Pneumatic tire

Abstract

A pneumatic tire includes a tread portion provided with a shoulder main groove and a crown main groove to form a middle land portion therebetween. The middle land portion is provided with a first middle lug groove including a first groove wall and a second groove wall, wherein the first groove wall includes a protrusion protruding toward the second groove wall on the side of the shoulder main groove. The protrusion includes a front wall located so as to form a sipe portion between the front wall and the second groove wall, a top wall, a first lateral wall located axially outward of the front wall and a second lateral wall located axially inward of the front wall. The front wall is configured to a triangular shape.

Claims

1. A pneumatic tire comprising: a tread portion having a ground contact surface, the tread portion being provided with a circumferentially extending shoulder main groove arranged proximate to a tread edge and a circumferentially extending crown main groove to form a middle land portion therebetween; the middle land portion being provided with a first middle lug groove extending axially inwardly from the shoulder main groove and terminating within the middle land portion; the first middle lug groove comprising a first groove wall and a second groove wall, the first groove wall comprising a protrusion protruding toward the second groove wall on the side of the shoulder main groove; the protrusion comprising a front wall located so as to form a sipe portion between the front wall and the second groove wall, a top wall, a first lateral wall located axially outward of the front wall and a second lateral wall located axially inward of the front wall; and the top wall comprising a step surface located radially inward of the ground contact surface of the tread portion and extending in parallel with the ground contact surface of the tread portion, the step surface configured to have a triangular shape comprising a bottom side on the side of the first groove wall, a vertex (P) protruding the second groove wall, a first oblique side extending from the vertex (P) to an axially outer end of the bottom side and a second oblique side extending from the vertex (P) to an axially inner end of the bottom side.

2. The pneumatic tire according to claim 1, wherein the first middle lug groove comprises the sipe portion and a remaining lug main portion, and a depth (Da) of the step surface from the ground contact surface of the tread portion is in a range of from 0.15 to 0.3 times a depth (D0) of the lug main portion.

3. The pneumatic tire according to claim 1, wherein the middle land portion is further provided with an auxiliary sipe extending from an axially inner end of the first middle lug groove and terminating within the middle land portion.

4. The pneumatic tire according to claim 1, wherein the middle land portion is further provided with a bent sipe comprising a longitudinal portion extending from the first middle lug groove in a circumferential direction of the tire and an inclined portion extending from the longitudinal portion to the crown main groove in parallel with the first middle lug groove.

5. The pneumatic tire according to claim 1, wherein the middle land portion is further provided with a second middle lug groove without having the protrusion.

6. The pneumatic tire according to claim 1, wherein the first middle lug groove comprises the sipe portion and a remaining lug main portion, and a depth (Db) of the sipe portion is equal to or less than a depth (D0) of the lug main portion.

7. A pneumatic tire comprising: a tread portion having a ground contact surface, the tread portion being provided with a circumferentially extending shoulder main groove arranged proximate to a tread edge and a circumferentially extending crown main groove to form a middle land portion therebetween; the middle land portion being provided with a first middle lug groove extending axially inwardly from the shoulder main groove and terminating within the middle land portion; the first middle lug groove comprising a first groove wall and a second groove wall, the first groove wall comprising a protrusion protruding toward the second groove wall on the side of the shoulder main groove; the protrusion comprising a front wall located so as to form a sipe portion between the front wall and the second groove wall, a top wall, a first lateral wall located axially outward of the front wall and a second lateral wall located axially inward of the front wall; the top wall comprising a step surface located radially inward of the ground contact surface of the tread portion and extending in parallel with the ground contact surface of the tread portion, the step surface configured to have a triangular shape comprising a bottom side on the side of the first groove wall, a vertex (P) protruding the second groove wall, a first oblique side extending from the vertex (P) to an axially outer end of the bottom side and a second oblique side extending from the vertex (P) to an axially inner end of the bottom side; the front wall configured to have a triangular shape comprising a bottom side extending on a bottom of the first middle lug groove in parallel with the second groove wall S2, a first oblique side extending from the vertex (p) to an axially outer end of the bottom side and a second oblique side extending from the vertex (P) to an axially inner end of the bottom side; the first lateral wall extending between the first oblique side of the step surface and the first oblique side of the front wall; and the second lateral wall extending between the second oblique side of the step surface and the second oblique side of the front wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a development view of a tread portion of a pneumatic tire according to an embodiment of the present invention.

