Patent Publication Number: US-6984006-B2

Title: Elastic flat tread

Description:
This application is a division of prior application Ser. No. 09/486,900 filed Mar. 3, 2000 now U.S Pat. No. 6,568,769. 

   TECHNICAL FIELD 
   The present invention relates to an elastic flat tread for an endless crawler belt, which is used for a hydraulic shovel, bulldozer, and other construction equipment, and particularly, to an elastic flat tread with improvements in the shapes and the materials of a core and an elastic solid covering the core. 
   BACKGROUND ART 
   Conventional construction equipment such as hydraulic shovels and bulldozers with steel crawler belts being attached has the disadvantage of damaging asphalt road surfaces when traveling on a public road on the move between work sites, and therefore increasing number of vehicles are equipped with rubber crawler belts recently. 
   The rubber crawler belts are formed by a number of core wires and cores embedded in rubber in an endless shape, but if problems such as a crack and peeling of rubber occurs, it is difficult to repair them, which necessitates the replacement of the crawler belt to a new one, thereby causing the disadvantage of increasing user cost. 
   In order to overcome the foregoing disadvantage, elastic flat treads formed by iron crawler plates with elastic solids such as rubber being bonded thereto are used. Recently, an art is developed, in which a core is embedded into an elastic solid to construct an elastic flat tread, a plurality of which are disposed in a longitudinal direction of a crawler to thereby form an endless crawler bell. 
   As a prior art of an elastic flat tread, for example, Japanese Patent Application Laid-open No. 7-152305 is known, which will be explained with reference to FIG.  53  and FIG.  54 . In an elastic flat tread  140 , a planar core  120  is covered with an elastic solid  130  from the entire ground-contacting side toward core end portions  121  and  121  in a longitudinal direction of the core  120  on the side not in contact with the ground, and bonded thereto by vulcanization. The core  120  is fastened to a link  150  by bolts not illustrated. Numeral  132  is a bolt hole for insertion of the bolt. 
   However, in the above elastic flat tread  140 , as shown in  FIG. 55 , elastic solid end portions  131  are locally bent to thereby cause the concentration of stress, when the elastic flat tread  140  runs on a protruding object such as a rock or stone A and a curb stone of a sidewalk not illustrated. As a result, the disadvantage of a crack P occurring in the elastic solid end portion  131  is caused. This is because the core  120  is designed to have high rigidity so as not to be deformed even if the vehicle weight W of construction equipment is exerted on the elastic flat tread  140  via a lower roller  145  and a link  150 . 
   Meanwhile, even the elastic solid  130  with higher rigidity in nature has lower rigidity than that of the core  120 . Consequently, when running on a protruding object such as a rock or stone A and a curb stone of a side walk, so long as the protruding object does not escape therefrom, distortion concentrates on the elastic solid  130  due to the difference in rigidity between the core  120  and the elastic solid  130 , thereby causing the crack P in the elastic solid end portion  131  shown in FIG.  55 . 
   Further, the head portions of bolts fastening the core  120  and the link  150  contact the elastic solid  130 , thus causing the disadvantage that a crack and peeling occur at the bolt insertion holes  132 . 
   DISCLOSURE OF THE INVENTION 
   The present invention is made in view of the disadvantages of the prior art, and its object is to provide an elastic flat tread capable of preventing an elastic solid from cracking when a vehicle runs on or collides with a rock or a stone, or a curb stone of a sidewalk during traveling. 
   In order to attain the above object, a first aspect of an elastic flat tread according to the present invention is an elastic flat tread having links of which end portions are connected to the adjacent end portions in a traveling direction of a crawler with a pin, and a core covered with an elastic solid at least on the round-contacting side, and characterized in that 
   the aforesaid core is any core of a core attached to the aforesaid link and a core attached to a metal plate which is attached to the aforesaid link, and in that 
   end portions in a longitudinal direction of the aforesaid any core are bent toward the side not in contact with the ground. 
   According to the above structure, even if the vehicle runs on or collides with a protruding object such as a rock or stone, or a curb stone of a sidewalk, since the end portions in a longitudinal direction of the core are bent toward the side not in contact with the ground, the rock or stone escapes from the elastic solid end portion formed along the bent portion of the core, thus making it possible to avoid local concentration of stress on the elastic solid. When the angle of bend of the core end portion is made larger, even if the elastic solid end portion formed along the bent portion collides with a curb stone of a sidewalk, local concentration of stress on the elastic solid can be avoided. The angle of bend of core end portion is appropriately set in the range of 10 degrees to 90 degrees, and the angle of bend of the core end portion is set in consideration of the weights of various kinds of models small to large in size, the sizes of the elastic flat treads, the lengths in the longitudinal direction of the cores, and the like. For example, in a small-sized model which frequently operates in a working site with many small rocks and stones, the angle of bend of the core end portion may be made smaller, and in a large-sized model which frequently operates in a working site with many large rocks and stones, the angle of bent of the core end portion may be larger. Consequently, even if the vehicle runs on a protruding object such as a rock or stone, or a curb stone of a sidewalk during traveling, a crack does not occur in the elastic solid end portion, thus increasing durability of the elastic flat tread. 
   A second aspect of the invention is characterized in that at least one layer of cable layers is provided inside the aforesaid elastic solid, under the aforesaid any core, near an end portion in a longitudinal direction of the aforesaid any core, in the structure of the first aspect of the invention. 
   According to the above structure, in addition to the operational effects of the first aspect of the invention, the cable layer is embedded near the end portion in a longitudinal direction of the core, thereby increasing the rigidity at this portion, which eliminates the occurrence of a crack in the elastic solid even if the elastic solid end portion runs on or collides with an protruding object such as a rock or stone, or a curb stone of a sidewalk. Consequently, durability of the elastic flat tread is improved, which makes the elastic flat tread useful to construction equipment operating in various working sites. 
   A third aspect of the invention is characterized in that a direction in which cable wires of the aforesaid cable layers are placed is either one of the parallel and diagonal directions relative to the longitudinal direction of the aforesaid any core, or the combination of two directions or more selected from the parallel and diagonal directions, in the structure of the second aspect of the invention. 
   According to the above structure, the elastic solid is strengthened by the cable layer with the direction of the cable wires being either one of or two or more of the parallel and diagonal directions relative to the longitudinal direction of the core, and therefore a crack does not occur in the elastic solid even if the elastic solid end portion runs on or collides with a protruding object such as a rock or stone, or a curb stone of a sidewalk. Consequently, durability of the elastic flat tread is improved, which makes the elastic flat tread useful to construction equipment operating in various working sites. 
