JP2008273435A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire largely enhancing drawing resistance of a carcass ply by largely enhancing physical restriction force of the carcass ply, more directly, the ply cord, by a pair of bead core portions of a division structure. <P>SOLUTION: The pneumatic tire has a bead part structure in which respective side part portions of the carcass ply 2a are clamped between the pair of bead core portions 3a, 3b of the division structure and respective side ends of the carcass ply 2a are projected to an inner side in a radial direction more than the bead core portions 3a, 3b. Thickness t of a clamped portion 4 between the bead core portions of the respective ply cords 4 forming the carcass ply 2a is made thinner than the thickness T of a projection end part 6 to an inner side in a radial direction more than the bead core portions 3a, 3b of the ply cord 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, and more particularly to a heavy duty pneumatic tire suitable for heavy duty vehicles such as trucks and buses. In particular, the present invention relates to a carcass ply forming a tire skeleton, more specifically, a carcass ply. The present invention proposes a technique for greatly improving the pull-out resistance of the ply cord forming the ply.

In recent years, instead of the bead portion structure that turns the side portion of the carcass ply around the bead core, a bead portion structure in which the side portion of the carcass ply is sandwiched between a pair of bead portions. However, in addition to what is disclosed in Patent Document 1, various proposals have been made.
Special table 2001-523608 gazette

  However, any conventional proposed technique in which the side portion of the carcass ply is sandwiched between the paired bead core portions of the split structure, the physical restraint on the carcass ply by the bead portion, or directly the ply cord, is achieved. Since the force is inevitably reduced, the carcass ply pull-out resistance against the filling air pressure and load load on the tire cannot be improved as expected, depending on the proposed technology. Is particularly serious in heavy-duty tires where the tire is filled with high air pressure and the load is increased.

  The object of the present invention is to solve such problems of the prior art, and the object of the present invention is to provide a carcass ply by a bead core portion of a split structure, directly. Is to provide a pneumatic tire in which the pull-out resistance of the carcass ply is greatly improved by greatly increasing the physical restraining force of the ply cord.

  The pneumatic tire according to the present invention sandwiches each side portion of the carcass ply between a pair or a plurality of pairs of bead core portions of a split structure, and each side end portion of the carcass ply is arranged in a radial direction from the bead core portions. The ply cord has a bead portion structure that protrudes inward and forms a carcass ply, and the thickness of the sandwiched portion between the bead core portions of a pair of ply cords that are mostly steel cords. This is thinner than the thickness of the protruding end portion inward in the radial direction from the bead core portion.

  In this case, the required thickness of each ply cord is such that the number of twists of the portion of the ply cord that becomes the twisted cord sandwiched between the bead core portions is less than the number of twists of the protruding end portion from the bead core portion. Or by making the cord diameter of the ply cord portion sandwiched between the bead core portions smaller than that of the projecting end portion from the bead core portion.

Here, in the former case, it is preferable to make the ply cord portion sandwiched between the bead core portions untwisted in order to further increase the difference in thickness.
In the former case, each ply cord may be arranged such that the ply cord portion sandwiched between the bead core portions is partially overlapped with the other adjacent ply cord portions between the bead core portions. It is preferable for the portion to exert pulling-out restraining force with respect to the other ply cord portion.

  In the latter case, the required diameter difference can be easily increased by making the twist pitch of the portion of the ply cord made of twisted cord sandwiched between the bead core portions larger than that of the protruding end portion from the bead core portion. It is preferable in realization.

  The pneumatic tire according to the present invention, in particular, according to the bead portion structure, each ply cord having a twisted structure and the like necessary for the carcass ply to perform a required function, and a bead core portion that forms a pair. By making the thickness of the portion sandwiched between the ply cords thinner than the thickness of the protruding end portion radially inward from the bead core portion, the protruding end portion of the ply cord is affected by the tensile force acting on the ply cord. Since the tensile force can be supported by the bead core portion when the bead core portion is engaged with the bead core portion, the ply cord and thus the carcass ply can be pulled out under sufficient breaking strength. It can be increased as expected.

