JPH0958223A - Pneumatic radial tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve resistance to edge separation at the end of a belt in a pneumatic radial tire for heavy load having a flat or wide tread. SOLUTION: A plurality of sipes 8 extending in the axial direction of a tire are disposed on a shoulder rib 6 at given intervals in the circumferential direction (T) of the tire. A depth (h) of the sipe 8 is made greater along the soulder end 6a and the touch-down length (m) of the shoulder end 6a side when the tread surface 1 touches to the ground is made shorter than the touch-down length (L) of the inner edge 6b side of the shoulder rib 6 facing a main groove 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy duty pneumatic radial tire used for trucks, buses and the like,
More specifically, the present invention relates to a pneumatic radial tire for heavy loads, which has a flattened or widened tread, and which suppresses edge separation occurring at the belt end portion.

[0002]

2. Description of the Related Art In recent years, heavy-duty pneumatic radial tires used for trucks, buses, etc. have tended to be flattened. By reducing the flatness ratio in this manner, the tire cross-section height is reduced, the volume of the sidewall portion is greatly reduced, the tread width is widened, and the wall thickness is reduced.

Therefore, when a large force is applied to the shoulder portion from the road surface during turning or the like when the steering wheel is turned,
The stress cannot be sufficiently absorbed, and as a result, stress concentrates on the belt end portion having a large difference in rigidity inside the tire, and edge separation easily occurs. Especially,
This tendency is remarkable in a heavy-duty pneumatic radial tire having a flatness of 70% or less. Further, the same problem as described above is also encountered in a heavy-duty pneumatic radial tire that has a wide tread in which the ratio between the tread width and the tire width is reduced.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a flat or wide-tread pneumatic radial tire for heavy loads, which is capable of improving edge separation resistance at the belt end portion. To provide tires.

[0005]

According to the present invention to achieve the above object, a flat groove having a main groove extending in the tire circumferential direction on a tread surface and having shoulder ribs defined by the main groove in a shoulder portion is provided. In a heavy-duty pneumatic radial tire having a wide tread, a plurality of sipes extending along the axial direction of the tire are arranged at the shoulder ribs at predetermined intervals in the tire circumferential direction, and the depth of the sipes is directed toward the shoulder end. The ground contact length m on the shoulder end side when the tread surface is grounded is set to be deeper, and the ground contact length L on the inner edge side of the shoulder rib facing the main groove is
It is characterized by being shorter than.

By arranging the sipes extending in the tire axial direction on the shoulder ribs at predetermined intervals in the tire circumferential direction in this manner, the rib rigidity of the shoulder portion can be reduced, so that the difference in rigidity can be reduced. While it is possible to disperse the stress by avoiding concentration on the belt end, make the depth of the sipe deeper toward the shoulder end,
Since the contact length m on the shoulder end side at the time of contact with the ground is made shorter than the contact length L on the inner edge side facing the main groove that defines the shoulder part, the shoulder end side is more likely to be deformed, and the shoulder part is easier to contact. Therefore, it is possible to avoid applying a large force from the road surface to the shoulder portion during turning traveling when the steering wheel is turned. As a result, it is possible to improve the edge separation resistance of the belt end portion. Further, since the sipes extend along the tire axial direction and are not inclined in the tire width direction, large uneven wear does not occur on the shoulder ribs.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The configuration of the present invention will be described in detail below with reference to the accompanying drawings. In FIG.
Reference numeral 1 denotes a tread surface of a flat pneumatic radial tire for heavy load, and a plurality of (4 in the figure) main grooves 2 extending straight along the tire circumferential direction T are provided on the tread surface 1.
A center rib 3 extending in the tire circumferential direction T is provided between the two main grooves 2 formed on the left and right sides with the tire center CL interposed therebetween.

Between the two main grooves 2 on the inner side of the tire and the two main grooves 2 on the outer side of the tire adjacent thereto, a plurality of narrow grooves 4 are formed, each of which extends obliquely in the tire width direction. A large number of blocks 5 are defined by the narrow grooves 4 and. Tread surface 1 divided by both outer main grooves 2
Shoulder ribs 6 extending along the tire circumferential direction T are provided on both shoulder portions.

