JP4392220B2 - Heavy duty radial tire - Google Patents

Description

  The present invention relates to a heavy duty radial tire that can suppress uneven wear by making the contact pressure of the tire uniform.

  In recent years, radial tires having increased rigidity by overlapping a plurality of belt plies made of steel cords on a belt layer are used as heavy duty tires used for trucks, buses and the like. In such heavy-duty radial tires, the problem of uneven wear tends to occur, and many proposals have been made to prevent such problems.

Japanese Patent Laid-Open No. 10-315772 JP 7-164824 A JP-A-7-164823 JP-A-8-2210 Japanese Patent Laid-Open No. 7-151971

  These prior documents particularly focus on the slip amount between the tire tread surface and the road surface and the contact pressure distribution, and make the slip amount uniform by making the tread surface discontinuous rather than a single arc. Or a tire that tries to prevent uneven wear by making the ground pressure distribution uniform, and a molding die for the tire, each of which has a corresponding effect.

  However, these proposals are still insufficient to prevent uneven wear in long-term use, especially in the present situation where the tread width tends to be expanded to increase the wear life. However, further improvement in the uneven wear resistance of the heavy duty radial tire is desired.

  An object of the present invention is to provide a heavy duty radial tire capable of suppressing uneven wear.

The invention according to claim 1 is a radial tire for heavy loads, wherein the carcass (6) has a radial arrangement that is folded around the bead core of the bead portion through the sidewall portion (3) from the tread portion (2). A belt layer (7) including two or more belt plies arranged outside the carcass (6) and having belt cords arranged at an angle of 10 to 40 degrees with respect to the tire circumferential direction, and in the tread portion At least two longitudinal main grooves G extending in the tire circumferential direction are provided, and the distance from the tread surface to the belt cord of the widest maximum belt ply is the belt cord distance BT, and the carcass ply closest to the tread surface from the tread surface The distance to the carcass cord is the carcass distance CT, the position a separating 50% of the tread half-width WT1 from the tire equatorial plane C, and 70%. When the intermediate region MA and the region between the positions b that, characterized by satisfying the following a) to e).
a) The intermediate area MA includes a portion in which a ratio BTm / BTq of the belt cord distance BTm in the intermediate area MA to the belt cord distance BTq in the tire equatorial plane q is expressed by the following equation.
0.950 ≦ BTm / BTq ≦ 0.975
b) The ratio BTc / BTq of the belt cord distance BTc at the edge c of the maximum width belt ply 7M to the belt cord distance BTq at the tire equatorial plane q is set to the following range.
1.00 ≦ BTc / BTq ≦ 1.025
c) The intermediate area MA has a portion in which the ratio CTm / CTq of the carcass cord distance CTm in the intermediate area MA to the carcass cord distance CTq in the tire equatorial plane q is as follows.
1.017 ≦ CTm / CTq ≦ 1.045
d) The ratio CTc / CTq of the carcass cord distance CTc at the edge c of the maximum width belt ply to the carcass cord distance CTq at the tire equatorial plane q is set to the following range.
1.350 ≦ CTc / CTq ≦ 1.550
e) The outer edge Go1 at which the groove wall on the outer side in the tire axial direction of the outer longitudinal main groove Go on the outermost side in the tire axial direction intersects the tread surface is the outer vertical main groove Go on both sides in the cross section including the tire shaft. The tread surface of the central area CA which is the area between them is regarded as a single arc and is located on the extended line EL extended.

The invention according to claim 2 is characterized in that the belt cord of the maximum width belt ply is a second belt ply inclined at an angle of 10 to 40 degrees with respect to the tire circumferential direction and second from the carcass side. In the invention according to claim 3, in the cross section including the tire shaft, the outer surface of the maximum width belt ply is substantially composed of a single belt arc RB, and the tread surface of the central region CA is substantially single. The belt arc RB and the tread surface center arc RT have the following relationship:
0.50 ≦ RB / RT ≦ 1.20

Furthermore, the invention according to claim 4 is characterized in that the belt arc RB is in a range of 400 mm to 700 mm .

