JP2005239068A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance controllability and stability without impairing ride comfort. <P>SOLUTION: The pneumatic tire is provided with a carcass 6; a bead apex 8; and a rubber chafer 9 and satisfies the following formulae: hr-ha≥10, hs×0.67>hr and Ha>Hr>Hs. Provided that hr is height of rubber chafer (mm), ha is height of bead apex (mm), has is height of tire cross section (mm), Ha is JISA hardness (°) of bead apex, Hr is JISA hardness (°) of rubber chafer and Hs is JISA hardness (°) of side wall rubber. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire that can improve steering stability without impairing riding comfort.

  FIG. 4 shows the structure of a bead portion a of a conventional radial tire for a passenger car. The bead portion a has a substantially U-shaped cross section arranged so as to wrap the bead core b via the carcass ply c1 and the carcass c formed of one carcass ply c1 folded and locked around the bead portion a. A rubber chafer d and a clinch apex e covering the outside thereof are arranged. The rubber chafer d is usually set to have a small height h1 from the bead base line BL. An inner liner rubber f excellent in air impermeability is disposed on the inner surface of the carcass c, and a sidewall rubber g extending from the clinch apex e to the sidewall region g is disposed on the outer surface of the carcass c. Further, a bead apex i made of hard rubber is disposed outside the bead core b.

  Conventionally, various improvements have been made to pneumatic tires in order to improve actual vehicle performance such as ride comfort and handling stability. For example, it is known that the handling stability can be improved by increasing the bead apex i without increasing the hardness or height. However, this method causes a significant deterioration in ride comfort. In order to minimize the deterioration of ride comfort, the bead apex i is divided into two layers inside and outside the tire in the radial direction, soft and hard two types of rubber are used, and a new one is added to the sidewall or bead. Providing a reinforcing rubber layer has also been proposed (see Patent Document 1 below). However, the method of forming two layers of bead apex or the method of newly adding a reinforcing rubber layer is not easy to realize due to restrictions on production facilities, and the productivity may be deteriorated.

Japanese Patent Laid-Open No. 3-193510

  The present invention has been devised in view of the above circumstances, paying attention to the rubber chafer arranged in the bead portion, and based on the optimum limitation of its height and rubber physical properties, An object of the present invention is to provide a pneumatic tire capable of improving the handling stability without causing deterioration in ride comfort.

The invention according to claim 1 of the present invention is a main body part that extends from the tread part through the sidewall part to the bead core of the bead part, and is connected to the main body part and folded around the bead core from the inner side to the outer side in the tire axial direction. A pneumatic tire comprising at least one carcass ply having a folded portion and a bead apex extending outward in the tire radial direction from the bead core, wherein at least an inner surface of the main body of the carcass ply A rubber chafer extending from the inner end in the tire radial direction of the main body portion to the outer side in the tire radial direction is attached, and the following expressions (1), (2), and (3) are satisfied.
hr-ha ≧ 10 (1)
hs × 0.67> hr (2)
Ha>Hr> Hs (3)
(Where, hr is the height of the rubber chafer (mm), ha is the height of the bead apex (mm), hs is the tire cross-sectional height (mm), Ha is the JIS hardness of the bead apex (°), and Hr is (The rubber chafer has JISA hardness (°), and Hs is the JISA hardness (°) of sidewall rubber.)

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein a height hr of the rubber chafer is 0.40 to 0.55 times a tire cross-section height hs.

  The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein a height hr of the bead apex is 0.15 to 0.40 times a tire cross-section height hs.

  According to a fourth aspect of the present invention, the rubber chafer has a sheet shape with the JISA hardness of 65 to 75 ° and 0.7 to 2.0 (mm). The pneumatic tire according to any one of 3.

