JP2001055014A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress a dirt blockage in a lag groove, and to improve steering stability on a dry road. SOLUTION: A tread surface 2S is provided with a tread groove including at least a lag groove 3. The sea area ratio (Sg/St) of the tread surface 2S is not less than 40%, the groove center line angle θ between a groove center line C of the lag groove 3 and a tire shaft direction line is 0 to 40 degrees, and the length Wg of the lag groove 3 in the tire shaft direction is 0.15 times or more of a tread width TW. A groove wall surface tilting angle α to a normal N stood on the tread surface 2S of a lag groove all surface 3S is increased from a groove wall surface tilting angle α1 at a tire shaft direction inner end of the lag groove 3 to a groove wall surface tilting angle α2 at an outer end.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for both off-road use and on / off-road use, and can reduce mud clogging in a lug groove, and can be operated on muddy ground without impairing steering stability on a dry road. The present invention relates to a pneumatic tire capable of improving the performance.

[0002]

2. Description of the Related Art Pneumatic tires for off-road use and on / off-road use, which enable traveling on muddy terrain,
In general, a block type or lug / rib type tread pattern in which the lug groove is used as the basis and the groove length and groove depth of the lug groove are increased is employed, and the sea area ratio of the tread pattern (the total area of the tread groove relative to the tread area St). The ratio (Sg / St) of the groove area Sg is, for example, 40%
The above is set to be large.

[0003] Thereby, the mud is firmly gripped in the lug groove, the mud is dug up, the frictional force and the shearing frictional force are increased,
It ensures traction in muddy areas. In order to further enhance the traction, the inclination angle of the lug groove wall surface is set to be as low as, for example, about 10 °, that is, arranged at an angle close to a right angle to the tread surface.

[0004]

However, the lengthening of the rug groove, the increase in the sea area ratio, and the decrease in the inclination angle on the rug groove wall surface cause a decrease in pattern rigidity, and the steering stability on a dry road is reduced. Lower. Further, this method has a problem that the mud repelling property is deteriorated, and the mud caught in the groove is not discharged and is easily clogged. In particular, when mud jam occurs in the rug groove, the traction property does not function, and the running performance on muddy ground is remarkably deteriorated.

Therefore, the present invention basically increases the groove wall inclination angle α of the lug groove 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. It is another object of the present invention to provide a pneumatic tire capable of effectively suppressing mud clogging in a lug groove, increasing cornering power by increasing the pattern rigidity at the tread end side, and improving steering stability on a dry road.

[0006]

In order to achieve the above object, the invention of claim 1 of the present application has a tread groove including at least a lug groove extending inward in the tire axial direction from a tread edge on a tread surface, In addition, the pneumatic tire is suitable for traveling on muddy terrain with a sea area ratio (Sg / St) of 40% or more, which is the ratio of the area St of the tread surface to the total groove area Sg of the tread groove in the tread surface. The lug groove has a groove center line angle θ of 0 to 40 degrees with respect to a tire axial direction line of the groove center line, and a tire axial length W of the lug groove.
g is not less than 0.15 times the tread width TW, and the lug groove wall surface sandwiching the lug groove includes the lug groove wall surface. The inclination angle α of the groove wall surface, which is an inclination angle in a plane perpendicular to the plane, is increased from the inclination angle α1 of the groove wall surface at the inner end in the tire axial direction of the lug groove to the inclination angle α2 of the groove wall surface at the outer end. I have.

According to the second aspect of the present invention, the difference (α2-α1) between the groove wall surface inclination angles α1 and α2 is 10 to 30 degrees.

In the invention according to claim 3, the lug groove is
On the inner side in the tire axial direction, the tire is characterized by being interrupted by intersecting with the tire circumferential groove.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 illustrate 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. , Tread surface 2S
A tread groove 4 including at least a lug groove 3 extending inward in the tire axial direction from the tread edge TE.

In the present embodiment, as the tread groove 4, tire circumferential grooves 5, 5 arranged on both sides of the tire equator CO are provided.
The lug grooves 3 extending inward in the tire axial direction from the tread edge TE and intersecting with the tire circumferential grooves 5 are cut off.
And a lateral groove 6 which crosses between the tire circumferential grooves 5, 5 is illustrated. Thereby, in the present example, a block type tread pattern including the middle blocks Bi arranged in the circumferential direction on the tire equator CO and the shoulder blocks Bo arranged in the circumferential direction along the tread edge TE is formed. I have.

