JPH0415108A - Radial tire for heavy load - Google Patents

Abstract

PURPOSE:To reduce tear in sipes in shoulder ribs without impairing wandering performance by providing a pair of tilted grooves on the equator face of tire in the shoulder ribs and locating the surface of land section which is partitioned by the tilted grooves toward the inside of direction of radius of tire. CONSTITUTION:A tread section 12 of a tire 10 is provided with main grooves 14 in peripheral direction which are mutually apart in the direction of tire width and extend in the peripheral direction, ribs 16 which are partitioned by these and extend in the peripheral direction of tire, and shoulder ribs 18. In this case, a pair of tilted grooves 20a and 20b are provided in the shoulder rib 18 in the peripheral direction of tire. One tilted groove 20a is formed in the range of 20 to 80% of rib width S0 of the shoulder rib 18 from the end of tread 22 of tire, and the other tilted groove 20b is formed apart on the central part side of tread by 5 to 65% of the width S0 of the shoulder rib from the tilted groove 20a. The surface of land section 24 which is partitioned by the tilted grooves which form a pair mutually and extend in the peripheral direction of tire is located on the inside of direction of radius of tire than the profile shape of tread section 12, forming stepped land section.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heavy-duty radial tire for trucks, buses, etc., which effectively suppresses the wandering phenomenon that is noticeable in heavy-duty radial tires.

(Prior art) A carcass ply consisting of cords arranged substantially uniformly in the radial direction of the tire is wrapped around a bead wire at both ends of the carcass. Tires with a radial structure equipped with a belt made of braais have an angle of 35° to 40° with respect to the tire's equatorial plane due to the so-called "hoop" effect of the belt.
Compared to tires with a bias structure that has carcass plies and breakers made of cord layers diagonally intersecting within the angular range of Because it has many advantages such as low rolling resistance, it tends to be widely used in heavy-duty vehicles such as trucks and buses with the development and maintenance of expressway networks in recent years.

On the other hand, it has been pointed out that radial tires cause a so-called wandering phenomenon in which the steering wheel is taken off when the vehicle runs over or tries to overcome ruts that are often seen on roads with heavy traffic.

This means that when a tire runs into a rut, it is almost equivalent to running a tire along an inclined surface, and in this case, for bias tires, it corresponds to the deformation of the tread rubber that forms the tire's tread. camber in the direction in which the angle is given, that is, in the direction in which the tire moves over the rut.
Thrust acts and the shear force in the braking direction that acts on the tread of the tire is that the shear force that acts on the tread located on the mountain side of the slope is stronger than the shear force that acts on the tread located on the valley side. Since the ruts are relatively large, a rotational force in the direction of climbing the slope, that is, camber torque, is applied, making it easier to get over the ruts.In contrast, with radial tires, the tread rubber is This is thought to be because the movement of the camber thrust and camber torque cannot be expected because the movement of the camber is restricted.

This wandering phenomenon does not pose much of a problem with radial tires used for relatively lightweight vehicles such as passenger cars, as their internal pressure is relatively low, but the tread portion is extremely rigid. This is a noticeable phenomenon in heavy-duty radial tires, which are reinforced with belts and subjected to high internal pressure, and because they force the driver to perform unnecessary steering operations, they have become more difficult to drive over long distances as the expressway network develops. In the case of heavy-duty radial tires, which have become increasingly popular, this has become a major problem that must be solved.

(Problem B that the invention attempts to solve) One of the technologies proposed to meet these demands is
There is one shown in Japanese Unexamined Patent Publication No. 105583/1983, and as shown in Fig. 2, there is a rib on the shoulder rib 3 of the tire l that extends in the circumferential direction of the tire and extends in the equatorial direction. An auxiliary groove 5 that is inclined is provided, and a large number of sipes 7 that are oriented in the axial direction of the tire are arranged in the circumferential direction of the tire so as to cross the land area located outward in the width direction of the tire defined by the auxiliary groove 5. The auxiliary grooves are formed at regular intervals, and the auxiliary grooves are inclined with respect to the tire's equator plane, and the sipes are provided in the land area divided by the auxiliary grooves.
The crushing of the shoulder ribs due to contact with the road surface causes a camber thrust along the slope, and a moment due to the shearing force acting in the tire braking direction, that is, camber thrust in the direction of overcoming the ruts. This generates torque and improves wandering performance. In addition, the code|symbol 9 is a circumferential direction main groove, and extends continuously in the tire circumferential direction.

However, due to the formation of a large number of sipes 7 in order to make the crutching of the shoulder ribs more effective, the portion divided by the sipes is easily torn off (hereinafter referred to as cyptear). When this happens, this becomes the core of wear, and the wear progresses gradually.

