JPH08488B2 - Radial tire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radial tire capable of improving one-sided flow of a vehicle and enhancing straight running performance.

[Conventional technology]

With the high performance of vehicles and the maintenance of road networks in recent years, in addition to various performances such as durability, steering stability and riding comfort, tires also travel a predetermined distance when the steering wheel is released. In the meantime, it is desired to further improve the driving comfort such as reducing the so-called one-way flow of a vehicle, which is displaced to one side with respect to the straight-ahead directional line, so-called a one-way flow, and improving straight running stability.

Conventionally, this one-sided flow of the vehicle is caused by what is called a cone-shaped consistency in the tire tread portion on the left and right in the tire axial direction, in particular, because the circumferential lengths of the belt layers are different, and therefore, the uniformity in the tire axial direction on the left and right sides is improved. Various measures have been taken in order to raise it.

[Problems to be Solved by the Invention]

However, it has been found that this improvement in the connectivity cannot sufficiently prevent the one-way flow of the vehicle.

On the other hand, due to recent progress in tire measurement technology, as schematically shown in FIG. 5, when a small slip angle α is applied to the tire traveling direction X, a cornering force generated in the tire lateral direction Y, that is, a lateral direction The force F and the self-aligning torque SAT that rotates in the direction of the slip angle α around the vertical axis Z passing through the tire center can be measured with high accuracy.

With such a measurement result, with the camber angle β set to 0,
For example, as shown in FIG. 6, the horizontal axis represents the self-aligning torque SAT, and the vertical axis represents the lateral force F using a straight line K. On the straight line K, the slip angle α is 0 degree and +0.
The case of 2 degrees and -0.4 degrees is indicated by black circles.

As described above, in the radial tire, the lateral force F and the self-aligning torque SAT are generally generated even in the straight traveling state. The lateral force F when the slip angle α and the camber angle β are both 0 is called LFD (lateral force deviation).

In such a relationship between the self-aligning torque SAT and the lateral force F, the lateral force F at the intersection k1 where the straight line K intersects the vertical axis, that is, the lateral force F when the self-aligning torque SAT does not occur is referred to as the residual CF. Name it. It was found that this residual CF affects the one-way flow of the vehicle. That is, when the residual CF is in the positive direction, it means that the vehicle unidirectionally flows to the right, so that the unidirectionality of the vehicle can be evaluated by the direction and size of the residual CF. It is necessary to reduce this residual CF.

The lateral force F and the self-aligning torque SAT
Are displayed for each slit angle α, the residual
CF and residual self-aligning torque SAT are shown in Fig. 7.

In the case of a tire with a so-called consistency that causes a difference in radius between the left and right of the tire equator, the residual CF and the self-aligning torque SAT change to the left or right on the large diameter side when the tire is assembled. However, when so-called front and back sets are performed, as shown in FIG.
The straight line K is two parallel straight lines as shown by a straight line K1 of the front set and a straight line K2 of the back set. Also, as shown in FIG.
In both cases, the average value of the lateral force when the slip angle α is 0 and the camber angle β is 0 is called a plysteer, and the deviation from each average value is defined as the community at the lateral force F.

Furthermore, in the relationship between the one-way flow of the vehicle, the residual CF, and the residual self-aligning torque SAT, the total self-aligning torque SA
Since T becomes 0, therefore, the residual CF on the tire at this time
Will occur. Normally, a force based on the community is further applied to this, and a resultant force of the residual CF and a lateral force based on the community are generated in the vehicle with respect to the tire.

An example of the residual CF and the flow of the vehicle is shown in FIG. This vehicle one-sided flow rate is the lateral displacement that occurs when the vehicle is running at 100 m at a speed of 50 km / h with the steering wheel released, and FIG. 9 is measured using tires of size 215SR15. In this way, it can be seen that the residual CF and the vehicle flow have a correlation, and it is better to reduce the residual CF to prevent the vehicle flow. Also, by setting the residual CF to +4 kg to -4 kg, the amount of one-sided flow is It was found that the vehicle flow was less than 0.5 m and was almost satisfactory.

The present inventor, on the premise that the conicity is set to a predetermined value or less, as a result of various studies to reduce the residual CF to 4 kg or less, the residual CF changes depending on the tread pattern of the tire and the structure of the belt layer. I found that.

Here, the effect of the tread pattern on the residual CF is, as shown in FIG. 11, particularly in the case where the block is divided by an oblique lateral groove, the block is caused by the radius difference between the tire equatorial CO side and the tread edge. Based on the generated traction FT and braking force FB, it is considered to be due to the rotational moment M acting on the tread surface of this block.

