JP5671503B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire in which noise performance, snow road performance, and ice road performance are improved in a balanced manner.

  Winter pneumatic tires run on asphalt roads as well as snow roads and ice roads. Therefore, such a pneumatic tire for winter is required to improve not only snow road performance and ice road performance but also noise performance.

  For example, in order to improve snow road performance, it has been proposed to increase the volume of the lateral groove of the tread portion in order to increase the snow column shear force. However, this method has a problem that the ice road performance deteriorates because the contact area of the tread portion is reduced. In addition, when the volume of the lateral groove is large, there is a problem that noise performance is also deteriorated because pumping sound and the like generated by the air flowing out of the lateral groove as the tire rolls increase. Thus, snow road performance, ice road performance, and noise performance have a reciprocal relationship, and it has been difficult to improve all of these performances in a well-balanced manner. Related technologies include the following.

JP 2011-042282 A

  The present invention has been devised in view of the above-described actual situation. Siping is provided in the center block and the middle block, the groove width and the arrangement angle of the center lateral groove and the middle lateral groove are defined, and the center lateral groove and the center main groove are provided. Noise performance, snowy road performance, and icy road are based on defining the tire circumferential direction distance between the first intersection where the groove intersects and the second intersection where the middle lateral groove and the center main groove intersect within a certain range. The main purpose is to provide a pneumatic tire with improved performance in a well-balanced manner.

According to the first aspect of the present invention, the tread portion includes 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 defined in the tire circumferential direction. A pair of shoulder main grooves extending continuously in the direction, a plurality of center lateral grooves extending between the center main grooves, and a plurality of middle lateral grooves extending between the center main grooves and the shoulder main grooves are provided. A center block row in which the center blocks divided by the pair of center main grooves and the center lateral grooves are separated in the tire circumferential direction, and divided by the shoulder main grooves, the center main grooves, and the middle lateral grooves A pneumatic tire comprising a pair of middle block rows in which the middle blocks are spaced apart in the tire circumferential direction, the center block and the center block Each of the dollar blocks is provided with a plurality of sipings, and the center lateral groove is inclined to one side in the tire axial direction at an angle of 5 to 20 ° with respect to the tire axial direction, and the average groove width is 7-15% of the maximum length of the center block in the tire circumferential direction, the middle lateral groove is inclined to the opposite side of the central lateral groove at an angle of 5-25 ° with respect to the tire axial direction, and The average groove width is 7 to 11% of the maximum length of the middle block in the tire circumferential direction, and the center block is formed with a center convex portion with a part protruding toward the center main groove side. The outer end of the convex portion that is the outermost side in the tire axial direction is formed on the outer side in the tire axial direction of the inner edge in the tire axial direction of the circumferential edge on the inner side in the tire axial direction of the middle block. Assembling The regulations inner pressure filling, yet in the ground plane of the normal load load state of being grounded plane camber angle of 0 degrees to load the normal load, the first intersection in which the center lateral grooves and the center main groove intersect, the center The distance in the tire circumferential direction between the first intersection and the second intersection where the middle lateral groove and the center main groove intersect with each other across the convex portion is the length of the ground contact surface at the tire equator position , It is 0.75 to 1.00 times the difference from the length in the tire circumferential direction of the ground contact surface at an intermediate position in the tire axial direction of the middle block.

The invention of claim 2, wherein the center lateral grooves, a pneumatic tire according to claim 1, wherein the groove width toward the end portions from the central portion in the tire axial direction increases gradually. According to a third aspect of the present invention, in the contact surface in the normal load state, the length of the contact surface at the tire equator position and the tire circumferential direction of the contact surface at an intermediate position in the tire axial direction of the middle block The pneumatic tire according to claim 1 or 2 , wherein a difference from the length of the tire is 0.015 to 0.045 times the length of the contact surface at the tire equator position . Or fourth aspect of the present invention has a front Kigaitan of the center convex portion, the tire axial direction of the length between the front Symbol inner end of the middle block is the 0.5~3.0mm The pneumatic tire according to claim 1 .

  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 center lateral grooves extending between the center main grooves, and a plurality of middle lateral grooves extending between the center main groove and the shoulder main grooves are provided. Accordingly, the tread portion includes a center block row in which center blocks divided by the pair of center main grooves and the center lateral grooves are spaced in the tire circumferential direction, and the shoulder main grooves, the center main grooves, and the A middle block divided by middle lateral grooves includes a pair of middle block rows spaced in the tire circumferential direction.

