JP2015223884A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire having excellent mud performance.SOLUTION: A pneumatic tire 1 comprises center blocks 3 on both sides of a tire equator. Each of the respective center blocks 3 has an inside edge 6 facing the tire equator side. The inside edge 6 is formed into an approximately V-shape having a first inclination edge 8 extending from an apex 6a on the tire equator C side and a second inclination edge 9 extending in a direction opposite to the first inclination edge 8 from the apex 6a. Length L2 of the second inclination edge 9 in a tire peripheral direction is shorter than length L1 of the first inclination edge 8 in the tire peripheral direction. The center block 3 comprises: a first part 3A having the first inclination edge 8; and a second part 3B having the second inclination edge 9. The second part 3B has an end part wall face 15 on a side opposite to the first part 3A. The end part wall face 15 includes a step-like part 16 extending stepwise toward a groove bottom.

Description

  The present invention relates to a pneumatic tire having excellent mud performance.

  All-season tires and M + S type pneumatic tires for running on rough terrain are required to have so-called mud performance that exhibits sufficient traction and soil removal performance in muddy areas, for example. In order to improve the mud performance, a tire having a block pattern in which a plurality of blocks are provided in a tread portion has been proposed.

Japanese Patent Application Laid-Open No. 09-300195

  However, conventional tires are prone to mud clogging in the grooves as they travel, and good mud performance has not been sustained.

  The present invention has been devised in view of the above circumstances, and provides a pneumatic tire that can exhibit good mud performance over a long period of time, based on improving the shape of the center block. The main purpose.

  The present invention is a pneumatic tire in which center blocks are provided on both sides of a tire equator of a tread portion, each center block having an inner edge facing the tire equator side, and the inner edge is a tire equator. A first inclined edge extending obliquely outward in the tire axial direction from the apex on the side, and a second inclined edge extending obliquely in the opposite direction to the first inclined edge outward from the apex in the tire axial direction The length of the second inclined edge in the tire circumferential direction is smaller than the length of the first inclined edge in the tire circumferential direction, and each center block includes a first portion having the first inclined edge; A second portion having the second inclined edge, and the second portion has an end wall surface opposite to the first portion, and the end wall surface is stepped toward the groove bottom. It includes a stepped portion that extends.

  In the pneumatic tire according to the present invention, it is desirable that the stepped portion includes a horizontal portion having an angle of 15 degrees or less with respect to the tread surface of the center block.

  In the pneumatic tire according to the present invention, the stepped portion includes an inner stepped portion provided on the tire equator side of the end wall surface, and an outer step provided outside the inner stepped portion in the tire axial direction. The end wall surface is preferably provided with a slope surface extending obliquely from the tread surface between the inner stepped portion and the outer stepped portion.

  In the pneumatic tire according to the present invention, it is preferable that the number of the horizontal portions of the inner stepped portion is larger than the number of the horizontal portions of the outer stepped portion.

  In the pneumatic tire according to the present invention, it is preferable that the center block is provided with siping, and the siping extends in a longitudinal direction of the second portion.

  In the pneumatic tire according to the present invention, it is preferable that the center blocks adjacent on both sides of the tire equator are arranged such that the first inclined edges face each other.

  Center blocks are provided on both sides of the tire equator in the tread portion of the pneumatic tire of the present invention. Each center block has an inner edge facing the tire equator side. The inner edge includes a first inclined edge extending obliquely outward from the apex on the tire equator side in the tire axial direction, and a second inclined edge extending obliquely outward from the apex in the tire axial direction and opposite to the first inclined edge. It is substantially V-shaped. Since such a 1st inclination edge and a 2nd inclination edge have a tire axial direction component, they can exhibit a shear force with respect to mud and can raise a traction.

