Abstract:
This tire has a buttress section to which a plurality of depressions ( 100 ) have been formed along the tire peripheral direction (D C ). The depressions ( 100 ) have: a first outer edge ( 110 ) that bulges inward in the tread width direction (D T ); and a second outer edge ( 120 ) that is continuous with the first outer edge ( 110 ) and that bulges outward in the tread width direction (D T ) with respect to the first outer edge ( 110 ). The distance between the deepest section ( 150 ) of the depressions ( 100 ) and the ground-contact end of the tread varies along the tire peripheral direction (D C ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/JP2012/069472 filed Jul. 31, 2012, claiming priority based on Japanese Patent Application No. 2011-171170 filed Aug. 4, 2011, the contents of all of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a tire having a plurality of recessed portions formed on a buttress portion along a tire circumferential direction. 
     BACKGROUND ART 
     Conventionally, in a tire mounted on a vehicle such as a passenger vehicle, various methods have been used to reduce tire noise generated when the tire rolls on a road surface having irregular recesses and bumps, such as a paved road with a rough road surface. For example, there is known a tire using rubber with high stiffness in the shoulder portion of a tread (refer to Patent Literature 1). According to such a tire, deformation of the tread can be suppressed when the bumps, of the recesses and bumps of the road surface, wedge into the tread. Due to this, the increase of the contact pressure of the tread is suppressed, and the increase of tire noise when the tire rolls on a rough road surface can be suppressed. 
     Incidentally, nowadays, as a result of progress in the intensive study on the mechanism of tire noise generated, it has been made clear that the vibration of the buttress portion due to recesses and bumps of the road surface is also a cause of tire noise. In other words, when the road surface is smooth, normally, the buttress portion does not contact the road surface. On the other hand, when there are small recesses and bumps on the road surface, such as a paved road with a rough road surface, the buttress portion does contact the road surface, and due to these recesses and bumps, the buttress portion vibrates. Vibration of the buttress portion like this increases tire noise. In order to suppress the generation of such tire noise, it is considered to form small recessed portions on the buttress portion. However, there is a problem that, when such small recessed portions are formed on the buttress portion that is severely deformed, cracks originating from the recessed portions easily progress. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Patent Application Publication No. 2008-24048. 
     SUMMARY OF INVENTION 
     A first feature is summarized as a tire comprising: a tread that contacts a road surface; a side wall provided on an inner side of the tread in the tire radial direction; and a buttress portion provided between the tread and the side wall, wherein a plurality of recessed portions are formed on the buttress portion along a tire circumferential direction, each of the recessed portions has: a first outer edge that bulges inward in a tread widthwise direction; and a second outer edge that continues to the first outer edge and bulges outward in the tread widthwise direction with respect to the first outer edge, and the distance between a deepest portion of the recessed portion and a grounding end of the tread varies as proceeding along the tire circumferential direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a part of a segmented pneumatic tire  10  according to an embodiment. 
         FIG. 2  is a view schematically showing a first recessed row  210  and  220  configured by recessed portions  100  according to the embodiment. 
         FIG. 3  is an enlarged view of the recessed portions  100  within an F 3  frame shown in  FIG. 2 . 
         FIG. 4  is a sectional view of a buttress portion  70 , which is taken along a line F 4 -F 4  shown in  FIG. 3 . 
         FIG. 5  is a sectional view of the buttress portion  70 , which is taken along a line F 5 -F 5  shown in  FIG. 3 . 
         FIG. 6  is a sectional view of the buttress portion  70 , which is taken along a line F 6 -F 6  shown in  FIG. 3 . 
         FIGS. 7( a )-7( c )  are views showing a shape of a recess according to modifications. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, an embodiment of a tire (a pneumatic tire) according to the present invention is described with reference to drawings. It is noted that, in the following description of the drawings, the same or similar reference numerals are used to designate the same or similar portions. It should be appreciated that the drawings are schematically shown and the ratio and the like of each dimension are different from the real ones. 
     Accordingly, specific dimensions and the like should be determined in consideration of the explanation below. Further, among the drawings, the respective dimensional relations or ratios may differ. 
     (1) Schematic Configuration of Pneumatic Tire 
       FIG. 1  is a perspective view of a part of a segmented pneumatic tire  10 . As shown in  FIG. 1 , the pneumatic tire  10  is provided with a tread  50  which contacts the road surface, a side wall  60  provided on the inner side, in a tire radial direction D R , of the tread  50 , and a buttress portion  70  provided between the tread  50  and the side wall  60 . It is noted that the pneumatic tire  10  may be filled with, instead of air, an inert gas such as nitrogen gas. The tread  50  is configured by a plurality of land blocks  51 , a plurality of circumferential grooves  52 , and a shoulder land portion  53 . Further, a plurality of recessed portions  100  are formed on the buttress portion  70  along a tire circumferential direction D C . 
