Patent Publication Number: US-2006011282-A1

Title: Run flat tire and method of manufacturing the tire

Description:
TECHNICAL FIELD  
      The present invention relates to a runflat tire capable of running for a certain distance even in a state where the inner pressure thereof has inordinately decreased or the tire has been punctured. In particular, the present invention is intended to remarkably improve a uniformity of the tire as well as to effectively inhibit both of pulling out of carcass cords and coming off of beads during running in the runflat state.  
     BACKGROUND ART  
      As a so-called runflat tire which is capable of running for a certain distance even when it gets an inordinate decrease in its inner pressure or it gets a puncture, there are two types of tires, i.e. a so-called core type runflat tire and a so-called side reinforced runflat tire. The former contains a supporting body in a tire/rim assembly, and the latter has a reinforcing rubber layer which consists of a relatively soft rubber and is arranged on the inner surface of the carcass at least in the sidewall portion.  
      A dimensional deviation of the tire may greatly affect on its uniformity especially for the side reinforced-type runflat tire, due to a material stiffness of its reinforcing rubber layer. Therefore, when such a runflat tire is to be built, it is necessary to satisfy a restrict standard in which a dimensional accuracy of the carcass as well as a thickness and a shape of the reinforcing rubber layer underneath the carcass are set higher than those of the ordinal tires.  
      A so-called core process (three dimensional process) is useful as a method of building a tire satisfying such a restrict standard. In this process, a green tire is formed in a shape similar to the product tire by attaching cords and rubber on the outer surface of a rigid core, and then the green tire along with the rigid core are vulcanized to yield the product tire without accompanying a large radial expansion caused due to a shaping step or the like. The tire built by the core process has a remarkably superior uniformity as compared with a tire built by a conventional process which includes a shaping step.  
      International Publication WO 00/73093, for example, discloses a tire built by a core process. However, as shown in  FIG. 9 , since each of cord layers  102 ,  103  of a carcass  101  has such a configuration that a plurality of cords  104  are arranged between both bead portions at a given pitch, this tire has a problem in which a force anchoring the carcass by means of the beads is insufficient and thus the cords  104  of such a carcass  101  are easily pulled out in the tire&#39;s radial direction. Where the arrangement pitch between the carcass cords  104  is narrowed and thereby increasing the carcass stiffness, it is useful that the adjacent cord layers are so arranged that cords thereof are shifted with each other at a given circumferential pitch. A tire having the configuration described in the above-mentioned International Publication WO 00/73093 inevitably needs to arrange a circumferential cord  105  extending in the circumferential direction between the cord layers  102  and  103 , which complicates the operation of attaching the cords.  
      In JP 11-115420 A, which was filed by the present applicant and was already laid-open, the present applicant disclosed a pneumatic tire that can facilitate the operation of attaching carcass cords and can effectively inhibit the carcass cords from pulling out by adopting a configuration in which split beads sandwich a carcass layer formed by arranging two layers of cord assemblies on the outer surface of the core while maintaining the overlap region and shifting the cord assemblies with each other at a given distance L in the circumferential direction.  
      In such a pneumatic tire, however, a distance between the radially innermost end of the split bead and the tire bead base is not particularly defined. When the distance becomes larger, the thickness of the rubber placed between the inner end of the split bead in the tire&#39;s radial direction and the tire bead base also becomes larger. Accordingly, such a pneumatic tire is not suitably applied to a runflat tire since the lower part of the bead portion largely deforms and thus the bead portion cannot exert a sufficient engagement force against the wheel rim when the inner pressure of the tire decreases.  
      U.S. Pat. No. 3,815,652 describes a tire which has a carcass layer built by using a continuous cord and arranging the cord while remaining the overlap region and shifting in the circumferential direction. This tire, however, cannot effectively prevent the carcass cords from pulling out, since a bead is arranged on a single side of the carcass layer and the tire does not employ a configuration in which the carcass layer is not sandwiched from the both sides.  
      U.S. Pat. No. 5,660,656 describes a tire which has such a configuration that split beads sandwich a carcass layer built by using a continuous cord and arranging the cord while shifting in the circumferential direction. This tire, however, has a problem in which a overlapping portion of the cords constituting the carcass layer present between the beads so that the tire cannot effectively prevent the carcass cords from pulling out.  
     DISCLOSURE OF THE INVENTION  
