Patent Publication Number: US-9902445-B2

Title: Crawler

Description:
TECHNICAL FIELD 
     The present invention relates to a crawler formed using an elastic material. 
     BACKGROUND ART 
     A rubber crawler is described in Japanese Utility Model Application Laid-Open (JP-U) No. H05-82773. The rubber crawler has lugs that extend in a straight line along the crawler width direction, formed at intervals along a crawler peripheral direction. The rubber crawler has a specified rotation direction, and a lug wall portion on an opposite side to the crawler rotation direction has a larger angle of inclination with respect to the crawler forward direction than a lug wall portion on the crawler rotation direction side. 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, although the rubber crawler of JP-U No. H05-82773 is capable of exhibiting sufficient traction performance when driving on rough ground due to the configuration of the lugs as described above, there is a tendency for side-slip to occur. 
     An object of the present invention is to provide a crawler that suppresses side-slip while securing traction performance during driving on rough ground. 
     Solution to Problem 
     A crawler of a first aspect of the present invention is a crawler that has a specified rotation direction. The crawler includes a crawler body that is formed from an elastic material in an endless shape entrained around a drive wheel and a follower wheel, and includes plural lugs. The plural lugs are provided at the crawler body, project out from an outer peripheral face of the crawler body, as viewed from a crawler outer peripheral side, are allocated to one side and another side in the crawler width direction so as to be alternately disposed on progression along the crawler peripheral direction on each side of a central line passing through a crawler width direction center, and extend at an angle to the crawler peripheral direction from an end portion on the central line side toward a crawler width direction outer side and toward an opposite side to a crawler rotation direction. In a cross-section taken along the crawler peripheral direction, an angle formed between each apex side portion of tread-in-side wall faces on the crawler rotation direction side and the outer peripheral face is 90 degrees or greater, and is smaller than an angle formed between each apex side portion of kick-out-side wall faces on the opposite side to the crawler rotation direction and the outer peripheral face. 
     Advantageous Effects of Invention 
     As explained above, the crawler of the first aspect of the present invention is able to suppress side-slip while securing traction performance during driving on rough ground. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a rubber crawler of an exemplary embodiment of the present invention, as viewed from the side (along a crawler width direction). 
         FIG. 2  is a perspective view including a partial cross-section of a rubber crawler of an exemplary embodiment of the present invention. 
         FIG. 3  is a perspective view including a partial cross-section of respective cord layers of a rubber crawler of an exemplary embodiment of the present invention. 
         FIG. 4  is a plan view of a rubber crawler of an exemplary embodiment of the present invention, as viewed from a crawler outer peripheral side. 
         FIG. 5  is a side view of the rubber crawler of  FIG. 4  as viewed from the arrow  5 X direction. 
         FIG. 6  is a cross section taken along line  6 X- 6 X of the rubber crawler in  FIG. 4 . 
         FIG. 7  is a cross-section taken along line  7 X- 7 X of the rubber crawler in  FIG. 4 . 
         FIG. 8  is a cross-section taken along line  8 X- 8 X of the rubber crawler in  FIG. 4 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Explanation follows regarding a crawler according to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 1  and  FIG. 2 , an endless rubber crawler  10 , serving as a crawler, according to the exemplary embodiment of the present invention is what is referred to as a coreless type rubber crawler that does not have a metal core, and has a specified rotation direction. 
     As illustrated in  FIG. 1 , the rubber crawler  10  is employed entrained around a drive wheel  100  coupled to a drive shaft of a tracked vehicle serving as a vehicle body, and an idle wheel  102  that is attached to the tracked vehicle so as to be freely rotatable. Plural rollers  104 , disposed between the drive wheel  100  and the idle wheel  102  and attached to the tracked vehicle so as to be freely rotatable, roll against an inner circumference of the rubber crawler  10 . 
     Note that the drive wheel  100  of the present exemplary embodiment is an example of a drive wheel of the present invention, and the idle wheel  102  and the rollers  104  of the present exemplary embodiment are each examples of a follower wheel of the present invention. 
     In the present exemplary embodiment, a peripheral direction (illustrated by the arrow CD in  FIG. 2 ) of the endless rubber crawler  10  is referred to as the “crawler peripheral direction”, and a width direction (illustrated by the arrow WD in  FIG. 2 ) of the rubber crawler  10  is referred to as the “crawler width direction”. Note that the crawler peripheral direction (synonymous with the length direction of the rubber crawler  10 ) and the crawler width direction are orthogonal to each other as viewed from an inner peripheral side or an outer peripheral side of the rubber crawler  10 . 
