JP5239504B2 - Pneumatic tire - Google Patents

Description

  In the present invention, the snow traction index (STI) is 180 or more, the JIS hardness of the tread rubber in contact with the road surface is 45 to 55 (0 ° C.), and the two circumferential main grooves sandwich the tire equator line. The present invention relates to a pneumatic tire, particularly a studless tire, in which a plurality of tread block rows are arranged in the tire circumferential direction.

Conventionally, studless tires (winter tires) use a block pattern as a pattern of a tread portion, and improve performance on snow by means of a spring elastic force or the like by a groove between each block. In addition, sipes extending in the tire width direction are formed in each block to improve the performance on ice.
In such a steady tire, in order to improve the performance on ice, the groove area ratio representing the ratio of the groove area to the ground contact area of the tire tread portion is reduced in order to increase the contact area between the ice and the tire tread portion. It is necessary. However, if this groove area ratio is reduced, the number of grooves themselves is reduced, so that there is a trade-off problem that the elasticity of the snow in the snow is reduced and the performance on snow is reduced.

Patent Document 1 listed below proposes a tire that significantly improves driving and braking performance as a studless tire while ensuring skid resistance with excellent performance on snow and performance on ice.
Patent Document 2 listed below provides a tire capable of improving wet braking performance and snow traction while ensuring on-ice performance.

JP 2001-191740 A WO2005 / 005170

  Under such circumstances, compatibility between on-ice performance and on-snow performance, in particular, both on-ice performance and on-snow handling stability and on-snow drive performance is further required.

  Therefore, an object of the present invention is to provide a pneumatic tire in which the performance on ice and the performance on snow are compatible with each other at a high level with respect to the conventional technology.

In order to achieve the above object, according to the present invention, the snow traction index (STI) is 180 or more, the JIS hardness of the tread rubber in contact with the road surface is 45 to 55 (0 ° C.), and the tire equator line is sandwiched. In a pneumatic tire in which two circumferential main grooves are provided and a plurality of tread block rows are arranged in the tire circumferential direction, the plurality of tread blocks are provided on a shoulder side of the circumferential main groove; When the tire block is divided into a center block through which the tire equator line passes and an intermediate block provided between the center block and the circumferential main groove, the intermediate block extends in the tire circumferential direction, which is divided in the tire width direction. The inclination angle of the first groove with respect to the tire circumferential direction is 5 to 30 degrees, and the center block and the intermediate block are The second groove extending in the circumferential direction of the cut has an inclination angle of 30 to 60 degrees with respect to the tire circumferential direction, extends from the circumferential main groove in the tire width direction, and communicates with the second groove. of a tilt angle of 0 to 30 degrees with respect to the tire width direction, the first groove, the second groove, and the third groove are those composed of linear grooves, the first The groove 3 extends from the circumferential main groove on one side across the tire equator line, crosses the second groove, and passes through the tire equator line without passing through the tire equator line. The present invention provides a pneumatic tire characterized by including a groove that gradually decreases and closes .

At that time, it is preferable that the first groove and the second groove communicate with each other.
Further, the third groove includes a groove extending from the circumferential main groove on one side across the tire equator line and communicating with the second groove on the other side through the tire equator line. It is preferable.

In addition, when each position in the tire width direction between the circumferential main grooves is made one round in the tire circumferential direction, the ratio of the length of the groove portion to the entire circumference in the tire circumferential direction is defined as a groove ratio. Is in the range of 10 to 70% at each position in the tire width direction between the circumferential main grooves, and the difference between the maximum value and the minimum value of the groove ratio is preferably 50% or less.
In that case, it is preferable that the groove ratio at a position passing through the equator line is 10% or less. Furthermore, in the region on the shoulder side from the circumferential main groove in the tire width direction, the groove ratio is preferably 10% or less.

