JP2018086962A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire having a structure that optimizes a ground contact form.SOLUTION: A pneumatic tire has: cap rubber 50 forming a ground plane E; and base rubber 51 provided in an inner side of the cap rubber 50 in a tire radial direction RD. The cap rubber 50 is formed with: a main groove 5a extending in a tire circumferential direction CD; and a rib Rb defined by the main groove 5a. The main groove 5a has: a groove wall surface 30 forming the rib Rb; a groove bottom surface 31; and a groove curved surface 32 connecting the groove wall surface 30 with the groove bottom surface 31. Low hardness rubber 52 having lower rubber hardness than the cap rubber 50 is disposed at a first area Ar1 that is located within the cap rubber 50, below an upper end P1 of the groove curved surface 32, and at a groove outer side of a lower end P2 of the groove curved surface 32. The low hardness rubber 52 overlaps with an entire portion of the groove curved surface 32 in a side view and overlaps with an entire portion of the groove curved surface 32 in a plan view.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a pneumatic tire.

  The tread pattern of the pneumatic tire is formed by grooves formed in the cap rubber. Main grooves extending in the tire circumferential direction in the tread define ribs or blocks. The rib is a land portion extending continuously in the tire circumferential direction, and the blocks are partitioned by a main groove and a lateral groove, and a plurality of blocks are arranged in the tire circumferential direction. Since the rib has higher rigidity than the block, it is considered that the grounding property is poor.

  FIG. 6B is a schematic diagram illustrating a ground contact shape of the rib. As shown in FIG. 6B, when the rib Rb is grounded, that is, when pressure is applied, the shape of the ground contact ends on both sides in the tire circumferential direction CD becomes distorted. Specifically, the end of the rib Rb (indicated by a dotted circle in the figure) swells and the center of the rib is recessed. In order to improve the braking performance, it is preferable that the shape of the ground contact end is a straight line perpendicular to the tire circumferential direction. It is because the pressure at the time of braking can be received appropriately.

  It is considered that the cause of the ground contact end shape of the rib Rb being distorted is the sectional shape of the groove. As shown in FIG. 6A, generally, a portion where the groove wall surface 30 and the groove bottom surface 31 of the main groove 5a forming the rib Rb intersect with each other is formed on a curved surface 32. If the straight lines intersect each other, the rubber will be cracked starting from the intersection, so a curved surface is employed to prevent rubber cracking. However, when the curved surface 32 is adopted, the foundation of the groove wall surface 30 becomes strong, the lower part of the groove wall surface 30 is firmly supported, and the upper part of the groove wall surface 30 becomes easy to move. As a result, as indicated by a dotted line in FIG. 6A, the upper portion of the groove wall surface 30 swells toward the inside of the groove. Naturally, since the material is rubber, a reaction force is generated in the direction in which the bulging returns, the pressure at the end of the rib increases, the end of the rib escapes in the tire circumferential direction, and the ground contact end is thought to be distorted.

  Although not directly related to the above, as a prior art, Patent Documents 1 and 2 describe pneumatic tires that suppress cracks in grooves. However, Patent Documents 1 and 2 do not describe the shape of the grounding end.

Japanese Patent Laying-Open No. 2015-157547 JP2015-85700A

  This indication is made paying attention to such a situation, and the object is to provide a pneumatic tire which has a structure which makes a grounding shape appropriate.

  In order to achieve the above object, the present disclosure takes the following measures.

  That is, the pneumatic tire according to the present disclosure includes a cap rubber that forms a contact surface, and a base rubber that is provided on the inner side in the tire radial direction of the cap rubber, and the cap rubber extends in a tire circumferential direction. A groove and a rib defined by the main groove are formed, the main groove includes a groove wall surface forming the rib, a groove bottom surface, and a groove curved surface connecting the groove wall surface and the groove bottom surface. In a first region inside the cap rubber and below the upper end of the groove curved surface and outside the groove than the lower end of the groove curved surface, the rubber hardness is lower than that of the cap rubber. Rubber is disposed, and the low hardness rubber overlaps the entire groove curved surface in a side view and overlaps the entire groove curved surface in a plan view.

  With this configuration, the low-hardness rubber covers the entire groove curved surface from the side and below, so that the support of the groove wall surface by the groove curved surface becomes weak, and the low-hardness rubber is compressed before the cap rubber. , Pressure is consumed as thermal energy. As a result, the reaction force that appears at the top of the groove wall surface is reduced, so that the ground contact shape is improved. As the ground contact shape improves, braking performance improves.