(2) FIG. 2 is a perspective view of a first middle lug groove.

(3) FIG. 3A is a plan view of the first middle lug groove, and FIG. 3B is a cross-sectional view taken along a line I-I of FIG. 3A.

(4) FIG. 4 is a partial perspective view illustrating a first groove wall of with a protrusion of the first middle lug groove.

(5) FIG. 5A is a perspective view of a second middle lug groove, and FIG. 5B is a plan view thereof.

(6) FIGS. 6A and 6B are a plan view and a perspective view respectively each illustrating the protrusion in accordance with another embodiment of the invention.

(7) FIGS. 7A and 7B are a plan view and a perspective view respectively each illustrating the protrusion in accordance with yet another embodiment of the invention.

(8) FIGS. 8A and 8B are a plan view and a perspective view respectively each illustrating the protrusion in accordance with yet another embodiment of the invention.

(9) FIGS. 9A and 9B are a plan view and a cross-sectional view respectively each illustrating a conventional tie-bar with a sipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) An embodiment of the present invention will be explained below with reference to the accompanying drawings. As illustrated in FIG. 1, a pneumatic tire 1 in accordance with the present embodiment includes a tread portion 2 provided with a pair of circumferentially extending shoulder main grooves 3 each arranged proximate to each tread edge Te and a pair of circumferentially extending crown main grooves 4 each arranged axially inward of each shoulder main groove 3. Thus, the tread portion 2 in accordance with the embodiment is separated into five land portions that include a central land portion 5 disposed between the crown main grooves 4 and 4, a pair of middle land portions 6 each disposed between the crown main groove 4 and the shoulder main groove 3 on each side of the tire equator Co, and a pair of shoulder land portions 7 each disposed between the shoulder main groove 3 and the tread edge Te on each side of the tire equator Co. Alternatively, a single crown main groove 4 may be provided. In this case, the tread portion 2 may be separated into four land portions that include a pair of middle land portions 6 and a pair of shoulder land portions 7.

(11) In this embodiment, the shoulder main grooves 3 and 3 have the same width and are located apart from the tire equator Co at the same axial distance. Similarly, the crown main grooves 4 and 4 have the same width and are located apart from the tire equator Co at the same axial distance. Furthermore, the central land portion 5, the middle land portions 6 and the shoulder land portions 7 have widths W5, W6 and W7 respectively, wherein the widths satisfy the following relationship:
W5<=W6<=W7.
In this embodiment, the tread pattern illustrated in FIG. 1 is configured as a substantially point-symmetrical pattern with respect to a point on the tire equator Co except variable pitches.

(12) Widths W3 and W4 of the shoulder main grooves 3 and the crown main grooves 4 respectively and depths thereof are not particularly limited, but may be employed conventional ranges. Preferably, the widths W3 and W4 are in a range of from 2% to 9% of a tread width TW and the depths are in a range of from 7.0 to 10.0 mm, for passenger car tires.

(13) Each middle land portion 6 is provided with a plurality of first middle lug grooves 8 which are spaced in the circumferential direction of the tire. In this embodiment, a second middle lug groove 9 is further provided between circumferentially adjacent first middle lug grooves 8 and 8. Thus, the first middle lug groove 8 and the second middle lug groove 9 are arranged alternately in the circumferential direction of the tire. The first middle lug grooves 8 and second middle lug grooves 9 are inclined in the same direction at an angle of from 30 to 60 degrees with respect to the circumferential direction of the tire.

