JP2015013514A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that is improved in on-snow performance while maintaining on-ice performance.SOLUTION: In a tread portion 2 are provided shoulder main grooves 3 and a center main groove 4 so that shoulder land portions 5 and middle land portions 6 are partitioned. In the shoulder land portions 5 are formed shoulder lateral grooves 10. The middle land portions 6 are partitioned into first middle land portions 31 and second middle land portions 32 by middle sub grooves 30. In the first middle land portions 31 are formed first middle lateral grooves 34. In the shoulder land portions 5 and the first middle land portions 31 are formed dimples 20 which have edges 21 and have recessed regions surrounded by the edges 21. The dimples 20 are adjacent to the shoulder lateral grooves 10 or the first middle lateral grooves 34. Lengths L1 in a tire circumferential direction of the dimples 20 are larger than widths W1 in a tire axial direction of the dimples 20.

Description

  The present invention relates to a pneumatic tire that can improve performance on snow while maintaining performance on ice.

  In order to improve running performance on snowy roads (hereinafter referred to as “on-snow performance”), a pneumatic tire having a lateral groove extending in the tire axial direction has been proposed. When such a pneumatic tire travels on a snowy road, the snow on the road surface is compressed in a lateral groove to form a snow column, and the reaction force when shearing the snow column (hereinafter referred to as “snow column shear force”). ) To obtain driving force.

  In order to achieve both performance on snow and running performance on ice (hereinafter referred to as “performance on ice”), the tread block has a notch shape that does not have a substantial thickness extending in the tire axial direction. A pneumatic tire provided with a sipe is proposed (for example, see Patent Document 1 below). Such a pneumatic tire improves on-ice performance due to the edge effect of the lateral grooves and sipes.

JP 2009-269500 A

  However, in the pneumatic tire as described above, the rigidity of the land portion is reduced by sipe. For this reason, when running on a snowy road, there is a problem in that the action of the lateral grooves compressing the snow is reduced and the snow column shear force is reduced.

  The present invention has been devised in view of the actual situation as described above, and is based on the provision of dimples having concave treads on the land, and a pneumatic tire that improves on-snow performance while maintaining on-ice performance. The main purpose is to provide.

  The present invention provides a pair of shoulder main grooves extending continuously in the tire circumferential direction on the tread ground end side most at the tread portion, and a center main extending continuously in the tire circumferential direction on the inner side in the tire axial direction than the shoulder main grooves. By providing the groove, the pair of shoulder land portions outside the tire axial direction from the pair of shoulder main grooves and the pair of middle land portions between the shoulder main groove and the center main groove are separated. The shoulder land portion is provided with a plurality of shoulder lateral grooves extending in the tire axial direction, and the middle land portion is formed in the tire axial direction by a middle sub-groove extending continuously in the tire circumferential direction. The first middle land portion is divided into an outer first middle land portion and a second middle middle land portion in the tire axial direction, and the first middle land portion has a plurality of first middle lateral grooves extending in the tire axial direction. The shoulder land portion and the first middle land portion are each provided with a dimple having a closed edge that appears in the tread surface and having a recessed region surrounded by the edge, Adjacent to a shoulder lateral groove or the first middle lateral groove, a length L1 of the dimple in the tire circumferential direction is larger than a width W1 of the dimple in the tire axial direction.

  In the pneumatic tire according to the present invention, the shoulder lateral groove extends from the tread ground end to the shoulder main groove, and the first middle lateral groove is smoothly connected to the shoulder lateral groove via the shoulder main groove. Is desirable.

  In the pneumatic tire according to the present invention, it is preferable that the edge of the dimple has an oval shape, an oval shape, or a rectangular shape.

  In the pneumatic tire according to the present invention, the total number Ns of the dimples provided in the one shoulder land portion is larger than the total number Nm of the dimples provided in the one first middle land portion. Is desirable.

