Patent Publication Number: US-2019176542-A1

Title: A Noise Reducing Tread

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to PCT International Patent Application Serial No. PCT/JP2016/066705, filed May 31, 2017, entitled “A NOISE REDUCING TREAD,” which claims priority to PCT/JP2016/066705, filed May 31, 2016. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a tread for a tire, in particular to a tread for a tire having a closing device enable to attenuate a noise generated by groove resonance in a primary groove. 
     2. Related Art 
     A groove resonance is generated by occurrence of resonance in an air column defined between a groove in a tread and a road surface in contact with the tire. The frequency of this groove resonance is dependent on a length of the air column formed between groove and the road surface in the contact patch. 
     This groove resonance has a consequence in an interior noise and an exterior noise on a vehicle equipping such tires, a frequency of which interior and exterior noise is often at around 1 kHz where human ear is sensitive. 
     In order to reduce such groove resonance, it is known to provide a plurality of closing device in the form of a flexible fence made of rubber-based material and relatively thin in thickness in each primary groove. It is effective that each flexible fence covers all or at least major part of the sectional area in the primary groove. Each flexible fence can extend from a groove bottom, or be fixed onto at least one of a groove sidewall delimiting such primary groove. Because being relatively thin in thickness, each flexible fence has to bend for opening the primary groove section to flow water on the road surface, in particular on the wet road. 
     Thanks to such flexible fences, the length of the air column is reduced so as to be shorter than the total length of primary groove in a contact patch, which leads to change the frequency of groove resonance. This change of resonance frequency makes the sound generated by the groove resonance less sensitive to human ear. 
     For preserving function of drainage, in case of driving in rainy weather, it is necessary that such flexible fence bends in a suitable way under the action of the pressure of water for opening the section of the primary groove. Several solutions have been proposed using this type of closing device to reduce groove resonance of the primary groove. 
     EP0908330B1 discloses, in  FIG. 4 a   , a tread having principal (primary) groove equipping with fence portions with three flexible fences, wherein two flexible fences extend inwardly from the opposite groove sidewalls, another flexible fence extends upwardly from the groove bottom which is offset from two flexible fences extending from the opposite groove sidewalls in an orientation the principal groove extends. However with such configuration, it is difficult to maintain satisfactory drainage capability, in particular when a groove depth is reduced with wear, as bending of the flexible fence extending from the groove bottom with hydrodynamic pressure occurs generally between middle part and bottom part of such flexible fence, and bending rigidity of such flexible fence increases with wear resulting disturbance of drainage. Moreover as there is always a gap between each the flexible fence not only in an orientation perpendicular to an orientation the principal groove extends but also in the orientation the principal groove extends, groove resonance attenuation capability is not satisfactory. 
     WO2013/072169A1 discloses, in  FIG. 1 , a tread having a groove providing with two flexible devices (flexible fences), both of which extend from each side of groove sidewalls, wherein the flexible devices are provided with a notch on their bottom wall. However, with such configuration, coverage of the section of the groove via the flexible fence becomes weak due to the notch and necessity to have a gap between two flexible fences in lateral orientation for securing bending capability and better productivity of the tread provided with the flexible fences. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     
         
         EP0908330 
       
    
     [PTL 2] 
     
