Patent Description:
In recent years, elastic crawlers have been widely used in travelling sections of agricultural machines, construction machines, civil engineering machines, etc. The elastic crawlers are generally formed in an endless belt-like shape using, e.g., rubber material. Such elastic crawlers are normally used in such a manner as to be wound around a drive wheel and track rollers of a travelling device, and each include a plurality of core bars, which are rigid members, embedded inside.

For example, the elastic crawler described in Patent Document <NUM> includes an endless belt-like elastic body and a plurality of core bars embedded inside the elastic body, and the core bars extend in a width direction of the elastic body and are embedded with predetermined spacing in a circumferential direction of the elastic body. Each core bar includes a long core bar base, a pair of projection portions that are located at a center portion in a longitudinal direction of the core bar base and project to the inner circumferential side of the elastic body, and a pair of rail portions that are located on opposite outer sides of a pair of projection portions and project to the inner circumferential side of the elastic body. The pair of rail portions each include a track roller support surface that supports a track roller, at a top portion, and the track roller support surface is larger in dimension in a core bar width direction than the core bar base.

In the elastic crawler described in Patent Document <NUM>, because of the rail portions being provided, a distance between core bars adjacent to each other in an elastic crawler circumferential direction (length of an area in which no core bar is provided) is shorter in a track roller passage area in which a track roller passes than in other areas. Consequently, when a track roller rolls from one core bar to another core bar adjacent to the core bar, an amount of depression of the track roller to the ground side can be reduced, enabling suppressing shaking of the track roller.

Further reference may be made to elastic crawlers as described in Patent Documents <NUM> to <NUM>.

If an elastic crawler is twisted as a result of driving over an obstacle such as a stone or travelling on an irregular surface, core bars embedded inside the elastic crawler are also twisted.

In a core bar including projection portions and rail portions, a twisting force acting on the core bar concentrates on connection portions located between the projection portions and the rail portions, the connection portions being smaller in width and strength than the projection portions and the rail portions, and thus, there is a need for a structure that is more durable against breakage of the core bar starting from the connection portions.

The present invention has been made in view of the aforementioned problem and an object of the present invention is to provide a core bar for an elastic crawler, the core bar having high durability against a twisting force acting during use, and an elastic crawler using the core bar.

In order to achieve the above object, a core bar for an elastic crawler according to claim <NUM> is a core bar for an elastic crawler, the core bar including: a core bar base that extends in a width direction of an endless belt-like elastic body and is embedded in the elastic body; a pair of projection portions that project to an inner circumferential surface side of the elastic body at a center portion in a longitudinal direction of the core bar base; and a pair of rail portions that project from the core bar base to the inner circumferential surface side of the elastic body on opposite outer sides of the pair of projection portions and each include a track roller support surface supporting a track roller rolling on the inner circumferential surface of the elastic body, wherein the core bar comprises a pair of rail extension portions that project from the core bar base to the inner circumferential surface side of the elastic body and each include a top surface formed in such a manner as to continue from the track roller support surface, the top surface extending from the rail portion toward the center side in the longitudinal direction of the core bar base, characterized in that: the projection portions comprise a head portion and a base portion having a dimension in a width direction of the core bar smaller than that of the head portion; in each rail extension portion, the top surface of rail extension portion is formed on both sides in the width direction of the core bar with the base portion therebetween; the top surfaces formed on both sides in the width direction of the core bar respectively extend from the rail portion to a distal end of the projection portion; and in each rail extension portion, the dimension, in a width direction of the core bar, of the rail extension portion including the base portion and the top surfaces on both sides thereof is decreases from the rail portion toward the distal end of the projection portion.

With this configuration, a strength of parts between the rail portions and the projection portions can be enhanced by the rail extension portions each including a top surface formed in such a manner as to continue from the track roller support surface, the top surface extending from the rail portion to the center side in the longitudinal direction of the core bar base. Consequently, it is possible to enhance durability of the core bar against a twisting force, enabling preventing breakage of the core bar due to twisting.

With this configuration, in which the top surface of each rail extension portion extends from the rail portion to an end portion on the center side in the longitudinal direction of the projection portion, it is possible to mitigate stress concentration occurring between the rail portions and the projection portions when a twisting force acts on the core bar, enabling more reliably preventing breakage of the core bar.