  The radial tire for heavy loads of the present invention can make the contact length in the tread uniform, and can suppress uneven wear.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, a heavy-duty radial tire 1 (hereinafter referred to as a tire 1) is located at a tread portion 2, sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and inner ends of the sidewall portions 3. The tire 1 includes a carcass 6 straddling the bead portions, and a belt layer wound around the carcass 6 in the radial direction of the tire and inside the tread portion 2. 7 is arranged.

  The tread portion 2 is provided with at least two longitudinal main grooves G continuous in the tire circumferential direction. The longitudinal main groove G means a wide longitudinal groove of about 8 to 23% of the tread half width WT1 in the tire axial direction. The vertical main groove G includes a vertical main groove Gi on both sides of the tire equatorial plane C and a vertical main groove Go on the outermost grounding end t side on the outermost side in the tire axial direction, and is indicated by a one-dot chain line. In addition, a central longitudinal main groove Gq can also be arranged on the tire equator plane q. The outer longitudinal main groove Go can be disposed at the middle position in the tire axial direction between the tire equatorial plane q and the ground contact end t, or on the ground contact end t side from the intermediate position. Further, the tire 1 can adopt various tread patterns such as a rib pattern, a block pattern, or a lug and a rib lug pattern by forming or not forming other lateral grooves and lug grooves.

  The carcass 6 is composed of one or more of a radial arrangement in which carcass cords are arranged at an angle of 70 to 90 degrees with respect to the tire circumferential direction, in this example, one carcass ply, and the carcass ply includes the tread portion. From 2 to the side wall part 3, it is folded and locked around a bead core of a bead part (not shown). The carcass cord is made of a steel cord in this embodiment, and an inner liner 4 made of air-impermeable rubber such as butyl rubber is disposed inside the carcass 6 so as to face the tire lumen.

  The belt layer 7 includes a plurality of high-strength belt cords such as steel cords arranged at a cord angle of 10 to 65 ° with respect to the tire circumferential direction. In this embodiment, the belt layer 7 is arranged in order from the carcass 6 side toward the tread portion 2. The four belt plies comprising the first belt ply 71, the second belt ply 72, the third belt ply 73, and the narrow fourth belt ply 74 are used. The cord of the first belt ply 71 has an angle of 64 ° with respect to the tire equatorial plane C, and the belt cords of the second to fourth belt plies 72 to 74 have an angle of 16 ° with respect to the tire equatorial plane C. The belt cords of the cord 71 and the second belt ply 72 are inclined in the same direction as viewed from the outer surface of the tread, and the belt cord of the third belt ply 73 and the belt cord of the fourth belt ply 74 are the first and second belts. Inclined in the opposite direction to the ply cord. Accordingly, a triangle structure is formed by the first and third belt plies 71 and 73 to make the belt layer strong, and the fourth belt ply 7 protects the central area CA that is easily damaged. Further, in this embodiment, the second belt ply 72 is the maximum width belt ply 7M having the widest width, and the width WB is set to about 0.85 to 1.00 of the tire tread width WT (this embodiment) Then, the grounding end t constitutes a point forming the tire tread width WT).

  In the heavy duty radial tire having such a structure, it is known that the uneven wear of the tire and the shape of the contact surface are closely related. Focusing on the contact length in the direction, it was found that wear is promoted in a portion where the contact length is short.

  Therefore, 50% of the tread half width WT1, which is the distance from the tire equatorial plane q to the ground contact t when the tire 1 is mounted on the normal rim and filled with the normal internal pressure (referred to as the normal state), is the tire equatorial plane. Attention was paid to the ground contact state in the intermediate region MA between the position a separated from q and the position b separated by 70%.

  In a normal tire, the intermediate area MA is relatively easily swelled compared to other areas of the tread surface S, and the outer area OA of the intermediate area MA outside the tire axial direction is relatively easily reduced in diameter. There was found. This is because the tread surface S of the tire in the normal state is relatively large formed in a region from the inner region IA in the tire axial direction inside of the intermediate region MA to the intermediate region MA in the cross section including the tire shaft. This is because it tends to consist of two arcs, that is, an arc and a relatively small arc in the outer area OA. In such a tire, the contact length between the tread surface S of the outer region OA and the road surface is shortened. As a result, the slip amount is increased, and uneven wear of the shoulder portion is easily induced.

