JP2016068628A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving chipping resistance while maintaining mud performance.SOLUTION: There is provided a pneumatic tire in which a pair of main grooves 3 extending zigzag on both sides of a tire equator C continuing in a tire circumferential direction, and a plurality of crown lateral grooves 9 partitioning plural crown blocks 8C by joining between the main grooves 3 are formed on a tread 2. Each crown block 8C has a crown recessed part 10 in which a part of a tread 8S dents inside in a tire radial direction to continue into one adjacent crown lateral groove 9, and the crown recessed part 10 is formed departing from both side main grooves 3. In the pneumatic tire in this invention, difference between partial rigidities of the crown blocks 8C is reduced and furthermore, chipping resistance is improved.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire that achieves both mud performance and chipping resistance.

  Patent Document 1 below discloses a plurality of main grooves extending in a zigzag manner on the tread portion on both sides of the tire equator in the tire circumferential direction, and a plurality of crown blocks that are divided into a plurality of crown blocks by connecting the main grooves. An off-road pneumatic tire having a lateral groove is proposed. The crown block has a crown recess in which a part of the tread surface is recessed inward in the tire radial direction. Such tires generate large gripping force by driving and muddying the mud by the crown recess when traveling in the muddy area (hereinafter, the muddy road running performance is referred to as “mad performance”). There is.)

JP-A-5-278415

  Generally, since the main groove of the off-road tire has a large groove depth and groove width, the rigidity of the portion of the crown block facing the main groove is small. On the other hand, in the tire of Patent Document 1, the crown recess is formed at a position continuous with the main groove. As a result, the rigidity of the crown block in the vicinity of the crown recess facing the main groove is significantly reduced, and as a result, the difference in rigidity between the portion of the crown block facing the main groove and the portion away from the main groove tends to increase. It was. There is a problem in that stress concentrates on the portion having relatively small rigidity during traveling, and block chipping such as chipping is likely to occur near the crown recess facing the main groove of the crown block.

  This invention is made | formed in view of the above actual conditions, and makes it the main objective to provide the pneumatic tire which can improve chipping-proof performance, maintaining a mud performance.

  The present invention provides a tread portion having a pair of main grooves extending zigzag continuously on both sides of the tire equator in the tire circumferential direction, and a plurality of crown transverse grooves for dividing a plurality of crown blocks by connecting the main grooves. Each of the crown blocks has a crown recess in which a part of the tread surface is recessed inwardly in the tire radial direction so as to be connected to the adjacent one of the crown lateral grooves. The main grooves on both sides are formed apart from each other.

  In the pneumatic tire according to the present invention, it is desirable that the depth of the crown recess is smaller than the depth of the crown lateral groove.

  In the pneumatic tire according to the present invention, each main groove includes a first main groove and a second main groove, and each of the first main groove and the second main groove is one in the tire circumferential direction. A first inclined portion that is inclined to the side, a second inclined portion that is inclined to the opposite side of the first inclined portion, and an inner top portion that protrudes inward in the tire axial direction, wherein the crown transverse groove is a first crown transverse groove And a second crown transverse groove, wherein the first crown transverse groove joins each inner top portion of the first main groove and the first inclined portion of the second main groove, and the second crown transverse groove is It is desirable to connect each inner top part of the second main groove and the second inclined part of the first main groove.

  In the pneumatic tire according to the present invention, it is preferable that the first inclined portion and the second inclined portion are inclined at an angle of 30 to 40 degrees with respect to the tire circumferential direction.

  In the pneumatic tire according to the present invention, it is preferable that the groove width of the crown lateral groove is in a range of 35% to 75% of the groove width of the main groove.

  In the pneumatic tire according to the present invention, it is preferable that the crown lateral groove is inclined at an angle of 30 to 40 degrees with respect to the tire axial direction.

