JP2013010433A - Pneumatic tire and method for designing carcass profile thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving uniformity and improving endurance and the like, and a method for designing a carcass profile thereof.SOLUTION: The pneumatic tire has an aspect ratio of 60% or smaller. The profile Pf of a body of a carcass ply projects outward in the tire radial direction with the curvature of radius Rt gradually reduced toward the outside in the tire axial direction in a crown region Cr from a tire equator position A to an outer end position B in the tire axial direction of an innermost belt ply 7E disposed at the innermost side in the tire radial direction, and projects outward in the tire axial direction with the curvature of radius Rs gradually increased toward the inside in the tire radial direction in a side wall region Sw from the outer end position B in the tire axial direction of the innermost belt ply 7E to an equivalent bead position E that departs from a carcass maximum width position D inward in the tire radial direction by a distance that is 55% of a length h1 in the tire radial direction between the carcass maximum width position D and the tire equator position A.

Description

  The present invention relates to a pneumatic tire capable of improving uniformity and improving durability and a method for designing a carcass profile thereof.

  There is known a pneumatic tire to which a natural equilibrium type theory (see Non-Patent Document 1 below) is applied in order to suppress the shear strain and bending strain generated in each component of the pneumatic tire and improve the uniformity of the tire. Yes.

  However, the radius of curvature of the carcass profile obtained by the natural equilibrium theory is discontinuous at the outer end of the belt ply in the tire axial direction. Therefore, since such a pneumatic tire is distorted between the belt layer and the carcass, there is a problem that uniformity, durability, and the like are easily deteriorated.

JP-A-8-142602

“Tire Engineering”, Hideo Sakai, Grand Prix Publishing, Inc., 1987, P75

  The present invention has been devised in view of the above circumstances, and based on the development of a natural equilibrium type theory to improve the carcass profile of the tread portion, the uniformity is improved, and the durability is improved. The main object is to provide a pneumatic tire that can be improved and a method for designing a carcass profile thereof.

  According to the first aspect of the present invention, at least one carcass in which a body portion extending from the tread portion through the sidewall portion to the bead core of the bead portion is provided with a series of folded portions that are folded around the bead core. A pneumatic tire having a flatness ratio of 60% or less, including a carcass having a ply and a belt layer composed of at least two belt plies arranged on the outer side in the tire radial direction of the carcass and on the inner side of the tread portion, In the tire meridian cross section including a normal tire rotating shaft that is mounted on the rim and filled with a normal internal pressure, the profile of the carcass ply main body profile is from the tire equator position A to the innermost side in the tire radial direction. In the crown region Cr up to the outer end position B of the innermost belt ply in the tire axial direction, The convex radius of curvature Rt gradually decreases toward the outer side in the tire axial direction, and the reduction rate Hs is greater than 0 and less than or equal to 7.0, and from the outer end position B of the innermost belt ply in the tire axial direction. Sidewall from the carcass maximum width position D to the equivalent bead position E separated by 55% of the tire radial direction length h1 between the carcass maximum width position D and the tire equator position A. In the region Sw, it is convex toward the outer side in the tire axial direction and the curvature radius Rs gradually increases toward the inner side in the tire radial direction, and the increase rate Ks is greater than 0 and equal to or less than 0.17.

  In the invention according to claim 2, the profile of the main body portion is the length in the tire axial direction between the outer end position B and the tire equator position A from the outer end position B of the innermost belt ply in the tire axial direction. An intermediate position in the tire radial direction between a 25% position G, which is a distance of 25% of h2 inward in the tire axial direction, and a carcass maximum width position D and an outer end position B in the tire axial direction of the innermost belt ply The radius of curvature Rts of the shoulder profile So connecting H is a distance of 50% of the tire axial direction length h2 from the 25% position G and the outer end position B of the innermost belt ply in the tire axial direction. 2. The pneumatic tire according to claim 1, comprising a radius of curvature obtained by regressing a value of each radius of curvature at a 50% position J, the carcass maximum width position D, and the intermediate position H separated inward by a sixth-order function.

  In the invention according to claim 3, the profile of the main body is such that the bead profile Bd connecting the carcass maximum width position D and the outer surface position F of the bead core in the tire radial direction is the equivalent bead from the carcass maximum width position D. A side wall 25% position K separating a distance 25% of the tire radial direction length h3 between the position E and the outer surface position F of the bead core in the tire radial direction; and the carcass maximum width position D; A bead 50% position M, and a distance 50% of the tire radial direction length h3 from the outer radial position F3 of the bead core to the outer side in the tire radial direction, and the outer surface. 3. The sky according to claim 1, comprising a profile obtained by regressing each coordinate of the inner bead profile Bu connecting the position F with a cubic function. It is entered tire.

