JPS63258203A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve wandering-proof and eccentric abrasive resistance by forming a small circular shoulder part being inscribed with a tread surface circular arc, while installing a circumferential narrow side groove in a specific part in a shoulder rib, forming a narrow rib therein, and installing a lot of sipes in this narrow rib. CONSTITUTION:The surface of a tread 2 is formed into a circular arc 12 in a radius RT, while a shoulder part is inscribed with this circular arc 12, formed into a small circular arc 13 in a radius RS, and both these circular arcs 12 and 13 are made contact with each other at a contact point P1. And the ratio of three radii RS/RT should be set to a range from more than 0.5% to less than 5.0%. A side groove of 0.5-2.0mm in width, whose depth D2 is more than 30% but less than 100% to depth D1 of a main groove is installed in a point P2 at the more cross direction inside than the point P1 in setting an angle alpha with the normal erected in the contact P2 to a range of 0 deg.-12 deg.. And, a lot of sipes are installed a narrow rib 10 to be formed in a shoulder rib 8 at a pitch of more than 0.6 D2 but less than 10 D2. With this constitution, wandering-proof and eccentric abrasion resistance are improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a pneumatic radial tire with improved wandering resistance and uneven wear resistance, and in particular to a pneumatic radial tire for heavy loads used in trucks and buses. It is suitable for radial tires.

(Prior art) Radial tires, especially heavy-duty radial tires that have a tread reinforced with three or more layers of steel breakers and are used under cylinder pressure, may suffer from a wandering phenomenon when running. many. The wandering phenomenon refers to a phenomenon in which when a vehicle is driving on a paved road with undulations or ruts formed on the surface due to vehicle traffic, the steering wheel is taken off due to a change in the road surface, and the direction of travel of the vehicle becomes unstable.

For example, when the tires of a moving vehicle are in ruts on the road surface and you turn the steering wheel to change direction, a convex part of the road surface contacts a part of the tire shoulder, and the impact is transmitted through the tires to the steering wheel, causing the steering wheel to turn. It is a phenomenon that is taken. A similar phenomenon occurs even when driving straight on a wavy road surface.

-C This phenomenon rarely occurs with bias tires, but mainly occurs with radial tires. This is because bias tires have a tread that easily deforms and can absorb the shock from the road surface, making it difficult to transmit it to the handlebars, whereas radial tires have a radial carcass that does not easily change angle and a breaker that has a strong hoop effect. This is because the tread has high rigidity and cannot absorb shock from the road surface.

Reducing the rigidity of the tread of a radial tire is effective in reducing the wandering phenomenon, but it also reduces the excellent characteristics of radial tires such as low fuel consumption, long life, low noise, and high durability. becomes undesirable.

In particular, heavy-duty radial tires with three to four steel breaker layers have extremely high tread rigidity, and six
Since the tire is used at a high internal pressure of ~8 kg/-, the rigidity of the entire tire is high, and the wandering phenomenon described above is likely to occur.

Conventionally, in order to solve this problem, the tread shoulders have a rounded shoulder shape to increase the contact area with the road surface protrusions and reduce the impact from the road surface, and the tread shoulders have been given a large number of sipes to increase rigidity. Some designs have been devised, such as those in which the diameter is locally lowered, or those in which a tapered shoulder shape and sipes are combined, as shown in Japanese Patent Application Laid-open No. 155504/1983.

However, none of these methods completely solves the wandering phenomenon described above, and problems remain.

(Problems to be Solved by the Invention) An object of the present invention is to provide a tire in which the above-mentioned wandering phenomenon is reduced to such an extent that it does not become a problem in actual use. Another object of the present invention is to reduce local early wear at the tread shoulders, so-called shoulder drop wear. This shoulder drop wear is caused by the difference in outer diameter between a part of the tread center and the tread shoulder, and the amount of slippage between the road surface and the tread surface during braking and free rolling is greater at the tread shoulder than at the tread center. It is often found in radial tires and has a negative impact on appearance, noise, tire maintenance, tire life, etc.

The inventors of the present application focused on the fact that shoulder drop wear mainly occurs in radial tires, similar to the wandering phenomenon described above, and that the more rigid the tread part is, the more difficult it is to alleviate the difference in outer diameter in the ground contact area. We have developed a tread shape that is effective in reducing shoulder drop wear as well as reducing the wandering phenomenon.

