JP2014240204A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve performance on an ice road, abrasion resistance and drainage performance with good balance.SOLUTION: A pneumatic tire has one center land part 5, sectioned by a pair of center main grooves 3A on both sides in a tire shaft direction of a tire equator C, provided at a tread part 2. The center land part 5 is provided with a center notch part 15 that extends from the center main grooves 3A to the tire equator C side and terminates in the center land part 5. In the center notch part 15, a length and a depth in the tire circumferential direction of an opening end 15c are 15-25% of one pitch of the center notch part and 55-65% of the groove depth of the center main groove respectively.

Description

  The present invention relates to a pneumatic tire in which ice road performance, uneven wear resistance performance and drainage performance are improved in a well-balanced manner.

  In recent years, in winter pneumatic tires, opportunities to travel on wet roads as well as ice roads are increasing. Therefore, in such a pneumatic tire for winter, it is required to improve not only the icy road performance but also the drainage performance at a high level in a well-balanced manner.

  For example, in order to improve drainage performance, it has been proposed to increase the width of main grooves and lateral grooves in order to smoothly drain the water film between the land portion of the tread portion and the road surface. .

  However, in the pneumatic tire as described above, since the contact area of the land portion is small, there is a problem that the frictional force and the pattern rigidity are lowered, and the ice road performance and the uneven wear resistance performance are deteriorated. As a related technique, there is Patent Document 1 below.

JP 2009-214775 A

  The present invention has been devised in view of the actual situation as described above, and in the center land portion, provided with a center notch extending from the center main groove, and defining the shape of the center notch, The main purpose is to provide a pneumatic tire with improved icy road performance, uneven wear resistance and drainage performance in a well-balanced manner.

  According to the first aspect of the present invention, the tread portion has a pair of center main grooves extending continuously in the tire circumferential direction on both sides in the tire axial direction of the tire equator, and a tire axial direction outer side of the center main groove on the tire. A pair of shoulder main grooves extending continuously in the circumferential direction, a plurality of middle lateral grooves connecting between the center main groove and the shoulder main grooves, and a plurality of connecting between the shoulder main grooves and the grounding end By providing the shoulder lateral groove, one center land portion divided by the pair of center main grooves, the middle block divided by the center main groove, the shoulder main groove, and the middle lateral groove are arranged in the tire circumferential direction. A pair of middle block rows that are spaced apart and a shoulder block that is partitioned by the shoulder main groove, the ground contact end, and the shoulder lateral groove are spaced apart in the tire circumferential direction. A pneumatic tire having a pair of shoulder block rows, wherein the center land portion extends from the center main groove toward the tire equator and terminates in the center land portion, and is deeper than the groove depth of the center main groove. Center notch portions having a small length are provided in the tire circumferential direction, and the center notch portion has a length in the tire circumferential direction of an opening edge of 15 to 25% of one pitch of the center notch portion, and a depth. Is 55 to 65% of the groove depth of the center main groove.

  In the invention according to claim 2, the middle block is provided with a middle lug groove extending inward in the tire axial direction from the shoulder main groove and terminating in the middle block, and the middle lug groove has a maximum length in the tire axial direction. 2. The pneumatic tire according to claim 1, wherein the middle block has a maximum length in the tire axial direction of 25 to 35% and a groove depth of 55 to 65% of the groove depth of the center main groove.

  According to a third aspect of the present invention, the middle block includes a middle notch extending from the center main groove outward in the tire axial direction and terminating in the middle block and having a depth smaller than the groove depth of the center main groove. The middle notch has a maximum length in the tire axial direction of 15 to 25% of a maximum length in the tire axial direction of the middle block, and a depth of the groove depth of the center main groove. It is 55 to 65%, The pneumatic tire according to claim 1 or 2.

  According to a fourth aspect of the present invention, the land ratio, which is the ratio of the total surface area of the tread portion and the virtual surface area of the virtual tread surface obtained by filling all the grooves of the tread portion, is 68 to 72%. A pneumatic tire according to any one of claims 1 to 3.

