JP6848413B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire.

As a method of improving the wet performance of a pneumatic tire, it is generally performed to secure drainage by forming a lug groove extending in the tire width direction in addition to a main groove extending in the tire circumferential direction on the tread surface of the tire. There is. However, such a method has a problem that the rigidity of the land portion formed on the tread surface is lowered, so that the tread rubber is easily worn and the life of the tire is shortened.
Conventionally, in a tire having a main groove and a lug groove formed, a tread pattern in which one end of the lug groove is connected to the main groove and the other end is closed in the land region is known (see Patent Document 1). In a tire having such a main groove and a lug groove, drainage is ensured, and a decrease in rigidity of the land portion is suppressed as compared with a tire in which both ends of the lug groove are connected to the main groove, resulting in wet performance. It is considered that wear resistance can be achieved at a certain level.

Japanese Unexamined Patent Publication No. 2013-71633

In the tread pattern having the main groove and the lug groove of the above-described form, the lug groove connecting to the main groove exists on one side of both sides of the main groove, while the other side has the lug groove on the main groove. There is no connecting lug groove. For this reason, a difference in rigidity occurs between the land portions on both sides of the main groove, and uneven wear is likely to occur. In particular, uneven wear is likely to occur on both sides of the main groove near the tire center line.

An object of the present invention is to provide a pneumatic tire capable of suppressing the occurrence of uneven wear while achieving both wear resistance and wet performance.

One aspect of the present invention is a pneumatic tire having a tread pattern on the surface of the tread portion.
The tread pattern is
A pair of outer circumferential main grooves that are arranged at intervals in the tire width direction across the tire center line and extend in the tire circumferential direction.
A center circumferential main groove arranged between the pair of outer peripheral main grooves in the tire width direction and extending in the tire circumferential direction,
In the region of the first center land portion located between the center circumferential main groove and the first outer circumferential main groove of the outer circumferential main grooves, from the first outer circumferential main groove. A plurality of first lug grooves extending toward the side of the main groove in the center circumferential direction and closing in the area of the first center land portion and arranged at intervals in the tire circumferential direction.
A plurality of lug grooves extending from the closed end of the first lug groove toward the main groove in the center circumferential direction and closing in the area of the first center land portion, and arranged at intervals in the tire circumferential direction. Sipe and
In the region of the second center land portion located between the center circumferential main groove and the second outer circumferential main groove of the outer circumferential main grooves, the second from the center circumferential main groove. A plurality of second lug grooves extending toward the side of the main groove in the outer circumferential direction of the tire, which are closed in the area of the second center land portion, and which are arranged at intervals in the tire circumferential direction.
In the region of the third land portion outside the tire width direction from the second outer circumferential main groove, the third land extends from the second outer circumferential main groove toward the outside in the tire width direction. It has a plurality of third lug grooves, which are closed in the area of the portion and are arranged at intervals in the tire circumferential direction.
The length W1 in the tire width direction of the first center land region is longer than the length W2 in the tire width direction of the second center land region.
The groove length L1 of the first lug groove is 80 to 120% of the total of the groove length L2 of the second lug groove and the groove length L3 of the third lug groove. ..

The pneumatic tire is further arranged outside the tire width direction from the second outer circumferential main groove, has a groove width narrower than the groove width of the second outer circumferential main groove, and is in the tire circumferential direction. It has an extending circumferential groove, and the third land region is located between the circumferential groove and the second outer circumferential main groove.
The length W1 in the tire width direction of the first center land portion is the sum of the length W2 in the tire width direction of the second center land portion and the length W3 in the tire width direction of the third land portion. It is preferably 80 to 120%.

The first lug groove, the sipe, and the second lug groove are inclined with respect to the tire circumferential direction and the tire width direction so as to extend to one side in the tire circumferential direction as the distance from the center circumferential main groove increases. And
The closed end of the sipe is preferably located at the same tire circumferential position as the connection position of the second lug groove with the center circumferential main groove.

The third lug groove is inclined with respect to the tire circumferential direction and the tire width direction so as to extend to the one side in the tire circumferential direction as the distance from the center circumferential main groove increases.
The closed end of the third lug groove is preferably located at the same tire circumferential position as the connection position of the first lug groove with the first outer circumferential main groove.

The center circumferential main groove has a first groove wall that defines one end in the tire width direction of the first center land region and is connected to the tread surface.
It is preferable that the first groove wall extends uninterrupted in the tire circumferential direction on the tread surface.

