Patent Description:
An ordinary loader crane is provided with a crane boom system which normally comprises a first crane boom in the form of a so-called inner boom, which is articulately connected to a rotatable column of the crane, and a second crane boom in the form of a so-called outer boom, which is telescopically extensible and articulately connected to the inner boom. The outer boom comprises a hollow base section, through which the outer boom is articulately connected to the inner boom, and telescopic crane boom sections, which are hollow and carried by the base section. The telescopic crane boom sections are telescopically mounted to each other and displaceable in the longitudinal direction of the base section by means of hydraulic cylinders for adjustment of the extension length of the outer boom. In order to extend the reach of the crane, i.e. the possible range for the lifting operations, an additional crane boom, in the following referred to as a jib, may be detachably mounted to the outer end of the outer boom. Also the jib may be telescopically extensible and may comprise one or more telescopic crane boom sections of the above-mentioned type.

It is previously known to produce a telescopic crane boom section of the above-mentioned type from one single metal sheet, wherein the metal sheet is shaped by bending and opposite longitudinal edges of the metal sheet are joined to each other by a longitudinal welding joint in order to form a tubular beam. <CIT> discloses a telescopic crane boom section produced in this manner, wherein <CIT> teaches that a suitable location of the longitudinal welding joint is at the top or at the bottom of the crane boom section along the plane of symmetry.

Other examples of telescopic crane boom sections produced in the above-mentioned manner are known from <CIT> and discloses the preamble of claim <NUM>.

Also <CIT> teaches that a suitable location of the longitudinal welding joint is at the top or at the bottom of the crane boom section along the plane of symmetry.

<CIT> discloses different examples of telescopic crane boom sections comprising an upper part and a lower part joined to each other by means of two longitudinal welding joints located at the neutral layer on opposite sides of the vertical plane of symmetry.

The object of the present invention is to provide a telescopic crane boom section of a new and favourable design.

According to the invention, this object is achieved by means of a telescopic crane boom section having the features defined in claim <NUM>.

The telescopic crane boom section of the present invention has an elongated main body in the form of a straight tubular beam that is formed by one single bent metal sheet and consists of several wall portions which are distributed about a longitudinal centre axis of the tubular beam and connected to each other via bending corners formed in the metal sheet, wherein:.

The above-mentioned configuration of the telescopic crane boom section will not only result in a telescopic crane boom section of high strength, it also improves the reliability of the welding joint. The conventional location of the welding joint is at the lower or upper end of the crane boom section for manufacturing reasons. Such a location of the welding joint implies that the welding joint will be positioned on the plane of symmetry, where the welding joint is affected by high stresses. At the upper end of the crane boom section the tensile stresses are high and at the lower end the compressive stresses are high. With such a conventional location of the welding joint, the requirements on the quality of the welding joint are therefore very high in order to achieve a reliable welding joint that can endure the stresses. By having the welding joint located at a lateral wall portion that is intersected by the neutral layer, it will be possible to locate the welding joint rather close to the neutral layer, which implies reduced stresses on the welding joint as compared to the conventional location of the welding joint at the lower or upper end of the crane boom section. For manufacturing reasons, it is favourable to have the welding joint of the crane boom section located at a corner between two wall portions, and by moving the welding joint from the lower or upper end of the crane boom section to an edge of a lateral wall portion, it will be possible to have planar upper and lower wall portions with an extension perpendicular to the vertical plane of symmetry. The inclusion of planar upper and lower wall portions with an extension perpendicular to the vertical plane of symmetry will make it possible to arrange planar and horizontally extending sliding elements at the top and bottom of the crane boom section, wherein vertical loads on the crane boom section may be taken up by these horizontal sliding elements is an efficient and reliable manner, which in its turn creates opportunities for a high stiffness of a telescopic crane boom that is provided with crane boom sections according to the invention. The horizontal sliding elements may co-operate with other planar sliding elements at inclined wall portions on either side of the upper and lower wall portions in order to distribute the local loads on the crane boom section in a suitable manner and thereby achieve a favourable stress distribution in the upper and lower parts of the crane boom section at the areas where the tubular beam makes contact with the sliding elements. Furthermore, the telescopic crane boom section of the present invention may be produced in an efficient and cost-effective manner.

According to the invention, each one of said first and second lateral wall portions has a length that is <NUM>-<NUM>% of the height of the tubular beam, as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam. By such a restriction of the length of the lateral wall portions that are intersected by the neutral layer, it is ensured that the welding joint located at the upper or lower edge of one of these wall portions will be positioned rather close to the neutral layer. The above-mentioned range of <NUM>-<NUM>% has been found to be advantageous as it provides a good trade-off between a desired closeness of the upper or lower edge of the lateral wall portions to the neutral layer and a desire to make the manufacturing process less demanding when it comes to the bending of the metal sheet.

The welding joint is preferably located at a height above the lower wall portion that is <NUM>-<NUM>% of the height of the tubular beam, as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam.

Further advantageous features of the telescopic crane boom section according to the present invention will appear from the description following below and the dependent claims.

