JPH08164709A - Tire for passenger car - Google Patents

Abstract

PURPOSE: To reduce the weight of a belt layer without impairing steering stability during turning motion in a passenger car having such a wheel alignment as its camber angle is regulated, by specifying the radius of curvature of a crown arc in the tread part and the radius of curvature of a shoulder arc. CONSTITUTION: In a tire for a passenger car, especially an electric vehicle, having a camber angle of 8 to 18 deg. in its wheel alignment, a tread surface in the meridian cross section consists of a crown arc C1, which ranges over 50 to 80% of a tread width TW and whose radius of curvature is R1, and a shoulder arc C2, which is connected to the crown arc C1 and whose radius of curvature is R2. The radius of curvature C1 of the crown arc is determined so that the ratio of the radius to the tread width R1/TW becomes 0.6 to 0.95, while the radius of curvature R2 of the shoulder arc C2 is determined so that the ratio R2/TW becomes 0.3 to 0.7 and moreover the R2 becomes smaller than the radius of curvature R1. The belt layer 7 made up of steel or Aramid is formed by spirally winding the belt cord at an angle 5 degrees or less to the circumferential direction of the tire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire for a passenger vehicle which can be preferably used in an electric vehicle or the like where weight reduction of the tire is important.

[0002]

2. Description of the Related Art Generally, a tire having a small tire weight has a small rolling resistance and improves the fuel efficiency of a vehicle. In particular, for an electric vehicle that uses a battery as a driving source,
The extension of the mileage by charging once is regarded as a very important issue compared to the requirement of the engine type vehicle, and thus the weight reduction of the tire mounted on such an electric vehicle is most important.

As a means for reducing the weight of a tire, for example, a tire constituent member such as a carcass or a belt is improved,
Attempts have been made to reduce the number of ply layers.

[0004]

However, as described above, when the number of plies of the tire constituent member is reduced, particularly when the carcass ply forming the tire frame is reduced, the required tire shape cannot be maintained, and the load capacity is not maintained. In many cases, the original function of the tire is impaired, such as inferior.

When the number of plies in the belt layer is reduced, the lateral bending rigidity of the belt layer is generally lowered, and as a result, the generation of cornering force for turning the vehicle is reduced. That is, there is a problem that the steering stability performance during turning is deteriorated.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that even if the lateral bending rigidity of the belt layer is reduced,
By controlling the radius of curvature of the tread surface in relation to the wheel alignment of the vehicle, particularly in relation to the camber angle, so-called camber thrust can be taken in as the cornering force, and as a result, the weight of the belt layer is reduced without impairing the steering stability during the turning. The present invention has been completed by finding that it can be realized.

That is, an object of the present invention is to provide a passenger car tire which can be mounted on a passenger car having a wheel alignment with a regulated camber angle and which can reduce the weight of the tire without impairing the steering stability.

[0008]

DISCLOSURE OF THE INVENTION The present invention is directed to a carcass in which an organic fiber cord is arranged in the radial direction so as to fold back around a bead core of a bead part from a tread part to a side wall part, and a tread on the outside of the carcass in the radial direction. A tire for a passenger car equipped with a belt layer arranged inward of a portion and having a camber angle of 8 to 18 degrees, which is mounted on a passenger car, in a normal state in which a normal internal pressure is applied. The tread surface of the tread portion in the meridian section is the tread width T that forms the maximum tire width.
A crown arc C1 having a radius of curvature R1 over a width of 50 to 80% of W, and a shoulder portion axially outside of this crown part that is smoothly connected to the crown arc C1 and has a radius of curvature R2. The radius of curvature R1 of the crown arc C1 is 0.6 to 0.9 and the ratio (R1 / TW) to the tread width TW is 0.6 to 0.9.
5, and the radius of curvature R2 of the shoulder arc C2 has a ratio (R2 / TW) to the tread width TW of 0.3 to 0.7.
Moreover, while being smaller than the radius of curvature R1, the belt layer is formed by spirally winding a belt cord made of steel or aramid into one layer at an angle of 5 degrees or less with respect to the tire circumferential direction. It is a featured passenger car tire.

[0009]

The passenger car tire of the present invention has a camber angle of 8
It is mounted on a passenger car with a wheel alignment of ~ 18 degrees. Therefore, when the passenger car is traveling, the tire can generate a large camber thrust even if the slip angle is 0 based on the large camber angle.