The total ratio of the groove areas of the pair of circumferential main grooves and the center circumferential main groove to the ground contact area when the tread surface touches the road surface is preferably 15% or more.

It is suitable for passenger cars with a tire nominal width of 255 mm or less.

According to the present invention, it is possible to suppress the occurrence of uneven wear while achieving both wear resistance and wet performance.

It is a figure which shows an example of the profile cross section of the pneumatic tire of this embodiment. It is a figure which shows an example of the tread pattern of the tire T of FIG.

Hereinafter, the pneumatic tire of the present embodiment will be described.
FIG. 1 is a diagram showing an example of a profile cross section of a tire T when the pneumatic tire (hereinafter, also referred to as a tire) T of the present embodiment is cut in a plane along the tire radial direction including the tire rotation axis. .. The profile cross section shown in FIG. 1 is a cross section of the tire T when cut along the line I-I of FIG. 2, which will be referred to later.

In this specification, each direction and side is defined as follows.
The tire width direction is a direction parallel to the rotation axis of the pneumatic tire. The outside in the tire width direction is the side away from the tire center line CL representing the tire equatorial plane with respect to the position to be compared in the tire width direction. Further, the inside in the tire width direction is the side closer to the tire center line CL in the tire width direction with respect to the position to be compared. The tire circumferential direction is the direction in which the pneumatic tire 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 along the tire radial direction with respect to the position to be compared. Further, the inside in the tire radial direction refers to a side approaching the rotation axis along the tire radial direction with respect to the position to be compared.

As shown in FIG. 1, the tire T may be mounted in a direction with respect to the vehicle. In FIG. 1, the reference numeral IN is the side facing the vehicle side when the tire T is mounted on the vehicle (hereinafter referred to as the inside of the vehicle), and the reference numeral OUT is the vehicle with the tire T mounted on the vehicle. Represents the side facing the opposite side (hereinafter referred to as the outside of the vehicle). The tire T is composed of a tread portion 1, a sidewall portion 2, and a bead portion 3. The tread portion 1 has a tread pattern on its surface 10. A carcass layer 4 is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inside to the outside of the tire around the bead core 5 arranged in each bead portion 3. Further, a bead filler 6 is arranged on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by a main body portion and a folded portion of the carcass layer 4. On the other hand, a plurality of layers (two layers in FIG. 1) of belt layers 7 and 8 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each of the belt layers 7 and 8 includes a plurality of reinforcing cords that are inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. In these belt layers 7 and 8, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in the range of, for example, 10 ° to 40 °. Further, a belt reinforcing layer 9 is provided on the outer peripheral side of the belt layers 7 and 8. The belt reinforcing layer 9 contains an organic fiber cord oriented in the tire circumferential direction. In the belt reinforcing layer 9, the angle of the organic fiber cord with respect to the tire circumferential direction is set to, for example, 0 ° to 5 °.

As shown in FIG. 2, the tread pattern of the tire T includes a pair of outer circumferential main grooves 11 and 13, a center circumferential main groove 12, a first lug groove 31, a sipe 41, and a second lug. It has a groove 32 and a third lug groove 33. FIG. 2 is a diagram showing an example of the tread pattern of the tire T of FIG.

The outer circumferential main grooves 11 and 13 are a pair of main grooves extending in the tire circumferential direction, arranged at intervals in the tire width direction with the tire center line CL interposed therebetween. The outer circumferential main grooves 11 and 13 have a groove wall that defines the end of the land region inside each vehicle and is connected to the tread surface. This groove wall extends uninterrupted in the tire circumferential direction on the tread surface. In other words, there are no lug grooves or sipes connected to the outer circumferential main grooves 11 and 13 in the land area inside the vehicle of the outer circumferential main grooves 11 and 13. As described above, the lug grooves 31 and 33 connected to the main grooves 11 and 13 in the outer circumferential direction are present on one side, while the lug grooves connected to the lug grooves 31 and 33 are not present on the other side. The tread pattern of the tire T is asymmetric with respect to the tire center line CL.

