JP2657034B2 - Radial tires for heavy loads - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radial tire for heavy loads capable of effectively suppressing uneven wear at a tread shoulder portion of a tire.

[0002]

2. Description of the Related Art In a pneumatic tire, the tire is inevitably worn as the vehicle runs. Particularly in recent years, in a radial tire that is frequently used, a belt layer made of a high-tensile cord such as a steel cord is arranged outside a carcass arranged in the radial direction, and a large tag effect is given. Pressure distribution tends to be non-uniform, and in particular, uneven wear, in which the shoulder portion of the tire is worn earlier than the crown portion, tends to occur. On the other hand, the so-called heel-and-toe wear particularly found in radial tires for passenger cars, and only the shoulder portion wears stepwise as illustrated in FIG. 7 which is found in heavy-duty tires such as trucks and buses according to the present invention. Abnormal wear such as stepped wear M may also occur.

[0003] Such uneven wear in the shoulder portion is caused by the fact that the tread surface t becomes substantially arc-shaped in a cross section including the tire shaft as shown in FIGS. 4 (A) and 4 (B). However, when the tread surface is in contact with the ground, the crown portion forms a drag side, and the shoulder portion forms a drag side, as shown in FIG. 6, for example, as shown in FIG. In addition, a stepped portion a, particularly a protruding portion b, for rolling the tire
It is thought to be caused by the sliding friction generated between the vehicle and the road surface.

[0004] In particular, when the tire is used for a front wheel on the non-driving side, the stepped wear M is caused by the fact that the attitude angle of the tire promotes the wear of the contact end portion. Grows with the mileage of the tire and eventually spreads over the full width of the outer ribs, reducing the life of the tire. Such uneven wear is particularly remarkable in ribs and lug patterns in which lug grooves are formed on the tread surface.

[0005] It is known that such uneven wear and stepped wear are caused by uneven wear energy generated by contact with a road surface. The wear energy W is
The friction coefficient μ between the road surface and the tire, the contact pressure P, and the slip S between the road surface and the tire are affected by the following equation. W μ ・ P ・ S

However, under mild conditions of low wear rate, that is, under conditions of running on a good road surface at a constant speed with a light load and running on a road surface with a small curve, a slight difference in the wear energy in the tire contact surface is reduced. It accumulates and develops uneven wear.

Conventionally, to prevent such uneven wear,
Either increase the radius of curvature of the tread surface to reduce the circumferential difference between the crown and the shoulder, or increase the size of the block at the shoulder to increase its rigidity, and further enhance the rigidity of the belt layer, especially at the shoulder. Proposals such as have been made.

[0008]

However, when the radius of curvature is increased to reduce the difference in circumferential length simply carelessly, as shown in FIGS. 5A and 5B, the contact pressure of the shoulder portion increases and the shoulder pressure increases. The thickness of the rubber layer in the portion increases, so that heat is easily generated in the portion c, and the rubber is more likely to be peeled off at the end of the belt ply in this portion.

As described above, uneven wear and the like, and heat generation, that is, durability, have two trade-offs. In addition, the increase in the rigidity of the block and the belt layer cannot sufficiently solve the wear, and when the rigidity of the block and the belt layer in the shoulder portion is excessively increased, the tire noise and the riding comfort performance tend to be impaired. Become.

