an unpaved road is improved (see, for example, Patent Documents 1 and 2).

  When these tires of Patent Documents 1 and 2 are compared, it can be said that the tire of Patent Document 1 is a tire of a type that has a relatively small groove area and that takes into consideration the running performance on a paved road. On the other hand, it can be said that the tire of Patent Document 2 is a type of tire specialized in traveling performance on an unpaved road with a large groove area and large individual blocks. For this reason, the former has lower running performance on an unpaved road than the latter, and the latter tends to have lower performance during normal running than the former. In recent years, the demand performance for tires has been diversified, and there is also a demand for tires for running on unpaved roads that have an intermediate level of performance between these two types of tires. Measures to improve it are needed. In addition, as described above, since the tire for an unpaved road basically has a large groove area mainly composed of blocks, there is a tendency that the stone bite easily occurs on the unpaved road. The prevention performance is also required to be maintained or improved satisfactorily.

Japanese Patent Laid-Open No. 2016-007861 JP 2013-119277 A

  An object of the present invention is to provide a pneumatic tire with improved stone biting prevention performance and running performance on an unpaved road.

  In order to achieve the above object, a pneumatic tire according to the present invention includes a tread portion that extends in the tire circumferential direction to form an annular shape, a pair of sidewall portions disposed on both sides of the tread portion, and the sidewall portions. A pair of main grooves extending in a zigzag manner along the tire circumferential direction on both sides of the tire equator, in the pneumatic tire including a pair of bead portions disposed on the inner side in the tire radial direction of the tire A center land portion defined by the pair of main grooves and positioned on the tire equator, a shoulder land portion defined on the outer side in the tire width direction of the pair of main grooves, and a tire width direction on the shoulder land portions A shoulder lug groove extending along the center land portion and a center lug groove extending obliquely with respect to the tire width direction on the center land portion, and at least the center The groove depth of the groove is smaller than the groove depth of the main groove, and rises from the groove bottom of each of the main groove, the shoulder lug groove, and the center lug groove along the grooves. The convex portion formed in the main groove is composed of a plurality of divided pieces arranged at intervals in the longitudinal direction of the main groove, and each divided piece has a zigzag in the main groove. It extends over the bending part bent in the shape, and is bent, It is characterized by the above-mentioned.

  In the present invention, as described above, a tread pattern mainly composed of a main groove, a shoulder lug groove, and a center lug groove extending in a zigzag shape is formed to improve the running performance on an unpaved road, at least in the center. Since the lug groove is shallower than the main groove so that multiple levels of groove depth are included, the balance between groove volume and land rigidity is improved, and the running performance on unpaved roads is efficiently performed Can be improved. Moreover, since the groove bottom of each groove has a convex portion, it is possible to prevent stone biting by this convex portion. Furthermore, since this convex part functions as an edge component, the traveling performance on an unpaved road can be further improved. At this time, as described above, there are a plurality of groove depths at which the convex portions are formed, so that when the ground is touched, there are a plurality of convex portions at different distances from the road surface, and the three-dimensional edge effect is exhibited. It is possible to improve the running performance on an unpaved road.

  In the present invention, the difference between the groove depth of the main groove and the groove depth of the center lug groove is preferably 1.6 mm or more. As a result, the distance from the road surface to the convex part at the time of ground contact can be made sufficiently different between the main groove and the center lug groove, and the three-dimensional edge effect can be efficiently exhibited, and traveling on an unpaved road It is advantageous to increase performance.

  In the present invention, the protruding height of the convex portion from the groove bottom of the groove in which the convex portion is formed is 0.8 mm or more and is not more than 1/3 of the groove depth of the groove in which the convex portion is formed. It is preferable. Thereby, the magnitude | size of a convex part becomes favorable and the edge effect by a convex part and the stone biting prevention effect can be exhibited with sufficient balance.

  In the present invention, it is preferable that the width of the convex portion is 0.8 mm or more and not more than ½ of the groove width on the tread surface of the groove where the convex portion is formed. Thereby, the magnitude | size of a convex part becomes favorable and the edge effect by a convex part and the stone biting prevention effect can be exhibited with sufficient balance.

