JP7095374B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire suitable as a heavy load pneumatic tire, and more particularly to a pneumatic tire having improved snow traction performance while maintaining good running performance and uneven wear resistance on unpaved roads.

Heavy-duty pneumatic tires used for construction vehicles such as dump trucks are mainly required to have excellent running performance (traction performance) on unpaved roads. Therefore, a block-based tread pattern having a large number of lug grooves extending in the tire width direction is adopted (see, for example, Patent Document 1).

On the other hand, in recent years, the required performance for various tires has been increasing, and even for the above-mentioned tires, it is required to improve not only the running performance on unpaved roads but also the traction performance on snow. Furthermore, tires such as those described above cause uneven wear due to the fact that the tread pattern is block-based, the frequency of braking and driving is high due to the conditions of use, and the frequency of sharp curve driving is also high. Since it tends to be easy, it is required to maintain or improve the uneven wear resistance as well.

Japanese Patent No. 4676959

An object of the present invention is to provide a pneumatic tire having improved traction performance on snow while maintaining good running performance and uneven wear resistance on unpaved roads.

The pneumatic tire of the present invention for achieving the above object has a tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and these sidewall portions. In a pneumatic tire having a pair of bead portions arranged inside in the tire radial direction and whose rotation direction is specified, the tread portion extends on the tire equatorial line along the tire circumferential direction over the entire circumference of the tire. One narrow groove is formed, and a plurality of lug grooves extending from the narrow groove toward the outside in the tire width direction and reaching the tread end are formed on both sides of the tire equatorial line at intervals in the tire circumferential direction. The end of the lug groove communicating with the narrow groove is located on the stepping side of the end of the lug groove on the tread end side, and the distance in the tire width direction from the tire equatorial line to the tread end is W, and the tire is tired. The first region is the region between the 0.25W distance from the equator in the tire width direction and the tire equator, and the 0.25W distance from the tire equator in the tire width direction and 0.50W in the tire width direction from the tire equator. The region between the separated positions is the second region, and the region between the position 0.50 W away from the tire equatorial line in the tire width direction and the position 0.75 W away from the tire equatorial line in the tire width direction is the third region. When the region between the position separated from the tire equatorial line by 0.75 W in the tire width direction and the tread end is the fourth region, the lug grooves adjacent to each other in the tire circumferential direction are connected to the second to third regions. An auxiliary groove extending along the tire circumferential direction is formed, and a plurality of blocks are partitioned by the narrow groove, the lug groove, and the auxiliary groove, and the center of the plurality of blocks located on the tire equatorial side is located. A shallow groove terminating in the tread is provided on the tread of the block, and the shallow groove extends at least from the outer edge of the tread of the center block on the tread side and extends along the shape of the outer edge of the tread. The lug groove includes the kick-out side groove portion extending along the shape of the kick-out side outer edge and separated from the kick-out side outer edge of the tread of the center block, and the lug groove is the said in the first region. The average angle of the lug groove with respect to the tire circumferential direction in the second region is smaller than the average angle of the lug groove with respect to the tire circumferential direction, and the third is smaller than the average angle of the lug groove with respect to the tire circumferential direction in the second region. It is characterized in that it is curved or bent so that the average angle of the lug groove in the region and the fourth region with respect to the tire circumferential direction becomes large .

In the present invention, in order to secure traction performance on unpaved roads, a center that greatly contributes to traction performance on snow in a block-based pattern in which a plurality of blocks are divided by fine grooves, lug grooves, and auxiliary grooves as described above. Since the shallow groove is provided on the tread surface of the block as described above, the traction performance on snow can be efficiently improved by the edge effect of the groove component in the tire width direction (that is, the stepping side groove portion and the kicking side groove portion). .. At this time, the shallow groove is terminated in the tread surface of the block, and both the stepping gutter and the kicking gutter extend along the shape of the outer edge while being separated from the outer edge of the center block. It is possible to suppress the decrease in the gutter and maintain good uneven wear resistance.

In the present invention, it is preferable that at least a part of the stepping side groove portion and the kicking side groove portion overlap when the stepping side groove portion and the kicking side groove portion are projected in the tire circumferential direction. As a result, the groove component in the tire width direction of the shallow groove can be sufficiently secured, which is advantageous for improving the traction performance on snow.

In the present invention, it is preferable that the distance between the center block of the stepping gutter and the outer edge of the stepping side is 8 mm to 12 mm. As a result, it is possible to surely prevent the block rigidity from being lowered due to the shallow groove, which is advantageous for maintaining good uneven wear resistance.

In the present invention, the shallow groove extends along the shape of the outer edge of the center block in the tire width direction by connecting the stepping side groove portion, the kicking side groove portion, and the outer ends in the tire width direction. It is preferably composed of three elements with the connecting groove portion. By forming the shallow groove into a substantially U-shape along the shape of the outer edge of the block as a whole in this way, it is possible to secure a well-balanced groove component in the tire width direction and a groove component in the tire circumferential direction of the shallow groove. It is advantageous for improving traction performance on snow and ensuring stability during traction.

In the present invention, the tread of a shoulder block located on the tread end side of a plurality of blocks may be provided with a shallow groove extending along the tire width direction, having at least one bent portion, and terminating in the tread. preferable. As a result, the edge component due to the shallow groove can be secured even in the region outside the tire width direction of the tread portion, which is advantageous for improving the traction performance on snow.

In the present invention, the groove depth of the shallow groove is preferably 1 mm to 3 mm. As a result, it is possible to effectively obtain the effect of improving the traction performance by the shallow groove while maintaining the block rigidity at an appropriate level and maintaining good uneven wear resistance.