The present inventors have conducted various experiments to prevent uneven wear and stepped wear in the shoulder portion of a heavy-duty radial tire. As a result, in order to prevent uneven wear, a cross section of the belt layer in the tire axial direction was obtained. It has been found that it is necessary to regulate the ratio of the shape, particularly the width of the belt ply having the maximum width, which has the greatest reinforcing effect of the belt layer, to the maximum tire width and the contact width. Further, in the belt ply having the maximum width, by setting the curvature of the outer portion, that is, the portion located at the shoulder to a predetermined range,
They learned that uneven wear can be prevented efficiently.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heavy duty radial tire capable of effectively suppressing uneven wear that tends to occur on a shoulder portion.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a radially or semi-radially arranged carcass which is folded from a tread portion to a side wall portion with a bead core at a bead portion, and to a radially outer side of the carcass and an inner side of the tread portion. And at least three belt cords using belt cords arranged at an angle of 5 to 70 ° with respect to the tire equator and comprising a belt ply overlapping inside and outside, and extending circumferentially on the tread surface. A plurality of vertical grooves and tread edges are connected to the vertical groove closest to the tread edge, and the groove width is 2
A heavy-duty radial tire having a lug groove having a groove depth of 5 mm or more and a groove depth of 5 mm or more, wherein a maximum allowable load is applied to the tire in a standard state where the tire is mounted on a regular rim and filled with a regular internal pressure. The contact width SW, which is the width of the contact surface when the contact surface is formed in the tire axial direction, is 0.7 of the maximum tire width TW.
The ply width BWM of the belt ply having the maximum width in the belt ply is twice or more and 0.9 or less and the ground width SW.
0.84 times or more and 0.96 times or less of the ply width BWM of the belt ply having the maximum width and the tire maximum width TW
And a ratio of BWM / TW to 0.69 or more, and an inner portion between 1/4 points separating both sides from the tire equator by a quarter of the ply width BWM of the belt ply; In the outer portion virtually divided into the outer portion of the point in the tire axial direction, the radially inner surface of the belt ply having the maximum width is a cross section including the tire shaft,
A load comprising a circular arc having a radius of curvature BR not less than 1.6 times and not more than 2.3 times the maximum width TW of the tire, and the inner surface is smoothly connected to the inner portion at the quarter point. It is a heavy duty radial tire.

[0013]

The radial tire for heavy loads according to the present invention sets the degree of curvature of the tread in a standard state where the tire is assembled on a regular rim and filled with a regular internal pressure. Here, the regular rim is THE TIRE and RIM ASSOCIA
TION INC. Issued by YEAR BOOK (T
RA) or THE EUROPEANTY
RE AND RIM TECHNICAL ORGA
STANDARDS MA issued by NIZATION
This is a standard rim defined by NUAL (commonly called ETRTO), and the normal internal pressure is defined as the maximum air pressure of each tire in TRA or ETRTO.

In the present invention, the contact width SW is set to the tire maximum width TW.
0.7 times or more and 0.9 times or less. Contact width S
W affects traction performance and wear resistance. If the contact width SW is less than 0.7 times the maximum width TW of the tire, the contact pressure becomes abnormally high and wear is early at the center of the tread, resulting in poor durability. Also, the traction performance is inferior due to a decrease in the grip force. If it becomes larger than 0.9, the tread surface may slip near the edge in the contact direction and generate heat during traveling, thereby lowering the durability.

The ply width BWM of the belt ply having the maximum width
Is set to 0.84 times or more and 0.96 or less of the ground width SW.

FIG. 2 shows that the tire size is 12R22.5, 1
Ratio of the ply width BWM to the contact width SW for tires 1R22.5 and 10.00R20 BWM / SW
Is shown in a graph.

The uneven wear amount is obtained by measuring the shoulder drop wear cross-sectional area per 1 mm over the entire area of the wear portion and displaying the average value thereof. The symbols in the figure represent the types of tires shown in Table 1.

As can be understood from FIG. 2, the ratio BWM / SW
When it was 0.84 or more, it was confirmed that uneven wear was sharply reduced. If the ply width BMW is less than 0.84 times the contact width SW, the rolling resistance during tire running increases. On the other hand, if the ratio BWM / SW exceeds 0.96, the belt width becomes excessively large, and the rigidity of the tread portion increases, which may result in a loss of steering stability. Easy to invite.

The ply width BWM and the tire maximum width T
The ratio BWM / TM to W is set to 0.69 or more. When the ratio BMW / TM is 0.69 or less, the contact width SW satisfies the above-mentioned regulation values for the tire maximum width TM and the ply width BWM satisfies the regulation values for the contact width SW, respectively. This was regulated as described above based on the experimental result that when the vehicle traveled at high speed, the durability of the tread shoulder portion was significantly reduced due to the low rigidity of the tread shoulder portion.

