JP4783004B2 - Heavy duty radial tire - Google Patents

Description

  The present invention relates to a heavy-duty pneumatic radial tire that improves wet grip performance and steering stability performance without sacrificing uneven wear resistance performance, low noise performance, and the like by improving a tread pattern.

  In heavy-duty radial tires used in heavy vehicles such as trucks and buses, there is a great demand for tires for all-season use. In addition, these heavy-duty radial tires for all-season use can safely run on various road conditions. Therefore, it is necessary to maintain particularly high wet grip performance and steering stability performance. For this reason, in many cases, a block pattern is adopted as a tread pattern.

  On the other hand, it is generally known that increasing the number of lateral grooves and longitudinal grooves, the groove volume, etc. is effective for improving wet grip performance in tires. However, in the case of heavy duty radial tires, a large shearing force acts on the first and rear sides in the rotational direction during driving and braking, and sliding friction occurs between the road surface and the rotational direction of the block. So-called heel and toe wear, in which the first and second wear sides are locally worn, is likely to occur, and the steering stability tends to be impaired due to the lower rigidity of the tread surface.

  In addition, a so-called punching uneven wear phenomenon that wears earlier in the block row located in the middle portion in the tire axial direction between the equatorial plane and the tread end is more likely to occur than in other block rows. For these reasons, easily increasing the number of grooves and the volume of the groove increases the frequency of occurrence of such uneven wear. In addition, the increase in the groove is accompanied by a decrease in the contact area and a decrease in the tire wear life. Furthermore, the groove is one of the causes of noise generation.

  Conventionally, as a means for preventing uneven wear such as heel & toe wear of heavy load tires having a block pattern, for example, a shoulder block formed in the shoulder portion is divided into the inside and outside of the tire axial direction and the intermediate portion is curved outwardly. A heavy-duty radial tire provided with narrow grooves has been proposed (see, for example, cited document 1).

JP 2000-177326 A

  Although this proposed heavy-duty radial tire exhibits a tread pattern intended to suppress uneven wear, it is sufficient for the recent demand for heavy-duty radial tires for all-seasons that require improved wet grip performance. Does not fit.

  An object of the present invention is to provide a heavy-duty pneumatic radial tire having a block pattern and having improved wet grip performance without sacrificing uneven wear resistance, steering stability, and the like.

In order to achieve the above-mentioned object, the invention of claim 1 of the present application includes, on the tread surface T, a central longitudinal groove 2C intersecting the tire equator Q and zigzag, and an outer longitudinal groove 2S on the outer side in the tire axial direction. , At least five longitudinal grooves (2) extending in the tire circumferential direction with an intermediate longitudinal groove 2M passing between them,
And a central horizontal groove 3C connecting between the central vertical groove 2C and the intermediate vertical groove 2M, an intermediate horizontal groove 3M connecting between the intermediate vertical groove 2M and the outer vertical groove 2S, and an outer vertical groove ( 2S) by arranging the outer lateral groove 3S extending from the tread end E to
A central block 4C delimited by a central vertical groove 2C, an intermediate vertical groove 2M and a central horizontal groove 3C, and an intermediate block 4M delimited by an intermediate vertical groove 2M, an outer vertical groove 2S and an intermediate horizontal groove 3M And a block pattern using at least three types of blocks 4 consisting of an outer vertical groove 2S and an outer block 4S separated by an outer horizontal groove 3S extending from the outer vertical groove 2S to the tread end E. With
The longitudinal length L4C of the central block, the longitudinal length L4M of the intermediate block, and the vertical length L4S of the outer block, which are distances between the most projecting end points on both sides in the tire circumferential direction of each central, intermediate and outer block 4 , And the lateral length W4C of the central block, which is the distance in the tire axial direction between the most protruding end points on both sides in the tire axial direction of each central, intermediate, and outer block 4, the lateral length W4M of the intermediate block, and the lateral length of the outer block In W4S, the length ratio of each block ((L4C / W4C in the central block 4C), (L4M / W4M) in the intermediate block 4M, (L4S / W4S) in the outer block)
(L4S / W4S) <(L4M / W4M) <(L4C / W4C)
1.50 <L4C / W4C <1.80
1.30 <L4M / W4M <1.65
0.90 <L4S / W4S <1.10
The groove width w2C of the central vertical groove 2C, the groove width w2M of the intermediate vertical groove 2M, the groove width w2S of the outer vertical groove 2S, and the groove width w3C of the central horizontal groove 3C in the groove width perpendicular to each groove center line. The ratio of the groove width w2C of the central vertical groove 2C to the groove width w3C of the central horizontal groove 3C (w2C / w3C), where the groove width w3M of the intermediate horizontal groove 3M and the groove width w3S of the outer horizontal groove 3S are The ratio of the groove width w2S of the outer vertical groove 2S to the groove width w3S of the outer vertical groove 2S (w2S / w3S) of the intermediate vertical groove 2M to the groove width w3M of the horizontal groove 3M Satisfying the following equation:
0.85 <w2C / w3C <1.30
0.85 <w2M / w3M <1.10
0.9 <w2S / w3S <1.10
And the most protruding end portion in the tire axial direction of the central block 4C facing the central vertical groove 2C, the most protruding end portion in the tire axial direction of the intermediate block 4M facing the outer vertical groove 2S, and the outer vertical The most projecting end portion in the tire axial direction of the outer block 4S facing the groove 2S is formed in an arc shape with a radius of curvature r, and the block vertical length of each block is L and the horizontal length of each block is W. Sometimes, the radius of curvature rC, rM, rS (hereinafter collectively referred to as r in the equation) of each of the most protruding end portions is determined by the equation of r coefficient = r / (L × W) ^0.5. The r coefficient (r4C, r4M, r4S) is 0.05 to 0.30.

