Patent Publication Number: US-2002003018-A1

Title: Bead core and pneumatic tire using the same

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to a bead core of so-called monostrand type and a pneumatic tire using the same.  
       [0003] 2. Description of Related Art  
       [0004] In general, so-called monostrand type bead core is constructed by spirally winding a single cord and stacking such spiral windings to each other as plural stages, wherein the single cord is aligned in the plural stages at the cross section of the bead core. In such a bead core, the number of free ends of the single cord becomes minimum (start end and terminal end), so that the resistance to bead burst is excellent.  
       [0005] However, the start end of the single cord in the bead core locates in an axially outermost position of a radially innermost stage, so that the bead core is subjected to a restraint from only one side. As a result, when a large external force is applied to the start end of the bead core in the assembling of a bead filler onto the bead core, the start end slips outward from the above position in the radial direction through an elastic restoring force of the cord itself and may spring up to a sidewall portion of a pneumatic tire according to circumstances. When vulcanization is carried out at such a state to fix the start end to the above slipped position, there is a problem that the start end repeatedly press-contacts with a carcass ply during the running to damage the carcass ply.  
       SUMMARY OF THE INVENTION  
       [0006] It is, therefore, an object of the invention to provide a bead core capable of preventing the slipping of the start end in the winding of the single cord to easily maintain a normal aligning wound state and a pneumatic tire using the same.  
       [0007] According to a first aspect of the invention, there is the provision of in a bead core formed by spirally winding a single cord and stacking spiral windings to each other as plural stages in a radial direction, an improvement wherein a winding start end of the single cord is shifted from an axially outermost or innermost position of a radially innermost first stage to a next position at least corresponding to only one of the single cord, and after the single cord is spirally wound from the first stage to a second stage and arrives on a position above the start end, it is wound on the axially outermost or innermost empty position of the radially innermost first stage.  
       [0008] In the conventional monostrand-type bead core, the start end of the single cord usually locates in an axially outermost or innermost position of a radially innermost stage as previously mentioned. On the contrary, in the bead core according to the invention, the start end of the single cord is shifted from the axially outermost or innermost position to a next position at least corresponding to only one of the single cord to form an empty region in the axially outermost or innermost position. Then, in the winding of the single cord at a second stage next to the radially innermost first stage, after the single cord arrive at a position above start end of the first stage, the single cord is placed on the empty region of the first stage and thereafter returned to a position above the empty region filled with the single cord and further the winding is continues toward a subsequent third stage.  
       [0009] Thus, the start end is strongly restrained by sandwiching from both sides by the continuous single cord. As a result, even if an external force is applied to the start end in the bead core, the start end is not slipped from the given position nor sprung upward and hence the damaging of a carcass ply is prevented.  
       [0010] In a preferable embodiment of the first aspect, the single cord is aligned in checkers in the bead core.  
       [0011] According to a second aspect of the invention, there is the provision of a pneumatic tire comprising a pair of bead portion each including a bead core embedded therein, wherein said bead core is formed by spirally winding a single cord and stacking spiral windings to each other as plural stages in a radial direction in which a winding start end of the single cord is shifted from an axially outermost or innermost position of a radially innermost first stage to a next position at least corresponding to only one of the single cord, and after the single cord is spirally wound from the first stage to a second stage and arrives on a position above the start end, it is wound on the axially outermost or innermost empty position of the radially innermost first stage.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] The invention will be described with reference to the accompanying drawings, wherein:  
     [0013]FIG. 1 is a diagrammatically section view of an embodiment of the bead core according to the invention;  
     [0014]FIG. 2 is a diagrammatically section view illustrating a state of mounting a bead filler onto the bead core shown in FIG. 1;  
     [0015]FIG. 3 is a diagrammatically section view of a first embodiment of the pneumatic tire according to the invention;  
     [0016]FIG. 4 is a diagrammatically section view of a second embodiment of the pneumatic tire according to the invention; and  
     [0017]FIG. 5 is a diagrammatically section view of a third embodiment of the pneumatic tire according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0018] In FIG. 1 is shown an embodiment of the bead core according to the invention. The bead core  11  shown in FIG. 1 is a bead core generally called as a monostrand-type bead core, which is constructed by spirally and continuously winding a single cord  13 , a steel cord  14  coated with an insulation rubber  12  in the illustrated embodiment into a cylindrical form and stacking such spiral windings  15  of the cylindrical form to each other outward in a radial direction.  
     [0019] In the above bead core  11 , a start end M of the single cord  13  locates in a radially innermost stage, i.e. a first spiral winding  15   a.  In the first spiral winding  15   s,  the start end M has hitherto been located in an axially outermost position (left end in FIG. 1) or an axially innermost position (right end in FIG. 1). In this case, however, if the start end M is subjected to an external force, it is slipped outward or inward from the above position in the axial direction and may spring up outward in the radial direction as previously mentioned.  
     [0020] In the invention, therefore, the start end M of the single cord  13  is shifted from the axially outermost or innermost position of the radially innermost stage to a neat position at least corresponding to only one of the single cord  13 . In the illustrated embodiment, the start end M is shifted inward from the axially outermost position by only one of the single cord  13  in the axial direction to render the axially outermost position into an empty region K. Then, the single cord  13  is spirally wound inward from the start end M in the axial direction three turns to form a cylindrical spiral winding  15   a  of the first stage. Moreover, the winding order of the single cord  13  is represented by symbols T- 1 , T- 2 , . . . T- 11  in FIG. 1.  
