JP2012086700A - Pneumatic radial tire - Google Patents

Abstract

The present invention provides a pneumatic radial tire that achieves low fuel consumption and secures vehicle space, and has improved tire durability, uneven wear resistance, and cornering power.
A pneumatic radial tire regulates a ratio W / L between a cross-sectional width W and an outer diameter L, and the inner side in the tire radial direction of the belt layer 3 from the end of the innermost belt layer 3 in the tire radial direction. Thus, the reinforcing layer 5 is provided at a position on the outer side in the tire radial direction from the tire maximum width portion and at a position on the outer side in the tire width direction from the end portion of the innermost belt layer 3.
[Selection] Figure 3

Description

  The present invention relates to a pneumatic radial tire, in particular, a pneumatic radial tire that achieves both low fuel consumption and comfortable living when an electric vehicle tire is mounted on a vehicle, and has improved tire durability, uneven wear resistance, and cornering power. Regarding tires.

Until around 1960, the weight of the vehicle was light and the required speed of the vehicle was slow, so a bias tire with a light tire burden and a narrow tire cross-sectional width was used. With increasing speed and speed, tires are becoming more radial and wider (Patent Document 1, etc.).
A tire to which a radial carcass is applied has excellent uneven wear resistance because the rigidity of the tire crown is higher than that of a bias tire. In addition, since the crown portion has high rigidity and the propagation of movement between the tire constituent members is suppressed, the rolling resistance is reduced. For this reason, it is characterized by good fuel efficiency and high cornering power.
In addition, by increasing the width of the tire, the ground contact area of the tire can be increased and the cornering power can be increased.

However, widening of the tires compresses the vehicle space and reduces the comfortability. Moreover, since air resistance increases, there exists a problem that a fuel consumption worsens.
In recent years, the demand for low fuel consumption has become stricter due to increasing interest in environmental problems. In particular, electric vehicles that are being put into practical use for the future need to secure a space for housing driving parts such as a motor for controlling the torque that rotates the tire around the tire axle. The importance of securing space is increasing.

JP 7-40706

  An object of the present invention is to solve the above-mentioned problems, and both the air resistance value (Cd value) of a tire-equipped vehicle and the rolling resistance value (RR value) of a tire are low. An object of the present invention is to provide a pneumatic radial tire that can secure a space, and further improve durability, uneven wear resistance, and cornering power.

The inventor has intensively studied to solve the above problems.
As a result, it has been found that in radial tires, regulating the cross-sectional width W and the outer diameter L of the tire under an appropriate ratio is extremely effective in improving fuel efficiency and comfort.
In addition, the inventor has made extensive studies to improve the durability, uneven wear resistance, and cornering power of the radial tire regulated under the above ratio. We obtained new knowledge that durability, uneven wear resistance, and cornering power can be improved by optimizing the structure.

The gist configuration of the present invention for solving the above-described problems is as follows.
(1) A pneumatic radial tire including a belt composed of one or more belt layers and a tread in order on the outer side in the radial direction of the carcass composed of a ply of a radial arrangement cord straddling a toroidal shape between a pair of bead portions. And
The ratio W / L of the tire cross-sectional width W and outer diameter L is 0.24 or less,
Among the belt layers, the inner side in the tire radial direction from the end of the innermost belt layer in the tire radial direction, the outer side in the tire radial direction from the maximum tire width portion, and the outer side in the tire width direction from the end portion of the innermost belt layer. A pneumatic radial tire comprising a reinforcing layer at a position.

(2) The reinforcing layer comprises a cord extending in the tire circumferential direction, the Young's modulus of the cord is Y1 (GPa), the number of driving is n1 (pieces / 50 mm), the width of the reinforcing layer is d1 (mm), The number of layers of the reinforcing layer is m1 (layer),
X1 = Y1 × n1 × d1 × m1
When defining
9000 ≦ X1 ≦ 18000
The pneumatic radial tire according to the above (1), characterized in that:

