JP2014141189A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire in which uneven wear of a tread part can be suppressed.SOLUTION: There is provided the pneumatic tire in which a pair of shoulder land parts 40 and a pair of middle land parts 20 are partitioned by providing a pair of shoulder main grooves 10 and a center main groove 9. Both side edges 23 in the tire circular direction, of the middle land part 20 extend toward the tire axial direction outside while inclining in the range of an angle α of 5 to 12° to the tire axial direction. Both side edges 43 in the tire circular direction, of the shoulder land part 40 incline in the range of an angle β equal to or larger than α and equal to or less than 17° to the tire axial direction. A distance L1 in the tire circular direction between the inner edge 46 and the outer edge 47 in the tire axial direction, of the edge 43 of the shoulder land part 40 is 0.03 to 0.12 times of the ground contact length L2 in the tire circular direction, of the shoulder land part 40.

Description

  The present invention relates to a pneumatic tire with improved uneven wear resistance by improving the shape of the ground contact surface.

  As shown in FIG. 5, various pneumatic tires having a main groove a extending continuously in the tire circumferential direction in the vicinity of the tread grounding end b have been proposed. Such a pneumatic tire has a problem in that shoulder fall wear is likely to occur in which the outer end portion d of the shoulder land portion c between the main groove a and the tread ground contact end b in the tire axial direction is unevenly worn.

  For such a problem, for example, Patent Document 1 below specifies the number of sipings formed in the land portion, thereby optimizing the rigidity of each land portion extending in the tire circumferential direction, and reducing uneven wear of the land portion. Proposed pneumatic tires that are suppressed. However, even such a pneumatic tire has room for further improvement in suppressing uneven wear.

  In addition, if the contact pressure of the shoulder land portion c is increased to suppress slipping from the road surface in order to suppress shoulder drop wear, slippage between the middle land portion d and the road surface is likely to occur. There has been a problem in that track wear occurs in which the end e is unevenly worn like a rail.

JP 2007-182097 A

  The present invention has been devised in view of the actual situation as described above, and provides a pneumatic tire capable of suppressing uneven wear of the tread portion on the basis of improving the shape of the contact surface of the tread portion and the like. Is the main purpose.

  According to the first aspect of the present invention, the tread portion has a pair of shoulder main grooves extending continuously in the tire circumferential direction on the tread ground end side, and a center extending inward in the tire axial direction from the shoulder main grooves. By providing the main groove, a pair of shoulder land portions on the outer side in the tire axial direction of each shoulder main groove and a pair of middle land portions between the pair of shoulder main grooves and the center main groove are divided. The contact surface when the tread portion is pressed against a flat surface with a normal load, loaded with a normal load and loaded with a normal load at a camber angle of 0 °, is a tire equator. The contact length in the tire circumferential direction gradually decreases from the side toward the tread ground contact edge, and the edges on both sides in the tire circumferential direction of the middle land portion on the ground contact surface are tire shafts. Inclined in the range of an angle α of 5 to 12 ° with respect to the direction and extends outward in the tire axial direction, and the edges on both sides in the tire circumferential direction of the shoulder land portion are equal to or greater than the angle α with respect to the tire axial direction. The distance L1 in the tire circumferential direction between the inner end and the outer end in the tire axial direction of the end edge of the shoulder land portion is 0. It is 0.03 to 0.12 times the ground contact length L2 in the tire circumferential direction of the shoulder land portion at a position separated by a distance of 97 times.

  The invention according to claim 2 includes a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer disposed inside the tread portion and outside the carcass, The outer end of the tire in the tire axial direction is positioned on the outer side in the tire axial direction with respect to the pair of shoulder main grooves, and the center main groove is a single piece extending in the tire circumferential direction on the tire equator, and the middle land portion Is divided by a middle lateral groove having one end communicating with the center main groove and the other end communicating with the shoulder main groove, and the distance in the tire axial direction between the shoulder main groove and the tire equator is the tire axis of the belt layer. The pneumatic tire according to claim 1, which is 0.45 to 0.70 times the half width in the direction.