   A fourth aspect of the invention is characterized by including a synthetic resin member which is placed near the end portion in the longitudinal direction of the aforesaid any core, and which is fixed to the aforesaid elastic solid, in the structure of the first aspect of the invention. 
   According to the above structure, if the synthetic resin member with a smaller friction coefficient is fixed to the elastic solid, a rock or a stone slips and escapes, even if the synthetic resin member runs on a protruding object such as a rock or stone, or a curb stone of a sidewalk, thereby making it possible to avoid local concentration of stress. Further, by using the synthetic resin member with higher rigidity than the elastic solid, rigidity around the core end portion can be increased. Consequently, even if the elastic flat tread runs on a protruding object such as a rock or a stone, or a curb stone of a sidewalk during traveling, a crack does not occur, thus improving durability of the elastic flat tread. 
   A fifth aspect of the invention is characterized in that the aforesaid elastic solid is integrally formed by elastic solids with different hardnesses, in which the hardness at a portion in contact with the aforesaid any core is the highest and the hardness sequentially lowers toward the ground-contacting side, in the structure of the first aspect of the invention. 
   According to the aforesaid structure, in addition to the operational effects of the fist aspect of the invention, the elastic solid with a higher hardness is strong against an unbalanced load caused by deflection or the like, but provides poor riding quality and less wear resistance on the other hand, and thus the elastic solid is designed to have the highest hardness at the portion nearest to the core. To make the hardness sequentially lower toward the ground-contacting side, the elastic solid having a lower hardness is provided on the ground-contacting side in consideration of riding quality and wear resistance. Accordingly, even if the elastic solid end portion runs on a protruding object such as a rock or stone, or a curb stone of a sidewalk, a crack does not occur in the elastic solid end portion, thus improving durability of the elastic flat tread. 
   A sixth aspect of the invention is characterized in that the aforesaid any core is formed of spring steel, in the structure of the first aspect of the invention. 
   According to the above structure, as in the structure of the first aspect of the invention, the end portions in the longitudinal direction of the core formed of spring steel are bent toward the side not in contact with the ground, and therefore even if the elastic solid end portion formed along the bent portion of the core runs on a protruding object such as a rock or stone, or a curb stone of a sidewalk, the core formed of spring steel is displaced upward, thereby making it possible to avoid local concentration of stress on the elastic solid end portion. Consequently, even if the elastic solid end portion runs on a protruding object such as a rock or stone, or a curb stone of a sidewalk, a crack does not occur, thus improving durability of the elastic flat tread. 
   A seventh aspect of the invention is characterized in that the ratio between a height h, which is from a mounting surface for the aforesaid link up to a tip end in a height direction of the end portion in the longitudinal direction of the aforesaid any core, and a link pitch Lp is 0.05≦h/Lp≦0.25, in the structure of the first aspect of the invention. 
   An eighth aspect of the invention is characterized in that the ratio between a height h, which is from a mounting surface for the aforesaid link up to a tip end in a height direction of the end portion in the longitudinal direction of the aforesaid any core, and a height H of the elastic flat tread is 0.08≦h/H≦0.50, in the structure of the first aspect of the invention. 
   A ninth aspect of the invention is characterized in that the ratio between a width W 1  of the aforesaid any core, and a width W 2  of a tip end in the longitudinal direction of the aforesaid any core is 0.5≦W 2 /W 1 ≦0.9, in the structure of the first aspect of the invention. 
   In the above seventh aspect through the ninth aspect of the invention, the dimensional ratio of the core and the like of the first aspect of the invention is specified, and as in the operational effects of the first aspect of the invention, a crack does not occur in the elastic solid end portion, thus improving durability of the elastic flat tread. 
   A tenth aspect of the invention is, in an elastic flat tread having links of which end portions are connected to the adjacent end portions in a traveling direction of a crawler with a pin, and a core covered with an elastic solid at least on the ground-contacting side, characterized in that 
   the aforesaid core is any core of a core attached to the aforesaid link and a core attached to a metal plate which is attached to the aforesaid link, and is characterized in that 
   at least one layer of cable layers is provided inside the aforesaid elastic solid, under the aforesaid any core, near an end portion in a longitudinal direction of the aforesaid any core. 
   The above structure corresponds to the structure of the second aspect of the invention of which core is not bent, and thus the same operational effect as in the second aspect of the invention can be obtained. 
   An eleventh aspect of the invention is characterized in that a direction in which cable wires of the aforesaid cable layers are placed is either one of the parallel and diagonal directions relative to the longitudinal direction of the aforesaid any core, or the combination of two directions or more selected from the parallel and diagonal directions, in the structure of the tenth aspect of the invention. 
   The above structure corresponds to the structure of the third aspect of the invention, and the same operational effects as in the third invention can be obtained. 
   A twelfth aspect of the invention is, in an elastic flat tread having links of which end portions are connected to the adjacent end portions in a traveling direction of a crawler with a pin, and a core covered with an elastic solid at least on the ground-contacting side, is characterized in that 
   the aforesaid core is any core of a core attached to the aforesaid link and a core attached to a metal plate which is attached to the aforesaid link, and characterized by further including 
   a synthetic resin member placed near an end portion in a longitudinal direction of the aforesaid any core and fixed to the aforesaid elastic solid. 
   The above structure corresponds to the structure of the fourth aspect of the invention of which core is not bent, and thus the same operational effects as in the fourth invention can be obtained. 
   A thirteenth aspect of the invention is, in an elastic flat tread having links of which end portions are connected to the adjacent end portions in a traveling direction of a crawler with a pin, and a core covered with an elastic solid at least on the ground-contacting side, characterized in that 
   the aforesaid core is any core of a core attached to the aforesaid link and a core attached to a metal plate which is attached to the aforesaid link, and characterized in that 
   the aforesaid elastic solid is integrally formed by elastic solids with different hardness, in which the hardness at a portion in contact with the aforesaid any core is the highest and the hardness sequentially lowers toward the ground-contacting side. 
   The above structure corresponds to the structure of the fifth aspect of the invention of which core is not bent, and thus the same operational effects as in the fifth aspect of the invention can be obtained. 
   A fourteenth aspect of the invention is, in an elastic flat tread having links of which end portions are connected to the adjacent end portions in a traveling direction of a crawler with a pin, and a core covered with an elastic solid at least on the ground-contacting side, and is characterized in that 
   the aforesaid core is any core of a core attached to the aforesaid link and a core attached to a metal plate which is attached to the aforesaid link, and characterized in that 
   the aforesaid any core is formed of spring steel. 
   The above structure corresponds to the structure of the sixth aspect of the invention of which core is not bent, and the same operational effects can be obtained as in the sixth aspect of the invention. 
