JP6017794B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire used in various vehicles including passenger cars. In particular, the present invention relates to a pneumatic tire that has improved fuel efficiency while maintaining steering stability.

  In recent years, the demand for lower fuel consumption of automobiles has been increasing, and there is a strong demand for reducing the rolling resistance of tires. In order to reduce rolling resistance, (1) Hysteresis loss of the rubber composition after vulcanization is reduced by compounding a large amount of silica, and (2) rigidity of the shoulder portion and sidewall portion of the tire is increased. Attempts have been made to set it appropriately small.

  On the other hand, in order to reduce pattern noise caused by the tread pattern, the pitch in the tire circumferential direction formed by the tread pattern block (island land portion) is also periodically changed. In Patent Document 1 below, in order to further reduce the noise in such a tire, “in the portion where the pitch of the tread pattern is relatively large, the hardness (or modulus) of the tread rubber layer is relatively lowered, and the tread It has been proposed that the hardness (or modulus) of the tread rubber layer is relatively high in a portion where the pitch of the pattern is relatively small (such as paragraph 0006). By doing so, “the tread rigidity can be made substantially uniform regardless of the size of the pitch”, so “vibration can be reduced”, and “grip due to the size of the pitch” By “canceling the variation in force”, it is said that “the steering stability can be improved” (paragraph 0012).

  On the other hand, in Patent Document 2 below, while reducing the initial wear of the kicking edge of the block pattern, the stepping edge is rounded and kicked in order to “reduce the noise caused by the block hitting sound”. It has been proposed to arrange a rubber part having a large elastic modulus at the delivery edge part (paragraphs 0005, 0031, etc.).

  According to Patent Documents 1 and 2 described above, it is considered that it is preferable to make the degree of deformation on the tire circumferential surface as uniform as possible in order to exhibit various performances of the tire. In Patent Document 1, it is considered that the hardness of the rubber layer is adjusted so as to cancel the difference in the tire circumferential dimension of the block forming the tread pattern, and the degree of deformation or the like is made uniform. In Patent Document 2, since stress concentrates on the kick-out edge portion at the time of kicking out, it can be considered that uniformity is achieved by increasing the elastic modulus of this portion.

  In Patent Document 3 below, in a tire having a cap tread, the rubber hardness of the tread base portion (“under tread layer”) is increased at the center portion, thereby maintaining low fuel consumption and improving steering stability. It has been proposed to improve. According to the results in Table 2 of Patent Document 3, it is advantageous to steering stability that the rubber hardness is high in all regions from the center portion to the shoulder portion, and conversely, the low rubber hardness is rolling resistance in all regions. This is advantageous for reducing the above. Patent document 3 aims at steering stability and low rolling resistance by said structure.

JP 2005-047446 A JP-A-11-0778428 JP 05-246212 A

  While the present inventors are diligently studying to reduce the rolling resistance of pneumatic tires, there may be methods other than the improvement of the overall rubber compounding composition and the optimization of the rigidity distribution in the tire cross section. I came to think of it. That is, the present invention seeks to provide a new method for reducing rolling resistance.

  In the tire in which the present inventor further studies in view of the above, the pitch of the tread pattern is relatively changed in the tire in which the pitch in the tire circumferential direction formed by the block of the tread pattern is periodically changed as in the above-mentioned Patent Document 1. An attempt was made by chance to set a condition opposite to the above-mentioned uniformization, in which the hardness of the tread rubber was set to be relatively small in a very small region. Surprisingly, the present inventors have found that rolling resistance can be reduced with little adverse effect on other performance such as steering stability.

That is, in the pneumatic tire according to the present invention, in the tire in which the pitch of the tread pattern is periodically changed in the tire circumferential direction, the rubber hardness of the tread is changed according to the pitch of the tread pattern, and the region where the pitch is smaller The rubber hardness is set small, and the boundary where the rubber hardness is switched is set along a curve that smoothly connects the lateral grooves between the blocks at the position where the pitch is switched . Here, the rubber hardness is a value measured according to JIS K 6253 durometer hardness test (type A). In particular, it is a value measured at room temperature such as 23 ° C.

