TECHNICAL FIELD

The present technology relates to a pneumatic tire suitable as a tire used for driving on unpaved roads, and more specifically to a pneumatic tire that provides enhanced driving performance on unpaved roads and enhanced wear resistance performance.

BACKGROUND ART

For pneumatic tires used for driving on unpaved roads such as uneven ground, muddy ground, snowy roads, sandy ground, and rocky areas, a tread pattern is generally employed that is based on lug grooves or blocks including many edge components and that has a large groove area. For such a tire, driving performance on unpaved roads is improved by biting into mud, snow, sand, stone, rock, or the like (hereinafter, referred to collectively as “mud or the like”) on a road surface to achieve traction performance and preventing grooves from being blocked with mud or the like (for example, see Japan Unexamined Patent Publication No. 2009-220779).

However, in such a tire, the groove area is set to a large value in order to sufficiently bite into mud or the like, or a sipe is formed in each block in order to increase the number of edge components. Thus, there is a problem in that block rigidity is likely to decrease, leading to difficulty in providing both enhanced driving performance on unpaved roads (in particular, traction performance and starting performance) and securing wear resistance performance of the blocks in a compatible manner to a high degree. Thus, there is a demand for measures for effectively biting into mud or the like via grooves to improve driving performance on unpaved roads (in particular, muddy roads), while securing wear resistance performance of the blocks, and providing such performances in a well-balanced, compatible manner.

SUMMARY

The present technology provides a pneumatic tire suitable as a tire used for driving on unpaved roads, which provides enhanced driving performance on unpaved roads and enhanced wear resistance performance.

A pneumatic tire according to the present technology includes a tread portion extending in a tire circumferential direction and having an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged inward of the pair of sidewall portions in a tire radial direction, wherein the tread portion includes a plurality of longitudinal grooves extending in the tire circumferential direction, a plurality of lateral grooves extending in a tire lateral direction, and a plurality of blocks defined by the plurality of longitudinal grooves and the plurality of lateral grooves, at least three blocks of the plurality of blocks, which include an outermost block positioned on an outermost side in the tire lateral direction and are adjacent to each other in the tire lateral direction, and at least two longitudinal grooves positioned between the at least three blocks are present on a platform, which is raised from a groove bottom of each of the plurality of lateral grooves, has a flat top surface, and has a shape protruding toward both sides in the tire circumferential direction with respect to the at least three blocks, on a groove bottom of a longitudinal groove adjacent to the outermost block, a raised bottom portion raised from the groove bottom of the longitudinal groove is provided, and the raised bottom portion connects the outermost block and the block adjacent to the outermost block.

In the present technology, as described above, the platform is provided, and three or more blocks and the longitudinal grooves positioned therebetween are arranged on the platform. Thus, block rigidity can be enhanced, and wear resistance can be enhanced. Further, the outermost block in which uneven wear is likely to be caused is connected with the adjacent block by the raised bottom portion, and has further enhanced rigidity. Thus, uneven wear resistance can also be enhanced. Meanwhile, the platform and the raised bottom portion are provided, and thus recesses and protrusions in the grooves are increased. With this, an edge effect can be obtained with those recesses and protrusions. Further, the grooves are less likely to be clogged with mud and the like due to the increased recesses and protrusions, and hence discharge performance for mud and the like can be enhanced. With this, driving performance on unpaved roads (for example, mud performance) can be enhanced.

In the present technology, the platform preferably has a height from the groove bottom of the lateral groove, the height falling within a range from 5% to 25% of a maximum groove depth of the lateral groove. By setting the height of the platform to fall within an appropriate range as described above, the groove area of the lateral grooves is sufficiently secured, and satisfactory mud performance is obtained. At the same time, the platform secures block rigidity to enhance wear resistance. As a result, such performances can be achieved in a well-balanced, compatible manner.

In the present technology, a ratio of a total area of a road contact surface of the blocks present on the platform with respect to a projected area of the platform preferably falls within a range from 55% to 75%. With this, the platform and the blocks are well balanced, which is advantageous in achieving mud performance and wear resistance performance in a well-balanced, compatible manner.

