JPH0441086B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a heavy-duty pneumatic radial tire that reduces plysteer and improves straight running performance.

[Prior art]

Conventionally, in pneumatic radial tires for heavy loads such as trucks and buses or small trucks, the cord angle between the tread and the carcass layer and adjacent to the carcass layer is 40 degrees with respect to the tire circumferential direction. A belt reinforcing layer with an angle of 75° to 75°, and at least two layers whose cord angles intersect with each other at 15° to 30° and 150° to 165° with respect to the tire circumferential direction. It is constructed by laminating and arranging belt reinforcing layers consisting of belt tension-resistant layers. The carcass layer in this case consists of one layer or two or more layers, and the carcass cord is approximately 90 degrees with respect to the tire circumferential direction (substantially in the radial direction).
is doing.

Compared to bias tires, this type of radial tire has superior braking performance, fuel efficiency, wear resistance, etc. due to the effect of the belt reinforcement layer. There is a problem of poor running performance. In other words, when a radial tire rotates, even if the slip angle is zero, there is a phenomenon in which lateral force occurs in either the left or right direction with respect to the direction of travel, and this lateral force causes tires to move in a direction different from the direction intended by the driver. The vehicle may proceed to

In general, the lateral force at a slip angle of zero consists of force components generated by two different mechanisms, one of which is conicity (CT).
The other is called plysteer (PS) and is classified as part of the tire's uniformity characteristics. On the other hand, according to the uniformity test method for automobile tires (JASOC 607),
When the average value of lateral force when the tire rotates once is LFD, LFD _W measured on the surface of the tire, LFD _S measured with the tire replaced and placed on the back side, and the above-mentioned Conishity CT and Plysteer PS. From the definition, the relationship is expressed by the following equation.

LFD _W = PS + CT ... (1) LFD _S = PS - CT ... (2) Calculating PS and CT from equations (1) and (2) above is as follows.

CT=LFD _W −LFD _S /2 ...(3) PS=LFD _W +LFD _S /2 ...(4) If the relationships in (1), (2), (3), and (4) above are illustrated, 7th
It can be expressed as shown in the figure.

By the way, among the above-mentioned conicity and plysteer, conicity refers to the fact that the tire shape is geometrically asymmetric with respect to the circumferential center of the tire, that is, the force generated when the tire, which has become like a truncated cone, rolls. It is considered. This is mainly due to the position of the belt reinforcing layer inserted into the tire tread.
This can be reduced by manufacturing improvements. On the other hand, plysteer is an inherent force caused by the structure of the belt reinforcing layer, and it has been considered virtually difficult to significantly reduce it unless the structure of the belt reinforcing layer itself is changed.

Now, when considering the belt reinforcing layer, it can be represented as a three-layer laminate 4 consisting of belt tension-resistant layers 4u and 4d and a belt reinforcing layer 4r, as shown in FIG. 8A. When a tensile force is applied to this three-layer laminate 4 in the tire circumferential direction EE', the three-layer laminate 4 deforms not only within the two-dimensional plane where the tension acts, but also three-dimensionally out of the plane. It is well known that this causes twisting deformation as shown in FIG. 8B. The above-mentioned plysteer occurs due to such torsional deformation of the belt reinforcing layer.

Conventionally, various studies have been made to reduce this plysteer by adding a new belt reinforcing layer to the belt reinforcing layer, but adding a new belt reinforcing layer in this way is This could not be said to be very desirable since it would also impair characteristics such as fuel efficiency.

[Purpose of the invention]

An object of the present invention is to provide a heavy-duty pneumatic radial tire that reduces plysteer and improves straight running performance by specifying the belt structure of the tire.

