JP6371509B2 - Determination method of carcass shape of pneumatic tire - Google Patents

Description

  The present invention relates to a method for determining a carcass shape of a pneumatic tire, and a pneumatic tire manufactured by applying this method.

  Conventionally, in the replacement tire for commercial use, many sizes are lined up for one tread pattern. In many cases, there is a lineup exceeding 70 sizes for one tread pattern. The tire size is determined by a standard (for example, JATMA standard). For example, 195 / 65R15. 195 is a nominal width (mm), 65 is a nominal flatness, R is radial, and 15 is a nominal rim diameter (inch). Among these, as a method for expanding and expanding the tire width at one flatness ratio, first, the representative tire width of the flatness ratio is selected. A mold profile of this representative tire width is designed. A mold profile for each tire width is determined so as to be similar to the representative profile. Next, the necessary rubber gauge is taken into consideration, and a carcass profile for each tire width is designed. The carcass profile refers to the shape indicated by the center line (carcass line) of the carcass thickness.

  As described above, when expanding the tire width, it is necessary to design a carcass profile for each tire width. The design man-hour load increases according to the number of tire widths. Since the carcass profile is designed for each tire width, the design may vary. As a result, for a tire having a specific tire width, a change in the carcass profile before and after inflation becomes large, and there is a possibility that excessive distortion occurs in the rubber and the cord. In other words, the carcass profile may deviate from the natural equilibrium shape.

  The carcass profile based on the natural equilibrium shape theory is formed when the normal internal pressure is filled and the carcass tension receives no force other than the tire internal pressure and the reaction force from the belt layer. This is the equilibrium shape of the carcass. The carcass based on this natural equilibrium shape theory changes its overall shape approximately to a similar shape as the internal pressure increases or decreases. This means that the deformation of the carcass accompanying the increase or decrease of the internal pressure is almost uniform and small. In the case of a carcass that has lost its equilibrium state in which the carcass profile deforms in response to changes in internal pressure, that is, a carcass that has lost its natural equilibrium shape, the durability of the tire may be reduced due to concentration of strain and stress. There is.

  Japanese Laid-Open Patent Publication No. Hei 8-142601 proposes a method of manufacturing a radial tire using a natural equilibrium shape theory. In this manufacturing method, in order to improve vibration resistance performance and ride comfort performance, the carcass profile sticking out due to a change in tire internal pressure is defined. Japanese Patent Application Laid-Open No. 8-142602 also proposes a method for manufacturing a radial tire using a natural equilibrium shape theory. In this manufacturing method, the radius (curvature radius) of the carcass profile is specified in order to improve vibration resistance performance and ride comfort performance.

  However, even when a carcass profile is designed by applying the natural equilibrium shape theory, since the carcass profile is designed for each tire width, the load of design man-hours increases according to the number of tire widths.

JP-A-8-142601 JP-A-8-142602

  The present invention has been made in view of the present situation, and provides a carcass profile determination method that can easily and quickly determine a carcass profile when expanding a tire width series, and applies this method. The purpose is to provide a pneumatic tire manufactured in this way.

A method for determining a carcass profile of a tire according to the present invention includes:
A method for determining a carcass profile of a tire comprising a carcass, a belt laminated to the carcass, and a bead having a bead base,
A representative carcass profile forming step of applying a natural equilibrium shape theory to obtain a natural equilibrium shape carcass profile for a tire having a representative tire width among tires having a flatness ratio;
A point which is four specific points of tires of other tire widths having the same flatness as the tire of the representative tire width, corresponding to four specific points on the natural equilibrium shape carcass profile of the tire of the representative tire width, A carcass profile calculating step of calculating a carcass profile based on a natural equilibrium shape theory using the positions of the points B, C and D,
In this carcass profile calculation step, the following formula for calculating the tire pressure sharing ratio Tb of the belt layer at an arbitrary position Z on the carcass in the stacking range of the carcass and the belt layer is used.
Tb = τo−a (ZA−Z) / (ZA−ZB)
The ZA coincides with the coordinate position in the Z-axis direction of the following point A,
ZB coincides with the coordinate position in the Z-axis direction of the following point B,
The point A is a coordinate on the cross-section perpendicular to the circumferential direction of the tire, with the intersection of the tire rotation axis and the tire equatorial plane as the origin, the tire rotation axis direction as the Y axis, and the tire radial direction as the Z axis. It is the intersection of the carcass and the tire equator,
The point B is a separation start point from the carcass belt layer at the coordinates,
The τo is a share ratio of the tire internal pressure of the belt layer at the point A,
The a is a decrease in the sharing ratio τo at the point B,
For each value of τo and a, a selection range is prepared for each flatness of the tire.

