JP2005231430A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire for achieving both of a wet performance and a noise performance while securing good steering stability. <P>SOLUTION: This pneumatic tire having directional patterns comprises a rib-like land part 11 extending in a tire peripheral direction at a center part of a tread 1, a pair of right and left main grooves 21 extending in the tire peripheral direction adjacent to both sides of the land part 11, a pair of right and left land parts 12 extending in the tire peripheral direction adjacent to outside of the main grooves 21, a pair of right and left main grooves 22 extending in the tire peripheral direction adjacent to the outside of the land parts 12, and a pair of right and left land parts 13 extending in the tire peripheral direction adjacent to the outside of the main grooves 22. Lug grooves 31 closed to the main grooves 21 and opened to the main grooves 22, and slit-like traverse grooves 32 communicated with both of the main grooves 21 and the main grooves 22 are alternately arranged on the land parts 12. An average inclination angle α of the lug grooves 31 arranged on the land parts 12 against a tire equator E is 10-30°, and a main groove area rate Am in a grounding face and a total groove area rate At in the grounding face are constituted to satisfy the relationship of 0.5≤Am/At≤0.75. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire having a directional pattern in which a rotation direction when mounted on a vehicle is specified. More specifically, the present invention enables compatibility between wet performance and noise performance while ensuring good steering stability. Related to pneumatic tires.

  In order to improve the wet performance of pneumatic tires and reduce noise, the tread is provided with a plurality of main grooves extending in the tire circumferential direction and a plurality of lug grooves inclined with respect to the tire equator line. It is general (see, for example, Patent Document 1 and Patent Document 2). Here, it is effective to increase the groove area ratio in order to improve wet performance, and to reduce the groove area ratio in order to reduce noise. The conditions for improving these wet performance and noise performance are contradictory. ing. For this reason, it has been attempted to devise the inclination angle and width of the lug groove.

However, even if the inclination angle and width of the lug groove are devised, as long as the lug groove is provided, there is a limit to the compatibility between wet performance and noise performance, and it is difficult to meet further improvement requirements. Further, there is a problem that the steering stability is deteriorated when the groove area ratio is increased.
JP 7-290909 A JP 7-285303 A

  An object of the present invention is to provide a pneumatic tire that can achieve both wet performance and noise performance while ensuring good steering stability.

  In order to achieve the above object, a pneumatic tire according to the present invention includes a rib-shaped first land portion extending in the tire circumferential direction at the center portion of the tread, and extending in the tire circumferential direction adjacent to both sides of the first land portion. A pair of left and right first main grooves, a pair of left and right second land portions extending in the tire circumferential direction adjacent to the outside of the first main grooves, and extending in the tire circumferential direction adjacent to the outside of the second land portion In the pneumatic tire having a directional pattern including a pair of left and right second main grooves and a pair of left and right third land portions extending in the tire circumferential direction adjacent to the outside of the second main grooves, the second land Lug grooves that close to the first main groove and open to the second main groove and slit-shaped transverse grooves that communicate with both the first main groove and the second main groove are alternately arranged in the portion. And an average inclination angle of the lug groove disposed in the second land portion with respect to the tire equator line is 10 to 30 °. It is characterized in that the main grooves area ratio Am in the ground plane and the total groove area ratio At the ground plane satisfies the relationship 0.65 ≦ Am / At ≦ 0.75.

  In the present invention, a directional pattern is composed of a main groove extending in the tire circumferential direction, a lug groove that is inclined with respect to the tire equator line, and a slit-like transverse groove, and by devising its specific structure, it is high. Provided is a pneumatic tire capable of improving wet performance and noise performance while ensuring steering stability. In particular, on the basis of the relationship of 0.65 ≦ Am / At ≦ 0.75, the wet groove performance and noise performance are improved by increasing the main groove area ratio in the contact surface compared to the conventional case and suppressing the lug groove area ratio. Can be improved at the same time.

  The lug groove in the second land portion has an average inclination angle with respect to the tire equator line of 10 to 30 °, and is stopped halfway so as not to open in one main groove. This makes it difficult for the edge of the lug groove to coincide with the ground contact edge, and it is generated when the block vibration noise, impact sound generated when the block contacts the road surface, or when the air inside the groove is released at once. Reduces air pumping noise. The lug groove in the second land portion is opened at the end on the second main groove side that contacts the ground after the end on the first main groove side when rolling the tire, thereby enclosing air in the lug groove Do not. In addition, the inclination angle of the lug groove disposed in the second land portion with respect to the tire equator line may be reduced as the first main groove is approached.

