Abstract:
An inclined groove ( 11 ) has a first inclined groove ( 101 ) and a second inclined groove ( 102 ). The first inclined groove ( 101 ) intersects a tire equator line (CL) and extends to one side (W 1 ) outward in the tire width direction proceeding from the forward side (F) to the rearward side (B) in the rotation direction. The second inclined groove ( 102 ) intersects the tire equator line (CL) and the first inclined groove ( 101 ), and extends to the other side (W 2 ) outward in the tire width direction proceeding from the forward side (F) in the rotation direction to the rearward side (B) in the rotation direction. The first inclined groove ( 101 ) and the second inclined groove ( 102 ) have forward side curved grooves ( 111 ), ( 121 ) located at the forward side (F) in the rotation direction, and rearward side curved grooves ( 112 ), ( 122 ) located at the rearward side (B) in the rotation direction.

Description:
TECHNICAL FIELD 
     The present invention relates to a tire suitable for use in icy or snowy road surface. 
     BACKGROUND ART 
     Conventionally, a variety of proposals have been made as to a tire improving a cruising performance on an icy or snowy road surface (a snowy road surface or an icy road surface). In order to enhance a cruising performance such as an acceleration performance at the time of startup on an icy or snowy road surface a braking performance at the time of stoppage, it is preferable to increase a component of a side groove along a tread widthwise direction (a so called lag groove) and to increase a percentage of a groove area in a ground surface (a negative rate). 
     However, if the component of the lag groove is increased too much in order to increase the negative rate, since a stability of block lowers, a driving stability in a dry road surface also lowers. On the other hand, if the content of the lag component is increased without increasing the negative rate, since a groove (a rib groove) component in a circumferential direction along a tire circumferential direction is decreased, a drainage performance also lowers. 
     In order to ensure compatibility between the cruising performance and the drainage performance in the icy or snowy road surface described above for example, there is proposed a tire in which a lag groove crossing in the tread widthwise direction is formed in a substantially V shape so as to be symmetrical with a tire equator line (refer to Patent Literature 1). According to this tire, the drainage performance is improved by means of a lag groove formed in a substantially V shape so as to be symmetrical with the tire equator line and a main groove that are formed in parallel to each other along the tire circumferential direction at a tread center part including the tire equator line. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: International Publication No. WO2005/005170, FIG. 1 
     SUMMARY OF INVENTION 
     However, so far, the conventional tire has entailed the following problem. That is, while in the conventional tire, the drainage performance can be improved, a block surrounded by the main groove has a shape which is greater in length in the tire circumferential direction than in the tread widthwise direction. In addition, since a sipe along the tread widthwise direction is formed, there is a problem that rigidity of the tread center part lowers. The lowering of the rigidity of the tread center part leads to the lowering of traction at the time of cornering or at the time of fast cruising. 
     Therefore, a further modification is required to widely ensure compatibility between the cruising performance and the drainage performance in a variety of situations in icy or snowy road surface. 
     Accordingly, it is an object of the present invention to provide a tire enabling a cruising performance and a drainage performance in icy or snowy road surface to be compatible with each other at a high level. 
     To solve the above problem, the present invention is summarized as a tire comprising a plurality of inclined grooves (inclined grooves  11 ) which are inclined with respect to a tread widthwise direction line (tread widthwise direction line L) parallel to a tread widthwise direction and are disposed in a tread unit along a tire circumferential direction, and in which a rotational direction at a time of forward movement of a vehicle body is specified, wherein the inclined grooves have: a first inclined grooves (first inclined grooves  101 , for example) crossing a tire equator line and extending to the outside in one tire widthwise direction as the first inclined grooves go from a foreside (foreside F in the rotational direction) to a backside (backside B in the rotational direction) in the rotational direction; and a plurality of second inclined grooves (second inclined grooves  102 ) respectively crossing the tire equator line and the first inclined grooves and extending to an outside in another tire widthwise direction as the second inclined grooves go from the foreside to the backside in the rotational direction, the first inclined grooves and the second inclined grooves respectively comprise: a foreside curved groove (foreside curved grooves  111 ,  121 ) positioned at the foreside in the rotational direction and are formed of curves overhanging from the foreside to the backside in the rotational direction, the foreside curved groove crossing the tread widthwise direction line at an acute angle; and a backside curved groove (backside curved grooves  112 ,  122 ) connected to an end portion at the backside in the rotational direction of the foreside curved groove and crossing the tread widthwise direction line at an angle (φ 1 , φ 2 ) greater than a cross angle (θ 1 , θ 2 ) between the foreside curved groove and the tread widthwise direction line, the plurality of second inclined grooves respectively comprise: a foreside second inclined groove (foreside second inclined groove  102   a , for example); and a backside second inclined groove (backside second inclined groove  102   b , for example) disposed at the backside in the rotational direction more significantly than the foreside second inclined groove and is adjacent to the foreside second inclined groove in the tire circumferential direction, the foreside curved groove of the first inclined groove and the backside curved groove of the foreside second inclined groove cross each other, and the backside curved groove of the first inclined groove and the foreside curved groove of the backside second inclined groove cross each other. 
