Abstract:
A pneumatic tire includes a plurality of protrusions on a bottom of each of the grooves. The height of the protrusion is variable in a profile of the protrusion in a circumference direction of the pneumatic. The protrusion has at least one peak portion that protrudes away from a center of the pneumatic tire. The pneumatic tire further includes a connection member between the protrusion and an adjacent one of the lands, the connection member having a first end toward the land and a second end toward the peak portion, a height of the first end from the bottom of the groove being larger than that of the second end.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a pneumatic tire. The present invention specifically relates to a pneumatic tire capable of suppressing stone trapping.  
         [0003]     2. Description of the Related Art  
         [0004]     Stones are sometimes trapped within grooves that are formed on the tread area of pneumatic tires of vehicles. When the stones are trapped within the grooves, so-called “stone drilling” may occur. The stone drilling is a phenomenon that stones penetrate the bottoms of the grooves due to rolling of the pneumatic tire to cause damage to the tread area. To take care of this issue, some of the conventional pneumatic tires have protrusions in the grooves to minimize stone trapping in the grooves. Due to the provision of the protrusions, even if stones enter the grooves, the stones are ejected to the outside of the grooves by the elastic force of the protrusion.  
         [0005]     When manufacturing pneumatic tires having protrusions in the grooves, however, the protrusions become obstacle to flow of rubber for forming the tread area inward in the tire radial direction of the protrusion. This may increase the pressure of the rubber located inward of the protrusion in the tire radial direction, and associated with this, a breaker ply located inward of the protrusion in the tire radial direction can get deformed into a wavy shape. If the breaker ply is deformed in this manner, abnormal wear may occur to the pneumatic tire due to the deformation in the breaker ply when a vehicle to which the pneumatic tires are fit travels.  
         [0006]     Some of the conventional pneumatic tires have a configuration that makes it possible to suppress the deformation of the breaker ply when the protrusions are provided in the grooves. For example, in Japanese Patent Application Laid-Open No. S61-291203, a plurality of protrusions are provided in grooves that extend in a zigzag shape in the tire circumferential direction, and connection members for connecting the protrusions to the sidewalls of the grooves are provided in locations where the adjacent protrusions in the tire circumferential direction are provided alternately in the tire width direction. In such a structure, the rubber located inward of the protrusion in the tire radial direction can escape in the direction of a land during manufacture of the pneumatic tire. It is, therefore, possible to prevent the pressure of the rubber located inward thereof in the tire radial direction from becoming too high. Consequently, it is possible to suppress the deformation of the breaker ply located inward of the protrusion in the tire radial direction and to reduce the abnormal wear.  
         [0007]     The protrusion provided in the groove ejects the stone entering the groove to the outside of the groove by the elastic force of the protrusion, and prevents the stone trapped within the groove from reaching the breaker ply by the volume of the protrusion. Therefore, the protrusion needs to have a predetermined height and a predetermined volume to fulfill these functions. Greater effect of suppressing stone trapping can be obtained if the height is larger or if the volume is larger. However, if the protrusion is too large, then the rubber does not satisfactorily flow into a mold for forming the protrusion, and it is difficult to discharge the air present between the mold and the rubber during manufacture of the pneumatic tire. As a result, the pneumatic tire is manufactured without obtaining a targeted shape of the protrusion, which causes failure in manufacture, i.e., occurrence of “bare” (depressed area).  
       SUMMARY OF THE INVENTION  
       [0008]     It is an object of the present invention to at least partially solve the problems in the conventional technology.  
         [0009]     According to an aspect of the present invention, a pneumatic tire having a tread area, the tread area being divided into a plurality of lands by virtue of a plurality of grooves, includes a plurality of protrusions on a bottom of each of the grooves, a height of the protrusion from the bottom of the groove in a profile of the protrusion in a circumference direction of the pneumatic tire being variable, the protrusion including at least one peak portion that protrudes away from a center of the pneumatic tire; and a connection member between the protrusion and an adjacent one of the lands, the connection member having a first end toward the land and a second end toward the peak portion, a height of the first end from the bottom of the groove being larger than that of the second end.  
         [0010]     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a diagram of a tread area of a pneumatic tire according to an embodiment of the present invention;  
         [0012]      FIG. 2  is a detailed diagram of the portion A of  FIG. 1 ;  
         [0013]      FIG. 3  is a cross-section taken along the line B-B of  FIG. 2 ;  
         [0014]      FIG. 4  is a cross-section taken along the line C-C of  FIG. 3 ;  
         [0015]      FIG. 5  is a perspective view of a protrusion and a connection member;  
         [0016]      FIG. 6  is a cross-section of the pneumatic tire for explaining a state in which a stone is trapped within a groove of the pneumatic tire;  
         [0017]      FIG. 7  is a cross-section of the pneumatic tire for explaining how the stone shown in  FIG. 6  moves;  
         [0018]      FIG. 8  is a schematic of a mold and a tread rubber for explaining a state before the tread area is subjected to vulcanization molding;  
         [0019]      FIG. 9  is a schematic of the mold and the tread rubber for explaining the state in which the tread area is being subjected to the vulcanization molding;  
         [0020]      FIG. 10  is a schematic of the mold and the tread rubber for explaining the state in which the tread area is being subjected to the vulcanization molding and which is subsequent to the state shown in  FIG. 9 ;  
         [0021]      FIG. 11  is a detailed cross-section of a pneumatic tire according to another embodiment of the present invention; and  
         [0022]      FIG. 12  is a cross-section taken along the line D-D of  FIG. 11 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings. It is to be noted that the present invention is not limited by the embodiments. Constituent elements explained in the following embodiments include those easily replaceable therewith by persons skilled in the art, or those substantially equivalent thereto. Types of pneumatic tires include a block type tread, a ribbed tread, and a ribbed-lug tread. In the following embodiments, the pneumatic tire having the block type tread will be explained as an example of the pneumatic tire.  