The center circumferential main groove 12 is a main groove that is arranged between the pair of outer peripheral main grooves 11 and 13 in the tire width direction and extends in the tire circumferential direction. The center circumferential main groove 12 is located in the vicinity of the tire center line CL. Since the main groove 12 in the center circumferential direction is located near the tire center line CL, the drainage property is improved and the maneuvering performance on a wet road surface (hereinafter referred to as wet performance) is improved. The vicinity of the tire center line CL means a range of 30% of the length W of the tread pattern in the tire width direction on both sides in the tire width direction from the tire center line CL. The center position of the groove width of the main groove 12 in the center circumferential direction is preferably located within this range, and more preferably located on the tire center line CL. The center position of the groove width of the main groove 12 in the center circumferential direction does not have to be located on the tire center line CL.
The center circumferential main groove 12 has a first groove wall 12a (see FIG. 1) that defines the outer edge of the vehicle in the region of the first center land portion 21 and is connected to the tread surface. The first groove wall 12a extends on the tread surface without interruption in the tire circumferential direction. In other words, there are no lug grooves or sipes connected to the center circumferential main groove 12 in the land area inside the vehicle of the center circumferential main groove 12. As described above, the lug groove 32 connected to the main groove 12 in the center circumferential direction exists on one side (outside the vehicle), while the lug groove connected to the lug groove 32 exists on the other side (inside the vehicle). The tread pattern of the tire T is asymmetric with respect to the tire center line CL in that it has a form in which the tire T does not exist. By providing the above-described form in the region near the tire center line CL, the effect of ensuring the drainage property on the outside of the vehicle while ensuring the steering stability on the inside of the vehicle, which will be described later, is increased.

The main grooves extending in the tire circumferential direction (hereinafter, also referred to as the circumferential main grooves) provided in the tread pattern of the tire T are a total of three main grooves 11 and 13 in the outer circumferential direction and the main groove 12 in the center circumferential direction. Therefore, in the tread pattern of the tire T, the distance between the two adjacent circumferential main grooves is wider than that of the tread pattern having the same nominal width having four or more circumferential main grooves, and the first land portion 21 described later will be described. And the length (width) of the second land portion 22 in the tire width direction is wide. In the tread pattern of the tire T, the groove widths of the circumferential main grooves 11 to 13 are wider than those of the tread pattern having the same nominal width having four or more circumferential main grooves. The groove widths of the outer circumferential main grooves 11 and 13 and the center circumferential main groove 12 may be equal to or different from each other. The groove widths of the outer circumferential main grooves 11 and 13 and the center circumferential main groove 12 are, for example, 5.5 to 8.5 mm, respectively.

In the tread pattern of the tire T, the total ratio of the groove areas of the pair of circumferential main grooves 11 and 13 and the center circumferential main groove 12 to the ground contact area when the tread surface touches the road surface (main groove area ratio). Is preferably 15% or more. As a result, when the number of the circumferential main grooves included in the tread pattern is three, the groove widths of the circumferential main grooves 11 to 13 are secured, and the drainage property is ensured. The upper limit of the main groove area ratio is, for example, 25%.
The ground contact area is the area of the ground contact surface when the tire T is assembled to the regular rim, filled with the regular internal pressure, and grounded on the horizontal plane under the condition that 85% of the regular load is the load load. The regular rim is a "standard rim" specified by JATMA, a "Design Rim" specified by TRA, or a "Measuring Rim" specified by ETRTO. The normal internal pressure is the "maximum air pressure" specified by JATTA, the maximum value described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "INFLATION PRESSURES" specified by ETRTO. The normal load is the "maximum load capacity" specified by JATTA, the maximum value described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "LOAD CAPACITY" specified by ETRTO.

The first lug groove 31 is a first center land portion 21 located between the center circumferential main groove 12 and the first outer circumferential main groove 11 of the pair of outer circumferential main grooves 11 and 13. In the region of, a plurality of tires extend from the first outer circumferential main groove 11 toward the center circumferential main groove 12 and close in the region of the first center land portion 21 at intervals in the tire circumferential direction. Have been placed. The rigidity of the first land portion 21 is ensured because the first lug groove 31 is closed within the region of the first center land portion 21 and the width of the first land portion 21 is wide as described above. Has been done. This form contributes to the improvement of the wear resistance performance of the tire T.
The extending direction of the first lug groove 31 is preferably inclined with respect to the tire width direction in order to improve drainage. In the example shown in FIG. 2, the first lug groove 31 has a portion in the middle of the extending direction in which the inclination angle with respect to the tire width direction gradually increases. Therefore, the inclination angle of the first lug groove 31 with respect to the tire width direction is different between the portion including the connection position with the first outer peripheral direction main groove 11 and the tip portion having the closed end 31a. The inclination angle of the tip portion with respect to the tire width direction is, for example, 45 to 85 °.
The distance between the closed end 31a and the main groove 12 in the center circumferential direction in the tire width direction is the groove length of the second lug groove 32 from the viewpoint of ensuring the rigidity of the first land portion 21 while ensuring wet performance. The distance is preferably 0.5 to 1.5 times that of L2.