In the present invention, the angle of the auxiliary groove with respect to the tire circumferential direction is preferably 10 ° to 20 °. As a result, the groove component in the tire circumferential direction can be reliably added by the auxiliary groove, the tire can be prevented from laterally shifting during traction, and the stability can be improved.

In the present invention, as described above, the lug groove has a smaller average angle of the lug groove with respect to the tire circumferential direction in the second region than the average angle of the lug groove with respect to the tire circumferential direction in the first region, and the lug in the second region. It is curved or bent so that the average angle of the lug groove with respect to the tire circumferential direction in the third region and the fourth region is larger than the average angle of the groove with respect to the tire circumferential direction . By bending or bending the lug groove in this way, it is possible to improve the traction performance on unpaved roads and improve the low noise performance. That is, since the average angle of the lug groove with respect to the tire circumferential direction is relatively large in the first region near the tire equator and the third to fourth regions near the tread end, it is possible to sufficiently secure the component in the tire width direction. It can improve the traction performance. On the other hand, in the second region, the average angle of the lug groove with respect to the tire circumferential direction becomes small, and the entire lug groove is curved or bent as described above, so that the generation of air column resonance noise can be suppressed. Moreover, since it is possible to suppress the emission of noise from the inside of the vehicle to the outside of the vehicle through the lug groove, it is possible to improve the low noise performance.

In the present invention, the average angle of the lug groove with respect to the tire circumferential direction in the second region is 28 ° to 38 °, and the average angle of the lug groove with respect to the tire circumferential direction in the first region and the tire of the lug groove in the second region. The difference from the average angle with respect to the circumferential direction is 35 ° or more and 45 ° or less, and the difference between the average angle of the lug groove with respect to the tire circumferential direction in the second region and the average angle of the lug groove with respect to the tire circumferential direction in the third region is 35. It is preferably ° or more and 45 ° or less. By setting the average angle of each part of the lug groove in this way, the curved or bent shape of the lug groove becomes good, which is advantageous for ensuring the traction performance on the unpaved road. In addition, it is possible to improve low noise performance by suppressing the generation of air column resonance sound and the propagation of noise through the groove.

In the present invention, it is preferable that the angle of the corner portion on the stepping side of the center block and the equator side of the tire on the tread tread is 60 ° to 75 °. As a result, the rigidity of the stepping side of the center block can be reduced, and the hitting sound due to the block can be reduced, which is advantageous for improving the low noise performance.

In the present invention, it is preferable that the corners on the stepping side and the equator side of the tire of the center block are chamfered. As a result, the ground pressure of the center block becomes uniform, and uneven wear at the initial stage of wear can be suppressed.

In the present invention, on the tread tread surface, the contour line on the tread side between the corner portion on the stepping side and the equator side of the tire and the corner portion on the kicking side and the outer side in the tire width direction becomes convex toward the outside of the block. It is preferably an arc. As a result, the hitting sound produced by the center block can be dispersed, which is advantageous for improving the low noise performance.

In the present invention, on the tread tread, the contour line on the tire equator side of the center block is inclined so that the distance between the tire equator side contour line and the tire equator is larger on the kicking side than on the stepping side. preferable. As a result, the groove width of the fine groove can be varied to suppress the generation of air column resonance sound generated in the fine groove, which is advantageous for improving the low noise performance.

In the present invention, the groove depth of the auxiliary groove is preferably 75% to 85% of the groove depth of the lug groove. By making the auxiliary groove shallower than the lug groove in this way, the rigidity of the block adjacent to the auxiliary groove can be increased, which is advantageous for improving the traction performance.

In the present invention, the groove depth between the blocks of the fine grooves is preferably 15% to 85% of the groove depth of the lug groove. By providing the narrow groove with a region shallower than the lug groove in this way, the rigidity of the block adjacent to the fine groove can be increased, which is advantageous for improving the traction performance.

In the present invention, the groove depth of the lug groove is preferably 15 mm to 25 mm. Further, it is preferable that the JIS-A hardness of the tread rubber constituting the tread portion is 61 to 65, and the modulus at 100% elongation is 2.0 MPa to 2.8 MPa. INDUSTRIAL APPLICABILITY The present invention can exhibit particularly excellent performance in terms of traction performance, uneven wear resistance performance, and low noise performance in a heavy-duty pneumatic tire having such characteristics. In the present invention, the "JIS-A hardness" is a hardness measured using a type A durometer at a temperature of 23 ° C. in accordance with the durometer hardness test specified in JIS K6253. The "modulus at 100% elongation" is a value measured under each condition of a tensile speed of 500 mm / min and a temperature of 23 ° C. using a No. 3 type dumbbell test piece in accordance with JIS K6251.

In the present invention, the "tread ends" are both ends of the tread pattern portion of the tire in a state where the tire is rim-assembled on a regular rim, the regular internal pressure is applied, and no load is applied (no load state). The "distance W in the tire width direction from the tire equatorial line to the tread end" in the present invention is a tread expansion width (specified by JATTA) which is a linear distance between the tread ends measured along the tire width direction in the above-mentioned state. It corresponds to 1/2 of the "tread width"). The "regular rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, JATTA is a standard rim, TRA is "DesignRim", or ETRTO. If so, it is set to "Measuring Rim". "Regular internal pressure" is the air pressure defined for each tire in the standard system including the standard on which the tire is based. The maximum value described in "COLD INFLATION PRESSURES" is "INFLATION PRESSURE" for ETRTO, but 180 kPa when the tires are for passenger cars.