         [0024]     In the embodiments, a tire width direction means a direction parallel to a rotating axis of the pneumatic tire, an inward in the tire width direction means a direction toward an equatorial plane in the tire width direction, and an outward in the tire width direction means a direction opposite to the direction toward the equatorial plane in the tire width direction. Moreover, a tire radial direction means a direction orthogonal to the rotating axis, and a tire circumferential direction indicates a direction of the tire rotating around the rotating axis.  
         [0025]      FIG. 1  is a schematic of a tread area  10  of a pneumatic tire  1  according to an embodiment of the present invention. The tread area  10 , which is made of an elastic rubber material, is formed on an outermost side in the tire radial direction. A surface of the tread area  10 , namely, a portion of the pneumatic tire  1  contacting a surface of the road when a vehicle (not shown) on the pneumatic tires  1  runs, is formed as a tread surface  11 . A plurality of grooves  20  including those formed in predetermined directions is formed in the tread area  10 . The grooves  20  include a plurality of longitudinal grooves  21  formed in the tire circumferential direction and a plurality of lateral grooves  22  formed in the tire width direction. The tread area  10  is divided by the longitudinal grooves  21  and the lateral grooves  22  into a plurality of blocks  15 , which blocks are to serve as lands. Protrusions  30  are arranged at intervals in the grooves  20  for both the longitudinal grooves  21  and the lateral grooves  22 , respectively.  
         [0026]     The longitudinal groove  21  and the lateral groove  22  are not necessarily formed accurately in the tire circumferential direction or the tire width direction. It suffices that each longitudinal groove  21  is formed substantially in the tire circumferential direction. Namely, the longitudinal groove  21  can be formed aslant with respect to the tire width direction, formed to be curved, or formed into a zigzag shape. It suffices that each lateral groove  22  is formed substantially in the tire width direction. Namely, the lateral groove  22  can be formed aslant with respect to the tire circumferential direction, formed to be curved, or formed into a zigzag shape.  
         [0027]      FIG. 2  is a detailed diagram of the portion A of  FIG. 1 .  FIG. 3  is a cross section taken along the line B-B of  FIG. 2 .  FIG. 4  is a cross section taken along the line C-C of  FIG. 3 .  FIG. 5  is a perspective view of the protrusion  30  and a connection member  40 . The protrusion  30  made of the same rubber material as that of the tread area  10  is formed apart from the blocks  15  or from groove walls  23  of the grooves  20 . The protrusion  30  is formed to protrude outward in the tire radial direction from a groove bottom  24  of the groove  20 . The protrusion  30  is also formed so that its height is smaller than that of the block  15 , namely, smaller than a distance from the groove bottom  24  to the tread surface  11 .  
         [0028]     The height of the protrusion  30  thus formed, from the groove bottom  24 , is changed. In other words, the protrusion  30  includes a convex portion  31  and a slope  35 . The convex portion  31  protrudes outward in the tire radial direction. The slope  35  is formed such that its height from the groove bottom  24  is getting smaller as it is farther from the convex portion  31 . The convex portion  31  has a top  32  that is the highest from the groove bottom  24  and parallel to the groove bottom  24 . The slope  35  is provided on each side of the convex portion  31  in the direction in which the groove  20  is formed. The convex portion  31  and the slopes  35  of the protrusion  30  are respectively formed to be generally rectangle when the protrusion  30  is viewed in the depth direction of the groove  20 .  
         [0029]     The connection member  40  is formed between the protrusion  30  thus shaped and the block  15 . The connection member  40  is connected to both the convex portion  31  of the protrusion  30  and the block  15 . A connection end of the connection member  40 , which end is connected to the convex portion  31  is a convex-side end  41 , and a connection end of the connection member  40 , which end is connected to the block  15  is a block-side end  42  or a land-side end. The convex-side end  41  is connected to a block  15 -side surface of the convex portion  31 , and the block-side end  42  is connected to a protrusion  30 -side surface of the block  15  or to a portion of the groove wall  23  opposing the convex portion  31 . The block-side end  42  is formed so that its height from the groove bottom  24  is larger than that of the convex portion  31  from the groove bottom  24 .  
         [0030]     More specifically, an outward surface  43  of the connection member  40 , which surface is located outward in the tire radial direction, is inclined with respect to the groove bottom  24 . The outward surface  43  is inclined in the direction in which it is farther from the groove bottom  24  as it directs from the convex-side end  41  toward the block-side end  42 . Alternatively, the outward surface  43  is inclined to be gradually located outward in the tire radial direction. In other words, the connection member  40  is formed so that its height from the groove bottom  24  is getting larger from the convex-side end  41  toward the block-side end  42 . Therefore, the relation between the convex portion  31  and the connection member  40  is represented by h 2 &lt;h 1 , where h 1  is the height of the convex portion  31  from the groove bottom  24  and h 2  is the height of the connection member  40  from the groove bottom  24 . Namely, the height of any part of the connection member  40  from the groove bottom  24  is always larger than that of the convex portion  31  from the groove bottom  24 .  
         [0031]     An inclination angle θ of the outward surface  43  with respect to the groove bottom  24 , i.e. an inclination angle θ with respect to the groove bottom  24  from the convex-side connection end  41  over the block-side end  42  is preferably in a range from 3 degrees to 45 degrees. Furthermore, a width of the connection member  40  in the direction in which the groove  20  is formed is preferably almost the same as that of the convex portion  31  in the same direction or as that of the top  32  in the same direction. Moreover, the connection member  40  is preferably formed to satisfy the relation represented by 0.05h 1 ≦W≦1.0h 1 , where h 1  is the height of the convex portion  31  from the groove bottom  24  and W is the width of the connection member  40  in the direction in which the groove  20  is formed.  
