JP2006290234A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of making driveability and wet performance compatible. <P>SOLUTION: A circumferential thin groove 38 formed in a shoulder block row 24 is constituted such that groove width and groove depth are gradually increased as it advances from a terminal end 38A to an opening 38B. Thereby, water taken-in in the circumferential thin groove 38 is smoothly discharged from the terminal end 38A side to a lug groove 34 side through the opening 38B. Thereby, since water discharge property in the shoulder block row 24 can be made well, the wet performance can be ensured. Further, by the above constitution of the circumferential thin groove 38, a volume of the shoulder block 36 is increased as it advances from the opening 38B side of the circumferential thin groove 38 toward the terminal end 38A side. Thereby, since rigidity in the shoulder block row 24 is ensured, operation stability performance also becomes good. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having an improved shape of a circumferential narrow groove provided in a shoulder block in order to achieve both steering stability performance and wet performance.

  2. Description of the Related Art Conventionally, a pneumatic tire in which a circumferential narrow groove is provided in a shoulder block located on the tread end side is known in order to achieve both steering stability performance and wet performance.

  In this type of pneumatic tire, each shoulder block located on the tread end side is provided with a circumferential narrow groove, so that the drainage performance in the shoulder block row is improved, thereby ensuring the grip force in the shoulder block row. Therefore, the wet performance is said to be good.

  However, the configuration in which each shoulder block is simply provided with a circumferential narrow groove having a constant groove width and groove depth can improve the wet performance while lowering the rigidity of each shoulder block. The stability performance may be impaired.

  Then, the following techniques are proposed as a technique which suppresses the fall of steering stability performance, ensuring wet performance (for example, refer patent document 1).

  For example, in the example described in Patent Document 1, a sub circumferential groove as a circumferential thin groove formed in a shoulder block is formed in a flask shape with a round bottom.

  In other words, in the example described in Patent Document 1, the block portions on both sides sandwiching the outer portion in the tire radial direction (near the tread surface) of the sub circumferential groove are in contact with each other under the ground contact surface during load rolling. It is like that. Thereby, since the rigidity of each shoulder block is ensured, it is supposed that it can suppress that steering stability performance falls.

On the other hand, the block portions on both sides sandwiching the tire radial inner portion (groove bottom portion) of the secondary circumferential groove do not contact even under the ground contact surface at the time of load rolling. The drainage channel is secured. And it is supposed that wet performance is securable by this structure.
JP 62-194909 (FIG. 1)

  However, in the example described in Patent Document 1, as described above, the block portions on both sides sandwiching the outer circumferential portion of the tire in the tire radial direction are in contact with each other under the ground contact surface during load rolling. That is, the outer side in the tire radial direction of the secondary circumferential groove is closed under the ground contact surface during load rolling.

  For this reason, under the ground contact surface of the shoulder block row during load rolling, water between the shoulder block surface and the ground contact surface passes through the secondary transverse grooves located on both sides in the tire circumferential direction with the secondary circumferential groove interposed therebetween. The water in the sub-circumferential groove and in the tire radial inner portion of the sub-circumferential groove is discharged to the outside through the sub-cross groove.

  As described above, in the example described in Patent Document 1, water is not directly taken in and out between the auxiliary circumferential groove and the outside under the ground contact surface at the time of load rolling. There was a problem that the wet performance was not sufficient.

  At this time, in order to ensure wet performance, it may be considered to add sipes along the tire circumferential direction to each shoulder block. However, in this case, the rigidity of each shoulder block is reduced, resulting in a decrease in steering stability performance.

  The present invention has been made in view of the above circumstances, and its purpose is to achieve both steering stability performance and wet performance by ensuring drainage while ensuring rigidity in the shoulder block row. Is to provide a simple pneumatic tire.