  In a preferred embodiment, the rubber hardness (JIS K 6253, type A, 23 ° C.) is set in several steps within the range of 55 to 75. In one preferred embodiment, the pitch of the tread pattern is set to 3 or 5 steps, and the rubber hardness is also set to 3 or 5 steps accordingly. In one preferred embodiment, the central value of the rubber hardness is set to 62 to 66, and the rubber hardness is set to increase or decrease by 2 to 5, for example, 3 each time the pitch is switched to the next stage. That is, the rubber hardness in the region having the central pitch value is set to a value in the range of 62 to 66, for example, 64, and the rubber hardness is set to, for example, 67 in a region having a larger one-step pitch value.

  In a preferred embodiment, the boundary where the rubber hardness is switched is set along a groove (lateral groove) between blocks extending in the width direction of the tread or obliquely thereto. Further, in a preferred embodiment, when crossing a rib pattern (for example, center rib) continuous in the tire circumferential direction, the lateral grooves between the land blocks (for example, quarter blocks) sandwiching this pattern from both sides in the tread width direction Can be set along a smooth curve. Accordingly, the boundary where the rubber hardness is switched can be set along a curve that smoothly connects the lateral grooves over the entire width of the tread.

  According to the present invention, rolling resistance can be reduced while maintaining steering stability substantially only by setting the rubber hardness at or near the tread surface to an appropriate level for each region in the tire circumferential direction.

FIG. 2 is a pattern diagram (partially developed view of a tread surface) showing a tread pattern in the pneumatic tire of Example 1 and regions where different rubber hardnesses are set. It is a typical fragmentary sectional view of the tire peripheral direction which shows the mode of the interface of the rubber layers from which rubber hardness differs in the tread of the pneumatic tire of Example 1. 3 is a schematic partial cross-sectional view of a tire tread for a pneumatic tire of Example 2. FIG. An interface between rubber layers is schematically shown in a cross section cut so as to be perpendicular to the tread surface and extend in the tire circumferential direction. It is a pattern diagram corresponding to FIG. 1 about the pneumatic tire of Example 2. 3 is a partial cross-sectional view in the tire circumferential direction corresponding to FIG. 2 in the tread of the pneumatic tire of Example 2. FIG. FIG. 6 is a partial cross-sectional view in the tire circumferential direction corresponding to FIGS. 2 and 5 for a modified example in which the shape of the interface between rubber layers is stepped.

  In a preferred embodiment, the boundary where the rubber hardness is switched is formed by a band-shaped region where the rubber layers overlap. That is, the interface between the rubber layers having different rubber hardnesses is inclined with respect to the tread surface. The width of the band-like region is preferably 10 to 40% of the tire circumferential dimension in the main block (the block whose tire circumferential dimension substantially corresponds to the pitch value) with a larger pitch, more preferably 20 to 30%. Strictly speaking, the tire circumferential dimension of the main block is a dimension obtained by subtracting the width of the groove extending in the direction across the tread from the pitch dimension value. In addition, when the rubber layers are overlapped, one rubber layer may have a thin edge portion in a tail shape in cross section. In such a case, when the thickness of one rubber layer is less than 10%, particularly less than 5% of the total thickness (total thickness of the two rubber layers), the influence of the thin edge is ignored. be able to. That is, only when the thinner rubber layer has a sufficient thickness, the rubber layer can be a region where the rubber layers overlap each other.

  As described above, by overlapping the end portions of the rubber layers having different rubber hardnesses, it is possible to prevent the rigidity of the tread from changing abruptly and to prevent or suppress a decrease in steering stability. In particular, the change in rigidity can be further smoothed by taking a relatively large width for overlapping the rubber layers. Therefore, it is possible to prevent almost or completely the adverse effect on the steering stability caused by changing the rubber hardness in the circumferential direction.

