Patent Grant
8851130
This application is a National Stage of International Application No. PCT/JP2008/059826 filed May 28, 2008, claiming priority based on Japanese Patent Application No. 2007-140896, filed May 28, 2007, the contents of all of which are incorporated herein by reference in their entirety.
The present invention relates to a tire having, in a tread portion, plural block land portion rows constituted of a large number of block land portions demarcated with plural circumferential grooves extending along tire circumferential direction and plural lateral grooves in communication with two adjacent circumferential grooves, in, particular, a tire for heavy load having such a tread construction. The present invention aims at enhancing wear resistance of the tire.
In general, a tire for heavy load has a relatively large aspect ratio and high rigidity of a belt to support considerable weight. Further, tread pattern is generally designed such that entire area of tread portion is provided with block land portions to enable the vehicles to run in various conditions.
A heavier load is exerted on the heavy load tire having such tread pattern as described above than a tire for vehicles in general. Therefore, uneven wear due to heel and toe wear tends to occur in running of the heavy load tire in proportion to the load exerted thereon. “Heel and toe wear” is relatively little wear loss at a leading edge (a portion brought into contact with the ground first) and relatively significant wear loss at a trailing edge (a portion brought into contact with the ground lastly), generated in the tire circumferential direction due to excessive deformation of the block land portions in rotation of the tire with a load exerted thereon. In view of this, there arises a problem that product life of tire with regard to wear is shortened due to occurrence of difference in wear in most cases between respective edges in the tire circumferential direction of each block land portion.
As countermeasures against uneven wear, a number of measures for suppressing uneven wear have been conventionally attempted. Examples of a presumably effective method include the method disclosed by JP 06-171318, in which a lateral groove demarcating block land portions is partially shallowed, i.e. a partially raised bottom portion is provided in the lateral groove, to enhance stress resisting collapse-deformation of block lad portions in the tire circumferential direction, suppress increase in driving force exerted per unit area of the tread portion and prevent uneven wear due to the collapse-deformation from occurring.
In general, since a tire for heavy load has a relatively large aspect ratio and high rigidity of belt, when the tire is rotated with a load exerted thereon, difference in displacement occurs between a belt portion and a tread portion, as shown in
Accordingly, an object of the present invention is to provide a tire in which wear resistance has been enhanced by optimizing the shape and location of the block land portion, while good uneven wear resistance is maintained.
In order to achieve the aforementioned object, the present invention provides a tire having plural rows of block land portions constituted of a number of block land portions by demarcation by providing plural circumferential groove extending along tire circumferential direction and lateral grooves in communication with adjacent two circumferential grooves is characterized in that: in at least two rows of block land portions adjacent to each other with a circumferential groove therebetween the respective rows of block land portions are disposed to be offset with respect to each other in the tire circumferential direction; the extending direction of the groove portion between the block land portions adjacent to each other in the tire widthwise direction is inclined with respect to the tire widthwise direction and tire circumferential direction; and a distance between the block land portions adjacent to each other in the tire widthwise direction is shorter than a distance between the block land portions adjacent to each other in the tire circumferential direction. In the present invention, a “groove portion” represents a part of a circumferential groove extending between block land portions adjacent to each other in the tire widthwise direction, and being “disposed to be offset with respect to each other” represents differentiating starting points of disposure pitch in the tire circumferential direction of the block land portions adjacent to each other in the tire widthwise direction, with each other, so that the ends in the circumferential direction of one row of block land portions are not aligned with the ends in the circumferential direction of another row of block land portions adjacent to the one row in the tire widthwise direction.
In this regard, the inventor of the present invention has discovered that, as a is result of decrease in the ground-contact area in a tread surface caused by increase in belt rigidity, shear force in the circumferential direction in tread kicking-out situation, during which sliding wear may occur, excessively increases and wear resistance of the tire deteriorates accordingly.
Yet further, a length of each block land portion in a section in the tire widthwise direction thereof preferably increases from the respective ends in the tire circumferential direction of the block land portion toward the center portion thereof. In the present invention, “the center portion of a block land portion” represents a region extending, by the length of 5 to 30% of the length in the tire circumferential direction of the block land portion, from the center position to the respective ends in the tire circumferential direction of the block land portion. In short, “the center portion of a block land portion” represents a region obtained by excluding, from an entire block land portion, areas ranging from the respective end portions in the tire circumferential direction to positions inward therefrom by 20% of the length of the block land portion in the tire circumferential direction.
Yet further, the ratio of a distance between block land portions adjacent to each other in the tire widthwise direction and a distance between block land portions adjacent to each other in the tire circumferential direction is preferably in the range of 1:0.85 to 1:0.3.
Yet further, the ratio of a distance between block land portions adjacent to each other in the tire circumferential direction and the length in the tire circumferential direction of a block land portion is preferably in the range of 1:0.25 to 1:0.05.
Yet further, the distance between the block land portions adjacent to each other in the tire widthwise direction is preferably in the range of 1.0 to 5.0 mm.
Yet further, the distance between the block land portions adjacent to each other in the tire circumferential direction is preferably in the range of 3.0 to 10.0 mm.