  In the present invention, the center lug groove includes a first center lug groove that terminates after reaching the tire equator, and a second center lug groove that terminates without reaching the tire equator, It is preferable that the center lug grooves are alternately arranged in the tire circumferential direction, and the convex portions are formed only in the first center lug grooves. Thereby, the groove shape in a center land part becomes favorable, and the distribution of a convex part can improve the traveling performance in an unpaved road effectively. Further, the convex portions are appropriately arranged in the groove shape, and the running performance on the unpaved road and the stone biting prevention effect can be exhibited with a good balance.

  In the present invention, the divided pieces include a plurality of types having different length ratios on one side and the other side of the bent portion, and the separation distance between the divided pieces adjacent in the tire circumferential direction is 40% to the groove width of the shoulder lug groove. 60% is preferable. Thereby, the shape and arrangement | positioning of the division | segmentation piece which comprises the convex part formed in a main groove become favorable, and the edge effect by the convex part in a main groove and the stone biting prevention effect can be exhibited with sufficient balance.

  In this invention, the ratio of the length along the longitudinal direction of the said center lug groove of the said convex part formed in the said center lug groove with respect to the length of the center lug groove in which the convex part was formed is 60%-80%. It is preferable. Thereby, the ratio of the magnitude | size of the convex part which occupies for a center lug groove | channel becomes favorable, and the edge effect by a convex part and the stone biting prevention effect can be exhibited with sufficient balance.

  In the present invention, when the convex portion is viewed from the tread surface side, the contour line of the longitudinal end portion of the convex portion is a hypotenuse inclined with respect to the groove width direction of the groove in which the convex portion is formed, and one end of the hypotenuse It is preferable that the contour line on the side surface of the convex portion and the hypotenuse form an acute angle on the side, and the contour line on the side surface of the convex portion on the other end side of the hypotenuse side is smoothly connected via the hypotenuse and the arc. Thus, by setting the end shape of the convex portion, the edge effect by the convex portion and the stone biting prevention effect can be exhibited in a balanced manner. Further, the durability of the convex portion itself can be enhanced.

  In the present invention, the term “contacting end” refers to the tire axial direction of the contact region formed when a normal load is applied by placing the tire on a normal rim and filling the normal internal pressure in a vertical state on a plane. It is the both ends of. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO. Then, “Measuring Rim” is set. “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is JATMA, and the table “TIRE ROAD LIMITS AT VARIOUS” is TRA. The maximum value described in “COLD INFRATION PRESURES”, “INFLATION PRESSURE” in the case of ETRTO, is 180 kPa when the tire is for passenger cars. “Regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum load capacity is JATMA, and the table “TIRE ROAD LIMITS AT VARIOUS” is TRA. The maximum value described in “COLD INFORMATION PRESURES”, “LOAD CAPACITY” if it is ETRTO, but if the tire is for a passenger car, the load is equivalent to 88% of the load.

1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. It is a front view which shows the tread surface of the pneumatic tire which consists of embodiment of this invention. It is explanatory drawing which expands and shows the principal part of this invention. It is XX arrow sectional drawing of FIG. It is a schematic diagram for demonstrating the shape of the convex part of this invention.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the pneumatic tire of the present invention is disposed on a tread portion 1, a pair of sidewall portions 2 disposed on both sides of the tread portion 1, and on the tire radial direction inner side of the sidewall portion 2. And a pair of bead portions 3. In FIG. 1, reference sign CL indicates a tire equator, and reference sign E indicates a ground contact end. Although FIG. 1 is a meridian cross-sectional view and is not depicted, the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape. The toroidal basic structure is constructed. Hereinafter, the description using FIG. 1 is basically based on the meridian cross-sectional shape shown in the figure, but each tire component extends in the tire circumferential direction to form an annular shape.