  In the pneumatic tire of the present invention, the tread portion has a pair of center main grooves extending continuously in the tire circumferential direction on both sides in the tire axial direction of the tire equator, and the tire axial direction outer side of the center main groove is continuous in the tire circumferential direction. A pair of extending shoulder main grooves, a plurality of middle horizontal grooves that connect between the center main groove and the shoulder main grooves, and a plurality of shoulder horizontal grooves that connect between the shoulder main groove and the grounding end are provided. Thus, a pair of center land portions divided by a pair of center main grooves, middle blocks divided by a center main groove, a shoulder main groove, and a middle lateral groove are provided in the tread portion in the tire circumferential direction. And a pair of shoulder block rows in which a shoulder block divided by a shoulder main groove, a ground contact end, and a shoulder lateral groove is spaced apart in the tire circumferential direction.

  The center land portion extends from the center main groove toward the tire equator side, terminates in the center land portion, and has a center notch portion having a depth smaller than the groove depth of the center main groove in the tire circumferential direction. In the center notch, the length of the opening edge in the tire circumferential direction is 15 to 25% of one pitch of the center notch, and the depth is 55 to 65% of the depth of the center main groove. Since such a center notch has edge components in the tire axial direction and the tire circumferential direction, the frictional force against the road surface is increased. Further, the center cutout portion maintains the rigidity of the center land portion high. Furthermore, the center cutout portion smoothly drains the water film between the center land portion and the road surface into the center main groove. Therefore, in the pneumatic tire of the present invention, ice road performance, uneven wear resistance performance and drainage performance are improved in a well-balanced manner.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is an enlarged view of the center land part and middle block row | line | column of the left side of the tread part of FIG. It is sectional drawing of the XX part of FIG. It is an expanded view of the tread part of other embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire of this embodiment (hereinafter simply referred to as “tire”) can be suitably used as, for example, a winter tire, and the tread portion 2 includes a tire equator C. A pair of center main grooves 3A extending continuously in the tire circumferential direction on both sides in the tire axial direction and a pair of shoulder main grooves 3B extending continuously in the tire circumferential direction on the outer side in the tire axial direction of the center main groove 3A are provided. It is done. In the present embodiment, the tread portion 2 has a plurality of middle lateral grooves 4A that connect between the center main groove 3A and the shoulder main groove 3B, and a plurality of connections that connect between the shoulder main groove 3B and the grounding end Te. Shoulder lateral groove 4B is provided.

  As a result, the tread portion 2 of the present embodiment includes a center land portion 5 divided by a pair of center main grooves 3A, 3A, a plurality of portions divided by the center main groove 3A, the shoulder main groove 3B, and the middle lateral groove 4A. The middle block 6 is a pair of middle block rows 6R spaced apart in the tire circumferential direction, and a plurality of shoulder blocks 7 divided by the shoulder main groove 3B, the ground contact Te and the shoulder lateral groove 4B are arranged in the tire circumferential direction. A pair of spaced shoulder block rows 7R are arranged.

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

  The “grounding end” Te is applied to a flat tire with a camber angle of 0 ° by applying a normal load to an unloaded normal tire that is assembled to a normal rim (not shown) and filled with a normal internal pressure. Is defined as the contact position on the outermost side in the tire axial direction. The distance in the tire axial direction between the ground contact Te and Te is determined as the tread ground contact width TW. When there is no notice in particular, the dimension of each part of a tire is the value measured in the said 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. “Standard Rim” for JATMA, “Design Rim” for TRA For ETRTO, "Measuring Rim". In addition, the “regular internal pressure” is an air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. The maximum value described in TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES is "INFLATION PRESSURE" for ETRTO, but 180 kPa for tires for passenger cars.

  The “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. “Maximum load capacity” for JATMA, “Table for TRA” The maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” is “LOAD CAPACITY” in the case of ETRTO.

  The center main groove 3A of the present embodiment has a long side portion 8a inclined to one side (inclined to the left in FIG. 1) with respect to the tire circumferential direction, and an inclined direction opposite to the long side portion 8a (in FIG. 1). It is formed in a zigzag shape in which short side portions 8b that are inclined to the right) and shorter in the tire circumferential direction than the long side portions 8a are alternately arranged. Since the center main groove 3A includes an edge component in the tire axial direction, the driving force and the braking force are increased. Therefore, ice road performance is improved.

  The angle of the center main groove 3A is obtained as the angle of the groove center line 10. The long side portion 8a of the present embodiment has a groove center line 10a that is inclined to one side with respect to the tire circumferential direction (inclined to the left in FIG. 1). Further, the short side portion 8b of the present embodiment has a groove center line 10b that is inclined to the other side with respect to the tire circumferential direction (inclined upward in FIG. 1).