With this configuration, in which a dimension, in a width direction of the core bar base, of each rail extension portion decreases from the rail portion toward the projection portion side, the dimension in the width direction of the rail extension portions is large at boundary portions that are boundaries with the rail portions, the boundary portions being easily broken by being twisted, enabling maintenance of high durability against twisting, and furthermore, making the dimension in the width direction decrease toward the respective projection portion sides enables suppressing an increase in weight of the core bar and thus enabling weight reduction.

Also, the invention according to claim <NUM> provides the core bar for an elastic crawler according to claim <NUM>, comprising an upright portion that is located between the track roller support surface of each rail portion and the top surface of the rail extension portion, and the core bar base, and continues from the core bar base, wherein a dimension, in the width direction of the core bar base, of the upright portion is smaller than a width dimension of the core bar base.

With this configuration, it is possible to make the upright portions be recessed relative to the core bar base in the width direction of the core bar base, enabling an elastic material forming the elastic body enter the recessed parts and thus enabling enhancement in adhesion between the core bar and the elastic body.

Also, the elastic crawler according to claim <NUM> comprises: an endless belt-like elastic body; and a plurality of the core bars for an elastic crawler according to claim <NUM> or <NUM>, the core bars being embedded with spacing in a circumferential direction of the elastic body in such a manner as to extend in the width direction of the elastic body.

With this configuration, the strength of the parts between the rail portions and the projection portions of the core bar can be enhanced by the rail extension portions formed in each of the core bars for an elastic crawler, enabling enhancement in durability of the core bar against a twisting force, and thus, it is possible to, if a twisting force acts on the core bar as a result of the elastic crawler driving over an obstacle or travelling on an irregular surface, suppress breakage of the core bar due to the twisting force.

A core bar for an elastic crawler and an elastic crawler according to the present invention enable enhancement in durability of a core bar against a twisting force acting during use.

A core bar for an elastic crawler (hereinafter simply referred to as "core bar") and an elastic crawler using the core bar according to the present invention will be described below. <FIG> is a side view schematically illustrating a travelling device <NUM> using an elastic crawler <NUM> that is an embodiment of the present invention. <FIG> is a plan view illustrating an inner circumferential portion of the elastic crawler. <FIG> is a sectional view along line A-A in <FIG>. In <FIG> and <FIG>, a crawler body <NUM>, which is an elastic body, is illustrated by alternate long and two short dashes lines and a core bar <NUM> is illustrated by solid lines. The elastic crawler <NUM> is installed on a travelling device <NUM>, for example, an agricultural machine, a construction machine or a civil engineering machine.

In the travelling device <NUM>, the elastic crawler <NUM> is used in such a manner as to be wound around a sprocket <NUM>, which is a drive wheel, an idler <NUM>, which is a driven wheel, and a plurality of track rollers <NUM>. Each track roller <NUM> rolls on a track roller passage surface formed in an inner circumferential surface <NUM> of the elastic crawler <NUM>.

The elastic crawler <NUM> includes a crawler body (elastic body) <NUM> formed in an endless belt-like shape by an elastic material, and a plurality of core bars <NUM> embedded with predetermined spacing in a circumferential direction of the crawler body <NUM>.

The crawler body <NUM> includes a plurality of lugs <NUM> projecting from an outer circumferential surface <NUM>. The lugs <NUM> are formed with predetermined spacing in a circumferential direction of the outer circumferential surface <NUM>. Note that a shape, a width (length in a circumferential direction of the elastic crawler <NUM>), a pattern, etc., of the lugs <NUM> can appropriately be set according to usage of the elastic crawler <NUM>.

As illustrated in <FIG>, each core bar <NUM> includes a long core bar base <NUM> embedded in the crawler body <NUM>, a pair of projection portions <NUM>, 32R located at a center portion in a longitudinal direction of the core bar base <NUM>, a pair of rail portion <NUM>, 34R located on opposite outer sides of the pair of projection portions <NUM>, 32R, and a pair of rail extension portions <NUM>, 36R formed between the rail portions <NUM>, 34R and the projection portions <NUM>, 32R.

The core bar base <NUM> is formed in a substantially rectangular shape in plan view. The pair of projection portions <NUM>, 32R, the pair of rail portions <NUM>, 34R and the pair of rail extension portions <NUM>, 36R each projects from an upper surface 31a (surface facing the inner circumferential surface <NUM> side of the crawler body <NUM> in a state in which the core bar base <NUM> is embedded in the crawler body <NUM>) of the core bar base <NUM>. An engagement portion <NUM> that engages with the sprocket <NUM> is formed between the pair of projection portions <NUM>, 32R.