  In the pneumatic tire according to the present invention, the shoulder land portion is a block row in which shoulder blocks divided by a plurality of shoulder lateral grooves are arranged, and the shoulder blocks are formed by shoulder sub-grooves extending in a tire circumferential direction. It is desirable that the first shoulder block piece on the outer side in the tire axial direction is divided into the second shoulder block piece on the inner side in the tire axial direction.

  In the pneumatic tire according to the present invention, it is preferable that an angle θ1 of the shoulder lateral groove with respect to the tire axial direction and an angle θ2 of the first middle lateral groove with respect to the tire axial direction are respectively 5 to 25 °.

  In the pneumatic tire according to the present invention, it is desirable that the width W1 of the dimple is 1.0 to 2.5 mm.

  In the pneumatic tire according to the present invention, it is preferable that the length L1 of the dimple is 3.0 to 4.5 mm.

  In the pneumatic tire according to the present invention, the dimple depth d1 is preferably 0.5 to 3.0 mm.

  The pneumatic tire of the present invention has a pair of shoulder main grooves extending continuously in the tire circumferential direction at the tread ground end side most continuously on the tread portion, and continuously in the tire circumferential direction on the inner side in the tire axial direction than the shoulder main grooves. By extending the center main groove, the pair of shoulder land portions on the outer side in the tire axial direction than the pair of shoulder main grooves, and the pair of middle land portions between the shoulder main groove and the center main groove are provided. It is divided.

  The shoulder land portion is provided with a plurality of shoulder lateral grooves extending in the tire axial direction. The middle land portion is divided into a first middle land portion on the outer side in the tire axial direction and a second middle land portion on the inner side in the tire axial direction by middle sub-grooves extending continuously in the tire circumferential direction. The first middle land portion is provided with a plurality of first middle lateral grooves extending in the tire axial direction. Such shoulder lateral grooves and first middle lateral grooves exhibit an edge effect when traveling on an icy road, and exhibit a large snow column shear force when traveling on a snowy road. Therefore, on-ice performance is improved while maintaining on-ice performance.

  Each of the shoulder land portion and the first middle land portion is provided with a dimple having a closed edge that appears in the tread surface and in which a region surrounded by the edge is recessed. Such dimples effectively suppress a decrease in rigidity of the land portion because the edges do not communicate with the lateral grooves. Furthermore, such an edge exhibits an edge effect in multiple directions. Therefore, excellent performance on ice is exhibited.

  The dimple is adjacent to the shoulder lateral groove or the first middle lateral groove. A length L1 of the dimple in the tire circumferential direction is larger than a width W1 of the dimple in the tire axial direction. Such dimples increase the rigidity in the tire circumferential direction of the land portion compared to the conventional sipe, and effectively suppress the deformation of the groove wall of the lateral groove in the tire circumferential direction. For this reason, when running on a snowy road, the pressure acting on the snow in the lateral groove increases, and a stronger snow column is formed. Therefore, a large snow column shear force is exhibited and excellent on-snow performance is exhibited.

  For this reason, the pneumatic tire of the present invention can improve the performance on snow while maintaining the performance on ice.

It is an expanded view of the tread part which shows the pneumatic tire of this embodiment. It is AA sectional drawing of FIG. It is an expansion perspective view of the dimple of FIG. It is an enlarged view of the shoulder land part of FIG. It is an enlarged view of the middle land part of FIG.

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 (hereinafter sometimes simply referred to as “tire”) 1 of the present embodiment. The pneumatic tire 1 of this embodiment is suitably used as a winter tire for passenger cars, for example.

  As shown in FIG. 1, the tread portion 2 of the tire 1 is provided with a pair of shoulder main grooves 3 and 3 and a center main groove 4 therebetween.

  The shoulder main groove 3 extends continuously in the tire circumferential direction on the tread ground contact end Te side. The shoulder main groove 3 of the present embodiment has a substantially constant groove width and is linear. The shoulder main groove 3 may be wavy or zigzag-shaped.