(3) The reinforcing layer is composed of a plurality of layers made of cords extending in the tire circumferential direction.
The cords cross each other between adjacent layers;
The circumferential component of the Young's modulus of the cord is Y2 (GPa), the number of driving is n2 (pieces / 50 mm), the width of the reinforcing layer is d2 (mm), and the reinforcing layer is an m2 layer of the cords And consists of
X2 = Y2 × n2 × d2 × m2
When defining
9000 ≦ X2 ≦ 18000
The pneumatic radial tire according to the above (1), characterized in that:

  According to the present invention, both the air resistance value (Cd value) of the vehicle and the rolling resistance value (RR value) of the tire are reduced, and it is excellent in fuel efficiency and vehicle comfort, and further, the durability of the tire and uneven wear resistance. It is possible to provide a pneumatic radial tire with improved performance and cornering power.

FIG. 3 is a diagram showing a cross-sectional width W and an outer diameter L of a tire. (a) It is a figure which shows the vehicle equipped with the tire which diameter-expanded and narrowed of this invention. (b) It is a figure which shows the vehicle equipped with the conventional tire. It is a schematic sectional drawing of the radial tire used for the test of this invention. FIG. 5 is a diagram showing a relationship between a ratio W / L of a tire cross-sectional width W to an outer diameter L, a vehicle air resistance value (Cd value), and a tire rolling resistance value (RR value). (a) It is a figure which shows the deformation | transformation of a tire typically. (b) It is a figure which shows typically the change of a grounding shape. It is a figure for demonstrating the change of a contact shape. It is a schematic sectional drawing of each radial tire concerning one embodiment of the present invention. (a) It is a figure which shows the deformation | transformation of the rubber | gum near the side part when not arrange | positioning a reinforcement layer. (b) It is a figure which shows the deformation | transformation of the rubber | gum near the side part at the time of arrange | positioning a reinforcement layer. (a) It is a figure which shows the deformation | transformation of a tire typically. (b) It is a figure which shows typically the change of a grounding shape. It is a figure for demonstrating the arrangement position and width | variety of a reinforcement layer.

Hereinafter, the process which led to the pneumatic radial tire of the present invention will be described.
First, as shown in FIG. 1, the inventor pays attention to the cross-sectional width W of the radial tire, and by making this cross-sectional width W narrower than before, vehicle space can be secured as shown in FIG. In particular, it has been found that a space for installing the drive parts is secured in the vicinity of the inside of the vehicle where the tire is mounted.
Further, when the tire cross-sectional width W is narrowed, an area when the tire is viewed from the front (hereinafter referred to as a front projection area) is reduced, which has an effect of reducing the air resistance value of the vehicle.
However, since the deformation of the ground contact portion becomes large, there is a problem that the rolling resistance value of the tire becomes large at the same air pressure.

  On the other hand, the inventor has found that the above-mentioned problems can be solved by the properties specific to the radial tire. In other words, since the radial tire has a smaller tread deformation than the bias tire, paying attention to the outer diameter L of the radial tire shown in FIG. It was found that the rolling resistance value can be reduced in the case of the same air pressure. Also, by increasing the diameter, it is possible to improve the load capacity of the tire, and as shown in Fig. 2, the diameter of the radial tire increases to increase the wheel axle and expand the space under the floor. It has also been found that it is possible to secure the space for the trunk of the vehicle and the installation space for the drive parts.

  Here, as described above, both the narrowing of the tire and the increase in the diameter of the tire have an effect of securing the vehicle space, but the rolling resistance value is in a trade-off relationship. Further, the air resistance value of the vehicle can be reduced by narrowing the tire.

  Therefore, the inventor has intensively studied the air resistance value and the rolling resistance value in order to improve these characteristics over the conventional radial tire by optimizing the balance between the tire cross-sectional width and the tire outer diameter.

The inventor pays attention to the ratio W / L between the tire cross-sectional width W and the tire outer diameter L, and attaches tires of various tire sizes including those outside the standard to the vehicle, and the air resistance value and rolling resistance. A test to measure the value was conducted, and the condition of the ratio W / L was derived that both of these characteristics exceeded that of the conventional radial tire.
Hereinafter, the test results that led to deriving the preferred range of the ratio W / L will be described in detail.

