JP2017193222A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of enhancing a steering stability performance on a dry road surface, while maintaining a brake performance on the wet road surface.SOLUTION: A pneumatic tire comprises multiple main grooves 11 extending in a tire circumferential direction in a tread part 1. Multiple rows of land parts 10 are partitioned by the multiple main grooves 11. The main groove 11 comprises a pair of outermost main grooves 11B arranged on an outermost side in a tire width direction. The land part 10 comprises center land parts 20 arranged on an inner side of the outermost main groove 11B in the tire width direction to form rib-like shapes. The center land part 20 comprises multiple sipes 21 extending in the tire width direction. At least one hole part 21A is provided in a part of each of the sipes 21 in a longitudinal direction, extends in a tire radial direction, and has a width wider than that of the sipe 21. A cavity part 21B is provided in a bottom part of each of the sipes 21, extends in the tire width direction, and has a width wider than that of the sipe 21. The cavity part 21B is connected with the hole part 21A.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that can improve steering stability performance on a dry road surface while maintaining braking performance on a wet road surface.

  In general, as a technique for reducing rolling resistance of a tire, it is widely performed to reduce the volume of cap rubber constituting the tread portion by reducing the groove depth of the groove formed in the tread portion. However, since the groove volume of the tread portion decreases due to the shallow groove of the tread portion, there is a problem that the braking performance on the wet road surface is lowered.

  On the other hand, as a technique for improving the braking performance on the wet road surface, it is effective to increase the groove area of the groove formed in the tread portion. However, when the groove area is increased, the rigidity of the land portion and the ground contact area are decreased, and there is a problem that the steering stability performance on the dry road surface is deteriorated.

  Various types of pneumatic tires with sipes formed in the tread portion have been proposed (see, for example, Patent Documents 1 to 3). Such sipes contribute to the improvement of drainage. However, when a sipe is provided in the tread portion, the sipe causes a decrease in the rigidity of the land portion, and the drainage effect by the sipe is not always sufficient.

JP 2006-168462 A International Publication No. 2012/029125 JP-A-62-241712

  An object of the present invention is to provide a pneumatic tire capable of improving the steering stability performance on a dry road surface while maintaining the braking performance on a wet road surface.

  To achieve the above object, a pneumatic tire according to the present invention includes a plurality of main grooves extending in the tire circumferential direction in a tread portion, and a plurality of rows of land portions are defined by the plurality of main grooves. The main groove includes a pair of outermost main grooves positioned on the outermost side in the tire width direction, and the land portion is positioned on the inner side in the tire width direction of the outermost main groove and forms a rib shape. The center land portion has a plurality of sipes extending in the tire width direction, and at least one hole extending in the tire radial direction in a part of the longitudinal direction of the sipes and wider than the sipes. Is attached to the bottom of the sipe, which extends in the tire width direction and wider than the sipe, and the cavity is connected to the hole. .

  In the present invention, the center land portion having a plurality of sipes extending in the tire width direction and having a rib shape is disposed on the inner side in the tire width direction from the outermost main groove, thereby increasing the rigidity of the tread portion and increasing the contact area. Can be secured. As a result, it is possible to improve the steering stability performance on the dry road surface. Further, at least one hole extending in the tire radial direction and wider than the sipe is attached to a part of the longitudinal direction of the sipe, and the bottom of the sipe extends in the tire width direction and wider than the sipe. Since the hollow part which is formed is attached and the hollow part is connected to the hole part, the water absorption of the sipe is improved. Therefore, even if the center land portion is configured in a rib shape, the braking performance on the wet road surface can be maintained without deteriorating drainage.

  In the present invention, the groove depth of the main groove is preferably 5.0 mm or more and 6.0 mm or less. By making the main groove shallow, the thickness of the cap tread can be reduced and the rolling resistance can be reduced.

