JP4473810B2 - Heavy duty radial tire - Google Patents

Description

  The present invention relates to a radial tire for heavy loads that is suitable for a tire having a flatness ratio of 50% or less and that suppresses uneven wear and occurrence of cracks at the groove bottom by improving a belt layer.

  In heavy-duty radial tires for trucks and buses, as shown in FIG. 4, generally, a belt layer a disposed on the outer side in the radial direction of the carcass is composed of 3 to 4 belt plies b using steel belt cords. It is formed by. Conventionally, in the first belt ply b1 arranged on the innermost side in the radial direction, the cord angle with respect to the tire circumferential direction is set to 60 ± 15 °, and the second to third or second to second outside the cord angle. The cord angle of the belt ply No. 4 with respect to the tire circumferential direction is 10 to 35 °, and the inclination directions of the cords of the second and third belt plies b2 and b3 are opposite to each other. This forms a triangle structure in which the belt cords cross each other between the first and second belt plies b1 and b2 and between the second and third belt plies b2 and b3. It has an effect and is reinforced.

  On the other hand, along with the improvement of highways and the improvement in vehicle performance, even in heavy-duty radial tires, the flatness, which is the ratio of the tire cross section height to the tire cross section width (tire cross section height / tire cross section width), is reduced. Flat tires with improved handling stability are being used.

  However, in such a flat tire, particularly a flat tire with a flatness ratio of 50% or less, the tread portion is wide and the tread contour shape is flattened. The outer diameter growth of the portion, particularly the outer diameter growth in the tread shoulder region, becomes large. As a result, the contact pressure in the tread shoulder region increases and induces uneven wear. Further, the stress acting on the groove bottom of the tread groove disposed in the tread shoulder region is increased, and there is a tendency to cause damage such as cracks at the groove bottom.

  Therefore, the present invention can increase the restraining force of the belt layer over a wide range in a well-balanced manner, and in particular, in a flat heavy load radial tire with a flatness ratio of 50% or less, the outer diameter growth of the tread portion, particularly in the tread shoulder region. An object of the present invention is to provide a heavy duty radial tire that suppresses the growth of the outer diameter and prevents the occurrence of uneven wear and cracks at the bottom of the tread groove.

Japanese Patent No. 3398065

In order to achieve the above object, the invention of claim 1 of the present application includes a carcass extending from a tread portion through a sidewall portion to a bead core of the bead portion, and a belt layer disposed on the radially outer side of the carcass and within the tread portion. A heavy-duty radial tire with
The belt layer is disposed on a radially innermost first belt ply in which a belt cord is arranged at an angle of 10 to 45 ° with respect to a tire circumferential direction, and on a radially outer side of the first belt ply. A third belt ply in which a belt cord is arranged at an angle of 10 to 45 ° with respect to a tire circumferential direction and an inclination direction is opposite to a belt cord of the first belt ply, and the first and third belt plies At least a second belt ply disposed between the belt plies and spirally wound around the belt cord at an angle of 5 ° or less with respect to the tire circumferential direction;
The ply widths W1 and W3 in the tire axial direction of the first and third belt plies are 85% or more of the tread contact width Tw, the difference W1-W3 is 14 mm or more, and the ply width W2 of the second belt ply Is not less than 70% of the tread grounding width Tw and smaller than the ply widths W1 and W3 of the first and third belt plies,
Provided between the first and third belt plies is a reinforcing rubber layer extending outward in the tire axial direction from the outer end in the tire axial direction of the second belt ply,
Moreover, the reinforcing rubber layer is connected to the outer end of the second belt ply and extends in the tire axial direction with a substantially constant thickness T1, and has a complex elastic modulus E * 1 of 8.0 to 14.0 MPa. Reinforcing rubber portion on the inner side in the tire axial direction, and a tire shaft that is connected to the reinforcing rubber portion and has a complex elastic modulus E * 2 of 6.0 to 12.0 MPa and smaller than the complex elastic modulus E * 1 It consists of a reinforcing rubber part on the outside in the direction,
Moreover, the thickness T1 of the inner reinforcing rubber portion is 1.5 to 4.0 mm, and the thickness T2e of the outer reinforcing rubber portion at the outer end in the tire axial direction of the third belt ply is 2.0 mm or more. A heavy duty radial tire characterized by

In the invention of claim 2, the inner reinforcing rubber portion has a rubber hardness Hs1 of 69 to 79 degrees , and the outer reinforcing rubber portion has a rubber hardness Hs2 of 65 to 75 degrees and is more than the rubber hardness Hs1. It is characterized by being small.
According to a third aspect of the invention, the thickness T2e of the outer reinforcing rubber portion is equal to or greater than the thickness T1 of the inner reinforcing rubber portion.
According to a fourth aspect of the present invention, the outer reinforcing rubber portion includes a gradually increasing portion extending from the outer end of the inner reinforcing rubber portion to the outer side in the tire axial direction while gradually increasing the thickness T2. .