         [0032]      FIG. 6  is a cross-section of the pneumatic tire  1  for explaining a state in which a stone  50  is trapped within the groove.  FIG. 7  is cross-section of the pneumatic tire for explaining how the stone  50  shown in  FIG. 6  moves. When the vehicle with the pneumatic tires  1  runs, the pneumatic tire  1  rotates while a lower part of the tread surface  11  is in contact with the road surface (not shown). At this time, the stone  50  is often present on the road surface. If the groove  20  passes through the road surface on which the stone  50  is present, the stone  50  often enters the groove  20  and is trapped within the groove  20 . If the stone  50  is trapped within the groove  20 , then the stone  50  contacts with the road surface through rotation of the pneumatic tire  1 , and is forced inward in the tire radial direction. The stone  50  forced inward in the tire radial direction contacts with the groove bottom  24  or the protrusions  30 .  
         [0033]     When the vehicle is running, the pneumatic tire  1  rotates even in this state. Therefore, the stone  50  that is pushed out of the groove  20  due to its size which is greater than the depth of the groove  20 , that is, the stone  50  protruding from the tread surface  11  outward in the tire radial direction contacts with the road surface when the stone  50  is present on the road surface side by rotation of the pneumatic tire  1 . At this time, frictional force acts between the stone  50  in contact with the road surface and the road surface. Furthermore, because of the rotation of the pneumatic tire  1 , a force for moving the stone  50  in the opposite direction to the rotation direction of the pneumatic tire  1  in the groove  20  in the direction in which the groove  20  is formed acts on the stone  50 .  
         [0034]     The protrusions  30  are provided at intervals in the groove  20 , and each of the protrusions  30  includes the slopes  35 . Each of the slopes  35  is formed so that its height from the groove bottom  24  is getting smaller as it is farther from the convex portion  31 . In other words, the slope  35  is formed so that its height from the groove bottom  24  is getting larger from a location apart from the convex portion  31  toward the convex portion  31 .  
         [0035]     The protrusion  30  is made of the same rubber material as that of the tread area  10  is formed. Therefore, the protrusion  30  has an elastic force. Because of the elastic force of the protrusion  30 , if the stone  50  is to touch the protrusion  30 , the stone  50  is affected by the force that moves the stone  50  from the state in which it is trapped within the groove  20 .  
         [0036]     When the pneumatic tire  1  rotates, the force for moving the stone  50  in the direction opposite to the rotation direction also acts on the stone  50  trapped within the groove  20 . The stone  50 , therefore, moves in the direction in which the groove  20  is formed. If the stone  50  touches the slope  35  of the protrusion  30 , the stone  50  moves along the slope  35 . Furthermore, if the moving direction of the stone  50  along the slope  35  is a moving direction from a position apart from the convex portion  31  toward the convex portion  31 , the stone  50  moves toward the top  32  of the convex portion  31  along the slope  35 . The moving direction of the stone  50  along the slope  35  is often a moving direction from a position near the convex portion  31  toward a position apart from the convex portion  31 . In the latter case, similarly to the former case, the stone  50  further moves to touch the slope  35  of the adjacent protrusion  30  because a plurality of protrusions  30  are formed at intervals in the groove  20 . The stone  50  thereby moves toward the top  32  of the convex portion  31  when moving along the slope  35 .  
         [0037]     In either case, the stone  50  moving in the groove  20  moves in the direction in which the groove  20  is formed, and also moves outward in the tire radial direction. When the stone  50  reaches the position of the top  32 , a large part of the stone  50  is exposed from the groove  20  and a part thereof trapped within the groove  20  decreases. As a result, the stone  50  is ejected to the outside of the groove  20 . Consequently, penetration of the stone  50  into the tread area  10  such as the groove bottom  24  can be suppressed. That is, the occurrence of stone drilling can be minimized.  
         [0038]     The movement of the stone  50  trapped within the groove  20  in the direction in which the groove  20  is formed according to the rotation of the pneumatic tire  1  occurs mainly when the stone  50  is trapped within the longitudinal groove  21 . However, if the lateral groove  22  is formed aslant or if the vehicle with the pneumatic tire  1  is in the cornering mode, i.e., taking a turn at a corner of the road, the stone  50  trapped within the lateral groove  22  sometimes moves in the direction in which the lateral groove  22  is formed due to the rotation of the pneumatic tire  1 . Therefore, whether the groove  20  trapping the stone  50  is the longitudinal groove  21  or the lateral groove  22 , the stone  50  moves in the direction in which the groove  20  is formed, and the protrusion  30  causes the stone  50  to move outward in the tire radial direction and to be ejected to the outside of the groove  20 . Consequently, penetration of the stone  50  into the tread area  10  such as the groove bottom  24  can be suppressed, and the occurrence of stone drilling can be minimized.  
         [0039]      FIG. 8  is a schematic of a mold  60  and a tread rubber  70  for explaining a state before the tread area  10  is subjected to vulcanization molding. Part of manufacturing processes for the pneumatic tire  1  is explained below. If the tread area  10  is to be molded during manufacture of the pneumatic tire  1 , the mold  60  is used for vulcanizing the tread area  10 . The mold  60  is formed into such a shape that convex and concave portions of the tread surface  11  are reversed. More specifically, the mold  60  includes a block-part mold  61  and a groove-part mold  62 . The block-part mold  61  is of the concavely shape, which is reverse to the shape of the block  15  formed on the tread surface  11 . The groove-part mold  62  is of the convex shape, which is reverse to the shape of the groove,  20  formed in the tread area  10 . The groove-part mold  62  includes a protrusion-part mold  63  and a connection-member-part mold  64  which are of the concave shapes, which are reverse to the protrusion  30  and the connection member  40  formed convexly in the groove  20 , respectively.  
         [0040]     The connection-member-part mold  64  is located between the protrusion-part mold  63  and the block-part mold  61  and connected to both the protrusion-part mold  63  and the block-part mold  61 . This is similar to the connection member  40  of the pneumatic tire  1  which is connected to both the protrusion  30  and the block  15 . A vent hole  65  is formed in the block-part mold  61  to communicate the block-part mold  61  with the outside of the mold  60 .  