  Each of the center block and the middle block is provided with a plurality of sipings. Ice edge performance is improved by the edge effect of siping.

  The center lateral groove is inclined to one side in the tire axial direction at an angle of 5 to 20 ° with respect to the tire axial direction, and the average groove width is 7 to 15% of the maximum length of the center block in the tire circumferential direction. It is. Further, the middle lateral groove is inclined to the opposite side of the center lateral groove at an angle of 5 to 25 ° with respect to the tire axial direction, and the average groove width is 7 to the maximum length of the middle block in the tire circumferential direction. 11%. The center lateral groove and the middle lateral groove that are inclined at such an angle ensure the rigidity of the center block and the middle block in the tire axial direction, and improve the turning performance on an icy road. In addition, the inclined lateral grooves suppress deformation of the lateral grooves accompanying the rolling of the tire in the groove and reduce the outflow of air, so that pumping noise is reduced. Furthermore, the center lateral groove and the middle lateral groove whose average groove width is defined in this way further suppresses the outflow of air in the groove. Therefore, noise performance is greatly improved.

  Further, the center lateral groove and the center main groove intersect at the ground contact surface in the normal load state where the normal rim is assembled and filled with the normal internal pressure, and the normal load is applied and the camber angle is 0 degrees to contact the plane. The distance in the tire circumferential direction between the first intersection point and the second intersection point where the middle lateral groove and the center main groove intersect is the length of the ground contact surface at the tire equator position and the contact point at the middle position of the middle block in the tire axial direction. It is 0.75 to 1.00 times the difference from the length in the tire circumferential direction of the ground. That is, since the first intersection and the second intersection are always misaligned, the center lateral groove and the middle lateral groove are prevented from being grounded at the same time. Thereby, the overlapping of pitch sounds is prevented. Further, the air flowing in the center lateral groove comes into contact with the middle block and the pumping sound is reduced. Similarly, the air flowing through the middle lateral groove contacts the center block 5 and the pumping sound is reduced. Therefore, noise performance is improved. Further, the center lateral groove and the middle lateral groove are close to each other. As a result, the center lateral groove and the middle lateral groove appear almost simultaneously in the central region in the vicinity of the leading edge. At this time, the ground contact area of the central region is reduced, and the contact pressure of the central region is increased. Therefore, a snow column with high rigidity is formed by each lateral groove in the central region, and snow road performance is improved.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is an enlarged view including the center block and middle block of FIG. It is a figure showing the contact shape of the tire of FIG. It is the A section enlarged view of FIG.

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, a plurality of center lateral grooves 4A extending between the center main grooves 3A and 3A, a plurality of middle lateral grooves 4B extending between the center main groove 3A and the shoulder main grooves 3B, and a shoulder main groove 3B A plurality of shoulder lateral grooves 4C extending between the ground contact Te are provided.

  Thereby, in the tread portion 2 of the present embodiment, a center block row 5R in which the center blocks 5 divided by the pair of center main grooves 3A, 3A and the center lateral grooves 4A are separated in the tire circumferential direction, the center main grooves 3A, a shoulder main groove 3B and a middle lateral groove 4B are divided into a middle block row 6R in which a middle block 6 is separated in the tire circumferential direction, and a shoulder main groove 3B, a ground contact end Te, and a shoulder lateral groove 4C. A shoulder block row 7R in which a plurality of segmented shoulder blocks 7 are arranged in the tire circumferential direction is arranged.

  In this embodiment, as a winter tire, the ratio between the total area Mb of the treads of all the blocks 5 to 7 and the total surface area Ma of the tread obtained by filling all the grooves 3A, 3B and 4A to 4C of the tread portion 2 The land ratio represented by (Mb / Ma) is set to 68 to 72%. Thereby, ice road performance, snow road performance, and drainage performance are improved with good balance.

  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. It is determined as the contact position on the outermost side in the tire axial direction in the normal load application state. 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” in the case of ETRTO.

  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. In addition, since the main grooves 3A and 3B disturb the air column resonance in the grooves, the noise performance is improved.

