Abstract:
A tire wherein a first bulge part and a second bulge part are formed in a circumferential direction groove. The first bulge part has a narrow-tip shape such that, in the tire tread plan view, the size in the tread width direction diminishes along a first direction in the tire circumferential direction. The second bulge part has a narrow-tip shape such that, in the tire tread plan view, the size in the tread width direction diminishes along a second direction opposite to the first direction in the tire circumferential direction. A plurality of first bulge parts and second bulge parts are provided at predetermined intervals in the tire circumferential direction. A groove part which extends in the tire circumferential direction is provided between the first bulge part and the second bulge part which opposes the first bulge part in the tread width direction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a National Stage of International Application No. PCT/JP2012/069153 filed Jul. 27, 2012, claiming priority based on Japanese Patent Application No. 2011-164570 filed Jul. 27, 2011, the contents of all of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a tire in which a circumferential groove extending in a tire circumferential direction is formed, and particularly relates to a tire having a sufficient water drainage performance even when a lug groove component is reduced. 
     BACKGROUND ART 
     Conventionally, in a pneumatic tire (hereinafter, referred to as tire) mounted on a passenger vehicle, for example, a method for forming a plurality of circumferential grooves in a tread has been widely used in order to ensure a water drainage performance on a wet road surface. 
     Further, there is known a tire in which a plurality of protrusions to be inclined relative to a tire circumferential direction are formed on a groove bottom of a circumferential groove in order to aggressively drain rainwater that has entered such a circumferential groove (for example, Patent Literature 1). According to such a tire, a spiral water flow is hardly generated in the rainwater that has entered the circumferential grooves, resulting in the improvement of a water drainage performance. 
     In recent years, along with an introduction of an electric vehicle or a hybrid automobile in which both an internal combustion engine and an electric motor are used, a further reduction of noise generated by a tire is demanded. Further, even in an automobile mounted thereon with an internal combustion engine, along with a reduction of noise generated by the automobile itself, a further reduction of noise generated by a tire is demanded than ever. Main examples of the noise generated by a tire include a pattern noise resulting from a tread pattern (pitch noise) and a road noise resulting from an unevenness on a road surface. As a method of reducing a pattern noise, it is possible to consider reducing a lug groove component in a tread. 
     However, even with the tire in which a lug groove component is thus reduced, it is necessary to ensure a water drainage performance at least equal to that of a conventional tire. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Patent Publication No. 2005-170381 
     SUMMARY OF INVENTION 
     A tire according to a first feature comprises: a circumferential groove extending in a tire circumferential direction; and a land portion that is adjacent to the circumferential groove and that extends in the tire circumferential direction. The circumferential groove is formed with: a first swelling portion that swells from one lateral wall of the circumferential groove toward a center in a widthwise direction of the circumferential groove; and a second swelling portion that swells from the other lateral wall of the circumferential groove toward the center in the widthwise direction of the circumferential groove. The first swelling portion has, in a tread surface view of the tire, a tapered shape in which a size in the tread widthwise direction is narrower as it goes in a first direction in the tire circumferential direction. The second swelling portion has, in the tread surface view of the tire, a tapered shape in which a size in the tread widthwise direction is narrower as it goes in a second direction that is opposite to the first direction in the tire circumferential direction. The first swelling portion and the second swelling portion are formed in plural with a predetermined interval in the tire circumferential direction. A groove extending in the tire circumferential direction is formed between the first swelling portion and the second swelling portion opposite to the first swelling portion in the tread widthwise direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a development plan view illustrating a part of a pneumatic tire  10  according to an embodiment. 
         FIG. 2  is an enlarged perspective view of a circumferential groove  20  according to the embodiment. 
         FIG. 3  is an enlarged view of the circumferential groove  20  as seen from a tire circumferential direction D C  according to the embodiment. 
         FIG. 4  is a cross sectional view of the circumferential groove  20  according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, a tire (pneumatic tire) according to an embodiment will be explained 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 is 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. Moreover, among the drawings, the respective dimensional relations or ratios may differ. 
     (1) Schematic Configuration of Pneumatic Tire 
       FIG. 1  is a development plan view illustrating a part of a pneumatic tire  10  according to the present embodiment. As illustrated in  FIG. 1 , on the pneumatic tire  10 , a plurality of circumferential grooves  20  extending in a tire circumferential direction D C  are formed. Further, the pneumatic tire  10  includes a land portion  30  extending in the tire circumferential direction D C , adjacently to each circumferential groove  20 . It is noted that the pneumatic tire  10  may be filled with, instead of air, an inert gas such as nitrogen gas. 