   A fifteenth aspect of the invention is, in an elastic flat tread having links of which end portions are connected to the adjacent end portions in a traveling direction of a crawler with a pin, and a core covered with an elastic solid at least on the ground-contacting side, characterized in that 
   end portions in a longitudinal direction of the aforesaid core are bent toward the side not in contact with the ground, and characterized in that 
   end portions of the aforesaid elastic solid are protruded outward relative to the tip ends of the end portions in the longitudinal direction of the aforesaid core. 
   According to the above structure, when the vehicle runs on or collides with a protruding object such as a rock or stone, or a curb stone of a sidewalk during traveling, the end portion in the longitudinal direction of the core is bent toward the side not in contact with the ground, thus making it possible to avoid local concentration of stress on the elastic solid as a result that the rock or the stone escapes from the elastic solid end portion formed alone the bent portion of the core. Since the elastic solid end portion formed along the bent portion of the core is protruded outward from the end portion of the core, therefore in the elastic solid end portion, an impact caused by the collision with an protruding object such as a rock or stone, or a curb stone of a sidewalk can be lessened. Accordingly, even if the vehicle runs on or collides with a protruding object such as a rock or stone, or a curb stone of a sidewalk during traveling, a crack does not occur in the elastic solid end portion, thus improving durability of the elastic flat tread. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an explanatory view of a first embodiment of an elastic flat tread according to the present invention; 
       FIG. 2  is a view seen from the arrow Y in  FIG. 1 ; 
       FIG. 3  is a view explaining the traveling state of an elastic flat tread in  FIG. 1 ; 
       FIG. 4  is an explanatory view of an example in which an a core is covered with and bonded to an elastic solid from the ground-contacting side to the side not in contact with the ground; 
       FIG. 5  is an explanatory view of a second embodiment of the elastic flat tread according to the present invention; 
       FIG. 6  is a view seen from the arrow X in  FIG. 5 ; 
       FIG. 7  is a view explaining the traveling state of the elastic flat tread in  FIG. 5 ; 
       FIG. 8  is an explanatory view of an example in which the core in  FIG. 5  is covered with and bonded to the elastic solid from the ground-contacting side to the side not in contact with the ground; 
       FIG. 9  is a view explaining a first example of the core according to the present invention; 
       FIG. 10  is a view explaining a second example of the core according to the present invention; 
       FIG. 11  is a view explaining a third example of the core according to the present invention; 
       FIG. 12  is a view explaining a fourth example of the core according to the present invention; 
       FIG. 13  is a view explaining a fifth example of the core according to the present invention; 
       FIG. 14  is an explanatory view of the core in  FIG. 13  being covered with and bonded to the elastic body; 
       FIG. 15  is a view seen from the arrow W in  FIG. 14 ; 
       FIG. 16  is a view explaining another elastic flat tread according to the present invention; 
       FIG. 17  is an explanatory view of an essential part of a third embodiment of the elastic flat tread according to the present invention; 
       FIG. 18  is an explanatory view of the essential part, in which the elastic flat tread in  FIG. 17  is seen from the ground-contacting side; 
       FIG. 19  is a diagram regarding the durability evaluation of the elastic flat tread in  FIG. 17 ; 
       FIG. 20  to  FIG. 24  show examples of the core shapes applied to the third embodiment of the elastic flat tread of the present invention; 
       FIG. 20  is an explanatory view of the essential part of a core of which end portion is-bent in two stages; 
       FIG. 21  is an explanatory view of the essential part of another core of which end portion is bent in two stages; 
       FIG. 22  is an explanatory view of the essential part of a core of which end portion is formed with a predetermined curvature radius; 
       FIG. 23  is an explanatory view of the essential part of a core of which end portion is formed with a different curvature radius from that in  FIG. 22 ; and 
       FIG. 24  is an explanatory view of the essential part of a core of which end portion is formed by a plurality of curved surfaces; 
       FIG. 25  is an explanatory view of a fourth embodiment of the elastic flat tread according to the present invention; 
       FIG. 26  is a view seen from the arrow V in  FIG. 25 ; 
       FIG. 27  is a sectional view taken along the  27 — 27  line in  FIG. 25 ; 
       FIG. 28  is an explanatory view of an application of the fourth embodiment of the elastic flat tread according to the present invention; 
       FIG. 29  is an explanatory view of a fifth embodiment of the elastic flat tread according to the present invention; 
       FIG. 30  is a view seen from the arrow U in  FIG. 29 ; 
       FIG. 31  is an explanatory view of a sixth embodiment of the elastic flat tread according to the present invention; 
       FIG. 32  is a view seen from the arrow T in  FIG. 31 ; 
       FIG. 33  is an explanatory view of an application of the sixth embodiment of the elastic flat tread according to the present invention; 
       FIG. 34  is an explanatory view of a seventh embodiment of the elastic flat tread according to the present invention; 
       FIG. 35  is a sectional view taken alone the  35 — 35  line in  FIG. 34 ; 
       FIG. 36  is an explanatory view of an eighth embodiment of the elastic flat tread according to the present invention; 
       FIG. 37  is an explanatory view of an application of the eighth embodiment of the elastic flat tread according to the present invention; 
       FIG. 38  is an explanatory view of a ninth embodiment of the elastic flat tread according to the present invention; 
       FIG. 39  is an explanatory view of an application of the ninth embodiment of the elastic flat tread according to the present invention; 
       FIG. 40  is an explanatory view of a tenth embodiment of the elastic flat tread according to the present invention; 
       FIG. 41  is a view seen from the arrow S in  FIG. 40 ; 
       FIG. 42  is a view explaining a traveling state of the elastic flat tread in  FIG. 40 ; 
       FIG. 43  is an explanatory view of an eleventh embodiment of the elastic flat tread according to the present invention; 
       FIG. 44  is a view seen from the arrow R in  FIG. 43 ; 
       FIG. 45  is an explanatory view of an application of the eleventh embodiment of the elastic flat tread according to the present invention; 
       FIG. 46  is an explanatory view of another application of the eleventh embodiment of the elastic flat tread according to the present invention; 
       FIG. 47  is an explanatory view of a twelfth embodiment of the elastic flat tread according to the present invention; 
       FIG. 48  is an explanatory view of the elastic flat tread in  FIG. 47  seen from the ground-contacting side; 
       FIG. 49  is a sectional view taken along the  49 - 49  line in  FIG. 48 ; 
       FIG. 50  is an explanatory view of a thirteenth embodiment of the elastic flat tread according to the present invent ion; 
       FIG. 51  is an explanatory view of the elastic flat tread in  FIG. 50  seen from the ground-contacting side; 
       FIG. 52  is a sectional view taken along the  52 — 52  line in  FIG. 51 ; 
       FIG. 53  is a plan view of a conventional elastic flat tread seen from the ground-contacting side; 
       FIG. 54  is a view seen from the arrow Z in  FIG. 53 ; and 
       FIG. 55  is a view explaining a problem occurring to the conventional elastic flat tread flat during traveling. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   An elastic flat tread according to the present invention will be explained below with reference to FIG.  1  through FIG.  52 . Initially, a first embodiment of the elastic flat tread will be explained with reference to FIG.  1  through FIG.  4 . 