  FIG. 2 shows a partially enlarged view of the left half of the tread portion 2 of FIG. As shown in FIG. 2, the groove center line 10 of the center main groove 3A has an innermost point a1 in the tire axial direction of the inner groove edge 10x on the inner side in the tire axial direction of the center main groove 3A and the center main groove 3A. An intermediate point s1 of the outer groove edge 10y on the outer side in the tire axial direction with the innermost point a2 in the tire axial direction, and an outermost point a3 of the inner groove edge 10x in the tire axial direction and the outer groove edge 10y in the tire axial direction. It is formed by a straight line obtained by alternately connecting intermediate points s2 with the outermost point a4.

  When the angle α1 of the long side portion 8a with respect to the tire circumferential direction is small, the edge component in the tire axial direction may be reduced. When the angle α1 of the long side portion 8a is large, the drainage resistance of the center main groove 3A is increased, and the drainage performance may be deteriorated. For this reason, the angle α1 of the long side portion 8a is preferably 5 ° or more, more preferably 7 ° or more, preferably 20 ° or less, more preferably 18 ° or less.

  Although not particularly limited, the angle α2 of the short side portion 8b with respect to the tire circumferential direction is preferably 30 ° or more, more preferably 35 ° or more, preferably 60 ° or less, more preferably 55 ° or less. is there. When the angle α2 of the short side portion 8b is large, the drainage performance may be deteriorated. When the angle α2 of the short side portion 8b is small, the ice road performance may be deteriorated.

  As shown in FIG. 1, the shoulder main groove 3 </ b> B of the present embodiment has a linear shape along the tire circumferential direction. Such a main groove 3B smoothly drains the drainage water in the groove to the rear in the tire rotation direction, and ensures high rigidity in the tire circumferential direction of the middle block 6 and the shoulder block 7 to improve uneven wear resistance. Let

  The groove width of each main groove 3A, 3B (the groove width measured in the direction perpendicular to the groove center line, hereinafter the same applies to other grooves) W1, W2 and groove depths D1, D2 (in FIG. 3) (Shown) can be variously determined in accordance with common practice. However, when these groove widths or groove depths are reduced, drainage performance may be deteriorated. On the contrary, when these groove widths or groove depths are increased, the rigidity of the land portion 5 and each of the blocks 6 and 7 is decreased, and the uneven wear resistance performance may be deteriorated. For this reason, the groove widths W1 and W2 of the main grooves 3A and 3B are preferably 2 to 6% of the tread ground contact width TW, for example. As for groove depth D1, D2 of each main groove 3A, 3B, 10-15 mm is desirable, for example.

  The tire axial distance L1 between the center main groove 3A and the tire equator C is 5 to 13% of the tread ground contact width TW in order to ensure a good balance of the rigidity in the tire axial direction of the land portion 5 and the blocks 6 and 7. Is desirable. The tire axial distance L2 between the shoulder main groove 3B and the tire equator C is preferably 24 to 32% of the tread contact width TW. In addition, although each position of each main groove 3A, 3B is specified by those groove center lines (groove center line 14 of the shoulder main groove 3B), the center main groove 3A is zigzag like this embodiment. In the case of a non-straight line, the center line G1 having the amplitude of the groove center line 10 is used.

  The middle lateral groove 4A is linear and inclined in a certain direction (in FIG. 1, it is inclined upward to the left). Such middle lateral groove 4A can smoothly drain water in the groove from the center main groove 3A toward the shoulder main groove 3B.

  When the angle α3 of the middle lateral groove 4A with respect to the tire axial direction is large, the edge component of the middle block 6 in the tire axial direction becomes small, and the driving and braking force may be reduced. When the angle α3 is small, the edge component in the tire circumferential direction may not be effectively increased. For this reason, the angle α3 of the middle lateral groove 4A is preferably 2 ° or more, more preferably 4 ° or more, preferably 20 ° or less, and more preferably 15 ° or less.

  When the groove width W3 and the groove depth D3 (shown in FIG. 3) of the middle lateral groove 4A are large, the rigidity of the middle block 6 may be reduced. When the groove width W3 and the groove depth D3 of the middle lateral groove 4A are small, the drainage performance may be deteriorated. For this reason, the groove width W3 of the middle lateral groove 4A is preferably 2.0 mm or more, more preferably 2.3 mm or more, and preferably 4.3 mm or less, more preferably 4.0 mm or less. The groove depth D3 of the middle lateral groove 4A is preferably 6.5 mm or more, more preferably 7.0 mm or more, preferably 10.0 mm or less, more preferably 9.5 mm or less. The middle lateral groove 4A of the present embodiment has a uniform width.