     In the present exemplary embodiment, the inner peripheral side (the side in the direction indicated by the arrow IN in  FIG. 6 ) of the rubber crawler  10  entrained in an annular shape (encompassing circular annular shapes, elliptical annular shapes, polygonal annular shapes, and the like) around the drive wheel  100  and the idle wheel  102  is referred to as the “crawler inner peripheral side”, and the outer peripheral side of the rubber crawler  10  (the side in the direction indicated by the arrow OUT in  FIG. 6 ) is referred to as the “crawler outer peripheral side”. Note that the arrow IN direction (the direction toward the inside of the annular shape) and the arrow OUT direction (the direction toward the outside of the annular shape) in  FIG. 6  indicate in/out directions of the rubber crawler  10  when in an entrained state (synonymous with a thickness direction of the rubber crawler  10 ). 
     Note that although the present exemplary embodiment is configured such that the rubber crawler  10  is entrained around the drive wheel  100  and the idle wheel  102 , there is no limitation thereto. For example, depending on the layout of the drive wheel  100 , the idle wheel  102 , and the rollers  104 , the rubber crawler  10  may be entrained around one or plural rollers  104  in addition to the drive wheel  100  and the idle wheel  102 . 
     The drive wheel  100 , the idle wheel  102 , the rollers  104 , and the rubber crawler  10  entrained thereon configure a crawler traveling device  90  (see  FIG. 1 ), serving as a traveling section of the tracked vehicle. 
     As illustrated in  FIG. 1 , the drive wheel  100  includes a pair of circular disk shaped wheel portions  100 A that are coupled to the drive shaft of the tracked vehicle. Outer circumferential surfaces  100 B of the wheel portions  100 A respectively contact wheel-rotated faces  16  of a crawler body  12 , described later, and roll against the wheel-rotated faces  16 . The drive wheel  100  causes drive force from the tracked vehicle to act on the rubber crawler  10  (described in detail later), and circulates the rubber crawler  10  between the drive wheel  100  and the idle wheel  102 . 
     The idle wheel  102  includes a pair of circular disk shaped wheel portions  102 A attached to the tracked vehicle so as to be freely rotatable. Outer circumferential surfaces  102 B of the wheel portions  102 A respectively contact the wheel-rotated faces  16 , and roll against the wheel-rotated faces  16 . The idle wheel  102  is moved in a direction away from the drive wheel  100  and pressed against the wheel-rotated faces  16  by, for example, a hydraulic pressing mechanism, not illustrated in the drawings, provided at the tracked vehicle. Tension (pull) in the rubber crawler  10  entrained around the drive wheel  100  and the idle wheel  102  is maintained by pressing the idle wheel  102  against the wheel-rotated faces  16  in this manner. 
     The rollers  104  each include a pair of circular disk shaped wheel portions  104 A attached to the tracked vehicle so as to be freely rotatable. Outer circumferential surfaces  104 B of the wheel portions  104 A respectively contact the wheel-rotated faces  16  and roll against the wheel-rotated faces  16 . The weight of the tracked vehicle is supported by the rollers  104 . Note that the idle wheel  102  and the rollers  104  rotate following the rubber crawler  10  circulating between the drive wheel  100  and the idle wheel  102 . 
     Note that the rubber crawler  10  (crawler body  12 ) is entrained around the drive wheel  100  and the idle wheel  102  under a specific tension. Accordingly, frictional force arises between the outer circumferential surfaces  100 B of the drive wheel  100  and the wheel-rotated faces  16 , transmitting drive force of the drive wheel  100  to the rubber crawler  10 , and circulating the rubber crawler  10  between the drive wheel  100  and the idle wheel  102  such that the rubber crawler  10  travels. 
     As illustrated in  FIG. 1  and  FIG. 2 , the rubber crawler  10  includes the crawler body  12  configured by forming a rubber material, this being an example of an elastic material, into an endless belt shape. Note that the crawler body  12  of the present exemplary embodiment is an example of an endless belt shaped crawler body of the present invention. The peripheral direction, the width direction, the inner peripheral side, and the outer peripheral side of the crawler body  12  of the present exemplary embodiment respectively match the crawler peripheral direction, the crawler width direction, the crawler inner peripheral side, and the crawler outer peripheral side. 