[Structure of the invention]

For this reason, the present invention has at least one carcass layer in which the carcass cords are arranged substantially in the radial direction, and on the outside of this carcass layer, the first belt reinforcing layer counted from the carcass layer in the tread direction. A pneumatic radial tire in which a certain belt reinforcing layer is provided, and at least two belt tension-resistant layers, which are the second or later belt reinforcing layers counted from the carcass layer in the tread direction, are laminated on the outside of the belt reinforcing layer on a bias. In (1) the cord arrangement angle of the belt reinforcing layer with respect to the tire circumferential direction;
45° to 75°, (2) the cord arrangement angle of the belt tension-resistant layer is 15° to 30° with respect to the tire circumferential direction, and (3) each cord of the belt tension-resistant layer is When a bundle-twist type steel cord in which strands are twisted in the same direction at the same pitch is used, and when the twist direction of this steel cord is Z-twist, the belt tension-resistant layer has an S laminated structure, and the steel cord The object of the present invention is to provide a pneumatic radial tire for heavy loads, characterized in that when the twist direction of the belt is S-twist, the belt tension-resistant layer has a Z-layered structure.

In this way, in the present invention, the cord arrangement angles of the belt reinforcing layer and the belt tension-resistant layer are determined respectively, and bundle-strand type steel cords are used as the cords of the belt tension-resistant layer, and the twisting direction of the steel cords and the belt By determining the relationship between the tensile strength layer and the laminated structure, it is possible to reduce plysteer (PS) by reducing the inherent force caused by the belt reinforcing layer.

Hereinafter, the configuration of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a partially cutaway radial cross-sectional perspective view of an example of a heavy-duty pneumatic radial tire of the present invention. In FIG. 1, 1 is a tread, 2 is a sidewall part provided extending on both sides of the tread 1, and 3 is a part embedded in the lower end of the sidewall part 2 along the tire circumferential direction EE'. This is a bead wire. The bead wires 3 at both ends are wrapped around each other, and the cord angle with respect to the tire circumferential direction EE' is approximately
Carcass layer 5 which is 90° (substantially radial direction)
A belt reinforcing layer made of steel cord is interposed between the carcass layer 5 and the tread 1. At least one carcass layer 5 is provided. Further, the belt reinforcing layer includes a belt reinforcing layer 4r provided on the outside of the carcass layer 5, and a belt reinforcing layer 4r provided on the outside of the carcass layer 5.
A lower belt tension-resistant layer 4d provided on the outside of r and an upper belt tension-resistant layer 4u provided thereon.
At least three layers are arranged. FIG. 2 shows an enlarged view of these belt reinforcing layers. Here, the belt reinforcing layer 4r is the first belt reinforcing layer counting from the carcass layer 5 in the direction of the tread 1, and the cord angle is substantially in the radial direction.
This is to strengthen the carcass layer 5 by a hoop effect by surrounding the carcass layer 5 in the circumferential direction of the tire in order to prevent it from becoming loose. The lower belt tension-resistant layer 4d and the upper belt tension-resistant layer 4u are the second and third belt reinforcing layers counting from the carcass layer 5 to the tread 1, respectively,
This is to reinforce the belt reinforcing layer 4r and to prevent the tire from expanding radially outward due to centrifugal force while the tire is running.

In addition, in order to protect the belt reinforcing layer against the impact load from the tread 1, the upper belt tension-resistant layer 4 is
A belt protective layer 6 may be placed outside of u. This belt protective layer 6 is a layer that is arranged as necessary.

In the present invention, the following requirements are defined for the tire shown in FIG. 1 above.

(1) The cord arrangement angle of the belt reinforcing layer 4r is set at 45° to 75° with respect to the tire circumferential direction EE'.

By setting the cord arrangement angle of the belt reinforcing layer 4r adjacent to the carcass layer 5 at a high angle (45° to 75°) with respect to the tire circumferential direction EE', the bending rigidity of the tread 1 in the tire meridional section direction is increased. This is to improve straight-line stability.