  The tread ground contact width means the maximum width in the tire axial direction of the ground contact surface that comes into contact when a normal load is applied to a tire that is assembled with a normal rim and filled with a normal internal pressure. The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based, for example, a standard rim for JATMA, “Design Rim” for TRA, or ETRTO means "Measuring Rim". The “regular internal pressure” is the air pressure specified by the tire for each tire. The maximum air pressure in the case of JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA, If it is ETRTO, it means "INFLATION PRESSURE". The “regular load” is the load defined by the standard for each tire. The maximum load capacity shown in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” for JATA If it is ETRTO, it is "LOAD CAPACITY".

  The complex elastic modulus E * is a value measured using a viscoelastic spectrometer under the conditions of a temperature of 70 ° C., a frequency of 10 Hz, an initial tensile strain of 10%, and a dynamic strain amplitude of ± 2%. The rubber hardness is a durometer A hardness measured with a durometer type A based on JIS-K6253.

  As described above, in the present invention, the first and third belt plies in which the cord angle is 10 to 45 ° and the belt cords cross each other between the plies, and the belt cords are spiraled in the tire circumferential direction. A belt layer is formed with the second belt ply wound in a shape, and each belt ply is set to a predetermined width. As a result, an excellent tagging effect can be exhibited over a wide range, the outer diameter growth of the tread portion can be uniformly suppressed, and the occurrence of uneven wear and cracks at the tread groove bottom can be prevented.

  In order to prevent damage due to the adoption of this belt structure, a reinforcing rubber layer is disposed on the outer side in the tire axial direction of the second belt ply and between the first and third belt plies. Is formed of a high-elasticity reinforcing rubber portion and an outer reinforcing rubber portion having a slightly lower elastic modulus. Therefore, the inner reinforcing rubber portion can suppress the peeling damage between the first and third belt plies, and the outer reinforcing rubber portion allows the cord end loose at the first and third belt ply outer ends. Can be suppressed. Further, the reinforcing rubber layer can ensure excellent rigidity up to the outer end of the belt layer, can further enhance the above-mentioned uneven wear resistance and crack resistance, and can contribute to improvement of steering stability.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a radial tire for heavy loads according to the present invention, and FIG. 2 is an enlarged sectional view showing a tread portion thereof.
As shown in FIG. 1, the heavy duty radial tire 1 includes a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, the radially outer side of the carcass 6 and the inside of the tread portion 2. And at least a belt layer 7 disposed on the belt. In this example, the case of a flat tire in which the flatness, which is the ratio of the tire cross section height to the tire cross section width (tire cross section height / tire cross section width), is reduced to 50% or less is illustrated.

  The carcass 6 is formed of one or more, in this example, one carcass ply 6A in which carcass cords are arranged at an angle of, for example, 75 to 90 degrees with respect to the tire circumferential direction. The carcass ply 6A includes a series of folded portions 6b that are folded from the inner side to the outer side in the tire axial direction around the bead core 5 at both ends of the ply body portion 6a straddling the bead cores 5 and 5. A bead apex rubber 8 for bead reinforcement having a triangular cross section extending radially outward from the bead core 5 is disposed between the ply main body portion 6a and the folded portion 6b. As the carcass cord, a steel cord is suitable, but organic fiber cords such as aromatic polyamide, nylon, rayon, polyester, etc. can be adopted as required.

In this example, the bead apex rubber 8 includes a radially inner apex portion 8A made of a hard rubber having a rubber hardness of 80 to 95 degrees and an outer radial direction made of a soft rubber having a rubber hardness of 40 to 60 degrees . A two-layer structure including the apex portion 8B is formed, and the height H1 of the outer end 8e from the bead base line BL is increased to a range of 35 to 50% of the tire cross-section height H0. Thereby, while suppressing damage at the outer end 8e, the side rigidity of the tire is increased, and the steering stability is improved.