  In the present invention, on the inner side surface of the main body portion of the carcass ply, the height of the rubber chafer extending from the inner end in the tire radial direction of the main body portion to the outer side in the tire radial direction and the rubber physical properties are optimally limited. Steering stability can be improved without deteriorating comfort. Since the rubber chafer is a tire constituent member that is generally used in general, the present invention can be easily handled by changing its shape. Therefore, the pneumatic tire of the present invention does not cause an increase in the number of new parts, so that the productivity is good, and the pneumatic tire can be manufactured without being restricted by production facilities.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a tire meridian cross-sectional view including a tire shaft in a normal state of the pneumatic tire 1 of the present embodiment, and FIG. 2 shows an enlarged view of an enlarged bead portion 4 thereof. The normal state uniquely defines the attitude of the pneumatic tire 1 and is a no-load state in which the tire is assembled with a normal rim (not shown) and filled with a normal internal pressure. Unless otherwise specified, the dimensions and the like of each part of the tire are in the normal state.

  The “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, For ETRTO, use “Measuring Rim”. Furthermore, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum air pressure is for JATMA, and the table is “TIRE LOAD LIMITS” for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” if it is ETRTO, but if the tire is for passenger cars, it is uniformly 180 kPa.

  The pneumatic tire 1 includes a toroidal carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a belt disposed outside the carcass 6 in the tire radial direction and inside the tread portion 2. The present embodiment exemplifies a tubeless type radial tire for a passenger car.

  The carcass 6 is composed of one or a plurality of carcass plies 6A in this example. The carcass ply 6A is a cord ply in which a carcass cord is covered with a thin topping rubber. In the present embodiment, the carcass cord is used so as to be inclined at an angle of, for example, 75 ° to 90 ° with respect to the tire equator C. Yes. The carcass cord is preferably an organic fiber cord such as polyester cord, nylon, rayon, or aramid, but a steel cord can also be used if necessary.

  The carcass ply 6A includes a toroid-shaped main body portion 6a that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and extends around the bead core 5 from the inner side in the tire axial direction to the outer side. And a folded portion 6b that has been folded. A bead apex 8 made of hard rubber that extends in a tapered shape from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b.

  The belt layer 7 includes at least two belt plies 7A and 7B in which the belt cords are arranged at a small angle of, for example, 10 to 40 ° with respect to the tire equator C. The cords are superposed in a direction crossing each other. Steel cords are preferably used as the belt cords, but organic fiber cords such as aramid and rayon can also be used as necessary.

  On the outer surface of the carcass 6, a tread rubber 2G is disposed in the tread region, a sidewall rubber 3G is disposed in the sidewall region, and a clinch rubber 4G is disposed in the bead region, thereby forming an outer skin portion of the tire. Further, a rubber chafer extending at least from the inner end 6ai in the tire radial direction of the main body portion 6a to the outer side in the tire radial direction is attached to the inner surface of the main body portion 6a of the carcass ply 6A. The inner liner 10 excellent in air impermeability for holding 11 air is arranged in a toroid shape.

  The rubber chafer 9 of the present embodiment includes a main portion 9a extending along the inner side in the tire radial direction of the bead core 5 via the carcass ply 6A, and an inner surface of the main body portion 6a of the carcass ply 6A connected to the main portion 9a. The inner portion 9b extends outward in the tire radial direction, and the outer portion 9c continues to the main portion 9a and extends outward in the tire radial direction along the folded portion 6b with a small height. Are illustrated. Although details will be described later, the rubber chafer 9 according to the present embodiment is formed by using a rubber sheet having a substantially constant thickness t, and the outer end 9T is gradually reduced in thickness.

The pneumatic tire 1 of the present embodiment is characterized by satisfying the following formulas (1), (2), and (3).
hr-ha ≧ 10 (1)
hs × 0.67> hr (2)
Ha>Hr> Hs (3)

  First, according to the formula (1), in the pneumatic tire 1, the height hr of the rubber chafer 9 is larger than the height ha of the bead apex 8, and the height difference (hr-ha) is 10 mm. Determined above. In the conventional general radial tire for passenger cars, as shown in FIG. 4, the height hr of the rubber chafer 9 is set to be significantly smaller than the height ha of the bead apex 8. In the present invention, the bending rigidity of the bead portion 4 is increased by increasing the height hr of the rubber chafer 9. However, if the height difference (hr−ha) is less than 10 mm, the bending rigidity of the bead portion 4 cannot be sufficiently increased, and the outer end 8T of the bead apex 8 and the rubber chafer 9 Since the end 9T approaches, a rigidity step is likely to occur at this portion, and durability is likely to deteriorate. The difference (hr−ha) is particularly preferably 12 mm or more, more preferably 15 mm or more.

