Patent Publication Number: US-2023138951-A1

Title: Pneumatic tire

Description:
RELATED APPLICATIONS 
     This application claims the benefit of foreign priority to Japanese Patent Application No. JP2021-180451, filed Nov. 4, 2021, which is incorporated by reference in its entirety. 
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to a pneumatic tire. 
     BACKGROUND OF THE DISCLOSURE 
     The following Patent Document 1 discloses a pneumatic tire expected to have improved durability. A bead apex rubber is arranged in each bead portion in the pneumatic tire. The bead apex rubber includes a main body apex extending from the outer surface of the bead core in the tire radial direction and an outer apex arranged outside the main body apex in the tire axial direction. 
     PATENT DOCUMENT 
     
         
         [Patent Document 1] Japanese Unexamined Patent Application Publication 2020-93755 
       
    
     SUMMARY OF THE DISCLOSURE 
     As described above, the pneumatic tire having a so-called outer apex structure has room for improvement in the durability of the bead portion under high load conditions. 
     The present disclosure has been made in view of the above circumstances and has a main object to improve bead durability in a pneumatic tire having an outer apex structure. 
     In one aspect of the present disclosure, a pneumatic tire includes a pair of bead portions, a pair of bead cores each disposed in a respective one of the bead portions, and a carcass extending between the pair of bead cores. The carcass includes a carcass ply including a main portion extending between the pair of bead cores and a pair of turn-up portions each turned up around a respective one of the bead cores from inside to outside of the tire in a tire axial direction and extending outwardly in a tire radial direction. In at least one of the pair of bead portions, a reinforcing rubber layer is disposed outwardly and adjacently in the tire axial direction of the turn-up portion. The reinforcing rubber layer includes a first rubber layer and a second rubber layer arranged outwardly in the tire axial direction of the first rubber layer. A loss tangent tan δ1 of the first rubber layer is smaller than a loss tangent tan δ2 of the second rubber layer. 
    
    
     
       SUMMARY OF THE DISCLOSURE 
         FIG.  1    is a tire meridian cross-sectional view of a pneumatic tire according to an embodiment of the present disclosure; and 
         FIG.  2    is an enlarged view of a bead portion of  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. 
       FIG.  1    is a tire meridian cross-sectional view including the tire axis of a pneumatic tire (hereafter, it may be simply referred to as “tire”)  1  under a normal state according to an embodiment of the present disclosure. The present disclosure, for example, may be used in tires  1  for commercial vehicles and light trucks. However, the present disclosure may also be used for tires for passenger cars or heavy-duty vehicles. 
     As used herein, the “normal state” is such that the tire  1  is mounted onto a standard wheel rim (not illustrated) with a standard pressure but loaded with no tire load. Unless otherwise noted, dimensions of portions of the tire  1  are values measured under the normal state. 
     As used herein, the “standard wheel rim” is a wheel rim officially approved for each tire by standards organizations on which the tire is based, wherein the standard wheel rim is the “standard rim” specified in JATMA, the “Design Rim” in TRA, and the “Measuring Rim” in ETRTO, for example. 
     As used herein, the “standard pressure” is a standard pressure officially approved for each tire by standards organizations on which the tire is based, wherein the standard pressure is the “maximum air pressure” in JATMA, the maximum pressure given in the “Tire Load Limits at Various Cold Inflation Pressures” table in TRA, and the “Inflation Pressure” in ETRTO, for example. 
     As illustrated in  FIG.  1   , the tire  1  according to the present embodiment includes a pair of bead portions  4 , a pair of bead cores  5  each disposed in a respective one of the bead portions  4 , and a carcass extending between the bead cores  5 . 
     The carcass  6  includes a carcass ply  6 A which includes a main portion  6   a  extending between the bead cores  5  and a pair of turn-up portions  6   b  each turned up around a respective one of the bead cores  5  from inside to outside of the tire in the tire axial direction and extending outwardly in the tire radial direction. The carcass  6 , in the present embodiment, is composed of two carcass plies  6 A and  6 B which are superimposed with each other in the tire radial direction. Each carcass ply  6 A and  6 B includes the main portion  6   a  and the pair of turn-up portions  6   b . The carcass  6 , for example, may be composed of a single carcass ply  6 A (not illustrated). 
     In at least one of the pair of bead portions  4 , a reinforcing rubber layer  10  is disposed outwardly and adjacently in the tire axial direction of the turn-up portion  6   b . The reinforcing rubber layer  10  can enhance the rigidity of the bead portion  4 , improving durability thereof. 
     In the present embodiment, the reinforcing rubber layer  10  is arranged in each bead portion  4 . 
     Each reinforcing rubber layer  10 , for example, is adjacent to an outer surface in the tire axial direction of each turn-up portion  6   b  of the radially inner carcass ply  6 A. 
     Each reinforcing rubber layer  10  includes a first rubber layer  11  and a second rubber layer  12  arranged outwardly in the tire axial direction of the first rubber layer  11 . Further, a loss tangent tan δ1 of the first rubber layer  11  is smaller than a loss tangent tan δ2 of the second rubber layer  12 . Thus, the first rubber layer  11  has a small hysteresis loss, which can suppress its heat generation. This can prevent the carcass plies  6 A and  6 B from being damaged by heat. In addition, the second rubber layer  12  has the basic effect of suppressing the distortion of the bead portions  4 . Thus, the durability performance of the tire can be greatly improved. 
     In order to effectively exert the above-mentioned effects, the loss tangent tan δ1, for example, is preferably equal to or more than 0.07, more preferably equal to or more than 0.12, but preferably equal to or less than 0.17, more preferably equal to or less than 0.14. For example, the loss tangent tan δ1 is preferably equal to or more than 60% of the loss tangent tan δ2, more preferably equal to or more than 70%, but preferably equal to or less than 95% of the loss tangent tan δ2, more preferably equal to or less than 90%. 
     In this specification, loss tangent tan δ and complex elastic modulus E*described later are values measured under the following conditions using a viscoelastic spectrometer in accordance with the provisions of JIS K6394 “Rubber, vulcanized or thermoplastic-determination of dynamic properties-General guidance”.
         Initial distortion: 10%   Amplitude: plus/minus 2%   Frequency: 10 Hz   Deformation mode: Tension   Temperature: 70 degrees C.   Viscoelastic spectrometer: GABO “Iplexer” (registered trademark)       