     According to the present invention, since the first inclined grooves and the second inclined grooves are formed so as to extend to the outside in a tire widthwise direction as these grooves go from a foreside in a rotational direction (foreside F in the rotational direction) to a backside (backside B in the rotational direction), there can be enhanced an advantageous effect of discharging water on a road surface to the outside in the tire widthwise direction. 
     In addition, according to the present invention, a foreside curved groove is formed, whereby an edge effect at the time of acceleration or at the time of startup can be enhanced. 
     Further, the foreside curved grooves are positioned at the foreside in the rotational direction, and are constituted with curves overhanging from the foreside to the backside in the rotational direction. In addition, the foreside curved groove of the first inclined groove and the backside curved groove of the foreside second inclined groove on the foreside cross each other, and the backside curved groove of the first inclined groove and the foreside curved groove  121  of the backside second inclined groove on the backside cross each other. With these grooves, at a cross point, movements of snow in the grooves interfere with each other, a pressure associated with the snow in the grooves rises. In this manner, density of the snow in the grooves is increased, and a snow&#39;s shear force increases. Therefore, the cruising performance in icy or snowy road surface can be enhanced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG. 1 ]  FIG. 1  is an exploded view explaining a tread pattern of a pneumatic tire  1  according to a first embodiment. 
       [ FIG. 2 ]  FIG. 2  is an exploded view explaining the tread pattern of the pneumatic tire  1  according to the first embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of a tire according to the present invention will be described with reference to the drawings. Specifically, (1) Description of Pneumatic Tire, (2) Functions and Advantageous Effects, and (3) Other Embodiments will be described. 
     In the following description of the drawings, same or similar constituent elements are designated by same or similar reference numerals. However, it should be kept in mind that the drawings are merely schematic, and rates or the like of the respective dimensions are different from real ones. Therefore, specific dimensions or the like should be determined in consideration of the following description. In addition, in among the respective drawings, portions different from each other in dimensional interrelationship or rate are included. 
     (1) Description of Pneumatic Tire 
     A structure of a pneumatic tire  1  according to the embodiments will be described with reference to the drawings.  FIG. 1  and  FIG. 2  are exploded views explaining a tread pattern of a pneumatic tire  1  according to a first embodiment. The pneumatic tire is a general radial tire provided with a bead unit, a carcass layer, a belt layer, and a tread unit (not shown). In the pneumatic tire  1 , a rotational direction (R direction) at the time of forward movement of a vehicle body is specified. 
     The pneumatic tire  1  is provided with a plurality of inclined grooves  11  inclined with respect to a phantom line along a tread widthwise W direction (tread widthwise direction line L). 
     The inclined groove  11  has a plurality of first inclined grooves  101  and a plurality of second inclined grooves  102 . The first inclined groove  101  crosses a tire equator line CL, and extends to one outside W 1  in a tire widthwise direction as the groove goes from the foreside F in the rotational direction to the backside B in the rotational direction. The second inclined groove  102  crosses the tire equator line CL and the first inclined groove  101 , and extends to the other outside W 2  in the tire widthwise direction as the groove goes from the foreside F in the rotational direction to the backside B in the rotational direction. 