  The groove width of each of the main grooves 3A and 3B (the groove width perpendicular to the longitudinal direction of the groove, hereinafter the same applies to other grooves) W1 and the groove depth (not shown) are variously determined according to customs. be able to. However, when these groove widths or groove depths are small, snowy road performance may be deteriorated. On the other hand, when these groove widths or groove depths are large, there is a risk that the ice road performance and noise performance will deteriorate. 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 of the main grooves 3A and 3B is preferably 6 to 15 mm, for example.

  In order to ensure the rigidity of the blocks 5 to 7 in the tire axial direction with a good balance, the tire axial distance L1 between the center main groove 3A and the tire equator C is preferably 5 to 15% of the tread contact width TW. The tire axial distance L2 between the shoulder main groove 3B and the tire equator C is preferably 25 to 35% of the tread contact width TW. In addition, although each position of each main groove 3A, 3B is specified by those groove centerlines, when each main groove 3A, 3B is a zigzag non-linear as in this embodiment, the groove centerline Amplitude centerlines G1, G2 are used.

  FIG. 2 shows an enlarged view of the center block 5 and the middle block 6 of FIG. As shown in FIG. 2, the maximum width Wa of the center block 5 in the tire axial direction is preferably 1.04 to 1.14 times the maximum width Wb of the middle block 6 in the tire axial direction. Thereby, the driving force and braking force on icy roads and snowy roads are enhanced.

  The center lateral groove 4A is inclined to one side in the tire axial direction (upward to the right in FIG. 1) at an angle α1 of 5 to 20 ° with respect to the tire axial direction. That is, when the angle α1 is less than 5 °, the outflow of air in the center lateral groove 4A increases with the rolling of the tire, so that the pumping sound increases. When the angle α1 exceeds 20 °, the rigidity of the center block 5 in the tire axial direction is reduced, and the turning performance is deteriorated. For this reason, the angle α1 of the center lateral groove 4A is preferably 7 ° or more, and preferably 18 ° or less. The angle α1 of the center lateral groove 4A is defined by a virtual center line 8c that connects the middle points 8e of the opening ends 8 on both sides of the center lateral groove 4A with a straight line, and the opening end 8 has groove edges 9 and 9 on both sides of the lateral groove. Formed between the outer ends 9a, 9a. Hereinafter, the same applies to the angles of the other lateral grooves.

  The average groove width W2g (shown in FIG. 1) of the center lateral groove 4A is defined as 7 to 15% of the maximum length L3 of the center block 5 in the tire circumferential direction. When the average groove width W2g of the center lateral groove 4A is less than 7% of the maximum length L3 of the center block 5, the groove volume of the center lateral groove 4A is reduced, and the snow column shear force is deteriorated. On the other hand, when the average groove width W2g exceeds 15% of the maximum length L3 of the center block 5, the land area of the center block row 5R becomes small, and the ice road performance deteriorates. Further, when the average groove width W2g is large, the pumping sound increases and the noise performance is deteriorated. For this reason, the average groove width W2g of the center lateral groove 4A is preferably 9% or more, preferably 13% or less of the maximum length L3 of the center block 5. The “average groove width” refers to a groove width obtained by dividing the area of the lateral groove on the ground contact surface in the normal load load state by the length of the groove center line 8i. Hereinafter, the average groove width of other grooves is also referred to. The same shall apply.

  In the present embodiment, the center lateral groove 4A gradually increases in groove width from the central portion 10b in the tire axial direction toward both end portions 10a. Such a center lateral groove 4A smoothly discharges the snow in the groove to the center main groove 3A, and improves snow road performance. In addition, when the groove width W2e of the both ends 10a is excessively large, the pumping sound in the center lateral groove 4A may be increased, and the noise performance may be deteriorated. For this reason, the groove width W2e of the both end portions 10a is preferably 1.3 times or more, more preferably 1.5 times or more, preferably 3.0 times or less, more preferably, the groove width W2c of the central portion 10b. 2.8 times or less.

  The central portion 10b of the center lateral groove 4A has a constant width. The central portion 10b of the present embodiment has a larger angle with respect to the tire axial direction than the portions on both sides thereof. Thereby, the center lateral groove 4A is bent in a crank shape. The crank-shaped lateral groove 4A has a large snow column shear force when turning on a snowy road. Further, since the air flow in the center lateral groove 4A is hindered, the noise performance is improved.