  Here, the required thickness of the ply cord is, for example, that the number of twists of the portion of the ply cord made of a twisted cord sandwiched between the bead core portions is made smaller than the number of twists of the protruding end portion from the bead core portion. Such a reduction in the number of twists can be achieved by chucking both end portions of the ply cord to which the required twist is applied, adjacent to the portions to be sandwiched between the bead core portions. It can be easily brought about by unwinding the twist by rotating and displacing the chucking part in the direction opposite to the twisting direction of the cord, and this is continued until the twist of the ply cord is completely extinguished. Thus, when the ply cord sandwiched portion is in a state where there is no twist, the difference in the thickness of the ply cord can be particularly increased. From Dokoa portion of the projecting end portion can be a physical engagement to the bead core portion and more reliable.

  As described above, when the necessary reduction in the sandwiching thickness is brought about by reducing the number of twists of the ply cord, the ply cord portion sandwiched between the bead core portions is partially connected to another adjacent ply cord portion. It is preferable to sandwich the pair of bead core parts in a state where they are overlapped with each other. According to this, when the tensile force is applied to the ply cord, each ply cord part is attached to the other ply cord part. Since the pulling-out restraining force is exerted, the pulling-out restraining force of the ply cord and thus the carcass ply by the bead core portion can be further increased.

  Here, the thickness of the portion of the ply cord that is sandwiched between the pair of bead core portions is reduced by making the cord diameter of the ply cord portion sandwiched between the bead core portions smaller than that of the protruding end portion from the bead core portion. In the case of reducing the thickness in this way, as described above, the pride cord that becomes a twisted cord is untwisted and compared with the case where the required reduction in thickness is brought about. In addition, since the untwisting process is not required, there is an advantage that the fatigue of the ply cord itself can be reduced and a large cord strength can be ensured.

  And, such a reduction in the diameter of the cord diameter of the ply cord portion sandwiched between the bead core portions, the twist pitch of the portion of the ply cord composed of twisted cords sandwiched between the bead portions, the protruding end from the bead core portion When it is brought about by making it larger than that of the portion, the sandwiched portion of the ply cord is easily deformed, and the thickness of the sandwiched portion can be easily further reduced in the sandwiching process between the bead portions. Therefore, the difference in thickness between the ply cord and the projecting end portion from the bead core portion can be further increased, and the pull-out resistance can be further improved.

  Here, the reduction in the cord diameter based on the change in the twist pitch as required is, for example, by lowering the twisting speed of the rotating housing of the twisting machine disclosed in International Publication No. 04/048679, And / or it can be done easily by increasing the cord drawing speed.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the present invention together with a rim on which one bead portion is assembled, and FIG. 1 (a) is a meridian having a cross-section in the tire width direction of the bead portion. FIG. 1B is a cross-sectional view illustrating a carcass ply and a bead core portion. FIG. 1C is a partial arrow view taken along line bb in FIG. 1A, and FIG. It is a fragmentary sectional view which follows the -c line.
Although not shown in the figure, this tire, like a general pneumatic tire, is continuously inward in the radial direction to the tread portion and the respective side portions of the tread portion to the bead portion 1 as shown in the drawing. A radial carcass having a radial structure or a bias structure, for example, a single carcass ply 2a, including a pair of extending side wall portions and comprising one or more carcass plies and supplementing each of these portions. With

  1A, each bead portion 1 sandwiches a side portion of the carcass ply 2a between a pair of bead core portions 3a and 3b having a divided structure, and each side end portion of the carcass ply 2a. Is protruded inward in the radial direction from the bead core portions 3a and 3b, the carcass ply 2a, directly, the sandwiched portion 5 between the bead core portions 3a and 3b of each ply cord 4 forming the carcass ply 2a. The thickness t of the ply cord 4 is made thinner than the bead core portions 3a and 3b of the ply cord 4 and the thickness T of the protruding end portion 6 inward in the radial direction.