It goes without saying that the present invention does not reduce other performances of the radial tire, such as structural durability, fuel efficiency, handling stability, ride comfort, etc.

(Means for Solving the Problems) The present invention provides a surface shape of a small arc in which at least one shoulder of the tread is inscribed in the arc of the tread surface in a tire width direction cross section of the tire taken along a plane including the tire rotation axis;
It is a pneumatic radial tire having a so-called round shoulder shape, and is narrow enough in the circumferential direction of the tire that the opening closes at a point located inside the tire width direction from the point of contact between the arc of the tread surface and the small arc. It has a continuous side groove, and the narrow rib formed in the shoulder rib by the side groove is substantially discontinuous at both ends with a large number of sipes opening into the tread edge and the side groove, respectively. It is a pneumatic radial tire.

The present invention will be explained in detail below using the drawings.

FIG. 1 shows the right half of a tire widthwise cross-section of a tire according to an embodiment of the present invention taken along a plane including the tire rotation axis (not shown). The tire 1 consists essentially of cords arranged in the radial direction, and includes a carcass 4 wound from the inside to the outside of an annular bead core 5, and a relatively shallow 15 to 25 degrees to the tire circumferential direction on the outside of the carcass 4 in the tire radial direction. It has a breaker 6 consisting of at least two layers of substantially non-tensile cord intersecting at an angle. Although FIG. 1 shows a cross section of the carcass 4 having one layer and the breaker 6 having 4N layers, it also includes a case where the carcass 4 has multiple layers and the breaker 6 has two or three layers. The cord forming the carcass 4 is steel or nylon.

Organic fibers such as polyester and aromatic polyamide are used, and the cords forming the breaker 6 are made of substantially non-tensile cord materials such as steel, aromatic polyamides, glass fibers and the like.

The tread 2 is annularly placed on the radially outer side of the breaker 6 and has main grooves 7a and 7b continuous in the circumferential direction. Although this example shows a case where the tread has three leading grooves, the center groove 7a and the shoulder groove 7b, the present invention is not limited to this, and the present invention can also be applied to a tread having two or four or more leading grooves. In particular, the present invention is effective when the shoulder rib 8 formed by the shoulder Ya7b has a wide width and the shoulder portion is highly bidirectional, since the aforementioned wandering phenomenon is generally likely to occur.

The surface of the tread 2 forms a circular arc 12 with a radius RT having its center on the center line CL, which is the intersection line of the tire equatorial plane and the tire width direction cross section, and a small circular arc 13 with a radius R3 inscribed in this circular arc 12 at the shoulder part. has. The small arc 13 further contacts the arc of the buttress portion. In this example, the arc of the buttress part has a radius RB and its center of curvature is on the outside of the tire, but depending on the type of tire, it may be an arc with its center of curvature toward the inside of the tire, or it may be a straight line. However, in order to prevent the wandering phenomenon, it is necessary that the small arc 13 has a shape that is in smooth contact with the small arc 13 and has no sharp inflection points. The small arcs may be formed on both shoulders of the tread, or may be formed only on the shoulders located on the outside of the vehicle when the tire is mounted on the vehicle. The ratio of the radius R3 of this small arc to the radius RT of the tread surface arc R3/
Preferably, RT is set in a range of 0.5% to 5.0%.

If it is less than 0.5%, it is difficult to reduce the wandering phenomenon, and if it is more than 5.0%, adverse effects such as a shortened life due to a decrease in ground contact area are likely to occur. Although this example shows a case where the circular arc 12 has a single circular arc shape, the present invention can also be applied to a case where the circular arc 12 is composed of two or more circular arcs. Tread surface arc 12
The side groove 9 located at a point P2 located on the inside in the tire width direction from the contact point P1 of the small arc 13 has a width of preferably 0.5 to 2.0 am, such that its opening closes when touching the ground. If it is less than 0.5 mm, the effect of preventing the wandering phenomenon will not occur. If it exceeds 2.0 mm, the thin rib 1 degree formed by the side groove 9 will be removed when a lateral force is applied to the tire. Movement in the width direction becomes excessive, and uneven wear starting from the periphery of the side groove 9 is likely to occur. The side grooves 9 may be provided with an inclination angle α such that the openings of the narrow ribs 10 are inclined toward the groove bottom and toward the outside of the tire so that the narrow ribs 10 are easily deformed when subjected to impact from the road surface. .