  In the pneumatic tire according to the present invention, the tread portion is provided with a plurality of shoulder lateral grooves extending outward in the tire axial direction from the main groove, and each shoulder lateral groove includes a first lateral groove portion continuous with the main groove; A second lateral groove portion that is continuous with the outer side in the tire axial direction of the first lateral groove portion and has a larger groove width and depth than the first lateral groove portion, and one groove wall of the first lateral groove portion is It is desirable that the second lateral groove portion is smoothly continuous with one of the groove walls.

  The pneumatic tire according to the present invention includes a pair of main grooves extending in a zigzag shape continuously on the tread portion on both sides of the tire equator in the tire circumferential direction, and a plurality of crown blocks divided by connecting between the main grooves. Are formed. Since such a pneumatic tire generates a large reaction force when shearing mud compacted in the main groove and the crown lateral groove, it can exhibit excellent mud performance.

  Each crown block has a crown recess in which a part of the tread surface is recessed inward in the tire radial direction so as to be connected to one of the adjacent crown lateral grooves. Such a crown concave portion generates a large reaction force when shearing the mud pressed in the concave portion, and is useful for improving the mud performance.

  The crown recess is formed away from the main grooves on both sides. Since such a crown recess is provided apart from the main groove of the crown block, a local reduction in rigidity due to the crown recess is prevented. For this reason, in the crown block of the present invention, the difference in rigidity between the portion where the rigidity is relaxed by the crown recess apart from the main groove and the portion where the rigidity facing the main groove is small is small. Therefore, the crown block of the pneumatic tire of the present invention can reduce a portion having a small local rigidity, and thus improve the chipping resistance there.

It is an expanded view of the tread part of one Embodiment of this invention. It is AA sectional drawing of FIG. FIG. 2 is a partially enlarged view near the tire equator of FIG. 1. It is the elements on larger scale of the shoulder land part vicinity of the right side of FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a development view of the tread portion 2 of the pneumatic tire according to the present embodiment (hereinafter sometimes simply referred to as “tire”). The pneumatic tire of this embodiment can be suitably used for a four-wheel drive vehicle such as an SUV.

  As shown in FIG. 1, the tread portion 2 is provided with a main groove 3 extending on both sides of the tire equator C. The main groove 3 includes, for example, a first main groove 3a extending on one side (right side in the figure) of the tire equator C and a second main groove 3b extending on the other side (left side in the figure) of the tire equator C.

  Each of the first main groove 3a and the second main groove 3b extends in a zigzag shape continuously in the tire circumferential direction. The first main groove 3a and the second main groove 3b of the present embodiment have the same zigzag pitch and are arranged so that the phases of the zigzag are aligned with each other.

  The first main groove 3a and the second main groove 3b include first inclined portions 4 and second inclined portions 5 alternately in the tire circumferential direction, respectively. The first inclined portion 4 is inclined to one side with respect to the tire circumferential direction. The second inclined portion 5 is inclined to the opposite side to the first inclined portion 4.

  Each of the first main groove 3a and the second main groove 3b includes a zigzag top portion 6 between the first inclined portion 4 and the second inclined portion 5 that are adjacent to each other in the tire circumferential direction. The zigzag top portion 6 includes an outer zigzag top portion 6a that protrudes outward in the tire axial direction and an inner zigzag top portion 6b that protrudes inward in the tire axial direction.

  Such 1st main groove 3a and 2nd main groove 3b shear the mud compacted in the groove | channel by the 1st inclination part 4 and the 2nd inclination part 5, respectively. Thereby, in the tire of this embodiment, a large reaction force is generated even in a muddy area, and excellent mud performance can be exhibited. Further, the zigzag-shaped first main groove 3a and second main groove 3b are less likely to generate air column resonance sound while traveling on a dry road surface, and thus are useful for reducing passing noise. From these viewpoints, the first inclined portion 4 and the second inclined portion 5 are preferably inclined at an angle α of, for example, 25 to 35 degrees with respect to the tire circumferential direction. Moreover, as for the 1st inclination part 4 and the 2nd inclination part 5, it is desirable to each extend linearly.