In the radial tire for heavy load according to the present invention, the belt ply having the maximum width among the belt plies forming the belt layer is separated by 1/4 of the width BMW from the equator of the tire on both sides. The belt ply is virtually divided into an inner portion between the points and an outer portion outside the 1/4 point, and the inner surface of the belt ply at the outer portion has a curvature of 1.6 times or more and 2.3 times or less the maximum width of the tire. It is formed by a circular arc having a radius.

FIG. 3 shows that the tire size is 285 / 75R2.
For tires of 4.5 and 11R24.5, running tests were performed with the radius of curvature BR of the outer portion and the radius of curvature TR of the tread surface different from each other, and the occurrence of uneven wear in the tread shoulder portion is shown by a graph. .
The graph shows the ratio BR / TW of the radius of curvature BR of the outer portion of the belt ply having the maximum width to the tire maximum width TW on the horizontal axis, and the ratio TR / TW of the radius of curvature TR of the tread surface to the tire maximum width TW on the vertical axis. The magnitude of uneven wear is indicated by a sign.

The amount of uneven wear was measured by mounting each test tire on an actual vehicle, running 100,000 km on a test road, and then measuring the uneven wear on the left or right shoulder in the circumferential direction. The sectional area of the wear was measured at eight locations and the average value was measured. The determination was made according to the criteria shown in Table 2.

[0023]

[Table 2]

The results of the test are shown in FIG. In addition, the magnitude of the uneven wear amount is indicated by △, ×, Δ, × according to the standard shown in Table 2. As can be understood from FIG. 3, the relationship between the radius of curvature BR of the outer portion of the belt ply having the maximum width is not affected by the radius of curvature TR of the tread surface, but the ratio BR / TW is large. 2.0
Above, uneven wear is remarkably reduced. Based on the test results, the radius of curvature B of the outer portion of the outermost belt ply is
R was set to be 1.6 times or more the maximum tire width TW.

When the ratio BR / TW exceeds 2.3, the end of the belt ply comes close to the tread surface at the shoulder portion, so that the allowance during tire rehabilitation is insufficient and the rehabilitation rate decreases. Thus, the upper limit of the ratio BR / TW was regulated.

As described above, the invention of the present application is to increase the rolling resistance even in a tire in which each of the above-mentioned components is organically integrated and has a lug groove in which uneven wear is liable to occur particularly in a tread shoulder portion. In addition, it is possible to prevent uneven wear while maintaining steering stability.

[0027]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows that a heavy duty radial tire 1 has a regular rim R
Shows a standard state in which the rim is assembled and filled with a normal internal pressure. Here, the normal rim R is a standard rim defined by TRA or ETRTO as described above, and the normal internal pressure is defined as the maximum air pressure of each tire in the TRA or ETRTO.

The heavy-duty radial tire 1 has a tread portion 2, a sidewall portion 3 extending radially inward from both ends thereof, and bead portions 4 provided at both ends thereof.
A carcass 6 which is turned around from the inside of the tire to the outside around the bead core 5 of the bead portion 4 and is locked;
And a belt layer 7 disposed radially outside of the belt.

On the tread surface 2A, a plurality of, in this embodiment, four longitudinal grooves G extending in the tire circumferential direction and a tread edge E
And a plurality of lug grooves GL connecting the vertical groove G closest to the tread edge E are formed. The lug groove GL has a groove width of 2 mm or more, a groove depth of 5 mm or more, and a groove depth of the vertical groove G or less.

The tread surface 2A is provided with a grounding surface S which is in a standard state and is grounded at the time of maximum load. This ground plane S
, The maximum width in the tire axial direction is defined as the contact width SW. The contact width SW is set in a range of 0.7 times or more and 0.9 times or less of the tire maximum width TW.