The inclination angle α can be set in the range of 0 to 12 degrees with respect to the normal line to P2 depending on the shape of the buttress portion. If it is smaller than 0 degrees, that is, if the direction of inclination is reversed, the bending rigidity of the thin ribs 10 will be high and the effect will be small; if it exceeds 12 degrees, the thin ribs 10 will suffer from rib tear (a phenomenon in which ribs are damaged by external force). ), which is undesirable. Also, for the same reason, the depth D2 of the side gutter 9 is within the range of 30 to 100% of the leading depth Dl, preferably 60 to 10%.
It is set within the range of 0%.

FIG. 2 is a developed view of the tread surface of this example, and FIG. 3 is a diagram showing a detailed cross section near the shoulder of the tire. The narrow rib 10 formed in the shoulder rib 8 by the side groove 9 in FIG. 2 is divided by a large number of sipes 11 shown in FIG. 3. The narrow rib 10 is completely divided into each block 15 by opening one end of the slide 11 to the tread end and opening the other end to the side groove 9. As a result, each block 15 moves independently and follows changes in the road surface. If the sipe 11 does not open at either end, stress will be concentrated at that end and cranking will likely occur. The sipe interval W3 is determined by the depth D2 of the side gutter 9, and is in the range of 0.6 to 10 times, preferably 100 to 200%, of D2.

In FIG. 3, the depth Dj of the sipe 11 cannot exceed the depth D2 of the side groove 9, but in order to reduce the bending rigidity of the narrow rib IO and give the block 15 a movement that follows the road surface, it is necessary to % or more is required.

It is desirable that the width W2 of the narrow groove is less than or equal to 2 of the shoulder rib rll W1 and greater than the depth D2 of the side groove 9. When Wl is 2 or more than W2, the ridge 11 of the thin rib 10
The effect becomes larger and less effective.

Moreover, when it is smaller than D2, the rib tear is likely to occur. Note that Wl and W2 are measured along the arc 12 of the tread surface from the intersection of the extended lines of the arc 12 of the tread surface and the arc of the buttress portion to the edge of the shoulder rib and the center of the opening of the side groove 9. .

Further, as shown in FIG. 5, the sipes 11 can be inclined at an inclination angle β of 0 to 15 degrees with respect to the width direction of the tire. It is desirable that the sipe spacing W3 be uniform in the tire circumferential direction, but if a zigzag shape with irregular pitch variations is primarily used to reduce noise, it can be changed accordingly.

Although this example shows a case in which the side grooves 9 extend linearly in the circumferential direction, they may also have a zigzag shape within the scope of the present invention. The circumferential width of the sipe 11 (not shown) is 1.0
It is necessary that it is less than m. 1. When it exceeds On, step wear is likely to occur in the blocks before and after the sipe 11. When forming the sipe 11 with a tire mold, 1. By placing a blade with a thickness of less than Q u+ in the mold. Conventionally, when a shoulder sipe was formed by placing a thin blade in a mold, there was a problem with the blade deforming or coming off during vulcanization, but in the present invention, a mold in which the blade forms the side groove 9 is used. This problem has been solved because it is fixed by the part and the mold body.

Alternatively, the sipes 11 can be formed by cutting the sipes 11 with a knife after the tire is vulcanized.

In that case, the width of the sipe 11 in the circumferential direction becomes substantially zero.

(Function) In FIG. 4, while the tire 1 of the present invention is running on a road surface 14 on which ruts are formed, it shifts to the 1" position due to a course change, and at that time, it comes into contact with the 14 degree swing of the road surface convexity and moves away from the road surface. The reaction force of the tread is received by the tread shoulder.At this time, the shoulder having the small arc shape 13 gradually comes into contact with the convex part of the road surface and increases the contact area, so it has the effect of alleviating the sudden impact. The rope rip lO completely divided into blocks 15 is easily deformed, and the side grooves 9 are laterally compressed to absorb the reaction force from the road surface, thus reducing the wandering phenomenon.

Furthermore, when mounted on a free rolling wheel, the thin ribs 10, which are separated from the tread body by the side grooves 9 and divided into a large number of blocks 15, are caused by the difference in outer diameter between the tread shoulders and a part of the center during straight running and cornering. This prevents the amount of slippage between the road surface and the tread surface from increasing at the tread shoulders, reducing shoulder drop wear. In other words, the slippage of the tread shoulder mainly occurs at both ends of the tire contact surface, particularly at the sliding surface where the tire surface separates from the contact surface in the case of a steered wheel during cornering. At this time, the tire of the present invention has sipes 1 in the narrow lips 10 separated from the tread body.
1 opens easily and alleviates this slippage. Since both ends of the sipe 11 are open to the tread end and the side groove 9, this effect is greater than the conventional shoulder sipe in which only one end is open to the tread end.