     Preferably, a complex elastic modulus E*2 of the second rubber layer  12  is larger than a complex elastic modulus E*1 of the first rubber layer  11 . As a result, the rigidity of the second rubber layer  12 , which is located relatively outside in the tire axial direction, can be increased, the bead distortion can be suppressed under high load conditions, and the bead durability can be improved. When the complex elastic modulus E*2 of the second rubber layer  12  is excessively larger than the complex elastic modulus E*1 of the first rubber layer  11 , the heat generated by the second rubber layer  12  may be conducted to the carcass plies  6 A and  6 B via the first rubber layer  11 . Thus, the complex elastic modulus E*2 is preferably equal to or more than 120% of the complex elastic modulus E*l, more preferably equal to or more than 130%, but preferably equal to or less than 200% of the complex elastic modulus E*1, more preferably equal to or less than 190%. Although not particularly limited, the complex elastic modulus E*1 is preferably equal to or more than 20 MPa, more preferably equal to or more than 30 MPa, but preferably equal to or less than 110 MPa, more preferably equal to or less than 80 MPa. 
     Preferably, the innermost end  10   i  in the tire radial direction of each reinforcing rubber layer  10  is located within 10 mm in the tire radial direction from the outermost end  5   e  of the bead core  5  in the tire radial direction. When the innermost end  10   i  of the reinforcing rubber layer  10  is located more than 10 mm outward in the tire radial direction from the outermost end  5   e  of the bead core  5 , it may be difficult to suppress the distortion of the bead part  4 . When the innermost end  10   i  of the reinforcing rubber layer  10  is located more than 10 mm inward in the tire radial direction from the outermost end  5   e  of the bead core  5 , it may not contribute to the improvement of the rigidity of the bead portion  4 , and for example, the mass of the tire  1  may increase and the rim assembly property may decrease. 
     Preferably, a height H 1  in the tire radial direction from the bead baseline BL to an outermost end  10   e  of the reinforcing rubber layer  10  is equal to or more than 25% of the tire cross-sectional height H. As a result, the rigidity of a portion where the bead portion  4  is greatly distorted can be surely increased. When the height H 1  is excessively large, it may lead to an increase in tire mass, for example. From this point of view, the height H 1  is more preferably equal to or more than 30%, but preferably equal to or less than 50%, more preferably equal to or less than 45% of the tire cross-sectional height H. 
     As used herein, the “bead baseline BL” is the tire axial line passing through the rim diameter (see JATMA) position determined by the standard based on the tire  1 . Also, the “tire cross-sectional height H” is the distance in the tire radial direction from the bead baseline BL to the outermost position of the tire in the tire radial direction. 
       FIG.  2    is an enlarged view of one of the bead portions  4  of  FIG.  1   . As illustrated in  FIG.  2   , the first rubber layer  11  and the second rubber layer  12 , for example, are formed of sheet-shaped rubber members  13 . In other words, the reinforcing rubber layer  10  according to the present embodiment is formed as a laminated body  13 R in which the sheet-shaped rubber members  13  are laminated in the tire axial direction. Such a reinforcing rubber layer  10  can increase the rigidity of the bead portion  4  and suppress a large increase in mass. 
     Each of the sheet-shaped rubber members  13 , for example, has a constant thickness T in more than 90% of its length. The reinforcing rubber layer  10  formed of such rubber members  13  can be able to have high rigidity so that the durability of the bead portion  4  can be improved. As used herein, the above-mentioned “constant thickness” includes a portion where the thickness changes by 0.2 mm/mm or less in the direction orthogonal to the thickness of the sheet-shaped rubber member  13 . 