  In order to solve the above problems, in the pneumatic tire according to claim 1, a plurality of circumferential main grooves are formed along a tire circumferential direction on a tire tread surface of a tread portion, and the plurality of circumferential main grooves are formed. In the pneumatic tire in which a plurality of block rows in which a plurality of blocks are arranged along the tire circumferential direction are formed in the tire width direction by forming a plurality of lug grooves so as to intersect with each other, the tread of the block rows Each shoulder block of the shoulder block row located on the end side is formed along the tire circumferential direction, and a pair of tire lug grooves formed on both sides in the tire circumferential direction across the shoulder blocks. A circumferential narrow groove is formed in one of the lug grooves and terminates in each shoulder block, and the circumferential narrow groove terminates in each shoulder block. According from the terminal end to towards the opening portion that is opened in the lug groove, characterized in that it is configured so as to gradually gradually depth with the groove width increases becomes deeper.

  Next, the operation of the pneumatic tire according to claim 1 will be described.

  As in the pneumatic tire according to claim 1, the circumferential narrow groove formed along the tire circumferential direction has an opening that opens from a terminal portion terminating in each shoulder block to a lug groove in the shoulder block row. If the groove width is gradually increased and the groove depth is gradually increased as it goes, resistance to water taken into the circumferential narrow groove opens from the end of the circumferential narrow groove. Since it gradually decreases as it goes to the portion, the water taken into the circumferential narrow groove is smoothly discharged from the terminal end side of the circumferential narrow groove to the lug groove side through the opening. Thereby, since the drainage property in a shoulder block row | line can be made favorable, wet performance can be ensured.

  In addition, as described above, the groove width gradually increases and the groove depth gradually increases as the circumferential narrow groove extends from the terminal portion terminating in each shoulder block to the opening opening in the lug groove. If comprised in this way, the volume of a shoulder block will increase as it goes to the termination | terminus part side from the opening part side of the circumferential direction fine groove in each shoulder block. Therefore, even when the circumferential narrow groove is provided in each shoulder block, it is possible to suppress a decrease in the rigidity of each shoulder block. Thereby, the rigidity in the shoulder block row is ensured, and the steering stability performance is also improved.

  Thus, according to the pneumatic tire of the first aspect, it is possible to achieve both steering stability and wet performance by ensuring drainage while securing rigidity in the shoulder block row.

  The pneumatic tire according to claim 2 is the pneumatic tire according to claim 1, wherein the circumferential narrow groove has a triangular cross-section in the longitudinal direction of the groove.

  Next, the operation of the pneumatic tire according to claim 2 will be described.

  As in the pneumatic tire according to claim 2, the circumferential narrow groove formed along the tire circumferential direction has an opening that opens from a terminal portion terminating in each shoulder block to a lug groove in the shoulder block row. If the cross section in the longitudinal direction of the groove where the groove width gradually increases and the groove depth gradually becomes deeper as the head is made up of triangular grooves, even if the wear of each shoulder block progresses, it ends in each shoulder block. As the width of the groove gradually increases and the depth of the groove gradually increases as the distance from the terminal end to the opening of the lug groove increases, the state in which the groove depth gradually increases can be reliably maintained.

  Thereby, even if wear of each shoulder block progresses, it becomes possible to reliably maintain a state in which steering stability and wet performance are compatible.

  The pneumatic tire according to claim 3 is a pair of pneumatic tires according to claim 1 or 2, wherein each shoulder block includes a pair of tire tires formed on both sides in the circumferential direction of the tire. At least one pair of the circumferential narrow grooves is formed so as to open in each of the lug grooves.

  Next, the operation of the pneumatic tire according to claim 3 will be described.

  As described in claim 3, when at least one pair of circumferential narrow grooves is formed in each shoulder block, the drainage channel in each shoulder block increases, so that the wet performance is also good.

  Further, as described in claim 3, at least a pair of circumferential narrow grooves is formed in each shoulder block so as to open to each of a pair of lug grooves formed on both sides in the tire circumferential direction with each shoulder block interposed therebetween. If it is formed, a complete block portion without a groove portion is formed by discontinuing both circumferential narrow grooves between at least a pair of circumferential narrow grooves in each shoulder block.

  Thereby, since the rigidity in each shoulder block can be ensured reliably while increasing the drainage channel in each shoulder block, it becomes possible to ensure steering stability.