  According to a third aspect of the present invention, the carcass includes two or more carcass plies made of a polyester cord, and the belt layer includes two or more belt plies made of a steel cord. Tire.

  According to a fourth aspect of the present invention, the center main groove includes a first portion and a second portion having a larger groove width than the first portion, and the first portion and the second portion are tires. The pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire is provided alternately in a circumferential direction.

  According to a fifth aspect of the present invention, the middle land portion is divided by a middle lateral groove having one end communicating with the center main groove and the other end communicating with the shoulder main groove, and the middle lateral groove has a groove bottom surface. The pneumatic tire according to any one of claims 1 to 4, wherein a raised tie bar and a groove bottom siping opened by the tie bar are provided.

  According to a sixth aspect of the present invention, each middle land portion has a first middle siping having one end communicating with the center main groove and the other end terminating in the middle land portion, and one end being the shoulder main groove. And a second middle siping whose other end terminates in the middle land portion. The first middle siping and the second middle siping are alternately provided in the tire circumferential direction. A pneumatic tire according to any one of claims 1 to 5.

  According to a seventh aspect of the present invention, the shoulder land portion is provided with an outer shoulder siping whose outer end in the tire axial direction opens at the tread grounding end. Tire.

  The pneumatic tire according to the present invention has a rim assembled on a regular rim, filled with a regular internal pressure, loaded with a regular load, and a tread portion is pressed against a flat surface at a camber angle of 0 °. Edges on both sides in the tire circumferential direction are inclined in the range of an angle α of 5 to 12 ° with respect to the tire axial direction and extend outward in the tire axial direction. Thereby, the contact length of the contact surface of the middle land portion gradually decreases gradually toward the outer side in the tire axial direction. For this reason, the difference in the contact pressure between the inner end portion and the outer end portion in the tire axial direction of the middle land portion is reduced. Accordingly, slippage between the outer end portion of the middle land portion and the road surface is suppressed, and track wear at the outer end portion is suppressed.

  Edges on both sides in the tire circumferential direction of the shoulder land portion are inclined with respect to the tire axial direction in the range of the angle β of the angle α to 17 °. Thereby, the contact length of the contact surface of the shoulder land portion gradually decreases gradually and gradually toward the outer side in the tire axial direction with the contact length of the middle land portion. Therefore, the difference in the contact pressure between the shoulder land portion and the middle land portion becomes small, and the progress of wear of the shoulder land portion and the middle land portion becomes uniform.

  The distance L1 in the tire circumferential direction between the inner end and the outer end in the tire axial direction of the edge of the shoulder land portion is a shoulder land portion at a position separated from the tire equator by 0.97 times the tread ground half width. This is 0.03 to 0.12 times the contact length L2 in the tire circumferential direction. As a result, the difference in the contact pressure between the inner end portion and the outer end portion in the tire axial direction of the shoulder land portion is reduced, and as a result, shoulder wear at the outer end portion of the shoulder land portion is suppressed.

It is sectional drawing which shows one Embodiment of the pneumatic tire of this invention. FIG. 2 is a development view of the tread portion of FIG. 1. FIG. 3 is a development view of a ground contact surface of the tread portion of FIG. 2. It is the elements on larger scale of the middle land part and shoulder land part of FIG. It is sectional drawing of the tread part of the conventional pneumatic tire.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a tire meridian cross-sectional view including a tire rotation axis in a normal state of a pneumatic tire (hereinafter, simply referred to as “tire”) 1 of the present embodiment. FIG. 2 is a development view of the tread portion of the tire of FIG. 1. FIG. 1 corresponds to the AA cross-sectional view of FIG. Here, the normal state is a no-load state in which the tire is assembled on a normal rim (not shown) and filled with a normal internal pressure. Hereinafter, unless otherwise specified, the dimensions and the like of each part of the tire are values measured in the normal state.