  The “tread ground contact Te” is a ground contact position on the outermost side in the tire axial direction when a normal load is applied to the tire 1 in a normal state and grounded on a plane with a camber angle of 0 °.

  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, dimensions and the like of each part of the tire are values measured in this normal state.

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

  “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. “JAMATA” is the “highest air pressure”, TRA is the table “TIRE LOAD LIMITS AT” The maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO.

  “Regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. “JATMA” is “Maximum load capacity”, TRA is “TIRE LOAD LIMITS” The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” in the case of ETRTO.

  The center main groove 4 is provided on the inner side in the tire axial direction than the shoulder main groove 3. The center main groove 4 extends continuously in the tire circumferential direction. The center main groove 4 has a substantially constant groove width and is linear. The center main groove 4 of this embodiment consists of one, and is provided on the tire equator C. The center main groove 4 may be a pair of grooves provided on both sides of the tire equator C, for example.

  The groove width W2 of the shoulder main groove 3 and the groove width W3 of the center main groove 4 are, for example, 2.5 to 4.5% of the tread ground contact width TW. The shoulder main groove 3 and the center main groove 4 exhibit excellent wet performance while maintaining the rigidity of the tread portion 2. The tread contact width TW is a distance in the tire axial direction between the tread contact ends Te and Te of the tire 1 in the normal state.

  FIG. 2 is a cross-sectional view taken along the line AA in FIG. As shown in FIG. 2, the groove depth d2 of the shoulder main groove 3 and the groove depth d3 of the center main groove 4 are preferably, for example, 7.0 to 12.0 mm.

  As shown in FIG. 1, the tread portion 2 is divided into a pair of shoulder land portions 5, 5 and a pair of middle land portions 6, 6.

  The shoulder land portion 5 is provided on the outer side in the tire axial direction than the shoulder main groove 3. The width W4 of the shoulder land portion 5 in the tire axial direction is, for example, 0.20 to 0.30 times the tread ground contact width TW. Such a shoulder land portion 5 achieves both on-ice performance and on-snow performance.

  The shoulder land portion 5 is a block row in which shoulder blocks 14 divided by a plurality of shoulder lateral grooves 10 are arranged. Each shoulder lateral groove 10 extends in the tire axial direction from the tread ground contact Te to the shoulder main groove 3.

  The shoulder lateral groove 10 is inclined with respect to the tire axial direction. The angle θ1 of the shoulder lateral groove 10 with respect to the tire axial direction is preferably 5 ° or more, more preferably 10 ° or more, preferably 25 ° or less, more preferably 20 ° or less. Such a shoulder lateral groove 10 exhibits an edge effect with a good balance in the tire circumferential direction and the tire axial direction.

  The shoulder lateral groove 10 includes a first portion 11 and a second portion 12. The first portion 11 of the shoulder lateral groove 10 continues to the shoulder main groove 3 and has a substantially constant groove width. The second portion 12 of the shoulder lateral groove 10 is connected to the outer side in the tire axial direction of the first portion 11 via a step 8, and is displaced from the first portion 11 in the tire circumferential direction. Such a shoulder lateral groove 10 exhibits a large snow column shear force when turning on a snowy road.

  The width W5 of the shoulder lateral groove 10 is, for example, 1.25 to 1.35 times the groove width W2 of the shoulder main groove 3. Such a shoulder lateral groove 10 improves the performance on snow while maintaining the performance on ice.

  The middle land portion 6 is provided between the shoulder main groove 3 and the center main groove 4. The width W6 in the tire axial direction of the middle land portion 6 is preferably 0.15 to 0.25 times the tread ground contact width TW. Such a middle land portion 6 exhibits excellent on-snow performance while maintaining on-ice performance.

  A middle sub-groove 30 is provided in the middle land portion 6. The middle sub-groove 30 extends continuously in the tire circumferential direction. The groove width W7 of the middle sub groove 30 is smaller than the groove width W2 of the shoulder main groove 3, for example. The groove width W7 of the middle sub groove 30 is preferably 0.50 to 0.85 times the groove width W2 of the shoulder main groove 3.

