JP4230621B2 - Pneumatic tire - Google Patents

Description

【００３３】
【発明の効果】
叙上の如く本発明は、ラグ溝の溝壁面傾斜角度αを、ラグ溝のタイヤ軸方向内端部における溝壁面傾斜角度α１から外端部における溝壁面傾斜角度α２まで増加させているため、ラグ溝の泥づまりを効果的に抑制しうるとともに、乾燥路における操縦安定性を向上できる。
【図面の簡単な説明】
【図１】本発明の一実施例のタイヤのトレッドパターンの展開図である。
【図２】ラグ溝を示す断面図である。
【図３】ラグ溝を示す斜視図である。
【図４】（Ａ）、（Ｂ）は、ラグ溝の溝壁面傾斜角度α１、α２を示す断面図である。
【図５】ラグ溝をその溝壁面とともに示す平面図である。
【図６】本発明の作用効果の一つを説明する線図である。
【符号の説明】
２Ｓ トレッド面
３ ラグ溝
３Ｓ ラグ溝壁面
４ トレッド溝
５ タイヤ周方向溝
Ｃ ラグ溝の溝中心線
Ｎ トレッド面に立てた法線
ＴＥ トレッド縁
Ｙ１ ラグ溝の内端部
Ｙ２ ラグ溝の外端部[0001]
BACKGROUND OF THE INVENTION
The present invention is a pneumatic tire that is suitable for both off-road use and on-off road use, can reduce mud clogging in the lug groove, and can improve running performance in a muddy place without impairing the handling stability on a dry road. About.
[0002]
[Prior art]
For off-road and on / off-road pneumatic tires that can run in muddy areas, block type and lug / rib type with lug groove as the main tone and groove length and groove depth are generally used. The tread pattern is used, and the sea area ratio in this tread pattern (ratio Sg / St of the total groove area Sg of the tread groove to the tread area St) is set to be as large as 40% or more, for example.
[0003]
As a result, the mud is firmly gripped in the lug groove, the mud digging up and the frictional force and shearing frictional force are increased, and the traction property in the mudland is secured. In order to further improve the traction, the lug groove wall has an inclination angle as low as about 10 °, that is, an angle close to a right angle with respect to the tread surface.
[0004]
[Problems to be solved by the invention]
However, an increase in the length of the lug groove, an increase in the sea area ratio, and a decrease in the inclination angle on the wall surface of the lug groove reduce the steering stability on the dry road, for example, leading to a decrease in pattern rigidity. In addition, this has a problem that mud repellency is lowered, and mud caught in the groove is not discharged and is easily clogged. In particular, when mud clogging occurs in the lug groove, the traction property does not function, and the running performance in the muddy ground is remarkably deteriorated.
[0005]
Therefore, the present invention is based on the fact that the groove wall inclination angle α of the lug groove is increased from the groove wall inclination angle α1 at the inner end portion in the tire axial direction of the lug groove to the groove wall inclination angle α2 at the outer end portion. An object of the present invention is to provide a pneumatic tire capable of effectively suppressing mud clogging, increasing cornering power by increasing pattern rigidity on the tread end side and improving driving stability on a dry road.
[0006]
[Means for Solving the Problems]
In order to achieve the object, the invention of claim 1 of the present application
The tread surface includes a tread groove including at least a lug groove extending inward in the tire axial direction from the tread edge, and the sea area is a ratio of the area St of the tread surface to the total groove area Sg of the tread groove in the tread surface. A pneumatic tire suitable for traveling in a muddy area with a ratio (Sg / St) of 40% or more and 65% or less ,
The lug groove has a groove center line angle θ of 0 to 40 degrees with respect to the tire axial direction line of the groove center line, and the tire axial direction length Wg of the lug groove is 0.15 times the tread width TW or more and 0 .35 times or less ,
Inclination of the groove wall surface that is an inclination angle in a plane that includes this normal line and is perpendicular to the center line of the lug groove with respect to the normal line of the two lug groove wall surfaces that are opposed to each other with the lug groove interposed therebetween. The angle α is characterized in that, in the two opposing lug groove wall surfaces, the groove wall inclination angle α1 at the inner end portion in the tire axial direction of the lug groove is increased from the groove wall inclination angle α2 at the outer end portion.