  In the present embodiment, the shoulder lateral groove 4B has an inclined portion 13a inclined from the shoulder main groove 3B toward the grounding end Te toward one side (inclined upward in FIG. 1), the inclined portion 13a and the grounding end Te. And an axial portion 13b extending along the tire axial direction. The inclined part 13a and the axial direction part 13b of this embodiment extend linearly. Thereby, the drainage resistance of the shoulder lateral groove 4B becomes small. Moreover, the rigidity of the shoulder block 7 is ensured and the turning performance is improved.

  Although not particularly limited, the angle α4 of the inclined portion 13a with respect to the tire axial direction is preferably 10 ° or more, more preferably 12 ° or more, preferably 20 ° or less, more preferably 18 ° or less. .

  The groove width W4 of the inclined portion 13a is preferably 6% or more, more preferably 8% or more, preferably 16% or less, more preferably 14% or less, of one pitch P1 of the shoulder block row 7R. When the groove width W4 of the inclined portion 13a is large, the rigidity of the shoulder block 7 may be reduced. When the groove width W4 of the inclined portion 13a is small, the drainage performance may be deteriorated.

  In this embodiment, the groove width W5 of the axial part 13b is formed larger than the groove width W4 of the inclined part 13a. Thereby, the water from the inclined part 13a is smoothly discharged to the grounding end Te side. In order to ensure the rigidity of the shoulder block 7 while exhibiting the above-described action, the groove width W5 of the axial portion 13b is preferably 1.2 times or more, more preferably 1.3 times the groove width W4 of the inclined portion 13a. It is more than twice, preferably less than 2.4 times, more preferably less than 2.3 times.

  As shown in FIG. 3, the groove depth D4 of the inclined portion 13a is preferably 5.0 mm or more, more preferably 5.5 mm or more, preferably 8.0 mm or less, more preferably 7.5 mm or less. is there. In this embodiment, the groove depth D5 of the axial direction part 13b is made larger than the groove depth D4 of the inclined part 13a, and the waste water in the shoulder lateral groove 4B is smoothly discharged to the ground contact Te. For this reason, the groove depth D5 of the axial direction portion 13b is preferably 1.2 times or more, more preferably 1.3 times or more, preferably 1.8 times or less, preferably the groove depth D4 of the inclined portion 13a. More preferably, it is 1.7 times or less.

  As shown in FIG. 2, the center land portion 5 extends from the center main groove 3A toward the tire equator C and terminates in the center land portion 5 and has a depth D6 (d6) than the groove depth D1 of the center main groove 3A. A small center cutout 15 is provided (shown in FIG. 3). Since the center notch 15 has edge components in the tire axial direction and the tire circumferential direction, it increases the frictional force against the road surface and improves the ice road performance. The center cutout portion 15 ensures high rigidity in the tire axial direction of the center land portion 5. The center notch 15 smoothly drains the water film between the center land portion 5 and the road surface into the center main groove 3A.

  The center cutout portions 15 of the present embodiment are arranged so as to be alternately displaced in both sides of the center land portion 5 in the tire axial direction and in the tire circumferential direction. Thereby, the rigidity of the center land portion 5 in the tire axial direction is equalized in the tire circumferential direction.

  The opening edge 15c of the center notch 15 that faces the center main groove 3A and is a step with the center main groove 3A has a length L3 in the tire circumferential direction of the opening edge 15c of one pitch of the center notch 15. 15 to 25% of P2 and the depth D6 are 55 to 65% of the groove depth D1 of the center main groove 3A.

  When the length L3 of the opening edge 15c of the center notch 15 in the tire circumferential direction is less than 15% of one pitch P2 of the center notch 15, the drainage performance cannot be improved. When the length L3 in the tire circumferential direction of the opening edge 15c exceeds 25% of one pitch P2 of the center notch portion 15, the surface area of the tread surface of the center land portion 5 becomes small, and the rigidity of the center land portion 5 deteriorates. . For this reason, the length L3 of the opening edge 15c in the tire circumferential direction is preferably 17% or more and preferably 23% or less of the one pitch P2 of the center notch portion 15.