  The invention according to claim 4 is the pneumatic tire according to claim 3, wherein a radius of curvature of the inner bead profile Bu is 38 to 42 mm.

  Further, in the invention according to claim 5, the bead portion is provided with a reinforcing filler extending inward and outward in the tire radial direction along the folded portion of the carcass ply, and the outer end of the reinforcing filler in the tire radial direction is the bead profile. The pneumatic tire according to claim 3 or 4, wherein the pneumatic tire is arranged on an inner side in a tire radial direction from an inflection point (X) of a cubic function forming Bd.

  The invention according to claim 6 is the pneumatic tire according to any one of claims 1 to 5, wherein an outer end in a tire radial direction of the folded portion of the carcass ply is smaller than a rim flange height of the regular rim. .

  The invention according to claim 7 has at least one carcass ply provided with a series of folded portions that are folded around the bead core in the body portion extending from the tread portion to the side wall portion to the bead core of the bead portion. A method for designing the carcass profile of a pneumatic tire having a flatness ratio of 60% or less, including a carcass and a belt layer made of at least two belt plies arranged on the outer side in the tire radial direction of the carcass and on the inner side of the tread portion. The innermost belt ply disposed on the innermost side in the tire radial direction has a tire axial length h2 between the outer end position B in the tire axial direction and the outer end position B and the tire equator position A. % Distance G that is spaced inward in the tire axial direction, carcass maximum width position D, and outer end position B in the tire axial direction of the innermost belt ply The shoulder profile So connecting the intermediate position H in the tire radial direction between the 25% position G and the outer end position B in the tire axial direction of the innermost belt ply is 50% of the tire axial direction length h2. A carcass comprising a step of making a curve obtained by regression of a 50% position J, which is spaced inward in the tire axial direction, the carcass maximum width position D, and the intermediate position H by a sixth-order function. This is a profile design method.

  In the pneumatic tire of the present invention, the profile of the main body of the carcass ply has a crown region Cr from the tire equator position A to the outer end position B in the tire axial direction of the innermost belt ply disposed on the innermost side in the tire radial direction. Then, the convex radius toward the outer side in the tire radial direction and the curvature radius Rt gradually decrease toward the outer side in the tire axial direction, and the carcass maximum width position D and the tire from the outer end position B in the tire axial direction of the innermost belt ply. In the sidewall region Sw from the equator position A to the equivalent bead position E that is a distance of 55% of the tire radial direction length h1 from the inner side in the tire radial direction, the tire has a convex radius of curvature Rs toward the outer side in the tire axial direction. It gradually increases inward in the radial direction. Since such a pneumatic tire can prevent the occurrence of distortion between the belt layer and the carcass, the uniformity is enhanced and the durability and the like are improved.

It is sectional drawing of the pneumatic tire of one Embodiment of this invention. It is a conceptual diagram explaining the profile of the carcass ply of the pneumatic tire of the present invention. It is a diagram explaining the profile of a carcass ply. It is a diagram explaining the profile of a carcass ply. (A) is a diagram of the radius of curvature of the carcass ply near the outer end position B in the tire axial direction of the innermost belt ply, and (b) and (c) are the radius of curvature of the carcass ply near the outer end position B. Is a diagram obtained by regression with a quadratic function. (A) thru | or (c) are the diagrams which regressed the curvature radius of the carcass ply of the said outer end position B vicinity by the 4th, 5th, or 6th order function. It is a diagram explaining the profile of the carcass ply in the sidewall section and the bead section. (A) thru | or (c) is a diagram explaining the bead profile which regressed the inner side bead profile and the outer side bead profile by the 2, 3 or 4th-order function.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a normal state of a pneumatic tire for passenger cars (hereinafter, simply referred to as “tire”) 1 having a flatness ratio of 60% or less according to the present embodiment. In this specification, the “normal state” means that the tire is assembled to the normal rim V and filled with the normal internal pressure and is in an unloaded state. The value measured in the normal state.

  Here, the “regular rim” is a rim defined for each tire in the standard system including the standard on which the tire is based, and is “standard rim” for JATMA, and “for TRA” “Design Rim” or “Measuring Rim” for ETRTO. In addition, the “regular internal pressure” is an air pressure determined by each standard for each tire in the standard system including the standard on which the tire is based. TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES "Maximum value", ETRTO, "INFLATION PRESSURE".