      The object of the present invention is to provide a runflat tire which can remarkably improve its uniformity as well as can effectively inhibit both of pulling out of carcass cords and coming off of beads during running in the runflat state by using a continuous cord and appropriately arranging the end portion of at least one cord layers constituting the carcass.  
      To achieve the above-mentioned object, a runflat tire according to the present invention comprises a carcass toroidally extending over a pair of bead portions in which a bead core is embedded, a pair of sidewall portions and a tread portion, and a reinforcing rubber layer which has a crescent sectional shape and is arranged at the interior surface side of the carcass at least in the sidewall portions, and is characterized in that the carcass comprises at least one cord layers including a continuous cord and having a plurality of radial cord portions radially-arrayed between the bead portions at a given circumferential pitch P and a plurality of circumferential cord portions circumferentially connecting respective inner ends of adjacent radial cord portions in the bead portion.  
      It is also preferred that the carcass comprises n (n is greater than or equal to two) layers of the cord layers; the adjacent cord layers are so arranged that their radial cord portions are circumferentially spaced with each other by a distance L obtained when the circumferential pitch P is divided by the number n; the circumferential cord portions of the different cord layers are substantially contacted with each other to form an overlap portion in the bead portions; the bead consists of a pair of split bead cores, the split bead cores locating on both sides of the carcass to sandwich the carcass; the circumferential cord portions locate below a lower end of the split bead cores as viewed from the tire&#39;s radial direction; and an inner end in the tire&#39;s radial direction of the split bead core locating outside as viewed from the tire&#39;s width direction is so placed that a vertical distance from a tire bead base or its extension is not more than 5 mm, particularly not more than 3 mm.  
      It is further preferred that the split bead core constituting the bead is formed by helically winding a bead wire.  
      It is further preferred that the number n of the cord layers constituting the carcass is  3 , and that the overlap portion has a triple contact portion at which all of the circumferential cord portions of the different cord layers are substantially contacted with each other.  
      If it is more necessary to prevent the carcass cords from pulling out, it is preferred that the bead consist of a pair of split bead cores, the split bead cores locating on both sides of the carcass to sandwich the carcass; and the carcass comprises at least one turn-up cord layers folded around the split bead core locating outside as viewed form the tire&#39;s width direction from the inner side to the outer side in the tire&#39;s width direction; and wherein a folded end of the turn-up cord layer substantially consists of a plurality of the circumferential cord portions.  
      Meanwhile, if the bead consist not of a split bead but of an ordinal bead, it is preferred that a stiffener rubber tapered outwardly in the tire&#39;s radial direction is further arranged outside the bead in the tire&#39;s radial direction; the carcass comprises at least one turn-up cord layers folded around the bead and the stiffener rubber from the inner side to the outer side in the tire&#39;s width direction; and wherein a folded end of the turn-up cord layer substantially consists of a plurality of the circumferential cord portions.  
      It is further preferred that, as viewed in a section in the tire&#39;s width direction under a condition where the tire is assembled to its standard rim to form a tire/wheel assembly and then a small inner pressure of 15% of the maximum inner pressure is applied to the tire with no load applied thereto, the folded end of the turn-up cord layer is laid, in the tire&#39;s radial direction, inside of a line segment PA which connects an arc center point P of the flange contour and an intersection A of the inner surface of the tire and a line extending outwardly in the tire&#39;s radial direction from the center point P at an angle of 60 degrees in relation to a line parallel to the rim radial line.  
      It is also preferred, as viewed in a section in the tire&#39;s width direction under a condition where the tire is assembled to its standard rim to form a tire/wheel assembly and then a maximum load is applied to the tire with no inner pressure applied thereto, the folded end of the turn-up cord layer is laid, in the tire&#39;s radial direction, outside of a line segment QB which connects an outermost point Q of the rim guard in the tire&#39;s width direction and an intersection B of the inner surface of the tire and a line extending outwardly in the tire&#39;s radial direction from the outermost point Q at an angle of 60 degrees in relation to a line parallel to the rim radial line.  
      It is preferred, as viewed from the tire&#39;s width direction, the sectional area of the stiffener rubber is in a range between 20-25% of the sectional area of the reinforcing rubber.  
      As used herein, the term “standard rim” refers to a standard rim specified in an industrial specification, standard or the like such as JATMA, TRA and ETRTO which are effective in the area where the tire is manufactured, sold or used. The term “maximum pressure” refers to a maximum pressure (an inner pressure corresponding to the maximum load capability) specified in the abovementioned industrial specification or standard.  