  When the depth D6 of the center cutout portion 15 exceeds 65% of the groove depth D1 of the center main groove 3A, the rigidity of the center land portion 5 is lowered. When the depth D6 of the center notch 15 is less than 55% of the groove depth D1 of the center main groove 3A, the drainage performance cannot be sufficiently improved. For this reason, the depth D6 of the center notch 15 is preferably 57% or more and preferably 63% or less of the groove depth D1 of the center main groove 3A.

  Thus, by defining the length L3 and the depth D6 in the tire circumferential direction of the opening edge 15c of the center notch portion 15, the ice road performance, the uneven wear resistance performance, and the drainage performance are improved in a well-balanced manner.

  When the maximum length L4 in the tire axial direction of the center notch portion 15 is large, the rigidity of the center land portion 5 may be deteriorated. When the maximum length L4 in the tire axial direction of the center notch 15 is small, there is a risk that improvement in drainage performance is suppressed. Further, a large edge component of the center notch portion 15 cannot be secured, and there is a possibility that the ice performance cannot be improved. For this reason, the maximum length L4 of the center notch portion 15 in the tire axial direction is preferably 10% or more, more preferably 11% or more, and preferably 15% or less of the maximum length Wc of the center land portion 5. More preferably, it is 14% or less.

  The center cutout portion 15 is provided including an intersection 8k between the long side portion 8a and the short side portion 8b. The intersection point 8k of the present embodiment is a bending point on the side that protrudes and bends inward in the tire axial direction from the groove center line 10 of the center main groove 3A. Such a center notch 15 improves the uneven wear resistance in order to relieve stress concentration at the intersection 8k at the center land 5 where the distance from the tire equator C is small and the contact pressure is high, and to ensure a large rigidity. Let

  The center land portion 5 has a pair of land portion edges 17 extending in both the tire axial direction and the tire circumferential direction. The land portion edge 17 includes a center long edge portion 17A extending along the long side portion 8a and a center short edge portion 17B disposed between the center long edge portions 17A and 17A adjacent in the tire circumferential direction. The center long edge portion 17A of the present embodiment is a land portion edge that is inclined to one side (inclined to the left in FIG. 2). The center short edge portion 17B is a land portion edge that inclines to the other side opposite to the center long edge portion 17A (inclined upward in FIG. 2).

  The center cutout portion 15 has a first cutout edge 15a that is smoothly connected to the center short edge portion 17B, and a second cutout edge 15b that extends along the tire axial direction. Such a first notch edge 15a further relaxes the stress concentration at the intersection 8k and further increases the rigidity. The first notch edge 15a smoothly guides water and snow in the center notch 15 to the center main groove 3A. In this embodiment, the center short edge part 17B and the 1st notch edge 15a are formed in linear form. The second notch edge 15b has an edge component in the tire axial direction. Thereby, the ice road performance is further improved.

  The middle block 6 has a middle inner block edge 19 extending in the tire axial direction and in the tire circumferential direction. The middle inner block edge 19 has a middle inner short edge portion 19A inclined to one side with respect to the tire circumferential direction (inclined to the right in FIG. 2), and a middle inner short edge from both ends of the middle inner short edge portion 19A. It includes a pair of middle inner long edges 19B, 19B that are inclined to the opposite side of the portion 19A (inclined to the left in FIG. 2) and longer in the tire circumferential direction than the middle inner short edge 19A.

  The middle block 6 extends from the center main groove 3A outward in the tire axial direction, terminates in the middle block, and has a middle notch portion having a depth D7 (shown in FIG. 3) smaller than the groove depth D1 of the center main groove 3A. 20 and a middle lug groove 21 extending inward in the tire axial direction from the shoulder main groove 3B and terminating in the middle block 6. Since the middle notch 20 and the middle lug groove 21 have edge components in the tire axial direction and the tire circumferential direction, the frictional force with respect to the road surface is increased and ice road performance is improved. The middle notch 20 ensures high rigidity of the middle block 6 in the tire axial direction. The middle notch 20 and the middle lug groove 21 smoothly drain the water film between the middle block 6 and the road surface into the center main groove 3A or the shoulder main groove 3B.

  The middle notch 20 is provided in the short side 8b. Thus, since the middle notch part 20 is provided in the short side part 8b with large drainage resistance, the drainage resistance of the center main groove 3A and the shoulder main groove 3B is reduced, and drainage performance further improves.

  In the present embodiment, the opening edge 20c of the middle notch 20 is formed over the entire length of the middle inner short edge 19A. Thereby, the water in the middle notch part 20 can be smoothly discharged to the long side part 8a via the short side part 8b. Accordingly, the drainage performance is further improved. The opening edge 20c of the middle notch 20 faces the center main groove 3A and forms a step with the center main groove 3A.