  A carcass layer 4 is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back around the bead core 5 disposed in each bead portion 3 from the vehicle inner side to the outer side. A bead filler 6 is disposed on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by the main body portion and the folded portion of the carcass layer 4. On the other hand, a plurality of layers (two layers in FIG. 1) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and is disposed so that the reinforcing cords cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. Further, a belt reinforcing layer 8 is provided on the outer peripheral side of the belt layer 7. The belt reinforcing layer 8 includes an organic fiber cord oriented in the tire circumferential direction. In the belt reinforcing layer 8, the organic fiber cord has an angle with respect to the tire circumferential direction set to, for example, 0 ° to 5 °.

  The present invention is applied to a pneumatic tire having such a general cross-sectional structure, but its basic structure is not limited to the above.

  On the surface of the tread portion 1 of the pneumatic tire of the present invention, as shown in FIGS. 2 and 3, a pair of main grooves 10 extending in a zigzag shape along the tire circumferential direction is formed on both sides of the tire equator CL. The A zigzag shape means that the part that goes straight in a predetermined direction and the part that goes straight in a different direction from this part are alternately repeated and bent along the tire circumferential direction, as shown in the example in the figure. It is. As shown in FIGS. 3 and 4, the main groove 10 has a groove width w1 of, for example, 8 mm to 18 mm, and a groove depth d1 of 10 mm to 20 mm. In addition, the groove width w1 and the groove depth d1 of the main groove 10 are values measured in the above-described straight traveling portion.

  By the pair of main grooves 10, a shoulder land portion 11 that is partitioned outside the main groove 10 in the tire width direction and a center land portion 12 that is partitioned between the pair of main grooves 10 are formed in the tread portion 1. The In the example shown in FIG. 2, a shoulder lug groove 20 extending along the tire width direction is formed in the shoulder land portion 11, and a center lug extending obliquely with respect to the tire width direction is formed in the center land portion 12. A groove 30 is formed. Hereinafter, the description will be made based on the embodiment of FIG. 2, but the present invention mainly relates to a convex portion 40 described later formed on the groove bottoms of the main groove 10, the shoulder lug groove 20, and the center lug groove 30. Therefore, the specific tread pattern is not necessarily limited to the illustrated example.

  One end of the shoulder lug groove 20 communicates with the main groove 10 and the other end extends beyond the grounding end E to partition the shoulder land portion 11 into a shoulder block 11 ′. The width and depth of the shoulder lug groove 20 can be equal to or less than those of the main groove 10. Specifically, the groove width w2 of the shoulder lug groove 20 at the opening position with respect to the main groove 10 is preferably 50% to 100% of the groove width w1 of the main groove 10, and the groove depth d2 of the shoulder lug groove 20 is the main groove 10. Preferably, the groove depth d1 can be set to 75% to 100%. In the shoulder block 11 ', a sipe S and a stud pin implantation hole P can be provided as in the illustrated example in order to further improve the running performance on an unpaved road.

  The center lug groove 30 has one end communicating with the main groove 10 and the other end terminating in the center land portion 12. In the illustrated example, the center lug groove 30 includes two types of a first center lug groove 31 and a second center lug groove 32 having different terminal positions in the center land portion 12. Specifically, the first center lug groove 31 reaches the tire equator CL and terminates, and the second center lug groove 32 terminates without reaching the tire equator CL. These first center lug grooves 31 and second center lug grooves 32 are alternately arranged in the tire circumferential direction. Any of the center lug grooves 30 (the first center lug 31 and the second center lug groove 32) are inclined at an angle of, for example, 45 ° to 70 ° with respect to the tire width direction. The groove width w3 of the center lug groove 30 can be made equal to or less than the groove width w1 of the main groove 10. For example, the groove width w 3 of the center lug groove 30 at the center position in the longitudinal direction of the center lug groove 30 can be set to 50% to 100% of the groove width w 1 of the main groove 10. On the other hand, the groove depth d3 of the center lug groove 30 is set smaller than the groove depth d1 of the main groove 10. That is, in the present invention, the groove depth d3 of the center lug groove 30 and the groove depth d1 of the main groove 10 always satisfy the relationship d1> d3. The magnitude relationship between the groove depth d3 of the center lug groove 30 and the groove depth d2 of the shoulder lug groove 20 is not particularly limited, but preferably satisfies the relationship of d2> d3.