Here, FIG. 3 is a schematic cross-sectional view in the tire width direction of the radial tire used in the above test. FIG. 3 shows only a half portion with the tire equator CL as a boundary.
As a test tire, a pneumatic radial tire having a carcass 2 arranged in a radial manner straddling a pair of bead cores 1 (only one side in FIG. 3) in a toroidal manner as shown in FIG. 3 is used as a tire. Several prototypes were made with different sizes.
In addition, regarding tire sizes, tire sizes outside these standards are included, without being bound by conventional standards such as JATMA (Japanese tire standards), TRA (American tire standards), ETRTO (European tire standards), etc. Widely studied.
Here, in the illustrated tire, the carcass 2 is composed of organic fibers, and a plurality of belts 3 and treads 4 in the illustrated example on the outer side in the tire radial direction of the crown portion of the carcass 2 are sequentially arranged. Has been placed. The two belt layers in the illustrated example are inclined belt layers that are inclined at an angle of 20 to 40 ° with respect to the tire equatorial plane CL, and are arranged so that the belt cords intersect between the layers. A belt reinforcing layer 5 made of a rubberized layer of cords extending along the tire equatorial plane CL is disposed outside the belt layer in the tire radial direction.
Further, the tread 4 is provided with a plurality of main grooves 6 extending in the tire circumferential direction, one in the half in the illustrated example.
Based on the tire structure described above, a large number of tires having various cross-sectional widths and outer diameters were manufactured.
In addition, as a conventional tire serving as an evaluation standard for the test, a tire with a tire size of 175 / 65R15 having a structure in accordance with the above-mentioned custom was prepared. Tires of this tire size are used in most general-purpose vehicles and are most suitable for comparing tire performance.
Here, the specifications of each tire are shown in Table 1.

Each test was performed as follows.
<Air resistance value (Cd value)>
In the laboratory, each tire was mounted on a vehicle with a displacement of 1500 cc, and the air force when the air was blown at a speed equivalent to 100 km / h was measured using a floor balance under the wheel. It was evaluated by the index. The smaller the value, the smaller the air resistance.
<Rolling resistance value (RR value)>
Each of the above tires was assembled to a specified rim, and rolling resistance was measured under the conditions of an air pressure of 220 kPa, a load load of 3.5 kN, and a drum rotation speed of 100 km / h.
The evaluation results are shown as an index with the conventional tire as 100. It means that rolling resistance is so small that this index value is small.
The test results are shown in Table 2 and FIG.

  From the test results shown in Table 2 and FIG. 4, the tire size radial tire having a ratio W / L of the tire cross-sectional width W to the tire outer diameter L of 0.24 or less is a conventional tire of tire size 175 / 65R15. It was found that both the air resistance value and the rolling resistance value were reduced from the tire.

  Next, in order to confirm that the fuel efficiency and comfort of the vehicle are actually improved by setting the ratio W / L of the tire cross-sectional width W and the tire outer diameter L to 0.24 or less, for the above test tire, The following tests were conducted.

<Actual fuel consumption>
The test by JOC8 mode running was done. The evaluation result is expressed as an index with the evaluation result of the conventional tire as 100, and a larger index indicates better fuel consumption.
<Residence>
The rear trunk width when a tire was mounted on a 1.7m-wide vehicle was measured. The evaluation results are expressed as an index with the evaluation result of the conventional tire as 100, and the larger the index, the better the comfortability.
The test results are shown in Table 3 below.

As shown in Table 1 and Table 3, in the test tires with a ratio W / L of 0.28 or 0.31, there were test tires in which at least one of fuel economy and comfortability was lower than that of the conventional tire, respectively. It can be seen that the test tires 1 to 7 having a ratio W / L of 0.24 or less are both better in fuel efficiency and comfort than the conventional tire.
In this way, the inventor, in the pneumatic radial tire, by setting the ratio W / L to 0.24 or less, both the air resistance value of the vehicle and the rolling resistance value of the tire are improved while improving the habitability of the vehicle. It has been found that the fuel efficiency can be improved by reducing the fuel consumption.