  Each of the first main groove 3a and the second main groove 3b preferably has a zigzag amplitude W1 in the range of 20% to 30% of the tread width TW, which is the distance between the tread ends Te, for example. When the zigzag amplitude W1 is less than 20% of the tread width TW, there is a possibility that a large reaction force is not generated by the first inclined portion 4 and the second inclined portion 5 when traveling in a muddy area. On the other hand, when the zigzag amplitude W1 is larger than 30% of the tread width TW, it may be difficult to compact mud in the grooves of the first main groove 3a and the second main groove 3b. In either case, there is a possibility that the mud performance cannot be fully exhibited.

  In the present specification, the “tread end” is a position on the outermost side in the tire axial direction of the contact surface of the tread portion 2 when a normal tire is loaded with a normal load and brought into contact with a plane with a camber angle of 0 °. It is.

  The “normal state” is a no-load state in which a tire is assembled on a normal rim (not shown) and filled with a normal internal pressure. In the present specification and claims, unless otherwise specified, the dimensions of each part of the tire are values in a normal state.

  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, “Standard Rim” for JATMA, “Design Rim” for TRA, For ETRTO, "Measuring Rim".

  “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. For example, “maximum air pressure” for JATMA, “TIRE” for TRA The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” in the case of ETRTO.

  “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. For example, “maximum load capacity” for JATMA, “table for TRA” The maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” in the case of ETRTO.

  FIG. 2 shows an AA end view of FIG. As shown in FIG. 2, the maximum groove width W2 of the first main groove 3a is, for example, in the range of 5% to 10% of the tread width TW (shown in FIG. 1) from the same viewpoint as the zigzag amplitude W1. Is desirable. From the same point of view, the groove depth D1 of the first main groove 3a and the second main groove 3b is preferably in the range of 10 to 20 mm, for example. In addition, it is desirable that the maximum groove width and the groove depth of the second main groove 3b of the present embodiment are approximately the same as the maximum groove width W2 and the groove depth D1 of the first main groove 3a.

  FIG. 3 is a partially enlarged view of the vicinity of the tire equator C in FIG. As shown in FIG. 1 or FIG. 3, in the present embodiment, the crown land portion 8 is divided between the first main groove 3a and the second main groove 3b.

  In the crown land portion 8 of the present embodiment, the zigzag phases of the first main groove 3a and the second main groove 3b are aligned with each other, so that the width in the tire axial direction is constant and the zigzag shape in the tire circumferential direction is formed. It is extended. The crown land portion 8 is provided with a plurality of crown lateral grooves 9. Thereby, the crown land portion 8 is divided into a plurality of crown blocks 8C.

  The crown lateral groove 9 connects between the first main groove 3a and the second main groove 3b. The crown lateral grooves 9 of the present embodiment include first crown lateral grooves 9a and second crown lateral grooves 9b that are alternately arranged in the tire circumferential direction.

  The first crown lateral groove 9a is inclined in the same direction as the second inclined portion 5 of the first main groove 3a. The second crown lateral groove 9b is inclined in the same direction as the first inclined portion 4 of the second main groove 3b, that is, is inclined to the opposite side to the first crown lateral groove 9a. Each of the first crown lateral groove 9a and the second crown lateral groove 9b preferably extends linearly.

  The first crown lateral groove 9a of the present embodiment connects between the inner zigzag top 6b of the first main groove 3a and the first inclined portion 4 of the second main groove 3b. Preferably, the first crown lateral groove 9a is connected to, for example, an intermediate portion in the longitudinal direction of the first inclined portion 4 of the second main groove 3b.

  The second crown lateral groove 9b of the present embodiment is connected between the inner zigzag top portion 6b of the second main groove 3b and the second inclined portion 5 of the first main groove 3a. Preferably, the second crown lateral groove 9b is connected to, for example, an intermediate portion in the longitudinal direction of the second inclined portion 5 of the first main groove 3a.

