JP2000006616A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a wandering performance while suppressing partial wear. SOLUTION: In a cross section including a tire axis, a tread surface 2a is formed with a center arc part 4 made from an arc having the center on a tire equator surface, and a shoulder arc part 5 made from a small arc having a radius of curvature Rs of 10 to 50 mm, wherein one end of the small arc is inscribed in the center arc part 4 and the other end is communicated to a side wall surface 3a. A circumferential direction narrow groove 9 continuously extending in a tire circumferential direction is formed close to the shoulder arc part 5. In a sectional center line extending from a groove bottom to an opening end in the cross section of the circumferential direction narrow groove 9, the groove bottom forms an angle θ1 of 0 to 20 degrees to a tread normal to a virtual tread surface including the sectional center line, on the outside in a tire axial direction. A axial direction narrow groove 10 extending in the tire axial direction is provided on the shoulder arc part 5. A groove bottom of the axial direction narrow groove 10 forms a concave arc having a radius of curvature Ra of 0 to 50 mm in a cross section along the groove bottom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a pneumatic tire capable of improving wandering performance.

[0002]

2. Description of the Related Art A pneumatic tire, particularly a pneumatic tire for a small truck, has a higher tread rigidity than a tire for a passenger car. Easy to be taken. Therefore, there is a strong demand for small truck tires to have improved stability performance during such rutted traveling, that is, improved wandering performance.

Conventionally, in order to improve such wandering performance, a radius of curvature on the shoulder side is reduced on the tread surface to provide a sipe in the tire axial direction (see, for example, JP-A-63-258203). Japanese Patent Application Laid-Open No. 1-95911) and the like have been proposed to provide narrow grooves in the shoulder portion in the circumferential direction of the tire (for example, Japanese Patent Application Laid-Open No. 1-95911), but the effect is not yet sufficient.

Generally, in order to improve the wandering performance, the rigidity of the tread shoulder portion is reduced,
It is effective to generate a lateral force (camber thrust) for trying to climb a rut on a tire. As a result, the tire climbs the rut without difficulty, and at this time, the driver of the vehicle hardly gets the steering wheel.

However, since a large load acts on the shoulder portion of the tread surface of a pneumatic tire during turning or the like, depending on the method of reducing the rigidity, steering stability is likely to be deteriorated and uneven wear is likely to occur. There's a problem.

The present invention has been devised in view of such a problem, and the axial end of the tread surface is formed by a small arc, and the small arc extends in the tire axial direction and has a groove bottom. Air that can greatly improve wandering performance by reducing the rigidity of the tread shoulder while suppressing the deterioration of steering stability and the occurrence of uneven wear, based on the provision of a concave narrow arcuate axial groove. An object of the present invention is to provide a pneumatic tire, particularly a pneumatic tire most suitable for a light truck.

[0007]

According to a first aspect of the present invention, there is provided a tread main portion comprising a circular arc having a center on the tire equatorial plane, and one end point A having the central circular portion. And the other end point B is connected to the sidewall surface and the radius of curvature Rs has a shoulder arc portion formed of a small arc of 10 to 50 mm to form a tread surface in a cross section including the tire axis, and the tire equatorial plane, Distance L between 95 and 100% of distance Z along tread surface between one end point A
1 continuously extends in the tire circumferential direction at a position separated from the equatorial plane of the tire in the tire axial direction and has a groove width W1 of 0.5 to 2.
0 mm, a groove depth d1 of which is 50-100% of a groove depth d of the circumferential main groove formed in the central arc portion, and a groove in the cross section of the circumferential thin groove. The cross-section center line extending from the bottom to the opening end has a groove bottom side with respect to a tread normal to a virtual tread surface through which this cross-section center line passes, and forms an angle θ of 0 to 20 ° with respect to a side that is outward in the tire axial direction, The groove width W2 extends beyond the other end point B outward in the tire axial direction starting from a position separated from the equatorial plane of the tire by a distance L2 of 102 to 105% of the distance Z in the tire axial direction.
Is provided with an axial narrow groove of 0.5 to 1.5 mm and a maximum groove depth d2 of 3 to 7 mm, and the groove bottom of the axial thin groove has a radius of curvature Ra of 10 to 10 in a cross section along the groove bottom. This is a pneumatic tire having a concave arc shape of 50 mm.

