Pneumatic tires

Abstract: A pneumatic tire has a tread pattern defined by at least one straight circumferential groove (2,3) and a plurality of lateral grooves (4) extending from tread ends toward the vicinity of a circumferential line perpendicular to a meridional line of the tire and extending slantwise and upward toward the tread end. In this tire, the lateral groove (4) is composed of a main lateral groove portion (5) and an auxiliary lateral grove portion (6). The main lateral groove portion (5) is comprised of a first slant segment (7) at an inclination angle of 5-30° with respect to the circumferential direction of the tire, a second slant segment (8) at an inclination angle of 60-80° with respect to the circumferential direction, and a curved segment (9) smoothly connecting the slant segments (7,8), and the auxiliary lateral groove portion (6) extends substantially parallel with the second slant segment (8) and opens to the tread end at the first slant segent (7).

Description: This invention relates to a pneumatic tire, and more particularly to a high-running performance tire having an effectively improved resistance to hydroplaning on wet road surfaces while maintaining a steering stability on dry road surfaces at a sufficiently high level. In this type of the tire, it is widely known to provide in the tread pattern thereof a combination of a plurality of straight circumferential grooves extending in a circumferential direction of the tread and a plurality of lateral grooves extending slantwise and upward from the vicinity of the center of the tread toward a tread end when viewing the tread pattern from the front of the tire mounted onto a vehicle. In such a conventional tire, when a negative ratio of the grooves is increased or an angle of each lateral groove inclined with respect to the circumferential direction of the tread is made small in order to improve the resistance to hydroplaning on wet road surfaces, there are caused problems that the effective ground contact area of land portions in the tread is decreased and the rigidity of a block against force in the widthwise direction of the tread is reduced to lower the steering stability on dry road surfaces. Attention is also drawn to the disclosure of DE-U-9002986, in particular the embodiment of figures 3 to 6 thereof. It is, therefore, an object of the present invention to overcome the aforementioned problems of the conventional technique and to provide a pneumatic tire capable of sufficiently improving the resistance to hydroplaning during straight running and turning while maintaining the steering stability on dry road surfaces mainly by improving the lateral grooves extending in the widthwise direction of the tread. The present invention in one aspect provides a pneumatic tire having a tread pattern defined by at least one straight circumferential groove extending substantially in the circumferential direction of the tread, and a plurality of lateral grooves each extending slantwise from a respective end of the tread and inwards of the tire, when viewed from the front of a vehicle when the tire is mounted onto the vehicle, characterized in that one of said straight circumferential grooves extends on the mid-circumferential line or is offset from the tread center toward the outside of the vehicle when the fire is mounted on the vehicle, and said lateral groove is composed of a main lateral groove portion continuously extending from the vicinity of the circumferential groove toward the vicinity of the tread end and an auxiliary lateral groove portion, and said main lateral portion is comprised of a first slant segment extending in the vicinity of the circumferential groove at an inclination angle of 5-30° with respect to the circumferential direction of the tire, a second slant segment extending toward the vicinity of the tread end at an inclination angle of 60-80° with respect to the circumferential direction, and a curved segment smoothly connecting the said first and second slant segments with each other, and said auxiliary lateral groove portion is a slant groove portion extending substantially parallel with said second slant segment and opening to each of said tread end and said first slant segment. The invention in another aspect provides a pneumatic tire having a tread pattern defined by at least one straight circumferential groove extending substantially in the circumferential direction of the tread, and a plurality of lateral grooves each extending slantwise from a respective end of the tread and inwards of the tire so as to define a circumferential rib in a central portion of the tread pattern when viewed from the front of a vehicle when the tire is mounted onto the vehicle, characterized in that said lateral groove is composed of a main lateral groove portion continuously extending from the vicinity of the mid-circumferential line of the tire toward the vicinity