In this tread pattern, the sea area ratio (Sg / Sg), which is the ratio of the area St of the tread surface 2S to the total groove area Sg of the tread groove 4 in the tread surface.
t) is set to 40% or more. This is because when traveling on bad roads, especially on muddy ground, the sea area ratio (Sg / St)
It is also important in the present application. If it is 40% or less, the influence of buoyancy becomes large, and it becomes difficult for the block B to penetrate deep into the ground to firmly grip the mud, so that good traction on muddy ground cannot be obtained. Because.
If the sea area ratio (Sg / St) exceeds 65%, steering stability on a dry good road (for example, asphalt road surface) is undesirably deteriorated.

Next, in the present application, the lateral groove opening at the tread edge TE is defined as "lug groove 3", and the lug groove 3 is formed in the tire axial direction with respect to the groove center line C for the traction. The groove centerline angle θ with respect to the line is restricted to 0 to 40 degrees. When the groove center line angle θ exceeds 40 degrees,
The circumferential frictional force of the mud gripped in the lug groove 3 and the circumferential frictional force generated by the mud digging up are significantly reduced, making it difficult to ensure traction. Here, the “groove center line C” means a line passing through the center between the ridge lines E on the tread surface 2S of the lug groove 3.

In the lug groove 3, the length Wg in the tire axial direction is set to 0.15 times or more the tread width TW. Here, the length Wg of the lug groove 3 in the tire axial direction (hereinafter referred to as a lug groove length Wg) means a distance from a point P where the groove center line C ends to the tread edge TE, and in this example. As described above, when the lug groove 3 intersects the tire circumferential groove 5,
As shown in FIG. 1, the groove center line C means a distance from a point P at which the tire circumferential groove 5 intersects a ridge line L on the outer side in the tire axial direction to a 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 too small.
Conversely, when the lug groove length Wg is larger than 0.35 × TW, side slip tends to occur due to a decrease in rigidity and edge components at the center of the tread. In FIG. 1, for convenience, the tread pattern is shown using the ridge line of the tread groove 4 on the tread surface 2S. Therefore, in FIG. 1, the groove bottom and the groove wall surface are not distinguished.

Here, the "tread width TW" means the distance between the tread edges TE in the axial direction of the tire.
In this example, the tread surface 2S and the tread side surface BS (buttress surface) form a so-called square shoulder in which the tread edge TE intersects the tread edge TE by the square intersection.
Is formed as an example. In addition, although it is not generally adopted 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 the tread surface 2S intersects via a small arc surface is used. In this case, the tread edge TE is formed by the intersection of the tread surface 2S and the inclined surface or the small arc surface.

In the present application, as shown in FIGS. 3 and 4, the groove wall surface inclination angle α (inclination angle) of the lug groove wall surface 3S.
Is greatly increased from the groove wall surface inclination angle α1 at the inner end Y1 in the tire axial direction of the lug groove 3 to the groove wall surface inclination angle α2 at the outer end Y2.

Here, the "groove wall surface inclination angle α" is, as shown in FIGS. 4 and 5, a normal line N to a normal line N set on the tread surface 2S where the lug groove wall surfaces 3S are continuous. And the inclination angle of the lug groove wall surface 3S in a plane NS orthogonal to the lug groove center line C.

The inner end Y1 and the outer end Y2 are
The distance of 0.15 times or less the length of the lug groove wall surface 3S at the ridge line E means a region separated from the inner end point P1 and the outer end point P2 of the ridge line E.

At the inner end Y1, the groove wall inclination angle α1 does not increase at least toward the inner end point P1.
That is, it is substantially constant or gradually decreases toward the inner end point P1. At the outer end portion Y2, the groove wall surface 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.

As described above, the lug grooves 3 increase the groove wall surface inclination angle α from the inner end portion Y1 to the outer end portion Y2, so that the lug grooves 3 are formed by the lug groove wall surfaces 3S and 3S.
Gradually falls outward in the tire axial direction, that is, has a trumpet-like shape in which the groove width extends radially outward.

As a result, due to the centrifugal force of the rotation of the tire, the mud that has entered the lug groove 3 tends to be discharged radially outward.

In addition, since mud enters the lug groove 3 newly,
For example, a force that squeezes outward in the tire axial direction is generated, such as the original mud moving along the inclination of the lug groove wall surface 3S.

Further, as shown in FIG. 6, in the shoulder block Bo between the lug grooves 3, 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 is larger on the inner side than on the outer side in the tire axial direction,
The mud in the lug groove 3 is guided outward in the tire axial direction.

These functions are organically combined with each other to function, and as a result, the earth discharging property is greatly improved, and the mud clogging of the lug grooves can be effectively suppressed.

