JP5932761B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire in which snow road performance and ice road performance are improved in a well-balanced manner while suppressing deterioration in drainage performance.

  Winter pneumatic tires travel not only on snowy and icy roads but also on wet roads. Therefore, such a pneumatic tire for winter is required to have high drainage performance as well as snow road performance and ice road performance.

  For example, in order to improve ice road performance, it has been proposed to increase the ground contact area of the tread portion for the purpose of increasing pattern rigidity and frictional force. However, this method has a problem that the drainage performance and snow road performance are deteriorated because the groove width of the main groove and the lateral groove is reduced. Thus, the ice road performance, the drainage performance, and the snow road performance have a reciprocal relationship, and it has been difficult to improve all these performances in a well-balanced manner. Related technologies include the following.

JP 2008-308010 A

  The present invention has been devised in view of the actual situation as described above, and regulates the average groove width of the middle lateral groove, and the edge extending in the tire axial direction on both sides in the tire circumferential direction of the middle block, and the middle block The main purpose is to provide a pneumatic tire that improves the snow road performance and ice road performance in a well-balanced manner while suppressing the deterioration of drainage performance based on specifying the shapes of the edges on both sides in the tire axial direction. Yes.

This onset Ming, the tread portion, a pair of the most and a pair of shoulder main grooves grounding end side extending continuously in the circumferential direction, extending the tire axial direction inner side of the shoulder main grooves continuous in the tire circumferential direction center By providing a main groove and a middle horizontal groove extending between the shoulder main groove and the center main groove, the middle block divided by the shoulder main groove, the center main groove, and the middle horizontal groove has a tire circumference. A pneumatic tire having a row of middle blocks separated in a direction, wherein an average groove width of the middle lateral groove is 7 to 11% of a maximum length of the middle block in a tire circumferential direction; The lateral edge of the middle block, which is an edge extending in the tire axial direction on both sides of the tire circumferential direction, is a tire circumferential direction at an angle of 3 to 15 ° with respect to the tire axial direction from the center main groove. A middle inner portion extending in a slanted direction on one side of the tire, bent to the one side in the tire circumferential direction, connected to the middle inner portion, and has a length in the tire circumferential direction of 75 to 100% of an average groove width of the middle lateral groove. A middle middle portion, and a middle outer portion that is connected to the middle middle portion and is inclined to the one side in the tire circumferential direction at an angle of 3 to 15 ° with respect to a tire axial direction, and is connected to the shoulder main groove, The middle inner vertical edge which is an edge extending in the tire circumferential direction on the tire equator side of the block and the middle outer vertical edge which is an edge extending in the tire circumferential direction on the ground contact end side of the middle block are respectively the center main groove or a plurality of circumferential strips and inclined with respect to the side and the tire circumferential direction of the inner middle portion inclined at an angle of 3 to 15 ° with respect to the tire circumferential direction in the opposite direction to project the shoulder main grooves, Wherein the irregularities in a plurality of axial strips splicing between circumferential strips are formed.

  According to a second aspect of the present invention, the middle block includes a semi-open type first siping having one end opened at the center main groove and the other end terminated without reaching the shoulder main groove, and one end at the shoulder. 2. The pneumatic tire according to claim 1, wherein the semi-open type second siping which opens at the main groove and terminates without the other end reaching the center main groove is alternately arranged in the tire circumferential direction.

  According to a third aspect of the present invention, there is provided a ratio (Lc / Lb) between a length Lb of the middle block horizontal edge along the middle inner portion and a length Lc of the middle inner vertical edge perpendicular to the middle inner portion. The pneumatic tire according to claim 1 or 2, wherein Lb) is 0.9 to 1.1.

The pneumatic tire according to the present invention, the axial piece, a first arm portion which is inclined in the same direction as the inclination with respect to the tire circumferential direction of the circumferential piece from one end in the tire circumferential direction of the circumferential strip The second piece portion is inclined from the one end portion in the tire circumferential direction of the circumferential piece provided at a position different from the circumferential piece in a direction opposite to the inclination of the circumferential piece with respect to the tire circumferential direction. Is desirable.