  The “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based. For example, “Standard Rim” for JATMA, “Design Rim” for TRA, For ETRTO, "Measuring Rim".

  As shown in FIG. 1, the pneumatic tire 1 of the present embodiment includes a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of the bead portion 4, and the carcass 6 has an outer side in the tire radial direction and a tread. A pneumatic tire for a light truck is shown in the present embodiment, including a belt layer 7 disposed inward of the portion 2.

  The carcass 6 includes, for example, two carcass plies 6A and 6B. The carcass plies 6 </ b> A and 6 </ b> B are folded back from the inner side in the tire axial direction to the outer side around the bead core 5 connected to the main body part 6 a from the tread part 2 through the sidewall part 3 to the bead core 5 of the bead part 4. And a folded portion 6b. As the carcass cords of the carcass plies 6A and 6B, for example, organic fiber cords such as polyester, aramid, and rayon are adopted. The carcass cord is arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator C.

  In the present embodiment, the belt layer 7 includes three belt plies 7A, 7B, and 7C in which the belt cord is inclined with respect to the tire equator C at an angle of, for example, 15 to 45 °, and the belt cords are mutually connected. It is formed by overlapping in the tire radial direction in the intersecting direction. In the belt layer 7 of this embodiment, the maximum width belt ply 7M having the largest width in the tire axial direction, and the belt plies 7A and 7C are overlapped on the inside and outside of the maximum width belt ply 7M in the tire axial direction. As the belt cord, for example, an organic fiber cord such as aramid or rayon or a steel cord is suitably employed.

  In the tire meridian cross section including the tire rotation axis, the radius of curvature R1 of the maximum width belt ply 7M is preferably 450 mm or more, more preferably 480 mm or more, preferably 550 mm or less, more preferably 520 mm or less. When the curvature radius R1 of the maximum width belt ply 7M is large, there is a possibility that the middle land portion 20 slips and the track wear occurs. On the other hand, when the radius of curvature R1 of the maximum width belt ply 7M is small, there is a possibility that shoulder drop wear may occur in the shoulder land portion 40.

  As shown in FIG. 2, the tire 1 includes a pair of shoulder main grooves 10 and 10 extending continuously in the tire circumferential direction on the tread portion 2 closest to the tread ground end Te, and the shoulder main grooves 10 and 10. Also, by providing one center main groove 9 extending inward in the tire axial direction, the pair of middle land portions 20 and 20 between the shoulder main groove 10 and the center main groove 9 and the shoulder main groove 10 are provided. The pair of outer shoulder land portions 40, 40 are separated.

  The tread contact end Te means a contact position on the outermost side in the tire axial direction when a normal load is applied to the tire in the normal state and contacted with a flat surface with a camber angle of 0 °. The “regular load” is a load determined by each standard for each tire in a standard system including the standard on which the tire is based. “JATMA” indicates “maximum load capacity”, and TRA indicates The maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is “LOAD CAPACITY” in the case of ETRTO, but when the tire is used for a passenger car, the load corresponds to 88% of the load. The distance between the tread ground contact ends Te and Te in the tire axial direction is the tread ground contact width TW.

  In order to satisfy drainage performance, steering stability, brake performance, and the like, the groove width W1 of the center main groove 9 and the groove width W2 of the shoulder main groove 10 are, for example, 3.0 to 6.0% of the tread ground contact width TW. Is desirable. The groove depth D1 of the center main groove 9 and the groove depth D2 of the shoulder main groove 10 are preferably 6 to 12 mm, for example. The groove widths of the center main groove 9 and the shoulder main groove 10 are measured in a direction perpendicular to the groove center line, and the same applies to other grooves.

