JPH05131458A - Vulcanizing mold - Google Patents

Abstract

PURPOSE:To improve stability of operation, by a method wherein a contour line on a meridional section of a tread molding surface is established by a specific general formula not having an inflection point. CONSTITUTION:A vulcanizing mold 1 is provided with a mold main body 3, which is provided with a recessed part 2 holding a green tire Ta, and at the time of vulcanization, the green tire to be held into the recessed part 2 is expanded by filling inner pressure, through which a tire T possessing an outside form fitting to an inner wall surface s of the recessed part 2 is formed. Then a contour line 5 in a meridional surface of a tread molding surface Sa molding a tread surface 21 of the tire T is established by a formula (aj is a coefficient) in coordinates where x and y axes are decided respectively in a tire axis direction outward and radial direction inward from a tire equatorial point. Since a curve y not having an inflection point indicated by the sum total of a 2i degree function (i=1,...n) is used like this, formation of a change point of a curvature in a state of a difference in level is removable. Therefore, in the tire formed by making use of the vulcanizing mold having the contour line like this, stable function of operation is improvable drastically.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention can improve steering stability by imparting a proper tread profile to a tire, and can be suitably applied to the production of a radial tire for high speed running, which is particularly used for automobile racing. Regarding sulfur mold.

[0002]

2. Description of the Related Art In recent years, with the increase in speed and performance of vehicles,
Flat radial tires are used that have improved high-speed running performance by tightening the outside of the carcass with a tough belt layer to greatly reduce the flatness.

Since this tire has a high tire rigidity, especially a tread rigidity, the tread deformation amount at the time of ground contact is small, and the ground contact width is wide, so that the contour shape of the outer surface of the tread (hereinafter referred to as tread profile) extends to the ground surface shape. The degree of influence is extremely large.

Therefore, in order to impart a proper ground contact surface shape having a wide ground contact width and a uniform ground contact pressure to the tire and sufficiently exert its original excellent running performance, the tire size, tire rigidity, etc. have been conventionally changed. The ideal tread profile determined in accordance with the above is determined in advance in the trial production stage, while the tread molding surface of the vulcanization mold for tire vulcanization molding is formed so as to approximate this ideal tread profile. And, the approximation of this tread molding surface is as shown in FIG.
As shown in FIG. 6, a plurality of arcs B ... Partially approximating the ideal tread profile A are connected by the contact points C, respectively.

[0005]

However, the tread surface of the tire formed by using the conventional tread molding surface composed of such arcs can be extremely smoothly continuous because the arcs B ... Are inscribed at the contact points C. On the other hand, the radii of curvature change stepwise on both sides of each contact C.

As a result, when the ground contact area moves laterally in the tire axial direction, for example, at the time of turning, the shape of the ground contact surface changes abruptly during traveling with the contact point C as a boundary, and steering stability, especially transient characteristics, is increased. Falls to the width.

[0007] In such a tread surface, when the tire expands due to filling with internal pressure, each radius of curvature sometimes changes unevenly,
There is also a problem that the tread profile deviates from the ideal tread profile when the internal pressure is filled by using, for example, bending around the contact point c on the tread surface.

That is, the present invention is based on that the contour line of the tread molding surface is approximated to an ideal tread profile by using the 2i-order function fx of x shown in Formula 1, and the tread surface of the tire to be vulcanized and molded. It is an object of the present invention to provide a vulcanizing mold capable of gradually changing the curvature of the slab toward the tread end and solving the above problems.

[0009]

In order to achieve the above object, the vulcanization mold of the present invention is a vulcanization mold for vulcanization molding of a tire, and a tread molding for molding the tread surface of the tire. The contour line in the meridional section of the plane is the following formula that does not have an inflection point at the coordinates where the x-axis is defined outward from the tire equator and the y-axis is defined radially inward from the tire equator. It is set by 1.

[0010]

In this way, the contour line of the tread forming surface of the vulcanizing die has an inflection point represented by the sum of the 2i quadratic functions of x (i = 1, 2 ... n) shown in Equation 1. It is approximated to the ideal tread profile by using the non-existent curve y. Since the curvature of this curve y changes continuously with the value of x, it is extremely smooth, and it is possible to eliminate the formation of stepwise change points of curvature corresponding to the conventional contact point.