It is a meridian sectional view of the pneumatic tire which comprises embodiment of this invention. It is a front view which shows the tread surface of the pneumatic tire which comprises embodiment of this invention. It is explanatory drawing which enlarges and shows the center block of FIG. It is explanatory drawing which shows typically another embodiment of the shallow groove of this invention. It is a front view which shows an example of the tread surface of the conventional example pneumatic tire.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the pneumatic tire of the present invention is arranged inside the tread portion 1, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and the sidewall portion 2 in the tire radial direction. It is provided with a pair of bead portions 3. In FIG. 1, reference numeral CL indicates a tire equator, and reference numeral E indicates a tread end. In the illustrated example, the tread end E coincides with the tire width outer edge of the outermost block in the tire width direction (the edge formed by the tread of the outermost block in the tire width direction and the outer side surface in the tire width direction). ing. Although FIG. 1 is a cross-sectional view of the meridian, it is not depicted, but the tread portion 1, the sidewall portion 2, and the bead portion 3 each extend in the tire circumferential direction to form an annular shape, whereby the toroidal of the pneumatic tire is formed. The basic structure of the shape is constructed. Hereinafter, the description using FIG. 1 is basically based on the illustrated meridian cross-sectional shape, but each tire component extends in the tire circumferential direction to form an annular shape.

A carcass layer 4 is mounted between the pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inside to the outside of the vehicle around the bead core 5 arranged in each bead portion 3. Further, a bead filler 6 is arranged on the outer periphery of the bead core 5, and the bead filler 6 is wrapped by a main body portion and a folded portion of the carcass layer 4. On the other hand, a plurality of layers (four layers in FIG. 1) of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to intersect each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cord with respect to the tire circumferential direction is set to, for example, in the range of 10 ° to 60 °. Although not adopted in the pneumatic tire of FIG. 1, in the present invention, a belt reinforcing layer (not shown) may be further provided on the outer peripheral side of the belt layer 7. When the belt reinforcing layer is provided, the belt reinforcing layer includes, for example, an organic fiber cord oriented in the tire circumferential direction, and the angle of the organic fiber cord with respect to the tire circumferential direction can be set to, for example, 0 ° to 5 °.

A tread rubber layer R1 is arranged on the outer peripheral side of the carcass layer 4 and the belt layer 7 in the tread portion 1. A side rubber layer R2 is arranged on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the sidewall portion 2. The rim cushion rubber layer R3 is arranged on the outer peripheral side (outside in the tire width direction) of the carcass layer 4 in the bead portion 3. The tread rubber layer R1 may have a structure in which two types of rubber layers (cap tread rubber layer and under tread rubber layer) having different physical properties are laminated in the tire radial direction.

The present invention is applied to such a general pneumatic tire, but the cross-sectional structure thereof is not limited to the above-mentioned basic structure. The present invention is mainly intended to be used as a pneumatic tire for heavy loads, and in that case, the rubber composition constituting the tread rubber layer R1 has a JIS-A hardness of 61 to 65 and is 100%. It is preferable to use a rubber composition having a modulus at the time of stretching of 2.0 MPa to 2.8 MPa.

As shown in FIG. 2, on the surface of the tread portion 1 of the pneumatic tire of the present invention, one narrow groove 11 extending along the entire circumference of the tire along the tire circumferential direction is provided on the equator CL of the tire. Will be. The fine groove 11 has a groove width of, for example, 4 mm to 10 mm and a groove depth of, for example, 5 mm to 25 mm, and is a groove having a groove width smaller than that of the lug groove 12, which will be described later.

On both sides of the tire equator CL, a plurality of lug grooves 12 extending from the narrow grooves 11 toward the outside in the tire width direction and reaching the tread end E are formed at intervals in the tire circumferential direction. In each lug groove 12, the end portion communicating with the narrow groove 11 is located on the stepping side of the end portion on the tread end E side. That is, the pneumatic tire of the present invention is a tire in which the rotation direction R is specified, but each lug groove 12 is inclined in the direction opposite to the rotation direction R from the tire equator CL side toward the outside in the tire width direction. .. The lug groove 12 is a groove having a groove width of, for example, 13 mm to 30 mm and a groove depth of, for example, 15 mm to 25 mm.

Further, an auxiliary groove 13 extending along the tire circumferential direction is formed so as to connect the lug grooves 12 adjacent to each other in the tire circumferential direction. As shown in FIG. 2, each auxiliary groove 13 has a distance in the tire width direction from the tire equatorial line CL to the tread end E as W, a position separated from the tire equatorial line CL by 0.25 W in the tire width direction, and the tire equatorial line CL. The region between them is defined as the first region A, and the region between the position separated from the tire equatorial CL by 0.25 W in the tire width direction and the region between the position separated from the tire equatorial CL by 0.50 W in the tire width direction is the second region B. The region between the position 0.50 W away from the tire equatorial CL in the tire width direction and the position 0.75 W away from the tire equatorial CL in the tire width direction is defined as the third region C, and the tire width direction from the tire equatorial CL. When the region between the position separated by 0.75 W and the tread end E is the fourth region D, the tires are arranged in the second region B to the third region C.

The tread portion 1 is divided into a plurality of blocks by the fine groove 11, the lug groove 12, and the auxiliary groove 13. In the following description, among these blocks, the block divided by the narrow groove 11, the lug groove 12, and the auxiliary groove 13 and located on the tire equatorial CL side is the center block 21, the fine groove 11, the lug groove 12, and the auxiliary groove 13. The block partitioned by and located on the Tread end E side is called a shoulder block 22.

