Rubber crawler

The present invention relates to a rubber crawler including: a joint formed by joining together opposite ends of a crawler body comprising an elastic member shaped like a belt having the opposite ends; and lugs projected at predetermined space intervals along a longitudinal direction of the belt and arranged on an outer circumferential surface of the crawler body. The joint is disposed on the outer circumferential surface of the crawler body, as located in a ground non-engaging portion and at different positions with respect to the longitudinal direction of the belt, the ground non-engaging portion defining an area excluding the lugs. In this way, stress acting on the joint is distributed or reduced.

FIELD OF THE INVENTION

The present invention relates to an endless-belt rubber crawler for use in belted-track mobile apparatuses such as construction machines and agricultural machines.

DESCRIPTION OF THE PRIOR ART

The rubber crawler is used widely because it is more advantageous than an iron crawler in terms of lower noises, higher ride quality, better road-surface conservation characteristic and the like. While the rubber crawler includes a type wherein core bars are covered with rubber, a coreless type and the like, all those types are manufactured by forming rubber into an endless belt. Such an endless rubber belt may be formed by joining together opposite ends of a rubber belt cut in a certain length. As disclosed in Japanese Unexamined Patent Publication No. 2001-38818 (claim 1, FIG. 2), the joining of the opposite ends of the rubber belt is normally accomplished by curing an un-cured or semi-cured rubber belt with its opposite ends in butt connection. In some cases, the endless rubber belt may be formed by interconnecting a plurality of rubber belts, the respective ends of which are joined to each other.

An outer circumferential surface of the rubber crawler is formed with lugs as a ground-engaging portion, the lugs projected at predetermined space intervals along a longitudinal direction (circumferential direction) of the belt. A lug layout pattern includes a so-called stagger pattern, as disclosed in Japanese Unexamined Patent Publication No. 2000-177658 (FIG. 1, FIG. 4, FIG. 6), wherein the lugs are separated into left-hand and right-hand lug groups via a portion near a widthwise center of the rubber crawler and wherein a respective pair of the left-hand and right-hand lugs have their phases shifted from each other along the longitudinal direction of the belt.

OBJECT AND SUMMARY OF THE INVENTION

As described above, the rubber crawler having the endless belt shape has the following problem because of the inclusion of a joint at which the opposite ends of the rubber belt are joined together. That is, the crawler sustains cracks originating from the joint and growing therefrom, so that the crawler suffers a serious damage which results in a lowered durability of the crawler. Conventionally, the joint at which the opposite ends of the rubber belt is joined together to form the endless belt shape is disposed on the outer circumferential surface of the crawler as extended in a straight line substantially along a widthwise direction of the crawler. Therefore, the joint on the outer circumferential surface of the crawler encounters a serious stress concentration because the joint is subjected to stress which is not distributed along the longitudinal direction of the belt. Furthermore, the joint on the outer circumferential surface of the crawler is in the form of the straight line substantially along the widthwise direction of the crawler, so that the joint often cuts across the lug. Since the joint on a surface of such a lug or within such a lug is subjected to a greater stress associated with traction and the like, the joint is susceptible to interfacial separation and cracks. In addition, the cracks grow to cause a serious damage to the crawler. This results in the lowered durability of the crawler.

The invention is directed to the augmentation of the durability of the rubber crawler by distributing or reducing the stress on the joint thereby preventing the occurrence or growth of the cracks originating from the joint.

According to the invention for achieving the above object, a rubber crawler comprises: a joint formed by joining together opposite ends of a crawler body comprising an elastic member shaped like a belt having the opposite ends; and lugs projected at predetermined space intervals along a longitudinal direction of the belt and arranged on an outer circumferential surface of the crawler body, and is characterized in that the joint is disposed on the outer circumferential surface of the crawler body as located in a ground non-engaging portion and at different positions with respect to the longitudinal direction of the belt, the ground non-engaging portion defining an area excluding the lugs. According to this arrangement, the joint is not located at the lug which is subjected to the great stress associated with the traction (drive force) during a ground engaging operation, but at an outside surface of the ground non-engaging portion subjected to a relatively small stress. Accordingly, the joint is less susceptible to the cracks on its surface, while the growth of the cracks is suppressed. Furthermore, the joint is disposed on the outer circumferential surface of the crawler as located at different positions with respect to the longitudinal direction of the belt. Hence, the stress on the joint is distributed along the longitudinal direction of the belt.