The inventor conducted a test for evaluating other performances of the tire with the ratio W / L set to 0.24 or less.
For the test items, the durability, uneven wear resistance, and cornering power of the test tires 1 and 7 having the structure shown in FIG. 3 and the conventional tire were evaluated. The evaluation method for each test is as follows.
<Durability>
After assembling each of the above test tires on the specified rim, a high-speed durability drum test was performed under the conditions of an internal pressure of 220 kPa and a load of 3.5 kN. Starting from 120 km / h on the drum under the above conditions, the speed was increased by 10 km / h every 5 minutes, and the speed until the tire failed was measured and evaluated based on this measured value. The evaluation is expressed as an index when the failure occurrence rate in the conventional tire is 100. The larger the index, the better the durability.
<Uneven wear resistance>
The internal pressure of each tire was 220 kPa. Then, a drum test was performed in which a load of 350 kgf was applied to the tire and the vehicle traveled 30000 km at a speed of 80 km / h.
The evaluation of uneven wear resistance is performed by calculating the difference in wear amount between the center portion of the tread and the end portion of the tread after running the drum, and is expressed as an index with the uneven wear resistance of a conventional tire as 100. The smaller the index, the better the uneven wear resistance.
<Cornering power>
In a flat belt cornering tester, measurement was performed at an internal pressure of 220 kPa, a load of 3.5 kN, and a speed of 100 km / h.
The cornering power was evaluated by an index with the cornering power of a conventional tire as 100. The larger the index, the greater the cornering power.

  From the evaluation results shown in Table 4, the test tires 1 and 7 having a ratio W / L of 0.24 or less have tire durability, uneven wear resistance, and cornering power, and the ratio W / L is 0.28. It has been newly found that it is lower than the conventional tire. Therefore, in order to market a pneumatic radial tire having a ratio W / L of 0.24 or less, it was found that it is important to improve these characteristics, particularly to improve the durability of the tire.

The inventor has earnestly investigated the cause of the deterioration of the tire performance.
As a result, it has been found that the above characteristics are deteriorated due to a cause peculiar to a radial tire having a ratio W / L of 0.24 or less.
As schematically shown in Fig. 5 (a) (the dotted line indicates the shape of the tire after deformation), radial tires with a ratio W / L of 0.24 or less have a narrow tire width, so input from the road surface (pressure) The tread surface is greatly deformed.
FIG. 5 (b) schematically shows changes in the shape of the ground contact surface due to input from the road surface. As shown in FIG. 5 (b), in the radial tire having the ratio W / L of 0.24 or less, the vicinity of the tire tread is locally deformed and the ground contact shape changes greatly. The inventor has found that this is the cause of uneven wear resistance and reduced cornering power.
Further, in general, in a tire, rubber is greatly deformed in a side portion in the vicinity of the tire tread due to bending under load, and repeated deformation of the rubber causes heat generation particularly in the vicinity of the end portion of the belt. In particular, a radial tire having a ratio W / L of 0.24 or less has a narrow tire width and an increased contact length in the tire circumferential direction, so that the amount of rubber deformed at the side portion increases. For this reason, the inventors have also newly found that in radial tires having a ratio W / L of 0.24 or less, heat generation particularly near the belt end increases and the durability of the tire decreases.
Hereinafter, a test for evaluating changes in the contact shape of the test tires 1 and 7 and the conventional tire will be described.

First, as shown in FIG. 6, when the slip length is 4 °, the contact length of the center O in the width direction of the contact surface S is t, and the contact width is w, as shown in FIG. When the ground contact length at the location w × 0.4 away from the center O in the tire direction on both sides in the tire width direction is t1, t2 (t1 ≦ t2), the contact shape change index I is
I = t1 / t2 × 100
Define as The smaller the index, the greater the change in the ground contact shape.
The test tires 1 and 7 and the conventional tire were subjected to a test for determining the contact shape change index. Evaluation was made with a slip angle of 4 °, a rim assembled on a specified rim, a load of 350 kg was applied to each tire with a specified internal pressure, and the ground contact shape when running at a speed of 3 km / h was measured. This was done by finding t2.
The evaluation results are shown in Table 5 below.