     As illustrated in  FIG. 2  and  FIG. 3 , at intervals around the crawler peripheral direction, the crawler body  12  is formed with plural rubber projections  14  projecting out from an inner peripheral surface  12 A toward the crawler inner peripheral side. The rubber projections  14  are disposed along a central line CL passing through the crawler width direction center of the crawler body  12 . The rubber projections  14  restrict movement of the wheels in the crawler width direction by contacting the wheels (referring to the drive wheel  100 , the idle wheel  102 , and the rollers  104 ) rolling against the wheel-rotated faces  16 . In other words, by contacting the wheels, the rubber projections  14  are capable of suppressing relative movement of the rubber crawler  10  and the wheels in the crawler width direction. Namely, the rubber projections  14  are capable of suppressing lateral misalignment of the rubber crawler  10  with respect to the wheels. Note that the rubber projections  14  of the present exemplary embodiment are examples of projections of the present invention. 
     In the present exemplary embodiment, the rubber projections  14  are laid out on the crawler body  12  such that the crawler width direction center of the rubber projections  14  is positioned on the central line CL; however, the present invention is not limited to such a configuration. It is sufficient to lay out the rubber projections  14  on the crawler body  12  such that part of the rubber projections  14  is positioned on the central line CL. For example, the crawler width direction center of the rubber projections  14  may be shifted to one side or the other side in the crawler width direction with respect to the central line CL. 
     As illustrated in  FIG. 2  and  FIG. 6 , the respective wheel-rotated faces  16  are formed extending along the crawler peripheral direction at a crawler width direction outer side of the crawler body  12 , with the rubber projections  14  interposed therebetween. The wheel-rotated faces  16  are configured with flat profiles, and configure a portion of the inner peripheral surface  12 A of the crawler body  12 . 
     Note that although in the present exemplary embodiment configuration is such that the faces between the rubber projections  14  and the wheel-rotated faces  16  on the inner peripheral surface  12 A of the crawler body  12  are in the same plane (at the same height in this case) as each other, the present invention is not limited to such a configuration. For example, the wheel-rotated faces  16  may be configured so as to rise up more toward the crawler inner peripheral side than the faces between the rubber projections  14 , or may be configured so as to be hollowed out toward the crawler outer peripheral side (a configuration provided with indentations). 
     Lugs 
     As illustrated in  FIG. 1  and  FIG. 2 , plural lugs  18  are provided on the crawler body  12  so as to project out from the outer peripheral face  12 B toward the crawler outer peripheral side. As illustrated in  FIG. 4 , the lugs  18  are allocated to one side (the left side in  FIG. 4 ) and another side (the right side in  FIG. 4 ) in the crawler width direction on each side of the central line CL of the crawler body  12  so as to be alternately disposed on progression along the crawler peripheral direction on the one side or the other side. For convenience, the lugs  18  on the one side in the crawler width direction will be referred to below as the lugs  18 L, and the lugs  18  on the other side in the crawler width direction will be referred to below as the lugs  18 R. 
     Note that in the present exemplary embodiment, the placement interval of the lugs  18 L in the crawler peripheral direction is the same placement interval as the placement interval of the rubber projections  14 . Similarly, the placement interval of the lugs  18 R in the crawler peripheral direction is the same placement interval as the placement interval of the rubber projections  14 . 
     The lugs  18  extend from an inner side end  18 A on the central line CL side thereof toward the crawler width direction outer side and toward the opposite side to the crawler rotation direction side (at an angle toward the upper side in  FIG. 4 ) so as to extend at inclination to the crawler peripheral direction. Note that reference here to the “crawler rotation direction” means the rotation direction of the rubber crawler  10  when the tracked vehicle is driven (advances) (the arrow R direction in  FIG. 4 ). Due to configuration as described above, the inner side end  18 A side of the lugs  18  makes ground contact before the outer side end  18 B side thereof. Note that reference here to the inner side end  18 A means the inner side end on the central line CL side at the base portion  18 D of the lugs  18 , and the outer side end  18 B means the outer side end on the crawler width direction outer side at the base portion  18 D of the lugs  18 . 