     In the pneumatic tire  10 , a plurality of circumferential grooves  20  are formed; a lug groove component extending in a tread widthwise direction D T  is not formed. It is noted that a thin groove or a siping not illustrated extending in the tread widthwise direction D T  may be formed. The pneumatic tire  10  may be favorably used for an electric automobile or a hybrid automobile in which both an internal combustion engine and an electric motor are used because a pattern noise is reduced due to a reduction in lug groove component. 
     Inside the circumferential groove  20 , a first swelling portion  110  and a second swelling portion  120  are arranged. Between the first swelling portion  110  and the second swelling portion  120  opposite to the first swelling portion  110  in the tread widthwise direction D T , a groove  200  extending in the tire circumferential direction D C  is formed. Specifically, the groove  200  is formed to be inclined relative to the tire circumferential direction D C , and a plurality of grooves  200  are repeatedly formed in the tire circumferential direction D C . 
     (2) Shape of Circumferential Groove 
       FIG. 2  is an enlarged perspective view of the circumferential groove  20 .  FIG. 3  is an enlarged view of the circumferential groove  20  as seen from the tire circumferential direction D C .  FIGS. 4( a ) to ( c )  are cross sectional views of the circumferential groove  20 . Specifically,  FIG. 4( a )  is a cross sectional view, of the circumferential groove  20 , taken along a line F 4 A to F 4 A illustrated in  FIG. 3 .  FIG. 4( b )  is a cross sectional view, of the circumferential groove  20 , taken along a line F 4 B to F 4 B illustrated in  FIG. 3 .  FIG. 4( c )  is a cross sectional view, of the circumferential groove  20 , taken along a line F 4 C to F 4 C illustrated in  FIG. 3 . 
     As illustrated in  FIG. 2  to  FIG. 4 , the first swelling portion  110  and the second swelling portion  120  are formed in plural with a predetermined distance (for example, about 30 mm) in the tire circumferential direction D C . 
     The first swelling portion  110  swells from one lateral wall  21  of the circumferential groove  20  toward a center in a widthwise direction of the circumferential groove  20 . Further, the first swelling portion  110  has, in a tread surface view of the pneumatic tire  10 , a tapered shape in which the size in the tread widthwise direction D T  is narrower as it goes in a first direction (upward direction in  FIG. 2  and  FIG. 3 ) in the tire circumferential direction D C . 
     The second swelling portion  120  has a shape similar to that of the first swelling portion  110 . Specifically, the second swelling portion  120  swells from the other lateral wall  22  of the circumferential groove  20  toward a center in the widthwise direction of the circumferential groove  20 . Further, the second swelling portion  120  has, in a tread surface view of the pneumatic tire  10 , a tapered shape in which the size in the tread widthwise direction D T  is narrower as it goes in a second direction (downward direction in  FIG. 2  and  FIG. 3 ) opposite to the first direction in the tire circumferential direction D C . 
     A lateral surface  111  of the first swelling portion  110  along the lateral wall  21  has, in the cross section along the tread widthwise direction D T  and the tire radial direction D R , an arc-like shaped portion recessed toward the lateral wall  21  (see  FIG. 4( c ) ). Similarly, a lateral surface  121  of the second swelling portion  120  along the lateral wall  22  has, in the cross section along the tread widthwise direction D T  and the tire radial direction D R , an arc-like shaped portion recessed toward the lateral wall  22  (see  FIG. 4( a ) ). 
     Further, an end  110   b  at a wider width side in the tread widthwise direction D T  of the first swelling portion  110  and the second swelling portion  120  is located inside, in the tire radial direction D R , from a tread surface of the land portion  30  adjacent to the circumferential groove  20 . On the other hand, an end  110   a  at a narrower width side in the tread widthwise direction D T  of the first swelling portion  110  is located at the approximately same height as that of a tread surface of the land portion  30  in the tire radial direction D R . Similarly, an end (end  120   a  described later) at a narrower width side in the tread widthwise direction D T  of the second swelling portion  120  is located at the approximately same height as that of a tread surface of the land portion  30  in the tire radial direction D R . According to the shape of such first swelling portion  110  and second swelling portion  120 , the groove  200  can be formed as a spiral-like form inside the circumferential groove  20 . 