  The middle land portion 6 is divided by a middle sub-groove 30 into a first middle land portion 31 on the outer side in the tire axial direction and a second middle land portion 32 on the inner side in the tire axial direction.

  The first middle land portion 31 is provided with a plurality of first middle lateral grooves 34. Each first middle lateral groove 34 extends from the shoulder main groove 3 to the middle sub-groove 30 in the tire axial direction.

  The first middle lateral groove 34 is inclined with respect to the tire axial direction, for example. The angle θ2 of the first middle lateral groove 34 with respect to the tire axial direction is preferably 5 ° or more, more preferably 10 ° or more, preferably 25 ° or less, more preferably 20 ° or less. Such first middle lateral grooves 34 exhibit an edge effect with a good balance in the tire circumferential direction and the tire axial direction.

  The first middle lateral groove 34 has a substantially constant groove width W8. The groove width W8 of the first middle lateral groove 34 is, for example, 0.9 to 1.0 times the groove width W2 of the shoulder main groove 3.

  The first middle lateral groove 34 is preferably smoothly connected to the shoulder lateral groove 10 via the shoulder main groove 3, for example. As a result, a large snow column is formed at the intersection 9 of the shoulder main groove 3, the shoulder lateral groove 10, and the first middle lateral groove 34 when traveling on a snowy road. For this reason, a snow column shear force becomes large and the performance on snow improves.

  A dimple 20 is provided on the shoulder land portion 5 and the first middle land portion 31. The dimple 20 has a closed edge 21 that appears in the tread. The dimple 20 has a recessed area surrounded by the edge 21. Such a dimple 20 effectively suppresses a decrease in rigidity of the shoulder land portion 5 and the first middle land portion 31 because the edge 21 does not communicate with the lateral groove. Furthermore, the edge 21 of the dimple 20 exhibits an edge effect in multiple directions. Therefore, excellent performance on ice is exhibited.

  The dimple 20 is adjacent to the shoulder lateral groove 10 or the first middle lateral groove 34. “The dimple is adjacent to the groove” means that the distance between the edge of the dimple and the groove edge of the groove is smaller than the groove width of the groove, and the sipe and others between the dimple and the groove. This means that no groove is provided.

  FIG. 3 shows an enlarged perspective view of the dimple 20. FIG. 3 is an enlarged perspective view of a region a surrounded by a broken line in FIG. As shown in FIG. 3, the length L1 of the dimple 20 in the tire circumferential direction is larger than the width W1 of the dimple 20 in the tire axial direction. Such dimple 20 keeps the rigidity in the tire circumferential direction of the land portion larger than that of the conventional sipe, and effectively suppresses the deformation in the tire circumferential direction of the groove wall of the lateral groove. For this reason, when running on a snowy road, the pressure acting on the snow in the lateral groove increases, and a stronger snow column is formed. Therefore, a large snow column shear force is exhibited and excellent on-snow performance is exhibited.

  The ratio L1 / W1 between the length L1 of the dimple 20 in the tire circumferential direction and the width W1 of the dimple 20 in the tire axial direction is greater than 1, but preferably 1.8 or more, more preferably 2.3. It is above, Preferably it is 4.5 or less, More preferably, it is 4.0 or less. When the ratio L1 / W1 is smaller than 1.8, the rigidity in the tire circumferential direction of the land portion is lowered, and the above-described effect may not be obtained. On the contrary, when the ratio L1 / W1 is larger than 4.0, the rigidity of the land portion in the tire axial direction is lowered, and the steering stability performance on the dry road surface may be lowered.

  The length L1 of the dimple 20 in the tire circumferential direction is preferably 3.0 mm or more, more preferably 3.5 mm or more, preferably 4.5 mm or less, more preferably 4.0 mm or less. When the length L1 of the dimple 20 is smaller than 3.0 mm, the edge component in the tire circumferential direction becomes small and the turning performance on an icy road may be deteriorated. On the other hand, when the length L1 of the dimple 20 is larger than 4.5 mm, the steering stability performance on the dry road surface may be deteriorated.