  The middle notch 20 of the present embodiment has a notch edge 20a that smoothly extends the middle inner long edge 19B. Such a notch edge 20a relieves stress concentration at the intersection of the middle inner long edge 19B and the middle inner short edge 19A, and increases the rigidity of the intersection. Moreover, the water in the middle notch 20 is smoothly drained into the center main groove 3A. In the present embodiment, the middle inner long edge 19B and the notch edge 20a are formed in a straight line.

  The middle lug groove 21 has an axial edge 21a extending inward in the tire axial direction along the tire axial direction from the shoulder main groove 3B, and an inclined edge 21b inclined inward in the tire axial direction from the shoulder main groove 3B. . Such middle lug grooves 21 ensure a large edge component in the tire axial direction and also ensure an edge component in the tire circumferential direction. This further improves ice road performance.

  When the maximum length L5 of the middle notch 20 in the tire axial direction is large, the rigidity of the middle block 6 is reduced, and the uneven wear resistance may be deteriorated. When the maximum length L5 of the middle notch 20 in the tire axial direction is small, the edge component of the middle notch 20 is small. For this reason, the maximum length L5 of the middle notch portion 20 in the tire axial direction is preferably 15% or more, more preferably 16% or more, and preferably 25% of the maximum length Wm of the middle block 6 in the tire axial direction. % Or less, more preferably 24% or less. From the same viewpoint, the maximum length L6 of the middle lug groove 21 in the tire axial direction is preferably 25% or more, more preferably 27% or more, preferably 35% or more of the maximum length Wm of the middle block 6 in the tire axial direction. % Or less, more preferably 33% or less.

  As shown in FIG. 3, the depth D7 of the middle notch 20 is preferably 55% or more, more preferably 57% or more, preferably 65% or less of the groove depth D1 of the center main groove 3A. More preferably, it is 63% or less. That is, when the depth D7 of the middle notch portion 20 is large, the rigidity of the middle block 6 is reduced, and the uneven wear resistance may be deteriorated. When the depth D7 of the middle notch 20 is small, the drainage performance may not be improved. From the same viewpoint, the depth D8 of the middle lug groove 21 is preferably 55% or more, more preferably 57% or more, preferably 65% or less, more preferably 63% of the groove depth D2 of the shoulder main groove 3B. It is as follows.

  Although not particularly limited, as shown in FIG. 2, when the length L7 of the opening edge 20c of the middle notch 20 in the tire circumferential direction is large, the rigidity of the middle block 6 is reduced, and uneven wear resistance is obtained. Performance may deteriorate. When the length L7 in the tire circumferential direction of the opening edge 20c of the middle notch 20 is small, the drainage performance may be deteriorated. For this reason, the length L7 of the opening edge 20c in the tire circumferential direction is preferably 12% or more, more preferably 13% or more, preferably 20% or less, more preferably 19% of one pitch P3 of the middle block row 6R. % Or less. From the same viewpoint, the average length L8 of the middle lug groove 21 in the tire circumferential direction is preferably 7% or more, more preferably 8% or more, preferably 13% or less of one pitch P3 of the middle block row 6R. More preferably, it is 12% or less.

  As shown in FIG. 1, the shoulder block 7 is provided with shoulder narrow grooves 23 extending linearly continuously in the tire circumferential direction. Thus, the shoulder block 7 is divided into an inner block 7A disposed on the inner side in the tire axial direction than the shoulder narrow groove 23 and an outer block 7B disposed on the outer side in the tire axial direction from the inner block 7A. Such shoulder narrow grooves 23 exhibit a large edge effect in the tire circumferential direction and improve turning performance.

  When the groove width W6 of the shoulder narrow groove 23 is large, the rigidity of the inner block 7A or the outer block 7B in the tire axial direction is reduced, and the uneven wear resistance may be deteriorated. When the groove width W6 of the shoulder narrow groove 23 is small, the drainage performance may be reduced. For this reason, the groove width W6 of the shoulder narrow groove 23 is preferably 0.5 mm or more, more preferably 1.0 mm or more, preferably 2.0 mm or less, more preferably 1.5 mm or less. From the same viewpoint, the groove depth D9 (shown in FIG. 3) of the shoulder narrow groove 23 is preferably 5.0 mm or more, more preferably 5.5 mm or more, and preferably 8.0 mm or less, more preferably 7.5 mm or less.