In the invention of claim 2, the groove width w2C of the central vertical groove 2C, the groove width w2M of the intermediate vertical groove 2M, and the groove width w2S of the outer vertical groove 2S are:
w2C <w2M <w2S
It is characterized by being.

In the invention of claim 3, the groove width w3C of the central lateral groove 3C, the groove width w3M of the intermediate lateral groove 3M, and the groove width w3S of the outer lateral groove 3S are:
w3C <w3M <w3S
It is characterized by being.

  The block according to claim 1, wherein at least five longitudinal grooves are provided to improve wet grip performance, and the drainage in the tread pattern, the circumferential rigidity of the block, and the rigidity of the block in the tire axial direction. The ratio of the circumferential length and the tire axial length is optimized according to the center, middle, and outer blocks, so that the circumferential and axial rigidity of the block is optimized, and traction and handling stability are improved. As well as improving the groove arrangement around the block, the drainage can be improved and the wet grip performance can be improved. Also, by adjusting the ratio of the groove width of the vertical groove that affects the wet turning performance and the groove width of the horizontal groove that affects the traction / brake performance to a wet grip by optimizing the value according to the center, middle and outer blocks Performance, hornability, brake performance, and low noise.

  Further, in the inventions of claims 2 and 3, since the groove widths of the vertical and horizontal grooves on the shoulder side are increased toward the shoulder side, drainage can be made smoother than conventional patterns, and wet grip properties are improved. sell.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a developed plan view showing a tread pattern of a tread portion in which a tread portion of a heavy duty radial tire of the present invention (hereinafter sometimes simply referred to as a tire) is developed, and tread edges E and E of the tire 1 are shown. The tread surface T in between consists of a single or a plurality of curvature radii in the cross section including the tire axis. Further, the tread surface T is divided into blocks 4 by providing a plurality of vertical grooves 2 extending in the tire circumferential direction and a plurality of horizontal grooves 3 extending in the direction intersecting with the vertical grooves 2. . The tread edge E refers to a ridgeline when the tread surface T forms an edge-like ridgeline with an inclined surface continuous with the buttress surface or the buttress surface, and when the tread surface T and the buttress intersect with an arc, the tread surface T It is defined as the position of the line of intersection between the extended surface and the extended surface from the buttress surface.

  The longitudinal groove 2 intersects the tire equator Q and extends in the tire circumferential direction in a zigzag manner in the center, and the outer longitudinal groove 2S extends in the tire circumferential direction in a zigzag manner in the present embodiment outside the tire axial direction. And at least five intermediate longitudinal grooves 2M extending in a zigzag shape with a moderate angle in the tire circumferential direction between the central longitudinal groove 2C and the outer longitudinal groove 2S. Thus, wet grip performance is improved by making the longitudinal groove 2 into five or more in the circumferential direction.