When a passenger car tire is mounted on a passenger car having a wheel alignment with a large camber angle, the ground contact pressure of the shoulder portion on the side where the camber angle is inclined is significantly increased, and as a result, uneven wear is apt to occur in such a portion. Therefore, in the present invention, the crown arc C of the tread surface is used.
The radius of curvature R1 of 1 is the ratio (R1 / T
W) is regulated within the range of 0.6 to 0.95.

Conventional passenger car tires have the above ratio (R1 /
Since the TW) is approximately 2.1 to 5.2, the crown portion of the passenger car tire of the present invention has the above ratio (R1 / T
It can be understood that W) is small, that is, the radius of curvature of the crown is small, and it is possible to prevent the contact pressure of the tread surface from being significantly increased by mainly contacting the crown portion, and uneven wear is suppressed.

Next, the radius of curvature R2 of the shoulder arc C2 on the outer side of the crown portion in the axial direction of the tire was examined as a result of various experiments in relation to the large camber angle of a passenger car, and the ratio (R2 / TW) to the tread width Has been found to be 0.3 to 0.7 and smaller than the radius of curvature R1, which is advantageous because the camber thrust is greatly generated.

The belt layer is formed by spirally winding a belt cord made of steel or aramid into one layer at an angle of 5 degrees or less with respect to the tire circumferential direction. The weight of the belt layer is reduced by reducing the amount of topping rubber compared to the ply, and the tire weight is also reduced.

When such a tire is used with a camber angle smaller than 8 degrees, the cornering force generated is naturally small due to the decrease in belt lateral bending rigidity. However, by giving the camber angle of 8 to 18 degrees, the large camber thrust can be compensated for the cornering force generated based on the slip angle, and as a result, a cornering force equivalent to that of a conventional tire is ensured and the turning is ensured. It is possible to maintain the steering stability during operation.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a normal state in which a passenger car tire according to the present invention is assembled on a standard rim and a normal internal pressure is applied, and is folded around a bead core 5 of a bead part 4 through a tread part 2 through a sidewall part 3. A carcass 6 is provided, and a belt layer 7 is arranged radially outside of the carcass 6 inside the tread portion and has a flatness ratio of 0.55.
A bead apex 9 is erected on the bead portion 4 from the bead core 5 toward the outer side in the radial direction.

The tread width TW of the tread portion 2 is
It has a cross-sectional shape that forms the maximum width of the tire, and is configured to generate a large camber thrust when given a camber angle.

The carcass 6 comprises one or more carcass cords arranged at an angle of 75 to 90 degrees with respect to the tire equator C to form a substantially radial structure.
The carcass ply 6A, 6B is composed of a sheet, and the carcass cord can be made lighter than the steel cord by using an organic fiber cord such as nylon, rayon, polyester, or aromatic polyamide. Further, in this embodiment, the end portions of the folded-back portions of the two carcass plies reach the vicinity of the shoulder of the tread portion 2 and extend at different heights to completely cover the bead apex 9.

The belt layer 7 is a belt cord 7A made of steel or aramid outside the carcass 6 in the radial direction.
Is formed by spirally winding one layer without laminating each other at an angle of 5 degrees or less with respect to the tire circumferential direction.

The belt layer 7 formed by spirally winding the cord is inferior in lateral bending rigidity as compared with a belt ply in which the belt cord 7A is topped into a rubber sheet, but the belt layer itself does not require a topping rubber. In addition to making it possible and easy to reduce the weight, it does not have a seam like ply and is excellent in tire uniformity. in this way,
The belt layer of the present invention, by placing the most importance on weight reduction,
Although the lateral bending rigidity is inferior, the cord angle is set to 5 degrees or less, preferably substantially 0 degrees to mainly secure the hoop effect.

The belt cord 7A is made of a highly elastic cord such as steel or aramid, preferably aramid having a smaller specific gravity, in order to ensure the minimum required rigidity by forming the belt layer into a single layer structure. It is necessary, and when the tire is subjected to normal internal pressure, the number of belt cords driven per 5 cm along the belt layer is 2
The number is 8 to 50, preferably 35 to 49.
Further, the belt cord 7A may include a cord whose periphery is covered with rubber.

Such a belt layer 7 has, for example, the belt cord 7A spirally formed on a peripheral surface of a rotatable profile drum or the like whose outer peripheral surface is formed into the same convex curved surface as the warp of the belt layer of the finished tire. Winding, first, a tread ring is formed by attaching a tread rubber to an annular belt ring having a bulge approximately equal to the radius of curvature at the time of tire molding.