Therefore, the tire formed by using the vulcanizing mold having the contour line of such a curve y can suppress the bending deformation of the tread surface at the time of internal pressure filling and can be expanded to a state close to an ideal tread profile. .. Moreover, since the change in the shape of the ground contact surface is smooth even during lateral movement of the ground contact area that occurs during turning, grip performance and the like in a transient state can be stabilized, and steering stability performance can be greatly improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In the figure, a vulcanization mold 1 comprises a mold body 3 provided with a recess 2 for accommodating a raw tire Ta, and during vulcanization, the raw tire Ta accommodated in the recess 2 is expanded by a filling internal pressure. Thus, a tire T having an outer surface shape that matches the inner wall surface s of the recess 2 is formed.

In the present invention, among the inner wall surfaces s,
Tread molding surface S for molding the tread surface 21 of the tire T
The contour line 5 in the meridional section of a is expressed by the function y =
It is set by fx.

[0014]

[Formula 1]

The vulcanization mold 1 can be suitably used for forming a high-performance tire for high-speed running used in, for example, automobile races. The vulcanization mold 1 is vulcanized and molded by using the vulcanization mold 1 as follows. The tire T will be described.

As shown in FIG. 2, the tire T includes a bead portion 23 through which the bead core 22 passes, a sidewall portion 24 extending outward from the bead portion 23 in the tire radial direction, and a tread portion 25 connecting the outer ends thereof. In the flat radial tire having the above, the flatness ratio H / SW, which is the ratio of the tire sectional height H to the tire width SW, is set to 0.25 to 0.70, and the tread width is expanded.

Between the bead portions 23, there are tread portions 25,
Both ends passing through the sidewall portion 24 are the bead cores 22.
As the carcass 27 that folds around is hung,
A strong belt layer 29 is wound around the outside of the carcass 27 and inside the tread portion 25.

The carcass 27 is formed of two carcass plies in this example in which organic fiber cords of nylon, polyester, aromatic polyamide or the like are arranged at an angle of 60 to 90 ° with respect to the tire equator CO. 27
The turn-up end ends in the vicinity of the maximum width position of the tire.
The bead portion 23 includes a bead core 22 and a carcass 27.
A hard bead apex rubber 30 is provided that extends outward in the tire radial direction between the main body portion and the folded-back portion of the tire, and cooperates with the high turn-up structure of the carcass 27 to increase the tire lateral rigidity. I am raising.

The belt layer 29 is, in this example, the carcass 27.
Is formed from two inner and outer belt plies adjacent to each other, and the belt width is 0.7 times or more and 0.85 times or less of the tire width SW. When it is less than 0.7 times, the restraining force at the shoulder portion is insufficient, and the outer diameter growth is induced due to the centrifugal force and the like accompanying the high speed rotation, and the ground contact pressure at this portion is unevenly increased. When it exceeds 0.85 times, the tire rigidity is excessively increased. Also, each belt ply is 10 to 10 in the tire circumferential direction.
Formed by a belt cord inclined at an angle of 30 °,
The belt cord has a tensile elastic modulus of 2500 kg / cm ²
Alternatively, higher modulus cords such as organic fiber cords such as aromatic polyamide fibers and carbon fibers and inorganic fiber cords such as metal fibers and glass fibers are used.

At the end of the belt layer 29, a soft breaker cushion rubber 31 filling the space between the carcass 27 is interposed to relax stress, and a reinforcing band 32 is provided outside the belt layer 29. It is provided to suppress lifting of the belt layer 29 due to centrifugal force or the like. The reinforcing band 32 covers only the outer end portion of the belt layer 29 and prevents the separation from the outer end portion of the first band ply 3.
2A and the second band ply 3 that covers the entire width of the belt layer 29 together with the band ply 32A to uniformly increase the in-plane rigidity.
2B, both of which are made of an organic fiber cord having a relatively high strength and a low mass, such as nylon.