(Example) The present invention was applied to a tire having a size of 11R22,51APR and having a 4N steel breaker and one layer of steel carcass based on FIGS. 1 to 3 and FIG. 5. Below, the tire is assembled on an 8.25X 22.5 rim with an internal pressure of 7
．． The basic tread pattern and structure, showing the dimensions of each part when filled with 25 kg/cd, are the same as in FIGS. 3 and 1.

First Example WT=216 Crane W 1 = 49.5 Dragon W2=18. Om1 W 3 = 14 am (W3/D2=1.0) W 4 = 2. Otm DI=14 Dragon D2=14 Crane (D3/D2=1.0) α=10' β=0″ RT=550 Dragon R3=25m (RS/RT=0.045) RB=100 Dragon 2nd Example WT = 216 awards W 1 - 4 9. 5 1 time W
2-2 0. O fin W3=17 Crane (W3/D2=2.0) W 4 = 1. O-chan D1 = 14 Rhyme D 2 = 8. 5 Crane (D2/DI=0.61) D3=4 Crane (D3/D2=0.47) α = O @ β = 0 @ RT=550 Fin R3=5 Seal■ (RS/RT=0.OO9) Both of the above two examples were compared with actual tires of the same size and pattern without side grooves (comparative example) and without side grooves and sipes (comparative example 2).

Good results were obtained in laboratory tests. Among the examples, the first example performed well in both the actual vehicle test and the two-vehicle test.

(Effects of the Invention) According to the present invention, the wandering phenomenon was reduced to such an extent that it would not be a problem in actual use, and uneven wear at the tread shoulders could be prevented.

[Brief explanation of the drawing]

1 and 2 are views showing an embodiment of the pneumatic radial tire according to the present invention, FIG. 3 is a detailed view thereof, FIG. 5 is a view showing another embodiment, and FIG. Schematic l for detailed explanation of the present invention... Pneumatic radial tire according to the present invention, 2... Tread, 6... Breaker 1 7a... Lead 7b... Lead 8...・Shoulder rib 9... Side groove 10... Thin rib 11... Sipe 13... Small arc W3... Sipe interval D2... Side groove depth R3... Radius of small arc Patent applicant Sumitomo Rubber Industries Co., Ltd. Representative Patent Attorney Yoshihei Nakamura Figure 1 Figure 2 Figure 3

Claims (5)

[Claims] (1) A pneumatic radial tire in which at least one shoulder of the tread has a surface shape of a small circular arc (13) inscribed in a circular arc (12) on the tread surface in a cross section in the tire width direction, and is characterized by the following features. (a) A tire with such a width that the opening closes at a point (P2) located inside in the width direction of the tire from the point of contact (P1) between the arc (12) on the tread surface and the small arc (13) on the tread shoulder. Having side grooves (9) that are generally continuous in the circumferential direction. (b) The narrow rib (10) formed in the shoulder rib (8) by this side groove (9) has a large number of sipes (11) that open on both sides to the tread end and the side groove (9), respectively.
be substantially discontinuous due to (2) Groove width (W4) on the tread surface of the side groove (9)
is 0.5 mm or more and 2.0 mm or less, and the depth (D2
) is 30% or more and 100% or less of the main groove depth (D1). (3) The side groove (9) has a shape that is inclined outward from the opening toward the groove bottom, and this inclination angle (α)
3. The pneumatic radial tire according to claim 1 or 2, wherein the angle is within a range of 0 degrees to 12 degrees with respect to the normal line to the point (P2). (4) The sipes (11) are arranged in the tire circumferential direction at a pitch (W3) that is 0.6 times or more and 10 times or less the depth (D2) of the side groove, and ranges from 0 degrees to 15 degrees with respect to the width direction of the tire. and the depth (D2) of the gutter is 40
The pneumatic radial tire according to any one of claims 1 to 3, wherein the pneumatic radial tire has a depth (D3) of % or more and 100% or less. (5) The radius of curvature (RS) of the small arc of the tread shoulder is 5.0% or more of the radius of curvature (RT) of the tread surface.
% or less, the pneumatic radial tire according to any one of claims 1 to 4.