The sipe 41 extends from the closed end 31a of the first lug groove 31 to the side of the main groove 12 in the center circumferential direction and closes in the region of the first center land portion 21, and a plurality of sipes 41 are spaced apart from each other in the tire circumferential direction. Have been placed. By providing such a sipe 41, the rigidity of the first land portion 21 is relaxed. The sipe 41 preferably extends at an angle with respect to the tire width direction, but may extend in the tire width direction. When the sipe 41 is tilted with respect to the tire width direction, the tilt angle of the sipe 41 is, for example, 45 to 85 °. In the example shown in FIG. 2, the sipe 41 has the same inclination direction as the tip of the first lug groove 31, but may have a different inclination angle from the tip of the first lug groove 31. Further, the length L4 of the sipe 41 in the extending direction is preferably, for example, 80 to 120% of the groove length L1 of the first lug groove 31. The distance between the closed end of the sipe 41 and the main groove 12 in the center circumferential direction in the tire width direction is first from the viewpoint of keeping the difference in rigidity between the first land portion 21 and the second land portion 23 in an appropriate range. The distance is preferably 10 to 50% of the length of the land portion 21 in the tire width direction.

The second lug groove 32 is a second center land portion 22 located between the center circumferential main groove 12 and the second outer circumferential main groove 13 of the pair of outer circumferential main grooves 11 and 13. In the region of, a plurality of tires extend from the center circumferential main groove 12 toward the side of the second outer circumferential main groove 13 and close in the area of the second center land portion 22 at intervals in the tire circumferential direction. Have been placed. The rigidity of the second land portion 22 is ensured because the second lug groove 32 is closed in the region of the second center land portion 22 and the width of the second land portion 22 is wide as described above. Has been done. This form contributes to the improvement of the wear resistance performance of the tire T.
The extending direction of the second lug groove 32 is preferably inclined with respect to the tire width direction in order to improve drainage. The inclination angle of the second lug groove 32 with respect to the tire width direction is, for example, 20 to 80 °. In the example shown in FIG. 2, the second lug groove 32 is on the side opposite to the tire circumferential direction (lower side in FIG. 2) where the first lug groove 31 is inclined with respect to the tire width direction (upper side in FIG. 2). However, the first lug groove 31 may extend to the same side as the side in the tire circumferential direction in which the first lug groove 31 is inclined.

The third lug groove 33 is located outside the tire width direction from the second outer circumferential main groove 13 in the region of the third land portion 23 outside the tire width direction from the second outer circumferential main groove 13. It extends toward the tire and closes in the area of the third land portion 23, and a plurality of tires are arranged at intervals in the tire circumferential direction. The rigidity of the third land portion 23 is ensured because the third lug groove 33 is closed within the region of the third land portion 23 and the width of the third land portion 23 is wide. This form contributes to the improvement of the wear resistance performance of the tire T.
The extending direction of the third lug groove 33 is preferably inclined with respect to the tire width direction in order to improve drainage. The inclination angle of the third lug groove 33 with respect to the tire width direction is, for example, 20 to 80 °. In the example shown in FIG. 2, the third lug groove 33 extends to the side opposite to the side in the tire circumferential direction in which the first lug groove 31 is inclined with respect to the tire width direction. The third lug groove 33 may extend to the same side as the tire circumferential direction in which the first lug groove 31 is inclined with respect to the tire width direction.

In the tread pattern of the tire T, the total ratio of the groove areas of the lug grooves 31 to 33 (also referred to as the lug groove area ratio) to the ground contact area when the tread surface 10 touches the road surface is 5% or more. preferable. The fact that the lug groove area ratio is within the above range contributes to the improvement of drainage. The upper limit of the lug groove area ratio is, for example, 15%. The lug groove area ratio does not include the area of the sipe.