  In the pneumatic tire of the present invention, a pair of shoulder main grooves extending continuously in the tire circumferential direction on the tread portion, and the inner side in the tire axial direction of the shoulder main grooves extending continuously in the tire circumferential direction. By providing a pair of center main grooves and a middle horizontal groove extending between the shoulder main groove and the center main groove, the middle block divided by the shoulder main groove, the center main groove, and the middle horizontal groove is arranged in the tire circumferential direction. It is equipped with spaced middle block rows.

  The average width of the middle lateral groove is defined as 7 to 11% of the maximum length of the middle block in the tire circumferential direction. Thereby, the rigidity in the tire circumferential direction of the middle block, the drainage resistance of the middle lateral groove, and the groove volume are enhanced in a well-balanced manner. Therefore, the braking force and snow column shearing force on the icy road are exhibited, and the icy road performance, the snowy road performance and the drainage performance are improved.

  Further, the middle block lateral edge, which is an edge extending in the tire axial direction on both sides in the tire circumferential direction of the middle block, is on one side of the tire circumferential direction at an angle of 3 to 15 ° with respect to the tire axial direction from the center main groove. An inner middle part extending obliquely, a middle middle part connected to the inner middle part, bent to one side in the tire circumferential direction and having a length in the tire circumferential direction of 75 to 100% of the average groove width of the middle lateral groove, and It consists of a middle outer portion that is connected to the middle portion of the middle and is inclined to one side in the tire circumferential direction at an angle of 3 to 15 ° with respect to the tire axial direction and is continuous with the shoulder main groove. Such a middle inner part and a middle outer part exhibit a large edge effect in the tire axial direction to further increase the braking force and snow column shear force. Since the middle middle part is inclined in the same direction as the middle inner part and the middle outer part, the drainage resistance of the middle lateral groove is ensured to be small. Also, the edge component in the tire circumferential direction is increased. Accordingly, a decrease in drainage performance is suppressed, and ice road performance and snow road performance are further improved in a balanced manner.

  The middle inner vertical edge, which is the edge extending in the tire circumferential direction on the tire equator side of the middle block, and the middle outer vertical edge, which is the edge extending in the tire circumferential direction on the ground contact end side of the middle block, are respectively the middle inner part. A plurality of circumferential pieces inclined in an opposite direction and at an angle of 3 to 15 ° with respect to the tire circumferential direction; and a first axial piece connecting the circumferential pieces with an inclination opposite to the circumferential piece; As a result, irregularities are formed. Such unevenness increases the edge component in the tire axial direction. Moreover, the circumferential piece formed at the above-described angle ensures rigidity in the tire circumferential direction. Furthermore, the circumferential piece keeps the drainage resistance small. Accordingly, a decrease in drainage performance is suppressed, and ice road performance and snow road performance are further improved in a balanced manner.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is an expanded sectional view of the XX part of FIG. FIG. 2 is an enlarged view of a left middle block in FIG. 1. It is an expanded view of the tread part of a prior art example.

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 has the most ground contact end. A pair of shoulder main grooves 3A extending continuously in the tire circumferential direction on the Te side and a pair of center main grooves 3B extending continuously in the tire axial direction on the inner side in the tire axial direction of the shoulder main grooves 3A are provided. Further, the tread portion 2 of the present embodiment includes a plurality of shoulder lateral grooves 4A extending between the shoulder main groove 3A and the ground contact Te, and a plurality of middle extending between the shoulder main groove 3A and the center main groove 3B. A plurality of center lateral grooves 4C extending between the lateral grooves 4B and the center main grooves 3B, 3B are provided.

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

  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, etc. 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. “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” if it is ETRTO, but if the tire is for a passenger car, the load is equivalent to 88% of the above load.

  Each main groove 3A, 3B of this embodiment extends in a zigzag shape in the tire circumferential direction. Such main grooves 3A and 3B increase the edge component in the tire axial direction, and thus increase the snow column shear force, driving force, braking force, and the like. Therefore, snow road performance and ice road performance are improved.

