JP5845019B2 - Pneumatic radial tire for passenger cars and method of using the same - Google Patents

Description

  The present invention relates to a pneumatic radial tire for passenger cars and a method for using the same.

  Vehicles up to about 1960 A.D. were used because of the light weight of the vehicle and the cruising speed required for the vehicle, so that the burden on the tire was light and the tire had a narrow cross-sectional width. However, with the recent increase in vehicle output and the development of highway networks, improvements in handling stability and wear resistance during high-speed driving have come to be demanded. Tires with a wide, flat radial structure Are becoming mainstream (Patent Document 1, etc.).

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

  Furthermore, the wide flat tire as described above has a wide tread surface as shown by arrows in FIG. It is not easy to be discharged and the drainage is not good. Further, since the contact length L of the wide flat tire is shortened, as shown in FIG. 1A, the tread surface is lifted by a water film entering from the stepping surface, the actual contact area is reduced, and the grip is lost. There is a problem that a planing phenomenon is likely to occur and wet performance is deteriorated.

Therefore, conventionally, particularly in a wide flat radial tire, a main groove having a large groove cross section and extending in the tread circumferential direction has to be disposed on the tread surface.
However, when the main groove having a deep groove depth is provided, it is necessary to increase the tread accordingly, which causes a problem that the weight of the tire is increased and the running performance is deteriorated. In addition, when a main groove with a wide groove width is provided, the negative rate increases and the ground contact area decreases, so grip strength, that is, steering stability, braking performance on dry road surfaces, wear resistance, and noise performance This also causes a problem of lowering.

  Further, it is known that, in a wide flat radial tire, it is effective to use a tread rubber having a small hysteresis loss in order to reduce rolling resistance and reduce fuel consumption. However, when rubber having a small hysteresis loss is used, there arises a problem that grip performance on a wet road surface is lowered.

Japanese Patent Laid-Open No. 7-40706

  As described above, it is generally difficult to achieve both tire fuel efficiency, comfort (vehicle space), wet performance, and dry performance, and a fundamental technology to achieve both of these performances. Was sought after.

  Therefore, an object of the present invention is to solve the above-mentioned problems, and both an air resistance value (Cd value) and a tire rolling resistance value (RR value) are low, and low fuel consumption and vehicle space are achieved. It is an object of the present invention to provide a pneumatic tire for a passenger car and a method of using the same that are capable of ensuring the above-mentioned performance and are excellent in running performance on a dry road surface and on a wet road surface.

The inventors have intensively studied to solve the above problems.
As a result, first, in order to improve the fuel efficiency and the comfortability of the radial tire, the width and the diameter of the tire are reduced, that is, the cross-sectional width SW and the outer diameter OD of the tire are regulated under an appropriate ratio. We found that it was extremely effective.

  Furthermore, the inventors of the above-mentioned tire having a narrow width and a large diameter can achieve both the driving performance on the dry road surface and the driving performance on the wet road surface by optimizing the tread pattern. I got new knowledge that

This invention is made | formed based on said knowledge, The summary structure is as follows.
(1) A pneumatic radial tire for a passenger car comprising a carcass made of a ply of a radial arrangement code straddling a toroidal shape between a pair of bead portions, and a tread,
The ratio SW / OD of the tire cross-sectional width SW to the outer diameter OD is 0.24 or less,
When the tread surface is equally divided into six regions in the tread width direction, the two regions in the center of the tread width direction are the center portion, and the other four regions on both sides of the center portion in the tread width direction are the shoulder portions. ,
The tread surface includes at least one lateral groove extending in the tread width direction from the shoulder portion of one half bordered by the tire equator surface to the other half portion across the tire equator surface and extending in the tread width direction. A groove pattern consisting only of grooves is formed,
Each of said lateral grooves, the inclination angle θ1 with respect to the tread circumferential direction in the center portion is rather larger than the inclination angle θ2 with respect to the tread circumferential direction in the shoulder portion,
A pneumatic radial tire for a passenger car , wherein at least one end of the lateral groove is open to a tread end .

(2) The pneumatic radial for a passenger car according to (1) above, wherein an inclination angle θ2 of the horizontal groove with respect to a tread circumferential direction at an opening portion where at least one end of the horizontal groove opens at a tread end is 30 ° to 70 °. tire.