As shown in an enlarged view in FIG. 3, the tread surface of the center block 21 is provided with a shallow groove 30 terminating in the tread surface of the center block 21. The shallow groove 30 is a groove having a smaller groove depth than the above-mentioned fine groove 11, lug groove 12, and auxiliary groove 13, and the groove depth of the shallow groove 30 is, for example, 1 mm to 3 mm. The shallow groove 30 is separated from the outer edge of the tread side of the center block 21 and extends along the shape of the outer edge of the tread side, and the stepping gutter portion 31 and the kicking side of the tread surface of the center block 21. It includes a kick-out gutter 32 that is separated from the outer edge and extends along the shape of the kick-out side outer edge. In the examples of FIGS. 2 and 3, the shallow groove 30 connects the outer ends of the stepping gutter 31 and the kicking gutter 32 in the tire width direction to each other to connect the outer edges of the center block 21 in the tire width direction. It also includes a connecting groove portion 33 extending along the shape of the above, and has a substantially U-shape composed of three elements of a stepping side groove portion 31, a kicking side groove portion 32, and a connecting groove portion 33.

In the present invention, in order to ensure traction performance on an unpaved road, a block-based tone in which a plurality of blocks (center block 21 and shoulder block 22) are partitioned by a fine groove 11, a lug groove 12, and an auxiliary groove 13 as described above. In the pattern, since the shallow groove 30 is provided on the tread surface of the center block 21 which greatly contributes to the traction performance on snow as described above, the groove component in the tire width direction (that is, the stepping side groove portion 31 and the kicking side groove portion 32). The edge effect of can effectively improve the traction performance on snow. At this time, since the shallow groove 30 is terminated in the tread of the block and extends along the shape of the outer edge while being separated from the outer edge of the center block 21, it is possible to suppress a decrease in block rigidity due to the shallow groove 30. Uneven wear resistance can be maintained well.

At this time, if the shallow groove 30 is opened in any of the narrow groove 11, the lug groove 12, and the auxiliary groove 13 without terminating in the tread of the block, it becomes difficult to sufficiently secure the rigidity of the center block 21. , It becomes difficult to maintain good uneven wear resistance. In addition, the block is easily deformed during traction, making it difficult to secure the edge effect. If the shallow groove 30 does not include the above-mentioned stepping side groove portion 31 and the kicking side groove portion 32, the groove component in the tire width direction cannot be secured, and the effect of improving the traction performance on snow cannot be sufficiently expected.

Since the shallow groove 30 only needs to have at least the stepping gutter portion 31 and the kicking gutter portion 32, for example, as shown in FIG. 4A, only the stepping gutter portion 31 and the kicking gutter portion 32 are included. It may be a structure. In other words, the structure may be such that a pair of divided shallow grooves 30 (stepping side groove portion 31 and kicking side groove portion 32) are provided on the tread surface of one center block 21. Further, as shown in FIG. 4B, in addition to the stepping side groove portion 31, the kicking side groove portion 32, and the connecting groove portion 33, the inner ends of the stepping side groove portion 31 and the kicking side groove portion 32 in the tire width direction are further provided. The structure may include a second connecting groove portion 34 that connects the portions and extends along the shape of the outer edge of the center block 21 on the inner side in the tire width direction. In this structure, the shallow groove 30 has a substantially square shape along the shape of the outer edge of the center block 21. In any case, by having the stepping side groove portion 31 and the kicking side groove portion 32, the groove component in the tire width direction of the shallow groove 30 can be secured, so that the traction performance on snow can be effectively improved. Can be done. As shown in FIG. 3, the shallow groove 30 has a substantially U-shape including a stepping-side groove portion 31, a kick-out side groove portion 32, and a connecting groove portion 33, which is a block rigidity and a groove component in the tire width direction. It is effective to improve the balance with the groove component in the circumferential direction and to achieve both traction performance on snow and uneven wear resistance.

As described above, the stepping side groove portion 31 and the kicking side groove portion 32 constituting the shallow groove 30 increase the groove component in the tire width direction to improve the traction performance on snow, so that each of them is in the tire circumferential direction. It is preferable to increase the amount of the groove component in the tire width direction so that at least a part of the stepping side groove portion 31 and the kicking side groove portion 32 overlap each other when projected. As a result, the groove component of the shallow groove 30 in the tire width direction can be sufficiently secured, which is advantageous for improving the traction performance on snow.

As described above, the shallow groove 30 extends while being separated from the outer edge of the center block 21, but in particular, the separation distance of the stepping gutter 31 from the outer edge of the stepping side of the center block 21 is 8 mm to 12 mm. preferable. By appropriately separating the stepping gutter portion 31 from the outer edge of the block in this way, it is possible to reliably prevent the block rigidity from being lowered by the shallow groove 30, which is advantageous for maintaining good uneven wear resistance. Become. The distance from the outer edge of the block of other parts of the shallow groove 30 is not particularly limited, but the distance from the outer edge of the kicking side of the center block 21 to the kicking side groove portion 32 may be, for example, 5 mm or more. .. When the connecting groove portions 33 and 34 are provided, the distance between the connecting groove portions 33 from the outer outer edge of the center block 21 in the tire width direction is, for example, 5 mm or more, and the connecting groove portion from the inner outer edge of the center block 21 in the tire width direction. The separation distance of 34 may be, for example, 5 mm or more.

As described above, the shallow groove 30 is for improving the traction performance on snow, and it is effective to provide the shallow groove 30 on the tread surface of the center block 21 which greatly contributes to the traction performance on snow, but further, the tread surface of the shoulder block 22. A shallow groove (hereinafter referred to as a shoulder shallow groove 40) may be provided in the shallow groove. The shape of the shoulder shallow groove 40 is not particularly limited, and various modes can be adopted depending on the shape of the shoulder block 40. In order to further improve the traction performance on snow, it is preferable that the shoulder shallow groove 40 extends along the tire width direction, has at least one bent portion, and terminates in the tread. As a result, the edge component can be increased also in the shoulder block 22 (that is, the region outside the tire width direction of the tread portion 1) while maintaining the rigidity of the shoulder block 22, which is advantageous for improving the traction performance on snow. become.

