JP2019182073A - Pneumatic tire - Google Patents

Abstract

To improve a brake performance by averaging the ground pressures of a shoulder side land part and an intermediate land part.SOLUTION: In a tread part 2 of a pneumatic tire, a shoulder land part of an outermost side in a tire width direction, an intermediate land part 4B adjacent to the inside of the shoulder land part in the tire width direction while interposing a circumferential main groove therebetween, and a center land part provided inside the intermediate land part 4B in the tire width direction, and adjacent on a tire equatorial plane or adjacent while interposing the circumferential main groove disposed on the tire equatorial plane therebetween, are formed by at least the four circumferential main grooves extending along a tire circumferential direction. Further, an intermediate block 6B divided in the tire circumferential direction in at least the intermediate land part 4B is formed by lateral grooves 5 crossing with the circumferential main groove. In the intermediate block 6B of the intermediate land part 4B, the outer contour line of a ground plane in a view from the tire width direction is formed expanded in an arc shape while having a maximum protrusion point G in the middle in the tire circumferential direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire.

  Conventionally, for example, the pneumatic tire described in Patent Document 1 is intended to exhibit heel and toe resistance. This pneumatic tire has a block-perpendicular cross-sectional profile with an arc shape with a smaller curvature than the tire radius, and a point that protrudes most outward in the radial direction is provided at the end of the kick-out side. A rib extending in the circumferential direction is provided at the end. For this reason, the stepped-end side, which is a portion having a low height and a low contact pressure, slides much with respect to the road surface, the wear progressing speed increases, and the progress of heel and toe wear after the initial wear is delayed. At the stepped-in end of the block, the tire equatorial plane side bears more contact pressure, but the shoulder-side contact pressure is further reduced, further promoting the wear progress from the stepped-in end and improving the heel and toe wear suppression effect to the initial block shape It becomes possible to put it out reliably.

Japanese Patent Laid-Open No. 7-186630

  By the way, in the pattern in which the tread portion is composed of four or more circumferential main grooves and lug grooves intersecting the circumferential main grooves, the land portion forms a block, the contact pressure of the shoulder side land portion is high, and the tire width There is a tendency that the ground contact pressure of the intermediate land portion on the inner side in the direction is lowered and the braking performance is lowered. In particular, with a studless tire, the braking performance on an icy road surface decreases.

  The present invention has been made in view of the above, and an object of the present invention is to provide a pneumatic tire that can improve the braking performance by averaging the contact pressure of the shoulder side land portion and the intermediate land portion. .

  In order to solve the above-described problems and achieve the object, a pneumatic tire according to one aspect of the present invention includes a tire width direction by at least four circumferential main grooves extending along the tire circumferential direction in the tread portion. An outermost shoulder land portion, an intermediate land portion adjacent to the inner side in the tire width direction of the shoulder land portion with the circumferential main groove interposed therebetween, and a tire equator provided on the inner side in the tire width direction of the intermediate land portion A center land portion adjacent to the circumferential main groove disposed on the surface or on the tire equatorial plane, and a tire formed at least in the intermediate land portion by a lateral groove intersecting the circumferential main groove. A pneumatic tire in which a block divided in the circumferential direction is formed, and in the block of the intermediate land portion, the outer contour line of the contact surface viewed from the tire width direction is maximum in the middle of the tire circumferential direction. It is formed by bulges in a circular arc shape having a outlet point.

  In the pneumatic tire according to an aspect of the present invention, in the block of the intermediate land portion, the distance r from the rotation axis of the maximum protrusion point and the distance R from the rotation axis of the reference contour line forming the tread profile. Preferably satisfies the relationship of 1.000 <r / R ≦ 1.005.

  Further, in the pneumatic tire according to one aspect of the present invention, a block is formed in the shoulder land portion, and in the shoulder land portion block, the radially outermost contour line of the contact surface viewed from the tire width direction. It is preferable that the distance rs from the rotation axis of the outer point and the distance r satisfy the relationship of 1.001 ≦ r / rs ≦ 1.003.