  FIG. 2 is a sectional view taken along line XX in FIG. As shown in FIGS. 1 and 2, the groove widths of the main grooves 3A and 3B (the groove width perpendicular to the longitudinal direction of the grooves, the same applies to other grooves hereinafter) W1 and the groove depth D1 Can be variously determined in accordance with common practice. However, when these groove widths or groove depths are small, drainage performance and snow road performance may be deteriorated. On the contrary, when these groove widths or groove depths are large, the ground contact area and rigidity of each block 5 to 7 may be reduced, and the ice performance may be deteriorated. For this reason, the groove width W1 of the main grooves 3A and 3B is desirably 3 to 9% of the tread ground contact width TW, for example. The groove depth D1 of the main grooves 3A and 3B is preferably 6 to 15 mm, for example.

  In order to ensure a good balance between the rigidity in the tire axial direction and the drainage performance of each block 5 to 7, the tire axial distance L1 between the shoulder main groove 3A and the tire equator C is 25 to 35% of the tread ground contact width TW. Is desirable. From the same viewpoint, the tire axial direction distance L2 between the center main groove 3B and the tire equator C is desirably 5 to 15% of the tread contact width TW. Each position of the main grooves 3A and 3B is specified by the groove center line. However, when the main groove 3 is a zigzag non-linear line as in this embodiment, the center of the amplitude of the groove center line is used. Lines G1 and G2 are used.

  In the present embodiment, the middle lateral groove 4B is bent with a certain width and extends in the same direction with respect to the tire axial direction, so that the drainage performance is improved. Moreover, since such a middle horizontal groove 4B ensures the land area of the middle block 6, the performance on ice is improved.

  The average groove width W2g of the middle lateral groove 4B is defined as 7 to 11% of the maximum length La of the middle block 6 in the tire circumferential direction. When the average groove width W2g of the middle horizontal groove 4B is less than 7% of the maximum length La of the middle block 6, the groove volume of the middle horizontal groove 4B becomes small, and the snow column shear force and drainage performance deteriorate. On the contrary, if the average groove width W2g exceeds 11% of the maximum length La, the land area of the middle block 6 becomes small, and the ice road performance deteriorates. For this reason, the average groove width W2g of the middle lateral groove 4B is preferably 8% or more and 10% or less of the maximum length La of the middle block 6. The “average groove width” refers to the area of the lateral groove on the ground contact surface along the inclination of the groove center line 8c when a normal load is applied to the tire in the normal state and grounded on a flat surface with a camber angle of 0 °. The groove width divided by the length (hereinafter, the length along such an inclination is referred to as “actual length” in this specification).

  In the present embodiment, the shoulder lateral groove 4A is formed as a zigzag groove extending in a zigzag shape over the longitudinal direction. Such shoulder lateral grooves 4A enhance the edge component in the tire axial direction and increase the snow column shear force.

  The width W3 of the shoulder lateral groove 4A is preferably 1.0% or more of the tread ground contact width TW, more preferably 1.5% or more, preferably 7.0% or less, more preferably 6.5% or less. is there.

  In this embodiment, in the center lateral groove 4C, the groove width W4 of the center lateral groove 4C gradually increases from the central portion 4x in the tire axial direction toward both end portions 4y. Such a center lateral groove 4C can smoothly discharge the snow in the center lateral groove 4C to the center main groove 3B. Further, since the center lateral groove 4C has a large groove volume at both ends 4y, the snow column shear force is improved.

  The groove width W4 of the center lateral groove 4C is preferably 0.5% or more of the tread ground contact width TW, more preferably 1.0% or more, preferably 3.5% or less, more preferably 3.0% or less. is there.

  In addition, the groove depth D3 of the shoulder lateral groove 4A, the groove depth D2 of the middle lateral groove 4B, and the groove depth D4 of the center lateral groove 4C are preferably in order to ensure the rigidity and the groove volume of each of the blocks 5 to 7 in a balanced manner. It is 4 mm or more, more preferably 6 mm or more, preferably 12 mm or less, more preferably 10 mm or less.

  FIG. 3 is a partially enlarged view of the vicinity of the middle block 6 provided in the left half of the tread portion 2 of FIG. As shown in FIG. 3, a middle block lateral edge 10, which is an edge extending in the tire axial direction on both sides in the tire circumferential direction of the middle block 6, includes a middle inner portion 11 extending from the center main groove 3 </ b> B, and the middle inner portion 11. A middle middle portion 12 extending from the outer end portion 11e in the tire axial direction and a middle outer portion 13 extending from the outer axial end portion 12e of the middle central portion 12 and continuing to the shoulder main groove 3A. Composed.