  As shown in FIG. 1, the middle lateral groove 4 </ b> B is inclined at an angle α <b> 2 of 5 to 25 degrees with respect to the tire axial direction, and is opposite to the center lateral groove 4 </ b> A (upward left in FIG. 1). When the angle α2 is less than 5 °, the outflow of air in the middle lateral groove 4B accompanying the rolling of the tire increases, so that the pumping noise increases. When the angle α2 exceeds 25 °, the rigidity of the middle block 6 in the tire axial direction is reduced, and the turning performance on an icy road is deteriorated. For this reason, the angle α2 of the middle lateral groove 4B is preferably 7 ° or more, and preferably 23 ° or less.

  Although not particularly limited, it is desirable that the angle α2 of the middle lateral groove 4B is larger than the angle α1 of the center lateral groove 4A. That is, when the angle α1 of the center lateral groove 4A is larger than the angle α2 of the middle lateral groove 4B, the snow column shearing force of the center lateral groove 4A to which a large ground pressure acts is reduced during straight traveling, and the straight running stability performance may be deteriorated. is there. In addition, when the angle α2 of the middle lateral groove 4B is excessively larger than the angle α1 of the center lateral groove 4A, the rigidity of the middle block 6 in the tire axial direction is reduced, and the turning performance on an icy road may be deteriorated. For this reason, the angle difference α2-α1 is preferably 2 ° or more, more preferably 4 ° or more, preferably 8 ° or less, more preferably 6 ° or less.

  The average groove width W3g of the middle lateral groove 4B is defined as 7 to 11% of the maximum length L4 (shown in FIG. 2) of the middle block 6 in the tire circumferential direction. When the average groove width W3g of the middle lateral groove 4B is less than 7% of the maximum length L4 of the middle block 6, the groove volume of the middle lateral groove 4B is reduced, and the snow column shear force is deteriorated. On the contrary, when the average groove width W3g exceeds 11% of the maximum length L4 of the middle block 6, the noise performance and the ice road performance are deteriorated. For this reason, the average groove width W3g of the middle lateral groove 4B is preferably 8% or more, preferably 10% or less of the maximum length L4 of the middle block 6. In the present embodiment, the middle lateral groove 4B is formed with a constant groove width. Thereby, the rigidity in the tire circumferential direction of the middle block 6 is equalized in the tire axial direction, and the braking force and the driving force are increased.

  The middle lateral groove 4B extends between the pair of middle outer portions 12a and the pair of middle outer portions 12a, 12a that are linearly inclined at both sides in the longitudinal direction at a constant angle with respect to the tire axial direction. A crank shape including a middle inner portion 12b inclined at an angle larger than 12a is formed. Such a middle lateral groove 4B improves noise performance because the middle inner portion 12b prevents the air flow in the middle lateral groove 4B.

  In this embodiment, the shoulder lateral groove 4C is inclined to the opposite side to the middle lateral groove 4B (lower left in FIG. 1). Thereby, the center lateral groove 4A, the middle lateral groove 4B, and the shoulder lateral groove 4C are alternately arranged in different directions with respect to the tire axial direction. Therefore, the pumping sound in the groove is disturbed by the horizontal grooves 4A to 4C, and the noise performance is further improved.

  The shoulder lateral grooves 4C are preferably inclined at an angle α3 of 5 to 20 ° with respect to the tire axial direction. Thereby, the pumping sound in a groove | channel and the air column resonance sound from the shoulder main groove | channel 4B can be reduced.

  The shoulder lateral groove 4C extends in a zigzag shape in the tire axial direction. Such shoulder lateral grooves 4C effectively disturb the air column resonance from the shoulder main grooves 3B and further improve the noise performance.

  The groove width W4 of the shoulder lateral groove 4C is preferably 3 to 7 mm, for example, in order to improve the snow drainage performance and the noise performance in a balanced manner.

  The groove depth (not shown) of the center lateral groove 4A, the middle lateral groove 4B and the shoulder lateral groove 4C is preferably 4 mm or more, more preferably 6 mm in order to improve the snow road performance, the ice road performance and the noise performance in a balanced manner. It is above, Preferably it is 12 mm or less, More preferably, it is 10 mm or less.

  Each of the center block 5 and the middle block 6 is provided with a plurality of sipings 14. For this reason, the ice road performance is improved by the edge effect of the siping 14.