The invention also relates to a telescopically extensible crane boom having the features defined in claim <NUM> and a hydraulic crane comprising such a crane boom.

Further advantageous features of the crane boom according to the present invention will appear from the description following below and the dependent claims.

With reference to the appended drawings, a specific description of embodiments of the invention cited as examples follows below. In the drawings:.

A hydraulic loader crane <NUM> according to an embodiment of the present invention is illustrated in <FIG>. The illustrated crane <NUM> comprises a crane base <NUM>, which for instance may be connected to the chassis of a lorry. Adjustable support legs <NUM> for supporting the crane <NUM> are fixed to the crane base <NUM>. The crane <NUM> further comprises:.

The expression "liftable and lowerable crane boom" here refers to a crane boom which can be pivoted in a vertical plane so as to thereby perform liftings and lowerings of a load carried by the crane. The expression "hydraulic cylinder for lifting and lowering the crane boom" here refers to the hydraulic cylinder which is associated with the liftable and lowerable crane boom and which carries out the pivoting thereof in a vertical plane.

The outer boom <NUM> is telescopically extensible to enable an adjustment of the extension length thereof. The outer boom <NUM> comprises a hollow base section <NUM>, through which the outer boom <NUM> is articulately connected to the inner boom <NUM>, and several hollow telescopic crane boom sections <NUM> which are carried by the base section <NUM> and displaceable in the longitudinal direction of the base section by means of hydraulic cylinders <NUM> for adjustment of the extension length of the outer boom <NUM>.

In the illustrated example, an additional telescopically extensible crane boom in the form of a jib <NUM> is detachably and articulately connected to the outer boom <NUM> in such a manner that it is pivotable in relation to it about an essentially horizontal axis of rotation. The hydraulic crane <NUM> further comprises a hydraulic cylinder <NUM> for lifting and lowering of the jib <NUM> in relation to the outer boom <NUM>.

The jib <NUM> is telescopically extensible to enable an adjustment of the extension length thereof. The jib <NUM> comprises a hollow base section <NUM>, through which the jib <NUM> is articulately connected to the outer boom <NUM>, and a hollow telescopic crane boom section <NUM> which is carried by the base section <NUM> and displaceable in the longitudinal direction of the base section by means of a hydraulic cylinder <NUM> for adjustment of the extension length of the jib <NUM>.

One of the telescopic crane boom sections <NUM> of the outer boom <NUM> shown in <FIG> is illustrated in closer detail in <FIG>.

The crane boom section <NUM> has an elongated main body in the form of a straight tubular beam <NUM> formed by one single metal sheet <NUM>, preferably of steel, which is shaped by bending. A collar <NUM> is mounted to the tubular beam <NUM> at a front end thereof, wherein the piston rod of the hydraulic cylinder <NUM> that is connected to the crane boom section <NUM> in order to effect an axial displacement thereof is fixed to the tubular beam <NUM> via the collar <NUM>. The tubular beam <NUM> consists of several wall portions W1-W12, which are distributed about a longitudinal centre axis of the tubular beam <NUM> and connected to each other via bending corners <NUM> (see <FIG>) formed in the metal sheet <NUM>. Opposite longitudinal edges 34a, 34b of the metal sheet <NUM> are joined to each other by a welding joint <NUM>, which extends in the longitudinal direction of the tubular beam <NUM>.

The tubular beam <NUM> has a vertical plane of symmetry <NUM> (see <FIG>) as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam. A neutral layer <NUM> of the tubular beam <NUM> extends across a first lateral wall portion W1 on a first side of the vertical plane of symmetry <NUM> and across an opposite second lateral wall portion W2 on the opposite side of the vertical plane of symmetry <NUM>.

Each one of said first and second lateral wall portions W1, W2 has a length L that is in the range of <NUM>-<NUM>% of the height H of the tubular beam <NUM>, as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam. The first and second lateral wall portions W1, W2 are preferably parallel to each other and parallel to the vertical plane of symmetry <NUM>, which implies that these wall portions W1, W2 are vertically arranged in the boom system.

In the illustrated example, the welding joint <NUM> is located at an upper edge <NUM> of the first lateral wall portion W1. As an alternative, the welding joint <NUM> could be located at a lower edge <NUM> of the first lateral wall portion W1 or at the upper or lower edge <NUM>, <NUM> of the second lateral wall portion W2.

The welding joint <NUM> is preferably located at a height h above the lower end of the tubular beam <NUM> that is in the range of <NUM>-<NUM>%, preferably <NUM>-<NUM>%, of the height H of the tubular beam, as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam.

The welding joint <NUM> may be produced by any suitable type of welding technique, such as for instance laser welding or arc welding.