      It is also preferred that a plurality of the circumferential cord portions constituting the folded end of the turn-up cord layer are so arranged that their positions in the tire&#39;s radial direction differ with each other.  
      It is further preferred that an overlap portion at which the circumferential cord portions in the different cord layers substantially contact with each other is formed in the bead portions.  
      A method of building a tire including a carcass having the abovementioned turn-up cord layer, for example, comprises the steps of attaching, as needed, an inner liner, a reinforcing rubber, a carcass ply rubber and the like on a toroidal shaping core of a shaping body which has the shaping core, a bladder stored inside the periphery of the shaping core, and a detachable folding core enclosing the bladder when it is stored; forming, thereafter, a carcass by attaching a continuous cord while radially displacing it back and forth between the both bead portions at a given circumferential pitch P; and then folding ends of the carcass around the beads by removing the folding core and expanding the bladder stored therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a partially exploded perspective view of a representative embodiment of a runflat tire according to the present invention;  
       FIG. 2  is a sectional view of the bead portion  5  of the tire shown in  FIG. 1  in the tire&#39;s width direction;  
      FIGS.  3 ( a )-( c ) are schematic views for illustrating a procedure of arranging the carcass cord  2  of the tire shown in  FIG. 1 ;  
      FIGS.  4 ( a )-( c ) are schematic views for illustrating another procedure of arranging the carcass cord  2  of the tire shown in  FIG. 1 ;  
      FIGS.  5 ( a )-( c ) are schematic views for illustrating yet another procedure of arranging the carcass cord  2  of the tire shown in  FIG. 1 ;  
       FIG. 6 ( a ) is a sectional view showing a state of the circumferential cord portion  16  in the overlap region K 2  of the tire shown in  FIG. 1  in the tire&#39;s width direction;  
       FIG. 6 ( b ) is a sectional view showing another state of the circumferential cord portion  16  in the overlap region K 2  of the tire shown in  FIG. 1  in the tire&#39;s width direction;  
       FIG. 6 ( c ) is a sectional view showing yet another state of the circumferential cord portion  16  in the overlap region K 2  of the tire shown in  FIG. 1  in the tire&#39;s width direction;  
       FIG. 7  is a schematic view for illustrating an example of a procedure of arranging the carcass cord  2  of a tire which has three cord layers  3 ;  
       FIG. 8  is a sectional view showing a state of the circumferential cord portion  16  in the overlap region K of the tire shown in  FIG. 7  in the tire&#39;s width direction;  
       FIG. 9  is a schematic view showing an arrangement of the cords in a tire manufactured according to the conventional core process;  
       FIG. 10  is a partially exploded perspective view of another embodiment of a runflat tire according to the present invention;  
       FIG. 11  is a partially exploded perspective view of another embodiment of a runflat tire according to the present invention;  
       FIG. 12  is a half sectional view of another embodiment of a runflat tire according to the present invention in the tire&#39;s width direction;  
       FIG. 13  is a half sectional view of the tire shown in  FIG. 11  in the tire&#39;s width direction when the inner pressure is zero and the steady state load is applied;  
       FIG. 14  is a half sectional view of another embodiment of a tire according to the present invention in the tire&#39;s width direction; and  
       FIG. 15  is a sectional view of Comparative Example showing a configuration of its bead portion. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Hereinafter, an embodiment of the present invention will be described with reference to the drawings.  FIG. 1  is a partially exploded perspective view of a representative embodiment of a runflat tire according to the present invention and  FIG. 2  is a sectional view of the bead portion  5  of the runflat tire shown in  FIG. 1 .  
      The runflat tire (hereinafter referred to as “tire”) N shown in  FIGS. 1 and 2  has a carcass  4  which is arranged outside a carcass liner  1  and which consists of a layer  3  of a cord  2 . The carcass  4  toroidally extends over a pair of bead portions  5 , a pair of sidewall portions  6  and a tread portion  7 . A reinforcing rubber layer  8  having a crescent sectional shape is provided on the inner surface side of the sidewall portion  6  in relation to the carcass  4 . On the periphery of the crown portion of the carcass  4 , there is provided a belt  10  built by laminating, in the tire&#39;s radial direction, a plurality of cord layers in which a plurality of cords  9  are aligned in parallel and are coated with rubber. A tread rubber layer  11  is arranged on the belt  10 .  
      A constitutional feature of the present invention is to optimize the carcass cords and the configuration of the bead, and more specifically the feature is that the carcass comprises at least one cord layer including a continuous cord and having a plurality of radial cord portions radially-arrayed between the bead portions at a given circumferential pitch P and a plurality of circumferential cord portions circumferentially connecting respective inner ends of adjacent radial cord portions in the bead portion. As such a configuration is adopted to the tire that a plurality of circumferential cord portions circumferentially connect the respective inner ends of the adjacent radial cord portions in the bead portion, the stiffness near the bead portion has been improved and thus the beads are prevented from coming off especially during running in the runflat state. In addition, as the ends of the carcass cords are connected by the circumferential cord portions, which increases a force of anchoring the carcass by means of the beads, the carcass cords are effectively prevented from pulling out even when a force of pulling out the carcass cord is activated.  
