JPS63173703A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve durability at belt portion, uneven abrasion performance and manuevering stability, by specifying a cord angle of a belt layer between central region and shoulder region, number of cords to be implanted and the lateral length of the cross-section of tire in the central region. CONSTITUTION:In belt layers composed of metallic cords, the cord angle of first belt layer 31 near to a carcass ply is set to 40-75 deg., while the cord angle of second and third belt layers 32, 33 is set to 10-30 deg. and the cord angle of fourth belt layer 34 is set to 10-30 deg.. Ratios of average cord angles theta1, theta2 and average numbers of cores to be implanted N1, N2 in central region A1 and shoulder region A2 of the second and third belt layers 32, 33 are set within predetermined ranges shown by formula I. Lateral length of the cross-section of tire in the central region A1 is set to be 0.40-0.60 times of the developed width of tread. With such arrangement, durability at the belt portion, uneven adrasion performance and manuevering stability can be improved.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention improves belt durability and uneven wear resistance by optimally changing and arranging the cord angle and number of cords in the center region and shoulder region of the belt layer. , relates to a pneumatic radial tire with improved handling stability.

[Prior art]

In general, radial tires for trucks and buses or radial tires for light trucks are based on two intersecting belt layers that can essentially act as tension members, and two or more belt layers on the carcass ply and tread. It is located in the pinched area. For example, in radial tires for trucks and buses used in trucks, buses, heavy goods transportation vehicles, etc., the belt layer is composed of four layers, and the tire of the cord of the first belt layer counting from the carcass ply The angle with respect to the circumferential direction is 40° to 75°, that of the second and third belt layers is 10° to 30°, the cords cross each other between the plies, and the fourth layer is a protector bridle layer. The cord angle with respect to the tire circumferential direction is 10°~
It is 30°. The 2Nth and third belt layers are belt layers that can substantially act as tension members;
As far as the layers are concerned, the material may be a metal cord or a cord having a function as a protector brace, such as aramid fiber. Further, the cord angle of each belt layer is the same over the entire width of the belt layer within the aforementioned cord angle range.

In particular, the cord angle and the number of cords inserted in the second and third belt layers have a large effect on tire performance such as belt durability, uneven wear resistance, and handling stability. There is a causal relationship. That is, when the cord angle is increased, the outer diameter increases, resulting in negative effects such as a decrease in belt durability, occurrence of center wear, and deterioration of straight running stability. On the other hand, however, the increase in stiffness in the cross-sectional direction of the tire suppresses shoulder wear, and it also has positive effects such as increasing self-lining torque in cornering characteristics and improving maneuverability. On the other hand, reducing the cord angle suppresses outer diameter growth, resulting in improved belt durability, reduced center wear, and improved straight-line stability. Adverse effects such as occurrence of wear and deterioration of maneuverability due to the aforementioned decrease in self-lining torque are also unavoidable. Regarding the number of cords driven in, increasing the number of cords driven in when the cord angle is large increases the strength of the belt layer, which in turn increases the rigidity in the cross-sectional direction of the tire, which is highly effective in suppressing shoulder wear. Separation resistance at the end of the belt layer deteriorates as the number of cords increases.

Conversely, if the number of cords is reduced when the cord angle is large, the outer diameter will grow larger, which will exacerbate the aforementioned negative effects of reduced belt durability and center wear. On the other hand, increasing the number of cords driven when the cord angle is small increases the strength of the belt layer, which has a greater effect on suppressing center wear and improving straight-line stability, but this is still due to the increased number of cords driven. Separation resistance at the edge of the belt layer deteriorates. Conversely, if the number of cords is reduced when the cord angle is small, the strength of the belt layer will decrease, resulting in a greater decrease in the cross-sectional stiffness of the tire, promoting shoulder wear, and at the same time decreasing the durability of the belt section. let

Therefore, although various techniques have been proposed and implemented in order to achieve both of these conflicting performances, none of them are perfect, and efforts are still being made.

[Purpose of the invention]

The present invention provides a pneumatic radial tire that achieves improved belt durability, suppressed uneven wear such as center wear and shoulder wear, and improved handling stability, which were difficult to achieve with conventional belt structures. With the goal.

[Structure of the invention]

For this reason, the present invention has at least two belt layers sandwiched between a carcass ply and a tread, and the belt layers include a set of mutually intersecting layers that can essentially act as tension members. In a pneumatic radial tire comprising: (1) a set of intersecting belt layers which can act substantially as tension members; The average cord angle of the shoulder area is 1.20 to 1.60 times, and (2) the average number of cords in the shoulder area is 0.63 to 0 times the average number of cords in the center area. The gist is a pneumatic radial tire characterized by: It is something to do.

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

FIG. 1 is a cross-sectional explanatory view of a tread portion showing a belt structure of an example of a pneumatic radial tire of the present invention, and FIG. 2 is a plan view explanatory view of the belt structure.