A tire having such a low flatness and a high tread rigidity is provided on the stepping-in side and the bulging-out side, as shown in FIG. 3, in order to sufficiently exhibit its running performance. It is necessary to provide the tire with a laterally long rectangular contact surface shape k in which the outer contact edges ka and kb extend substantially linearly in the axial direction of the tire and the contact pressure is made uniform.

Therefore, in the vulcanization mold 1, the contour line 5 of the tread molding surface Sa for molding the tread surface 21 is formed.
Is approximated to the ideal tread profile 6 using the function y = fx shown in Expression 1.

[0023]

[Formula 1]

The ideal tread profile 6 is a profile that is derived at the trial manufacture stage of a tire in order to obtain the ground contact surface shape K, and differs depending on the tire size, belt rigidity, rubber hardness, etc. Determined by repeated experiments.

Therefore, it is difficult to exactly represent such an ideal tread profile 6 by a mathematical expression. Therefore, in the present invention, the ideal tread profile 6 is represented by the function y = fx shown in the expression 1 and the ideal tread profile 6 is obtained. The vulcanization mold 1 is formed by using the approximate contour lines 5.

Here, the function y = fx is such that the coordinate axis facing outward in the tire axial direction with the origin at the tire equator point PO where the tread surface intersects with the tire equator CO is the x axis, and the tire equator point P is
The coordinate axis that points inward in the tire radial direction with O as the origin is represented as the y-axis, and the least-squares method is used to approximate the function y = fx to the ideal profile 6, that is, to set the coefficient ai. In Expression 1, i is an arbitrary positive integer, and in order to obtain the contour line 5 with higher accuracy, it is preferable that i is an integer of 4 or more.

The least squares method is a method used for fitting the correlation of a plurality of data to a curve in statistical analysis, and in this example, as shown in FIG. M points Pm (xm, y
m) and the m points Qm (xm, f (xm)) on the contour line 5 having the x coordinate equal to the point Pm, the sum of squares of the distances (shown in Equation 2) is obtained, The contour 5 can be specified by estimating ai which minimizes the value of the expression 2 and determining the value of ai in which the function y = fx shown in the expression 1 is the closest to the ideal profile 6. ..

[0028]

[Formula 2]

Since the contour line 5 is set by the function y = fx as described above, it is possible to obtain the tread molding surface Sa whose curvature changes smoothly and continuously as x increases. It should be noted that the tread molding surface Sa may be provided with ribs 11 ... Which project the tread pattern 10 including the vertical groove 10A, the horizontal groove 10B and the like on the tread surface 21 inwardly in the tire radial direction as required. it can.

(Concrete Example) A radial tire having a tire size of 205 / 60R15 having the structure shown in FIG. 2 is formed by using a vulcanizing mold having a contour line 5 having the specifications shown in Table 1, while running the tire. The performance was evaluated by a feeling test by running in an actual vehicle.

[0031]

[Table 1]

The evaluation is represented by an index with the conventional tire 1 being 100, and the larger the index value, the better.

[0033]

As described above, in the vulcanizing mold of the present invention, the contour line of the tread molding surface is set by the function y = fx shown in Formula 1, so that the tread surface of the vulcanized tire is optimized. The tire performance can be improved.

[Brief description of drawings]

FIG. 1 is a meridional sectional view of a vulcanizing mold showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of a tire vulcanized and molded thereby.

FIG. 3 is a diagram showing an ideal ground plane shape.

FIG. 4 is a diagram illustrating an approximation unit of a expression 1;

FIG. 4 is a diagram showing an example of a contour line represented by b expression 1.

FIG. 5 is a diagram of a tread profile illustrating a conventional technique.

FIG. 6 is a diagram of a tread profile illustrating the prior art.

[Explanation of symbols]

 5 contour line 21 tread surface T tire PO tire equator point

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Claims (1)

[Claims] 1. A vulcanizing mold for vulcanizing and molding a tire, comprising:
The contour line in the meridional section of the tread molding surface for molding the tread surface of the tire is changed at the coordinates where the x axis is defined outward from the tire equator point in the axial direction of the tire and the y axis is defined radially inward from the tire equator point. A vulcanization mold set by the following formula 1 having no bending point. [Formula 1]