  The pneumatic tire according to claim 4 is the pneumatic tire according to claim 3, wherein the pair of circumferential narrow grooves are line-symmetric with respect to a tire circumferential center line of each shoulder block. It is formed.

  Next, the operation of the pneumatic tire according to claim 4 will be described.

  When the pair of circumferential narrow grooves are formed in line symmetry with respect to the center line in the tire circumferential direction of each shoulder block as described in claim 4, It can be a tire circumferential direction center part of a block. As a result, the amount of collapse of the shoulder block can be made uniform during braking and driving, so that rigidity in the shoulder block row can be ensured without causing uneven wear on the shoulder block.

  Moreover, the pneumatic tire according to claim 5 is the pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire extends from the end portion of the circumferential narrow groove to the opening. The groove width is set to a dimension that is 10% to 50% of an average groove width in a circumferential main groove adjacent to the shoulder block row among the plurality of circumferential main grooves.

  Next, the operation of the pneumatic tire according to claim 5 will be described.

  As described in claim 5, in the pneumatic tire according to any one of claims 1 to 4, the groove width from the terminal end of the circumferential narrow groove to the opening is a plurality of circumferences. Even if the wear of the shoulder block progresses when the dimension is set to a dimension of 10% to 50% of the average groove width in the circumferential main groove adjacent to the shoulder block row among the directional main grooves, the drainage performance in the shoulder block row Can be secured. In addition, even when the article is new, the shoulder block can be prevented from falling down and the rigidity of the shoulder block can be sufficiently secured.

  When the groove width at the terminal end of the circumferential narrow groove is set to a dimension that is less than 10% of the average groove width in the circumferential main groove adjacent to the shoulder block row among the plurality of circumferential main grooves, the shoulder Even if the block is slightly worn, the drainage by the circumferential narrow groove cannot be secured. That is, the drainage property in the shoulder block row can be ensured only when it is new.

  Further, when the groove width in the opening of the circumferential narrow groove is set to a dimension larger than 50% of the average groove width in the circumferential main groove adjacent to the shoulder block row among the plurality of circumferential main grooves, Sometimes, the shoulder block collapses greatly, and it is impossible to ensure the rigidity of the shoulder block.

  Moreover, the pneumatic tire according to claim 6 is the pneumatic tire according to any one of claims 1 to 5, wherein the pneumatic tire extends from the end portion of the circumferential narrow groove to the opening. The groove depth is set to a dimension of 5% to 70% of the block height of the shoulder block.

  Next, the operation of the pneumatic tire according to claim 6 will be described.

  As described in claim 6, in the pneumatic tire according to any one of claims 1 to 5, the groove depth from the terminal end of the circumferential narrow groove to the opening is a shoulder block. When the dimension is set to 5% to 70% of the block height, the drainage property in the shoulder block row can be ensured even when the wear of the shoulder block proceeds. In addition, even when the article is new, the shoulder block can be prevented from falling down and the rigidity of the shoulder block can be sufficiently secured.

  If the groove depth at the end of the circumferential narrow groove is set to a dimension that is less than 5% of the block height of the shoulder block, the drainage by the circumferential narrow groove is only caused by slight wear of the shoulder block. Cannot be secured. That is, the drainage property in the shoulder block row can be ensured only when it is new.

  In addition, if the groove depth at the opening of the circumferential narrow groove is set to a dimension larger than 70% of the block height of the shoulder block, the shoulder block collapses greatly when new, and the rigidity of the shoulder block is increased. Can not be secured.

  The pneumatic tire according to claim 7 is the pneumatic tire according to any one of claims 1 to 6, wherein a groove bottom portion of the circumferential narrow groove has a curvature radius of 0.7 mm or more. It is comprised by the concave curved surface which has.

  Next, the operation of the pneumatic tire according to claim 7 will be described.

  As described in claim 7, when the groove bottom portion of the circumferential narrow groove is formed of a concave curved surface having a radius of curvature of 0.7 mm or more, strain concentrates on the groove bottom portion of the circumferential narrow groove. Since it can prevent, it becomes possible to suppress that a crack arises in the groove bottom part of a circumferential direction fine groove by this.