of the tread end and an auxiliary lateral groove portion, and said main lateral portion is comprised of a first slant segment extending in the vicinity of the mid-circumferential line at an inclination angle of 5-30° with respect to the circumferential direction of the tire, a second slant segment extending toward the vicinity of the tread end at an inclination angle of 60-80° with respect to the circumferential direction, and a curved segment smoothly connecting the said first and second slant segments with each other, and said auxiliary lateral groove portion is a slant groove portion extending substantially parallel with said second slant segment and opening to each of said tread end and said first slant segment, wherein said circumferential rib is continuous to a land portion in a side region of the tread pattern between said main lateral groove portions. The term "circumferential line" used herein means an equatorial line of the tire and a line parallel with the equatorial line. In preferable embodiments of the invention, each of the lateral grooves is comprised of one main lateral groove portion and two auxiliary lateral groove portions; and the lateral grooves are arranged on both sides with respect to the circumferential groove; and at least one straight circumferential groove having a width wider than those of the main lateral groove portion and the auxiliary lateral groove portion and extending across the second slant segment of the main lateral groove portion and the auxiliary lateral groove portion is arranged between the circumferential groove and the tread end facing the inside of a vehicle when the tire is mounted on the vehicle; and the width of the first slant segment of the main lateral groove portion is wider than that of the second slant groove segment thereof. The invention will be further described with reference to the accompanying drawings, wherein: Fig. 1 is a schematic view of a first embodiment of the tread pattern of a pneumatic tire according to the invention; Fig. 2 is a schematic view of a second embodiment of the tread pattern of a tire according to the invention; Fig. 3 is a schematic view of a third embodiment of the tread pattern of a tire according to the invention; Fig. 4 is a schematic view of a fourth embodiment of the tread pattern of a tire according to the invention; and Fig. 5 is a schematic view of a conventional tread pattern. In the pneumatic tire according to the invention, the drainage effect can be sufficiently improved by locating the first slant segment of the main lateral groove portion at a region extending in the vicinity of the circumferential line and largely exerting an effect upon the resistance to hydroplaning. Further, the first slant segment contacts with the ground so as to cut a water film in the stepping-in of the rotating tire, so that the rising of blocks defined in the tread through hydraulic pressure can effectively be prevented. Moreover, the first slant segment discharges water flowed therein slantwise and laterally, so that the amount of water discharged ahead of the tire can effectively be reduced. On the other hand, the second slant segment of the main lateral groove portion and the auxiliary lateral groove portion are located at a region extending toward the vicinity of the tread end and largely exerting an effect upon the steering stability on dry road surfaces, whereby the ground contacting property of the tire is sufficiently improved and also the high rigidity of the blocks against force in the widthwise direction of the tread is ensured and at the same time water is discharged rapidly and efficiently from the vicinity of the circumferential line toward the side of the tread end. These effects become particularly conspicuous when a plurality of the above lateral grooves are arranged on both sides with respect to the circumferential line. Further, when two auxiliary lateral groove portions are opened to the single main lateral groove portion, the drainage property can be further improved. This is true even when a straight circumferential groove having a width wider than those of the main lateral groove portion and the auxiliary lateral groove portion is arranged in a region of the tread facing the inside of a vehicle when the tire is mounted on the vehicle. In the latter case, the straight circumferential groove is located at the inside of the vehicle, so that danger of lowering the block rigidity and hence the steering stability can be sufficiently overcome. Moreover, when the width of the first slant segment in the main lateral groove portion is made wider than that of the second slant segment, a greater amount of water can be retained in the first slant segment to further enhance the drainage efficiency. In the main lateral groove portion, the reason why the inclination angle of the first slant segment with respect to the circumferential direction of the