  Further, in the pneumatic tire according to one aspect of the present invention, a block is formed in the center land portion, and in the block of the center land portion, the radial direction outermost contour line of the ground contact surface viewed from the tire width direction. It is preferable that the distance rc from the rotation axis of the outer point and the distance r satisfy the relationship of 0.999 ≦ r / rc ≦ 1.02.

  Further, in the pneumatic tire according to one aspect of the present invention, the rotation direction is specified, and the tire from the stepping side end to the maximum protruding point with respect to the tire circumferential direction length L in the block of the intermediate land portion The circumferential position “a” is preferably in the range of 0.3 ≦ a / L <0.5.

  Further, in the pneumatic tire according to one aspect of the present invention, in the block of the intermediate land portion, fine unevenness is formed on the ground contact surface, and the tire circumference extends from the maximum protruding point with respect to the tire circumferential direction length L. When the range b in the direction is 0.1 ≦ b / L ≦ 0.4 and the range c is other than the range b, the density of the fine irregularities may be 1.0 <b / c ≦ 1.2. preferable.

  According to the present invention, in the block of the intermediate land portion, the outer contour line of the ground contact surface viewed from the tire width direction is formed to bulge in an arc shape with the maximum protruding point in the middle of the tire circumferential direction. As a result, the contact pressure of the intermediate land portion is improved. For this reason, the contact pressure of the shoulder land portion and the intermediate land portion can be averaged. As a result, the braking performance can be improved. In particular, in a studless tire, the braking performance on the road surface on ice can be improved.

FIG. 1 is a plan view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is a sectional view in the tire width direction of an intermediate land portion in the pneumatic tire according to the embodiment of the present invention. FIG. 3 is a cross-sectional view in the tire width direction of the shoulder land portion or the center land portion in the pneumatic tire according to the embodiment of the present invention. FIG. 4 is an enlarged plan view of an intermediate land portion in the pneumatic tire according to the embodiment of the present invention. FIG. 5 is an enlarged plan view of an intermediate land portion in the pneumatic tire according to the embodiment of the present invention. FIG. 6 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. Further, a plurality of modifications described in this embodiment can be arbitrarily combined within the scope obvious to those skilled in the art.

  FIG. 1 is a plan view of the pneumatic tire according to the present embodiment. FIG. 2 is a sectional view in the tire width direction of an intermediate land portion in the pneumatic tire according to the present embodiment. FIG. 3 is a sectional view in the tire width direction of the shoulder land portion or the center land portion in the pneumatic tire according to the present embodiment. FIG. 4 is an enlarged plan view of an intermediate land portion in the pneumatic tire according to the present embodiment. FIG. 5 is an enlarged plan view of an intermediate land portion in the pneumatic tire according to the present embodiment.

  In the following description, the tire circumferential direction refers to a circumferential direction having a rotation axis (not shown) of the pneumatic tire 1 as a central axis. Further, the tire width direction means a direction parallel to the rotation axis, the inner side in the tire width direction means the side toward the tire equator plane (tire equator line) CL in the tire width direction, and the outer side in the tire width direction means the tire width direction. Is the side away from the tire equatorial plane CL. The tire radial direction refers to a direction orthogonal to the rotation axis, the inner side in the tire radial direction refers to the side toward the rotation axis in the tire radial direction, and the outer side in the tire radial direction refers to the side away from the rotation axis in the tire radial direction. The tire equatorial plane CL is a plane that is orthogonal to the rotation axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1. The tire equator line is a line along the tire circumferential direction of the pneumatic tire 1 on the tire equator plane CL. In the present embodiment, the same sign “CL” as that of the tire equator plane is attached to the tire equator line.

  The pneumatic tire 1 of the present embodiment has a tread portion 2 as shown in FIG. The tread portion 2 is made of a rubber material, and is exposed at the outermost side in the tire radial direction of the pneumatic tire 1, and its surface serves as an outer contour of the pneumatic tire 1 as a ground contact surface 2 </ b> A.