  The shoulder block undergoes deformation called wiping because it receives a large input from the lateral direction of the tire during cornering. This is a deformation that also occurs during straight running. For this reason, compression and tensile deformation are repeatedly generated at the groove bottom portion of the circumferential narrow groove as the tire rolls, and strain is concentrated thereby. Therefore, if the groove bottom of the circumferential narrow groove is configured with a concave curved surface having a radius of curvature of less than 0.7 mm, or the circumferential narrow groove is configured with a V-shaped cross section, There is a risk of cracks occurring at the bottom of the groove.

  The pneumatic tire according to claim 8 is the pneumatic tire according to any one of claims 1 to 7, wherein the shoulder blocks are provided at a variable pitch in the shoulder block row. It is characterized by being.

  Next, the operation of the pneumatic tire according to claim 8 will be described.

  As described in claim 8, when the shoulder blocks are provided at a variable pitch in the shoulder block row, pattern noise caused by the shoulder block row can be reduced.

  As described above, according to the pneumatic tire of the present invention, it is possible to achieve both steering stability and wet performance by ensuring drainage while ensuring rigidity in the shoulder block row.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the members, configurations, arrangements, and the like described below do not limit the present invention, and it is needless to say that various modifications can be made in accordance with the spirit of the present invention.

(Composition of pneumatic tire)
First, the configuration of the pneumatic tire 10 according to an embodiment of the present invention will be described.

  The pneumatic tire 10 according to an embodiment of the present invention is suitably used as, for example, a high-performance radial tire for passenger cars, and has a tire section width of 205 or more and a flatness ratio of 55 series or less. Is.

  Explaining the tread pattern of the pneumatic tire 10 of this example, a pair of circumferential main grooves 16 are formed along the tire circumferential direction on the center side of the tire tread surface of the tread portion 12 formed in the pneumatic tire 10. A pair of circumferential main grooves 18 are formed on both sides of the pair of circumferential main grooves 16 along the tire circumferential direction. The circumferential main grooves 16, 18 are configured with a groove width of about 1 mm to 10 mm.

  And in the pneumatic tire 10 which concerns on this embodiment, the circumferential direction main grooves 16 and 18 are formed in the tire tread of the tread part 12 as mentioned above, From the tire equatorial plane CL side to the tread end 14 side A central rib 20, an intermediate block row 22, and a shoulder block row 24 are formed toward the surface.

  In the central rib 20, inclined narrow grooves 26 extending in an oblique direction are alternately formed, and in the intermediate block row 22, inclined narrow grooves 28 and lug grooves 30 are formed. In addition, a plurality of intermediate blocks 32 are arranged in the intermediate block row 22 by forming lug grooves 30.

  A plurality of lug grooves 34 are formed in the shoulder block row 24 so as to intersect with the circumferential main groove 18, whereby a plurality of shoulder blocks 36 are arranged in the shoulder block row 24.

  And in this embodiment, when the length of the tire circumferential direction which match | combined each shoulder block 36 and one of the lug grooves 34 which divides the shoulder block row | line | column 24 in a tire circumferential direction is made into a pitch, the pneumatic tire of this example 10 has a configuration with a plurality of pitches (three types of small, medium and large in this example).

  That is, in the pneumatic tire 10 of this example, a so-called pitch variation is introduced into the pattern of the tread portion 12. For example, the shoulder block row 24 includes a shoulder block 36 having a small pitch P1 and a shoulder block 36 having a medium pitch P2. And a combination with the shoulder block 36 having a large pitch P3 is repeated in the tire circumferential direction.

  Each shoulder block 36 has at least a pair of circumferential narrow grooves 38 formed along the tire circumferential direction. The circumferential narrow groove 38 is formed in line symmetry with respect to the center line in the tire circumferential direction of each shoulder block 36.

  Each circumferential narrow groove 38 is formed so as to open to each of the pair of lug grooves 34 formed on both sides in the tire circumferential direction with the shoulder block 36 interposed therebetween, and terminate in each shoulder block 36.