(3) A value obtained by dividing the total extension of the groove extending in the tread width direction in the tread tread surface projected on the cross section in the tread width direction by the area of the tread tread is an edge component per unit area of the tread tread,
When the edge component per unit area at the center portion is ρc (mm / mm ² ) and the edge component per unit area at the shoulder portion is ρs (mm / mm ² ),
ρc ≧ 1.2ρs
The pneumatic radial tire for passenger cars according to (1) or (2), wherein

(4) When the groove depth of the lateral groove on the tire equator surface is δg, and the thickness of the tread rubber from the tread tread surface to the tire radial direction outermost reinforcing member on the tire equator surface is δt,
δg / δt ≦ 0.85
The pneumatic radial tire for passenger cars according to any one of (1) to (3), wherein

(5) The tire size is any one of 155 / 55R21, 165 / 55R21, 155 / 55R19, 155 / 70R17, 165 / 55R20, 165 / 65R19, 165 / 70R18, 155 / 45R21 above (1 The pneumatic radial tire for passenger cars according to any one of (1) to (4).
(6) The pneumatic radial tire for a passenger car according to any one of (1) to (5), wherein the center portion includes at least one sipe between the lateral grooves adjacent to each other in the tread circumferential direction.
(7) The lateral groove extends in the tread width direction from the tread end toward the tread circumferential direction in one half portion of the tread tread with the tire equatorial plane as a boundary, and the tread tread tread tread In the other half part which makes a surface a boundary, it extends in the tread width direction toward the direction opposite to the one direction of the tread circumferential direction from the tread end, and is described in any one of the above (1) to (6). Pneumatic radial tires for passenger cars.
(8) A value obtained by dividing a total extension obtained by projecting the groove extending in the tread width direction in the tread width direction on the cross section in the tread width direction by the area of the tread surface is defined as an edge component per unit area of the tread surface,
When the edge component per unit area at the center portion is ρc (mm / mm ² ) and the edge component per unit area at the shoulder portion is ρs (mm / mm ² ),
ρc ≦ 3ρs
The pneumatic radial tire for passenger cars according to any one of (1) to (7), wherein
(9) When the groove depth of the lateral groove on the tire equator plane is δg, and the thickness of the tread rubber from the tread tread surface to the tire radial direction outermost reinforcing member on the tire equator surface is δt,
δg / δt ≧ 0.65
The pneumatic radial tire for passenger cars according to any one of (1) to (8), wherein
(10) A method for using a pneumatic radial tire for a passenger car, wherein the tire according to any one of (1) to (9) is used at an internal pressure of 250 kPa or more.

  According to the present invention, the air resistance value (Cd value) and the tire rolling resistance value (RR value) are both low, low fuel consumption and securing of vehicle space can be realized, and driving performance on a dry road surface and It is possible to provide a pneumatic radial tire for a passenger car having excellent running performance on a wet road surface.

(A) It is a figure for demonstrating the wet performance of a wide radial tire. (B) It is a figure for demonstrating the wet performance of a radial tire of a narrow width. It is a figure which shows the cross-sectional width SW and outer diameter OD of a tire. (A) It is a figure which shows the vehicle equipped with the tire which expanded the diameter of this invention and narrowed. (B) It is a figure which shows the vehicle equipped with the conventional tire. It is a figure which shows the relationship between the rolling resistance value of each tire, and an air resistance value. It is an expanded view which shows the tread pattern concerning the 1st Embodiment of this invention. It is an expanded view which shows the tread pattern concerning the 2nd Embodiment of this invention. It is an expanded view which shows the tread pattern concerning the 3rd Embodiment of this invention. It is a figure for demonstrating the edge component of a horizontal groove. FIG. 6 is a schematic cross-sectional view in the tire width direction for explaining a ratio δg / δt. It is an expanded view which shows the tread pattern concerning a comparative example. It is an expanded view which shows the tread pattern concerning a comparative example. It is an expanded view which shows the tread pattern concerning a comparative example. It is an expanded view which shows the conventional tread pattern. It is an expanded view which shows the conventional tread pattern. It is a figure for demonstrating the inclination-angle of a horizontal groove.

Hereinafter, the process which led to the pneumatic radial tire for passenger cars (hereinafter also referred to as a tire) of the present invention will be described.
First, the inventors have made it possible to secure a vehicle space by making the tire cross-sectional width SW (see FIG. 2) of the radial tire narrower than before, and in particular, in the vicinity of the tire mounting inner side of the tire. It paid attention to the installation space being secured (see FIG. 3).
Further, when the tire cross-sectional width SW 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 (Cd value) of the vehicle.
However, since the deformation of the ground contact portion becomes large, there is a problem that the rolling resistance value (RR value) of the tire becomes large at the same air pressure.

  On the other hand, the inventors have found that the above-described problems can be solved by the properties unique to the radial tire. That is, since the radial tire is smaller in tread deformation than the bias tire, increasing the outer diameter OD (see FIG. 2) of the radial tire is less affected by the roughness of the road surface. It was noted that the rolling resistance value (RR value) can be reduced in the case of the same air pressure. Further, by increasing the diameter, it is possible to improve the load capacity of the tire. Further, as shown in FIG. 3, the diameter of the radial tire increases to increase the wheel axle and expand the space under the floor. It was also found that a space for a vehicle trunk or the like and an installation space for driving parts can be secured.