The groove depth of the shallow groove 30 is preferably set to 1 mm to 3 mm as described above. With a groove depth of this degree, it is possible to effectively obtain the effect of improving the traction performance by the shallow groove while maintaining the block rigidity at an appropriate level and maintaining good uneven wear resistance. If the groove depth of the shallow groove 30 is less than 1 mm, the shallow groove 30 is too shallow and the edge effect of the shallow groove 30 cannot be sufficiently secured. If the groove depth of the shallow groove 30 exceeds 3 mm, the block rigidity is lowered and it becomes difficult to maintain good uneven wear resistance. When the shoulder shallow groove 40 is provided, it is preferable that the groove depth of the shoulder shallow groove 40 is also set to 1 mm to 3 mm.

Since the present invention mainly improves the traction performance on snow by the shallow groove 30 (shoulder shallow groove 40) as described above, the center block 21 and the shoulder block 22 are mainly provided by the fine groove 11, the lug groove 12, and the auxiliary groove 13. As long as the tread pattern is mainly a block in which and is partitioned, the specific structure of the various grooves and blocks is not limited to the illustrated embodiment. However, in order to obtain good performance (particularly, traction performance on unpaved roads) as a heavy-duty pneumatic tire intended to apply the present invention, it is preferable to adopt the following structure.

In each lug groove 12, the average angle θb of the lug groove 12 with respect to the tire circumferential direction in the second region B is smaller than the average angle θa of the lug groove 12 with respect to the tire circumferential direction in the first region A, and the lag in the second region B The lug groove 12 is curved or bent so that the average angle θcd of the lug groove 12 in the third region C and the fourth region D with respect to the tire circumferential direction is larger than the average angle θb of the groove 12 with respect to the tire circumferential direction. preferable. In other words, each lug groove 12 has a smooth curved shape from the tire equator CL to the tread end E, and there is an inflection point in the second region B or the third region C where the direction of the curve is reversed. There is one, or there are two bending points in the second region B or the third region C, with a bending shape that is bent twice from the tire equator CL to the tread end E. It is good to be there.

The average angle of the lug grooves 12 can be obtained as an angle formed by a straight line connecting the midpoints of the lug grooves 12 in the groove width direction at the boundary position of each region with respect to the tire circumferential direction. However, for the first region A and the fourth region D, as shown in the figure, the midpoint of the extension line of the lug groove 12 drawn toward the tire equator CL or the tread end E at the tire equator CL or the tread end E is used. It shall be. Further, the average angle (for example, the average angle θcd) straddling the two regions is the midpoint in the groove width direction of the lug groove 12 at the boundary position on the tire equator CL side of the third region C and the tread of the fourth region D. It can be obtained as an angle formed by a straight line connecting the midpoint in the width direction of the lug groove 12 at the boundary position on the end E side (that is, the tread end E) with respect to the tire circumferential direction.

In this way, by bending or bending the lug groove 12 at an appropriate angle with respect to the tire circumferential direction in each of the first to fourth regions A to D, the traction performance on an unpaved road is improved. , Low noise performance can be improved. That is, the average angle of the lug groove 12 with respect to the tire circumferential direction is relatively large in each of the first region A near the tire equator CL and the third to fourth regions C and D near the tread end E, so that the tire width direction The groove component of the tire can be sufficiently secured, and the traction performance can be improved. On the other hand, in the second region B, the average angle of the lug groove 12 with respect to the tire circumferential direction becomes small, and the entire lug groove 12 is curved or bent as described above, so that the generation of air column resonance noise is suppressed. Moreover, it is possible to suppress the emission of noise from the inside of the vehicle to the outside of the vehicle through the lug groove 12, so that the low noise performance can be improved.

In setting the angle of the lug groove 12 as described above, the difference between the average angle θa of the lug groove 12 with respect to the tire circumferential direction in the first region A and the average angle θb of the lug groove 12 with respect to the tire circumferential direction in the second region B. Is preferably 35 ° or more and 45 ° or less. Similarly, the difference between the average angle θb of the lug groove 12 with respect to the tire circumferential direction in the second region B and the average angle θc of the lug groove 12 with respect to the tire circumferential direction in the third region C is 35 ° or more and 45 ° or less. preferable. By setting the angle difference of the lug groove 12 between the regions to an appropriate range in this way, the lug groove 12 can be appropriately curved or bent while sufficiently securing the groove component in the tire width direction of the lug groove 12. This is advantageous for improving low noise performance while ensuring traction performance. At this time, if these angle differences are less than 35 °, they are substantially equivalent to a groove that is not curved or bent, and the effect of improving low noise performance cannot be sufficiently obtained. If these angle differences exceed 45 °, the curvature or bending of the lug groove 12 becomes too large, and it becomes rather difficult to secure a good balance between the tire width direction component and the tire circumferential direction component of the lug groove 12, and the unpaved road. It becomes difficult to improve the traction performance and the low noise performance in a well-balanced manner.

