JP2006103522A - Pneumatic tire for icy road - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for an icy road making a draining property on a wet road surface and a braking property on an icy road compatible at high level. <P>SOLUTION: In the tire, a plurality of lateral grooves 2 extending in a tire width direction, and a plurality of vertical grooves 3 extending so as to intersect the lateral grooves 2 are arranged on a tread portion 1. At least one line of block land part lines 5a to 5b made from a large number of block land parts 4 is partitioned thereby. In each block land part 4, a plurality of sipes 6 extending in the tire widthwise direction are arranged. In at least one block land part lines 5b, 5c, sipe density obtained by dividing the total sum of the sipe width w<SB>1</SB>arranged in the same block land part 4 by a tire circumferential length l of the block land part 4 is in a range of 0.08 to 0.15. A lateral groove 2 width ratio obtained by dividing the groove width w<SB>2</SB>of the lateral grooves 2 by the tire circumferential length l of the block land part 4 is in a range of 0.10 to 0.20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, a plurality of horizontal grooves extending in the tire width direction and a plurality of vertical grooves extending across the horizontal grooves are disposed in the tread portion, so that at least one row of a plurality of block land portions is provided. The present invention relates to a pneumatic tire for icy and snowy roads, in particular, a studless tire, in which a block land portion row is partitioned and a plurality of sipes extending in the tire width direction are disposed on the block land portion. Both braking performance on tires on snowy and snowy road surfaces and drainage on wet road surfaces are made compatible at a high level.

  As shown in FIG. 5, in the pneumatic tire for snowy and snowy roads, a plurality of horizontal grooves 102 extending in the tire width direction and a plurality of vertical grooves 103 extending so as to intersect these horizontal grooves are disposed in the tread portion 101. In general, a plurality of block land portions 104 are partitioned and a plurality of width direction sipes 105 are provided in the block. In order to improve the braking performance on ice of such a tire, the edge effect is increased by increasing the number of sipes disposed, or the friction coefficient is increased by increasing the contact area. However, if there are too many sipes, uneven wear of the block land portion is likely to occur, and the edge effect may not be sufficiently exhibited due to a decrease in block rigidity, which may reduce the braking performance on ice. . Increasing the ground contact area improves braking performance on ice, but these tires may run on wet roads as well as snowy and snowy roads. There is a problem of being damaged. That is, braking performance on icy and snowy road surfaces and drainage performance on wet road surfaces are in a trade-off relationship, and it has been considered difficult to realize a tire that achieves both of these performances. However, in view of today's road conditions, there are many opportunities to run on general dry road surfaces and wet road surfaces even for icy and snowy road pneumatic tires, and tires that satisfy both of these performances have been demanded.

  In order to achieve both such braking performance and drainage performance, for example, in Patent Document 1, the longitudinal grooves are formed in a zigzag shape, and the lateral grooves extend in opposite directions from the ends of both treads toward the tire equatorial plane. There is described a tire having a directional tread pattern which is an inclined groove and has a contour shape of a block land portion to be partitioned as a polygonal shape of a pentagon or more. In such a tire, the drainage is improved by inclining the lateral groove to impart directionality, and the braking performance is improved by providing the block land portion with a polygonal shape and imparting edge components in various directions to each block. However, since such a tire has a directional tread pattern, it cannot be rotated so as to change the rotation direction of the tire, and is particularly resistant to uneven wear in light truck tires that are prone to uneven wear. There was a problem of being inferior.

JP 2001-191739 A

  Accordingly, an object of the present invention is to provide a pneumatic tire for icy and snowy roads that achieves a high level of drainage on wet roads and braking performance on icy and snowy roads.

  In order to achieve the above object, the present invention provides a plurality of blocks by disposing a plurality of transverse grooves extending in the tire width direction and a plurality of longitudinal grooves extending across the transverse grooves in the tread portion. In a pneumatic tire for snowy and snowy roads, in which at least one block land portion row composed of land portions is defined and a plurality of sipes extending in the tire width direction are disposed on the block land portion. In this block land portion row, a value obtained by dividing the sum of the sipe widths of sipes arranged in the same block land portion by the tire circumferential direction length of the block land portion (hereinafter referred to as “sipe density”) is 0.08. The value obtained by dividing the width of the lateral groove by the tire circumferential direction length of the block land portion (hereinafter referred to as “lateral groove width ratio”) is in the range of 0.10 to 0.20. Pneumatic tire characterized by A.