In the block shown in FIG. 11, as shown in FIG.
It has been found that generally the residual CF is increased, and that the block shown in FIG. 12 lowers the residual CF.

In addition, due to the residual CF based on the tread pattern,
Tires of tread patterns SA, SB, SC having different orientations of the outer lateral grooves Gs in the outer region of the tire shown in FIGS. 14 (a) to 14 (c) were prototyped. In the same figure, the belt cord 7a of the outermost belt ply 7B is indicated by a chain line. As a result of measuring the residual CF in such patterns SA, SB, and SC, the residual CF in the patterns SA, SB, and SC are -14.4 kg and -7.8 k, respectively.
It can be seen that the residual CF of the pattern SC provided with the lateral groove Gs having a direction g different from that of the outer belt cord 7a is g, −3.6 kg.

Further, the belt cord 7a shown in FIGS. 15 (a) to 15 (c).
The residual CF in the case of the pattern CA in which the inner lateral groove Gc tilts in the same direction, the pattern CB tilting in the tire axial direction, and the pattern CC tilting in the opposite direction were −5.9 kg, −8.1 kg, and −12.1 kg, respectively. .

Thus, the tread pattern affects the residual CF,
It can be seen that the direction of the belt cord, that is, the structure of the belt layer is also closely related to the one-way flow of the vehicle.

The residual CF exerted by the structure of the belt layer is caused by the expansion and contraction of the belt in the ground contact portion, and the radial tire belt disposed on the cross ply is subjected to in-plane shear such that the cord moves in parallel due to expansion and contraction. It is considered that the residual CF is generated due to the deformation, which causes the tread rubber to undergo the in-plane shear deformation together with the deformation of the outermost belt ply.

It was also found that the structure of this belt layer can be judged by the belt stiffness index x. Here, the belt stiffness index x is a value defined by the following equation, and the belt stiffness index x
Has been found to be substantially linearly correlated with the one-way flow of the vehicle as shown in FIG.

x = Bw ² · Bm · 10 ⁻⁵ / sin θ ° …… Bw: Width of the outermost belt ply (mm) θ: Inclination angle of the belt cord with respect to the tire equator Bm: n × d ² × N (n: belt cord Number of strands in, d: radius of strands, N: number of cords per 5 cm) When the belt rigidity index x exceeds 4.5, the rigidity of the tread becomes excessive and the riding comfort decreases, while it is less than 1. It is known that the steering stability is deteriorated when

Further, the belt stiffness index x and the residual CF (K2) are K2
= -Ax (A = 3.3 when the belt is upright, A when it is upside down)
= -3.3). Therefore, by knowing the amount of influence of the tread pattern on the vehicle flow, by adjusting the belt stiffness index x within the above range, it is possible to obtain a tire with a residual CF within ± 4 kg.

However, the tread pattern residual CF is significantly affected by the structure of the belt layer at that time, as described above.

Therefore, the present inventor has variously studied how to measure the influence amount of the tread pattern on the vehicle flow without being affected by the belt layer, and as a result, in a tire having the same tread pattern, each belt of the belt ply of the belt layer. By manufacturing a tire with only the direction of the cord reversed, measuring it and finding the average value,
I noticed that it is possible to find the amount of influence of the tread pattern only on the vehicle flow excluding the influence of the belt layer, that is, the pattern residual CF (K1) by the tread pattern.

Therefore, an object of the present invention is to provide a radial tire capable of reducing vehicle flow.

[Means for solving the problem]

The present invention provides a carcass in which a carcass cord is radially arranged from a tread portion having a tread pattern recessed on the outer surface to a side wall portion and is folded back at a bead core of a bead portion, and the carcass is arranged radially outside and inside the tread portion. A radial tire having a belt layer made of one or more belt plies formed by arranging steel belt cords in parallel with each other and crossing the tire equator, the residual CF (CF1) of the radial tire. ) And the residual CF (CF2) of the contralateral radial tire in which only the direction of the inclination of the belt cord of the belt ply with respect to the tire equator is reversed and other configurations are the same [(CF1 + CF2) / 2] Belt residual CF (K2) obtained by the following from the pattern residual CF (K1) and the belt stiffness index (x) obtained by the following formula
-4kg of tire residual CF (K) [= K1 + K2]
Radial tires that weigh more than 4kg.

x = Bw ² · Bm · 10 ⁻⁵ / sin θ ° …… Bw: Width of the outermost belt ply (mm) θ: Inclination angle of the belt cord with respect to the tire equator Bm: n × d ² × N (n: belt cord Number of strands inside, d: Radius of strands, N: Number of cords per 5 cm) K2 ＝ Ax (A is −3.3 when the belt is upright, +3.3 when it is upright) …… [Action] Radial The average value of the residual CF (CF1) of the tire and the residual CF (CF2) of the contralateral radial tire in which only the direction of the inclination of the belt cord of the belt ply with respect to the tire equator is reversed and the other configurations are the same [( CF1 + CF2) / 2] which is the pattern residual CF (K1). As a result, the pattern residual CF (K1), which is the residual CF due to the tread pattern itself without the influence of the belt layer, can be obtained.