  Although the positional relationship between the shoulder lug groove 20 and the center lug groove 30 is not particularly limited, for example, a part of the main groove 10 extending in a zigzag shape is inclined in the same direction as the center lug groove 30 as in the illustrated example. This part relays between the shoulder lug groove 20 and the center lug groove 30, and the shoulder lug groove 20, a part of the main groove 10 and the center lug groove 30 are smoothly continuous. It is preferable in terms of soil properties and edge effect.

  In addition to the above-described center lug groove 30, a connection groove 50 that connects the center lug grooves 30 can also be provided in the center land portion 12 in order to further improve traveling performance on an unpaved road. The groove width of the connection groove 50 is preferably smaller than the groove width of the center lug groove 30, and the groove depth d5 of the connection groove 50 is preferably smaller than the groove depth d3 of the center lug groove 30. The connecting groove 50 is not formed with a protrusion 40 described later. The center land portion 12 may be provided with a sipe S as in the illustrated example in order to further improve the running performance on an unpaved road.

  In the present invention, convex portions 40 are formed on the respective groove bottoms of the main groove 10, the shoulder lug groove 20, and the center lug groove 30 so as to protrude from the groove bottom of each groove and extend along each groove. The In the following description, among these convex portions 40, those formed in the main groove, those formed in the first convex portion 41, and the shoulder lug groove 20 are formed in the second convex portion 42 and the center lug groove 30. May be referred to as a third convex portion 43. Each raised portion 40 does not occupy the entire width of the groove at the site when it rises from the groove bottom of each groove, but is provided at the center of each groove apart from the groove wall of each groove as shown in the figure. is there.

  The 1st convex part 41 formed in the main groove 10 does not extend continuously over the perimeter along the main groove 10 extended over the tire perimeter, but the extension direction of the main groove 10 Are formed of a plurality of divided pieces 41a and 41b spaced apart from each other. Each divided piece 41a, 41b extends across a bent portion where the main groove 10 is bent in a zigzag shape, and each divided piece 41a, 41b itself is also bent. Each of the divided pieces 41a and 41b may have the same shape, but from the viewpoint of efficiently exhibiting the edge component, one of the bending points where the divided pieces 41a and 41b bend as the divided pieces 41a and 41b. It is preferable to provide a plurality of types having different length ratios on the side and the other side. For example, in the illustrated example, the length ratio is different between one side and the other side of the bending point between the divided piece 41a and the divided piece 41b.

  In the present invention, as described above, a tread pattern mainly composed of the main groove 10, the shoulder lug groove 20, and the center lug groove 30 extending in a zigzag shape is formed to enhance the running performance on an unpaved road. Since at least the center lug groove 20 is shallower than the main groove 10 so that a plurality of groove depths are included, the balance between the groove volume and the land portion rigidity is improved, and the vehicle runs on an unpaved road. The performance can be improved efficiently. Moreover, since the convex part 40 is provided in the groove bottom of each groove | channel, the stone biting can be prevented by this convex part 40. Furthermore, since this convex part 40 functions as an edge component, the running performance on an unpaved road can be further improved. At this time, as described above, there are a plurality of levels of groove depths at which the protrusions 40 are formed. Therefore, the plurality of protrusions 40 are present at different distances from the road surface when grounded, resulting in a three-dimensional edge effect. Can be exhibited, and the running performance on an unpaved road can be improved efficiently.

At this time, if the main groove 10, the shoulder lug groove 20 and the center lug groove 30 have the same groove depth, the groove volume becomes too large, the rigidity of the land portion decreases, and good running performance on an unpaved road is ensured. It becomes difficult to do. In addition, the above-described three-dimensional edge effect cannot be obtained.
In order to effectively exhibit the above-described three-dimensional edge effect, the groove depth d1 of the main groove 10, the groove depth d2 of the shoulder lug groove 20, and the groove depth d3 of the center lug groove 30 are d1 = d2>. d3 is set to the relationship of d3, or the groove depth d1 of the main groove 10, the groove depth d2 of the shoulder lug groove 20, and the groove depth d3 of the center lug groove 30 are set to d1. It is preferable to set the relationship of>d2> d3 and set the groove depth to three levels. With other groove depth relationships, the relationship between the position in the width direction of the tread portion 1 and the groove depth (block rigidity, position from the road surface of the convex portion 40 at the time of ground contact) is not necessarily appropriate, and the unpaved road The effect of improving the running performance is limited.