In the pneumatic tire of the present invention, the first groove extending in the tire circumferential direction dividing the intermediate block in the tire width direction has an inclination angle with respect to the tire circumferential direction of 5 to 30 degrees, and the circumferential direction separating the center block and the intermediate block The inclination angle of the second groove extending in the tire circumferential direction is 30 to 60 degrees, the third groove extending from the circumferential main groove in the tire width direction and communicating with the second groove is in the tire width direction. The inclination angle is 0 to 30 degrees, and the first groove, the second groove, and the third groove are constituted by linear grooves. Thereby, the performance on ice and the performance on snow can be compatible in a high dimension.
In the pneumatic tire, the groove ratio is in a range of 10 to 70% at each position in the tire width direction between the circumferential main grooves, and the difference between the maximum value and the minimum value of the groove ratio is 50% or less. By providing the pattern, the braking performance on ice and the driving performance on ice can be improved. In particular, the on-ice driving performance can be improved by setting the groove ratio at a position passing through the equator line to 10% or less. The braking performance on ice can be improved by providing a portion having a groove ratio of 10% or less in the region on the shoulder side from the circumferential main groove in the tire width direction.

  Hereinafter, the pneumatic tire of the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 is an external perspective view of a studless tire (hereinafter referred to as a tire) 10 which is an embodiment of the pneumatic tire of the present invention.
The tire 10 is provided with a tread pattern in which a plurality of tread block rows are arranged in the tire circumferential direction in the tread portion. The snow traction index (STI) in the tread pattern of the tire 10 is 180 or more, and the JIS hardness of the tread rubber in contact with the road surface is 45 to 55 (0 ° C.). The snow traction index (STI) is an index indicating the on-snow performance level calculated by the tire width direction component and the groove depth of the groove and sipe length of the tread surface described in SAE Paper 8203345. Specifically, STI = −6.8 + 2202ρg + 672ρs + 7.6Dg, and ρg is (total groove length projected in the tire width direction) / (contacting width × tire circumference) (1 / mm), ρs represents (total sipe length projected in the tire width direction) / (contact width × tire circumference) (1 / mm), and Dg represents an average groove depth (mm).

In the present invention, the groove means a groove having a width of 1.6 mm or more and a depth of 4 mm or more. A sipe is one having a width of less than 1.6 mm and a depth of 4 mm or more.
The ground contact width of the ground contact surface in the tire width direction when mounted on a standard rim determined by JATMA and applied with a load equivalent to an internal pressure of 200 kPa and 85% of the maximum load capacity determined by JATMA and grounded on a horizontal surface. The maximum width. In the following, the ground contact width is defined as described above.
The tire circumferential direction refers to the rotation direction when the tread portion rotates about the tire rotation axis, and the tire width direction refers to a direction parallel to the tire rotation axis.
Each dimension of the tread pattern given in the following description is an example of a dimension that can be effectively used for a tire having a tread width of 175 to 315 mm, centering on a tire of 225 / 65R17.

Fig.2 (a) is detail drawing of the tread pattern shown by FIG. 1, FIG.2 (b) is arrow sectional drawing along the XX line of (a).
The tread pattern 12 shown in FIG. 2A includes circumferential main grooves 14a and 14b, first inclined grooves 16a and 16b, second inclined grooves 18a and 18b, and third inclined grooves 20a to 20d. And having. The tread pattern 12 has a plurality of blocks separated by these grooves. The circumferential main grooves 14a and 14b, the first inclined grooves 16a and 16b, the second inclined grooves 18a and 18b, and the third inclined grooves 20a to 20d are all combined with linear grooves. It is the groove comprised.

  The circumferential main grooves 14a and 14b are provided at symmetrical positions with respect to the center line CL (equatorial line) and extend substantially in the tire circumferential direction. More specifically, the term “extending substantially in the tire circumferential direction” means that, in the circumferential grooves 14a and 14b, at the starting positions where the third inclined grooves 20a to 20d extend, both sides of the circumferential grooves 14a and 14b. The side walls of the tire are shifted by a predetermined amount in the tire width direction. However, this shift amount is a shift amount within a range where the see-through portions exist in the circumferential grooves 14a and 14b. The see-through portion refers to a tire main meridian cross section (cross section cut along line XX shown in FIG. 2A) in the tire circumferential direction, and the circumferential main groove can be seen over the entire circumference of the tire. Say part. That is, when each position of the circumferential main groove in the tire width direction is examined over the entire circumference of the tire, it refers to a portion located in the circumferential main groove over the entire circumference of the tire. The reason why the see-through portions are required in the circumferential main grooves 14a and 14b is to secure snow removal performance on the road surface on snow. For example, the circumferential main grooves 14a and 14b preferably have a groove width of 5.0 to 11.0 mm and a groove depth of 8.0 to 12.5 mm. The center positions of the circumferential grooves 14a and 14b are preferably set within a range of 30 to 45% of the ground contact width from the center line CL. That is, the length between the center position of the circumferential groove 14a and the center position of the circumferential groove 14b is preferably 60 to 90% of the ground contact width.