     [0021] Subsequently, the single cord  13  is spirally wound from a position above the axially innermost position of the first stage in a winding direction opposite to that of the first stage to form a cylindrical spiral winding  15   b  of a second stage. In the formation of the spiral winding  15   b  of the second stage, after the winding is carried out above the start end M (sixth turn T- 6 ), the single cord  13  is wound at the empty region K in the axially outermost position of the first stage (seventh turn T- 7 ) and then the winding is carried out at the axially outermost position of the second stage (eighth turn T- 8 ).  
     [0022] Thus, the start end M of the single cord  13  is strongly restrained from both sides by sandwiching between second turn T- 2  and seventh turn T- 7  of the continuous single cord  13  and hence the winding of the single cord  13  is easily maintained at a normal aligning state and the slipping of the start end M from the given position is never caused even if the external force is applied to the start end M in the bead core  11 .  
     [0023] Then, the single cord  13  is spirally wound from a position above the axially outermost position of the second stage in a winding direction opposite to that of the second stage three turns to form a cylindrical spiral winding  15   c  of a third stage.  
     [0024] When the above spiral windings  15  are stacked to each other in the radial direction, the single cords  13  are accurately overlapped with each other in the radial direction, so that the single cord  13  is aligned at a checkers state in the bead core  11 . Moreover, the number of the stages is favorable to be a range of 2 to 6.  
     [0025] Then, an operation of mounting a bead filler  21  onto the above bead core  11  will be described with reference to FIG. 2. In this case, two bead cores  11  are provided at a joined state in the axial direction. On the other hand, a pair of bead fillers  21  are extruded through an extruder at a state of connecting their base portions to each other as shown in FIG. 2 in order to improve the operation efficiency. The thus extruded bead filler pair are wound on the outside of the two bead cores  11  in the radial direction.  
     [0026] Thereafter, the connected portion of the bead filler pair is cut by a cutter  22  to divide into two bead fillers  21  and at the same time the joined bead cores are separated into individual bead cores  11 . In this case, the cutter  22  gives an external force to the single cord  13  constituting the bead core  11 , particularly the single cords  13  located at a side adjacent to the cutter.  
     [0027] In the bead core according to the invention, however, the start end M as a free end of the single cord is shifted inward from the axially outermost position of the first stage only by one of the single cord, so that the external force applied to the start end M is fairly decreased. And also, the start end M is strongly restrained between turns T- 2  and T- 7  of the single cord  13  from both sides, so that the start end M is never slipped out outward from the given position and does not spring up. Further, the single cords  13  located at the radially outermost positions are never slipped out even if external force is applied because they continue to front and back windings of the single cord  13  in any stages.  
     [0028] In FIG. 3 is shown a first embodiment of incorporating the above bead core  11  into a pneumatic tire  25  according to the invention. This tire  25  comprises a pair of bead portions  26  each containing the bead core  11  embedded therein, a pair of sidewall portions  27  extending outward from these bead portions  26  in substantially a radial direction, and a substantially cylindrical tread portion  28  connecting outer ends of the sidewall portions  27  in the radial direction.  
     [0029] The sidewall portions  27  and the tread portion  28  are reinforced by a carcass  29  extending substantially in a toroidal form, and both widthwise end portions of the carcass  29  are wound around the bead cores  11  from an inside of the tire toward an outside thereof and moored thereto.  
     [0030] In the bead core  11  embedded in the bead portion  26   a  (axially left side in FIG. 3), the start end M locates at a bead heel side, while in the bead core  11  embedded in the bead portion  26   b  (axially right side in FIG. 3), the start end M locates at a bead toe side.  
     [0031] When the start end M locates at the bead toe side as in the bead core  11  embedded in the bead portion  26   b,  the single cord  13  in the vicinity of the start end M intends to be slipped out by a dragging force directing outward from the carcass  29  in the radial direction (external force) during the vulcanization of the green tire. When the bead core  11  is constructed as mentioned above, however, the start end M is restrained by the single cord  13  from both sides and also the single cord  13  located inward from the start end M in the axial direction continues to front and back windings of the single cord  13 , so that the start end M is never slipped out and is easily maintained at the normal aligned state.  
     [0032]FIG. 4 is a second embodiment of the pneumatic tire according to the invention. In the illustrated embodiment, the start ends M in both the bead cores  11  are located so as to approach to each other, so that the start ends M of the bead cores  11  locate at the bead toe side in both the bead portions  26   a,    26   b.  In this case, the slipping of the single cord  13  in the separation and cutting through the cutter  22  can be prevented in both the bead cores  11 .  
     [0033]FIG. 5 is a third embodiment of the pneumatic tire according to the invention. In the illustrated embodiment, the start ends M of both the bead cores  11  are located so as to separate away from each other, so that the start ends M of the bead cores  11  in both the bead portions  26   a,    26   b  locate at the bead heel side. In this case, the slipping of the single cord  13  during the vulcanization of the green tire can be prevented in both the bead cores  11 .  
     [0034] Although the shifting quantity of the start end M corresponds to only one of the single cord  13  in the above embodiments, it may be two or more of the single cord. And also, the above embodiments are described with respect to the bead core  11  having substantially a rectangular form at section, the invention can be applied to a bead core having substantially a hexagonal form at section.  
     [0035] As mentioned above, according to the invention, the normal aligning state of the single cord in the bead core can easily be maintained by preventing the slipping of the start end of the single cord.