In the below description, a longitudinal direction of the core bar <NUM> (arrow X direction in <FIG>) is simply referred to as "longitudinal direction" and a width direction of the core bar <NUM> (arrow Y direction in <FIG>) is referred to as "core bar width direction" and a thickness direction of the core bar <NUM> (arrow Z direction in <FIG>) is referred to as "core bar thickness direction". The X direction, the Y direction and the Z direction are orthogonal to one another. The core bar <NUM> further includes a pair of first restricting projections <NUM>, 40R at one side surface 30b in the core bar width direction and a pair of second restricting projections <NUM>, 42R at another side surface 30c. The core bar <NUM> is generally one formed of metal via means such as casting or forging, but may be one formed of hard resin or a sheet metal.

In the present embodiment, as illustrated in <FIG>, the pair of projection portions <NUM>, 32R, the pair of rail portions <NUM>, 34R and the pair of rail extension portions <NUM>, 36R are formed in such a manner as to be symmetrical to each other with respect to a center point P of the core bar <NUM> in plan view, respectively; however, the present invention is not limited to this example and the pair of projection portions <NUM>, 32R, the pair of rail portions <NUM>, 34R and the pair of rail extension portions <NUM>, 36R may be each formed in such a manner as to be symmetrical to each other with respect to a center line CL of the core bar <NUM>. The pair of first restricting projections <NUM>, 40R and the pair of second restricting projections <NUM>, 42R are each formed in such a manner as to be symmetrical with respect to the center line CL. In the below description, of the paired projection portions <NUM>, 32R, the paired rail portions <NUM>, 34R and the paired rail extension portions <NUM>, 36R, one projection portion 32R, one rail portion 34R and one rail extension portion 36R will be described in detail, and parts of the other projection portion <NUM>, the other rail portion <NUM> and the other rail extension portion <NUM>, the parts corresponding to those of the projection portion 32R, the rail portion 34R and the rail extension portion 36R, are provided with reference numerals that are the same as those of the projection portion 32R, the rail portion 34R and the rail extension portion 36R, and detailed description thereof will be omitted.

The projection portion 32R includes a base portion 33A that continues from the core bar base <NUM> and a head portion 33B that projects from the base portion 33A in the core bar width direction. As illustrated in <FIG> and <FIG>, a dimension W2 in the core bar width direction of the base portion 33A is smaller than a width dimension W1 of the core bar base <NUM> and a dimension in the core bar width direction of the head portion 33B is substantially equal to a width dimension W1 of the core bar base.

The rail portion 34R is formed in an area in which the track rollers <NUM> pass when the elastic crawler <NUM> travels. As illustrated in <FIG>, the rail portion 34R includes an upright portion 39A that continues from the core bar base <NUM> and a top portion 39B that projects from the upright portion 39A in the core bar width direction and includes a track roller support surface <NUM> that supports a track roller <NUM>, at the top portion 39B. The track roller support surface <NUM> is formed in a substantially planar shape at a position that is lower than the head portion 33B of the projection portion 32R (that is, a position at which the base portion 33A is present in the core bar thickness direction), and as illustrated in <FIG>, has a dimension W3 in the core bar width direction that is set to be larger than the width dimension W1 of the core bar base <NUM>. The track roller support surface <NUM> of the present embodiment is formed in a rectangular shape that is long in the core bar width direction in plan view. The rail portion 34R further includes a rib 39C that projects from the upper surface 31a of the core bar base <NUM> and supports the top portion 39B. The rib 39C extends from one side surface in the core bar width direction of the upright portion 39A (more specifically, a side surface on the side on which a part of the track roller support surface <NUM> projects relative to the core bar base <NUM>) in the core bar width direction in the plan view illustrated in <FIG>.

As illustrated in <FIG>, each track roller <NUM> includes a shaft portion 56A rotatably supported on the travelling device <NUM> and wheel portions 56B fixed to opposite end portions in an axis direction of the shaft portion 56A, and the wheel portions 56B roll on the track roller support surfaces <NUM>.

The rail extension portion 36R is formed between the rail portion 34R and the projection portion 32R. As illustrated in <FIG>, the rail extension portion 36R includes an upright portion 38A that continues from the core bar base <NUM> and a top portion 38B that projects from the upright portion 38A in the core bar width direction. A top surface <NUM> of the rail extension portion 36R, which is formed at the top portion 38B, continues from the track roller support surface <NUM>, and in the present embodiment, is substantially flush with the track roller support surface <NUM>.