  In the present invention, the maximum width WVh in the tire circumferential direction of the hole located in the center land portion is preferably 2 to 5 times the sipe width Ws of the sipe. On the other hand, the maximum width WLh in the tire width direction of the hole located in the center land portion is preferably 2 to 5 times the sipe width Ws of the sipe. By appropriately setting the size of the hole in this manner, the sipe can exhibit a sufficient water absorption effect, and contributes to the maintenance of the braking performance on the wet road surface. In addition, it is possible to minimize the reduction in the contact area due to the increase in the groove area, and it is possible to effectively improve the steering stability performance on the dry road surface.

  In the present invention, the maximum width Wp in the tire circumferential direction of the hollow portion located in the center land portion is preferably not less than 2 times and not more than 4 times the sipe width Ws of the sipe. On the other hand, it is preferable that the maximum width Dp in the tire radial direction of the hollow portion located in the center land portion is 0.2 to 0.5 times the sipe depth Ds of the sipe. Thus, by appropriately setting the dimensions of the hollow portion, the sipe can exert a sufficient drainage effect, and contributes to the maintenance of the braking performance on the wet road surface. In addition, it is possible to minimize the decrease in rigidity of the land portion due to the increase in the groove volume, and it is possible to effectively improve the steering stability performance on the dry road surface.

It is meridian sectional drawing which shows the pneumatic tire which consists of embodiment of this invention. It is a top view which shows a part of tread part of the pneumatic tire which concerns on this invention. It is a perspective view which shows the center land part formed in the tread part of the pneumatic tire which concerns on this invention. It is a top view which shows the sipe and hole part of FIG. It is XX arrow sectional drawing of FIG.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. 1 to 5 show a pneumatic tire according to an embodiment of the present invention. 1 and 2, CL is a tire center line.

  As shown in FIG. 1, the pneumatic tire of the present embodiment includes a tread portion 1 that extends in the tire circumferential direction and has an annular shape, and a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1. And a pair of bead portions 3 and 3 disposed inside the sidewall portion 2 in the tire radial direction.

  A carcass layer 4 is mounted between the pair of bead portions 3 and 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded from the inside of the tire to the outside around the bead core 5 disposed in each bead portion 3. A bead filler 6 made of a rubber composition having a triangular cross-section is disposed on the outer periphery of the bead core 5.

  On the other hand, a plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. In the belt layer 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set in a range of, for example, 10 ° to 40 °. A steel cord is preferably used as the reinforcing cord of the belt layer 7. For the purpose of improving high-speed durability, at least one belt cover layer 8 in which reinforcing cords are arranged at an angle of, for example, 5 ° or less with respect to the tire circumferential direction is disposed on the outer peripheral side of the belt layer 7. Yes. As the reinforcing cord of the belt cover layer 8, an organic fiber cord such as nylon or aramid is preferably used.

  In addition, although the tire internal structure mentioned above shows the typical example in a pneumatic tire, it is not limited to this.

  2 to 4 show a part of the tread portion 1, Tc indicates the tire circumferential direction, and Tw indicates the tire width direction. As shown in FIG. 2, the tread portion 1 is formed with three main grooves 11 extending in the tire circumferential direction. The main groove 11 includes an inner main groove 11A located on the tire center line CL and a pair of outermost main grooves 11B and 11B located on the outermost side in the tire width direction. The three main grooves 11 define a plurality of rows of land portions 10 in the tread portion 1. The land portion 10 includes a pair of center land portions 20 and 20 positioned on both sides of the tire center line CL, and a pair of shoulder land portions 30 and 30 positioned on the outer side in the tire width direction of each center land portion 20.

  The center land portion 20 is configured in a rib shape. A plurality of sipes 21 that are inclined in the same direction with respect to the tire width direction are formed in the center land portion 20 at intervals in the tire circumferential direction. These sipes 21 have one end communicating with the inner main groove 11A and the other end communicating with the outermost main groove 11B. That is, the sipe 21 is an open sipe. The sipe 21 is a narrow groove having a groove width of 1.5 mm or less. The center land portion 20 is subdivided by a sipe 21, but has a structure that is substantially continuous in the tire circumferential direction without being divided by a lug groove having a groove width of 2.0 mm or more.

