JP5375377B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly, to improve the braking performance on ice in a tire having a sipe formed on a tread surface, and to secure a volume of incision in the late stage of wear after having finished its role as a winter tire. It is related with the pneumatic tire which improved wet performance by doing.

  In general, in order to improve running performance on wet road surfaces and icy and snowy road surfaces, it is widely performed to improve water absorption by providing sipes on the tread surface. However, if too many sipes are arranged on the tread surface, the tread rigidity is lowered and the steering stability and braking performance are deteriorated. Therefore, many proposals have conventionally been made regarding the form of the sipes and their arrangement ( For example, see Patent Documents 1 and 2).

  Among the proposals described above, Patent Document 1 improves on-ice stability while preventing sipe cracking failure and chunk-out failure by crossing two or more sipes extending in different directions on the block surface. Propose to let you. Further, Patent Document 2 proposes to improve riding comfort while ensuring steering stability and wet braking performance by forming a sipe with a torsion around a torsion shaft extending in the tire radial direction. doing.

  However, in Patent Document 1, although the water absorption of the tread surface can be improved to some extent, if the number of sipes is further increased to increase the water absorption, there is a limit that it is difficult to maintain steering stability due to a decrease in tread rigidity. . Further, in Patent Document 2, since the torsion angle is set to a size exceeding 135 °, the releasability from the mold after tire molding vulcanization is deteriorated, and the tread surface is likely to be damaged. There is.

  In addition, a studless tire having a sipe provided on the tread surface may be used as a summer tire after the wear has progressed and has finished its role as a winter tire. In general, the tread rubber for studless tires uses softer rubber than the tread rubber for summer tires, so after running as a winter tire, the running performance as a summer tire is ensured. There is a problem that you can not. Therefore, in these studless tires, how to ensure the running performance as a summer tire is an important issue in the late stage of wear after completing the role as a winter tire.

JP-A-9-263111 JP 2006-27306 A

  The object of the present invention is to improve the braking performance on ice in a tire having a sipe formed on the tread surface, and to ensure the volume of the notch in the late stage of wear after finishing the role as a winter tire, thereby improving the wet performance. An object of the present invention is to provide a pneumatic tire that is improved.

The pneumatic tire of the present invention for achieving the above object comprises two inventions, and the first invention (hereinafter referred to as the first invention) is a land formed on the tread surface as described in claim 1. A closed sipe in which at least three cuts extending in a radial direction with respect to a virtual axis extending in the depth direction of the land portion and terminating in the land portion are disposed, and the virtual axis is provided in the cut of the closed sipe In a pneumatic tire in which a spiral twist is applied in a depth direction centered on the center, a twist angle from the surface of the land portion to the bottom surface of the incision is set to 10 ° or more and less than 135 ° In addition, the length of the cut in the radial direction is formed to be shorter on the tread surface side in the depth direction of the closed sipe than on the bottom surface side , and the radial length L2 on the bottom surface of the cut and the tread The relationship with the length L1 in the radial direction on the plane is 1.2 ≦ L2 / L1 ≦ 2.0 .

  Further, in the above-described configuration, the width of the notch is formed so as to be narrower than the bottom surface side on the tread surface side in the depth direction of the closed sipe, or formed so as to be wider than the bottom surface side on the tread surface side. Good.

According to a second aspect of the present invention (hereinafter referred to as a second aspect), the land portion formed on the tread surface is radial with respect to a virtual axis extending in the depth direction of the land portion. A closed sipe having at least three incisions extending in the land and terminating in the land, and a spiral twist is applied to the incision of the closed sipe toward a depth direction centering on the virtual axis. In the pneumatic tire, a torsion angle from the surface of the land portion to the bottom surface of the incision is set to 10 ° or more and less than 135 °, and the width of the incision is set on the tread surface side in the depth direction of the closed sipe. It is formed so as to be narrower than the bottom surface side, and the relationship between the width W2 at the bottom surface of the notch and the width W1 at the tread surface is 0.2 ≦ W1 / W2 ≦ 0.7 .

  Further, in the above-described configuration, the length of the cut in the radial direction may be formed so as to be longer on the tread surface side in the depth direction of the closed sipe than on the bottom surface side.

  Moreover, in the 1st invention and the 2nd invention, it is preferable to comprise as described in the following (1)-(3).

(1) The number of the cuts is 3 to 6.