  The horizontal groove 3 includes a central horizontal groove 3C that connects between the central vertical groove 2C and the intermediate vertical groove 2M, an intermediate horizontal groove 3M that connects between the intermediate vertical groove 2M and the outer vertical groove 2S, and an outer side. The outer lateral groove 3S extending from the longitudinal groove 2S to the tread end E is included.

Accordingly, the block 4 includes a central block 4C, an intermediate vertical groove 2M, an outer vertical groove 2S, and an intermediate horizontal groove that are separated by a central vertical groove 2C , an intermediate vertical groove 2M, and a central horizontal groove 3C. Includes at least three types of blocks 4 including an intermediate block 4M divided into 3M, an outer vertical groove 2S, and an outer block 4S which is divided by the outer horizontal groove 3S and the tread edge E and is located at the shoulder portion. The tread surface T is formed as a block pattern.

  This block pattern is a repeating pattern of the pattern constituent unit d. For example, the upper and lower pitch lines y1 that are located immediately above (in the drawing) the lateral grooves 3S and 3S on the left end of FIG. 1 and extend in the tire axial direction. , Y2 is assumed as a repeating pattern constituent unit d. The length of the pattern constituent unit d in the tire circumferential direction is referred to as a pitch p. In this embodiment, a plurality of different types of pattern constituent units d are arranged in a length range of about 1.0 to 1.3 times the pitch p. The frequency is dispersed by using a block pattern using a so-called variable pitch method.

  As is apparent from FIG. 1, in this embodiment, at this pitch center position p0 where the tire equator Q and the central longitudinal groove 3C intersect at the pitch center position p0, in this embodiment, each pattern constituent unit d is on both sides in the tire axial direction. Is formed as a point-symmetric pattern. Various patterns such as a line target shape can also be adopted.

  Further, in FIG. 1, the central longitudinal groove 2C is a vertex c1 projecting to the left (in this specification, a vertex projecting to the left is called a mountain vertex if necessary, and a vertex projecting to the right is called a valley vertex. 1 is a circumferentially repeated body of the groove 2c having a position or angle in each groove, which is a position at the groove center line and an angle with respect to the center line), and is located above the groove 2c in FIG. The slant piece 2c1 has its length center point cc1 at the intersection of the pitch line y1 and the tire equator Q, and the lower slant piece 2c2 has its center point cc2 intersecting the tire equator Q. In this embodiment, the center point cc1 of the length of the upper oblique piece 2c1 of the next groove 2c continuous below the lower oblique piece 2c2 is located at the intersection of the pitch line y2 and the tire equator Q. In other words, in the present example, the one rectangular groove 2c has a length of the pitch p, and the center point cc2 of the lower oblique piece 2c2 is located at the center of the pitch p and on the tire equator Q. Accordingly, the upper inclined piece 2c1 preferably has a circumferential length twice as long as the lower inclined piece 2c2.

  Both of the intermediate longitudinal grooves 2M on both sides of the tire equator Q are repeated in the circumferential direction of the rectangular groove 2m having the apex m1 (mountain apex) protruding to the left, and the length of the upper slope 2m1 of the rectangular groove 2m. The pitch line y1 passes near the central point cm1. In this embodiment, it intersects with the pitch line y2 in the vicinity of the center point cm1 of the length of the upper oblique piece 2m1 next to the continuous groove 2m2 below the lower oblique piece 2m2. In other words, in the present example, the one rectangular groove 2m has a length of the pitch p, and the upper oblique piece 2m1 and the lower oblique piece 2m2 are set to have the same length. The intermediate longitudinal grooves 2M on both sides are formed in the same phase.

  The outer vertical groove 2S is a circumferentially repeated body of a rectangular groove 2s having a vertex s1 protruding to the left in FIG. 1, like the central and intermediate vertical grooves 2C and 2M, In the longitudinal grooves 2S, 2S, the position of the apex s1 is shifted in the tire circumferential direction by about 0.05 to 0.30 times the pitch p, and the right outer longitudinal groove 2S is displaced downward (in the drawing). Yes.