With respect to the land portions 21 and 22 on both sides of the center circumferential main groove 12, the width W1 of the region of the first center land portion 21 is longer than the width W2 of the region of the second center land portion 22. The tread pattern of the tire T is asymmetric with respect to the tire center line CL from the viewpoint of ensuring steering stability. In the tread pattern of the tire T, the ground contact area inside the vehicle is increased to ensure steering stability, and the groove area outside the vehicle is increased to ensure drainage.
Further, in the tread pattern of the tire T, the groove length L1 of the first lug groove 31 is 80 to 80, which is the total of the groove length L2 of the second lug groove 32 and the groove length L3 of the third lug groove 33. It is 120%. In general, if the widths of the land portions on both sides of the circumferential main groove are different, a difference in rigidity occurs between the two land portions. In particular, if there is a lug groove connected to the circumferential main groove only in the narrower land part on both sides of the circumferential main groove, the difference in rigidity between the two land parts is even larger. Become. In the tread pattern of the tire T, the lug grooves 31, 32, 33 are closed in the regions of the land portions 21, 21, 22, and 23, and the groove length L1 of the lug groove 31 is the groove length of the lug groove 32. The first land portion 21, the second land portion 22, and the second land portion 22 and that are 80 to 120% of the total L2 + L2 of the groove length L3 of the tire L2 and the lug groove 33, that is, L1 is about the same as L2 + L3. The difference in rigidity of the third land portion 23 is relaxed. Therefore, the occurrence of uneven wear can be suppressed. If L1 is less than 80% of L2 + L3, the difference in rigidity between the first land portion 21 and the second land portion 22 and the third land portion 23 cannot be sufficiently alleviated. When L1 exceeds 120% of L2 + L3, the rigidity of the first land portion 21 is reduced with respect to the rigidity of the second land portion 22 and the third land portion 23, and the rigidity difference may be rather large. ..
The groove lengths L1, L2, and L3 are lengths along the extending direction of the center position of the groove widths of the lug grooves 31, 32, and 33, respectively. The groove length L2 and the groove length L3 may be equal to or different from each other. L1 is preferably 90 to 110% of L2 + L3.

According to the tire T of the present embodiment, it is possible to suppress the occurrence of uneven wear while achieving both wear resistance and wet performance.

The tread pattern of the present embodiment further has a circumferential groove 14, and the region of the third land portion 23 is located between the circumferential groove 14 and the second outer circumferential main groove 13. The width W1 of the first center land portion 21 is 80 to 120% of the total W2 + W3 of the width W2 of the second center land portion 22 and the width W3 of the third land portion 23, that is, W1. Is preferably about the same as W2 + W3. The third lug groove 33 extends from the second outer circumferential main groove 13 toward the circumferential narrow groove 14. Since W1 is about the same as W2 + W3, the difference in rigidity between the land portions on both sides of the main groove 12 in the center circumferential direction can be made evenly close to each other, and the effect of suppressing uneven wear in a tread pattern asymmetric with respect to the tire center line CL. Will be higher. The width W2 of the second land portion 22 and the width W3 of the third land portion 23 may be equal to or different from each other. W1 is preferably 90 to 110% of W2 + W3.

The circumferential narrow groove 14 is arranged outside the tire width direction from the second outer circumferential main groove 13, has a groove width narrower than the groove width of the second outer circumferential main groove 13, and extends in the tire circumferential direction. It is a groove. By providing the circumferential groove 14, the drainage property in the region outside the vehicle is improved. The circumferential fine groove 14 has a groove width narrower than the groove widths of the three circumferential main grooves 11 to 13, for example, 1 to 5 mm. Further, the groove depth of the circumferential narrow groove 14 is shallower than the groove depth of the circumferential main grooves 11 to 13.