      In a preferred embodiment of the present invention, the carcass  4  includes n (n is greater than or equal to two, and three in  FIG. 3 ) layers of the cord layers  3   a ,  3   b  and  3   c  which are composed of a continuous cord  2  and has a plurality of radial cord portions  15  and circumferential portions  16  connecting the respective inner ends of the adjacent radial cord portions  15  in the bead portion  5 . Sets of adjacent cord layers  3   a  and  3   b ,  3   b  and  3   c  are so arranged that their radial cord portions  15  are circumferentially spaced with each other by a distance L obtained when the circumferential pitch P is divided by the number n (three in  FIG. 1 ). The circumferential cord portions  16   a ,  16   b  and  16   c  of the different cord layers  3   a ,  3   b  and  3   c , respectively, are substantially contacted with each other to form an overlap portion K in the bead portions  5 . The bead  12  consists of a pair of split bead cores  13  and  14  which locate on both sides of the carcass  4  to sandwich the carcass  4 . The circumferential cord portions  16   a ,  16   b  and  16   c  locate below the lower end of the split bead cores  13  and  14  as viewed from the tire&#39;s radial direction. The inner end  21  in the tire&#39;s radial direction of the split bead core  14  locating outside as viewed from the tire&#39;s width direction is so placed that a vertical distance from a tire bead base  17  or its extension is not more than 5 mm.  
      That is, when the three cord layers  3   a ,  3   b  and  3   c  are arranged to have the circumferential distance L therebetween, the circumferential cord portions  16   a ,  16   b  and  16   c  of these cord layers  3   a ,  3   b  and  3   c  partly overlap and contact with each other in the tire&#39;s width direction to form overlap portions K 1 , K 2  and K 3  in the bead  5 . In these overlap portions, the circumferential cord portions  16   a ,  16   b  and  16   c  contact and hold one another. Even when a force acts on the radial cord portions  15  outwardly in the tire&#39;s radial direction and thus the circumferential cord portion  16   a  continuing thereto is pulled outwardly, the circumferential cord portion  16   a  is prevented from moving due to the adjacent circumferential cord portion  16   b , thereby inhibiting the carcass cord  2  from pulling out. Further, the adjacent circumferential cord portions  16   a ,  16   b  and  16   c  contact and restrain with each other in the overlap portions K 1 , K 2  and K 3 , as shown in  FIG. 2 , so that they are integrated to give a diameter of the circumscribed circle larger than that of a single carcass cord  2 , while the pair of split bead cores  13  and  14  are arranged to sandwich the carcass  4  at near the border of the radial carcass cord portion  15  and the circumferential cord portion  16  so that the space therebetween is slightly larger than the diameter of the carcass cord  2 . The overlap portion K is difficult to pass through the space between the pair of the split bead cores  13  and  14  since the circumferential cord portions  16  are placed inside the inner ends  21  of the bead as viewed from the tire&#39;s radial direction. Moreover, since the radial cord portion  15  and the circumferential portion  16  are continuously formed, the circumferential cord portion  16  continuing to the radial cord portion  15  is restrained by the bead  12  even when a force acts on the carcass  4  outwardly in the tire&#39;s radial direction and the radial cord portion  15  is pulled out, resulting an effective prevention of pulling down the carcass cords  2 .  
      Further, the radial cord portion  15  and the circumferential cord portion  16  connect with each other, so that a device for attaching a carcass cord, for example, described in JP 2000-52448 A, which is also filed by the present applicant, can be used to continuously form the carcass  4 . This may improve the uniformity and the productivity of the tire.  
      In addition, according to the conventional process, a smaller distance between the radial cords yields a smaller feed of the tire&#39;s constitutional members per an arrangement of the radial cord, resulting poor accuracy and productivity, while a larger distance between the radial cords yields a smaller strength of the carcass so that a cord with a larger diameter is needed to prevent this. In contrast, according to the present invention, even if the distance L between the radial cord portions  15  is small, the arrangement pitch P of the radial cord portions  15  is large enough to be able to facilitate a manufacturing of the carcass with closely arranged cords.  
      Moreover, as the vertical distance between the radially innermost end of the split bead core  14  which locates outside as viewed from the tire&#39;s width direction and the tire bead base  17  or its extension is set to 5 mm or less, the stiffness near the bead heal portion  18  becomes higher. As a result, even when the inner pressure decreases, the lower part of the bead portion  5  is less deformed and thus the bead portion  5  exerts a sufficient engagement force against the rim of the wheel (not shown) so that the bead is effectively prevented from coming off.  