  The center main groove 9 is composed of a single line extending linearly on the tire equator C in the tire circumferential direction. The center main groove 9 of the present embodiment includes a first portion 9a and a second portion 9b having a larger groove width than the first portion 9a, and the groove width changes in the tire circumferential direction. It is desirable that the first portions 9a and the second portions 9b are alternately provided in the tire circumferential direction. Such a center main groove 9 maintains the rigidity in the vicinity of the tire equator C, improves the steering stability, and improves the wet performance.

  The ratio W1a / W1b between the groove width W1a of the first portion 9a and the groove width W1b of the second portion 9b is, for example, 0. 0 in order to improve the wet performance of the tire while maintaining the rigidity of the middle land portion 20. It is 60 or more, more preferably 0.65 or more, preferably 0.80 or less, more preferably 0.75 or less.

  The shoulder main groove 10 extends linearly in the tire circumferential direction. As shown in FIG. 1, the shoulder main grooves 10 and 10 are provided on the inner side in the tire axial direction of the outer ends 7 e and 7 e of the belt layer 7 in the tire axial direction, respectively. On the other hand, if the shoulder main groove 10 is too close to the tire equator C, partial wear may occur in the middle land portion 20. For this reason, the distance L8 in the tire axial direction between the shoulder main groove 10 and the tire equator C is preferably 0.50 times or more, more preferably 0.55 times or more the half width BWh of the belt layer 7 in the tire axial direction. , Preferably 0.70 times or less, more preferably 0.65 times or less.

  FIG. 3 shows a developed view of the ground contact surface 2s of the tread portion 2. As shown in FIG. The contact surface 2s shown in FIG. 3 is obtained by assembling a rim on a normal rim, filling a normal internal pressure, and applying a normal load and pressing the tread portion 2 against a flat surface at a camber angle of 0 °.

  The contact pressure of the tread portion 2 gradually decreases from the tire equator C toward the tread contact end Te side with the curvature of the contact surface of the tread portion 2. For this reason, the tire circumferential direction length L0 of the contact surface 2s is gradually reduced from the tire equator C side toward the tread contact end Te.

  On the contact surface 2s, the edges 23 and 23 on both sides in the tire circumferential direction of the middle land portion 20 are inclined in the range of an angle α of 5 to 12 ° with respect to the tire axial direction and extend outward in the tire axial direction. Thereby, the contact length L3 of the contact surface 22 of the middle land portion 20 gradually decreases toward the outer side in the tire axial direction. For this reason, the difference in the contact pressure between the inner end 24 and the outer end 25 in the tire axial direction of the middle land portion 20 is reduced. Therefore, slip between the outer end portion 25 of the middle land portion 20 and the road surface is suppressed, and track wear of the outer end portion 25 is suppressed.

  When the angle α is smaller than 5 °, the contact pressure of the inner end portion 24 of the middle land portion 20 is excessively lowered, and there is a risk that track wear occurs at the inner end portion 24. Conversely, when the angle α is larger than 12 °, the difference in the contact pressure between the inner end 24 and the outer end 25 of the middle land portion 20 increases, and the slippage increases between the outer end 25 and the road surface. Then, there is a possibility that the track wear of the outer end portion 25 may occur. For this reason, the angle α is more preferably 7 ° or more, further preferably 8 ° or more, more preferably 10 ° or less, and further preferably 9 ° or less.

  Edges 43 and 43 on both sides in the tire circumferential direction of the shoulder land portion 40 are inclined with respect to the tire axial direction in the range of the angle β of the angle α to 17 °. Thereby, the ground contact length L4 of the ground contact surface 42 of the shoulder land portion 40 is gradually decreased toward the outer side in the tire axial direction continuously with the ground contact length L3 of the middle land portion 20. Therefore, the difference in the contact pressure between the shoulder land portion 40 and the middle land portion 20 becomes small, and the progress of wear of the shoulder land portion 40 and the middle land portion 20 becomes uniform.