  Preferably, in the carcass profile calculation step, a selection range of each coordinate position of at least three points among A point, B point, C point, and D point, which are four specific points of the tire of the other tire width, A numerical range setting step for a specific point prepared by applying natural equilibrium shape theory is included.

  Preferably, the Y coordinate value B (y) of the B point is set with a range for each tire width, and the Z coordinate value D (z) of the D point is set for each tire width. It is set with a range.

Preferably, the Z coordinate value A (z) of the above point A is determined by the inner diameter of the mold defined in the standard, the thickness of the tread rubber in the central portion in the tire axial direction of the tread, and the thickness of all the belt layers,
The Y-coordinate value C (y) of the above point C depends on 1/2 of the total mold width defined in the standard, the thickness of the sidewall, and the thickness of the carcass when the carcass has a high turn-up structure. Determined.

The pneumatic tire according to the present invention is
A tread, a pair of sidewalls extending substantially inward in the tire radial direction from both ends of the tread, a pair of beads positioned on the inner side in the tire axial direction of each sidewall, and along the inside of the tread and the sidewall A carcass spanned between one bead and the other bead, and a belt layer laminated on the outer side in the tire radial direction of the carcass,
The shape of the carcass when assembled to the rim and filled with the internal pressure is determined based on the natural equilibrium shape theory, and when determining the shape of the carcass, any one of the above-mentioned A method for determining a carcass profile is applied.

  In the method for determining a carcass profile of a tire according to the present invention, when expanding a series of tire widths within the same flatness ratio, carcass profiles of different tire widths can be easily and quickly determined.

FIG. 1 is a cross-sectional view perpendicular to the tire circumferential direction showing an example of a tire to which a carcass profile determination method according to an embodiment of the present invention can be applied. FIG. 2 is a schematic cross-sectional view showing the tire internal pressure sharing ratio of the belt layer of the tire of FIG. FIG. 3 shows a preferable range of the tire layer pressure distribution ratio τo of the belt layer at the intersection (point A) of the equatorial plane and the carcass at each flatness ratio of FIG. It is a graph which shows the preferable range of the reduction | decrease amount a of the tire internal pressure share rate (tau) in B point). 4 is an enlarged cross-sectional view of a portion IV in FIG. 1, showing a separation start point (point B) between the carcass and the belt layer of the tire in FIG. FIG. 5 is an enlarged cross-sectional view of a portion V in FIG. 1 showing a point (point C) at the maximum width position of the carcass of the tire in FIG. FIG. 6 is a schematic cross-sectional view showing an intersection (point D) between the carcass line of the tire of FIG. 1 and a straight line in the tire radial direction passing through the clip width end of the tire.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 shows a pneumatic tire 2 to which a carcass profile determination method according to an embodiment of the present invention can be applied. In FIG. 1, the vertical direction is the tire radial direction (hereinafter also simply referred to as the radial direction), the left-right direction is the tire axial direction (hereinafter also simply referred to as the axial direction), and the direction perpendicular to the paper surface is the tire circumferential direction ( Hereinafter, it is also simply referred to as a circumferential direction). A one-dot chain line CL in FIG. 1 is a center line of the meridian section of the tire 2 and also represents an equatorial plane. The shape of the tire 2 is symmetrical with respect to the equator plane except for the tread pattern. A two-dot chain line BL represents a bead base line of the tire 2.

  The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, a belt 12, an inner liner 14, and a chafer 16. The tire 2 is a tubeless type. The tire 2 can be attached to a passenger car.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 20 that contacts the road surface. A groove 22 is carved in the tread surface 20. The groove 22 forms a tread pattern.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. A radially outer end of the sidewall 6 is joined to the tread 4. This sidewall 6 is made of a crosslinked rubber having excellent cut resistance and weather resistance. The sidewall 6 prevents the carcass 10 from being damaged.

  The bead 8 is located inside the sidewall 6 in the radial direction. The bead 8 includes a core 24 and an apex 26 that extends radially outward from the core 24. The core 24 has a ring shape and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 26 is tapered outward in the radial direction. The apex 26 is made of a highly hard crosslinked rubber.

  The carcass 10 includes a carcass ply 28. The carcass ply 28 is spanned between the beads 8 on both sides, and extends along the tread 4 and the sidewall 6. The carcass ply 28 is folded around the core 24 from the inner side to the outer side in the axial direction. By this folding, the carcass ply 28 is formed with a main portion 28a and a folded portion 28b.

  The carcass ply 28 includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 75 ° to 90 °. In other words, the carcass 10 has a radial structure. The cord is made of organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. The carcass 10 may be formed from two or more plies.