According to the second aspect of the present invention, in the shoulder arc portion, a lug-shaped groove having a groove width larger than the axial narrow groove is spaced apart in the tire circumferential direction, and the shoulder arc is formed between the lug-shaped grooves. 2. The pneumatic tire according to claim 1, wherein up to four narrow grooves in the axial direction are formed. 3.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the pneumatic tire according to the present embodiment includes a carcass 6 including, for example, three carcass plies 6A, 6B, and 6C from a tread portion 2 to a bead portion of a bead portion (not shown) via a sidewall portion 3; A radial tire for a small truck having a belt layer 7 disposed inside the tread portion 2 and outside the carcass 6 in the tire radial direction, for example, having a load acting on one tire of 1 ton or more. ing.

In the carcass 6, the carcass cords are arranged at an angle of, for example, 70 to 90 degrees with respect to the tire equator,
As the carcass cord, for example, an organic fiber cord such as polyester, nylon, or rayon is adopted. It should be noted that a steel cord can be used if necessary. Further, the belt layer 7 has a cord, for example, 15 to 4 with respect to the tire equator.
At least two, in this example, two inner and outer belt plies 7A and 7B, which are arranged at an angle of small 5 ° and are superposed in a direction in which the cords cross each other, and the tread portion 2 is loosely fastened. Thereby increasing its rigidity.

The pneumatic tire has a tire equatorial plane CP.
A central arc portion 4 which is composed of an arc C1 having a center O on the upper side and forms a main portion of the tread; and a sidewall surface 3a in which one end point A is inscribed in the central arc portion 4 and the other end point B is the surface of the sidewall portion 3 And the radius of curvature Rs is 10
A tread surface 2a is formed in a cross section including the tire axis by the shoulder arc portion 5 formed of a small arc C2 of about 50 mm.

As described above, the shoulder circular arc portion 5 of the tread surface 2a is formed into a small circular arc C2 having a limited radius of curvature.
It is a premise that a large camber thrust is generated on the tire. When the radius of curvature Rs is less than 10 mm,
In the case where the thickness exceeds 50 mm, the effect of increasing the camber thrust is not so high in any case, so that the object of the present invention of improving wandering performance cannot be achieved.

As shown in FIGS. 1 and 2, the central arc portion 4 has one or more, preferably two or more, extending in the tire circumferential direction in the present embodiment, and in this embodiment, the tread surface 2a (the central arc portion 4). ) Shows four main grooves G (two shown in the figure, only the left half of the tire is shown). In order to exhibit a good drainage function, the main groove G has, for example, a groove width W of 3 to 7%, preferably 4 to 6% of the tread width TW, and a groove depth d of 6 mm.
As described above, 5 to 9% of the tread width TW, preferably 6 to 9%
It is preferred that In this specification, the “tread width” is the distance between the tread edges E, E in the tire axial direction, and the tread edge E is a virtual extension of the surface of the central arc portion 4 and the surface of the sidewall portion 3. The tire radial direction line passing through the intersection point intersects with the tread surface 2a.

Between these main grooves G, G and between the main groove G and the tread edge E, rib-like portions 13A, which contact the road surface,
13B and 13C are formed. Further, these rib-shaped portions are provided with appropriate lateral grooves, cuts, and the like, and the rigidity thereof is adjusted.

In this embodiment, the tread surface 2a has a tread surface 2 between the tire equatorial plane CP and the one end point A.
A circumferential narrow groove 9 having a groove center line at a position separated from the tire equatorial plane CP in the tire axial direction by a distance L1 of 95 to 100% of the distance Z along the a, and extending continuously in the tire circumferential direction is formed. Have been. Such a circumferential narrow groove 9 reduces the rigidity of the tread surface 2a on the shoulder side, and helps to further increase the camber thrust of the tire.

As a result of various experiments by the present inventors, in order to improve the wandering performance, the shoulder circular arc portion 5 is provided with the circumferential narrow groove 9 near one end point A in which the central circular arc portion 4 is inscribed.
When the distance L1 is less than 95% or more than 100% of the distance Z, the camber thrust due to the synergistic action with the shoulder arc portion 4 is effective. It was found that no significant improvement could be achieved, and that no improvement in wandering performance could be expected.

In the present embodiment, the circumferential narrow groove 9 extends linearly and continuously in the tire circumferential direction, and has a groove width W.
1 is set to 0.5 to 2.0 mm, and the groove depth d1 is set to 50 to 100% of the groove depth d of the main groove G.