  If the angle β is smaller than the angle α, orbital wear may occur at the outer end portion 25 of the middle land portion 40. On the other hand, when the angle β is larger than 17 °, the amount of slip between the shoulder land portion 40 and the road surface becomes large, and shoulder fall wear occurs in the shoulder land portion 40. For this reason, the angle β is more preferably 12 ° or more, further preferably 13 ° or more, more preferably 16 ° or less, and further preferably 15 ° or less.

  The distance L1 in the tire circumferential direction between the inner end 46 and the outer end 47 in the tire axial direction of the edge 43 of the shoulder land portion 40 is separated from the tire equator C by 0.97 times the tread grounding half width TWh. It is 0.03 to 0.12 times the contact length L2 in the tire circumferential direction of the shoulder land portion 40 at the position. Thereby, the difference in the contact pressure between the inner end portion 44 and the outer end portion 45 in the tire axial direction of the shoulder land portion 40 is reduced, and as a result, the shoulder drop wear of the outer end portion 45 of the shoulder land portion 40 is suppressed.

  The shape of the contact surface 2s of the tread portion 2 can vary greatly depending on, among other things, the profile of the tread portion 2 in the normal state and the rubber volume of the tread rubber Tg of the tread portion 2. For this reason, it is desirable that the profile of the tread portion 2 is convex outward in the tire radial direction. The tread rubber thickness from the outer surface of the maximum width belt ply of the tread rubber to the contact surface of the tread portion is preferably constant in the tire axial direction or gradually decreased from the tire equator C toward the outer side in the tire axial direction.

  In order to obtain the shape of the contact surface 2s of the tread portion 2 described above, it is desirable that the thickness of the tread rubber Tg is defined. Specifically, the inner land portion thickness t1 that is the thickness of the tread rubber at a position 0.30 times the tread ground half width TWh from the tire equator C is, for example, the tread rubber thickness on the tire equator C. It is desirable to set it to 0.96 to 0.97 times the reference land portion thickness tb. Further, the intermediate land portion thickness t2, which is the thickness of the tread rubber at a position 0.65 times the tread ground half width TWh from the tire equator C, is, for example, 0.89 to 0.95 times the reference land portion thickness tb. It is desirable to set to. Further, the outer land portion thickness t3, which is the thickness of the tread rubber at a position 0.90 times the tread ground half width TWh from the tire equator C, is, for example, 0.86 to 0.92 times the reference land portion thickness tb. It is desirable to set to.

  In addition, when the groove | channel is provided in the measurement position of inner land part thickness t1, intermediate | middle land part thickness t2, and outer land part thickness t3, each said thickness t1 thru | or t3 filled the groove virtually It is a value measured in the state.

  As shown in FIG. 4, the middle land portion 20 of the present embodiment is provided with a middle lateral groove 26 having one end 27 communicating with the center main groove 9 and the other end 28 communicating with the shoulder main groove 10. Thereby, the middle block 29 is spaced apart in the tire circumferential direction. Each middle block 29 is provided with a middle siping 30.

  The groove width W7 of the middle lateral groove 26 is preferably smaller than the groove width W2 (shown in FIG. 1) of the shoulder main groove 10, and is, for example, 0.30 times or more of the groove width W2, more preferably 0. It is 35 times or more, preferably 0.45 times or less, more preferably 0.40 times or less. Such middle lateral grooves 26 achieve both steering stability and wet performance.

  It is desirable that one end 27 of the middle lateral groove 26 communicates with the second portion 9 b of the center main groove 9. Thereby, the drainage performance of the middle lateral groove 26 is improved, and consequently the wet performance is improved.

  The other end 28 of the middle lateral groove 26 is preferably continuous with a recess 32 in which an edge 31 on the outer side in the tire axial direction of the middle land portion 20 is recessed toward the inner side in the tire axial direction. Thereby, the deformation | transformation area | region of a middle block is ensured. Therefore, when the contact pressure from the road surface acts on the contact surface 2s, the middle block 29 is deformed along the road surface while suppressing slippage with the road surface. For this reason, uneven wear of the middle block 29 is suppressed.