  The belt 12 is located on the inner side in the radial direction of the tread 4. The belt 12 is laminated with the carcass 10. The belt 12 reinforces the carcass 10. The belt 12 includes an inner belt layer 30 and an outer belt layer 32 superimposed on the radially outer side of the inner belt layer 30. As apparent from FIG. 1, the width of the inner belt layer 30 is slightly larger than the width of the outer belt layer 32 in the axial direction. Although not shown, each of the inner belt layer 30 and the outer belt layer 32 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The absolute value of the tilt angle is usually 10 ° to 35 °. The inclination direction of the cord of the inner belt layer 30 with respect to the equator plane is opposite to the inclination direction of the cord of the outer belt layer 32 with respect to the equator plane. A preferred material for the cord is steel. An organic fiber may be used for the cord.

  The inner liner 14 is located inside the carcass 10. The inner liner 16 is made of a crosslinked rubber. The inner liner 14 is made of rubber having excellent air shielding properties. A typical base rubber of the inner liner 14 is butyl rubber or halogenated butyl rubber. The inner liner 14 maintains the internal pressure of the tire.

  The chafer 16 is located in the vicinity of the bead 8. When the tire 2 is incorporated into the rim, the chafer 16 comes into contact with the rim. By this contact, the vicinity of the bead 8 is protected. The chafer 16 can be formed of, for example, a cloth and a rubber impregnated in the cloth.

  A double arrow WC in FIG. 1 indicates the maximum width of the carcass 10. The maximum width WC of the carcass 10 is measured as a linear distance in the axial direction. This maximum width WC is measured as the distance from the thickness center of the carcass 10 to the thickness center.

  A double arrow WB 1 in FIG. 1 indicates the width of the outer belt layer 32. A double-headed arrow WB2 indicates a width of a range in which the belt 12 including the inner and outer layers 30 and 32 and the carcass 10 are overlapped without being separated. Specifically, both ends of the double-pointed arrow WB2 indicate separation start points PP between the inner belt layer 30 and the carcass 10, respectively. These widths WB1 and WB2 are both measured as linear distances in the axial direction of the tire 2.

  A double arrow WL in FIG. 1 indicates the clip width of the tire 2. This clip width WL is measured as a linear distance in the axial direction. The clip width WL is usually designed to be larger than the width of the normal rim defined in the standard (reference rim width). This is because the tire shrinks after vulcanization. However, if the clip width WL is too larger than the reference rim width, compression distortion has already occurred in the bead portion from the stage of rim assembly. Therefore, there is a possibility that it will not be able to withstand an increase in compressive strain due to a load. If the clip width WL is too smaller than the normal rim width, the bead portion tends to stand (along the tire radial direction) when the rim is assembled and inflated.

  In this specification, the normal rim means a rim defined in a standard on which a tire depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims.

  Hereinafter, a method for determining the profile of the carcass 10, which is an important process in the design of the tire 2, will be described. Here, a method for determining a carcass profile when expanding a series of tire widths (nominal widths of tires) within the same aspect ratio will be described.

  For the determination of the carcass profile, natural equilibrium shape theory is applied so that shape changes accompanying changes in tire internal pressure are similar. The carcass profile based on this natural equilibrium shape theory means that when the tire is filled with normal internal pressure, if the tension of the carcass receives no force other than the internal pressure of the tire and the reaction force from the belt layer, it balances with these forces. This is the equilibrium shape of the carcass formed. In this specification, the normal internal pressure means an internal pressure defined in a standard on which the tire depends. “Maximum air pressure” in JATMA standard, “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures.

  According to this natural equilibrium shape theory, the tension acting on the carcass cord is constant. Therefore, assuming that elongation occurs in the carcass cord, the carcass profile based on this theory can be deformed substantially uniformly from the original shape. As a result, the amount of deformation becomes small. Many theoretical formulas for setting a natural equilibrium carcass line are known. In the present embodiment, the technique introduced in “Tire Engineering” by Hideo Sakai is adopted.

  First, a carcass profile of a tire having one representative tire width among tires having one flatness ratio is obtained by applying a natural equilibrium shape theory. This carcass profile is on a cross section perpendicular to the circumferential direction of the tire (hereinafter also referred to as a meridian cross section). Then, a preferable tire internal pressure distribution ratio τo of the belt on the center line CL and a decrease a thereof of the tire having the flatness ratio are selected. At the same time, four specific points (A, B, C, D) of tires having other tire widths for which the carcass profile is to be determined are set on the carcass line of the natural balance shape of the representative tire width. For example, if τo and a associated with the natural equilibrium shape theory and at least three of the four specific points (A, B, C, D) are determined, the carcass profile having the natural equilibrium shape is quantified. Is determined.