  In the tread portion 2, a plurality of (four in the present embodiment) circumferential main grooves 3 extending along the tire circumferential direction are provided side by side in the tire width direction on the ground contact surface 2 </ b> A. In the present embodiment, the two circumferential main grooves 3 at the center in the tire width direction across the tire equatorial plane CL are defined as the center main grooves 3A. The circumferential main grooves 3 on both outer sides in the tire width direction of the center main grooves 3A are referred to as shoulder main grooves 3B. The circumferential main groove 3 has a groove width of 4 mm or more and 15 mm or less and a groove depth of 5 mm or more and 15 mm or less (the tire radial dimension from the opening position of the ground contact surface 2A to the groove bottom). Is a groove in which is disposed. A groove extending along the tire circumferential direction that is narrower than the groove width of the circumferential main groove 3 or shallower than the groove depth of the circumferential main groove 3 is not the circumferential main groove 3.

  In the tread portion 2, a plurality of land portions 4 (5 in this embodiment) are formed in the tire width direction along the tire circumferential direction by the circumferential main grooves 3 on the ground contact surface 2 </ b> A. In the present embodiment, the land portion 4 disposed on the tire equatorial plane CL between the center main grooves 3A is defined as the center land portion 4A. The land portion 4 disposed between the center main groove 3A and the shoulder main groove 3B on the outer side in the tire width direction is defined as an intermediate land portion 4B. Further, the land portion 4 on the outer side in the tire width direction of each shoulder main groove 3B is defined as a shoulder land portion 4C.

  Although not clearly shown in the drawing, the circumferential main groove 3 may be disposed on the tire equatorial plane CL depending on the number of circumferential main grooves 3 (for example, five). In this case, one circumferential main groove 3 on the tire equatorial plane CL is defined as a center main groove 3A. A circumferential main groove 3 is also present on the outer side in the tire width direction of the center main groove 3A and on the inner side in the tire width direction of the shoulder main groove 3B. The circumferential main groove 3 is used as an intermediate main groove. In this case, the two land portions 4 defined by one center main groove 3A and the intermediate main groove on the tire equatorial plane CL are defined as the center land portion 4A, and are divided by the intermediate main groove and the shoulder main groove 3B. The land portions 4 to be used are defined as intermediate land portions 4B, and the land portions 4 on the outer sides in the tire width direction of the respective shoulder main grooves 3B are defined as shoulder land portions 4C.

  Although not shown in the figure, the circumferential direction is also on the outer side in the tire width direction of the center main groove 3A and on the inner side in the tire width direction of the shoulder main groove 3B depending on the number (for example, 6) of the circumferential main grooves 3. A main groove 3 is present, and this circumferential main groove 3 is an intermediate main groove. In this case, the intermediate land portion 4B is also partitioned between the center main groove 3A and the intermediate main groove. In the present embodiment, this intermediate land portion 4B is referred to as a center intermediate land portion. Thus, only the land portion adjacent to the inner side of the shoulder land portion 4C on the inner side in the tire width direction of the shoulder main groove 3B is referred to as the intermediate land portion 4B, and all the intermediate land portions on the inner side in the tire width direction are also centered. It is called Yoriku Chubu.

  Further, the tread portion 2 is provided with a plurality of lateral grooves 5 that intersect the circumferential main groove 3 side by side in the tire circumferential direction. At least the intermediate land portion 4B is formed with a plurality of blocks 6 divided by a plurality of lateral grooves 5 in the tire circumferential direction. The block 6 of the intermediate land portion 4B is referred to as an intermediate block 6B. In the present embodiment, also in the center land portion 4A, a plurality of blocks 6 (center block 6A) divided in the tire circumferential direction by a plurality of lateral grooves 5 are partitioned. Also in the shoulder land portion 4 </ b> C, a plurality of blocks 6 (shoulder blocks 6 </ b> C) divided in the tire circumferential direction by a plurality of lateral grooves 5 are defined. The lateral groove 5 has a groove width of 3 mm or more and 10 mm or less and a groove depth of 1.5 mm or more and 15 mm or less (a tire radial direction dimension from the opening position of the ground contact surface 2A to the groove bottom). In the pneumatic tire 1 of the present embodiment, the intermediate land portion 4B needs to be formed with the block 6, but the other land portions 4 may not have the block 6 formed therein.