  Furthermore, in this embodiment, as shown in FIGS. 2 and 3, the circumferential narrow groove 38 extends from the terminal end portion 38 </ b> A that terminates in each shoulder block 36 toward the opening 38 </ b> B that opens to the lug groove 34. The longitudinal section in which the groove width is gradually increased and the groove depth is gradually increased is formed by triangular grooves.

  At this time, the groove width from the end portion 38A of the circumferential narrow groove 38 to the opening portion 38B (the groove width of the end portion 38A is W1 and the groove width of the opening portion 38B is W2) is the circumferential main groove 18. The groove depth from the terminal end 38A of the circumferential narrow groove 38 to the opening 38B (the groove depth of the terminal end 38A is D1 and the opening 38B is set to a size of 10% to 50% of the average groove width in FIG. ) Is set to a dimension of 5% to 70% of the block height H of the shoulder block 36.

  Further, the groove bottom portion 38C of the circumferential narrow groove 38 is constituted by a concave curved surface having a radius of curvature of 0.7 mm or more.

  Here, although not shown, left and right sidewalls are formed on both sides in the tire width direction of the tread 12 in the pneumatic tire 10 of this example, and carcass is provided on the inside of the sidewalls and the tread 12. It has been.

  Further, a belt is interposed between the tread 12 and the carcass. In addition, the pneumatic tire 10 of this example is provided with a conventionally known member such as a bead core.

  In the present embodiment, a pair of circumferential narrow grooves 38 is formed in each shoulder block 36. However, when the rigidity of each shoulder block 36 is ensured, the circumferential narrow grooves 38 are formed in each shoulder block 36. Two or more pairs may be formed.

  In this embodiment, the combination of the shoulder block 36 with the small pitch P1, the shoulder block 36 with the medium pitch P2, and the shoulder block 36 with the large pitch P3 is not limited to the present embodiment, and various modifications are made. Of course it can be done.

  For example, as shown in this example, the combination of the small pitch P1 shoulder block 36 to the large pitch P3 shoulder block 36 arranged in ascending order is not repeated in the tire circumferential direction, and the small pitch P1 shoulder block 36 is large. Alternatively, the shoulder blocks 36 having the pitch P3 may be arranged in ascending order and then arranged in descending order from the shoulder blocks 36 having the large pitch P3 to the shoulder blocks 36 having the small pitch P1, and this combination may be repeated in the tire circumferential direction.

  Furthermore, the shoulder block 36 with the small pitch P1, the shoulder block 36 with the medium pitch P2, and the shoulder block 36 with the large pitch P3 may be randomly arranged in the tire circumferential direction.

(Functional effects of pneumatic tires)
Next, the function and effect of the pneumatic tire 10 having the above configuration will be described.

  Like the pneumatic tire 10 according to the present embodiment, the circumferential narrow groove 38 is configured such that the groove width gradually increases and the groove depth gradually increases from the terminal portion 38A toward the opening 38B. In this case, the resistance to water taken into the circumferential narrow groove 38 gradually decreases from the terminal end portion 38A of the circumferential narrow groove 38 toward the opening 38B.

  Accordingly, the water taken into the circumferential narrow groove 38 is smoothly discharged from the terminal end 38A side of the circumferential narrow groove 38 to the lug groove 34 side through the opening 38B. Thereby, since the drainage property in the shoulder block row | line | column 24 can be made favorable, wet performance can be ensured.

  Further, as described above, when the circumferential narrow groove 38 is configured so that the groove width gradually increases and the groove depth gradually increases from the terminal end 38A toward the opening 38B, each shoulder The volume of the shoulder block 36 increases as it goes from the opening 38B side to the terminal end 38A side of the circumferential narrow groove 38 in the block 36.

  Therefore, even when the circumferential narrow groove 38 is provided in each shoulder block 36, it is possible to suppress the rigidity of each shoulder block 36 from being lowered. Thereby, the rigidity in the shoulder block row 24 is ensured, and the steering stability performance is also good.

  As described above, according to the pneumatic tire 10 according to the present embodiment, it is possible to achieve both steering stability and wet performance by ensuring drainage while securing rigidity in the shoulder block row 24. .