As shown in Table 5, in the radial tire having the ratio W / L of 0.24 or less, it is understood that the contact shape change index I is small.
Therefore, a tire structure for improving the durability, uneven wear resistance, and cornering power of the tire by suppressing the contact shape change in a radial tire having a ratio W / L of 0.24 or less will be described next.

The inventor conducted extensive studies on the tire structure capable of improving the various performances of the tire described above. As a result, the inventor intends to increase the circumferential rigidity in the vicinity of the tire side portion, and among the belt layers, High rigidity in the tire circumferential direction at the inner side in the tire radial direction from the end portion of the inner belt layer, the outer side in the tire radial direction from the maximum tire width portion, and the outer side in the tire width direction from the end portion of the innermost belt layer The present inventors have obtained new knowledge that various performances of the tire can be improved by arranging the reinforcing layer.
Hereinafter, with reference to the drawings, a specific tire structure for realizing improvement of tire durability, uneven wear resistance, and cornering power will be described in detail.

7 (a) and 7 (b) are schematic cross-sectional views in the tire width direction of the radial tire of one embodiment of the present invention. FIGS. 7 (a) and 7 (b) show only a half portion with the tire equator CL as a boundary.
The difference between the tire shown in FIG. 7 (a) and the tire shown in FIG. 3 is as follows.
The tire shown in FIG. 7 (a) is inside in the tire radial direction from the end of the innermost belt layer in the tire radial direction, outside in the tire radial direction from the tire maximum width portion E, and from the end of the innermost belt layer. 3 is different from the tire shown in FIG. 3 in that a reinforcing layer 7a having high rigidity in the tire circumferential direction is arranged at a position outside in the tire width direction. In the illustrated example, the reinforcing layer 7a is made of a cord extending in the tire circumferential direction.
Further, the tire shown in FIG. 7 (b) is the tire shown in FIG. 7 (a), and a plurality of layers of cords extending at an angle of 10 ° to 30 ° with respect to the tire circumferential direction, illustrated example However, the difference is that a reinforcing layer 7b having a two-layer structure is disposed, and that cords cross each other between adjacent layers.
Hereinafter, the function and effect of the present invention will be described in detail.

According to the tire structure of the present invention, the circumferential rigidity in the vicinity of the tire side portion is increased by the reinforcing layer.
FIG. 8 shows the amount of rubber deformation (elongation) in the vicinity of the tire tread in the case where (a) the reinforcing layer is not arranged and (b) the case where the reinforcing layer is arranged (arrows). Is schematically shown).
As shown in FIGS. 8 (a) and 8 (b), according to the tire structure of the present invention, since the circumferential rigidity near the tire side portion is increased, the deformation (elongation) in the tire circumferential direction of the rubber near the tire side portion is increased. It will be suppressed.
Therefore, due to the incompressibility of rubber, as shown schematically in FIG. 9 (a) in comparison with FIG. 5 (a) (the dotted line indicates the shape of the tire after deformation), Deformation in the tire width direction is also suppressed.
Accordingly, as schematically shown in FIG. 9 (b) in comparison with FIG. 5 (b), the change in the ground contact shape with respect to the input in the tire width direction from the road surface is reduced, and uneven wear resistance and cornering power are reduced. Can be improved.
Further, as described above, since the deformation of the rubber is suppressed, heat generation due to the deformation of the rubber can be suppressed, and the durability of the tire is also improved.

  Here, with respect to the position where the reinforcing layer is arranged, as shown in FIG. 10, in a tire with no load and an air pressure of 220 kPa, when the tire equator is P, the reinforcing layer 7 is arranged in the tire radial direction. It is preferable to dispose it across the center position Q between the maximum width portion E and the tire equator P. This is because, when the tire rolls, the deformation of the rubber is the largest at the above-mentioned central position Q. Therefore, by arranging the reinforcing layer at this position, the elongation of the side portion can be effectively suppressed. .