(2) The end of the notch on the virtual axis side is connected to the virtual axis or is not continuous. In the former case, a small hole may be formed along the virtual axis in the depth direction of the closed sipe.

(3) A linear sipe extending in the tire width direction together with the closed sipe is provided on the land portion. In this case, when the land portion is a block, the closed sipes may be arranged along the tire width direction at the front end portion and / or the rear end portion in the tire circumferential direction of the block.

  According to the above-described present invention, the land portion formed on the tread surface is provided with the closed sipes in which at least three cuts extending in the radial direction with respect to the virtual axis extending in the depth direction and terminating in the land portion are arranged. A spiral twist was given to the incision in the depth direction centered on the virtual axis, and the twist angle was set to 10 ° or more and less than 135 °, so that there was no hindrance to mold release from the mold. In addition, while suppressing a decrease in the tread rigidity, the water absorption performance can be improved by increasing the volume accompanying the twisting of the cut, and the braking performance on ice can be improved.

Further, in the first invention, the radial length of the cut is formed so as to be shorter on the tread surface side in the depth direction of the closed sipe than on the bottom surface side, and the radial length L2 and the tread on the bottom surface of the cut. The relationship with the radial length L1 of the surface is 1.2 ≦ L2 / L1 ≦ 2.0. In the second aspect of the invention, the width of the cut is the bottom side on the tread surface side in the depth direction of the closed sipe. And the relationship between the width W2 on the bottom surface of the cut and the width W1 on the tread surface is 0.2 ≦ W1 / W2 ≦ 0.7 . while favorably ensuring the releasability from the mold, since the volume cut with the progress of the wear is increased gradually, the wear late after finishing the role as winter tires, improve the wet performance Door can be.

It is explanatory drawing which shows an example of the closed sipe by 1st invention formed in the tread surface of the pneumatic tire of this invention, (a) is the top view, (b) is a perspective view which shows the outer wall shape. It is explanatory drawing which shows an example of the closed sipe by 2nd invention formed in the tread surface of the pneumatic tire of this invention, (a) is the top view, (b) is a perspective view which shows the outer wall shape. (A) And (b) is a top view which shows an example of the closed sipe by other embodiment of this invention, respectively. It is a top view which shows an example of the closed sipe by other embodiment of this invention. It is a top view which shows a part of tread surface of the pneumatic tire by embodiment of this invention. It is a top view which shows a part of tread surface of the pneumatic tire by other embodiment of this invention. It is a top view which shows a part of tread surface of the pneumatic tire employ | adopted in the Example.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 (a) is a plan view showing an example of a closed sipe formed on the tread surface of the pneumatic tire of the present invention according to the first invention in a square frame, and FIG. 1 (b) is a closed view of FIG. 1 (a). It is a perspective view which shows the outer wall shape of a sipe.

  In FIG. 1A, the land portion 3 formed on the tread surface 1 of the pneumatic tire of the present invention has a land portion extending radially and centering on a virtual axis 2 extending in the depth direction of the land portion 3. A closed sipe 5 consisting of at least three (four in the figure) incisions 4 terminating in 3 is formed. In the closed sipe 5 of the present invention, each notch 4 is provided with a helical twist (see FIG. 1 (b)) in the depth direction around the virtual axis 2, and from the surface of the land portion 3. The torsion angle θ up to the bottom surface is set to 10 ° or more and less than 135 °, preferably 90 to 120 °. The dotted line in the figure indicates the bottom surface of the cut 4.

  As a result, the water absorption performance is enhanced by the increase in the volume associated with the twist of the notch 4 and the braking performance on ice is improved while preventing a decrease in the tread rigidity without hindering the releasability from the mold. be able to.

  Furthermore, in the closed sipe 5 according to the first invention shown in FIGS. 1A and 1B, the radial length of the cut 4 is shorter on the tread surface 1 side in the depth direction of the closed sipe 5 than on the bottom surface side. It is formed as follows. As a result, the cutting volume gradually increases as the wear progresses, so that the wet performance can be improved in the late stage of wear after having finished its role as a winter tire.

  The torsion angle θ from the surface of the land portion 3 to the bottom surface of the notch 4 described above refers to the torsion angle from the upper edge of the notch 4 to the lower edge of the tread surface 1 side. The same applies to the second invention.