  In particular, in the tread pattern in which the outer vertical main groove Go is provided, for example, continuously in the circumferential direction in the region of the intermediate region MA or in the vicinity of the outer side in the tire axial direction, the vertical main groove Go has the curvature radius of the tread surface S. This results in increased discontinuity and promotes uneven wear. The term “provided in the vicinity” means that the inner groove edge Go2 (the position where the groove wall on the inner side in the tire axial direction intersects the tread surface S) of the longitudinal main groove Go in the tire axial direction is in the intermediate region MA, or It means that it is separated from the intermediate region MA by about 1/4 or less of the groove width of the longitudinal main groove G.

  Further, in order to reduce uneven wear, as shown in FIGS. 3 to 4, in the cross section including the tire shaft of the tire in a normal state, the outer side where the groove wall on the outer side in the tire axial direction of the longitudinal main groove Go intersects the tread surface S An end edge Go1 (that is, an inner edge of a region (shoulder region) between the ground contact end t and the outer vertical main groove Go) is defined as a region between the outer vertical main grooves Go on both sides (inner sides on both sides). The tread surface S of the central area CA, which is the area between the side groove edges Go2, is regarded as a single arc and is present at a position on the extended line EL extended.

  Here, when the tread surface S of the central region S is regarded as a single arc, the arc passes through a point on the tire equator plane q, the inner end edge Go2, and an intermediate point of the tread surface S therebetween. When the intermediate point is a groove, the point is on the tire equatorial plane q side of the groove.

Tend to intermediate region MA is bulged as described above, then the outer side edge Go1 is easily located Go1a point radially inward of Figure 3 of the extension line EL, is at that time, the tire is rolling This is because the relative movement with respect to the road surface is large and tends to be a starting point for uneven wear. If the outer side edge Go1 is positioned Go1b point radially outward of the imaginary line EL (shown in FIG. 3), the slip amount of the inner edge Go2 opposite longitudinal main groove Go becomes large, wherein Therefore, uneven wear tends to occur.

Ground terminal t is radially outward of the extension line EL, as shown in FIG. 4, or may be located radially inward of the tire as shown in FIG. 5, the outer side edge as shown in FIG. 3 It is desirable that both the edge Go1 and the ground end t are positioned on the extension line EL. The contact end t is a position that is most outward in the tire axial direction within a region that is in contact with the ground when a normal load is applied in a normal state. 4 and 5 show the top and bottom of the grounding end t in an extremely enlarged manner.

  Here, the normal rim is a standard rim specified by JATMA, “Design Rim” specified by TRB, or “Measuring Rim” specified by ETRTO, and the normal internal pressure is the highest air pressure specified by JATMA, the TRB The maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFRATION PRESURES” or “INFLATION PRESSURES” specified by ETRTO, and the normal load is the maximum load capacity specified by JATMA, the maximum described in the above table of TRB Value or “LOAD CAPACITY” defined by ETRTO.

  As described above, in order to position the outer edge Go1 on the extension line EL, the modification of the outer shape simply by modifying the mold shape is not essential. In the ground pressure distribution, the intermediate region MA tends to be discontinuous and insufficient. Therefore, in order to basically suppress uneven wear, in the present invention, the distance from the tread surface S to the belt cord of the widest maximum belt ply 7M is the belt cord distance BT, the tread surface S, and the tread surface. When the distance to the carcass cord of the carcass ply closest to S is the carcass distance CT, the following a) to d) are satisfied.

a) The intermediate region MA has a portion in which a ratio BTm / BTq of the belt cord distance BTm in the intermediate region MA to the belt cord distance BTq in the tire equatorial plane q is expressed by the following formula: 0.950 ≦ BTm / BTq ≦ 0.975
b) The ratio BTc / BTq of the belt cord distance BTc at the edge c of the maximum width belt ply 7M to the belt cord distance BTq at the tire equatorial plane q,
1.00 ≦ BTc / BTq ≦ 1.025
c) The intermediate region MA has a portion in which the ratio CTm / CTq of the carcass cord distance CTm in the intermediate region MA to the carcass cord distance CTq in the tire equatorial plane q is as follows:
1.017 ≦ CTm / CTq ≦ 1.045
d) The ratio CTc / CTq of the carcass cord distance CTc at the edge c of the maximum width belt ply to the carcass cord distance CTq at the tire equatorial plane q,
1.350 ≦ CTc / CTq ≦ 1.550

  As described above, the outer end edge Go1 of the outer longitudinal main groove Go1 at the outermost outermost side in the tire axial direction is an extension obtained by regarding the tread surface of the central area CA as a single arc in a cross section including the tire axis. As described above, it is located on the line EL.