   As FIG.  1  and  FIG. 2  show, a core  1  is covered with and bonded to an elastic solid  2  such as rubber. A tread which is formed by the core  1  covered with and bonded to the elastic solid  2  is called an elastic flat tread  3 . Bolts not illustrated are inserted into bolt insertion holes  2   c  provided in the elastic solid  2 , thereby attaching the elastic flat tread  3  to a link  6 . A number of elastic flat treads  3  are disposed in a traveling direction of a crawler, and end portions of the links  6  adjacent to each other are connected to each other with pins  6   a  to form an endless crawler belt. A lower roller  5  attached to a vehicle body not illustrated abuts to the tread surface of the link  6  to thereby rotate. The weight of the vehicle body is exerted on the core  1  via the lower roller  5  and the link  6 . Consequently, the core  1  is made of a material with high rigidity so as not to be deformed. Core end portions  1   a  and  1   b  are bent toward the side not in contact with the ground. An angle of bend α 1  in this case is set at, for example, 45 degrees. 
   The operation in FIG.  1  and  FIG. 2  will be explained based on FIG.  3 . As  FIG. 3  shows, when the vehicle runs on, or collides with a protruding object such as a rock A or a curb stone during traveling the end portion  1   b  in a longitudinal direction of the core  1  is bent toward the side not in contact with the ground, thus allowing the rock A to escape in the X direction from an elastic solid end portion  2   b  formed along a bent portion of the core  1 . As a result, the elastic solid  2  can avoid the local concentration of stress at the end portion  2   b.    
   In the first embodiment, the angles of bend α 1  of the core end portions  1   a  and  1   b  are set at 45 degrees, but they can be appropriately set in the range of 10 degrees to 90 degrees. Specifically, the angles of bend α 1  of the core end portions  1   a  and  1   b  are set in consideration of the weights of various types of vehicles which are small to large in size, the size of the elastic flat tread  3 , and the dimension of the core  1  in its longitudinal direction. For example, in a small-sized vehicle which is frequently operated in a work site with a large number of small rocks and stones, it is suitable to reduce the angles of bend α  1  of the core end portions  1   a  and  1   b , while in a large-sized vehicle which is frequently operated in a work site with a large number of large rocks and stones, it is suitable to increase the angles of bend α 1  of the core end portions  1   a  and  1   b . Thus, even if the vehicle runs on a protruding object such as the rock A and a curb stone, a crack does not occur in the elastic solid end portions  2   a  and  2   b , thereby increasing durability of the elastic flat tread  3 . 
   An elastic flat tread  3 A shown in  FIG. 4  is an example in which the sides of the core end portions  1   a  and  1   b , which are not in contact with the ground, are also covered with and bonded to end portions  2   c  and  2   d  of the elastic solid  2 . In the other points, the elastic flat tread  3 A has the same structure and effects as the elastic flat tread  3  in  FIG. 1 , therefore omitting the explanation thereof. 
   According to the structure in  FIG. 4 , compared to the elastic flat tread  3  in the first embodiment in  FIG. 1 , the core  1  is covered with and bonded to the elastic solid  2  up to the sides not in contact with the ground, thus preventing the core  1  and the elastic solid  2  from peeling away. 
   Subsequently, a second embodiment of the elastic flat tread will be explained with reference to FIG.  5  through FIG.  8 . 
   As FIG.  5  and  FIG. 6  show, a core  10  is covered with and bonded to an elastic solid  20  such as rubber. A tread which is formed by the core  10  covered with and bonded to the elastic solid  20  is called an elastic flat tread  3 B. Bolts not illustrated are inserted into bolt insertion holes  20   c  provided in the elastic solid  20  to thereby attach the elastic flat tread  3 B to the link  6 . A number of elastic flat treads  3 B are disposed in a traveling direction of a crawler, and end portions of the links  6  adjacent to each other are connected to each other with pins  6   a  to thereby form an endless crawler belt. The lower roller  5  attached to the vehicle body not illustrated abuts to the tread surface of the link  6  to thereby rotate. The weight of the vehicle body is exerted on the core  10  via the lower roller  5  and the link  6 . Consequently, the core  10  is made of a material with high rigidity so as not to be deformed. Core end portions  10   a  and  10   b  are bent toward the side not in contact with the ground. An angle of bend α 2  in this case is set at 90 degrees. 
   The operation in FIG.  5  and  FIG. 6  will be explained based on FIG.  7 . Even if the vehicle collides with, or runs on a curb stone of a sidewalk or the like during traveling, since the end portion  10   b  in a longitudinal direction of the core  10  is bent toward the side not in contact with the ground, the elastic solid  20  can avoid the local concentration of stress at an end portion  20   b  owing to the elastic effect of the elastic solid end portion  20   b  formed along the bent portion of the core  10 . As a result, a crack does not occur in the elastic solid end portions  20   a  and  20   b , thereby increasing durability of the elastic flat tread  3 B. As in the first embodiment, the angles of bend α 2  of the core end portions  10   a  and  10   b  are appropriately set in the range of 10 degrees to 90 degrees. 
   An elastic flat tread  3 C shown in  FIG. 8  is an example in which the sides of the core end portions  10   a  and  10   b , which are not in contact with the ground, are covered with and bonded to end portions  20   c  and  20   d  of the elastic solid  20 . In the other points, the elastic flat tread  3 C has the same structure and effects as the elastic flat tread  3 B in  FIG. 5 , therefore omitting the explanation thereof. 
   According, to the structure in  FIG. 8 , compared to the elastic flat tread  3 B in the second embodiment in  FIG. 5 , the core  10  is covered with and bonded to the elastic solid  20  up to the sides not in contact with the ground, thus preventing the core  10  and the elastic solid  20  from peeling away. 
   Next, the shapes of the cores according to the elastic flat tread of the present invention will be explained with reference to FIG.  9  through FIG.  13 . Only the end portions on one side of the cores are shown in FIG.  9  through  FIG. 13 , and it is noted that the end portions on both sides are formed in the same shape. 