  2, 4, 5, and 6 show the positions of the four specific points (A, B, C, and D). Point A is the position of the intersection of the carcass 10 and the center line (equatorial plane) CL. Point B is the position of the separation start point PP between the carcass 10 and the belt 12. Point C is the position of the end point of the maximum width of the carcass 10. Point D is the position of the intersection of the carcass line CCL defined by the three points (A, B, C) and the radial straight line RL passing through the bead heel 34 that is the end of the clip width WL.

A belt 12 is laminated on the carcass 10 in the tread portion of the tire 2. Between this point A and point D, the belt 12 also shares the tire internal pressure with the carcass 10 only in this laminated region, so that tension is generated in the belt 12. In the natural equilibrium shape theory, the internal pressure sharing ratio Tb of the belt 12 is expressed as a function of the position Z on the Z-axis at that position as shown in the following equation (1). The coordinates defining Z, ZA, and ZB are the origin of the intersection of the tire rotation axis (tire central axis) RA and the tire center line (equatorial plane) CL in the plane coordinates on the meridian cross section. The rotational axis direction is the Y axis, and the tire radial direction is the Z axis.
Tb = τo−a {(ZA−Z) / (ZA−ZB)} (1)
In this formula (1), τo is a tire internal pressure sharing ratio of the belt 12 on the center line CL. a is a decrease in the tire internal pressure sharing ratio τo at the separation start point PP of the belt 12 from the carcass 10. ZA is a position on the Z-axis of the point A. ZB is a position on the Z-axis of the point B. Both τo and a can be arbitrarily determined according to the belt 12 to be used.

In this case, from the balance condition between the tension tc acting on the cord of the carcass 10 and the tire internal pressure p, the following equation (2) is calculated between the section curvature radius Rs at the point of the radius z with the tire rotation axis RA as the center position. ) Is established.
N · tc / 2π · z = p · Tc · Rs (2)
Here, Tc is a tire internal pressure sharing ratio of the carcass 10. From point A to point B, which is the stacking range of the carcass 10 and the belt 12, Tc = 1−Tb. From point B to point D where the belt 12 or the like is not laminated on the carcass 10, Tc = 1.

Rs in the formula (2) is expressed as the following formula (3) which is a geometric relational expression.
^{1 / Rs = y "/ (} 1 + y '2) 3/2 (3)
By substituting this equation (3) and the above-mentioned internal pressure sharing rate Tc of the carcass 10 into the above equation (2) and integrating, the carcass profile is obtained by the following equations (4) and (5).

The shape of the carcass 10 in the stacking range (between points A and B) of the carcass 10 and the inner belt layer 30 in the tread 4 is obtained by the following formula (4).
y = −∫G ₁ (z) dz (4)
The shape of the carcass 10 at the side wall (between points B and D) 6 is obtained by the following formula (5).
y = −∫G ₁ (z) dz−∫G ₂ (z) dz (5)

Here, G ₁ (z) and G ₂ (z) are both functions of Z,
G ₁ (z) = [ZB ² −ZC ² + {1−τo + aZA / (ZA−ZB)} (Z ² −ZB ² ) −2a (Z ³ −ZB ³ ) / 3 (ZA−ZB)] ×
[B ² − {ZB ² −ZC ² + {1−τo + aZA / (ZA−ZB)}
^{(Z 2 -ZB 2) -2a (} Z 3 -ZB 3) / 3 (ZA-ZB)} 2] -1/2 (6)
^{_{G 2 (z) = (Z}} 2 -ZC 2) {B 2 - (Z 2 -ZC 2) 2} -1/2 (7)
It is.

here,
^{B = ZB 2 -ZC 2 + {} 1-τo + aZA / (ZA-ZB)} (ZA 2 -ZB 2)
^{-2a (ZA 3 -ZB 3) /} 3 (ZA-ZB)] (8)
It is.
Here, τo, a, ZA, and ZB are as described above. ZC is the position on the Z-axis of the point C.

  A carcass profile having a natural equilibrium shape for each tire width can be determined by performing sequential calculation while appropriately applying τo, a, ZA, ZB, and ZC to the equations (1) to (8). The selection of each value of τo, a, ZA, ZB, ZC will be described below.

  As shown in Table 1 and FIG. 3, in this embodiment, preferable τo and a for each of a plurality of predetermined flatness ratios (80, 70, 65, 60, 55, 50, 45, 40, 35) of the tire. The numerical range of is defined. As for the numerical values of τo and a, preferable ranges are defined for the flatness ratios of 80 to 35 regardless of the tire width. τo and a are preferably selected from the range shown in Table 1. By selecting and determining the values of τo and a, the distribution of the tire internal pressure sharing ratio of the belt 12 from the point A to the point B is determined, and the carcass profile and the belt profile along the carcass are determined. Is done. The range of numerical values shown in Table 1 and FIG. 3 was determined by using the finite element method as a numerical value for obtaining an appropriate grounding shape and grounding pressure distribution and uniformity of the protruding amount of the profile. As is clear from Table 1, the value of τo increases and the value of a decreases as the flatness ratio decreases. This means that the lower the flatness of the tire, the stronger the restraining force by the belt, and the flatter the shape of the belt.