Also, as shown in FIG. 10, in the tire width direction cross section, the length (hereinafter referred to as the width of the reinforcing layer) that the reinforcing layer 7 extends in the direction parallel to the tire equatorial plane CL is d (mm). The width d (mm) of the reinforcing layer is preferably 20% to 40% of the distance h (mm) between the tire maximum width portion E and the point P in the direction parallel to the tire equatorial plane CL.
This is because if it is less than 20%, the effect of improving the rigidity in the tire circumferential direction near the tire side portion by the reinforcing layer is not sufficient, while if it exceeds 40%, the rigidity in the tire circumferential direction becomes too high and the contact length becomes too long. This is because the maximum cornering force may be reduced.
Specifically, the width d (mm) of the reinforcing layer is preferably 10 to 40 (mm).

Here, the “stiffness of the reinforcing layer” is defined as follows.
First, when the cord of the reinforcing layer extends in the tire circumferential direction, the Young's modulus of the cord is set to Y1 (GPa), the number of drivings is n1 (pieces / 50 mm), and the number of reinforcing layers is set to m1 (layer).
As shown in FIG. 10, the width of the reinforcing layer is d1 (mm),
X1 = Y1 × n1 × d1 × m1
It is defined as
By defining the parameter using the width of the reinforcing layer as in the above formula, it represents the rigidity of the entire structure that can suppress the circumferential expansion of the rubber regardless of the material of the reinforcing layer. be able to.
At this time, the rigidity of the reinforcing layer is the Young's modulus of the cord, the number of drivings, the reinforcing layer width in the tire radial direction, and the number of reinforcing layers. It is preferable that the parameter X1 calculated from
The Young's modulus means the Young's modulus with respect to the tire circumferential direction, and is obtained in accordance with JIS L1017 8.8 (2002) after being tested in JIS L1017 8.5 a) (2002).
Here, the number of driving when the cord is spirally wound in the tire circumferential direction refers to the number of driving when viewed in a sectional view in the tire width direction.

Here, more specifically, regarding the rigidity of the belt reinforcing layer, the parameter X1 based on the above evaluation method and definition is preferably 9000 or more, and more preferably 12000 or more.
This is because if it is less than 9000, the effect of improving the circumferential rigidity in the vicinity of the side portion of the tire cannot be sufficiently obtained, while by setting it to 12000 or more, not only the durability is improved but also the rolling resistance value. It is because it can also be reduced.
The parameter X1 is preferably 18000 or less.
This is because if the parameter X1 is larger than 18000, the rigidity in the tire circumferential direction becomes too high, and the cornering force may decrease.

In order to set the parameter X1 in the above range, the Young's modulus of the cord used for the reinforcing layer is 15 GPa to 30 GPa, the number of driving is 40 to 60 (pieces / 50 mm), the width of the reinforcing layer is 10 to 40 (mm), The number of reinforcing layers is preferably one or two.
The cord is preferably made of organic fibers such as Kevlar having a fineness of 1500 to 1800 dtex.

Here, even when the tire structure shown in FIG. 7 (b), that is, when the cord of the reinforcing layer is inclined with respect to the tire circumferential direction, the Young's modulus of the cord is Y (GPa) and the number of driving is n2 / 50mm), the number of reinforcing layers is m2 (layers), the width of the reinforcing layer is d2 (mm), and the parameter X2 representing the rigidity in the circumferential direction is defined as these functions, and the preferred range of the parameter X2 is specified can do.
That is, for example, when the circumferential component of the Young's modulus of the cord is Y2 (GPa),
Y2 = F (Y)
The relationship F between Y and Y2 is obtained through experiments and the like, as in the case of the tire structure shown in FIG.
X2 = Y2 × n2 × d2 × m2
And define parameter X2 in the same way
9000 ≦ X2 ≦ 18000
By arranging the reinforcing layer in the range, the same effect as that obtained when the cord extends in the tire circumferential direction can be obtained.
Specifically, for example, the intersection of the circumference around the rotation axis of the tire and the cord of the reinforcing layer is hypothesized, and the included angle (on the acute angle side) with respect to the tangent to the circumference at this intersection (hereinafter referred to as the inclination angle). The relationship between the inclination angle θ and the contribution of the Young's modulus Y of the cord to the tire circumferential direction component can be defined.
As an example of the relational expression F, when the inclination angle θ of the reinforcing layer cord with respect to the tire circumferential direction is a low angle of about 10 to 20 °, the cord is inclined with respect to the tire circumferential direction. Because you can almost ignore the impact that your code breaks along the way,
Y2 = Y × cosθ
This relational expression is a good approximation, and by this relational expression, the same definition as in the case where the cord extends in the tire circumferential direction as described above (in the case of FIG. 7A) can be made.
The circumferential component of the Young's modulus of the cord can be measured, for example, using a tensile tester by cutting out a portion including the reinforcing layer of the vulcanized tire.
Further, the number of driving of the cord when the cord is inclined with respect to the tire circumferential direction refers to the number of driving when viewed in the sectional view in the tire width direction.