  If the average inclination angle of the lug groove of the second land portion with respect to the tire equator line is reduced, it is necessary to reduce the number of pitches of the lug groove in order to ensure the rigidity of the second land portion partitioned thereby. In this case, the rigidity in the tire circumferential direction of the second land portion becomes too high, and there is a risk of impairing the ground contact property (trackability to the road surface). Therefore, a slit-shaped transverse groove is disposed between the lug grooves. Thereby, since the bending rigidity of the tire circumferential direction of the 2nd land part falls moderately, grounding property improves and steering stability improves. Moreover, since the edge amount increases, the braking performance on the wet road surface is improved. In addition, it is preferable that the pitch number of the repeating element of a tread containing a lug groove or a slit-shaped crossing groove is 24-33.

  The slit-shaped transverse groove has an average inclination angle with respect to the tire equator line of 14 to 42 °, and it is preferable that the inclination angle becomes larger as it approaches the first main groove. This is to ensure the rigidity of the land portion at the end of the slit-shaped transverse groove communicating with the first main groove and to improve the uneven wear resistance.

  Further, it is preferable to provide a raised portion having a depth of 20 to 50% of the depth of the second main groove at a portion of the lug groove disposed in the third land portion near the tire equator line. Ribbing the third land without connecting the lug groove, which has the greatest impact on noise, to the main groove is effective in reducing noise and improving uneven wear resistance, but it is completely ribbed. Is not preferable because it reduces the edge amount and reduces the braking performance on wet road surfaces. In contrast, if the depth of the bottom raised portion is 20 to 50% of the depth of the second main groove, all of noise performance, uneven wear resistance, and wet braking performance can be achieved at a high level.

  In the present invention, the main groove has a width of 6.0 to 20 mm and a depth of 6.0 to 8.5 mm. Even grooves extending in the tire circumferential direction are narrower than the above dimensions are excluded from the calculation of the main groove area ratio Am because the drainage effect is insufficient. The slit-shaped transverse grooves have a width of 0.5 to 2.0 mm and a depth of 2.0 to 5.0 mm. If the cross-sectional dimension of the slit-shaped transverse groove is too large, the rigidity of the second land portion is lowered and the steering stability is lowered. On the other hand, the lug groove may have a width of 0.5 to 8.0 mm and a depth of 0.5 to 8.5 mm. The lug groove basically has a larger cross-sectional dimension than the slit-shaped transverse groove, but the end may be shallower or narrower. Therefore, the cross-sectional dimension of the lug groove can be selected in a wide range as described above.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a tread pattern of a pneumatic tire according to an embodiment of the present invention, and FIG. 2 shows its ground contact shape. This pneumatic tire has a designated rotational direction R when mounted on the vehicle. As shown in FIG. 1, the tread 1 has a rib-like land portion 11 (first land portion) extending in the tire circumferential direction at the center thereof, and extends in the tire circumferential direction adjacent to both sides of the land portion 11. A pair of left and right main grooves 21, 21 (first main groove), a pair of left and right land parts 12, 12 (second land part) extending in the tire circumferential direction adjacent to the outside of the main grooves 21, 21; A pair of left and right main grooves 22, 22 (second main grooves) extending in the tire circumferential direction adjacent to the outside of the land portions 12, 12, and extending in the tire circumferential direction adjacent to the outside of the main grooves 22, 22. A pair of left and right land portions 13 and 13 (third land portion) are arranged.

  The land portion 12 located outside the rib-shaped land portion 11 includes a plurality of lug grooves 31 that are not in communication with the main groove 21 and communicate with the main groove 22, and the main groove 21 and the main groove 22. A plurality of slit-shaped transverse grooves 32 communicating with both are alternately arranged. A plurality of lug grooves 33 extending in the tire width direction are disposed on the land portion 13 located outside the land portion 12. The lug grooves 31 and 33 and the slit-shaped transverse groove 32 are inclined in the direction opposite to the rotation direction R from the tread center side toward the shoulder side. Directional patterns are formed based on the inclination of the grooves 31 to 33.