The average angle of each region can be appropriately set depending on the performance to be emphasized in the tire, but the average angle θa of the lug groove 12 in the first region A with respect to the tire circumferential direction is, for example, 70 ° to 85 °, and the second region B. The average angle θb of the lug groove 12 with respect to the tire circumferential direction in the third region C is, for example, 30 ° to 40 °, the average angle θc of the lug groove 12 with respect to the tire circumferential direction in the third region C is, for example, 70 ° to 80 °, and the lag in the fourth region D. The average angle θd of the groove 12 with respect to the tire circumferential direction may be set to, for example, 75 ° to 85 °. Among these angles, setting the average angle θb of the lug groove 12 in the second region B with respect to the tire circumferential direction is effective for improving the low noise performance, and more preferably the average angle θb is 28 ° to 38 °. It is good to set to. By setting the average angle in this way, the curved or bent shape of the lug groove 12 becomes better, which is advantageous for improving the traction performance and the low noise performance in a well-balanced manner. If the average angle θb is less than 28 °, the curvature or bending of the lug groove 12 becomes too large, and it becomes rather difficult to secure the tire width direction component and the tire circumferential direction component of the lug groove 12 in a well-balanced manner. It becomes difficult to improve the traction performance and low noise performance on paved roads in a well-balanced manner. If the average angle θb exceeds 38 °, it becomes difficult to appropriately bend or bend the lug groove 12, and the effect of improving low noise performance cannot be sufficiently obtained.

As described above, when the auxiliary groove 13 is provided, it is preferable to arrange the auxiliary groove 13 in the second region B to the third region C. For example, in the illustrated example, the auxiliary groove 13 is provided in the second region B. Further, it is preferable that the angle α of the auxiliary groove 13 with respect to the tire circumferential direction is set to 10 ° to 20 °. By providing the auxiliary groove 13 in this way, it is possible to reliably secure the groove component in the tire circumferential direction, prevent the tire from laterally shifting during traction, and improve stability. When the auxiliary groove 13 is formed in the first region A, the center block 21 becomes relatively small, and when the auxiliary groove 13 is formed in the fourth region D, the shoulder block 22 becomes relatively small. Since it becomes difficult to secure the rigidity of the relatively small block, the traction performance may be affected. When the angle α of the auxiliary groove 13 is less than 10 °, the component in the tire width direction obtained by the auxiliary groove 13 is substantially eliminated, so that the improvement of the traction performance by the auxiliary groove 13 cannot be expected. When the angle α of the auxiliary groove 13 exceeds 20 °, it becomes difficult for the auxiliary groove 13 to efficiently add the component in the tire circumferential direction, and the effect of improving the stability during traction is limited.

In the present invention, the shape of the block (center block 21, shoulder block 22) formed in the tread portion 1 is as long as it is the shape obtained by the configuration of the above-mentioned grooves (fine groove 11, lug groove 12, auxiliary groove 13). Although not particularly limited, the center block 21 is preferably configured as follows in order to improve the noise performance. That is, the angle β of the corner portion on the stepping side of the center block 21 and the tire equatorial CL side on the block tread may be set to 60 ° to 75 °. As a result, the rigidity of the stepping side of the center block 21 can be reduced, and the hitting sound due to the block can be reduced, which is advantageous for improving the low noise performance. If the angle β is less than 60 °, the corner portion may become too sharp and the durability of the block itself may be affected. When the angle β exceeds 75 °, the effect of reducing the rigidity of the stepping side of the center block 21 is limited, and it becomes difficult to efficiently improve the low noise performance.

Further, on the tread tread surface, the contour line on the tread side between the corner portion on the stepping side and the tire equatorial CL side of the center block 21 and the corner portion on the kicking side and the outer side in the tire width direction becomes convex toward the outside of the block. It is preferably an arc. By forming the center block 21 in such a shape, it becomes possible to disperse the hitting sound by the center block 21, which is advantageous for improving the low noise performance.

Further, on the tread tread, the contour line of the center block 21 on the tire equator CL side is inclined so that the distance between the tire equator CL side contour line and the tire equator CL is larger on the kicking side than on the stepping side. Is preferable. In particular, in the illustrated example, the lug groove 12 on one side of the tire equator CL and the lug groove 12 on the other side are arranged so as to be offset in the tire circumferential direction, and the center block 21 on one side of the tire equator CL and the other side are arranged. The center block 21 of the above is also arranged so as to be offset in the tire circumferential direction. Therefore, the contour lines on the tire equator CL side having the above-mentioned inclined shape form a C-shape shifted in the tire circumferential direction on both sides of the tire equator CL. With such a shape, the air column resonance sound generated in the narrow groove 11 can be reduced, which is advantageous for improving the low noise performance.

As described above, the present invention is intended as a heavy-duty pneumatic tire mainly used for construction vehicles such as dump trucks, but in that case, in addition to the tread pattern being a block tone, due to usage conditions. Since the frequency of braking and driving is high, and the frequency of sharp curve driving is also high, uneven wear tends to occur. Therefore, in addition to the above structure, it is preferable to chamfer the corners of the center block 21 on the stepping side and the tire equatorial CL side. As a result, the ground pressure of the center block 21 becomes uniform, and uneven wear at the initial stage of wear can be suppressed.

As described above, in the present invention, the fine groove 11, the lug groove 12, and the auxiliary groove 13 are optionally provided, but among these grooves, the lug groove 12 is the deepest, and the fine groove 11 and the auxiliary groove 13 are more than the lug groove 12. It is preferable that the groove depth is small. Specifically, it is preferable that the groove depth of the auxiliary groove 13 is 75% to 85% of the groove depth of the lug groove 12. By making the auxiliary groove 13 shallower than the lug groove 12 in this way, the rigidity of the blocks (center block 21 and shoulder block 22) adjacent to the auxiliary groove 13 can be increased, which is advantageous for improving the traction performance. Become. Further, it is preferable that the groove depth between the blocks of the fine groove 11 is 15% to 85% of the groove depth of the lug groove 12. By providing the narrow groove 11 with a region shallower than the lug groove 12 in this way, the rigidity of the block (center block 21) adjacent to the fine groove 11 can be increased, which is advantageous for improving the traction performance.