  The shoulder land portion 30 is formed with a plurality of sipes 31 extending in the tire width direction and connected to the outermost main groove 11B. That is, the sipe 31 is a semi-closed sipe. The sipe 31 is a narrow groove having a groove width of 1.5 mm or less. The shoulder land portion 30 is formed with a plurality of lug grooves 32 that are inclined in the same direction with respect to the tire width direction and are not communicated with the outermost main groove 11B at intervals in the tire circumferential direction. ing.

  A part of the sipe 21, 31 in the longitudinal direction is provided with one hole 21 </ b> A, 31 </ b> A that extends in the tire radial direction and is wider than the sipe 21, 31. The shape of the holes 21A and 31A in plan view is not particularly limited, but the shape of the holes 21A and 31A shown in FIG. 2 is a circular shape in plan view. Thus, when the shape of hole 21A, 31A is circular shape, it is excellent in mold release property and is advantageous on manufacture. In addition, a triangular, rectangular, or polygonal shape can also be employed.

  In the sipe 21, as shown in FIGS. 2 and 3, a cavity 21B extending in the tire width direction and wider than the sipe 21 is attached to the bottom of the sipe 21, and the cavity 21B is connected to the hole 21A. . That is, the sipe 21, the hole 21A, and the cavity 21B form an integrated space in which the sipe 21, the hole 21A, and the cavity 21B are connected. The cross-sectional shape of the cavity portion 21B is not particularly limited, but the cross-sectional shape of the cavity portion 21B shown in FIG. 3 is a circular shape. Thus, when the cavity 21B has a circular cross-sectional shape, it is excellent in mold release and advantageous in manufacturing.

  As shown in FIGS. 2 and 3, the hollow portion 21 </ b> B communicates with the main grooves 11 </ b> A and 11 </ b> B located on both sides of the center land portion 20. By forming the hollow portion 21B in this way, the drainage performance of the sipe 21 is improved. On the other hand, both ends of the hollow portion 21B may be configured to be in communication with the main grooves 11A and 11B and terminated in the center land portion 20.

  Further, in the sipe 31, a cavity 31B extending in the tire width direction and wider than the sipe 31 is attached to the bottom of the sipe 31, and the cavity 31B is connected to the hole 31A. That is, the sipe 31, the hole portion 31A, and the hollow portion 31B form an integral space in which each is connected. The cavity 31B has the same cross-sectional shape as the cavity 21B of the sipe 21, and one end thereof communicates with the main groove 11B. One end of the cavity 31B communicates with the main groove 11B, which is advantageous for improving the drainage of the sipe 31. On the other hand, both ends of the hollow portion 31B may be configured to be in communication with the main groove 11B and terminated in the shoulder land portion 30.

  In the pneumatic tire, the center land portion 20 having a plurality of sipes 21 extending in the tire width direction and the rib-shaped center land portion 20 is disposed on the inner side in the tire width direction with respect to the outermost main groove 11B. The rigidity can be increased and the ground contact area can be secured. As a result, it is possible to improve the steering stability performance on the dry road surface. Further, at least one hole 21A extending in the tire radial direction and wider than the sipe 21 is attached to a part of the sipe 21 in the longitudinal direction, and the bottom of the sipe 21 extends in the tire width direction. Since the cavity 21B having a width wider than 21 is provided and the cavity 21B is connected to the hole 21A, the water absorption of the sipe 21 is improved. Therefore, even if the center land portion 20 is configured in a rib shape, the braking performance on the wet road surface can be maintained without causing deterioration of drainage.

  In the pneumatic tire, the sipes 21 are preferably arranged so as to be aligned in the tire circumferential direction at intervals of 20% to 50% with respect to the width L of the center land portion 20 in the tire width direction. By arranging a large number of the sipes 21 in the center land portion 20 in this way, it becomes possible to achieve both improvement in the steering stability performance on the dry road surface and the improvement of the braking performance on the wet road surface.