         
         WO2013/072169 
       
    
     Definitions 
     A “radial direction/orientation” is a direction/orientation perpendicular to axis of rotation of the tire. This direction/orientation corresponds to thickness orientation of the tread. 
     An “axial direction/orientation” is a direction/orientation parallel to axis of rotation of the tire. 
     A “circumferential direction/orientation” is a direction/orientation which is tangential to any circle centered on axis of rotation. This direction/orientation is perpendicular to both the axial direction/orientation and the radial direction/orientation. 
     A “tire” means all types of elastic tire whether or not subjected to an internal pressure. 
     A “tread” of a tire means a quantity of rubber material bounded by lateral surfaces and by two main surfaces one of which is intended to come into contact with ground when the tire is rolling. 
     A “groove” is a space between two rubber faces/sidewalls, which do not contact between themselves under usual rolling condition, connected by another rubber face/bottom. A groove has a width and a depth. 
     A “primacy groove” is a groove having relatively wider width as primarily responsible for liquid drainage. Often such primary groove extends towards generally circumferential orientation in a form of straight, zigzag and so on. The primary groove can also be understood as a groove extending in oblique orientation having relatively wider width as primarily responsible for liquid drainage. 
     A “contact patch” is a footprint of a tire mounted onto its standard rim as identified in tire standards such as ETRTO, JATMA or TRA, and inflated at its nominal pressure and under its nominal load. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     It is thus an object of the disclosure to provide a tread for a tire, which tread can provide further satisfactory reduction on groove resonance and productivity for manufacturing such tread. 
     The present disclosure provide a tread for a tire having a contact face intended to come into contact with ground during rolling and comprising at least one primary groove having depth D and being delimited by two opposite groove sidewalls, these groove sidewalls being axially connected by a groove bottom, the primary groove being provided with a plurality of closing device including at least two flexible fences, the closing device covering at least equal to 70% of sectional area of the primary groove, the at least two flexible fences of the closing device being at least one first flexible fence having thickness t 1  and extending from the groove bottom in a radially outward orientation of the tire, and at least one second flexible fence having thickness t 2  and extending from one of groove sidewall toward the other groove sidewall, the at least two flexible fences of the closing device being distant each other in an orientation the primary groove extends with a gap g, the first flexible fence and the second flexible fence overlap partly in sectional view of the primary groove, and the gap g is at most equal to 1.0 mm. 
     This arrangement provides further satisfactory reduction on groove resonance and productivity for manufacturing such tread. 
     According the above arrangement, the primary groove is provided with the plurality of closing device comprising at least two flexible fences as to cover at least equal to 70% of the cross sectional area of the primary groove. Therefore, the length of the air column of the primary groove formed with the road surface is different from that formed in case there is no closing device, and the peak of groove resonance is shifted to an outside of the frequency range audible to the human ear. As a result, groove resonance due to air column resonance of the primary groove can be improved. 
     Since the closing device includes at least two flexible fences, each the flexible fence can be relatively smaller for covering at least 70% of cross sectional area of the primary groove. As a result, productivity of the tread provided with the closing device can be improved. 
     Since the at least two flexible fences of the closing device are at least one first flexible fence having thickness t 1  and extending from the groove bottom in a radially outward orientation of the tire, and at least one second flexible fence having thickness t 2  and extending from one of groove sidewall toward the other groove sidewall, it is possible to cover as broader cross sectional area of the primary groove as effectively as possible by the closing device, while maintaining good productivity of the tread with the flexible fences as closing device, as the sectional area covered by each flexible fence can be reduced using simple tool for manufacturing the tread with the flexible fences which serve as the closing device. 
     Since the first flexible fence and the second flexible fence overlap partly in sectional view of the primary groove, it is possible to further effectively attenuate groove resonance due to air column resonance of the primary groove, as the sound wave generated by groove resonance has more difficulty in propagating between each the flexible fences of the closing device. 