     The first inclined groove  101  has a forward first inclined groove  101   a  and a backward first inclined groove  101   b . The forward first inclined groove  101   a , and the backward first inclined groove  101   b , are adjacent to each other in the tire circumferential direction. The forward first inclined groove  101   a , is positioned at the foreside F in the rotational direction more significantly than the backward first inclined groove  101   b . The backward first inclined groove  101   b , is positioned at the backside B in the rotational direction more significantly than the forward first inclined groove  101   a.    
     The second inclined groove  102  has a forward second inclined groove  102   a , and a backward second inclined groove  102   b . The forward second inclined groove  102   a , and the backward second inclined groove  102   b , are adjacent to each other in the tire circumferential direction. The forward second inclined groove  102   a , is positioned at the foreside F in the rotational direction more significantly than the backward second inclined groove  102   b . The backward second inclined groove  102   b , is positioned at the backside B in the rotational direction more significantly than the forward second inclined groove  102   a.    
     The first inclined groove  101  and the second inclined groove  102  both are formed so as to cross the tire equator line CL. The shape of the first inclined groove  101  and the shape of the second inclined groove  102  are respectively linearly symmetrical with each other with respect to the tire equator line CL. The first inclined groove  101  and the second inclined groove  102 , each of which has the shape of linear symmetry with respect to the tire equator line CL, are formed so as to be displaced forward and backward in the tire circumferential direction in the tread unit. 
     The first inclined groove  101  has a foreside curved groove  111  that is positioned at the foreside F in the rotational direction and a backside curved groove  112  that is positioned at the backside B in the rotational direction. The foreside curved groove  111  and the backside curved groove  112  are connected to each other. The first inclined groove  101  bends at this coupling portion. 
     Like the first inclined groove  101 , the second inclined groove  102  also has a foreside curved groove  121  that is positioned at the foreside F in the rotational direction and a backside curved groove  122  that is positioned at the backside B in the rotational direction. The foreside curved groove  121  and the backside curved groove  122  are connected to each other. The second inclined groove  102  bends at this coupling portion. 
     In addition, the foreside curved grooves  111  and  121  and the backside curved grooves  112  and  122  both are formed of curves overhanging from the foreside F in the rotational direction to the backside B in the rotational direction. 
     In the embodiment shown in  FIG. 1  and  FIG. 2 , the foreside curved grooves  111  and  121  are formed so that their lengths that over the tire circumferential direction are respectively smaller than those of the backside curved grooves  112  and  122 . The foreside curved grooves  111  and  121  cross the line L in the tread widthwise direction at an acute angle (angle θ 1  or θ 2 ). 
     The backside curved grooves  112  and  122  are connected to end portions  111   r , and  121   r , at the backside B in the rotational direction of the foreside curved grooves  111  and  121 . The backside curved grooves  112  and  122  cross the line L in the tread widthwise direction at angle φ 1  or φ 2  that is greater than the cross angle θ 1  or θ 2  between the foreside curved grooves  111  and  121  and the tread widthwise direction L. Here, the ranges of angles of θ 1  and θ 2  and φ 1  and φ 2  can be set at the values as shown below. 30, degrees&lt;θ 1 , θ 2 &lt;80, degrees, 60, degrees&lt;φ 1 , and φ 2 &lt;100, degrees 
     In the embodiment shown in  FIG. 1  and  FIG. 2 , the foreside curved grooves  111  and  121  are formed so as to extend in the tread widthwise direction, and the backside curved grooves  112  and  122  are formed so as to extend in the tire circumferential direction. 
     In the embodiment, the foreside curved groove  111  of the first inclined groove  101  and the backside curved groove  122  of the second inclined groove  102  cross each other. The backside curved groove  112  of the first inclined groove  101  and the foreside curved groove  121  of the second inclined groove  102  cross each other. Specifically, the foreside curved groove  111  of the first inclined groove  101  and the backside curved groove  122  of the foreside second inclined groove  102   a , cross each other, and the backside curved groove  112  of the first inclined groove  101  and the foreside curved groove  121  of the backside second inclined groove  102   b , cross each other. Similarly, the foreside curved groove  121  of the second inclined groove  102  and the backside curved groove  112  of the foreside first inclined groove  101   a  cross each other, and the backside curved groove  122  of the second inclined groove  102  and the foreside curved groove  111  of the backside first inclined groove  101   b , cross each other. 