  The length of the second inclined edge in the tire circumferential direction is smaller than the length of the first inclined edge in the tire circumferential direction. The center block has a first portion having a first inclined edge and a second portion having a second inclined edge. Since the first inclined edge is applied with a greater force from the road surface than the second inclined edge, the first portion has a larger amount of deformation at the time of grounding than the second portion. For this reason, the mud is effectively discharged from the groove around the center block by unbalanced deformation of the first part and the second part at the time of ground contact, so that excellent soil removal properties can be obtained.

The second part has an end wall surface opposite to the first part. The end wall surface includes a stepped portion extending stepwise toward the groove bottom. Thereby, when mud is clogged in the groove including the end wall surface, the mud is cracked at the stepped portion, and the mud is effectively discharged starting from the crack. Further, by providing such a stepped portion in the second portion with a small deformation amount at the time of ground contact, the mud in the groove near the second portion is effectively discharged. For this reason, the more excellent soil removal property is obtained.
By the above operation, the pneumatic tire of the present invention can exhibit excellent mud performance.

It is an expanded view of the tread part of the pneumatic tire of one embodiment of the present invention. It is an enlarged view of the center block of FIG. It is a fragmentary perspective view of a center block. It is AA sectional drawing of FIG. It is an enlarged view of the adjacent center block of FIG. It is an expanded view of the tread part of other embodiment of this invention. It is an expanded view of the tread part of embodiment of a comparative example.

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

  As shown in FIG. 1, the tread portion 2 is provided with a center block 3 disposed on both sides of the tire equator C and a shoulder block 4 disposed on the tread end Te side with respect to the center block 3. . The tread portion 2 of the present embodiment includes a pair of center block rows 3R in which a plurality of center blocks 3 are arranged in the tire circumferential direction, a pair of shoulder block rows 4R in which a plurality of shoulder blocks 4 are arranged in the tire circumferential direction, and the center block 3 3, a groove 5 extending between the shoulder blocks 4, 4 or between the center block 3 and the shoulder block 4 is provided.

  The tread pattern of the present embodiment is formed in a substantially point-symmetric pattern except for a variable pitch with an arbitrary point on the tire equator C as the center.

  The “tread end” Te is obtained when a normal load is applied to a normal tire 1 that is assembled with a normal rim and filled with a normal internal pressure, and a normal load is applied to the flat tire with a camber angle of 0 degrees. It is determined as the ground contact position on the outermost side in the tire axial direction. In the normal state, the distance in the tire axial direction between the tread ends Te and Te is determined as the tread contact width TW. Unless otherwise noted, the dimensions and the like of each part of the tire are values measured 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, ETRTO Then "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. “JAMATA” is the “maximum air pressure”, TRA is the table “TIRE LOAD LIMITS” The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” in the case of ETRTO. When the tire is for a passenger car, the normal internal pressure is 180 kPa.

  “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. “JATMA” is “maximum load capacity”, TRA is “TIRE LOAD” The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” in the case of ETRTO. When the tire is for a passenger car, the normal load is a load corresponding to 88% of the load.

  FIG. 2 is an enlarged view of the center block 3 of FIG. As shown in FIG. 2, the center block 3 has an inner edge 6 facing the tire equator C side and an outer edge 7 facing the tread end Te side. The inner edge 6 and the outer edge 7 are edges between the tread surface 3a of the center block 3 and the block wall surface 3b (shown in FIG. 3). For the sake of convenience, the center block 3 in FIG. 2 has a stepped portion, a siping, and a concave portion, which will be described later, removed.

  The inner edge 6 extends obliquely from the apex 6a on the tire equator C side to the outer side in the tire axial direction and obliquely extends from the apex 6a to the outer side in the tire axial direction in the opposite direction to the first inclined edge 8. It has a substantially V shape having a second inclined edge 9. Since the first inclined edge 8 and the second inclined edge 9 have a tire axial direction component, they can exert a shearing force against mud and enhance traction.