  With respect to the shoulder lug groove 20 and the center lug groove 30 arranged at intervals in the tire circumferential direction, it is not always necessary to provide the convex portions 40 in all the grooves. For example, the effect of the present invention can be sufficiently exerted if the convex portions 40 are formed in more than half of the lug grooves included in the ground plane. In the illustrated example, with respect to the shoulder lug grooves 20, convex portions 40 (second convex portions 42) are formed in all the shoulder lug grooves 20, and with respect to the center lug grooves 30, two types of center lug grooves having different end positions are formed. Of the 30 (first center lug groove 31 and second center lug groove 32), the convex part 40 (third convex part 43) is formed only in the first center lug groove 31. In particular, when two types of center lug grooves 30 (first center lug groove 31 and second center lug groove 32) having different end positions are included as in the illustrated example, only the first center lug groove 31 has a convex portion. By providing 40 (third convex portion 43), the balance between the rigidity of the center land portion 12, the groove volume of the center lug groove 30, and the amount of the convex portion 40 can be improved, and the running performance on an unpaved road. It will be advantageous to improve.

  In the present invention, as described above, the center lug groove 30 is configured to be shallower than the main groove 10, but at this time, the difference between the groove depth d 1 of the main groove 10 and the groove depth d 3 of the center lug groove 30. Δd (= d1−d3) is preferably set to 1.6 mm or more, more preferably 2 mm to 8 mm. By setting the groove depth difference Δd in this way, the distance from the road surface to the convex portion 40 at the time of ground contact can be made sufficiently different between the main groove 10 and the center lug groove 30, and the three-dimensional edge effect It is advantageous for improving the running performance on an unpaved road. At this time, if the difference Δd in the groove depth is less than 1.6 mm, the difference in depth between the main groove 10 and the center lug groove 30 is reduced, and it becomes difficult to sufficiently secure the three-dimensional edge effect. .

  Although the groove depth d2 of the shoulder lug groove 20 is not particularly limited as described above, for example, when the groove depth of each groove satisfies the relationship d1> d2> d3, the groove depth d1 of the main groove 10 And the groove depth d2 of the shoulder lug groove 20 may be set to 2 mm to 8 mm, for example, and the difference between the groove depth d2 of the shoulder lug groove 20 and the groove depth d3 of the center lug groove 30 may be set to 2 mm to 6 mm, for example. .

  As schematically shown in FIG. 5, each convex portion 40 has a groove G (main groove 10, shoulder) in which convex portions 40 (first convex portion 41, second convex portion 42, third convex portion 43) are formed. The raised height h from the groove bottom of the lug groove 20 and the center lug groove 30) is 0.8 mm or more, and the convex portion 40 (first convex portion 41, second convex portion 42, third convex portion 43). It is preferable that it is 1/3 or less of the groove depth D (d1, d2, d3) of the groove G (the main groove 10, the shoulder lug groove 20, the center lug groove 30) in which is formed. Further, the width w4 of the convex portion 40 (first convex portion 41, second convex portion 42, third convex portion 43) is 0.8 mm or more, and the convex portion 40 (first convex portion 41, second convex portion). The groove 42 (the main groove 10, the shoulder lug groove 20, and the center lug groove 30) in which the portion 42 and the third convex portion 43) are formed is ½ or less of the groove width W (w1, w2, w3) on the tread surface. Preferably there is. Thus, by setting the dimension of each convex part 40 (the 1st convex part 41, the 2nd convex part 42, the 3rd convex part 43), the magnitude | size of each convex part 40 becomes favorable and it depends on the convex part 40. The edge effect and the stone biting prevention effect can be exhibited with a good balance. In addition, the groove | channel G of FIG. 5 simplified the shape of the main groove 10, the shoulder lug groove 20, and the center lug groove 30 in order to demonstrate the shape of the convex part 40, and was shown as a common drawing.