     The foreside curved groove  111  of the first inclined groove  101  crosses the tire equator line CL. The foreside curved groove  121  of the second inclined groove  102  crosses the tire equator line CL. 
     In the tire widthwise direction, circumferential grooves  130  and  150  extending along the tire circumferential direction are respectively formed at the outside of the first inclined groove  101  and the second inclined groove  102 . 
     The circumferential grooves  130  and  150  are formed in a zigzag shape with respect to the line M in the tire circumferential direction parallel to a tire circumferential direction. 
     In the embodiment shown in  FIG. 1  and  FIG. 2 , when the tread unit is expanded all over the tire circumferential direction, the circumferential grooves  130  and  150  are grooves (so called see-through grooves) in which from arbitrary one end (an end portion Tf of the foreside F in the rotational direction in  FIG. 2 ), the other end (an end portion Tb of the backside B in the rotational direction in  FIG. 2 ) can be seen. 
     The backside curved groove  112  is in communication with the circumferential groove  130 . The backside curved groove  122  is in communication with the circumferential groove  150 . 
     At a communication portion between the backside curved groove  112  and the circumferential groove  130 , an end portion T 2  of a wall surface of the foreside F in the rotational direction of the backside curved groove  112  is positioned in a location closer to the tire equator line CL than an end portion T 1  of the wall surface of the backside B in the rotational direction of the backside curved groove  112 . Similarly, at a communication portion between the backside curved groove  122  and the circumferential groove  150 , an end portion of the wall surface of the foreside F in the rotational direction of the backside curved groove  122  is positioned in a location closer to the tire equator line CL than an end portion of the wall surface of the backside B in the rotational direction of the backside curved groove  122 . It is to be noted that the end portion of the wall surface is an end portion in the tread widthwise direction. 
     In the tire widthwise direction W, a plurality of side grooves  140  extending in the tread widthwise direction are formed at the outside W 1  of the circumferential groove  130 . In the tire widthwise direction W, a plurality of side grooves  160  extending in the tread widthwise direction are formed at the outside W 2  of the circumferential groove  150 . An end portion  112   b , of the outside in the tire widthwise direction of the backside curved groove  112  couples with the side groove  140 . In addition, an end portion  122   b , at the outside in the tire widthwise direction of the backside curved groove  122  couples with the side groove  160 . 
     The blocks B 1  and B 2  that are formed by being defined in the first inclined groove  101  and the second inclined groove  102  has an elongated portion in which a length Wa in he tread widthwise direction is greater than a length Wb in the tire circumferential direction. At the elongated portion, a thin groove (referred to as a sipe) is formed, although not shown. Here, the thin groove is referred to as a groove such that wall parts forming the thin groove are brought into contact with each other by means of a grounding pressure exerted when the pneumatic tire  1  is grounded. 
     (2) Functions and Advantageous Effects 
     In the pneumatic tire  1 , the first inclined groove  101  and the second inclined groove  102  are formed so as to extend to the outside in the tire widthwise direction as these grooves go from the foreside F in the rotational direction to the backside B in the rotational direction. Thus, an advantageous effect of discharging the water on a road surface to the outside in the tire widthwise direction can be enhanced. 
     In the embodiment shown in  FIG. 1  and  FIG. 2 , the foreside curved grooves  111  and  121  are formed so as to extend in the tread widthwise direction. Thus, the foreside curved grooves  111  and  121  can contribute to an edge effect at the time of acceleration or at the time of startup. The backside curved grooves  112  and  122  are formed so as to extend in the tire circumferential direction. Therefore, the backside curved grooves  112  and  122  can contribute to drainage property. 
     In the embodiment, the first inclined groove  101  and the second inclined groove  102 , each of which has the shape of linear symmetry with respect to the tire equator line CL, are formed so as to be displaced forward and backward in the tire circumferential direction in the tread unit. In this manner, a change of a negative rate on the tread widthwise direction line exerted by tire rolling can be reduced, and tire noise exerted by edging can be reduced. 