  Here, the sipe width is a tire rim assembled on a standard or design rim, such as JATMA, TRA, ETRTO, etc., which is effective in the area where the tire is manufactured, sold, or used, and which is effective in the region. Measurement shall be performed with no load filled with 100% internal pressure defined in the air pressure to load capacity correspondence table defined in standards, standards, etc., and in a state where no foreign matter is caught in the sipe.

  The sipe is preferably a zigzag sipe extending in the tire width direction while being bent in a zigzag shape at least on the land surface, and the sipe width is preferably in the range of 0.4 to 0.7 mm.

  Furthermore, it is preferable that the sipe disposed at least adjacent to the lateral groove has at least one bent portion in the cut depth direction. Here, the “bending portion” refers to a portion where the extending direction of the sipe greatly changes with respect to the cutting depth direction.

  Furthermore, 4 to 8 sipes are arranged in the same block land portion, the negative rate is in the range of 27 to 35%, and the rubber hardness at 0 ° C. of the rubber constituting the tread portion is 45. It is preferable that it exists in the range of -55, and the rubber which comprises a tread part is foamed rubber. In addition, "rubber hardness" here means the rubber hardness obtained by the spring type hardness tester A type specified in JIS K 6253.

  According to the present invention, it is possible to provide a pneumatic tire for icy and snowy roads that achieves a high level of drainage performance on wet road surfaces and braking performance on icy and snowy road surfaces.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a development view of a part of a tread portion of a typical pneumatic tire for snowy road (hereinafter referred to as “tire”) according to the present invention, and FIG. 2 (a) is a block diagram of the tire shown in FIG. FIG. 2B is an enlarged view of a land portion, and FIG. 2B shows a state in which snow is caught in a sipe disposed in the block land portion of FIG. In the tire, a plurality of lateral grooves 2 extending in the tire width direction and a plurality of (three in FIG. 1) longitudinal grooves 3 extending so as to intersect the lateral grooves 2 are disposed in the tread portion 1. Block land portion rows 5a to 5b of at least one row (four rows in FIG. 1) composed of the individual block land portions 4 are partitioned. Each block land portion 4 is provided with a plurality of sipes 6 extending in the tire width direction, as shown in FIG.

The main structural features of the present invention are that at least one block land portion row, in FIG. 1, two block land portion rows 5b and 5c, are arranged in the same block land portion 4. The sipe density obtained by dividing the sum of the sipe widths w ₁ of 6 by the tire circumferential direction length l of the block land portion 4 is in the range of 0.08 to 0.15, and the groove width w ₂ of the lateral groove _{2 is changed} to the block land portion 4 The transverse groove width ratio divided by the tire circumferential direction length 1 is in the range of 0.10 to 0.20.

  As described above, from the viewpoint of improving the braking performance on the icy and snowy road surface, it is preferable to increase the negative ratio of the tread part tread to increase the ground contact area, while from the viewpoint of improving the drainage performance on the wet road surface, the tread part tread. It is preferable to reduce the negative rate of the road to reduce the ground contact area, and the required ground contact areas are completely different on both road surfaces. The inventor believes that the actual icy and snowy road surface is mainly the snowy road surface, and occasionally the icy road surface appears, so that when driving on the icy road surface where the friction coefficient between the road surface and the tire is the smallest, the snow bites into the sipe. If it is possible to change the apparent ground contact area between the icy and snowy road surfaces by using this phenomenon, the icy and snowy road surface that was previously considered difficult to achieve at the same time I got the idea that both the braking performance and the drainage performance on wet roads can be achieved at a high level. When the inventor conducted extensive research based on this idea, if the ratio of the sum of the sipe widths of the sipe disposed in the block land portion and the tire circumferential direction length of the block land portion is optimized, FIG. As shown in (2), it was found that the sipe 6 was expanded by the snow biting into the sipe 6 and the block land portion 4 was extended in the tire circumferential direction, resulting in an increase in the apparent ground contact area. However, simply increasing the sum of the sipe widths reduces the rigidity of the block land portion, and the block land portion tends to deform during braking, which may offset the effect of increasing the apparent ground contact area. . Therefore, the inventor conducted further research and optimized the ratio between the groove width of the lateral groove and the tire circumferential length of the block land portion to bite snow into the sipe, and the block land portion extended in the tire circumferential direction. In this case, as shown in FIG. 3, the width of the lateral groove 2 is narrowed, and the block land portion rows 5b and 5c become rib-like land portion rows. As a result of the substantially equal intervals between the edges, substantially equal contact pressure is applied to all edges, so that it is possible to effectively prevent local block land deformation due to large contact pressure being applied only to some edges. I found out that I can do it.

