Patent Publication Number: US-2016221396-A1

Title: Tire

Description:
TECHNICAL FIELD 
     The present invention relates to a tire including a tread portion having a ground contacting tread surface. 
     BACKGROUND ART 
     A tire is known in the art which includes a pair of bead portions assembled to a rim flange, a pair of side portions contiguous with the pair of bead portions on the outer side in a tire radial direction, and a tread portion having a ground contacting tread surface that comes into contact with a road surface. 
     Various methods for designing the contour of the tread portion (hereinafter referred to as a “tread profile”) in a cross-section taken along a tire width direction and a tire radial direction have been studied. For example, Patent Literature 1 discloses a design method for a tread profile that is intended to improve ride comfort and handling stability. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2005-53260 A 
     SUMMARY OF INVENTION 
     However, there is room for improvement in the design method for a tread profile in terms of wear resistance and uneven wear resistance. 
     Accordingly, the present invention has been made to solve the above problem and is directed to a tire capable of improving wear resistance and uneven wear resistance. 
     A tire according to the first feature includes a tread portion having a ground contacting tread surface that comes into contact with a road surface. The ground contacting tread surface includes a pair of ground contacting ends forming outermost ends in a tire width direction. The tread portion includes a shoulder region having a range from one of the pair of ground contacting ends to 0.20W to 0.30W inward of the one ground contacting end in the tire width direction where a distance between the pair of ground contacting ends is a ground contact width W. A tread profile that is a contour of the shoulder region is defined by N radii of curvature SR(n)(n=1 to N) in order from inner side in the tire width direction in a cross-section taken along the tire width direction and a tire radial direction. The above N and the radii of curvature SR(n) satisfy a condition of: N≧3 and SR(n)/SR(n+1)≦3. 
     In the first feature, the shoulder region includes an inner shoulder end forming an innermost end in the tire width direction. The tread portion includes a center region having a range from a tire equator line to the inner shoulder end. A tread profile that is a contour of the center region is defined by M radii of curvature CR(n) (n=1 to M) in order of proximity to the tire equator line in the cross-section taken along the tire width direction and the tire radial direction. SR( 1 ) and CR(M) satisfy a condition CR(M)/SR( 1 )≧5, where SR( 1 ) defines an innermost portion in the tire width direction of the radii of curvature SR( 1 ) to SR(N) and CR(M) defines an outermost portion in the tire width direction of the radii of curvature CR( 1 ) to CR(M). 
     In the first feature, the tread portion includes an out-of-shoulder region having a range from one of the pair of ground contacting ends to 0.05W outward of the one ground contacting end in the tire width direction. A tread profile that is a contour of the out-of-shoulder region is defined by L radii of curvature SR(n) (n=N + 1 to N+L) in order from inner side in the tire width direction in the cross-section taken along the tire width direction and the tire radial direction. The radii of curvature SR(n) satisfy a condition SR(n)/SR(n+1)≦3. 
     According to the present invention, it is possible to provide a tire capable of improving wear resistance and uneven wear resistance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating part of a tire  100  according to a first embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a susceptor according to an embodiment of the present invention will be described with reference to the drawings. Note that, in the following description of the drawings, same or similar reference signs denote same or similar elements and portions. 
     It is to be noted that the drawings are schematic and the dimensions or ratios are different from actual values. Accordingly, specific dimensions and the like should be determined by taking the following description into consideration. Needless to say, a relationship or a ratio of mutual dimensions may differ among the drawings. 
     Overview of Embodiment 