     Moreover, as illustrated in  FIG. 4 , there is a larger angle on the acute angle side to the crawler peripheral direction further to the crawler width direction outer side of the lugs  18  than that on the central line CL side thereof. Note that the lugs  18  in the present exemplary embodiment are configured so as to extend in a straight line at an angle to the crawler peripheral direction, and to be bent partway along (a 2-stage angled configuration). Each of the lugs  18  of the present exemplary embodiment accordingly includes a tread-in-side wall face  18 E also referred to as forward wall face  18 E) and a kick-out-side wall face  18 F also referred to as rearward wall face  18 F), described later, that are each angled in 2-stages with respect to the crawler peripheral direction. Note that the present invention is not limited to the above configuration. For example, the lugs  18  may adopt a multi-stage angled configuration with respect to the crawler peripheral direction (a configuration in which the tread-in-side wall face  18 E and the kick-out-side wall face  18 F are respectively angled in multiple stages with respect to the crawler peripheral direction), or a configuration curved in a curved line with respect to the crawler peripheral direction (a configuration in which the tread-in side wall face  18 E and the kick-out side wall face  18 F are respectively curved with respect to the crawler peripheral direction). 
     As illustrated in  FIG. 7  and  FIG. 8 , in a cross-section taken along the crawler peripheral direction, the tread-in-side wall face  18 E on the crawler rotation direction side (in other words, on the tread-in-side) of the lugs  18  is angled (which has the same meaning here as tilted) with respect to the outer peripheral face  12 B of the crawler body  12 . More specifically, the tread-in-side wall face  18 E is sloped at a fixed angle to the outer peripheral face  12 B from the vicinity of an apex portion  18 C of the lugs  18  to the vicinity of the base portion  18 D thereof. Moreover, an angle θ 1  formed between the tread-in-side wall face  18 E and the outer peripheral face  12 B is 90 degrees or greater, but is smaller than an angle θ 2 , described later. 
     Moreover, in a cross-section taken along the crawler peripheral direction, the kick-out-side wall face  18 F, on the opposite side of the lugs  18  to the crawler rotation direction (in other words, on the kick-out-side), is angled (which has the same meaning here as tilted) in 2-stages with respect to the outer peripheral face  12 B of the crawler body  12 . Specifically, the kick-out-side wall face  18 F is angled with respect to the outer peripheral face  12 B at a fixed angle θ 2  from the vicinity of the apex portion  18 C of the lugs  18  to a lug projection height intermediate portion thereof, and is angled with respect to the outer peripheral face  12 B at a fixed angle θ 3  from the intermediate portion to the vicinity of the base portion  18 D. The kick-out-side wall face  18 F is set here such that the angle θ 2 , formed between an apex side portion  18 FA on the apex portion  18 C side and the outer peripheral face  12 B, is larger than the angle θ 3 , formed between a base side portion  18 FB on the base portion  18 D side and the outer peripheral face  12 B. The angle θ 3  is set so as to exceed 90 degrees. 
     The angle θ 1  of the tread-in-side wall face  18 E of the lugs  18  is smaller on the outer side end  18 B side than on the inner side end  18 A side of the lugs  18 . Moreover, the angle θ 2  of the kick-out-side wall face  18 F of the lugs  18  is smaller on the outer side end  18 B side than on the inner side end  18 A side of the lugs  18 . Note that the angle θ 3  of the kick-out-side wall face  18 F may be the same on the outer side end  18 B side as on the inner side end  18 A side of the lugs  18 , or may be smaller on the outer side end  18 B side than on the inner side end  18 A side thereof. 
     The angle θ 1  of the lugs  18  is preferably set within a range of from 102 degrees to 115 degrees, and the angle θ 2  is preferably set within a range of from 118 degrees to 132 degrees, and the angle θ 3  is preferably set within a range of from 104 degrees to 118 degrees. 
     As illustrated in  FIG. 4 , lugs  18  that are adjacent to each other in the crawler width direction (a lug  18 L and a lug  18 R) have inner side ends  18 A that respectively overlap with each other when viewed along the crawler width direction. In  FIG. 4 , the range over which the inner side ends  18 A respectively overlap when viewed along the crawler width direction as described above (the overlap range) is indicated by the label P. 
     As viewed from the crawler outer peripheral side, the inner side ends  18 A of lugs  18  that are adjacent to each other in the crawler width direction respectively overlap with a single rubber projection  14 . Moreover, as viewed from the crawler outer peripheral side, the inner side ends  18 A of lugs  18  adjacent to each other in the crawler width direction are respectively disposed at positions separated from each other in the crawler width direction. Specifically, a length W 1  along a crawler width direction between inner side ends  18 A of respective lugs  18  adjacent to each other in the crawler width direction is set so as to be within a range of from 4% to 10% of a length W 0  along the crawler width direction of the crawler body  12 . 