The present invention was made in view of such problems,
The purpose is to provide a heavy-duty pneumatic tire in which cyptear in shoulder ribs is reduced without impairing wandering performance.

(Means for Achieving the Object) In order to achieve this object, the present invention provides a tread portion of a tire with a plurality of circumferential main grooves extending continuously in the circumferential direction, and a plurality of circumferential main grooves extending in the circumferential direction thereof. A heavy-duty radial tire having a plurality of ribs partitioned by a main groove, the tire having a plurality of ribs partitioned by a circumferential main groove outward in the width direction of the tire. , A pair of inclined grooves are provided that are inclined toward the tire equatorial plane at an angle range of 0° to 60° with respect to the tread surface, and one of the minor grooves is provided within a range of 20% to 80% of the shoulder rib width from the tread edge. Then, the other inclined groove is located inward in the tire width direction from one inclined groove within a range of 5% to 65% of the shoulder rib width, and the land area defined by the inclined grooves and extending in the tire circumferential direction is The surface of the tread portion is located inward in the tire radial direction from the contour shape of the tread portion.

(Function) The shoulder ribs defined by the circumferential main grooves on the outside in the width direction of the tire will be compressed and deformed when the tire runs onto the slope of a rut, but the ribs have inclined grooves formed on them. Therefore, the deformation is large in the direction opposite to the slope direction of the groove, and therefore, a shear force directed outward in the trend width direction, that is, camber thrust, acts from the slope.
This will push the tires up the mountain side of the slope.

On the other hand, since the surface of the land section divided by the pair of inclined grooves formed in the shoulder rib is located inward in the tire radial direction to form the step land section, the step land section is dragged by the road surface when the tire is transferred. Furthermore, since the sum of the shear forces in the driving and braking directions acting on a unit area of the tire ground area is considered to be approximately constant, the shearing forces in the braking direction will be concentrated on the stepped land portion. However, since the ground pressure acting on the shoulder ribs located on the mountain side of the slope is greater than that acting on the ribs located on the valley side,
The shear force in the braking direction that acts on the stepped land portion on the mountain side of the slope is large, and therefore, a moment, ie, camber torque, is applied to the tire due to the difference in the shear forces in the braking direction. Since this direction is the direction in which the tire climbs the slope, it cooperates with the camber thrust to make it easier for the tire to overcome the rut.

Moreover, since there is no need to provide a large number of sipes in the land section divided by the inclined groove and the trend end, cyptairs do not occur. In addition, for shoulder ribs located on the valley side of a slope, the shear force in the tire braking direction is concentrated on the stepped land area provided there, so it is important to avoid other land areas adjacent to the stepped land area, especially the edges. This suppresses the occurrence of uneven wear along the tire and increases the wear life of the tire as a whole.

(Example) Hereinafter, preferred examples of the tire of the present invention will be described with reference to the drawings.

FIG. 1 is a developed view showing a tread pattern of a tire 10 according to the present invention, in which the tread portion 12 of the present embodiment has a tread pattern that is spaced apart from each other in the tire width direction and extends in the circumferential direction. There are four circumferential main grooves 14 and a rib 1 partitioned by the circumferential main grooves and extending in the tire circumferential direction.
6, and a shoulder rib 18 defined by a circumferential main groove located outward in the tire width direction. Note that the internal structure of the tire 10 is similar to a conventional radial structure, so its explanation will be omitted here.

A pair of inclined grooves 20a are provided in each shoulder rib 18.
and 20b are arranged to extend in the tire circumferential direction, and one inclined groove 20a located on the tread end side is in the range of 20% to 80% of the rib width S0 of the shoulder rib 18 from the tread end 22 of the tire. the other inclined groove 20b.
is 5% to 6% of the shoulder rib width S0 from the inclined groove 20a.
5%, and is formed at a distance toward the center of the tread. In addition,
It is preferable that the groove depth H of these inclined grooves 20a and 20b is 30% to 95% of the groove depth Ho of the circumferential main groove 14.

Then, these inclined grooves 20a and 20b are formed as shown in FIG.
), 10° to 60° in the direction of the tire's equatorial plane.
The width of each groove is 0.5~3.
．． The value shall be within the range of 0-. Further, the surface of the land portion 24, which is partitioned by a pair of inclined grooves and extends in the tire circumferential direction, is positioned inward in the tire radial direction from the contour shape of the tread portion 12 to form a stepped land portion. The height difference h between the contour shape of the trend portion and the surface of the stepped land portion, that is, the distance in the tire radial direction, is determined by
It is sufficient that the groove depth H can come into contact with the road surface, and specifically, it has been found that it is preferable to set the groove depth H to 5% to 20% of the groove depth H of the inclined groove.