The first inclined grooves 16a and 16b are grooves extending in the tire circumferential direction that divide the intermediate block in the tire width direction. The intermediate block refers to a block provided between the center block through which the center line CL passes and the circumferential main grooves 14a and 14b. For example, in the blocks A to E in FIG. 2A, the block C passing through the center line CL is a center block, and the blocks A and A sandwiched between the center block and the circumferential main grooves 14a and 14b. B, D, and E are intermediate blocks.
The first inclined grooves 16a and 16b are provided at an inclination angle of 5 to 30 degrees with respect to the tire circumferential direction. The first inclined grooves 16a and 16b are adjacent to each other in the tire circumferential direction starting from the position of the intermediate portion of the third inclined grooves 20a and 20b. The inclined grooves 20a and 20b are the end points. For this reason, the first inclined grooves 16a and 16b cross the third inclined grooves 20c and 20d provided between the third inclined grooves 20a and 20b adjacent in the tire circumferential direction. For example, the first inclined grooves 16a and 16b preferably have a groove width of 2.0 to 6.0 mm and a groove depth of 4 to 12.5 mm. Note that the inclination angles of the first inclined grooves 16a and 16b are set so that the first inclined grooves 16a and 16b are arranged symmetrically about the center line CL. The groove center positions of the first inclined grooves 16a and 16b are preferably set in a range away from the center line CL by 17.5 to 27.5% of the ground contact width.

  The second inclined grooves 18a and 18b are grooves that divide the center block and the intermediate block through which the center line CL passes. In the example of FIG. 2 (a), the groove extends in the tire circumferential direction separating the block A and the intermediate block C. The groove is provided with an inclination angle of 30 to 60 degrees with respect to the tire circumferential direction. For example, the groove width is preferably 4 to 9 mm and the groove depth is 8 to 12.5 mm. The second inclined grooves 18a and 18b are connected over the entire circumference while changing the inclination direction to the upper right or upper left in FIG. 2A while maintaining a substantially parallel relationship with each other. 18a and 18b are provided so as to meander around the center line CL. The center positions of the second inclined grooves 18a and 18b are preferably set within a range of 5 to 20% of the ground contact width from the center line CL.

The third inclined grooves 20a, 20b extend from the circumferential main grooves 14a, 14b in the tire width direction, cross the second inclined grooves 18a, 18b, and then communicate with the second inclined grooves 18b, 18a. is there. In the example shown in FIG. 2A, the third inclined grooves 20a, 20b extend in the tire width direction from the circumferential main grooves 14a, 14b, pass through the center line CL, and the second inclined grooves 18b on the opposite side, It communicates with 18a. The communication position is a bent portion where the inclination angle of the second inclined grooves 18b, 18a changes. In the present invention, it is not always necessary to communicate with the second inclined grooves 18b and 18a.
The third inclined grooves 20a and 20b communicate with the second inclined grooves 18b and 18a while gradually decreasing the groove width after crossing the second inclined grooves 18a and 18b.
This groove is provided with an inclination angle of 0 to 30 degrees with respect to the tire width direction. For example, the groove width is 4 to 9 mm and the groove depth is 8 to 12.5 mm except for a bent portion where the groove width gradually decreases. It is preferable.