  The pneumatic tire 1 according to the present embodiment is disposed on a carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and on the radially outer side of the carcass 6 and inside the tread portion 2. Belt layer 7.

  The carcass 6 includes a main body portion 6a straddling a pair of bead cores 5 and 5 in a toroidal manner, and a folded portion 6b which is continuous from both sides of the main body portion 6a and is folded from the inner side to the outer side in the tire axial direction around the bead core 5. It consists of at least one carcass ply 6A provided in series, in this embodiment, one carcass ply 6A. In the carcass ply 6A, the carcass cord is inclined at an angle of, for example, 75 to 90 ° with respect to the tire equator Ca direction. As the carcass cord, for example, an organic fiber cord is employed.

  The belt layer 7 is composed of at least two belt plies 7A and 7B, in the present embodiment, in the tire radial direction, and in the outer two. That is, in this specification, the belt ply 7A in the tire radial direction is defined as the innermost belt ply 7E disposed on the innermost side in the tire radial direction. Each belt ply 7A, 7B has a highly elastic belt cord such as a steel cord inclined at an angle of 15 to 40 ° with respect to the tire equator Ca. The belt plies 7A and 7B are overlapped so that the belt cords intersect each other.

  Further, as shown in FIG. 1, the bead portion 4 includes a bead apex 8 made of hard rubber and extending in a tapered shape on the outer side in the tire radial direction of the bead core 5, and the tire of the bead apex 8. A reinforcing filler 9 is provided that extends axially outside and inside the folded portion 6b inward and outward in the tire radial direction. Since such a bead part 4 has improved rigidity, the strain can be reduced. Therefore, tire uniformity is improved.

  Here, it is well known that the natural equilibrium shape theory is proposed for the design of the carcass ply profile. This natural equilibrium shape theory is that when the outer end of the belt layer in the tire axial direction and the bead portion fixing position point are given (assuming that these two points do not move), the carcass cord interval or the maximum carcass width It is a theory that can determine the profile of the carcass ply uniquely by determining either.

  A feature of this natural equilibrium shape theory is that the tension acting on the carcass cord is constant. Therefore, if it is considered on the assumption that the carcass cord is stretched, the carcass ply profile based on this theory can be expanded and deformed from the original shape in a similar and substantially uniform manner to improve uniformity.

  The natural equilibrium shape theory is described in W.W. Hofferberth, Kautsch. Details are available in the literature discussed in Gummi (8-1955, 124-130).

  As shown in FIG. 2, the carcass ply profile Pf based on the natural equilibrium shape theory takes, for example, the y axis on the tire rotation axis and the z axis in the radial direction through the position of the tire equator Ca. A sidewall section sandwiched between the outer end 7e of the belt layer 7 in the tire axial direction and the outer end 8e of the bead apex 8 in the tire radial direction or the outer end 9e of the reinforcing filler 9 in the tire radial direction on a coordinate system taking 21 (between B and U) can adopt the natural equilibrium shape theory because the membrane theory can be applied, but the crown section 20 from the tire equator position A to the outer end position B in the tire axial direction of the innermost belt ply 7E. (Between A and B), an outer end 8e in the tire radial direction of the bead apex 8 or an outer end 9e in the tire radial direction of the reinforcing filler 9, and an outer end 5e in the tire radial direction of the bead core 5 Bead section 22 which sandwich (between U-F) are added to modifications as follows.

  As shown in FIG. 3A, most of the crown section has the tire internal pressure shared by the belt layer 7 as indicated by the arrows of the carcass cord of the carcass 6 and the belt cord of the belt layer 7. It is thought that there is.

  Here, the belt internal pressure sharing ratio Tb that the belt layer 7 shares the tire internal pressure can be expressed by approximating as a function of Z as shown in Equation (1).

  However, “a” is arbitrary depending on the belt layer, and the belt internal pressure sharing ratio Tb is a = 0, and the pressure distribution is uniformly b across the entire belt layer 7, and at a = b, the pressure sharing is 0 at both ends of the belt layer. Next, it forms a parabola that becomes b on the equator. ZA and ZB are the coordinate values of points A and B.

  Next, as shown in FIG. 3 (b), the bead internal pressure sharing ratio Te in which the bead apex 8 and the reinforcing filler 9 in the bead section 22 share the tire internal pressure is approximated as a function of Z as shown in equation (2). Can be expressed as ZF is the Z coordinate at the outer end 5e of the bead core 5 in the tire radial direction, ZU is the Z coordinate of the outer end 9e in the radial direction of the reinforcing filler 9, and C is at the outer end 5e in the radial direction of the bead core 5 tire. This is the internal pressure sharing rate.