[0007]
The invention according to claim 2 is characterized in that a difference (α2−α1) between the groove wall inclination angles α1 and α2 is 10 to 30 degrees.
[0008]
According to a third aspect of the invention, the lug groove intersects with the tire circumferential groove and is interrupted on the inner side in the tire axial direction.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 exemplify a tread portion 2 when the pneumatic tire 1 of the present invention is formed as a tire for a four-wheel drive vehicle for both on and off-road use. The tread surface 2S is provided with a tread groove 4 including at least a lug groove 3 extending inward in the tire axial direction from the tread edge TE.
[0010]
As the tread groove 4, in this example, the tire circumferential grooves 5 and 5 disposed on both sides of the tire equator CO, and the tire circumferential direction groove 5 extend inward in the tire axial direction from the tread edge TE. The case where it forms from the lug groove 3 ... which interrupts, and the horizontal groove 6 ... which crosses between the said tire circumferential direction grooves 5 and 5 is illustrated. Thus, in this example, a block type tread pattern is formed that includes blocks Bi arranged in the circumferential direction on the tire equator CO and shoulder blocks Bo arranged in the circumferential direction along the tread edge TE. Yes.
[0011]
In this tread pattern, the sea area ratio (Sg / St), which is the ratio between the area St of the tread surface 2S and the total groove area Sg of the tread groove 4 in the tread surface, is 40% or more. This is because the sea area ratio (Sg / St) is also important in the present application when traveling on rough roads, especially in muddy areas, and the influence of buoyancy increases below 40%, and block B enters deeply into the ground. This is because it becomes difficult to grip mud firmly, and good traction characteristics in mudland cannot be obtained. A sea area ratio (Sg / St) exceeding 65% is not preferable because steering stability on a dry good road (for example, an asphalt road surface) is impaired.
[0012]
Next, in the present application, the lateral groove that opens at the tread edge TE is defined as “lug groove 3”, and this lug groove 3 is a groove with respect to the tire axial direction line of the groove center line C for the traction property. The center line angle θ is regulated to 0 to 40 degrees. If the groove center line angle θ exceeds 40 degrees, the shear frictional force obtained from the mud gripped in the lug groove 3 and the circumferential component force of the mud digging frictional force are significantly reduced, making it difficult to ensure traction. Become. Here, the “groove center line C” means a line passing through the center between the ridge lines E and E on the tread surface 2S of the lug groove 3.
[0013]
Moreover, in the said lug groove 3, the tire axial direction length Wg is 0.15 times or more of the tread width TW. Here, the tire axial direction length Wg of the lug groove 3 (hereinafter referred to as the lug groove length Wg) means the distance from the point P where the groove center line C terminates to the tread edge TE. Thus, when the lug groove 3 intersects with the tire circumferential groove 5, as shown in FIG. 1, the groove center line C intersects the ridge line imaginary line L outside the tire circumferential groove 5 in the tire axial direction. Means the distance from the point P to the tread edge TE. When the lug groove length Wg is smaller than 0.15 × TW, the shear frictional force itself obtained from the gripped mud becomes excessively small. On the other hand, when the lug groove length Wg is larger than 0.35 × TW, side slip is likely to occur due to the rigidity of the tread central portion and the reduction of the edge component. In FIG. 1, for the sake of convenience, the tread pattern is shown by using the ridgeline on the tread surface 2S of the tread groove 4, and therefore, the groove bottom and the groove wall surface are not distinguished in FIG.
[0014]
Here, the “tread width TW” means a distance in the tire axial direction between the tread edges TE and TE, and in this example, the so-called tread surface 2S and the tread side surface BS (buttress surface) intersect in a square shape. A case where the tread edge TE is formed by this square intersection by forming a square shoulder is illustrated. Although not generally used for both off-road use and on / off-road use, a so-called tapered shoulder where the tread surface 2S and the tread side surface BS intersect via a slope, or a so-called round shoulder where a small arc surface intersects. In this case, the tread edge TE is formed by the intersection of the tread surface 2S and the inclined surface or the small circular arc surface.