  The third inclined grooves 20c and 20d are grooves extending from the circumferential main grooves 14a and 14b in the tire width direction and crossing the second inclined grooves 18a and 18b. Regarding the arrangement in the tire circumferential direction, the third inclined grooves It is provided between the grooves 20a and 20b. The third inclined grooves 20c and 20d are blocked by gradually decreasing the groove width in the center block region without crossing the center line CL. The third inclined grooves 20c and 20d change their orientations by bending after crossing the first inclined grooves 16a and 16b and before crossing the second inclined grooves 18a and 18b. It is comprised so that 18a and 18b may be crossed. Similar to the third inclined grooves 20a and 20b, this groove is provided with an inclination angle with respect to the tire width direction of 0 to 30 degrees. For example, the groove width is 4 to 9 mm at a portion other than the bent portion where the groove width gradually decreases. The groove depth is preferably 8 to 12.5 mm.

The third inclined groove 20a and the third inclined groove 20d extend in the tire width direction from substantially the same position in the tire circumferential direction from the circumferential main grooves 14a and 14b, and the third inclined groove 20b. The third inclined groove 20c extends in the tire width direction from the circumferential main grooves 14a and 14b with the substantially same position in the tire circumferential direction as a base point.
The third inclined grooves 20a to 20d extend to the shoulder side across the circumferential main grooves 14a and 14b to form a shoulder block, and the groove depth gradually decreases in the shoulder side region.

  The first inclined grooves 16a and 16b start from the position of the intermediate portion of the third inclined grooves 20a and 20b, and the second inclined grooves 18a and 18b communicate with each other at the position of the starting point. . Accordingly, the first inclined grooves 16a and 16b communicate with the second inclined grooves 18a and 18b.

The center block through which the center line CL passes, the shoulder block located on the shoulder side from the circumferential grooves 14a and 14b, and the intermediate block surrounded by the center block and the circumferential main grooves 14a and 14b are all wavy. Sipes are provided to help improve the performance on ice. The sipe has a width of 0.2 mm or more and less than 1.6 mm and a depth of 4 to 10 mm.
In addition, the tread surface of the tire 10 is provided with a group of minute grooves that are narrower than the wavy sipe provided in each block and have an extremely shallow depth inclined by 42 to 60 degrees with respect to the tire circumferential direction. However, it is preferable in terms of improving performance on ice and performance on snow in the initial state of the tire.

As described above, the length between the center position of the circumferential groove 14a and the center position of the circumferential groove 14b is 60 to 90% of the ground contact width, and the tire circumference with respect to the inclined grooves defining the center block and the intermediate block. By defining the inclination angle with respect to the direction or the tire width direction within the predetermined range described above and configuring each inclined groove with a linear groove, excellent steering stability performance on the road surface on snow can be exhibited together with the performance on ice.
In particular, since the first inclined grooves 16a and 16b and the second inclined grooves 18a and 18b communicate with each other, the snow drainage performance and drainage performance on the snow are also improved.
Further, the center block is formed by the second inclined grooves 18a and 18b and the third inclined grooves 20a and 20b, so that the snow drainage performance and the drainage performance are improved.

Further, in the tire 10, each position in the tire width direction between the circumferential main grooves 14a and 14b makes one round in the tire circumferential direction, and the ratio of the length of the groove portion to the circumferential length in the tire circumferential direction is defined as a groove ratio. The groove ratio is in the range of 10 to 70% at each position in the tire width direction between the circumferential main grooves, and the difference between the maximum value and the minimum value of the groove ratio is 50% or less. preferable. Note that the above-described wavy sipe is not included in the groove.
Since the tire having the groove ratio in the above range can reduce the occurrence of a water film due to the friction of the tread portion with respect to the road surface on ice, the performance on ice is improved. As a result, the steering stability performance on snow, the driving performance on snow, and the performance on ice are balanced.

FIG. 3 is a diagram showing a tire width direction distribution of the groove ratio of the tire 10 when the horizontal axis indicates the position in the tire width direction and the vertical axis indicates the groove ratio (%).
In the drawing, 14a and 14b indicate positions of the circumferential main grooves 14a and 14b. The groove ratio distribution of the tire 10 is distributed between 14a and 14b in a range of a minimum value of approximately 18% and a maximum value of approximately 50%, and the difference between the maximum value and the minimum value is approximately 32%. ing.