     FIG. 9  shows the core  1  shown in the first embodiment in  FIG. 1 , and the angle of bend α 1  at the core end portion  1   b  is set at 45 degrees.  FIG. 10  shows the core  10  shown in the second embodiment in  FIG. 5 , and the angle of bend α 2  at the core end portion  10   b  is set at 90 degrees. 
   A core  30 A in  FIG. 11  shows an example in which a square end portion  30   a  is formed. A core  30 B in  FIG. 12  shows an example in which a circular end portion  30   b  is formed. A core  30 D in  FIG. 13  shows an example in which an end portion  30   d  in a shape of the bottom of a ship is formed. 
   With the core  30 D shown in  FIG. 13  cited as an example, the structure of the covering of the elastic-solid will be explained. Since the cores shown in FIG.  9  through  FIG. 12  have the same structure, the explanation thereof will be omitted. As FIG.  14  and  FIG. 15  show, an elastic solid  31  covers and bonds to the core  30 D from the ground-contacting side to an end portion  31   b  on the side not in contact with the ground. In such a elastic flat tread, the same effects can be obtained as in the embodiments shown in FIG.  1  and FIG.  5 . 
     FIG. 16  shows a plan view of another elastic flat tread according to the present invention, in which an elastic solid  32  covers and bonds to a core  30 E. An end portion  30   e  of the core  30 E is formed to be square, and corner portions  32   a  and  32   a  are formed at the end portion of the elastic solid  32  for covering and bonding to the core end portion  30   e . As a result that the corner portions  32   a  and  32   a  are formed, a crack and the like do not occur in the elastic solid  32  even if the elastic flat tread collides with, or runs on a protruding object such as a rock and stone. 
   Subsequently, a third embodiment of the elastic flat tread will be explained with reference to FIG.  17  through FIG.  24 . 
   As FIG.  17  and  FIG. 18  show, in the elastic flat tread  33 , a core  11  other than a link mounting surface  6   b  is covered with and bonded to an elastic solid  22  such as rubber. Only one side of the elastic flat tread  33  is illustrated, and the other side is omitted, since the other side is in a form symmetrical with the one side. In the elastic flat tread  33 , the link  6  (See  FIG. 1 ) is attached on the link mounting surface  6   b  with bolts being inserted into bolt insertion holes  22   c  provided in the elastic solid  22 . As in the first embodiment, the elastic flat treads  33  form an endless crawler belt. 
   The core  11  is made of a material with high rigidity so as not to be deformed, and the end portion  11   a  is bent toward the side not in contact with the ground at a predetermined angle of bend α. The core end portion  11   a  is formed in such a shape that tapers toward a tip end  11   c  in a longitudinal direction of the core  11 . In the third embodiment, chamfered portions  11   d  are formed on the ground-contacting side at both ends in a lateral direction of the core  11 , but they may be omitted. 
   The characteristics of the elastic flat tread  33  according to the above structure will be explained.  FIG. 19  shows the relationship between the angle of bend a of the core end portion  11   a , and the durability evaluation index regarding a crack occurrence in the elastic solid end portion  22   a . Here, the durability evaluation index of the angle of bend α=0° is the data of a conventional elastic flat tread, which is almost the same as an elastic flat tread  140  shown in FIG.  53 . As is obvious from  FIG. 19 , the core end portion  11   a  is bent toward the side not in contact with the ground, thereby increasing the durability against a crack occurrence in the elastic solid end portion  22   a.    
   Consequently, the durability increases at the angle of bend α&gt;0° as compared with the prior art (the angle of bend α=0°), and in obtaining excellent durability, 10°≦the angle of bend α≦90° is preferable. Further, in order to achieve a suitable thickness for an elastic solid thickness T 1  shown in  FIG. 17 , it is more preferable that the angle of bend α≧15°, specifically, 15°≦the angle of bend α≦90°. Meanwhile, in order to reduce the concentration of stress occurring at the elastic solid end portion  22   a  near a bent portion  11   e  (See FIG.  17 ), it is more preferable that the angle of bend α≦45°, specifically, 10≦the angle of bend α≦45°. From the above, in obtaining extremely excellent durability, it is still more preferable that 15°≦the angle of bend α≦45°. 
   As a factor of the durability evaluation index, the relationship with the angle of bend α is explained, but other factors may be used. For example, the explanation can be made by the relationship between a height h shown in  FIG. 17 , specifically, the height h from the link mounting surface  6   b  up to a tip end  11   b  in a height direction of the core end portion  11   a , and a link pitch, specifically, the distance between axes of the pins  6   a  and  6   a  (See  FIG. 1 ) for connecting the links  6  and  6  (See  FIG. 1 ) adjacent in a fore-and-aft direction of the crawler traveling direction (hereinafter called a link pitch Lp). In this case, an excellent durability evaluation index can be obtained when 0.05≦h/Lp≦0.25. Further, in order to achieve an appropriate thickness for the elastic solid thickness T 1 , it is more preferable that h/Lp≧0.09. Meanwhile, in order to reduce the adverse possibility that interference may occur between the elastic flat tread  33  and components around the vehicle body or the like, it is more preferable that h/Lp≦0.13. Accordingly, it is a still more preferable condition that 0.09≦h/Lp≦0.13. 
   Further, as another factor of the durability evaluation index, the relationship between the above height h and a height H of the elastic flat tread  33  shown in  FIG. 17  may be suitable. In this case, a preferable durability evaluation index can be obtained when 0.08≦h/H≦0.5. Further, in order to achieve an appropriate thickness for the elastic solid thickness T 1 , it is more preferable that h/H≧0.16. Meanwhile, in order to reduce the adverse possibility of the interference as in the above, it is more preferable that h/H≦0.23. Accordingly, it is a still more preferable condition that 0.16≦h/H≦0.23. 
   Further, as still another factor of the durability evaluation index, the relationship between a width W 1  of the core  11  shown in  FIG. 18 and a  width W 2  of the tip end  11   c  in a longitudinal direction of the core  11  may be suitable. In this case, a preferable durability evaluation index can be obtained when 0.5≦W 2 /W 1 ≦0.9. Further, in order to reduce the concentration of stress occurring at the elastic solid end portion  22   a  near the tip end  11   c  in the longitudinal direction when the vehicle runs on a protruding object such as a rock and stone, it is more preferable that W 2 /W 1 ≧0.65. Meanwhile, in order to reduce the concentration of stress occurring at the elastic solid end portion  22   a  near a corner portion  11   g  of the core end portion  11   a  when the vehicle runs on a protruding object, it is more preferable that W 2 /W 1 ≦0.8. Accordingly, it is a still more preferable condition that 0.65≦W 2 /W 1 ≦0.80. 
