JP5664825B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire having a tread pattern.

Along with the recent demand for lower fuel consumption of vehicles, pneumatic tires (hereinafter simply referred to as tires) are also required to have reduced rolling resistance. The rolling resistance of the tire can be effectively reduced by changing the physical properties of the tread rubber that generally contributes most to the rolling resistance of the tire.
For example, tread rubber includes silica as a reinforcing material in addition to carbon, and is compounded into tread rubber in a state where carbon and silica are bonded. Thereby, steering stability performance (grip force) can be ensured while reducing rolling resistance.

By the way, in passenger car tires, two circumferential main grooves extending in the tire circumferential direction are provided in each of the half tread regions divided on both sides in the tire width direction with the tire center line as a boundary, and the groove area ratio is A tire having a tread pattern in the range of 20 to 40% is generally used. This circumferential main groove is important for ensuring steering stability on wet road surfaces including drainage. An example of such a tread pattern is a tire described in Patent Document 1 below.
Moreover, in the tire for passenger cars, a tread pattern is formed using a two-part mold having an upper mold and a lower mold in the vulcanization process of the tire manufacturing process.

JP 2000-43511 A

Thus, when a tire having a tread pattern having a circumferential main groove in each of the half tread regions is manufactured using a tread rubber for reducing rolling resistance, tread chipping may occur due to tire vulcanization. .
Specifically, when a tire is vulcanized using a two-part mold to form a tread pattern, tread chipping occurs in which the vicinity of the end of the land portion sandwiched between the two circumferential grooves is damaged. Immediately after vulcanization, the mold used for vulcanization is pulled out of the tire, but the convex part of the mold corresponding to the circumferential groove of the tread pattern is forcibly separated from the circumferential main groove in the groove width direction. Next, the mold is moved relative to the tire. At this time, the convex portion of the mold is rubbed in the tire width direction while pressing the land portion of the tread pattern. On the other hand, since the tread rubber used for lowering rolling resistance has a small elongation at break, a large force in the tire width direction is applied to the land portion by rubbing the surface of the tread rubber with the convex portion of the mold. The vicinity of the end of the chip tends to be chipped.

  In order to eliminate such tread chipping, a split mold in which a mold for forming a tread pattern is divided into a plurality of sections in the tire circumferential direction is used. However, since a split mold having irregularities corresponding to the tread pattern is expensive to manufacture, it is difficult to manufacture a passenger car tire at a low cost.

  Therefore, an object of the present invention is to provide a pneumatic tire having a tread pattern that does not increase manufacturing cost, is less likely to cause tread chipping in the tire manufacturing process, and has excellent steering stability on a dry road surface.

One embodiment of the present invention is a pneumatic tire having a tread pattern in a tread portion. At least one of the half tread regions on both sides in the tire width direction with the tire center line of the tread portion of the pneumatic tire as a boundary,
Two circumferential main grooves extending in the tire circumferential direction;
A circumferential narrow groove that is provided between the two circumferential main grooves, has a narrower groove width and a smaller groove depth than the circumferential main groove, and extends in the tire circumferential direction;
A plurality of inclined grooves provided in the tire circumferential direction that are inclined with respect to the tire width direction connecting between the shoulder-side main groove located on the shoulder side of the circumferential main groove and the circumferential narrow groove;
A plurality of inclined grooves provided in the tire circumferential direction that are inclined with respect to the tire width direction connecting between the shoulder-side main groove located on the shoulder side of the circumferential main groove and the circumferential narrow groove;
A land portion continuously formed in the tire circumferential direction, formed between the center-side main groove located on the tire center line side of the circumferential main groove and the circumferential narrow groove;
Of the inclined grooves, the side walls on both sides of the circumferential narrow groove between the connection positions where the two adjacent adjacent inclined grooves adjacent to each other along the tire circumferential direction and the circumferential narrow groove are connected to each other. Each of the chamfered portions is provided with a chamfering angle with respect to a normal direction of the tread as the first side wall among the side walls proceeds from the first connection position toward the second connection position among the connection positions. A first chamfer that is gradually reduced and a tread method provided on a second side wall of the side wall that faces the first side wall and proceeds from the first connection position toward the second connection position. And a chamfered portion including a second chamfer in which the chamfer angle with respect to the line direction gradually increases.

