JP2000264015A - Tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reconcile the traveling performance of a tire on an icy road and the steering stability on a dry road-surface. SOLUTION: Tread rubber 9 contains at least a crown rubber part 9A brought in contact with a road surface and arranged in the middle part of the tread and a shoulder rubber part 9B brought in contact with the road surface and arranged on both sides of the crown rubber part 9A. The crown rubber part 9A is formed out of the soft rubber material containing short fibers, which is obtained by mixing short fibers into rubber base material containing natural rubber and butadiene rubber and whose JIS-A hardness is not less than 55 deg. but not more than 62 deg.. The shoulder rubber part 9B is formed out of hard rubber material which contains no short fibers and whose JIS-A hardness is higher than 62 deg. but not more than 70 deg.. When the tire is brought in contact with a flat ground-surface, with the tire inflated to the normal pressure and placed under a normal load, the maximum ground-touching width CW in the tire-axial direction of the crown rubber part 9A is 0.5 to 0.7 times the tread width TW.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty tire capable of achieving both running performance on ice and snow road surfaces and steering stability on dry pavement roads.

[0002]

2. Description of the Related Art
In heavy vehicles such as buses and trucks running on an area with a lot of snowy roads, the mounting rate of studless tires is increasing. Such a heavy load stud rest tire reduces the rubber hardness of the tread rubber that contacts the road surface, and secures grip on ice and snow roads by means of siping provided on the tread surface.

[0003] However, the soft tread rubber reduces the steering stability, for example, when the vehicle is turning on a dry pavement, so that the tread rubber is only stiff, and causes the tread rubber to be chipped when the tire chain is mounted. There is a problem.

The present invention has been devised in view of the above-described problems. A tread rubber is provided on a road surface and in contact with a crown rubber portion disposed at the center of the tread, and on both sides of the crown rubber portion. And at least a shoulder rubber portion disposed, and the crown rubber portion is formed from a soft rubber material containing short fibers obtained by mixing short fibers into a rubber base material containing natural rubber and butadiene rubber, and the shoulder rubber portion. It is made of a hard rubber material that does not contain short fibers, and on the basis of regulating the contact width of the crown rubber portion in the tire axial direction, the driving performance on ice and snow roads and the steering stability against dry road surface running are improved. It is an object of the present invention to provide a heavy-duty tire that can solve the above-mentioned problems while being compatible.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a load comprising a carcass comprising a single carcass ply having a toroidal shape extending from a tread portion to a sidewall portion to a bead core of a bead portion and having steel cords arranged in parallel. A heavy tire, wherein a tread rubber disposed on a tread portion is grounded on a road surface and a crown rubber portion disposed on a tread central portion, and a shoulder rubber portion disposed on a road surface and ground on both sides of the crown rubber portion. The crown rubber portion has a JISA hardness of 55 ° or more and 6 in which short fibers are mixed in a rubber base material containing natural rubber and butadiene rubber.
The shoulder rubber portion is made of a soft rubber material containing not more than 2 mm of short fibers, and the shoulder rubber portion does not contain short fibers and is JIS.
The crown rubber portion is formed from a hard rubber material having an A hardness of greater than 62 ° and not more than 70 °, and is assembled to a regular rim, filled with a regular internal pressure, loaded with a regular load, and grounded on a flat surface. Is characterized in that the maximum contact width CW in the tire axial direction is 0.5 to 0.7 times the tread contact width TW.

As described above, according to the present invention, a rubber base material containing natural rubber and butadiene rubber having excellent cold resistance is used for the crown rubber portion which is disposed at the center of the tread and has the highest contact pressure, and has a JISA hardness. Adopting low rubber prevents rubber hardening at ice temperature and improves running performance on icy and snowy roads. Also, by mixing short fibers into the rubber base material, fine irregularities can be formed on the rubber surface, improving the edge effect on the icy road surface and generating a large frictional force, improving the running performance on icy roads Can.