In FIGS. 1 and 2, at least one layer of metal cords is sandwiched between a carcass ply 1 and a tread 2 made of one or more layers of metal cords arranged substantially perpendicular to the tire circumferential direction, or a carcass ply 1 made of organic fiber cords and a tread 2. Two belt layers (in this example, four layers 31 to 34 are arranged).

The belt layer is composed of four layers, and the carcass ply l
The cord angle of the first belt layer 3I with respect to the tire circumferential direction is 40° to 75° over the entire width.

The belt layer of the second layer 3t and the third layer 33 is lO"~3
0° and intersect each other. However, in these two layers, the cord angle is different between the center area A1 and the shoulder area At, and the cord angle is smaller in the center area A+, and the number of cords is also different between the center area A and the shoulder area A2. , this is smaller in shoulder area A2.

The fourth layer 34 is a belt layer as a protector ply, and the cord angle with respect to the tire circumferential direction is 10° to 30°.
It is. As for the belt layer 34, its material may be a metal cord or a cord having a function as a protector brace, such as aramid fiber. Note that EE'
represents the tire circumferential direction.

(a) In the present invention, a set of intersecting belt layers which can essentially act as tension members;
That is, in FIGS. 1 and 2, for the second belt layer 3□ and the third belt layer 33, the average cord angle θ1 and the average number of cords N in the center area A+ are determined by the positions on both sides of the belt layer 3□ and the third belt layer 33. The following relationship is established for the average cord angle θ2 of the shoulder area A2 and the average number of cords N2.

1.20≦θ! /θ, ≦1.60 0.63≦N, /Nl ≦0.85 In other words, the average cord angle and average number of cords in the center area are smaller and larger than the average cord angle and average number of cords in the shoulder area, respectively. Increase. Here, center area AIs shoulder area A
Regarding the cord angle of t and the number of cords inserted, there is no sharp bend at the boundary between the center area and shoulder area (it is continuous with a gentle gradual change, so the numbers are There are slight differences depending on the measurement point.Therefore, when referring to the cord angle and number of cords inserted in each area, the average is taken and called the average cord angle (θ1.θt) and the average number of cords implanted (N+, N*), respectively. This year,
The boundary between the two regions is defined as the point where the virtual extension lines of the respective average chord angles intersect. Note that the number of cords to be inserted refers to the number of cords existing within 50n in the perpendicular direction to the cord.

Hereinafter, the contents of this component will be explained in detail.

In the belt layer of conventional tires, the cord angle and number of cords are the same across the entire belt width, so if the cord angle is made smaller to improve the durability of the belt, shoulder wear is likely to occur. Invariably, some kind of performance has been sacrificed. In the present invention, among these belt layers, in a set of intersecting belt layers that can substantially act as tension members, the center region of the belt width has an average cord angle and the average number of cords driven, and the average cord of the shoulder region has an average cord angle and an average number of cords. By making the angle and the average number of cords implanted smaller and larger, respectively, contradictory performances can be achieved. When the cord is continuous over the entire width of the belt, θ2/θ1 and Nt/N+ do not exist independently, but are mutually related values. In other words, when θ and N1 are determined, N! is determined by the value of 02! will be decided. Table 1 below shows the study and results of the average cord angle and average number of cords driven. The ratio of the center area to the tread width is 0.5 for now.
It was set to 4. The following can be seen from Table-1.

■ θ! /θ+<1.20 and Ng/Nt>0.85.

Due to the effect of suppressing outer diameter growth, the durability of the belt portion is almost the same as that of conventional tires, and the straight-line stability is also significantly improved, but the amount of uneven wear on the shoulder portion is large, and the maneuverability is also worse than that of conventional tires. The reason why the belt part durability of Tire A is slightly worse than that of the conventional tire is considered to be because the separation resistance of the belt layer ends deteriorates due to the increased number of ends of the belt layer.

■ θt/θ+ >1.60 and Ng/N+<0.63
When.

The center area of the belt layer is firmly held down due to the low cord angle and high number of cords driven in, and the high cord angle in the shoulder area improves both belt durability and maneuverability compared to conventional tires. The amount of uneven wear is large. This is thought to be due to the decrease in stiffness in the cross-sectional direction of the tire in the shoulder area due to the large reduction in the number of cords driven in, although the cord angle in the shoulder area has increased.

Therefore, from the above (2) and (2), the relationship between the average cord angle and the average number of cords must be set to 1.20≦θ2/θ1≦1.60 and 0.63≦Nz/N+≦0.85.

(Margin below this page) (b) In addition, in the present invention, the center area A,
, the relationship with the tread width T is as shown below.