According to a preferred aspect of the invention, the rubber crawler comprises: the lugs separated into left-hand and right-hand lug groups via a portion near a widthwise center of the crawler body or near a sprocket engagement hole, and staggeredly arranged in opposing relation; the crawler body including an outer circumferential member constituting the outer circumferential surface thereof, and an inner circumferential member disposed on an inner side of the outer circumferential member so as to constitute an inner circumferential surface of the crawler body; and the joint including an outer circumferential joint portion formed by joining together opposite ends of the outer circumferential member for forming an endless belt shape, and an inner circumferential joint portion formed by joining together opposite ends of the inner circumferential member for forming an endless belt shape, and is characterized in that the outer circumferential joint portion is located in the ground non-engaging portion whereas the inner circumferential joint portion is formed substantially along a widthwise direction of the crawler body. In this case, the lugs are staggered so that the left-hand and right-hand lugs are shifted from each other in phase. Therefore, time when the stress transmitted from a ground-engaging face is peaked differs between the left-hand lug and the right-hand lug. This prevents the great stress from acting on the left-hand and right-hand lugs simultaneously. Furthermore, the outer circumferential joint portion is located in the ground non-engaging portion, so that the positions thereof with respect to the lateral sides of an outer-circumferential ground-engaging portion are shifted from each other along the longitudinal direction of the belt as a result of that the outer circumferential joint portion circumvents the staggered lugs. This prevents the great stress from acting on the lateral sides of the outer-circumferential ground-engaging portion simultaneously. Furthermore, the outer circumferential joint portion, the lateral positions of which are shifted from each other along the longitudinal direction of the belt, is configured differently from the inner circumferential joint portion extended substantially along a widthwise direction of the crawler. This is effective to the distribute the stress on the joint.

According to another preferred aspect of the invention, the rubber crawler comprises: the lugs arranged along the longitudinal direction of the belt at a substantially equal pitch; and the outer circumferential joint portion, positions of which at widthwise opposite ends of the crawler are shifted from each other along the longitudinal direction of the belt by 0.2 or more times the pitch and 1.5 or less times the pitch.

In this case, the crawler may be formed uniformly with respect to the longitudinal direction of the belt by virtue of the lugs arranged at the substantially equal pitch. The widthwise opposite ends of the outer circumferential joint portion are shifted from each other along the longitudinal direction of the belt by 1.5 or less times the pitch and hence, the length of the outer circumferential joint portion is never greater than necessary. By the same reason, it is preferred that the widthwise opposite ends of the outer circumferential joint portion are shifted from each other along the longitudinal direction of the belt by 0.8 or less times the pitch. In addition, the widthwise opposite ends of the outer circumferential joint portion are shifted from each other along the longitudinal direction of the belt by 0.2 or more times the pitch, so that the phase shift of the lateral positions of the joint portion provides an adequate effect.

According to another preferred aspect of the invention, the rubber crawler comprises: widthwise reinforcing members embedded at space intervals along the longitudinal direction of the belt for the purpose of widthwise reinforcement of the crawler; and the inner circumferential joint portion located substantially centrally of the space between the widthwise reinforcing members.

In this case, the crawler is increased not only in the torsional rigidity thereof but also in the endurance against stress acting in the widthwise direction of the crawler. Although the elastic member has a relatively small thickness at its portion where the widthwise reinforcing members are embedded, the inner circumferential joint portion may be spaced away from the thin portion because the inner circumferential joint portion is located near the center of the space between the widthwise reinforcing members. Thus, the inner circumferential joint portion may achieve an increased joining strength.

The joint portion on the outer circumferential surface of the crawler body may include a portion inclined at 10° or more and 60° or less relative to the widthwise direction of the crawler body as seen in plan viewed from the outer circumferential surface of the crawler. In this case, the stress may be adequately distributed along the longitudinal direction of the belt by defining the angle of inclination to be 10° or more. In the meantime, the angle of inclination defined to be 60° or less affords the ease of locating the joint in the ground non-engaging portion defining the area excluding the lugs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the invention will hereinbelow be described with reference to the accompanying drawings.