  Here, when the sipe density is in the range of 0.08 to 0.15, when this is less than 0.08, the rigidity of the block land portion is too high, and it is difficult for snow to bite into the sipe. This is because the sipe cannot be sufficiently expanded even if it is bitten, and if it exceeds 0.15, the rigidity of the block land portion will be too low, and the block land portion will be easily deformed during braking, which makes the apparent ground contact area This is because the increased effect is offset. Moreover, the reason why the lateral groove width ratio is set to the range of 0.10 to 0.20 is that when this is less than 0.10, the drainage on the wet road surface is deteriorated, and when it exceeds 0.20. This is because the groove width of the lateral groove is too large for the extension of the block land portion in the tire circumferential direction when snow is bitten into the sipe, and the block land portion row does not have a rib shape. It is not necessary for the lateral groove to be completely closed when the sipe is expanded by snow, and the lateral groove may be open within a range in which deformation of the block land portion during braking can be suppressed.

  Thus, in the tire according to the present invention, even if the contact area of the tread surface is set to a value suitable for the wet road surface, the apparent contact area increases on the icy and snowy road surface. It is possible to satisfy both of the drainage properties at a high level. Also, when the road surface temperature is relatively high and the snow is present in a sherbet-like or water-like state, hydroplaning occurs due to the poor drainage performance of conventional tires with a high contact area. However, in the tire according to the present invention, the sherbet-like or water-film-like snow is easily discharged from the sipe, so that the apparent ground contact area does not increase and the width of the lateral groove also narrows. Therefore, high drainage can be ensured.

  The snow caught in the sipe 6 is discharged from the sipe 6 by centrifugal force when the tire rolls. If there are many snow road surfaces, even if the snow is discharged, it will not be a problem because new snow will be caught in the sipe 6 when the block land portion comes in contact with the road surface next time. When the road surface increases, it is preferable that snow is held in the sipe 6 over a certain travel distance from the viewpoint of ensuring braking performance on the ice road surface. Specifically, it is preferable that the sipe 6 is a zigzag sipe that extends in the tire width direction while being bent in a zigzag shape at least on the land surface. This is because in such a zigzag sipe, the friction between the snow bitten by the bent portion and the sipe wall is large, so that the centrifugal force required for discharging the snow is larger than that of the straight sipe. Furthermore, the zigzag sipe has a large sipe wall area as compared with the straight sipe, and the snow is not easily discharged even when the snow caught in not only the tire circumferential direction but also the tire width direction is restrained.

Further, it is preferable that the sipe width _{w 1} is in the range of 0.4-0.7 mm. This is because if it is less than 0.4 mm, it may become difficult to bite snow into the sipe, and if it exceeds 0.7 mm, it will bite into the sipe due to the centrifugal force generated by the rolling of the tire. This is because snow is easily discharged and the apparent ground contact area may not increase. In addition, if the sipe width w ₁ is less than 0.4 mm, the durability of the blade provided in the molding mold to form the sipe may be insufficient, and manufacturing may be difficult. This is because the sipe is likely to open greatly on the dry road surface, and there is a concern that uneven wear will increase.