[0015]
In the present application, as shown in FIGS. 3 and 4, the groove wall inclination angle α (inclination angle) of the lug groove wall surface 3 </ b> S is outside the groove wall inclination angle α <b> 1 at the tire axial direction inner end Y <b> 1 of the lug groove 3. The feature is that the groove wall inclination angle α2 at the end Y2 is increased. Here, the lug groove wall surface 3S is “the lug groove wall surface 3S sandwiching the lug groove 3” as described in the first claim, and as shown in FIG. 3 and FIGS. There are two lug groove wall surfaces 3S, 3S that are opposed to each other with the lug groove 3 interposed therebetween, and in these two lug groove wall surfaces 3S, 3S (ie, respectively), the groove wall inclination angle α (inclination angle) is set to the lug groove 3 It is obvious that the groove wall inclination angle α1 at the inner end portion Y1 in the tire axial direction is increased from the groove wall inclination angle α2 at the outer end portion Y2. This description states that “the lug groove 3 of [0019] has a trumpet shape in which the lug groove wall surfaces 3S and 3S are gradually tilted outward in the tire axial direction, that is, the groove width spreads outward in the radial direction. It is clear from the description.
[0016]
Here, as shown in FIGS. 4 and 5, the “groove wall inclination angle α” means a lag including the normal N with respect to the normal N standing on the tread surface 2S where the lug groove wall 3S is continuous. It means the inclination angle of the lug groove wall surface 3S in the plane NS orthogonal to the groove center line C.
[0017]
Further, the inner end Y1 and the outer end Y2 are a range in which a distance of 0.15 times or less the length of the lug groove wall surface 3S at the ridge line E is separated from the inner end point P1 and the outer end point P2 of the ridge line E. Means the area.
[0018]
At the inner end Y1, the groove wall inclination angle α1 does not increase at least toward the inner end point P1, that is, is substantially constant or gradually decreases toward the inner end point P1. In the outer end Y2, the groove wall inclination angle α2 does not decrease at least toward the outer end point P2, that is, is substantially constant, or gradually increases toward the outer end point P2.
[0019]
Thus, since the lug groove 3 increases the groove wall inclination angle α from the inner end Y1 to the outer end Y2, the lug groove 3 includes the lug groove wall surfaces 3S and 3S on the tire shaft. It becomes a trumpet shape that gradually falls outward in the direction, that is, the groove width spreads outward in the radial direction.
[0020]
As a result, the mud that has entered the lug groove 3 is easily discharged radially outward by the centrifugal force of the tire rotation.
[0021]
Further, when mud newly enters the lug groove 3, a force in the direction of squeezing outward in the tire axial direction is generated, for example, the original mud moves along the inclination of the lug groove wall surface 3S.
[0022]
As shown in FIG. 6, in the shoulder block Bo between the lug grooves 3 and 3, the rigidity on the inner side in the tire axial direction is larger than the rigidity on the outer side. Therefore, due to the difference in rigidity in the block, the movement of the shoulder block Bo becomes larger on the inner side than on the outer side in the tire axial direction, and mud in the lug groove 3 is guided outward in the tire axial direction.
[0023]
These functions function by organically bonding to each other. As a result, the soil removal performance is greatly improved, and mud clogging in the lug grooves can be effectively suppressed.
[0024]
Further, as described above, the rigidity of the shoulder block Bo is increased on the outer side in the tire axial direction, so that the cornering power is increased. Therefore, the rigidity feeling and the behavioral stability in the driving on the dry road, particularly the turning driving are greatly increased. The improved steering stability can be improved. Here, the difference (α2−α1) between the groove wall inclination angles α1 and α2 is preferably 10 to 30 degrees, and if the difference is less than 10 degrees, the effect of improving the soil removal property and the improvement of the handling stability are obtained. The effect is not fully exhibited. On the other hand, if it exceeds 30 degrees, the cross-sectional area of the lug groove 3 becomes too small, which is disadvantageous for the running performance of the muddy ground.