  Next, the belt layer 7 includes three to four sheets using steel cords as belt cords, and in this example, four sheets composed of first to fourth belt plies 7A to 7D that are sequentially stacked from the inner side to the outer side in the radial direction. The structure is illustrated.

  Among these, as shown in FIG. 3, the first belt ply 7A arranged on the innermost side in the radial direction has the belt cords inclined and arranged at an angle α1 of 10 to 45 ° with respect to the tire circumferential direction. The second belt ply 7B has a belt cord wound spirally at an angle α2 of 5 ° or less with respect to the tire circumferential direction. The third belt ply 7C has a belt cord inclined at an angle α3 of 10 to 45 ° with respect to the tire circumferential direction and with the inclination direction opposite to the belt cord of the first belt ply 7A. . The fourth belt ply 7D is not particularly restricted, but in this example, the belt cord is inclined at an angle α4 of 10 to 45 ° with respect to the tire circumferential direction and in the same direction as the belt cord of the third belt ply 7C. Arranged.

  At this time, the ply widths W1 and W3 in the tire axial direction of the first and third belt plies 7A and 7C are respectively 85% or more of the tread contact width Tw, and the tire axial direction of the second belt ply 7B. The ply width W2 is set to 70% or more of the tread grounding width Tw and smaller than the ply widths W1 and W3. The ply widths W1 and W3 have a difference W1-W3 of 14 mm or more, that is, the outer ends of the first and third belt plies 7A and 7C are separated from each other by a distance L of at least 7 mm in the tire axial direction. As a result, the stress concentrated on the outer ends of the first and third belt plies 7A and 7C is relieved. The ply width W4 of the fourth belt ply 7D is at least smaller than the ply width W3. In this example, the ply width W4 is larger than the ply width W2, thereby increasing the reinforcing effect. The upper limit of the ply widths W1 and W3 is 100% or less of the tread ground contact width Tw.

  The belt layer 7 configured as described above can ensure the necessary belt rigidity because the belt cords of the first to third belt plies 7A to 7C intersect each other to form a triangle structure. Moreover, since the belt cord of the second belt ply 7B is spirally wound in the circumferential direction, the restraining force on the tread portion 2 can be greatly increased, and an excellent tagging effect can be exhibited over a wide range. By uniformly suppressing the growth of the outer diameter, uneven wear, generation of cracks at the tread groove bottom, and the like can be effectively suppressed.

  The ply widths W1 and W3 of the first and third belt plies 7A and 7C are less than 85% of the tread grounding width Tw, and the ply width W2 of the second belt ply 7B is less than 70% of the tread grounding width Tw. In this case, the tag effect is insufficient in the tread shoulder region, and the effect of suppressing the uneven wear and the effect of suppressing the occurrence of cracks at the tread groove bottom cannot be achieved sufficiently.

  However, when such a belt structure is employed, separation damage such as separation tends to occur between the first and third belt plies 7A and 7C at the outer end portion of the belt layer 7. Therefore, as shown in FIG. 2, a reinforcing rubber layer 10 extending outward in the tire axial direction from the outer end Be in the tire axial direction of the second belt ply 7B is provided between the first and third belt plies 7A and 7C. Arranged.

  The reinforcing rubber layer 10 is connected to the outer end Be of the second belt ply 7B and extends in the tire axial direction at a substantially constant thickness T1 and has a complex elastic modulus E * 1 of 8.0 to 14.0 MPa. Reinforcing rubber portion 10A on the inner side in the tire axial direction, and continuous elastic rubber portion 10A, and complex elastic modulus E * 2 of 6.0 to 12.0 MPa and smaller than the complex elastic modulus E * 1 The outer reinforcing rubber portion 10B outside the tire axial direction.

  Such a reinforcing rubber layer 10 reinforces the outer side in the tire axial direction from the second belt ply 7B and reaches the outer end of the belt layer 7 to ensure excellent rigidity, thereby preventing the above-mentioned uneven wear resistance and crack resistance. Further enhance sex. Moreover, the inner reinforcing rubber portion 10A has high elasticity, so that the movement between the first and third belt plies 7A and 7C can be suppressed, and the separation can be prevented. Further, the outer reinforcing rubber portion 10B has a lower elasticity than the inner reinforcing rubber portion 10A, so that the shearing force concentrated on the outer ends of the first and third belt plies 7A and 7C is alleviated. Cord end looseness can be suppressed.