  In the present embodiment, the siping 14 is a semi-open type siping in which one end terminates in each of the blocks 5 and 6 and the other end opens into the main grooves 3A and 3B. Such a siping 14 ensures a good balance between the edge effect and the rigidity of the block.

  In this embodiment, the sipings 14 of the center block 5 are alternately provided at the circumferential edges 5a on both sides of the center block 5 in the tire axial direction. Thereby, the rigidity of the center block 5 in the tire circumferential direction is ensured to be high. From the same viewpoint, the opening ends of the sipings 14 of the middle block 6 are alternately provided on the circumferential edges 6a on both sides of the middle block 6 in the tire axial direction.

  In this embodiment, the shoulder block 7 has a semi-open type siping 15a having one end opened in the shoulder main groove 3B and the other end terminated in the shoulder block 7, and a closed type terminated in the shoulder block 7 at both ends. A siping 15b is provided. Thereby, the rigidity of the shoulder block 7 to which a large lateral force acts during turning is ensured.

  FIG. 3 shows the ground contact surface S in the normal load state of the pneumatic tire of the present embodiment. As shown in FIG. 3, the ground contact surface S is a first arrival edge Sa (upper edge in FIG. 3) which is an end edge on the first arrival side in the rotation direction, and a rear end which is an end edge on the rear arrival side in the rotation direction. And an edge Sb (the lower edge in FIG. 3). The first landing edge Sa has a convex shape that protrudes most toward the first landing side at the tire equator position Ce. Further, the trailing edge Sb has a convex shape that protrudes most toward the trailing edge at the tire equator position Ce. That is, in the ground contact surface S of the present embodiment, the length L5 of the ground contact surface at the tire equator position Ce is greater than the length L6 of the ground contact surface in the tire circumferential direction at the middle position 6c of the middle block 6 in the tire axial direction. large.

In the ground contact surface S, the distance La in the tire circumferential direction between the first intersection K1 where the center lateral groove 4A and the center main groove 3A intersect and the second intersection K2 where the middle lateral groove 4B and the center main groove 3A intersect is the tire 0.75 to 1 of the difference (L5-L6) between the length L5 of the contact surface at the equator position Ce and the length L6 in the tire circumferential direction of the contact surface at the middle position 6c in the tire axial direction of the middle block 6 It is specified as 0.00. That is, since the first intersection K1 and the second intersection K2 are always displaced, it is possible to suppress the center lateral groove 4A and the middle lateral groove 4B from being grounded at the same time. Thereby, the overlapping of pitch sounds is prevented. Further, the air flowing in the center lateral groove 4A contacts the middle block 6 and the pumping sound is reduced. Similarly, the air flowing through the middle lateral groove 4B comes into contact with the center block 5 and the pumping sound is reduced. Therefore, noise performance is improved. Further, the center lateral groove 4A and the middle lateral groove 4B are close to each other. As a result, the center lateral groove 4A and the middle lateral groove 4B appear almost simultaneously in the central region Sc near the leading edge Sa. At this time, the ground area of the central region Sc is small, and the ground pressure of the central region Sc is large. Therefore, a snow column with high rigidity is formed by the lateral grooves 4A and 4B in the central region Sc, and snow road performance is improved. The central region Sc includes a first edge S, a tire circumferential position at a distance of 16% of the tread contact width TW in the tire circumferential direction from one end Sd closest to the first edge Sa, and a middle block. 6 is a region (indicated by hatching in FIG. 3) sandwiched between both ends 6 n and 6 n in the tire axial direction. Further, the intersection point K1 is the midpoint 8e of the center lateral groove 4A. Further, the intersection K2 is a midpoint 13e of the open end 13 of the middle lateral groove 4B.