     A bottom surface of the groove  200  is communicated, as one seamless surface, to the lateral surface  111  of the first swelling portion  110 . Further, the bottom surface of the groove  200  is communicated, as one seamless surface, to the lateral surface  121  of the second swelling portion  120 . That is, the bottom surface of the groove  200  has no portion in which an unevenness or a ridge is formed, and has a shape that little disturbs a flow of rainwater that has entered the groove  200 . 
     (3) Operation and Effect 
     According to the pneumatic tire  10 , between the first swelling portion  110  and the second swelling portion  120 , a plurality of grooves  200  extending in the tire circumferential direction D C  are formed. The first swelling portion  110  has, in a tread surface view of the pneumatic tire  10 , a tapered shape in which the size in the tread widthwise direction D T  is narrower as it goes in a first direction in the tire circumferential direction D C . Similarly, the second swelling portion  120  has, in a tread surface view of the pneumatic tire  10 , a tapered shape in which the size in the tread widthwise direction D T  is narrower as it goes in a second direction in the tire circumferential direction D C . 
     Rainwater flowing in such a groove  200  flows in a spiral form from the bottom surface of the groove  200  toward the lateral surface  111  of the first swelling portion  110  and the lateral surface  121  of the second swelling portion  120 . Thus, the rainwater that has entered the circumferential groove  20  flows smoothly without creating a large turbulence inside the circumferential groove  20 . That is, even when a lug groove component is reduced as in the pneumatic tire  10 , it is possible to provide a sufficient water drainage performance. 
     In the present embodiment, the lateral surface  111  of the first swelling portion  110  is of arc-like shape recessed toward the lateral wall  21 . Further, in the present embodiment, the lateral surface  121  of the second swelling portion  120  is of arc-like shape recessed toward the lateral wall  22 . Thus, the rainwater that has entered the circumferential groove  20  is more easily flown in a spiral form, resulting in further increasing a water drainage performance. 
     In the present embodiment, the end  110   b  (end  120   b ) at a wider width side of the first swelling portion  110  (second swelling portion  120 ) is located inside, in the tire radial direction D R , from a tread surface of the land portion  30 . Further, the end  110   a  (end  110   b ) at a narrower width side of the first swelling portion  110  (second swelling portion  120 ) is located at the approximately same height as that of a tread surface of the land portion  30  in the tire radial direction D R . Moreover, the bottom surface of the groove  200  is communicated, as one seamless surface, to the lateral surface  111  of the first swelling portion  110 , and communicated, as one seamless surface, to the lateral surface  121  of the second swelling portion  120 . 
     As a result, it is possible to bring a flow of rainwater having entered the circumferential groove  20  in a spiral form having a large radius of rotation, resulting in a further improvement of water drainage performance. 
     In particular, the water led to the first direction along a direction in which the groove  200  extends travels over the end  110   b  at a wider width side of the first swelling portion  110 , and thereafter, the water is prevented by the end  110   a  at a narrower width side of the first swelling portion  110  after which it is led to the other lateral wall  22  of the circumferential groove  20  from one lateral wall  21  of the circumferential groove  20 . Further, the water is prevented by the end  120   a  at a narrower width side of the second swelling portion  120  and the other lateral wall  22  of the circumferential groove  20 , resulting in a turbulent flow to be led to the first direction. As a result of such a flow of water being continuing, the flow of water is brought in a spiral form. 
     (4) Other Embodiments 
     So far, the contents of the present invention are disclosed through the above embodiment of the present invention. However, it should not be interpreted that the statements and drawings constituting a part of the present 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, in the above-described embodiment, the bottom surface of the groove  200  is communicated, as one seamless surface, to the lateral surface  111  of the first swelling portion  110 , and communicated, as one seamless surface, to the lateral surface  121  of the second swelling portion  120 ; however, the bottom surface of the groove  200  may not necessarily be communicated, as one seamless surface like this, and may have a portion where a slight unevenness or ridge is formed. 
     In the above-described embodiment, the lateral surface  111  of the first swelling portion  110  and the lateral surface  121  of the second swelling portion  120  are of arc-like shape; however, may not necessarily be of arc-like shape, and may be liner in a cross section along the tread widthwise direction D T  and the tire radial direction D R . 
     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. 
     INDUSTRIAL APPLICABILITY 
     According to a characteristic of the present invention, even when a lug groove component is reduced, it is possible to provide a tire having a sufficient water drainage performance.