In the present embodiment, the carcass 6 comprises a single ply of a radial structure in which the carcass cords are arranged at an angle of 90 ° with respect to the tire equatorial plane CO, and a steel cord is used as the carcass cord. I have. The carcass may have a radial or semi-radial structure in which carcass cords are arranged at 60 to 90 degrees. In addition to the steel cord, aramid, nylon,
An organic fiber cord such as rayon or polyester can be used as a plurality of plies. In addition, the carcass folded the bead core 5 and the folded end 6A
Is interrupted above the bead core 5 and below the maximum width position of the tire. The bead portion 4 includes a reinforcing layer that prevents abrasion between the carcass 6 and the bead core 5 that move with deformation of the tire due to ground contact or the like and that increases the rigidity of the bead portion.
In addition to chafers (both not shown) for preventing rim shift,
Another reinforcing layer 8 or the like that covers the folded portion of the carcass 6 may be provided. Further, the tread portion 2 may be provided with a band layer (not shown) made of an organic fiber cord that covers an end portion of the belt layer 7 in the tire axial direction.

Further, the bead portion 4 is provided with a bead apex 10 made of a rubber material tapering radially outward from the bead core 5 to improve lateral rigidity.

The belt layer 7 is formed of a carcass 6 in this embodiment.
A four-layer structure including a first belt ply 11, a second belt ply 12, a third belt ply 13, and a narrow fourth belt ply 14 arranged in this order from the side toward the tread portion 2 is formed. The ply width W2, which is the length between the outer edges of the second belt ply 12 in the tire axial direction, is larger than the ply width W1 of the first belt ply 11, and the ply width W1 of the third belt ply 13 is larger. The width W3 is substantially the same as the ply width W1. That is, the second belt ply 12 has the maximum width BWM of the four belt plies.

The second belt ply, that is, the belt ply having the maximum width, has its ply width BWM changed to the ground width S.
W is 0.84 times or more and 0.96 times or less of W, and a ratio BWM / T between the ply BWM and the tire maximum width TW
M is set to 0.69 or more.

The ply width BWM of the belt ply 12
1/4 of the distance from the tire equator CO on both sides
/ 4 point A is temporarily provided, and the belt ply 12 is connected to the inner portion 12A located between １ ／ points A, A,
It is virtually divided into four points and an outer part 12B located on the outer side in the tire axial direction, and the outer part 12B has a radially inner inner surface 12a formed by an arc.
The end of the outer portion 12B on the tire equator side is smoothly connected to the inner portion 12A.

The radius of curvature BR of the inner surface 12a of the outer portion 12B is measured by using an X-RAY CT caster, and the radius of curvature BR is regulated in a ratio with respect to the tire maximum width TW. It is 1.6 times or more and 2.3 times or less.

Further, the belt cord is inclined at an angle of 5 to 70 degrees with respect to the tire equator CO.
The first belt ply 11 inclines its belt cord at an angle of 50 to 70 degrees with respect to the tire equator CO, and the second belt ply 12 places the belt cord in the same direction as the first belt cord. The third belt ply 13 has an inclination angle of 14 to 22 degrees with respect to the equator CO.
The belt cord is disposed in the opposite direction to the second belt cord and at an inclination angle of 14 to 22 degrees with respect to the tire equator CO.

Accordingly, the belt layer 7 has the first and second belt cords crossing each other, but the first and second belt cords are inclined in the same direction. While alleviating the shear strain between the two belt plies 11 and 12, the belt cord angles of the plies 11 to 13 intersect to form a rigid and large triangle structure having a high binding force over the end of the belt layer. .

Further, the cord angle of the first belt ply 11 and the cord angle of the carcass 7 and the second belt ply 12
, The rigidity step between the carcass 7 and the belt 9 is reduced to prevent peeling damage. The fourth belt ply 14 is a ply 15 made of a steel cord that is 45 to 10% narrower than the width of the third belt ply 13, and protects the first to third belt plies 11, 12, and 13 from external damage. .

