JP5481949B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire that improves steering stability without significantly reducing tire mass without reducing tire durability.

  In recent years, there has been an increasing demand for weight reduction of tires from the viewpoint of improving fuel efficiency. As a representative measure, weight reduction has been achieved by reducing the amount of use of members constituting the tire. For example, means such as reducing the number of carcass layers or reducing the amount of rubber constituting the tire are employed.

  On the other hand, in order to improve the steering stability of the tire, it is effective to increase the tire rigidity, and it is particularly effective to increase the casing rigidity. In order to increase the tire rigidity, there are means such as increasing the number of carcass layers or thickening the carcass cord. However, these means are accompanied by a significant increase in tire mass, and thus go against weight reduction of the tire and increase fuel efficiency. For this reason, it has been difficult to achieve both weight reduction of the tire and improvement of steering stability by such measures.

  In Patent Document 1, as a measure for improving steering stability without increasing the mass of the tire, the folded portion of the carcass layer is extended to the inner side in the tire radial direction of the belt layer, and between the folded portion and the carcass main body portion. It has been proposed to provide a cord reinforcement layer between layers in the shoulder portion. That is, since the tire rigidity can be increased by the cord reinforcing layer, it is possible to achieve both weight reduction of the tire and improvement of steering stability without increasing the number of used carcass layers and the amount of rubber.

  However, if a cord reinforcing layer is provided between the carcass body portion and the folded portion, the cord constituting the cord reinforcing layer and the carcass cord cross each other, and a relative movement occurs between the two cords during traveling. There was a problem that delamination was likely to occur between the cord reinforcing layer and the carcass layer, and the durability was poor.

JP 7-179101 A

  An object of the present invention is to solve the above-described problems, and to provide a pneumatic tire that improves steering stability without significantly increasing tire mass without reducing tire durability. It is in.

In order to achieve the above object, a pneumatic tire according to the present invention includes a carcass layer mounted between a pair of left and right bead portions, a belt layer disposed on an outer periphery of the carcass layer, and folded back at the bead portion. In a pneumatic tire in which the folded end of the layer extends to the inner side in the tire radial direction of the belt layer, at least on the side that becomes the vehicle outer side when the vehicle is mounted, a JIS hardness is provided between the body portion and the folded portion of the carcass layer. The rubber reinforcing layer of 65 to 85 is disposed, the outer end in the tire radial direction of the rubber reinforcing layer is extended inward in the tire width direction from the end of the belt layer, and the inner end in the tire radial direction of the rubber reinforcing layer parts while the Ru is positioned radially outside the tire maximum width position, wherein the rubber reinforcing layer constituted by splicing the three rubber layers having different hardness, the three rubber The maximum hardness in the tire radial direction of the intermediate rubber layer of, characterized in that a lower rubber layer hardness than the rubber layer in between on both sides.

Moreover, in the structure mentioned above, it is preferable to comprise as described in (1)-( 4 ) below.

(1) The amount of overlap between the end portion of the rubber reinforcing layer in the tire radial direction and the end portion of the belt layer is 5 to 10 mm, and the inner end portion in the tire radial direction of the rubber reinforcing layer and the maximum tire width The distance from the position in the tire radial direction is 0 to 35% of the tire cross-section height.
(2) The maximum thickness of the rubber reinforcing layer is 1 to 3 mm.
(3) providing a pre-SL rubber reinforcing layer symmetrically with respect to the tire equator.
( 4 ) One carcass layer is formed.

  According to the present invention, a rubber reinforcing layer having a JIS hardness of 65 to 85 is disposed between the main body portion and the folded portion of the carcass layer at least on the vehicle outer side when the vehicle is mounted. Since the end is located on the inner side in the tire width direction from the end of the belt layer, and the inner end in the tire radial direction of the rubber reinforcing layer is located on the outer side in the tire radial direction from the maximum tire width position, the tire mass is greatly increased. Without increasing the rigidity of the shoulder portion, the steering stability can be improved. Furthermore, since the rubber reinforcing layer is sandwiched between the main body portion and the folded portion of the carcass layer, delamination due to friction between the cords between the carcass main body portion and the folded portion is suppressed, and durability is improved. Can be maintained.

1 is a circumferential sectional view of a pneumatic tire according to an embodiment of the present invention. The reinforcing rubber used for a pneumatic tire of the present invention is a cross-sectional view illustrating.

  In the pneumatic tire shown in FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. Both ends of the carcass layer 4 are mounted between the pair of left and right bead portions 3 so as to be folded around the bead core 5 from the inside to the outside of the tire. In the tread portion 1, a plurality of belt layers 6 are arranged on the outer peripheral side of the carcass layer 4 so that the cords cross each other.