0.40≦2AI/T≦0.60 Regarding the ratio of the center area to the tread width, based on the results in Table 1, 2A+/T is
A number of models were set, and the amount of uneven wear on the shoulder portion and the handling stability were evaluated as shown in Table 2 below. The results are shown in FIG.

In FIG. 3, the white circles represent uneven wear amount t, and the shaded area represents maneuverability. The following can be seen from Table 2 and Figure 3.

■ When 2Al/T<0.40.

Due to the wide shoulder area with a large cord angle, the stiffness of the shoulder area in the cross-sectional direction of the tire is increased, so the amount of uneven wear is quite small, and the maneuverability is also better than conventional tires, but the straight-line stability deteriorates. In order to improve straight-line stability, it is necessary to increase the tire circumferential stiffness, but in Tire H, the portion that greatly contributes to circumferential stiffness is too narrow, and it is thought that the effect on straight-line stability is rather reduced.

■ When 2 A I/T > 0.60.

Tires J and K, which have a large center area, tend to have increased uneven wear in the shoulder area and decreased maneuverability. This is because the cross-sectional rigidity of the tire is insufficient.

Therefore, from the above ■ and ■, the ratio of the center area to the tread width (2AI/T) is 0.4≦2A, /T≦0
．． It is better to set it to 60.

(Blank below next summer) As mentioned above, the three performances that the present invention aims to improve, namely belt durability, uneven wear resistance, and straight-line stability/manoeuvrability, are all important; Part durability is a basic performance.

Even if uneven wear does not occur and straight-line stability and maneuverability are good, it is meaningless if the tires are damaged early. Therefore, as shown in Table 1, center area A,
is approximately the middle value of the tread development width T, and θ1. θt,
The optimal range of the relationship between N+ and Nt is determined based on the above-mentioned engineering performance, with belt durability as the first priority, and then the optimal range of <2AI/T as shown in Table 2 is determined for uneven wear resistance and straight-line stability.・The experiment was conducted in such a way that judgment was made based on two characteristics: maneuverability. The tires used in these experiments were 11R22.5
-14PR size, tread development width T is 1861
101s The metal cords that make up each belt layer are 3 (
0,20) +6(0,38). The belt durability was evaluated using an indoor rotating tester under high speed conditions. As for the evaluation of uneven wear resistance, 30,000k was carried out in an actual vehicle test (front wheel mounted) under the load and air pressure specified by JIS.
Uneven wear amount t of the shoulder part shown in Fig. 4 after running for m
(mm) was measured. Straight-line stability and maneuverability were evaluated in an actual vehicle feeling test using a scoring method established by internal standards. The test conditions were the load and air pressure specified by JIS, similar to the uneven wear resistance evaluation. The results are in Table-1
As shown in Table 2 and Figure 3, it was found that the belt durability (index display) could be improved by 10% compared to the conventional tire if the optimal value of the setting range was taken. The amount of wear is reduced by 30% to 50%, and straight-line stability and
It was confirmed that maneuverability improved by 1 to 1.5 points.

〔Effect of the invention〕

As explained above, according to the present invention, the center area AI
, average cord angle of shoulder area A2 (θ1.θt)
, the average number of code inputs (N1゜Nz) is 1.20≦θ
t/θ1 ≦1.60 and 0.63≦N! 7Nl ≦
0.85, and the ratio of the center area A1 to the tread width T was set to 0.4≦2A, /T≦0.6, so that a ■ tire that could not be achieved with conventional tires was basically required. The goal is to achieve a well-balanced combination of engineering performance: improving belt durability, ■ suppressing uneven wear in the center and shoulder areas that shortens tire life, and improving straight-line stability and maneuverability, which are related to driver comfort. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view of the tread portion showing the belt structure of an example of the pneumatic radial tire of the present invention, FIG. 2 is an explanatory plan view of the belt structure, and FIG. 3 is an explanatory diagram showing tire performance in a graph. FIG. 4 is an explanatory cross-sectional view of the tread portion showing the uneven wear amount t of the shoulder portion. l...Carcass ply, 2...Tread, 31...
・First belt layer, 3□・・・Second belt layer, 3
, . . . 3rd belt layer, 34 . . . 4th belt layer. 3 going down - (εE) 0's 501 sun - + [lsu (to)

Claims (1)

[Claims] An air conditioner having at least two belt layers sandwiched between a carcass ply and a tread, the belt layers including a set of intersecting layers that can substantially act as tension members. In a cored radial tire, for the above-mentioned set of intersecting belt layers that can substantially act as tension members, (1) the average cord angle of the shoulder regions located on both sides of the average cord angle of the center region; Cord angle 1.20 times ~ 1
．． 60 times, (2) the average number of cords in the shoulder area is 0.63 to 0.85 times the average number of cords in the center area, and (3) the cross-sectional width of the tire in the center area. A pneumatic radial tire characterized in that the length in the direction is 0.40 to 0.60 times the expanded tread width.