  In the configurations a) to d), the configuration of a) makes the belt shape appropriate, the configuration of b) optimizes the belt shape, and the configuration of c) optimizes the carcass shape. By doing so, the bulging of the intermediate region MA is suppressed, and the configuration of d) is intended to prevent relative shrinkage of the shoulder portion by optimizing the carcass shape.

  Here, the ground contact end t is the outermost point in the tire axial direction on the tread contact surface when a normal load is applied to the tire 1 in the normal state, and coincides with the tread end e in FIG. The ground contact end t may be located inward of the tire axial direction from the tread end, or may be located outward in the case of a round edge or the like (in the round edge, the tread edge e is the tread surface S and the buttress surface). Can be defined as the point of intersection with the extended surface). In many cases, the tread half width WT1 is ½ of the tread width WT which is the distance in the tire axial direction between the ground contact ends t and t. For example, in the case of an asymmetrical tire with respect to the tire equatorial plane q The tread half width WT1 will not be equal to 0.5WT.

  As described above, the intermediate area MA is an area between the position a separating 50% of the tread half width WT1 and the position b separating 70% from the tire equatorial plane q, and the belt cord distance BT. Means the length from the tread surface S to the belt cord of the maximum width belt ply 7M in the normal to the tread surface S. The carcass cord distance CT refers to the length from the tread surface S to the carcass cord of the outermost carcass ply 6A in the normal to the tread surface S.

  Therefore, the belt cord distance BTm in the intermediate region MA is the distance from the tread surface S to the point where the normal to the tread surface S intersects the belt cord outer surface of the maximum width belt ply 7M in the intermediate region MA. Say distance. Belt cord distance BTq at the tire equatorial plane q, belt cord distance BTc at the edge c of the maximum width belt ply 7M, carcass cord distance CTq at the tire equatorial plane q, and at the edge c of the maximum width belt ply 7M. The carcass cord distance CTc can be set similarly.

  When the ground contact width WT is relatively narrow or the end edge c of the maximum width belt ply 7M exceeds the tread edge e outward in the tire axial direction, an extension line of the tread surface S in the central area CA as shown in FIG. The distance from the extension line EL to the point where the normal to EL passes through the edge c is defined as the belt cord distance BTc at the edge c of the maximum width belt ply 7M (72), and similarly the carcass cord distance CTc. To do.

  In a), when the ratio BTm / BTq of the belt cord distance BTm in the intermediate region MA to the belt cord distance BTq in the tire equatorial plane q is 0.950> BTm / BTq, the intermediate region by normal internal pressure filling The bulge of MA becomes too small, the contact length and contact pressure of the intermediate area MA are insufficient, and early wear occurs in the intermediate area MA. In the case of BTm / BTq> 0.975, the bulging of the intermediate region is large as before, and uneven wear of the shoulder portion is easily induced. Only a part of the intermediate area MA may satisfy the configuration. The ratio BTm / BTq is more preferably 0.953 to 0.974.

  In b), when the ratio BTc / BTq of the belt cord distance BTc at the edge c of the maximum width belt ply 7M (72) to the belt cord distance BTq at the tire equatorial plane q is 1.000> BTc / BTq. The diameter of the shoulder portion is easily reduced, increasing the possibility of so-called shoulder wear. When BTc / BTq> 1.025, the ground contact pressure of the shoulder portion becomes too high, resulting in deterioration of uneven wear in the vicinity of the outer longitudinal main groove Go, and deterioration of structural durability performance due to increased heat generation of the shoulder portion. The ratio BTc / BTq is more preferably 1.000 to 1.021.