      Although  FIG. 1  shows an embodiment in which the cord layers  3   a ,  3   b  and  3   c  are serially arranged with circumferentially shifted by the distance L, as shown in  FIG. 3 ( a ), the order in arranging the cord layer  3   a ,  3   b  and  3   c  is not particularly limited as far as the radial cord portions  15  can be evenly spaced after the carcass layer  4  is built. For example, the cord layer  3   c  may be arranged between the cord layers  3   a  and  3   b , as shown in  FIG. 4 , or the cord layer  3   a  may be arranged between the cord layers  3   b  and  3   c  as shown in  FIG. 5 .  
      Furthermore, the pair of the split bead cores  13  and  14  constituting the bead  12  is preferably formed by helically winding bead wires  19  and  20 , respectively. As the bead wires  19  and  20  are helically winded to arrange them in piles substantially parallel to the circumferential cord portion  16 , the overlap portion K is difficult to pass through the space between the pair of the split beads  13  and  14  so that the effect of restricting the carcass  4  by means of the bead is enhanced. In addition, as the split bead core  14  especially locating outwardly in the tire&#39;s width direction is formed by aligning a plurality of arrays of bead wires  20  in the tire&#39;s width direction, the stiffness near the bead heal portion  18  is further enhanced to effectively prevent the pulling out of the carcass cord  2  and the coming off of the bead.  
      The vertical distance D between the radially innermost end  21  of the split bead core  14  locating outwardly as viewed from the tire&#39;s width direction is preferably not more than 3 mm. The closer the bead wire  20  is placed to the bead heal portion  18 , the larger the stiffness near the bead heal portion  18 . This reduces the deformation of the shape near the bead heal portion  18  and ensures a sufficient engagement force of the bead portion  5  of the tire against the rim of the wheel (not shown) even when the inner pressure decreases.  
      In this regard, the overlap portion K may be so formed that only the circumferential cord portion  16   b  substantially contacts with the other two cord portions  16   a  and  16   c , as shown in  FIG. 2 , and more preferably the overlap portion K has a triple contact portion at which all of the circumferential cord portions  16   a ,  16   b  and  16   c  are substantially contacted with each other. That is, in the second overlap portion K 2  shown in  FIG. 1 , if each of the circumferential cord portions  16   a ,  16   b  and  16   c  is placed at a vertex of a equilateral triangle, as shown in  FIG. 6 ( c ), positional relationships of the circumferential cord portions  16   a ,  16   b  and  16   c  are stabilized and mutual restriction forces therebetween are further increased by the contact. This makes the anchoring of the overlap portion K by means of the bead  12  stronger when a force is applied outwardly to the carcass  4  in the tire&#39;s radial direction.  
      Although  FIGS. 1-6  show embodiments in which the cord layer- 3  consist of three layers, the cord layer  3  may consist of two layers in another embodiment. In that case, the overlap portion K has an arrangement shown in  FIGS. 7 and 8 .  
       FIG. 6 ( a ) shows an embodiment in which the circumferential cord portions  16   a ,  16   b  and  16   c  constituting the overlap portion K are placed at vertexes of an equilateral triangle and one of the vertexes is directed inwardly in the tire&#39;s radial direction. The circumferential cord portions  16   a ,  16   b  and  16   c , however, may be placed on the equilateral triangles shown in FIGS.  6 ( b ) and  6 ( c ) which are rotationally symmetry with the equilateral triangle shown in  FIG. 6 ( a ). The circumferential cord portions  16   a ,  16   b  and  16   c  may be placed at any vortexes of an equilateral triangle.  
      The runflat tire having the above-mentioned configuration and according to the present invention has superior uniformity and can effectively inhibit both of pulling out of carcass cords and coming off of beads during running in the runflat state.  
      However, under a more severe condition where the tire is used in the runflat state with a higher load being applied, it may be necessary to further inhibit both of pulling out of carcass cords and coming off of beads during running in the runflat state.  
      In this case, it is preferred that the bead  12  consists of a pair of split bead cores  13  and  14  which locate on both sides of the carcass  4  to sandwich the carcass  4 , the carcass  4  comprises at least one turn-up cord layers  22  folded around the split bead core  14  located outside as viewed form the tire&#39;s width direction from the inner side to the outer side in the tire&#39;s width direction, and a folded end  23  of the turn-up cord layer  22  substantially consists of a plurality of the circumferential cord portions  24   a ,  24   b  and  24   c.    