  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 (RR value) is in a trade-off relationship. Further, the air resistance value (Cd value) of the vehicle can be reduced by narrowing the tire.

  Accordingly, the inventors have made these characteristics suitable for conventional radial tires by optimizing the balance between the tire cross-sectional width and the tire outer diameter with respect to the air resistance value (Cd value) and the rolling resistance value (RR value). We studied earnestly to improve it.

The inventors pay attention to the ratio SW / OD of the tire cross-sectional width SW and the outer diameter OD of the tire, attach tires of various tire sizes including those outside the standard to the vehicle, and set the air resistance value (Cd Value) and rolling resistance value (RR value) were tested, and the condition of the ratio SW / OD was derived, in which both of these characteristics exceeded that of a conventional radial tire.
Hereinafter, the experimental results that led to deriving the preferred range of the ratio SW / OD will be described in detail.

Based on the above knowledge, the inventors have investigated specific conditions that can achieve both a reduction in tire air resistance and a reduction in rolling resistance by increasing the tire diameter and width. .
First, a tire having a tire size of 195 / 65R15, which is used in the most general-purpose vehicles and is suitable for comparison of tire performance, was prepared as a reference tire.
Moreover, tires of various tire sizes were prepared, incorporated into rims, the internal pressure was set to 220 kPa, and the following tests were performed.
Table 1 shows the specifications of each tire. The specifications of the tire not shown in Table 1 such as the internal structure of the tire are the same as those of a general tire, and each tire has a carcass made of a ply of a radial arrangement code straddling a toroidal shape between a pair of bead portions. And tread.
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. And studied extensively.

<Air resistance value>
In the laboratory, each tire is mounted on a vehicle with a displacement of 1500 cc, and the air force when the air is blown at a speed corresponding to 100 km / h is 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>
Each tire was mounted on a rim to form a tire / rim assembly, the maximum load specified for each vehicle on which the tire was mounted was applied, and the rolling resistance was measured under a drum rotation speed of 100 km / h.
The evaluation results are indicated by an index with the reference tire as 100. It means that rolling resistance is so small that this index value is small.
The evaluation 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 SW / OD of the tire cross-sectional width SW to the tire outer diameter OD of 0.24 or less is a tire size 195 / The knowledge that both the air resistance value (Cd value) and the rolling resistance value (RR value) were reduced from the tire 65R15.

  Next, in order to confirm that the ratio SW / OD of the tire cross-sectional width SW and the tire outer diameter OD is 0.24 or less, the fuel efficiency and comfort of the vehicle are actually improved. The following tests were conducted.

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

As shown in Table 3, in the test tires having a ratio SW / OD of more than 0.24, there were test tires in which at least one of the fuel economy and the habitability was lower than that of the reference tire. It can be seen that the test tires 1 to 7 and 17 having SW / OD of 0.24 or less are both better in fuel efficiency and comfort than the reference tire.
In this way, the inventors have set the ratio SW / OD to 0.24 or less in the pneumatic radial tire, thereby improving the air comfort of the vehicle and the rolling resistance of the tire. It has been found that the fuel efficiency can be improved by reducing both values.

  Next, in the pneumatic radial tire having the above ratio SW / OD of 0.24 or less, a tire tread pattern for achieving both the running performance on the dry road surface and the running performance on the wet road surface will be described.

FIG. 5 is a development view showing a tread pattern of a pneumatic radial tire for passenger cars (hereinafter referred to as a tire) according to the first embodiment of the present invention.
As shown in FIG. 5, the tire according to the first embodiment is divided into at least one, 10 in the illustrated example, a lateral groove 2 extending in the tread width direction, the lateral groove 2 and the tread end TE. And land portion 3 to be provided. Further, in the tire according to the first embodiment, only the lateral groove 2 extending in the tread width direction is disposed on the tread tread surface 1 and does not have a main groove extending in the tread circumferential direction.
The tread tread is the maximum load specified for each vehicle on which the tire is mounted, with the tire mounted on the rim, filled with the maximum air pressure specified for each vehicle on which the tire is mounted, and placed vertically on a flat plate. The surface area of the tread rubber that comes into contact with the flat plate when a weight corresponding to is applied.