It is preferable that the circumferential main groove, the circumferential narrow groove, the land portion, and the chamfered portion are provided in each of the half tread regions on both sides in the tire width direction with the tire center line of the tread portion as a boundary.
The center in the tire width direction of the circumferential narrow groove is provided on the tire center line side with respect to the center position in the tire width direction of the region between the shoulder side main groove and the center side main groove. Is preferred.
In that case, when the width along the tire width direction of the region between the shoulder side main groove and the center side main groove is A, the center of the circumferential narrow groove in the tire width direction is the center position. It is more preferable that it is offset in the range of 30% to 40% of the width A to the tire center line side.

The maximum width of the first chamfer and the second chamfer along the tire width direction is preferably 20 to 30% of the width of the land portion.
It is preferable that the depth of the first chamfering and the second chamfering is 15 to 25% of the groove depth of the center side main groove.

It is preferable that the elongation at break (JIS K6251) of the tread rubber of the tread portion at 100 ° C. is 300 to 400%.
It is preferable that tan δ at 60 ° C. of the tread rubber of the tread portion is 0.18 or less.

  Furthermore, in the region of the shoulder land portion provided on the outer side in the tire width direction of the shoulder side main groove, the shoulder side main groove extends from the pattern end of the tread pattern toward the shoulder side main groove and is not connected to the shoulder side main groove. A plurality of shoulder lug grooves provided in the tire circumferential direction, and sipes provided in the tire circumferential direction extending from the shoulder side main groove toward the pattern end and closing in the middle. preferable.

  The tread portion can be formed using, for example, a pair of molds that separately form tread patterns positioned on both sides in the tire width direction with the tire center line as a boundary.

  According to the pneumatic tire of the present invention, it is possible to provide a pneumatic tire having a tread pattern that does not incur manufacturing costs, does not cause tread chipping during the tire manufacturing process, and has excellent steering stability on a dry road surface.

It is sectional drawing of the profile of the tire of this embodiment. FIG. 2 is a plan development view of a tread pattern formed on a tread portion of the tire shown in FIG. 1. (A) is an enlarged plan view around the circumferential narrow groove of the tread pattern shown in FIG. 2, and (b) and (c) are cross-sectional views of the circumferential narrow groove. It is a plane development view showing a tread pattern of a conventional example. (A)-(c) is a plane expanded view which shows the tread pattern of a comparative example.

  Hereinafter, the pneumatic tire of the present invention will be described in detail. The pneumatic tire according to the embodiment described below can be applied to a tire for a small truck or a tire for a bus / truck in addition to a tire for a passenger car. For example, passenger car tires are defined in Chapter A of JATMA YEAR BOOK 2011 (Japan Automobile Tire Association Standard), and small truck tires are tires defined in Chapter B of JATMA YEAR BOOK 2011, bus and truck tires. Is a tire defined in Chapter C of JATMA YEAR BOOK 2011. The pneumatic tire of this embodiment described below is a passenger tire.

The tire width direction is a direction parallel to the rotation axis of the pneumatic tire. The outer side in the tire width direction is the side away from the tire center line CL in two directions in the tire width direction. The inner side in the tire width direction is the side closer to the tire center line CL in the two directions in the tire width direction. The tire circumferential direction is a direction in which the tire tread portion rotates with the rotation axis of the pneumatic tire as the center of rotation. The tire radial direction is a direction orthogonal to the rotation axis of the pneumatic tire. The outer side in the tire radial direction refers to the side away from the rotation axis. The inner side in the tire radial direction refers to the side approaching the rotation axis.
The tire contact width described below is the contact surface formed on the flat plate when the tire is mounted on a normal rim and loaded in the vertical direction on the flat plate under the conditions of normal internal pressure and 80% of the normal load. The maximum linear distance between the ground contact edges in the tire width direction. The ground terminal E is indicated by a dotted line in FIG. The groove area ratio refers to the ratio of the area of the groove opening portion that opens toward the outer side in the tire radial direction within the ground contact region to the area of the tread region for one turn of the tire located within the range of the ground contact width.
Here, the regular rim means “standard rim” defined in JATMA, “Design Rim” defined in TRA, or “Measuring Rim” defined in ETRTO. The normal internal pressure means “maximum air pressure” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The normal load means the “maximum load capacity” defined in JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined in TRA, or “LOAD CAPACITY” defined in ETRTO.

(Tire structure)
FIG. 1 shows a profile cross-sectional view of a tire 10 of the present embodiment. The tire 10 includes a carcass ply layer 12, a belt layer 14, and a bead core 16 as a skeleton material. Around these skeleton members, a tread rubber member 18, a side rubber member 20, a bead filler rubber member 22, a rim cushion rubber member 24, and an inner liner rubber member 26 are mainly provided.