         [0041]     When the pneumatic tire  1  is to be vulcanized using the mold  60  thus formed, the mold  60  is situated in the outward of the tread rubber  70  in the tire radial direction. The tread rubber  70  is rubber that corresponds to the tread area  10 , and that is part of a green tire which is the pneumatic tire  1  before the vulcanization molding. At this time, the mold  60  is directed so that the block-part mold  61 , the groove-part mold  62 , the protrusion-part mold  63 , and the connection-member-part mold  64  oppose the tread rubber  70 .  
         [0042]      FIG. 9  is a schematic of the mold  60  and the tread rubber  70  for explaining the state in which the tread area  10  is being subjected to the vulcanization molding. When the pneumatic tire  1  is to be vulcanized, pressure is applied to the green tire from the inward to the outward in the tire radial direction. As a result, the tread rubber  70  contacts with the mold  60 . The pressure is further applied to the green tire outward in the tire radial direction. The tread rubber  70  is thereby deformed to fit the shape of the mold  60  of the part opposing the tread rubber  70 . In other words, the tread rubber  70  located in the block-part mold  61  flows into the concave block-part mold  61 . Likewise, the tread rubber  70  flows into the concave protrusion-part mold  63  and the concave connection-member-part mold  64 . Conversely, the tread rubber  70  contacts with the convex groove-part mold  62  in the early stage of the vulcanization molding.  
         [0043]     In this manner, the tread rubber  70  is pressurized against the mold  60  from the inward to the outward in the tire radial direction during the vulcanization molding. However, because the tread rubber  70  contacts with the mold  60  from its part located inward of the mold  60  in the tire radial direction, the air present between the mold  60  and the tread rubber  70  flows from the inward to the outward in the tire radial direction. For example, the tread rubber  70  flows into the protrusion-part mold  63  from the inward to the outward in the tire radial direction. The air in the protrusion-part mold  63  flows to the outward in the tire radial direction. Furthermore, the convex portion  31  is formed on the protrusion  3  and is a portion of the protrusion  30 , which portion protrudes outward in the tire radial direction. The air flowing in the tire radial direction during the vulcanization molding, therefore, flows to a portion of the protrusion-part mold  63  where the convex portion  31  is molded.  
         [0044]     The connection-member-part mold  64  is connected to the protrusion-part mold  63 . The connection-member-part mold  64  is formed outward in the tire radial direction relative to the protrusion-part mold  63 , and connected to both the protrusion-part mold  63  and the block-part mold  61 . This is similar to the connection member  40  formed so that its height from the groove bottom  24  is larger than that of the convex portion  31 . Therefore, the tread rubber  70  flows into the protrusion-part mold  63 . The air in the protrusion-part mold  63  flowing outward in the tire radial direction thereby flows in the direction of the block-part mold  61  through the connection-member-part mold  64 .  
         [0045]     More specifically, the connection member  40  is formed so that its height from the groove bottom  24  is getting larger from the convex-side end  41  toward the block-side end  42 . The connection-member-part mold  64  is, therefore, formed to correspond to the connection member  40 . Namely, the connection-member-part mold  64  is formed to gradually extend outward of the protrusion-part mold  63  in the tire radial direction from the protrusion-part mold  63  to the block-part mold  61 . Therefore, the air flowing between the protrusion-part mold  63  mold  64  and the tread rubber  70  easily flows from the position corresponding to the convex-side end  41  toward the position corresponding to the block-side end  42 . The air can thereby flow more surely from the  18 . direction of the protrusion-part mold  63  to the direction of the block-part mold  61 .  
         [0046]     The air in the block-part mold  61  flows outward in the tire radial direction by the flow of the tread rubber  70  into the block-part mold  61 . Because the vent hole  65  is provided in the block-part mold  61 , the air in the block-part mold  61  flowing outward in the tire radial direction flows into the vent hole  65 , and is discharged from the vent hole  65  to the outside of the mold  60 . With this discharge, the air in the protrusion-part mold  63  flowing in the direction of the block-part mold  61  through the connection-member-part mold  64  is also discharged to the outside of the mold  60  through the vent hole  65 .  
         [0047]      FIG. 10  is a schematic of the mold  60  and the tread rubber  70  for explaining the state in which the tread area  10  is being subjected to the vulcanization molding and which is subsequent to the state shown in  FIG. 9 . The tread rubber  70  is pressed outward in the tire radial direction during the vulcanization molding of the pneumatic tire  1  as shown in  FIG. 9 . The air in the protrusion-part mold  63  thereby flows in the direction of the block-part mold  61  through the connection-member-part mold  64 , while the tread rubber  70  contacts with the mold  60  from its inward part in the tire radial direction.  
         [0048]     Therefore, during the vulcanization molding of the pneumatic tire  1 , the tread rubber  70  in the protrusion-part mold  63  contacts with the mold  60  more early than the tread rubber  70  in the connection-member-part mold  64 . Consequently, almost all of the air present between the protrusion-part mold  63  of the mold  60  and the tread rubber  70  flows in the direction of the block-part mold  61  through the connection-member-part mold  64 . Therefore, when the tread rubber  70  located in the protrusion-part mold  63  contacts with the protrusion-part mold  63  while the tread rubber  70  is continuously pressed, no air is left between the protrusion-part mold  63  and the tread rubber  70 . In addition, almost all the tread rubber  70  located in and opposing the protrusion-part mold  63  directly contacts with the protrusion-part mold  63 .  
         [0049]     The tread rubber  70  located in the connection-member-part mold  64  contacts with the connection-member-part mold  64  after almost all the tread rubber  70  located in and opposing the protrusion-part mold  63  contacts with the protrusion-part mold  63 . At this time, almost all the air between the connection-member-part mold  64  and the tread rubber  70  flows in the direction of the block-part mold  61  because the connection-member-part mold  64  is connected to the block-part mold  61 . Therefore, when the tread rubber  70  in the connection-member-part mold  64  contacts with the connection-member-part mold  64 , no air is left between the connection-member-part mold  64  and the tread rubber  70 . In addition, almost all the tread rubber  70  located in and opposing the connection-member-part mold  64  directly contacts with the connection-member-part mold  64 .  