  In the present embodiment, the outer end of the inclined portion 13 a in the tire axial direction is connected to the shoulder narrow groove 23.

  The center land portion 5, the middle block 6, the inner block 7A and the outer block 7B of the present embodiment are provided with sipings 25 extending in the tire axial direction. Such a siping 25 has an edge component in the tire axial direction, and further improves ice road performance. The siping 25 of the present embodiment has a semi-open type in which one end is opened by the main grooves 3A, 3B or the shoulder narrow groove 23 and the other end is terminated in the center land portion 5, the middle block 6, the inner block 7A and the outer block 7B. And an open type siping 25b having both ends opened by the center main groove 3A. In this embodiment, the open-type siping 25b is provided only in the center land portion 5. As a result, the driving / braking force of the center land portion 5 to which a large ground pressure acts during straight traveling is increased, and in particular, straight running stability performance on an icy road is improved. In addition, the siping 25 of this embodiment is formed in linear form. As a result, the edge component in the tire axial direction is further increased, and ice road performance is further improved. The siping 25 is not limited to such a shape, and may be, for example, a wave shape.

  In order to ensure a large driving force and braking force, the siping 25 desirably has an angle αs of 0 to 30 ° with respect to the tire axial direction.

  The siping 25 provided in the center land portion 5 is not connected to the center notch portion 15 in this embodiment. Thereby, the rigidity of the center land part 5 is ensured high, and uneven wear-proof performance improves.

  The center land portion 5 and each of the blocks 6, 7 </ b> A, and 7 </ b> B are provided with a cross siping 26 that is orthogonal to the siping 25 and that is smaller in size in the longitudinal direction than the siping 25. Such a cross siping 26 includes an edge component in the tire circumferential direction, and improves turning performance. In this embodiment, the cross siping 26 is one in the outer region So in the tire axial direction of the center land portion 5 and each block 6, 7A, 7B, respectively, and the center land portion 5, each block 6, 7A, 7B. Two are arranged in each of the inner regions Si in the tire axial direction. Such a cross siping 26 equalizes the rigidity of the land portion 5 and the blocks 6, 7 </ b> A, 7 </ b> B in the tire axial direction, and further ensures high anti-wear performance. In this specification, as shown in FIG. 2, for example, in the center land portion 5, the inner region Si is centered on both outer sides in the tire axial direction from the intermediate point Cp in the tire axial direction of the center land portion 5. The outer region So is a region within 25% of the maximum length Wc of the land portion 5, and the outer region So is a region on both sides in the tire axial direction of the inner region Si of the center land portion 5 (middle block 6, inner block). 7A and the outer block 7B are also defined in the same ratio area).

  Although not particularly limited, the pitch Pa of the two cross sipings 26 and 26 provided in the inner region Si is set to the center land where the cross siping 26 is provided in order to effectively exhibit the above-described operation. 4 to 8% of the maximum width in the tire axial direction of the portion 5, the middle block 6 and the block portions 7A and 7B is desirable.

  In the present embodiment, as the winter tire, the total surface area Mb of all the land portions 5 and the tread surfaces of the blocks 6 and 7, all the grooves 3 </ b> A, 3 </ b> B, 4 </ b> A, 4 </ b> B, 21, each notch portion 15 of the tread portion 2. , 20 and the sipings 25 and 26, the land ratio represented by the ratio (Mb / Ma) to the virtual surface area Ma of the virtual tread is set to 68 to 72%. Thereby, ice road performance, uneven wear resistance performance, and drainage performance are enhanced in a well-balanced manner.

  FIG. 4 shows a development view of the tread portion 2 of another embodiment. As shown in FIG. 4, a zigzag-shaped siping 27 is provided in the center land portion 5, the middle block 6, and the shoulder block 7. Such a siping 32 can exhibit edge effects in multiple directions, and can further improve the running performance on snowy roads.

