JP2007191083A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire exhibiting operation stability from a low load area to a high load area by providing a proper belt protecting layer to restrict an increase in the grounding length of a shoulder area of a tread corresponding to both ends of the belt layer, in which rigidity is low, without remarkably increasing the mass, rolling resistance and manufacturing cost of a tire. <P>SOLUTION: The pneumatic radial tire is provided with a radial carcass 3 extended toroidally, a belt 6 positioned on the peripheral side of a crown 4 of the carcass 3 and constituted of the belt layers 5a and 5b formed by coating cords with rubber and formed with crossing cord layers crossing each other, while pinching a tire equator between the belt layers, and a belt protecting layer 7 positioned outside in the tire radial direction of the belt 6 and formed by coating the cords extended in the tire circumferential direction with rubber. In the cross section of the tire cross direction, the cords structuring a central area 10 of the belt protecting layer 7 have elasticity smaller than that of the cords constituting both ends area 11 and 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention comprises a radial carcass extending in a toroidal shape and at least two belt layers positioned on the outer peripheral side of the crown portion of the carcass and coated with rubber, and the cord is a tire equatorial plane between adjacent belt layers. A belt formed by forming an intersecting belt layer that intersects with each other across the belt, and a belt protective layer formed by rubber-covering a cord that is positioned on the outer side in the tire radial direction of the belt and extends substantially along the tire circumference. In particular, it is intended to improve steering stability without significantly increasing the mass, rolling resistance, and manufacturing cost of the tire.

  In a conventional pneumatic radial tire, a cord extending in a direction intersecting with the cord constituting the carcass is rubber-coated on the outer periphery of the crown portion of the radial carcass configured by rubber-covering the cord extending substantially in the tire width direction. Generally, at least one belt layer configured as described above is disposed.

  For example, in Patent Document 1, a first belt-like ply in which a first belt cord is covered with a first topping rubber, and a second belt cord made of a material different from the first belt cord are referred to as a first topping rubber. Was formed by arranging two or more kinds of belt-like plies including at least a second belt-like ply covered with a second topping rubber having a different composition in the tire width direction and spirally winding the tire equatorial plane at a small angle. A pneumatic radial tire having a belt layer composed of one or more belt plies is described. According to this, the rigidity of the tread portion can be easily tuned by selecting the material of the belt cord, and by using the topping rubber suitable for each belt cord, the rubber separation of the belt cord is suppressed and the deterioration of the durability is prevented. be able to.

  In particular, in the case of a recreational vehicle (RV), the load changes relatively greatly between the two-passenger state and the full load state, but there is little change in the ground contact shape in any state, and the handling stability is not impaired. Desired. Conventionally, in a pneumatic radial tire to which a relatively high load is applied, for the purpose of improving durability, a cross belt layer in which cords cross each other across the tire equatorial plane is formed between adjacent belt layers, and the belt layer and the tread. A belt protective layer is also disposed between the portions so as to cover the belt layer.

  For example, Patent Document 2 describes that a belt protective layer is formed by spirally winding a ribbon-like body formed by covering a plurality of organic fiber cords with rubber in a substantially tire circumferential direction.

JP 2003-34109 A JP-A-1-109108

  The tire described in Patent Document 1 has a problem that the cost of raw materials is high and the manufacturing is complicated because the manufacturing is complicated. Further, in the tire described in Patent Document 2, when only the so-called cap layer covering the entire belt layer is disposed, the contact length of the shoulder region of the tread portion corresponding to both ends of the belt layer having low rigidity increases, There was a risk that steering stability would be reduced. On the other hand, in the tire described in Patent Document 2, in addition to the cap layer, when a so-called layer layer having a narrow width is disposed at a position corresponding to both end portions of the belt layer, the contact length of the shoulder region of the tread portion is reduced. Although the increase can be suppressed and the steering stability can be maintained, the thickness of the tire is increased by the amount of the layer layer, which may lead to an increase in mass, rolling resistance and manufacturing cost.