This is the tread pattern DA, DB, shown in Figures 16-18,
Remaining CF for normal and reverse tension of DC tires
(CF1, CF2) DA is -1.93, +1.80, DB is +0.70, +
5.23, DC was −4.95, −0.68, and their average value [(CF1
+ CF2) / 2], that is, -0.07, + 3.0-2.8 is the pattern residual C
Do F (K1).

Also, from the belt rigidity index (x) obtained by the following equation, the belt residual CF (K2) is obtained by the following equation, and the tire residual CF (K) [= K1 + K2], which is the sum of them, is set to -4 kg or more and 4 kg or less. Of.

x = Bw ² · Bm · 10 ⁻⁵ / sin θ ° …… Bw: Width of the outermost belt ply (mm) θ: Inclination angle of the belt cord with respect to the tire equator Bm: n × d ² × N (n: belt cord Number of strands inside, d: radius of strands, N: number of cords per 5 cm) K2 = Ax (A is −3.3 when the belt is upright, +3.3 when it is upright). "" Means that the belt cord of the outer belt ply is wound in a direction of the right spiral inclining with respect to the tire equator, and "contrast" means that the belt cord is wound in the left spiral.

The belt stiffness index x correlates with the bending stiffness of the belt layer, and when this value is greater than 4.5, it reduces riding comfort,
If it is less than 1.0, the steering stability will be impaired.

Furthermore, the tire residual CF (K) [= K1
+ K2] within ± 4kg, the pattern residual CF (K1)
The value of is limited to the range of +20 to -20kg. Further, by presetting the pattern residual CF (K1) of the tread pattern in the above range, the belt rigidity index x in the above range can be obtained.
The residual CF can be adjusted to a range of ± 4 kg.

After setting the belt stiffness index x to the above range, the residual CF
It is also possible to select and determine the pattern residual CF (K1) so that (K) becomes the above value.

Such a radial tire has a residual CF within ± 4 kg, and is a tire having a favorable vehicle flow while maintaining riding comfort and steering stability.

In addition, the belt stiffness index may be brought close to 1 in order to keep the tire residual CF (K) within ± 4 kg. In the normal case, when it is not less than 1, substantially satisfactory steering stability can be obtained.

However, there are some vehicles, such as those traveling at high speed on rough roads, in which it is desirable to maintain high steering stability. At this time, increasing the rigidity of the carcass or the like to increase the rigidity of the tread portion without changing the belt cord tends to increase the weight of the tire and impair other tire performance.

Also in this respect, the present inventor has found that in order to improve the steering stability, it is preferable to increase the rigidity of the bead portion of the tire.

Moreover, the rigidity of the bead portion is defined as the bead portion rigidity index y.
It is given by the following formula.

This value should be 4.6-5.2. Moreover, it is preferable to set the belt-bead index Z of the expression obtained from the belt rigidity index x and the bead portion rigidity index y to 130 to 150.

z = Bl ² · Bh · Fg · C · F · 10 ^-6 …… Bl: Length of bead apex Bh: JIS A hardness of bead apex Fg: Total thickness of clinch on bead C: Number of carcass plies, carcass ply Constants determined in Table 1 according to height and carcass cord thickness.

F: A constant defined in Table 2 according to the material of the reinforcement cord of the bead reinforcement layer.

(1) "HTU" is the winding height h
Is 0.35 times the tire cross-section height H or more.
U ”means smaller than 0.35 times.

(2) In terms of thickness, “thick” means 1250d / 2 or more, and “thin” means smaller than 1250d / 2.

z = x ^1/4 · y ³ ...... This is the ^{fourth where} the riding comfort and steering stability are qualitatively plotted on the vertical axis when the belt stiffness index x and the bead portion stiffness index y are plotted on the horizontal axis. As shown in the figure, the riding comfort and the steering stability show characteristic curves that are contradictory with respect to the belt stiffness index x and the bead portion stiffness index y, and the belt stiffness index x
Is in the range of 1 to 4.5, and the riding comfort is inferior as it approaches 4.5, but the steering stability is excellent, and the bead portion rigidity index y is 4.6 to 5.2, and as it approaches 4.6, Show the characteristics.