  When τo becomes smaller than the lower limit of the selection range shown in Table 1, the carcass profile becomes an outwardly convex round shape, and the belt 12 becomes too round. As a result, it is necessary to make the gauge of the tread 4 thicker from the middle part in the axial direction of the tread 4 to the shoulder part. There is a risk that it will be difficult to achieve the desired ground contact shape. The same applies when a is smaller than the lower limit of the selection range shown in Table 1. On the other hand, when τo becomes larger than the upper limit of the selection range in Table 1, the carcass profile becomes too flat, and the belt 12 also becomes flat. As a result, it may be difficult to achieve compatibility with the target grounding shape. The same applies when a is larger than the upper limit of the selection range shown in Table 1.

  Next, a method for setting the points A, B, C, and D will be described. First, point A is a drawing start point on the carcass line. The point A can be defined as a coordinate position with the intersection point of the tire rotation axis (Y axis) RA and the tire center line (Z axis) CL as the origin. As shown in FIG. 1, the Y coordinate position A (y) of point A is fixed on the center line CL. The Z coordinate position A (z) of point A is defined by the diameter on the center line CL. That is, A (z) is the thickness of the tread rubber in the center line CL portion and the thickness of all the belt layers based on the inner diameter of the mold (corresponding to the outer diameter of the tire) defined by the standard for each tire width. From this, it is calculated for each tire width. In general, A (z) = ½ (standard inner diameter of mold) − (thickness of tread rubber at center line CL portion + thickness of belt 12). The standards in which the inner diameter of the mold is defined are JATMA standard, TRA standard, and ETRTO standard.

  Point B is a separation start point PP with respect to the inner belt layer 30 in the carcass 10 and is a position of an end of a range in which the belt 12 shares the internal pressure. Similarly to the A point, the B point can also be defined as a coordinate position with the intersection point of the tire rotation axis RA and the center line (Z axis) CL as the origin. The Y coordinate position B (y) of point B is defined by the distance in the tire rotation axis direction from the origin. The Z coordinate position B (z) of point B is defined by the distance in the tire radial direction from the tire rotation axis RA. B (z) is a value calculated as a result of uniformly determining the carcass profile and the profile of the belt 12 laminated on the carcass 10 based on τo and a.

  Table 2 shows the range of the ratio of the width of the outer belt layer 32 to the nominal width of the tire and the additional dimension L. From the description of Table 2, in this embodiment, a preferable numerical range of B (y) is obtained for each of a plurality of predetermined flatness ratios (80, 70, 65, 60, 55, 50, 45, 40, 35) of the tire. It can be easily calculated. In Table 2, it can be said that for each flatness ratio from 80 to 35, a substantially preferable range of numerical values of B (y) according to the tire width is defined. B (y) is preferably calculated from the range shown in Table 2.

  B (y) is a position separated from the end of the outer belt layer 32 by a predetermined dimension L in the axial direction. L is an additional dimension that is negative inward in the axial direction and positive in the outward direction.

As shown in Table 2, in the present embodiment, the width of the outer belt layer 32 includes a lower limit value obtained by multiplying the tire nominal width by a predetermined small coefficient, and an upper limit value obtained by multiplying the tire nominal width by a predetermined large coefficient. Is preferably set to a value between. The value of B (y) is obtained by the following formula.
B (y) = 1/2 × (width of outer belt layer 32) + L
That is, the value of B (y) has a preferable selection range corresponding to the selection range defined by the lower limit value and the upper limit value of the outer belt layer 32. The selection range of the ratio and the additional dimension L described in Table 2 are such that the grounding shape and the ground pressure distribution are optimal from the small nominal width to the large nominal width (conforming to JATMA standard) for each flatness ratio. Determined using the finite element method.

  Hereinafter, as an example, the value of B (y) is calculated for a tire having a flatness ratio of 65 and a tire nominal width of 195 using the values in Table 2. The following can be understood from the description in Table 2. That is, the range of the width of the outer belt layer 32 is 0.708 × (tire nominal width) 195 = 138.06 or more, and 0.748 × (tire nominal width) 195 = 145.86 or less. Since the additional dimension L is −1.0, a preferable range of B (y) is ½ × 138.06−1.0 = 68.03 or more, and ½ × 145.86-1. 0 = 71.93 or less.