In the present invention, a shoulder rubber portion made of a hard rubber material is disposed on both sides of the crown rubber portion, so that a large lateral force during turning can be generated due to its high rigidity. Stability, especially handling stability on dry road surfaces, can be improved. In addition, since the shoulder rubber portion is formed from a hard rubber material, damage such as cracks and chips caused by friction with the tire chain and slippage can be suppressed, and durability can be improved.

When the tire is assembled on a regular rim, filled with a regular internal pressure, a regular load is applied, and the tire is grounded on a flat surface, the maximum contact width CW of the crown rubber portion in the tire axial direction is obtained.
Is regulated to 0.5 to 0.7 times the tread contact width TW, so that traveling performance on ice and steering stability on a dry road surface can be compatible with a good balance.

Here, the definitions used in this specification are as follows. First, a “regular rim” is a rim defined for each tire in a standard system including a standard on which a tire is based. For example, a standard rim for JATMA, a “Design Rim” for TRA, or an ETRT
If it is O, it will be "Measuring Rim". In addition, the "normal internal pressure" is the air pressure that each standard defines for each tire in a standard system including the standard on which the tire is based,
JATMA for maximum air pressure, TRA for table "TI
RE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE
Maximum value described in "S", or "INFLATION P" for ETRTO
RESSURE ". Further," regular load "refers to the load specified by each standard in the standard system including the standard on which the tire is based. Table "TIRELOAD LIMITS AT V
ARIOUS COLD INFLATION PRESSURES "
If it is ETRTO, set it to "LOAD CAPACITY".

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a heavy duty tire according to the present invention will be described below with reference to the drawings. FIG. 1 shows a tubeless type heavy duty studless tire (hereinafter, referred to as a truck, a bus, etc.) for running on icy and snowy roads.
Sometimes simply referred to as a "tire." 1) is illustrated. 1 shows a non-loaded right half cross-sectional view (the left half cross-section is substantially symmetrical thereto) in which the tire 1 is assembled to the normal rim J and filled with the normal internal pressure.

In FIG. 1, a tire 1 has a tread 2
The carcass 6 includes a toroidal carcass 6 extending from the first through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a belt layer 7 disposed radially outside the carcass 6 and inside the tread portion 2.

The carcass 6 is a tread portion 2 in this embodiment.
A single carcass ply 6A integrally provided with a folded portion 6b that folds the periphery of the bead core 5 from the inside in the tire axial direction to the outside in the body portion 6a extending from the side wall portion 3 to the bead core 5 of the bead portion 4. Consists of
The carcass ply 6A is formed in a sheet shape in which both sides of a cord array in which steel cords are arranged are covered with thin topping rubber. In addition, the carcass 6 has a steel cord, for example, 75 to 90 degrees with respect to the tire equator C,
In the present embodiment, an example in which the components are arranged at an angle of about 90 ° is illustrated. A hard bead apex rubber 8 that extends from the outer surface of the bead core 5 in the tire radial direction to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b of the carcass ply 6A.

In the present embodiment, the belt layer 7 includes a steel cord with respect to the tire equator C and an innermost belt ply 7A in which the steel cord is inclined at an angle of, for example, about 60 ± 10 °. For example, there is illustrated a four-layer structure in which belt plies 7B, 7C, and 7D arranged at an angle of a small angle of 30 ° or less and at least one or more locations where the belt cords cross each other between the plies are provided. I have. In addition to the belt layer 7, the belt layer 7
And a structural member such as a band layer that is disposed radially outward of the belt layer and that prevents lifting of the belt layer 7 may be provided.

In the present embodiment, four longitudinal grooves 10 extending continuously in the circumferential direction are formed in the tread portion 2, and between the longitudinal grooves 10, 10 and between the longitudinal grooves 10 and the tread edge E are formed. Between them, five land portions 11 are formed. In this example, the land portion 11 forms a block row in which blocks are arranged in the tire circumferential direction, and can improve running performance on a snowy road.