  The number of holes 21A attached to the sipe 21 is not particularly limited, but the embodiment shown in FIGS. 2 to 4 is an example where one hole is provided, and a plurality of holes 21A can be attached. When attaching a plurality of hole portions 21A, it is preferable to arrange along the sipe 21 at intervals of 20% or more with respect to the width L in the tire width direction of the center land portion 20. By arranging the hole 21A along the sipe 21 as described above, it is possible to achieve both improvement in the steering stability performance on the dry road surface and the braking performance on the wet road surface.

  In particular, the groove depth of the main groove 11 is preferably 5.0 mm or more and 6.0 mm or less. Thus, by making the main groove 11 shallow, the thickness of the cap tread can be reduced. As a result, since the volume of the cap tread rubber can be reduced, the rolling resistance can be reduced.

  As shown in FIG. 4, the maximum width WVh in the tire circumferential direction of the hole 21 </ b> A may be configured to be 2 to 5 times the sipe width Ws of the sipe 21. On the other hand, the maximum width WLh in the tire width direction of the hole 21 </ b> A may be configured to be 2 to 5 times the sipe width Ws of the sipe 21. In this way, by appropriately setting the size of the hole 21A, the sipe 21 can exhibit a sufficient water absorption effect, and contributes to the maintenance of the braking performance on the wet road surface. In addition, it is possible to minimize the reduction in the contact area due to the increase in the groove area, and it is possible to effectively improve the steering stability performance on the dry road surface.

  Here, when the maximum width WVh or the maximum width WLh of the hole 21A is less than twice the sipe width Ws of the sipe 21, the sipe 21 cannot obtain a sufficient water absorption effect, and braking performance on a wet road surface. The sufficient improvement effect cannot be obtained. On the other hand, when the maximum width WVh or the maximum width WLh of the hole 21A exceeds 5 times the sipe width Ws of the sipe 21, the steering stability on the dry road surface is reduced due to a decrease in rigidity of the center land portion 20 and a reduction in the contact area. Performance will be reduced.

  As shown in FIG. 5, the maximum width Wp in the tire circumferential direction of the hollow portion 21 </ b> B may be configured to be 2 to 4 times the sipe width Ws of the sipe 21. On the other hand, the maximum width Dp of the hollow portion 21B in the tire radial direction may be configured to be 0.2 to 0.5 times the sipe depth Ds of the sipe 21 in the tire radial direction. By appropriately setting the size of the hollow portion 21B in this way, the sipe 21 can exhibit a sufficient drainage effect, contributing to maintenance of braking performance on a wet road surface. Moreover, the rigidity fall of the center land part 20 by the increase in groove volume can be minimized, and it becomes possible to improve the steering stability performance on a dry road surface effectively.

  Here, the maximum width Wp of the cavity portion 21B is less than twice the sipe width Ws of the sipe 21, or the maximum width Dp of the cavity portion 21B is less than 0.2 times the sipe depth Ds of the sipe 21. In this case, the sipe 21 cannot obtain a sufficient drainage effect, and a sufficient improvement effect of the braking performance on the wet road surface cannot be obtained. On the other hand, the maximum width Wp of the cavity 21B exceeds 4 times the sipe width Ws of the sipe 21, or the maximum width Dp of the cavity 21B is 0.5 times the sipe depth Ds of the sipe 21. If exceeded, the steering stability performance on the dry road surface is lowered due to the rigidity of the center land portion 20 being lowered.

  In a pneumatic tire having a tire size of 155 / 65R14 and having a plurality of main grooves extending in the tire circumferential direction in a tread portion, and a plurality of rows of land portions being partitioned by the plurality of main grooves, a lug groove in a center land portion Presence / absence, presence / absence of sipe hole, presence / absence of sipe cavity, groove depth (mm) of main groove, ratio of maximum width WVh in tire circumferential direction to sipe width Ws (WVh / Ws), sipe The ratio of the maximum width WLh in the tire width direction of the hole to the width Ws (WLh / Ws), the ratio of the maximum width Wp in the tire circumferential direction of the cavity to the sipe width Ws (Wp / Ws), and the cavity to the sipe depth Ds Tires of conventional examples, comparative examples 1 to 3 and examples 1 to 6 in which the ratio of the maximum width Dp in the tire radial direction (Dp / Ds) was set as shown in Table 1 were manufactured.