  In such a case, from the balance condition of the cord tension tc acting on the carcass cord and the tire internal pressure P, the relational expression of Equation 3 is established between the curvature radius R at the point of the coordinate Z and the number of carcass cords around the entire tire is N. Holds.

  Tc is an internal pressure sharing ratio of the carcass 6 and is a function of Z. In the crown section 20, Tc = 1−Tb (Tb: belt internal pressure sharing ratio), and in the bead section 22, Tc = 1−Te (Te: bead). (Internal pressure sharing rate), otherwise Tc = 1. Tc is the tension of one carcass cord. Further, the radius of curvature R can be expressed as in Equation 4 from the geometrical relationship.

  By substituting Equation 4 and each carcass internal pressure sharing ratio Tc into Equation 3 for integration, the carcass shape of the crown section 20 (between A and B) is represented by Expression 5, and the carcass of the sidewall section 21 (between B and U). The shape of the carcass in the form 6 and the bead section 22 (between U and F) can be specified as in the form 7.

  However, the code | symbol W of several 5-7 is shown in several 8.

  And by the inventors' research, by setting the radius of curvature of the profile Pf of the carcass ply based on the natural equilibrium shape that can be drawn using the formulas expressed by the above formulas 5 to 7 within a specified range. Furthermore, a pneumatic tire excellent in uniformity was invented. In general, the balance of the forces in the crown section 20 is a film force (Nθ, N), in the tire circumferential direction (hereinafter simply referred to as “circumferential direction”) and in the tire radial direction (hereinafter also simply referred to as “radial direction”). Nφ), the radius of curvature (Rθ, Rφ) in the circumferential direction and the radial direction, and the tire internal pressure P are used to establish Equation (9). Tφ and Tθ represent the internal pressure sharing ratios in the radial direction and the circumferential direction that share the tire internal pressure.

Here, when Expressions 10-1 and 10-2 are used, Expression 9 is expressed as Expression 11.

  In the present embodiment, the radius of curvature Rt of the crown region Cr from the tire equator position A to the outer end position B of the innermost belt ply 7E in the tire axial direction is represented by Rφ of Formula 9, and From this, the equation 12 is derived.

  Further, the internal pressure sharing ratio Tθ in the circumferential direction is large at the tire equator position A, and gradually decreases toward the outer end position B in the tire axial direction of the innermost belt ply 7E. On the other hand, the internal pressure sharing ratio Tφ in the radial direction is small at the tire equator position A and gradually increases toward the outer end position B in the tire axial direction of the innermost belt ply 7E. Therefore, the internal pressure sharing ratios Tθ and Tφ are expressed by Equations 13-1 and 13-2.

  Therefore, from Equation 12, the radial internal pressure sharing ratio Tφ increases from the tire equator position A toward the outer end position B, so that the radius of curvature Rt of the carcass ply in the crown region Cr gradually decreases outward in the tire axial direction. It turns out that there is a need to do.

  Further, a distance of 55% of the tire radial direction length h1 between the carcass maximum width position D and the tire equator position A is separated from the outer end position B in the tire axial direction of the innermost belt ply inward in the tire radial direction. The radius of curvature Rs of the carcass ply in the sidewall region Sw up to the equivalent bead position E is expressed by the Rφ of the equation 9 similarly to the tread portion, and the equation 14 can be derived from the equation 10-2.

  Here, in the sidewall region Sw, since the tire internal pressure P is shared only by the carcass, a radial sharing ratio Tφ = 1 holds. Therefore, Equation 14 is established as Equation 15.

  Further, the membrane force Nφ is expressed as Equations 16-1 and 16-2 when cord tension tc and end (number of carcass cords per unit width) n are used.

  That is, from the equations 16-1 and 16-2, in order to keep the tension tc constant, the radius of curvature Rs must be changed according to the change of n. Therefore, in order to maintain a stable carcass ply profile shape, the cord tension tc per cord must be the same at any position in the sidewall region, so that the radius of curvature Rs is directed from the bead side to the tread side. It became clear that it was necessary to increase gradually.

  Based on such knowledge, in the pneumatic tire 1 of the present invention, the profile Pf of the main body portion 6a of the carcass ply 6A is convex toward the outer side in the tire radial direction and the curvature radius Rt is in the tire axial direction in the crown region Cr. While gradually decreasing outward, the sidewall region Sw is convex outward in the tire axial direction and the radius of curvature Rs gradually increases inward in the tire radial direction.