(14) As illustrated in FIGS. 2 and 3, the first middle lug grooves 8 include axially outer ends 8o in communication with the shoulder main groove 3 and axially inner ends 8i terminating within the middle land portion 6.

(15) Each first middle lug groove 8 includes a first groove wall Si and a second groove wall S2. The first groove wall S1 includes a protrusion 12 protruding toward the second groove wall S2 at an opening 10 on the side of the shoulder main groove 3. The protrusion 12 raises from a groove bottom 11.

(16) The protrusion 12 is provided such that a narrow sipe portion 13 is formed between the protrusion 12 and the second groove wall S2. That is, the first middle lug groove 8 includes the sipe portion 13 and a remaining lug main portion 14. The sipe portion 13 has a width W13 in a range of equal to or less than 1.2 mm same as conventional sipes.

(17) As illustrated in FIGS. 3 and 4, the protrusion 12 includes a front wall 15 located to form the sipe portion 13 between the front wall 15 and the second groove wall S2, a top wall 16, a first lateral wall 17 located axially outward of the front wall 15 and a second lateral wall 18 located axially inward of the front wall 15. The top wall 16 includes a step surface 16A located radially inward of the ground contact surface TS of the tread portion 2 and extending in parallel with the ground contact surface TS of the tread portion 2. In this embodiment, the top wall 16 includes a sub portion 16B constituting a part of the ground contact surface TS and the step surface 16A connected to the sub portion 16B through a step K.

(18) The step surface 16A is configured to a substantially triangular shape that includes a bottom side 16a on the side of the first groove wall S1, a vertex (P) protruding toward the second groove wall S2, a first oblique side 16b extending from the vertex (P) to an axially outer end of the bottom side 16a and a second oblique side 16c extending from the vertex (P) to an axially inner end of the bottom side 16a. Preferably, the bottom side 16a extends in parallel with the first groove wall S1. Note that the above-mentioned substantially triangular shape refers to as not only a triangular shape in which the first and second oblique sides 16b and 16c extend from the vertex (P) to the axially outer and inner ends of the bottom side 16a respectively but also an imperfect triangular shape in which a part J1 of the triangular shape is cut on the side of the shoulder main groove 3 or the sipe portion 13, as illustrated in FIGS. 6A, 6B, 7A and 7C. In case of the former, the vertex (P) is preferably located on the perpendicular bisector of the bottom side 16a. In the latter case, the vertex (P) is preferably located on the perpendicular bisector of the bottom side 16a in a shape before being cut the part J1.

(19) Referring back to FIG. 4, the front wall 15 is configured to a substantially triangular shape that includes a bottom side 15a extending on a bottom 11 of the first middle lug groove 8 in parallel with the second groove wall S2, a first oblique side 15b extending from the vertex (P) to an axially outer end of the bottom side 15a and a second oblique side 15c extending from the vertex (P) to an axially inner end of the bottom side 15a. The front wall 15 extends substantially in parallel with the second groove wall S2. Note that the above-mentioned substantially triangular shape refers to as not only a triangular shape in which the first and second oblique sides 15b and 15c extend from the vertex (P) to the axially outer and inner ends of the bottom side 15a respectively but also an imperfect triangular shape in which a part J2 of the triangular shape is cut on the side of the shoulder main groove 3 or the sipe portion 13, as illustrated in FIGS. 6A, 6B, 7A and 7C. In case of the former, the vertex (P) is preferably located on the perpendicular bisector of the bottom side 15a. In the latter case, the vertex (P) is preferably located on the perpendicular bisector of the bottom side 15a in a shape before being cut the part J2.