  FIG. 4 is a tire radial direction cross-sectional view of the block land portion. As shown in FIG. 4, at least the sipes 6a and 6e arranged adjacent to the lateral groove 2 preferably have at least one (two in FIG. 4) bent portions 7a and 7b in the cut depth direction. According to this, the rigidity of both ends of the block land portion 4 is reduced, and the block land portion 4 easily extends toward the lateral groove 2 when snow is bitten into the sipes 6a to 6e. The area increasing effect is enhanced.

  Moreover, it is preferable that the number of sipes arrange | positioned in the same block land part shall be 4-8. This is because if the number is less than three, the edge effect due to the sipe arrangement is insufficiently improved, and there is a possibility that the improvement in braking performance on an icy and snowy road surface may not be expected. This is because the rigidity is excessively reduced and the block land portion is easily deformed during braking, thereby canceling the effect of increasing the apparent ground contact area.

  Furthermore, the negative rate is preferably in the range of 27 to 35%. If this is less than 27%, there is a concern that the drainage performance on wet roads may be reduced. If it exceeds 35%, the ground contact area will be insufficient even after the apparent ground contact area has increased. This is because there is a risk that the amount becomes insufficient.

  Furthermore, the rubber hardness at 0 ° C. of the rubber constituting the tread portion 1 is preferably in the range of 45 to 55. By using rubber having such rubber hardness, it is possible to achieve high performance required for tires such as wear resistance, drivability and braking performance on dry road surfaces, wet road surfaces, and icy and snow road surfaces. Because it can. In particular, when rubber having too high rubber hardness is used, it is difficult to bite snow into the sipe, and there is a concern that the sipe cannot be sufficiently spread even if the snow is bitten.

  In addition, the rubber constituting the tread portion 1 is preferably foamed rubber. This is because the water film existing on the surface of the icy road surface is quickly absorbed into the foamed rubber bubbles, and as a result, the braking performance is further improved.

In addition, from the viewpoint of maximizing the effect of deforming the block land portion row 5 in a rib shape on the snowy and snowy road surface while ensuring drainage on the wet road surface, the groove width w2 of the lateral groove ₂ is 2 to 4 mm. It is a range, and it is preferable that the tire circumferential direction length l of the block land part 4 is the range of 15-35 mm.

  In addition, the place mentioned above only showed a part of embodiment of this invention, and can add a various change in a claim. For example, FIG. 1 shows a mode having a tread pattern composed of rectangular block land portions 4, but the tread pattern is not limited to this, and the shape of the block land portions is a rhombus and a parallelogram as in a normal studless tire. The shape may be a pentagon or more polygon, and the arrangement may be a so-called directional pattern. In addition, FIG. 1 shows a mode in which only the block land portion row 5 arranged adjacent to the tire equator plane E becomes a rib-like land portion when traveling on an icy and snowy road surface. Such a configuration may be adopted. However, from the viewpoint of ensuring drainage and enhancing the braking performance on ice, it is particularly preferable that the block land portion row in the central area of the tread becomes a rib-like land portion when traveling on an icy and snowy road surface as shown in FIG.

  Next, tires according to the present invention were prototyped and performance evaluations were performed, which will be described below.

  The tires of Examples 1 and 2 are vanless studless tires having a tire size of 195 / 80R15, and the tread portion is composed of foamed rubber having a rubber hardness of 50 at 0 ° C. Have yuan. Further, these tires have a tread pattern similar to that shown in FIG. 1 except that the number of sipes disposed in the same block land portion is six.

  For comparison, although the tire size and the rubber constituting the tread portion are the same as those in Examples 1 and 2, the tire has the specifications shown in Table 1 and has a negative rate equivalent to that of a conventional studless tire (conventional example). In addition, tires with comparatively low negative rates (Comparative Examples 1 and 2) were also manufactured. Further, the conventional tire has a tread pattern similar to that shown in FIG. 5 except that the number of sipes disposed in the same block land portion is four, and the tires of Comparative Examples 1 and 2 are The tread pattern is the same as that shown in FIG. 5 except that the number of sipes disposed in the same block land portion is five.

  Each of the test tires was attached to a rim of size 51 / 2JJ to form a tire wheel. The tire wheels were mounted on a test vehicle, and the following tests were performed by applying air pressure: 300 kPa (relative pressure) to the front wheels and air pressure: 400 kPa (relative pressure) to the rear wheels.