  In the present specification, the profile Pf of the main body 6a is represented by an outline 6B in which the center points of the carcass cords of the main body 6a are smoothly connected as shown in FIG. To do.

  Further, the reduction rate Hs of the radius of curvature Rt in the crown region Cr needs to be limited to be larger than 0 and 7.0 or less. That is, when the reduction rate Hs increases, the rubber on the tire equator Ca side of the tread portion 2 protrudes during running, and the contact pressure of the portion increases, so that the tire uniformity, rolling resistance, and steering stability performance may be deteriorated. is there. Further, when the decrease rate Hs is reduced, the rubber on the outer end position B side of the tread portion 2 protrudes during traveling, and the contact pressure of the portion increases, and it becomes easy to pick up unevenness on the road surface. There is a risk that tire uniformity will deteriorate. From such a viewpoint, the reduction rate Hs is preferably 1.0 or more, more preferably 1.7 or more, and preferably 5.9 or less, more preferably 4.9 or less.

  Further, the increasing rate Ks of the radius of curvature Rs in the sidewall region Sw needs to be limited to be larger than 0 and not more than 0.17. When the increase rate Ks increases, the rubber in the sidewall region SW protrudes toward the inside in the tire axial direction during running, and conversely, the rubber on the bead portion 4 side protrudes toward the outside in the tire axial direction. For this reason, the tire uniformity is deteriorated and, in particular, the tire radial strain remains with respect to the rubber in the sidewall region SW, so that the durability of the bead portion 4 may be deteriorated. When the increase rate Ks decreases, the rubber in the sidewall region SW protrudes outward in the tire axial direction during traveling, and conversely, the rubber in the bead portion 4 protrudes inward in the tire axial direction. For this reason, in addition to the tire uniformity being deteriorated, in particular, there is a possibility that the steering stability performance is deteriorated because distortion in the tire axial direction remains with respect to the rubber in the sidewall region SW. From such a viewpoint, the increase rate Ks is preferably 0.12 or more, more preferably 0.13 or more, and preferably 0.16 or less.

  The decrease rate Hs is obtained by connecting the tire equator position A and the outer end position B by the difference (Ra−Rb) between the curvature radius Ra of the tire equator position A and the curvature radius Rb of the outer end position B according to Equation 12. It is represented by (Ra−Rb) / Rab divided by an average curvature radius Rab (not shown) of the arc Lab (not shown). Further, the increase rate Ks is the difference (Rc−Rb) between the curvature radius Rb of the outer end position B and the curvature radius Rc of the equivalent bead position E according to Equation 16-2, and the curvature radius Rd of the carcass maximum width position D. (Rc-Rb) / Rd divided by.

  Further, in such integral calculation (Equation 5), the denominator of the integrand F1 is extremely small in the vicinity of the tire equator position A, and cannot be obtained accurately. In particular, in the tread portion of a pneumatic tire having a flatness ratio of 60% or less, since the range of the Z value is small with respect to the Y value, the Y value near the tire equator position A cannot be obtained with high accuracy.

  Accordingly, the radius of curvature of the arc passing through the 10 mm points A ′ and A ′ 10 mm apart from the tire equator position A on both sides in the tire axial direction and the tire equator position A is obtained from the following equation 17 and is in contact with the profile obtained in the above equation 5. Thus, the carcass ply profile of the tread portion in the vicinity of the tire equator position A could be obtained.

  In addition, since the undetermined multipliers a and b are included in the right side of the equation 17, the profile is calculated by sequential calculation so that the profile passes through the tire equator position A, the outer end position B, and the carcass maximum width position D. In addition, the accuracy of these calculations is improved by using double precision calculations.

  FIG. 5A is a graph showing the radius of curvature of the carcass ply with respect to the distance from the tire equator position A obtained by the above natural equilibrium theory. As shown in FIG. 5A, at the outer end position B, the radius of curvature R of the carcass ply is discontinuous. And it turned out that such a pneumatic tire 1 produces a distortion between the belt layer 7 and the carcass 6, and worsens uniformity. For this reason, researchers conducted various studies to correct the discontinuity at the outer end position B, and obtained the following results.