  The outer edge 7 extends from the outer end 8e of the first inclined edge 8 to the outer side in the tire axial direction from the third inclined edge 10 extending obliquely in the opposite direction to the first inclined edge 8, and from the outer end 9e of the second inclined edge 9. A fourth inclined edge 11 extending obliquely in the direction opposite to the second inclined edge 9 outward in the tire axial direction; a fifth inclined edge 12 extending along the first inclined edge 8 from the outer end 10e of the third inclined edge 10; And a sixth inclined edge 13 extending from the inner end 12 i of the fifth inclined edge 12 along the second inclined edge 9. In the present embodiment, the fifth inclined edge 12 and the sixth inclined edge 13 are formed in a substantially V shape with the tire equator C side as the apex. Note that the term “extend along” includes not only extending in the same direction with respect to the tire axial direction but also including an inclined edge having an angle with respect to the tire axial direction of 85 degrees or more.

  The fifth inclined edge 12 includes a fifth gently inclined edge 12a inclined at a small angle with respect to the tire axial direction, and a fifth steeply inclined edge 12b inclined at a larger angle than the fifth gently inclined edge 12a. The fifth steeply inclined edge 12 b extends from the outer end 10 e of the third inclined edge 10. The sixth inclined edge 13 includes a sixth gently inclined edge 13a inclined at a small angle with respect to the tire axial direction, and a sixth steeply inclined edge 13b inclined at a larger angle than the sixth gently inclined edge 13a. The sixth gentle inclined edge 13 a extends from the inner end 12 i of the fifth inclined edge 12.

  The center block 3 includes a first portion 3 </ b> A having a first inclined edge 8 and a second portion 3 </ b> B having a second inclined edge 9. In the present embodiment, the first portion 3 </ b> A includes a first inclined edge 8, a third inclined edge 10, and a fifth inclined edge 12. The second portion 3 </ b> B includes a second inclined edge 9, a fourth inclined edge 11, and a sixth inclined edge 13. That is, the tread surface 3a of the center block 3 is substantially V-shaped and bent at the apex 6a between the first portion 3A and the second portion 3B.

  In the present embodiment, the first inclined edge 8 and the second inclined edge 9 are continuously inclined on one side or the other side with respect to the tire axial direction. Thereby, a load efficiently acts on the first inclined edge 8 and the second inclined edge 9, and the first portion 3A and the second portion 3B are smoothly deformed, and the first portion 3A and the second portion 3B The mud can be grabbed effectively between them, and excellent mud performance is demonstrated.

  The length L2 of the second inclined edge 9 in the tire circumferential direction is smaller than the length L1 of the first inclined edge 8 in the tire circumferential direction. As a result, since the first inclined edge 8 is applied with a greater force from the road surface than the second inclined edge 9, the first portion 3A has a larger deformation amount at the time of grounding than the second portion 3B. For this reason, when the first part 3A and the second part 3B are deformed unbalanced at the time of grounding, the mud grasped by the first part 3A and the second part 3B can be effectively discharged, which is excellent. A good soil removal property is obtained.

  If the length L2 of the second inclined edge 9 is excessively smaller than the length L1 of the first inclined edge 8, the deformation of the first portion 3A becomes excessively large, and the traction due to friction with the road surface may be reduced. is there. For this reason, the length L2 of the second inclined edge 9 is preferably 40% to 60% of the length L1 of the first inclined edge 8.

  In order to effectively exhibit the above-described action, the length L4 of the second inclined edge 9 in the tire axial direction is preferably 15% to 35% of the length L3 of the first inclined edge 8 in the tire axial direction. .

  FIG. 3 is a perspective view of the center block 3 in the vicinity of the second portion 3B. 4 is a cross-sectional view taken along line AA in FIG. As shown in FIGS. 3 and 4, the second portion 3 </ b> B has an end wall surface 15 opposite to the first portion 3 </ b> A. The end wall surface 15 of the present embodiment is a block wall surface that continues to the fourth inclined edge 11.