     A tire according to an embodiment includes a tread portion having a ground contacting tread surface that comes into contact with a road surface. The ground contacting tread surface includes a pair of ground contacting ends forming outermost ends in a tire width direction. The tread portion includes a shoulder region having a range from one of the pair of ground contacting ends to 0.20W to 0.30W inward of the one ground contacting end in the tire width direction where a distance between the pair of ground contacting ends is a ground contact width W. A tread profile that is a contour of the shoulder region is defined by N radii of curvature SR(n) (n=1 to N) in order from inner side in the tire width direction in a cross-section taken along the tire width direction and a tire radial direction. The above N and the radii of curvature SR(n) satisfy the condition of: N≧3 and SR(n)/SR(n+1)≦3. 
     In this embodiment, N and the radii of curvature SR(n) satisfy the condition of: N≧3 and SR(n)/SR(n+1)≦3. That is, the surface (i.e. tread profile) of the shoulder region in the tire radial direction is gradually varied along the tire width direction in the cross-section taken along the tire width direction and the tire radial direction. This prevents or reduces the deviation of a ground contact pressure between the shoulder region and the road surface even when the shoulder region is deformed during rotation of the tire, and wear resistance and uneven wear resistance can be improved. 
     First Embodiment 
     Structure of Tire 
     A tire according to a first embodiment is described below.  FIG. 1  is a view illustrating part of a tire  100  according to the first embodiment. In particular,  FIG. 1  illustrates a partial cross-section of the tire  100  taken along a tire width direction TW and a tire radial direction TR. 
     The tire  100  includes a pair of bead portions assembled to a rim flange, side portions contiguous with the pair of bead portions on the outer side in the tire radial direction TR, and a tread portion having a ground contacting tread surface that comes into contact with a road surface. 
     Specifically, the tire  100  includes a tread portion  10  having a ground contacting tread surface as illustrated in  FIG. 1 . The tread portion  10  includes center regions  10 C, shoulder regions  10 S, and out-of-shoulder regions  10 Sout. 
     Here, the ground contacting tread surface is a surface of the tread portion  10  in contact with a road surface under the condition that the tire  100  is mounted on a normal rim as defined by JATMA, the internal pressure of the tire  100  is a normal internal pressure as defined by JATMA, a load applied to the tire  100  is 80% of the maximum load capacity as defined by JATMA, and a camber angle is 0 degrees. The ground contacting tread surface includes a pair of ground contacting ends  11 E,  11 E forming outermost ends in the tire width direction TW. A distance between the pair of ground contacting ends  11 E,  11 E, i.e., a ground contact width of the ground contacting tread surface in the tire width direction TW, is denoted by “W”. 
     The center region  10 C is provided on the inner side of the shoulder region  10 S in the tire width direction TW. Specifically, the center region  10 C has a range from a tire equator line CL to an inner shoulder end  11 Sin. 
     The shoulder region  10 S is provided on the outer side of the center region  10 C in the tire width direction TW. Specifically, the shoulder region  10 S has a range from the ground contacting end  11 E to 0.20W to 0.30W inward of the ground contacting end  11 E in the tire width direction TW. The shoulder region  10 S includes the inner shoulder end  11 Sin forming an innermost end in the tire width direction TW. In the shoulder region  10 S, an outermost end in the tire width direction TW is the ground contacting end  11 E. 
     The out-of-shoulder region  10 Sout is provided on the outer side of the center region  10 C in the tire width direction TW. Specifically, the out-of-shoulder region  10 Sout has a range from the ground contacting end  11 E to 0.05W outward of the ground contacting end  11 E in the tire width direction TW. 
     Tread Profile 
     A tread profile according to the first embodiment is described below. The tread profile means a contour (i.e. surface shape) of the tread portion  10  in the cross-section taken along the tire width direction TW and the tire radial direction TR. However, it should be noted that the tread profile means an outline of the tread portion  10  assuming the tread portion  10  has no grooves. 
     In the first embodiment, the profile of the center region  10 C defined by M radii of curvature CR(n) (n=1 to M) in order of proximity to the tire equator line CL.  FIG. 1  shows CR( 1 ) and CR( 2 ) as an example of the radii of curvature CR(n). M is an integer and it is sufficient if M satisfy the condition M≧1. The greater the value of n, a portion defined by CR(n) is located further outward in the tire width direction TW. 