  In the pneumatic tire 1 having the above-described configuration, as shown in FIG. 2, the intermediate block 6B of the intermediate land portion 4B is configured such that the tire 1 The outer contour line of the ground contact surface 2A viewed from the direction has a maximum protruding point G in the middle of the tire circumferential direction and is formed to bulge out in an arc shape.

  Specifically, as shown in FIG. 2, in the intermediate block 6 </ b> B of the intermediate land portion 4 </ b> B, the outer contour line of the contact surface 2 </ b> A has a maximum protruding point G in the middle of the tire circumferential direction with respect to the tread profile PR. Arcs outward from the tire circumferential ends P1 and P2 in the tire radial direction (when the radii of the arcs on both sides in the tire circumferential direction of the maximum projecting point G are the same and the radii of the arcs on both sides in the tire circumferential direction of the maximum projecting point G) Are formed to bulge in). Ends P1, P2 in the tire circumferential direction of the intermediate block 6B are intersections between the ground contact surface 2A and the groove wall 5a of the lateral groove 5. When a process such as chamfering is performed at the intersection, the intersection point between the extension line of the ground contact surface 2A and the extension line of the groove wall 5a of the lateral groove 5 is the end P1 of the intermediate block 6B in the tire circumferential direction. , P2.

  Here, the tread profile PR is a reference contour line in which the pneumatic tire 1 is assembled to a normal rim and the inner pressure is not filled and no load is applied. In the tire width direction sectional view shown in FIG. In addition to the two tire circumferential ends P1 and P2 of the intermediate block 6B that define the tire block, in the tire circumferential direction of two other intermediate blocks 6B adjacent to both sides of the tire circumferential direction with the lateral groove 5 sandwiched between the intermediate block 6B. An arc passing through the two points P1 and P2 in the tire circumferential direction of the intermediate block 6B defining the outer contour line and the other one of the four points of the end P1 and the end P2, and the center of the arc Is an arc that can be drawn with a maximum radius of curvature located on the inner side in the tire radial direction from the ground contact surface 2A.

  The regular rim is “standard rim” defined by JATMA, “Design Rim” defined by TRA, or “Measuring Rim” defined by ETRTO. In addition, the internal pressure is a normal internal pressure, and is the “maximum air pressure” specified by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” specified by TRA, or “INFLATION PRESSURES” specified by ETRTO. . In addition, the load is a regular load, and is the “maximum load capacity” specified by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” specified by TRA, or “LOAD CAPACITY” specified by ETRTO. is there.

  Thus, according to the pneumatic tire 1 of the present embodiment, in the intermediate block 6B of the intermediate land portion 4B, the outer contour line of the ground contact surface 2A viewed from the tire width direction is the maximum protruding point in the middle of the tire circumferential direction. The ground pressure of the intermediate land portion 4B is improved by having G and bulging in an arc shape. For this reason, the ground contact pressure of the shoulder land portion 4C and the intermediate land portion 4B can be averaged. As a result, the braking performance can be improved. In particular, in a studless tire, the braking performance on the road surface on ice can be improved.

  Moreover, in the pneumatic tire 1 of this embodiment, as shown in FIG. 2, in the intermediate block 6B of the intermediate land portion 4B, the distance r from the rotation axis of the maximum protrusion point G and the reference contour line forming the tread profile PR. The distance (radius) R from the rotation axis preferably satisfies the relationship of 1.000 <r / R ≦ 1.005. Specifically, it is preferable to satisfy the relationship of 1.001 ≦ r / R ≦ 1.005.

  According to this pneumatic tire 1, since 1.000 <r / R (1.001 ≦ r / R), the contact pressure of the intermediate land portion 4B is improved, and the shoulder land portion 4C and the intermediate land portion 4B are improved. The ground contact pressure can be averaged. On the other hand, by setting r / R ≦ 1.005, a radial force variation (RFV: Radial) which is a radial direction (tire radial direction) force among fluctuations of the force generated on the contact surface in the rolling pneumatic tire 1. It is possible to prevent the situation where Force Variation is worsened. That is, when r / R exceeds 1.005, radial force variation tends to deteriorate. Note that the distance r and the distance (radius) R satisfy the relationship of 1.001 ≦ r / R ≦ 1.003 in order to average the ground contact pressure of the shoulder land portion 4C and the intermediate land portion 4B, and thus radial It is more preferable in preventing the deterioration of the force variation.