     The lugs  18  are set such that an angle α formed between an inner side wall face  18 G on the central line CL side thereof and an outer peripheral face  12 B is within a range of from 110 degrees to 120 degrees. 
     In the present exemplary embodiment, the lugs  18  are configured so as to have left-right symmetry about the central line CL; however, the present invention is not limited to such a configuration. For example, the lugs  18  may be configured so as to have left-right asymmetry about the central line CL. 
     Cord Layer 
     As illustrated in  FIG. 3  and  FIG. 5 , a main cord layer  20 , a first bias cord layer  22 , a second bias cord layer  23 , and a protection cord layer  28  are embedded in the crawler body  12  in that sequence from the crawler inner peripheral side. 
     The main cord layer  20  is an endless belt shape, and is superimposed at the crawler outer peripheral side of a body inner peripheral portion  12 C forming the inner peripheral surface  12 A of the crawler body  12 . The main cord layer  20  includes main cords  20 A extending along the crawler peripheral direction. The main cords  20 A are configured by plural strands twisted together. In the present exemplary embodiment, as an example, the strands are formed by twisting together plural filaments; however, the present invention is not limited to such a configuration. The main cords  20 A are covered in rubber. 
     Moreover, although in the present exemplary embodiment steel cords having excellent tensile strength are employed as the main cords  20 A, the present invention is not limited to such a configuration, and organic fiber cords configured by organic fibers (for example, nylon fibers, aromatic polyamide fibers or the like) may be employed as the main cords  20 A, as long as they have sufficient tensile strength. 
     The first bias cord layer  22  is configured in an endless belt shape, and is superimposed on the main cord layer  20  at the crawler outer peripheral side thereof. The first bias cord layer  22  includes an endless belt shaped bias ply  24  formed by embedding bias cords  24 A in belt shaped rubber, such that the bias cords  24 A extend at an angle with respect to the crawler peripheral direction and plural of the bias cords  24 A lie side-by-side in the crawler peripheral direction. Note that the bias ply  24  of the present exemplary embodiment is an example of a first bias ply of the present invention. 
     The second bias cord layer  23  is configured in an endless belt shape, and is superimposed on the first bias cord layer  22  at the crawler outer peripheral side thereof. The second bias cord layer  23  includes an endless belt shaped bias ply  26  formed by embedding bias cords  26 A in belt shaped rubber, such that the bias cords  26 A extend at an angle with respect to the crawler peripheral direction and intersect the bias cords  24 A, and plural of the bias cords  26 A lie side-by-side in the crawler peripheral direction. Specifically, the bias cords  26 A are angled in the opposite direction to the bias cords  24 A with respect to the crawler peripheral direction. Note that the bias ply  26  of the present exemplary embodiment is an example of a second bias ply of the present invention. 
     In the present exemplary embodiment, the bias cords  24 A and the bias cords  26 A are configured by the same steel cords. The bias cords  24 A and the bias cords  26 A employ steel cords with a smaller diameter than the main cords  20 A, from the perspective of the bending flexibility of the rubber crawler  10 . Note that the present invention is not limited to such a configuration, and organic fiber cords configured by organic fibers (for example, nylon fibers, aromatic polyamide fibers or the like) may be employed as the bias cords  24 A and the bias cords  26 A as long as they have sufficient tensile strength. 
     The protection cord layer  28  is configured in an endless belt shape, and is superimposed on the second bias cord layer  23  at the crawler outer peripheral side thereof, and is superimposed at the crawler inner peripheral side of a body outer peripheral portion  12 D forming the outer peripheral face  12 B of the crawler body  12 . The protection cord layer  28  is formed by superimposing plural layers of endless belt shaped protection plies  30  (two plies in the present exemplary embodiment). Note that the protection plies  30  in the present exemplary embodiment are examples of the protection plies of the present invention. 
     The protection plies  30  are formed by plural strands of protection cord  30 A that extend along the crawler width direction (in other words a direction orthogonal to the central line CL), that are arranged side-by-side in the crawler peripheral direction, and that are embedded in belt shaped rubber. 
     Due to the protection cords  30 A extending along the crawler width direction, the protection cord layer  28  has high rigidity in the crawler width direction, or, in other words, is not liable to deform in the crawler width direction. 