  If the raised height h of the convex portion 40 is less than 0.8 mm, the convex portion 40 does not sufficiently rise, and it becomes difficult to sufficiently secure the edge effect and the stone biting prevention effect by the convex portion 40. When the protruding height h of the convex portion 40 exceeds 1/3 of the groove depth D of the groove G, the ratio of the convex portion 40 to the groove G becomes excessive, and there is a possibility that the soil removal property may be affected. When the width w4 of the convex portion 40 is less than 0.8 mm, the convex portion 40 becomes too small, and it becomes difficult to sufficiently secure the edge effect and the stone biting prevention effect by the convex portion 40. Moreover, it becomes difficult to ensure the durability of the convex portion 40 itself. When the width w4 of the convex portion 40 exceeds 1/2 of the groove width W, the proportion of the convex portion 40 in the groove G becomes excessive, and there is a possibility that the soil removal property may be affected. In order to satisfy this dimension, in order to further improve the proportion of the convex portion 40 in the groove G, the cross-sectional area of the convex portion 40 is preferably set to, for example, 15% to 30% of the cross-sectional area of the groove G.

  The first convex portion 41 formed in the main groove 10 is composed of the plurality of divided pieces 41a and 41b as described above, but the separation distance between the divided pieces 41a and 41b adjacent in the tire circumferential direction is the shoulder lug groove. It is preferably 40% to 60% of the groove width w2 of 42. Thus, by appropriately separating the divided pieces 41a and 41b, the arrangement and distribution of the first convex portions 41 (divided pieces 41a and 41b) in the main groove 10 are improved, and the first convex portions in the main groove 10 are obtained. The edge effect by 41 and the stone biting prevention effect can be exhibited with good balance. If the separation distance between the divided pieces 41a and 41b is less than 40% of the groove width w2 of the shoulder lug groove 42, the divided pieces 41a and 41b are too close to each other, and the first convex portion 41 continues over the entire circumference of the tire. Substantially the same as the case where it extends, the flow of water, mud, etc. from the shoulder lug groove 20 or the center lug groove 30 to the main groove 10 is likely to be obstructed, and the function of the main groove 10 may be reduced. There is. When the separation distance between the divided pieces 41a and 41b exceeds 60% of the groove width w2 of the shoulder lug groove 42, the area where the first convex portion 41 (the divided pieces 41a and 41b) does not exist in the main groove 10 becomes large, It becomes difficult to sufficiently secure the effect of the one convex portion 41.

  It is preferable that the 2nd convex part 42 formed in the shoulder lug groove 20 extends over the full length of the shoulder lug groove 20 in which the 2nd convex part 42 was formed like the example of illustration. That is, one end in the longitudinal direction of the second convex portion 42 extends beyond the ground contact end E and reaches the end on the side wall 2 side of the shoulder block 11 ′, while the longitudinal direction of the second convex portion 42 is reached. It is preferable that the other end reaches the opening of the shoulder lug groove 20. In particular, when the length along the longitudinal direction of the shoulder lug groove 20 from the ground contact E to the opening is Ls, the length L2 of the second protrusion 42 is 100% to 115% of the length Ls. It is preferable.

  On the other hand, the third protrusion 43 formed in the center lug groove 30 does not need to extend over the entire length of the center lug groove 30 in which the third protrusion 43 is formed. Rather, the third convex portion 43 should be reasonably short with respect to the center lug groove. Specifically, when the length along the groove longitudinal direction from the opening end to the end of the center lug groove 30 is Lc, The length L3 of the third convex portion 43 is preferably 60% to 80% of the length Lc. Thereby, the ratio of the magnitude | size of the convex part which occupies for the center lug groove | channel 30 becomes favorable, and the edge effect and the stone biting prevention effect by the 3rd convex part 43 can be exhibited with sufficient balance. If the length L3 of the third convex portion 43 is less than 60% of the length Lc of the center lug groove 30, the third convex portion 43 becomes excessively small, and the edge effect and the stone biting prevention effect by the third convex portion 43 are obtained. It becomes difficult to fully demonstrate. When the length L3 of the third convex portion 43 exceeds 80% of the length Lc of the center lug groove 30, the ratio of the third convex portion 43 to the center lug groove 30 increases, and the groove volume of the center lug groove 30 is reduced. It becomes difficult to secure enough.