         [0050]     Because the vent hole  65  is formed in the block-part mold  61 , the air present between the block-part mold  61  and the tread rubber  70  is discharged to the outside of the mold  60  through the vent hole  65 . By continuously pressing the tread rubber  70 , therefore, the air present between the block-part mold  61  and the tread rubber  70  is discharged to the outside of the mold  60 . Accordingly, when the tread rubber  70  in the block-part mold  61  contacts the block-part mold  61 , no air is left between the block-part mold  61  and the tread rubber  70  and almost all the tread rubber  70  located in and opposing the block-part mold  61  directly contacts with the block-part mold  61 .  
         [0051]     In this manner, the pneumatic tire  1  includes the protrusion  30  provided in each of the grooves  20  of the tread area  10  and formed so that its height from the groove bottom  24  is changed. The convex portion  31  of the protrusion  30  and the block  15  are connected to each other by the connection member  40 . The connection member  40  is formed so that its height from the groove bottom  24  in the block-side end  42  is larger than that in the convex-side end  41 . During manufacture of the pneumatic tire  1 , the mold  60  for molding the tread area  10  is disposed outward of the tread rubber  70  in the tire radial direction, and the pressure is applied to the tread rubber  70  from inward to outward of the tread rubber  70  in the tire radial direction, thereby vulcanization-molding the tread area  10 . During the vulcanization molding, the air present between the tread rubber  70  and the mold  60  flows into the portion located further outward in the tire radial direction. Accordingly, the air present between the tread rubber  70  and the protrusion-part mold  63  flows into the portion of the protrusion-part mold  63 , which portion corresponds to the convex portion  31  of the protrusion  30 . Furthermore, the height of the connection member  40  from the groove bottom  24  is larger than that of the convex portion  31 . Therefore, the air present between the tread rubber  70  and the mold  60  flows from the protrusion-part mold  63  for molding the convex portion  31  to the connection-member-part mold  64 . Moreover, because of the connection of the connection-member-part mold  64  to the block-part mold  61 , the air between the connection-member-part mold  64  and the tread rubber  70  flows from the connection-member-part mold  64  to the block-part mold  61 . Furthermore, the vent hole  65  is formed in the block-part mold  61 .  
         [0052]     With these features, during the vulcanization molding, the air between the protrusion-part mold  63  and the tread rubber  70  moves in the direction of the block-part mold  61  through the connection-member-part mold  64 , and is discharged from the vent hole  65  to the outside of the mold  60 . Therefore, the tread rubber  70  easily flows into the protrusion-part mold  63 . Consequently, even if the height of the protrusion  30  is made larger or the volume thereof is increased to ensure the capability of preventing the stone  50  from being trapped within the groove  20  when the stone  50  enters the groove  20 , that is, to ensure anti-stone-trapping capability, the tread rubber  70  can more reliably flow into the mold  60  for forming the protrusion  30  during manufacture of the pneumatic tire  1 . Therefore, it is possible to reduce failure in manufacture or so-called “occurrence of bare”, and to more surly obtain the targeted shape of the protrusion  30 . Consequently, the occurrence of bare can be reduced while the anti-stone-trapping capability is ensured.  
         [0053]     The height of the connection member  40  from the groove bottom  24  becomes gradually larger from the convex-side end  41  toward the block-side end  42 . Therefore, when the pneumatic tire  1  is manufactured, the air between the protrusion-part mold  63  of the mold  60  and the tread rubber  70  and flowing from the protrusion-part mold  63  to the block-part mold  61  through the connection-member-part mold  64  more easily flows in the direction of the portion corresponding to the block-side end  42  which is the portion located outward in the tire radial direction. With this feature, the tread rubber  70  can more reliably flow into the protrusion-part mold  63 , which makes it possible to more surely obtain the targeted shape of the protrusion  30 . Consequently, the occurrence of bare can be more reliably reduced.  
         [0054]     When the connection member  40  is formed so that its inclination angle θ with respect to the groove bottom  24  from the convex-side end  41  over the block-side end  42  is in the range from 3 degrees to 45 degrees, the occurrence of bare can be reduced while the anti-stone-trapping capability is more reliably ensured. More specifically, the inclination angle θ with respect to the groove bottom  24  from the convex-side end  41  over the block-side end  42  is set to 3 degrees or more, and it is thereby possible to prevent a difference in the tire radial direction between the convex portion  31  and the block-side end  42  from becoming too small. Therefore, because the block-part mold  61  side of the connection-member-part mold  64  is formed more surely outward in the tire radial direction than the protrusion-part mold  63  side thereof, the air flowing from between the protrusion-part mold  63  of the mold  60  and the tread rubber  70  to the direction of the block-part mold  61  through the connection-member-part mold  64  can more reliably flow in this direction during the vulcanization molding. With this feature, the tread rubber  70  can more surely flow into the protrusion-part mold  63 , thus more reliably obtaining the targeted shape of the protrusion  30 .  
         [0055]     The inclination angle θ with respect to the groove bottom  24  from the convex-side end  41  over the block-side end  42  is set to 45 degrees or less. It is thereby possible to prevent the rigidity of the connection member  40  from becoming too high, and associated with this, the rigidity of the protrusion  30  connected to the connection member  40  can be prevented from being too high. With this feature, the protrusion  30  is formed to be elastic, and this allows the ejection action on the stone  50  by the elastic force of the protrusion  30  to be ensured, and the anti-stone-trapping capability can thereby be ensured. Therefore, by forming the connection member  40  so that its inclination angle θ with respect to the groove bottom  24  is in the range from 3 degrees to 45 degrees, the targeted shape of the protrusion  30  can be more surely obtained, and the stone  50 , which has entered the groove  20 , can be more reliably ejected. Consequently, the occurrence of bare can be reduced while the anti-stone-trapping capability is more surely ensured.  