Here, the tread tread surface 1 is equally divided into six regions in the tread width direction, and the two regions at the center in the tread width direction sandwiching the tire equator surface CL are the center portion 4 and the other regions on both outer sides of the center portion 4 in the tread width direction. The four regions are referred to as a shoulder portion 5.
In the example shown in FIG. 5, the lateral groove 2 has a designated tire rotation direction from one end (starting end) that opens at the tread end TE of one half in the width direction of the tread tread surface 1 with the tire equatorial plane CL as a boundary. In the direction of R, it extends inward in the tread width direction and extends to the other half in the width direction of the tread surface 1 across the tire equatorial plane CL. The other end (terminal) of the lateral groove 2 remains in the land portion 3 (in the illustrated example, in the center portion 4) of the other half of the tread surface 1.
In the example shown in FIG. 5, the lateral grooves 2 adjacent to each other in the tread circumferential direction are disposed so as to extend from opposite tread ends TE with the tire equatorial plane CL as a boundary.

なお、「あるセンタ部内の幅方向位置ｙにおける、横溝２とタイヤ周方向とがなす挟角θ（ｙ）」は、微分により求めるものとする。
また、「ショルダ部でのトレッド周方向に対する傾斜角度」とは、図１５（ａ）〜（ｃ）に示すように、トレッド幅方向をｙ軸とし、あるショルダ部内の幅方向位置ｙにおける、横溝２とタイヤ周方向とがなす挟角（鋭角）θ（ｙ）を、ショルダ部での横溝の延在範囲の全域にわたって、「ｙ」で積分した値をショルダ部での横溝の幅方向延在範囲の全域（定義域）で除した値をいうものとする。すわわち、図１５（ｂ）に示すように、横溝２が一方の幅方向半部のショルダ部から他方の幅方向半部のショルダ部まで延びている場合は、θ２は、次式で表される（ただし、ｙｃは、ショルダ部の幅方向最内側の正のｙ座標であり、ｙ３、ｙ４は、ショルダ部における横溝の端部の座標とし、ｙ３が負、ｙ４が正とする）。

また、図１５（ａ）、（ｃ）に示すように、横溝２が一方の幅方向半部のショルダ部から他方の幅方向半部のショルダ部まで延びずに、他方の半部のセンタ部内に留まる場合には、θ２は次式で表される。
まず、図１５（ａ）に示すように、ｙ座標が正であるショルダ部から他方の半部のセンタ部まで横溝が延びている場合には、以下の式で表される。

一方で、図１５（ｃ）に示すように、ｙ座標が負であるショルダ部から他方の半部のセンタ部まで横溝が延びている場合には、以下の式で表される。

Furthermore, in the first embodiment, as shown in FIG. 5, the lateral groove 2 is disposed so as to have a shape along the tread width direction as it extends inward in the tread width direction, and the tread circumference at the center portion 4 is arranged. The inclination angle θ <b> 1 with respect to the direction is larger than the inclination angle θ <b> 2 with respect to the tread circumferential direction at the shoulder portion 5.
Here, the “inclination angle with respect to the tread circumferential direction at the center portion” means that, as shown in FIGS. 15A to 15C, the tread width direction is the y axis, and the width direction position y in a certain center portion is A value obtained by integrating the sandwiched angle (acute angle or right angle) θ (y) formed by the lateral groove 2 and the tire circumferential direction with “y” over the entire region extending in the width direction of the groove at the center portion is represented by It shall be the value divided by the width direction extension distance. That is, θ1 is expressed by the following equation (where “y1” and “y2” are the y-coordinates of the ends of the lateral grooves in the center portion, as shown in FIGS. y2> y1).

Note that “the included angle θ (y) between the lateral groove 2 and the tire circumferential direction at a position y in the width direction within a certain center portion” is obtained by differentiation.
In addition, the “inclination angle with respect to the tread circumferential direction at the shoulder portion” means, as shown in FIGS. 15A to 15C, the transverse groove at the position y in the width direction within a certain shoulder portion with the tread width direction as the y axis. 2 and the circumferential angle of the lateral groove in the shoulder portion obtained by integrating “y” over the entire extending range of the lateral groove in the shoulder portion. The value divided by the entire range (defined area). That is, as shown in FIG. 15B, when the lateral groove 2 extends from the shoulder portion of one width direction half portion to the shoulder portion of the other width direction half portion, θ2 is expressed by the following equation. (Where yc is the positive y coordinate on the innermost side in the width direction of the shoulder portion, y3 and y4 are the coordinates of the end of the lateral groove in the shoulder portion, y3 is negative, and y4 is positive).

Further, as shown in FIGS. 15A and 15C, the lateral groove 2 does not extend from the shoulder portion of one width direction half portion to the shoulder portion of the other width direction half portion, but in the center portion of the other half portion. When θ remains, θ2 is expressed by the following equation.
First, as shown in FIG. 15A, when a lateral groove extends from a shoulder portion having a positive y coordinate to the center portion of the other half, it is expressed by the following equation.