  The left outer vertical groove 2S has a lower part of the upper oblique piece 2s1 located on the upper side in FIG. 1 constituting the pattern constituting unit d within the pitch line y1, and a part of the upper oblique piece 2s1. The rectangular groove 2s is formed by the lower inclined piece 2s2 and the upper inclined piece 2s1 of the next rectangular groove 2s connected to the lower end of the lower inclined piece 2s2. The upper oblique piece 2s1 and the lower oblique piece 2s2 have the same length and are connected to each other to form a rectangular groove 2s having a pitch length p.

  In addition, each peak and trough of each longitudinal groove 2C, 2M, 2S is arranged in parallel in the tire circumferential direction at the same position in the tire axial direction.

  Further, an inclination angle α2s1 on the acute angle side formed by the upper inclined piece 2c1 of the central longitudinal groove 2C with respect to the tire circumferential direction line (parallel to the tire equator Q) is 15 to 35 °, preferably 20 to 30 °. The inclination angle α2s2 of 2c1 is set to about 30 to 45 °, preferably about 20 to 35 °, thereby improving the grip performance and the handling stability.

  On the other hand, the outer vertical groove 2S has an acute inclination angle α2s formed with respect to the tire circumferential direction line in the upper inclined piece 2s1 and the lower inclined piece 2s2 of the square groove 2s. Preferably, it is larger than the inclination angle α2c1 of the upper inclined piece 2c1 of the central longitudinal groove 2C and smaller than the inclination angle α2c2 of the lower inclined piece 2c2. The inclination angle α2m on the acute angle side of the intermediate longitudinal groove 2M with respect to the tire circumferential direction line is the same in the upper slant piece 2m1 and the lower slant piece 2m2 of the square groove 2m, and is compared in consideration of drainage. In this embodiment, it is formed at 1 to 15 °, preferably about 2 to 8 °, and an angle α2c (average value of upper and lower inclined pieces) with respect to the tire circumferential direction of the central longitudinal groove 2C and the outer longitudinal groove 2S, It is smaller than α2s. Thereby, it becomes easy to discharge | emit the water between the tread surface 1 and a road surface in a tire center part and a tire shoulder part to a tire peripheral direction, and improves wet grip performance.

  Further, on the left side of the tire equator Q of FIG. 1, the central lateral groove 3C connects the peak of the central vertical groove 2C and the peak of the intermediate vertical groove 2M, and the intermediate horizontal groove 2M is the intermediate vertical groove. The 2M trough apex and the trough apex of the outer vertical groove 2S are joined. The outer lateral groove 3S extends from the top of the outer vertical groove 2S to the tread edge E. On the right side, the central horizontal groove 3C connects the valley vertex of the central vertical groove 2C and the valley vertex of the intermediate vertical groove 2M, and the intermediate horizontal groove 2M is connected to the peak of the intermediate vertical groove 2M and the outer vertical groove. It joins the peak of the groove 2S. The outer lateral groove 3S extends from the top of the valley of the outer vertical groove 2S to the tread edge E. As a result, it is possible to configure a tying block in which the central blocks 4C and 4C face each other with the tire equator Q sandwiched between the intermediate longitudinal grooves 2m and 2m, so that rigidity can be improved and drainage can be enhanced and steering stability can be exhibited.

  Further, the central lateral groove 3C and the intermediate lateral groove 3M are inclined in the same direction, for example, the left side is upward, and the inclination angles β3c and β3m on the acute angle side with respect to the tire circumferential direction line are Are the same and are set in the range of 50 ° to less than 90 °, preferably in the range of 65 to 85 °. Further, the equivalent angle β3s of the outer lateral groove 3S is set within a range of ± 10 °, preferably about ± 6 ° with respect to the tire axial direction or the tire axial direction line.

  The block patterns of the vertical grooves 2 and the horizontal grooves 3 are preferably point-symmetric about the center point cc1 of the lower slant piece 2c2 of the central vertical groove 2C for each pattern constituent unit d. Thus, drainage is improved and wet grip is improved, and left and right variations are eliminated and steering stability is improved.

  Next, the central block 4C of the block 4 is shown in FIG. 2, the intermediate block 4M is shown in FIG. 3, and the outer block 4S located at the shoulder is shown in FIG. Further, in each block 4, the distance between two tire axial direction lines yc1, yc2, ym1, ym2, and ys1, ys2 extending in the tire axial direction through the uppermost and lowermost projecting ends in the tire circumferential direction, that is, ys1, ys2, respectively. The distances in the tire circumferential direction between the central, intermediate, and outer blocks 4 are referred to as a central block vertical length L4C, an intermediate block vertical length L4M, and an outer block vertical length L4S.