  That is, as shown in FIG. 6C, 25% of the length h2 in the tire axial direction between the outer end position B and the tire equator position A from the outer end position B of the innermost belt ply 7E in the tire axial direction. A shoulder profile that connects a 25% position G, which is spaced inward in the tire axial direction, and an intermediate position H in the tire radial direction between the carcass maximum width position D and the outer end position B in the tire axial direction of the innermost belt ply 7E. The curvature radius Rts of So is a 25% position G, and a 50% position J that is a distance of 50% of the tire axial direction length h2 from the outer end position B of the innermost belt ply in the tire axial direction. It has been known that the coordinates of the radius of curvature at the carcass maximum width position D and the intermediate position H can be represented by a smooth curve by regressing with a sixth-order function. Therefore, the tire according to the present embodiment can be in a smooth continuous state even when the radius of curvature of the profile Pf of the carcass ply is at the outer end position B, so that the uniformity of the tire is improved.

  As shown in FIGS. 5B and 5C and FIGS. 6A to 6C, even if the radius of curvature R is regressed by a quadratic to quintic function, the radius of curvature R is gradually increased or decreased. However, there was a tendency to diverge and the uniformity could not be improved. Further, a function of 7th order or higher (not shown) has a demerit that a calculation processing time becomes longer than that when a 6th order function is used. That is, it can be understood that the most preferable mode is to perform regression using a sixth-order function.

  Further, when a carcass profile of a tire having a flatness ratio of 60% or less is created using Equations 6 and 7 of the natural equilibrium theory, the carcass profile on the bead section 22 side and the carcass profile on the sidewall section 21 side are It has been found that there is a possibility that the two parts are not connected by being divided into the inner and outer sides in the axial direction. FIG. 7 shows an example in which the carcass profile on the bead section 22 side and the carcass profile on the sidewall section 21 side cannot contact the carcass profile on the bead section 22 side even when the bead internal pressure sharing ratio Te is 1. .

  For this reason, as shown in FIG. 8A, the profile of the main body portion 6a of the present embodiment is the bead profile Bd connecting the carcass maximum width position D and the outer surface position F of the bead core in the tire radial direction. A sidewall 25% position K that divides a distance of 25% of the tire radial direction length h3 from the equivalent bead position E to the outer surface position F of the bead core in the tire radial direction from the carcass maximum width position D; An outer bead profile Bs connecting the carcass maximum width position D, and a bead 50 separating a distance of 50% of the tire radial direction length h3 from the outer surface position F in the tire radial direction of the bead core to the outer side in the tire radial direction. It is formed by smoothly connecting each coordinate of the inner bead profile Bu connecting the% position M and the outer surface position F by a cubic function. That is desirable.

  Note that, as shown in FIGS. 8B and 8C, those obtained by regressing with the quadratic function and the quartic function are larger than the profile regressed with the cubic function shown in FIG. 8A. There was a shift. Therefore, it is most preferable to perform regression with a cubic function.

  Moreover, as for the profile of a main-body part, it is desirable that the curvature radius of the said inside bead profile Bu is 38-42 mm. That is, when the tire is filled with the normal internal pressure, the bead portion 4 is pressed against the rim. For this reason, the closer the profile of the carcass ply is to the rim shape, the more the strain and shear force can be suppressed. Accordingly, the radius of curvature of the inner bead profile Bu is more preferably 39 mm or more, and more preferably 41 mm or less. The inner bead profile Bu is convex toward the inner side in the tire axial direction.

  The outer end 9e of the reinforcing filler 9 in the tire radial direction is preferably arranged on the inner side in the tire radial direction from the inflection point X of the cubic function forming the bead profile Bd. That is, when the outer end 9e is disposed radially outward from the inflection point X, the internal pressure sharing region by the carcass and the bead reinforcing layer (reinforcing filler 9) increases, and the carcass moves by lateral force or load. There is a risk that fluctuations in ply will increase and uniformity will deteriorate. In addition, if the outer end 9e is disposed excessively inside the inflection point from the inflection point, the rigidity of the bead portion 4 is reduced and the behavior of the tread portion 2 is increased, so that the rolling resistance may be easily deteriorated. There is. For this reason, it is desirable that the outer end 9e is located on the inner side in the tire radial direction from the inflection point X, preferably 2 mm or more, more preferably 3 mm or more, and preferably 6 mm or less, more preferably 5 mm or less. It is desirable to be located.