  The height ha of the bead apex 8 that serves as a reference for the height hr of the rubber chafer 9 is not particularly limited. However, if the height ha is too small, the basic bending rigidity of the bead portion 4 tends to decrease, and conversely If it is too large, the ride quality tends to deteriorate. From such a viewpoint, the height ha of the bead apex 8 is desirably 0.15 to 0.40 times, more preferably 0.25 to 0.32 times the tire cross-section height hs.

  Preferably, the height hc of the folded portion 6b of the carcass ply 6A is also suitably adjusted according to these heights. That is, it is desirable that the outer end 6be of the folded portion 6b is positioned so as not to approach the outer ends 8T and 9T of the bead apex 8 and the rubber chafer 9, and the maximum tire width position M. In the present embodiment, the height hc of the folded portion 6 b is smaller than the height ha of the bead apex 8. In particular, the difference in height (ha−hc) is 5 mm or more, more preferably about 5 to 15 mm, which helps to further relax the rigidity step of the bead portion 4 and improve the durability.

  Further, according to the expression (2), in the pneumatic tire 1 of the present invention, the upper limit of the height hr of the rubber chafer 9 is determined to be less than 0.67 times the tire cross-section height hs. Even if the height hr of the rubber chafer 9 is increased, the effect of improving the steering stability reaches a peak, and there is a possibility that the rolling resistance is deteriorated due to an increase in tire weight. Particularly preferably, the height hr of the rubber chafer 9 is 0.40 to 0.55 times, more preferably 0.45 to 0.50 times the tire cross-section height hs. Note that if the outer end of the rubber chafer 9 and the outer end of the folded portion 6b of the carcass ply 6A overlap, the change in rigidity becomes significant, and the strain tends to concentrate on that portion. Therefore, | hr−hc | is desirably 10 mm or more.

  Further, according to the expression (3), the pneumatic tire 1 of the present invention has the JISA hardness Hr of the rubber chafer 9 larger than the JISA hardness Hs of the side wall rubber 3G and the JISA hardness Ha of the bead apex 8. Are also defined as small. As the side wall rubber 3G, a relatively soft rubber material having excellent flexibility is usually used. For this reason, if the JISA hardness Hr of the rubber chafer 9 is smaller than the JISA hardness Hs of the side wall rubber 3G, the bending rigidity of the bead portion 4 cannot be sufficiently increased. The bead apex 8 is made of a very hard rubber among the rubber constituting the tire. If a rubber harder than this is used for the rubber chafer 9, the ride comfort is significantly deteriorated. The preferable JISA hardness of each rubber material will be specifically described as follows.

  First, the bead apex 8 passing through the bending neutral line ML of the bead portion 4 has a JISA hardness Ha of preferably 80 ° or more, more preferably 85 ° or more, and further preferably 90 ° or more. If the angle is less than 80 °, the basic bending rigidity of the bead portion 4 tends not to be obtained. On the contrary, even if the JISA hardness Ha of the bead apex 8 is too large, the ride comfort tends to deteriorate, so the upper limit is preferably 95 ° or less.

  Further, the rubber chafer 9 has a JISA hardness Hr of preferably 65 ° or more, more preferably 68 ° or more. If the hardness Hr is less than 68 °, not only the effect of reinforcing the bending rigidity of the bead portion 4 can be obtained, but also damage tends to occur during rim assembly, and durability tends to deteriorate. The rubber chafer 9 is positioned on the inner side in the tire axial direction with respect to the bending neutral line ML of the bead portion 4 and mainly bears a tensile load during load running. For this reason, if the JISA hardness Hr of the rubber chafer 9 is too large, not only will the ride comfort be deteriorated, but the rubber will be liable to crack and the durability will be deteriorated. From such a viewpoint, the upper limit of the JISA hardness of the rubber chafer 9 is preferably 75 ° or less, more preferably 72 ° or less.