  In the pneumatic tire 1 of the present embodiment, as shown in FIG. 3, in the shoulder block 6 </ b> C of the shoulder land portion 4 </ b> C, the radially outermost point (maximum) of the outer contour line of the ground contact surface 2 </ b> A viewed from the tire width direction. Projection point) The distance rs from the rotation axis of Gs and the distance r from the rotation axis of the maximum projection point G in the intermediate block 6B of the intermediate land portion 4B shown in FIG. 2 are 1.001 ≦ r / rs ≦ 1. It is preferable to satisfy the relationship of 003.

  That is, the distance r from the rotation axis of the maximum protrusion point G in the intermediate block 6B of the intermediate land portion 4B is the distance from the rotation axis of the radially outermost point (maximum protrusion point) Gs in the shoulder block 6C of the shoulder land portion 4C. It is preferable that it is larger than rs (rs <r).

  According to this pneumatic tire 1, the contact pressure of the intermediate land portion 4B can be improved, and the contact pressure of the shoulder land portion 4C and the intermediate land portion 4B can be further averaged.

  As shown in FIG. 3, in the shoulder block 6 </ b> C of the shoulder land portion 4 </ b> C, the outer contour line of the ground contact surface 2 </ b> A viewed from the tire width direction is the radially outermost point (maximum protruding point) in the middle of the tire circumferential direction. It has Gs and bulges in an arc shape. A distance rs from the rotation axis of the radially outermost point (maximum protrusion point) Gs and a distance (radius) Rs from the rotation axis of the reference contour line forming the tread profile PR are 1.000 ≦ rs / Rs. ≦ 1.005 (preferably 1.001 ≦ rs / Rs ≦ 1.003) satisfies the ground contact pressure of the shoulder land portion 4C and the intermediate land portion 4B, thereby deteriorating the radial force variation. It is more preferable in preventing.

  Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 3, in the center block 6A of the center land portion 4A, the radially outermost point (maximum in the outer contour line of the ground contact surface 2A viewed from the tire width direction) Protrusion point) The distance rc from the rotation axis of Gc and the distance r from the rotation axis of the maximum protrusion point G in the intermediate block 6B of the intermediate land portion 4B shown in FIG. 2 are 0.999 ≦ r / rc ≦ 1. It is preferable to satisfy the relationship of 02.

  That is, the distance r from the rotation axis of the maximum protrusion point G in the intermediate block 6B of the intermediate land portion 4B is the distance from the rotation axis of the radially outermost point (maximum protrusion point) Gc in the center block 6A of the center land portion 4A. It is preferably larger than rc (rc <r).

  According to this pneumatic tire 1, the contact pressure of the intermediate land portion 4B can be improved, and the contact pressures of the center land portion 4A and the intermediate land portion 4B can be averaged. As a result, the braking performance can be improved. In particular, in the studless tire, the braking performance on the road surface on ice can be improved.

  As shown in FIG. 3, in the center block 6A of the center land portion 4A, the outer contour line of the ground contact surface 2A viewed from the tire width direction is the radially outermost point (maximum protruding point) in the middle of the tire circumferential direction. It has Gc and bulges in an arc shape. The distance rc from the rotation axis of the radially outermost point (maximum protrusion point) Gc and the distance (radius) Rc from the rotation axis of the reference contour line forming the tread profile PR are 1.000 ≦ rc / Rc. ≦ 1.005 (preferably 1.001 ≦ rc / Rc ≦ 1.003) satisfies the ground contact pressure of the center land portion 4A and the intermediate land portion 4B, and the deterioration of radial force variation It is more preferable in preventing.

  The radial outermost point (maximum protrusion point) Gc of the center land portion 4A from the rotation axis of the center block 6A and the radial outermost point (maximum protrusion point) of the shoulder block 6C of the shoulder land portion 4C. The distance rs from the rotation axis of Gs is preferably in the relationship of rs <rc (rs <rc <r) in order to average the contact pressure over the entire contact surface of the pneumatic tire 1.