As described above, the shoulder block Bo
The stiffness of the tire increases on the outer side in the tire axial direction, so that the cornering power increases.Therefore, driving stability such as rigidity and behavioral stability on a dry road, particularly on cornering, is greatly improved. Can improve. Here, the difference (α2−α1) between the groove wall surface 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 earth discharging property and the improvement of steering stability are improved. The effect is not fully exhibited. Conversely, if the angle exceeds 30 degrees, the cross-sectional area of the lug groove 3 becomes too small, which is disadvantageous for the running performance on muddy ground.

The value itself of the groove wall surface inclination angle α1 is:
Although not particularly limited, the range of 2 to 10 degrees is generally used, and the groove depth Dg of the lug groove 3 is also 12 to 18 m as in the conventional case.
m is preferred. It is most preferable to increase the groove wall inclination angle α between the inner end portion Y1 and the outer end portion Y2 continuously and smoothly as in this example, but it is also possible to increase the angle stepwise. At this time, it is preferable to divide the step into at least three or more steps so as to minimize the step.

The shape, size (groove width and groove depth), number 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 freely changed as required. it can.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pneumatic tire having a tread pattern of FIG. 1 and a tire size of 235 / 85R16 was prototyped based on the specifications shown in Table 1, and each of the test tires was discharged on a muddy ground, traction force (traction force), and start acceleration. Thyme as well as steering stability on dry roads were tested.

(1) Discharge property on muddy ground: A test tire was mounted on a rim (6J × 16) under the conditions of internal pressure (200 kPa).
Attached to all wheels of a vehicle (RWD vehicle with four-wheel drive), depth of about 2
×, △, ○, ◎ by visual observation of the mud jam condition when traveling on a muddy ground test course with a mud layer of 00 mm
Was determined in four steps.

(2) Traction force on muddy ground (traction force)
Each of the measurements was performed 10 times by a climbing test, and the average value was used to make a judgment in four stages of ×, Δ, ○, and ◎.

(3) Start acceleration time on muddy ground: The start time required for traveling from a stationary state to 20 m on the test course was measured 10 times, and the average value was used to determine ×, Δ, ○, ◎. Was determined in four steps.

(4) Driving stability on a dry road: Driving stability on a test course on a dry asphalt road surface using the above vehicle was evaluated by a sensory evaluation of a driver as x, Δ, 、, ◎. It was judged at the stage.

[0032]

[Table 1]

[0033]

As described above, according to the present invention, the groove wall inclination angle α1 at the inner end in the tire axial direction of the lug groove is changed from the groove wall inclination angle α1 at the outer end to the groove wall inclination angle α2 at the outer end.
Since it is increased, the mud clogging of the rug groove can be effectively suppressed, and the steering stability on the dry road can be improved.

[Brief description of the drawings]

FIG. 1 is a developed view of a tread pattern of a tire according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a lug groove.

FIG. 3 is a perspective view showing a lug groove.

FIGS. 4A and 4B are groove wall inclination angles α of lug grooves.
1 is a sectional view showing α2.

FIG. 5 is a plan view showing a lug groove together with its groove wall surface.

FIG. 6 is a diagram illustrating one of the functions and effects of the present invention.

[Description of References] 2S Tread surface 3 Lug groove 3S Lug groove wall surface 4 Tread groove 5 Tire circumferential groove C Lug groove groove center line N Normal line on tread surface TE Tread edge Y1 Inner end of lug groove Y2 Lug Outer end of groove

Claims (3)

[Claims] 1. A tread surface comprising a tread groove including at least a lug groove extending inward in the tire axial direction from a tread edge, and furthermore, an area St of the tread surface and a total groove area Sg of the tread groove in the tread surface. A pneumatic tire suitable for running on muddy ground with a sea area ratio (Sg / St) of 40% or more, wherein the lug groove has a groove centerline angle θ with respect to a tire axial direction line of the groove centerline. 0 to 40 degrees, and the tire axial length Wg of the lug groove is set to 0.15 times or more the tread width TW, and the lug groove wall surface sandwiching the lug groove is connected to the tread surface. The groove wall surface inclination angle α, which is an inclination angle in a plane including the normal line and perpendicular to the lug groove center line with respect to the established normal, is outside of the groove wall surface inclination angle α1 at the tire axial direction inner end of the lug groove. At the end Groove wall surface inclination angle α2
A pneumatic tire characterized by increasing the number of tires. 2. The difference (α2) between the groove wall inclination angles α1, α2.
The pneumatic tire according to claim 1, wherein -α1) is 10 to 30 degrees. 3. The pneumatic tire according to claim 1, wherein the lug groove intersects with the tire circumferential groove and is interrupted on the inner side in the tire axial direction.