The tread rubber 9 provided on the tread portion 2 is provided with a crown rubber portion 9A which is in contact with the road surface and is provided in the central portion of the tread, and is provided on both sides of the crown rubber portion 9A which is in contact with the road surface and is provided with ground. And at least a shoulder rubber portion 9B. The tread rubber 9 of the present embodiment includes a base rubber portion 9C disposed radially inward of the crown rubber portion 9A in the tire radial direction and connected to the shoulder rubber portion 9B.
A tread central portion has a two-layer structure, and shoulder portions on both sides thereof have a single-layer structure.

The crown rubber portion 9A is connected to the tread portion 2
And the groove surface 10a of the vertical groove 10 is disposed. Further, the crown rubber portion 9A is made of JI made by mixing short fibers into a rubber base material containing natural rubber and butadiene rubber.
It is made of a soft rubber material containing short fibers having an SA hardness of 55 ° or more and 62 ° or less. Generally, in order to obtain a good gripping force when traveling on ice and snowy roads, it is important how to prevent the rubber from hardening due to the low temperature. Therefore, in this embodiment,
A rubber base material containing natural rubber and butadiene rubber having low molecular cohesion energy and excellent cold resistance is used for the crown rubber portion 9A arranged at the center of the tread and having the highest ground pressure, and has a JISA hardness of 55 ° or more. And 6
By adopting a soft rubber of 2 mm or less, rubber hardening at ice temperature can be prevented and running performance on icy and snowy roads can be improved.

If the soft rubber material containing short fibers constituting the crown rubber portion 9A has a JISA hardness of less than 55 °, it is difficult to employ the material under heavy load because the wear is large and the durability is poor. When the value exceeds ゜, sufficient grip force cannot be obtained when traveling on an ice-snow road, and the traction performance and the braking performance tend to decrease. More preferably, the soft rubber material containing short fibers has a JISA hardness of 5
It is desirable to set it to 8 ° to 60 °.

The soft rubber material containing short fibers can form fine irregularities due to short fibers on the rubber surface that is in contact with the road surface, and can increase frictional force, particularly by increasing the edge effect on the icy road surface. Grip performance and braking performance can be improved. Here, short fibers include organic fibers such as nylon, rayon, polyester, aromatic polyamide, cellulose resin, crystalline polybutadiene, cotton thread, and carbon fiber, and inorganic materials such as metal fibers, whiskers, boron, and glass fibers. And these can be used alone or in combination of two or more. Preferably, the short fibers have been subjected to a surface treatment in order to improve the adhesion to the rubber component. In the present embodiment, crushed natural vegetable fibers are used as the short fibers.

The short fibers are not particularly limited, but preferably have an average fiber diameter of 0.1 μm to 0.5 mm and an average fiber length of 20 μm to 2 mm. If the average diameter and the average length of the short fibers are smaller than the above-mentioned values, the effect of increasing the frictional force on the surface of the crown rubber portion 9A tends to relatively decrease. , In particular, the crack resistance tends to deteriorate.

In this embodiment, the short fibers are oriented in a range of ± 20 ° with respect to the tire circumferential direction. Thereby, the circumferential rigidity of the crown rubber portion 9A is increased, and the rolling resistance and the like can be reduced. Short fibers are
Orientation can be performed at an angle of ± 20 ° with respect to the tire axial direction. In this case, the axial stiffness of the crown rubber portion 9A is increased, so that riding comfort and steering stability can be improved. Such staple fibers can be extruded,
90% or more of the short fibers are oriented in the extrusion direction by being kneaded with a rubber base by a calender or the like and extruded.

The crown rubber portion 9A contains 5 to 30 parts by weight of short fibers, preferably 15 to 25 parts by weight, more preferably 20 to 2 parts by weight, based on 100 parts by weight of the rubber base material.
It is desirable to mix 5 parts by weight. If the blending amount of the short fibers is less than 5 parts by weight, the running performance on ice and snow roads tends to be relatively deteriorated, and if it exceeds 30 parts by weight, the crack resistance of the crown rubber portion 9A is increased. Etc. tend to decrease. A preferable combination as the rubber base material of the crown rubber portion 9A is 40 to 60 parts by weight of natural rubber,
Butadiene rubber 60 to 40 parts by weight.