     The profile of the shoulder region  10 S is defined by N radii of curvature SR(n) (n=1 to N) in order from inner side in the tire width direction TW.  FIG. 1  shows SR( 1 ), SR( 2 ), and SR( 3 ) as an example of the radii of curvature SR(n). N is an integer and it is sufficient if N satisfy the condition N≧3. The greater the value of n, a portion defined by SR(n) is located further outward in the tire width direction TW. 
     The profile of the out-of-shoulder region  10 Sout is defined by L radii of curvature SR(n) (n=N+1 to N+L).  FIG. 1  shows SR 4  and SR 5  as an example of the radii of curvature SR(n) in order from inner side in the tire width direction TW. L is an integer and it is sufficient if L satisfy the condition L≧1. The greater the value of n, a portion defined by SR(n) is located further outward in the tire width direction TW. 
     In such a case, first, the profile of the shoulder region  10 S satisfies the following condition. Specifically, N and the radii of curvature SR(n) satisfy condition (1): N≧3 and SR(n)/SR(n+1)≦3. In the case illustrated in  FIG. 1 , for example, the condition of SR( 1 )/SR( 2 )≦3 and SR( 2 )/SR( 3 )≦3 is satisfied. 
     Second, the profile of the center region  10 C preferably satisfies the following condition. Specifically, SR( 1 ) and CR(M) preferably satisfy condition (2): CR(M)/SR( 1 )≧5, where SR( 1 ) defines an innermost portion in the tire width direction of the radii of curvature SR( 1 ) to SR(N) and CR(M) defines an outermost portion in the tire width direction of the radii of curvature CR( 1 ) to CR(M). In the case illustrated in  FIG. 1 , for example, the condition CR( 2 )/SR( 1 )≧5 is satisfied. 
     Third, the profile of the out-of-shoulder region  10 Sout preferably satisfies the following condition. Specifically, the radii of curvature SR(n) preferably satisfy condition (3): SR(n)/SR(n+1)≦3. In the case illustrated in  FIG. 1 , for example, the condition SR( 4 )/SR( 5 )≦3 is satisfied. 
     Note that if the condition (3) is satisfied, SR(N+1) and SR(N) also satisfy the condition SR(N)/SR(N+1)≦3, where SR(N+1) defines an innermost portion in the tire width direction of the radii of curvature SR(N+1) to SR(N+L) and SR(N) defines an outermost portion in the tire width direction of the radii of curvature SR( 1 ) to SR(N). In the case illustrated in  FIG. 1 , for example, the condition SR( 3 )/SR( 4 )≦3 is satisfied. 
     In the first embodiment, it should be noted that portions adjacent to each other share a tangent at the boundary of the portions adjacent to each other of portions defined by the radii of curvature (SR(n) or CR(n)). 
     Preferably, SR(n) is in a range of 10 to 500 mm in the first embodiment. Preferably, CR(n) is in a range of 800 to 3000 mm. 
     Advantageous Effects 
     In the first embodiment, N and the radii of curvature SR(n) satisfy the condition (1) of N≧3 and SR(n)/SR(n+1)≦3. That is, the surface (i.e. tread profile) of the shoulder region  10 S in the tire radial direction TR is gradually varied along the tire width direction TW in the cross-section taken along the tire width direction TW and the tire radial direction TR. This prevents or reduces the deviation of a ground contact pressure between the shoulder region  10 S and a road surface even when the shoulder region  10 S is deformed during rotation of the tire  100 , and wear resistance and uneven wear resistance can be improved. 
     In the first embodiment, SR( 1 ) and CR(M) satisfy the condition (2) of CR(M)/SR( 1 )≧5, where SR( 1 ) defines the innermost portion in the tire width direction of the radii of curvature SR( 1 ) to SR(N) and CR(M) defines the outermost portion in the tire width direction of the radii of curvature CR( 1 ) to CR(M). That is, the tread profile of the entire tread portion  10  approaches a rectangular shape, thereby improving wear resistance. 
     In the first embodiment, the radii of curvature SR(n) also satisfy the condition (3) of SR(n)/SR(n+1)≦3 in the out-of-shoulder region  10 Sout. Therefore the deviation of the ground contact pressure between the shoulder region  10 S and the road surface is prevented or reduced even when a camber angle is large, and wear resistance and uneven wear resistance can be improved. 
     Evaluation Results 
     Evaluation results are described below. In particular, uneven wear resistance and wear resistance are evaluated by preparing samples (conventional example, Example 1, and Example 2) having different radii of curvature defining the tread profile. 
     Test conditions are as follows:
     Tire size: 245145R18   Load: 45 kN   Camber angle: −2 degrees   