  The first crown transverse groove 9a and the second crown transverse groove 9b can generate a large reaction force by shearing the mud compacted in the groove in the muddy ground, thereby further improving the mud performance. From such a viewpoint, it is desirable that the first crown lateral groove 9a is inclined at an angle β of, for example, 30 to 40 degrees with respect to the tire axial direction. From the same point of view, it is desirable that the second crown lateral groove 9b is inclined at the same angle as the first crown lateral groove 9a, for example, with respect to the tire axial direction.

  As shown in FIG. 2 or 3, the groove width W3 of the first crown lateral groove 9a is, for example, in the range of 35% to 75% of the groove width W2 of the first main groove 3a in order to maintain high mud performance. It is desirable that Similarly, the groove depth D2 of the first crown lateral groove 9a is desirably in the range of 70% to 90% of the groove depth D1 of the first main groove 3a and the second main groove 3b, for example. From the same viewpoint, it is desirable that the groove width and the groove depth of the second crown lateral groove 9b are approximately the same as the groove width W3 and the groove depth D2 of the first crown lateral groove 9a.

  As shown in FIG. 3, the crown block 8 </ b> C preferably has a polygonal tread surface in order to increase the frictional force with respect to the road surface by causing its edges to act in various directions. The main groove 3a, the second main groove 3b, the first crown lateral groove 9a, and the second crown lateral groove 9b are divided into substantially pentagonal shapes.

  In the crown block 8C of the present embodiment, the maximum width W4 in the tire axial direction is, for example, 20 of the tread width TW (shown in FIG. 1) in order to ensure frictional force with the road surface while maintaining high mud performance. It is desirable to be in the range of% -50%. The crown block 8C has a maximum length L1 in the tire circumferential direction in the range of, for example, 50% to 200% of the maximum width W4 in the tire axial direction in order to maintain mud performance and chipping resistance. desirable.

  A crown recess 10 is provided in the crown block 8C. The crown recess 10 is a recess in which a part of the tread surface 8S is recessed inward in the tire radial direction. The crown recess 10 is provided so as to continue to one of the first crown lateral grooves 9a or the second crown lateral grooves 9b adjacent to the crown block 8C. The crown recess 10 terminates in the crown block 8C. Such a crown recess 10 generates a large reaction force when the mud is solidified and sheared in the recess, and helps to further improve the mud performance.

  The crown recess 10 is formed away from the first main groove 3a and the second main groove 3b. Since such a crown recess 10 is provided apart from the first main groove 3a and the second main groove 3b of the crown block 8C, a local rigidity reduction in the crown recess 10 is prevented. For this reason, in the crown block 8C of the present embodiment, the portion whose rigidity is relaxed by the crown recess 10 separated from the first main groove 3a and the second main groove 3b, and the first main groove 3a and the second main groove 3b are provided. The difference in stiffness from the facing portion with small stiffness is small. Therefore, the crown block 8C of the pneumatic tire of the present embodiment can reduce a portion having a small local rigidity, and thus improve the chipping resistance performance there.

  The maximum width W5 in the tire axial direction of the crown recess 10 is, for example, 25% to 35% of the maximum width W4 in the tire axial direction of the crown block 8C from the viewpoint of improving chipping resistance while maintaining mud performance. A range is desirable. From the same viewpoint, the maximum length L2 in the tire circumferential direction of the crown recess 10 is desirably in the range of 20% to 30% of the maximum length L1 in the tire circumferential direction of the crown block 8C, for example.

  As shown in FIG. 2, the depth D3 of the crown recess 10 is smaller than the groove depth D2 of the first crown lateral groove 9a so that the rigidity in the vicinity of the crown recess 10 of the crown block 8C does not become excessively small. desirable. In a more preferred embodiment, the depth D3 of the crown recess 10 is, for example, in the range of 50% to 70% of the first crown lateral groove 9a.