  In the present embodiment, the middle inner portion 11 and the middle outer portion 13 both extend linearly. As a result, the edge component in the tire axial direction of the middle block 6 and the drainage resistance of the middle lateral groove 4B are enhanced in a well-balanced manner.

  The middle inner portion 11 is inclined to one side in the tire circumferential direction (upward to the left in FIG. 3) at an angle α1 of 3 to 15 ° with respect to the tire axial direction. The middle outer portion 13 is also inclined to one side (upward in FIG. 3) in the tire circumferential direction at an angle α2 of 3 to 15 ° with respect to the tire axial direction. Since the middle inner portion 11 and the middle outer portion 13 have a large edge component in the tire axial direction, the braking force and the snow column shear force are increased.

  When the angle α1 of the middle inner portion 11 and the angle α2 of the middle outer portion 13 are less than 3 °, the edge component in the tire circumferential direction cannot be increased, and the turning performance cannot be improved. Conversely, when the angle α1 of the middle inner portion 11 and the angle α2 of the middle outer portion 13 exceed 15 °, the edge component in the tire axial direction becomes small, and the braking force and snow column shearing force are reduced. For this reason, the angle α1 of the middle inner portion 11 and the angle α2 of the middle outer portion 13 are preferably 5 ° or more, and preferably 13 ° or less.

  The middle central portion 12 extends linearly in the present embodiment. For this reason, the effect of reducing drainage resistance is enhanced. Further, the middle central portion 12 ensures a large rigidity in the tire axial direction of the middle block 6.

  The middle center portion 12 is inclined in the same direction as the middle inner portion 11 and the middle outer portion 13 with respect to the tire axial direction. Thereby, the drainage resistance of the middle lateral groove 4B is kept small. The middle middle portion 12 has a length L3 in the tire circumferential direction of 75 to 100% of the average groove width W2g (shown in FIG. 1) of the middle lateral groove 4B. Thereby, the edge component of the tire circumferential direction of the middle block 6 becomes large. Therefore, ice road performance, drainage performance and snow road performance are further improved in a balanced manner.

  When the length L3 in the tire circumferential direction of the middle middle portion 12 exceeds 100% of the average groove width W2g of the middle lateral groove 4B, the drainage resistance of the middle lateral groove 4B increases and the drainage performance deteriorates. Moreover, when the length L3 is large, the rigidity of the middle block 6 becomes small and the edge effect is not exhibited. On the other hand, when the length L3 of the middle central portion 12 is less than 75% of the average groove width W2g, the edge component in the tire circumferential direction becomes small, and the turning performance on an icy road deteriorates. For this reason, the length L3 of the middle central portion 12 is preferably 80% or more, preferably 95% or less of the average groove width W2g of the middle lateral groove 4B.

  In order to effectively exhibit the above-described action, the angle α3 of the middle middle portion 12 with respect to the tire axial direction is preferably 45 ° or more, more preferably 50 ° or more, preferably 75 ° or less, more preferably 70 °. It is as follows.

  By the middle inner portion 11, the middle middle portion 12, and the middle outer portion 13 as described above, vertical convex portions 14 and 14 are formed on both sides of the middle block 6 in the tire circumferential direction so that the ends of the middle block 6 protrude outward. Is done. In the present embodiment, the middle outer portion 13 and the middle central portion 12 form a vertical convex portion 14 a on one side (upper side in FIG. 3) of the middle block 6 in the tire circumferential direction, and the middle inner portion 11 and the middle central portion 12. Thus, a vertical convex portion 14b on the other side (lower side in FIG. 3) of the middle block 6 in the tire circumferential direction is formed.

  When the actual length L4 of the middle inner portion 11 that forms the other longitudinal convex portion 14b in the tire circumferential direction is large, the average groove width W2g of the middle lateral groove 4B becomes small, and drainage performance and snowy road performance may deteriorate. There is. On the other hand, when the actual length L4 is small, the rigidity in the tire axial direction of the vertical convex portion 14b becomes small, and there is a possibility that the turning performance cannot be improved. For this reason, the actual length L4 of the middle inner part 11 is preferably 25% or more, more preferably 30% or more, preferably 45% of the length Lb of the middle block lateral edge 10 along the middle inner part 11. Below, more preferably 40% or less.