  The carcass ply layer 12 is made of a carcass ply material in which organic fibers are covered with rubber, which is wound between a pair of annular bead cores 16 to form a toroidal shape. The carcass ply layer 12 is wound around the bead core 16. A belt layer 14 composed of two belt members 14a and 14b is provided outside the carcass ply layer 12 in the tire radial direction. Each of the belt members 14a and 14b is a member in which a rubber is coated on a steel cord disposed at a predetermined angle, for example, 20 to 30 degrees with respect to the tire circumferential direction, and the lower belt member 14b is an upper layer. The width in the tire width direction is wider than that of the belt material 14a. The inclination directions of the steel cords of the two-layer belt materials 14a and 14b are opposite to each other. For this reason, belt material 14a, 14b is a crossing layer, and controls expansion of carcass ply layer 12 by the filled air pressure.

A tread rubber member 18 is provided on the outer side in the tire radial direction of the belt material 14a. Side rubber members 20 are connected to both ends of the tread rubber member 18 to form side portions. A rim cushion rubber member 24 is provided at an end of the side rubber member 20 on the inner side in the tire radial direction, and comes into contact with a rim on which the tire 10 is mounted. It is sandwiched between the portion of the carcass ply layer 12 before being wound around the bead core 16 and the portion of the carcass ply layer 12 wound around the bead core 16 on the outer side in the tire radial direction of the bead core 16. A bead filler rubber member 22 is provided. An inner liner rubber member 26 is provided on the inner surface of the tire 10 facing the tire cavity region filled with air surrounded by the tire 10 and the rim.
In addition, a belt cover layer 15 that covers the belt layer 14 from the outer side in the tire radial direction of the belt layer 14 and reinforces the belt layer 14 that is coated with organic fibers with rubber is provided. In addition, the tire 10 may include a bead reinforcing material between the carcass ply layer 12 wound around the bead core 16 and the bead filler rubber member 22.

  Although the tire 10 has such a tire structure, the tire structure of the pneumatic tire of the present invention is not limited to the tire structure shown in FIG.

(Tread pattern)
A tread pattern 50 is formed on the tire tread portion of the tire 10. FIG. 2 is a pattern development view of an example in which a part on the tire circumference of the tread pattern 50 formed in the tire tread portion of the tire 10 shown in FIG. 1 is developed on a plane. In the tread pattern 50, the tread pattern having the same configuration is formed in the half tread regions on both sides of the tire center line, but the following tread pattern may be formed in any one of the half tread regions.

Two circumferential main grooves 52, 54, a circumferential narrow groove 56, and an inclined groove 58 are provided in each of the half tread regions on both sides in the tire width direction with the tire center line CL of the tread portion of the tire 10 as a boundary. And a shoulder lug groove 60 and a shoulder sipe 62.
A center land portion 53 extending in the tire circumferential direction is provided between the circumferential main grooves 52 located on both sides in the tire width direction across the tire center line CL. The center land portion 53 is not provided with any lug grooves or sipes. By providing the center land portion 53, the steering stability on the dry road surface, particularly the responsiveness at the start of steering is improved.

The circumferential main groove 52 is a center side main groove that extends in the tire circumferential direction and is provided on the tire center line CL side with respect to the circumferential main groove 54. The circumferential main groove 54 is a shoulder side main groove provided on the shoulder side with respect to the circumferential main groove 52 and extending in the tire circumferential direction. Center in the tire width direction of the circumferential direction main grooves 52, and the distance between the tire centerline CL and a ground terminal E of FIG. 2 was set to W _1, for example, 13% of the distance W ₁ from the tire center line CL ~ 16% away from the outside in the tire width direction. The center of the circumferential main groove 54 in the tire width direction is, for example, 55% to 65% of the distance W ₁ away from the tire center line CL on the outer side in the tire width direction.

  A plurality of shoulder lug grooves 60 are provided in the tire circumferential direction in the shoulder region on the outer side in the tire width direction of the circumferential main groove 54. The shoulder lug groove 60 extends from the pattern end PE toward the inner side in the tire width direction, and is closed on the way without being connected to the circumferential main groove 54. The shoulder lug groove 60 is slightly inclined with respect to the tire width direction and extends outward in the tire width direction. When the closed end close to the circumferential main groove 54 of the shoulder lug groove 60 is virtually extended and virtually connected to the circumferential main groove 54, a plurality of inclined connection positions 58 are provided in the tire circumferential direction. Is near the position in the tire circumferential direction connected to the circumferential main groove 54. A plurality of shoulder lug grooves 60 are provided in the tire circumferential direction. The shoulder lug groove 60 extends outward in the tire width direction to the vicinity of the pattern end PE, and bends and changes its direction in the vicinity of the pattern end PE into a “<” shape (dogleg shape).