The tire meridian cross-sectional view showing an example of a pneumatic tire according to the present disclosure. Sectional drawing which shows the positional relationship of a main groove and low-hardness rubber. Sectional drawing which shows typically the deformation | transformation of the groove | channel at the time of grounding. The top view which shows the earthing | grounding end shape of a rib. Sectional drawing which shows the low hardness rubber | gum of a modification. Sectional drawing which shows the low hardness rubber | gum of a modification. Sectional drawing which shows the low hardness rubber | gum of a modification. Sectional drawing which shows the low hardness rubber | gum of a modification. Sectional drawing which shows typically the deformation | transformation of the groove | channel at the time of earthing | grounding in a conventional structure. The top view which shows the earthing | grounding end shape of the conventional rib.

  Hereinafter, a pneumatic tire according to an embodiment of the present disclosure will be described with reference to the drawings.

  As shown in FIG. 1, the pneumatic tire T includes a pair of bead portions 1, sidewall portions 2 that extend outward from the respective bead portions 1 in the tire radial direction RD, and outer sides in the tire radial direction RD of both sidewall portions 2. And a tread portion 3 connected to the end. The bead portion 1 is provided with an annular bead core 1a formed by covering a converging body such as a steel wire with rubber and a bead filler 1b made of hard rubber.

  The tire T includes a toroidal carcass layer 4 that extends from the tread portion 3 through the sidewall portion 2 to the bead portion 1. The carcass layer 4 is provided between a pair of bead portions 1 and is constituted by at least one carcass ply, and its end is locked in a state of being wound up via a bead core 1a. The carcass ply is formed by covering a cord extending substantially perpendicular to the tire equator CL with a topping rubber. Inside the carcass layer 4 is disposed an inner liner rubber 4a for maintaining air pressure.

  Further, a sidewall rubber 6 is provided outside the carcass layer 4 in the sidewall portion 2. A rim strip rubber 7 is provided outside the carcass layer 4 in the bead portion 1 so as to come into contact with a rim (not shown) when the rim is mounted. In the present embodiment, the topping rubber and rim strip rubber 7 of the carcass layer 4 are made of conductive rubber, and the side wall rubber 6 is made of non-conductive rubber.

  On the outer side of the carcass layer 4 in the tread portion 3, a belt 4b for reinforcing the carcass layer 4, a belt reinforcing material 4c, and a tread rubber 5 are provided in order from the inner side to the outer side. The belt 4b is composed of a plurality of belt plies. The belt reinforcing member 4b is configured by covering a cord extending in the tire circumferential direction with a topping rubber. The belt reinforcing material 4b may be omitted as necessary.

  As shown in FIGS. 1 and 2, the tread rubber 5 includes a cap rubber 50 that is formed of a non-conductive rubber and that constitutes the ground contact surface E, and a base rubber 51 that is provided inside the tire rubber in the tire radial direction. Have A plurality of main grooves 5 a extending along the tire circumferential direction are formed on the surface of the cap rubber 50.

  In the above, the ground contact surface E is a surface that is assembled to a regular rim and filled with a regular internal pressure, and the tire is placed vertically on a flat road surface and contacted to the road surface when a regular load is applied. The outermost position of WD is the grounding end. The normal load and the normal internal pressure are the maximum load (design normal load in the case of passenger car tires) specified in JIS D4202 (specifications of automobile tires) and the air pressure corresponding to this, and the normal rim is As a rule, the standard rim specified in JIS D4202 etc. shall be used.

  In the present embodiment, a side wall on tread (SWOT) structure in which the side wall rubber 6 is placed on both end portions of the tread rubber 5 is adopted, but the present invention is not limited to this structure. It is also possible to adopt a tread on side (TOS) structure in which both end portions of the tread rubber are placed on the outer end in the tire radial direction RD of the sidewall rubber.

Here, the conductive rubber is exemplified by a rubber having a volume resistivity of less than 10 ⁸ Ω · cm. For example, the conductive rubber is produced by blending carbon black as a reinforcing agent in a high ratio with a raw material rubber. In addition to carbon black, carbon fibers such as carbon fiber and graphite, and metal-based known conductivity imparting materials such as metal powders, metal oxides, metal flakes, and metal fibers can also be blended.

Further, the non-conductive rubber is exemplified by a rubber having a volume resistivity of 10 ⁸ Ω · cm or more, and a rubber blended with a raw material rubber in a high ratio as a reinforcing agent is exemplified. For example, the silica is blended in an amount of 30 to 100 parts by weight with respect to 100 parts by weight of the raw rubber component. As silica, wet silica is preferably used, but those commonly used as reinforcing materials can be used without limitation. The nonconductive rubber may be prepared by blending calcined clay, hard clay, calcium carbonate, or the like, in addition to silicas such as precipitated silica and anhydrous silicic acid.