  The lug groove 31 disposed in the land portion 12 becomes smaller as the inclination angle with respect to the tire equator line E approaches the main groove 21, and the average inclination angle α with respect to the tire equator line E is in the range of 10 to 30 °. Is set. The average inclination angle α is an inclination angle between a straight line passing through the groove width center position at both ends of the lug groove 31 and the tire equator line E. If the average inclination angle α is less than 10 °, the rigidity of the land portion 12 at the end of the lug groove 31 is lowered, so that uneven wear resistance and steering stability are lowered. Conversely, if it exceeds 30 °, noise is reduced. The effect is insufficient.

  In addition, the slit-shaped transverse groove 32 disposed in the land portion 12 increases as the inclination angle with respect to the tire equator line E approaches the main groove 21, and the average inclination angle β with respect to the tire equator line E is 14 to 42. It is set in the range of °. The average inclination angle β is an inclination angle between a straight line passing through the groove width center position at both ends of the slit-like transverse groove 32 and the tire equator line E. If the average inclination angle β is less than 14 °, the rigidity of the land portion 12 at the end of the slit-like transverse groove 32 is lowered, so that uneven wear resistance and steering stability are lowered, and conversely if it exceeds 42 °. Noise reduction effect is insufficient.

  The slit-shaped transverse groove 32 has a width of 0.5 to 2.0 mm and a depth of 2.0 to 5.0 mm. That is, the slit-shaped transverse groove 32 does not carry drainage, but adjusts the rigidity of the land portion 12 based on the above dimensions. If the cross-sectional dimension of the slit-shaped transverse groove 32 is too large, the rigidity of the land portion 12 is lowered and the steering stability is lowered.

  In the pneumatic tire, the main groove area ratio Am in the ground contact surface X and the total groove area ratio At in the ground contact surface X satisfy the relationship of 0.65 ≦ Am / At ≦ 0.75 (FIG. 2). reference). The main groove area ratio Am is the ratio of the total main groove area to the area of the ground plane X. The total groove area ratio At is the ratio of the total groove area to the area of the ground plane X. Therefore, the larger Am / At means that the ratio of the main groove extending in the tire circumferential direction is relatively high and the ratio of the lug groove is relatively low. If Am / At is out of the above range, it becomes difficult to achieve both wet performance and noise performance. In addition, the area of the contact surface is the tire mounted on the measurement rim specified in JATMA Yearbook (2003 edition), filled with air pressure corresponding to the maximum load capacity, and the load of 88% of the maximum load capacity is This is the area of the ground plane (including the groove portion) formed when hung.

  In the pneumatic tire configured as described above, directionality from the main grooves 21 and 22 extending in the tire circumferential direction, the lug grooves 31 and 33 inclined with respect to the tire equator line E, and the slit-shaped transverse grooves 32. Since the pattern is configured and the structure is specified as described above, the wet performance and the noise performance can be improved while ensuring good steering stability.

  FIG. 3 shows a lug groove arranged in the third land portion. As shown in FIG. 3, a bottom raised portion 33 a having a depth d of 20 to 50% of the depth D of the main groove 22 is formed at a portion near the tire equator line of the lug groove 33 arranged in the land portion 13. Has been. The raised portion 33a contributes to improvement in noise performance and uneven wear resistance. However, when the depth d of the bottom raised portion 33a is less than 20% of the depth D of the main groove 22, the wet braking performance becomes insufficient. Conversely, when the depth d exceeds 50%, the noise performance and uneven wear resistance are improved. Becomes insufficient.

  In the pneumatic tire, the number of pitches of the repeating elements such as the lug grooves 31 and 33 of the tread 1 and the slit-shaped transverse grooves 32 per tire circumference is preferably 24 to 33. By setting the number of pitches of the repeating elements within the above range, it is possible to improve the steering stability, the wet performance, and the noise performance in a balanced manner. If the number of pitches of the repeating elements is too small, sufficient wet performance cannot be exhibited. Conversely, if the number is too large, the rigidity is lowered and steering stability becomes insufficient.

  In a pneumatic tire having a tire size of 235 / 45R17, a tread pattern as shown in FIG. 1 is formed, and an average inclination angle α of lug grooves arranged in the second land portion, an average inclination angle β of slit-like transverse grooves, and a contact surface Table 1 shows the total groove area ratio At, the ratio Am / At of the main groove area ratio Am within the ground contact surface to the total groove area ratio At within the ground contact surface, and the number of tread repeating elements as shown in Table 1. The tires of Examples 1 to 5 and Comparative Examples 1 to 4 were manufactured. For comparison, a conventional tire having a tread pattern shown in FIG. 4 was manufactured. In FIG. 4, 41 is a shallow groove, and 42 and 43 are lug grooves.