As shown in FIG. 2, the first lug groove 31, the sipe 41, and the second lug groove 32 extend in the tire circumferential direction and one side in the tire circumferential direction as the distance from the center circumferential main groove 12 increases. It is preferable that the closed end of the sipe 41 is inclined with respect to the tire width direction and is at the same tire circumferential position as the connection position of the second lug groove 32 with the center circumferential main groove 12. In other words, it is preferable that the first lug groove 31 and the sipe 41 and the second lug groove 32 have a V shape. In the example shown in FIG. 2, the V-shape has a sipe 41 and a second lug in the extending direction of the tip end portion of the first lug groove 31 and the sipe 41 and the extending direction of the second lug groove 32. The grooves 32 intersect in the tire width direction. These two extending directions intersect between the sipe 41 and the tire width direction of the center circumferential main groove 12. Note that the same tire circumferential position means that the distance between the two target positions (for example, the closed end of the sipe 41 and the connection position of the second lug groove 32) in the tire circumferential direction is the distance between the tires T. It means that it is within the range of 30% of the pitch length.
Further, in the above-described V-shaped form, the third lug groove 33 extends in the tire circumferential direction and the tire width direction so as to extend to the one side in the tire circumferential direction as the distance from the center circumferential main groove 12 increases. It is more preferable that the third lug groove 33 is inclined and is at the same tire circumferential position as the connection position of the first lug groove 31 with the first outer circumferential main groove 11. In this embodiment, the second lug groove 32 and the third lug groove 33 are located so as to form an outer portion of the vehicle among the two V-shaped portions. In order to obtain such a form, the extending direction of the second lug groove 32 and the extending direction of the third lug groove 33 are such that the main groove 13 in the outer circumferential direction and the third lug groove 33 are located. It is preferable that they intersect or match within the range in the tire width direction. In the example shown in FIG. 2, the two extending directions intersect at the connection position with the outer circumferential main groove 13 of the third lug groove 33.

Since the first lug groove 31 and the sipe 41 and the second lug groove 32 have a V shape, among the ground contact shapes when the tread surface 10 comes into contact with the road surface, the center circumferential main groove 12 The shape near the opening end of is almost symmetrical on both sides of the main groove 12 in the center circumferential direction. By obtaining such a ground contact shape, the difference in the amount of water flowing from the center circumferential main groove 12 to both sides thereof is small, and the water is efficiently drained to both the outside of the vehicle and the inside of the vehicle.
Further, even when the main groove 12 in the center circumferential direction is not located on the tire center line CL, the first lug groove 31 and the sipe 41 and the second lug groove 32 have a V shape. Then, the inclination angle of the first lug groove 31 and the sipe 41 and the inclination angle of the second lug groove 32 are adjusted, so that the ground contact shape near the opening end of the main groove 12 in the center circumferential direction can be easily adjusted. For example, when the main groove 12 in the center circumferential direction is located inside the vehicle with respect to the tire center line CL, the inclination angle of the lug groove 31 and the sipe 41 forming the inside portion of the vehicle in the V shape with respect to the tire width direction is small ( By increasing (steeply) the inclination angle of the lug groove 32 forming the outer part of the vehicle with respect to the tire width direction, the contact length of both sides of the main groove 12 in the center circumferential direction can be adjusted to the entire contact shape. It will be easier to make the length along the contour.

It is preferable that the edges in the tire width direction in contact with the tread surface are chamfered in the circumferential main grooves 11 to 13. The main groove area ratio is calculated based on the area of the main groove expanded by chamfering.
Further, the portion of the land portion 21 to 23 in which the lug grooves 31 to 33 are connected to the main grooves 11 to 13 in the circumferential direction at an acute angle may be chamfered. In the example shown in FIG. 2, the portion of the first land portion 21 in which the first lug groove 31 connects to the first outer circumferential main groove 11 at an acute angle is chamfered. The lug groove area ratio is calculated based on the area of the lug groove expanded by chamfering, which will be described later.

The tire T of the present embodiment is suitable for a passenger car having a tire nominal width of 255 mm or less. The tire nominal width is preferably 145 to 185 mm. Tire nominal widths in such a range are common in light passenger car tires. Light passenger cars generally have a higher number of revolutions than ordinary passenger cars when traveling the same distance, and are prone to wear. Since the tire T of the present embodiment has improved wear resistance as described above, it is suitable as a tire to be mounted on a light passenger car. From such a viewpoint, the tire T of the present embodiment is more suitable when the tire nominal width is in the above range and the tire T is mounted on a light passenger car having a rim diameter of 14 to 16 inches.

The tread pattern of the tire T further has shoulder lug grooves 34, 35.
A plurality of shoulder lug grooves 34 are formed in the region of the shoulder land portion 24 located inside the vehicle of the first outer peripheral direction main groove 11 at intervals in the tire circumferential direction. The shoulder lug groove 34 extends from the inner end of the tread pattern toward the side of the first outer circumferential main groove 11, and is closed within the region of the shoulder land portion 24. A sipe extending toward the first outer circumferential main groove 11 and connected to the first outer circumferential main groove 11 is connected to the closed end of the shoulder lug groove 34.
A plurality of shoulder lug grooves 35 are formed in the region of the shoulder land portion 25 located on the outside of the vehicle in the second outer peripheral direction main groove 13 at intervals in the tire circumferential direction. The shoulder lug groove 35 extends from the outer end of the tread pattern toward the side of the second outer circumferential main groove 13, and is closed within the region of the shoulder land portion 25. A shoulder sipe is formed between the adjacent shoulder lug grooves 35.