     Since the at least two flexible fences of the closing device is distant each other in an orientation the primary groove extends with a gap g which is at most equal to 1.0 mm, a sound wave generated by groove resonance has difficulty in propagating through the gap between each the flexible fences of the closing device. As a result, groove resonance due to air column resonance of the primary groove can effectively be improved. 
     If the gap g is more than 1.0 mm, there is a risk of groove resonance attenuation capability degradation as the sound wave generated by groove resonance may propagate between each the flexible fences of the closing device. By setting this gap g at most equal to 1.0 mm, groove resonance due to air column can effectively be improved. 
     In another preferred embodiment, the gap g is at least equal to 0.05 mm and at most equal to 0.5 mm. 
     According to this arrangement, it is possible to further effectively attenuate groove resonance due to air column resonance of the primary groove while maintaining satisfactory drainage capability of the primary groove, as the sound wave generated by groove resonance has more difficulty in propagating through the gap between adjacent flexible fences of the closing device while ensuring enough gap between flexible fences for bending. Preferably this gap g is at least equal to 0.1 mm and at most equal to 0.3 mm, more preferably at least equal to 0.1 mm and at most equal to 0.2 mm. 
     In another preferred embodiment, the closing device includes one first flexible fence and two second flexible fences and each of the second flexible fences extends from each of opposite groove sidewalls. 
     According to this arrangement, it is possible to effectively cover as broader cross sectional area of the primary groove as possible by the closing device, while maintaining good productivity of the tread with the flexible fences which serve as closing device, as the sectional area covered by each flexible fence can be reduced using simple tool for manufacturing the tread with the flexible fences as the closing device, and to have higher flexibility of an arrangement of the flexible fences. 
     In another preferred embodiment, the two second flexible fences overlap partly in sectional view of the primary groove. 
     According to this arrangement, it is possible to further effectively attenuate groove resonance due to air column resonance of the primary groove, as the sound wave generated by groove resonance has more difficulty in propagating between each the flexible fences of the closing device. 
     In another preferred embodiment, the thickness t 1  of the first flexible fence is different from the thickness t 2  of the second flexible fence. 
     According to this arrangement, performance compromise by the flexible fences can be achieved. By making the thickness t 1  of the first flexible fence thicker than the thickness t 2  of the second flexible fence, it is possible to have a regular wear of the first flexible fence with tread wear by increased bending rigidity of the first flexible fence relative to the second flexible fence. Contrarily by making the thickness t 1  of the first flexible fence thinner than the thickness t 2  of the second flexible fence, it is possible to achieve easier bending of the first flexible fence even with reduced groove depth which results in further improvement on drainage capability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the disclosure arise from the description made hereafter in reference to the annexed drawings which show, as nonrestrictive examples, the embodiments of the disclosure. 
       In these drawings: 
         FIG. 1  is a schematic view of a portion of a tread for a tire according to a first embodiment of the present disclosure; 
         FIG. 2  is an enlarged schematic view showing a portion indicated as II in  FIG. 1 ; 
         FIG. 3  is a schematic cross sectional view taken along line in  FIG. 1 ; 
         FIG. 4  is an enlarged schematic view of a portion according to a second embodiment of the present disclosure; 
         FIG. 5  is a schematic cross sectional view according to the second embodiment of the present disclosure; 
         FIG. 6  is an enlarged schematic view of a portion according to a third embodiment of the present disclosure; and 
         FIG. 7  is a schematic cross sectional view according to the third embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE ENABLING EMBODIMENTS 
     Preferred embodiments of the present disclosure will be described below referring to the drawings. 
     A tread  1  for a tire according to a first embodiment of the present disclosure will be described referring to  FIGS. 1, 2 and 3 .  FIG. 1  is a schematic view of a portion of a tread  1  according to the first embodiment of the present disclosure.  FIG. 2  is an enlarged schematic view showing a portion indicated as II in  FIG. 1 .  FIG. 3  is a schematic cross sectional view taken along line in  FIG. 1 . 