  At this time, the thickness T1 of the inner reinforcing rubber portion 10A is set to 1.5 to 4.0 mm, and the thickness T2e of the outer reinforcing rubber portion at the outer end of the third belt ply 7C is set to 2.0 mm or more. Is necessary.

  When the thickness T1 is less than 1.5 mm, separation tends to occur. When the thickness T1 exceeds 4.0 mm, the reinforcing effect is reduced and cracks and the like tend to occur. If the thickness T2e is less than 2.0 mm, the cord end loose tends to occur at the outer ends of the first and third belt plies 7A and 7C. The upper limit of the thickness T2e is not particularly limited, but is preferably 4.5 mm or less.

Similarly, when the complex elastic modulus E * 1 of the inner reinforcing rubber portion 10A exceeds 14.0 MPa, separation tends to occur. Conversely, when the elastic modulus E * 1 falls below 8.0 MPa, the reinforcing effect decreases and cracks tend to occur. . If the complex elastic modulus E * 2 of the outer reinforcing rubber portion 10B exceeds 12.0 MPa, the cord end looseness tends to occur. Conversely, if it falls below 6.0 MPa, the reinforcing effect decreases and cracks and the like tend to occur. Become. The complex elastic modulus difference E * 1-E * 2 is preferably in the range of 1.0 to 4.0 MPa. For the same reason, the rubber hardness Hs1 of the inner reinforcing rubber portion 10A is in the range of 69 to 79 degrees , and the rubber hardness Hs2 of the outer reinforcing rubber portion 10B is in the range of 65 to 75 degrees and the rubber hardness Hs1. It is also preferable to set a smaller value.

  The length Li of the reinforcing rubber portion 10A in the tire axial direction is in the range of 20 to 50% of the total length L0 of the reinforcing rubber layer 10 in the tire axial direction. From the viewpoint of balance. In the outer reinforcing rubber portion 10B, it is preferable from the viewpoint of suppressing cord end looseness that the thickness T2e is set to be equal to or greater than the thickness T1 and further larger than the thickness T1. Therefore, as in this example, the outer reinforcing rubber portion 10B is provided with a thickness increasing portion 10Ba extending outward from the outer end of the inner reinforcing rubber portion 10A while gradually increasing its thickness T2. In particular, it is preferable to form the gradually increasing thickness portion 10Ba up to the outer end of the second belt ply 7B.

  Further, the outer end portion of the first belt ply 7A is gradually separated from the carcass 6 toward the outer side in the tire axial direction. The spacing portion J is provided with a cushion rubber 11 having a triangular elastic section E * 3 of 2.0 to 5.0 Mpa and E * 3 <E * 2 ≦ E * 1, and a belt ply Damage at the outer end of 7A is further suppressed. In the present invention, since the cord angle α1 of the first belt ply 7A is smaller than the conventional one, the shearing force between the first belt ply 7A and the carcass ply 6A tends to increase. Therefore, in this example, the cushion rubber 11 is provided with a thin auxiliary layer portion 11A having a thickness of 0.5 to 2.0 mm extending between the first belt ply 7A and the carcass ply 6A and extending to the tire equator, The shearing force is relaxed.

In the present embodiment, the tread portion 2 is provided with a tread rubber 2G through an adhesive rubber layer 12 that is thinner (for example, 0.5 mm or less) than the auxiliary layer portion 11A. The adhesive rubber layer 12 extends along the outer surface of the fourth belt ply 7D, the outer surface of the third belt ply 7C, the outer end surface of the reinforcing rubber layer 10, and the outer surface of the cushion rubber 11. The outer end surface of the reinforcing rubber layer 10 is adjacent to the base rubber portion 2Gb of the tread rubber 2G through the adhesive rubber layer 12. The base rubber portion 2Gb has a rubber hardness of about 64 degrees and a complex elastic modulus of about 5 Mpa, as in the prior art. The inner and outer reinforcing rubber portions 10A and 10B are harder than the base rubber portion 2Gb. High elasticity is set.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

  A radial heavy load tire having a tire size of 435 / 45R22.5 having the structure shown in FIG. 1 was made on the basis of the specifications shown in Table 1, and the partial wear resistance, crack resistance at the groove bottom, and tread durability of each sample tire were tested. Tested and evaluated for sex.