The tire size is 315 / 80R22.5, and it has the basic structure illustrated in FIG. 1, and has the basic tread pattern, the presence or absence of the stepping side groove of the shallow groove, the presence or absence of the kicking side groove, the presence or absence of the connecting groove, and the stepping. Existence of overlap between the side groove and the kicking side groove, the distance between the stepping side groove and the outer edge of the stepping side of the center block, the presence or absence of the shoulder shallow groove, the groove depth of the shallow groove, the tire of the lug groove in the first region A. Average angle θa with respect to the circumferential direction, average angle θb of the lug groove with respect to the tire circumferential direction in the second region B, average angle θc with respect to the tire circumferential direction of the lug groove in the third region C, tire circumferential direction of the lug groove in the fourth region D The average angle θd with respect to the tire, the average angle θcd of the lug groove in the third region C and the fourth region D with respect to the tire circumferential direction, the magnitude relationship between the average angles θa and θb, the magnitude relationship between the average angles θb and θcd, and the difference in the average angle | θa. -Θb |, difference in average angle | θb-θc |, position of auxiliary groove, angle α of auxiliary groove with respect to tire circumferential direction, angle β of corner on the stepping side and tire equatorial CL side of the center block on the block tread, center The shape of the contour line on the stepping side (shape of the contour line on the stepping side) between the corner on the stepping side and the tire equatorial CL side of the block and the corner on the kicking side and the outer side in the tire width direction, the stepping side and the center block Presence / absence of chamfering treatment of corners on the tire equatorial CL side (presence / absence of chamfering of corners), shape of contour line on the tire equatorial CL side of the center block, ratio of the groove depth of the fine groove to the groove depth of the lug groove, Twenty-seven types of pneumatic tires of Conventional Example 1, Comparative Examples 1 to 5 , and Examples 1 to 21 in which the ratio of the groove depth of the auxiliary groove to the groove depth of the lug groove was set as shown in Tables 1 to 3, respectively, were produced. did.

In the "tread pattern" column of Tables 1 to 3, the corresponding drawing numbers are described. In Comparative Examples 4 to 5 , although the patterns have less bending or bending of the lug groove, the numerical values and the like of each item are displayed as corresponding to the pattern of FIG. 2 for convenience. Regarding the shape of the shallow groove, if there is a corresponding drawing, the drawing number is described in the column of "corresponding drawing" in Tables 1 to 3. The column of "presence or absence of overlap between the stepping side groove portion and the kicking side groove portion" in Tables 1 to 3 indicates whether or not each portion overlaps when the stepping side groove portion and the kicking side groove portion are projected in the tire circumferential direction. It is a column, and when at least a part of it overlaps, it is displayed as "Yes", and when it does not overlap, it is displayed as "No". Regarding the column of "Shape of stepping side contour line" in Tables 1 to 3, if the contour line is an arc that is convex toward the outside of the block, it is "arc", and the contour line is bent and the center block is on the stepping side. In addition, when the corner is located outside in the tire width direction, it is indicated as "corner". Regarding the column of "Shape of contour line on the equator side" in Tables 1 to 3, if the contour line is tilted so that the distance from the tire equator is larger on the kicking side than on the stepping side, "tilt", When the contour line is parallel to the tire equator and the distance between the contour line and the tire equator is constant, it is displayed as "parallel".

These pneumatic tires were evaluated for traction performance, snow traction performance, and uneven wear resistance on unpaved roads by the following evaluation methods, and the results are also shown in Tables 1 to 3.

Traction performance on unpaved roads Each test tire was assembled to a wheel with a rim size of 22.5 x 9.00, and the air pressure was set to 850 kPa, and it was mounted on the drive shaft of the test vehicle (truck with an axle arrangement of 6 x 4). Sensory evaluation was performed by a test driver on each test course consisting of paved roads. The evaluation result is shown by an index with the value of Conventional Example 1 as 100. The larger this index value is, the better the traction performance is.

Snow traction performance Each test tire is attached to a wheel with a rim size of 22.5 x 9.00, the air pressure is 850 kPa, and it is mounted on the drive shaft of a test vehicle (a truck with an axle arrangement of 6 x 4), and consists of a snow road. Sensory evaluation was performed by a test driver on each test course. The evaluation result is shown by an index with the value of Conventional Example 1 as 100. The larger this index value is, the better the traction performance is.

Uneven wear resistance performance Each test tire is assembled to a wheel with a rim size of 22.5 x 9.00, and the air pressure is set to 850 kPa, and it is mounted on the drive shaft of a test vehicle (truck with an axle arrangement of 6 x 4), and a pattern of 40,000 km. The amount of wear (heel-and-toe wear) of the block after running was measured. The evaluation result is shown by an index with the value of Conventional Example 1 as 100 using the reciprocal of the measured value. The larger this index value is, the smaller the amount of wear is and the better the uneven wear resistance performance is. If the index value is "98" or more, it means that the good uneven wear resistance performance equivalent to that of the conventional level is maintained.

As is clear from Tables 1 to 3, all of Examples 1 to 21 have improved traction performance on snow while maintaining good traction and uneven wear resistance on unpaved roads as compared with Conventional Example 1. did.

On the other hand, Comparative Example 1 did not have a shallow groove, so that the effect of improving the traction performance on snow could not be obtained. Comparative Examples 2 and 3 do not have either a stepping gutter or a kicking gutter, and the shape of the shallow gutter is inappropriate, so that the effect of improving the traction performance on snow could not be sufficiently obtained. ..