  In the present invention, in order to improve the on-ice driving performance, the groove ratio at the center position passing through the center line CL (equator line) in the tire width direction is preferably 10% or less. More preferably, it is 5% or less. Furthermore, in order to improve the braking performance on ice, it is preferable to have a portion having a groove ratio of 10% or less in the region on the shoulder side from the circumferential main groove in the tire width direction. More preferably, it is 5% or less.

[Example 1]
It was confirmed by making the following tires and carrying out vehicle evaluation that such a tire 10 has a high level of compatibility between performance on ice and performance on snow.
The tire size is 225 / 65R17 101Q. The produced tires are the four patterns shown in FIGS. 4A to 4C and 5 and the pattern of the tire 10 shown in FIG.
The pattern shown in FIG. 4A includes an inclination angle of the first groove corresponding to the first inclined grooves 16a and 16b, an inclination angle of the second groove corresponding to the second inclined grooves 18a and 18b, and the inclination angle of the third groove corresponding to the third inclined groove 20a~d is a pattern respectively, it is included in the scope of the present invention.
The pattern shown in FIG. 4B is the same as the pattern shown in FIG. 4A, but the first groove corresponding to the first inclined grooves 16a and 16b and the second corresponding to the second inclined grooves 18a and 18b. This is a pattern in which the first groove is improved so as to communicate with the groove.
In the pattern shown in FIG. 4C, the third groove corresponding to the third inclined grooves 20a and 20b is located on the opposite side across the center line CL (equator line) in the pattern shown in FIG. 4B. This is a pattern in which the third groove is improved so as to communicate with the second groove corresponding to the second inclined grooves 18b, 18a, and corresponds to the invention.
The pattern shown in FIG. 5 shows a tire pattern of a conventional example, and is the tire pattern described in Patent Document 2 described above. This pattern is constituted by four circumferential main grooves and curved lug grooves, and corresponds to the first grooves and the second inclined grooves 18a and 18b corresponding to the first inclined grooves 16a and 16b. The second groove and the third groove corresponding to the third inclined grooves 20a to 20d do not exist and do not correspond to the product of the present invention.

Each dimension of the pattern shown to Fig.2 (a) is as follows.
-Circumferential main grooves 14a, 14b:
Groove depth: 10.5mm
Groove width: 10.0mm
Amount of displacement of the side wall in the tire width direction: 2.0 mm
Groove center position: 35% of ground contact width from center line CL
・ First inclined grooves 16a and 16b
Groove depth: 8.9mm
Groove width: 4.0mm
Inclination angle with respect to tire circumferential direction: 10 degrees Groove length: 60 to 76 mm
Groove center position: 20 to 21.5% of ground contact width from center line CL
・ Second inclined grooves 18a and 18b
Groove depth: 10.5mm
Groove width: 6mm
Inclination angle with respect to tire circumferential direction Inclination angle: 30 degrees Groove center position: 10-15% of ground contact width from center line CL
・ Third inclined grooves 20a and 20b
Groove depth: 10.5mm
Groove width: 8mm
Inclination angle with respect to tire width direction: 20 degrees Groove length: 63 mm
・ Third inclined grooves 20c, 20d
Groove depth: 10.5mm
Groove width: 7mm
Inclination angle with respect to tire width direction: 20 degrees Groove length: 50 mm
・ Sipe
Width: 0.4mm
-Snow traction index (STI): 200
・ JISA hardness of tread rubber (0 ° C.): 50

Below each of the patterns in FIGS. 4A to 4C and FIG. 5, a graph showing the distribution of the groove ratio in accordance with the position in the tire width direction of the pattern is shown. In the patterns shown in FIGS. 4A to 4C and FIG. 5, the groove area ratios of the patterns within the tire contact width range are the same.
In the distribution of the groove ratio shown in FIG. 4A, the maximum value is approximately 75% and the minimum value is approximately 8% in the region R located between the two circumferential main grooves.
In the distribution of the groove ratio shown in FIG. 4B, the maximum value is approximately 70% and the minimum value is approximately 8% in the region R located between the two circumferential main grooves.
In the distribution of the groove ratio shown in FIG. 4C, the maximum value is approximately 75% and the minimum value is approximately 15% in the region R located between the two circumferential main grooves.
In the distribution of the groove ratio shown in FIG. 5, the maximum value is approximately 100% and the minimum value is approximately 18% in the region R located between the two circumferential main grooves.
From the above, the patterns shown in FIGS. 4A to 4C and FIG. 5 are all in the range of the groove ratio described above, and the difference between the maximum value and the minimum value of the groove ratio is as follows. The pattern does not satisfy the preferable condition of 50% or less. On the other hand, the pattern shown in FIG. 2A is a pattern that satisfies this condition.