This cord arrangement angle is preferably around 55°. By setting the angle to around 55 degrees, it is possible to arrange the carcass cords of the carcass layer 5 adjacent to the belt reinforcing layer 4r in a substantially radial direction, thereby particularly improving the tire uniformity. This is because it can be done. That is, when the cord arrangement angle of the belt reinforcing layer 4r is around 55 degrees, shearing deformation is least likely to occur in the belt reinforcing layer 4r even if a tensile force acts on the belt reinforcing layer 4r in the tire circumferential direction. This is because cord disorder is not caused in the carcass layer 5 adjacent to the reinforcing layer 4r.

(2) The cord arrangement angle of the belt tension-resistant layers 4d and 4u is set at 15° to 30° with respect to the tire circumferential direction EE'.

This is because it becomes possible to maintain sufficient rigidity in the tire circumferential direction EE'.

(3) When a bundle-type steel cord in which each strand is twisted at the same pitch and in the same direction is used as the cord for the belt tension-resistant layers 4d and 4u, and the direction of twist of this steel cord is Z-twist, the above-mentioned The belt tension-resistant layer has an S-layer structure, and when the steel cord is twisted in the S-twist direction, the belt tension-resistant layer has a Z-layer structure.

Here, the S-twist and Z-twist refer to a way of twisting a cord in a certain twisting direction, and are generally known. That is, in the S twist, as shown in FIG. 3A, the twist direction a of the cord goes from the upper left to the lower right, and the cord is twisted as if drawing an S-shape. Further, in the Z twist, as shown in FIG. 3B, the cord is twisted in a direction b from the upper right to the lower left, as if the cord were twisted in a Z-shape.

The S laminated structure and Z laminated structure refer to a laminated structure in which the belt tension layers 4d and 4u are defined by the difference in the inclination direction of the cords of each layer when viewed from the outside of the tire (or viewed from the inside of the tire). . In the S laminated structure, as shown in FIG. 4A, the cord 4dc of the lower belt tension-resistant layer 4d is inclined from the upper right to the lower left with respect to the tire circumferential direction EE', and the cord 4dc of the lower belt tension-resistant layer 4d is inclined from the upper right to the lower left with respect to the tire circumferential direction EE'. The cord 4uc is inclined from the upper left to the lower right with respect to the tire circumferential direction EE', and the cord 4dc and the cord 4uc form an S-shape. As shown in FIG. 4B, the Z laminated structure has a cord 4 of the lower belt tension-resistant layer 4d.
dc is inclined from the upper left to the lower right with respect to the tire circumferential direction EE', and the cord 4uc of the upper belt tension layer 4u is inclined from the upper right to the lower left with respect to the tire circumferential direction EE'. The code 4dc and code 4uc have a structure that looks like a Z-shape.

Conventionally, the steel cord for the belt tension-resistant layers 4d and 4u has a layer twist type of 3 (0.20) + 6.
(0.38), 3+9+15(0.22)1w, etc. were used. This is because the twisting direction of the inner layer and the outer layer are opposite to each other, which prevents the cord from rotating due to untwisting when tension is applied to the cord. This is due to the structure of the belt reinforcing layer. It suppresses its inherent power. In contrast, in the present invention, a bundle-twisted steel cord in which each strand is twisted in the same direction at the same pitch is used as the cord for the belt tension-resistant layers 4d and 4u. for example,
A bundled type steel cord with 12 to 37 strands, all of which are twisted at the same pitch and in the same direction (e.g. 1 x 12 (0.32), 1 x 27
(0.22) etc.). In the case of bundle-stranded steel cord, this is as shown in Figure 5.
When tension is applied to the cord, the rotation of the cord due to the untwisting of the cord is greater than that of the conventional steel cord mentioned above, which can be attributed to the belt reinforcement layer by appropriately combining it with the lamination method as described below. The idea is to reduce the inherent force.

