Patent Publication Number: US-2016221402-A1

Title: Pneumatic vehicle tire

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of application Ser. No. 13/127,639, filed Jul. 29, 2011, which is a national phase application based on PCT/EP2008/065776, filed Nov. 18, 2008, the content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a runflat pneumatic vehicle tire comprising a carcass, said carcass being associated with two bead cores in respective bead portions of the tire, a belt structure provided between the carcass and a tread strip, a pair of sidewalls located at an intermediate portion of the tire between each bead portion and the tread strip, a runflat reinforcement arranged at the inner side of each sidewall, a reinforcer arranged in each bead portion of the tire, and a bead filler extending from each bead core along the respective reinforcer. 
     Such runflat tires feature a stiffer internal construction, which is capable of temporarily carrying the weight of the vehicle, even after the tire has lost all air pressure. To provide the self-supporting capability, a runflat reinforcement is provided at the inner side of each sidewall. 
     PRIOR ART 
     EP-B-1 013 482 discloses a vehicle tire comprising a carcass which extends between two bead rings, a belt arrangement provided between the carcass and a tread strip, and also rubber reinforcing plies arranged in the sidewall regions, which adopt a supporting function when the tyre is deflated. A single rubber reinforcing ply is arranged radially within a first carcass ply and its maximum thickness is disposed in the upper half of the sidewall height. The rubber reinforcing ply extends from the bead apex region up to and beneath the edge region of the belt ply. The bead apex, which extends approximately up to the half sidewall height, is surrounded by the first carcass ply. A reinforcing or stiffening strip is provided between the bead apex and the turned around end of the carcass ply, consisting of a textile material which extends up to and into the direct vicinity of the bead ring. 
     SUMMARY OF THE INVENTION 
     The applicant has tackled the problem of providing an improvement of the driving performance of runflat tires, particularly of the handling and comfort properties of a runflat tire. 
     This problem is solved by a pneumatic vehicle tire comprising a carcass, said carcass being associated with two bead cores in bead portions of the tire, a belt structure provided between the carcass and a tread strip, a pair of sidewalls, a runflat reinforcement arranged at the inner side of each sidewall, a reinforcer arranged in each bead portion of the tire, and a bead filler extending from the bead core along the reinforcer, characterized in that the reinforcer is arranged internally of the bead filler, the reinforcer comprises metal cords, the bead filler extends beyond an end of the reinforcer, and the bead filler is made of a soft rubber compound with an IHRD hardness lower than 80. 
     The pneumatic vehicle tire according to the invention thus comprises a reinforcer which is arranged at the inner side of each bead portion of the tire. The reinforcer comprises metal cords, for example steel cords. The bead filler extends beyond the end tip of the reinforcer. Thus, risk of damage of the carcass by the reinforcer can be reduced. 
     The bead filler is made of a soft rubber compound with an IHRD hardness lower than 80, preferably between 75 and 79. It has been found that the soft rubber compound of the bead filler contributes to give better comfort properties to the runflat tire. In particular, the use of a soft compound for the bead filler effects better dampening properties which provide better comfort and noise properties. 
     The metallic reinforcer improves the handling properties of the runflat tire, since the torsional stiffness of the tire is improved. Positioning of the reinforcer at the inner side of the bead provides a direct transmission of the forces from the carcass to the rim which further increases the torsional stiffness. 
     The runflat tire according to the invention features higher runflat performance, less rolling resistance and improved comfort properties. 
     The reinforcer is preferably directly connected to an inner portion of the carcass. Owing to the direct contact between the reinforcer and the inner carcass, the torsional stiffness of the tire is increased. 
     In an alternative embodiment the reinforcer is arranged between two carcass layers. This embodiment also provides an increase of the torsional stiffness due to the direct contact between the reinforcer and the carcass layers. 