(20) The first lateral wall 17 intersects with a groove wall 3w of the shoulder main groove 3. Furthermore, the first lateral wall 17 intersects with the step surface 16A at the first oblique side 16b, and intersects with the front wall 15 at the first oblique side 15b. In this embodiment, the first lateral wall 17 is configured as a triangular shape. The second lateral wall 18 intersects with the first groove wall S1. Furthermore, the second lateral wall 18 intersect with the step surface 16A at the second oblique side 16c, and intersects with the front wall 15 at the second oblique side 15c. In this embodiment, the front wall 15, the step surface 16A, the first lateral wall 17 and the second lateral wall 18 are configured as a plane.

(21) Preferably, a depth (Da) of the step surface 16A from the ground contact surface TS of the tread portion 2 is in a range of from 0.15 to 0.3 times a depth (D0) of the lug main portion 14 as illustrated in FIG. 3B. When the depth (Da) is less than 0.15 times the depth (D0), drainage performance may be lowered. On the other hand, when the depth (Da) is more than 0.3 times the depth (D0), steering stability of the tire may be lowered. Furthermore, a depth (Db) of the sipe portion 13 from the ground contact surface TS of the tread portion 2 is preferably equal to or less than the depth (D0) of the lug main portion 14. More preferably, the depth (Db) is in a range of from 0.70 to 0.95 times the depth (D0).

(22) The protrusion 12 may increase rigidity of a portion around the middle lug groove 8 on the side of the opening 10, and thus improves steering stability of the tire. Furthermore, the protrusion 12 may prevent inflow of an air compressed by the middle lug groove 8 to the shoulder main groove 3 to improve noise performance. In addition, wet performance of the tire can be ensured since water introduced in the middle lug groove 8 is drained toward the shoulder main groove 3 through the sipe portion 13 and the step surface 16A.

(23) Each of the step surface 16A and the front wall 15 is configured as a triangular shape, and the second lateral wall 18 is formed into an oblique plane including the second oblique sides 15c and 16c. That is, the second lateral wall 18 is inclined so as to approach the step surface 16A and the sipe portion 13 to the axially outwardly. This configuration would smoothly guide water introduced in the middle lug groove 8 to the shoulder main groove 3 through the sipe portion 13 as well as a space between the step surface 16A and the ground while ensuring noise performance to improve drainage performance.

(24) Furthermore, since the first lateral wall 17 is also formed into an oblique plane including the first oblique sides 15b and 16b, the protrusion 12 is configured as a quadrangular pyramid shape having the front wall 12 increasing its width toward the bottom 11 and the top wall increasing its width toward the first groove wall S1. This configuration of the protrusion 12 may have high rigidity to improve steering stability while offering better drainage of the sipe portion 13 as compared with a tie-bar formed as a rectangular parallelepiped shape.

(25) In this embodiment, an auxiliary sipe 20 is provided on the middle land portion to further improve drainage performance while ensuring the rigidity, wherein the auxiliary sipe 20 extends axially inwardly from the axially inner end 8i of each first middle lug groove 8.

(26) The auxiliary sipe 20 extends substantially in parallel with the middle lug groove 8 and has an axially inner end terminating within the middle land portion 6. As illustrated in FIG. 1, the middle land portion 6 is further provided with a bent sipe 21. The bent sipe 21 includes a longitudinal portion 21A extending from the first middle lug groove 8 in the circumferential direction of the tire and an inclined portion 21B extending from the longitudinal portion 21A to the crown main groove in parallel with the first middle lug groove 8. The longitudinal portion 21A extends on or around the axially center of the middle land portion 6. Preferably, the longitudinal portion 21A may be located within 10% of a width W6 of the middle land portion 6 from the axially center.