  Further, as in the pneumatic tire 10 according to the present embodiment, as the circumferential narrow groove 38 formed along the tire circumferential direction moves from the terminal portion 38A that terminates in each shoulder block 36 toward the opening 38B, If the groove longitudinal section in which the groove width gradually increases and the groove depth gradually increases is configured by a triangular groove, even if the wear of each shoulder block 36 progresses, it terminates in each shoulder block 36. It is possible to reliably maintain a state in which the groove width is gradually increased and the groove depth is gradually increased from the end portion 38A toward the opening 38B.

  Further, when at least a pair of circumferential narrow grooves 38 are formed in each shoulder block 36 as in the pneumatic tire 10 according to the present embodiment, the drainage channels in each shoulder block 36 increase, so that the wet performance is also good. It becomes.

  Further, as in the present embodiment, when at least a pair of circumferential narrow grooves 38 are formed in each shoulder block 36 so as to open into the lug grooves 34, at least a pair of circumferential narrow grooves in each shoulder block 36 is formed. A complete block portion 36A having no groove portion is formed by discontinuing the circumferential narrow grooves 38 between them.

  As a result, the rigidity in each shoulder block 36 can be reliably ensured while increasing the drainage channels in each shoulder block 36, so that the steering stability can also be reliably ensured.

  At this time, when the pair of circumferential narrow grooves 38 are formed in line symmetry with respect to the center line in the tire circumferential direction of each shoulder block 36 as in the present embodiment, the most rigid of the shoulder blocks 36. The high portion can be the central portion of the shoulder block 36 in the tire circumferential direction.

  As a result, the amount of fall of the shoulder block 36 can be made uniform during braking and driving, so that rigidity in the shoulder block row 24 can be ensured without causing uneven wear on the shoulder block 36. Become.

  Furthermore, in the pneumatic tire 10 according to the present embodiment, the groove width (W1 to W2) from the terminal end 38A of the circumferential narrow groove 38 to the opening 38B is 10 of the average groove width in the circumferential main groove 18. The groove depth (D1 to D2) from the terminal end 38A of the circumferential narrow groove 38 to the opening 38B is set to 5% to 70% of the block height H of the shoulder block 36. When the size is set to%, the drainage performance in the shoulder block row 24 can be ensured even when the wear of the shoulder block 36 progresses.

  In addition, even when new, the shoulder block 36 can be prevented from falling down and the shoulder block 36 can have sufficient rigidity.

  The groove width W1 at the end portion 38A of the circumferential narrow groove 38 is set to a dimension that is less than 10% of the average groove width of the circumferential main groove 18 or at the end portion 38A of the circumferential narrow groove 38. If the groove depth D1 is set to a dimension less than 5% of the block height H of the shoulder block 36, the drainage by the circumferential narrow groove 38 cannot be ensured only by slightly wearing the shoulder block 36.

  That is, the drainage property in the shoulder block row 24 can be ensured only when new.

  Further, the groove width W2 in the opening 38B of the circumferential narrow groove 38 is configured to have a dimension larger than 50% of the average groove width in the circumferential main groove 18 or in the opening 38B of the circumferential narrow groove 38. If the groove depth D2 is configured to be larger than 70% of the block height of the shoulder block 36, the shoulder block 36 will be greatly deformed when new, and the rigidity of the shoulder block 36 can be secured. Disappear.

  And if the groove bottom part 38C of the circumferential direction fine groove 38 is comprised by the concave curved surface which has a curvature radius of 0.7 mm or more like the pneumatic tire 10 which concerns on this embodiment, the circumferential direction fine groove 38 of Since the strain can be prevented from concentrating on the groove bottom portion 38C, it is possible to suppress the occurrence of cracks in the groove bottom portion 38C of the circumferential narrow groove 38.

  The shoulder block 36 undergoes deformation called wiping because it receives a large input from the tire lateral direction during cornering. This is a deformation that also occurs during straight running.

  For this reason, compression and tensile deformation are repeatedly generated in the groove bottom portion 38C of the circumferential narrow groove 38 as the tire rolls, thereby concentrating strain.