  The width W1 of the dimple 20 in the tire axial direction is preferably 1.0 mm or more, more preferably 1.5 mm or more, preferably 2.5 mm or less, more preferably 2.0 mm or less. Such a dimple 20 exhibits an excellent edge effect while maintaining the rigidity of the land portion.

  The depth d1 of the dimple 20 is preferably 0.5 mm or more, more preferably 1.0 mm or more, preferably 3.0 mm or less, more preferably 2.5 mm or less. If the depth d1 of the dimple 20 is smaller than 0.5 mm, the edge effect cannot be obtained and the on-ice performance may be deteriorated. On the other hand, when the depth d1 of the dimple 20 is larger than 3.0 mm, the steering stability performance on the dry road surface may be deteriorated.

  The edge 21 of the dimple 20 of this embodiment is elliptical. Such dimple 20 effectively suppresses deformation of the land portion in the tire circumferential direction. The edge 21 of the dimple 20 may be oval or rectangular. Such an edge 21 of the dimple 20 increases an edge component in the tire circumferential direction, and effectively suppresses a skid on an icy road.

  As shown in FIG. 1, the total number Ns of dimples 20 provided in one (one row) shoulder land portion 5 is equal to the dimple 20 provided in one (one row) middle land portion 6. It is desirable that it is larger than the total number Nm. Thereby, the rigidity of the middle land portion 6 is maintained, and the shoulder land portion 5 edge component increases. For this reason, excellent on-ice performance is exhibited while maintaining stable driving performance on a dry road surface.

  The ratio Ns / Nm between the total number Ns of dimples 20 provided in one shoulder land portion 5 and the total number Nm of dimples 20 provided in one middle land portion 6 is preferably 1.3 or more. Preferably it is 1.5 or more, Preferably it is 2.0 or less, More preferably, it is 1.8 or less. Thereby, the steering stability performance on ice and the on-ice performance are improved in a well-balanced manner.

  FIG. 4 shows an enlarged view of the shoulder land portion 5. As shown in FIG. 4, each shoulder block 14 is provided with one shoulder sub-groove 13. The shoulder minor groove 13 extends in the tire circumferential direction. The shoulder sub-groove 13 has a substantially constant groove width and is linear. The shoulder sub-groove 13 of this embodiment is inclined at an angle θ3 of 5 to 15 ° with respect to the tire circumferential direction.

  The groove width W11 of the shoulder sub-groove 13 is smaller than the groove width W2 of the shoulder main groove 3, for example. The groove width W11 of the shoulder sub-groove 13 is preferably 0.25 times or more, more preferably 0.28 times or more, preferably 0.35 times or less, more preferably 0 than the groove width W2 of the shoulder sub-groove 13. .32 times or less.

  As shown in FIG. 2, the groove depth d5 of the shoulder sub-groove 13 is smaller than, for example, the groove depth d2 of the shoulder main groove 3 and the groove depth d4 of the shoulder lateral groove 10. The groove depth d5 of the shoulder sub-groove 13 is preferably 1.0 to 2.0 mm.

  As shown in FIG. 4, each shoulder block 14 is divided into a first shoulder block piece 15 on the outer side in the tire axial direction and a second shoulder block piece 16 on the inner side in the tire axial direction by the shoulder sub-groove 13. ing.

  The first shoulder block piece 15 has a substantially trapezoidal shape with end edges 15e and 15e on both sides in the tire circumferential direction extending in parallel to each other.

  The length L2 in the tire circumferential direction of the first shoulder block piece 15 is smaller than the width W4 in the tire axial direction of the shoulder land portion 5, for example. The length L2 of the first shoulder block piece 15 is preferably 0.55 times or more, more preferably 0.60 times or more, and preferably 0.70 times the width W4 of the shoulder land portion 5 in the tire axial direction. Hereinafter, it is more preferably 0.65 times or less. Such first shoulder block piece 15 improves on-ice performance while maintaining wandering performance.