These five types of tires were mounted on a SUV (Sports Utility Vehicle) type vehicle, and the snow handling stability performance, on ice performance, and snow driving (traction) performance were examined.
Steering performance on snow was evaluated by running the vehicle on the snow surface of the test course. Evaluation was performed by sensory evaluation with a driver, and indexed with the pattern of FIG. The index indicates that the higher the value, the better the performance.
The performance on ice was evaluated based on the braking distance until the vehicle stopped on the road running on the ice surface in the test course at a speed of 40 km / h, and braking was started in this state. At this time, the pattern of FIG. 5 was indexed. The index indicates that the higher the value, the better the performance.
As snow driving performance, in a snowy road test course including a sherbet-like snowy road, the vehicle engine was fully opened and the time from starting to reaching 35 km / h was measured. The result is shown as an index value based on the pattern of FIG. The index indicates that the higher the value, the shorter the measurement time and the better the on-snow driving performance. An index of 105 or more has a remarkable effect.
The evaluation results are shown in Table 1 below.

As is evident from Table 1, the pattern shown, that the prior art is in exponential with respect to the pattern shown in FIG. 5 5% or more performance improves FIG. 2 (a) and FIG. 4 (a) ~ (c) I understand. In particular, the pattern shown in FIG. 2A satisfying the preferable condition that the groove ratio is in the range of 10 to 70% and the difference between the maximum value and the minimum value of the groove ratio is 50% or less is shown in FIG. It can be seen that the performance on ice is improved by 10% compared to the conventional pattern shown.

[Example 2]
Next, the patterns shown in FIGS. 6A to 6D and the pattern shown in FIG. 5 were prepared, and the performance on ice, particularly the driving performance on ice and the braking performance were examined. In the patterns shown in FIGS. 6A to 6D and FIG. 5, the groove area ratios of the patterns within the tire contact width range are the same.
FIGS. 6A to 6D show diagrams of patterns and distribution of groove ratios similarly to FIGS. 4A to 4C and FIG.

6A to 6D, as described above, satisfy the preferable condition that the groove ratio is in the range of 10 to 70% and the difference between the maximum value and the minimum value of the groove ratio is 50% or less. Pattern.
In the pattern shown in FIG. 6A, the groove width of the third groove is wider in the region S than the pattern shown in FIG. The maximum groove width in the region S is expanded from 7 mm to 9 mm.
The pattern shown in FIG. 6B has a portion where the groove ratio is 10% or less at the center position through which the center line CL passes, and is extremely lower than the surrounding groove ratio.
The pattern shown in FIG. 6C has a groove ratio of 10% or less on the shoulder side of the circumferential main groove, and is provided with a portion that is extremely lower than the surrounding groove ratio.
In the pattern shown in FIG. 6D, the groove ratio is 10% or less at the center position where the center line CL passes, and is extremely lower than the surrounding groove ratio. Furthermore, on the shoulder side of the circumferential main groove, the groove ratio is 10% or less, and a portion that is extremely lower than the surrounding groove ratio is provided.

In the same manner as in Example 1, these five types of tires were mounted on an SUV type vehicle, and on-ice performance, on-ice driving performance and on-ice braking performance were examined.
The driving performance on ice is evaluated by the driver's sensory evaluation of the climbing ability when starting from a stop on each of the climbing slopes of 4, 6 and 8% on the test course. As an index. The index indicates that the higher the value, the better the performance.
The braking performance on ice was evaluated based on the braking distance until the braking on the ice surface in the test course started at an initial speed of 40 km / h and stopped, and was indexed based on the pattern of FIG. The higher the index, the better the performance.
The evaluation results are shown in Table 2 below.