  Accordingly, an object of the present invention is to solve such problems of the prior art, and the object is to optimize the belt protective layer, thereby reducing the mass, rolling resistance and manufacturing cost. An object of the present invention is to provide a tire that exhibits stable steering stability from a low load range to a high load range without a significant increase.

  In order to achieve the above-mentioned object, the present invention comprises a radial carcass extending in a toroid shape, and at least two belt layers which are positioned on the outer peripheral side of the crown portion of the carcass and covered with rubber, and are adjacent to each other. A belt formed by forming an intersecting belt layer in which the cords cross each other across the tire equatorial plane between the belt layers, and a cord that is positioned on the outer side in the tire radial direction of the belt and that extends in the tire circumferential direction is rubber-coated 1 In a pneumatic radial tire including a belt protective layer, a cord constituting a central region when the belt protective layer is divided into a central region and both end regions in a tire width direction cross section constitutes both end regions. A pneumatic radial tire having an elastic modulus smaller than that of a cord. By adopting such a configuration, an increase in the contact length of the shoulder region of the tread portion corresponding to both ends of the belt layer having low rigidity can be suppressed without significantly increasing the mass, rolling resistance, and manufacturing cost.

  Here, “substantially tire circumferential direction” means a direction within a range of ± 10 °, preferably ± 5 ° with respect to the tire circumferential direction, and “central region” of the belt protective layer means a tire equator. The region including the surface is referred to, and the “both end regions” refer to regions located on both sides of the central region.

  Further, it is preferable that the belt protective layer is formed by spirally winding a ribbon-shaped member formed by covering the cord with rubber in the tire circumferential direction.

  Furthermore, it is preferable that the cord constituting the central region of the belt protective layer is a nylon cord, and the cord constituting both end regions is a polyethylene terephthalate cord.

  Furthermore, the central region preferably has a width within the range of 33 to 90% of the width of the belt protective layer with the tire equatorial plane as the center, and more preferably has a width within the range of 60 to 80%.

  In addition, it is preferable that the belt layer has two layers, and the end region of the belt protective layer extends to cover an end portion of the second belt layer that is a belt layer positioned on the outer side in the tire radial direction. In this case, the first belt layer, which is a belt layer located on the inner side in the tire radial direction, is wider than the second belt layer, and both end portions of the belt protective layer are the end portions of the first belt layer and the second belt layer, respectively. More preferably, it is located between the ends of the two.

  According to the present invention, by optimizing the belt protective layer, the shoulder region of the tread portion corresponding to both ends of the belt layer having low rigidity can be obtained without significantly increasing the mass, rolling resistance and manufacturing cost of the tire. It is possible to suppress the increase in the contact length and to exhibit stable steering stability from a low load range to a high load range.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a tire width direction cross section of a typical pneumatic radial tire (hereinafter referred to as “tire”) according to the present invention, and FIG. 2 schematically shows the cord arrangement of the tire belt shown in FIG. Show.

  A tire 1 shown in FIG. 1 includes a carcass 3 extending in a toroidal shape between bead portions 2 and 2 and a belt layer of at least two layers (two layers in FIG. 1) located on the outer periphery of the crown portion 4 of the carcass 3. A belt 6 composed of 5a and 5b and a single belt protective layer 7 positioned on the outer side in the tire radial direction of the belt 6 are provided. The belt layers 5a and 5b are formed by covering the cords with rubber like the belt layers of the conventional radial tires, and are laminated so that the cords cross each other across the tire equatorial plane E. The so-called cross belt layer is formed. In this cross belt layer, as shown in FIG. 2, the cord 8 between adjacent belt layers forms a rhombus mesh 9, and the inside of the mesh is filled with rubber, and these cords are restrained in a viscoelastic manner. Yes. As a result, resistance to deformation caused by the internal pressure of the tire or external input is generated, so that high rigidity can be exhibited. The protective belt layer 7 is formed by covering a cord with rubber, and is arranged so that the cord extends in a substantially circumferential direction. In a tire having a cross belt layer, when the tire rolls under load, shear strain is generated between adjacent belt layers constituting the cross belt layer, and separation between belt layers is likely to occur, but a belt protective layer is disposed on the outer periphery of the belt. The belt interlayer separation is prevented by suppressing the extension of the belt in the tire circumferential direction.