      Such a tire has the bead  12  consisted of the split beads  13  and  14 , so that, as mentioned in the above, the overlap portion is difficult to pass through the space between the split beads  13  and  14 . In addition, the tire has the carcass  4  provided with the turn-up layer  22  which is formed in a turn-up configuration, so that the carcass cord  2  is further difficult to be pulled out even when a force is applied to the carcass  4  outwardly in the tire&#39;s radial direction and the radial cord portions  15  are pulled outwardly. Moreover, the tire has the circumferential cord portions which circumferentially connect the respective inner ends of the adjacent radial cord portions, so that the bonding area between the carcass cord  2  and the rubber is increased and the carcass cord  2  is formed in a key-like shape (a configuration capable of hooking the rubber). Such a configuration makes the carcass cord  2  difficult to be pulled out, thereby exerting a remarkable effect especially in a state where a large force is applied, such as in a severe runflat running state.  
      The tire shown in  FIG. 12  is another embodiment of the present invention which has a turn-up configuration. In this tire, a stiffener rubber  25  tapered outwardly in the tire&#39;s radial direction is further arranged outside the bead  12  as viewed from the tire&#39;s radial direction. The carcass  4  comprises at least one turn-up cord layers  22  folded around the bead  12  and the stiffener rubber  25  from the inner side to the outer side in the tire&#39;s width direction. The folded end  23  of the turn-up cord layer  22  substantially consists of a plurality of the circumferential cord portions  24   a - 24   c  ( FIG. 11 ). Such a configuration may also exert the same effect as the above-mentioned turn-up configuration. In  FIG. 12 , although shown is an embodiment in which the carcass  4  has a so-called up-and-down configuration consisting of one turn-up cord layer  8  and one downward cord layer, the carcass  4  may have various configurations.  
      It is preferred that, as viewed in a section in the tire&#39;s width direction under a condition where the tire is assembled to its standard rim to form a tire wheel and then a small air pressure of 15% of the maximum inner pressure is applied to the tire (so-called a free-standing state) with no load applied thereto ( FIG. 12 ), the folded end of the turn-up cord layer is laid in the tire&#39;s radial direction inside of a line segment PA which connects an arc center point P of said flange contour and an intersection A of the inner surface of the tire and a line extending outwardly in the tire&#39;s radial direction from the center point P at an angle of 60 degrees in relation to a line parallel to the rim radial line. In other words, the turn-up cord layer preferably has a so-called low turn-up configuration in which the height of the folded portion of the turn-up cord layer is smaller than the height of the rim flange. Such a configuration may avoid a large force caused by contacting with the rim especially in a normal running state. As a result, a separation can be effectively prevented at the folded ends of the carcass. In addition, the turn-up card layer having the low turn-up configuration is advantageous in the point where it may avoid a large force caused by contacting with the rim even in a runflat running state.  
      In order to effectively prevent a separation at the folded ends of the carcass in a runflat running state, it is also preferred that, as viewed in a section in the tire&#39;s width direction under a condition where the tire is assembled to its standard rim to form a tire wheel and then a maximum load is applied to the tire with no air pressure applied thereto, the folded end of the turn-up cord layer is laid in the tire&#39;s radial direction outside of a line segment QB which connects an outermost point Q of the rim guard in the tire&#39;s width direction and an intersection B of the inner surface of the tire and a line extending outwardly in the tire&#39;s radial direction from the outermost point Q at an angle of 60 degrees in relation to a line parallel to the rim radial line.  
      If the tire necessarily has a stable and sufficient runflat performance, as viewed from the tire&#39;s width direction, the sectional area S 1  of the stiffener rubber  25  is preferably in a range between 20-25% of the sectional area S 2  of the reinforcing rubber  8 , as shown as a hatched portion in  FIG. 14 . This is because the stiffness tends to be insufficient when the sectional area S 1  of the stiffener rubber  25  is less than the sectional area S 2  of the reinforcing rubber  8 , while problems such as a heat generation, a weight increase and a deterioration in the riding quality may arise when the sectional area S 1  is more than the sectional area S 2 .  
      Furthermore, in order to disperse the stress acting on the folded ends and to effectively prevent an occurrence and growth of a separation, the circumferential cord portions  24   a - 24   c  constituting the folded end  23  of the turn-up cord layer  22  are preferably arranged in such a manner that their positions in the tire&#39;s radial direction differ with each other, as shown in  FIG. 11 .  
      In the turn-up cord layer  22  constituting the carcass, the circumferential cord portions of the adjacent cord layers may be arranged without overlapping with each other, as shown in  FIG. 15 ( b ), since it can be effectively prevent the carcass cords from pulling out. If the carcass cord should be more strictly prevented from pulling out, an overlap portion at which the circumferential cord portions  24   a - 24   c  in the different cord layers  3   a - 3   c  substantially contact with each other is preferably formed at the position of each of the bead portions  5 .  