  From the same point of view, the actual length L5 of the middle outer portion 13 forming the one longitudinal protrusion 14a in the tire circumferential direction is preferably the length Lb of the middle block lateral edge 10 along the middle inner portion 11. It is 25% or more, more preferably 30% or more, preferably 45% or less, more preferably 40% or less.

  Further, in the present embodiment, the middle block 6 has a middle inner vertical edge 17 that is an edge on the tire equator C side and a middle outer vertical edge 18 that is an edge on the ground contact Te side of the middle block 6.

  The middle inner vertical edge 17 and the middle outer vertical edge 18 of the present embodiment are respectively a plurality of circumferential pieces 20 which are opposite to the middle inner portion 11 and inclined at an angle α4 of 3 to 15 ° with respect to the tire circumferential direction. And the unevenness | corrugation is formed by the some axial direction piece 21 which connects between this circumferential direction piece 20 and 20. FIG. Such unevenness increases the edge component of the middle block 6 in the tire axial direction.

  When the angle α4 of the circumferential piece 20 is less than 3 °, the edge component in the tire axial direction becomes small. Conversely, when the angle α4 of the circumferential piece 20 exceeds 15 °, the drainage resistance of each of the main grooves 3A and 3B is deteriorated. Further, when the angle α4 is large, the rigidity in the tire circumferential direction is small. For this reason, the angle α4 of the circumferential piece 20 is preferably 5 ° or more, and preferably 13 ° or less.

  The circumferential pieces 20 of the middle inner vertical edge 17 and the middle outer vertical edge 18 of this embodiment are irregularly formed. Specifically, the circumferential piece 20 of the middle inner vertical edge 17 includes two or more (two kinds in this embodiment) circumferential pieces 20a and 20b having different angles α4. Similarly, the circumferential piece 20 of the middle outer vertical edge 18 includes two or more kinds (three kinds in this embodiment) of circumferential pieces 20c, 20d, and 20e having different angles α4. Thereby, the edge effect of the circumferential piece 20 can be exhibited largely according to the turning angle of the vehicle.

  Moreover, in this embodiment, each circumferential direction piece 20 of the middle inner vertical edge 17 has a different actual length L6. Similarly, each circumferential direction piece 20 of the middle outer vertical edge 18 has a different actual length L6. As a result, the arrangement positions of the axial pieces 21 of the middle inner vertical edge 17 and the middle outer vertical edge 18 are shifted in the tire circumferential direction, respectively, so the middle inner vertical edge 17 of the circumferential piece having the same actual length L6. As compared with the middle outer vertical edge 18, the edge effect in the tire axial direction is closely exhibited in the tire circumferential direction, and the braking force is improved. If the actual length L6 of the circumferential piece 20 is small, the rigidity of the middle block 6 may be excessively small. For this reason, the actual length L6m of the largest circumferential piece 20 of the middle inner vertical edge 17 is preferably 1.5 to 3.0 times the actual length L6n of the smallest circumferential piece 20. Moreover, the actual length L6m of the largest circumferential piece 20 of the middle outer vertical edge 18 is preferably 1.5 to 3.0 times the actual length L6n of the smallest circumferential piece 20.

  In the present embodiment, the average tire circumferential angle (not shown) of the circumferential pieces 20 of the middle inner vertical edge 17 and the middle outer vertical edge 18 is inclined at 3 to 15 °. Thereby, the middle block 6 becomes a substantially rectangular shape by the middle block horizontal edge 10, the middle inner vertical edge 17 and the middle outer vertical edge 18, and the rigidity in the tire circumferential direction and the axial direction of the middle block 6 is enhanced. The “average tire circumferential direction angle” is an angle obtained by dividing the sum of the products of the actual length L6 of each circumferential piece 20 and the angle α4 by the sum of the actual lengths of each circumferential piece 20. It is.