tread is within a range of 5-30° is due to the fact that when the inclination angle is less than 5°, the distance between adjoining first slant segments in the circumferential direction becomes narrower to make the rigidity of land portions insufficient and hence there are caused problems such as uneven wear and the like, while when said inclination angle exceeds 30°, the drainage efficiency considerably lowers. Further, the reason why the inclination angle of the second slant segment with respect to the circumferential direction of the tread is within a range of 60-80° is due to the fact that when the inclination angle is less than 60°, sufficient block rigidity against input force during the cornering cannot be maintained, while when said inclination angle exceeds 80°, the drainage property in a ground contacting direction is considerably degraded and the advantage of the directional tread pattern may be lost. Fig. 1 shows a first embodiment of the tread pattern in a tire according to the invention, in which the circumferential line of the tire is coincident with the equatorial line of the tire or the tread center. In this tire, a straight circumferential groove 2 along the equatorial line of the tire is arranged in a central portion of a ground contact area 1 of the tread, and a straight circumferential groove 3 is arranged in each side portion of the ground contact area 1. Viewing from the front of the tire mounted onto a vehicle as shown in Fig. 1, a plurality of lateral grooves 4 extending slantwise and upward from the vicinity of the tread center toward each tread end and opening to the tread end are arranged at given intervals in the circumferential direction of the tread. Each of the lateral grooves 4 is composed of a main lateral groove portion 5 and an auxiliary lateral groove portion 6. The main lateral groove portion 5 is comprised of a first slant segment 7 extending in the central portion of the tread at an inclination angle of 5-30° with respect to the circumferential direction of the tread, a second slant segment 8 extending in each side portion of the tread at an inclination angle of 60-80° with respect to the circumferential direction, and a curved segment 9 smoothly connecting these slant segments 7, 8 with each other. On the other hand, the auxiliary lateral groove portion 6 is a slant groove portion extending substantially in parallel with the second slant segment 8 of the main lateral groove portion 5 beneath the main lateral groove portion 5 and opening to the tread end and to the first slant segment 7 of the main lateral groove portion 5. In this embodiment, the width of the first slant segment 7 in the main lateral groove portion 5 is somewhat wider than that of the second slant segment 8. Further, a circumferential rib 10 is formed between the straight circumferential groove 2 and a row of the lateral grooves 4 arranged in the circumferential direction so as to have a sawteeth-like shape. According to the tire of the above structure, the resistance to hydroplaning can effectively be improved while maintaining the steering stability on dry road surfaces at a sufficiently high level under the action of the lateral grooves 4 as previously mentioned. In such a tire, the three straight circumferential grooves 2, 3 are arranged in the ground contact area 1, so that the drainage property can be further improved. Fig. 2 shows a second embodiment of the tread pattern in a tire according to the invention, and has substantially the same structure as in the first embodiment except that the circumferential line of the tire is somewhat offset from the tread center toward the outside of a vehicle when the tire is mounted onto the vehicle, and a straight circumferential groove 11 is arranged at a position corresponding to the circumferential line, and two straight circumferential grooves 12 each extending across the second slant segment 8 of the main lateral groove portion 5 and having a width wider than those of the main lateral groove portion 5 and the auxiliary lateral groove portion 6 are arranged in a region between the circumferential line and the tread end facing the inside of the vehicle. Even in this embodiment, substantially the same function and effect as in the first embodiment can be obtained under the action of the lateral grooves 4. In addition, the circumferential groove is not arranged in a region facing the outside of the vehicle, so that the block rigidity in this region can be increased to further improve the steering stability on dry road surfaces. Fig. 3 shows a third embodiment of the tread pattern in a tire according to the invention. This tire is different from the tire of the first embodiment in that the arrangement of the straight circumferential groove is omitted in the central portion of the tread, and the first slant segment 7 of the main lateral groove portion 5 has a longer extension length and a