     In the embodiment, the foreside curved groove  111  of the first inclined groove  101  and the backside curved groove  122  of the foreside second inclined groove  102   a , cross each other, and the backside curved groove  112  of the first inclined groove  101  and the foreside curved groove  121  of the backside second inclined groove  102   b , cross each other. Similarly, the foreside curved groove  121  of the second inclined groove  102  and the backside curved groove  112  of the foreside first inclined groove  101   a , cross each other, and the backside curved groove  122  of the second inclined groove  102  and the foreside curved groove  111  of the backside first inclined groove  101   b , cross each other. In addition, the foreside curved groove  111  of the first inclined groove  101  crosses the tire equator line CL. The foreside curved groove  121  of the second inclined groove  102  crosses the tire equator line CL. 
     In this manner, at a cross portion, movements of snow in the grooves interfere with each other, and a pressure associated with the snow in the grooves rises. For example, at the time of acceleration, at a cross portion of the grooves, the snow in the grooves moves in the direction indicated by the filled arrow, and its related movements interfere with each other, whereby the pressure associated with the snow in the grooves rises. In this manner, density of the snow in the grooves is enhanced, and a snow&#39;s shear force increases. In addition, at the time of braking, at the cross portion, the snow in the grooves moves in the direction indicated by the open arrow, and its related movements interfere with each other, whereby the pressure associated with the snow in the grooves rises. Therefore, the braking performance and the acceleration performance in icy or snowy road surface can be enhanced. 
     Here, the ranges of the angles of θ 1 , θ 2 , φ 1 , and φ 2  can be set at the values shown below. 30, degrees&lt;θ 1 , θ 2 &lt;80, degrees, 60, degrees&lt;φ 1 , and φ 2 &lt;100, degrees. In particular, if the cross angles θ 1  and θ 2  between the foreside curved grooves  111  and  121  and the line L in the tread widthwise direction, are set to be 30, degrees&lt;θ 1  and θ 2 &lt;50, degrees, a good edge effect can be obtained. In addition, the cross angles φ 1  and φ 2  between the backside curved grooves  112  and  122  and the line L in the tread widthwise direction are set to be 70, degrees&lt;φ 1  and φ 2 &lt;90, degrees, a good drainage property can be obtained. 
     In addition, in a case where the cross angles θ 1  and θ 2  between the foreside curved grooves  111  and  121  and the line L in the tread widthwise direction are set to be shallow, the snow entering the foreside curved grooves  111  and  121  is hardly released. Thus, the snow&#39;s shear force can be further increased. Therefore, the cruising performance in icy or snowy road surface (in particular, steering wheel handling performance) can be enhanced. In this case, it is preferable that a relationship between the cross angles of θ 1  and θ 2  meet θ 1  and θ 2 &lt;OO degrees. 
     At the outside in the tire widthwise direction, there are formed the circumferential grooves  130  and  150  extending along the tire circumferential direction and having a zigzag shape with respect to the line M in the tire circumferential direction parallel to a tire circumferential direction. In the embodiment, at the communication portion between the backside curved groove  112  and the circumferential groove  130 , the end portion T 2  of the wall surface of the foreside F in the rotational direction of the backside curved groove  112  is positioned in a location closer to the tire equation line CL than the end portion T 1  of the wall surface of the backside B in the rotational direction of the backside curved groove  112 . Similarly, at the communication portion between the backside curved groove  122  and the circumferential groove  150 , an end portion of the wall surface of the foreside F in the rotational direction of the backside curved groove  122  is positioned in a location closer to the tire equation line CL than an end portion of the wall surface of the backside B in the rotational direction of the backside curved groove  122 . 
     By having such shape, the snow in the grooves is easily caught in the wall surface, and the snow in the grooves can be effectively compressed by means of rolling. Therefore, the snow&#39;s shear force can be effectively generated. In addition, since the circumferential grooves  130  and  150  are so called see-through grooves, these grooves have an edge effect, and can enhance a snow cruising performance and a drainage performance. 