  Moreover, in preferable embodiment, the strip | belt-shaped area | region where rubber layers overlap is biased to the area | region side where the pitch value of a tread pattern is relatively large. That is, the center line of the belt-like region where the rubber layers overlap is located at a position shifted toward the block having a larger pitch value than the center line of the groove between the blocks. In a preferred embodiment, one edge of the strip region is at or near the groove region and the other edge extends to pass through the interior of the block with the higher pitch value. In this way, if the belt-like region where the rubber layers overlap is arranged so as to be biased toward the block having a larger pitch value, the region having a relatively small rubber hardness is located near the groove, It is thought that the deformation at the nearby location is promoted. That is, it is considered advantageous in realizing reduction of rolling resistance due to “falling”.

  In a preferred embodiment, in a region where the rubber layers overlap each other, a rubber layer having a lower rubber hardness is located on the surface side of the tread. Therefore, in the cross section perpendicular to the tire rotation axis and the tread surface, the interface between the rubber layers having different rubber hardnesses moves from the boundary line exposed on the tread surface toward the inside of the tread toward the region where the pitch value is larger. It extends to head. With such a configuration, when the tread comes into contact with the road surface, the influence of the rubber layer having a smaller rubber hardness appears first, and the influence can be further reduced by switching the rubber hardness in the tire circumferential direction. It is done. That is, it is considered more advantageous in maintaining steering stability.

  In a preferred embodiment, the boundary line at which the interface between the rubber layers appears on the tread surface is at a position off the groove. As described above, when the width at which the rubber layers overlap is large to some extent, the boundary line comes to a position out of the groove. In particular, when the overlapping region is biased toward a block having a larger pitch value, the boundary line appearing on the tread surface is further separated from the groove. In particular, when the width of the overlapping region is 20 to 30% of the tire circumferential dimension of the block having the larger pitch value, the boundary line appearing on the tread surface is located far away from the groove region. It will be. In addition, the other edge of the area | region where rubber layers overlap in the inside of a tread can be arrange | positioned in the area | region which overlaps with a groove | channel, or its vicinity. In a preferred embodiment, the belt-like region where the rubber layers overlap is a region between the boundary line that appears offset on the tread surface from the groove part and the edge of the groove far from the boundary line. Yes.

  In one embodiment, the difference in the blending of the rubber composition for changing the rubber hardness for each region in the tire circumferential direction is realized by the difference in the ratio of the blending components. For example, when the rubber component is a mixture of two types of diene rubbers and one diene rubber contributes to wear resistance performance compared to the other diene rubber, but reduces grip properties, the blending ratio of these two types of diene rubbers is It can be realized by adjusting. It can also be realized by adjusting the blending ratio of a filler such as carbon black or silica. In other preferred embodiments, the type of filler is used, for example, by blending only a drive wheel tire with a styrene butadiene rubber having a high glass transition point (Tg), or using another type of carbon black. It is realized by making a difference.

  In a preferred embodiment, the tread portion of the pneumatic tire is provided with three or more main grooves that are continuous or partially interrupted in the circumferential direction, thereby forming four or more rows of land portions. Here, the land portion is typically formed by a row of blocks, but one or a plurality of land portions may be a rib pattern continuous in the tire circumferential direction. In the present application, the case where the tires are partially continuous in the tire circumferential direction is regarded as a row of blocks.

  When the tire tread is composed of a cap tread and a base tread, either or both of them can be formed of rubber layers having different rubber hardness for each predetermined region in the tire circumferential direction. However, in this case, it is preferable to form at least the cap tread with a rubber layer having a different rubber hardness. In order to simplify the manufacturing process, it is preferable to form only the cap tread with a rubber layer having a different rubber hardness. . In order to dispose a predetermined rubber layer in a predetermined region, for example, a method and apparatus for adhering a ribbon-like unvulcanized member to a predetermined position of a tire molding drum while appropriately cutting (Japanese Patent Laid-Open No. 2005-53083) Etc.) can be used. The method described in Patent Document 1 can also be used.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated still in detail, this invention is not limited to an Example.