When the groove width W1 of the circumferential narrow groove 9 is less than 0.5 mm, or the groove depth d1 is 5 times the groove depth d of the main groove G.
When it is less than 0%, the rigidity of the tread surface 2a on the shoulder side cannot be effectively reduced, and no improvement in the wandering performance can be expected. Conversely, when the groove width W1 of the circumferential narrow groove 9 exceeds 2.0 mm, or when the groove depth d1 exceeds 100% of the groove depth d of the main groove G, the rigidity of the shoulder portion is excessively reduced. Therefore, there is a problem that steering stability and abrasion resistance are deteriorated.

As shown in FIG. 3, the center line 9c extending from the groove bottom 9b to the open end in the cross section of the circumferential narrow groove 9 is the virtual tread surface 2V through which the center line 9c passes. Groove bottom 9 for tread normal N to
The side b forms an angle θ of 0 to 20 ° with respect to the outer side in the tire axial direction. When the angle θ exceeds 20 °, or when the sectional center line 9c of the circumferential narrow groove 9 is inclined inward in the tire axial direction with respect to the tread normal N, the tread edge Since the rigidity of the region sandwiched between E and the circumferential narrow groove is excessively reduced,
Abrasion resistance deteriorates.

As shown in FIG. 2, the shoulder arc 5 has a distance Z of 102 mm from the tire equatorial plane CP.
A narrow axial groove 10 extending beyond the other end point B of the small arc C2 is provided on the outer side in the tire axial direction from a position separated by a distance L2 of about 105% in the tire axial direction as a starting point. The axial narrow groove 10 is formed without communicating with the circumferential narrow groove 9, and suitably reduces the rigidity of the tread surface 2 a on the shoulder side, and can further contribute to the improvement of the wandering performance.

If the distance L2 from the tire equatorial plane CP to the starting point of the axial narrow groove 10 is less than 102% of the distance Z, the axial narrow groove 10 communicates with the circumferential narrow groove 9 to tread. There is a problem that the rigidity of the surface 2a on the shoulder side is excessively reduced, and steering stability is deteriorated and uneven wear occurs. Conversely, if the distance L2 is set to be greater than 105% of the distance Z, it becomes difficult for the axial narrow groove 10 to contact the road surface, and the effect of improving wandering performance cannot be obtained.

The present invention is characterized in that the groove bottom 10b of the axial narrow groove 10 has a concave arc shape having a curvature radius Ra of 10 to 50 mm in a cross section along the groove bottom 10b. As a result of various experiments by the inventors, it is possible to make the shoulder side of the tread surface 2a flexible by making the groove bottom of the axial narrow groove 10 formed in the shoulder arc portion 5 into a concave arc shape. It has been found that not only the ring performance can be improved, but also uneven wear caused by a decrease in rigidity on the shoulder side due to tire wear can be prevented.

That is, as shown in FIG. 5, when the groove bottom of the axial narrow groove 10 is formed substantially parallel to the tread surface 2a, the axial narrow groove 10 and the circumferential narrow groove 9 The rigidity of the intervening region X is significantly reduced, and uneven wear such as so-called step wear is likely to occur due to wear (indicated by a dashed line) due to running of the tire. On the other hand, in the axial narrow groove 10 having the concave arc-shaped groove bottom of the present embodiment, an extremely rigid step is hardly generated in a region between the axial narrow groove 10 and the circumferential narrow groove 9, The occurrence of uneven wear is suppressed.

If the radius of curvature Ra of the groove bottom of the concave narrow arc of the axial narrow groove 10 is less than 10 mm, the effect of suppressing uneven wear cannot be sufficiently obtained. Conversely, if it exceeds 50 mm, the tread surface 2a Therefore, the reduction in rigidity on the shoulder side cannot be effectively achieved, and the improvement of the wandering performance cannot be expected much.

The axial narrow groove 10 has a groove width W2 of 0.5 to 1.5 mm and a maximum groove depth d2 of 3 to 7 mm. This groove width W2 is less than 0.5 mm or the maximum groove depth d2
Is less than 3 mm, the wandering performance cannot be improved. Conversely, when the groove width W2 exceeds 1.5 mm or when the maximum groove depth d2 exceeds 7 mm, there is a problem that the wear resistance is poor.

In this embodiment, a lug-shaped groove 12 having a groove width W3 larger than the axial narrow groove 10 is provided in the shoulder arc portion 5 in the tire circumferential direction.
The figure shows that two to four, in this example, two, axially narrow grooves 10 are formed between 2 and 12. Such a lug-shaped groove 12 extends from the vicinity of the tread edge E to the outside in the tire axial direction, and reduces the rigidity on the shoulder side to reduce the rigidity in the axial direction.
This is preferable in that it can be performed together with.