         [0056]     When the connection member  40  is formed so that the relation between the height h 1  of the convex portion  31  and the width W of the connection member  40  is in the range of 0.05h 1 ≦W≦1.0h 1 , the occurrence of bare can be reduced while the anti-stone-trapping capability is more reliably ensured. More specifically, by setting the width W of the connection member  40  to be 0.05 times or more of the height h 1  of the convex portion  31 , the width of the connection member  40  can be increased to a predetermined width or more, and associated with this, the width of the connection-member-part mold  64  can be made to a predetermined width or more. This allows the air to easily flow between the connection-member-part mold  64  and the tread rubber  70  during the vulcanization molding. The air can, therefore, easily flow from the protrusion-part mold  63  to the block-part mold  61  during the vulcanization molding, and hence, the tread rubber  70  can easily flow into the protrusion-part mold  63 . It is thereby possible to more surely obtain the targeted shape of the protrusion  30 .  
         [0057]     By setting the width W of the connection member  40  to be 1.0 time or less of the height h 1  of the convex portion  31 , the rigidity of the connection member  40  can be prevented from becoming too high, and associated with this, the rigidity of the protrusion  30  connected with the connection member  40  can be prevented from becoming too high. By so setting, the protrusion  30  can be formed to be elastic, and hence, the ejection action on the stone  50  by the elastic force of the protrusion  30  can be ensured, and the anti-stone-trapping capability can thereby be ensured. Therefore, by forming the connection member  40  so that the relation between the height h 1  of the convex portion  31  and the width W of the connection member  40  is in the range of 0.05h 1 ≦W≦1.0h 1 , the targeted shape of the protrusion  30  can surely be obtained, and the stone  50 , which has entered the groove  20 , can thereby be more reliably ejected therefrom. Consequently, the occurrence of bare can be reduced while the anti-stone-trapping capability is more surely ensured.  
         [0058]      FIG. 11  is a detailed cross-section of a pneumatic tire according to another embodiment of the present invention.  FIG. 12  is a cross-section taken along the line D-D of  FIG. 11 . In the preceding embodiment, one convex portion  31  is formed in one protrusion  30 , but a plurality of convex portions  31  can be formed in one protrusion  30 . For example, as shown in  FIG. 11  and  FIG. 12 , in the protrusion  30 , concavity and convexity may be repeated in the tire radial direction and a plurality of convex portions  31  which are convex outward in the tire radial direction are obtained. In this case, a plurality of connection members  40  may be formed so as to connect a plurality of the convex portions  31  to blocks  15 , respectively. The convex portions  31  are formed on the protrusion  30 , which allows improvement of the anti-stone-trapping capability. In addition, by connecting the connection members  40  to the convex portions  31 , the targeted shape can be more surely obtained even if the convex portions  31  are formed in the protrusion  30 . Consequently, the occurrence of bare can be reduced while the anti-stone-trapping capability is more reliably ensured.  
         [0059]     Although only one connection member  40  is connected to one convex portion  31 , a plurality of connection members  40  can be connected to one convex portion  31 . For example, the connection member  40  is provided from one convex portion  31  toward both of opposite groove walls  23 , and the connection members  40  can be connected to the respective groove walls  23 , i.e. the respective blocks  15 . In other words, the two blocks  15 , which include the opposite groove walls  23 , and the convex portion  31  of the protrusion  30 , which is located between these blocks  15 , can be connected to each other by the two connection members  40 . With this structure, when the vulcanization molding is carried out, the air in the protrusion-part mold  63  is allowed to flow in the directions of two block-part molds  61  through two connection-member-part molds  64 . Therefore, the tread rubber  70  can more surely flow into the protrusion-part mold  63 . Consequently, the occurrence of bare can be more reliably reduced.  
         [0060]     Although the height of the connection member  40  is getting larger from the convex-side end  41  toward the block-side end  42 , the height of the connection member  40  from the groove bottom  24  can be changed step by step. Even if the height of the connection member  40  does not gradually change, the air between the protrusion-part mold  63  of the mold  60  and the tread rubber  70  can flow from the connection member  40  to the block-part mold  61  if the height of the connection member  40  from the groove bottom  24  is larger than that of the convex portion  31  from the groove bottom  24 . This allows the tread rubber  70  to more surely flow into the protrusion-part mold  63 . Consequently, the occurrence of bare can be more surely reduced.  
         [0061]     Even if the height of the connection member  40  is not gradually changed, the connection member  40  is preferably formed so that its inclination angle θ with respect to the groove bottom  24  from the convex-side end  41  over the block-side end  42  is in the range from 3 degrees to 45 degrees. More specifically, even if the height of the connection member  40  is not gradually changed, the connection member  40  is preferably formed so that its inclination angle θ with respect to the groove bottom  24  is in the range from 3 degrees to 45 degrees, the inclination angle being from a portion of the convex-side end  41  located in its outside end in the tire radial direction to a portion of the block-side end  42  located in its outside end in the tire radial direction. By forming the connection member  40  so that the relation between the convex-side end  41  and the block-side end  42  falls within the range, the occurrence of bare can be reduced while the anti-stone-trapping capability is more reliably ensured.  
         [0062]     The width of the connection member  40  in the direction in which the groove  20  is formed is almost equivalent to the width of the convex portion  31  of the protrusion  30  in the same direction as above. However, the width of the connection member  40  can be set different from the width of the convex portion  31 . Widths of the connection member  40  and the convex portion  31  can be either equal to or different from each other. If both of them are connected to each other, the air can flow from the protrusion-part mold  63  of the mold  60  to the connection-member-part mold  64  during the vulcanization molding. In addition, the tread rubber  70  can more reliably flow into the protrusion-part mold  63 . Consequently, the occurrence of bare can be more surely reduced.  