  Further, the side wall rubber 3G has a JISA hardness Hs of preferably 45 ° or more, more preferably 48 ° or more, and further preferably 50 ° or more. If it is less than 45 °, the trauma resistance tends to deteriorate and the appearance of the tire tends to be impaired at an early stage. Conversely, if the JISA hardness Hs of the sidewall rubber 3G is too large, the flexibility is lowered and damage such as cracks is likely to occur. Therefore, the upper limit is preferably 60 ° or less, more preferably 58 ° or less, Preferably it is 55 ° or less.

  Moreover, as long as Formula (3) is satisfy | filled, each rubber material can be variously set within the said range, Preferably, the difference (Ha-Hr) and / or (Hr-Hs) of a JISA hardness can be adjusted appropriately. desirable.

  As shown in FIG. 2, in the deformation region Y1 of the bead portion 4 during load running, bending and compressive loads mainly act on the bead apex 8 as the carcass 6 deforms, but the rubber chafer 9 mainly pulls. A load acts. In order to improve steering stability such as turning, it is effective to increase the JISA hardness of the bead apex 8 to reduce the compressive strain and suppress the amount of vertical deflection of the tire. Further, the rubber chafer 9 is preferably provided with an appropriate flexibility so as not to cause a crack or the like against a tensile strain. However, if the difference in hardness between the two rubber materials is too large, stress concentration occurs between the interface of the carcass ply, and the carcass cord and the rubber are easily separated. This significantly deteriorates the durability of the tire. From such a viewpoint, the difference in JIS hardness (Ha-Hr) between the bead apex 8 and the rubber chafer 9 is preferably set to 5 to 20 °, more preferably 10 to 15 °.

  The carcass 6 is mainly subjected to bending deformation as indicated by an arrow B in the deformation region Y2 of the sidewall portion 3 during load traveling. Along with this deformation, bending and compression loads are mainly applied to the rubber chafer 9, and tensile loads are mainly applied to the sidewall rubber 3G. In order to enhance the ride comfort, it is desirable to secure a larger amount of bending deformation and increase shock absorption. From this point of view, the difference in JISA hardness (Hr-Hs) between the rubber chafer 9 and the sidewall rubber 3G is preferably 5 to 20 °, more preferably 10 to 15 °.

  Further, the thickness t of the rubber chafer 9 is preferably 0.7 to 2.0 mm. If the thickness t of the rubber chafer 9 is too large, the tire weight tends to increase and the ride comfort deteriorates. Conversely, if the thickness is too small, the steering stability tends not to be improved.

  The pneumatic tire 1 of the present invention can be manufactured according to a conventional method. An example is shown by the manufacturing process of such a pneumatic tire 1 by FIG. 3 (A) thru | or (C). As shown in FIG. 3 (A), an inner liner 10 having a wide rubber chafer 9 pre-assembled at both ends and a carcass ply 6A are wound around the molding drum D, and a bead apex is wound on the outside thereof. The bead core 5 to which 8 is attached is fitted. Next, as shown in FIG. 3B, part of the rubber chafer 9 is folded together with the carcass ply 6A, and the sidewall rubber 3G, the clinch rubber 4G, and the like are attached to the outside thereof. Thereafter, as shown in FIG. 3C, the carcass ply 6A and the like are deformed into a toroid shape and integrated with the belt layer 7, the tread rubber 2G, and the like to form a raw cover. By vulcanizing this, the pneumatic tire 1 shown in FIGS. 1 and 2 can be manufactured. Therefore, the actual vehicle performance of the tire can be improved without changing the current tire manufacturing equipment.