The change in the radial length of the notch 4 described above may be formed so as to increase gradually or stepwise from the tread surface 1 side toward the bottom surface side. Here, the radial lengths of the cuts 4 at the tread surface 1 and the bottom surface of the closed sipe 5 are appropriately set according to the required performance of the tire . In the first invention described above, the tire after vulcanization is used. From the viewpoint of securing the releasability from the mold, the relationship between the radial length L2 on the bottom surface of the notch 4 and the radial length L1 on the tread surface 1 is 1.2 ≦ L2 / L1 ≦ 2. Adjustment is made to be zero .

  Furthermore, in the first invention described above, the width of the cut 4 can be changed with respect to the depth direction of the closed sipe 5. Here, when the width of the cut 4 is made narrower on the tread surface 1 side than on the bottom surface side, the cut volume increases with the progress of wear, so that the water absorption effect in the later stage of wear increases. Therefore, it is preferably applied to tires that place importance on wet performance.

  On the other hand, when the width of the incision 4 is wider on the tread surface 1 side than on the bottom surface side, the incision volume can be adjusted according to the progress of wear. It is preferably applied to tires that place an emphasis on balance.

  2 (a) and 2 (b) show the form of the closed sipe 5 according to the second invention. In the closed sipe 5 according to the second invention, the width of the notch 4 is set to the tread in the depth direction of the closed sipe 5. The surface 1 side is formed to be narrower than the bottom surface side. As a result, like the closed sipe 5 according to the first invention described above, the cutting volume gradually increases with the progress of wear, so that the wet performance is improved in the late stage of wear after having finished its role as a winter tire. Can do.

Here, the change in the width of the notch 4 is preferably formed so as to increase gradually or stepwise from the tread surface 1 side toward the bottom surface side. The widths of the cuts 4 at the tread surface 1 and the bottom surface of the closed sipe 5 are appropriately set according to the required performance of the tire . In the second invention described above , the release from the mold of the tire after vulcanization is performed. From the viewpoint of ensuring a good balance between the wettability and the late wear performance, the relationship between the width W2 of the bottom surface of the notch 4 and the width W1 of the tread surface 1 is adjusted to satisfy 0.2 ≦ W1 / W2 ≦ 0.7. It is .

  In the second invention described above, the length of the cut 4 in the radial direction can be formed to be longer on the tread surface 1 side in the depth direction of the closed sipe 5 than on the bottom surface side. In this case, it is necessary to devise in order to ensure releasability from the mold, but since it becomes possible to adjust the cut volume according to the progress of wear, the wet performance and steering stability in the late wear stage It is preferably applied to tires that place an emphasis on balance.

  In the pneumatic tire of the present invention configured as described above, the closed sipe 5 is formed by at least three notches 4 provided with a twist around the virtual axis 2 extending in the depth direction of the land portion 4. When the tire after vulcanization is removed from the mold, the tread surface 1 is easily damaged by the forming blade of the cut 4. From this point of view, the inner surface of the mold for vulcanizing and molding the pneumatic tire of the present invention is provided with a molding blade of a notch 4 that is rotatable about the virtual axis 2 and is vulcanized by this mold. It is good to do.

  In the above-described embodiment, the case where the number of the cuts 4 constituting the closed sipe 5 is four is shown, but the number of the cuts 4 constituting the closed sipe 5 in the present invention is not limited to this, and the tread is not limited thereto. It is good to comprise within the range of 3-6 according to the form of a pattern. If the number of the cuts 4 is 7 or more, cracks are likely to occur on the tread surface 1 during tire travel.

  Further, in the above-described embodiment, the case where the end portion of the cut 4 on the virtual axis 2 side is connected to the virtual axis 2 is illustrated, but the pneumatic tire of the present invention is illustrated in FIG. In addition, the end 4a on the virtual axis 2 side of the notch 4 constituting the closed sipe 5 may be discontinuously arranged with respect to the virtual axis 2 in some cases. The effect in this case is not different from the case according to the above-described embodiment.

  In the present invention, when the ends of the cuts 4 on the virtual axis 2 side are connected to the virtual axis 2 respectively, they are closed along the virtual axis 2 as illustrated in FIGS. 3 (a) and 3 (b). The small hole 9 can be formed toward the depth direction of the sipe 5. As a result, the water absorption on the icy road surface is further increased, and the braking performance during traveling on the icy road surface can be further improved.