FIG. 1is a plan view showing an outer circumferential surface (ground-engaging surface) of a rubber crawler1according to a first embodiment of the invention.FIG. 2is a plan view depicting core bars as a widthwise reinforcing member with broken lines which are added toFIG. 1.FIG. 3is a plan view showing an inner circumferential surface of the rubber crawler1.FIG. 4is a sectional view taken on the line A-A inFIG. 1throughFIG. 3.FIG. 5is a sectional view taken on the line B-B inFIG. 1throughFIG. 3.FIG. 6is a sectional view taken on the line C-C inFIG. 1throughFIG. 3.FIG. 7is a sectional view taken on the line D-D inFIG. 1throughFIG. 3.

As shown inFIG. 1andFIG. 2, the rubber crawler1includes: lugs7, as ground-engaging portions, projected at predetermined space intervals along a longitudinal direction of belt; and a ground non-engaging portion8defining an area excluding the lugs7. The lugs7are separated into left-hand and right-hand lug groups via a portion near a widthwise center of the rubber crawler1, and are staggeredly arranged in opposing relation. As indicated by a broken line inFIG. 3, core bars5elongated in a widthwise direction of a crawler body4are embedded in the rubber crawler1at predetermined space intervals along the longitudinal direction of the belt. The core bars5serve as a widthwise reinforcing member for reinforcing the crawler body4in the widthwise direction thereof.FIG. 2depicts the core bars5with the broken line which are added to the plan view ofFIG. 1.

While the lugs7are separated into the left-hand and the right-hand lug groups via the portion near the widthwise center of the rubber crawler1and staggeredly arranged in opposing relation, as shown inFIG. 1, a respective pair of adjacent right-hand and left-hand lugs7are disposed in overlapping relation with respect to the longitudinal direction of the belt. In the rubber crawler1, therefore, the lugs7are arranged such that a cross-section passing through any point on the longitudinal direction of the belt substantially along the widthwise direction of the crawler body cuts across at least a part of the lug. For instance, a cross-section taken on a widthwise line A-A with respect to the crawler body cuts across one (the left-hand lug7inFIG. 1) of the left-hand and right-hand lugs7. Similarly, a cross-section taken on a widthwise line E-E with respect to the crawler body (seeFIG. 1) cuts across both of the left-hand and right-hand lugs7. If a straight-line joint extended along the widthwise direction of the crawler is to be provided on the outer circumferential surface of the crawler, as practiced in the prior art, the joint necessarily cuts across any part of the lug7. According to the embodiment, a joint9(an outer-circumferential joint portion9ato be described hereinlater) on the outer circumferential surface of the crawler is bent so that the lug7may not contain therein the joint9. It is noted that “to cut across the lug” means not only to cut across a top face (ground-engaging face) of the lug7but also to cut across any part of the lug7(projected portion).

As shown in the sectional view ofFIG. 4, the crawler body4of the rubber crawler1is constructed such that an outer circumferential member2and an inner circumferential member3are laminated, the outer circumferential member constituting the outer circumferential surface of the rubber crawler1, the inner circumferential member3constituting the inner circumferential surface of the crawler body4as disposed on an inner side of the outer circumferential member2. As shown in the sectional view ofFIG. 5, the individual core bars5are embedded as sandwiched between the outer circumferential member2and the inner circumferential member3.

As shown inFIG. 1throughFIG. 3, sprocket engagement holes6are formed centrally of the width of the rubber crawler1as arranged at regular space intervals along the longitudinal direction of the belt. A sprocket engages the sprocket engagement holes6thereby applying a drive force to the rubber crawler1. The sprocket engagement hole6is a through hole extended from the outer circumferential surface to the inner circumferential surface of the rubber crawler1. In some cases, a thin rubber film may be provided on an inside surface of the through hole. As shown inFIG. 2andFIG. 3, the core bar5is embedded in space between a respective pair of adjoining sprocket engagement holes6with respect to the longitudinal direction of the belt. Thus, the core bars5are arranged longitudinally of the belt with equal spacing, while the crawler body4fills a space between a respective pair of adjoining core bars5.

As shown inFIG. 5, the core bar5includes: lateral wings5aindividually extended transversely of the rubber crawler1; a central portion5bconstituting a longitudinally central portion of the core bar5; and anti-disengagement projections5cindividually projecting from laterally opposite sides of the central portion5btoward the inner circumferential surface of the crawler. While the core bar5is embedded in the crawler body4of the rubber crawler1, only the anti-disengagement projection5cis partially exposed from the inner circumferential surface of the rubber crawler1. As shown inFIG. 4andFIG. 5, a plurality of tensioning members10such as formed of a steel cord are also embedded in the crawler body4along the longitudinal direction of the belt.

