Pneumatic tire

Abstract

A pneumatic tire having a specified rotational direction and including land portions formed compartmentally on the tread of the pneumatic tire by disposing plural inclined grooves extending from both tread ends respectively toward the tire equator and inclined toward the rotational direction with respect to a tire width direction, and also including branch grooves on the tread, each of the branch grooves diverging from a portion of the inclined groove within an area till ¼ of the tread width from the tread, extending to the tire equator in the opposite tire circumferential direction of the inclined groove with respect to the tire width direction and terminating within the land portions.

Claims

1. A pneumatic construction vehicle tire having a specified rotational direction, the pneumatic tire comprising: land portions formed compartmentally on the tread of the pneumatic tire by disposing a plurality of inclined grooves extending from both tread ends respectively toward the tire equator and inclined toward the rotational direction, and branch grooves also on the tread, each of the branch grooves diverging from a portion of a corresponding inclined groove within an area till ¼ of the tread width from the tread end to an inner side in the tire width direction, extending toward the tire equator in the opposite tire circumferential direction of the inclined groove and terminating within the land portions, wherein the position in which each branch groove diverges from the inclined groove, is disposed within an inside area of 1/16 of the tread width from the tread end in the tire width direction.

2. A pneumatic tire according to claim 1, wherein the shortest distance between the branch groove and the inclined groove neighboring the branch groove in the opposite side of the rotational direction is within the range of 15% to 30% of the tread width.

3. A pneumatic tire according to claim 1, wherein an extending direction of the branch grooves is within the angle range of 30° to 60° with respect to the tire width direction.

4. A pneumatic tire according to claim 2, wherein an extending direction of the branch grooves is within the angle range of 30° to 60° with respect to the tire width direction.

5. A pneumatic tire according to claim 1, wherein an extending direction of the inclined grooves is within the angle range of 5° to 45° with respect to the tire width direction.

6. A pneumatic tire according to claim 1, wherein a distance I.sub.2 of each branch groove between an end edge thereof and an end branching into its corresponding inclined groove is within the range of 50% to 90% of a distance I.sub.1 between one end of the inclined groove connecting with the tread end and the other end edge thereof.

7. A pneumatic tire according to claim 1, wherein an average width w.sub.2 of the branch grooves is within a range of 0.5% to 4% of the tread width.

8. A pneumatic tire according to claim 1, wherein a depth of the branch grooves is ⅓ or more of a depth of the inclined grooves.

9. A pneumatic tire according to claim 1, wherein an average width w.sub.1 of the inclined grooves is within a range of 10% to 30% of the tread width.

10. A pneumatic tire according to claim 1, wherein a depth of the inclined grooves is within a range of 60% to 90% of a thickness of the tread rubber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an exploded view showing a part of the tread of a pneumatic tire as an embodiment of the present invention.

(2) FIGS. 2(a) and 2(b) are exploded views showing a part of the tread of conventional examples 1 and 2 respectively, and FIGS. 2(c), 2(d) and 2(e) are exploded views showing a part of the tread of the comparative examples 1, 2 and 3 respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

(3) An embodiment according to the present invention will be described in detail below based on the drawings. In accordance with the custom, a pneumatic tire of the embodiment is provided with a pair of bead portions, a pair of side wall portions extending from the bead portions to an outer side in the tire diameter direction and a tread portion between the side wall portions. In the configuration of the pneumatic tire, there are a carcass toroidally extending between each bead core embedded in the bead portions and a belt composed of a plurality of belt layers at a crown portion of the carcass to an outer side in the tire radial direction.

(4) FIG. 1 is an exploded view showing a part of the tread of a pneumatic tire of an embodiment according to the present invention. A pneumatic tire 1 of the embodiment has a specified rotational direction R and is provided with land portions formed compartmentally on a tread portion 3 by disposing a plurality of inclined grooves 5 that are configured at an interval with each other in the tire circumferential direction and extending from both tread ends 11 toward the tire equator e of the tire 1. Each of the inclined grooves 5 is composed of an extending part 5a in the tire width direction and an inclined part 5b at an angle α with respect to the tire width direction. Each of branch grooves 9 diverges from the inclined groove 5 within an area till ¼ of the tread width from the tread end 11, extends to the tire equator e in the opposite direction of the inclined groove 5 with respect to the tire width direction with an inclination at an angle β with respect to the tire width direction and terminates respectively either within land portions 6a or 6b of each half tread width area defined by the equator e.