Next, the tread ring thus formed is positioned outside the toroidal carcass and the carcass is loaded with an internal pressure to form a raw tire. The passenger car tire 1 can be formed. In addition to such a two-stage molding method, it is also possible to mold by a one-stage molding method.

The passenger car in which the tire of the present invention is used has a camber angle of 8 to 18 degrees, preferably 10 to 1.
An example is an electric vehicle that uses a battery as a driving source, which is premised on having a wheel alignment of 5 degrees. Generally, the camber angle of a passenger car is about 3 degrees.

As shown in FIG. 2, the camber angle is, for example, the center line CL of the tire T when the vehicle is viewed from the front.
The camber thrust CT is generated in the direction in which the tire is tilted at an angle α formed by the vertical line N. Particularly in a motorcycle or the like, when making a turn, the camber angle is positively given by tilting the vehicle. The camber angle α defines the front wheels when viewed from the front side, and is a negative camber having a “C” shape when viewed from the front.

Therefore, the passenger car tire of the present invention mounted on such a passenger car can always generate a large camber thrust based on a relatively large camber angle even if the slip angle is 0, and the slip angle during steering can be increased. By supplementing the cornering force generated with the increase of the steering force, the steering stability during turning can be maintained.

FIG. 3 shows the relationship between the slip angle and the cornering force when the camber angle is changed. The conventional 2-cut ply steel belt has a camber angle of 0 °. The spirally wound single-layer belt according to the embodiment of the present invention uses steel as the belt cord.

As is clear from the figure, the camber angle is 0.
In the example, the cornering force generated is small, but for the camber angles of 9 degrees and 15 degrees, a cornering force comparable to the conventional 2-cut ply steel belt is generated when the slip angle is around 1 degree. I can understand that. It has been found that this result also appears in a belt cord using aramid.

Next, in the normal state, the tread surface of the tread portion 2 in the meridional section of the tire has a width CW of 50 to 80% of the tread width TW with the tire equator C as the center.
The region extending over is the crown portion 2A, and this crown portion 2A
The area on the outer side in the tire axial direction is defined as the shoulder portion 2B.

The crown portion is formed by a crown arc C1 having a radius of curvature R1, and the shoulder portion is formed by a shoulder arc C2 having a radius of curvature R2 which is smoothly connected to the crown arc C1 at an intersection S.

The radius of curvature R1 of the crown arc C1
Has a ratio (R1 / TW) to the tread width TW of 0.6.
To 0.95, for example, when the tread width TW is 180 mm, the radius of curvature R1 of the crown arc C1 is 108 to 171 mm.
It is about degree. As already described, the mounted vehicle has a large camber angle, and the ratio (R1 / TW) is regulated from the viewpoint of suppressing uneven wear.

Especially, as a result of various experiments in relation to the range of the camber angle, the ratio (R1 / TW) is 0.6.
If it is less than 1.0, the crown arc C1 becomes too small to secure a sufficient ground contact area, and the ground contact pressure tends to be excessively increased. On the other hand, if it exceeds 0.95, the crown portion before grounding is flattened and grounds. In any case, such as locally increasing the pressure, the ground pressure cannot be optimized and wear is promoted, which is not preferable.

Next, the radius of curvature R of the shoulder arc C2
2 has a ratio (R2 / TW) to the tread width of 0.3 to
It is important to be 0.7 and smaller than the radius of curvature R1. This is mainly regulated from the viewpoint of obtaining the camber thrust in an advantageous manner.

When the ratio (R2 / TW) is less than 0.3, the shoulder arc C2 becomes a too small arc so that the ground contact cannot be achieved, and the camber thrust can be advantageously obtained despite giving a sufficient camber angle. I can't. If the ratio (R2 / TW) exceeds 0.7, the shoulder arc is relatively large, and although the camber thrust is obtained, the tire friction becomes too large, and conversely the rolling resistance increases, which is not preferable.

With such a ratio (R2 / TW), the radius of curvature R2 of the shoulder arc C1 can be about 54 to 126 mm in the size of the tread width TW (180 mm).

In the tread portion 2, a tread rubber having a small hysteresis loss, for example, a low heat-generating rubber composition having a loss coefficient (tan δ) of about 0.05 to 0.2 is attached to the outside of the belt layer 7 in the radial direction. It is preferable.