(Ice road surface braking test)
The tire load is set to 5.1kN for the front wheel and 3.6kN for the rear wheel. After sufficiently running on the snowy road surface and having the snow squeezed into the sipe, from the running state of 30km / h on the icy road surface. Sudden braking was performed without using an ABS device, and the braking distance until the vehicle was stationary was measured. This test was repeated 5 times for each test tire, and the braking performance was evaluated with an average value of 5 times. The evaluation results are shown in Table 1. In addition, this evaluation result represents the reciprocal number of the average value of braking distance by the index ratio when the conventional example is set to 100, and the performance is excellent, so that a numerical value is large.

(Wet road drainage test)
The tire load was set to 5.1 kN for the front wheels and 3.6 kN for the rear wheels. The test course with a water depth of 5 mm was accelerated until the hydroplaning phenomenon occurred, and drainage was evaluated at the speed at which the hydroplaning phenomenon occurred. The evaluation results are shown in Table 1. This evaluation result is expressed as an index ratio when the conventional example is set to 100, and the larger the value, the better the performance.

  From the evaluation results shown in Table 1, although the tires of Examples 1 and 2 are inferior in drainage compared with the tires of the conventional examples, the braking performance is significantly superior, and the tires of Comparative Example 1 having the same negative rate Compared with the tire of Comparative Example 2, the drainage performance is improved, and the braking performance is improved. Compared with the tire of Comparative Example 2, the braking performance is equivalent, but the drainage performance is greatly improved. It turns out that all are excellent in overall performance.

  As is apparent from the above description, according to the present invention, it is possible to provide a pneumatic tire for snowy and snowy roads that achieves a high level of drainage on wet road surfaces and braking performance on snowy and snowy road surfaces.

1 is a development view of a part of a tread portion of a typical tire for a snowy road according to the present invention. (A) is an enlarged view of the block land portion of the tire shown in FIG. 1, and (b) shows a state in which snow is caught in a sipe disposed in the block land portion of (a). Fig. 2 shows a state in which snow is caught in the sipe of the tire shown in Fig. 1. It is tire radial direction sectional drawing of a block land part. FIG. 3 is a development view of a part of a tread portion of a tire of a conventional example and Comparative Examples 1 and 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Horizontal groove 3 Vertical groove 4 Block land part 5, 5a, 5b, 5c, 5d Block land part row | line | column 6, 6a, 6b, 6c, 6d, 6e Sipe 7a, 7b Bending part

Claims (8)

By arranging a plurality of horizontal grooves extending in the tire width direction and a plurality of vertical grooves extending so as to intersect the horizontal grooves in the tread portion, at least one block land portion row composed of a plurality of block land portions is provided. In the pneumatic tire for snowy and snowy roads formed by arranging a plurality of sipes extending in the tire width direction on the block land portion,
The value obtained by dividing the sum of the sipe widths of the sipes disposed in the same block land portion by the tire circumferential direction length of the block land portion in at least one block land portion row is in the range of 0.08 to 0.15. A pneumatic tire having a value obtained by dividing the groove width of the lateral groove by the tire circumferential direction length of the block land portion is in a range of 0.10 to 0.20.   2. The pneumatic tire according to claim 1, wherein the sipe is a zigzag sipe extending in a tire width direction while being bent in a zigzag shape at least on a surface of a land portion.   The pneumatic tire according to claim 1 or 2, wherein the sipe has a sipe width in a range of 0.4 to 0.7 mm.   The pneumatic tire according to any one of claims 1 to 3, wherein the sipe disposed at least adjacent to the lateral groove has at least one bent portion in a cutting depth direction.   The pneumatic tire according to any one of claims 1 to 4, wherein 4 to 8 sipes are disposed in the same block land portion.   The pneumatic tire according to any one of claims 1 to 5, wherein a negative rate is in a range of 27 to 35%.   The pneumatic tire according to any one of claims 1 to 6, wherein rubber constituting the tread portion has a rubber hardness at 0 ° C in a range of 45 to 55.   The pneumatic tire according to any one of claims 1 to 7, wherein the rubber constituting the tread portion is foamed rubber.

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