     Other features and advantages of the present invention will become apparent from the following more detailed description of the embodiments, which describe, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-section of a vehicle tire according to the invention; 
         FIG. 2  is an enlarged view of the sidewall region of  FIG. 1 ; 
         FIG. 3  is a schematic cross-section through a second embodiment of the invention; 
         FIG. 4  is an enlarged view of the sidewall according to  FIG. 3 ; and 
         FIG. 5  is a table with test results. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to  FIGS. 1 and 2 , a pneumatic tire  10  according to the invention comprises a tread strip  19  and a pair of sidewalls  20 , connected to the tread strip  19 . A carcass  11  is associated with two bead cores  15  which are arranged in a bead portion of the tire  10 . The carcass  11  is turned up around the bead rings  15  as can be taken from  FIG. 2 . Thus, the carcass  11  comprises two portions  11   a,    11   b  in the bead portion and in the area of the sidewalls  20 . In the bead portion of the tire  10  the inner carcass portion  11   a  and the outer carcass portion  11   b  are separated by the bead core  15  and the bead filler  14 . The carcass portions  11   a,    11   b  join together at a ply join  12 . In the area of the sidewall  20  the carcass portions  11   a  and  11   b  are directly connected with each other. The outer carcass portion  11   b  leads up to a belt structure  18  which is arranged between the carcass  11  and the tread strip  19 . Typically, the belt structure  18  comprises a pair of layers including metal (e.g. steel) cords, inclined with respect to the equatorial plane of the tyre. A further radially outer layer comprising textile, e.g. nylon, cords can also be advantageously provided in the belt structure  18 , the textile cords being arranged at a small angle with respect to the equatorial plane of the tyre (e.g. within 5°). 
     A runflat sidewall reinforcement  17  is provided at the inner side of each of the sidewalls  20 . The runflat reinforcement  17 , which adopts a supporting function when the tire is deflated, is arranged at the axial inner side of the sidewall  20  and is limited by an inner liner  21 . At the axial outer side the runflat reinforcement  17  is directly connected to the carcass  11 . 
     A reinforcer  13  comprising steel cords is directly connected with the outer wall of the inner carcass portion  11   a.  The reinforcer  13  extends from about the bead core  15  towards the sidewall  20 , in contact with bead filler  14 . In particular, the end portion  13   a  of the reinforcer  13  is covered by a portion of the bead filler  14 , which extends up to the ply join  12 . Thus, the end portion  13   a  of the reinforcer  13  is practically embedded in the bead filler  14 . In this way, damage to the ply join  12  of the carcass  11  by the reinforcer  13  is avoided. The reinforcer  13  preferably has a thickness comprised between 0.9 and 1.5 mm. The reinforcer consists eg. of steelcord 3×0.22 HT F75 (HT=high tensile, F 75=75 single cords 3×0.22 over a length of 10 cm) which is embedded in a rubber composition. The reinforcer  13  may comprise one layer. The reinforcer cords may be preferably arranged at an angle of 18° to 35°, preferably 22°, with respect to the radial direction of the tire  10 . 
     The bead filler  14  is made of a soft rubber compound with an IHRD hardness, lower than 80, preferably between 75 and 79, e.g. 78. The IRHD measurement (international rubber hardness degree) is carried out in accordance with the test method DIN 53519 sheet 2 at 23° C. In a preferred embodiment, the bead filler  14  comprises a rubber mixture with a NR/BR (Natural Rubber/Butadiene Rubber) ratio of 80 to 20. It has been found that the soft compound of the bead filler  14  effects better dampening properties which provide better comfort and noise properties of the tire. 
     The runflat sidewall reinforcement  17  comprises a rubber mixture having an IHRD hardness substantially similar to that of the bead filler  14  or slightly lower, e.g. of 75. The bead core  15  is typically embedded in a bead protection portion  16  having similar hardness to the bead filler  14 . 
     The radial height R of the reinforcer  13  may be comprised between 30 and 45 mm, depending on the size of the tire. The radial height F of the bead filler  14  may be comprised between 35 and 55 mm, depending on the size of the tire. Thus, the bead filler  14  extends beyond the tip  13   a  of the reinforcer  13  by about 5 mm to 15 mm. The ratio bead filler height F/sidewall height H may be comprised between 0.35 and 0.50. The ratio reinforcement height R/filler height f may be comprised between 0.65 and 0.90, depending on the size of the tire. 