The shoulder rubber portion 9B is disposed from the end of the crown rubber portion 9A to the tread end E, and is formed of a hard rubber material having a JISA hardness of more than 62 ° and 70 ° or less, Short fibers are not included. By using the hard rubber material for the shoulder rubber portion 9B in this manner, a large lateral force can be generated during turning and traveling, and the steering stability particularly on dry asphalt road surface can be improved.

The tread shoulder portion tends to cause friction, slippage, and the like with the tire chain when the tire chain is mounted due to the curvature of the tread surface and the like, as compared with the center portion of the tread. It is susceptible to damage such as cracks and chipping by chains. In particular, if short fibers are mixed in the rubber, these cracks are likely to occur starting from the bonding portion between the short fibers and the rubber. Therefore, in the present embodiment, by forming the shoulder rubber portion 9B from a hard rubber material containing no short fiber, damages such as cracks and chips caused by slipping with the tire chain and the like are suppressed, and durability is improved. I have.

If the hard rubber material forming the shoulder rubber portion 9B has a JISA hardness of 62 ° or less, the steering stability on a dry road surface or the like tends to be reduced and the tire chain tends to be damaged. If the hardness exceeds 70 °, the difference in hardness between the crown rubber portion 9A and the crown rubber portion 9A tends to be excessive, and uneven wear tends to occur early. Preferably, the hard rubber material has a JISA hardness of 65 ° to 68 °. In this embodiment, the hard rubber material also includes a material containing natural rubber and butadiene rubber having excellent cold resistance.
5 parts by weight, 35 to 15 parts by weight of butadiene rubber.

The base rubber portion 9C disposed radially inward of the crown rubber portion 9A in the tire radial direction is formed of the same hard rubber material as the shoulder rubber portion 9B. Therefore, the central portion of the tread is located at the base rubber portion 9C.
Thereby, the rigidity inside the tire in the radial direction can be reinforced, and the steering stability on a dry road surface is improved.

In this embodiment, the vertical groove 1 is formed at the boundary between the crown rubber portion 9A and the shoulder rubber portion 9B.
0, the outer longitudinal groove 10 which is arranged most outward in the tire axial direction.
o is recessed. For this reason, as shown in FIG. 2, the outer land portion 11e sandwiched between the outer vertical groove 10o and the tread end E.
However, the outer land portion 11e is substantially formed of the hard rubber, and the rigidity of the outer land portion 11e can be made uniform, and the occurrence of uneven wear of the outer land portion 11e can be effectively suppressed.

The soft rubber material and the hard rubber material containing short fibers are mixed with carbon black as a reinforcing material. Examples of the carbon black include HAF and ISAF having a nitrogen adsorption specific surface area of 70 m ² / g or more determined by the BET method.
Although grades can be used, it is more preferable to use ISAF having a nitrogen adsorption specific surface area of 100 m ² / g or more from the viewpoint of preventing chain damage. Specifically, Show Black N220 (I) manufactured by Showa Cabot Co., Ltd.
SAF) and the like.
It is desirable to add about 40 to 60 parts by weight, preferably about 40 to 50 parts by weight, in parts by weight.

When the central portion of the tread forms two layers of the crown rubber portion 9A and the base rubber portion 9C as in this example, the thickness t of the crown rubber portion 9A measured at the non-groove portion is used.
Is preferably about 30 to 70% of the total thickness T of the tread rubber 9. If the thickness t of the crown rubber portion 9A is less than 30% of the total thickness T, the performance on ice tends to decrease. Conversely, if it exceeds 70%, the life of the tire is shortened due to early wear of the tread central portion. Tends to invite.

In the present embodiment, when the tire 1 is assembled on a regular rim J, filled with a regular internal pressure and loaded with a regular load and grounded on a flat surface, as shown in FIG. The maximum axial contact width CW is 0.5 to 0.7 times the tread contact width TW. If the maximum contact width CW of the crown rubber portion 9A in the tire axial direction is less than 0.5 times the tread contact width TW, the running performance on ice is reduced, and if it exceeds 0.7 times, the shoulder rubber This is because the width of the portion 9B is small, so that the above-described chain damage is likely to occur, and the steering stability on a dry road surface is reduced.