  A first shoulder sipe 17 is provided on the first shoulder block piece 15. The first shoulder sipe 17 has a wave shape or a zigzag shape. The first shoulder sipe 17 includes an axial sipe 17a extending in the tire axial direction and a circumferential sipe 17b extending in the tire circumferential direction.

  The axial sipe 17a communicates with the shoulder sub-groove 13 and extends outward in the tire axial direction. The axial sipe 17 a terminates in the first shoulder block piece 15. A plurality of axial sipes 17a are provided in the tire circumferential direction. The plurality of axial sipes 17a are provided in parallel to each other. Such an axial sipe 17a exhibits an excellent edge effect and suppresses uneven wear of the first shoulder block piece 15 on the outer side in the tire axial direction.

  The circumferential sipe 17b is provided outside the axial sipe 17a in the tire axial direction. The circumferential sipe 17 b is a closed type in which both ends are terminated in the first shoulder block piece 15. Such a circumferential sipe 17b improves wandering performance and suppresses uneven wear of the first shoulder block piece 15.

  The second shoulder block piece 16 has a substantially rectangular shape. The second shoulder block piece 16 is provided with a second shoulder sipe 18 and the dimple 20.

  The second shoulder sipe 18 extends from the shoulder sub-groove 13 to the shoulder main groove 3 in the tire axial direction. The second shoulder sipe 18 has a wave shape or a zigzag shape. A plurality of second shoulder sipes 18 are spaced apart in the tire circumferential direction. The plurality of second shoulder sipes 18 are provided in parallel to each other. Such a second shoulder sipe 18 exhibits excellent wet performance and on-ice performance.

  It is desirable that a plurality of dimples 20 provided on the shoulder land portion 5 are spaced apart in the tire axial direction. Three dimples 20 provided in the shoulder land portion 5 of the present embodiment are spaced apart in the tire axial direction. Thereby, the edge component of the shoulder land part 5 increases, and the performance on ice improves.

  The distance W10 between the dimples 20 and 20 adjacent in the tire axial direction in the tire axial direction is preferably 1.05 times or more, more preferably 1.10 times or more, preferably the width W1 of the dimple 20 in the tire axial direction. 1.20 times or less, more preferably 1.15 times or less. Such dimple 20 increases the edge effect while effectively suppressing deformation of the groove wall 10w of the shoulder lateral groove 10 in the tire circumferential direction.

  It is desirable that at least one of the dimples 20 provided in the shoulder land portion 5 is adjacent to the shoulder main groove 3. Such dimple 20 effectively suppresses the deformation of the corner portion 16c of the second shoulder block piece 16 as compared with the case where the sipe is provided. For this reason, when running on a snowy road, a stronger snow column is formed at the intersection 9a between the shoulder main groove 3 and the shoulder lateral groove 10. Therefore, the snow column shear force is increased and the performance on snow is improved.

  FIG. 5 shows an enlarged view of the first middle land portion 31 and the second middle land portion 32. As shown in FIG. 5, the first middle land portion 31 is a block row in which the first middle blocks 36 are spaced apart in the tire circumferential direction. The first middle block 36 is divided by a first middle lateral groove 34.

  The first middle block 36 has a substantially trapezoidal shape with end edges 36a, 36a on both sides in the tire circumferential direction being parallel to each other.

  The first middle block 36 is provided with the dimple 20 and a first middle sipe 37.

  The dimple 20 is preferably provided adjacent to the shoulder main groove 3 or the middle sub-groove 30. Thereby, the deformation | transformation of the corner | angular part 40 of the 1st middle block 36 is suppressed. Therefore, when running on a snowy road, a stronger snow column is formed and the performance on snow is improved.