(Comparative Examples, Examples)
In order to investigate the effect of the pneumatic tire of the present embodiment, the tread pattern of the tire was variously changed, and the wet performance, wear resistance performance, and uneven wear resistance performance were investigated. The prototype tire had a size of 155 / 65R14, had the cross-sectional shape shown in FIG. 1, and was based on the tread pattern shown in FIG. 2 except for the forms shown in Table 1, Table 2, and the following.

Tables 1 and 2 show the morphology of each tire with respect to the tread pattern and the evaluation results thereof.
In Comparative Example 1, lug grooves extending from the circumferential main groove to the outside of the vehicle (in order from the inside of the vehicle) are provided in each of the four land regions between the four circumferential main grooves and the one circumferential narrow groove. The first lug groove to the fourth lug groove) were provided, and a sipe connecting to the first lug groove was provided in the region of the first land portion on the innermost side of the vehicle. Further, the first lug groove and the sipe and the second lug groove are inclined to the same side in the tire circumferential direction with respect to the tire width direction, and the third lug groove and the fourth lug groove are these lug grooves. And tilted to the opposite side of the sipe. With respect to the widths W1 to W4 of each land portion, W1 <W2, W1> W3 and W4 were set. Further, with respect to the groove lengths L1 to L4 of each lug groove, L1 = 1/2 × L2 and L1 = L3 + L4. In Table 1, the relationship between W1 and W2 and the description of Comparative Example 1 in the columns of L1 / (L2 + L3) and W1 / (W2 + W3) are omitted.
In both the comparative example and the example, the main groove area ratio was set to 20% and the lug groove area ratio was set to 9%.

In Tables 1 and 2, "sipe" means a sipe connected to a first lug groove in a first land region.
Among the items shown in Table 1, those not shown in Table 2 (presence or absence of sipes, etc.) were the same as those in the first embodiment.

Wet performance Each test tire is assembled on a wheel with a rim size of 14 x 6J, mounted on a test vehicle (front wheel drive vehicle) with a displacement of 0.5L with an air pressure of 230kPa, and pylon is installed at intervals of 35m at a depth of 2 to 3mm. On a 175 m slalom test road composed of an asphalt road surface, the time required for the test driver to travel in slalom was measured. The evaluation result is shown by an index with Comparative Example 1 as 100 using the reciprocal of the measured value. The larger this index is, the shorter the required time is, and the better the wet performance is.

The wear resistance test tire was mounted on the same test vehicle used in the wet performance evaluation test, and a 12000 km pattern run was carried out on the test course. After the test, the groove depth of the main groove in the center circumferential direction was measured, and the amount of reduction (height) of the tread rubber was calculated. The evaluation result is shown by an index with Comparative Example 1 as 100 using the reciprocal of the calculated value. The larger this index is, the smaller the amount of tread rubber is reduced, which means that the wear resistance is excellent.

Uneven wear resistance performance After the evaluation test of wear resistance performance, the groove depths of the two main grooves in the outer circumferential direction were measured, and the difference in the amount of reduction (height) of the tread rubber was calculated. The evaluation result is shown by an exponent with Comparative Example 1 as 100 using the reciprocal of the calculated value. The larger this index is, the smaller the difference in the amount of reduction of the tread rubber is on both sides in the tire width direction, which means that the uneven wear resistance is excellent.
As a result of these tests, those having a total of 304 or more of the indexes of the three performances were evaluated as being able to suppress the occurrence of uneven wear while achieving both wear resistance performance and wet performance.

As shown in Tables 1 and 2, Examples 1 to 7 were superior in wet performance, wear resistance performance, and uneven wear resistance performance as compared with Comparative Examples 1 to 6. From this result, in the tread pattern having three circumferential main grooves, there is a sipe connected to the first lug groove and extending toward the center circumferential main groove, W1> W2, and L1 is L2 + L3. It can be seen that when the content is 80 to 120%, the occurrence of uneven wear can be suppressed while achieving both wear resistance and wet performance.
Further, from Examples 4 to 6 and Examples 1 to 3 and 7, W1 is 80 to 120% of W2 + W3, so that uneven wear is achieved at a higher level while achieving both wear resistance and wet performance. It can be seen that the occurrence can be suppressed.