(5) Next, a mechanism will be described for suppressing the partial wear by a tread pattern according to the present invention. First of all, the inclined grooves 5 are provided. In particular, the inclined groove part 5b of each inclined groove 5, which is inclined toward the rotational direction R, produces an effect for suppressing tread rubber deformation in the tire width direction involved in the belt deformation. In addition, each inclined groove 5 is provided with the branch groove, which diverges from the inclined groove 5 within the area till ¼ of the tread width from the tread end 11, making it possible to decrease the tire width directional elements of the rubber deformation in the above stated side portion area. In case the branch grooves extend in the tire circumferential direction and cross the land portions (see FIG. 2(d)), the independent land portions are thus formed. As a result, tread rubber deformation in the tire circumferential direction may be promoted. Therefore, it is important to incline the branch grooves 9 toward the tire equator e as shown in FIG. 1. That is, according to such a configuration of the branch grooves 9, the land portions formed compartmentally between the mutual inclined grooves 5 are divided at an angle with respect to the tire circumferential direction by the branch grooves 9. At ground contact of the land portions, as shown by an arrow in FIG. 1, the tread deformation is led to a deformation M.sub.1 from a side of the tread end 11 and a deformation M.sub.2 from a side of the equator e, and both deformations M.sub.1 and M.sub.2 are proceeding along the branch groove 9 toward the end edge thereof. The deformation M.sub.2 from the side of the equator e suppresses the rubber behavior in the tire width direction involved in the belt deformation. At the end edge of the branch groove 9, both deformations M.sub.1 and M.sub.2 join together so that tire width directional elements of both sides across the branch groove 9 act to compensate with each other and are dissolved. And remaining tire circumferential elements join together an the end edge of the branch groove 9 and then form the tire circumferential elements in the opposite direction of the rotational direction R.

(6) Here, FIG. 2 (c) shows a part of a tire in which the land portions are formed compartmentally on the tread by the inclined grooves. As shown by an arrow M.sub.3, the tread rubber deformation involved in the above stated belt deformation proceeds along the inclined grooves 5 toward the rotational direction R and the tire width directional elements affect each other in the facing direction across the tire equator and act to compensate. As a result, mostly tire circumferential elements remain. These tire circumferential elements have been the principal cause of the partial wear. Now that the above stated tire circumferential elements in the opposite direction of the rotational direction R are formed by the branch grooves 9 and thus the tire circumferential elements act to compensate with each other. Consequently, it is achieved to suppress the partial wear in the tire circumferential direction.

(7) As shown in FIG. 1, it is noted that the shortest distance d between the branch groove 9 and the inclined groove 5 neighboring the branch groove 9 in the opposite side of the rotational direction is preferably within the range of 15% to 30% of the tread width, thereby making it possible to reduce the slip phenomena of the tread more surely. In case the shortest distance between the branch groove 9 and the inclined groove neighboring the branch groove 9 in the opposite side of the rotational direction is less than 15% of the tread width W, it is impossible to cause sufficient rubber deformation in the tire circumferential direction in the branch groove end, therefore, the partial wear cannot be suppressed. Moreover, in case the shortest distance between the branch groove and the inclined groove neighboring the branch groove in the opposite side of the rotational direction is more than 30% of the tread width W, rubber deformation will not arise sufficiently in an inner side of the branch groove in the tire width direction, thus, the partial wear cannot be suppressed.

(8) It is also preferable to dispose the position in which each branch groove 9 diverges from the inclined groove 5 within an inside area of 1/16 of the tread width W from the tread end 11 in the tire width direction, thereby making it possible to reduce the slip phenomena of the tread more surely.

(9) It is also preferable that an inclination angle β of the branch grooves 9 with respect to the tire width direction is within the angel range of 30° to 60°, thereby making it possible to strike the rubber deformation balance both in the tire width and circumferential directions, and thus leading to the total reduction of the partial wear.

(10) Furthermore, it is preferable that an inclination angle α of the inclined grooves 5 with respect to the tire width direction is within the range of 5° to 45°

(11) The inclined grooves 5 extend preferably from the tread ends 11 at least beyond 3/10 of the tread width W to inner side areas in the tire width direction, and an average width W.sub.1 of the inclined grooves 5 is preferably within the range of 10% to 30% of the tread width. In addition, a depth of the inclined grooves 5 is preferably within the range of 60% to 90% of a thickness of the tread rubber.

(12) A distance I2 of each branch groove 9 between an end edge thereof and an end branching into the inclined groove 9 is preferably within the range of 50% to 90% of a distance I1 between one end of the inclined groove 5 connecting with the tread end and the other end edge thereof. And an average width w2 of the branch grooves is preferred to be within the range of 0.5% to 4% of the tread width. In addition, a depth of the branch grooves is preferably ⅓ or more of a depth of the inclined grooves.