The embodiment of the present invention has been described in detail above.
The present invention is not limited to the illustrated form, and various modifications are possible. For example, as shown in FIG. 4, the central arc portion may be formed by a plurality of arcs having a center on the tire equatorial plane CP. good. Further, the present invention can be suitably applied to a light truck tire, but is not limited to this tire category.

[0028]

EXAMPLES A pneumatic tire of the present invention having a tire size of 205 / 75R16 and shown in FIGS. 1 and 2 and Table 1 was prototyped (Examples 1 to 4), and the camber thrust per camber angle of the tire was obtained. Canvas stiffness, handling stability and abrasion resistance were tested. For comparison, tires (Comparative Examples 1 to 7) having the groove bottom shown in FIG. A similar test was performed. The test method is as follows.

<Camber stiffness> A camber thrust when a camber angle of 2 ° was given while a test tire was filled with an internal pressure of 600 (KPa) and a load of 9.5 KN was applied, and a camber angle of 1 ° was measured. The camber stiffness given per camber thrust was calculated.

<Manipulation Stability> The test tire is mounted on a small truck, and the characteristics related to steering wheel responsiveness, stiffness, grip, etc. are displayed on a dry asphalt road surface of the tire test course in a 10-point method by a sensory evaluation of a driver. are doing. The larger the value, the better.

<Abrasion resistance> A test tire was mounted on a small truck, and a total of 3000 km was run on a general road and an expressway, and the difference in the amount of wear between the inner side and the outer side in the tire axial direction of the circumferential narrow groove was determined and compared. It is indicated by an index with Example 1 being 100. The larger the value, the more uniform the abrasion and the more excellent the abrasion resistance. Table 1 shows the test results and the like.

[0032]

[Table 1]

[0033]

As described above, the pneumatic tire of the present invention can improve the wandering performance by increasing the camber thrust while suppressing the decrease in steering stability and uneven wear.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a pneumatic tire showing one embodiment of the present invention.

FIG. 2 is a development view of a tread portion and the like in FIG. 1;

FIG. 3 is an enlarged sectional view showing a shoulder arc portion of FIG. 1;

FIG. 4 is a contour diagram of a tread surface showing another embodiment of a central arc portion.

FIG. 5 is a partial sectional view showing a shoulder portion of a conventional pneumatic tire.

[Explanation of symbols]

 2 Tread portion 2a Tread surface 3 Side wall portion 3a Side wall surface 4 Central arc portion 5 Shoulder arc portion 6 Carcass 9 Circumferential narrow groove 10 Axial narrow groove G Main groove

Claims (2)

[Claims] 1. A central arc portion comprising an arc centered on the tire equatorial plane and constituting a tread main portion, one end point A is inscribed in the central arc portion and the other end point B is connected to the sidewall surface and has a radius of curvature. A shoulder arc portion formed of a small arc having a radius of 10 to 50 mm forms a tread surface in a cross section including the tire axis. The distance Z along the tread surface between the tire equatorial plane and the one end point A is 95 to A distance L1 of 100% is spaced apart from the equatorial plane of the tire in the tire axial direction, continuously extends in the tire circumferential direction, the groove width W1 is 0.5 to 2.0 mm, and the groove depth d1 is in the central arc portion. 5 of groove depth d of the formed circumferential main groove
A cross-sectional center line extending from the groove bottom to the open end of the circumferential narrow groove at the cross-section is defined by a tread normal to a virtual tread surface through which the cross-sectional center line passes. On the other hand, the groove bottom side forms an angle θ of 0 to 20 ° with respect to the side that is the outer side in the tire axial direction, and originates from a position separated from the equatorial plane by a distance L2 of 102 to 105% of the distance Z in the tire axial direction. An axial narrow groove extending beyond the other end point B and having a groove width W2 of 0.5 to 1.5 mm and a maximum groove depth d2 of 3 to 7 mm outside the tire axial direction; The pneumatic tire is characterized in that the groove bottom has a concave arc shape having a curvature radius Ra of 10 to 50 mm in a cross section along the groove bottom. 2. The shoulder arc portion has a lug-like groove having a groove width larger than the axial narrow groove and is spaced apart in the tire circumferential direction, and two to four axial lugs are provided between the lug-like grooves. The pneumatic tire according to claim 1, wherein a narrow groove is formed.