On the other hand, as shown in FIG. 15C, when the lateral groove extends from the shoulder portion having a negative y coordinate to the center portion of the other half, it is expressed by the following equation.

As described above, in the present invention, the ratio SW / OD of the tire cross-sectional width SW to the outer diameter OD is 0.24 or less, and the tread tread surface 1 has one half of the tire equatorial plane CL as a boundary. A groove pattern consisting only of grooves extending in the tread width direction, including at least one horizontal groove 2 extending in the tread width direction from the shoulder portion 5 to the other half portion across the tire equatorial plane CL is formed. It is important that the inclination angle of the center portion 4 with respect to the tread circumferential direction is larger than the inclination angle of the shoulder portion 5 with respect to the tread circumferential direction.
Hereinafter, the operation and effect of the present invention when the vehicle is mounted on the vehicle with the direction R of the arrow in FIG. 5 as the tire rotation direction will be described.

According to the first embodiment of the present invention, first, the ratio SW / OD is 0.24 or less and the width of the stepping surface is narrow. As schematically shown by the line, water is likely to be discharged to both sides of the tire in the width direction, so that drainage is enhanced and an actual ground contact area can be secured. Further, since the inclination angle of the lateral groove with respect to the tire circumferential direction is large in the center portion where the contact length becomes long, the edge component in the width direction of the center portion increases, and wet braking performance is improved. Further, in the tire according to the first embodiment, the circumferential edge component of the lateral groove is increased in the shoulder portion, so that the wet turning performance is also improved.
In addition, regarding the traveling on the dry road surface, the tire according to the first embodiment does not have the main groove extending in the tire circumferential direction on the tread surface, and thus the rigidity of the land portion is high, so that the steering stability, the braking performance, Noise and wear resistance can be ensured.
Therefore, according to the first embodiment, it is possible to achieve low fuel consumption and secure vehicle space, and to achieve both driving performance on a dry road surface and driving performance on a wet road surface.

FIG. 6 is a development view showing a tread pattern of a tire according to the second embodiment of the present invention. As shown in FIG. 6, this tire includes at least one lateral groove 2 extending in the tread width direction on the tread tread surface 1, and in the illustrated example, a land groove 3 defined by the lateral groove 2 and the tread end TE. Have
In the example shown in FIG. 6, the lateral grooves 2 are arranged symmetrically about the tire equatorial plane CL, and the designated tire rotation direction from the tread end TE in the half of the tread width direction with the tire equatorial plane CL as a boundary. It extends inward in the tread width direction toward the direction of R.
Further, as shown in FIG. 6, the lateral groove 2 is arranged in the tread half so as to have a shape along the tread width direction as it extends inward in the width direction from the tread end TE. The inclination angle θ1 with respect to the tread circumferential direction at is greater than the inclination angle θ2 with respect to the tread circumferential direction at the shoulder portion 5.
In addition, the tire according to the second embodiment has a total of six sipes 6 in the center portion 4, at least one in the center portion 4, in the illustrated example, one between the lateral grooves 2 adjacent in the tread circumferential direction. Yes.
Here, the lateral groove 2 is a groove extending in the tread width direction and having a groove width of 1.5 mm or more, and the sipe 6 is a groove extending in the tread width direction and having a groove width of less than 1.5 mm. . The width of the lateral groove is not particularly limited, but is preferably 20 mm or less, for example.
Hereinafter, the operation and effect when the tire according to the second embodiment is attached to the vehicle with the direction R of the arrow in FIG. 6 as the tire rotation direction will be described.

According to the second embodiment of the present invention, first, similarly to the first embodiment, since the width of the stepping surface is narrow, on the wet road surface, a streamline of water is schematically shown by arrows in FIG. As shown in the figure, water is easily discharged to both sides in the width direction of the tire, so that drainage is improved and an actual contact area can be secured. Further, since the inclination angle of the lateral groove with respect to the tire circumferential direction is large at the center portion where the contact length becomes long, the edge component in the width direction of the center portion increases and wet braking performance is improved. Furthermore, in the example shown in FIG. 6, since the circumferential edge component of the lateral groove increases in the shoulder portion, the wet turning performance is improved.
Furthermore, according to the second embodiment, the edge component in the width direction in the center portion is secured by a sipe having a small groove width, the negative rate is low, and the rigidity of the land portion is high, so that the dry performance is further improved.
Therefore, according to the second embodiment of the present invention, low fuel consumption and securing of the vehicle space can be realized, and traveling performance on a dry road surface and traveling performance on a wet road surface can both be achieved.