  First, the structure of the pneumatic tire 1 of Example 1 is demonstrated using FIGS. In the specific example shown in the tread pattern diagram of FIG. 1, three main grooves 13 extending in the tire circumferential direction and four land portions are provided. In the illustrated example, each land portion is formed by a row of shoulder blocks 11-1, 11-5, a row of quarter blocks (mediate blocks) 11-2, 11-4, and a row of center blocks 11-3. It has a point-symmetric pattern as a whole. In the land portion on the center line, the blocks 11-3 are continuous with each other in the tire circumferential direction in the vicinity of the center line. Further, the blocks 11 adjacent to each other in the tire circumferential direction are separated from each other by a lateral groove 12 narrower than the main groove 13, and in the illustrated example, the lateral grooves 12 in each row of the blocks 11-1 to 11-5 are the main grooves. The position where the horizontal groove 13 is aligned with 13 is close to the position where the lateral groove 12 of the adjacent row is aligned with the main groove 13. That is, when the horizontal grooves 12 in adjacent rows are connected to each other, one smooth curve (curved curve) over the entire width of the tread can be assumed.

  On the other hand, in the specific example shown in the tread pattern diagram of FIG. 1, the pitch in the tire circumferential direction of the tread pattern varies periodically, and takes any one of the three pitches PL, PM, and PS in order. In the example shown in the figure, the large pitch PL, the medium pitch PM, the small pitch PS, the medium pitch PM, and the large pitch PL are repeated. The tire tread consists of three types of rubber layers HL, HM, and HS with different rubber hardness ("JIA AH" in the figure). The region of medium pitch PM is formed by the rubber layer HM having a medium rubber hardness (rubber hardness 65), and the region of small pitch PS is formed by the rubber layer HS having a low rubber hardness (rubber hardness 62). Is formed. The boundary line 14 between the rubber layers HL, HM, and HS is located inside the groove 12 between the blocks 11L, 11M, and 11S having different pitches, particularly at the groove bottom. Therefore, as shown by the thick broken line in the figure, the boundary line 14 between the rubber layers HL, HM, and HS coincides with the above-described one smooth curve over the entire width of the tread.

  In FIG. 2, the location of the boundary line 14 between the rubber layers HL and HM is shown by a schematic cross-sectional view along the tire circumferential direction. As shown in FIG. 2, the interface 15 between the rubber layers HL and HM is located in the vicinity of the lateral groove 12, and in particular, the boundary line 14 that appears on the tread surface is located on the bottom surface of the lateral groove 12. In the illustrated example, the interface 15 extends obliquely in the cross section in the tire circumferential direction so as to obtain a sufficient adhesion area between the rubber layers HL and HM. That is, the edge 17 of the interface 15 that appears on the back surface of the cap tread 21 is in the vicinity of the lateral groove 12 but is slightly spaced from the boundary line 14 in the tire circumferential direction.

  As shown in FIG. 2, a tire tread (tread rubber) 25 includes a cap tread 21 and a base tread 22, and only the cap tread 21 is formed of rubber layers having a plurality of types of rubber hardness. That is, the base tread 22 is formed of a single rubber composition. In the illustrated example, a belt layer 23 and a carcass layer 24 are laminated on the inner surface side of the base tread 22.

  Next, the structure of the pneumatic tire 1 ′ of Example 2 will be described with reference to FIGS. As shown in FIG. 5 which is a cross-sectional view corresponding to FIG. 2 and a schematic cross-sectional view of FIG. 3 schematically showing a region larger than this, in Example 2, the rubber layers HL having different rubber hardnesses are used. , HM, and HS have a large width of the region 16 where they overlap each other. The other points are exactly the same as those in the first embodiment.