     The tread  1  is a tread for a tire having dimension 225/45R17 and comprises a contact face  2  intended to come into contact with the ground during rolling, a plurality of primary groove  3  extending in a tire circumferential orientation indicated as XX′. The primary grooves  3  are delimited by two groove sidewalls  31 ,  32  facing each other and being connected by a groove bottom  33 . The primary groove  3  has a width W at a level of the contact face  2  and a depth D (as shown in  FIG. 3 ). 
     As shown in  FIG. 1 , a contact patch  5  has a contact patch length L in a tire circumferential orientation when the tire with the tread  1  is mounted onto its standard rim and inflated at its nominal pressure and its nominal load is applied. According to ‘ETRTO Standard Manual 2015’ the standard rim for this size is 7.5 J, the nominal pressure is 250 kPa and the nominal load is 615 kg. 
     As shown in  FIG. 1 , in the primary groove  3 , a plurality of closing device  4  is provided. The closing device  4  comprises one first flexible fence  41  and two second flexible fences  42  for dividing an air column created between the ground and the primary groove  3  in the contact patch  5  during rolling. Each closing device  4  is spaced from each other by distance P in the tire circumferential orientation in the primary groove  3 . The distance P is preferably shorter than the contact patch length L so that at least one closing device  4  is always located in the contact patch  5  during rolling in each primary groove  3 . 
     The first flexible fence  41  has a thickness of t 1  and extends from the groove bottom  33  of the primary groove  3  and two second flexible fences  42  have a thickness of t 2  and extend from each of the opposite groove sidewalls  31 ,  32 . Two second flexible fences  42  are offset each other in a circumferential orientation in the primary groove  3 . The first flexible fence  41  is placed at a circumferential position between two second flexible fences  42 ,  42  and distant in circumferential orientation (an orientation the primary groove  3  extends) with a gap g which is at most equal to 1.0 mm, from both of the second flexible fences  42  in the primary groove  3 , as shown in  FIG. 2 . 
     The thickness t 1  of the first flexible fence  41  is thinner than the thickness t 2  of the second flexible fence  42 , as shown in  FIG. 2 . The first and the second flexiblea fences  41 ,  42  partly overlap in a circumferential orientation (in sectional view of the primary groove  3 ), and the two second flexible fences  42 ,  42  also overlap partly in a circumferential orientation (in sectional view of the primary groove  3 ). The first and the second flexible fences  41 ,  42  cover at least equal to 70% of the cross sectional area of the primary groove  3 , as shown in  FIG. 3 . 
     As shown in  FIG. 3 , the first flexible fence  41  has a pentagon shape as to extend in radially outward orientation of the tread  1  from the groove bottom  33 . The width of the first flexible fence  41  is less than the width W of the primary groove  3  and the height of the first flexible fence  41  is less than the depth D of the primary groove  3   
     Further, a radially inner edge of the second flexible fence  42  extends obliquely upwardly from the groove sidewall  31 ,  32  so as to form a triangular space defined by the radially inner edges of the two second flexible fences  42  and the groove bottom  33 . A radially outer edge of the second flexible fence  42  extends substantially parallel to the contact face  2 . The axial width of the second flexible fence  42  is less than the width W of the primary groove  3 . 
     The tread  1  has the same structure as the conventional tread except for an arrangement regarding the closing device  4  and is intended to be applied to a conventional pneumatic radial tire and other non-pneumatic tire. Thus, description of the internal construction of the tread  1  will be omitted. 
     The primary groove  3  is provided with the plurality of closing device  4  each covering at least equal to 70% of the radial cross sectional area of the primary groove  3 . Therefore, the length of the air column formed by the primary groove  3  in the contact patch  5  is shifted to a length whose groove resonance peak is outside of the frequency audible range for the human ear. Thus, groove resonance due to air column resonance of the primary groove  3  can be harmless. 
     The flexible fences of the closing device  4  are provided so as to be distant each other with the gap g which is at most equal to 1.0 mm in an orientation along which the primary groove  3  extends. Therefore, it is possible to effectively improve groove resonance due to air column as a sound wave generated by groove resonance has difficulty in propagating between each the flexible fences of the closing device  4 . This effect of improving groove resonance due to air column is further emphasized by setting this gap g at least equal to 0.05 mm and at most equal to 0.5 mm while ensuring enough gap between flexible fences to bend. Preferably this gap g is at least equal to 0.1 mm and at most equal to 0.3 mm, and more preferably at least equal to 0.1 mm and at most equal to 0.2 mm. 