  Examples of the raw rubber include natural rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), and butyl rubber (IIR). These may be used alone or in combination of two or more. Used. A vulcanizing agent, a vulcanization accelerator, a plasticizer, an anti-aging agent and the like are appropriately blended with the raw rubber.

The conductive rubber has a nitrogen adsorption non-surface area: N ₂ SA (m ² / g) × carbon black content (mass%) of 1900 or more, preferably 2000 or more, from the viewpoint of improving durability and improving current carrying performance. In addition, it is desirable that the blending amount of the dibutyl phthalate oil absorption: DBP (ml / 100 g) × carbon black is 1500 or more, preferably 1700 or more. N ₂ SA is determined according to ASTM D3037-89, and DBP is determined according to ASTM D2414-90.

  In the present embodiment, as shown in FIG. 2, the cap rubber 50 is formed with ribs Rb partitioned by the main groove 5a. As shown in the figure, the main groove 5 a has a groove wall surface 30 that forms the rib Rb, a groove bottom surface 31, and a groove curved surface 32 that connects the groove bottom surface 31 and the groove wall surface 30. All or part of the groove wall surface 30 is a flat surface, and the groove bottom surface 31 is a flat surface. The groove curved surface 32 is a combination of one or a plurality of curved surfaces. The average radius of curvature of the groove curved surface 32 is 1.5 to 2.0 mm, but is not limited thereto. The average radius of curvature is an average value of the curvature radii of the curved surfaces constituting the groove curved surface 32.

  As shown in FIG. 2, a low hardness rubber 52 having a rubber hardness lower than that of the cap rubber 50 is disposed inside the cap rubber 50 and around the groove curved surface 32. The rubber hardness here means the hardness measured according to JISK6253 durometer hardness test (type A). The low hardness rubber 52 is disposed in the first region Ar1 inside the cap rubber 50, below the upper end P1 of the groove curved surface 32 and outside the groove from the lower end P2 of the groove curved surface 32. The first region Ar1 is a region indicated by hatching in FIG. The low hardness rubber 52 overlaps the entire groove curved surface 32 in a side view and covers the entire groove curved surface 32 from the side. Further, the low hardness rubber 52 overlaps the entire groove curved surface 32 in plan view and covers the entire groove curved surface 32 from below.

  FIG. 3A is a cross-sectional view schematically showing the deformation of the groove at the time of grounding. In FIG. 3A, the shape when not grounded is drawn by a solid line, and the shape when grounded is drawn by a broken line. Since the low hardness rubber 52 covers the entire groove curved surface 32 from the side and below, the support of the groove wall surface 30 by the groove curved surface 32 becomes weak. Then, as shown in FIG. 3A, the low-hardness rubber 52 is compressed before the cap rubber 50, and the pressure is consumed as heat energy. Since the low hardness rubber 52 is preferentially compressed, the reaction force RF is mainly developed below the groove wall surface 30. As a result, the reaction force that appears on the upper surface of the groove curved surface 32 is reduced, so that the ground contact shape is improved. FIG. 3B shows a ground contact shape, and the swelling of the end of the rib Rb is reduced as shown in FIG. 6B.

  As shown in FIG. 2, the low-hardness rubber 52 disposed in the first region Ar <b> 1 is disposed within a range where the distance R <b> 1 from the groove curved surface 32 is 1.7 mm along the normal direction of the groove curved surface 32. Preferably it is. If the low-hardness rubber 52 is in this range, the low-hardness rubber 52 is likely to compress preferentially.

  Furthermore, it is preferable that the low hardness rubber 52 extends upward from the first region Ar1 to the ground contact surface E. Of course, as shown in FIG. 4A, the low hardness rubber 52 does not have to extend to the ground contact surface E. The thickness D2 of the low hardness rubber 52 in the first region Ar1 is larger than the thickness D1 of the low hardness rubber 52 exposed to the ground contact surface E. The thickness D1 is preferably 0.1 to 1.0 mm, and the thickness D2 is preferably 0.4 to 1.5 mm. In this embodiment, since the cap rubber 50 is a non-conductive rubber and the low-hardness rubber 52 is a conductive rubber, the volume of the conductive rubber is suppressed to suppress the deterioration of rolling resistance, and the low-hardness rubber 52 It is a viewpoint which makes compatible that a grounding end shape is improved by being compressed. Of course, there is an effect even outside this numerical range.