  The carcass layer 4 reaches the inner side in the tire radial direction and the inner side in the tire width direction of the end portion 6a of the innermost belt layer 6 where the extended end of the folded portion 4a has the maximum width, and the folded portion 4a and the belt layer 6 respectively The ends of each other overlap each other.

  A rubber reinforcing layer 7 made of rubber having a JIS hardness of 65 to 85 is disposed between the folded portion 4a and the main body portion 4b of the carcass layer 4. The rubber reinforcing layer 7 has a tire radial direction outer side end portion 7a positioned on the inner side in the tire width direction from the end portion 6a of the belt layer 6 and a tire radial direction inner side end portion 7b from the tire maximum width position A in the tire radial direction. It is located on the outside and is arranged mainly in a region corresponding to the buttress portion.

  By providing the rubber reinforcing layer 7 in this way, the rigidity of the buttress portion can be improved and the steering stability can be improved. In addition, since it is only necessary to provide the rubber reinforcing layer 7 as a means for improving steering stability, the tire mass is not significantly increased, and low fuel consumption can be maintained.

  Since the buttress portion is a portion where the deformation is large in the tire cross section, if the rubber reinforcing layer 7 is disposed on the outer side of the tire with respect to the folded portion 4a of the carcass layer 4, the body portion 4b of the carcass layer 4 and the carcass folded back. Delamination is likely to occur due to stress concentrated between the layers with the portion 4a. However, as in the configuration described above, when the rubber reinforcing layer 7 is disposed between the carcass folded portion 4a and the carcass main body portion 4b, the rubber reinforcing layer 7 disperses stress and suppresses delamination. Durability can be improved. Further, when a fiber reinforcement layer is disposed instead of the rubber reinforcement layer, the cord of the fiber reinforcement layer intersects with the cord of the main body portion 4b and the folded portion 4a of the carcass layer 4 and breakage easily occurs.

  In the present invention, if the hardness of the rubber constituting the rubber reinforcing layer 7 is less than 65 in terms of JIS hardness, sufficient tire rigidity cannot be obtained, so that the steering stability improvement effect cannot be obtained. On the contrary, if the hardness of the rubber is more than 85 in terms of JIS hardness, the difference in rigidity between the rubber reinforcing layer 7 and its peripheral part becomes large, causing stress concentration at the interface and causing failure. Here, JIS hardness refers to the hardness of type A as defined by JIS, and the hardness measured at a temperature of 20 ° C.

  In the present invention, the length in which the tire radial direction outer side end portion 7a of the rubber reinforcing layer 7 overlaps the end portion 6a of the belt layer 6 is preferably 5 to 10 mm. If the overlap amount is less than 5 mm, the rigidity change from the rubber reinforcing layer 7 to the belt layer 6 is not smooth, and there is a risk of causing a peeling failure. Conversely, if the overlap amount is more than 10 mm, the effect of the overlap is saturated, and conversely, there is a disadvantage that the tire mass increases.

  The tire radial inner end 7b of the rubber reinforcing layer 7 preferably has a tire radial distance Hb from the tire maximum width position A of 0 to 35% of the tire cross-section height SH, more preferably 10 to 25. % Is good. When the rubber reinforcing layer 7 extends beyond the tire maximum width position A to the bead side, it is not preferable because it causes deterioration in riding comfort and an increase in mass. On the contrary, when the distance Hb exceeds 35% of SH, the rigidity improvement of the buttress portion is small and the steering stability cannot be improved. Here, the maximum width position A of the tire is a position where the width of the tire is maximized in a no-load state in which the tire is assembled on a standard rim and filled with normal internal pressure.

  It is preferable that the rubber reinforcing layer 7 has a maximum thickness of 1 to 3 mm. The shape of the rubber reinforcing layer 7 is preferably substantially rectangular in cross-section, but a substantially triangular shape or a substantially trapezoidal shape can also be employed depending on the application. If the maximum thickness of the rubber reinforcing layer 7 is less than 1 mm, an effective improvement effect of tire rigidity cannot be obtained, and if it exceeds 3 mm, the mass is greatly increased and further bending of the carcass is induced, resulting in a decrease in durability. Here, the maximum thickness of the rubber reinforcing layer 7 is the maximum thickness between the carcass folded portion 4b and the carcass main body portion 4c.