         [0063]     As one example of the pneumatic tire  1 , the pneumatic tire  1  including the block type tread has been explained above. However, the pneumatic tire  1  to which the present invention is applied can be the pneumatic tire  1  including any one of the ribbed tread, the ribbed-lug tread, and the like other than the block type tread. Even if the pneumatic tire  1  is other than the pneumatic tire  1  including the block type tread, it suffices that the connection member  40  is formed such that its height from the groove bottom  24  is larger than the height of the convex portion  31  of the protrusion  30  from the groove bottom  24 . In addition, it suffices to form such a connection member  40  in the groove  20 , in which it is connected to both the convex portion  31  and the land, similarly to the pneumatic tire  1  including the block type tread. In this manner, if the pneumatic tire  1  is the one that the protrusion  30  and the connection member  40  made in the above manner can be formed in the groove  20 , a desired pattern can be used for the pattern shape of the tread. Even if the pneumatic tire  1  has any pattern shape, the occurrence of bare can be reduced while the anti-stone-trapping capability is ensured by forming the protrusion  30  and the connection member  40  in the groove  20  in the above manner.  
         [0064]     Performance evaluation tests conducted on the conventional pneumatic tire and the pneumatic tire.  1  according to the embodiments of the present invention are explained below. The performance evaluation test was conducted on two items, i.e., anti-bare capability and the anti-stone-trapping capability.  
         [0065]     The performance evaluation test was conducted using the pneumatic tire  1  of 11R22.5 size. Each test item was evaluated as follows. The anti-bare capability was evaluated by vulcanization-molding 20 pieces of pneumatic tires  1  and by determining how many pieces out of the 20 pneumatic tires  1  bare occurred to. It is assumed that if bare occurred to fewer pneumatic tires  1 , then the pneumatic tires  1  are determined more excellent in the anti-bare capability. It is also assumed that if bare occurred to two pieces or less out of the 20 pieces of the pneumatic tires  1 , then the pneumatic tires  1  are determined effective in the anti-bare capability.  
         [0066]     The anti-stone-trapping capability was evaluated by attaching each of the pneumatic tires  1  to be tested assembled with a rim to a vehicle, performing a test run of the vehicle on a fixed course, and determining how many stones were trapped within the grooves  20  after the test run. The number of stones were evaluated using an index in which the number of stones in comparative example 1 explained later was set to 100. It is assumed that a higher index indicates more excellence in the anti-stone-trapping capability. It is also assumed that the anti-stone-trapping capability is ensured if the index is up to 95.  
         [0067]     The pneumatic tires  1  to be tested include those according to seven examples (hereinafter, “examples 1 to 7”) of the present invention, and those according to two comparative examples (hereinafter, “comparative examples 1 and 2”). These pneumatic tires  1  were tested in the above method. Each of the pneumatic tires  1  according to the examples 1 to 7 and the comparative examples 1 and 2 includes zigzag-shaped longitudinal grooves  21 . In addition, a plurality of protrusions  30  are formed in each longitudinal groove  21 . Each of the protrusion  30  has a height from the groove bottom  24  of four millimeters, a width in the groove width direction of 2.5 millimeters, and a length in the direction, in which the longitudinal groove  21  is formed, of 40 millimeters.  
         [0068]     Among the pneumatic tires  1  including the protrusions  30  thus formed and to be tested, the pneumatic tire  1  according to the comparative example  1  includes no connection member  40 . The pneumatic tire  1  according to comparative example 2 includes the connection member  40 . However, the relation between the height h 1  of the convex portion  31  from the groove bottom  24  and the height h 2  of the connection member  40  from the groove bottom  24  is h 2 =h 1 . The inclination angle of the outward surface  43  of the connection member  40  with respect to the groove bottom  24  is zero degree. In addition, the ratio (W/h 1 ) of the width W of the connection member  40  to the height h 1  of the convex portion  31  is 0.15.  
         [0069]     On the other hand, according to the examples 1 to 7, the relation between the height h 1  of the convex portion  31  from the groove bottom  24  and the height h 2  of the connection member  40  from the groove bottom  24  is h 2 &lt;h 1 . Furthermore, in the example 1, the inclination angle of the outward surface  43  of the connection member  40  with respect to the groove bottom  24  is two degrees, and the ratio (W/h 1 ) of the width W of the connection member  40  to the height h 1  of the convex portion  31  is 0.5. Likewise, in the example 2, the inclination angle is four degrees and the ratio (W/h 1 ) is 0.5. In the example 3, the inclination angle is four degrees and the ratio (W/h 1 ) is 0.05. In the example 4, the inclination angle is 15 degrees and the ratio (W/h 1 ) is 0.5. In the invention  5 , the inclination angle is 40 degrees and the ratio (W/h 1 ) is 0.5. In the example 6, the inclination angle is 50 degrees and the ratio (W/h 1 ) is 0.2. In the example 7, the inclination angle is 4 degrees and the ratio (W/h 1 ) is 1.0.  
         [0070]     The evaluation tests were conducted on the pneumatic tires  1  according to the comparative example 1 and the comparative example 2 and according to the examples 1 to 7 using the method. Test results are shown in Table 1 to Table 2. Table 1 depicts the results of the evaluation tests conducted on the pneumatic tires  1  according to the comparative example 1 and the comparative example 2 and the pneumatic tires  1  according to the examples 1 to 3. Table 2 depicts the results of the evaluation tests conducted on the pneumatic tires  1  according to the examples 4 to 7.  
                                                                 TABLE 1                                   Com-   Com-                       parative   parative           Example 1   Example 2   Example 1   Example 2   Example 3                                    Connection   Not   h2 = h1   h2 &gt; h1   h2 &gt; h1   h2 &gt; h1       Member   provided       Inclination   —   0   2   4   4       angle (°)       Width of   —   0.15   0.5   0.5   0.05       Connection       Member       (W/h1)       Number of   18   9   2   0   1       occurrences       of bare       (/20 pieces)       Anti-stone-   100   100   100   100   100       trapping       capability                  
 