  As shown in FIG. 2, the low hardness rubber 52 arranged in the first region Ar1 has a crescent shape. As shown in FIGS. 5A and 5B, the low hardness rubber 52 may be shaped like one side of a trapezoid. In addition, the low hardness rubber 52 is preferably disposed between the center RCL of the rib Rb and the center GCL of the main groove 5a. If it is out of this range, the effect of improving the ground contact end shape may not be exhibited, or another part may be adversely affected.

  As shown in FIG. 1, the main groove 5 a has a tire wear indicator TWI protruding from the groove bottom surface 31. The tire wear indicator TWI is a protrusion indicating the replacement time of the tire, and has a height of 1.6 mm from the groove bottom surface 31. As shown in FIG. 2, the thickness of the low hardness rubber 52 above the tire wear indicator TWI is relatively small, and the thickness of the low hardness rubber 52 below the tire wear indicator TWI and in the first region Ar1. Is preferably relatively large. This is because the area above the tire wear indicator TWI is exposed as a ground contact surface, so that exposure of the conductive rubber in this region is suppressed, and deterioration of rolling resistance and wet performance is suppressed.

  As shown in FIG. 2, the low-hardness rubber 52 is formed of a conductive rubber and extends from the ground contact surface E to the bottom surface of the cap rubber 50. With this configuration, the low hardness rubber 52 also functions as a conductive path from the ground contact surface E to the base rubber 51. Of course, if the conductive path is unnecessary, the low hardness rubber 52 may not extend to the bottom surface of the cap rubber 50 as shown in FIGS. 4A and 4B. Further, the low hardness rubber 52 may not be formed of conductive rubber, and may be non-conductive rubber. From the viewpoint of optimizing the shape of the ground end, the cap rubber 50 may not be a non-conductive rubber, and may be a conductive rubber.

  In order to specifically show the configuration and effects of the present disclosure, the following evaluations were performed on the following examples.

(1) Braking performance Measure the braking distance when the ABS is operated from a state where the tire is mounted on a Japanese sedan car (2000cc) and the road surface is running at 100 km / h. The reciprocal was calculated. The result of Comparative Example 1 is evaluated with an index of 100, and the larger the index, the better the braking performance.

Comparative Example 1
As shown in FIG. 6A, a rib Rb is formed by a main groove 5a, and the main groove 5a is a groove wall surface 30 that forms the rib Rb, a groove bottom surface 31, and a groove curved surface that connects the groove wall surface 30 and the groove bottom surface 31. Thus, a tire having a structure of a general cap rubber 50 having 32 is manufactured.

Example 1
As shown in FIG. 2, a crescent-shaped low-hardness rubber 52 is disposed in the first region. The low hardness rubber 52 extends upward from the first region Ar1 and reaches the ground contact surface E. The low hardness rubber 52 extends downward and reaches the bottom surface of the cap rubber 50. Otherwise, it was the same as Comparative Example 1.

  From Table 1, it can be seen that Example 1 is superior to Comparative Example 1 in terms of braking performance. This is considered to be because the contact end shape is improved, and the contact end easily receives a force appropriately during braking.

  As described above, the pneumatic tire of the present embodiment includes the cap rubber 50 that forms the ground contact surface E, and the base rubber 51 provided inside the tire rubber radial direction RD of the cap rubber 50. Is formed with a main groove 5a extending in the tire circumferential direction CD, and a rib Rb defined by the main groove 5a. The main groove 5a includes a groove wall surface 30 that forms the rib Rb, a groove bottom surface 31, and A groove curved surface 32 that connects the groove wall surface 30 and the groove bottom surface 31, and is inside the cap rubber 50, below the upper end P <b> 1 of the groove curved surface 32, and outside the groove from the lower end P <b> 2 of the groove curved surface 32. A low-hardness rubber 52 having a lower hardness than the cap rubber 50 is disposed in the first region Ar1, and the low-hardness rubber 52 overlaps the entire groove curved surface 32 in a side view and also has a groove curved surface 32 in a plan view. It overlaps with the whole.

  With this configuration, the low-hardness rubber 52 covers the entire groove curved surface 32 from the side and below, so that the support of the groove wall surface 30 by the groove curved surface 32 becomes weak and lower than the cap rubber 50. Hard rubber 52 is compressed and pressure is consumed as thermal energy. As a result, the reaction force that appears at the top of the groove wall surface 30 is reduced, so that the ground contact shape is improved. When the ground contact shape is improved, the braking performance is improved.

  In the present embodiment, the low hardness rubber 52 extends upward from the first region Ar1 to the ground contact surface E.