     The closing device  4  includes one first flexible fence  41  and two second flexible fences  42  and each of the second flexible fences  42  extends from each of opposite groove sidewalls  31 ,  32 . Therefore, it is possible to cover as broader cross sectional area of the primary groove  3  as effectively as possible by the closing device  4 , while maintaining good productivity of the tread  1  with the flexible fences as closing device  4 , as the sectional area covered by each flexible fence can be reduced using simple tool for manufacturing the tread  1  with the flexible fences as the closing device  4 , and to have higher flexibility of an arrangement of the first and the second flexible fences. 
     The first flexible fence  41  and the second flexible fence  42  of the closing device  4  overlap partly in a circumferential orientation (in sectional view of the primary groove  3 ). Also, two second flexible fences  42  of the closing device  4  overlap partly in a circumferential orientation (in sectional view of the primary groove  3 ). Therefore, it is possible to further effectively attenuate groove resonance due to air column resonance of the primary groove  3 , as the sound wave generated by groove resonance has more difficulty in propagating between each the flexible fences of the closing device  4 . 
     The thickness t 1  of the first flexible fence  41  is thinner than the thickness t 2  of the second flexible fence  42 . It is possible to achieve easier bending of the first flexible fence  41  even when the groove depth decreases, which results further improvement on drainage capability. Both the thickness t 1  of the first flexible fence  41  and the thickness t 2  of the second flexible fence  42  is preferably less than or equal to 1.5 mm, more preferably between 1.0 mm and 0.2 mm, and a difference between two thicknesses t 1  and t 2  is preferably less than or equal to 1.0 mm, more preferably less than or equal to 0.5 mm. 
     The gap g between the flexible fences  41 ,  42  of the closing device  4  may have different value position by position, and the thickness t 2  of the second flexible fence  42  may have different thickness one another. 
     A tread  21  according to a second embodiment of the present disclosure will be described referring to  FIGS. 4 and 5 .  FIG. 4  is an enlarged schematic view of a portion according to the second embodiment of the present disclosure.  FIG. 5  is a schematic cross sectional view according to the second embodiment of the present disclosure. The constitution of this second embodiment is similar to that of the first embodiment other than the arrangement shown in  FIGS. 4 and 5 , thus description will be made referring to  FIGS. 4 and 5 . 
     In the second embodiment, a closing device  24  comprises one first flexible fence  241  having a thickness of t 1  and extending from a groove bottom  233  of a primary groove  23  and two second flexible fences  242  having a thickness of t 2  and extending from each of opposite groove sidewalls  231 ,  232 . Two second flexible fences  242  are substantially in line each other in an axial orientation in the primary groove  23 . The first flexible fence  241  is placed as to be distant in circumferential orientation (an orientation along which the primary groove  23  extends) from the second flexible fences  242  with a gap g which is at most equal to 1.0 mm, in the primary groove  23 . 
     The thickness t 1  of the first flexible fence  241  is thicker than the thickness t 2  of the second flexible fence  242 , as shown in  FIG. 4 . The first and the second flexible fences  241 ,  242  partly overlap in a circumferential orientation (in sectional view of the primary groove  23 ). The first and the second flexible fences  241 ,  242  cover at least equal to 70% of the cross sectional area of the primary groove  23 , as shown in  FIG. 5 . The width of the first flexible fence  241  is less than the width W of the primary groove  23 . Side portions of the second flexible fences  242  facing to the primary groove  23  overlap the each side of the first flexible fence  241 . 
     As shown in  FIG. 5 , the first flexible fence  241  has a rectangular shape as to extend in radially outward orientation of the tread  21  from the groove bottom  233  to substantially same level as a contact face  22 , and covers major part of the primary groove  23 . 
     Further, a radially inner edge of the second flexible fence  242  extends obliquely upwardly from the groove sidewall  231 ,  232  so as to form a triangular space thereunder with the groove bottom  233 . A radially outer edge of the second flexible fence  242  extends substantially parallel to the contact face  22  at radially inward level from the contact face  22  and covers relatively minor part of the primary groove  23  without overlapping each other in circumferential orientation (in sectional view of the primary groove  23 ). 