  When B (y) is larger than the upper limit value calculated from Table 2, both τo and a become large. In addition, the radius of curvature of the carcass line is reduced at the bead portion. As a result, the carcass line becomes a line that passes inside the target point D. Depending on the tire width, there is a possibility that a cushion layer cannot be secured inside the belt layer in the tire radial direction. Conversely, if B (y) is narrower than the upper limit calculated from Table 2, the carcass line of the bead portion passes outside the point D. Thus, the range of B (y) is an important point for the carcass line to pass through point D. Further, it may be difficult to secure a belt width corresponding to the tire width.

  Point C is the point at the end of the maximum width of the carcass. Similarly to the points A and B, the point C can also be defined as a coordinate position with the intersection point of the tire rotation axis (Y axis) RA and the tire center line (Z axis) CL as the origin. The Y coordinate position C (y) of point C is defined by the distance in the tire rotation axis direction from the origin. The Z coordinate position C (z) of point C is defined by the distance in the tire radial direction from the origin. The Z-axis direction position C (z) of the C point is determined uniformly by the carcass profile and the profile of the belt 12 laminated on the carcass 10 by the above τo and a, similarly to the above-described B (z). The result is a calculated value.

  C (y) is a high turn as shown in FIG. 1 in which the thickness TS of the sidewall 6 and the carcass 10 are based on the total mold width (corresponding to the tire width) WM defined in the standard. In the case of an up structure, it is calculated from the thickness TC of the carcass 10. That is, generally, C (y) = standard total mold width WM × 1 / 2− (side wall thickness TS + thickness TC of carcass 10 when carcass 10 has a high turn-up structure. ). The standards in which the inner diameter of the mold is defined are JATMA standard, TRA standard, and ETRTO standard.

  If C (y) is larger than the value obtained from the above formula, it means that the tire deviates from the standard. Conversely, if C (y) is smaller than the value obtained from the above formula, the actual width of the tire is narrower than the specified nominal width, and the range of the internal pressure sharing ratio τo (Table 1) is not satisfied. When the above A (y, z), B (y, z), and C (y, z) are determined, a natural equilibrium shape line can be drawn.

  As shown in FIG. 6, the point D coincides with the intersection of the carcass line CCL determined by the points A, B and C and the radial straight line RL passing through the bead heel 34 which is the clip width WL end. . Point D is a position near the upper end of the range in which the carcass 10 shares the internal pressure with the bead 8. Therefore, the range from point B to point D is a range where only the carcass receives the tire internal pressure, and is a range where the membrane theory can be applied.

  Unlike the points A to C, the point D can be defined as a coordinate position with the intersection point of the bead base line (Y axis) BL and the tire center line (Z axis) CL as the origin. The Y coordinate position D (y) of point D is defined by the distance in the tire rotation axis direction from the origin. D (y) coincides with the position of the end of the clip width WL. The Z coordinate position D (z) of point D is defined by the distance in the tire radial direction from the origin.

  The clip width WL of the tire that serves as a basis for specifying the point D is determined according to the rim width of the rim to which the tire is assembled. Usually, the clip width WL is designed to be larger than the reference rim width defined in the standard. However, if the clip width WL is too larger than the reference rim width, compression distortion already occurs in the bead portion from the stage of rim assembly. Therefore, there is a possibility that it cannot withstand the increase in compressive strain due to a load. Conversely, if the difference obtained by subtracting the reference rim width from the clip width WL is too small, the bead portion tends to stand (along the tire radial direction) when the rim is assembled and inflated. For this reason, D (z) becomes high (moves outward in the tire radial direction).

  Table 3 shows a formula for obtaining D (z) in consideration of an appropriate value α of the “clip width WL−reference rim width”. Here, the calculated value obtained by this formula is denoted as D (z) c for convenience. This formula is defined for each flat rate. In the present embodiment, a formula is defined for each tire having a flatness ratio of 80, 70, 65, 60, 55, 50, 45, 40, and 35.

  As shown in Table 3, in this embodiment, the calculated value D (z) c is calculated by adding and subtracting a predetermined plurality of coefficients to the tire nominal width and multiplying it. Further, this formula includes a difference α obtained by subtracting the reference rim width from the aforementioned clip width WL. As shown in Table 4, an appropriate range is defined for this value α for each flatness. Further, Table 5 defines a preferable range of D (z). That is, in Table 5, a preferable range of D (z) is defined by giving a width to D (z) c calculated based on the definitions of Tables 3 and 4.