  The end wall surface 15 of the present embodiment includes a stepped portion 16 extending stepwise toward the groove bottom, and a slope surface 17 extending obliquely from the tread surface 3a to the groove bottom. Such end wall surface 15 can cause the mud to crack at the stepped portion 16 where the thickness (depth) of the mud is reduced when the groove 5 including the end wall surface 15 is clogged. The mud can be effectively discharged from the crack. Moreover, mud can be discharged | emitted more effectively by providing the step-shaped part 16 in the 2nd part 3B with a small deformation amount at the time of grounding. For this reason, the more excellent soil removal property is obtained.

  The stepped portion 16 includes an inner stepped portion 16A provided on the tire equator C side of the end wall surface 15 and an outer stepped portion 16B provided on the outer side in the tire axial direction than the inner stepped portion 16A. Yes. In the present embodiment, the inner stepped portion 16 </ b> A is provided including the inner end 11 a of the fourth inclined edge 11. The outer stepped portion 16 </ b> B is provided including the outer end 11 b of the fourth inclined edge 11. Thereby, since a crack can be produced in two places of the center block 3, the soil removal property is further improved. Further, cracks starting from the inner stepped portion 16 </ b> A and the outer stepped portion 16 </ b> B are propagated to the mud of the groove 5 along the second inclined edge 9 and the sixth inclined edge 13 adjacent to the fourth inclined edge 11. Therefore, the soil removal property is further improved.

  As shown in FIG. 4, in this embodiment, the stepped portion 16 extends at an angle θ <b> 1 of 15 degrees or less with respect to the tread surface 3 a of the center block 3, and extends at an angle θ <b> 2 larger than the horizontal portion 18. And a rising portion 19. The stepped portion 16 of the present embodiment includes a first horizontal portion 18A provided on the groove bottom side and a second horizontal portion 18B provided on the outer side in the tire radial direction than the first horizontal portion 18A. Yes. Such a stepped portion 16 can promote the generation of cracks in the region of the second horizontal portion 18B where the thickness of the mud is small while ensuring the groove volume, so that the soil removal and traction are well balanced. Enhanced.

  In order to exhibit the above-described action more effectively, the height H2 from the groove bottom of the second horizontal portion 18B is preferably 64% to 72% of the height Ha of the center block 3. Further, from the viewpoint of ensuring a good balance between the rigidity of the second portion 3B and the groove volume, the height H1 of the first horizontal portion 18A from the groove bottom is preferably 30% to 38% of the height Ha of the center block 3. %.

  When the depth length L5 of the horizontal portion 18 is large, the volume of the groove 5 becomes small, and mud cannot be gripped effectively, and traction may be reduced. When the depth length L5 of the horizontal portion 18 is small, the effect of causing mud cracking may be reduced. For this reason, the depth length L5 of the horizontal portion 18 is preferably 10% to 30% of the height Ha of the center block 3.

  As shown in FIG. 3, in this embodiment, the horizontal portions 18A of the inner stepped portion 16A are formed in the same number as the horizontal portions 18B of the outer stepped portion 16B. Thereby, the rigidity in the vicinity of both end sides of the end wall surface 15 is ensured with a good balance, and the occurrence of cracks is equalized.

  In the present embodiment, the slope surface 17 extends continuously and smoothly from the tread surface 3a to the groove bottom. Such a slope surface 17 exhibits a large shearing force against mud in order to suppress an excessive decrease in the rigidity of the end wall surface 15.

  The slope surface 17 of the present embodiment is provided between the inner stepped portion 16A and the outer stepped portion 16B. Thus, the slope surface 17 of the present embodiment is provided in the central portion of the fourth inclined edge 11. For this reason, since the rigidity of the end part wall surface 15 can be improved with sufficient balance, the excessive deformation | transformation of the 2nd part 3B at the time of grounding can be suppressed.

  FIG. 5 is an enlarged view of the center blocks 3 and 3 adjacent on both sides of the tire equator C. FIG. As shown in FIG. 5, the center block 3 is provided with a siping 20. Such siping 20 effectively reduces the rigidity of the center block 3, promotes the deformation of the first part 3A and the second part 3B at the time of ground contact, and between the first part 3A and the second part 3B. Grab and drain mud effectively.