  A plurality of shoulder sipes 62 are provided in the tire circumferential direction. The shoulder sipe 62 is provided between the shoulder lug grooves 60 adjacent to each other in the tire circumferential direction, and is connected to the circumferential main groove 54. The shoulder lug sipe 62 inclines in the tire width direction in parallel with the shoulder lug groove 60 and closes in the vicinity of the ground contact end E.

  The shoulder lug groove 60 has a groove width of, for example, 1.7 mm to 5.2 mm, and a groove depth of, for example, 4.0 mm to 7.0 mm. The width of the shoulder sipe 62 is, for example, 0.5 mm to 1.0 mm, and the depth is, for example, 3.3 mm to 5.5 mm.

A circumferential narrow groove 56 is provided between the circumferential main groove 52 and the circumferential main groove 54. The circumferential narrow groove 56 is a groove extending in the tire circumferential direction, and has a narrower groove width and a smaller groove depth than the circumferential main grooves 52 and 54. The groove width of the circumferential narrow groove 56 is, for example, 1.5 mm to 4.5 mm, and the groove depth is, for example, not less than 2.0 mm and less than 6.0 mm. On the other hand, the groove width of the circumferential main grooves 52 and 54 is, for example, 4.0 mm to 15 mm, and the groove depth is, for example, 6.0 mm to 9.0 mm. The circumferential narrow groove 56 can be distinguished from the circumferential main grooves 52 and 54 in terms of groove width and depth.
The circumferential narrow groove 56 is preferably provided on the circumferential main groove 52 side with respect to the center position in the tire width direction in the region between the circumferential main groove 52 and the circumferential main groove 56.

A land portion 57 that extends continuously in the tire circumferential direction is formed between the circumferential main groove 52 and the circumferential narrow groove 56. The land portion 57 is not provided with lug grooves and sipes.
An inclined groove 58 is provided between the circumferential narrow groove 56 and the circumferential main groove 54. For this reason, between the circumferential narrow groove 56 and the circumferential main groove 54, a plurality of circumferential circumferential grooves 56, the circumferential main grooves 54, and the inclined grooves 58 adjacent to the tire circumferential direction are provided in the tire circumferential direction. Blocks are formed. The inclined groove 58 extends from the circumferential narrow groove 56 while being inclined with respect to the tire width direction, and is connected to the circumferential main groove 54. The groove width of the inclined groove 58 is, for example, 1.7 mm to 5.0 mm, and the groove depth is, for example, 2.0 mm to 8.0 mm.
The provision of the inclined groove 58 between the circumferential narrow groove 56 and the circumferential main groove 54 suppresses tire noise generated when the tire rolls on the road surface in a passenger car tire, and ensures steering stability on a wet road surface. It is to do. In particular, by providing the inclined groove 58, it is possible to reduce the hitting sound of the tire hitting the road surface when the tire contacts the road surface. Therefore, by providing the inclined groove 58, tire noise when the vehicle is running with a tire mounted thereon is reduced.

FIG. 3A is an enlarged plan view around the circumferential narrow groove 56. 3B and 3C are cross-sectional views of the circumferential narrow groove 56. FIG. 3B is a cross-sectional view taken along the line AA ′ in FIG. 3A, and FIG. 3C is a cross-sectional view taken along the line BB ′ in FIG.
Of the inclined grooves 58, two connection positions where two adjacent adjacent inclined grooves adjacent to each other in the tire circumferential direction and the circumferential narrow groove 56 are connected are a first connection position 56c and a second connection position. 56d. At this time, chamfered portions are provided on the side walls on both sides of the circumferential narrow groove 56 between the first connection position 56c and the second connection position 56d. The chamfered portion includes chamfers 56a and 56b. Among the chamfers 56a and 56b, the chamfer 56a provided on one side wall (first side wall) is a tread as it proceeds from the first connection position 56c toward the second connection position 56d among the two connection positions. The chamfer angle θ with respect to the normal direction (see FIGS. 3B and 3C) is gradually reduced. On the other hand, the chamfer 56b is provided on the other side wall (the second side wall opposite to the first side wall), and the chamfer angle θ gradually increases as it proceeds from the first connection position 56c toward the second connection position 56d. It has become. The tread normal direction refers to the direction of the normal that is orthogonal to the surface of the tread portion (land portion).