     In the present exemplary embodiment, in a state in which the rubber crawler  10  is not yet mounted to a wheel (namely, in a state in which tension is not being applied), the protection cords  30 A extend along the crawler width direction. Note that reference here to “extend along the crawler width direction” includes cases in which they are angled with respect to the crawler width direction by about ±3 degrees. 
     Although in the present exemplary embodiment steel cords are employed as the protection cords  30 A in order to raise the rigidity in the crawler width direction, the present invention is not limited to such a configuration, and organic fiber cords configured by organic fibers (for example, nylon fibers, aromatic polyamide fibers or the like) may be employed as the protection cords  30 A as long as they have sufficient rigidity in the crawler width direction. 
     Moreover, as illustrated in  FIG. 6 , a thickness T 1  of the body inner peripheral portion  12 C on the central line CL is thicker than a thickness T 2  of the body outer peripheral portion  12 D. Moreover, on the central line CL, the thickness T 1  is preferably set to a thickness within a range of from 35% to 45% of a thickness T 0  of the crawler body  12 , and the thickness T 2  is preferably set to a thickness within a range of from 16% to 26% of the thickness T 0 . 
     In the present exemplary embodiment, the main cords  20 A are disposed at a central portion in the thickness direction (which means the same as the crawler in/out directions) of the crawler body  12 . 
     Next, explanation follows regarding operation and advantageous effects of the rubber crawler  10  of the present exemplary embodiment. 
     In the rubber crawler  10 , as illustrated in  FIG. 7  and  FIG. 8 , in a cross-section taken along the crawler peripheral direction, the angle θ 1  formed between the apex side portion of the tread-in-side wall face  18 E and the outer peripheral face  12 B is 90 degrees or greater, but is smaller than the angle θ 2  formed between the apex side portion  18 FA of the kick-out-side wall face  18 F and the outer peripheral face  12 B. Hence, traction is improved in the rubber crawler  10  since the force component of the driving force applied to the soil in the horizontal direction when driving on rough ground is increased compared, for example, to cases in which the angle θ 1  is larger than the angle θ 2 . Moreover, even in cases in which the soil of the rough ground is a sandy substance, by adopting the configuration described above, soft dirt can be suppressed from being swept away from the area of the apex portion  18 C of the lugs  18  that makes contact with the soil, using the tread-in-side wall face  18 E. This thereby enables sliding between the apex portion  18 C and the soil to be suppressed, and secures traction in the machinery body forward direction. This thereby enables traction performance to be secured by the rubber crawler  10  when driving on rough ground. 
     On the other hand, in the rubber crawler  10 , the lugs  18  each extend from the inner side end  18 A on the central line CL side toward the crawler width direction outer side, and toward the opposite side to the crawler rotation direction at an angle with respect to the crawler peripheral direction. Thus due to the projected surface area of the lugs  18  in the crawler width direction being increased in the rubber crawler  10  compared, for example, to cases in which the lugs  18  extend in a straight line along the crawler width direction, the resistance to lateral force in the crawler width direction is improved when driving on rough ground. The rubber crawler  10  thereby enables side-slip when driving on rough ground to be suppressed. 
     Moreover, in the rubber crawler  10 , in a cross-section of the lugs  18  taken along the crawler peripheral direction, the angle θ 3  formed between the base side portion  18 FB of the kick-out-side wall face  18 F and the outer peripheral face  12 B is 90 degrees or greater, but is smaller than angle θ 2 . Thus in the rubber crawler  10 , the spacing in the crawler peripheral direction between lugs  18  adjacent in the crawler peripheral direction can be widened compared to cases in which, for example, the angle θ 3  is larger than the angle θ 2 . Thus in the rubber crawler  10 , earth and mud can be suppressed from becoming lodged between lugs  18  adjacent in the crawler peripheral direction, and due to increasing the efficacy of earth and mud discharge, the lugs  18  reliably penetrate into the earth and mud, and traction and resistance to lateral force are further improved. 
     Moreover, in the rubber crawler  10 , the angle θ 1  of the tread-in-side wall face  18 E of the lugs  18  is smaller at the crawler width direction outer side (the outer side end  18 B side) than at the central line CL side (the inner side end  18 A side). Due to such a configuration, in the rubber crawler  10 , due to the force component of the driving force applied to the soil in the horizontal direction being increased at the crawler width direction outer side, the traction performance when driving on rough ground is effectively improved. Moreover, due to the above configuration, when driving on rough ground, the lugs  18  readily penetrate into the earth and mud, and traction and resistance to lateral force are further improved. 