  Although not clearly shown in the figure, when the center landing middle land portion has a center landing middle land portion, the distance r ′ from the rotation axis of the maximum protrusion point G is the maximum protrusion point in the intermediate block 6B of the intermediate land portion 4B. The distance r from the rotation axis of G may be equal to the distance r from the rotation axis of the radial outermost point (maximum protrusion point) Gc in the center block 6A of the center land portion 4A. In this case, in order to average the contact pressure, a relationship of rc <r ′ <r is preferable. Further, in the center-side middle land portion, the distance r ′ from the rotation axis of the maximum protrusion point G and the distance (radius) R ′ from the rotation axis of the reference contour line forming the tread profile PR are 1.000 <r The relationship of '/R'≦1.005 (specifically, 1.001 ≦ r ′ / R ′ ≦ 1.005, preferably 1.001 ≦ r ′ / R ′ ≦ 1.003) may be satisfied. . Further, in the center-side middle land portion, the distance r ′ from the rotation axis of the maximum protrusion point G and the distance (radius) R ′ from the rotation axis of the reference contour line forming the tread profile PR are 1.000 ≦ r The relationship of “/R”≦1.005 (preferably 1.000 ≦ r ′ / R ′ ≦ 1.001) may be satisfied.

  Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 2, the rotation direction is specified, and the stepping side end P1 with respect to the tire circumferential direction length L in the intermediate block 6B of the intermediate land portion 4B. The position a in the tire circumferential direction from the maximum protrusion point G to the maximum protrusion point G is preferably in the range of 0.3 ≦ a / L <0.5. Specifically, it is preferable to satisfy the relationship of 0.3 ≦ a / L ≦ 0.49.

  Here, the tire circumferential direction length L of the intermediate block 6B is the length at the position where the distance between the ends P1, P2 is the longest when viewed from the tire width direction.

  According to this pneumatic tire 1, the maximum protrusion point G in the tire circumferential length L is 0.3 ≦ a / L <0.5 (0.3 ≦ a / L ≦ 0.49). Because it is located closer to the stepping side, there is a maximum protrusion point G in the portion that contacts the road surface faster in the intermediate block 6B, and it is possible to improve braking performance and traction performance. Especially in studless tires, on the ice road surface The braking performance and traction performance can be improved. In order to further improve the braking performance and traction performance on the road surface on ice, it is preferable to satisfy the relationship of 0.4 ≦ a / L <0.5 (0.4 ≦ a / L ≦ 0.49). When the rotation direction is specified, the bulging arc of the intermediate block 6B (including other blocks) has a tire tread surface (the side that comes into contact with the ground first) in order to ensure braking performance and traction performance. The arc must start from the block end (P1 in FIG. 2) and pass through the maximum protruding point G, but the tire kicking surface end does not need to start from the block end (P2 in FIG. 2). In addition, when the rotation direction is not designated, the bulging arc of the intermediate block 6B (including other blocks) is used to secure the braking performance and the traction performance in order to secure the braking performance and the traction performance. It is desirable to start from P2) and pass through the maximum protruding point G.

  In the pneumatic tire 1 of the present embodiment, as shown in FIG. 4, in the intermediate block 6 </ b> B of the intermediate land portion 4 </ b> B, the sipe 7 is formed on the ground contact surface 2 </ b> A. When the range b in the tire circumferential direction from the maximum protrusion point G is 0.1 ≦ b / L ≦ 0.4 and the range c other than the range b is the range c, the density of the sipe 7 is 1.0 <b / c ≦ 1. .2 (1.05 ≦ b / c ≦ 1.2) is preferable.

  The sipe 7 is a cut formed in the ground contact surface 2A and is also referred to as fine unevenness. The sipe 7 has a groove width of less than 1.0 mm and a groove depth of 2.0 mm or more. The upper limit of the groove depth of the sipe 7 is not particularly limited, but is generally shallower than the groove depth of the circumferential main groove 3. The density of the sipe 7 is the sum of the groove lengths of the sipe 7, and the higher the sum of the groove lengths, the higher the density.

  Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 5, in the intermediate block 6 </ b> B of the intermediate land portion 4 </ b> B, the uneven portion 8 is formed on the ground contact surface 2 </ b> A, and the tire circumferential direction length L is When the range b in the tire circumferential direction from the maximum protrusion point G is 0.1 ≦ b / L ≦ 0.4 and the range c other than the range b is the range c, the density of the concavo-convex portions 8 is 1.0 <b / c. ≦ 1.2 (1.05 ≦ b / c ≦ 1.2) is preferable. Here, the range b is a range on both sides in the tire circumferential direction from the maximum protrusion point G.

  The uneven portion 8 is a fine surface processed portion formed on the ground contact surface 2A of the intermediate block 6B, and is also referred to as fine uneven portion. The concavo-convex portion 8 includes fine concave portions such as thin shallow grooves and fine dimples, and fine convex portions such as fine fine ribs and fine protrusions. On the other hand, the concavo-convex portion 8 does not include, for example, a deep narrow groove, a sipe that closes when the tire contacts the ground, a deep dimple, and a notch. Conceptually, dimples having a long structure correspond to grooves, and protrusions having a long structure correspond to ribs. The concavo-convex portion 8 has a concavo-convex amount (dimension in the tire radial direction) in a range of 0.1 mm to 1.0 mm and a width (a short plane dimension) in a range of 0.1 mm to 0.8 mm. . The density of the concavo-convex portion 8 is the sum of the volumes of the concavo-convex portions 8 and indicates that the density having a large sum of the volumes is high.

  According to the pneumatic tire 1, the range b including the maximum protruding point G with respect to the tire circumferential direction length L in the sipe 7 and the fine irregularities that are the irregularities 8 formed in the intermediate block 6 </ b> B of the intermediate land portion 4 </ b> B. Is 0.1 ≦ b / L ≦ 0.4, and when the range c is other than the range b, the density of fine irregularities is 1.0 <b / c ≦ 1.2 (1.05 ≦ b / c ≦ 1). .2), the edge effect of fine irregularities can be efficiently obtained within a range where the contact pressure is improved. As a result, the braking performance can be improved. In particular, in the studless tire, the braking performance on the road surface on ice can be improved.

  In this example, performance tests on braking performance (on-ice braking performance) and RFV (radial force variation) performance were performed on a plurality of types of pneumatic tires having different conditions (see FIG. 6).

  In the performance test of braking performance (braking performance on ice), a pneumatic tire (test tire) with a tire size of 195 / 65R15 91Q is assembled to a regular rim of 15 × 6.0J and filled with internal pressure (front wheel 250 kPa / rear wheel 240 kPa). The vehicle was mounted on a front engine front wheel drive passenger car (test vehicle) having a displacement of 1800 cc.

  In the evaluation method of the braking performance, the test vehicle travels on the icy road surface of the icy test site, and the braking distance from the traveling speed of 40 km / h is measured. Then, based on this measurement result, index evaluation using the conventional example as a reference (100) is performed. This evaluation shows that the greater the value, the shorter the braking distance and the better the braking performance (on-ice braking performance).

  In the performance test of RFV performance, a pneumatic tire (test tire) with a tire size of 195 / 65R15 91Q is assembled to a regular rim of 15 × 6.0J, filled with internal pressure (200 kPa), a load (438 kg) is applied, and a force is applied. RFV (longitudinal stiffness balance) based on JASO C607 standard is measured by a variation testing machine.

  In the RFV performance evaluation method, index evaluation is performed based on the measurement result with the conventional example as a reference (100). This evaluation shows that the smaller the index, the smaller the vibration and the better the vibration characteristics.

  In FIG. 6, the pneumatic tires of the conventional example and Examples 1 to 12 have a center land portion on the tire equator plane and an intermediate land portion on the outer side in the tire width direction of the center land portion by four circumferential main grooves. A shoulder land portion is formed on the outer side in the tire width direction of the intermediate land portion, and a block is formed by a lateral groove in each land portion. In the conventional pneumatic tire, the contact surface of each block is formed along the tread profile and does not bulge in the tire circumferential direction. In the pneumatic tires of Examples 1 to 12, at least the ground contact surface of the intermediate block in the intermediate land portion bulges in the tire circumferential direction.