wider width, and each of the lateral grooves 4 is composed of the main lateral groove portion 5 and two auxiliary lateral portions 6, 16 extending substantially in parallel with each other and with the second slant segment 8 and opening to the first slant segment 7 and the tread end, respectively. In this case, a circumferential rib 10' having the shape similar to that of the circumferential rib 10 is formed in the central portion of the tread between a pair of rows of the lateral grooves 4. According to the third embodiment, the drainage property can be ensured by the first slant segment 7 instead of the circumferential groove located in the central portion of the tread, and also a great amount of water can rapidly be discharged by providing the additional auxiliary lateral groove portion 16. Fig. 4 shows a fourth embodiment of the tread pattern in a tire according to the invention, in which sipes are added to the circumferential rib 10 in the tread pattern shown in Fig. 1. In this case, a sipe 21 is formed in a region from a second slant segment 8 of a first main lateral groove portion 5 to a top of a first slant segment 7 of an adjoining second main lateral groove portion 5, and a sipe 22 is formed in a region from a middle position of an auxiliary lateral groove portion 6 facing to the first slant segment 7 of the second main lateral groove portion 5 to the straight circumferential groove 2 located at the tread center and substantially in parallel with the sipe 21, whereby the land portion located at the tread center is made flexible to improve the ground contacting property of the tire. A comparative test between a conventional tire and invention tires will be described with respect to the steering stability on dry road surfaces and resistance to hydroplaning on wet road surfaces. o ○ Test tires having a tire size of 225/50 R16 and a tread ground contact width of 200 mm as mentioned later. ○ Invention tire 1 This tire has a tread pattern shown in Fig. 1, in which the width of each of the straight circumferential grooves 2, 3 is 10 mm, and the first slant segment 7 of the main lateral groove portion 5 has an inclination angle of 14° with respect to the circumferential direction of the tread and a width of 6.5 mm, and each of the second slant segment 8 and the auxiliary lateral groove portion 6 has an inclination angle of 50-70° with respect to the circumferential direction of the tread and a width of 5-6 mm. ○ Invention tire 2 This tire has a tread pattern shown in Fig. 2, in which each width and inclination angle are the same as in the invention tire 1. ○ Invention tire 3 This tire has a tread pattern shown in Fig. 3, in which the straight circumferential groove 3 has a width of 12 mm, and the first slant segment 7 of the main lateral groove portion 5 has an inclination angle of 8° with respect to the circumferential direction of the tread and a width of 9 mm, and each of the second slant segment 8 and the auxiliary lateral groove portion 6 has an inclination angle of 55-70° with respect to the circumferential direction of the tread and a width of 5-6 mm. ○ Conventional tire This tire has a tread pattern shown in Fig. 5 in which the width of the straight circumferential groove is 10 mm and the width of the slant groove is 4-5 mm. o ○ Test method The test tire is inflated under an internal pressure of 2.2 kgf/cm 2 and mounted on a vehicle, which is actually run with two persons riding in the vehicle. The steering stability on dry road surfaces is evaluated by a feeling test of a driver when the vehicle is run on a dry test course under various running modes. The resistance to hydroplaning in straight running is evaluated by measuring a remaining area of the ground contact area when running on a wet road surface having a water depth of 6 mm, while the resistance to hydroplaning in cornering is evaluated by measuring a lateral gravity during running on a wet road surface having a radius of 100 m. o ○ Test results The measured results are shown in Table 1 by an index value on the basis that the conventional tire is 100. The larger the index value, the better the result. Conventional tire Invention tire 1 Invention tire 2 Invention tire 3 Steering stability on dry road surface 100 100 105 100 Resistance to hydroplaning in straight running 100 110 105 110 Resistance to hydroplaning in cornering 100 110 105 110 As seen from Table 1, the resistance to hydroplaning can effectively be improved without reducing the steering stability in all of the invention tires. In the invention tire 2, the steering stability can be further improved by omitting the straight circumferential groove from the region facing to the outside of the vehicle. As mentioned above, according to the invention, the resistance to hydroplaning on wet road surfaces can effectively be improved while maintaining the steering stability on dry road surfaces at a satisfactory level.