  The dimple 20 is provided at a corner portion 40a where an angle θ4 formed by an end edge 36c of the first middle block 36 extending in the tire circumferential direction and an end edge 36a of the first middle block 36 extending in the tire axial direction is an acute angle. It is desirable. Thereby, the progress of wear at the corner 40a and the corner 40b at which the angle θ4 is an obtuse angle becomes uniform, and uneven wear is suppressed.

  The first middle sipes 37 are wavy or zigzag shaped. The first middle sipe 37 extends in the tire axial direction from the shoulder main groove 3 to the middle sub-groove 30. A plurality of first middle sipes 37 are spaced apart in the tire circumferential direction. The plurality of first middle sipes 37 are parallel to each other. Such a first middle sipe 37 exhibits excellent performance on ice.

  The second middle land portion 32 is a block row in which the second middle blocks 38 are spaced apart in the tire circumferential direction. The second middle block 38 is divided by a second middle lateral groove 35.

  It is desirable that the second middle lateral groove 35 has a groove width W9 that increases toward the outer side in the tire axial direction. The second middle lateral groove 35 exhibits a large snow column shear force in the tire axial direction when turning on a snowy road. For this reason, performance on snow improves.

  The groove width W9 of the second middle lateral groove 35 is preferably 0.62 times or more, more preferably 0.72 times or more, preferably 0.88 times or less, more preferably less than the groove width W2 of the shoulder main groove 3. It is 0.78 times or less. Such a second middle lateral groove 35 exhibits excellent on-snow performance while maintaining on-ice performance.

  It is desirable that the second middle lateral groove 35 is displaced from the first middle lateral groove 34 in the middle sub-groove 30 in the tire circumferential direction. Such a second middle lateral groove 35 suppresses a decrease in rigidity of the middle land portion 6 and maintains steering stability performance and on-ice performance on a dry road surface.

  The second middle block 38 is provided with a second middle sipe 39. The second middle sipe 39 has a wave shape or a zigzag shape. The second middle sipe 39 extends in the tire axial direction from the center main groove 4 to the middle sub-groove 30. A plurality of second middle sipes 39 are provided in the tire circumferential direction. The plurality of second middle sipes 39 are parallel to each other. Such a second middle sipe 39 increases the edge component of the middle land portion 6 and exhibits excellent performance on ice.

  As the winter tire of the present embodiment, for example, a rubber composition of preferably 40 degrees or more, more preferably 45 degrees or more, preferably 60 degrees or less, more preferably 53 degrees or less as tread rubber is suitable. Used. When the rubber hardness of the tread rubber is less than 40 degrees, the rigidity of the shoulder land portion 5 and the middle land portion 6 is lowered, and the steering stability performance on the dry road surface and the ice road may be lowered. On the contrary, when the rubber hardness of the tread rubber is larger than 60 degrees, the grip force on the dry road surface may be reduced. In this specification, rubber hardness means durometer A hardness measured in a 23 ° C. environment by durometer type A based on JIS-K6253.

  From the same point of view, as a winter tire, the land ratio of the tread portion 2 is preferably 60% or more, more preferably 65% or more, preferably 75% or less, more preferably 70% or less. When the land ratio of the tread portion 2 is smaller than 60%, the rigidity of the tread portion 2 is lowered, and the steering stability performance on the dry road surface may be lowered. On the contrary, when the land ratio of the tread portion 2 is larger than 70%, the edge effect and snow column shear force exerted by the grooves, sipes and dimples are reduced, and there is a possibility that the performance on ice and the performance on snow are lowered. The land ratio is a ratio of the total contact area of the actual tread portion to the total contact area of the tread portion 2 measured in a state where all the grooves, sipes, and dimples are filled.

  Although the pneumatic tire of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be implemented with various modifications.