  From the same viewpoint, it is desirable that the upper end 6b1 in the tire radial direction of the folded portion 6b of the carcass ply is located on the inner side in the tire radial direction than the rim flange height Hf. When the upper end 6b1 is positioned on the inner side in the tire radial direction with respect to the rim flange height Hf, the rigidity variation of the folded portion 6b of the carcass ply is eliminated and the uniformity is improved. For this reason, the upper end 6b1 is preferably located on the inner side in the tire radial direction from the rim flange height Hf, preferably 1 mm or more, and preferably 4 mm or less. When the upper end 6b1 is separated from the height Hf by more than 4 mm inward in the tire radial direction, the carcass 6 at the time of internal pressure filling is deteriorated due to the deterioration of the adhesive performance between the carcass cord forming the carcass 6 and the rubber. There is a possibility that the carcass 6 may slip through because it cannot be held by the bead core 5.

Next, a method for designing the carcass ply profile Pf of such a pneumatic tire 1 will be described.
In the present embodiment, as described above, it is based on the natural equilibrium shape theory. Specifically, the profile of the crown section 20 is designed according to the formula 5, the profile of the sidewall section 21 is designed as the formula 6, and the profile of the bead section 22 is designed according to the formula 7.

  In the crown region Cr from the tire equator position A to the outer end position B in the tire axial direction of the innermost belt ply disposed on the innermost side in the tire radial direction, the convex radius of curvature Rt is outward in the tire radial direction. The correction design is made so as to gradually decrease toward the outer side in the tire axial direction. Further, an equivalent bead in which a distance of 55% of the tire radial direction length h1 between the carcass maximum width position D and the tire equator position A from the outer end position B is separated from the carcass maximum width position D inward in the tire radial direction. In the sidewall region Sw up to the position E, correction design is performed so that the convexity is outward toward the tire axial direction and the curvature radius Rs is gradually increased toward the inner side in the tire radial direction.

  Next, since the radius of curvature of the profile of the carcass ply is discontinuous at the outer end position B in the tire axial direction of the innermost belt ply 7E, the outer end position B in the tire axial direction of the innermost belt ply 25% position G, which is a distance of 25% of the tire axial direction length h2 between the outer end position B and the tire equator position A, and the carcass maximum width position D and the tire axis of the innermost belt ply. The radius of curvature Rts of the shoulder profile So that connects the intermediate position H in the tire radial direction with the outer end position B in the direction is from the 25% position G, the outer end position B in the tire axial direction of the innermost belt ply to the tire. It was obtained by regression of the radius of curvature at 50% position J, the carcass maximum width position D, and the intermediate position H separated by 50% of the axial length h2 in the tire axial direction with a sixth-order function. It is corrected on the basis of the line.

  Further, when the bead profile Bd connecting the carcass maximum width position D and the outer surface position F of the bead core in the tire radial direction has a carcass internal pressure sharing ratio of 0, the equivalent bead position E and the bead core are separated from the carcass maximum width position D. An outer bead profile Bs connecting a sidewall 25% position K, which is a distance of 25% of the tire radial direction length h3 with the outer surface position F in the tire radial direction, and the carcass maximum width position D; And an inner bead that connects the outer surface position F and a bead 50% position M, which is a distance of 50% of the tire radial direction length h3 from the outer surface position F in the tire radial direction of the bead core. Each coordinate of the profile Bu is corrected based on a curve obtained by regression with a cubic function.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and can be implemented with various modifications.

A pneumatic tire (size: 215 / 45R17) having the tire structure of FIG. 1 and based on the specifications of Table 1 was manufactured and tested for durability, uniformity, and handling stability. The reduction rate Hs is set so that all the rubber thicknesses of the tread portion 2 are the same. The common specifications are as follows.
Rim size: 17 × 7.0J
Tread contact width TW: 186mm
The test method is as follows.

<Durability>
Using a drum tester, the test tire was run at an internal pressure of 220 kPa and a load of 8.36 kN at a speed of 80 km / h, and the running distance until damage to the bead apex rubber was measured. Example 1 was evaluated with an index of 100. A larger value is better.

<Uniformity>
Based on the uniformity test conditions of JASO C607, the average value (N) of radial force variation (RFV) was calculated for 20 tires. The reciprocal of each result was calculated and evaluated with an index with Example 1 as 100. A larger value is better.

<Rolling resistance>
The rolling resistance when the sample tire was run on a drum having a diameter of 1.7 m under a condition of an internal pressure of 220 kPa and a load of 4.2 kN under a speed of 60 km / h was measured by a rolling resistance tester. The results are displayed as an index with the reciprocal of Example 1 as 100. A larger value is better.
The test results are shown in Table 1.