  On the other hand, tire shafts between the tire circumferential direction lines xc1 and xc2, between xm1 and xm2, and between xs1 and xs2 that pass through the most projecting end points on both sides in the tire axial direction of each center, middle, and outer block 4 The central block horizontal length W4C, which is the directional distance, the intermediate block horizontal length W4M, and the outer block horizontal length W4S are named.

At this time, the following expression is satisfied in the longitudinal ratio of each block ((L4C / W4C) in the central block 4C, (L4M / W4M) in the intermediate block 4M, (L4S / W4S) in the outer block). .
(L4S / W4S) <(L4M / W4M) <(L4C / W4C)

  In this way, the vertical length ratio L4 / W4 of the block 4 is made smaller as it goes from the central block 4C to the outer block 4S, and the degree of the vertical length of the block is reduced to approach a square shape. The vertical length L of each block 4 corresponds to a length obtained by subtracting the groove width W3 of the horizontal groove 3 above and below the block 4 from the pitch p of the pattern constituent unit d, and accordingly, the vertical length ratio of the block (L4S / W4S). , (L4M / W4M) and (L4C / W4C) mainly correlate with the length of the lateral groove 4 in the tire axial direction, and the length ratio L / W increases as the length decreases.

  By the way, in general, in a heavy duty pneumatic tire, the center portion of the tire, that is, the crown portion is grounded first, and then the intermediate portion or the shoulder portion is grounded. Therefore, on a wet road surface, water between the tread surface T and the road surface flows from the center portion of the tread to both sides in the tire axial direction. At this time, drainage is better when the length of the central lateral groove 3C in the tire axial direction is shorter.

  Further, the force applied to the central block 4C is greater in the tire circumferential direction than in the tire axial direction. Therefore, when the tire circumferential direction is viewed vertically and the tire axial direction is viewed horizontally as shown in FIG. 1, the central block 4 </ b> C has a vertically long shape to enhance the traction performance and the effect of suppressing uneven wear of the block.

On the other hand, since the tread surface T of the tire inevitably has a curvature, the amount of slip is generally larger than that of the tire center. For this reason, the outer lateral groove 3S has a high so-called wiping effect for sweeping out a water film formed on the road surface. For this reason, as compared with the central lateral groove 3C, a longer one in the tire axial direction is advantageous in improving wet grip performance. Further, the lateral force applied to the outer block 4S is larger than the lateral force applied to the central block 4C. This is particularly noticeable when turning, and the lateral rigidity of the outer block 4S greatly affects the steering stability performance. Therefore, when viewing the tire circumferential direction as shown in FIG. 1 vertically, the horizontal the tire axial direction, should be square shape, it is of the wet grip performance and steering stability preferred. The intermediate block 4M is required to have intermediate characteristics between the central block 4C and the outer block 4S, and therefore, the shape characteristics need to be intermediate.

The length ratio of each block (center block 4C: (L4C / W4C), middle block 4M: (L4M / W4M), outer block: (L4S / W4S)) is set as follows. Is good.
1.50 <L4C / W4C <1.80
1.30 <L4M / W4M <1.65
0.90 <L4S / W4S <1.10

Preferably,
1.60 <L4C / W4C <1.70
1.40 <L4M / W4M <1.55
0.95 <L4S / W4S <1.05
It is. It was proved that the above-mentioned effects were excellent by setting the above range.

Further, the groove width w2C of the central vertical groove 2C, the groove width w2M of the intermediate vertical groove 2M, the groove width w2S of the outer vertical groove 2S, and the groove width w3C of the central horizontal groove 3C measured in a direction perpendicular to each groove center line. When the groove width w3M of the intermediate horizontal groove 3M and the groove width w3S of the outer horizontal groove 3S are set, the ratio of the vertical and horizontal groove widths w3 / w2, that is, the central vertical groove 2C with respect to the groove width w3C of the central horizontal groove 3C. The groove width ratio of the groove width w2C (w2C / w3C), the groove width ratio of the intermediate vertical groove 2M to the groove width w3M of the intermediate lateral groove 3M (w3M / w3M), the outer vertical width of the outer horizontal groove 3S with respect to the groove width w3S The groove width ratio (w2S / w3S) of the groove width w2S of the groove 2S is formed so that the following expression is satisfied.
0.85 <w2C / w3C <1.30
0.85 <w2M / w3M <1.10
0.9 <w2S / w3S <1.10