A pneumatic tire of size 195 / 65R15 having the basic pattern of FIG. As a comparative example, a pneumatic tire having no dimples was prototyped. Each test tire was tested for driving stability performance on ice, performance on ice, and performance on snow. The common specifications and test methods for each tire are as follows.
Wearing rim: 15 × 6J
Tire internal pressure: 230kPa
Test vehicle: Front-wheel drive vehicle, displacement 1500cc
Tire mounting position: all wheels

<Operation stability on dry road>
The driving stability performance when the test vehicle was run on the test course consisting of a dry asphalt road surface was evaluated based on the driver's sensory performance. A result is a score which sets the comparative example 1 to 100, and shows that steering stability performance is excellent, so that a numerical value is large.

<Performance on ice>
Using the test vehicle, on a test course consisting of an icy road, sudden braking was performed from a straight traveling state at 40 km / h, and the braking distance was measured. The result is the reciprocal of the braking distance, and is displayed as an index with Comparative Example 1 being 100. A result is so good that a numerical value is large.

<Snow performance>
The performance on snow when running on the snow with the test vehicle was evaluated based on the driver's sensuality. A result is a score which sets the comparative example 1 to 100, and shows that the steering stability performance on a snowy road is excellent, so that a numerical value is large.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the performance of the pneumatic tire of the example was improved while maintaining the performance on ice.

2 Tread portion 3 Shoulder main groove 4 Center main groove 5 Shoulder land portion 6 Middle land portion 10 Shoulder lateral groove 30 Middle sub-groove 31 First middle land portion 32 Second middle land portion 34 First middle transverse groove 20 Dimple 21 Edge

Claims (9)

A pair of shoulder main grooves extending continuously in the tire circumferential direction at the tread ground end side and a center main groove extending continuously in the tire axial direction on the inner side in the tire axial direction than the shoulder main grooves are provided in the tread portion. A pair of shoulder land portions on the outer side in the tire axial direction than the pair of shoulder main grooves and a pair of middle land portions between the shoulder main grooves and the center main groove. Because
The shoulder land portion is provided with a plurality of shoulder lateral grooves extending in the tire axial direction,
The middle land portion is divided into a middle middle groove extending continuously in the tire circumferential direction into a first middle land portion on the outer side in the tire axial direction and a second middle land portion on the inner side in the tire axial direction,
The first middle land portion is provided with a plurality of first middle lateral grooves extending in the tire axial direction,
Each of the shoulder land portion and the first middle land portion is provided with a dimple having a closed edge appearing in the tread surface and having a recessed region surrounded by the edge,
The dimple is adjacent to the shoulder lateral groove or the first middle lateral groove,
A pneumatic tire characterized in that a length L1 of the dimple in the tire circumferential direction is larger than a width W1 of the dimple in the tire axial direction. The shoulder lateral groove extends from the tread ground end to the shoulder main groove,
The pneumatic tire according to claim 1, wherein the first middle lateral groove is smoothly connected to the shoulder lateral groove via the shoulder main groove.   The pneumatic tire according to claim 1 or 2, wherein the edge of the dimple has an oval shape, an oval shape, or a rectangular shape.   4. The total number Ns of the dimples provided in the one shoulder land portion is larger than the total number Nm of the dimples provided in the one first middle land portion. 5. Pneumatic tire. The shoulder land portion is a block row in which shoulder blocks divided by a plurality of the shoulder lateral grooves are arranged,
The shoulder block is divided into a first shoulder block piece on the outer side in the tire axial direction and a second shoulder block piece on the inner side in the tire axial direction by a shoulder sub-groove extending in the tire circumferential direction. The pneumatic tire according to Crab.   6. The pneumatic tire according to claim 1, wherein an angle θ <b> 1 of the shoulder lateral groove with respect to the tire axial direction and an angle θ <b> 2 of the first middle lateral groove with respect to the tire axial direction are respectively 5 to 25 °.   The pneumatic tire according to any one of claims 1 to 6, wherein the width W1 of the dimple is 1.0 to 2.5 mm.   The pneumatic tire according to any one of claims 1 to 7, wherein the length L1 of the dimple is 3.0 to 4.5 mm.   The pneumatic tire according to any one of claims 1 to 8, wherein a depth d1 of the dimple is 0.5 to 3.0 mm.

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