  However, since the cord 8 is cut at both width ends of the belt 6, a complete mesh cannot be formed, and the inside is open. As a result, the rigidity of the end region of the belt 6 is lowered, the contact length of the tread shoulder region having low rigidity is increased when a load is applied, and the contact length of the tread center region is relatively shortened. If the entire belt in the tread area has sufficient tension, the force from the road surface is transmitted well to the tires and the driving stability is improved, but the contact area of the tread shoulder area is relatively increased in this way. As a result, the load sharing ratio of the tread shoulder region that does not sufficiently maintain the tension increases, leading to a decrease in steering stability.

  Therefore, in the present invention, when the belt protective layer 7 is divided into the center region 10 including the tire equatorial plane E and the both end regions 11, 11 located outside the center region 10 in the width direction, 11 is composed of a cord having an elastic modulus larger than that of the cord constituting the central region 10, thereby reinforcing the rigidity of both end regions 11 of the belt 6 and suppressing an increase in the contact length of the tread shoulder region. ing. That is, the material of the cord used is changed so that the rigidity distribution corresponding to the required characteristics is obtained in one belt protective layer. As a result, the steering stability can be improved without increasing the thickness of the tire as in the so-called cap-and-layer structure, and thus without significantly increasing the mass, rolling resistance and manufacturing cost. .

  Such a belt protective layer is formed by covering a parallel-arranged cord with rubber, making a sheet-like member having the same width as the belt protective layer once in the tire circumferential direction, and joining both ends. However, in this case, since the joint portion of the sheet-like member exists on the circumference, the uniformity of the tire is lowered. From the viewpoint of minimizing the presence of such joints and improving uniformity, it is preferable to form the belt protective layer 7 by spirally winding a ribbon-like member formed by covering a cord with rubber in a substantially tire direction. . Further, by forming the belt protective layer 7 in this manner, two types of ribbon-shaped members, that is, a low-elasticity ribbon-shaped member for configuring the central region 10 and a high-elasticity ribbon-shaped member for configuring the end region 11 are used. By preparing the above, it becomes unnecessary to make various sheet-like members according to the tire size and required performance, and an increase in manufacturing cost can be avoided.

  The cord constituting the central region 10 of the belt protective layer 7 is preferably an organic fiber cord, particularly a nylon cord. The reason why the nylon cord is particularly suitable is that it is relatively light and inexpensive and has sufficient tensile strength, so that the central region of the belt can be used without deteriorating other performance such as mass, grounding performance, and rolling resistance. This is because it can be effectively reinforced.

  Moreover, as a code | cord | chord which comprises the both ends area | region 11 of the belt protective layer 7, an organic fiber cord, especially a polyethylene terephthalate cord are preferable. The reason why the polyethylene terephthalate cord is particularly suitable is that the both end regions of the belt can be efficiently reinforced without a significant increase in mass because it has a high tensile strength while being relatively light.

  The ratio between the central region 10 of the belt protective layer 7 and both end regions 11 and 11 can be appropriately changed according to the performance required for the tire, but the width of the central region 10 is changed to the overall width W of the belt protective layer 7. It is preferable to be within the range of 33 to 90% of the above. This is because when the width of the central region 10 is less than 33% of the width W, the cost is increased, and the load dependency improvement of the steering stability is small, and when this exceeds 90% of the width W, This is because it is somewhat advantageous in terms of cost, but the improvement in load dependency of steering stability is still small.