  In the conventional tire, in the first to fourth belt plies, the cord angle α1 (+ 50 °), the cord angle α2 (+ 18 °), the cord angle α3 (−18 °), and the cord angle α4 (−18 °). It is said. In the tires of Examples and Comparative Examples, in the first to fourth belt plies, the cord angle α1 (+ 18 °), the cord angle α2 (approximately 0 ° (spiral winding)), the cord angle α3 (−18 °), The cord angle α4 (−18 °) is used.

(1) Uneven wear resistance:
A sample tire is mounted on all wheels of a 2-D / 4 test vehicle under the conditions of a rim (22.5 × 14.00) and internal pressure (900 kPa), and includes the highway, urban area, and mountain road. I drove 10,000 km. And the remaining groove depth of the shoulder groove | channel after driving | running | working was measured and it compared by the index | exponent which set the conventional example to 100. The larger the value, the better the uneven wear resistance.

(2) Crack resistance:
After running, the presence or absence of cracks at the bottom of the shoulder groove was visually inspected.

(3) Tread durability:
After the running, the tire was disassembled, and the presence or absence of separation between the first and third belt plies and the presence or absence of a cord end rule at the outer ends of the first and third belt plies were inspected.

  As shown in the table, it can be confirmed that the tires of the examples can suppress the occurrence of uneven wear and cracks at the bottom of the tread groove while ensuring the durability of the tread portion.

It is sectional drawing which shows one Example of the radial tire for heavy loads of this invention. It is sectional drawing which expands and shows the tread part. It is drawing explaining the code arrangement | sequence of each belt ply. It is drawing explaining the cord arrangement of the belt ply of the conventional tire.

Explanation of symbols

2 Tread portion 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 7 Belt layer 7A First belt ply 7B Second belt ply 7C Third belt ply 10 Reinforcing rubber portion 10B in reinforcing rubber layer 10A Outside reinforcing rubber Part 10Ba Thickness increasing part

Claims (4)

A heavy duty radial tire comprising a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a belt layer disposed radially outside the carcass and within the tread portion,
The belt layer is disposed on a radially innermost first belt ply in which a belt cord is arranged at an angle of 10 to 45 ° with respect to a tire circumferential direction, and on a radially outer side of the first belt ply. A third belt ply in which the belt cord is arranged at an angle of 10 to 45 ° with respect to the tire circumferential direction and the inclination direction of the belt cord of the first belt ply is opposite; and the first and third belt plies At least a second belt ply disposed between the belt plies and spirally wound around the belt cord at an angle of 5 ° or less with respect to the tire circumferential direction;
The ply widths W1, W3 in the tire axial direction of the first and third belt plies are 85% or more of the tread contact width Tw, the difference W1-W3 is 14 mm or more, and the ply width W2 of the second belt ply is , 70% or more of the tread grounding width Tw and smaller than the ply widths W1 and W3 of the first and third belt plies,
Provided between the first and third belt plies is a reinforcing rubber layer extending outward in the tire axial direction from the outer end in the tire axial direction of the second belt ply,
Moreover, the reinforcing rubber layer is connected to the outer end of the second belt ply and extends in the tire axial direction with a substantially constant thickness T1, and has a complex elastic modulus E * 1 of 8.0 to 14.0 MPa. Reinforcing rubber portion on the inner side in the tire axial direction, and a tire shaft that is connected to the reinforcing rubber portion and has a complex elastic modulus E * 2 of 6.0 to 12.0 MPa and smaller than the complex elastic modulus E * 1 It consists of a reinforcing rubber part on the outside in the direction,
Moreover, the thickness T1 of the inner reinforcing rubber portion is 1.5 to 4.0 mm, and the thickness T2e of the outer reinforcing rubber portion at the outer end in the tire axial direction of the third belt ply is 2.0 mm or more. A heavy duty radial tire characterized by The inner reinforcing rubber portion has a rubber hardness Hs1 of 69 to 79 degrees , and the outer reinforcing rubber portion has a rubber hardness Hs2 of 65 to 75 degrees and smaller than the rubber hardness Hs1. The radial tire for heavy loads according to claim 1.
  The radial tire for heavy loads according to claim 1 or 2, wherein the thickness T2e of the outer reinforcing rubber portion is equal to or greater than the thickness T1 of the inner reinforcing rubber portion.   4. The outer reinforcing rubber portion includes a thickness increasing portion extending from the outer end of the inner reinforcing rubber portion to the tire axial direction outside while increasing the thickness T2. Heavy duty radial tire as described in 1.

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