阅读说明：本技术 充气轮胎 (Pneumatic tire ) 是由 茶谷瞳 于 2019-02-12 设计创作，主要内容包括：提供一种能够改善冰上制动性能并且降低滚动阻力的充气轮胎。所述充气轮胎具备胎面部(1)、一对胎侧部(2)以及一对胎圈部(3),在胎圈部(3)之间架设有胎体层(4),胎面部(1)具有顶胎面橡胶层(11A)和底胎面橡胶层(11B)的层叠构造,雪地牵引指数STI为180以上,其中,胎面部(1)的子午线截面中的胎面半径(TR)为轮胎外径(OD)的80％～140％,胎面部(1)的接地宽度(TCW)为轮胎截面宽度(SW)的66％～83％,胎圈填胶(6)的高度(BFH)为轮胎截面高度(SH)的40％以下。(Provided is a pneumatic tire capable of improving braking performance on ice and reducing rolling resistance. The pneumatic tire is provided with a tread portion (1), a pair of side portions (2) and a pair of bead portions (3), wherein a carcass layer (4) is provided between the bead portions (3), the tread portion (1) has a laminated structure of a top tread rubber layer (11A) and a bottom tread rubber layer (11B), and the snow traction index STI is 180 or more, wherein the Tread Radius (TR) in the meridian section of the tread portion (1) is 80-140% of the tire Outer Diameter (OD), the ground contact width (TCW) of the tread portion (1) is 66-83% of the tire Section Width (SW), and the height (BFH) of the bead filler (6) is 40% or less of the tire Section Height (SH).)

1. A pneumatic tire comprising a tread portion extending in a tire circumferential direction and having a ring shape, a pair of side portions disposed on both sides of the tread portion, and a pair of bead portions disposed on inner sides of the side portions in a tire outer diameter direction, wherein a carcass layer is provided between the pair of bead portions, the tread portion has a laminated structure of a top tread rubber layer and a bottom tread rubber layer, and grooves and sipes are formed in the tread portion, and a snow traction index STI based on the grooves and sipes is 180 or more, the pneumatic tire being characterized in that,

the tread radius in the meridian section of the tread portion is 80% -140% of the tire external diameter, the ground contact width of the tread portion is 66% -83% of the tire section width, and the height of the bead filler arranged on the periphery of the bead core of the bead portion is less than 40% of the tire section height.

2. A pneumatic tire according to claim 1,

the maximum width position of the tire is in the range of 50% to 60% of the tire section height.

3. A pneumatic tire according to claim 1 or 2,

the rubber thickness at the maximum width position of the tire is 1mm to 4mm on the outer side of the carcass layer.

4. A pneumatic tire according to any one of claims 1 to 3,

the carcass layer is wound up around the bead core from the inner side to the outer side of the tire, and the wound-up height of the carcass layer is 10% to 40% of the tire sectional height.

Technical Field

The present invention relates to a pneumatic tire suitable for use on an icy or snowy road, and more particularly, to a pneumatic tire capable of improving braking performance on ice and reducing rolling resistance.

Background

In a pneumatic tire for an ice and snow road represented by a studless tire, in general, a tread portion is formed with a plurality of longitudinal grooves extending in a tire circumferential direction and a plurality of lateral grooves extending in a tire width direction, and a plurality of blocks are divided by the longitudinal grooves and the lateral grooves. Further, a plurality of sipes are formed in each block.

Such a pneumatic tire can exhibit excellent running performance on ice and snow based on grooves and sipes formed in a tread portion, but further improvement in braking performance on ice has been demanded in recent years.

In addition, in a pneumatic tire for an ice and snow road, a laminated structure of a top tread rubber (hereinafter, referred to as "cap tread rubber") layer and a bottom tread rubber (hereinafter, referred to as "under tread rubber") layer is employed in a tread portion, but in this case, a soft top tread rubber layer exhibits a following property to a road surface, and on the other hand, a bottom tread rubber layer as a base portion thereof contributes to improvement of steering stability (for example, see patent documents 1 to 2).

However, since the rubber composition constituting the under tread rubber layer generally has a high tan, when the under tread rubber layer is thickened, the rolling resistance tends to be deteriorated. Therefore, in recent years, a reduction in rolling resistance has been demanded also in pneumatic tires for ice and snow road, in which rolling resistance has not been regarded as a problem.