By thus reducing the internal loss of the tread rubber, it helps to reduce the rolling resistance. The loss coefficient (tan δ) is 4mm width × 30mm length × 1.5mm thickness under the conditions of 70 ° C, frequency 20Hz, static strain rate 10%, dynamic strain rate 2% using a viscometer manufactured by Iwamoto Seisakusho. It is defined as the value measured using a strip-shaped sample.

Further, in this embodiment, the normal internal pressure to be filled when the tire is used is set to a high internal pressure of 2.9 kgf / cm ² or more to contribute to the reduction of rolling resistance, and the tread surface may be appropriately arranged in the tire circumferential direction or the tire axial direction. It goes without saying that the tread groove extending to each can be arranged.

(Concrete Example) With respect to the tire of the present invention having a tread width TW of 180 mm, an aspect ratio of 0.55 and a rim diameter of 7 inches, a tire having the specifications shown in FIG. 1 and Table 1 was manufactured (Example 1, 2), the tire is a standard rim (17 × M)
It was attached to T5.50) and various tests were conducted. In addition, as a comparative example, the carcass, the belt, and the embodiment in which the tread profile was prototyped according to the specifications shown in Table 1 and the conventional passenger car tire (tread width of 165 mm) in which the maximum tire width and the flatness ratio are substantially the same are also included. The performance was comparatively evaluated. The test procedure is as follows.

B) Tire weight The weight per tire is shown as an index with Comparative Example 1 being 100. The smaller the value, the lighter the weight.

(B) Cornering force Using a force variation (FV) tester, the tire under test was subjected to a cornering force under a load of kgf while changing the slip angle to 1.5 degrees and the camber angle α to 0 degrees, 10 degrees and 15 degrees. Is measured, and is displayed as an index with Comparative Example 1 being 100. The larger the value, the larger the cornering force.

C) Abrasion index A domestic FR vehicle of 2500CC was mounted with Comparative Example 1 and Example 1, and Comparative Example 1 and Example 2 with the wheel positions of the front, rear, left and right crossed, and after traveling about 6000 km in the city area. , The degree of uneven wear and the wear state such as the amount of wear are displayed as an index. The smaller the value, the better the abrasion resistance.

D) Grounding pressure index The grounding pressure of the tire crown portion under the conditions of an internal pressure of 2.9 kgf / mm ² and a load of 350 kgf is expressed by an index. The higher the number, the higher the ground pressure. The test results are shown in Table 1.

[0043]

[Table 1]

As a result of the test, the tires of the examples were made light in weight, and by supplementing the camber thrust,
It was confirmed that when the camber angle was 10 degrees or more, the cornering force could be generated to about the same extent as in the comparative example. It was also found that both the wear index and the ground contact pressure index were maintained at the same level as in the comparative example.

[0045]

As described above, the passenger car tire of the present invention is
Tire weight can be reduced while maintaining steering stability.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating a camber angle when the vehicle is viewed from the front.

FIG. 3 is a graph showing the relationship between slip angle and cornering force.

[Explanation of symbols] 2 tread portion 2A crown portion 2B shoulder portion 3 sidewall portion 4 bead portion 5 bead core 6 carcass 7 belt layer C1 crown arc C2 shoulder arc R1 radius of curvature of crown arc R2 radius of curvature of shoulder arc

Claims (3)

[Claims] 1. A carcass in which an organic fiber cord is folded in a radial direction from a tread portion to a side wall portion and folded back around a bead core of a bead portion, and the carcass is arranged radially outside of the carcass and inside the tread portion. A tread surface for a tread portion in a meridional section of a tire in a normal state in which a normal internal pressure is applied, the tread surface including a belt layer and being mounted on a passenger car having a camber angle of 8 to 18 degrees in wheel alignment. Is a crown arc covering a width of 50 to 80% of the tread width TW that forms the maximum tire width, and a crown arc C1 having a radius of curvature R1; And a shoulder arc C2 having a radius of curvature R2 that is smoothly continuous with the radius of curvature R of the crown arc C1. Has a ratio (R1 / TW) to the tread width TW of 0.6 to 0.95, and a radius of curvature R2 of the shoulder arc C2 has a ratio (R2 / TW) to the tread width TW of 0.3. ˜0.7 and smaller than the radius of curvature R1, the belt layer is formed by spirally winding a belt cord made of steel or aramid into one layer at an angle of 5 degrees or less with respect to the tire circumferential direction. A tire for passenger cars characterized by being formed. 2. The passenger car is an electric vehicle.
The passenger car tires described. 3. The tire for passenger cars according to claim 1, wherein the camber angle is 10 to 15 degrees.