     Under such conditions, a tire was mounted on a vehicle, the vehicle was caused to travel, and uneven wear resistance and wear resistance were measured. The uneven wear resistance and the wear resistance are represented by an index based on the amount of wear, and the index means that the greater the value of the index, the better result is obtained. 
     A ground contact width W, radii of curvature, and switching positions of the radii of curvature of each of the samples are shown in Tables 1 to 4, and the evaluation results are shown in Table 1. 
     Here, the ground contact width W is a width in the tire width direction of the surface of the tread in contact with a road surface under the condition that the tire is mounted on a normal rim as defined by JATMA, the internal pressure of the tire is a normal internal pressure as defined by JATMA, a load applied to the tire is 80% of the maximum load capacity as defined by JATMA, and a camber angle is 0 degrees. The radii of curvature define a tread profile. Of portions defined by the radii of curvature, portions adjacent to each other share a tangent at the boundary of the portions adjacent to each other. The switching position of a radius of curvature is a position at which the radius of curvature changes. The switching position of the radius of curvature is represented by the proportion (%) of a width from the tire equator line to the switching position to a width from the tire equator line to the ground contacting end. For example, L1 indicates a position at which R1 changes to R2. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Conventional 
                   
                   
               
               
                   
                 Example 
                 Example 1 
                 Example 2 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Ground Contact Width W (mm) 
                 179.5 
                 180.0 
                 186.3 
               
            
           
           
               
               
               
               
               
            
               
                 Shoulder 
                 Number of Radii of 
                 3 
                 18 
                 17 
               
               
                 Region 
                 Curvature 
               
               
                   
                 Radii of Curvature 
                 Table 2 
                 Table 3 
                 Table 4 
               
               
                   
                 (mm) 
               
               
                   
                 Satisfy Condition 
                 No 
                 Yes 
                 Yes 
               
               
                   
                 (1) 
               
               
                 Center 
                 Number of Radii of 
                 1 
                 1 
                 1 
               
               
                 Region 
                 Curvature 
               
               
                   
                 Radii of Curvature 
                 Table 2 
                 Table 3 
                 Table 4 
               
               
                   
                 (mm) 
               
               
                   
                 Satisfy Condition 
                 No 
                 No 
                 Yes 
               
               
                   
                 (2) 
               
               
                 Out-of- 
                 Number of Radii of 
                 — 
                 — 
                 2 
               
               
                 Shoulder 
                 Curvature 
               
               
                 Region 
                 Radii of Curvature 
                 Table 2 
                 Table 3 
                 Table 4 
               
               
                   
                 (mm) 
               
               
                   
                 Satisfy Condition 
                 No 
                 No 
                 Yes 
               
               
                   
                 (3) 
               
               
                 Evaluation 
                 Uneven Wear 
                 100 
                 130 
                 125 
               
               
                 Results 
                 Resistance 
               
               
                   
                 Wear Resistance 
                 100 
                 102 
                 125 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Conventional Example 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Radius of 
                   
                   
                   
               
               
                   
                 Curvature 
                   
                 Switching 
               
               
                   
                 [mm] 
                   
                 Position [%] 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Center Region 
                 R1 
                 700 
                 L1 
                 51.1 
               
               
                   
                 Shoulder Region 
                 R2 
                 300 
                 L2 
                 71.5 
               
               
                   
                   
                 R3 
                 300 
                 L3 
                 85.6 
               
               
                   
                   
                 R4 
                 35 
                 L4 
                 100 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Example 1 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Radius of 
                   
                 Switching 
                   
               
               
                   
                 Curvature [mm] 
                   
                 Position [%] 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Center Region 
                 R1 
                 700 
                 L1 
                 51 
               
               
                   
                 Shoulder Region 
                 R2 
                 300 
                 L2 
                 54 
               
               
                   
                   
                 R3 
                 284 
                 L3 
                 57 
               
               
                   
                   
                 R4 
                 269 
                 L4 
                 59 
               
               
                   
                   
                 R5 
                 253 
                 L5 
                 62 
               
               
                   
                   
                 R6 
                 238 
                 L6 
                 65 
               
               
                   
                   
                 R7 
                 222 
                 L7 
                 67 
               
               
                   
                   
                 R8 
                 206 
                 L8 
                 70 
               
               
                   
                   
                 R9 
                 191 
                 L9 
                 73 
               
               
                   
                   
                 R10 
                 175 
                 L10 
                 76 
               
               
                   
                   
                 R11 
                 160 
                 L11 
                 78 
               
               
                   
                   
                 R12 
                 144 
                 L12 
                 81 
               
               
                   