  According to this, in the action of the tensile force on the ply cord 4, and eventually the carcass ply 2a, the tensile force is applied under the physical engagement state between the bead core portions 3a and 3b and the projecting end portion 6. The carcass ply 2a can be reliably supported by the bead core portions 3a and 3b without fear of pulling out the carcass ply 2a.

  By the way, such a reduction in the thickness of the ply cord 4 at the sandwiching portion 5 is, for example, on both sides adjacent to the portion of the ply cord 4 made of a steel twist cord that is to be sandwiched between the bead core portions. The part is chucked with a jig or the like, and the twisting of the cords on both sides of the parts is securely held, and the part between both chucking parts is rotated in the direction opposite to the twisting direction of the cords. As shown in FIG. 1B, it can be easily realized by loosening the twist of the cord as required. In this case, the twist of the cord between the two chucking portions is completely achieved. When extinguished, the thickness t of the sandwiched portion 5 of the ply cord 4 can be minimized.

  In the case where the thickness of the sandwiched portion 5 of the ply cord 4 is reduced as necessary by unwinding the cord as described above, it is preferable that the thickness is shown in FIGS. 1B and 1C. As is apparent from FIG. 2, the sandwiched portion 5 is sandwiched between the pair of bead core portions 3a and 3b in a state where the sandwiched portion 5 is partially overlapped with another sandwiched portion 5 adjacent thereto, whereby the ply cord 4 and thus The pull-out resistance of the carcass ply 2a is further improved by generating a pull-out drag force by the other pinching portion 5 partially overlapping the pinching portion 5 against the action of the tensile force on the pinching portion 5. Can be made.

  When the carcass ply 2a, for example, is used to form a radial structure or a bias structure carcass 2, when the side portion of each carcass ply 2a is sandwiched between different bead core portions, For example, three bead core portions arranged side by side in the tire width direction can be dealt with by putting two adjacent ones as a pair and sandwiching the side portion of each carcass ply 2a between each of them. For three or more carcass plies 2a, the bead core portions arranged side by side in the tire width direction are increased one by one from the above, and each side portion is sandwiched between the bead core portions adjacent to each other. You can deal with it.

  FIG. 2 is a cross-sectional view similar to FIG. 1A showing another example of the thickness of the sandwiched portion of the ply cord. This is a cross-sectional view of each ply cord 4 between the bead core portions 3a and 3b. In order to make the thickness t of the sandwiching portion 5 smaller than the thickness T of the projecting end portion 6, the cord diameter of the sandwiching portion 5 is made smaller than that of the projecting end portion 6. Specifically, for this reason, The twist pitch of the sandwiching portion 5 between the bead core portions 3a and 3b of the ply cord 4 made of a twisted cord, for example, by lowering the twisting speed of the twisting machine and / or increasing the drawing speed of the cord, This is larger than the twist pitch of the protruding end 6.

  Also by this, because of the difference in diameter between the sandwiching portion 5 and the protruding end portion 6, the tensile force acting on the ply cord 4 is under the engagement between the protruding end portion 6 and the bead core portions 3a and 3b. It will be effectively supported by 3a and 3b, and the pull-out resistance of the carcass ply will be greatly improved.

  In addition, 7 in a figure shows the wire chafer arrange | positioned from the outer part of a tire width direction to a bead base part.

By the way, in the embodiment shown in FIG. 2, even if the carcass ply 2a and the bead core portions 3a and 3b have respective coating rubbers such as thermal deterioration, the carcass ply 2a has high pull-out resistance. In order to provide, the relative relationship between the cord diameter d of the sandwiching portion 5 and the cord diameter D of the protruding end 6 is
0.2D ≦ d ≦ 0.8D
It is preferable to set it as the range.

  In other words, a bead portion sample (length 130 mm in the direction perpendicular to the paper surface) as shown in FIG. 2 is prepared with the relative ratio of the cord diameters d and D of the ply cord 4 made of steel cord as a parameter. Was placed in an oven at 100 ° C. for 6 hours to promote thermal degradation of the rubbery material, and the lower end portion of the figure including the bead core portion was fixed with a jig. When a tensile test in which a tensile force was applied to one existing ply cord was performed, the result shown in FIG. 3 was obtained, and the cord diameter d of the sandwiching portion 5 was 0.2D to This is because a high pull-out resistance is obtained in the range of 0.8D, in particular, in the range of 0.3D to 0.6D.