   Regarding the core  11  in the third embodiment, the shapes other than that in  FIG. 17  will be explained with reference to  FIG. 20  to FIG.  24 . In the core  11  in  FIG. 20 , the core end portion  11   a  is bent at two kinds of angles of bend α 3  and α 4 , and α 3 &gt;α 4 . In the core  11  in  FIG. 21 , the core end portion  11   a  is bent at two kinds of angles of bend α 5  and α 6 , and α 5 &lt;α 6 . FIG.  20  and  FIG. 21  show the examples in which the core end portion  11   a  is bent in two stages, but the core end portion  11   a  may be bent in three stages or more as necessary. The core  11  in  FIG. 22  has a structure in which the core end portion  11   a  is formed with a radius of curvature R 1  and the core end portion  11   a  is in contact with the core  11 . The core  11  in  FIG. 23  shows the example in which the core end portion  11   a  is formed with a radius of curvature R 2  and the core end portion  11   a  forms the bent portion  11   e . The core  11  in  FIG. 24  shows the example in which the core end portion  11   a  is formed by a plurality of curved surfaces. The core end portion  11   a  in  FIG. 24  may be a combination of curved surfaces and flat surfaces. 
   Next, a fourth embodiment of the elastic flat tread will be explained with reference to  FIG. 25  trough FIG.  27 . 
   An elastic flat tread  3 F is formed by a core  40  covered with and bonded to an elastic solid  50  such as rubber. The elastic flat tread  3 F is fastened to the link  6  by bolts not illustrated being inserted into bolt insertion holes  50   c  provided in the elastic solid  50 . An end portion  50   b  of the elastic solid  50  is in a form protruding outward relative to an end portion  40   b  of the core  40 . A cable layer  60 A is placed inside the elastic solid  50  and under the core  40 . 
   As FIG.  26  and  FIG. 27  show, the cable layer  60 A consisting of a plurality of cable wires parallel with the core  40  is placed under the core  40 . 
     FIG. 25  shows the cable layer  60 A embedded in the elastic solid  50  only on one side, specifically, only on the outer side of the vehicle, but it may be provided on both sides. The length of the portion of an end portion  50   a  of the elastic solid  50 , which is protruded outward from an end portion  40   a  of the core  40 , and the length of the portion of the end portion  50   b  of the elastic solid  50 , which is protruded outward from the end portion  40   b  of the core  40  may be symmetric. The lengths? of the portion protruded outward may be asymmetric as in FIG.  25 . The above is appropriately designed in consideration of the weights of various model from small to large in size, the size of the elastic flat tread  3  and the like. 
   The operation of FIG.  25  through  FIG. 27  will be explained. As a result that the cable layer  60 A is embedded near the end portion  40   b  in the longitudinal direction of the core  40 , rigidity increases in this portion. Thereby, even if the elastic solid end portion  50   b  runs on or collides with a protruding object such as a rock and stone, a curb stone of a sidewalk and the like, a crack does not occur at the elastic solid end portion  50   b . Further, since the elastic solid end portion  50   b  is protruded outward relative to the end portion  40   b  of the core  40 , even if the elastic solid end portion  50   b  collides with a protruding object such as a curb stone of a sidewalk or the like during traveling, the impact caused by the collision with the protruding object can be lessened. As described above, even if the elastic flat tread  3 F runs on or collides with a protruding object such as a curb stone of a sidewalk or the like during traveling, a crack does not occur at the elastic solid end portion  50   b , thus increasing durability of the elastic flat tread  3 F. 
   As an application of the fourth embodiment, the cable layer  60 A may be provided in the elastic flat tread  33  (See FIG.  17 ). For example, as  FIG. 28  illustrates, in an elastic flat tread  33 F, the cable layer  60 A is embedded inside an end portion  22   d  of the elastic solid  22  under an end portion  11   h  in the longitudinal direction of the core  11 . According to the above structure, as in the above, durability of the elastic flat tread  33 F is increased. 
   A fifth embodiment of the elastic flat tread will be explained with reference to FIG.  29  and FIG.  30 . 
   An elastic flat tread  3 E is formed by the core  40  covered with and bonded to the elastic solid  50  such as rubber. The elastic flat tread  3 E is attached to the link  6  by bolts not illustrated being inserted into the bolt insertion holes  50   c  provided in the elastic solid  50 . The end portion  50   b  of the elastic body  50  is formed to protrude outward relative to the end portion  40   b  of the core  40 . A cable layer  60 B is diagonally placed inside the elastic solid  50  and under the core  40 . FIG.  29  and  FIG. 30  show only one layer of the cable layer  60 B, but the configuration with a plurality of layers of the cable layers  60 B may be suitable. 
     FIG. 29  shows the cable layer  60 B embedded in the elastic solid  50  only on one side, but it may be provided on both sides. The length of the portion of the end portion  50   a  of the elastic solid  50 , which is protruded outward from the end portion  40   a  of the core  40 , and the length of the portion of the end portion  50   b  of the elastic solid  50 , which is protruded outward from the end portion  40   b  of the core  40  may be symmetric. The lengths of the portions protruded outward may be asymmetric as in FIG.  29 . 
   The operation in FIG.  29  and  FIG. 30  will be explained. The cable layer  60 B consisting of a plurality of cable wires diagonally placed is embedded near the end portion  40   b  in the longitudinal direction of the core  40 . As the result, rigidity increases in the area near the portion where it is embedded, and thus even if the elastic solid end portion  50   b  runs on, or collides with a protruding object, a crack does not occur at the elastic solid end portion  50   b . Further, since the elastic solid end portion  50   b  is protruded outward relative to the end portion  40   b  of the core  40 , even if the elastic solid end portion  50   b  collides with a curb stone of a sidewalk or the like during traveling, the impact caused by the collision with the curb stone or the like can be lessened. As the result, as in the above embodiment, a crack does not occur at the elastic solid end portion  50   b , thus increasing durability of the elastic flat tread  3 E. 
   A sixth embodiment of the elastic flat tread will be explained with reference to FIG.  31  and FIG.  32 . 
   An elastic flat tread  3 G is formed by the core  40  covered with and bonded to the elastic solid  50  such as rubber. The elastic flat tread  3 G is attached to the link  6  by bolts not illustrated being inserted into the bolt insertion holes  50   c  provided in the elastic solid  50 . 