  As shown in FIG. 1, the middle horizontal groove 26 is preferably provided with a tie bar 33 with a groove bottom surface 26 d raised and a groove bottom siping 34 opened with the tie bar 33. Thereby, the movement of the middle block 29 (shown in FIG. 3) is suppressed, and the wear resistance of the middle block 29 is improved.

  In order to further enhance the above action, the height h1 of the tie bar 33 is preferably 0.40 times or more, more preferably 0.45 times or more, preferably 0.45 times or more the groove depth D1 of the center main groove 9. 60 times or less, more preferably 0.55 times or less. Similarly, the depth D3 of the groove bottom siping 34 is preferably 0.80 times or more, more preferably 0.85 times or more, preferably 1.00 times or less, more preferably the height h1 of the tie bar 33. Is 0.95 times or less.

  As shown in FIG. 4, for example, one middle siping 30 is provided in the middle portion 29 m in the tire circumferential direction of each middle block 29 in parallel with the middle lateral groove 26. The middle siping 30 has one end 35a communicating with the center main groove 9 and the other end 35b terminating in the middle land portion 20, and one end 36a communicating with the shoulder main groove 10 and the other end. 36 b includes a second middle siping 36 that terminates in the middle land portion 20. The first middle siping 35 and the second middle siping 36 are provided in the middle block 29 so as to be alternately arranged in the tire circumferential direction, for example. Such a middle siping 30 improves wet performance, makes the progress of wear of the middle land portion 20 and the shoulder land portion 40 uniform, and suppresses uneven wear.

  The shoulder land portion 40 of the present embodiment is formed by ribs that are continuous in the tire circumferential direction. The shoulder land portion 40 includes, for example, an inner lug groove 48 and an inner shoulder siping 49 that communicate with the shoulder main groove 10, and an outer lug groove 50 and an outer shoulder siping 51 that open at the tread grounding end Te. Yes. Such a shoulder land portion 40 makes the progress of wear of the inner end portion 44 and the outer end portion 45 of the shoulder land portion 40 uniform, and suppresses shoulder drop wear of the shoulder land portion 40.

  The inner lug groove 48 has one end 52 communicating with the shoulder main groove 10 and the other end 53 terminating in the shoulder land portion 40. The inner lug groove 48 communicates with the shoulder main groove 10 and has a first portion 48a in which the groove width gradually decreases toward the outer side in the tire axial direction. The inner lug groove 48 continues to the first portion 48a. And a second portion 48b that terminates. For example, the inner lug grooves 48 are spaced at equal intervals in the tire circumferential direction. Thereby, the deformation | transformation area | region of the shoulder land part 40 is ensured, and the slip with the outer surface of the shoulder land part 40 and a road surface is suppressed. Further, such an inner lug groove 48 reinforces the drainage performance of the shoulder main groove 10 and consequently improves the wet performance of the tire.

  In order to enhance such an action, the length L5 of the inner lug groove 48 in the tire axial direction is preferably 1.10 times or more, more preferably 1 of the groove width W2 (shown in FIG. 2) of the shoulder main groove 10. .15 times or more, preferably 1.30 times or less, more preferably 1.25 times or less.

  For example, the inner shoulder siping 49 has one end 54 communicating with the shoulder main groove 10 and the other end 55 terminating in the shoulder land portion 40. In addition, a plurality of inner shoulder sipings 49 are provided between the inner lug grooves 48, for example, 1 to 5, for example, three in this embodiment. Such an inner shoulder siping 49 makes the progress of wear uniform between the inner end 44 of the shoulder land portion 40 and the outer end 25 of the middle land portion 20, and orbital wear of the outer end portion 25 of the middle land portion 20. Suppress.

  In order to further enhance such an action, the length L6 of the inner shoulder siping 49 in the tire axial direction is preferably 0.40 times or more, more preferably 0.43 times or more the length L5 of the inner lug groove 48. Preferably, it is 0.50 times or less, more preferably 0.47 times or less.