In the present embodiment, the axial piece 21 includes a first piece portion 21x that is inclined in a direction opposite to the circumferential piece 20 from one end portion (lower end in FIG. 4) of the circumferential piece 20 in the tire circumferential direction, and a circumferential piece. It consists of the 2nd piece part 21y which inclines in the same direction as the circumferential direction piece 20 from one edge part of the tire circumferential direction of the direction piece 20. As shown in FIG. And in the area | region where the 1st piece part 21x and the 2nd piece part 21y adjoin a tire circumferential direction, the unevenness | corrugation (it becomes convex from the main grooves 3A and 3B side) formed with the circumferential direction piece 20 and the axial direction piece 21 A concave portion 22 or a convex portion 23) that protrudes toward the main grooves 3 </ b> A and 3 </ b> B is formed in a substantially rectangular shape. Such concave portions 22 and convex portions 23 are secured with high rigidity, and braking force and turning performance are enhanced. Moreover, the recessed part 22 and the convex part 23 exhibit a big snow column shear force, and improve snowy road performance.

  Moreover, in the area | region where the 1st piece part 21x and the 1st piece part 21x are adjacent in a tire circumferential direction, the unevenness | corrugation formed with the circumferential direction piece 20 and the axial direction piece 21 is formed in a substantially square shape. Such unevenness improves the edge component in the tire axial direction and drainage resistance in a well-balanced manner. In the present embodiment, each of the middle inner vertical edge 17 and the middle outer vertical edge 18 is provided with a substantially rectangular concave portion 22 and convex portion 23 and a plurality of substantially square-shaped concave and convex portions, respectively. Thereby, drainage performance, snow road performance, and ice road performance are improved in a well-balanced manner.

  In the present embodiment, the middle block 6 has a ratio (Lc) between the length Lb of the middle block lateral edge 10 along the middle inner portion 11 and the length Lc of the middle inner vertical edge 17 perpendicular to the middle inner portion 11. / Lb) is 0.9 to 1.1. In such a middle block 6, the rigidity in the tire circumferential direction and the rigidity in the tire axial direction are improved in a well-balanced manner.

  The ratio (L3 / Lc) between the length L3 of the middle middle portion 12 in the tire circumferential direction and the length Lc of the middle inner vertical edge 17 perpendicular to the middle inner portion 11 is 0.05 to 0.15. . Thereby, the edge component of the tire circumferential direction of the middle inner side vertical edge 17 and the middle outer side vertical edge 18 is ensured largely. Further, the rigidity of the middle block 6 in the tire axial direction is ensured.

  The middle block 6 has a semi-open type first siping 24a having one end opened at the center main groove 3B and the other end terminated without reaching the shoulder main groove 3A, and one end opened at the shoulder main groove 3A. Semi-open type second sipes 24b that end without the other end reaching the center main groove 3B are alternately arranged in the tire circumferential direction. Thereby, the edge effect of siping is exhibited and ice road performance improves. Further, the rigidity of the middle block 6 in the tire circumferential direction is equalized, and the driving force and braking force are improved.

  As shown in FIG. 1, in this embodiment, sipings 25 are also arranged in the shoulder block 5 and the center block 7. The shoulder block 5 is provided with a closed type siping 25a whose both ends terminate in the shoulder block 5. Thereby, the rigidity of the shoulder block 5 on which a large lateral force acts during turning can be ensured. In addition, semi-open type sipings 25b are alternately arranged in the center block 7 in the tire circumferential direction.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, this invention is not limited to said specific embodiment, It can implement by changing into a various aspect.

A pneumatic tire of size 195 / 80R15 having the basic pattern of FIGS. 1 and 4 was prototyped based on the specifications in Table 1, and the drainage performance, ice performance (braking force) and snow performance of each sample tire were tested. It was. The common specifications are as follows.
Tread contact width TW: 161mm
<Main groove>
Groove width W1: 4.0 to 6.8 mm
Groove depth: 12.5mm
Ratio of tire axial direction distance L1 of shoulder main groove to tread contact width TW (L1 / TW): 0.28
Ratio (L2 / TW) between the tire axial direction distance L2 of the center main groove and the tread contact width TW (0.10): 0.10
<Horizontal groove>
Center lateral groove width W4: 2.1 to 4.5 mm
Shoulder lateral groove width W3: 2.7 to 5.9 mm
Middle groove width average groove width W2g: 3.0mm
Groove depth: 7.0 to 10.5 mm
<Middle block>
Middle inner angle α1: 8 °
Middle outer angle α2: 9 °
Middle length of tire in the middle of the middle / Average groove width of middle groove: 85%
The test method is as follows.