  According to this configuration, the portion of the cap rubber 50 that forms the groove wall surface 30 is partitioned by the low-hardness rubber 52. Therefore, the entire portion that forms the groove wall surface 30 moves downward, and the low-hardness rubber 52 is preferentially used. Compressed. As a result, the reaction force that appears at the upper part of the groove wall surface 30 is further reduced, so that the ground contact shape is further improved.

  In the present embodiment, the thickness D2 of the low hardness rubber 52 in the first region Ar1 is larger than the thickness D1 of the low hardness rubber 52 exposed to the ground contact surface E.

  According to this configuration, since the thickness D2 of the low-hardness rubber 52 in the first region Ar1 that is easily compressed at the time of grounding is relatively large, the effect of improving the grounding shape can be enhanced. When the cap rubber 50 is a non-conductive rubber and the low hardness rubber 52 is a conductive rubber, the volume of the conductive rubber can be suppressed and deterioration of rolling resistance can be suppressed.

  In the present embodiment, the low-hardness rubber disposed in the first region is disposed within a range in which the distance R1 from the groove curved surface is 1.7 mm along the normal direction of the groove curved surface.

  According to this configuration, the effect of preferentially compressing the low-hardness rubber is easily exhibited, and the ground contact shape is likely to be improved.

  In the present embodiment, the cap rubber 50 is made of non-conductive rubber, and the low hardness rubber 52 is made of conductive rubber and extends from the ground surface E to the bottom surface of the cap rubber 50.

  According to this configuration, it is possible to secure a conductive path using the low hardness rubber 52.

  In the present embodiment, the main groove 5a has a tire wear indicator TWI protruding from the groove bottom surface 31, the thickness D1 of the low hardness rubber 52 above the tire wear indicator TWI is relatively small, and the tire wear indicator TWI. The thickness D2 of the low-hardness rubber 52 in the first region Ar1 is lower than the thickness D2.

  According to this configuration, the area above the tire wear indicator TWI is an area exposed as a ground contact surface, and the exposure of the conductive rubber in this area can be suppressed, and deterioration of rolling resistance and wet performance can be suppressed.

  The structure employed in each of the above embodiments can be employed in any other embodiment. The specific configuration of each unit is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present disclosure.

  In the present embodiment, the low hardness rubber 52 is provided on the side of the groove wall surface 30 that forms the rib Rb in the main groove 5a between the rib Rb and the block. However, the present invention is not limited to this. For example, in the main groove 5a between the ribs, the low hardness rubber 52 may be provided on both the groove wall surfaces 30 side.

30 ... groove wall 31 ... groove bottom surface 32 ... groove curved surface 50 ... cap rubber 51 ... base rubber 52 ... low hardness rubber 5a ... main groove E ... ground surface Rb ... rib P1 ... upper end of groove curved surface P2 ... lower end of groove curved surface Ar1 ... 1st region TWI ... Tire wear indicator

Claims (6)

A cap rubber that forms a ground contact surface, and a base rubber provided on the inner side in the tire radial direction of the cap rubber,
The cap rubber is formed with a main groove extending in the tire circumferential direction and a rib defined by the main groove,
The main groove has a groove wall surface that forms the rib, a groove bottom surface, and a groove curved surface that connects the groove wall surface and the groove bottom surface,
A low-hardness rubber having a rubber hardness lower than that of the cap rubber is disposed in a first region inside the cap rubber and below the upper end of the groove curved surface and outside the groove lower end of the groove curved surface. The low-hardness rubber is a pneumatic tire that overlaps the entire groove curved surface in a side view and overlaps the entire groove curved surface in a plan view.   The pneumatic tire according to claim 1, wherein the low-hardness rubber extends upward from the first region to a ground contact surface.   The pneumatic tire according to claim 2, wherein the thickness of the low-hardness rubber in the first region is larger than that of the low-hardness rubber exposed on the ground contact surface.   The low-hardness rubber disposed in the first region is disposed in a range in which a distance from the groove curved surface is 1.7 mm along a normal direction of the groove curved surface. The pneumatic tire according to Crab. The cap rubber is made of non-conductive rubber,
The pneumatic tire according to any one of claims 1 to 4, wherein the low hardness rubber is formed of a conductive rubber and extends from a ground contact surface to a bottom surface of the cap rubber. The main groove has a tire wear indicator protruding from the groove bottom surface,
The thickness of the low-hardness rubber above the tire wear indicator is relatively small, and the thickness of the low-hardness rubber below the tire wear indicator and in the first region is relatively large. Item 6. The pneumatic tire according to Item 5.

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