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

A pneumatic tire of size 195 / 80R15 having the basic pattern of FIG. 1 was prototyped based on the specifications of Table 1, and the drainage performance, ice road performance, and uneven wear resistance performance of each sample tire were tested. A pneumatic tire of size 195 / 80R15 having the basic pattern of FIG. 4 was prototyped based on the specifications in Table 2, and the drainage performance, ice road performance, and uneven wear resistance performance of each sample tire were tested. The common specifications for each tire are as follows. Except for the grooves described in Table 1 or 2, the groove width and angle of each groove are as shown in FIG. 1 or FIG.
Tread contact width TW: 160mm
<Each main groove>
Groove depth D1, D2: 12.5mm
<Horizontal groove>
Middle lateral groove depth D3: 9.0 mm
Groove depth D4 of the inclined part: 7.0 mm
Axial groove depth D5: 10.5mm
Shoulder narrow groove depth D9: 7.0 mm
<Others>
Depth of each siping: 7.0mm
Depth of each cross siping: 2.0mm
The test method is as follows.

<Drainage performance>
Each sample tire was mounted on all wheels of a 2700cc four-wheel drive vehicle under the following conditions, and one driver took the test course on an asphalt road surface with a water depth of 2 to 5 mm. The driving characteristics at this time, such as steering response, rigidity, and grip, were evaluated by the driver's sensuality. The results are displayed with a score of 100 for Example 1 and Example 1R. The larger the value, the better. In addition, 95 or less is rejected.
Rims: 15 × 6.0J
Internal pressure: 350kPa (front wheel)
Internal pressure: 425 kPa (rear wheel)

<Ice performance>
With the above test vehicle, a driver on the icy road (ice barn) traveled with one driver, and characteristics relating to steering response, rigidity, grip, etc. were evaluated by sensory evaluation of the driver. The results are displayed with a score of 100 for Example 1 and Example 1R. The larger the value, the better. In addition, 95 or less is rejected.

<Uneven wear resistance>
In the above test vehicle, drive on a dry asphalt road for 10,000 km, and the wear amount of the land edge on both sides of the center land portion and the wear amount of the block edge on both sides of one middle block are the same in the tire circumferential direction. Measurements were made at eight locations on the tire circumference. Then, the difference between the maximum value and the minimum value of the wear amount was calculated. The results were expressed as an index with the reciprocal of the difference between Example 1 and Example 1R as 100. The larger the value, the better. In addition, 95 or less is rejected.
The test results are shown in Table 1.

  As a result of the test, in both Tables 1 and 2, it was confirmed that the tires of the examples had significantly improved drainage performance, ice road performance, and uneven wear resistance performance as compared with the comparative examples.

2 tread portion 3A center main groove 5 center land portion 15 center notch portion 15c opening edge of center notch portion C tire equator

Claims (4)

A pair of center main grooves extending continuously in the tire circumferential direction on both sides in the tire axial direction of the tire equator on the tread portion, and a pair of shoulder main grooves extending continuously in the tire circumferential direction on the outer side in the tire axial direction of the center main groove. And a plurality of middle lateral grooves that connect between the center main groove and the shoulder main groove, and a plurality of shoulder lateral grooves that connect between the shoulder main groove and the grounding end,
A pair of middle blocks in which one center land portion divided by the pair of center main grooves, middle blocks divided by the center main grooves, the shoulder main grooves, and the middle lateral grooves are spaced apart in the tire circumferential direction. A pneumatic tire comprising a row and a pair of shoulder block rows in which the shoulder block divided by the shoulder main groove, the ground contact end and the shoulder lateral groove is spaced in the tire circumferential direction;
The center land portion extends from the center main groove toward the tire equator side, terminates in the center land portion, and has a center notch portion having a depth smaller than the groove depth of the center main groove. ,
The center notch has a length in the tire circumferential direction of the opening edge of 15 to 25% of one pitch of the center notch and a depth of 55 to 65% of the depth of the center main groove. Pneumatic tire characterized by. The middle block is provided with a middle lug groove extending inward in the tire axial direction from the shoulder main groove and terminating in the middle block,
In the middle lug groove, the maximum length in the tire axial direction is 25 to 35% of the maximum length in the tire axial direction of the middle block, and the groove depth is 55 to 65% of the groove depth of the center main groove. The pneumatic tire according to claim 1. The middle block is provided with a middle notch portion extending from the center main groove outward in the tire axial direction and terminating in the middle block and having a depth smaller than the depth of the center main groove,
The middle notch has a maximum length in the tire axial direction of 15 to 25% of the maximum length of the middle block in the tire axial direction, and a depth of 55 to 65% of the groove depth of the center main groove. The pneumatic tire according to claim 1 or 2.   The land ratio, which is the ratio of the total surface area of the tread surface of the tread part and the virtual surface area of the virtual tread surface obtained by filling all the grooves of the tread part, is 68 to 72%. Pneumatic tire described in 2.

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