                   
                 R13 
                 129 
                 L13 
                 84 
               
               
                   
                   
                 R14 
                 113 
                 L14 
                 86 
               
               
                   
                   
                 R15 
                 97 
                 L15 
                 89 
               
               
                   
                   
                 R16 
                 82 
                 L16 
                 92 
               
               
                   
                   
                 R17 
                 66 
                 L17 
                 95 
               
               
                   
                   
                 R18 
                 51 
                 L18 
                 97 
               
               
                   
                   
                 R19 
                 35 
                 L19 
                 100 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Example 2 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Radius of 
                   
                 Switching 
                   
               
               
                   
                 Curvature [mm] 
                   
                 Position [%] 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Center Region 
                 R1 
                 1800 
                 L1 
                 45 
               
               
                   
                 Shoulder Region 
                 R2 
                 300 
                 L2 
                 48 
               
               
                   
                   
                 R3 
                 284 
                 L3 
                 52 
               
               
                   
                   
                 R4 
                 269 
                 L4 
                 55 
               
               
                   
                   
                 R5 
                 253 
                 L5 
                 58 
               
               
                   
                   
                 R6 
                 238 
                 L6 
                 62 
               
               
                   
                   
                 R7 
                 222 
                 L7 
                 65 
               
               
                   
                   
                 R8 
                 206 
                 L8 
                 68 
               
               
                   
                   
                 R9 
                 191 
                 L9 
                 72 
               
               
                   
                   
                 R10 
                 175 
                 L10 
                 75 
               
               
                   
                   
                 R11 
                 160 
                 L11 
                 78 
               
               
                   
                   
                 R12 
                 144 
                 L12 
                 82 
               
               
                   
                   
                 R13 
                 129 
                 L13 
                 85 
               
               
                   
                   
                 R14 
                 113 
                 L14 
                 88 
               
               
                   
                   
                 R15 
                 97 
                 L15 
                 92 
               
               
                   
                   
                 R16 
                 82 
                 L16 
                 95 
               
               
                   
                   
                 R17 
                 66 
                 L17 
                 98 
               
               
                   
                 Out-of-Shoulder 
                 R18 
                 51 
                 L18 
                 102 
               
               
                   
                 Region 
                 R19 
                 35 
                 L19 
                 105 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 1, good results have been obtained with respect to both uneven wear resistance and wear resistance in Examples 1 and 2 where the condition (1) of N≧3 and SR(n)/SR(n+1)≦3 is satisfied, as compared with the conventional example. A good result has been obtained with respect to the wear resistance in Example 2 where the condition (2) of CR(M)/SR( 1 )≧5 is satisfied, as compared Example 1. 
     It should be further noted that, although not shown in the evaluation results, the wear resistance and the uneven wear resistance in the out-of-shoulder region  10 Sout are also improved in Example 2 where the condition (3) of SR(n)/SR(n+1)≦3 is satisfied even when a camber angle is large, as compared with Example 1. 
     Other Embodiments 
     While the present invention has been described in accordance with the above embodiment, it should be understood that the discussion and drawings forming a part of this disclosure does not limit the present invention. Various alternative embodiments, examples, and operation techniques will become apparent to those skilled in the art in view of this disclosure. 
     Although not specifically described in the above embodiment, the number (N) of radii of curvature defining the tread profile in the shoulder region  10 S may be determined based on the ratio (SR(N)/SR( 1 )) of SR(N) defining the outermost portion in the tire width direction to SR( 1 ) defining the innermost portion in the tire width direction of the radii of curvature SR( 1 ) to SR(N). If SR(N)/SR( 1 ) is equal to or greater than 10% and is less than 20%, N preferably satisfies the condition N≧4. If SR(N)/SR( 1 ) is equal to or greater than 20% and is less than 30%, N preferably satisfies the condition N≧5. It should be noted that N satisfies the condition N≧3 even when SR(N)/SR( 1 ) is less than 10%. 
     Note that the entire content of Japanese Patent Application No. 2013-189128 (filed on Sep. 12, 2013) is incorporated by reference in the present specification. 
     INDUSTRIAL APPLICABILITY 
     As described above, the present invention provides a tire capable of improving wear resistance and uneven wear resistance and, thus, is particularly useful for a tire including a tread portion having a ground contacting tread surface.