Disclosure of Invention

Problems to be solved by the invention

The invention aims to provide a pneumatic tire capable of improving braking performance on ice and reducing rolling resistance.

Means for solving the problems

A pneumatic tire according to the present invention for achieving the above object is a pneumatic tire including a tread portion extending in a tire circumferential direction and having a ring shape, a pair of side portions disposed on both sides of the tread portion, and a pair of bead portions disposed on inner sides of the side portions in a tire outer diameter direction, a carcass layer being provided between the pair of bead portions, the tread portion having a laminated structure of a top tread rubber layer and a bottom tread rubber layer, and grooves and sipes being formed in the tread portion, and a Snow Traction Index (STI) based on the grooves and sipes being 180 or more,

the tread radius in the meridian section of the tread portion is 80% -140% of the tire external diameter, the ground contact width of the tread portion is 66% -83% of the tire section width, and the height of the bead filler arranged on the periphery of the bead core of the bead portion is less than 40% of the tire section height.

ADVANTAGEOUS EFFECTS OF INVENTION

In the present invention, by adopting a flat tread profile and increasing the ground-contact width of the tread portion, the ground-contact area of the tread portion can be increased, improving the on-ice braking performance. Further, since the vertical spring constant (constant バネ in Japanese) of the tire is reduced by reducing the height of the bead filler, and the sidewall portion is easily deflected, the energy loss of the tread portion can be relatively reduced, and the rolling resistance can be reduced. Further, the promotion of the deflection of the sidewall portion increases the ground contact area at the time of braking, and therefore contributes to the improvement of the braking performance on ice. Thereby, the on-ice braking performance can be improved, and the rolling resistance can be reduced.

In the present invention, it is preferable that the tire maximum width position is in the range of 50% to 60% of the tire section height. By setting the tire maximum width position in the above range, the longitudinal spring constant of the tire is reduced, and the sidewall portion is easily bent, so that the rolling resistance can be reduced by relatively reducing the energy loss of the tread portion, and the ground contact area can be increased by bending the sidewall portion.

Preferably, the rubber thickness at the tire maximum width position on the outer side of the carcass layer is 1mm to 4 mm. By reducing the rubber thickness on the outer side of the carcass layer at the tire maximum width position, the longitudinal spring constant of the tire can be reduced, the ground contact area can be increased, and the rolling resistance can be reduced by reducing the energy loss in the sidewall portion.

Preferably, the carcass layer is wound up around the bead core from the inner side to the outer side of the tire, and the wound-up height of the carcass layer is 10% to 40% of the tire sectional height. By reducing the rolling height of the carcass layer in this way, the longitudinal spring constant of the tire can be reduced, the contact patch can be increased, and the rolling resistance can be reduced.

In the present invention, the snow traction index STI is set to 180 or more in order to satisfy the required characteristics as a pneumatic tire for an ice and snow road. The snow traction index STI is calculated by the following formula (1).

STI＝－6.8+2202ρg+672ρs+7.6Dg…(1)

Wherein ρ g: cell density (mm/mm)²) Total length (mm) of extended component in tire width direction of groove/total area (mm) of ground contact region²)

ρ s: sipe Density (mm/mm)²) Total length (mm) of extension component in tire width direction of sipe/total area (mm) of ground contact region²)

And Dg: average groove depth (mm)