Yet further, the block land portion is preferably provided with a narrow groove which is in communication in the tire widthwise direction, with the two circumferential grooves each adjacent to the block land portion.
Yet further, the narrow groove provided in the block land portion preferably opens to the circumferential grooves at the center portion of the block land portion.
Yet further, the length in the tire circumferential direction of the narrow groove provided in the block land portion is preferably in the range of 5 to 20% of the groove depth of the lateral groove.
According to the present invention, it is possible to provide a tire, in which wear resistance has been enhanced by optimizing the shape and location of the block land portions.
a) is a view showing a block land portion in contact with the ground due to being pushed horizontally with respect to a road surface.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the tire of the present invention, as shown in
Yet further, as shown in
Further, the respective groove portions 6 in one block land portion 4 facing the same circumferential groove 2, which groove portions 6 are between the one block land portion and the other block land portion adjacent to each other in the tire widthwise direction, are preferably inclined with respect to the tire equatorial plane in directions opposite to each other. If the extending direction of the aforementioned groove portions 6 between the block land portions adjacent to each other in the tire widthwise direction were to be inclined with respect to the equatorial plane in the same direction, although sliding wear would be effectively prevented for an input from a certain direction, an input from other directions would not be effectively addressed and sliding wear derived from the input from other directions would not be successfully prevented. Further, since the inclined extending directions of the groove portions between the block land portion adjacent to each other in the tire widthwise direction described above are complementarily combined, in arrangement, with the inclinations of the walls of the block land portion 4 resulted from the shape in which the length of the block land portion 4 in a section in the tire widthwise direction thereof is increased toward the center portion 8 of the block land portion 4, a block pattern can be designed without creating meaningless spaces in the tire widthwise direction, such that wear resistance performance is effectively demonstrated without marring either the structures or effects resulted from the aforementioned two inclinations. Accordingly, a pattern designing by combining the aforementioned block pattern with a second rib, a shoulder rib, a lug and the like is made easy.
Yet further, the ratio of a distance d1 between block land portions adjacent to each other in the tire circumferential direction with respect to a distance d2 between block land portions adjacent to each other in the tire widthwise direction is preferably in the range of 1:0.85 to 1:0.3 and more preferably in the range of 1:0.7 to 1:0.4. In a case where the ratio of a distance d2 between block land portions adjacent to each other in the tire widthwise (circumference) direction with respect to a distance di between block land portions adjacent to each other in the tire circumferential direction is larger than 1:0.3, although the distance d1 between block land portions adjacent to each other in the tire circumferential direction is sufficient, the distance d2 between block land portions adjacent to each other in the tire widthwise direction is too short. Due to this, the block land portions 4 adjacent to each other in the tire widthwise direction are brought into contact with each other when the tire is rotated with a load exerted thereon and deforming force to collapse-deform is not effectively transferred from one block land portion 4 to another block land portion 4 adjacent thereto, whereby shear force in the block land portion 4 is not effectively dissipated and sliding wear may be resulted. In a case where the ratio of a distance d2 between block land portions adjacent to each other in the tire widthwise direction with respect to a distance d1 between block land portions adjacent to each other in the tire circumferential direction is smaller than 1:0.85, although the distance d2 between block land portions adjacent to each other in the tire widthwise direction is sufficient, the distance d1 between block land portions adjacent to each other in the tire circumferential direction is too short. Accordingly, the block land portions 4 are in contact with each other in the tire circumferential direction when these block land portions 4 are brought into contact with a road surface, whereby deformation due to expansion of rubber occurs, as shown in
Yet further, the ratio of the length d1 in the tire circumferential direction of the block land portion 4 with respect to a distance d1 between block land portions 4 adjacent to each other in the tire circumferential direction is preferably in the range of 1:0.25 to 1:0.05 and more preferably in the range of 1:0.17 to 1:0.07. In a case where the ratio of a distance di between block land portions 4 adjacent to each other in the tire circumferential direction with respect to the length d3 in the tire circumferential direction of the block land portion 4 exceeds 1:0.05, the block land portions 4 adjacent in the tire circumferential direction contact with each other too close when these block land portions 4 collapse-deform in rotation of the tire with a load exerted thereon. Accordingly, as shown in
Yet further, the distance d2 between the block land portions adjacent to each other in the tire widthwise direction is preferably in the range of 1.0 to 5.0 mm and more preferably in the range of 1.5 to 3.5 mm. In a case where the distance d2 between the block land portions exceeds 5.0 mm, the distance d2 between the block land portions adjacent to each other in the tire widthwise direction is too long. As a result, deformation force to collapse-deform one block land portion 4 cannot be transferred to another block laud portion 4 adjacent thereto in the widthwise direction, whereby excessive collapse-deformation in the tire circumferential direction of the one block land portion is caused and wear due to sliding of the block land portion 4 may be resulted. In a case where the distance d2 between the block land portions is shorter than 1.0 mm, the distance d2 between the block land portions adjacent to each other in the tire widthwise direction is too short. As a result, the block land portions 4 adjacent in the tire widthwise direction contact with each other when the tire is rotated with a load exerted thereon and deformation force to collapse-deform one block land portion 4 cannot be effectively transferred to another block land portion 4 adjacent thereto in the widthwise direction, whereby excessive collapse-deformation is caused and wear due to sliding of the block land portion 4 may be resulted.