In the present embodiment, the chamfer 56a gradually decreases from the first connection position 56c toward the second connection position 56d, and the chamfer angle θ gradually decreases from the first connection position 56c to the second connection position 56c. The chamfering angle θ gradually increases as it proceeds toward the position 56d. However, as the chamfer 56a advances from the first connection position 56c toward the second connection position 56d, the chamfer angle θ gradually increases, and the chamfer 56b increases from the first connection position 56c toward the second connection position 56d. Therefore, the chamfering angle θ may be gradually reduced. The maximum value of the chamfering angle θ is preferably in the range of 35 to 55 degrees, more preferably in the range of 40 to 50 degrees. The minimum value of the chamfer angle θ is preferably in the range of 2 to 6 degrees, and more preferably in the range of 3 to 5 degrees.
Thus, in the tread pattern 50 in which the inclined groove 58 is provided between the circumferential narrow groove 56 and the circumferential main groove 54, the inclined groove 58 does not extend toward the circumferential main groove 52, and the circumferential direction A land portion 57 extending in the tire circumferential direction is provided between the groove 52 and the circumferential narrow groove 56, and chamfers 56 a and 56 b are provided in the circumferential narrow groove 56. This realizes a tread pattern in which tread chipping does not occur in the tire manufacturing process and steering stability on a dry road surface is excellent. Hereinafter, this point will be described.

As described above, in the vulcanization step of the tire manufacturing process, a two-part mold is used as the vulcanization mold. The mold is tired so that the convex portion of the mold corresponding to the circumferential groove 52 of the mold used for vulcanization immediately after vulcanization is forcibly separated from the circumferential main groove 52 in the tire groove width direction. Move relative to. At this time, since the land portion 57 is continuously extended in the tire circumferential direction and the land portion 57 has high block rigidity, even if the convex portion of the mold moves while rubbing the surface of the land portion 57, Unlike conventional ones, chipping of tread is unlikely to occur.
The circumferential narrow groove 56 has a narrower groove width than the circumferential main grooves 52 and 54 and a shallower groove depth than the circumferential main grooves 52 and 54, but the circumferential narrow groove 56 and the circumferential main groove 54 Since a plurality of inclined grooves 58 are provided in the circumferential direction of the tire to form a plurality of blocks, the block rigidity is small. Therefore, immediately after vulcanization, when the convex portion of the mold corresponding to the circumferential main groove 52 is forcibly separated from the circumferential main groove 52 in the groove width direction, the convex portion of the mold corresponding to the circumferential narrow groove 56 is removed. The portion rubs the surface of the block (land portion) surrounded by the circumferential narrow groove 56, the circumferential main groove 54, and the inclined groove 58, and tread chipping is likely to occur. For this reason, chamfers 56a and 56b are provided on both sides of the circumferential narrow groove 56 so as not to cause tread chipping. Further, since the chamfering angles θ of the chamfers 56a and 56b change according to the position in the tire circumferential direction, the land portion that contacts the ground as compared with the chamfering in which the chamfering angle θ is constant regardless of the position in the tire circumferential direction. Increases the area. Also, the block rigidity is increased. For this reason, the steering stability on the dry road surface is improved.
Thus, the tread pattern 50 does not generate a tread chip during the tire manufacturing process and has excellent steering stability on a dry road surface.

  Further, immediately after vulcanization, when the convex portion of the mold corresponding to the circumferential main groove 54 is forcibly separated from the circumferential main groove 54 in the groove width direction, the convex portion of the mold corresponding to the circumferential main groove 54 However, it rubs the land surface of the shoulder region. However, since the shoulder lug groove 60 is closed in the middle without being connected to the circumferential main groove 54, a land portion extending continuously in the tire circumferential direction is formed at the end in the vicinity of the circumferential main groove 54 in the shoulder region. Therefore, the block rigidity in this part is high. For this reason, generation | occurrence | production of the tread chip | tip of the land part in a shoulder area | region is suppressed.