  The outer lug groove 50 opens, for example, at the tread ground contact end Te, and the inner end 57 in the tire axial direction terminates in the shoulder land portion 40. The outer lug groove 50 includes, for example, a first portion 50a extending at a constant groove width on the outer side in the tire axial direction, and a second portion that continues to the first portion 50a and ends in the shoulder land portion 40 with the groove width gradually decreasing. 50b. The outer lug grooves 50 are desirably provided at equal intervals in the tire circumferential direction. Thereby, the deformation | transformation area | region of the shoulder land part 40 is ensured, and the slip with the outer surface of the shoulder land part 40 and a road surface is suppressed. Such an outer lug groove 50 makes the rigidity of the shoulder land portion 40 appropriate and improves the wandering performance.

  In order to further enhance such an action, the groove width W8 of the outer lug groove 50 is preferably 0.60 times or more, more preferably 0.65 times or more, preferably 0.65 times or more of the length L5 of the inner lug groove 48, preferably It is 0.75 times or less, More preferably, it is 0.70 times or less.

  The outer shoulder siping 51 opens, for example, at the tread grounding end Te, and the inner end 58 ends in the shoulder land portion 40. The outer shoulder siping 51 extends parallel to the tire axial direction, for example. For example, a plurality of outer shoulder sipings 51 are provided between the outer lug grooves 50, 50, for example, 1 to 5, for example, three in this embodiment. Such an outer shoulder siping 51 improves wet performance and wandering performance.

  The length L7 in the tire axial direction from the inner end 58 of the outer shoulder siping 51 to the tread ground contact end Te is preferably 2.2 times or more, more preferably, the length L6 of the inner shoulder siping 49 in the tire axial direction. It is 2.3 times or more, preferably 2.6 times or less, more preferably 2.5 times or less. Such an outer shoulder siping 51 makes the progress of wear of the inner end portion 44 and the outer end portion 45 of the shoulder land portion 40 uniform, and suppresses uneven wear.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, this invention can be changed into various aspects, without being limited to said specific embodiment, and can be implemented.

A pneumatic tire for a light truck of size 185 / 65R15 having the basic structure of FIG. 1 and the tread pattern of FIG. 2 was prototyped based on the specifications in Table 1, and the amount of uneven wear and shoulder wear of each sample tire was Presence / absence, wandering performance and exothermicity of the shoulder land were tested.
The test method is as follows.

<Uneven wear>
Each sample tire was mounted on an actual vehicle under the following conditions, and the amount of uneven wear after running 8000 km was measured. The uneven wear amount means a difference between the remaining groove depth of the center main groove and the remaining groove depth of the shoulder type groove. The result is an index with the uneven wear amount of Comparative Example 1 being 100, and the smaller the numerical value, the smaller the uneven wear amount and the better.
Wearing rim: 5.0J × 15
Internal pressure: 600 kPa
Installed vehicle: Light truck with maximum loading capacity of 2t, 2-D vehicle Tire mounting position: Front wheel

<Existence of shoulder wear>
When measuring the amount of uneven wear, the presence or absence of shoulder drop wear on the shoulder land was examined with the naked eye. The results are displayed in the following three-level evaluation.
A: Good shoulder wear is not generated.
B: Although shoulder fall wear has occurred, it is at a level that can be commercialized.
C: Shoulder drop wear has occurred at a level that cannot be commercialized.