  As a result of the test, it can be confirmed that the tires of the examples have improved various performances as compared with the comparative examples.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 6A Carcass ply 6a Main part 6b Folding part 7 Belt layer 7E Innermost belt ply Pf Profile

Claims (7)

A carcass having at least one carcass ply provided with a series of folded portions that are turned around the bead core in the main body portion extending from the tread portion to the bead core through the sidewall portion, and the tire radial direction of the carcass A pneumatic tire having a flatness ratio of 60% or less, including a belt layer composed of at least two belt plies arranged outside and inside the tread portion,
In the tire meridian cross section including the tire rotating shaft in a normal state that is mounted on a regular rim and is filled with a regular internal pressure,
The profile of the carcass ply main body has a profile in the crown region Cr from the tire equator position A to the outermost position B in the tire axial direction of the innermost belt ply disposed on the innermost side in the tire radial direction. The convexity and the curvature radius Rt gradually decrease toward the outer side in the tire axial direction, and the reduction rate Hs is greater than 0 and less than or equal to 7.0.
From the outer end position B in the tire axial direction of the innermost belt ply, a distance of 55% of the tire radial direction length h1 between the carcass maximum width position D and the tire equator position A is from the carcass maximum width position D. In the sidewall region Sw up to the equivalent bead position E separated on the inner side in the tire radial direction, the curvature radius Rs is convex toward the inner side in the tire radial direction, and the rate of increase Ks is larger than 0. And a pneumatic tire characterized by being 0.17 or less. The profile of the main body portion is a distance of 25% of a tire axial direction length h2 between the outer end position B and the tire equator position A from the outer end position B of the innermost belt ply in the tire axial direction. The curvature of the shoulder profile So connecting the 25% position G separated inward in the direction and the intermediate position H in the tire radial direction between the carcass maximum width position D and the outer end position B in the tire axial direction of the innermost belt ply. Radius Rts is
The 25% position G, the 50% position J that is 50% of the tire axial direction length h2 from the outer end position B in the tire axial direction of the innermost belt ply, and the carcass maximum width. The pneumatic tire according to claim 1, comprising a radius of curvature obtained by regressing a value of each radius of curvature at the position D and the intermediate position H with a sixth-order function. The profile of the main body is a bead profile Bd that connects the carcass maximum width position D and the outer surface position F of the bead core in the tire radial direction.
Side wall 25% position that is 25% of the distance in the tire radial direction h3 between the equivalent bead position E from the carcass maximum width position D and the outer surface position F of the bead core in the tire radial direction. An outer bead profile Bs connecting K and the carcass maximum width position D;
And an inner bead that connects the outer surface position F and a bead 50% position M, which is a distance of 50% of the tire radial direction length h3 from the outer surface position F in the tire radial direction of the bead core. The pneumatic tire according to claim 1 or 2, comprising a profile obtained by regressing each coordinate of the profile Bu with a cubic function.   The pneumatic tire according to claim 3, wherein a radius of curvature of the inner bead profile Bu is 38 to 42 mm.   The bead portion is provided with a reinforcing filler extending inward and outward in the tire radial direction along the folded portion of the carcass ply, and the outer end of the reinforcing filler in the tire radial direction is a change of a cubic function forming the bead profile Bd. 5. The pneumatic tire according to claim 3, wherein the pneumatic tire is disposed on an inner side in a tire radial direction than the bending point (X).   The pneumatic tire according to any one of claims 1 to 5, wherein an outer end in a tire radial direction of the folded portion of the carcass ply is smaller than a rim flange height of the regular rim. A carcass having at least one carcass ply provided with a series of folded portions that are turned around the bead core in the main body portion extending from the tread portion to the bead core through the sidewall portion, and the tire radial direction of the carcass A method of designing the carcass profile of a pneumatic tire having a flatness ratio of 60% or less including an outer side and a belt layer made of at least two belt plies arranged on the inner side of the tread portion,
A distance of 25% of the tire axial direction length h2 between the outer end position B and the tire equator position A from the outer end position B in the tire axial direction of the innermost belt ply arranged on the innermost side in the tire radial direction. A shoulder profile So connecting a 25% position G separated inward in the tire axial direction, and an intermediate position H in the tire radial direction between the carcass maximum width position D and the outer end position B in the tire axial direction of the innermost belt ply. The
The carcass, the 25% position G, and a 50% position J, which is a distance of 50% of the tire axial direction length h2 from the outer end position B of the innermost belt ply in the tire axial direction; A method of designing a carcass profile, comprising a step of making a maximum width position D and the intermediate position H into a curve obtained by regression with a sixth-order function.

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