  When the cord diameter d is less than 0.2D, the pull-out drag is caused by the decrease in the shear holding force between the ply cord 4 and the covering rubber due to the thermal deterioration of the rubber. Will be reduced.

A bead part sample having a bead part structure having a bead part structure as exemplified in the meridian cross-sectional views in FIGS. 4 (a), (b) and (c) is prepared, and the sample is heated at 100 ° C. for 48 hours. After the thermal deterioration of the ply cord, and thus the carcass ply covering rubber, is promoted, an Instron tensile tester is used to pull out one of the steel ply cords located at the center of the steel ply cord. The release characteristics were measured.
The maximum tensile force at this time is displayed as an index with a graph in FIG. The index value means that the structure shown in FIG. 4B is used as a control, and the larger the value, the larger the maximum tensile force.

In addition, the structure shown in FIG. 4A is a structure in which the side portion of the carcass ply is simply sandwiched between a pair of bead core portions,
The structure shown in FIG. 4 (b) is obtained by winding the side portion of the carcass ply around a bead core having a hexagonal cross section.
The structure shown in FIG. 4 (c) relates to the present invention, and is a structure in which a pinched portion of a ply cord that is completely untwisted is sandwiched between a pair of bead core portions.

  Also, here, the tensile test is performed after the sample is heated.If the tensile test is performed directly without passing through the thermal history, the cord is pulled out until the ply cord is broken in all samples. Therefore, since the sample cannot be directly compared and evaluated for resistance to pull-out, the sample is heated to cause thermal degradation of the coated rubber, thereby reducing the shear holding force between the ply cord and the coated rubber. This is for facilitating the evaluation of pull-out resistance.

  According to FIG. 5, the ply cord is pulled out by the action of a relatively small tensile force under the simple pinching structure shown in FIG. 4A, whereas according to the present invention shown in FIG. In the structure in which the thickness of the ply cord is thin, it is clear that the cord breaks before the ply cord is pulled out, and the tensile force at the time of breaking is shown in FIG. It turns out that it becomes larger than a general winding structure, in other words, there is little decrease in the cord strength in the bead portion.

It is a figure which shows embodiment of this invention. It is meridian sectional drawing similar to Fig.1 (a) which shows other embodiment of this invention. It is a graph which shows the pull-out drag of a ply cord. It is meridian sectional drawing which shows the bead part structure of an Example. It is a graph which shows the result of an Example with an index value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Carcass 2a Carcass ply 3a, 3b Bead core part 4 Ply cord 5 Clamping part 6 Projection end part t, T thickness

Claims (6)

A bead portion structure in which each side portion of the carcass ply is sandwiched between paired bead core portions of the split structure, and each side end portion of the carcass ply is protruded radially inward from the bead core portion. In a pneumatic tire having
A pneumatic tire in which each ply cord forming a carcass ply has a thickness of a sandwiched portion between bead core portions thinner than a thickness of a protruding end portion of the ply cord radially inward from the bead core portion.   2. The pneumatic tire according to claim 1, wherein the number of twists of a portion of the ply cord that becomes a twist cord sandwiched between the bead core portions is smaller than the number of twists of the protruding end portion from the bead core portion.   The pneumatic tire according to claim 2, wherein the ply cord portion sandwiched between the bead core portions is not twisted.   The pneumatic tire according to claim 2 or 3, wherein a ply cord portion sandwiched between bead core portions is partially overlapped with another adjacent ply cord portion.   The pneumatic tire according to claim 1, wherein a cord diameter of a ply cord portion sandwiched between bead core portions is smaller than that of a protruding end portion from the bead core portion.   The pneumatic tire according to claim 5, wherein a twist pitch of a portion of the ply cord made of a twisted cord sandwiched between the bead core portions is made larger than that of the protruding end portion from the bead core portion.

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