Here, among the inclined grooves 20a and 20b forming a pair, the inclined groove 20a located on the trend end side is connected to the trend end 20a.
2 to 20% to 80 of the rib width S0 of the shoulder rib 18
% is formed so that the distance between the inclined groove 20a and the tread edge 22 is the rib width S0 of the shoulder rib 18.
If it is less than 20%, the inclined groove 20a and the tread edge 22
This is because the rigidity in the tread width direction of the rib 24 defined by the tread width direction becomes too small, and although the ground contact pressure of the rib 24 increases, the shear force from the road surface corresponding to the deformation, that is, the camber thrust, decreases. On the other hand, 80%
This is because, if the stiffness exceeds this value, the rigidity of the rib 24 increases, making it difficult for the rib to deform, and the occurrence of camber thrust due to crushing of the rib 24 cannot be expected.

Further, the other inclined groove 20b is replaced with one inclined groove 2 of the pair.
If the distance between a pair of inclined grooves is less than 5% of the shoulder rib width, the distance between the inclined grooves is Since the width of the stepped land area formed in the tire becomes smaller and the stiffness of the stepped land area in the braking direction decreases, it is not possible to expect the generation of shear force acting in the tire braking direction, which reduces wandering performance. Camber that contributes to improvement
Torque cannot be expected to be generated, and on the other hand, if the interval between the inclined grooves exceeds 65% of the shoulder rib width S0, the width of the step land formed between the inclined grooves will increase. This is because the stiffness of the step land portion in the braking direction becomes too high, so that it is impossible to expect concentration of shear force in the braking direction on the step land portion, and therefore generation of significant camber torque.

Then, the groove depth H of these inclined grooves 20a and 20b is
The reason why the groove depth Ho of the circumferential main groove 14 is 30% to 95% is that the groove depth H of the inclined groove is 30% of the groove depth Ho of the circumferential main groove.
%, the circumferential main groove 1 located on the tread end side
4 and the tread end 22, the rigidity of the rib 24 becomes too high, so crushing due to contact with the road surface cannot be expected. If it exceeds 95% of the groove depth Ho, the groove depth of the inclined groove becomes too deep and the rigidity of the rib 24 decreases.
This is because problems such as rib tear and stone entrapment may occur.

In addition, in order to make each of the inclined grooves 20a and 20b inclined within the range of 10° to 60° with respect to the tread surface in the direction of the tire's equatorial plane, the angle θ between the inclined groove and the tread surface is 10°.
If the angle θ is less than 60°, the camber thrust caused by the crushing of the ribs 24 will be small, and therefore good wandering performance cannot be expected, whereas if the angle θ exceeds 60°, the rigidity of the ribs 24 will decrease. This is because it becomes too low and the camber thrust due to clubbing and two-singing cannot be obtained. In addition, the width of the inclined grooves 20a and 20b is set to 0.5 mm to 3.0 mm because
If the groove width of the inclined groove is smaller than 0.5 m, the groove walls of the inclined groove will come into contact with each other during tire transfer, increasing the coefficient of friction and reducing the rigidity of the individual ribs separated by the inclined groove. becomes higher. This is because the crushing effect of the ribs 24, which is advantageous for the generation of camber thrust, cannot be expected.If the groove width of the inclined groove is larger than 3.0 m, the stiffness of the shoulder ribs will be extremely reduced. This is because the movement of a part of the shoulder during transfer becomes slow, which worsens and accelerates uneven wear.

By the way, when a tire is transferred, shear force also acts in the braking direction, but the magnitude of the shear force in the braking direction differs in the tread width direction, and is larger on the trend end side.
It is known that the shear force tends to decrease at the center of the tread, and that the sum of the shear forces in the driving and braking directions acting on a unit area of the tread is indefinite.

On the other hand, when the tire rolls under the normal load, the stepped land portion 2 formed on the shoulder rib on the tread end side
4 will come into contact with the road surface, but since that surface is located inward in the tire radial direction from the tread contour shape, it will be dragged by the road surface due to the diameter difference with the tread surface, and the stepped land area will not be able to brake. In contrast, the shearing force in the braking direction acting on each rib adjacent to the stepped land portion substantially shifts to the driving direction.