The rubber crawler1is formed into an endless belt by joining together opposite ends of the crawler body4formed from an elastic member shaped like a belt having the opposite ends. Therefore, the rubber crawler1includes the joint9at which the opposite ends of the crawler body are joined to each other. The crawler body4of the rubber crawler1includes the outer circumferential member2and the inner circumferential member3, as described above, and each of the inner and outer circumferential members2,3is formed into the endless belt by joining together the opposite ends of the belt member. Accordingly, the joint9includes the outer circumferential joint portion9aformed by joining together the opposite ends of the outer circumferential member2for forming the endless belt shape; and an inner circumferential joint portion9bformed by joining together the opposite ends of the inner circumferential member3for forming the endless belt shape. These joint portions9(the outer circumferential joint portion9a,the inner circumferential joint portion9b) are indicated by the broken lines inFIG. 1throughFIG. 3,FIG. 6andFIG. 7.

As shown inFIG. 1,FIG. 6andFIG. 7, the outer circumferential joint portion9adoes not exist in the lug7but exists in the ground non-engaging portion8. Thus, the outer circumferential joint portion9aof the joint9is disposed on the outer circumferential surface of the crawler body4as located in the ground non-engaging portion8. More specifically, the outer circumferential joint portion9ais divided into lateral segments via a portion near the widthwise center of the rubber crawler body4, the lateral joint segments located at different positions with respect to the longitudinal direction of the belt. The lateral joint segments at the individually different longitudinal positions are extended substantially along the widthwise direction while the joint portion near the widthwise center is extended along the longitudinal direction of the belt.

In this manner, the outer circumferential joint portion9ais located in the ground non-engaging portion8as circumventing the staggered lugs7. Hence, the right-hand and the left-hand segments of the outer circumferential joint portion9aare shifted from each other with respect to the longitudinal direction of the belt. On the other hand, the inner circumferential joint portion9bis formed substantially in the straight line along the widthwise direction of the crawler body4, as shown inFIG. 3. As a result, the outer circumferential joint portion9aand the inner circumferential joint portion9bhave a positional relation with respect to the longitudinal direction of the belt such that the outer circumferential joint portion and the inner circumferential joint portion are close to each other on the right side of the rubber crawler1as seen inFIG. 1(see the sectional view ofFIG. 6taken on the line C-C), whereas the outer and inner circumferential joint portions are spaced away from each other on the left side of the rubber crawler (see the sectional view ofFIG. 7taken on the line D-D).

In the rubber crawler1, as shown inFIG. 1, the lugs7are arranged along the longitudinal direction of the belt at a substantially equal pitch P, whereas a distance d between widthwise opposite ends h1, h2of the outer circumferential joint portion9awith respect to the longitudinal direction of the belt is 0.2 or more times the pitch P and 0.8 or less times the pitch P.

While the rubber crawler1includes the core bars5, as the widthwise reinforcing member for widthwise reinforcement, which are embedded therein at space intervals S along the longitudinal direction of the belt (seeFIG. 3), as described above, the inner circumferential joint portion9bis located substantially centrally of the space S, as shown inFIG. 3.

The rubber crawler1constructed in the aforementioned manner has the following working effects.

During a ground-engaging operation of the crawler, the lugs7receive a traction force (the drive force) as engaging the ground, so that the lugs7are subjected to a great stress. The rubber crawler1is constructed such that the joint9is disposed on the outer circumferential surface of the crawler body4as located on the surface of the ground non-engaging portion8which is subjected to a relatively smaller stress, rather than on the surface of the lug7or in the lug7which is subjected to a particularly great stress. Therefore, the rubber crawler is less susceptible to cracks originating from an outer circumferential surface of the joint9. If the cracks should occur, the growth of the cracks will be suppressed. Furthermore, the joint portion has a smaller elongation at bent than the surface or interior of the lug7and hence, the joint portion is less likely to encounter the crack occurrence or the crack growth.

Furthermore, the outer circumferential joint portion9ais disposed on widthwise opposite portions of the rubber crawler body4as located at the positions shifted from each other with respect to the longitudinal direction of the belt. Hence, the stress (such as tensile stress) acting on the outer circumferential joint portion9ais distributed along the longitudinal direction of the belt. Accordingly, the stress concentration is alleviated so that the cracks originating from the outer circumferential joint portion9aare obviated or that the crack growth is suppressed.