     Moreover, in the rubber crawler  10 , due to the angle θ 1  of the tread-in-side wall face  18 E of the lugs  18  being set within a range of from 102 degrees to 115 degrees, the traction performance when driving on rough ground can be further improved. Note that in cases in which the angle θ 1  is smaller than 102 degrees, earth and mud is difficult to dislodge, and sufficient traction cannot be obtained. However, if the angle θ 1  exceeds 115 degrees, then sufficient spacing cannot be secured between lugs  18  adjacent in the crawler peripheral direction, and sufficient traction cannot be obtained. Thus the angle θ 1  is preferably set within a range of from 102 degrees to 115 degrees. 
     In the rubber crawler  10 , as illustrated in  FIG. 4 , the inner side ends  18 A on the central line CL side of each of the lugs  18  adjacent in the crawler width direction respectively overlap with a single rubber projection  14  as viewed from the crawler outer peripheral side. Thus in the rubber crawler  10 , the rigidity to bending at the areas corresponding to the rubber projections  14  is larger, and the rigidity to bending at the areas corresponding to between the rubber projections  14  is smaller. Thus in the rubber crawler  10 , due to the areas corresponding to between the rubber projections  14  at the sections entrained around the drive wheel  100  and the idle wheel  102  bending so as to have a curvature greater than that of the areas corresponding to the rubber projections  14 , mud lodged between the lugs  18  when driving on rough ground can be dislodged starting from the areas corresponding to between the rubber projections  14 . 
     In the rubber crawler  10 , as viewed from the crawler outer peripheral side, each of the inner side ends  18 A of the lugs  18  adjacent to each other in the crawler width direction are disposed at positions separated in the crawler width direction. Thus in the rubber crawler  10 , since there are no projecting objects such as lugs  18  formed on the central line CL, mud can be suppressed from becoming lodged in the crawler width direction central portion, and even if mud were to become lodged, dislodging of the lodged mud is facilitated. 
     Moreover, in the rubber crawler  10 , each of the inner side ends  18 A of the lugs  18  that are respectively adjacent to each other in the crawler width direction overlap with each other when viewed along the crawler width direction. Thus in the rubber crawler  10 , due to being able to achieve a wide spacing between the inner side ends  18 A of the lugs  18  respectively adjacent to each other in the crawler peripheral direction, mud can be further suppressed from lodging in the central portion in the crawler width direction, and even if mud does become lodged, dislodging of the lodged mud is facilitated. 
     Moreover, in the rubber crawler  10 , the angle of the lugs  18 , on the acute angle side, to the crawler peripheral direction is larger at the crawler width direction outer side than that on the central line CL side thereof. Thus in the rubber crawler  10  the force component of the driving force applied to the soil in the horizontal direction is increased at the crawler width direction outer side of the lugs  18 , and traction is improved. 
     The rubber crawler  10  accordingly suppresses lodging of mud when driving on rough ground, and improves traction performance. 
     Moreover, in the rubber crawler  10 , the length W 1  along the crawler width direction between inner side ends  18 A of lugs  18  respectively adjacent to each other in the crawler width direction is set so as to be within a range of from 4% to 10% of a length W 0  along the crawler width direction of the crawler body  12 . Hence in the rubber crawler  10 , the occurrence of mud lodging between each of the inner side ends  18 A of the lugs  18  that are adjacent to each other in the crawler width direction can be suppressed. Note that in cases in which the length W 1  is less than 4% of the length W 0 , sufficiently effective mud lodging suppression is not obtained. However, in cases in which the length W 1  exceeds 10% of the length W 0 , due to the length of the lugs  18  along the crawler width direction being shorter, sufficient traction performance is not obtained. The length W 1  is accordingly preferably set within a range of from 4% to 10% of the length W 0 . 
     Moreover, in the rubber crawler  10 , due to the angle α formed between the inner side wall face  18 G of the lugs  18  and the outer peripheral face  12 B being set within a range of from 110 degrees to 120 degrees, occurrences of mud lodging between each of the inner side ends  18 A of the lugs  18  can be further suppressed. Note that when the angle α is smaller than 110 degrees, sufficiently effective suppression of mud lodging between each of the inner side ends  18 A of lugs  18  is not obtained. However, if the angle α exceeds 120 degrees, due to the length of the apex portions  18 C of the lugs  18  along the crawler width direction being shorter, sufficient traction performance is not obtained. The angle α is accordingly preferably set within a range of from 110 degrees to 120 degrees. 