When the distance La in the tire circumferential direction between the intersections K1 and K2 is less than 0.75 times the difference in length in the tire circumferential direction (L5-L6), the air flowing through the center lateral groove 4A comes into contact with the middle block 6. Without flowing into the middle lateral groove 4B. Further, the air that has flowed through the middle lateral groove 4 </ b> B does not contact the center block 5. For this reason, the pumping sound is not reduced. Further, since the center lateral groove 4A and the middle lateral groove 4B are grounded almost simultaneously, overlapping of pitch sounds occurs. Therefore, noise performance is deteriorated. Further, when the distance La exceeds 1.00 times the difference (L5−L6), the center lateral groove 4A and the middle lateral groove 4B are separated from each other. Therefore, the ground contact area of the central region Sc and thus the ground pressure of the central region Sc are small. Become . Thereby, the rigidity of the snow column of each horizontal groove 4A, 4B becomes small, and snow road performance deteriorates. Therefore, the distance La in the tire circumferential direction between the intersections K1 and K2 is preferably 0.80 times or more, and preferably 0.95 times or less the difference in length in the tire circumferential direction (L5-L6).

  In addition, although not particularly limited, in order to increase the contact pressure in the central region Sc when the difference in length in the tire circumferential direction (L5-L6) is reduced, the tire circumferential direction between the intersections K1 and K2 is increased. Since it is necessary to reduce the distance La, noise performance may not be improved. Conversely, when the difference in the tire circumferential length (L5-L6) increases, the area of the contact surface S decreases and snow road performance may deteriorate. For this reason, the difference in length in the tire circumferential direction (L5−L6) is preferably 0.015 times or more, more preferably 0.020 times or more of the length L5 of the contact surface at the tire equator position Ce, Preferably it is 0.045 times or less, More preferably, it is 0.040 times or less.

  FIG. 4 shows an enlarged view of part A of FIG. As shown in FIG. 4, in the present embodiment, a part of the center block 5 is protruded toward the center main groove side in the tire circumferential region R between the first intersection K1 and the second intersection K2. A center projection 17 is formed. Such center convex part 17 raises the contact pressure of the center main groove 3A vicinity between the center convex parts 17 and 17 adjacent to a tire circumferential direction. Thereby, a hard snow column is formed in the center main groove 3A. For this reason, a snow column shear force becomes large and snow road performance improves. In addition, in order to exhibit the above-mentioned operation, in the tire circumferential direction region R, instead of the center convex portion 17, a middle convex portion (not shown) in which a part of the middle block 6 protrudes toward the center main groove side is provided. It may be formed.

  The center convex portion 17 of the present embodiment includes a pair of center axis direction edges 17a and 17a extending in the tire axial direction and spaced apart in the tire circumferential direction, and a center circumferential direction edge connecting one end of the pair of center axis direction edges 17a and 17a. 17b is formed in a substantially rectangular shape. The center axis direction edge 17a is inclined at an angle α4 of 0 to 20 ° with respect to the tire axial direction. Thereby, the snow column shear force of the center main groove 3A is further increased.

  In order to exhibit the above-described action more effectively, the outer end 17e that forms the outermost side in the tire axial direction of the center convex portion 17 is the inner end in the tire axial direction of the circumferential edge 6i on the inner side in the tire axial direction of the middle block 6 It is desirable that it be formed on the outer side in the tire axial direction than 6e.

  In addition, if the outer end 17e of the center convex portion 17 is disposed on the outer side in the tire axial direction excessively than the inner end 6e of the circumferential edge 6i, the rigidity in the tire circumferential direction of the center convex portion 17 may be deteriorated. . For this reason, the length L7 in the tire axial direction between the outer end 17e and the inner end 6e is preferably 0.5 mm or more, more preferably 1.0 mm or more, and preferably 3.0 mm or less, more preferably. Is 2.0 mm or less.

  On the ground contact surface S, a large ground pressure is generated along the inclination direction of the first edge Sa. For this reason, as shown in FIG. 3, in the present embodiment, one middle lateral groove 4B in the tire axial direction (the left middle lateral groove in FIG. 3) is inclined in the same direction as the leading edge Sa. The snow column formed by the middle lateral groove 4B is formed with high rigidity.

  Further, the other middle lateral groove 4B in the tire axial direction (the right middle lateral groove in FIG. 3) is formed on the opposite side to the inclination direction of the leading edge Sa with respect to the tire axial direction. In such a middle lateral groove 4B, since the deformation of the groove due to grounding is small, the outflow of air in the middle lateral groove 4B is small. Accordingly, the other middle lateral groove 4B reduces the pumping sound and improves the noise performance. That is, in this embodiment, the noise performance and the snow road performance are improved in a balanced manner by the one middle lateral groove 4B in the tire axial direction and the other middle lateral groove 4B in the tire axial direction.