Yet further, the distance d1 between the block land portions 4 adjacent to each other in the tire circumferential direction is preferably in the range of 3.0 to 10.0 mm and more preferably in the range of 4.0 to 8.0 mm. In a case where the distance d1 between the block land portions adjacent to each other in the tire circumferential direction exceeds 10.0 mm, the distance d1 between the block land portions adjacent to each other in the tire circumferential direction is too long. As a result, the ground-contact pressure of the block land portion 4 rises up excessively, possibly causing wear resistance to deteriorate. In a case where the distance d1 between the block land portions adjacent to each other in the tire circumferential direction is shorter than 3.0 mm, the distance d1 between the block land portions adjacent to each other in the tire circumferential direction is too short. As a result, the block land portions 4 contact with each other in the tire circumferential direction when these block land portions 4 are brought into contact with a road surface and deformation due to expansion of rubber as shown in
Yet further, as shown in
Yet further, the narrow groove 11 provided in the block land portion 4 preferably opens to the circumferential grooves 2 at the center portion 8 of the block land portion 4. In a case where the narrow groove 11 opens in a region other than the center portion 8 of the block land portion 4, gripping force as the driving force can no longer be dissipated with good balance within the block land portion 4, whereby there is a possibility that torque from the engine cannot be efficiently converted into driving force.
Yet further, the length in the tire circumferential direction of the narrow groove 11 provided in the block land portion 4 is preferably in the range of 5 to 20% and more preferably in the range of 7 to 18% of the groove depth (depth in the radial direction) of the lateral groove 3. In a case where the length in the tire circumferential direction of the narrow groove 11 is shorter than 5% of the groove depth of the lateral groove 3, the length in the tire circumferential direction of the narrow groove 11 is too short. As a result, gripping force from the leading edge 10 toward the trailing edge 9 deteriorates to the level of gripping force observed in a case where no narrow groove is provided in the block land portion 4, possibly rendering provision of the narrow groove 11 meaningless. In a case where the length in the tire circumferential direction of the narrow groove 11 exceeds 20% of the groove depth of the lateral groove 3, the length in the tire circumferential direction of the narrow groove 11 is too long. As a result, the block land portions 4, each of which is sectioned into sub-portions by the narrow groove 11, can no longer transfer force by reaction between the block land portions 4, whereby excessive collapse-deformation may occur, followed by sliding wear due to the deformation. In order to obtain a satisfactory effect until the final stage of wear, the groove depth of the narrow groove 11 in the block land portion 4 is preferably 60 to 100% of the groove depth of the lateral groove 3.
The foregoing descriptions only explain a part of the embodiments of the present invention. The structures described above may be combined with each other or subjected to various modification, unless such combination or modification digresses the spirit of the present invention. For example, although the tire having the structure as shown in
Next, there were produced pneumatic tires according to the present invention (Example tires 1 to 8), pneumatic tires having conventional tread pattern (Conventional Example tire), and pneumatic tires having the same structure as the pneumatic tire of the present invention, except that the distance between the block land portions is beyond the scope of the present invention (the Comparative example tire), as test tires (pneumatic tires for heavy load having tire size of 495145R22.5), respectively, and performances thereof were evaluated as described below.
Examples tires 1 to 8 are pneumatic tires having tread portions corresponding to
As shown in
Measurement was made by: assembling each of the test tires with a rim having size of 17.00×22.5 to obtain a tire wheel; mounting, as a driving wheel, each tire wheel thus obtained to a tractor vehicle for use in the tests; applying an air pressure of 900 kPa (relative pressure) and a load of 57 kN to the tires; and measuring wear amount in center portion of block land portion after running the vehicle for 50000 km on the highway. The wear resistance was then evaluated by: using the wear amount by the Comparative Example tire as the reference value and expressing the wear amount of other tires as relative values thereto (comparing Example tire: 100), and comparing the results thus obtained. The smaller value of the wear amount represents the better wear resistance. The results are shown in Table 2,
As is obvious from the results shown in Table 2, due to the optimization of distance between the block land portions adjacent to each other in the tire circumferential direction and widthwise direction, wear amount in center portion of block land portion was smaller in the tires of Examples 1 to 8, as compared with the tires of Conventional Example and Comparative Example. Further, due to optimization of shape of block land portion, in the tires of Examples 3, 4, and 6 to 8, wear amount were particularly small and wear resistance is effectively enhanced. In Example tires 6 to 8, due to the enhancement of gripping force by providing narrow groove in block land portion, in particular, wear resistance is improved, as compared with the tires of Examples 1 and 2.
As is obvious from the foregoing descriptions, according to the present invention, it is possible to provide a tire, in which wear resistance has been enhanced by optimizing the shape and location of the block land portions.
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|---|---|---|---|
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|---|---|---|---|---|
| PCT/JP2008/059826 | 5/28/2008 | WO | 00 | 12/11/2009 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2008/146851 | 12/4/2008 | WO | A |
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| Number | Date | Country | |
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