According to the present invention, in the flat pneumatic radial tire for heavy load having the above-mentioned structure, the shoulder rib 6 has a plurality of notches extending along the tire axial direction (the tire width direction orthogonal to the tire circumferential direction T). Sipe 8 is provided. The plurality of sipes 8 are arranged in the tire circumferential direction T.
Are arranged at predetermined intervals along the depth of each sipe 8
2, has a configuration in which the depth is increased toward the shoulder end 6a of the shoulder rib 6 facing the outside of the tire.

The sipe 8 is formed so as to be gradually deeper from the inner edge 6b of the shoulder rib 6 facing the outer main groove 2, and the outer end 8a thereof is open to the side wall portion W side. The inner end 8b of the sipe 8 is in a closed state without opening in the outer main groove 2. As shown in FIG. 3, when the tread surface 1 is in contact with the road surface (filling reference air pressure for each tire), the contact length m on the shoulder end 6a side is shorter than the contact length L on the inner edge 6b side. It is configured.

By disposing a plurality of sipes 8 extending in the tire width direction on the shoulder ribs 6 at predetermined intervals in the tire circumferential direction in this manner, the rigidity of the shoulder ribs 6 is lowered, and the shoulder ribs 6 are arranged on the tire inner diameter side. While dispersing the stress concentrated on the end portion 10a of the arranged belt 10,
Make the depth h of the sipe 8 deeper toward the shoulder end,
By making the ground contact length m on the shoulder end 6a side at the time of ground contact shorter than the ground contact length L on the inner edge 6b side facing the outer main groove 2, the shoulder end 6a side is more easily deformed, and the handle It is possible to make the shoulder portion slippery during turning traveling when the vehicle is turned, and thereby avoid applying a large force from the road surface to the shoulder portion. Therefore, it is possible to suppress the occurrence of edge separation at the belt end portion 10a.

Further, since the sipe 8 is arranged to extend along the tire axial direction and is not arranged so as to be inclined with respect to the tire width direction, occurrence of large uneven wear on the shoulder rib 6 is avoided. be able to. The sipe 8 is
The number of sipes may be appropriately selected and provided so that the ratio m / L of the ground contact length m on the shoulder end 6a side and the ground contact length L on the inner edge 6b side is 0.7 to 0.9. preferable.
When m / L is smaller than 0.7, the shoulder drop wear on the shoulder end 6a side becomes large, so that the effect of improving the edge separation cannot be obtained. Also, m / L is 0.9
When it exceeds, the difference between the contact lengths m and L becomes small, so that the effect of improving the edge separation is reduced.

The depth h of the sipe 8 at the shoulder end 6a is preferably in the range of 20 to 80% with respect to the groove depth D of the outer main groove 2 which defines the shoulder rib 6. The present invention is not particularly limited as long as it is a flattened pneumatic radial tire for heavy loads, but preferably, it can be suitably used for a flattening ratio of 70% or less at which edge separation remarkably occurs. .

Further, in the above-mentioned embodiment, the flattened pneumatic radial tire for heavy load has been described. However, the present invention has a tread width A defined by a length between both shoulder ends and both sidewall portions W. Even in a heavy-duty pneumatic radial tire with a wide tread in which the ratio with the tire width S indicated by the maximum width in the tire width direction is smaller than in the conventional case, by providing the sipe 8 as described above on the shoulder rib, The same effect can be obtained. In particular, it can be preferably applied to the one in which the wide tread ratio represented by the ratio A / S of the tread width A and the tire width S is 0.7 or less.

[0015]

[Examples] Tires of the present invention having the same tire size of 295 / 70R22.5 and having the sipe shown in FIG. 1 provided on the shoulder ribs and a conventional tire having no sipe shown in FIG. 1 were manufactured. The tire of the present invention has m / L =
0.8, the conventional tire has m / L = 1.0. The depth h at the shoulder end of the sipe in the tire of the present invention is 50% of the groove depth D of the outer main groove.