The tubular beam <NUM> has a planar upper wall portion W3 at its top, wherein this upper wall portion W3 is perpendicular to the vertical plane of symmetry <NUM>. Thus, the upper wall portion W3 is horizontally arranged. The upper wall portion W3 is connected to each one of said first and second lateral wall portions W1, W2 via one or more intermediate wall portions W4-W7, each of which being planar and inclined in relation to the vertical plane of symmetry <NUM>. In the illustrated example, the upper wall portion W3 is connected to the first lateral wall portion W1 via two intermediate wall portions W4, W5 and to the second lateral wall portion W2 via two opposite intermediate wall portions W6, W7. Having two or more intermediate wall portions between the upper wall portion W3 and each lateral wall portion W1, W2 adds flexibility in the shaping of the crane boom section <NUM> to provide room for the hydraulic cylinders <NUM>. Furthermore, it may also improve the resistance to buckling, owing to the fact that an increase of the number of intermediate wall portions will make it possible to reduce the length of each individual intermediate wall portion, as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam.

The tubular beam <NUM> also has a planar lower wall portion W8 at its bottom, wherein this lower wall portion W8 is perpendicular to the vertical plane of symmetry <NUM>. Thus, the lower wall portion W8 is horizontally arranged. The lower wall portion W8 is connected to each one of said first and second lateral wall portions W1, W2 via one or more intermediate wall portions W9-W12, each of which being planar and inclined in relation to the vertical plane of symmetry <NUM>. In the illustrated example, the lower wall portion W8 is connected to the first lateral wall portion W1 via two intermediate wall portions W9, W10 and to the second lateral wall portion W2 via two opposite intermediate wall portions W11, W12.

The tubular beam <NUM> has a polygonal cross-sectional shape and it is preferably designed as a drop-shaped polygon, as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam, wherein a lower end of the drop-shaped polygon is wider than an upper end thereof. In the illustrated examples, the essentially drop-shaped cross-sectional shape of the tubular beam <NUM> is mainly achieved in that the inclined wall portions W5, W7 connected to the upper edges <NUM> of the first and second lateral wall portions W1, W2 are considerably longer than the inclined wall portions connected to the lower edges <NUM> of the first and second lateral wall portions W1, W2 and in that the inclined wall portions W4, W6 connected to the upper wall portion W3 are shorter than the inclined wall portions W9, W11 connected to the lower wall portion W8, as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam. The tubular beam <NUM> preferably has ten or more sides. In the embodiment illustrated in <FIG> and <FIG>, the tubular beam <NUM> is twelve-sided. In the embodiment illustrated in <FIG>, the tubular beam <NUM> is ten-sided. In the latter case, the lower wall portion W8 is connected to the first lateral wall portion W1 via one single intermediate wall portion W9 and to the second lateral wall portion W2 via an opposite intermediate wall portion W11.

<FIG> illustrates how the tubular beam <NUM> of the crane boom section <NUM> illustrated in <FIG> and <FIG> is telescopically mounted within a tubular beam <NUM>' of another crane boom section <NUM> of corresponding design, wherein:.

The above-mentioned first, second and third sliding elements S1-S3 are fixed to the outer side of the inner tubular beam <NUM> at the rear end thereof and the other sliding elements S4-S8 are fixed to the inner side of the outer tubular beam <NUM>' at the front end thereof.

The telescopic crane boom section <NUM> of the jib <NUM> shown in <FIG> is designed in the same manner as the telescopic crane boom section <NUM> that has been described above with reference to <FIG>.

Claim 1:
A telescopic crane boom section intended to form part of a telescopically extensible crane boom, the crane boom section (<NUM>) having an elongated main body in the form of a straight tubular beam (<NUM>) formed by one single bent metal sheet (<NUM>) and consisting of several wall portions (W1-W12) which are distributed about a longitudinal centre axis of the tubular beam (<NUM>) and connected to each other via bending corners (<NUM>) formed in the metal sheet, wherein:
- opposite longitudinal edges (34a, 34b) of the metal sheet (<NUM>) are joined to each other by a welding joint (<NUM>) extending in the longitudinal direction of the tubular beam (<NUM>);
- the tubular beam (<NUM>) has a vertical plane of symmetry (<NUM>) as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam;
- a neutral layer (<NUM>) of the tubular beam (<NUM>) extends across a first lateral wall portion (W1) on a first side of the vertical plane of symmetry (<NUM>) and across an opposite second lateral wall portion (W2) on an opposite side of the vertical plane of symmetry (<NUM>);
- the tubular beam (<NUM>) has a planar upper wall portion (W3) at its top, wherein this upper wall portion (W3) is perpendicular to the vertical plane of symmetry (<NUM>) and is connected to each one of said first and second lateral wall portions (W1, W2) via one or more intermediate wall portions (W4-W7);
- the tubular beam (<NUM>) has a planar lower wall portion (W8) at its bottom, wherein this lower wall portion (W8) is perpendicular to the vertical plane of symmetry (<NUM>) and is connected to each one of said first and second lateral wall portions (W1, W2) via one or more intermediate wall portions (W9-W12);
characterized in:
- that the welding joint (<NUM>) is located at an upper edge (<NUM>) or lower edge (<NUM>) of one of said first and second lateral wall portions (W1, W2); and
- that each one of said first and second lateral wall portions (W1, W2) has a length (L) that is <NUM>-<NUM>% of the height (H) of the tubular beam (<NUM>), as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam (<NUM>).