  As shown in the test results of FIG. 6, it can be seen that the pneumatic tires of Examples 1 to 12 have improved braking performance (on-ice braking performance). Further, as shown in the test results of FIG. 6, in the pneumatic tires of Examples 1 to 12, the outer contour line of the ground contact surface viewed from the tire width direction in the block has a maximum protruding point in the middle of the tire circumferential direction. If it is formed to bulge in an arc shape, vibration tends to increase and RFV performance tends to decrease, but the relationship between the maximum protrusion point distance r and the tread profile distance R (r / R) is specified. By defining the relationship between the intermediate block and the shoulder block (r / rs) and by defining the relationship between the intermediate block and the center block (r / rc), the increase in the RFV figure of merit can be suppressed to less than 115, It can be seen that RFV performance is maintained.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 2A Grounding surface 3 Circumferential main groove 3A Center main groove 3B Shoulder main groove 4 Land part 4A Center land part 4B Middle land part 4C Shoulder land part 5 Horizontal groove 5a Groove wall 6 Block 6A Center block 6B Middle Block 6C Shoulder block 7 Sipe (fine irregularities)
8 Concavities and convexities (fine irregularities)
a Position in the tire circumferential direction from the stepping side end to the maximum protruding point b Range from the maximum protruding point to the tire circumferential direction c Range other than range b CL Tire equatorial plane G Maximum protruding point Gc Radial outermost point (maximum protruding point)
Gs radially outermost point (maximum protruding point)
P1, P2 end PR tread profile r distance R distance rc distance rs distance

Claims (6)

In the tread portion, at least four circumferential main grooves extending along the tire circumferential direction, the outermost shoulder land portion in the tire width direction and the shoulder land portion in the tire width direction with the circumferential main groove interposed therebetween An intermediate land portion adjacent to the inside, and a center land portion adjacent to each other with the circumferential main groove provided on the tire equator plane or on the tire equator plane provided inside the intermediate land portion in the tire width direction. And a pneumatic tire in which a block divided in the tire circumferential direction is formed at least in the intermediate land portion by a lateral groove intersecting the circumferential main groove,
In the intermediate land block, a pneumatic tire in which an outer contour line of a ground contact surface viewed from the tire width direction has a maximum protruding point in the middle of the tire circumferential direction and is bulged in an arc shape.   In the intermediate land block, the distance r from the rotation axis of the maximum protrusion point and the distance R from the rotation axis of the reference contour forming the tread profile are 1.000 <r / R ≦ 1.005. The pneumatic tire according to claim 1, satisfying the relationship:   A block is formed in the shoulder land portion, and in the shoulder land portion block, the distance rs from the rotation axis of the radially outermost point of the outer contour line of the ground contact surface viewed from the tire width direction, and the distance The pneumatic tire according to claim 2, wherein r satisfies a relationship of 1.001 ≦ r / rs ≦ 1.003.   A block is formed in the center land portion, and in the block of the center land portion, the distance rc from the rotation axis of the radially outermost point of the outer contour line of the ground contact surface viewed from the tire width direction, and the distance The pneumatic tire according to claim 2 or 3, wherein r satisfies a relationship of 0.999 ≦ r / rc ≦ 1.02.   The rotation direction is specified, and in the block of the intermediate land portion, the position a in the tire circumferential direction from the stepping side end to the maximum protruding point with respect to the tire circumferential direction length L is 0.3 ≦ a / L The pneumatic tire according to any one of claims 1 to 4, which is in a range of <0.5.   In the block of the intermediate land portion, fine unevenness is formed on the contact surface, and a range b in the tire circumferential direction from the maximum protrusion point with respect to the tire circumferential length L is 0.1 ≦ b / L ≦ 0. The pneumatic tire according to any one of claims 1 to 5, wherein the density of the fine unevenness is 1.0 <b / c ≦ 1.2, when .4 is set and the range c is other than the range b. .

Images