A plurality of tires having the structure shown in FIG. 7 (a) were prototyped and tests for evaluating various performances of the tires were conducted. The specifications of each tire are shown in Tables 6 to 9, and the evaluation results are shown in Table 10.
Here, in Tables 6, 8, and 9, the cord used for the reinforcing layer is spirally wound in the tire circumferential direction, and the number of driving is 50 (pieces / 50 mm).
In Tables 6, 7, and 8, the width of the reinforcing layer is 20 (mm).
The reinforcing layer is made of nylon and has a fineness of 1400 dtex, and the number of reinforcing layers is one unless otherwise indicated in the table.
In Table 10, durability, uneven wear resistance, and cornering power are shown as indices when the conventional tire in Table 4 is taken as 100. The higher the durability and cornering power, the better the performance, and the lower the wear resistance, the better the performance.

From Table 10, tires with a high-rigidity reinforcing layer with parameter X1 of 9000 to 18000 shown in FIG. 7 (a) have little change in ground contact shape, and are excellent in tire durability, uneven wear resistance, and cornering power. I understood it.
Further, it can be seen from Table 10 that when the parameter X1 is 12000 or more, the tire is particularly excellent in durability, uneven wear resistance, and cornering power.

  ADVANTAGE OF THE INVENTION According to this invention, the pneumatic radial tire which was excellent in low-fuel-consumption property and comfortability, and improved the durability of tire, uneven wear resistance, and cornering power can be manufactured, and can be provided to the market.

1 Bead core
2 Carcass
3 belt
4 tread
5 Belt reinforcement layer
6 Circumferential main groove
7, 7a, 7b Reinforcement layer
W Tire cross-sectional width
L Tire outer diameter
S Ground plane
O Center of ground plane width direction
t, t1, t2 Grounding length
w Grounding width

Claims (3)

A pneumatic radial tire comprising a belt composed of one or more belt layers on the outer side in the tire radial direction of a carcass composed of a ply of a radial arrangement cord straddling a toroidal shape between a pair of bead portions, and a tread in order,
The ratio W / L of the tire cross-sectional width W and outer diameter L is 0.24 or less,
Among the belt layers, the inner side in the tire radial direction from the end of the innermost belt layer in the tire radial direction, the outer side in the tire radial direction from the maximum tire width portion, and the outer side in the tire width direction from the end portion of the innermost belt layer. A pneumatic radial tire comprising a reinforcing layer at a position. The reinforcing layer is composed of a cord extending in the tire circumferential direction, the Young's modulus of the cord is Y1 (GPa), the number of driving is n1 (pieces / 50 mm), the width of the reinforcing layer is d1 (mm), and the reinforcing layer If the number of layers is m1 (layers),
X1 = Y1 × n1 × d1 × m1
When defining
9000 ≦ X1 ≦ 18000
2. The pneumatic radial tire according to claim 1, wherein The reinforcing layer is composed of a plurality of layers composed of cords extending in a slanting direction in the tire circumferential direction,
The cords cross each other between adjacent layers;
The circumferential component of the Young's modulus of the cord is Y2 (GPa), the number of driving is n2 (pieces / 50 mm), the width of the reinforcing layer is d2 (mm), and the reinforcing layer is an m2 layer of the cords It shall consist of
X2 = Y2 × n2 × d2 × m2
When defining
9000 ≦ X2 ≦ 18000
2. The pneumatic radial tire according to claim 1, wherein

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