     The flexible fences of the closing device  24  are provided so as to be distant from each other with the gap g which is at most equal to 1.0 mm in an orientation the primary groove  23  extends. Therefore, it is possible to effectively improve groove resonance due to air column as a sound wave generated by groove resonance has difficulty in propagating between each the flexible fences of the closing device  24 . This effect of improving groove resonance due to air column is further emphasized by setting this gap g at least equal to 0.05 mm and at most equal to 0.5 mm while ensuring enough gap between flexible fences to bend. Preferably this gap g is at least equal to 0.1 mm and at most equal to 0.3 mm, and more preferably at least equal to 0.1 mm and at most equal to 0.2 mm. 
     The closing device  24  includes one first flexible fence  241  and two second flexible fences  242  and each of the second flexible fences  242  extends from each of opposite groove sidewalls  231 ,  232 . Therefore, it is possible to effectively cover as broader cross sectional area of the primary groove  23  as possible by the closing device  24 , while maintaining good productivity of the tread  21  with the flexible fences as closing device  24 , as the sectional area covered by each flexible fence can be reduced using simple tool for manufacturing the tread  21  with the flexible fences as the closing device  24 , and to have higher flexibility of an arrangement of the first and the second flexible fences. 
     The first flexible fence  241  and the second flexible fence  242  of the closing device  24  overlap partly in a circumferential orientation (in sectional view of the primary groove  23 ). Therefore, it is possible to further effectively attenuate groove resonance due to air column resonance of the primary groove  23 , as the sound wave generated by groove resonance has more difficulty in propagating between each the flexible fences of the closing device  24 . 
     The thickness t 1  of the first flexible fence  241  is thicker than the thickness t 2  of the second flexible fence  242 . Therefore it is possible to have a regular wear of the first flexible fence  241  with tread wear by increased bending rigidity of the first flexible fence  241  relative to the second flexible fence  242 . Both the thickness t 1  of the first flexible fence  241  and the thickness t 2  of the second flexible fence  242  is preferably less than or equal to 1.5 mm, more preferably between 1.0 mm and 0.2 mm, and a difference between two thicknesses t 1  and t 2  is preferably less than or equal to 1.0 mm, more preferably less than or equal to 0.5 mm. 
     A tread  51  according to a third embodiment of the present disclosure will be described referring to  FIGS. 6 and 7 .  FIG. 6  is an enlarged schematic view of a portion according to the third embodiment of the present disclosure.  FIG. 7  is a schematic cross sectional view according to the third embodiment of the present disclosure. The constitution of this third embodiment is similar to that of the first embodiment other than the arrangement shown in  FIGS. 6 and 7 , thus description will be made referring to  FIGS. 6 and 7 . 
     In the third embodiment, a closing device  54  comprises one first flexible fence  541  having a thickness t 1  and extending from a groove bottom  533  of the primary groove  53  and one second flexible fence  542  having a thickness t 2  and extending from one groove sidewall  531 . The thickness t 1  of the first flexible fence  541  is substantially equal to the thickness t 2  of the second flexible fence  542 , as shown in  FIG. 6 . The first flexible fence  541  is placed as to be distant in circumferential orientation (an orientation the primary groove  53  extends) from the second flexible fence  542  with a gap g which is at most equal to 1.0 mm, in the primary groove  53 . 
     As shown in  FIG. 7 , the first flexible fence  541  has a rectangular shape as to extend in radially outward orientation of the tread  51  from the groove bottom  533 , and a radially outer edge of the first flexible fence  541  offsets radially inwardly from the level of the contact face  52 , and the first flexible fence  541  covers major part of the primary groove  53 . 
     Further, a radially inner edge of the second flexible fence  542  extends substantially parallel to the groove bottom  533  and quadrantly notched at connecting part to the groove sidewall  531 . A radially outer edge of the second flexible fence  542  extends substantially parallel to the contact face  52  at radially inwardly offset level from the level of the contact face  52  and the second flexible fence  542  covers relatively minor part of the primary groove  53 . The first and the second flexible fences  541 ,  542  cover at least equal to 70% of the cross sectional area of the primary groove  53 , as shown in  FIG. 7 . 