  About these test tires, using a turbo-equipped vehicle with a displacement of 2000 cc, under the conditions of a front wheel pressure of 220 kPa and a rear wheel pressure of 190 kPa, the following test methods were used to evaluate the handling stability, drainage performance, wet braking performance, and noise performance. The results are shown in Table 1.

Steering stability:
An actual car sensory test was conducted at the circuit. The evaluation results are shown as an index with the conventional example being 100. The larger the index value, the better the steering stability.

Drainage performance:
In a straight hydroplaning test on a wet road surface with a water depth of about 10 mm, the hydroplaning generation rate was measured. The evaluation results are shown as an index with the conventional example being 100. A larger index value means better drainage performance. In particular, when the index value is 105 or more, a remarkable improvement effect is recognized.

Wet braking performance:
Braking was performed while operating the ABS from a traveling state at a speed of 100 km / h on a wet road surface with a water depth of 3 mm, and the braking distance was measured. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. A larger index value means better wet braking performance. In particular, when the index value is 105 or more, a remarkable improvement effect is recognized.

Noise performance:
The vehicle interior sound (pattern noise) when traveling on a dry road surface at a speed of 60 km / h was measured. The evaluation results are shown as an index with the conventional example being 100, using the reciprocal of the measured value. A larger index value means better noise performance. In particular, when the index value is 105 or more, a remarkable improvement effect is recognized.

  As can be seen from Table 1, the tires of Examples 1 to 5 can greatly improve drainage performance, wet braking performance, and noise performance while maintaining good steering stability in comparison with the conventional example. did it. In contrast, the tires of Comparative Examples 1 to 4 that did not satisfy the conditions defined in the present invention did not satisfy all the required performances.

It is an expanded view which shows the tread pattern of the pneumatic tire which consists of embodiment of this invention. It is a top view which shows the tread grounding surface of the pneumatic tire which consists of embodiment of this invention. It is sectional drawing which shows the lug groove arrange | positioned at the 3rd land part. It is an expanded view which shows an example of the tread pattern of the conventional pneumatic tire.

Explanation of symbols

1 tread 11 land (1st land)
12 Land (second land)
13 Land (third land)
21 Main groove (first main groove)
22 Main groove (second main groove)
31 Lug groove 32 Slit-shaped transverse groove 33 Lug groove 33a Bottom raised part E Tire equator line

Claims (7)

A rib-shaped first land portion extending in the tire circumferential direction at the center of the tread; a pair of left and right first main grooves extending in the tire circumferential direction adjacent to both sides of the first land portion; and A pair of left and right second land portions extending in the tire circumferential direction adjacent to the outside, a pair of left and right second main grooves extending in the tire circumferential direction adjacent to the outside of the second land portion, and the second main grooves In a pneumatic tire having a directional pattern including a pair of left and right third land portions extending in the tire circumferential direction adjacent to the outside, the second land portion is closed with respect to the first main groove, and the first 2. Lug groove tires disposed in the second land portion by alternately arranging lug grooves that open to the two main grooves and slit-shaped transverse grooves that communicate with both the first main groove and the second main groove The average inclination angle with respect to the equator line is 10 to 30 °, the main groove area ratio Am in the ground contact surface and the ground contact surface A pneumatic tire, wherein a and the groove area ratio At satisfies the relationship 0.65 ≦ Am / At ≦ 0.75. 2. The pneumatic tire according to claim 1, wherein an inclination angle of the lug groove disposed in the second land portion with respect to the tire equator line decreases as the first main groove approaches. The pneumatic tire according to claim 1 or 2, wherein an average inclination angle of the slit-shaped transverse groove with respect to a tire equator line is 14 to 42 °. The pneumatic tire according to any one of claims 1 to 3, wherein an inclination angle of the slit-shaped transverse groove with respect to the tire equator line increases as the first main groove is approached. The pneumatic tire according to any one of claims 1 to 4, wherein the slit-shaped transverse groove has a width of 0.5 to 2.0 mm and a depth of 2.0 to 5.0 mm. The bottom raising part which has a depth of 20 to 50% of the depth of the said 2nd main groove was provided in the site | part near the tire equator line of the lug groove arrange | positioned at the said 3rd land part. The pneumatic tire in any one of -5. The pneumatic tire according to any one of claims 1 to 6, wherein a pitch number of the repeating elements of the tread is 24 to 33.

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