<Wandering performance>
The wandering performance when a test vehicle with a fixed volume condition under the following conditions traveled on a rough road surface was evaluated by the driver's sensuality. The wandering performance means the steering stability and riding comfort of the vehicle when entering the heel, going straight in the heel, and escaping from the heel. A result is a score which sets the comparative example 1 to 100, and shows that it is excellent in the wandering performance, so that a numerical value is large.
Wearing rim: 5.0J × 15
Internal pressure: 600 kPa
Installed vehicle: Light truck with maximum loading capacity of 2t, 2-D vehicle Tire mounting position: Front wheel Speed: 60km / h

<Exotherm of shoulder land>
The temperature of the shoulder land portion when measured on the drum test machine under the following conditions was measured. A result is an index which sets comparative example 1 as 100, and shows that heat generation of a shoulder land part is so small that a numerical value is small, and durability of a shoulder land part is high.
Wearing rim: 5.0J × 15
Internal pressure: 600 kPa
Longitudinal load: 12kN
Speed: 80km / h
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the tire of the example had improved uneven wear resistance compared to the tire of the comparative example.

2 Tread portion 9 Center main groove 10 Shoulder main groove 20 Middle land portion 23 Edge 40 Shoulder land portion 43 Edge

Claims (7)

Each shoulder is provided with a pair of shoulder main grooves extending continuously in the tire circumferential direction on the tread ground end side and a center main groove extending inward in the tire axial direction from the shoulder main grooves. A pneumatic tire in which a pair of shoulder land portions on the outer side in the tire axial direction of the main groove and a pair of middle land portions between the pair of shoulder main grooves and the center main groove are divided,
The ground contact surface when the tread is pressed against a flat surface with a normal load and a normal load filled with a normal load and a camber angle of 0 ° is the tire from the tire equator side toward the tread ground contact end. The circumferential contact length is gradually reduced, and in the contact surface,
Edges on both sides in the tire circumferential direction of the middle land portion are inclined in the range of an angle α of 5 to 12 ° with respect to the tire axial direction and extend outward in the tire axial direction,
Edges on both sides in the tire circumferential direction of the shoulder land portion are inclined with respect to the tire axial direction in the range of the angle β of the angle α to 17 °,
The distance L1 in the tire circumferential direction between the inner end and the outer end in the tire axial direction of the edge of the shoulder land portion is a position separated from the tire equator by a distance 0.97 times the tread ground half width. A pneumatic tire characterized by being 0.03 to 0.12 times the contact length L2 in the tire circumferential direction of the shoulder land portion. A carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer disposed inside the tread portion and outside the carcass,
The outer end of the belt layer in the tire axial direction is located on the outer side in the tire axial direction than the pair of shoulder main grooves,
The center main groove consists of one piece extending on the tire equator in the tire circumferential direction,
The middle land portion is divided by a middle lateral groove having one end communicating with the center main groove and the other end communicating with the shoulder main groove,
The pneumatic tire according to claim 1, wherein a distance in the tire axial direction between the shoulder main groove and the tire equator is 0.45 to 0.70 times a half width of the belt layer in the tire axial direction. The carcass includes two or more carcass plies made of a polyester cord,
The pneumatic tire according to claim 2, wherein the belt layer includes two or more belt plies made of a steel cord. The center main groove includes a first portion and a second portion having a groove width larger than the first portion,
The pneumatic tire according to any one of claims 1 to 3, wherein the first portion and the second portion are provided alternately in a tire circumferential direction. The middle land portion is divided by a middle lateral groove having one end communicating with the center main groove and the other end communicating with the shoulder main groove,
The pneumatic tire according to any one of claims 1 to 4, wherein the middle lateral groove is provided with a tie bar having a raised groove bottom surface and a groove bottom siping opened by the tie bar. Each middle land portion has a first middle siping having one end communicating with the center main groove and the other end terminating in the middle land portion, and one end communicating with the shoulder main groove and the other end of the middle main groove. A second middle siping that terminates in the land,
The pneumatic tire according to any one of claims 1 to 5, wherein the first middle siping and the second middle siping are alternately provided in a tire circumferential direction.   The pneumatic tire according to any one of claims 1 to 6, wherein the shoulder land portion is provided with an outer shoulder siping whose outer end in the tire axial direction opens at the tread grounding end.

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