  In the illustrated example, the edge 17 of the interface 15 that appears on the back surface side is in the vicinity of one edge of the lateral groove 12, as in the specific example of Example 1, but the boundary line 14 that appears on the tread surface is the lateral groove 12. Greatly shifted to the other side. Therefore, the interface 15 between the rubber layers HL, HM, and HS forms an inclined surface in a cross section in the tire circumferential direction perpendicular to the tread surface. By forming the inclined surface in this way, the change in rigidity in the tire circumferential direction is continuously performed without a step. Therefore, it is possible to prevent or suppress an adverse effect on steering stability. Moreover, the effect which enlarges the adhesion area of rubber layers is also acquired.

  As shown in FIGS. 3 and 5, the boundary lines 14 appearing on the tread surface are positioned in the blocks 11L and 11M having a larger pitch at the interfaces between the rubber layers HL, HM and HS. For this reason, in the region 16 where the rubber layers HL, HM and HS overlap each other, as a result, the rubber layers HM and HS having a lower rubber hardness are located on the tread surface side. Further, as shown in FIGS. 3 and 5, in the illustrated example, the inclined surface formed by the interface 15 between the rubber layers HL, HM, and HS is substantially perpendicular to the tread surface in the vicinity of the boundary line 14 of the tread surface. The slope gradually decreases as it goes to the edge 17 on the back surface side. Therefore, when the tire tread surface comes into contact with the road surface during traveling of the vehicle, the influence of the rubber layer having a lower rubber hardness is likely to occur.

  FIG. 4 which is a tread pattern diagram similar to FIG. 1 specifically shows a band-like region 16 where rubber layers overlap each other. In the specific example shown in the figure, the edge 17 on the back surface side forms a smooth curve that connects the edges of each lateral groove 12 with the smaller pitch in a single stroke. The boundary line 14 on the tread surface is a curve having the same shape obtained by translating the curve formed by the edge 17 on the back surface side in the tire circumferential direction. That is, the width of the band-like region 16 is constant over the entire width of the tread.

  Further, in the specific example shown in FIG. 4, the width of the band-like region 16 is set to 25% of the tire circumferential direction dimension of the block 11 having a larger pitch. Therefore, in the illustrated specific example, the block 11L with the largest pitch is adjacent to the block 11M with the smaller pitch from both sides in the tire circumferential direction, so that almost half of the tire circumferential direction is the region 16 where the rubber layers overlap. It has become.

  Next, FIG. 6, which is a cross-sectional view corresponding to FIG. 5, shows a main part of a modified pneumatic tire 1 ″. This modified example differs from Example 2 only in the shape of the interface between the rubber layers. The interface between the rubber layers is stepped to increase the area of the interface, but the manufacturing process is somewhat complicated.

  Hereinafter, specific tests and the results will be described. This produced the pneumatic tires of Examples 1-2 above, the pneumatic tires of Comparative Examples 1-2 corresponding to Patent Documents 1-2, and conventional conventional pneumatic tires. The performance is evaluated.

  The pneumatic tires of Examples 1 and 2 and Comparative Examples 1 and 2 and the conventional example are such that each rubber layer constituting the cap tread has a rubber hardness value of 65, 62, or 68. is there. In one example of the composition, the rubber layer forming the cap tread is composed of 100 parts by weight of a rubber component composed of styrene butadiene rubber and butadiene rubber having a high cis content, about 40 parts by weight of oil, about 5 parts by weight of carbon black, and silica. About 55 parts by weight of powder, sulfur, vulcanization accelerator, anti-aging agent and the like are blended. By adjusting the blending ratio of styrene butadiene rubber and butadiene rubber as appropriate, the rubber hardness can be Adjusted to a predetermined value.