The top surface <NUM> of the rail extension portion 36R extends from the rail portion 34R toward the center side in the longitudinal direction of the core bar base <NUM>. The top surface <NUM> extends from the rail portion 34R preferably to the center line CL side (that is, the center side in the longitudinal direction of the core bar base <NUM>) relative to a proximal end 32a of the projection portion 32R, more preferably to an end portion on the center line CL side of the projection portion 32R. In the present embodiment, the top surface <NUM> extends from the rail portion 34R to a distal end 32b of the projection portion 32R. In the present embodiment, as illustrated in <FIG> and <FIG>, a dimension in the core bar width direction of the top surface <NUM> decreases from the rail portion 34R toward the projection portion 32R side, a maximum dimension W4 of the top surface <NUM> is set to be substantially equal to the width dimension W1 of the core bar base <NUM> and a minimum dimension W5 of the top surface <NUM> is set to be substantially equal to or larger than the dimension in the core bar width direction of the base portion 33A of the projection portion 32R.

As illustrated in <FIG> and <FIG>, the upright portion 39A of the rail portion 34R and the upright portion 38A of the rail extension portion 36R are located at a center portion in the core bar width direction of the core bar base <NUM> and are linearly continuous with each other in the longitudinal direction of the core bar <NUM>. A dimension W6 in the core bar width direction of the upright portions 38A, 39A is smaller than the width dimension W1 of the core bar base <NUM>.

The first restricting projections <NUM>, 40R are paired with the engagement portion <NUM> therebetween and the second restricting projections <NUM>, 42R are paired with the engagement portion <NUM> therebetween. The first restricting projections <NUM>, 40R and the second restricting projections <NUM>, 42R are tapered and a distance between tip portions of the second restricting projections <NUM>, 42R is larger than that of the first restricting projections <NUM>, 40R.

In a state in which the core bar <NUM> is embedded in the crawler body <NUM>, the core bar <NUM> is disposed in such a manner that: the core bar base <NUM> extends in a width direction of the crawler body <NUM>; and the engagement portion <NUM>, the projection portions <NUM>, 32R, the rail portions <NUM>, 34R and the rail extension portions <NUM>, 36R are covered by the elastic material forming the crawler body <NUM> and face the inner circumferential surface <NUM> side of the crawler body <NUM>. As illustrated in <FIG>, the pair of projection portions <NUM>, 32R form elastic projections <NUM> that project from the inner circumferential surface <NUM> of the elastic crawler <NUM>. The circumferential direction and a width direction of the elastic crawler <NUM> (that is, the circumferential direction and the width direction of the crawler body <NUM>) are orthogonal to each other. In a state in which the core bar <NUM> is embedded, the core bar thickness direction coincides with a thickness direction of the elastic crawler <NUM> and the longitudinal direction of the core bar <NUM> coincides with the width direction of the elastic crawler <NUM>.

As already described, the plurality of core bars <NUM> are disposed in such a manner as to be spaced in the circumferential direction of the crawler body <NUM>, and as illustrated in <FIG>, core bars <NUM> adjacent to each other in the circumferential direction are disposed in such a manner that on the outer sides in the crawler width direction of the first restricting projections <NUM>, 40R of one core bar <NUM>, the second restricting projections <NUM>, 42R of the other core bar <NUM> are disposed. Such disposition enables restriction of movement in the crawler width direction of the core bars <NUM>.

Each core bar <NUM> can be disposed in such a manner that the core bar base <NUM> entirely or partly overlaps with lugs <NUM> in the thickness direction. Also, instead of this disposition, each core bar <NUM> may be disposed in such a manner that the core bar base <NUM> does not overlap with lugs <NUM> in the thickness direction.

As illustrated in <FIG>, in the crawler body <NUM>, on the crawler body <NUM> outer circumferential surface <NUM> side of the core bar <NUM>, an endless belt-like reinforcement layer <NUM> extending in the crawler circumferential direction is embedded on opposite sides in the crawler width direction across the engagement portion <NUM> located between the pair of projection portions <NUM>, 32R. The reinforcement layer <NUM> is formed by covering with rubber a single reinforcement cord helically wound along the crawler circumferential direction or a plurality of reinforcement cords arranged in parallel along the crawler circumferential direction. For the reinforcement cord(s), for example, a steel cord having good tensile strength or a cord formed of, e.g., organic fiber can be used.