The center in the tire width direction of the circumferential narrow groove 56 is provided on the tire center line CL side with respect to the center position in the tire width direction between the circumferential main groove 54 and the circumferential main groove 52. This is preferable in that no tread chipping occurs.
When the center in the tire width direction of the circumferential narrow groove 56 is provided on the shoulder side (outer in the tire width direction) with respect to the center position in the tire width direction between the circumferential main groove 54 and the circumferential main groove 52, Since the block rigidity between the directional narrow groove 56 and the circumferential main groove 54 (the rigidity of the land portion between the circumferential directional groove 56 and the circumferential main groove 54) decreases, the circumferential narrow groove 56 is chamfered 56a. , 56b, tread chipping is likely to occur.
When the width along the tire width direction of the region between the circumferential main groove 52 and the circumferential main groove 54 is A (see FIG. 2), the center in the tire width direction of the circumferential narrow groove 56 is the circumferential main. Offset from the center position in the tire width direction in the region between the groove 54 and the circumferential main groove 52 to the circumferential main groove 52 side (in the tire width direction) within a range of 30% to 40% of the width A; It is preferable to suppress the occurrence of tread chipping and improve the handling stability on the dry road surface.

  The maximum width W of the chamfers 56a and 56b along the tire width direction (see FIGS. 3B and 3C) is the width of the land portion 57 (the width in the tire width direction on the tread surface of the land portion 57). ) Is preferably 20 to 30% from the viewpoint of improving steering stability on a dry road surface and suppressing tread chipping. When the maximum width of the chamfers 56a and 56b is less than 20% of the width of the land portion 57, the width of the chamfers 56a and 56b is reduced, and the area of the land portion in contact with the ground is increased. However, since the chamfer width becomes small, tread chipping is likely to occur. On the other hand, when the maximum width of the chamfers 56a and 56b exceeds 30% of the width of the land portion 57, tread chipping is difficult to occur, but the area of the land portion in contact with the ground is reduced and the block rigidity is also reduced. Steering stability on dry road surface is reduced.

  Further, the depth D of the chamfers 56a and 56b (see FIGS. 3A and 3B) is 15 to 25% of the groove depth of the circumferential main groove 52. It is preferable in terms of improving and suppressing tread chipping. When the depth D of the chamfers 56a and 56b is less than 15% of the groove depth of the circumferential main groove 52, the steering stability on the dry road surface is improved, but since the chamfer width is reduced, tread chipping is likely to occur. . On the other hand, when the depth D of the chamfers 56a and 56b exceeds 25% of the groove depth of the circumferential main groove 52, tread chipping is difficult to occur, but the block rigidity is lowered and the steering stability on the dry road surface is lowered. To do.

Moreover, it is preferable that the breaking elongation at 100 degrees C of the tread rubber of a tread part is 300 to 400% in the point which reduces rolling resistance. Such a tread rubber is a rubber in which tread chipping is likely to occur because the elongation at break is low. However, in the tread pattern 50, the land portion 57, the circumferential narrow groove 56, and the chamfers 56a and 56b are provided between the circumferential groove 52 and the circumferential groove 54 so that tread chipping is difficult to occur. Even if the tread rubber has an elongation at break of 300 to 400%, tread chipping hardly occurs. The breaking elongation (tensile breaking elongation) is measured by a method according to JIS K6251.
In order to reduce rolling resistance, tan δ at 60 ° C. of the tread rubber is preferably 0.18 or less. Therefore, in the tire of this embodiment, in order to produce a tire having low rolling resistance, tread chipping is not caused even when the tan δ of the tread rubber is 0.18 or less and the elongation at break is 300 to 400%. It is difficult to generate, and the steering stability on the dry road surface can be improved. Note that tan δ is measured by a method based on JIS K5394. For example, tan δ is obtained by using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. according to JIS K6394 for the dynamic viscoelasticity of a sheet-like rubber sample obtained by cutting a tread rubber into a predetermined size. It is measured under the measurement conditions of% ± 2% and vibration frequency 20 Hz. The lower limit of tan δ of the tread rubber is not particularly limited, but is 0.10, for example.

Such a tread pattern 50 can be formed using a pair of molds (upper mold and lower mold) that separately form tread patterns positioned on both sides of the tire center line. As described above, since the tread pattern 50 is formed so that the tread chipping does not occur immediately after the vulcanization, the tread chipping occurs in the tire even when the split mold composed of the upper mold and the lower mold is used. Hateful. A tire manufactured using a split mold composed of an upper mold and a lower mold is formed by extending a burr on the tire surface formed at the time of vulcanization by one round in the tire circumferential direction near the tire center line CL. Can be specified.
Moreover, the tire of this embodiment can be suitably applied with a tire size of 135 to 285 in nominal width. Even if a split mold consisting of an upper mold and a lower mold is produced within the range of the nominal width, tread chipping can be suppressed and steering stability on a dry road surface can be improved. The nominal width means a portion of “175” when the tire size is displayed on the side portion of each tire, for example, “175 / 65R14”.
The groove area ratio of the tread pattern 50 of the tire 10 in the present embodiment is preferably 25 to 40%, and more preferably 28 to 32%.