FIG. 7 is a development view showing a tread pattern of a tire according to the third embodiment of the present invention. As shown in FIG. 7, the tire according to the third embodiment includes at least one lateral groove 2 extending in the tread width direction on the tread tread surface 1, and in the illustrated example, the lateral groove 2 and the lateral grooves 2 and the tread ends TE1 and TE2. And a land portion 3 partitioned by The lateral grooves 2 are disposed asymmetrically with the tire equatorial plane CL as a boundary.
Here, one half T1 with the tire equatorial plane CL of the tread tread 1 as a boundary is defined as T2, and the other half T2.
As shown in FIG. 7, the lateral groove 2 extends in the tread width direction from the tread end TE1 toward one direction in the tread circumferential direction in one half T1. Further, the lateral groove 2 extends in the tread width direction from the tread end TE2 toward the opposite direction of the one direction in the other half portion T2.

Furthermore, as shown in FIG. 7, the lateral groove 2 has a shape along the tread width direction as it extends inward in the width direction from the tread end TE1 toward the tire equatorial plane CL in one half T1. Further, in the other half portion T2, as it extends inward in the width direction from the tread end TE2 toward the tire equatorial plane CL, it is disposed so as to have a shape along the tread width direction. Therefore, the inclination angle θ <b> 1 of the lateral groove 2 in the tread circumferential direction at the center portion 4 is larger than the inclination angle θ <b> 2 of the lateral groove 2 in the shoulder portion 5 with respect to the tread circumferential direction.
Hereinafter, the operation and effect when the tire according to the third embodiment is mounted on a vehicle will be described.

According to the third embodiment, first, similarly to the first and second embodiments, since the width of the stepping surface is narrow, when running on a wet road surface, the flow of water is indicated by an arrow in FIG. As schematically shown by the line, water is likely to be discharged to both sides of the tire in the width direction, so that drainage is enhanced and an actual ground contact area can be secured. Further, since the inclination angle of the lateral groove with respect to the tire circumferential direction is large at the center portion where the contact length becomes long, the edge component in the width direction of the center portion increases and wet braking performance is improved. Further, in the example shown in FIG. 7, the circumferential edge component of the lateral groove is increased in the shoulder portion, so that the wet turning performance is improved.
Even on dry road surfaces, the tire has no circumferential main groove, so the land portion has high rigidity, and driving stability, braking performance, noise resistance, and wear resistance can be ensured.
Furthermore, since there is no designation of the tire rotation direction, cross rotation between the inner side and the outer side of mounting is possible, uneven wear due to improper distribution of right and left loads can be suppressed, and the life of the tire can be improved.
Therefore, according to the third embodiment of the present invention, it is possible to achieve low fuel consumption and secure vehicle space, and to achieve both driving performance on a dry road surface and driving performance on a wet road surface.

Here, in the present invention, as shown in FIGS. 5 to 7, at least one end of the lateral groove 2 opens at the tread end, and the inclination angle θ <b> 2 of the lateral groove 2 with respect to the tread circumferential direction is 30 at the opening. It is preferable that it is (degree)-70 degree.
By setting the angle to 30 ° or more, chipping of the block in the vicinity of the opening of the lateral groove can be suppressed and the wear resistance can be improved. Because it can be done.

Further, a value obtained by dividing the total extension of the grooves (lateral grooves 2 and sipes 6) extending in the tread width direction in the tread tread surface 1 on the tread width direction cross section by the area of the tread tread surface 1 per unit area of the tread tread surface 1 Edge component.
Here, as shown in FIG. 8, the total extension is an extension length including overlapping portions when a plurality of (three in FIG. 8) grooves overlap when projected onto the cross section in the tread width direction. , “2A + B”.
When the edge component per unit area at the center portion 4 is ρc (mm / mm ² ) and the edge component per unit area at the shoulder portion 5 is ρs (mm / mm ² ),
ρc ≧ 1.2ρs
It is preferable to satisfy.
This is because, by setting the above range, the edge component at the center portion can be further secured and the wet braking performance can be further improved.
It should be noted that the extreme increase in edge density decreases the block rigidity and reduces the braking performance on the dry road surface and the wet braking performance in the low speed range.
ρc ≦ 3ρs
It is preferable to satisfy.

Furthermore, as shown in FIG. 9, the groove depth of the lateral groove 2 at the tire width direction center position (tire equatorial plane CL) is δg, and the tire from the tread tread surface 1 at the tire width direction center position (tire equatorial plane CL). When the thickness of the tread rubber to the radially outermost reinforcing member (in the illustrated example, the outermost belt layer 7a of the two belt layers 7a and 7b) is δt,
δg / δt ≦ 0.85
It is preferable to satisfy.
This is because, by setting the ratio δg / δt to 0.85 or less, it is possible to further secure the rigidity of the land portion and improve the running performance on the dry road surface.
In addition, considering the balance between the groove volume required for drainage and ensuring wear resistance,
δg / δt ≧ 0.65
It is preferable to satisfy.
The reinforcing member is a belt and a belt protective layer.