  When the belt layer has two layers as shown in FIG. 1, the end region 11 of the belt protective layer 7 covers the end portion 12 of the second belt layer 5b, which is a belt layer located on the outer side in the tire radial direction. preferable. From the viewpoint of reinforcing the belt layer, the belt protective layer 7 is preferably at least as wide as the second belt layer 5b, but the end of the belt protective layer 7 and the end of the second belt layer 5b are tires. If they are at the same position in the width direction, there is a risk that the strain will concentrate here and separation will occur, so by arranging the belt protection layer 7 so as to cover the second belt layer 5b, both reinforcement and prevention of separation are achieved. It is to do.

  FIG. 3 shows a cross section in the tire width direction of another embodiment according to the present invention. When the belt layer is two layers and the first belt layer 5a, which is a belt layer located on the inner side in the tire radial direction, is wider than the second belt layer 5b, as shown in FIG. The end portions 13 and 13 are preferably located between the end portion 14 of the first belt layer 5a and the end portion 12 of the second belt layer 5b. The end portion 14 of the first belt layer 5a is greatly distorted during running. If the end portion 14 is covered with the belt protective layer 7 to suppress the strain, the large stress is concentrated on the end portion 14 of the first belt 5a. However, there is a risk of so-called belt edge separation. In the embodiment shown in FIG. 3, the end portion 13 of the belt protective layer 7 is disposed between the end portion 15 of the first belt layer 5a and the end portion 12 of the second belt layer 5b. The movement of the end 15 is released to avoid such stress concentration. In this configuration, although the range of reinforcement by the belt protective layer 7 is narrowed, the second belt layer 5b is disposed on the end portion 14 of the first belt layer 5a where the belt protective layer 7 is not disposed. Since there is no mesh, therefore, there is little influence on steering stability.

  Note that the above description shows only a part of the embodiment of the present invention, and these configurations can be combined with each other or various modifications can be made without departing from the gist of the present invention. . For example, in the illustrated embodiment, there are two belt layers, but the belt layers can be four layers or six layers depending on the load conditions in which the tire is used.

  Next, tires according to the present invention were prototyped and performance evaluations were performed, which will be described below.

  The tire according to the example is a radial tire for passenger cars having a tire size of 195 / 65R15, and has a structure as shown in FIG. The tire belt protective layer has a central region made of a ribbon-like member coated with nylon cord with rubber, and an end region made of a ribbon-like member coated with polyethylene cord with rubber. The width of the central region with respect to the entire width is 72. %.

  For comparison, the tire size is the same as that of the tire of the example, and has the same carcass and belt as the tire of the example, but the configuration of the belt protective layer is different from that of the tire of the example. 2 tires were also prototyped. In the tire of Conventional Example 1, the belt protective layer is composed only of a ribbon-like member in which a nylon cord is covered with rubber, and the width of the belt protective layer is the same as that of the tire of the example. Further, in the tire of Conventional Example 2, the belt is formed by disposing a layer layer made of a ribbon-like member made of rubber coated nylon cord on both ends of a cap layer made of only a ribbon-like member coated with nylon cord rubber. The protective layer is comprised and the width | variety is the same as the tire of Example 1. FIG.

  Each of the test tires was mounted on a rim of size 6J × 15 to form a tire wheel, and the following tests were performed.

(Maneuvering stability change test)
The tire wheel is mounted on four wheels of an RV vehicle capable of riding eight people, and an air pressure of 230 kPa (relative pressure) is applied, and the circuit includes a long straight line portion under a load condition equivalent to two passengers and eight passengers. And driving on a test course consisting of a handling evaluation road with many gentle curves in a speed range from low speed to 150 km / h, the steering stability (handle response) at that time is a 10-point feeling by a professional driver Scored by evaluation. Then, the change in steering stability was evaluated based on the difference in scoring between when two people were riding and when eight people were riding. The evaluation results are shown in Table 1. The evaluation results shown in Table 1 represent the increase or decrease in the score when eight people are on board, based on the score when two people are on board. The positive value is 8 rather than the steering stability when two people are on board. It indicates that the handling stability when the passenger is equivalent is excellent, and a negative value indicates that the steering stability when the passenger is equivalent to 8 is worse than the steering stability when the passenger is equivalent. The zero indicates that the score when two passengers are equivalent is the same as the score when eight passengers are equivalent.