As shown in FIG. 2 , the rubber reinforcing layer 7 has different hardness so as to maximize the hardness of the intermediate rubber layer 7d in the tire radial direction and to splice rubber layers 7c and 7e having lower hardness on both sides thereof. It is composed of a plurality of rubber layers 7c, 7d, 7e. When the rubber reinforcing layer 7 is composed of a plurality of rubber layers having different hardnesses as described above, a gradual change in rigidity can be provided. At this time, it is preferable to connect the splice portions obliquely and gradually change the rigidity at the interface. However, even when the reinforcing layer is constituted by a plurality of rubber layers, the maximum thickness of the reinforcing layer is preferably 1 to 3 mm.

  In the present invention, the rubber reinforcing layer described above may be provided at least on the tire side located on the vehicle outer side when the vehicle is mounted. Preferably, the side portions on both the left and right sides of the tire are axisymmetric with respect to the tire equator. It is good to provide. Thus, the uniformity of the tire can be maintained by providing it symmetrically on both sides of the tire.

Eleven types of pneumatic tires of Conventional Examples 1 and 2, Test Examples 1 to 5, and Comparative Examples 1 to 4 having tire sizes common to 275 / 70R16 and different specifications as shown in Tables 1 and 2 were manufactured. .
Conventional Example 1 is an example in which no reinforcing layer is provided. Conventional example 2 is an example in which a cord reinforcing layer of nylon cord is provided between carcass layers. Test Examples 1 to 5 are all examples in which a rubber reinforcing layer is provided between the carcass layers, and the carcass folded end position, the positions of both ends of the reinforcing layer, and the JIS hardness of the rubber are common, and the carcass folded portion and the belt layer The overlap amount and the maximum thickness of the reinforcing layer are different. Comparative Examples 1 and 2 are examples in which the JIS hardness of the rubber is out of the prescribed range of the present invention with respect to Test Example 1. Comparative example 3 is an example in which the arrangement position of the reinforcing layer and the carcass folding end position deviate from the definition of the present invention. Comparative Example 4 is an example in which the radially inner end of the reinforcing layer is extended closer to the bead than the tire maximum width position with respect to Test Example 1.

  These 11 types of tires are assembled on a 16x7JJ rim, each mounted on a 4WD vehicle with a displacement of 3.0L, and handling stability (dry handling) and tire durability with the axle load equivalent to two passengers in the following manner And tire mass were measured.

<Steering stability (dry handling)>
The evaluation was based on the average value of the sensory test when the circuit was run by five test drivers. The evaluation value is indicated by an index with Conventional Example 1 being 100, and the higher the index, the better the dry handling property.

<Tire durability>
The test tire was filled with an air pressure of 140 kPa, and the presence or absence of a failure was compared when running on a drum rotating at a speed of 120 km / h for 3 hours. ○ means no failure, × means failure.

<Tire mass>
The mass was measured by measuring the mass of each test tire and indicated by an index with the tire mass shown in Conventional Example 1 being 100. The smaller the index value, the lighter the mass and the better.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 4a Folding part 4b Body part 6 Belt layer 7 Rubber reinforcement layer 7a Tire radial direction outer side edge 7b Tire radial direction inner side edge part

Claims (5)

A carcass layer is mounted between a pair of left and right bead portions, a belt layer is disposed on the outer periphery of the carcass layer, and the folded end of the carcass layer folded at the bead portion extends to the inside in the tire radial direction of the belt layer. In the pneumatic tire that was made to
A rubber reinforcing layer having a JIS hardness of 65 to 85 is disposed between the main body portion and the folded portion of the carcass layer at least on the vehicle outer side when the vehicle is mounted, and an outer end in the tire radial direction of the rubber reinforcing layer is disposed. while the belt layer end portion extending inwardly in the tire width direction than the, and Ru the radially inner end of the rubber reinforcing layer is positioned radially outside the maximum tire width position, hardness the rubber reinforcing layer Are formed by splicing three rubber layers having different diameters, and the hardness of the intermediate rubber layer in the tire radial direction is maximized among the three rubber layers, and the rubber layers having lower hardness than the intermediate rubber layer on both sides thereof Placed pneumatic tire.   The amount of overlap between the tire radial outer end of the rubber reinforcing layer and the end of the belt layer is 5 to 10 mm, and the tire radial inner end of the rubber reinforcing layer and the tire maximum width position The pneumatic tire according to claim 1, wherein a distance in a tire radial direction is 0 to 35% of a tire cross-sectional height.   The pneumatic tire according to claim 1 or 2, wherein the rubber reinforcing layer has a maximum thickness of 1 to 3 mm. The pneumatic tire according to any one of claims 1 to 3 , wherein the rubber reinforcing layer is provided line-symmetrically with respect to the tire equator. The pneumatic tire according to any one of claims 1 to 4, wherein the carcass layer is one.

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