[0025]
The value of the groove wall inclination angle α1 itself is not particularly limited, but is generally in the range of 2 to 10 degrees, and the groove depth Dg of the lug groove 3 is preferably 12 to 18 mm as in the conventional case. Further, it is most preferable to increase the groove wall inclination angle α between the inner end Y1 and the outer end Y2 continuously and smoothly as in this example, but it can also be increased stepwise. At this time, it is preferable to divide into at least three steps to make the step as small as possible.
[0026]
Further, the shape, size (groove width and groove depth), the number, etc. of the tread grooves 4 other than the lug grooves 3, that is, the tire circumferential grooves 5 and the lateral grooves 6, can be changed in any manner as required.
[0027]
【Example】
A pneumatic tire having a tire size of 235 / 85R16 having the tread pattern shown in FIG. 1 is manufactured on the basis of the specifications shown in Table 1, and the soil removal performance, traction force (traction force) and start acceleration time of each sample tire in the muddy ground, and drying. Tested on road stability.
[0028]
(1) Soil removal in a muddy area:
A test course for a muddy ground with a mud layer with a depth of about 200 mm is mounted on all wheels of a vehicle (four-wheel drive RV vehicle) under the conditions of a rim (6J × 16) and internal pressure (200 kPa). The state of mud clogging when traveling was visually judged in four stages, x, Δ, ○, and ◎.
[0029]
(2) Traction force (traction force) in a muddy area
The traction force when running on the test course was measured 10 times in each of the climbing tests, and the average value was determined in four stages of x, Δ, ○, and ◎.
[0030]
(3) Start acceleration time in a muddy area:
In the test course, the time required for starting from a stationary state to 20 m was measured 10 times, and the average value of the time was determined in four stages of x, Δ, ○, and ◎.
[0031]
(4) Steering stability on dry road:
Steering stability when running on a dry asphalt road test course using the vehicle was judged in four stages of ×, Δ, ○, and ◎ by sensory evaluation of the driver.
[0032]
[Table 1]

[0033]
【The invention's effect】
As described above, the present invention increases the groove wall inclination angle α of the lug groove from the groove wall inclination angle α1 at the tire axial direction inner end of the lug groove to the groove wall inclination angle α2 at the outer end. It is possible to effectively suppress mud clogging in the lug grooves and improve steering stability in the dry road.
[Brief description of the drawings]
FIG. 1 is a development view of a tread pattern of a tire according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing lug grooves.
FIG. 3 is a perspective view showing a lug groove.
4A and 4B are cross-sectional views showing groove wall inclination angles α1 and α2 of lug grooves.
FIG. 5 is a plan view showing a lug groove together with a groove wall surface thereof.
FIG. 6 is a diagram illustrating one of the operational effects of the present invention.
[Explanation of symbols]
2S tread surface 3 lug groove 3S lug groove wall surface 4 tread groove 5 tire circumferential groove C groove center line N normal line TE standing on tread surface T1 edge Y1 inner end Y2 of lug groove outer end of lug groove

Claims (3)

The tread surface includes a tread groove including at least a lug groove extending inward in the tire axial direction from the tread edge, and the sea area is a ratio of the area St of the tread surface to the total groove area Sg of the tread groove in the tread surface. A pneumatic tire suitable for traveling in a muddy area with a ratio (Sg / St) of 40% or more and 65% or less ,
The lug groove has a groove center line angle θ of 0 to 40 degrees with respect to the tire axial direction line of the groove center line, and the tire axial direction length Wg of the lug groove is 0.15 times the tread width TW or more and 0 .35 times or less ,
Inclination of the groove wall surface that is an inclination angle in a plane that includes this normal line and is perpendicular to the center line of the lug groove with respect to the normal line of the two lug groove wall surfaces that are opposed to each other with the lug groove interposed therebetween. The angle α is increased from the groove wall inclination angle α1 at the inner end in the tire axial direction of the lug groove to the groove wall inclination angle α2 at the outer end in the two opposing lug groove wall surfaces. Enter tire.   The pneumatic tire according to claim 1, wherein a difference (α2-α1) between the groove wall inclination angles α1 and α2 is 10 to 30 degrees.   3. The pneumatic tire according to claim 1, wherein the lug groove is interrupted by intersecting with the tire circumferential groove on the inner side in the tire axial direction.

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