  For these test tires, the following test methods were used to evaluate rolling resistance, steering stability performance on a dry road surface, and braking performance on a wet road surface, and the results are also shown in Table 1.

Rolling resistance:
Each test tire was assembled on a wheel having a rim size of 14 × 4.5 J, filled with an air pressure of 230 kPa, and rolling resistance was measured using a drum testing machine having a drum diameter of 2000.0 mm in accordance with ISO regulations. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. It means that rolling resistance is so small that this index value is large.

Steering stability on dry roads:
Each test tire is assembled on a wheel with a rim size of 14 x 4.5 J and mounted on a light vehicle. The air pressure after warm-up (F / R) is 240 kPa / 240 kPa, and the steering performance from low speed to high speed on dry roads Sensory evaluation with a test driver was performed for stability. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the steering stability performance on the dry road surface.

Braking performance on wet surfaces:
Each test tire is mounted on a wheel with a rim size of 14 x 4.5 J and mounted on a mini vehicle. A distance measurement was performed. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. The larger the index value, the better the braking performance on the wet road surface.

  As can be seen from Table 1, a rib-shaped center land portion having a plurality of sipes extending in the tire width direction is arranged on the inner side in the tire width direction from the outermost main groove, and a hole portion and a cavity portion are provided in the sipe. By providing the tires of Examples 1 to 6, the rolling resistance and the steering stability performance on the dry road surface were simultaneously improved while maintaining the braking performance on the wet road surface.

  On the other hand, in Comparative Example 1, since the lug groove was provided in the center land portion, the improvement effect of the steering stability performance on the dry road surface could not be obtained. In Comparative Examples 2 and 3, the sipe was not provided with a cavity and a hole, respectively, so that the drainage and water absorption of the sipe were insufficient, and the braking performance on the wet road surface was deteriorated.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 10 Land part 11 Main groove 11A Inner main groove 11B Outermost main groove 20 Center land part 21,31 Sipe 30 Shoulder land part

Claims (6)

In a pneumatic tire provided with a plurality of main grooves extending in the tire circumferential direction in the tread portion, and a plurality of rows of land portions are partitioned by the plurality of main grooves,
The main groove includes a pair of outermost main grooves positioned on the outermost side in the tire width direction, and the land portion includes a center land portion that is located on the inner side in the tire width direction than the outermost main groove and forms a rib shape. The center land portion has a plurality of sipes extending in the tire width direction, and at least one hole extending in the tire radial direction and wider than the sipes is attached to a part of the longitudinal direction of the sipes. A pneumatic tire characterized in that a hollow portion extending in the tire width direction and wider than the sipe is attached to the bottom portion of the sipe, and the hollow portion is connected to the hole portion.   The pneumatic tire according to claim 1, wherein a groove depth of the main groove is 5.0 mm or more and 6.0 mm or less.   3. The air according to claim 1, wherein a maximum width WVh in the tire circumferential direction of the hole located in the center land portion is not less than 2 times and not more than 5 times the sipe width Ws of the sipe. Enter tire.   The maximum width WLh in the tire width direction of the hole located in the center land portion is 2 to 5 times as large as the sipe width Ws of the sipe. The described pneumatic tire.   5. The maximum width Wp in the tire circumferential direction of the hollow portion located in the center land portion is 2 to 4 times as large as the sipe width Ws of the sipe. The described pneumatic tire.   The maximum width Dp in the tire radial direction of the hollow portion located in the center land portion is 0.2 to 0.5 times the sipe depth Ds of the sipe. The pneumatic tire according to any one of 5.

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