  The crown recess 10 is formed in, for example, a substantially trapezoidal shape in a plan view of the crown block 8C. More specifically, the crown recess 10 is formed such that a pair of groove edges that are continuous with the crown lateral groove 9 are close to each other toward the terminal end in the crown block 8C, for example. Such a crown concave portion 10 can guide mud toward the terminal end of the concave portion along each groove edge at the time of ground contact, and can solidify the mud more reliably in the concave portion, thereby further improving the mud performance. To help.

  In order to exhibit the above-described action more effectively, each crown recess 10 of the present embodiment is desirably formed on the tire equator C. When the crown block 8C is in contact with the ground, a larger contact pressure acts on the tire equator C side of the crown block 8C. For this reason, by forming the crown concave portion 10 on the tire equator C, mud in the concave portion can be hardened with a larger ground pressure.

  By providing the crown recess 10, the tread surface 8S of the crown block 8C is formed, for example, in a substantially C shape. In such a crown block 8C, for example, a restoring force in a direction in which the recess is contracted acts on the crown recess 10 that is expanded by mud in the recess and the ground pressure. For this reason, when the crown recessed part 10 is contracted, mud in the recessed part is pushed into the crown lateral groove 9, for example. Thereby, in the crown block 8C of this embodiment, mud can be prevented from accumulating in the recess, and excellent mud performance can be maintained.

  As shown in FIG. 3, the crown block 8 </ b> C is preferably provided with a siping 13. The siping 13 extends in a substantially C shape so as to surround the crown recess 10. The siping 13 is, for example, a closed sipe whose both ends are terminated in the crown block 8C. Moreover, the siping 13 may be formed by arranging a plurality of closed sipes in a substantially C shape, for example. Such a siping 13 can partially suppress the rigidity of the crown block 8C, and thus further improves the chipping resistance. In the present specification, “siping” means a cut having a width of about 0.5 to 1.5 mm, and is distinguished from a groove for drainage.

  The crown block 8C is preferably provided with a chamfer 14. It is desirable that the chamfered portion 14 is provided at the top facing the main groove 3 on the tread surface of the crown block 8C. Such a chamfered portion 14 can suppress the chipping of the block starting from the top portion having a small rigidity facing the main groove 3, and thus further improves the chipping resistance. From the same point of view, the chamfered portion 14 of the present embodiment may be provided, for example, at an acute apex facing the crown recess 10.

  As shown in FIG. 1, the tread portion 2 of the present embodiment includes a shoulder land portion between the first main groove 3a and the tread end Te and between the second main groove 3b and the tread end Te. 15 is divided.

  The shoulder land portion 15 of the present embodiment is provided with a plurality of shoulder lateral grooves 16 that connect between the first main groove 3a and the tread end Te or between the second main groove 3b and the tread end Te. . Thus, the shoulder land portion 15 is divided into a plurality of shoulder blocks 15S.

  FIG. 4 shows a partially enlarged view near the shoulder land portion 15 on the right side of FIG. As shown in FIG. 4, each shoulder lateral groove 16 includes, for example, a first lateral groove portion 16 a continuous with the first main groove 3 a and a second lateral groove portion 16 b continuous with the outer side in the tire axial direction of the first lateral groove portion 16 a. It is out.

  The first lateral groove portion 16a is connected to, for example, the first inclined portion 4 of the first main groove 3a, is inclined in the same direction as the second inclined portion 5, and extends outward in the tire axial direction. The first lateral groove portion 16a of the present embodiment is connected to the first inclined portion 4 so as to form a T-shaped three-way.

  In general, at the position of the zigzag top portion 6 where the first inclined portion 4 and the second inclined portion 5 of the main groove 3 intersect, the direction of the air flowing therein changes. For this reason, for example, if the first lateral groove portion 16a is connected to the zigzag top portion 6, there is a problem that air easily flows into the shoulder lateral groove 16 from the main groove 3 and the passage noise increases. However, the shoulder lateral groove 16 of this embodiment is connected to the first inclined portion 4 so as to form a T-shaped three-way. Therefore, the tire according to the present embodiment suppresses the inflow of air from the main groove 3 to the shoulder lateral groove 16 during traveling on the dry road surface, so that the passing noise is reduced without reducing the groove volume of the main groove 3 or the shoulder lateral groove 16. It can be reduced.