  When α is smaller than the preferred range, that is, when D (y) is smaller than the preferred range, the bead-to-bead distance becomes small. If the distance between the rim humps is narrower, it is difficult to inject air and the rim assembly workability is reduced. On the contrary, if α is larger than the above preferred range, that is, if D (y) is larger than the preferred range, the difference from the actual rim width becomes large, and initial strain tends to remain in the bead portion when assembling the rim. As a result, the durability of the bead portion decreases.

As an example, for a tire having a flatness ratio of 65 and a tire nominal width of 195, for example, when 1.0 is selected as α, a preferable range of the value of D (z) is calculated.
D (z) c = 0.899 * (0.116 * 195 + 2.556) + 1.620 * 1.0 + 0.920 = 25.17. Since the preferable range of the value of D (z) is the range of the calculated value D (z) c ± 4, it is 21.17 mm or more and 29.17 mm or less.

  If the above D (z) is larger than the preferred range (D point is too high), it becomes necessary to increase the height of the bead apex and increase the thickness. As a result, the longitudinal spring constant becomes high, and the ride comfort becomes worse. If D (z) is less than the preferred range (D point is too low), the bead apex must be low and thin. As a result, the lateral spring constant is lowered and the steering stability is lowered.

  As described above, in the present embodiment, the technique introduced in “Tire Engineering” by Hideo Sakai is adopted. In this method, the carcass profile of the tire when mounted on the standard rim can be drawn by the equations (4) and (5) in addition to the above equation (1). Carcass diameter (diameter in the tire radial direction) rc, carcass width WC, belt width BW, rim width, clip width for specifying points A, B, C and D with respect to the above formulas (1) to (8) A carcass profile having a natural equilibrium shape for each tire width can be determined by appropriately giving WL and the internal pressure sharing ratio Tb of the belt. At that time, in the present invention, by setting the four points (A, B, C, D) for each tire width as plane coordinates on the carcass profile obtained based on the natural equilibrium shape theory in advance. By designating the nominal width and flatness of the tire, a carcass profile having a natural equilibrium shape for each tire width can be easily determined.

  As described above, if at least three of the above-described τo and a associated with the natural equilibrium shape theory and four specific points (A, B, C, D) are determined, the carcass having the natural equilibrium shape. The profile is determined quantitatively. In the carcass profile calculation step, τo, a, A (y), A (z), B (y), B (z), C (y), C (z), and D, which are undetermined multipliers, are used. If at least seven of (y) and D (z) are determined in association with the natural equilibrium shape theory, a carcass profile having a natural equilibrium shape is quantitatively determined.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

  The tires listed below as examples and comparative examples have all tire sizes of 195 / 65R15. For each tire, the contact shape and contact pressure distribution were measured. The ground contact shape was evaluated by a factor FSF (Foot Print Shape Factor). The evaluation was made with an index of 5 points. Larger numbers are preferable. About each tire, the well-known test for evaluating uneven wear-proof performance was performed with the table | surface wear energy test apparatus. The tire tread was evaluated based on the ratio of the wear energy of the crown portion to the wear energy of the shoulder portion. The evaluation was made with an index of 5 points. Larger numbers are preferable. For each tire, the amount of protrusion of the carcass profile by filling the specified internal pressure was calculated at the design stage. The calculation of this protrusion amount was based on the finite element method. In particular, the amount of protrusion of the buttress portion and the amount of protrusion of the bead portion were calculated. The uniformity of the deformation of the carcass profile was evaluated by the ratio of the protruding amounts of both parts. A ratio closer to 1 is preferred. For each tire, the riding comfort performance was evaluated by an actual vehicle running test using a test vehicle. The evaluation is a sensory evaluation related to pushing up on a rough road by the driver of the test vehicle. The evaluation was made with an index of 5 points. Larger numbers are preferable. Each tire was evaluated for road noise resistance by an actual vehicle running test using a test vehicle. The sound pressure level during traveling was measured by a measuring instrument installed at a predetermined position in the driver's seat of the test vehicle. The evaluation was made with an index of 5 points. Larger numbers are preferable.

[Example 1]
As Example 1, a tire having the basic structure shown in FIG. 1 was manufactured. Table 6 shows the values of τo, a, B (y) and D (z) described above at the design stage of the tire carcass. Table 6 shows the evaluation results of the contact shape, the protruding amount of the carcass profile, the uneven wear resistance performance, the riding comfort performance, and the road noise resistance performance.

[Example 2]
As Example 2, a tire having the basic structure shown in FIG. 1 was manufactured. Table 6 shows the values of τo, a, B (y) and D (z) described above at the design stage of the tire carcass. Other configurations and the points of the evaluation test are the same as those in Example 1. Table 6 shows the evaluation results of the contact shape, the protruding amount of the carcass profile, the uneven wear resistance performance, the riding comfort performance, and the road noise resistance performance.