In the present invention, the various dimensions including the tread radius, the outer diameter of the tire, and the height of the tire section are measured in a state where the tire rim is assembled to a regular rim (japanese: size リム) and filled with a regular internal pressure (japanese: size). The ground contact width of the tread portion is a ground contact width in the tire axial direction measured when a tire rim is assembled to a regular rim and filled with a regular internal pressure, and the tire rim is placed on a flat surface in a vertical state and a regular load (japanese: a regular weight loss) is applied. The "regular Rim" means a Rim specified for each tire in a standard system including a standard on which tires are based, and is set as a standard Rim (japanese publication: pre-registration リム) in case of JATMA, as a "Design Rim" in case of TRA, or as a "Measuring Rim" in case of ETRTO. The "normal internal PRESSURE" is an air PRESSURE determined for each TIRE in a standard system including standards based on TIREs, and is a maximum value described in a table of "TIRE PRESSURE limit AT VARIOUS COLD INFLATION PRESSUREs" in JATMA (japanese: highest air permeability), in TRA (TRA), and "INFLATION PRESSURE" in ETRTO (for passenger vehicles), but is 180 kPa. The "normal LOAD" is a LOAD that is determined for each TIRE according to each standard in a standard system including standards based on which TIREs are based, and is a maximum LOAD CAPACITY in case of JATMA, a maximum value described in a table "TIRE LOAD limit AT variable cold inflation PRESSURES" in case of TRA, and a LOAD CAPACITY in case of ETRTO, but is a LOAD corresponding to 88% of the LOAD in case of a passenger vehicle.

Drawings

Fig. 1 is a meridian cross-sectional view showing a pneumatic tire constituted by an embodiment of the present invention.

Fig. 2 is a development view showing a tread pattern of the pneumatic tire of fig. 1.

Detailed Description

Hereinafter, the structure of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 and 2 are views showing a pneumatic tire according to an embodiment of the present invention. In fig. 1 and 2, Tc is the tire circumferential direction, Tw is the tire width direction, CL is the tire equator, and TCW is the contact patch width.

As shown in fig. 1, the pneumatic tire of the present embodiment includes a tread portion 1 extending in a tire circumferential direction and having a ring shape, a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3, 3 disposed on the inner side of the sidewall portions 2 in the tire radial direction.

A carcass layer 4 is provided between the pair of bead portions 3, 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the tire inner side to the outer side around bead cores 5 disposed in the respective bead portions 3. A bead filler 6 made of a rubber composition having a triangular cross section is disposed on the outer periphery of the bead core 5.

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

In the pneumatic tire described above, the top tread rubber layer 11A and the bottom tread rubber layer 11B are disposed on the outer side of the carcass layer 4, the belt layer 7, and the belt cover layer 8 in the tread portion 1. The top tread rubber layer 11A is located further outward in the tire radial direction than the bottom tread rubber layer 11B, and is exposed on the tire outer surface. The undertread rubber layer 11B is composed of a rubber composition harder than the rubber composition constituting the top tread rubber layer 11A. More specifically, the rubber composition constituting the top tread rubber layer 11A has a JIS hardness of 50 to 65, and the rubber composition constituting the bottom tread rubber layer 11B has a JIS hardness of 56 to 66. The JIS hardness is a durometer hardness (Japanese: デュロメータ hard さ) measured at a temperature of 20 ℃ in accordance with JIS K-6253 using a type A durometer.

Further, a side rubber layer 12 is disposed on the outer side of the carcass layer 4 in the side portion 2. A rim cushion rubber layer 13 is disposed on the outer side of the carcass layer 4 at the bead portion 3. An inner liner 14 is disposed along the carcass layer 4 on the inner surface of the tire.

As shown in fig. 2, the tread portion 1 is formed with a plurality of longitudinal grooves 21 extending in the tire circumferential direction Tc and a plurality of lateral grooves 22 extending in the tire width direction Tw. These vertical grooves 21 and horizontal grooves 22 define a plurality of block-shaped land portions 23 in the tread portion 1. Further, a plurality of sipes 24 extending in the tire width direction are formed in each land portion 23. The sipe may extend in a zigzag shape along the tire width direction, or may extend linearly. The sipe 24 has a groove width of about 1.5mm or less. The tread pattern is not particularly limited, but the snow traction index STI is set to 180 or more, and more preferably set in the range of 180 to 240, in order to satisfy the required characteristics as a pneumatic tire for an ice and snow road.

In the pneumatic tire described above, as shown in fig. 1, the tread radius TR in the meridian section of the tread portion 1 is set in the range of 80% to 140% of the tire outer diameter OD, the ground contact width TCW of the tread portion 1 is set in the range of 66% to 83% of the tire section width SW, and the height BFH of the bead filler 6 disposed on the outer periphery of the bead core 5 of the bead portion 3 is set in the range of 40% or less of the tire section height SH.