Since the lugs7are staggered with the left-hand and right-hand lugs mutually shifted in phase, time when the stress transmitted from the ground-engaging face is peaked differs between the left-hand lug and the right-hand lug. This prevents a great stress from acting on the left-hand and right-hand lugs simultaneously. Therefore, the outer circumferential joint portion9as a whole is prevented from receiving the great stress at a time. The outer circumferential joint portion9ais located in the ground non-engaging portion8in a manner to circumvent the staggered lugs7. Hence, the positions of the left-hand and right-hand segments of the outer circumferential joint portion9aare shifted from each other along the longitudinal direction of the belt. This prevents the great stress from acting on the left-hand and right-hand segments of the outer circumferential joint portion9asimultaneously. That is, the effect provided by the staggered the lugs7work synergistically with the effect provided by the outer circumferential joint portion9ahaving the left-hand and right-hand segments thereof shifted from each other along the longitudinal direction of the belt, whereby the stress is distributed and the outer circumferential joint portion9ais effectively prevented from suffering the occurrence or growth of the cracks.

The inner circumferential joint portion9bis extended substantially in the straight line substantially along the widthwise direction of the crawler, whereas the outer circumferential joint portion9alocated in the ground non-engaging portion8between the staggered lugs7is extended in a non-straight line as seen in plan ofFIG. 1. In the rubber crawler1, therefore, the outer circumferential joint portion9aand the inner circumferential joint portion9bon the right-hand side of the width of the rubber crawler1are located close to each other with respect to the longitudinal direction of the belt, as shown inFIG. 6. However, the outer circumferential joint portion9aand the inner circumferential joint portion9bon the left-hand side of the width of the rubber crawler1are spaced away from each other with respect to the longitudinal direction of the belt, as shown inFIG. 7. Thus, the longitudinal positions of the outer circumferential joint portion9aand the inner circumferential joint portion9bwith respect to the belt are shifted from each other at least on one of the right-hand side and the left-hand side of the width of the crawler. The all length of the outer circumferential joint portion9ais not in proximity of the inner circumferential joint portion9bwith respect to the whole width of the crawler. Accordingly, the cracks produced in the outside surface of the outer circumferential joint portion9aare less likely to grow to reach the inner circumferential joint portion9b.This results in the augmented durability of the joint9. Furthermore, the location of the joint9is distributed along the longitudinal direction of the belt, so that the stress on the joint9is effectively distributed. Accordingly, the cracks are less likely to occur while the growth of the cracks is suppressed.

In the rubber crawler1, the lugs7are arranged along the longitudinal direction of the belt at the substantially equal pitch P. In this case, the crawler may be formed uniformly with respect to the longitudinal direction of the belt by virtue of the lugs7arranged along the longitudinal direction of the belt substantially with equal spacing. This results in a preferred crawler endlessly rotating in the longitudinal (circumferential) direction of the belt.

The outer circumferential joint portion9ais designed such that the distance d between the longitudinal positions thereof at the widthwise opposite ends h1, h2of the rubber crawler1is 1.5 or less times the pitch P (seeFIG. 1). In this case, the length of the outer circumferential joint9awith respect to the longitudinal direction of the belt is never greater than necessary. A specific description is made on this regard. As shown inFIG. 1, the lugs7are staggered in the rubber crawler1, so that the left-hand and right-hand lugs7have different phases with respect to the longitudinal direction of the belt. Accordingly, the left-hand and right-hand ground non-engaging portions8also have different phases with respect to the longitudinal direction of the belt. The outer circumferential joint portion9ais disposed at the left-hand and right-hand ground non-engaging portions8having the different phases. If the left-hand ground non-engaging portion8provided with the outer circumferential joint portion9ais spaced too far away from the right-hand ground non-engaging portion8provided with the outer circumferential joint portion9a,the outer circumferential joint portion9aof the rubber crawler1has an excessively great longitudinal length r (seeFIG. 1). For this reason, the aforesaid distance d is defined to be 1.5 or less times the pitch P. This prevents the outer circumferential joint portion9aof the rubber crawler1from having the excessively great longitudinal length r (seeFIG. 1) and hence, the outer circumferential joint portion9amay achieve an increased joining strength. By the same reason as the above, the aforesaid distance d may more preferably be 0.8 or less times the pitch P.