     In the rubber crawler  10 , the protection cord layer  28  formed overlapping the plural protection plies  30  is disposed at the crawler outer peripheral side of the second bias cord layer  23 . Thus in the rubber crawler  10 , the speed with which cracking caused by external damage to the outer peripheral face  12 B of the crawler body  12  propagates to the first bias cord layer  22  and the second bias cord layer  23  can be slowed. By extending the time until cracking reaches the bias cords  24 A and the bias cords  26 A in this manner, problems with the bias cords  24 A and the bias cords  26 A due to the penetration of water from outside can be suppressed for a long period of time, and the durability of the rubber crawler  10  is improved. 
     Moreover, in the rubber crawler  10 , the first bias cord layer  22  is superimposed at the crawler outer peripheral side of the main cord layer  20 , and the second bias cord layer  23  is superimposed at the crawler outer peripheral side of the first bias cord layer  22 . Hence the bias ply  24  and the bias ply  26  are close to the main cord layer  20 , enabling the deflection amount of the bias cords  24 A and the bias cords  26 A during turning to be reduced. This thereby enables buckling of the bias cords  24 A and the bias cords  26 A to be suppressed from arising. The occurrence of problems with the bias cords  24 A and the bias cords  26 A arising due to such buckling can thereby be suppressed for a long period of time, improving the durability of the rubber crawler  10 . Moreover, as described above, due to the bias ply  24  and the bias ply  26  being close to the main cord layer  20 , an action to prevent twisting of the main cords  20 A can be effectively obtained, improving the directionality of the rubber crawler  10 . 
     In the rubber crawler  10 , due to the thickness T 1  of the body inner peripheral portion  12 C of the crawler body  12  being thicker than the thickness T 2  of the body outer peripheral portion  12 D, problems can be suppressed from arising in the body inner peripheral portion  12 C that receives load from the drive wheel  100 , the idle wheel  102 , and the rollers  104 . 
     In the rubber crawler  10 , the main cord layer  20  is the neutral axis of bending for the sections entrained around the drive wheel  100  and the idle wheel  102 . Thus by disposing the main cords  20 A at the central portion in the crawler body thickness direction, a balance can be achieved between compression force acting on the inner peripheral surface  12 A of the crawler body  12  and tension force acting on the outer peripheral face  12 B. This thereby enables the durability of the crawler body  12  to be improved. 
     Although in the exemplary embodiment described above a configuration is adopted in which each of the inner side ends  18 A of the lugs  18  that are adjacent to each other in the crawler width direction are respectively disposed at positions separated from each other in the crawler width direction, the present invention is not limited to such a configuration. For example, a configuration may be adopted in which each of the inner side ends  18 A of the lugs  18  that are adjacent to each other in the crawler width direction overlap as viewed from the crawler peripheral direction. 
     Moreover, although in the exemplary embodiment described above the lugs  18  extend angled in 2-stages with respect to the crawler peripheral direction, the present invention is not limited to such a configuration. For example, the lugs  18  may extend in a straight line at an angle to the crawler peripheral direction. 
     Moreover, although in the exemplary embodiment described above a configuration is adopted in which the main cord layer  20 , the first bias cord layer  22 , the second bias cord layer  23 , and the protection cord layer  28  are embedded in the crawler body  12  in this sequence from the crawler inner peripheral side, the present invention is not limited to such a configuration. For example, the sequence may be changed for each of the cord layers, and the first bias cord layer  22 , the second bias cord layer  23 , or the protection cord layer  28  may be omitted. 
     Although embodiments of the present invention have been explained by giving exemplary embodiments thereof, these exemplary embodiments are merely examples, and various modifications may be implemented within a range not departing from the spirit thereof. It also goes without saying that the scope of rights of the present invention is not limited by these exemplary embodiments. 
     The disclosure of Japanese Patent Application No. 2014-083143 filed on Apr. 14, 2014 is incorporated by reference in its entirety in the present specification. 
     All publications, patent applications and technical standards mentioned in the present specification are incorporated by reference in the present specification to the same extent as if the individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.