In addition, in the tire of the present invention, it is preferable to use an internal pressure of 250 kPa or more.
This is because, by setting the high internal pressure, the belt tension increases and the contact pressure increases, thereby improving the hydroplaning property.
The internal pressure is preferably 350 kPa or less.
The tire of the present invention preferably has an air volume of 15000 cm ³ or more. This is because it is necessary to maintain the minimum load capacity of the tire.

In order to confirm the effect of the present invention, tires according to Invention Examples 1 to 3 and Comparative Examples 1 to 3 were manufactured as trials, and tires according to Conventional Examples 1 and 2 were prepared.
The specifications of each tire are shown in Table 4 below.

Each of the above tires was subjected to tests for evaluating wet braking performance, wet turning performance, steering stability on a dry road surface, wear resistance, and quietness.
The evaluation method is as follows.

<Wet braking performance>
The vehicle equipped with each of the tires was run on a wet road surface at an initial speed of 40 km / h, and the stop distance (mm) during full braking was evaluated as an index. The results are shown in Table 1.
In evaluation, it represents with the index | index which made the conventional tire 1 100, and the one where a numerical value is large shows that the performance is excellent.
<Wet swirl>
A vehicle equipped with a test tire was turned on an asphalt road course with a turning radius of 30 m (with an average water depth of 2 mm), the lateral acceleration during turning was measured, and the turning performance was evaluated based on the magnitude of the lateral acceleration. .
In the evaluation, it is represented by an index with the conventional tire 1 being 100, and a larger numerical value indicates better performance.
<Steering stability>
For each of the above tires, run in a speed range from low speeds to around 150 km / h on a test course consisting of a circumference circuit including a long straight part and a handling evaluation road with many gentle curves. The driver evaluated the feeling. Steering stability is evaluated by indexing the conventional tire 1 as 100, and a larger numerical value indicates better performance.
<Abrasion resistance>
The amount of wear was calculated from the remaining groove measurement after traveling 100,000 km. The index was evaluated with the evaluation value in Conventional Example 1 being 100. Smaller value indicates better wear resistance <Silent>
The quietness was evaluated by feeling by a professional driver running a vehicle equipped with the above tires on a circuit road at a speed of 60 to 120 km / h. At this time, the quietness of the conventional tire 1 was converted to 100, and the other tires were relatively evaluated. In addition, it shows that it is excellent in quietness, so that a numerical value is large.
These evaluation results are shown in Table 5 below.

  As shown in Table 5, the tires according to Comparative Examples 1 to 3 are inferior to Conventional Example 1 in any of wet braking performance, wet turning performance, steering stability, wear resistance, and quietness. It can be seen that all the tires according to Invention Examples 1 to 3 are superior to Conventional Example 1 in all of these performances.

Next, in order to see the effect of the lateral groove opening at the tread end and setting the lateral groove at the opening to an appropriate inclination angle with respect to the tread circumferential direction, the tires according to Invention Examples 4 and 5 were prototyped, A test was conducted to evaluate the performance.
Table 6 shows the specifications and evaluation results of each tire. Inventive Example 1 and Inventive Examples 4, 5 are common to specifications not shown in Table 6.

Next, to see the effect of optimizing the relationship between the edge component ρc at the center portion and the edge component at the shoulder portion ρs, a tire according to Invention Example 7 is prototyped and the performance of the tire is evaluated. A test was conducted.
The specifications and evaluation results of each tire are shown in Table 7 below. The invention example 1 and the invention example 7 are common about the item which is not shown in Table 7.

Furthermore, in order to see the effect of optimizing the ratio δg / δt, a tire according to Invention Example 8 was prototyped and a test for evaluating tire performance was performed.
The specifications and evaluation results of each tire are shown in Table 8 below. It should be noted that Invention Example 1 and Invention Example 8 are common to specifications not shown in Table 8. In Table 8, it is evaluated by an index when Invention Example 1 is set to 100, and a larger value indicates better performance.

In addition, in order to see the effect of using the tire at a high internal pressure, the test tire 17 was subjected to a test for evaluating the tire performance by changing the internal pressure.
The specifications and evaluation results of each tire are shown in Table 9 below. In Table 9, the evaluation results are expressed as an index when the internal pressure is 250 kPa, and a larger numerical value indicates better performance.