(27) As illustrated in FIGS. 5A and 5B, the second middle lug groove 9 includes an axially outer end 9o that opens at the shoulder main groove 3 and an axially inner end 9i that terminates within the middle land portion 6. The middle lug groove 9 has no protrusions 12 on the side of the opening 22, and extends in parallel with the middle lug groove 8 with a width same as the lug main portion 14 of the first middle lug groove 8. Furthermore, the axially inner end of the second middle lug groove 9 is connected to an auxiliary sipe 23 which is similar to the auxiliary sipe 20. As illustrated in FIG. 1, the second middle lug groove 9 has an axial length L.sub.9 which is smaller than an axial length L.sub.8 of the first middle lug groove 8, and preferably the length L.sub.9 is 40% to 60% of the length L.sub.8. In this embodiment, an acute corner Q between the second middle lug groove 9 and the shoulder main groove 3 is configured as a triangular chamfered portion 24 to prevent the corner Q from chipping.

(28) As illustrated in FIG. 1, the middle land portion 6 is further provided with a plurality of second auxiliary sipes 25 extending axially outwardly from the crown main groove 4 and terminating within the middle land portion 6. In this embodiment, the second auxiliary sipes 25 extend in parallel with the inclined portion 21B of the bent sipe 21. The auxiliary sipes 25 and the inclined portions 21B are arranged alternately in the circumferential direction of the tire so that pattern rigidity of the middle land portion 6 is uniformized. The respective acute corners formed between the auxiliary sipes 25 and the crown main groove 4 as well as between the inclined portion 21B and the crown main groove 4 are chamfered in a triangular shape to prevent these corners from chipping (not illustrated).

(29) The shoulder land portions 7 is provided with a plurality of shoulder lug grooves 26 that extend axially inwardly from a location axially outside the tread edge Te and have axially inner ends terminating within the shoulder land portions 7, and a plurality of auxiliary sipes 27 that extend from the axially inner ends of the shoulder lug grooves 26 to the shoulder main groove 3, for example. In this embodiment, a sipe 28 is provided between circumferentially adjacent shoulder lug grooves 26 and 26, wherein the sipe 28 extends axially inwardly from a location axially outside the tread edge Te and terminating within the shoulder land portions 7. The sipe 28 extends substantially in parallel with the shoulder lug grooves 26. Furthermore, the shoulder lug grooves 26 and the sipe 28 have an angle 90 degrees plus/minus 10 degrees with respect to the circumferential direction of the tire at the tread edge Te.

(30) FIGS. 6A and 6B illustrate a plan view and a perspective view respectively each illustrating the protrusion 12 in accordance with another embodiment of the invention. In this embodiment, the step surface 16A and the front wall 15 are formed into a substantially triangular shape (e.g. imperfect triangular shape). Specifically, the step surface 16A is exemplified as a substantially triangular shape which is deficient in a small part J1 on the side of the shoulder main groove 3 with respect to a reference triangular shape imaginary formed by the bottom side 16a, the first oblique side 16b and the second oblique side 16c.

(31) Similarly, the front wall 15 is exemplified as a substantially triangular shape which is deficient in a small part J2 on the side of the shoulder main groove 3 with respect to a reference triangular shape imaginary formed by the bottom side 15a, the first oblique side 15b and the second oblique side 15c. In any case, a deficient area of a substantially triangular shape is preferably less than 15%, more preferably less than 10% of the reference triangular shape. Such a protrusion 12 may also exert the same effects as the protrusion 12 described above in which both the step surface 16A and the front wall 15 have a reference triangular shape.

(32) Note that the depth (Db) of the sipe portion 13 may be set same as the depth (D0) of the lug main portion 14.

(33) FIGS. 7A and 7B illustrate a plan view and a perspective view of another embodiment of the protrusion respectively, wherein the step surface 16A and the front wall 15 are formed into a substantially triangular shape. Specifically, the step surface 16A is exemplified as a substantially triangular shape which is deficient in a small part J1 on the side of the vertex (P) with respect to a reference triangular shape imaginary formed by the bottom side 16a, the first oblique side 16b and the second oblique side 16c. In this embodiment, the step surface 16A having the substantially triangular shape may be similar to a trapezoidal shape. Similarly, the front wall 15 is also exemplified as a substantially triangular shape which is deficient in a small part J2 on the side of the vertex (P) with respect to a reference triangular shape imaginary formed by the bottom side 15a, the first oblique side 15b and the second oblique side 15c. In this embodiment, the front wall 15 having the substantially triangular shape may be similar to a trapezoidal shape. In any case, a deficient area of a substantially triangular shape is preferably less than 15 %, more preferably less than 10% of the reference triangular shape. Such a protrusion 12 may also exert the same effects as the protrusion 12 described above in which both the step surface 16A and the front wall 15 have a reference triangular shape.