[Comparative Example 1-4]
As Comparative Examples 1 to 4, tires having the basic structure shown in FIG. 1 were manufactured. Table 6 shows the values of τo, a, B (y) and D (z) described above at the design stage of the tire carcass. Other configurations and the points of the evaluation test are the same as those in Example 1. Table 6 shows the evaluation results of the contact shape, the protruding amount of the carcass profile, the uneven wear resistance performance, the riding comfort performance, and the road noise resistance performance.

[Example 3-7]
As Examples 3 to 7, tires having the basic structure shown in FIG. 1 were manufactured. Table 6 shows the values of τo, a, B (y) and D (z) described above at the design stage of the tire carcass. Other configurations and the points of the evaluation test are the same as those in Example 1. Table 7 shows the evaluation results of the ground contact shape, the protruding amount of the carcass profile, the uneven wear resistance performance, the riding comfort performance, and the road noise resistance performance.

  As shown in Tables 6 and 7, the tires of the examples have higher evaluations regarding the uniformity of the protruding amount than the tires of the comparative examples. As a result, the evaluation regarding the contact shape, contact pressure distribution and uneven wear resistance is also high. Moreover, it can be said that there is no difference between an Example and a comparative example about riding comfort performance and road noise-proof performance.

  The carcass profile determination method described above can be applied to various passenger cars.

2 ... tyre 4 ... tread 6 ... side wall 8 ... bead 10 ... carcass 12 ... belt 14 ... inner liner 16 ... chafer 20 ... tread surface 22 ... Groove 24 ... Core 26 ... Apex 28 ... Carcass ply 30 ... Inner belt layer 32 ... Outer belt layer 34 ... Bead heel BL ... Bead baseline CL ...・ Center line CCL ・ ・ ・ Carcass line PP ・ ・ ・ Separation start point (carcass and belt) RA ・ ・ ・ Tire rotation axis RL ・ ・ ・ Radial straight line passing through the clip width end TC ・ ・ ・ Carcass thickness TS ・ ・ ・ Thickness of sidewall rubber WB1 ・ ・ ・ Width of outer belt layer WB2 ・ ・ ・ Width of inner belt layer and carcass WC ・ ・ ・ Maximum width of carcass L ··· clip width WM ··· mold the total width

Claims (3)

A method for determining a carcass profile of a tire comprising a carcass, a belt laminated to the carcass, and a bead having a bead base,
A representative carcass profile forming step of applying a natural equilibrium shape theory to obtain a natural equilibrium shape carcass profile for a tire having a representative tire width among tires having a flatness ratio;
A point which is four specific points of tires of other tire widths having the same flatness as the tire of the representative tire width, corresponding to four specific points on the natural equilibrium shape carcass profile of the tire of the representative tire width , A carcass profile calculating step of calculating a carcass profile based on a natural equilibrium shape theory using the positions of the points B, C and D;
In this carcass profile calculation step, the following formula for calculating the tire pressure sharing ratio Tb of the belt layer at an arbitrary position Z on the carcass in the stacking range of the carcass and the belt layer is used.
Tb = τo−a (ZA−Z) / (ZA−ZB)
The ZA coincides with the coordinate position in the Z-axis direction of the following point A,
ZB coincides with the coordinate position in the Z-axis direction of the following point B,
The point A is a coordinate on the cross-section perpendicular to the circumferential direction of the tire, with the intersection of the tire rotation axis and the tire equatorial plane as the origin, the tire rotation axis direction as the Y axis, and the tire radial direction as the Z axis. It is the intersection of the carcass and the tire equator,
The point B is a separation start point from the carcass belt layer at the coordinates,
The τo is a share ratio of the tire internal pressure of the belt layer at the point A,
The a is a decrease in the sharing ratio τo at the point B,
The point C is a point at the end of the maximum width of the carcass,
The point D is an intersection of the carcass and a radial straight line RL passing through a bead heel that is an end of the clip width WL.
A method for determining a carcass profile, wherein each value of τo and a is selected from a selection range prepared in advance for each flatness of a tire. The preferred Y coordinate value B (y) of the B point is set with a range for each tire width, and the preferred Z coordinate value D (z) of the D point is a range for each tire width. The method for determining a carcass profile according to claim 1, wherein the carcass profile is set. The Z coordinate value A (z) of the above point A is determined by the inner diameter of the mold specified in the standard, the thickness of the tread rubber in the central portion in the tire axial direction of the tread, and the thickness of all the belt layers,
The Y-coordinate value C (y) of the above point C depends on 1/2 of the total mold width defined in the standard, the thickness of the sidewall, and the thickness of the carcass when the carcass has a high turn-up structure. The method for determining a carcass profile according to claim 1 or 2, wherein the carcass profile is defined.

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