      As an example of a method of building the above-mentioned runflat tire having the carcass consisted of the turn-up cord layer, a method may be mentioned by way of example, which comprising the steps of attaching, as needed, an inner liner, a reinforcing rubber, a carcass ply rubber and the like on a toroidal shaping core of a shaping body which has the shaping core, a bladder stored inside the periphery of the shaping core, and a detachable folding core enclosing the bladder when it is stored; forming, thereafter, a carcass by attaching a continuous cord while radially displacing it back and forth between the both bead portions at a given circumferential pitch P; and then folding ends of the carcass around the beads by removing the folding core and expanding the bladder stored therein.  
      Although illustrative embodiments of the present invention have been described above, variations and modifications may be made without departing from the scope of the invention as defined by the appended claims.  
     EXAMPLES  
      Pneumatic tires according to the present invention were experimentally manufactured and their performances in durability and bead-securing forces were evaluated. The details will be described below.  
      Examples 1-14 were runflat tires for passenger vehicles and their tire sizes were 215/65 R15. Each of Examples 1-4 provided with a carcass, which did not have a turn-up cord layer but had overlap portions, and beads, which consist of split bead cores formed by helically winding a bead wire. Each of Examples 5-13 provided with a carcass, which had a turn-up cord layer but did not have overlap portions, and beads, which consist of a single bead core formed by helically winding a bead wire. Example 15 provided with a carcass, which had a turn-up cord layer and overlap portions, and beads, which consist of a single bead core formed by helically winding a bead wire. Examples 1-14 had parameters shown in Table 1 or 2. In Table 1, “Distance between the bead inner end and the bead base” and “Distance between the circumferential cord portion and the bead base” are indicated as vertical distances the inner end of the bead or the circumferential cord portion in the tire&#39;s radial direction and the tire bead base or its extension. In Table 2, “Sectional area of stiffener rubber” is indicated as a percentage of the sectional area of the stiffener rubber to the sectional area of the reinforcing rubber layer. In Table 2, “Position of the folded end” means the position of the folded portion of the turn-up cord layer of the carcass, “BQ-PA” means that the folded portion locates between the line segments BQ and PA, and “&gt;QB” means that the folded portion locates inside the line segment QB in the tire&#39;s radial direction.  
      For the purpose of comparison, a tire having the conventional carcass configuration (Conventional Example) and a tire having the carcass configuration shown in  FIGS. 15   a  and  15   b  (Comparative Example), both of which had the same tire size as those of Examples 1-14, were also experimentally manufactured.  
      The durability was evaluated in the following procedures. The abovementioned test tires were equipped on standard rims specified by JATMA to form tire/wheel assemblies. Then, the bulb cores were removed to set their inner pressure at 0 kPa (relative pressure). These tires were pressed against a drum rotating at the surface velocity of 89 km/h with a loading force of 5.3 kN, and the distances until the tires were broken were measured. The durability was evaluated based on the measured distance. The evaluated results are shown in Tables 1 and 2.  
      The bead-securing force was evaluated in the following procedures. The above-mentioned test tires were equipped on standard rims specified by JATMA to form tire/wheel assemblies. Then, by means of a device for measuring the bead-securing force which is commercially available from Hofmann, the bead portion was expanded at some segments and an expansion force was measured when the segment was expanded to the specific value defined for the standard rim. The bead-securing force was evaluated based on the measured force. The evaluated results are shown in Tables 1 and 2.  
      In Tables 1 and 2, each performance was represented by an index provided the performance of the Conventional Example is set to 100. The larger index means the better performance.  
                                           TABLE 1                                   Conventional   Comparative   Example   Example   Example   Example           Example   Example   1   2   3   4                                                                Pitch P   1.5   1.5   3   4.5   6   4.5       Number of carcasses n   1   1   3   3   4   3       L = P/n   1.5   1.5   1.5   1.5   1.5   1.5       Type of bead   Single   Split   Split   Split   Split   Split       Overlap portion   No   No   Yes   Yes   Yes   Yes       Distance between the bead     5 mm     5 mm     5 mm     5 mm     3 mm     3 mm       inner end and the bead base       Distance between the   2.5 mm   2.5 mm   2.5 mm   2.5 mm   0.5 mm   0.5 mm       circumferential cord portion       and the bead base       Durability   100   82   108   110   112   112       Bead-securing force   100   75   102   106   108   108                  
 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 5 
                 6 
                 7 
                 8 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Pitch P 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 4.5 
               