(34) FIGS. 8A and 8B illustrate a plan view and a perspective view of the protrusion 12 respectively in accordance with yet another embodiment of the invention. In this embodiment, the top wall 16 is configured by only the step surface 16A, and the sub portion 16B is not provided.

(35) While the particularly preferable embodiments in accordance with the present invention have been described in detail, the present invention is not limited to the illustrated embodiments, but can be modified and carried out in various aspects.

EXAMPLE

(36) In order to confirm the effects of the invention, passenger car tires (195/65R15) having a basic tread pattern illustrated in FIG. 1 were manufactured based on the detail shown in Table 1. Then, noise performance, wet performance and steering stability of each test tire was tested. Note that the tire of Ref 1 had no protrusions on the middle lug groove and the tire of Ref 2 was provided with a tie-bar with a groove bottom sipe on the middle lug groove 8 at its opening 10 as illustrated in FIGS. 9A and 9B. Each tire has substantially same specification except the detail as shown in Table 1. Common specification and test method are as follows:

(37) Common specification:

(38) Protrusion Step surface shape: triangle Front wall shape: triangle Step surface depth Da: 1.5 mm Sipe portion depth Db: 5.3 mm Lug main portion depth D0: 6.0 mm Auxiliary sipe width: 0.8 mm Bent sipe width: 0.8 mm
Noise performance test:

(39) Each test tire mounted on a rim (156JJ) with an inner pressure (230 kPa) and was installed to a front wheel drive test vehicle having a displacement of 1800cc as its all wheels, and then a driver drove the test vehicle on a noise measurement road with a rough asphalt surface at speed of 60 km/h to evaluate a car interior noise by his sense. The test results are shown with an index base on Ref 1 being 100. The larger the value, the better the performance is.

(40) Wet Performance Test:

(41) The above-mentioned test vehicle was entered into a course with a water puddle of 5 mm deep and 20 m long, on an asphalt road surface with a radius of 100 m, with stepwise speed increase. Then, lateral acceleration (lateral G) of the test vehicle was measured, and average lateral at speeds of 50 to 80 km/h was calculated. The test results are shown with an index base on Ref. 1 being 100. The larger the value, the better the performance is.

(42) Steering Stability Test:

(43) The driver drove the above mentioned test vehicle on a tire test course with a dry asphalt surface to evaluate the steering stability by his sense. The test results are shown with an index base on Ref. 1 being 100. The larger the value, the better the performance is.

(44) As shown in Table 1, it is confirmed that the tire, which has the protrusion in which both the step surface and the front wall are configured as a triangular shape, exerts excellent steering stability, wet performance and noise performance at a high level, as compared with the tire of Ref 2 having a tie-bar with a sipe.

(45) TABLE-US-00001 TABLE 1 Ref. 1 Ref. 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Tread pattern FIG. 1 Middle lug groove Presence Protrusion Absence Tie-bar Presence Step surface Absence Presence (triangular shape) Front wall Absence Presence (triangular shape) Sipe portion Absence Sipe Presence Auxiliary sipe Absence Absence Absence Presence Presence Absence Bent sipe Absence Absence Absence Presence Presence Absence Second middle lug Absence Absence Absence Absence Presence Presence groove Noise performance 100 110 110 110 110 110 Wet performance 100 90 97 105 110 108 Steering stability 100 107 110 110 110 110 (TOTAL) 300 307 317 325 330 328