(Experimental example)
Hereinafter, in order to investigate the effect of the tire 10 of the present embodiment, the tire was evaluated by performing a handling stability test on tread chips and dry road surfaces when various tread patterns were produced.
The tire size of the manufactured tire is 175 / 65R14. A tread rubber having a breaking elongation at 100 ° C. of 360% and a tan δ at 60 ° C. of 0.18 was used for the production of a tire. The breaking elongation was obtained by a tensile breaking elongation test of a sheet-like rubber sample cut into a predetermined size of tread rubber. tan δ is a dynamic viscoelasticity of a sheet-like rubber sample obtained by cutting a tread rubber into a predetermined size in accordance with JIS K6394, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. The measurement was performed under the measurement conditions of 2% and a vibration frequency of 20 Hz.
For the tread chipping, the inspector will evaluate the appearance of the tire immediately after vulcanization, and depending on the number of tread chippings and the degree of chipping, it will be “large”, “slightly high”, “medium”, “low”, “nothing” It was evaluated in five stages. Among the evaluation results, “none”, “small”, and “medium” are acceptable product ranges.
On the other hand, for the driving stability test, four tires having the same tread pattern were produced and a running test was performed. The tire was assembled on a rim of 14 × 5 JJ and filled with air pressure of 230 kPa. These four tires were mounted on a passenger car having a displacement of 1.3 liters, and a sensory evaluation was performed by a driver while traveling on a dry road surface at a traveling speed of 60 to 120 (km / hour). The sensory evaluation was a relative evaluation based on a conventional example described later as a reference (100). The higher the evaluation value, the better the steering stability.

Table 1 below shows the specifications and evaluation results of the tires of the conventional example, the actual example 1, and the comparative examples 1 to 3.
The chamfering in Table 1 means the first chamfering and the second chamfering shown in FIGS. According to the evaluation results shown in Table 1, it can be seen that Example 1 has less tread chipping than the conventional example, and the steering stability on the dry road surface is improved. On the other hand, compared to Example 1 and Comparative Examples 1 to 3, in order to reduce tread chipping and improve steering stability on a dry road surface, chamfers 56a and 56b are provided in the circumferential narrow groove 56, and the tire circumference It is necessary that a land portion 57 extending continuously in the direction exists.

  Further, tires of Examples 2 to 7 were manufactured, and a preferable range of the center position of the circumferential narrow groove 56 in the tire width direction was examined. When the center in the tire width direction of the circumferential narrow groove 56 is offset with respect to the center position of the region between the circumferential main groove 52 and the circumferential main groove 54, the width A of the offset distance (see FIG. 2). In Table 2, the ratio (%) to ()) is expressed as a value of “position of circumferential narrow groove (%)”. The position (%) of the circumferential narrow groove in Example 1 is + 35%.

  In the “circumferential narrow groove position (%)” in Table 2 above, the center in the tire width direction of the circumferential narrow groove 56 is the tire width direction in the region between the circumferential main groove 52 and the circumferential main groove 54. The case where it is located on the tire center line CL side from the center position is positive, and the case where it is located on the shoulder side is negative.

  From Table 2, Examples 1, 3, and 4 are superior to Examples 2, 5, 6, and 7 in terms of handling stability on a dry road surface and lack of tread rubber. From this, it is understood that the circumferential narrow groove 56 is preferably provided on the tire center line CL side with respect to the center position in the tire width direction between the circumferential main groove 54 and the circumferential main groove 52. Further, the center in the tire width direction of the circumferential narrow groove 56 is 30% to 40% of the width A from the center position in the tire width direction between the circumferential main groove 54 and the circumferential main groove 52 to the circumferential main groove 52 side. It can be seen that the offset is preferably in the range of%.

  In Table 3 below, tires of Examples 8 to 11 having various widths of the chamfering W while the width of the land portion 57 was made were manufactured, and a preferable range of the chamfering width W was examined. The chamfering width W of the first embodiment is 25% of the width of the land portion 57.