  The siping 20 of the present embodiment has an outer portion 21 disposed in the first portion 3A and an inner portion 22 provided on the inner side in the tire axial direction than the outer portion 21. Thereby, since the rigidity of the center block 3 is reduced uniformly, the first portion 3A and the second portion 3B are deformed as a whole, and thus mud can be effectively grasped.

  The outer portion 21 and the inner portion 22 are separated from each other without overlapping in the tire axial direction and the tire circumferential direction. Thereby, the above-mentioned effect is further exhibited.

  The outer portion 21 joins the third inclined edge 10 and the first inclined edge 8.

  The inner part 22 extends in the longitudinal direction of the second part 3B. The inner portion 22 of the present embodiment joins the fourth inclined edge 11 and the first inclined edge 8 linearly. As a result, the rigidity of the second portion 3B, which is harder to deform than the first portion 3A, is effectively reduced, and the occurrence of cracks on the end wall surface 15 is further promoted.

  The length B of the tire circumferential component of the siping 20 is preferably 45% or more of the sum (A + B) of the length A of the tire axial component and the length B of the tire circumferential component. When the length B of the tire circumferential component of the siping 20 is less than 45% of the sum (A + B) of the length A of the tire axial component and the length B of the tire circumferential component, the tire axial direction of the center block 3 There is a possibility that a decrease in the rigidity of the first portion 3A and the second portion 3B is suppressed. Further, when the length B of the tire circumferential direction component of the siping 20 exceeds 70% of the sum (A + B) of the lengths, the rigidity of the center block 3 in the tire axial direction becomes excessively small, and the shearing force against mud is increased. May decrease. For this reason, the length B of the tire circumferential direction component of the siping 20 is preferably 70% or less of the sum (A + B) of the lengths. In FIG. 5, the tire axial components a1 to a4 obtained by disassembling the length A of the tire axial component of the siping 20 of the present embodiment, and the tire circumferential components b1 obtained by decomposing the length B of the tire circumferential component. To b4.

  As such siping, the width is preferably 1.0 mm or less, and the depth (not shown) is preferably 9.0 to 14.0 mm.

  Further, the center blocks 3 adjacent on both sides of the tire equator C are arranged so that the first inclined edges 8 and 8 face each other. Thereby, mud, sand, etc. can be easily grasped by the groove 5a formed between the first inclined edges 8 and 8, traction can be enhanced, and mud performance and dirt performance can be improved. In order to effectively exhibit such an action, the length La in the tire circumferential direction of the overlapping portion K where the adjacent first inclined edges 8 and 8 overlap in the tire axial direction is preferably 5% of the tread contact width TW. Or more, more preferably 7% or more. If the length La of the overlapping portion K is excessively large, mud may not be smoothly discharged from the overlapping portion K. For this reason, the length La in the tire circumferential direction of the overlapping portion K is preferably 20% or less of the tread contact width TW.

  From the viewpoint of effectively exhibiting the above-described action, the length Lb of the first inclined edge 9 in the tire circumferential direction is preferably 10% to 30% of the tread contact width TW.

  As shown in FIG. 3, the center block 3 has a concave portion 25 having a gentle slope 26 in which the block wall surface of the portion where the outer edge 7 is greatly recessed toward the tire equator C side is gently inclined outward in the tire axial direction. Is provided. Such a recess 25 improves the mud performance because the gentle slope 26 can effectively discharge mud in the recess 25. The concave portion 25 of the present embodiment is provided on the fifth gently inclined edge 12a and the sixth slowly inclined edge 13a.

  In the recessed portion 25 of the present embodiment, the edge 26a of the gentle slope 26 is located outside the groove bottom in the tire radial direction. Such a recess 25 secures the rigidity of the center block 3, suppresses excessive deformation of the first portion 3A and the second portion 3B, and increases the shearing force of the first inclined edge 8 and the second inclined edge 9. be able to. In addition, the recessed part 25 is not limited to such an aspect, A depth may be smaller than a groove bottom and a fixed aspect may be sufficient (illustration omitted).