     The blocks B 1  and B 2  that can be formed after defined into the first inclined groove  101  and the second inclined groove  102  has an elongated portion in which the length Wa in the tread widthwise direction is greater than the length Wb in the tire circumferential direction. At the elongated portion, a thin groove (referred to as a sipe) is formed, although not shown. In this manner, since an elongated groove that is long in the tread widthwise direction is formed in the blocks B 1  and B 2 , an edge effect can be enhanced. 
     (3) Other Embodiments 
     As described above, while the contents of the present invention were disclosed through the embodiments of the present invention, it should not be understood that the statements and drawings forming a part of this disclosure limit the present invention. From this disclosure, a variety of alternative embodiments and examples would be self-explanatory to one skilled in the art. For example, the embodiments of the present invention can be modified as follows. 
     For example, while in  FIG. 1 , it is shown that the angles θ 1  and θ 2  are equal to each other, as long as the angle relationship described above is met, there does not always need to be θ 1 =θ 2 . As is the case with a relationship between the angles of φ 1  and φ 2  as well, as long as the angle relationship described above is met, there does not always need to be φ 1 =φ 2 . 
     While, in the embodiment shown in  FIG. 1 , the circumferential groove extending along the tire circumferential direction is formed at each of one outside W 1  in the tire widthwise direction and the other outside W 2  in the tire widthwise direction, the circumferential groove may be formed at only one side. 
     While, in the embodiment shown in  FIG. 1 , the rotational direction (R direction) at the time of forward movement of a vehicle body was specified, the rotational direction at the time of forward movement of the vehicle body does not always need to be specified. One direction parallel to a tire circumferential direction is a first direction, and the other direction parallel to a tire circumferential direction is a second direction. The second direction is a direction opposite to the first direction. 
     In a case where the first direction at the time of forward movement of the vehicle body is not specified, it may be that the tire is provided with a plurality of inclined grooves that are inclined with respect to the tread widthwise direction line parallel to a tread widthwise direction, and are disposed in a tread unit along the tire circumferential direction, the inclined grooves have: first inclined grooves crossing the tire equation line and extending to the outside in one wire widthwise direction as these grooves go from the foreside to the backside in the first direction; and a plurality of second inclined grooves respectively crossing the tire equation line and the first inclined grooves and extending to the outside in the other tore widthwise direction as these grooves go from the foreside to the backside in the first direction, the first inclined grooves and the second inclined grooves are formed of: foreside curved grooves that are positioned at the foreside in the first direction and are formed of curves overhanging from the foreside to the backside in the first direction, the foreside curved grooves crossing the tread widthwise direction line at an acute angle; and backside curved grooves connected to an end portion at the backside in the first direction of the foreside curved groove and crossing the tread widthwise direction line at an angle that is greater than the cross angle between the foreside curved groove and the tread widthwise direction line, the plurality of second inclined grooves have foreside second inclined grooves and backside second inclined grooves that are disposed at the backside in the first direction more significantly than the foreside second inclined grooves, and are adjacent to the foreside second inclined grooves in the tire circumferential direction, the foreside curved grooves of the first inclined grooves and the backside curved grooves of the foreside second inclined grooves cross each other, and the backside curved grooves of the first inclined grooves and the foreside curved grooves of the backside second inclined grooves cross each other. As long as the tire mentioned above is mounted on the vehicle body so that the rotational direction at the time of forward movement of the vehicle body is coincident with the first direction, there can be attained functions and advantageous effects similar to those of the embodiment shown in  FIG. 1 . In order to prevent a mistaken mounting direction, it is preferable that the rotational direction at the time of forward movement of the vehicle body be specified. 
     Thus, of course, the present invention includes a variety of embodiments or the like described herein. Therefore, the technical scope of the present invention is defined only by the specified matter of the invention associated with reasonable scope of claims from the foregoing description. 
     All the contents of Japanese Patent Application No. 2010-225771 (filed on Oct. 5, 2010) are incorporated therein by reference. 
     [Industrial Applicability] 
     According to the present invention, there can be provided a tire enabling a cruising performance and a drainage performance in icy or snowy road surface to be compatible with each other at a high level.