Claims: A pneumatic tire having a tread pattern defined by at least one straight circumferential groove (2,3;11,12) extending substantially in the circumferential direction of the tread, and a plurality of lateral grooves (4) each extending slantwise from a respective end of the tread and inwards of the tire, when viewed from the front of a vehicle when the tire is mounted onto the vehicle, characterized in that one of said straight circumferential grooves (2,11) extends on the mid-circumferential line or is offset from the tread center toward the outside of the vehicle when the tire is mounted on the vehicle, and said lateral groove (4) is composed of a main lateral groove portion (5) continuously extending from the vicinity of the circumferential groove toward the vicinity of the tread end and an auxiliary lateral groove portion (6), and said main lateral portion (5) is comprised of a first slant segment (7) extending in the vicinity of the circumferential groove at an inclination angle of 5-30° with respect to the circumferential direction of the tire, a second slant segment (8) extending toward the vicinity of the tread end at an inclination angle of 60-80° with respect to the circumferential direction, and a curved segment (9) smoothly connecting the said first and second slant segments (7,8) with each other, and said auxiliary lateral groove portion (6) is a slant groove portion extending substantially parallel with said second slant segment (8) and opening to each of said tread end and said first slant segment (7). A pneumatic tire as claimed in Claim 1, characterized in that each of said lateral grooves (4) is comprised of one main lateral groove portion (5) and two auxiliary lateral groove portions (6, 16). A pneumatic tire as claimed in Claim 1 or 2, characterized in that said lateral grooves (4) are arranged on both sides with respect to said circumferential groove (2, 11). A pneumatic tire as claimed in any of Claims 1 to 3, characterized in that at least one straight circumferential groove (3; 12) having a width wider than those of said main lateral groove portion (5) and auxiliary lateral groove portion (6) and extending across said second slant segment (8) of said main lateral groove portion (5) and auxiliary lateral groove portion (6) is arranged between said circumferential groove (2, 11) and said tread end facing the inside of a vehicle when the tire is mounted on the vehicle. A pneumatic tire as claimed in any of Claims 1 to 4, characterized in that the width of said first slant segment (7) of said main lateral groove portion (5) is wider than that of said second slant groove segment (8) thereof. A pneumatic tire having a tread pattern defined by at least one straight circumferential groove (3) extending substantially in the circumferential direction of the tread, and a plurality of lateral grooves (4) each extending slantwise from a respective end of the tread and inwards of the tire so as to define a circumferential rib (10') in a central portion of the tread pattern when viewed from the front of a vehicle when the tire is mounted onto the vehicle, characterized in that said lateral groove (4) is composed of a main lateral groove portion (5) continuously extending from the vicinity of the mid-circumferential line of the tire toward the vicinity of the tread end and an auxiliary lateral groove portion (6), and said main lateral portion (5) is comprised of a first slant segment (7) extending in the vicinity of the mid-circumferential line at an inclination angle of 5-30° with respect to the circumferential direction of the tire, a second slant segment (8) extending toward the vicinity of the tread end at an inclination angle of 60-80° with respect to the circumferential direction, and a curved segment (9) smoothly connecting the said first and second slant segments (7, 8) with each other, and said auxiliary lateral groove portion (6) is a slant groove portion extending substantially parallel with said second slant segment (8) and opening to each of said tread end and said first slant segment (7), wherein said circumferential rib (10') is continuous to a land portion in a side region of the tread pattern between said main lateral groove portions. A pneumatic tire as claimed in Claim 6, characterized in that said tread pattern includes a straight circumferential groove (3) between said mid-circumferential line and said tread end and extending substantially in the circumferential direction of the tread, and in that said straight circumferential groove intersects said lateral grooves (4). A pneumatic tire as claimed in Claim 6 or 7, characterized in that said straight circumferential groove (3) has a width wider than a width of said main lateral groove portion (5). A pneumatic tire as claimed in any of Claims 6 to 8, characterized in that said straight circumferential groove (3) has a width wider than a width of said auxiliary lateral groove portion (6). A pneumatic tire as claimed in any of Claims 6 to 9, characterized in that said straight circumferential groove (3) intersects said second slant segment (8) and said auxiliary lateral groove portion (6). A pneumatic tire as claimed in any of Claims 6 to 10, characterized in that each of said lateral grooves (4) is comprised of a main lateral groove portion (5) and at least two auxiliary lateral groove portions (6, 16). A pneumatic tire as claimed in any of Claims 6 to 11, characterized in that said tread pattern includes at least one straight circumferential groove (3) on each side of said mid-circumferential line and extending substantially in the circumferential direction of the tread. A pneumatic tire as claimed in any of Claims 6 to 12, characterized in that said land portion in the side region of the tread pattern is unitary.

Inventors: HIMURO YASUO, HIMURO, YASUO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1993
Main classification: B60C11
IPC codes: B60C11