  Accordingly, when the groove bottom portion 38C of the circumferential narrow groove 38 is configured with a concave curved surface having a radius of curvature of less than 0.7 mm, or when the circumferential narrow groove 38 is configured with a V-shaped cross section, the circumferential direction There is a possibility that a crack may occur in the groove bottom 38C of the narrow groove 38.

  Further, when the shoulder blocks 36 are provided at a variable pitch in the shoulder block row 24 as in the pneumatic tire 10 according to the present embodiment, it is possible to reduce pattern noise caused by the shoulder block row 24. Become.

  As described above in detail, according to the pneumatic tire 10 according to the present embodiment, it is possible to achieve both steering stability and wet performance by ensuring drainage while ensuring rigidity in the shoulder block row 24. It becomes.

  In particular, the above-described effects can be exhibited even in a configuration with a wide tire section width, a high inch, and a low flatness.

  Therefore, even if the pneumatic tire 10 has a wide tire section width, a high inch, and a low flatness, the hydroplaning phenomenon can be made less likely to occur when the wet road surface is traveling at high speed.

  Further, on the dry road surface, a high braking force and a driving force can be obtained by adopting a configuration in which the tire section width is wide and high, and the flatness is low.

(Test example)
Next, performance evaluation of the pneumatic tire 10 according to the present embodiment will be described.

  In order to confirm the effect of the present invention, a comparative test is performed on the pneumatic tire 10 according to the present example, the pneumatic tire 40 according to the conventional example, and the pneumatic tire 50 according to the comparative example.

  As shown in FIG. 4, the pneumatic tire 40 according to the conventional example has a configuration in which the circumferential narrow groove 38 formed in the shoulder block 36 is omitted from the pneumatic tire 10 according to the present embodiment.

  Further, as shown in FIG. 5, the pneumatic tire 50 according to the comparative example includes circumferential circumferential grooves 58 formed in the shoulder block 36 along the tire circumferential direction with respect to the pneumatic tire 10 according to the present embodiment. Thus, the groove width and groove depth are constant.

  The circumferential narrow groove 58 of the pneumatic tire 50 according to the comparative example is formed by additionally processing the circumferential narrow groove 38 of the pneumatic tire 10 according to the present embodiment with a groover.

  In the pneumatic tire 40 according to the conventional example and the pneumatic tire 50 according to the comparative example, the same reference numerals are used for the same configuration as the pneumatic tire 10 according to the present embodiment.

  In the comparative test, wet performance and turning motion performance are evaluated for each pneumatic tire. For wet performance, brake performance on wet roads is evaluated, and for steering stability, turning motion performance on dry roads is evaluated.

  At this time, the braking performance on a wet road surface is evaluated by measuring the braking distance until the vehicle stops at a speed of 80 km / h on an asphalt road surface with a water depth of 2 mm. As for the number of times of execution, the first 5 times are used as a break-in test, and thereafter, the test is performed 5 times continuously, and the average braking distance at this time is evaluated.

  Further, the reciprocal of the braking distance is used for the evaluation value of the braking performance on the wet road surface. At this time, index evaluation is performed by setting the braking performance of the pneumatic tire 40 according to the conventional example to 100. That is, the larger the index value, the better the braking performance on wet roads.

  As for the turning motion performance on a dry road surface, a vehicle is used when a constant speed turning with a radius of 30 m is performed and the speed is gradually increased from 50 km / h by 5 km / h, and the turning with a radius of 30 m cannot be maintained. Measure lateral acceleration.

  Further, the evaluation value of the turning motion performance on the dry road surface is index-evaluated assuming that the acceleration in the vehicle lateral direction of the pneumatic tire 40 according to the conventional example when the turning traveling with a radius of 30 m cannot be maintained is 100. That is, the larger the numerical value of the index, the better the turning motion performance on the dry road surface.

  Each pneumatic tire has a size of 235 / 45R17, and conditions such as air pressure and alignment of each pneumatic tire are those specified by the vehicle.