As is apparent from Table 2, it can be seen that the performance of the patterns shown in FIGS. 6A to 6D is improved by an index of 5 to 10% or more with respect to the pattern shown in FIG. In particular, the pattern shown in FIG. 6B in which the groove ratio is 10% or less at the center position has an on-ice driving performance improved by 10%, and the shoulder region has a groove ratio of 10% or less in FIG. 6C. The pattern shown in FIG. 6 (d) has a 10% improvement in braking performance on ice, a groove ratio of 10% or less at the center position, and a groove area having a groove ratio of 10% or less in the shoulder region. It can be seen that both the driving performance on ice and the braking performance on ice are improved by 10%.
Accordingly, in order to improve the on-ice driving performance, the groove ratio at the center position passing through the center line CL (equator line) in the tire width direction is preferably 10% or less. To improve on-ice braking performance, the tire It can be seen that it is preferable to have a portion having a groove ratio of 10% or less in the region on the shoulder side from the circumferential main groove in the width direction.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, this invention is not limited to the said embodiment, Of course, in the range which does not deviate from the main point of this invention, you may make a various improvement and change. is there.

1 is an external perspective view of a studless tire that is an embodiment of a pneumatic tire of the present invention. (A) is detail drawing of the tread pattern shown by FIG. 1, (b) is arrow sectional drawing along the XX line of (a). It is a figure which shows distribution in the tire width direction of the groove ratio of the tire shown in FIG. (A)-(c) is a figure which shows the pattern used in Example 1, and distribution of a groove ratio. It is a figure which shows distribution of the pattern and groove ratio of a prior art example. (A)-(d) is a figure which shows the pattern used in Example 2, and distribution of a groove ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pneumatic tire 12 Tread pattern 14a, 14b Circumferential main groove 16a, 16b 1st inclination groove 18a, 18b 2nd inclination groove 20a, 20b, 20c, 20d 3rd inclination groove

Claims (6)

The snow traction index (STI) is 180 or more, the JIS hardness of the tread rubber contacting the road surface is 45 to 55 (0 ° C.), and two circumferential main grooves are provided across the tire equator line. In the pneumatic tire in which the tread block row of is arranged in the tire circumferential direction,
A shoulder block provided on the shoulder side of the circumferential main groove, the center block through which the tire equator line passes, and an intermediate block provided between the center block and the circumferential main groove. When divided into
The inclination angle of the first groove extending in the tire circumferential direction dividing the intermediate block in the tire width direction with respect to the tire circumferential direction is 5 to 30 degrees,
The inclination angle of the second groove extending in the circumferential direction separating the center block and the intermediate block with respect to the tire circumferential direction is 30 to 60 degrees,
The inclination angle of the third groove extending from the circumferential main groove in the tire width direction and communicating with the second groove with respect to the tire width direction is 0 to 30 degrees,
The first groove, the second groove, and the third groove are constituted by linear grooves ,
The third groove extends from the circumferential main groove on one side across the tire equator line, crosses the second groove, and passes through the tire equator line without passing through the tire equator line. A pneumatic tire comprising a groove that gradually closes and closes .   The pneumatic tire according to claim 1, wherein the first groove and the second groove communicate with each other.   The third groove includes a groove that extends from the circumferential main groove on one side across the tire equator line, and that communicates with the second groove on the other side through the tire equator line. The pneumatic tire according to 1 or 2. When each position in the tire width direction between the circumferential main grooves is rounded in the tire circumferential direction, when the ratio of the length of the groove portion to the entire circumference in the tire circumferential direction is defined as a groove ratio, the groove ratio is: in the range from 10 to 70% at each position in the tire width direction between the circumferential main grooves, and any one of claims 1 to 3 the difference between the maximum value and the minimum value of the groove ratio is 50% or less The pneumatic tire according to item 1. The pneumatic tire according to claim 4 , wherein the groove ratio at a position passing through the equator line is 10% or less. In the region of the shoulder side from the circumferential main groove in the tire width direction, the pneumatic tire according to claim 4 or 5 having a portion the groove ratio is 10% or less.

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