Although the pneumatic tire of the present invention has been described in detail above, the pneumatic tire of the present invention is not limited to the above-described embodiment or embodiment, and various improvements and changes have been made without departing from the gist of the present invention. Of course, it may be.

1 Tread portion 10 Tread portion surface 11, 13 Outer circumferential main groove 12 Center circumferential main groove 12a First groove wall 14 Circumferential narrow groove 21 First center land portion 22 Second center land portion 23 Third 31 First lug groove 31a Closed end of first lug groove 32 Second lug groove 33 Third lug groove 41 Sipe

Claims (7)

A pneumatic tire with a tread pattern on the surface of the tread.
The tread pattern is
A pair of outer circumferential main grooves that are arranged at intervals in the tire width direction across the tire center line and extend in the tire circumferential direction.
A center circumferential main groove arranged between the pair of outer peripheral main grooves in the tire width direction and extending in the tire circumferential direction,
In the region of the first center land portion located between the center circumferential main groove and the first outer circumferential main groove of the outer circumferential main grooves, from the first outer circumferential main groove. A plurality of first lug grooves extending toward the side of the main groove in the center circumferential direction and closing in the area of the first center land portion and arranged at intervals in the tire circumferential direction.
A plurality of lug grooves extending from the closed end of the first lug groove toward the main groove in the center circumferential direction and closing in the area of the first center land portion, and arranged at intervals in the tire circumferential direction. Sipe and
In the region of the second center land portion located between the center circumferential main groove and the second outer circumferential main groove of the outer circumferential main grooves, the second from the center circumferential main groove. A plurality of second lug grooves extending toward the side of the main groove in the outer circumferential direction of the tire, which are closed in the area of the second center land portion, and which are arranged at intervals in the tire circumferential direction.
In the region of the third land portion outside the tire width direction from the second outer circumferential main groove, the third land extends from the second outer circumferential main groove toward the outside in the tire width direction. It has a plurality of third lug grooves, which are closed in the area of the portion and are arranged at intervals in the tire circumferential direction.
The length W1 in the tire width direction of the first center land region is longer than the length W2 in the tire width direction of the second center land region.
The groove length L1 of the first lug groove is 80 to 120% of the total of the groove length L2 of the second lug groove and the groove length L3 of the third lug groove. Pneumatic tires. Further, a circumferential narrow groove that is arranged outside the tire width direction from the second outer circumferential main groove, has a groove width narrower than the groove width of the second outer circumferential main groove, and extends in the tire circumferential direction. The third land region is located between the circumferential narrow groove and the second outer circumferential main groove.
The length W1 in the tire width direction of the first center land portion is the sum of the length W2 in the tire width direction of the second center land portion and the length W3 in the tire width direction of the third land portion. The pneumatic tire according to claim 1, which is 80 to 120%. The first lug groove, the sipe, and the second lug groove are inclined with respect to the tire circumferential direction and the tire width direction so as to extend to one side in the tire circumferential direction as the distance from the center circumferential main groove increases. And
The pneumatic tire according to claim 1 or 2, wherein the closed end of the sipe is located at the same tire circumferential position as the connection position of the second lug groove with the center circumferential main groove. The third lug groove is inclined with respect to the tire circumferential direction and the tire width direction so as to extend to the one side in the tire circumferential direction as the distance from the center circumferential main groove increases.
The pneumatic tire according to claim 3, wherein the closed end of the third lug groove is located at the same tire circumferential position as the connection position of the first lug groove with the first outer circumferential main groove. The center circumferential main groove has a first groove wall that defines one end in the tire width direction of the first center land region and is connected to the tread surface.
The pneumatic tire according to any one of claims 1 to 4, wherein the first groove wall extends on the surface of the tread without interruption in the tire circumferential direction. Any of claims 1 to 5, wherein the ratio of the total groove area of the pair of circumferential main grooves and the center circumferential main groove to the ground contact area when the tread surface touches the road surface is 15% or more. The pneumatic tire described in item 1. The pneumatic tire according to any one of claims 1 to 6, wherein a passenger car having a tire nominal width of 255 mm or less is applied.

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