As shown in Table 6, it can be seen that Invention Example 1 in which the groove pattern is optimized is superior to Invention Examples 4, 5, and 6 in wet swirlability.
Further, as shown in Table 7, it can be seen that Invention Example 1 in which the value of the ratio ρc / ρs is optimized is superior in wet braking performance to Invention Example 7.
Furthermore, as shown in Table 8, it can be seen that Invention Example 1 in which the value of the ratio δg / δt is optimized has an RR value reduced from Invention Example 8.
In addition, as shown in Table 9, it can be seen that according to the usage method in which the internal pressure of the tire is optimized, the RR value is reduced and the wet braking performance is also improved.

DESCRIPTION OF SYMBOLS 1 Tread surface 2 Horizontal groove 3 Land part 4 Center part 5 Shoulder part 6 Sipe 7a, 7b Reinforcement material (belt layer)
10 Tread tread 20 Horizontal groove 30 Main groove 40 Land

Claims (10)

A pneumatic radial tire for a passenger car, comprising a carcass made of a ply of a radial arrangement code straddling a toroidal shape between a pair of bead parts, and a tread,
The ratio SW / OD of the tire cross-sectional width SW to the outer diameter OD is 0.24 or less,
When the tread surface is equally divided into six regions in the tread width direction, the two regions in the center of the tread width direction are the center portion, and the other four regions on both sides of the center portion in the tread width direction are the shoulder portions. ,
The tread surface includes at least one lateral groove extending in the tread width direction from the shoulder portion of one half bordered by the tire equator surface to the other half portion across the tire equator surface and extending in the tread width direction. A groove pattern consisting only of grooves is formed,
Each of said lateral grooves, the inclination angle θ1 with respect to the tread circumferential direction in the center portion is rather larger than the inclination angle θ2 with respect to the tread circumferential direction in the shoulder portion,
A pneumatic radial tire for a passenger car , wherein at least one end of the lateral groove is open to a tread end . 2. The pneumatic radial tire for a passenger car according to claim 1, wherein an inclination angle θ <b> 2 of the transverse groove with respect to a tread circumferential direction at an opening portion where at least one end of the transverse groove opens at a tread end is 30 ° to 70 °. A value obtained by dividing the total extension obtained by projecting the groove extending in the tread width direction in the tread tread surface on the tread width direction cross section by the area of the tread tread is an edge component per unit area of the tread tread,
When the edge component per unit area at the center portion is ρc (mm / mm ² ) and the edge component per unit area at the shoulder portion is ρs (mm / mm ² ),
ρc ≧ 1.2ρs
The pneumatic radial tire for passenger cars according to claim 1 or 2, wherein When the groove depth of the lateral groove on the tire equator surface is δg, and the thickness of the tread rubber from the tread tread surface to the tire radial direction outermost reinforcing member on the tire equator surface is δt,
δg / δt ≦ 0.85
The pneumatic radial tire for a passenger car according to any one of claims 1 to 3, wherein The tire size of the tire is any one of 155 / 55R21, 165 / 55R21, 155 / 55R19, 155 / 70R17, 165 / 55R20, 165 / 65R19, 165 / 70R18, and 155 / 45R21. The pneumatic radial tire for passenger cars as described in any one of Claims. The pneumatic radial tire for a passenger car according to any one of claims 1 to 5, wherein the center portion has at least one sipe between the lateral grooves adjacent to each other in the tread circumferential direction. The lateral groove extends in the tread width direction from one end of the tread toward the tread circumferential direction in one half of the tread tread with the tire equatorial plane as a boundary, and the tread tread has a tire equatorial boundary as a boundary. The pneumatic radial for a passenger car according to any one of claims 1 to 6, wherein the other half portion extends in the tread width direction from the tread end in a direction opposite to the one direction in the tread circumferential direction. tire. A value obtained by dividing the total extension obtained by projecting the groove extending in the tread width direction in the tread tread surface on the tread width direction cross section by the area of the tread tread is an edge component per unit area of the tread tread,
The edge component per unit area at the center is ρc (mm / mm ² ), And the edge component per unit area in the shoulder portion is ρs (mm / mm ² )
ρc ≦ 3ρs
The pneumatic radial tire for passenger cars according to any one of claims 1 to 7, wherein When the groove depth of the lateral groove on the tire equator surface is δg, and the thickness of the tread rubber from the tread tread surface to the tire radial direction outermost reinforcing member on the tire equator surface is δt,
δg / δt ≧ 0.65
The pneumatic radial tire for passenger cars according to any one of claims 1 to 8, wherein A method for using a pneumatic radial tire for a passenger car, wherein the tire according to any one of claims 1 to 9 is used at an internal pressure of 250 kPa or more.

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