  The depth (maximum depth) D1 of the recess 25 is preferably 50% to 80% of the height Ha of the center block 3. If the depth D1 of the recess 25 exceeds 80% of the height Ha of the center block 3, the rigidity of the center block 3 may be excessively reduced, and traction may be reduced. When the depth D1 of the recess 25 is less than 50% of the height Ha of the center block 3, there is a possibility that mud cannot be effectively grasped.

  As shown in FIG. 5, in order to effectively exhibit the above-described action, the incision length L6 in the tire axial direction of the recess 25 is preferably the maximum width Wa in the tire axial direction of the center block 3 passing through the recess 25. 10% to 30%.

  From the same viewpoint, the virtual surface area of the recess 25 is 3% to 10% of the area of the tread surface 3a of the center block 3. The virtual surface area of the recess 25 is the surface area of the virtual tread surface of the recess 25 obtained by filling the recess 25.

  As shown in FIG. 1, the tread surface 4a of the shoulder block 4 has a gently inclined portion 4A extending from the tread end Te side toward the tire axial direction at an angle of 15 degrees or less with respect to the tire axial direction, and a gently inclined portion 4A. A steeply inclined portion 4B that is inclined at a larger angle than the gently inclined portion 4A with respect to the tire axial direction. Such a shoulder block 4 is deformed by a load from the road surface, and mud can be effectively grasped between the gently inclined portion 4A and the steeply inclined portion 4B. Therefore, since a large traction on rough terrain can be obtained, the mud performance is further improved.

  In this embodiment, the steeply inclined portion 4B includes a first block edge 30a that defines an inner side in the tire axial direction, a second block edge 30b that defines an outer side in the tire axial direction, and a first block edge 30a and a second block edge 30b. And a third block edge 30c. The third block edge 30c is inclined in the opposite direction to the first block edge 30a.

  The first block edge 30a and the second block edge 30b are inclined in the same direction. Thereby, since the rigidity of the steeply inclined portion 4B is made uniform over the longitudinal direction, a large shearing force can be exhibited against mud and the like, and traction can be enhanced.

  The steeply inclined portion 4B is arranged so as to be continuous with the first portion 3A and the groove 5b interposed therebetween. As a result, one smooth groove 5c is formed between the shoulder blocks 4, 4 adjacent to each other in the tire circumferential direction and between the first portions 3A, 3A. Since the mud in the groove 5c is easily discharged from the tread end Te, the soil removal performance is improved. Note that “continuous” means that the first imaginary line 30e in which the first block edge 30a of the steeply inclined portion 4B is smoothly extended to the tire equator C side or the second block edge 30b is smooth to the tire equator C side. One of the second imaginary lines 30 i extended in the above-described manner is in communication with the third inclined edge 10.

  The groove 5d formed between the gently inclined portions 4A and 4A adjacent in the tire circumferential direction has an angle α with respect to the tire axial direction of preferably 15 degrees or less. As a result, during turning, the mud in the groove 5d in the vicinity of the tread end Te on which a large lateral force acts can be discharged smoothly.

  The height of each of the blocks 3 and 4 is preferably 12 to 18 mm in order to improve the mud performance and the steering stability performance with a good balance.

  The groove width (measured at right angles to the groove center line) W1 of the groove 5 is not particularly limited, but the rigidity of each block 3, 4 is secured to increase the shearing force against mud, etc., and From the viewpoint of effectively discharging mud and the like, it is preferably 5 to 15% of the tread ground contact width TW.