     Preferably, a thickness T 2  of the second rubber layer  12  is greater than a thickness T 1  of the first rubber layer  11 . As a result, the reinforcing rubber layer  10  has greater rigidity, and thus the durability performance can further be improved. Although not particularly limited, the thickness T 2  of the second rubber layer  12  is preferably equal to or more than 130% of the thickness T 1  of the first rubber layer  11 , more preferably equal to or more than 140%, but preferably equal to or less than 170% of the thickness T 1  of the first rubber layer  11 , more preferably equal to or less than 160%. The thickness T 2  of the second rubber layer  12  is preferably equal to or more than 1.0 mm, more preferably equal to or more than 1.2 mm, but preferably equal to or less than 2.5 mm, more preferably equal to or less than 2.0 mm. 
     Preferably, the outermost end  11   e  in the tire radial direction of the first rubber layer  11  is located outwardly in the tire radial direction of the outermost end  12   e  in the tire radial direction of the second rubber layer  12 . Such a first rubber layer  11  can effectively suppress the heat generated by the second rubber layer  12  from being conducted to the carcass  6 . A separation distance Ha in the tire radial direction between the outermost end  11   e  of the first rubber layer  11  and the outermost end  12   e  of the second rubber layer  12  is preferably equal to or more than 2% of a tire radial length H 2  of the first rubber layer  11 , more preferably equal to or more than 5%, but preferably equal to or less than 20% of the tire radial length H 2  of the first rubber layer  11 , more preferably equal to or less than 10%. 
     In the present embodiment, in order to exert the same effect, the innermost end  11   i  in the tire radial direction of the first rubber layer  11  is located inwardly in the tire radial direction of the innermost end  12   i  of the second rubber layer  12 . A separation distance Hb in the tire radial direction between the innermost end  11   i  of the first rubber layer  11  and the innermost end  12   i  of the second rubber layer  12  is preferably equal to or more than 2% of the tire radial length H 2  of the first rubber layer  11 , more preferably equal to or more than 5%, but preferably equal to or less than 20% of the tire radial length H 2  of the first rubber layer  11 , more preferably equal to or less than 10%. 
     Each bead portion  4  according to the present embodiment is provided with a bead apex rubber  8  extending outwardly in the tire radial direction from the bead core  5  and a clinch rubber  4 G arranged outwardly in the axial direction of the reinforcing rubber layer  10 . In addition, a sidewall rubber  3 G is arranged outwardly in the tire axial direction of the clinch rubber  4 G, for example. The sidewall rubber  3 G and the clinch rubber  4 G form an outer surface of the tire. 
     In each bead portion  4 , the bead apex rubber  8  is formed in a triangular shape, for example, in a tire meridian cross-sectional view. Although not particularly limited, the first rubber layer  11  and the second rubber layer  12  are arranged at the height position in the tire radial direction of the outermost end  8   e  in the tire radial direction of the bead apex rubber  8 . 
     Preferably, a complex elastic modulus E*3 of each bead apex rubber  8 , for example, is larger than the complex elastic modulus E*1 of the first rubber layer  11 . Preferably, the complex elastic modulus E*3 of each bead apex rubber  8 , for example, is smaller than the complex elastic modulus E*2 of the second rubber layer  12 . 
     The complex elastic modulus E*of sidewall rubber  3 G and clinch rubber  4 G are both smaller than the complex elastic modulus E*1 of the first rubber layer  11 . This can be helpful to provide basic ride comfort performance. 
     Although an embodiment of the present disclosure has been described in detail above, the present disclosure is not limited to the specific embodiment described above but may be modified and carried out in various aspects. 
     Example 
     Some kinds of pneumatic tires with the basic structure shown in  FIG.  1    were prepared based on the specifications in Table 1. Then, the durability performance of each test tire was tested. The common specifications of each test tire and the test method are as follows. 
     Durability Test: 
     Each test tire was run on a drum tester under the following conditions, and the mileage until damage occurred in either one of the bead portions was measured. The test results were shown in Table 1 using an index with Comparative Example 1 as 100. The larger the value, the better.
         Tire size: 225/85R16   Rim: 6.0 J   Internal pressure: 220 kPa   Load: 19.84 kN   tan δ1:0.13   E*1:30 MPa       