  The first lateral groove portion 16a is inclined in the same direction as the second inclined portion 5 of the main groove 3, for example. The first lateral groove portion 16 a of the present embodiment extends linearly along the second inclined portion 5. Such a first lateral groove portion 16a guides water to the tread end Te side by utilizing the inertia when the water in the second inclined portion 5 moves to the first inclined portion 4 side, for example, during wet running. To do.

  In order to effectively exhibit the above-described action, the groove width W6 of the first lateral groove portion 16a is, for example, in the range of 4.0 to 8.0 mm, and preferably in the range of 5.0 to 7.0 mm. From the same viewpoint, the groove depth of the first lateral groove portion 16a is, for example, in the range of 6.0 to 9.0 mm.

  For example, the second lateral groove portion 16b extends in the tire axial direction from the first lateral groove portion 16a to the tread end Te. As a preferred embodiment, the inclination angle of the second lateral groove portion 16b with respect to the tire axial direction is gradually reduced toward the outer side in the tire axial direction, for example.

  The 2nd horizontal groove part 16b of this embodiment has a larger groove width than the 1st horizontal groove part 16a. The groove width W7 at the tread end Te of the second horizontal groove portion 16b is preferably in the range of 3.5 to 6.0 times the groove width W6 of the first horizontal groove portion 16a, for example.

  The 2nd horizontal groove part 16b of this embodiment has a larger groove depth than the 1st horizontal groove part 16a. The groove depth of the second horizontal groove portion 16b is preferably in the range of 1.25 to 1.65 times the groove depth of the first horizontal groove portion 16a, for example.

  In the first horizontal groove portion 16a and the second horizontal groove portion 16b, the amount of air flowing from the main groove 3 to the second horizontal groove portion 16b is restricted by the first horizontal groove portion 16a, thereby reducing the pumping sound. it can.

  The groove wall on one side (the lower side in FIG. 4) of the tire circumferential direction of the second lateral groove portion 16b is smoothly continuous with the groove wall on one side of the first lateral groove portion 16a. Thereby, the air flowing in from the main groove 3 does not generate a turbulent flow in the shoulder lateral groove 16, and smoothly flows along the groove wall of the continuous first lateral groove portion 16a and the second lateral groove portion 16b on the tread end Te side. To be discharged. For this reason, the instantaneous increase in the air pressure in the shoulder lateral groove 16 at the time of grounding is mitigated, and the pumping noise is further suppressed.

  From the same viewpoint as the crown block 8C (shown in FIG. 1), the shoulder block 15S preferably has a polygonal tread surface. In this embodiment, the shoulder block 15S is formed by the zigzag phase of the first main groove 3a and the shoulder lateral groove 16. It is divided into a substantially Y shape.

  The shoulder block 15S of the present embodiment is provided with a siping 17 extending from the first main groove 3a and the shoulder lateral groove 16, for example, in order to reduce the rigidity. The siping 17 extends toward the center of the shoulder block 15S and terminates in the shoulder block 15S. Further, the shoulder block 15S is preferably provided with a sub-groove 18. The sub-groove 18 is connected, for example, between the terminal end of the siping 17 and the tread end Te. Such sub-grooves 18 are useful for improving drainage performance toward the outer side in the tire axial direction.

  The shoulder block 15S is preferably provided with a chamfer 19. It is preferable that the chamfered portion 19 is provided at an edge facing the shoulder lateral groove 16 on the tread surface of the shoulder block 15S. Such a chamfered portion 19 can suppress block chipping starting from an edge portion caused by a large stress acting at the time of acceleration or deceleration, and thus helps to further improve the chipping resistance. From the same viewpoint, it is desirable that the chamfered portion 19 of the present embodiment is also provided at the top portion facing the first main groove 3a, for example.