       FIGS. 3 and 4  show a second embodiment of the present invention. In the following description the same reference numbers are used as already introduced in connection with the description of the embodiment of  FIGS. 1 and 2 . 
     Referring to  FIG. 3 , the tire  30  comprises a carcass  11  which has a double-layer structure. The carcass  11  comprises a first layer  11   c  and a second layer  11   d.  Both layers  11   c,    11   d  of the carcass  11  are turned up around the bead core  15 . The first carcass layer  11   c  extends up to a first ply end  23  positioned in the middle portion of the sidewall  20 . The second carcass layer  11   d  extends up to a second ply end  22  positioned close to the radially outer portion of the bead core  15 . 
     In this embodiment, the reinforcer  13  is positioned between the carcass layers  11   c  and  11   d.  The bead filler  14  extends from the bead core  15  towards the second ply end  23  thus extending beyond the end portion  13   a  of the reinforcer  13 . Thus, damage by the end portion  13   a  is avoided. 
     The bead filler  14  and the runflat reinforcement  17  have the same properties as the tire  10  shown in  FIGS. 1 and 2 . 
     Owing to the double layer construction of the carcass  11  the tire  30  is able to take up higher loads. 
     The construction and effects of the pneumatic tire according to the invention will be further explained with reference to the following test results. 
     Test Results 
     Comparative tests were carried out with tires of different construction. In all test the tires had a tire size of 225/45 RF 91 W and a tread pattern Pirelli PZERO. 
     Variant 1 (Prior Art) 
     Construction: 2-ply carcass below tread strip, 2-ply carcass in sidewall; 
     Bead filler made of hard rubber with IHRD hardness of 98; no reinforcer 
     Variant 2 (Embodiment according to  FIGS. 1 and 2 ) 
     Construction: 1-ply carcass below tread strip, 2-ply carcass in sidewall; internal reinforcer comprising steel cords; bead filler made of soft rubber compound with IHRD hardness of 78; 
     Variant 3 (Embodiment according to  FIGS. 3 and 4 ) 
     Construction: 2-ply carcass below tread strip; 2-ply carcass in sidewall; internal reinforcer comprising steel cords embedded between two carcass plies; bead filler made of soft rubber compound with IHRD hardness of 78. 
     The same sidewall runflat reinforcement was used in the three tires, having IHRD hardness of 75. 
     The runflat performance was tested with the following test parameters:
         Inflation: 0 psi, valve core removed   Load: 470 Kg   Speed: 80 km/h   Duration: To tire failure (excessive vibration)       

     The tire properties as to steering, straight running, curve characteristics, damping and noise of the inflated tire are subjective results determined in driving tests by test drivers. 
     The test results can be gathered from the table according to  FIG. 5 . The evaluation is made on a scale from 0 to 10 wherein 10 is the best grade. 
     As can be seen, in Variant 2 the runflat performance is nearly three times higher than in the prior art tire according to Variant 1, The rolling resistance which is proportional to the consumption is reduced. Furthermore the subjective tire properties as to steering, straight running, curve characteristics, damping and noise are improved. The tire according to Variant 3 also shows significantly better properties than the prior art tire according to Variant 1. 
     As explained above in detail, the pneumatic tires  10 ,  30  comprise an internal reinforcer  13  comprising metal, e.g. steel, cords. The internal reinforcer  13  improves the handling properties of the inflated tire since the torsional stiffness of the tire is improved. Use of a soft compound for the bead filler  14  effects better dampening properties which provide better comfort and noise properties of the inflated tire. Runflat performance of the deflated tire is high since the reinforcer  13  is covered by the bead filler  14  and embedded in the same. Thus, any damage of the carcass by the end portion  13   a  of the reinforcer  13  is avoided.