  The size and cross-sectional shape of the small hole 9 formed along the virtual axis 2 are not particularly limited, and may be substantially circular or polygonal as illustrated in FIG. ), It may be formed into a star shape corresponding to the number of cuts 4 according to the number of cuts 4 constituting the closed sipes 5.

  In the above-described embodiment, the case where the cuts 4 constituting the closed sipes 5 are linearly extended in the radial direction has been described. However, the planar form of the cuts 4 in the present invention is not limited to this, and a curved line is used. It can be formed in an (arc) shape, a wave shape or a zigzag shape.

  In the pneumatic tire of the present invention, it is preferable that the above-described closed sipes 5 are dispersed and arranged over the entire land portion 3 formed on the tread surface 1. In this case, it is preferable to arrange the cuts 4 constituting the closed sipe 5 so as not to approach each other from the viewpoint of uniformly maintaining the rigidity distribution of the land portion 3 and suppressing uneven wear.

  Further, according to the required characteristics of the tire, as illustrated in FIGS. 5 and 6, a linear sipe 6 extending in the tire width direction together with the closed sipe 5 is combined with the land portion 3 formed on the tread surface 1. Can be arranged. Thereby, steering stability and on-ice braking performance can be achieved at a high level by increasing the edge effect accompanying the arrangement of the linear sipes 6.

  In the embodiment of FIG. 5, a plurality of closed sipes 5 arranged in parallel on the surface of the rib 7 formed on the tread surface 1 and a linear sipe 6 extending zigzag in the tire width direction are arranged in the tire circumferential direction T. However, the shape of the linear sipes 6 and the arrangement thereof are not limited to this, and can be appropriately changed according to the shape of the tread pattern. Examples of the form of the linear sipe 6 include a substantially linear or wavy shape and a three-dimensional shape.

  Further, as illustrated in FIG. 6, when the land portion 3 formed on the tread surface 1 is a block 8, the block 8 is partitioned by a linear sipe 6 extending in the tire width direction, and then the closed sipe 5. May be arranged along the tire width direction of the front end portion and / or the rear end portion (front end portion and rear end portion in the drawing) of the block 8 in the tire circumferential direction corresponding to the kicking side and / or the stepping side of the tire.

  In particular, the linear sipes 6 extending in the tire width direction as much as possible are not formed in the region at the front end portion and / or the rear end portion corresponding to approximately 30% or less of the tire circumferential direction length of the block 8, and The closed sipes 5 may be arranged along the tire width direction. This ensures block rigidity at the front end and / or rear end of the block 8, improves steering stability while suppressing the occurrence of uneven wear, and increases water absorption to improve braking performance on ice. Can do.

As described above, the pneumatic tire according to the present invention has at least three land portions formed on the tread surface extending in the radial direction around the virtual axis extending in the depth direction of the land portion and terminating in the land portion. Provide a closed sipe consisting of cuts, and give these cuts a helical twist in the depth direction centered on the virtual axis, and set the twist angle to 10 ° or more and less than 135 °, and then the radial direction of the cut Late wear after finishing the role as a winter tire while improving the braking performance on ice as a winter tire by making the length or cut width of the tire smaller at a predetermined rate on the tread surface side than the bottom surface side In order to improve the wet performance by securing a cutting volume, it has a simple structure and has excellent effects. It can be widely applied to studless tires.

  The tire size is 195 / 65R15 91Q, the tire pattern is FIG. 7, the plane form on the tread surface of the closed sipe 5 provided on the land portion is FIG. 1 (a), and the radial lengths on the tread surface and the bottom surface of the closed sipe 5 The tires of the present invention (Examples 1 to 4) and comparative tires (Comparative Examples 1 and 2) in which the cutting width and the twisting angle of the cutting were made different as shown in Table 1 were produced. In each tire, the depth of the closed sipes 5 was 7 mm.

  For these six types of tires, evaluation of releasability when the vulcanized tire is taken out from the mold is performed, and on the test method described below, evaluation of braking performance on ice at the time of a new article and wet performance in the later stage of wear Was evaluated.

  In addition, regarding the releasability from the mold of the tire after vulcanization, in Table 1, “O” indicates that the tread surface was not damaged, and “X” indicates that the tread surface was damaged. Displayed. Then, the evaluation of braking performance on ice at the time of new article and the evaluation of wet performance at the late stage of wear were carried out excluding those in which the tread surface was damaged.