In order to confirm the effect of the present invention, a tire having a size of “195 / 65R15 91H” was prototyped based on the specifications shown in Table 1. As actual vehicle performance, steering stability, riding comfort, tire weight, rim assembly damage performance and durability were tested.
The test method is as follows.

<Steering stability>
Each test tire is assembled on a rim (15x6.0J) and mounted on a 1800cm ³ domestic FF vehicle with four wheels, filled with an internal pressure of 200 kPa and driven on a dry asphalt road test course by one driver. In addition, characteristics relating to steering wheel response, rigidity, grip, etc. were evaluated by sensory evaluation of the driver. The results were displayed by a 10-point method with Comparative Example 1 as 6. The larger the value, the better.

<Ride comfort>
Using the same test vehicle as above, on a stepped road on dry asphalt road, Berjaso road (cobblestone road surface), Bitzman road (road surface covered with pebbles), etc. Sensory evaluation was performed, and the results were displayed by a 10-point method with Comparative Example 1 as 6. The larger the value, the better.

<Tire weight>
The weight per tire was measured and displayed as the amount of increase or decrease based on Comparative Example 1.

<Rim assembly damage resistance>
Each test tire was assembled to a rim (15 × 6.0 J) using a tire mounter (automatic rim assembling machine) and tested. After assembly, the tire was removed from the rim and examined for damage to the bead. Each tire was tested five by one, and even if one of them was damaged, it was rejected, and the others were accepted.

<Drum durability>
Each sample tire was mounted on a rim (15 × 6.0J), and a drum having a diameter of 1.7 m was run at an internal pressure of 190 kPa, a longitudinal load of 6.96 kN, a speed of 80 km / h, and completed 30,000 km without damage. The test was accepted, and any damage that could be visually confirmed during the test was rejected. Table 1 shows the test results.

  As a result of the test, it can be confirmed that the actual tire performance of the tire of the example is significantly improved as compared with the comparative example. Also, the increase in tire weight is very small. Moreover, the tire of an Example can be produced in the same process as the tire of Comparative Example 1, and it has also been confirmed that the productivity does not deteriorate.

It is sectional drawing of the pneumatic tire of this embodiment. It is sectional drawing which expands and shows the bead part. It is a cross-sectional schematic diagram which shows an example of the manufacturing process of the pneumatic tire of this embodiment. It is sectional drawing of the conventional pneumatic tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 3g Side wall rubber 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 8 Bead apex 9 Rubber chafer 9a Rubber chafer main part 9b Rubber chafer inner part 9c Rubber chafer Outside of

Claims (4)

From at least one carcass ply having a main body part that extends from the tread part through the sidewall part to the bead core of the bead part, and a folded part that is connected to the main body part and is folded around the bead core from the inner side to the outer side in the tire axial direction. Carcass
A pneumatic tire comprising a bead apex extending radially outward from the bead core,
On the inner side surface of the main body portion of the carcass ply, a rubber chafer extending at least from the inner end in the tire radial direction of the main body portion to the outer side in the tire radial direction is attached, and the following formulas (1), (2) and ( A pneumatic tire characterized by satisfying 3).
hr-ha ≧ 10 (1)
hs × 0.67> hr (2)
Ha>Hr> Hs (3)
(Where, hr is the height of the rubber chafer (mm), ha is the height of the bead apex (mm), hs is the tire cross-sectional height (mm), Ha is the JIS hardness of the bead apex (°), and Hr is (The rubber chafer has JISA hardness (°) and Hs is the JISA hardness (°) of sidewall rubber.)   The pneumatic tire according to claim 1, wherein a height hr of the rubber chafer is 0.40 to 0.55 times a tire cross-section height hs.   The pneumatic tire according to claim 1, wherein a height hr of the bead apex is 0.15 to 0.40 times a tire cross-sectional height hs.   The pneumatic rubber according to any one of claims 1 to 3, wherein the rubber chafer has a sheet shape with the JISA hardness of 65 to 75 ° and 0.7 to 2.0 (mm). tire.

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