     The test results are shown in Table 1. In Table 1, “A” indicates a separation distance in the tire radial direction between the innermost end of the reinforcing rubber layer and the outermost end of the bead core in each bead portion, and the outermost end of the bead core is located outwardly in the tire radial direction than the innermost end of the reinforcing rubber layer. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Comparative 
                 Comparative 
                   
                   
                   
                   
                   
                   
               
               
                   
                 ex. 1 
                 ex. 2 
                 ex. 3 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ex. 6 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Number of rubber sheets 
                 1 
                 2 
                 2 
                 2 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 of reinforcing rubber layer 
               
               
                 Ratio tanδ1/tanδ2 (%) 
                 — 
                 100 
                 125 
                 75 
                 90 
                 75 
                 75 
                 75 
                 75 
               
               
                 Ratio E*2/E*1 (%) 
                 — 
                 100 
                 80 
                 180 
                 180 
                 130 
                 180 
                 180 
                 180 
               
               
                 Separation distance A (mm) 
                 8 
                 8 
                 8 
                 8 
                 8 
                 8 
                 12 
                 8 
                 8 
               
               
                 Ratio H1/H (%) 
                 30 
                 30 
                 30 
                 30 
                 30 
                 30 
                 30 
                 20 
                 20 
               
               
                 First rubber layer 
                 1.5 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.5 
               
               
                 thickness T1 (mm) 
               
               
                 Second rubber layer 
                 — 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
                 1.0 
               
               
                 thickness T2 (mm) 
               
               
                 T1 + T2 (mm) 
                 1.5 
                 2.5 
                 2.5 
                 2.5 
                 2.5 
                 2.5 
                 2.5 
                 2.5 
                 2.5 
               
               
                 Durability test [index] 
                 100 
                 110 
                 105 
                 150 
                 120 
                 125 
                 130 
                 130 
                 140 
               
               
                   
               
            
           
         
       
     
     As a result of the test, it is confirmed that the tires of the examples have improved durability performance as compared to the tires of the comparative examples. 
     [Additional Notes] 
     The present disclosure includes the following aspects. 
     [Note 1] 
     A pneumatic tire comprising: 
     a pair of bead portions: 
     a pair of bead cores each disposed in a respective one of the bead portions; and 
     a carcass extending between the pair of bead cores, wherein 
     the carcass comprises a carcass ply comprising a main portion extending between the pair of bead cores and a pair of turn-up portions each turned up around a respective one of the bead cores from inside to outside of the tire in a tire axial direction and extending outwardly in a tire radial direction, 
     in at least one of the pair of bead portions, a reinforcing rubber layer is disposed outwardly and adjacently in the tire axial direction of the turn-up portion, 
     the reinforcing rubber layer comprises a first rubber layer and a second rubber layer arranged outwardly in the tire axial direction of the first rubber layer, and 
     a loss tangent tan δ1 of the first rubber layer is smaller than a loss tangent tan δ2 of the second rubber layer. 
     [Note 2] 
     The pneumatic tire according to note 1, wherein 
     a complex elastic modulus E*2 of the second rubber layer is larger than a complex elastic modulus E*1 of the first rubber layer. 
     [Note 3] 
     The pneumatic tire according to note 2, wherein 
     the complex elastic modulus E*2 of the second rubber layer is equal to or more than 150% of the complex elastic modulus E*1 of the first rubber layer. 
     [Note 4] 
     The pneumatic tire according to any one of notes 1 to 3, wherein an innermost end in the tire radial direction of the reinforcing rubber layer is located within 10 mm in the tire radial direction from an outermost end of the bead core in the tire radial direction. 
     [Note 5] 
     The pneumatic tire according to any one of notes 1 to 4, wherein 
     a height in the tire radial direction from a bead baseline to an outermost end of the reinforcing rubber layer is equal to or more than 25% of a tire cross-sectional height. 
     [Note 6] 
     The pneumatic tire according to any one of notes 1 to 5, wherein a thickness of the second rubber layer is greater than a thickness of the first rubber layer. 
     [Note 7] 
     The pneumatic tire according to any one of notes 1 to 6, wherein 
     an outermost end in the tire radial direction of the first rubber layer is located outwardly in the tire radial direction of an outermost end in the tire radial direction of the second rubber layer. 
     [Note 8] 
     The pneumatic tire according to any one of notes 1 to 7, wherein 
     an innermost end in the tire radial direction of the first rubber layer is located inwardly in the tire radial direction of an innermost end in the tire radial direction of the second rubber layer.