  Table 1 shows the specification values of the pneumatic tire according to the conventional example, the comparative example, and the present embodiment, and the evaluation values for the braking performance on the wet road surface and the turning motion performance on the dry road surface.

  From the above tests, as shown in Table 1, the pneumatic tire 50 according to the comparative example has improved drainage due to the provision of the circumferential narrow groove 58 as compared with the pneumatic tire 40 according to the conventional example. The result was excellent braking performance on wet roads.

  On the other hand, since the groove width and groove depth of the circumferential narrow groove 58 are constant along the tire circumferential direction, the rigidity of the shoulder block row 24 cannot be ensured, and the turning motion of the dry road surface The result was inferior in performance.

  On the other hand, the pneumatic tire 10 according to the present embodiment is configured such that the groove width and the groove depth gradually increase as the circumferential narrow groove 38 moves from the terminal end portion 38A toward the opening portion 38B. The drainage performance can be improved while ensuring the rigidity in the shoulder block row 24.

  As a result, the pneumatic tire 10 according to this example is superior to the pneumatic tire 40 according to the conventional example in terms of both braking performance on wet road surfaces and turning motion performance on dry road surfaces. .

  From the above, it can be said that the pneumatic tire 10 of the present embodiment is a well-balanced pneumatic tire having both steering stability performance and wet performance.

FIG. 1 is a developed view of a tread portion of a pneumatic tire according to the present embodiment. FIG. 2 is a perspective view showing the configuration of the circumferential narrow groove according to the present embodiment. FIG. 3 is a side view showing the configuration of the circumferential narrow groove according to the present embodiment. FIG. 4 is a developed view of a tread portion of a pneumatic tire according to a conventional example. FIG. 5 is a developed view of a tread portion of a pneumatic tire according to a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pneumatic tire 12 Tread part 14 Tread end 16,18 Circumferential main groove 24 Shoulder block row 36 Shoulder block 38 Circumferential thin groove 38A Termination part 38B Opening part 38C Groove bottom part

Claims (8)

A plurality of circumferential main grooves are formed along the tire circumferential direction on the tire tread surface of the tread portion, and a plurality of lug grooves are formed intersecting with the plurality of circumferential main grooves. In a pneumatic tire in which a plurality of block rows in which a plurality of blocks are arranged are formed in the tire width direction,
Each shoulder block of the shoulder block row located on the tread end side of the block row is formed along the tire circumferential direction, and both sides of the tire circumferential direction across the shoulder blocks among the plurality of lug grooves A circumferential narrow groove that opens in either one of the pair of lug grooves formed in and ends in each shoulder block is formed,
The circumferential narrow groove is configured such that the groove width gradually increases and the groove depth gradually increases from the terminal portion terminating in each shoulder block toward the opening opening in the lug groove. A pneumatic tire characterized by   The pneumatic tire according to claim 1, wherein the circumferential narrow groove has a triangular cross section in the longitudinal direction of the groove.   Each of the shoulder blocks is formed with at least one pair of the circumferential narrow grooves so as to open to each of a pair of lug grooves formed on both sides in the tire circumferential direction across the shoulder blocks. The pneumatic tire according to claim 1 or 2.   4. The pneumatic tire according to claim 3, wherein the pair of circumferential narrow grooves are formed in line symmetry with respect to a tire circumferential center line of each shoulder block. 5.   The groove width from the terminal end of the circumferential narrow groove to the opening is 10% to 50% of the average groove width in the circumferential main groove adjacent to the shoulder block row among the plurality of circumferential main grooves. The pneumatic tire according to any one of claims 1 to 4, wherein the pneumatic tire is set to a dimension of%.   The groove depth from the terminal end of the circumferential narrow groove to the opening is set to a dimension of 5% to 70% of the block height of the shoulder block. The pneumatic tire according to any one of claims 5 to 5.   The pneumatic tire according to any one of claims 1 to 6, wherein a groove bottom portion of the circumferential narrow groove is formed of a concave curved surface having a radius of curvature of 0.7 mm or more.   The pneumatic tire according to any one of claims 1 to 7, wherein the shoulder blocks are provided at a variable pitch in the shoulder block row.

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