               
                 Number of carcasses n 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 1 
                 3 
               
               
                 L = P/n 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
               
               
                 Type of bead 
                 Single 
                 Single 
                 Single 
                 Single 
                 Single 
                 Single 
                 Single 
                 Single 
                 Single 
                 Single 
               
               
                 Overlap portion 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
                 No 
                 Yes 
               
               
                 Position of the folded end 
                 BQ-PA 
                 &lt;PA 
                 &gt;QB 
                 &lt;PA 
                 &lt;PA 
                 &lt;PA 
                 &lt;PA 
                 &lt;PA 
                 &lt;PA 
                 &lt;PA 
               
               
                 Sectional area of the 
                 25% 
                 25% 
                 23% 
                 18% 
                 20% 
                 23% 
                 25% 
                 27% 
                 23% 
                 23% 
               
               
                 stiffener rubber 
               
               
                 Durability 
                 120 
                 122 
                 128 
                 106 
                 114 
                 116 
                 114 
                 116 
                 118 
                 120 
               
               
                 Bead-securing force 
                 110 
                 100 
                 110 
                 110 
                 110 
                 110 
                 112 
                 112 
                 110 
                 114 
               
               
                   
               
            
           
         
       
     
      As seen from the results of Tables 1 and 2, it is clear that each of Examples 1-14 has superior durability and bead-securing force as compared with Conventional Example and Comparative Example.  
     INDUSTRIAL APPLICABILITY  
      According to the present invention, it is possible to provide a runflat tire which can effectively inhibit both of pulling out of carcass cords and coming off of beads during running in the runflat state.