  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 in Table 1, and the noise performance, ice performance (braking force) and snow performance of each sample tire were tested. The common specifications are as follows.
Tread contact width TW: 160mm
<Main groove>
Groove width W1: 3-5mm
Groove depth: 12.3 mm
Ratio (L1 / TW) of the tire axial direction distance L1 of the center main groove and the tread ground contact width TW: 0.09
Ratio of tire axial direction distance L2 of shoulder main groove to tread contact width TW (L2 / TW): 0.28
<Horizontal groove>
Center groove angle α1: 9 °
Middle lateral groove angle α2: 12 °
Shoulder width groove width W4: 3-5mm
Shoulder lateral groove angle α3: 10 °
Groove depth of each lateral groove: 6.5 to 10.0 mm
<Block>
Center axis direction angle α4: 8 to 11 °
Maximum width Wa of center block / Maximum width Wb of middle block: 1.09
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 in a 10-point method with Comparative Example 1 as 6 points. The larger the value, the better.
Rim 15 × 6.0J
Internal pressure: 350 kPa (front wheel)
Internal pressure: 425 kPa (rear wheel)
Load: 4.9kN

<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 Comparative Example 2 being 100. The larger the value, the better.

<Noise performance>
The test vehicle was run on an asphalt road test course at a speed of 80 km / h, and the noise heard in the passenger compartment was evaluated by the driver's sensuality. The results are displayed in a 10-point method with Comparative Example 1 as 6 points. The larger the value, the better.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the noise, snowy road performance, and icy road performance of the tire of the example were significantly improved as compared with the comparative example.

3A Center main groove 3B Shoulder main groove 4A Center horizontal groove 4B Middle horizontal groove 5 Center block 6 Middle block 14 Siping K1 First intersection K2 Second intersection

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, 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, By providing a plurality of center lateral grooves extending between the center main grooves, and a plurality of middle lateral grooves extending between the center main grooves and the shoulder main grooves,
A center block segmented by the pair of center main grooves and the center lateral grooves is separated by a center block row that is spaced in the tire circumferential direction, and by the shoulder main grooves, the center main grooves, and the middle lateral grooves. A pneumatic tire having a pair of middle block rows in which the middle blocks are spaced apart in the tire circumferential direction,
Each of the center block and the middle block is provided with a plurality of sipings,
The center lateral groove is inclined to one side in the tire axial direction at an angle of 5 to 20 ° with respect to the tire axial direction, and the average groove width is 7 to the maximum length in the tire circumferential direction of the center block. 15%,
The middle lateral groove is inclined to the side opposite to the center lateral groove at an angle of 5 to 25 ° with respect to the tire axial direction, and the average groove width is 7 which is the maximum length of the middle block in the tire circumferential direction. ~ 11%,
The center block is formed with a center convex portion, a part of which projects toward the center main groove, and the outer end of the center convex portion that is the outermost side in the tire axial direction is the inner side in the tire axial direction of the middle block. It is formed on the outer side in the tire axial direction than the inner end in the tire axial direction of the circumferential edge,
In the ground contact surface in the normal load state where the rim is assembled to the normal rim and filled with the normal internal pressure, and the normal load is applied and the camber angle is 0 degrees and grounded to the plane,
A tire circumference between a first intersection where the center lateral groove and the center main groove intersect with a second intersection where the middle lateral groove and the center main groove intersect with each other adjacent to the first intersection across the center convex portion The distance in the direction is 0.75 to 1.00 times the difference between the length of the ground contact surface at the tire equator position and the length of the ground contact surface in the tire circumferential direction at the middle position of the middle block in the tire axial direction. A pneumatic tire characterized by being. 2. The pneumatic tire according to claim 1 , wherein the center lateral groove has a groove width gradually increasing from a central portion in a tire axial direction toward both end portions . In the ground contact surface in the normal load loading state,
The difference between the length of the ground contact surface at the tire equator position and the length of the ground contact surface in the tire circumferential direction at the middle position in the tire axial direction of the middle block is the length of the ground contact surface at the tire equator position. The pneumatic tire according to claim 1, wherein the pneumatic tire is 0.015 to 0.045 times as large as . The pneumatic tire according to claim 1, wherein a length in a tire axial direction between the outer end of the center convex portion and the inner end of the middle block is 0.5 to 3.0 mm .

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