In the present technology, at least a part of the platform preferably has a step-like structure including one or more steps between the groove bottom of the lateral groove and the top surface of the platform. With this, block rigidity can be secured efficiently with the platform while securing the groove area of the lateral grooves, which is advantageous in achieving mud performance and wear resistance performance in a well-balanced, compatible manner. Further, edge components are increased in the step-like portions, and hence mud performance can further be enhanced.

In the present technology, a cut portion having a V-shape in which an end enters the longitudinal groove is preferably formed in at least one part of the platform. With this, while securing rigidity of the plurality of blocks as a whole on the platform, the cut portion can enhance road surface followability of the individual blocks, which is advantageous in achieving mud performance and wear resistance performance in a well-balanced, compatible manner.

In this case, an angle α of the end of the cut portion preferably falls within a range from 5° to 120°. By setting the angle α as described above, the above-mentioned effect of enhancing road surface followability can be exerted satisfactorily.

In the present technology, the tire circumferential direction length of the raised bottom portion preferably falls within a range from 35% to 75% of the circumferential length of the longitudinal groove in which the raised bottom portion is provided. With this, the groove capacity of the longitudinal groove in which the raised bottom portion is provided is secured sufficiently, and at the same time, an effect of enhancing uneven wear resistance, which is exerted by the raised bottom portion, can be exerted more satisfactorily, which is advantageous in achieving such performances in a well-balanced, compatible manner.

In the present technology, when the raised bottom portion is viewed from the block road contact surface side, both end portions of the raised bottom portion in the tire circumferential direction are preferably bent to recess in a V-shape, and a bend angle β thereof preferably falls within a range from 60° to 170°. With this, the end portion shape of the raised bottom portion is satisfactory, which is advantageous in achieving mud performance and wear resistance performance (particularly, uneven wear resistance performance) in a well-balanced, compatible manner.

In the present technology, the raised bottom portion preferably has a height from the groove bottom of the longitudinal groove, the height falling within a range from 35% to 75% of a maximum groove depth of the longitudinal groove in which the raised bottom portion is formed. By setting the height of the raised bottom portion to fall within an appropriate range, the groove area of the longitudinal groove in which the raised bottom portion is provided can be secured sufficiently to achieve satisfactory mud performance, and an effect of enhancing uneven wear resistance due to the raised bottom portion can be obtained satisfactorily, which is advantageous in achieving such performances in a well-balanced, compatible manner.

“Length” in the present technology is the length in the tread contact surface unless otherwise noted. “Road contact surface” of each block is a surface portion of each block actually contacting a plane on which the tire is placed under a state in which the tire is assembled on a regular rim and inflated to a regular internal pressure, and does not include, for example, a chamfered portion that does not actually contact the plane. Additionally, “ground contact edge” refers to both ends in the tire axial direction in this state. “Regular rim” is a rim defined by a standard for each tire according to a system of standards that includes standards on which tires are based, and refers to a “standard rim” in the case of JATMA (Japan Automobile Tyre Manufacturers Association, Inc.), refers to a “design rim” in the case of TRA (The Tire and Rim Association, Inc.), and refers to a “measuring rim” in the case of ETRTO (European Tire and Rim Technical Organization). “Regular internal pressure” is an air pressure defined by standards for each tire according to a system of standards that includes standards on which tires are based, and refers to a maximum air pressure in the case of JATMA, refers to the maximum value in the table of “TIRE ROAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, and refers to the “INFLATION PRESSURE” in the case of ETRTO. “Regular internal pressure” is 180 kPa for a tire on a passenger vehicle. “Regular load” is a load defined by standards for each tire according to a system of standards that includes standards on which tires are based, and refers to a maximum load capacity in the case of JATMA, refers to the maximum value in the table of “TIRE ROAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, and refers to the “LOAD CAPACITY” in the case of ETRTO. “Regular load” is a load equivalent to 88% of the load described above for a tire on a passenger vehicle.