In the elastic crawler <NUM> using the above-described core bars <NUM>, a strength of parts between the rail portions <NUM>, 34R and the projection portions <NUM>, 32R of each core bar <NUM> can be enhanced by the rail extension portions <NUM>, 36R, enabling enhancement in durability against a twisting force acting on the core bar <NUM> as a result of the elastic crawler <NUM> driving over an obstacle such as a stone. Consequently, it is possible to prevent breakage of the core bar <NUM> due to twisting. Also, the top surfaces <NUM> of the rail extension portions <NUM>, 36R are flush with the respective track roller support surfaces <NUM>, enabling mitigation of stress concentration occurring in respective boundary portions that are boundaries with the rail portions <NUM>, 34R, the boundary portions being easily broken by being twisted.

Also, a dimension in the core bar width direction of the rail extension portions <NUM>, 36R decreases from the rail portions <NUM>, 34R toward the respective projection portion <NUM>, 32R sides, enabling suppressing an increase in weight of the core bar <NUM> and thus enabling weight reduction while ensuring necessary strength against twisting. In particular, the width dimension of the rail extension portion <NUM>, 36R is large at the boundary portions that are boundaries with the rail portions <NUM>, 34R, from which breakage due to twisting easily starts, enabling maintenance of high durability against twisting.

Also, the upright portions 38A, 39A, which have a smaller dimension in the core bar width direction than the top portions 38B of the rail extension portions <NUM>, 36R and the top portions 39B of the rail portion <NUM>, 34R, are formed between the top portions 38B and the top portions 39B, and the core bar base <NUM> to make the upright portions 38A, 39A be recessed relative to the core bar base <NUM>, enabling the elastic material forming the crawler body <NUM> to enter the recessed parts. Consequently, the area of contact between the core bar <NUM> and the crawler body <NUM> can be increased, enabling enhancement in adhesion between the core bar <NUM> and the crawler body <NUM>. Also, it is possible to suppress an increase in weight of the core bar <NUM> and thus reduce the weight.

Claim 1:
A core bar (<NUM>) for an elastic crawler (<NUM>), the core bar including:
a core bar base (<NUM>) that extends in a width direction of an endless belt-like elastic body (<NUM>) and is embedded in the elastic body (<NUM>);
a pair of projection portions (<NUM>,32R) that project to an inner circumferential surface side of the elastic body (<NUM>) at a center portion in a longitudinal direction of the core bar base (<NUM>); and
a pair of rail portions (<NUM>,36R) that project from the core bar base (<NUM>) to the inner circumferential surface side of the elastic body (<NUM>) on opposite outer sides of the pair of projection portions (<NUM>,32R) and each include a track roller support surface (<NUM>) supporting a track roller (<NUM>) rolling on the inner circumferential surface of the elastic body (<NUM>),
wherein the core bar (<NUM>) comprises a pair of rail extension portions (<NUM>,36R) that project from the core bar base (<NUM>) to the inner circumferential surface side of the elastic body (<NUM>) and each include a top surface (<NUM>) formed in such a manner as to continue from the track roller support surface (<NUM>), the top surface (<NUM>) extending from the rail portion (<NUM>,36R) toward the center side in the longitudinal direction of the core bar base (<NUM>),
characterized in that
the projection portions (<NUM>,32R) comprise a head portion (33B) and a base portion (33A) having a dimension in a width direction of the core bar (<NUM>) smaller than that of the head portion (33B);
in each rail extension portion (<NUM>,36R), the top surface (<NUM>) of rail extension portion (<NUM>,36R) is formed on both sides in the width direction of the core bar (<NUM>) with the base portion (33A) therebetween;
the top surfaces (<NUM>) formed on both sides in the width direction of the core bar (<NUM>) respectively extend from the rail portion (<NUM>,34R) to a distal end (32b) of the projection portion (<NUM>,32R); and
in each rail extension portion (<NUM>,36R), the dimension, in a width direction of the core bar (<NUM>), of the rail extension portion (<NUM>,36R) including the base portion (33A) and the top surfaces (<NUM>) on both sides thereof is decreases from the rail portion (<NUM>,34R) toward the distal end (32b) of the projection portion (<NUM>, 32R) .