Further, the first belt ply 11 is separated from the carcass 6 on the outer side in the tire axial direction, and the second belt ply 12 extends in the tire axial direction along the first belt ply, and The belt ply 13 is separated from the second belt ply 12 at an end portion, and each separated portion has a cushion rubber 1 extending in the tire axial direction.
The interposition of 5 and 16 alleviates the stress concentration at the end of each ply and prevents separation.

As the belt cord, an organic fiber cord such as aramid, nylon, rayon, polyester or the like can be used as a plurality of plies in addition to the steel cord.

In this embodiment, the tread surface 2A is formed of an arc centered on the tire equator CO surface, and its tread radius of curvature TR is set to 1.89 times or more and 2.11 times or less of the tire maximum width TW. It is preferable to set it in the range. The magnitude of the radius of curvature of the tread is due to other factors than the above-mentioned uneven wear of the shoulder portion. If the radius is less than 1.89 times, stepped wear may occur as shown in FIG. If it exceeds twice, there is a risk that the tread portion will overheat during traveling.

[0043]

As described above, the radial tire for heavy load of the present invention can prevent uneven wear of the shoulder portion and improve durability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a tire axial direction right side showing one embodiment of the present invention.

FIG. 2 is a graph showing the occurrence of uneven wear in relation to the ratio between the ply width of the belt ply having the maximum width and the contact width.

FIG. 3 is a graph showing the occurrence of uneven wear in the relationship between the radius of curvature of the outer portion of the belt ply having the maximum width and the radius of curvature of the tread surface.

FIGS. 4A and 4B illustrate a ground contact state of a tire, in which FIG. 4A is a cross-sectional view and FIG.

5A and 5B show another example of a contact state of the tire, wherein FIG. 5A is a cross-sectional view thereof, and FIG. 5B is a plan view thereof.

FIG. 6 is a front view illustrating a grounding shape;

FIG. 7 is a cross-sectional view illustrating stepped wear.

[Explanation of symbols]

 2 Tread part 2A Side wall part 4 Bead part 5 Bead core 6 Carcass 7 Belt layer 12 Belt ply of maximum width 12A Inner part 12B Outer part A 1/4 point BR Radius of curvature of outer part BWM Belt width of maximum width belt ply G Vertical groove GL Lug groove S Grounding surface SW Grounding width TW Maximum tire width

[Table 1]

Claims (1)

(57) [Claims] 1. A radially or semi-radially arranged carcass which is folded from a tread portion to a side wall portion with a bead core of a bead portion, and disposed outside the carcass in the radial direction and inside the tread portion and at the tire equator. 5-7
A belt layer comprising at least three belt plies using a belt cord inclined at an angle range of 0 ° and overlapping inside and outside, and a plurality of longitudinal grooves and tread edges extending in a circumferential direction on a tread surface and the tread; A heavy duty radial tire having a lug groove having a groove width of 2 mm or more and a groove depth of 5 mm or more, which is connected to a vertical groove closest to the edge,
In a standard state where the tire is mounted on a regular rim and filled with a regular internal pressure, a contact width SW, which is a width in a tire axial direction formed by a contact surface when a maximum allowable load is applied to the tire, is 0 of the maximum tire width TW. The ply width B of the belt ply having a maximum width of not less than 7 times and not more than 0.9 times, among the belt plies.
WM is at least 0.84 times the grounding width SW and 0.96
The ply width B of the belt ply having the maximum width not more than twice
The ratio BWM / TW between WM and the maximum tire width TW is 0.69.
The ply width BW of this belt ply
1/4 of the distance from the tire equator to 1/4 of M
In the outer portion virtually divided into an inner portion between four points and an outer portion in the tire axial direction at the 1/4 point, a radially inner surface of the belt ply having the maximum width has a cross section including a tire axis. Wherein the inner surface is smoothly connected to the inner part at the quarter point by a radius of curvature BR of 1.6 times or more and 2.3 times or less the maximum tire width TW. Heavy duty radial tires.