  This is because the groove width w2 of the vertical groove 2 (the groove width w2C of the central vertical groove 2C, the groove width w2M of the intermediate vertical groove 2M, the groove width w2S of the outer vertical groove 2S) and the groove of the horizontal groove 3 connected thereto. By making the width w3 (the groove width w3C of the central lateral groove 3C, the groove width w3M of the intermediate lateral groove 3M, and the groove width w3S of the outer lateral groove 3S) substantially the same, This is a result of finding that water flow acceleration and uneven wear resistance are good, and the range of the difference is ± 10%, preferably 0.94 or more and 1.06 or less. .

The groove width w2C of the central vertical groove 2C, the groove width w2M of the intermediate vertical groove 2M, and the groove width w2S of the outer vertical groove 2S are larger as they approach the tread edge E, that is, satisfy the following equation: .
w2C <w2M <w2S

  In general, when the vehicle is traveling straight ahead and stopped, the ground contact pressure of the tire is maximized at the equator plane and becomes smaller toward the tread end. Therefore, on the dry road surface, the grip performance is higher and the wear resistance performance is better as the actual ground contact area at the center is larger. On the wet road surface, the wet grip performance increases as the width of the vertical groove 2 increases. However, if the groove width w2 of the vertical groove 2 in the central portion is increased, the above performance is liable to be adversely affected. In order to improve both of the conflicting performances, the longitudinal groove width w2 is set in the above relationship. In this embodiment, the groove width w2C2 of the lower oblique piece 2C2 is 1.05 to 1.60 times larger than the groove width w2C1 of the upper oblique piece 2C1 in the square groove 2c of the central vertical groove 2C. The water flow is good by increasing the degree. For example, the groove width w2C1 can be 4 mm, and the groove width w2C2 can be 6 mm. The groove width w2C of the central longitudinal groove 2c refers to the average groove width value of the total length.

In addition, Preferably, the ratio with respect to the contact width WT of the tread part with respect to the groove width w2 of the said vertical groove 2 is set as follows.
0.020 ≦ (w2C / WT) ≦ 0.040
0.025 ≦ (w2M / WT) ≦ 0.045
0.040 ≦ (w2S / WT) ≦ 0.060

Furthermore, for the same reason, the groove width w3 of the lateral groove (the groove width w3C of the central lateral groove 3C, the groove width w3M of the intermediate lateral groove 3M, and the groove width w3S of the outer lateral groove 3S) is also set as follows.
w3C <w3M <w3S

Preferably, the following range is set with respect to the ground contact width WT in the standard state under the above relationship.
0.015 ≦ (w3C / WT) ≦ 0.035
0.030 ≦ (w3M / WT) ≦ 0.050
0.035 ≦ (w3S / WT) ≦ 0.055

  By setting the groove width w3 of the horizontal groove 3 so as to be closer to the tread end, the water flow in the ground plane from the equator plane toward the tread end can be promoted, and the wet grip performance can be improved. In this case, the same effects can be obtained.

  In this specification, values such as the vertical length L of each block, the horizontal width W of the block, the groove width w, etc., or their reference positions are the values in the normal internal pressure state in which the tire is assembled on the normal rim and the normal internal pressure is applied. It is a value at the tread surface T, and when the tread surface T intersects with the groove wall via the arcuate portion, it is a numerical value at a position at the intersection line of each extended perpendicular plane. Here, “regular rim” is defined in accordance with either the standard rim defined by JATMA, “Design Rim” defined by TRA, or “Measuring Rim” defined by ETRTO, and “regular internal pressure” It is determined according to either the maximum air pressure specified in TRA table, the maximum value described in the TRA table “TIRE LOADLIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “INFLATION PRESSURE” specified in ETRTO. “Normal load” means the maximum load corresponding to the normal internal pressure in each standard. If the groove width or the like varies in the direction of the center line, the average value is taken.