The same applies to the distance CT to the carcass 6 in the intermediate area MA. In c), the ratio CTm of the carcass cord distance CTm in the intermediate area MA to the carcass cord distance CTq in the tire equator plane q. When / CTq is 1.017 > CTm / CTq, the bulging of the intermediate region MA due to normal internal pressure filling is too small, and when CTm / CTq> 1.045, the bulging of the intermediate region MA is excessive. The ratio CTm / CTq is more preferably 1.017 to 1.042.

  In d), when the ratio CTc / CTq of the carcass cord distance CTc at the edge of the maximum width belt ply to the carcass cord distance CTq at the tire equatorial plane q is 1.350> CTc / CTq, the vicinity of the tread edge The outer diameter becomes smaller, and uneven wear such as shoulder drop wear tends to occur. When CTc / CTq> 1.550, the bulge in the vicinity of the tread edge in the normal state becomes too large, the contact pressure and contact length become uneven, adversely affect the uneven wear resistance, and the shoulder portion. The heat generation increases and the durability performance also decreases. The ratio CTc / CTq is more preferably 1.387 to 1.524.

  Further, in the cross section including the tire shaft in the normal state, it is desirable that the second belt ply 72 which is the maximum width belt ply 7M is substantially in a single arc shape, and in the heavy duty radial tire, the second belt ply Has a single arc cross-sectional shape, so that the tread surface touches the road surface smoothly from the tread center to the end of the contact between the start of the contact and the end of contact during rolling of the tire. I can go. As a result, it is possible to prevent abnormal slipping at each minute portion of the ground contact surface, and to prevent occurrence of a portion that is a starting point of uneven wear. The first belt ply may have a maximum width, and the width may be gradually reduced toward the fourth belt ply.

Further, in the cross section including the tire shaft, the outer surface of the maximum width belt ply 7M is formed by the substantially single belt arc RB as described above, and the tread surface S of the central region CA is also substantially single. The belt arc RB and the tread surface center arc RT have the following relationship. “Substantially” means that the radius of curvature does not vary by more than 3%, preferably more than 1.5%.
0.50 ≦ RB / RT ≦ 1.20
If 0.05> RB / RT, the shear strain between the second and third belt plies from the carcass side increases when a load is applied, and there is a possibility that the belt ply peels off. Further, when RB / RT> 1.20, the distance between the third belt ply from the carcass side and the tread surface S is small, and the problem that the belt ply end is caught during rehabilitation is likely to occur.

Further, in a heavy-duty radial tire mounted on a truck having a maximum load capacity of 4t to 10t, it is preferable that RB is set to 400 mm or more and 700 mm or less.

  Further, the tread 2 of the present example is formed from a relatively low heat-generating rubber in a heat generating portion in a region extending from a position below the inner vertical main groove Gi (position about 1/5 away from the tire equator q) to a vicinity of the tread edge e. A base layer 22 is provided. Since the low heat-generating rubber constituting the base layer 22 is generally inferior in weather resistance and trauma resistance, the cap layer 21 having high wear resistance at the side portion and the side wall rubber layer having excellent weather resistance at the side portion. 31.

  A tire having a tire size of 11R22.5 and having the configuration shown in FIG. 1 is manufactured on the basis of the specifications shown in Table 1, and in the normal state of the sample tire, the ground contact lengths at four locations in the tire axial direction in a state where a normal load is applied. And the amount of wear after running was measured. The results are shown in Table 1.

Examples 1 to 4 and Comparative Examples 1 and 2 were each composed of a belt ply made of four steel cords and a one-ply carcass layer made of steel cords, and the specifications were all the same except for the items shown in Table 1. Each tire was mounted on a rim having a size of 22.5 × 7.50, filled with an internal pressure of 800 kPa, and a load of 26.72 kN was applied to measure the ground contact shape. Moreover, it mounted | worn to all the 22D type trucks 8 wheels of maximum load capacity 10t, and the amount of wear of each part was measured after driving | running 100,000 km.
In the table, (1), (2), (3), and (4) indicate the following positions on the tread surface.
(1): Position of the tire equatorial plane q (2): Position of 61 mm outward from the tire equatorial plane q in the axial direction of the tire (3): Position of 73 mm outward from the tire equatorial plane q in the axial direction of the tire (4 : Tread edge e

  As shown in Table 1, it was confirmed that the tires of the examples all suppressed the occurrence of uneven wear.