  When the convex portion 40 is viewed from the tread surface side, the end line of each convex portion 40 is inclined with respect to the groove width direction of the groove in which the convex portion 40 is formed. It is a hypotenuse, and the contour of the side surface of the convex portion 40 and the hypotenuse form an acute angle at one end of the hypotenuse, and the contour of the side of the convex portion 40 is smooth through the hypotenuse and the arc at the other end of the hypotenuse. It is preferable to connect to. In particular, in the case of the example shown in FIGS. 2 and 3, the hypotenuse of the first convex portion 41 may be inclined substantially parallel to the facing groove wall surface at the end facing the center lug groove 30. 12 is preferably inclined in a direction intersecting the opposing groove wall surface. The oblique side of the second convex portion 42 may be inclined in the same direction as the oblique side of the end portion of the first convex portion 41 located on the extension line of the second convex portion 42. The oblique side of the third convex portion 43 is preferably substantially parallel to the groove wall surface at the end of the center lug groove 30 and the land wall surface at the opening. Thus, by obtaining the edge part shape of the convex part 40, the edge effect by the convex part 40 and the stone biting prevention effect can be exhibited with sufficient balance. Moreover, durability of the convex part 40 itself can also be improved.

  The tire size is LT265 / 70R17 121Q, and has the basic structure illustrated in FIG. 1, based on the tread pattern of FIG. 2, and the groove depth d1 of the main groove, the groove width w1 of the main groove, and the first convex portion Width, raised height of the first convex part, type of divided piece, separation distance between adjacent divided pieces in the tire circumferential direction, groove depth d2 of the shoulder lug groove, groove width w2 of the shoulder lug groove, second convex part Width, raised height of second convex portion, groove depth d3 of center lug groove, groove width w3 of center lug groove, arrangement of center lug groove, width of third convex portion, raised height of third convex portion The length of the third convex part, the size relationship between the groove depths d1 to d3, the difference Δd between the groove depth d1 and the groove depth d3, and the end part shape of the convex part were set as shown in Tables 1 to 3, respectively. 24 types of pneumatic tires of Comparative Example 1 and Examples 1 to 23 were produced.

  About the column of “type of divided piece” in Tables 1 to 3, when two types of divided pieces having different length ratios are included on one side and the other side of the bending point of the divided piece, as in the illustrated example. “Two types”, and “one type” when the length ratio is the same on one side and the other side of the bending point of the divided pieces for all the divided pieces. In the column of “Separation distance of divided pieces” in Tables 1 to 3, the ratio (%) to the groove width of the shoulder lug groove is displayed. About the column of "arrangement of center lug groove" of Tables 1-3, the case where a convex part is formed in both the first center lug groove and the second center lug groove is only "all grooves", only the first center lug groove The case where the convex portion was formed was indicated as “first only”. About the column of "end part shape of a convex part" of Tables 1-3, when the edge part has the shape shown in figure, it is "illustration shape", the outline of the longitudinal direction edge part of a convex part when it sees from the tread tread side The case where is parallel to the groove width direction and perpendicular to the contour line of the side surface of the convex portion 40 is indicated as “rectangular”.

  About these pneumatic tires, the stone biting prevention performance and the start performance were evaluated by the following evaluation methods, and the results are also shown in Tables 1 to 3.

Stone biting prevention performance Each test tire is mounted on a wheel with a rim size of 17 x 8 J, mounted on a test vehicle (four-wheel drive SUV) with an air pressure of 350 kPa, and a test driver on a test road consisting of an unpaved road (gravel road surface). After carrying out a running test according to, the number of stone bites was counted. The evaluation results are shown as an index using the reciprocal of the count value and the value of Comparative Example 1 as 100. The larger the index value, the smaller the number of stone bites, which means that the stone biting prevention performance is excellent.