Therefore, when the tire runs on a flat road surface, the shear force that acts in the braking direction with respect to the center of the trend is equal, and therefore Although no moment acts on the tire, when the tire is running on a rut, the ground pressure of the tread part located on the mountain side of the slope is higher than the ground pressure of the tread part located on the valley side of the slope. Since the shear force in the braking direction generated on the mountain side portion is higher than the braking direction shear force generated on the valley side portion, the braking direction shear force acting on those tread portions is generated around the line segment. In response to the difference in force, a moment, or camber torque, acts on the tire in the direction of moving it over the slope, and this works together with the camber thrust caused by the crushing of the shoulder ribs, making it easier to get over the rut. do.

Since the shearing force in the braking direction is concentrated on the stepped land portion, occurrence of uneven wear along the ribs adjacent to the stepped land portion, particularly along the edges thereof, is suppressed. This also applies to the stepped land area located on the shoulder rib located on the valley side of the slope, where the shear force in the braking direction is concentrated, causing uneven wear due to drag in the rib area. suppress.

In this embodiment, a pair of inclined grooves are formed on both shoulder ribs of the tire, but the present invention is not limited to this embodiment. Even if an inclined groove is formed in the outer shoulder rib, the wandering performance can be improved, and various modifications can be made within the scope of the claims.

Incidentally, in order to investigate the wandering performance of such a tire, a comparative test was conducted using the tire according to the present tread invention and a conventional tire, and the results are shown in the following table. The tire used in the comparative test had a size of LSR750R16 and had four circumferential main grooves.

◎Test tire/invention tire: A tire with a tread pattern shown in Figure 1, with a tread width of 135 txm, a circumferential main groove width of 9.0 am, and a groove depth (Ho). 11.3 am, the shoulder rib width (So) is 23.0 am, the distance from the tread end to the inclined groove of the tread end is 60% of the shoulder rib width (So), and the other inclined groove forming a pair from that inclined groove The distance to the groove is 55% of the shoulder rib width (S, ), and the angle (θ) that these inclined grooves make with the tire equatorial plane is 10.
°, the groove width of the inclined groove is 2. Owa, groove depth of inclined groove (H)
is 88% of the groove depth (Ho) of the circumferential main groove, and the height difference (h) between the stepped land portion and the tread surface is 2.5 m.

Conventional Tire: A tire having the tread pattern shown in Figure 1, in which the groove width and groove depth of the circumferential main groove, the shoulder rib width, and the position of the inclined groove from the tread edge are the same as the inventive tire. A tire in which a plurality of ribs are formed at intervals of 4.5 degrees in the circumferential direction of the tire, intersecting the ribs located between the inclined groove and the tread edge.

◎Test method The invented tire and the conventional tire were subjected to 2D-
It was attached to the front wheels of four cars and driven on a test road with ruts.
Wandering performance was evaluated as an index using a feeling test, and the presence or absence of uneven wear was visually measured and compared.

◎Test results The test results are shown in the table below.

Note that the larger the index, the better the wandering performance, the presence or absence of cyptair refers to the number of areas where it has occurred, and the presence or absence of uneven wear refers to a state that cannot be determined by visual inspection.

As is clear from this table, it can be seen that the invention tire has improved wandering performance without causing uneven wear or cyptair.

(Effects of the Invention) Thus, according to the present invention, wandering performance can be improved without impairing various performances as a tire for heavy loads such as trunks and busses.

[Brief explanation of the drawing]

FIG. 1(a) is a developed view showing the tread pattern of the tire of the present invention, FIG. 1Φ) is a cross-sectional view of a part of the tire of the present invention, and FIGS. b) is a developed view of a tread pattern of a conventional tire and a cross-sectional view of a part thereof; 10-...Tire 12-...Tread portion 14-Circumferential main groove 16-Rib 18-Shoulder rib 20a, 20b-One inclined groove 22-1
-Red end 24-...Land @1 Figure (a) [b] Figure 2 (a) Procedural amendment July 13, 1990

Claims (1)

[Claims] 1. A heavy-load radial tire having a plurality of circumferential main grooves continuously extending in the circumferential direction of the tire and a plurality of ribs partitioned by the circumferential main grooves, the tire A pair of shoulder ribs extending in the circumferential direction of the tire and inclined toward the tire equatorial plane at an angle range of 10° to 60° with respect to the tread surface, on at least one shoulder rib defined by the outer circumferential main groove in the width direction. Provided with a slanted groove,
20 of the shoulder rib width from the tread edge to one inclined groove.
% to 80%, and move the other inclined groove inward in the tire width direction from one inclined groove by 5% to 65% of the shoulder rib width.
For heavy loads, the surface of the land section partitioned by the inclined grooves and extending in the circumferential direction of the tire is located inward in the radial direction of the tire from the contour shape of the tread section. radial tire.