On the other hand, the aforesaid distance d is also defined to be 0.2 or more times the pitch P, so that the left-hand and right-hand segments of the outer circumferential joint portion9ahaving the different longitudinal positions with respect to the belt may fully exhibit the aforementioned effect.

The lugs7are staggered in the rubber crawler1, so that the left-hand and right-hand lugs7have the mutually shifted phases with respect to the longitudinal direction of the belt and thence, the left-hand and right-hand ground non-engaging portions8also have the mutually shifted phases with respect to the longitudinal direction of the belt. Such a lug pattern may define the aforesaid distance d to be 0.2 or more times the pitch P and 1.5 or less times the pitch P, thereby providing the ease of locating the outer circumferential joint portion9aonly at the non-lug portions as circumventing the lugs.

On the other hand, the core bars5, as the widthwise reinforcing member for the widthwise reinforcement of the crawler body4, are embedded along the longitudinal direction of the belt at the space intervals S. Hence, the crawler body4is increased not only in the endurance against the stress acting in the widthwise direction thereof, but also in the torsional rigidity thereof.

In the rubber crawler1, as shown inFIG. 3, the inner circumferential joint portion9bis located substantially centrally of the space S. In this manner, the inner circumferential joint portion9bis located substantially centrally of the space S where the elastic member has a relatively great thickness, rather than at a portion where the elastic member is decreased in thickness due to the core bar5embedded therein. Therefore, the inner circumferential joint portion may achieve the increased joining strength. Furthermore, the inner circumferential joint portion9bmay be spaced far away from the thin portion of the elastic member, so that the inner circumferential joint portion9bis disposed at the portion of the elastic member that is relatively free to deform elastically. This results in a reduced stress on the inner circumferential joint portion9b.In addition, a greater joining area is attained because the inner circumferential joint portion9bis not located at the thin portion of the elastic member.

The inner circumferential joint potion9blocated substantially centrally of the space S is extended substantially along the widthwise direction, so that the whole length of the inner circumferential joint portion9bbetween the right end thereof and the left end thereof is substantially at the same position with respect to the longitudinal direction of the belt. Accordingly, the inner circumferential joint portion9bis configured differently from the outer circumferential joint portion9ahaving the right and left ends located at different longitudinal positions with respect to the belt. At least on one of the right side and the left side of the crawler body4with respect to the widthwise direction, therefore, the longitudinal positions of the inner and outer circumferential joint portions with respect to the belt are not close to each other or spaced away from each other. As described above, the joint9is less susceptible to the cracks. If the cracks should occur, the growth of the cracks will be suppressed.

While the rubber crawler1is constructed such that the outer circumferential joint portion9ais divided into the left-hand and right-hand segments via the portion near the widthwise center of the crawler body4, the left-hand and right-hand segments individually extended substantially in parallel with the widthwise direction of the crawler body4, the invention is not limited to this construction. Needless to say, the segments of the joint portion may be inclined relative to the widthwise direction of the crawler body4, or may take any suitable configuration such as a curved line or a polygonal line.

FIG. 8is a plan view showing an outer circumferential surface (ground engaging surface) of a rubber crawler20according to a second embodiment of the invention. In the rubber crawler20, the left-hand and right-hand lugs7are arranged in substantially an inverted V-fashion or inclined relative to the widthwise direction of the crawler body4. On the outer circumferential surface of the rubber crawler20, the outer circumferential joint portion9alocated in the ground non-engaging portion8is also inclined at their lateral segments but for the portion near the widthwise center of the crawler body4, the inclination of the segments being substantially in conformity with the layout of the lugs7. On the other hand, the inner circumferential joint portion9blocated on the inner circumferential surface, which is the back side as seen inFIG. 8, is formed substantially in the straight line along the widthwise direction of the rubber crawler20. In addition, the inner circumferential joint portion is located substantially centrally of the space S between the core bars5embedded in the crawler body along the longitudinal direction of the belt at the space intervals S. Just as in the aforementioned rubber crawler1, therefore, at least a part of the outer circumferential joint portion9ais spaced away from the inner circumferential joint portion9bwith respect to the longitudinal direction of the belt. As described above, therefore, the joint9is less susceptible to cracks. If the cracks should occur, the growth of the cracks will be suppressed.