In the pneumatic tire described above, by adopting a flat tread profile specified by the tread radius TR and increasing the ground contact width TCW of the tread portion 1, the ground contact area of the tread portion 1 can be increased, improving the on-ice braking performance. Further, by lowering the height BFH of the bead filler 6, the longitudinal spring constant of the tire is lowered, and the sidewall portion 2 is easily bent, so that the energy loss of the tread portion 1 can be relatively reduced to reduce the rolling resistance. Further, the promotion of the deflection of the sidewall portion 2 increases the ground contact area at the time of braking, and therefore contributes to the improvement of the on-ice braking performance. Thereby, the on-ice braking performance can be improved, and the rolling resistance can be reduced.

Here, if the tread radius TR in the meridian cross section of the tread portion 1 is smaller than 80% of the tire outer diameter OD, the ground contact area becomes insufficient, and conversely, if it is larger than 140%, the ground contact performance in the central region deteriorates, and therefore the effect of improving the on-ice braking performance decreases. In particular, the tread radius TR is preferably in the range of 110% to 130% of the tire outer diameter OD.

Further, if the ground contact width TCW of the tread portion 1 is smaller than 66% of the tire section width SW, the ground contact area becomes insufficient, whereas if it is larger than 83%, the ground contact performance in the shoulder region is improved, and on the other hand, the ground contact performance in the center region is deteriorated, so the improvement effect of the on-ice braking performance is reduced. In particular, the ground contact width TCW of the tread portion 1 is preferably in the range of 70% to 80% of the tire section width SW.

If the height BFH of the bead filler 6 is greater than 40% of the tire section height SH, the effect of reducing the rolling resistance cannot be obtained. In particular, the height BFH of the bead filler 6 is preferably in the range of 10% to 20% of the tire section height SH. Further, the height BFH of the bead filler 6 may also be 0% of the tire section height SH (i.e., a configuration without the bead filler 6).

In the pneumatic tire described above, the height Hmax in the tire radial direction from the heel position to the tire maximum width position Pmax may be in the range of 50% to 60% of the tire section height SH. By disposing the tire maximum width position Pmax in the above range, the longitudinal spring constant of the tire is reduced, and the sidewall portion 2 is easily flexed, so that the energy loss of the tread portion 1 can be relatively reduced, and the rolling resistance can be reduced. Moreover, the ground contact area can be increased by the deflection of the sidewall portion 2. Here, if the tire maximum width position Pmax is located inward in the tire radial direction from the position of 50% of the tire section height SH, the effect of lowering the longitudinal elastic constant is reduced, whereas if it is located outward in the tire radial direction from the position of 60% of the tire section height SH, an unreasonable structure is generated in the tire, and the durability is reduced. In particular, the height Hmax in the tire radial direction from the heel position to the tire maximum width position Pmax is preferably in the range of 52% to 56% of the tire section height SH.

In the pneumatic tire described above, the rubber thickness T on the outer side of the carcass layer 4 at the tire maximum width position Pmax may be 1mm to 4 mm. By reducing the rubber thickness T on the outer side of the carcass layer 4 at the tire maximum width position Pmax, the longitudinal spring constant of the tire can be reduced, the ground contact area can be increased, and the energy loss of the sidewall portion 2 can be reduced to reduce the rolling resistance. Here, if the rubber thickness T is smaller than 1mm, the cut resistance is lowered, whereas if it is larger than 4mm, the energy loss of the sidewall portion 2 becomes large. In particular, the rubber thickness T is preferably 2mm to 3 mm.

In the pneumatic tire described above, the carcass layer 4 is preferably turned up around the bead core 5 from the inner side to the outer side of the tire, and the turn-up height TUH of the carcass layer 4 is preferably 10% to 40% of the tire section height SH. By thus reducing the turn-up height TUH of the carcass layer 4, the longitudinal spring constant of the tire can be reduced, the ground contact area can be increased, and the rolling resistance can be reduced. Here, if the turn-up height TUH of the carcass layer 4 is smaller than 10% of the tire section height SH, the rigidity around the bead portion 3 becomes insufficient, and conversely, if it is larger than 40%, the effect of lowering the longitudinal elastic constant is reduced. In particular, the rolling height TUH of the carcass layer 4 is preferably 20% to 30% of the tire section height SH.