   The end portion  50   b  of the elastic body  50  is formed to protrude outward relative to the end portion  40   b  of the core  40 . Two layers of cable layers  60 C are placed inside the elastic solid  50  and under the core  40 . The first cable layer  60 C is a cable layer with a plurality of cable wires being diagonally placed. A plurality of cable wires of the second cable layer  60 C are placed diagonally in the reverse direction relative to the diagonal direction of the cable wires of the first cable layer  60 C so as to cross the cable wires of the first cable layer  60 C. FIG.  31  and  FIG. 32  show two layers of the cable layers  60 C, but three or more layers of the cable layers  60 C may be placed. Further, the cable layers  60 C embedded in the elastic solid  50  at only one side is illustrated, but they may be provided at both sides. 
   The operation in FIG.  31  and  FIG. 32  will be explained. A plurality of the cable layers  60 C each having a different placement direction of the cable wires are embedded near the end portion  40   b  in the longitudinal direction of the core  40 , thus increasing, rigidity in the area near the portion where they are embedded. As a result, as in the fifth embodiment, a crack does not occur at the elastic solid end portion  50   b , thus increasing durability of the elastic flat tread  3 G. 
   As an application of the sixth embodiment, a plurality of the cable layers  60 C may be provided in the elastic flat tread  33  (See FIG.  17 ). For example, as  FIG. 33  illustrates, in an elastic flat tread  33 G, two layers of the cable layers  60 C are embedded inside the end portion  22   d  of the elastic solid  22  under the end portion  11   h  in the longitudinal direction of the core  11 . According to the above structure, as in the above, durability of the elastic flat tread  33 G is increased. 
   A seventh embodiment of the elastic flat tread will be explained with reference to FIG.  34  and FIG.  35 . 
   In an elastic flat tread  3 H, the core  40  is covered with and bonded to the elastic solid  50  such as rubber as in  FIG. 29. A  plurality of cable layers  60 D are placed in parallel inside the elastic solid  50  and under the core  40 .  FIG. 34  shows three layers of the cable layers  60 D, but four or more layers of the cable layers  60 D may be placed.  FIG. 34  shows only one side of the elastic flat tread  3 H, but as in the aforesaid embodiment, the cable layers  60 D embedded in the elastic solid  50  may be provided at both sides. Further, the length of the portion of the end portion  50   b  of the elastic solid  50 , which is protruded outward from the end portion  40   b , may be symmetric or asymmetric. The above is appropriately designed in consideration of the weights of various kinds of models small to large in size, the size of the elastic flat tread  3 H and the like. According to the above structure, as in the fifth embodiment, a crack does not occur at the elastic solid end portion  50   b , thus increasing durability of the elastic flat tread  3 H. 
   As is shown in drawing  FIGS. 25-35  and discussed above, the invention includes separated, generally parallel cable wires  60 A (especially FIG.  27 ); cable wires only adjacent to the longitudinal end  40   b  of the core  40  (FIG.  25 ); two sets of cable wires  60 A at front and rear of the tread (FIG.  26 ); plural cable layers  60 D at different heights (FIG.  35 ); such layers of cables  60 D having different lengths or staggered edges (FIG.  34 ); and a cable layer does not extend to a central area of the core ( FIGS. 25 ,  26 , and  28 - 34 ). 
   An eighth embodiment of the elastic flat tread will be explained with reference to FIG.  36 . 
   An elastic flat tread  3 I is formed by a core  70  covered with and bonded to an elastic solid  80  such as rubber. The elastic flat tread  3 I is attached to the link  6  by bolts not illustrated being inserted into bolt insertion holes  80   c  provided in the elastic solid  80 . The core  70  is covered with and bonded to the elastic solid  80  including an elastic solid end portion  80   a  on the side not in contact with the ground from the ground-contacting side to the side not in contact with the ground. Thereby, the elastic solid  80  is prevented from peeling away from the core  70 . The elastic solid  80  is integrally formed by elastic solids with different hardnesses so that the hardness of the portion nearest to the core  70  is the highest and the hardness lowers gradually toward the ground-contacting side. 
   An elastic solid  80 X forming the portion nearest to the core  70 , an elastic solid  80 Z forming the portion nearest to the ground-contacting side, and an elastic solid  80 Y forming the middle portion between the elastic solid  80 X and the elastic solid  80 Z are respectively set at a hardness HS of  90 , a hardness HS of  70 , and a hardness HS of  80 . The hardnesses of the elastic solids  80 X,  80 Y, and  80 Z are appropriately set according to the specifications such as the weights of various kinds of models small to large in size, and the like. 
   The operation in  FIG. 36  will be explained. The elastic solid  80  with a higher hardness is strong against unbalanced load caused by defection or the like, but provides poor riding quality and less abrasive resistance on the other hand. Therefore, the elastic solid  80 X nearest to the core  70  is given the highest hardness. The hardness is sequentially lowered toward the ground-contacting side, and the portion at the ground-contacting side of the elastic solid  80  is formed by the elastic solid  80 Z with a lower hardness in consideration of riding quality and abrasive resistance. Consequently, even if the elastic flat tread  3 I runs on an protruding object such as a rock and stone, and a curb stone of a sidewalk during traveling, a crack does not occur at an elastic solid end portion  80   b , thus increasing durability of the elastic flat tread  3 I. 
   As an application of the eighth embodiment, the elastic solid  80  may be applied to the elastic flat tread  33  (See FIG.  17 ). For example, as  FIG. 37  illustrates, the elastic solid  80  of an elastic flat tread  33 I is integrally formed by the elastic solids  80 X,  80 Y, and  80 Z with different hardnesses so that the hardness of the portion nearest to the core  11  including the core end portion  11   h  is the highest, and the hardness sequentially lowers toward the ground-contacting side. According to the above structure, as in the above, durability of the elastic flat tread  33 I is increased. 
   A ninth embodiment of the elastic flat tread will be explained with reference to FIG.  38 . 
   An elastic flat tread  3 J is formed by a core  93  being covered with and bonded to an elastic solid  90 . The elastic flat tread  3 J is attached to the link  6  by bolts not illustrated being inserted in bolt insertion holes  90   c  provided in the elastic solid  90 . The elastic flat tread  3 J includes a synthetic resin member  95  fixed to the elastic solid  90  near an end portion in a longitudinal direction of the core  93 . The synthetic resin member  95  is provided near one end portion in the longitudinal direction of the core  93 , or near both ends portions thereof. 
   The operation in  FIG. 38  will be explained. If a material with a lower coefficient of friction is used for the synthetic resin member  95  which is fixed to the elastic solid  90 , even if the synthetic resin member  95  runs on a protruding object such as a rock and stone, and a curb stone of a sidewalk, the rock or the stone slips and escapes therefrom, thereby making it possible to avoid local concentration of stress in the synthetic resin member  95  and an elastic solid end portion  90   b . As a result, a crack does not occur even if the elastic flat tread  3 J runs on an protruding object such as a rock and stone, and a curb stone of a sidewalk during traveling, thus increasing durability of the elastic flat tread  3 J. 