  From Table 3, Examples 1, 8, and 9 are superior to Examples 10 and 11 in terms of handling stability on a dry road surface and lack of tread rubber. In Example 10, steering stability is improved, but tread chipping is slightly increased. On the other hand, in Example 11, there is little tread chipping, but the margin for improving steering stability is small. From this, it can be seen that the chamfering width W is preferably 20 to 30% of the width of the land portion 57.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, the pneumatic tire of this invention is not limited to the said embodiment, You may make various improvement and change in the range which does not deviate from the main point of this invention. .

DESCRIPTION OF SYMBOLS 10 Tire 12 Carcass ply layer 14 Belt layers 14a and 14b Belt material 15 Belt cover layer 16 Bead core 18 Tread rubber member 20 Side rubber member 22 Bead filler rubber member 24 Rim cushion rubber member 26 Inner liner rubber member 50 Tread pattern 52, 54 Circumferential direction Main grooves 53, 57 Land portion 56 Circumferential narrow grooves 56a, 56b Chamfer 56c First connection position 56d Second connection position 58 Inclined groove 60 Shoulder lug groove 62 Shoulder sipe

Claims (10)

A pneumatic tire having a tread pattern in a tread portion,
At least one of the half tread regions on both sides in the tire width direction with the tire center line of the tread portion of the tread pattern as a boundary,
Two circumferential main grooves extending in the tire circumferential direction;
A circumferential narrow groove that is provided between the two circumferential main grooves, has a narrower groove width and a smaller groove depth than the circumferential main groove, and extends in the tire circumferential direction;
A plurality of inclined grooves provided in the tire circumferential direction that are inclined with respect to the tire width direction connecting between the shoulder-side main groove located on the shoulder side of the circumferential main groove and the circumferential narrow groove;
A land portion continuously formed in the tire circumferential direction, formed between the center-side main groove located on the tire center line side of the circumferential main groove and the circumferential narrow groove;
Of the inclined grooves, the side walls on both sides of the circumferential narrow groove between the connection positions where the two adjacent adjacent inclined grooves adjacent to each other along the tire circumferential direction and the circumferential narrow groove are connected to each other. Each of the chamfered portions is provided with a chamfering angle with respect to a normal direction of the tread as the first side wall among the side walls proceeds from the first connection position toward the second connection position among the connection positions. A first chamfer that is gradually reduced and a tread method provided on the second side wall of the side wall that faces the first side wall and proceeds from the first connection position toward the second connection position. A chamfer including a second chamfer in which the chamfer angle with respect to the line direction gradually increases, and
A pneumatic tire characterized by having.   2. The circumferential main groove, the circumferential narrow groove, the land portion, and the chamfered portion are provided in each of the half tread regions on both sides in the tire width direction with the tire center line of the tread portion as a boundary. Pneumatic tire described in 2.   The center in the tire width direction of the circumferential narrow groove is provided on the tire center line side with respect to a center position in the tire width direction of a region between the shoulder side main groove and the center side main groove. The pneumatic tire according to 1 or 2.   When the width along the tire width direction of the region between the shoulder side main groove and the center side main groove is A, the center in the tire width direction of the circumferential narrow groove is the tire from the center position. The pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire is offset to the center line side within a range of 30% to 40% of the width A.   The maximum width of the width along the tire width direction of the first chamfer and the second chamfer is 20 to 30% of the width of the land portion, according to any one of claims 1 to 4. Pneumatic tire.   The pneumatic tire according to any one of claims 1 to 5, wherein a depth of the first chamfering and the second chamfering is 15 to 25% of a groove depth of the center side main groove. The pneumatic tire according to any one of claims 1 to 6, wherein the tread rubber of the tread portion has an elongation at break according to JIS K6251 at 100 ° C of 300 to 400%.   The pneumatic tire according to claim 6, wherein tan δ at 60 ° C of the tread rubber of the tread portion is 0.18 or less.   Furthermore, in the region of the shoulder land portion provided on the outer side in the tire width direction of the shoulder side main groove, the shoulder side main groove extends from the pattern end of the tread pattern toward the shoulder side main groove and is not connected to the shoulder side main groove. A plurality of shoulder lug grooves provided in the tire circumferential direction, and sipes provided in the tire circumferential direction extending from the shoulder side main groove toward the pattern end and closing in the middle. Item 10. The pneumatic tire according to any one of Items 1 to 8.   The pneumatic tire according to claim 2, wherein the tread portion is formed by using a pair of molds that separately form tread patterns positioned on both sides in the tire width direction with a tire center line as a boundary.

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