     (2) Shape of Recessed Portion  100   
     Next, the shape of each recessed portion  100  formed on the buttress portion  70  will be described. Specifically, description will be given for the schematic shape and the cross-sectional shape of the recessed portion  100 . 
     (2.1) Schematic Shape of Recessed Portion  100   
       FIG. 2  is a view schematically showing a first recessed row  210  and a second recessed row  220  configured by the recessed portions  100 .  FIG. 3  is an enlarged view of the recessed portions  100  within an F 3  frame shown in  FIG. 2 . 
     As shown in  FIG. 2 , the recessed portion  100  is in an elliptical shape and a plurality of the recessed portions  100  continue in the tire circumferential direction D C . In the present embodiment, the first recessed row  210  configured by the plurality of recessed portions  100  formed along the tire circumferential direction D C , and the second recessed row  220  configured by the plurality of recessed portions  100  formed along the tire circumferential direction D C  and disposed outside the first recessed row  210  in the tread widthwise direction D T , are provided. 
     A distance d between a deepest portion  150  of the recessed portion  100  and a grounding end  50   e  of the tread  50  (specifically, the shoulder land portion  53 ) varies in the tire circumferential direction D C . That is, the distance d varies as proceeding along the tire circumferential direction D C , and the variation in the distance d is repeated with the recessed portion  100  as a unit. 
     Further, the deepest portion  150  of the recessed portion  100  is curved in side view of the pneumatic tire  10 . It is noted that the grounding end  50   e  means an outer end in the tread widthwise direction D T  on the ground contact surface of the tread  50  in a state where a normal load is applied to the pneumatic tire  10  set to have a normal internal pressure regulated by the Japan Automobile Tire Manufacturers Association (JATMA) and the like. 
     (2.2) Cross-Sectional Shape of Recessed Portion  100   
       FIG. 4  is a sectional view of the buttress portion  70 , which is taken along a line F 4 -F 4  shown in  FIG. 3 .  FIG. 5  is a sectional view of the buttress portion  70 , which is taken along a line F 5 -F 5  shown in FIG.  3 .  FIG. 6  is a sectional view of the buttress portion  70 , which is taken along a line F 6 -F 6  shown in  FIG. 3 . 
     As shown in  FIG. 4  to  FIG. 6 , the recessed portion  100  has a first outer edge  110  that bulges inward in the tread widthwise direction D T . Further, the recessed portion  100  has a second outer edge  120  that is continuous with the first outer edge  110  and that bulges outward in the tread widthwise direction D T  with respect to the first outer edge  110 . 
     In the present embodiment, the first outer edge  110  is in an arc-like shape that is curved so as to bulge inward in the tread widthwise direction D T . Similarly, the second outer edge  120  is in an arc-like shape that is curved to bulge outward in the tread widthwise direction D T  with respect to the first outer edge  110 . That is, the recessed portion  100  is in an elliptical shape. Further, the recessed portion  100  has a first bottom surface  130  that extends from the first outer edge  110  to the deepest portion  150  and a second bottom surface  140  that extends from the second outer edge  120  to the deepest portion  150 . The first bottom surface  130  is formed so as to be point-symmetrical to the second bottom surface  140 . 
     Further, in the present embodiment, the recessed portion  100  included in the second recessed row  220  is formed between the two recessed portions  100  adjacent to each other in the tire circumferential direction D C  included in the first recessed row  210 . The deepest portion  150  has a first curved portion  151  that is curved so as to be closer to the first outer edge  110  in side view (viewpoint from the side wall  60 ) of the pneumatic tire  10  and a second curved portion  152  that continues to the first curved portion  151  and is curved so as to be closer to the second outer edge  120  in side view of the pneumatic tire  10 . 
     Further, as described above, the distance d between the deepest portion  150  and the grounding end  50   e  of the tread  50  varies in the tread widthwise direction D T  (see  FIG. 2 ). Therefore, as shown in  FIG. 4  to  FIG. 6 , the position of the deepest portion  150  in the tread widthwise direction D T  varies as proceeding along the tire circumferential direction D C . Specifically, positions, in the tread widthwise direction D T , of the deepest portion  150  of the recessed portion  100  that forms the first recessed row  210  and the deepest portion  150  of the recessed portion  100  that forms the second recessed row  220  vary, respectively, in the tire circumferential direction D C . Further, the distance between the deepest portion  150  and the first outer edge  110  and the distance between the deepest portion  150  and the second outer edge  120  also vary in the tire circumferential direction Dc. 