Each of the test tires was subjected to an evaluation test for edge separation resistance and uneven wear resistance of the belt end portion under the following measurement conditions, and the results shown in Table 1 were obtained. Edge separation resistance Each test tire was mounted on a rim of 22.5 x 9.00 rim size, mounted on an indoor drum tester with an air pressure of 825 kPa, and a slalom running with a slip angle of ± 2 ° under a load of 31.87 kN. Then, the running distance until edge separation occurred at the belt end was measured, and the result was evaluated by an index value with the conventional tire being 100. The larger this value, the better the edge separation resistance.

[0017]

[Table 1]

As can be seen from Table 1, the tire of the present invention can effectively improve the edge separation resistance. Further, the tire size and the depth h at the shoulder end of the sipe were set to the same as above, and test tires 1 to 5 were manufactured, respectively, in the tire having the configuration shown in FIG. 1 with m / L changed as shown in Table 2.

Each of the test tires was subjected to an evaluation test of the edge separation resistance of the belt end portion under the measurement conditions shown above, and an uneven wear resistance evaluation test of the shoulder ribs under the measurement conditions shown below. By the way, Table 2
Were obtained. Uneven wear resistance Each test tire was mounted on a rim with a rim size of 22.5 × 9.00, mounted on the front wheel of a 10t truck with an air pressure of 825kPa, and after running 10,000 km, the amount of shoulder drop wear of the shoulder rib was measured. The conventional tire was evaluated with an index value of 100. The larger this value, the better the uneven wear resistance.

[0020]

[Table 2]

As is apparent from Table 2, the shoulder end 6
It is understood that the ratio m / L of the contact length m on the a side to the contact length L on the inner edge 6b side should be 0.7 to 0.9.
If the decrease in uneven wear resistance is within 10, there is no particular problem.

[0022]

As described above, according to the present invention, a plurality of sipes extending along the axial direction of the tire are arranged on the shoulder rib at predetermined intervals in the tire circumferential direction, and the depth of the sipes is directed toward the shoulder end. Since the contact length m on the shoulder end side when the tread surface contacts the ground is made shorter than the contact length L on the inner edge side of the shoulder rib facing the main groove, the load is flattened or widened. In a heavy-duty pneumatic radial tire, it is possible to improve the edge separation resistance at the belt end portion.

[Brief description of drawings]

FIG. 1 is a plan view of essential parts showing an example of a tread pattern of a heavy duty pneumatic radial tire of the present invention.

FIG. 2 is a meridian half cross-sectional view of a heavy duty pneumatic radial tire of the present invention.

FIG. 3 is an explanatory diagram showing a state of a tread surface at the time of grounding.

[Explanation of symbols]

1 tread surface 2 main groove 6 shoulder rib 6a shoulder end 6b inner edge 8 sipe T tire circumferential direction W sidewall part

Claims (4)

[Claims] 1. A flat or wide-tread pneumatic radial tire for heavy loads, comprising a main groove extending in the tire circumferential direction on a tread surface, and having shoulder ribs defined by the main groove in a shoulder portion, A plurality of sipes extending along the axial direction of the tire are arranged at the shoulder ribs at a predetermined interval in the tire circumferential direction, and the depth of the sipes is made deeper toward the shoulder end,
A heavy-duty pneumatic tire in which the ground contact length m on the shoulder end side when the tread surface contacts the ground is shorter than the ground contact length L on the inner edge side of the shoulder rib facing the main groove. 2. The ratio m / L of the contact length is 0.7 to 0.
The pneumatic tire for heavy loads according to claim 1, wherein the sipe is provided so as to be 9. 3. The heavy-duty pneumatic radial tire according to claim 1, wherein the sipe is open to the side wall portion side. 4. The flatness ratio is 70% or less, or the wide tread ratio represented by the ratio of the tread width to the tire width is 0.7.
The pneumatic radial tire for heavy loads according to claim 1, which is as follows.