  The evaluation of the wet performance in the latter stage of wear described above is carried out in advance until the remaining groove depth of the main groove (maximum depth: 8.9 mm) formed on the tread surface becomes 40% of the depth when new. It was abraded and evaluated at that time.

[Evaluation of braking performance on ice when new]
Each tire is assembled in a rim of size 15 x 6 JJ, filled with air pressure of 230 kPa and mounted on the front and rear wheels of a domestic passenger car with a displacement of 2000 cc, and then a braking test is performed from the initial speed of 40 km / h on the ice surface. The braking performance on ice was evaluated by the reciprocal of the stopping distance. The results are also shown in Table 1 using an index with Comparative Example 1 as 100. The larger the value, the better the braking performance on ice.

[Evaluation of wet performance in late wear]
Each tire is installed in a rim of size 15 x 6 JJ, filled with air pressure of 230 kPa and mounted on the front and rear wheels of a domestic passenger car with a displacement of 2000 cc. From an initial speed of 100 km / h on an asphalt road surface with an average water depth of about 1.5 mm The wet performance was evaluated using the reciprocal of the braking stop distance. The results are also shown in Table 1 using an index with Comparative Example 1 as 100. Larger values indicate better wet performance.

  From Table 1, it can be seen that the tire according to the present invention improves the wet performance in the late stage of wear while substantially maintaining the braking performance on ice at the time of a new article as compared with Comparative Example 1. In Comparative Example 2 in which the twist angle of cutting was set to 140 °, it was confirmed that the releasability from the mold deteriorates.

1 Tread surface 2 Virtual axis 3 Land 4 Cut 5 Closed sipe 6 Linear sipe 7 Rib 8 Block 9 Small hole θ Torsion angle

Claims (11)

The land portion formed on the tread surface is provided with a closed sipe in which at least three cuts extending in a radial direction with respect to a virtual axis extending in the depth direction of the land portion and terminating in the land portion are disposed. In a pneumatic tire in which a spiral twist is given to the incision in the depth direction around the virtual axis,
The torsion angle from the surface of the land portion to the bottom surface of the cut is made 10 ° or more and less than 135 °, and the radial length of the cut is the bottom surface on the tread surface side in the depth direction of the closed sipe. The length L2 in the radial direction at the bottom surface of the notch and the length L1 in the radial direction at the tread surface are 1.2 ≦ L2 / L1 ≦ 2.0. pneumatic tire.   2. The pneumatic tire according to claim 1, wherein a width of the notch is formed to be narrower on a tread surface side in a depth direction of the closed sipe than on a bottom surface side.   The pneumatic tire according to claim 1, wherein a width of the cut is formed so as to be wider on a tread surface side in a depth direction of the closed sipe than on a bottom surface side. The land portion formed on the tread surface is provided with a closed sipe in which at least three cuts extending in a radial direction with respect to a virtual axis extending in the depth direction of the land portion and terminating in the land portion are disposed. In a pneumatic tire in which a spiral twist is given to the incision in the depth direction around the virtual axis,
The torsion angle from the surface of the land portion to the bottom surface of the cut is set to 10 ° or more and less than 135 °, and the width of the cut is narrower on the tread surface side in the depth direction of the closed sipe than the bottom surface side. A pneumatic tire formed so that the relationship between the width W2 at the bottom surface of the cut and the width W1 at the tread surface is 0.2 ≦ W1 / W2 ≦ 0.7 .   The pneumatic tire according to claim 4, wherein the radial length of the cut is formed to be longer on the tread surface side in the depth direction of the closed sipe than on the bottom surface side.   The pneumatic tire according to any one of claims 1 to 5, wherein the number of the cuts is 3 to 6.   The pneumatic tire according to any one of claims 1 to 6, wherein an end of the notch on the virtual axis side is connected to the virtual axis.   The pneumatic tire according to claim 7, wherein a small hole is formed in the depth direction of the closed sipe along the virtual axis.   The pneumatic tire according to any one of claims 1 to 6, wherein an end of the notch on the virtual axis side is discontinuous with respect to the virtual axis.   The pneumatic tire according to any one of claims 1 to 9, wherein a linear sipe extending in the tire width direction together with the closed sipe is provided in the land portion.   The pneumatic tire according to claim 10, wherein the land portion is a block, and the closed sipes are arranged along a tire width direction at a front end portion and / or a rear end portion in the tire circumferential direction of the block.

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