     (3) Advantageous Effect 
     According to the pneumatic tire  10 , the plurality of recessed portions  100  formed along the tire circumferential direction have the first outer edge  110  that bulges inward in the tread widthwise direction D T , and the second outer edge  120  that continues to the first outer edge  110  and bulges outward in the tread widthwise direction D T  with respect to the first outer edge  110 . Further, the distance d between the deepest portion  150  of the recessed portion  100  and the grounding end  50   e  of the tread  50  varies in the tire circumferential direction D C . 
     In general, a buttress portion does not contact a smooth road surface, but contacts a road surface with small recesses and bumps, such as a paved road with a rough road surface. Due to such recesses and bumps, the buttress portion vibrates, and road noise resulting from the vibration of the buttress portion is increased. However, in the embodiment, the recessed portion  100  is formed on the buttress portion and the distance d between the deepest portion  150  of the recessed portion  100  and the grounding end  50   e  of the tread  50  varies in the tire circumferential direction D C , thus it is possible to suppress the road noise resulting from the vibration of the buttress portion. 
     Further, the distance d between the deepest portion  150  of the recessed portion  100  and the grounding end  50   e  of the tread  50  varies in the tread widthwise direction D T , thus the progression of cracks resulting from the shape of the recessed portions  100  along the tire circumferential direction D C  is suppressed. 
     That is, according to the pneumatic tire  10 , it is possible to suppress, by the recessed portion  100  formed on the buttress portion  70 , the generation of tire noise resulting from a vibration of the buttress portion  70  and progression of cracks originating from the recessed portions  100 . 
     Further, since the distance d between the deepest portion  150  of the recessed portion  100  and the grounding end  50   e  of the tread  50  varies in the tire circumferential direction D C , curvature itself is suppressed, and generation of cracks is suppressed. Further, even when cracks are generated, progression of cracks is suppressed. 
     In the present embodiment, the first outer edge  110  and the second outer edge  120  are in an arc-like shape, and the deepest portion  150  is curved in the pneumatic tire  10 . Further, the recessed portion  100  has a first bottom surface  130  that extends from the first outer edge  110  to the deepest portion  150  and a second bottom surface  140  that extends from the second outer edge  120  to the deepest portion  150 . Thus, progression of cracks resulting from the shape of the recessed portion  100  along the tire circumferential direction D C  is further suppressed. 
     In the present embodiment, the deepest portion  150  has the first curved portion  151  that is curved so as to be closer to the first outer edge  110  and the second curved portion  152  that continues to the first curved portion  151  and is curved so as to be closer to the second outer edge  120 . Further, the first bottom surface  130  is formed so as to be point-symmetrical to the second bottom surface  140 . Therefore, progression of cracks in the recessed portion  100  can be suppressed. 
     In the present embodiment, the first recessed row  210  and the second recessed row  220  are formed and the recessed portion  100  included in the second recessed row  220  is formed between the two recessed portions  100  adjacent to each other in the tire circumferential direction D C  included in the first recessed row  210 . Therefore, vibration resulting from contact of the buttress portion  70  with the road surface is effectively reduced and progression of cracks resulting from the shape of the recessed portions  100  along the tire circumferential direction D C  is suppressed. 
     (4) Other Embodiments 
     As described above, the contents of the present invention are disclosed through the embodiment of the present invention. However, it should not be interpreted that the statements and drawings constituting a part of this disclosure limit the present invention. From this disclosure, a variety of alternate embodiments, examples, and applicable techniques will become apparent to one skilled in the art. For example, the shape of the recessed portion  100  may not necessarily be in an elliptical shape as described in the above-described embodiment.  FIGS. 7( a ) to ( c )  are views showing shapes of recessed portion according to modifications of the present invention. As shown in  FIGS. 7( a ) to ( c ) , a recess formed on the buttress portion  70  may be a polygonal recessed portion  100 A as shown in  FIG. 7( a ) . Alternatively, as shown in  FIGS. 7( b ) and ( c ) , the recessed portion may be rhomboidal recessed portions  100 B and  100 C. Further, the shape of the deepest portion of the recess may be a combination of straight lines like the recessed portion  100 B or in a curved shape like the recessed portion  100 C. 
     As described above, needless to say, the present invention includes various embodiments and the like not described here. Therefore, the technical range of the present invention is to be defined only by the inventive specific matter according to the adequate claims from the above description. 
     In addition, the entire content of Japanese Patent Application No. 2011-171170 (filed on Aug. 4, 2011) is incorporated in the present specification by reference. 
     INDUSTRIAL APPLICABILITY 
     According to a characteristic of the present invention, it is possible to provide a tire with which it is possible to suppress, by recessed portions formed on a buttress portion, the generation of tire noise resulting from vibration of the buttress portion and the progression of cracks originating from the recessed portions.