         [0071]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
               
               
                   
                 Example 4 
                 Example 5 
                 Example 6 
                 Example 7 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Connection Member 
                 h2 &gt; h1 
                 h2 &gt; h1 
                 h2 &gt; h1 
                 h2 &gt; h1 
               
               
                 Inclination angle (°) 
                 15 
                 40 
                 50 
                 4 
               
               
                 Width of 
                 0.5 
                 0.5 
                 0.2 
                 1.0 
               
               
                 Connection Member 
               
               
                 (W/h1) 
               
               
                 Number of 
                 0 
                 0 
                 0 
                 0 
               
               
                 occurrences of bare 
               
               
                 (/20 pieces) 
               
               
                 Anti-stone-trapping 
                 100 
                 100 
                 97 
                 96 
               
               
                 capability 
               
               
                   
               
             
          
         
       
     
         [0072]     As clear from the test results shown in Tables 1 and 2, if the connection member  40  is not formed, the air between the tread rubber  70  and the protrusion-part mold  63  in the mold  60  could not be easily discharged during the vulcanization molding, and the tread rubber  70  does not easily flow into the protrusion-part mold  63 . Due to this, bare easily occurs (see comparative example 1). If the connection member  40  is formed but the height h 2  of the connection member  40  from the groove bottom  24  is equal to the height h 1  of the convex portion  31  of the protrusion  30 , the air between the tread rubber  70  and the protrusion-part mold  63  in the mold  60  does not easily flow in the direction of the connection-member-part mold  64  during the vulcanization molding of the pneumatic tire  1 . Easiness of flow of the tread rubber  70  into the protrusion-part mold  63  is not, therefore, much improved. As a result, it is difficult to reduce the occurrence of bare (see comparative example 2).  
         [0073]     On the other hand, according to the examples 1 to 7, the connection member  40  is formed so that the relation between the height h 2  of the connection member  40  from the groove bottom  24  and the height h 1  of the convex portion  31  of the protrusion  30  is h 2 &lt;h 1 . The connection member  40  is connected to the protrusion  30 . Therefore, the air between the tread rubber  70  and the protrusion-part mold  63  in the mold  60  can easily flow in the direction of the connection-member-part mold  64  during the vulcanization molding of the pneumatic tire  1 . Easiness of flow of the tread rubber  70  into the protrusion-part mold  63  can be thereby improved, thus allowing reduction in the occurrence of bare. Because of the reduction in the occurrence of bare, the targeted shape of the protrusion  30  can be obtained. It is, therefore, possible to ensure the anti-stone-trapping capability by providing the protrusions  30  in the groove  20 .  
         [0074]     According to one aspect of the present invention, the occurrence of bare can be reduced while ensuring the anti-stone-trapping capability.  
         [0075]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.