Startability Each test tire is assembled to a wheel with a rim size of 17 × 8J, mounted on a test vehicle (SUV with four-wheel drive) at an air pressure of 350 kPa, and the startability is tested on a test road consisting of an unpaved road (gravel road surface). Sensory evaluation by a driver was performed. The evaluation results are shown as an index with the value of Comparative Example 1 as 100. A larger index value means better startability on an unpaved road.

  As is apparent from Tables 1 to 3, all of Examples 1 to 24 improved the stone biting prevention performance and the start performance effectively as compared with Comparative Example 1. Although only the startability on the gravel road surface was evaluated, the tire of the present invention can be used for mud and rocks on the road surface even when traveling on other unpaved roads (such as muddy roads, rocky places, and snowy roads). Since it acts effectively on snow and the like, it can exhibit excellent starting performance on any unpaved road.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Belt reinforcement layer 10 Main groove 11 Shoulder land part 11 'Shoulder block 12 Center land part 20 Shoulder lug groove 30 Center lug groove 31st One center lug groove 32 Second center lug groove 40 Convex part 41 First convex part 41a, 41b Dividing piece 42 Second convex part 43 Third convex part CL Tire equator E Grounding end

Claims (8)

An annular tread portion extending in the tire circumferential direction, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed on the inner side in the tire radial direction of the sidewall portions. In the provided pneumatic tire,
A pair of main grooves extending in a zigzag manner along the tire circumferential direction on both sides of the tire equator in the tread portion, a center land portion that is partitioned by the pair of main grooves and located on the tire equator; A shoulder land portion partitioned on the outer side in the tire width direction of the pair of main grooves, a shoulder lug groove extending along the tire width direction on the shoulder land portion, and a tire width direction on the center land portion And a center lug groove extending in an inclined manner, at least the groove depth of the center lug groove is smaller than the groove depth of the main groove,
The main groove, the shoulder lug groove, and the center lug groove are each formed with a convex portion that protrudes from the groove bottom of each groove and extends along each groove.
The convex portion formed in the main groove is composed of a plurality of divided pieces arranged at intervals in the longitudinal direction of the main groove, and each divided piece extends across the bent portion where the main groove is bent in a zigzag shape. A pneumatic tire characterized by being bent.   The pneumatic tire according to claim 1, wherein a difference between a groove depth of the main groove and a groove depth of the center lug groove is 1.6 mm or more.   The protruding height of the convex part from the groove bottom of the groove in which the convex part is formed is 0.8 mm or more, and is not more than 1/3 of the groove depth of the groove in which the convex part is formed. The pneumatic tire according to claim 1 or 2, characterized in that.   The width of the convex part is 0.8 mm or more, and is 1/2 or less of the groove width in the tread surface of the groove in which the convex part is formed. Pneumatic tires.   The center lug groove includes a first center lug groove that reaches the tire equator and terminates, and a second center lug groove that terminates without reaching the tire equator, and the first center lug groove and the second center The pneumatic tire according to any one of claims 1 to 4, wherein the lug grooves are alternately arranged in a tire circumferential direction, and the convex portion is formed only in the first center lug groove.   The divided pieces include a plurality of types having different length ratios on one side and the other side of the bent portion, and the separation distance between the divided pieces adjacent in the tire circumferential direction is 40% to 60% of the groove width of the shoulder lug groove. The pneumatic tire according to claim 1, wherein the pneumatic tire is a tire.   The ratio of the length along the longitudinal direction of the center lug groove of the convex portion formed in the center lug groove to the length of the center lug groove formed with the convex portion is 60% to 80%. The pneumatic tire according to any one of claims 1 to 6, characterized in that   When the convex portion is viewed from the tread tread side, the contour line of the longitudinal end portion of the convex portion is an oblique side inclined with respect to the groove width direction of the groove in which the convex portion is formed, and one end side of the oblique side The contour line of the side surface of the convex portion and the hypotenuse form an acute angle, and the contour line of the side surface of the convex portion is smoothly connected to the hypotenuse side via an arc on the other end side of the hypotenuse side. The pneumatic tire according to any one of claims 1 to 7.

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