  Further, in this embodiment, the groove depth is about 11.0 to 18.0 mm in the central vertical groove 2C and the horizontal groove 3C, and the groove depths of the outer vertical groove 2S and the horizontal groove 3S are the vertical groove 2S and the vertical groove 2C. On the other hand, the lateral groove 3S is about 0.2 to 5.0 mm deep, and the lateral groove 3S is shallower by about 7.0 to 13.0 mm than the lateral groove 3C. Even at the end of wear (at least 50% depth wear), the full depth depth at which the tread pattern of the vertical groove 2 and the horizontal groove 3 remains clearly is set. The groove width at the groove bottom is set to about 50 to 90% (surface width ratio) of the groove width on the tread surface. With this setting, wet grip performance and steering stability (particularly straight running stability) can be solved by securing the edge component at the end and improving the block rigidity of the crown portion.

  Further, with respect to the intermediate block 4M, the angle γ of the intersection j between the side facing the outer vertical groove 2S and the side facing the intermediate horizontal groove 3M is maintained at an obtuse angle at the top and bottom of the figure to prevent fear of punching wear. The width of the intermediate block 4M in the tire axial direction is uniform in the tire circumferential direction, for example, the ratio of the maximum value to the minimum value is about 1.0 to 1.3, and the rigidity on the first arrival side and the rear arrival side is set. It is intended to equalize and reduce heel and toe wear.

Further, in each of the blocks 4C, 4M, and 4S, each protruding end portion protruding in the tire axial direction is formed in an arc shape with a radius of curvature r to prevent uneven wear. The respective radii of curvature rC, rM, rS (hereinafter collectively referred to as r) of the blocks 4C, 4M, 4S are the r coefficients (r4C, r4M, r4S) of the blocks 4C, 4M, 4S obtained by the following equations. Set in the range of 0.05-0.30 . Note that L is the vertical length of each block, and W is the horizontal length of each block.
r coefficient = r / (L × W) ^0.5
If it is less than 0.05, the effect of preventing the above-mentioned block chipping and uneven wear is small, and if it exceeds 0.30, the wiping effect in the wet road surface by the block edge decreases.

  The heavy-duty radial tire of the present invention can be variously modified within the scope of the claims without being limited to the above-described configuration.

A heavy duty radial tire of size 11R22.5 having the tread pattern of FIG. 1 was prototyped (Table 1) and evaluated for each performance. The evaluation results are shown in Table 3. The r coefficient is shown in Table 2.
Various test conditions shown in Table 1 are as follows. In each test, the rim size is 7.50 × 22.5, the internal pressure is 800 kPa, and a domestic 10-ton truck 2-D vehicle (half-loading and loading in front of the loading platform) is used as the vehicle.

(1) WET turning performance Place: Sumitomo Rubber Industries, Ltd. Okayama Test Course Method: The lap time when making a round of a course with a radius of 30 m in a wet state is represented by the reciprocal of the ratio with Comparative Example 1. The comparative example 1 is set to 100, and a larger value indicates a better result.
(2) WET traction performance Location: Sumitomo Rubber Industries, Ltd. Okayama Test Course Method: The time of a certain section of the course in a wet state is represented by the reciprocal of the ratio with Comparative Example 1. The comparative example 1 is set to 100, and a larger value indicates a better result.
(3) WET brake performance Location: Sumitomo Rubber Industries, Ltd. Okayama Test Course Method: Enter the wet road surface area at a speed of 60 km / hr, apply the brake and stop the distance from the comparison example 1. Expressed as a reciprocal. The comparative example 1 is set to 100, and a larger value indicates a better result.
(4) Noise test place: Sumitomo Rubber Industries, Ltd. Anechoic Real Vehicle Laboratory Method: Using a drum type noise measuring device. Measures generated sound at 7.5m microphone position at 70km / h.
Rim size: 7.50 x 22.5
Internal pressure: 800 kPa
(5) Uneven wear resistance performance The distance traveled by the 2-D4 type box-type truck until the partial wear occurs and the position is changed is determined as an index ratio when the tire of Comparative Example 1 is set to 100. It was.
(6) Abrasion resistance performance A 2-D4 box-type truck travels 40,000 km under a constant load (10 tons) loading condition. The wear resistance performance index was calculated from the remaining grooves after running and compared. The wear resistance performance index is an index ratio in which the value of (new groove depth−groove depth after wear) / (new groove depth) / (new groove depth) of the test tire is 100.

It is a top view which shows the tread pattern of one embodiment of this invention. It is a top view which expands and shows the block. It is a top view which expands and shows another block. It is a plain view which expands and shows another block.