That is, in the present invention, the belt tension layers 4d, 4
When the twisting direction of the steel cord u is Z-twist, the belt tension-resistant layers 4d and 4u have an S laminated structure, and when the twisting direction of the steel cord is S-twisting, the belt tension-resistant layer 4d , 4u have a Z-layered structure. This means that when a tensile force is applied in the tire circumferential direction EE′, in the case of S lamination,
Torsional deformation occurs in the belt reinforcing layer as shown in FIG. 8B described above. On the other hand, if we consider the single cord, if a tensile force is also applied, in the case of S twist, it will change from the state shown in Figure 9 A to the 9
Torsional deformation occurs in the state shown in Figure B. A combination of the two may result in the belt reinforcing layer being twisted at any time, which is undesirable. In the combination of S lamination and Z twist, the torsional deformation due to S lamination is reduced to Z of the cord.
The twist caused by twisting acts to cancel each other out, and as a result, PS is reduced.
Therefore, in the present invention, the S-laminated structure is combined with the Z-twist, or the Z-laminated structure is combined with the S-twist so that they mutually cancel out the torsional deformation, thereby reducing plysteer. .

Examples are shown below.

Examples Trial tires of the following inventive tire, comparative tire, and conventional tire were produced with a tire size of 11R22.514PR, and plysteer (PS) was evaluated.

(a) Tire of the present invention The tire has the structure of the belt reinforcing layer and carcass layer shown in Fig. 1, and the carcass layer uses conventionally used steel cord 3+9+15 (0.175) 1w.

In each layer of the belt reinforcing layer, the two-layer bias laminated parts 4d and 4u as the belt tension-resistant layer have twisted pitches of strands of strands as bundled type steel cords.
16mm, 1×12 (0.32) with a breaking strength of 235Kg, belt reinforcement layer 4r is a layered steel cord with a Z-twist inner layer and a twist pitch of 10mm, and the outer layer is an S-twist with a twist pitch of 18mm and a breaking strength of 180Kg. (0.20)+6
(0.38), and double-stranded high elongation steel cord 4 x 4 (0.22) was used for the belt protection layer 6.

The arrangement angle of the steel cords in the two-layer bias laminated parts 4d and 4u is 18 degrees from the acute angle side with respect to the tire circumferential direction, the number of cords is 22.5 cords/50 mm, and the cords are twisted in the Z-twist direction for a tire with an S-laminated structure. A
and Tire B with a Z-laminated structure with the cords twisted in the S-twist direction.

Note that the cord arrangement angles of the belt reinforcing layer 4r and the belt protection layer 6 are respectively 62° and 18° from the acute angle side with respect to the tire circumferential direction, and the cord arrangement direction of each layer is It was set in the same direction as each of the layer bias laminated parts 4d and 4u. In addition, the number of steel cords inserted is 22/50mm for belt reinforcement layer 4r and 19.5/50 for belt protection layer 6.
mm.

(b) Comparison Tire S-twist with the same structure as the above-mentioned tire of the present invention except that the twisting direction and lamination structure of the cord are different.
We prototyped a tire C with a laminated structure and a tire D with a Z-laminated structure using Z twist.

(c) Conventional tire The two-layer bias laminated parts 4d and 4u are made of layer-twisted steel cord with an inner layer twist pitch of 10 mm.
Outer layer twist pitch is 18mm, breaking strength 180Kg 3
(0.20) + 6 (0.38), and the number of cords is set to 29/50 to make the strength equivalent to that of the tire of the present invention.
mm, and the cord arrangement angle was set at 18 degrees from the acute angle side with respect to the tire circumferential direction.

Tire A' has an S-laminated structure with the cords twisted in the Z-twist direction, tire B' has the Z-laminated structure with the S-twisted cord, tire C' has the S-laminated structure with the S-twisted cord, and tire D' has the Z-laminated structure with the Z-twisted cord. Trial production.

Note that the cord arrangement angle between the belt reinforcing layer 4r and the belt protection layer 6, the cord arrangement direction, the cord used,
The number of cords inserted was the same as in the above-mentioned present invention tire and the above-mentioned comparative tire.

Regarding plysteer (PS): According to the uniformity test method for automobile tires (JASO C607), PS was measured using a rim of 8.25 x 22.5, an air pressure of 7.0 Kg/cm ² and a load of 2450 Kg. The results are shown in FIG. In addition, in FIG. 6, ○ represents a bundle twist type, and ● represents a layer twist type.