It is sectional drawing which illustrates one embodiment of this invention. It is the diagram which takes out and describes the part. It is a diagram which shows the outer side edge Go1 and the extension line EL of a vertical main groove in contrast. It is a diagram which shows the outer side edge Go1 and the extension line EL of a vertical main groove in contrast. It is a diagram which shows the outer side edge Go1 and the extension line EL of a vertical main groove in contrast. It is sectional drawing which illustrates the case of a round edge.

Explanation of symbols

2 Tread part 3 Side wall part 6 Carcass 7 Belt layer a Position separating 50% of the tread half-width WT1 from the tire equatorial plane C b Position separating 70% 7M Maximum width belt ply BT Belt cord distance BTq Belt on the tire equatorial plane q Cord distance BTm The belt cord distance BTc at the intermediate area MA BTc Belt cord distance CT at the edge c of the maximum width belt ply 7M CT Carcass distance CT
CTq Carcass cord distance at the tire equatorial plane q CTm Carcass cord distance at the intermediate region MA CTc Carcass cord distance at the edge c of the maximum belt ply G Vertical main groove Go1 Outer vertical main groove Go on the outermost side in the tire axial direction The outer edge MA where the groove wall outside the tire axial direction and the tread surface intersect
S tread surface

Claims (4)

A radial arrangement of the carcass (6) folded from the tread portion (2) to the sidewall portion (3) and around the bead core of the bead portion, and the belt cord arranged on the outer side of the carcass (6) And a belt layer (7) including two or more belt plies arranged at an angle of 10 to 40 degrees with respect to the tire, and at least two longitudinal main grooves G extending in the tire circumferential direction are provided in the tread portion, The belt cord distance BT is the distance from the tread surface to the belt cord of the widest belt ply, the widest belt ply, the distance from the tread surface to the carcass ply of the carcass ply closest to the tread surface is the carcass distance CT, and the tire equatorial plane C is the tread. When the region between the position a separating 50% of the half width WT1 and the position b separating 70% is the intermediate region MA, the following a Heavy duty radial tire, characterized by satisfying to e).
a) The intermediate area MA includes a portion in which a ratio BTm / BTq of the belt cord distance BTm in the intermediate area MA to the belt cord distance BTq in the tire equatorial plane q is expressed by the following equation.
0.950 ≦ BTm / BTq ≦ 0.975
b) The ratio BTc / BTq of the belt cord distance BTc at the edge c of the maximum width belt ply 7M to the belt cord distance BTq at the tire equatorial plane q should be in the following range.
1.00 ≦ BTc / BTq ≦ 1.025
c) The intermediate area MA has a portion in which the ratio CTm / CTq of the carcass cord distance CTm in the intermediate area MA to the carcass cord distance CTq in the tire equatorial plane q is as follows.
1.017 ≦ CTm / CTq ≦ 1.045
d) The ratio CTc / CTq of the carcass cord distance CTc at the edge c of the maximum width belt ply to the carcass cord distance CTq at the tire equatorial plane q should be in the following range.
1.350 ≦ CTc / CTq ≦ 1.550
e) The outer edge Go1 at which the groove wall on the outer side in the tire axial direction of the outer longitudinal main groove Go on the outermost side in the tire axial direction intersects the tread surface is the outer vertical main groove Go on both sides in the cross section including the tire shaft. The tread surface of the central area CA which is the area between them is regarded as a single arc and is located on the extended line EL extended .
  The heavy duty belt ply according to claim 1, wherein the maximum width belt ply is a second belt ply whose belt cord is inclined at an angle of 10 to 40 degrees with respect to a tire circumferential direction and second from the carcass side. Radial tire. In the cross section including the tire shaft, the outer surface of the maximum width belt ply is substantially composed of a single belt arc RB, and the tread surface of the central region CA is substantially a single arc. The radial tire for heavy loads according to claim 1 or 2, wherein the radial tire is made of RT, and the belt arc RB and the tread surface center arc RT have the following relationship.
0.50 ≦ RB / RT ≦ 1.20   The radial tire for heavy loads according to claim 3, wherein the belt arc RB is in a range of 400 mm to 700 mm.

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