Explanation of symbols

T Tread surface 2 Vertical groove 3 Vertical groove 4 Block E Tread edge Q Tire equator

Claims (3)

On the tread surface T, at least five tires including a central longitudinal groove 2C that intersects the tire equator Q and extends in a zigzag shape, an outer longitudinal groove 2S on the outer side in the tire axial direction, and an intermediate longitudinal groove 2M that passes between them. Longitudinal groove (2) extending in the circumferential direction,
In addition, a central horizontal groove 3C connecting between the central vertical groove 2C and the intermediate vertical groove 2M, an intermediate horizontal groove 3M connecting between the intermediate vertical groove 2M and the outer vertical groove 2S, and an outer vertical groove 2S. By arranging the outer lateral groove 3S extending from the tread end E to
A central block 4C delimited by a central vertical groove 2C, an intermediate vertical groove 2M and a central horizontal groove 3C, and an intermediate block 4M delimited by an intermediate vertical groove 2M, an outer vertical groove 2S and an intermediate horizontal groove 3M And a block pattern using at least three types of blocks 4 consisting of an outer vertical groove 2S and an outer block 4S separated by an outer horizontal groove 3S extending from the outer vertical groove 2S to the tread end E. With
The longitudinal length L4C of the central block, the longitudinal length L4M of the intermediate block, and the vertical length L4S of the outer block, which are distances between the most projecting end points on both sides in the tire circumferential direction of each central, intermediate and outer block 4 , And the lateral length W4C of the central block, which is the distance in the tire axial direction between the most protruding end points on both sides in the tire axial direction of each central, intermediate, and outer block 4, the lateral length W4M of the intermediate block, and the lateral length of the outer block In W4S, the length ratio of each block ((L4C / W4C in the central block 4C), (L4M / W4M) in the intermediate block 4M, (L4S / W4S) in the outer block)
(L4S / W4S) <(L4M / W4M) <(L4C / W4C)
1.50 <L4C / W4C <1.80
1.30 <L4M / W4M <1.65
0.90 <L4S / W4S <1.10
As well as
The groove width w2C of the central vertical groove 2C, the groove width w2M of the intermediate vertical groove 2M, the groove width w2S of the outer vertical groove 2S, the groove width w3C of the central horizontal groove 3C, measured in a direction perpendicular to each groove center line, The ratio of the groove width w2C of the central vertical groove 2C to the groove width w3C of the central horizontal groove 3C (w2C / w3C), where the groove width w3M of the intermediate horizontal groove 3M and the groove width w3S of the outer horizontal groove 3S are The ratio (w2S / w3S) of the intermediate vertical groove 2M to the groove width w3M of the horizontal groove 3M (w2M / w3M) and the ratio of the outer vertical groove 2S to the groove width w3S (w2S / w3S) of the outer horizontal groove 3S are as follows. Satisfying the formula
0.85 <w2C / w3C <1.30
0.85 <w2M / w3M <1.10
0.9 <w2S / w3S <1.10
And the most protruding end portion in the tire axial direction of the central block 4C facing the central vertical groove 2C, the most protruding end portion in the tire axial direction of the intermediate block 4M facing the outer vertical groove 2S, and the outer vertical The most projecting end portion in the tire axial direction of the outer block 4S facing the groove 2S is formed in an arc shape with a radius of curvature r, and the block vertical length of each block is L and the horizontal length of each block is W. Sometimes, the radius of curvature rC, rM, rS (hereinafter collectively referred to as r in the equation) of each of the most protruding end portions is determined by the equation of r coefficient = r / (L × W) ^0.5. The heavy duty radial tire is characterized in that the r coefficient (r4C, r4M, r4S) of the tire is 0.05 to 0.30.
The groove width w2C of the central vertical groove 2C, the groove width w2M of the intermediate vertical groove 2M, and the groove width w2S of the outer vertical groove 2S are:
w2C <w2M <w2S
The radial tire for heavy loads according to claim 1, wherein: The groove width w3C of the central lateral groove 3C, the groove width w3M of the intermediate lateral groove 3M, and the groove width w3S of the outer lateral groove 3S are:
w3C <w3M <w3S
The radial tire for heavy loads according to claim 1, wherein the radial tire is for heavy loads.

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