<Snow road performance>
Each sample tire was mounted on all wheels of a 2700cc four-wheel drive vehicle under the following conditions, and was run on a snowy road test course by one driver. 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 the conventional example. The larger the value, the better.
Rim 15 × 6J
Internal pressure: 350 kPa (front wheel)
Internal pressure: 425 kPa (rear wheel)

<Ice performance (braking force)>
The test vehicle traveled on an icy road test course, suddenly braked from a speed of 30 km / h, and the braking distance until stopping was measured. The result is displayed as an index with the reciprocal of the braking distance of the conventional example as 100. The larger the value, the better.

<Drainage performance>
The test vehicle was run on a wet asphalt road test course having a total length of 2000 m, and the running time at that time was measured. In order to make the wet conditions the same, the water depth on the road surface was unified to 5 mm immediately before traveling. The result is displayed as an index with the reciprocal of the traveling time of the conventional example as 100. The larger the value, the better.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that in the tires of the examples, the snow road performance and the ice road performance were significantly improved while the deterioration of the drainage performance was suppressed as compared with the comparative example.

2 Tread 3A Shoulder main groove 3B Center main groove 4B Middle lateral groove
6 Middle block 10 Middle block lateral edge 11 Middle inner part 12 Middle central part 13 Middle outer part 17 Middle inner vertical edge 18 Middle outer vertical edge 20 Circumferential piece 21 Axial piece

Claims (4)

A pair of shoulder main grooves extending continuously in the tire circumferential direction on the tread portion, and a pair of center main grooves extending continuously in the tire circumferential direction on the inner side in the tire axial direction of the shoulder main grooves; By providing a middle lateral groove extending between the shoulder main groove and the center main groove, the middle block divided by the shoulder main groove, the center main groove and the middle lateral groove is separated in the tire circumferential direction. A pneumatic tire with a middle block row,
An average groove width of the middle lateral groove is 7 to 11% of a maximum length of the middle block in the tire circumferential direction,
A middle block lateral edge, which is an edge extending in the tire axial direction on both sides in the tire circumferential direction of the middle block, is located on one side in the tire circumferential direction at an angle of 3 to 15 ° with respect to the tire axial direction from the center main groove. Middle inner part that extends at an angle,
A middle middle portion that is continuous with the middle inner side portion and bent to the one side in the tire circumferential direction and has a length in the tire circumferential direction that is 75 to 100% of an average groove width of the middle lateral groove; and
Continuing from the middle of the middle, comprising a middle outer portion that is inclined to the one side in the tire circumferential direction at an angle of 3 to 15 ° with respect to the tire axial direction and is continuous with the shoulder main groove,
The middle inner vertical edge, which is an edge extending in the tire circumferential direction on the tire equator side of the middle block, and the middle outer vertical edge, which is an edge extending in the tire circumferential direction on the grounded end side of the middle block, are respectively A plurality of circumferential pieces inclined at an angle of 3 to 15 degrees with respect to the tire circumferential direction opposite to the inclination of the groove or the shoulder main groove on the side and the inner side of the middle with respect to the tire circumferential direction; A pneumatic tire is characterized in that irregularities are formed by a plurality of axial pieces that connect between the directional pieces.   The middle block has a semi-open type first siping having one end opened in the center main groove and the other end terminated without reaching the shoulder main groove, and one end opened in the shoulder main groove and the other end The pneumatic tire according to claim 1, wherein semi-open type second sipings that terminate without reaching the center main groove are alternately arranged in the tire circumferential direction.   The ratio (Lc / Lb) between the length Lb of the middle block lateral edge along the middle inner portion and the length Lc of the middle inner vertical edge perpendicular to the middle inner portion is 0.9-1. The pneumatic tire according to claim 1 or 2, which is .1. The axial piece is different from the circumferential piece in a first piece that is inclined in the direction opposite to the inclination of the circumferential piece with respect to the tire circumferential direction from one end of the circumferential piece in the tire circumferential direction. 4. The device according to claim 1, further comprising a second piece portion that is inclined in the same direction as the inclination of the circumferential piece with respect to the tire circumferential direction from one end portion of the circumferential piece provided in a position in the tire circumferential direction. The described pneumatic tire.

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