Therefore, when the belt rigidity index x is close to 1, it is possible to improve the steering stability while maintaining the riding comfort by making the bead portion rigidity index y large, that is, close to 5.2, and the belt rigidity index x
When .apprxeq.4.5, the bead stiffness index y can be set to a value close to 4.6 to compensate for the reduction in riding comfort.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a pneumatic radial tire 1 includes a carcass 6 which is folded from a tread portion 2 through a sidewall portion 3 at a bead core 5 of a bead portion 4, and a carcass 6 radially outside of the carcass 6 and inside the tread portion 2. The bead reinforcing layer 9 is provided on the bead portion 4 as appropriate.

The belt 7 is composed of two inner and outer layers of belt plies 7A and 7B, and the belt cords are inclined with respect to the tire equator CO at an inclination angle of 18 degrees or less. The belt cord is
Steel strands 7b are twisted together, eg 2 + 7 × 0.2
2, 1 x 5 x 0.23, 1 x 4 x 0.22, 1 x 3 / 0.175 + 6 / 0.22
Are used.

The tread portion 2 is provided with a tread pattern illustrated in FIG. 2, for example.

〔Concrete example〕

A tire of size 215SR / 15 was prototyped according to the specifications shown in FIGS. 1, 2 and 3 and the one-sided flowability, steering stability performance and riding comfort were measured. The results are also shown in Table 3. Also, the residual CF is MTS of the United States with an internal pressure of 1.9 kg / cm ² and a load of 475 kg.
It measured using the flat track machine of the company. In addition,
The one-sided flowability is indicated by the residual CF index with Comparative Example 1 being 100. The larger the index is, the more preferable it is. In addition, steering stability performance, riding comfort, mounted on a 2000cc passenger car, a driver's feeling test was performed, and a comparison order was 100
As evaluated. The higher the score, the better.

It is understood that the example products can improve the residual CF of the tire as a whole without impairing the riding comfort and steering stability.

〔The invention's effect〕

As described above, the present invention can improve the one-way flow performance of the vehicle without impairing the steering stability performance and the riding comfort.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a plan view showing the pattern, and FIG. 3 is a diagram illustrating the relationship between a belt layer and one-way flowability. , FIG. 4 is a diagram showing the relationship between the belt stiffness index x, the bead portion stiffness index y and the steering stability and riding comfort, and FIGS. 5-8 are diagrams for explaining the residual CF,
FIG. 9 is a diagram illustrating the measurement results of residual CF and unidirectional flow,
FIG. 10 is a diagram illustrating the radius of the crown portion and the shoulder portion of the tire, FIGS. 11 and 12 are diagrams illustrating the tread pattern, and FIG. 13 is a diagram illustrating the relationship between the tread pattern and the residual CF. FIGS. 14 to 18 are plan views illustrating the tread pattern. 2 ... tread part, 3 ... sidewall part, 4 ... bead part, 5 ... bead core, 6 ... carcass, 7 ... belt, 7A, 7B ... belt ply.

Claims (3)

[Claims] 1. A carcass in which a carcass cord is radially arranged from a tread portion having a tread pattern recessed on the outer surface to a side wall portion and folded back at a bead core of a bead portion, and a carcass radially outward of the carcass and inward of the tread portion. A radial tire having a belt layer made up of one or more belt plies, which are arranged in parallel with steel belt cords crossing the tire equator, the residual CF of the radial tire ( CF1) and the residual CF (CF2) of the contralateral radial tire in which only the direction of inclination of the belt cord of the belt ply with respect to the tire equator is reversed and the other configurations are the same [(CF1 + CF2) / 2] From the pattern residual CF (K1), which is, and the belt residual CF (K2) obtained by
-4kg of tire residual CF (K) [= K1 + K2]
Radial tires that weigh more than 4kg. x = Bw ² · Bm · 10 ⁻⁵ / sin θ ° …… Bw: Width of the outermost belt ply (mm) θ: Inclination angle of the belt cord with respect to the tire equator Bm: n × d ² × N (n: belt cord Number of strands inside, d: radius of strands, N: number of cords per 5 cm) K2 ＝ Ax (A is −3.3 when the belt is upright, 3.3 when it is upside down) …… 2. The radial tire according to claim 1, wherein the belt stiffness index (x) is in the range of 1.0 to 4.5. 3. The pattern residual CF (K1) is +20 to −20.
The radial tire according to claim 1, which is in a range of kgf.