FIG. 9is a plan view showing an outer circumferential surface of a rubber crawler30according to a third embodiment of the invention. The rubber crawler30has the same lug pattern as the rubber crawler20, except for the layout of the outer circumferential joint portion9a.That is, a difference between the rubber crawler20and the rubber crawler30consists in that the left-hand and right-hand segments of the outer circumferential joint portion9a,as divided via the portion near the widthwise center of the crawler body4, are at the longitudinal positions with respect to the longitudinal direction of the belt, which are defined in the opposite ways. It goes without saying that the rubber crawler30having such a construction provides the same working effects as the rubber crawler20. In both of the rubber crawler20and the rubber crawler30, the positions at the widthwise opposite ends h1, h2of the outer circumferential joint portion9aare shifted from each other along the longitudinal direction of the belt by the distance d which is 0.2 or more times the pitch P and 0.8 or less times the pitch P. As described above, therefore, the outer circumferential joint portion9amay achieve the increased joining strength.

According to the embodiment shown inFIG. 9, the outer circumferential joint portion9a,as the joint9on the outer circumferential surface, includes the segments inclined relative to the widthwise direction of the crawler body as seen in plan viewed from the outer circumferential surface of the crawler. The angle of inclination a is defined to be 10° or more and 60° or less relative to the widthwise direction of the crawler body4(such as represented by a broken line indicating the inner circumferential joint portion9binFIG. 9). The segments may be inclined at an angle of 10° or more, thereby adequately contributing to the aforementioned distribution of stress along the longitudinal direction of the belt. Furthermore, the segments inclined at an angle of 60° or less provides the ease of locating the joint in the ground non-engaging portion excluding the lugs. It is noted that the configuration of the segment inclined relative to the widthwise direction of the crawler body is not limited to the straight line and may also include a curved line. In this case, the aforesaid angle of inclination a may be determined from a tangent to the curved line.

FIG. 10is a plan view showing an outer circumferential surface of a rubber crawler40according to a fourth embodiment of the invention.FIG. 11is a plan view showing an inner circumferential surface of the rubber crawler40. Unlike the aforementioned rubber crawler1or the like, the rubber crawler40is of a so-called projection drive system, which does not include the sprocket engagement holes6but instead, includes driving rubber projections41on the inner circumferential surface. Furthermore, the rubber crawler40does not include the core bars5. As shown inFIG. 10, the lug7is not separated into the left-hand and right-hand segments with respect to the widthwise direction of the crawler body4. The lug7forms a substantially chevron-shaped pattern having a crest at place near the widthwise center of the crawler body4as seen in plan. The outer circumferential joint portion9ais formed in conformity with the configuration of the lug7, or substantially in a chevron shape as seen in plan. On the other hand, as shown inFIG. 11, the inner circumferential joint portion9bincludes: lateral segments which are shifted from each other in the longitudinal direction of the belt and are individually extended in straight lines along the widthwise direction of the crawler; and a central segment located centrally of the width of the crawler and extended along the longitudinal direction of the belt as interconnecting the lateral segments.

Such a rubber crawler40is adapted to reduce the stress on the joint9as described above, because the outer circumferential joint portion9ais disposed on the outer circumferential surface of the rubber crawler40as located in the ground non-engaging portion8. Furthermore, the outer circumferential joint portion9aand the inner circumferential joint portion9bhave different configurations as seen in plan, so that the outer circumferential joint portion9aand the inner circumferential joint portion9bare spaced away from each other along the longitudinal direction of the belt at least somewhere along the widthwise direction of the crawler body4. Accordingly, the occurrence of the cracks or the growth of the cracks is obviated as mentioned supra.

FIG. 12is a plan view showing an outer circumferential surface of a rubber crawler50according to a fifth embodiment of the invention. In the rubber crawler50, each of the lugs7includes a pair of transverse lugs7aextended substantially along the widthwise direction of the crawler and in parallel relation; and an intermediate lug7bextended substantially along the longitudinal direction of the crawler belt so as to interconnect the transverse lug pair7a.A surface of the intermediate lug7bis one step lower than that of the transverse lugs7aand hence, the transverse lugs7aprincipally engage the ground. The outer circumferential joint portion9ais disposed on an outer circumferential surface of the rubber crawler50and is located in the ground non-engaging portion8as circumventing the transverse lugs7aand the intermediate lug7b.It goes without saying that the invention is also applicable to the rubber crawler having such a lug pattern.