1 Tread part 2 Side wall part 3 Bead part 4 Carcus layer 5 Bead core 6 Bead filler 7 Belt layer 11 Fine groove 12 Rug groove 13 Auxiliary groove 21 Center block 22 Shoulder block 30 Shallow groove 31 Stepping side groove part 32 Kicking side groove part 33, 34 Connecting groove 40 Shoulder shallow groove A 1st area B 2nd area C 3rd area D 4th area CL Tire equator E Tread end

Claims (16)

A tread portion extending in the tire circumferential direction to form an annular shape, a pair of sidewall portions arranged on both sides of the tread portion, and a pair of bead portions arranged inside the tire radial direction of these sidewall portions. For pneumatic tires with a specified direction of rotation
On the equator of the tire in the tread portion, one narrow groove extending along the entire circumference of the tire is formed along the tire circumferential direction.
A plurality of lug grooves extending from the narrow groove toward the outside in the tire width direction and reaching the tread end are formed on both sides of the tire equator at intervals in the tire circumferential direction, and are formed in the fine grooves of the lug groove. The communicating end is located on the stepping side of the end on the tread end side of the lug groove.
The distance in the tire width direction from the tire equator to the tread end is W, the region between the position 0.25 W away from the tire equator in the tire width direction and the tire equator is the first region, and the tire equator to the tire width direction. The second region is the region between the position separated by 0.25 W and the position separated by 0.50 W from the tire equatorial line in the tire width direction, and the position separated by 0.50 W from the tire equatorial line in the tire width direction and the tire width from the tire equatorial line. When the region between the position separated by 0.75 W in the direction and the position separated by 0.75 W in the tire width direction from the tire equatorial line is defined as the fourth region, the region between the tread end is defined as the fourth region. Auxiliary grooves extending along the tire circumferential direction are formed by connecting adjacent lug grooves in the tire circumferential direction in the second to third regions.
A plurality of blocks are partitioned by the narrow groove, the lug groove, and the auxiliary groove, and among the plurality of blocks, a shallow groove terminating in the tread is provided on the tread of the center block located on the equator side of the tire.
The shallow groove is at least separated from the outer edge of the tread surface of the center block on the stepping side and separated from the outer edge of the tread surface of the center block on the kicking side and the stepping gutter extending along the shape of the outer edge of the stepping side. Including a kick-out gutter extending along the shape of the kick-out side outer edge.
The average angle of the lug groove with respect to the tire circumferential direction in the second region is smaller than the average angle of the lug groove with respect to the tire circumferential direction in the first region, and the lug groove in the second region A pneumatic tire characterized by being curved or bent so that the average angle of the lug groove in the third region and the fourth region with respect to the tire circumferential direction is larger than the average angle with respect to the tire circumferential direction . The air-filled portion according to claim 1, wherein when the step-on side groove portion and the kick-out side groove portion are projected in the tire circumferential direction, at least a part of the step-on side groove portion and the kick-out side groove portion overlap each other. tire. The pneumatic tire according to claim 1 or 2, wherein the distance from the outer edge of the center block on the stepping side of the stepping gutter portion is 8 mm to 12 mm. The shallow groove connects the stepping side groove portion, the kicking side groove portion, and these outer end portions in the tire width direction, and extends along the shape of the outer edge of the center block in the tire width direction. The pneumatic tire according to any one of claims 1 to 3, wherein the tire is composed of three elements including a groove portion. The tread of the shoulder block located on the tread end side of the plurality of blocks is provided with a shallow groove extending along the tire width direction, having at least one bent portion, and terminating in the tread. The pneumatic tire according to any one of claims 1 to 4. The pneumatic tire according to any one of claims 1 to 5, wherein the shallow groove has a groove depth of 1 mm to 3 mm. The pneumatic tire according to any one of claims 1 to 6, wherein the angle of the auxiliary groove with respect to the tire circumferential direction is 10 ° to 20 °. The average angle of the lug groove with respect to the tire circumferential direction in the second region is 28 ° to 38 °, and the average angle of the lug groove with respect to the tire circumferential direction in the first region and the lug groove in the second region. The difference from the average angle with respect to the tire circumferential direction is 35 ° or more and 45 ° or less, and the average angle of the lug groove with respect to the tire circumferential direction in the second region and the average of the lug groove with respect to the tire circumferential direction in the third region. The pneumatic tire according to any one of claims 1 to 7, wherein the difference from the angle is 35 ° or more and 45 ° or less. The pneumatic tire according to any one of claims 1 to 8 , wherein the angle of the corner portion on the tread tread side of the center block on the stepping side and the equator side of the tire is 60 ° to 75 °. The pneumatic tire according to any one of claims 1 to 9, wherein the corner portion on the stepping side and the equator side of the tire is chamfered. On the tread tread surface, the contour line on the tread side between the corner portion on the stepping side and the equator side of the tire and the corner portion on the kicking side and the outer side in the tire width direction of the center block is an arc that is convex toward the outside of the block. The pneumatic tire according to any one of claims 1 to 10 . The tread tread is characterized in that the contour line on the tire equator side of the center block is inclined so that the distance between the tire equator side contour line and the tire equator is larger on the kicking side than on the stepping side. The pneumatic tire according to any one of claims 1 to 11 . The pneumatic tire according to any one of claims 1 to 12 , wherein the groove depth of the auxiliary groove is 75% to 85% of the groove depth of the lug groove. The pneumatic tire according to any one of claims 1 to 13 , wherein the groove depth between the blocks of the fine grooves is 15% to 85% of the groove depth of the lug groove. The pneumatic tire according to any one of claims 1 to 14 , wherein the groove depth of the lug groove is 15 mm to 25 mm. The tread rubber constituting the tread portion has a JIS-A hardness of 61 to 65, and a modulus at 100% elongation of 2.0 MPa to 2.8 MPa, according to any one of claims 1 to 15 . The described pneumatic tire.

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