     The flexible fences of the closing device  54  are provided so as to be distant from each other with the gap g which is at most equal to 1.0 mm in an orientation along which the primary groove  53  extends. Therefore, it is possible to effectively improve groove resonance due to air column as a sound wave generated by groove resonance has difficulty in propagating between each the flexible fences of the closing device  54 . This effect of improving groove resonance due to air column is further emphasized by setting this gap g at least equal to 0.05 mm and at most equal to 0.5 mm while ensuring enough gap between flexible fences to bend. Preferably this gap g is at least equal to 0.1 mm and at most equal to 0.3 mm, and more preferably at least equal to 0.1 mm and at most equal to 0.2 mm. 
     The closing device  54  includes one first flexible fence  541  and one second flexible fence  542  and the second flexible fence  542  extends from one of the groove sidewall  531 . Therefore, it is possible to cover as broader cross sectional area of the primary groove  53  as effectively as possible by the closing device  54 , while maintaining good productivity of the tread  51  with the flexible fences as closing device  54 , as the sectional area covered by each flexible fence can be reduced using simple tool for manufacturing the tread  51  with the flexible fences as the closing device  54 , and to have higher flexibility of an arrangement of the first and the second flexible fences. 
     The first flexible fence  541  and the second flexible fence  542  of the closing device  54  overlap partly in a circumferential orientation (in sectional view of the primary groove  53 ). Therefore, it is possible to further effectively attenuate groove resonance due to air column resonance of the primary groove  53 , as the sound wave generated by groove resonance has more difficulty in propagating between each the flexible fences of the closing device  54 . 
     In order to confirm the effect of the present disclosure, three types of pneumatic tires of Example to which the present disclosure is applied and another type of pneumatic tire of Comparative Example were prepared. An internal construction of these tires was typical radial tire construction for passenger car tire. 
     The Examples were pneumatic tires having a tread as shown in  FIG. 3  described in the above embodiment with three different gap g between each the flexible fence of the closing device. The Comparative Example was a pneumatic tire having a tread as shown in  FIG. 3  with gap g out of the range of the present disclosure, and Reference was a pneumatic tire without having the closing device. 
     The tire dimension of the Examples, Comparative Example and Reference were all 205/55R16, mounted onto a rim of 6.5 J×16, and inflated to 180 kPa. 
     Noise Test: 
     A sound pressure level of the unused test tires mounted onto abovementioned rim, inflated to abovementioned internal pressure were measured while applying a load of 452 daN, running 90 kph on a drum of 2.7 m in diameter having ISO surface in a semi-anechoic chamber, via a microphone installed axially 1 m outward from a center of tire contact, radially 0.2 m backward from a tire rolling axis and 0.32 m in height. The data acquired through the measurements were processed to calculate an absorption level of a sound at groove resonance frequency. The results are shown in table 1. In this table 1, results are represented by an index of 100 for Reference, higher the number indicates better the noise performance. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 Com- 
                   
               
               
                   
                   
                   
                   
                 parative 
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 
                 Reference 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Gap g (mm) 
                 1.0 
                 0.5 
                 0.2 
                 2.0 
                 — 
               
               
                 Noise 
                 106 
                 107 
                 108 
                 103 
                 100 
               
               
                 performance 
               
               
                 (index) 
               
               
                   
               
            
           
         
       
     
     As seen from table 1, the Example tires show improvement on noise performance. 
     The disclosure is not limited to the examples described and represented and various modifications can be made there without leaving its framework. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  21 ,  51  tread 
           2 ,  22 ,  52  contact face 
           3 ,  23 ,  53  primary groove 
           31 ,  231 ,  531  groove sidewall of the primary groove 
           32 ,  232 ,  532  groove sidewall of the primary groove 
           33 ,  233 ,  533  groove bottom of the primary groove 
           4 ,  24 ,  54  closing device 
           41 ,  241 ,  541  first flexible fence 
           42 ,  242 ,  542  second flexible fence 
           5  contact patch