  As mentioned above, although especially preferable embodiment of this invention was described in full detail, this invention is not limited to this embodiment, It can deform | transform and implement in a various aspect.

Tires of Examples 1 to 7 (size: 225 / 95R16C) having the basic pattern shown in FIG. 1 and based on the specifications of Table 1 were prototyped and their performance was tested. As a comparative example, a tire in which a crown block in which a crown recess is formed at a position where it is continuous with a main groove was sectioned was manufactured and tested in the same manner. Further, as Example 8, a tire in which a crown block having a substantially rectangular shape with a tread surface is sectioned by making a crown lateral groove join the inner top portion and the outer top portion of each main groove while being based on FIG. Tested.
The test method is as follows.

<Mad performance>
Each sample tire was mounted on all the wheels of the test vehicle with internal pressure (front: 250 kPa, rear: 475 kPa), and after running on a test course including muddy areas, the traction performance in muddy areas was evaluated by the driver's sensuality. . A result is a score which sets the comparative example as 100, and it is excellent in mud performance, so that a numerical value is large.

<Chip resistance>
After causing the tire to idle on the gravel road in the test vehicle, the chipping generated in the crown block was confirmed by the inspector's visual observation. The result is a score based on the confirmed number and state of chipping, with the comparative example being 100. The larger the value, the better the chipping resistance.

  As shown in Table 1, it was confirmed that the tires of each example could improve the chipping performance while maintaining the mud performance.

2 Tread portion 3 Main groove 8C Crown block 8S Tread 9 Crown lateral groove 10 Crown recess C Tire equator

Claims (7)

A pair of main grooves extending in a zigzag manner on both sides of the tire equator in the tire circumferential direction and a plurality of crown lateral grooves that divide a plurality of crown blocks by connecting between the main grooves are formed in the tread portion. A pneumatic tire,
Each crown block has a crown recess in which a part of the tread surface is recessed inward in the tire radial direction so as to be continuous with the adjacent one of the crown lateral grooves,
The pneumatic tire according to claim 1, wherein the crown recess is formed apart from the main grooves on both sides.   The pneumatic tire according to claim 1, wherein a depth of the crown recess is smaller than a depth of the crown lateral groove. Each of the main grooves includes a first main groove and a second main groove,
Each of the first main groove and the second main groove includes a first inclined portion inclined to one side in the tire circumferential direction, a second inclined portion inclined to the opposite side of the first inclined portion, and a tire axial direction. Including an inner top that is convex inward,
The crown transverse groove includes a first crown transverse groove and a second crown transverse groove,
The first crown lateral groove joins each inner top portion of the first main groove and the first inclined portion of the second main groove,
The pneumatic tire according to claim 1 or 2, wherein the second crown lateral groove joins the inner top portions of the second main groove and the second inclined portion of the first main groove.   The pneumatic tire according to claim 3, wherein the first inclined portion and the second inclined portion are inclined at an angle of 30 to 40 degrees with respect to a tire circumferential direction.   The pneumatic tire according to any one of claims 1 to 4, wherein a groove width of the crown lateral groove is in a range of 35% to 75% of a groove width of the main groove.   The pneumatic tire according to claim 1, wherein the crown lateral groove is inclined at an angle of 30 to 40 degrees with respect to a tire axial direction. The tread portion is provided with a plurality of shoulder lateral grooves extending outward from the main groove in the tire axial direction,
Each of the shoulder lateral grooves has a first lateral groove portion that is continuous with the main groove, a second lateral groove portion that is continuous with the outer side in the tire axial direction of the first lateral groove portion, and has a groove width and a depth that are larger than the first lateral groove portion. Including lateral grooves,
The pneumatic tire according to any one of claims 1 to 6, wherein one groove wall of the first lateral groove portion is smoothly continuous with one groove wall of the second lateral groove portion.

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