   As an application of the ninth embodiment, the synthetic resin member  95  may be applied to the elastic flat tread  33  (See FIG.  17 ). For example, as  FIG. 39  illustrates, an elastic flat tread  33 J includes the synthetic resin member  95  fixed to the elastic solid  90  near the end portion  11   h  in the longitudinal direction of the core  11 . According to the above structure, as in the above, durability of the elastic flat tread  33 I is increased. 
   A tenth embodiment of the elastic flat tread will be explained with reference to  FIG. 40 ,  FIG. 41 , and FIG.  42 . 
   In an elastic flat tread  3 K, a core  100  is covered with and bonded to an elastic solid  110  such as rubber. The core  100  is formed of spring steel. According to the structure, even if the elastic flat tread  3 K runs on a protruding object during traveling, an end portion  101  in a longitudinal direction of the core  100  formed of spring steel is displaced upward, and thus local concentration of stress in an elastic solid end portion  111  can be avoided. Though the end portion  101  of the core  100  shown in  FIG. 40  is formed to be flat, if the end portion  101  of the core  100  is bent toward the side not in contact with the ground as in the first embodiment in  FIG. 1 , local concentration of stress in the elastic solid end portion  111  can be further avoided. As a result, even if the elastic flat tread  3 K runs on a protruding object during traveling, a crack does not occur in the elastic solid end portion  111 , thus increasing durability of the elastic flat tread  3 K. 
   An eleventh embodiment of the elastic flat tread will be explained with reference to FIG.  43  and FIG.  44 . 
   An elastic flat tread  3 L is formed by a core  115  covered with and bonded to an elastic solid  116 . End portions  115   a  and  115   b  of the core  115  are bent toward the side not in contact with the ground. Accordingly, the basic structure of the eleventh embodiment is the same as that in  FIG. 1  of the first embodiment. What makes the structure of the eleventh embodiment different from the first embodiment is a point in which a metal plate  9 A is attached (fixed) to a link  8  by welding or the like to be integrated therewith, and the metal plate  9 A is attached to the core  115  with bolts  9 . 
   According to the above structure, the end portions  115   a  and  115   b  of the core  115  are bent to the side not in contact with the ground, and thus local concentration of stress in the elastic solid end portions  116   a  and  116   b  can be avoided as in the first embodiment in FIG.  1 . As a result, even if the elastic flat tread  3 L runs on a protruding object during traveling, a crack does not occur in the elastic solid end portions  116   a  and  116   b , thus increasing durability of the elastic flat tread  3 L. Further, the core  115  is attached to the link  8  with the metal plate  9 A therebetween, thus making it unnecessary to provide boll insertion holes in the elastic solid  116 . As a result, problems such as a crack and peeling off resulting from the bolt insertion holes are eliminated. 
   As an application relating to the integration of the eleventh embodiment, the link and the core may be integrated. For example,  FIG. 45  shows integrated structure of the link  6  and the core  1  of the elastic flat tread  3 A in FIG.  4 . In an elastic flat tread  33 A, the link  6  is attached to a core  71  on the link mounting surface  6   a  by welding. As a result, the formation of the bolt insertion holes  2   c  provided in the core  1  and the elastic solid  2  in  FIG. 4  is eliminated and the bolts are made unnecessary. 
   As another example of the integration, it may be suitable to integrate the link  8 , the metal plate  9 A and the core  115  in FIG.  43 . For example, in an elastic flat tread  33 L in  FIG. 46 , the link  8 , a metal plate  73 , and a core  74  are attached to one another by welding to be integrated. As a result, the bolt insertion holes provided in the core  115  and the metal plate  9 A in  FIG. 43  are eliminated, and the bolts  9  are made unnecessary. 
   Further, still another application of the eleventh embodiment will be listed. 
   (1) Any one of the cable layers  60 A in  FIG. 28 ,  60 B in  FIG. 29 ,  60 C in  FIG. 33 , and  60 D in  FIG. 34  is placed inside the elastic solid  116  under the core  115  and near the core end portion  115   b.    
   (2) The elastic solid  116  is integrally formed by the elastic solids  80 X,  80 Y, and  80 Z (See  FIG. 37 ) with different hardnesses so that the elastic solid  116  has the same structure as the elastic solid  80  in  FIG. 37 , and the hardness is the highest at the portion nearest to the core  115  and sequentially lowers toward the ground-contacting side. 
   (3) The elastic solid  116  includes the synthetic resin member  95  fixed to the elastic solid  116  near the end portion  115   b  in a longitudinal direction of the core  115  (almost corresponds to the elastic solid end portion  116   b ) so as to have the same structure as the elastic solid  90  and the synthetic resin member  95  in FIG.  39 . 
   (4) The core  115  is formed of spring steel. 
   (5) Further, the core  115  in the above items (1) to (4) is formed to be flat, specifically, to be in a form in which the core end portions  115   a  and  115   b  are not bent. 
   A twelfth embodiment of the elastic flat tread will be explained with reference to FIG.  47  through FIG.  49 . The elastic flat tread  33  is substantially the same as the elastic flat tread  33  in FIG.  17  and  FIG. 18 , and the core  11  other than the link mounting surface  6   b  is covered with and bonded to the elastic solid  22  such as rubber. The end portions  11   a  and  11   h  in the longitudinal direction of the core  11  are bent toward the side not in contact with the ground. According to the structure, as in the above embodiments, even if the elastic flat tread  33  runs on a protruding object during traveling, a crack does not occur in the elastic solid end portions  22   a  and  22   d , thus increasing durability of the elastic flat tread  33 . 
   A thirteenth embodiment of the elastic flat tread will be explained with reference to FIG.  50  through FIG.  52 . In an elastic-flat tread  83 , a core  81  is covered with and bonded to an elastic solid  82  such as rubber. End portions  81   a  and  81   b  in a longitudinal direction of the core  81  are bent toward the side not in contact with the ground. According to the structure, as in the above embodiments, even if the elastic flat tread  83  runs on a protruding object during traveling, a crack does not occur in elastic solid end portions  82   a  and  82   b , thus increasing durability of the elastic flat tread  83 . 
   It goes without saying that the elastic flat treads according to the present invention described in detail thus far can be applied to construction equipment small to large in size as well as to endless crawler belts of industrial equipment, agricultural machinery and the like other than the construction equipment. 
   INDUSTRIAL AVAILABILITY 
   The present invention is useful as an elastic flat tread which can prevent a crack from occurring in an elastic solid when the elastic flat tread runs on or collides with an protruding object such as a rock and stone, and a curb stone of a sidewalk during traveling.