As is clear from FIG. 6, bundled type steel cords are used for the two-layer bias laminated parts 4d and 4u, and when the cord is twisted in the Z direction, the S-laminated structure is used, and when the cord is twisted in the S-twisted direction, the Z-laminated structure is used. It can be seen that the tire of the present invention has less plysteer than the conventional tire. Therefore, the tire of the present invention can improve straight running performance.

On the other hand, a comparison tire having a two-layer bias laminated portion in which bundled type steel cords have an S-twist S-laminate structure and a Z-twist Z-laminate structure has larger plysteer than the conventional tire.

In this embodiment, the cord arrangement direction of the belt protective layer 6 was made to be the same inclination direction with respect to the adjacent layer side of the two-layer bias laminated portions 4d, 4u and the tire equator line, but in the present invention, the cord arrangement direction is It is not restricted and may be arranged in an intersecting manner. Also,
In principle, the cords of the belt reinforcement layer 4r and the cords of the two-layer bias laminated portions 4d and 4u adjacent thereto are arranged in the same inclination direction with respect to the tire equator line, due to the nature of the belt reinforcement layer.

〔Effect of the invention〕

As explained above, according to the present invention, the cord arrangement angles of the belt reinforcing layer and the belt tension-resistant layer are determined respectively, and bundled and twisted steel cords are used as the cords of the belt tension-resistant layer, and the steel cords are By determining the relationship between the twist direction and the laminated structure of the belt tension-resistant layer, it is possible to reduce the inherent force caused by the belt reinforcement layer and reduce plysteer, thereby improving straight running performance. Become.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway radial cross-sectional perspective view of an example of a heavy-duty pneumatic radial tire of the present invention, and FIG.
The figure is an enlarged explanatory view of the belt reinforcing layer in Figure 1,
3A and 3B are explanatory diagrams showing the twisting direction of the cords in the belt reinforcing layer, respectively; FIGS. 4A and 4B are explanatory diagrams showing the laminated structure of the belt reinforcing layer, respectively; FIG. 5 is a diagram showing the relationship between the untwisting angle of the cord and the cord tensile force, and FIG. 6 is a diagram showing the relationship between the structure of the belt reinforcing layer and plysteer. Figure 7 is a diagram showing the relationship between tire travel distance and lateral force, Figures 8A and B are model diagrams showing the deformation of the belt reinforcing layer, and Figures 9A and B are torsional deformations in the cord. FIG. 1...Torezdo, 2...Side wall part, 3
...Bead wire, 4r...Belt reinforcement layer, 4d
...Lower belt tension-resistant layer, 4u...Upper belt tension-resistant layer, 5...Carcass layer, 6...Belt protective layer.

Claims (1)

[Claims] 1. It has at least one carcass layer in which carcass cords are arranged substantially in the radial direction, and a belt reinforcing layer that is the first belt reinforcing layer counted from the carcass layer in the tread direction is provided on the outside of this carcass layer. In addition, in a pneumatic radial tire in which at least two belt tension-resistant layers, which are the second and subsequent belt reinforcing layers counted from the carcass layer in the tread direction, are laminated on the outside of the belt reinforcing layer in a bias manner, (1) the above-mentioned The cord arrangement angle of the belt reinforcing layer is 45° to 75° with respect to the tire circumferential direction, and (2) the cord arrangement angle of the belt tension-resistant layer is 15° to 30° with respect to the tire circumferential direction; Furthermore, (3)
A bundle-type steel cord in which each strand is twisted in the same direction at the same pitch is used as the cord of the belt tension-resistant layer, and when the twisting direction of this steel cord is Z-twist, the belt tension-resistant layer is A pneumatic radial tire for heavy loads, characterized in that it has an S-laminated structure, and when the twisting direction of the steel cord is S-twist, the belt tension-resistant layer has a Z-laminated structure.