  FIG. 6 is a development view of the tread portion 2 according to another embodiment of the present invention. As shown in FIG. 6, in this embodiment, in the end wall surface 15, the number of horizontal portions 18a of the inner stepped portion 16A is larger than the number of horizontal portions 18b of the outer stepped portion 16B. . Thereby, since the thickness of the mud by the horizontal portion 18 provided on the outermost side in the tire radial direction is likely to be smaller at the inner stepped portion 16A than at the outer stepped portion 16B, the mud is difficult to be discharged on the tire equator C side. Cracking is more likely to occur, and the soil evacuation on the tire equator C side can be enhanced. Moreover, since the depth length of the horizontal part 18 can be made larger at the outer stepped portion 16B than at the inner stepped portion 16A, a greater shearing force can be exerted on mud during turning. For this reason, in the end part wall surface 15 of this embodiment, the soil removal performance and the traction are improved with a good balance. In the present embodiment, three horizontal portions 18a of the inner stepped portion 16A are provided, and two horizontal portions 18b of the outer stepped portion 16B are provided.

  As mentioned above, although embodiment of this invention was explained in full detail, it cannot be overemphasized that this invention is not limited to illustrated embodiment, and can be deform | transformed and implemented in a various aspect.

Tires for four-wheel drive vehicles having the basic pattern of FIG. 1 were prototyped based on the specifications in Table 1, and the mud performance and dirt performance of each sample tire were tested. The main common specifications and test methods for each sample tire are as follows.
Tread contact width TW: 240mm
Center block height: 17.1 mm
Shoulder block height: 17.1 mm

<Mad performance and dirt performance>
Each sample tire was mounted on all wheels of a 3600cc four-wheel drive vehicle under the following conditions. Then, the test driver ran the test course on the muddy road surface and the gravel road surface, and the running characteristics related to the traction and soil removal at this time were evaluated based on the sensuality of the test driver. The results are displayed with a score of Comparative Example 1 being 100. The larger the value, the better.
Size: 37 × 12.50R17
Rim: 9.0JJ
Internal pressure: 100kPa
Table 1 shows the test results.

  As a result of the test, it can be confirmed that the tire of the example has improved mud performance and dirt performance compared to the tire of the comparative example. In addition, the same test was carried out by changing the tire size, but showed the same tendency as the test result.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 3 Center block 3A 1st part 3B 2nd part 6 Inner edge
6a vertex 8 first inclined edge 9 second inclined edge 15 end wall surface 16 stepped portion C tire equator

Claims (6)

A pneumatic tire provided with center blocks on both sides of the tire equator of the tread,
Each center block has an inner edge facing the tire equator side,
The inner edge includes a first inclined edge extending obliquely outward in the tire axial direction from the apex on the tire equator side, and a second inclined edge extending obliquely outward in the tire axial direction from the apex in an opposite direction to the first inclined edge. And is substantially V-shaped,
The length of the second inclined edge in the tire circumferential direction is smaller than the length of the first inclined edge in the tire circumferential direction,
Each center block has a first portion having the first inclined edge and a second portion having the second inclined edge;
The second part has an end wall surface opposite to the first part,
The pneumatic tire according to claim 1, wherein the end wall surface includes a stepped portion extending stepwise toward the groove bottom.   The pneumatic tire according to claim 1, wherein the stepped portion includes a horizontal portion having an angle of 15 degrees or less with respect to the tread surface of the center block. The stepped portion includes an inner stepped portion provided on the tire equator side of the end wall surface, and an outer stepped portion provided on the outer side in the tire axial direction than the inner stepped portion,
The pneumatic tire according to claim 2, wherein the end wall surface is provided with a slope surface extending obliquely from the tread surface between the inner stepped portion and the outer stepped portion.   The pneumatic tire according to claim 3, wherein the number of the horizontal portions of the inner stepped portion is larger than the number of the horizontal portions of the outer stepped portion. The center block is provided with siping,
The pneumatic tire according to any one of claims 1 to 4, wherein the siping extends in a longitudinal direction of the second portion.   The pneumatic tire according to any one of claims 1 to 5, wherein the center blocks adjacent on both sides of the tire equator are arranged such that the first inclined edges face each other.

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