[0030]

EXAMPLE A heavy-duty tire having a tire size of 11R22.5 and having the basic structure shown in FIG. 1 was tested for performance on ice, performance on snow, dry steering stability and chain damage, and the performance was compared. For comparison, the value of CW / TW was not the present invention (Comparative Example 1,
For 2), a prototype was made and the performance was compared. The test method was as follows.

A) Performance test on ice A speedometer, a braking distance measuring device, and a test tire were mounted on a test vehicle, and the vehicle was driven at a constant speed of 40 km / H on a test road surface formed by an ice plate. The braking distance was measured until the vehicle was stopped after sudden braking was applied, and the friction coefficient was calculated from each value of the total weight, the speed and the braking distance of the test vehicle. The larger the value, the higher the friction coefficient and the better.

B) Snow Performance Test A snow-covered road surface was run at a constant speed of 40 km / H, and braking and evaluation were performed in accordance with the above-mentioned ice performance test.

C) Chain Damage Test A tire chain is wound around a test tire and mounted on an actual vehicle. After a specified maximum load is applied, the tire runs on a snow-covered road at a speed of 60 km / H for about 10 km, and then a shoulder is applied. The damage state, such as cracks and block hanging, which occurred in the part was examined.

D) Dry steering stability test The test tire was mounted on the above-mentioned vehicle, and the tire was run on a test course on a dry asphalt road surface, and evaluated by a 10-point method according to a driver's feeling. Table 1 shows the composition of each rubber material, and Table 2 shows the test results.

[0035]

[Table 1]

[0036]

[Table 2]

As a result of the test, it can be confirmed that the heavy load tire of the embodiment can maintain the running performance on the ice and snow road which is substantially the same as the tire of the comparative example, and that the steering stability on the dry road surface is improved. . Also regarding chain damage,
Good results were obtained with almost no cracks or the like.

[0038]

As described above, the heavy load tire of the present invention can achieve both running performance on icy and snowy roads and steering stability against running on dry road surfaces. Further, even when a tire chain is mounted, cracks in the shoulder portion can be suitably suppressed, and durability can be improved.

[Brief description of the drawings]

FIG. 1 is a right half sectional view of a tire showing one embodiment of the present invention.

FIG. 2 is a plan view of the tread portion.

[Description of Signs] 2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 7 Belt layer 9 Tread rubber 9A Crown rubber portion 9B Shoulder rubber portion 9C Base rubber portion

Claims (3)

[Claims] 1. A heavy-duty tire comprising a carcass comprising a single carcass ply having a toroidal shape extending from a tread portion to a bead core of a bead portion through a sidewall portion and having steel cords arranged in parallel. The crown rubber, which includes at least a crown rubber portion that is in contact with the road surface and is disposed at the center of the tread, and a shoulder rubber portion that is in contact with the road surface and is disposed on both sides of the crown rubber portion. The portion is formed from a soft rubber material containing short fibers having a JISA hardness of 55 ° or more and 62 ° or less in which short fibers are mixed into a rubber base material containing natural rubber and butadiene rubber, and the shoulder rubber portion is formed of short fibers. And made of a hard rubber material with a JISA hardness of more than 62 mm and 70 mm or less, The maximum contact width CW in the tire axial direction of the crown rubber portion when the normal internal pressure is charged and a regular load is applied to contact the flat surface is set to 0.5 to 0.7 times the tread contact width TW. A heavy duty tire characterized by the following. 2. The tread rubber includes a base rubber portion disposed radially inward of the crown rubber portion in the tire radial direction and connected to the shoulder rubber portion, and the base rubber portion is the same hard rubber material as the shoulder rubber portion. The heavy duty tire according to claim 1, wherein the tire is formed from: 3. The soft rubber material containing short fibers contains 5 to 30 parts by weight of short fibers in 100 parts by weight of the rubber base material, and the thickness of the crown rubber portion is less than the total thickness of the tread rubber. The heavy duty tire according to claim 1 or 2, wherein the content is 30 to 60%.