(13) It is noted that a negative ratio of the tread ground contact surface is preferably within the range of 15% to 30%, thereby making it possible to secure heat release resistance of the tread. A negative ratio in excess of 30% decreases stiffness of the land portions and thus wear resistance may deteriorate. And a negative ratio less than 15% makes heat release property worse, becoming a cause of malfunction such as heat separation and the like.

(14) In addition, an average value of a groove width of the branch grooves 9 is preferably smaller than that of the inclined grooves 5, thereby making it possible to reduce the slip phenomena of the tread more surely.

(15) It is noted that there is a means to dispose a displaying part such as an arrow at a visible position on a tire outer surface as a means for indicating a rotational direction. Any forms or characters indicating a rotational direction may be adopted as this means, and an indication of a mounting position to a vehicle or an inside and outside expression are also acceptable.

(16) As the aforementioned, explanation has been made according to the illustrated examples. However, the present invention is not limited to the above mentioned embodiments but can be modified as necessary within the scope of claims. For example, the inclined grooves 5 in FIG. 1 extend from the tread ends 11 with an approximately fixed groove width and terminate short of the tire equator e. However, the inclined grooves 5 can be shaped in such a manner that the width thereof expands partly or tapers to a point. Moreover the inclined grooves 5 may cross the equator e and extend further. In addition, the inclined grooves 5 may be shaped in such a manner as to extend linearly from the tread ends 11 to the end edge or extend circularly. The point is that the majority of the inclined grooves 5 is disposed according to the above stated inclined configuration. The branch grooves may be also shaped in such a manner as to extend in zigzags or to extend in a curving line.

Example

(17) Next, the pneumatic tire according to the present invention has been produced for performance evaluation and results thereof will be explained hereafter. Each of conventional examples 1 and 2 and each of comparative examples 1, 2 and 3 has a tire size of 46/90R57.

(18) The pneumatic tire of Conventional example 1 is provided with the tread pattern shown in FIG. 2(a), in which the inclined grooves connect the tread ends mutually. And the pneumatic tire of Conventional example 2 has the tread patter shown in FIG. 2(b), in which, in addition to the tread patter of Conventional example 1, the branch grooves extend in the tire circumferential direction and divide the land portions.

(19) The tire of Comparative example 1 is provided with the tread pattern shown in FIG. 2(c). In the tread pattern of Comparative example 2 shown in FIG. 2 (d), the branch grooves in the tire circumferential direction are added to the tread pattern of Comparative example 1. In Comparative example 3 shown in FIG. 2(e), the branch grooves of the tire of Comparative example 2 terminate in the kick-out sides of the land portion blocks.

(20) Each tread pattern of Conventional examples 1 and 2, and each tread pattern of Comparative examples 1, 2 and 3 is provide with the following groove configuration as shown in the below table 1. Here, the term “Inclined groove depth” refers to a depth in a position in which a tread wear indicator is disposed, the term “Inclined groove length” refers to a length of a line connecting centers of a groove width and the term “Inclined groove angle” refers to an angle of the inclined groove with respect to the tire width direction. In addition, the term “Branch groove length” means a length of a line connecting centers of a groove width and the term “Branch groove angle” means an angle of the branch groove with respect to the tire width direction.

(21) TABLE-US-00001 TABLE 1 Conventional Conventional Comparative Comparative Comparative Example of example 1 example 2 example 1 example 2 example 3 invention Inclined groove depth (mm) 97 97 97 97 97 97 Inclined groove length (mm) 364 364 364 364 364 364 Left-right symmetry No No Yes Yes Yes Yes Inclined groove angle (α) — — 30° 30° 30° 30° Branch groove No Yes No Yes Yes Yes Branch groove length (mm) — 237 — 237 158 158 Branch groove angle (β) — 90° — 90° 90° 45° Wear resistance (index) 100 105 100 105 110 120
(Performance Evaluation Test)

(22) Each test tire as above stated is mounted on a rim (29.0×6.0) under the conditions of tire internal pressure: 700 kPa and load applied: 60,000 kg. After using as a front tire for a construction vehicle at a site of a mine for 1,000 hours, each result was subject to evaluation. The results thereof are shown in Table 1.

(23) The evaluation results of Table 1 show that the example tire of the present invention has improved in wear resistance. Moreover, it is clear that by disposing the branch grooves with an inclination and terminating the branch grooves within the land portions, wear resistance is also enhanced.

INDUSTRIAL APPLICABILITY

(24) Consequently, according to the present invention, it is possible to provide a pneumatic tire which improves in partial wear resistance by suppressing slipping both in the tire width and circumferential directions effectively without deteriorating in heat release property.

DESCRIPTION OF REFERENCE NUMERALS

(25) 1 Pneumatic tire 3 Tread portion 5 Inclined groove 9 Branch groove 11 Tread end R Tire rotational direction E Tire equator