(Rolling resistance test)
An air pressure of 210 kPa (relative pressure) is applied to the tire wheel, the vehicle is run on a force type rolling resistance tester under the conditions of a speed of 80 km / h and a tire load load of 4.41 kN, and the rolling resistance at that time is measured and evaluated. did. The evaluation results are shown in Table 1. In addition, the evaluation result shown in Table 1 is shown by the index ratio when the evaluation result of the tire of Conventional Example 1 is 100, and the smaller the value, the smaller the rolling resistance and the better the performance.

(Mass of belt protective layer)
The mass of the belt protective layer of each test tire was measured. The evaluation results are shown in Table 1. In addition, the evaluation result shown in Table 1 is shown by the index ratio when the evaluation result of the tire of Conventional Example 1 is 100, and the larger the value, the larger the mass.

(Material cost of belt protective layer)
The material cost required to manufacture the belt protective layer of each test tire was calculated. The results are shown in Table 1. In addition, the evaluation result shown in Table 1 is shown by the index ratio when the evaluation result of the tire of Conventional Example 1 is set to 100, and the higher the numerical value, the higher the material cost.

  From the results shown in Table 1, the tire of the example is more effective in changing the steering stability than the tire of the conventional example 1 without significantly increasing the rolling resistance, mass and material cost like the tire of the conventional example 2. It can be seen that it can be suppressed.

  As is apparent from the above description, the present invention increases the contact length of the shoulder area of the tread portion corresponding to both ends of the belt layer having low rigidity without significantly increasing the mass, rolling resistance and manufacturing cost of the tire. This makes it possible to exhibit stable steering stability from a low load range to a high load range.

1 is a cross-sectional view in the tire width direction of a typical pneumatic radial tire according to the present invention. FIG. 2 is a plan view schematically showing the cord arrangement of the tire belt shown in FIG. 1. It is tire width direction sectional drawing of the other embodiment according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tire 2 Bead part 3 Carcass 4 Crown part 5a 1st belt layer 5b 2nd belt layer 6 Belt 7 Belt protective layer 8 Belt layer cord 9 Mesh formed by belt layer cord 10 Central region of belt protective layer 11 Belt End region of protective layer 12 End portion of second belt layer 13 End portion of belt protective layer 14 End portion of first belt layer

Claims (7)

It consists of a radial carcass extending in a toroid shape and at least two belt layers located on the outer peripheral side of the crown portion of the carcass and coated with rubber, and between the adjacent belt layers, the cords sandwich the tire equatorial plane. A pneumatic radial comprising a belt formed with intersecting belt layers, and a belt protective layer that is positioned outside the belt in the tire radial direction and covered with a rubber that extends substantially in the tire circumferential direction. In the tire,
In the tire width direction cross section, the cord constituting the central region when the belt protective layer is divided into the central region and both end regions has a smaller elastic modulus than the cord constituting the both end regions. Radial tire.   2. The pneumatic radial tire according to claim 1, wherein the belt protective layer is configured by spirally winding a ribbon-like member formed by covering a cord with a rubber in a substantially tire circumferential direction.   The pneumatic radial tire according to claim 1 or 2, wherein the cord constituting the central region of the belt protective layer is a nylon cord.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the cord constituting the both end regions of the belt protective layer is a polyethylene terephthalate cord.   The pneumatic radial tire according to any one of claims 1 to 4, wherein the central region has a width within a range of 33 to 90% of a width of the belt protective layer with the tire equatorial plane as a center.   The belt layer includes two layers, and an end region of the belt protective layer extends to cover an end portion of a second belt layer that is a belt layer positioned on the outer side in the tire radial direction. The pneumatic radial tire according to item.   The first belt layer, which is a belt layer positioned on the inner side in the tire radial direction, is wider than the second belt layer, and both end portions of the belt protective layer are the end portions of the first belt layer and the second belt layer, respectively. The pneumatic radial tire according to claim 6, which is located between the two.

Images