  The conventional example is exactly the same as Example 1 except for the tread pattern, etc., except that the entire cap tread is formed of a rubber layer having a medium rubber hardness (rubber hardness 65). Comparative Example 1 is a tire manufactured so as to have the same pitch change and tread pattern as Example 1 in accordance with Patent Document 1, and the pneumatic tire of Example 1 has a high rubber hardness. The arrangement region of the rubber layer HL having (rubber hardness 68) and the arrangement region of the rubber layer HS having a low rubber hardness (rubber hardness 62) are reversed. Further, in Comparative Example 2, the pitch is not changed, the rubber hardness of the kick-out edge portion is set to 68, and the rubber hardness of the other region is set to 65 in accordance with Patent Document 1 described above. In addition, the width | variety of the part which enlarges rubber hardness was made into the area | region to 25% of the tire circumferential direction dimension of a block from the kicking side edge.

  A tire with a specified structure is formed by affixing a ribbon-shaped rubber member to a specified location on a tire-forming drum, and the tire size is 175 / 65R14 by vulcanization molding at 160 ° C for 30 minutes. An inset tire was produced. And it tested by the following method.

<Low rolling resistance>
A test drum was run at a standard speed (60 km / hr), and the rolling resistance was measured. The measurement results are shown in Table 1 below as an index taking the reciprocal and taking the reciprocal of the measured value in the conventional example as 100. A larger index indicates a lower rolling resistance and better low rolling resistance.

<Moist surface stability>
Attached to each wheel of a 1800cc sedan with displacement and continued running at standard speed (60km / hr) without rotating tires on the test wear running course owned by the applicant company. In addition, the degree of wear at the central main groove was measured. Then, the travel distance per 1 mm of the tread groove depth was obtained. The measurement results are shown in Table 1 below as an index with the measured value in the conventional example as 100.

  In the comparative example 1, as a result of increasing the rubber hardness for the block (small block) in the region where the pitch is relatively small, the low rolling resistance is lower than when the rubber hardness is uniform (conventional example). . However, the handling stability has been improved by improving the overall rigidity. Moreover, in Comparative Example 2, as a result of increasing the rubber hardness only in the kicked-out portion, the low rolling resistance was lower than that of the conventional example, but higher than that of Comparative Example 1. Further, the steering stability was comparable to that of the conventional example.

  On the other hand, in Example 1, the low rolling resistance was remarkably improved as compared with the conventional example. However, the handling stability decreased slightly. In Example 2, the boundary line appearing on the tread surface was offset (shifted) by 25% of the size in the block having the larger pitch instead of being located at the groove bottom of the lateral groove as in Example 1. The steering stability can be made the same as the conventional example. Moreover, the same low rolling resistance as in Example 1 was obtained.

  The pneumatic tire of the present invention can be used by being mounted on a vehicle for various uses such as a light truck for a passenger car such as a sedan type small passenger car or a compact car.

1 ... Pneumatic tires; 11 ... Block (island land);
11L, 11M, 11S ... Blocks of large, medium and small pitches; 12 ... Transverse grooves;
13 ... Circumferential main grooves; 14 ... Boundaries of rubber layers with different hardness on the tread surface;
15 ... interface of rubber layers having different hardnesses; 16 ... band-like region where rubber layers overlap;
17 ... Edge of the interface on the back of the cap tread; 21 ... Cap tread;
22 ... base tread; 23 ... belt layer; 24 ... carcass layer;
25 ... tread rubber HL, HM, HS ... rubber layers of rubber hardness 68, 65 and 62;
PL, PM, PS: Large, medium and small pitches in tread pattern

Claims (2)

In the pneumatic tire in which the pitch in the tire circumferential direction of the tread pattern is periodically changed, the rubber hardness of the tread is changed according to the pitch, and the rubber hardness is set to be smaller as the pitch is smaller .
A pneumatic tire characterized in that the boundary where the rubber hardness changes is set along a curve that smoothly connects the lateral grooves between the blocks at the place where the pitch changes . The boundary portion is provided as a belt-like region in which rubber layers having different rubber hardness are overlapped, and the width of the belt-like region is set to 10 to 40% of the tire circumferential dimension in a block having a larger pitch. The pneumatic tire according to claim 1, wherein

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