EP2107033B1 - Boom of a tower crane with folding-unfolding mechanism - Google Patents

Description

The present invention relates to the technical field of tower cranes, usable in particular on construction sites. More particularly, it relates to a tower crane boom which is made of two or more articulated linkage elements, and which comprises a folding-unfolding mechanism, by means of which the boom is made collapsible for transport, and deployable for its use.

• un vérin hydraulique articulé par une extrémité sur l'un des éléments du bras,
• un levier à trois points d'articulation, disposés en triangle, l'un de ces points étant situé sur le premier élément à proximité de l'axe de pivotement le liant au second élément, tandis que l'autre extrémité du vérin est liée à un deuxième point d'articulation du levier, et
• une bielle liée par une extrémité au troisième point d'articulation du levier, et liée par son autre extrémité à un point situé sur le second élément à proximité de l'axe de pivotement de ce dernier.

By the patent document FR 2499354 a folding-unfolding device is already known for an agricultural machine arm consisting of two elements articulated together about a horizontal pivot axis, the folding-unfolding device comprising:

• a hydraulic cylinder articulated at one end to one of the elements of the arm,
• a lever with three articulation points, arranged in a triangle, one of these points being located on the first element near the pivot axis linking it to the second element, while the other end of the cylinder is connected to a second point of articulation of the lever, and
• a rod connected at one end to the third point of articulation of the lever, and linked at its other end to a point on the second element near the pivot axis of the latter.

Thus, in the retracted position of the jack, the second element is folded over the first element, considered as a fixed element, which corresponds to a folded transport position. By actuating the cylinder in the direction of the output of its rod, the second element pivots to be brought into the extension of the first element, which corresponds to an extended working position.

Also known in the field of tower cranes, arrows composed of at least two elements respectively designated as "foot of arrow" and "arrowhead", these cranes being equipped with two tie rods which are respectively a short tie intended to support the foot of arrow, and a tie of greater length intended to support the point of arrow. As examples, here reference is made to the French patent FR 2636616 or its equivalent the European patent EP 0360702 .

In the achievements of older cranes of this kind, the functions of unfolding and lifting of the boom are achieved by means of at least one motorized cable, an example of such an embodiment being given by the aforementioned patents.

More recent folding boom crane designs include the use of hydraulic cylinders to control the folding and unfolding of the boom. A particular solution consists in interposing a triangular intermediate short arrow element between the jib foot and the jib, the jack controlling the pivoting of the intermediate jib element relative to the jib foot, and a mechanism articulated then simultaneously imposing the pivoting of the arrowhead relative to the intermediate boom element. However, this solution remains heavy and it has a large number of mechanical parts; in particular, it requires splints on the lower chords of the different boom elements, chords which usually constitute the runway of the boom carriage.

To simplify the realization of folding arrows tower cranes, of the kind considered here, a solution that appears interesting is that of the patent FR 2499354 aforesaid, with a jack, three-point lever and connecting rod mechanism disposed between the jib foot and the jib tip. However, because of the specificity of tower cranes, the application of the teaching of this prior patent to a folding boom crane poses various problems.

In particular, in the case of a double-crane crane boom, equipped with a trolley on the lower chords of the boom elements, it is necessary to fold the boom tip by articulating the two boom elements at their upper chords. If one uses on such an arrow the folding-unfolding mechanism according to the French patent FR 2499354 , and when the boom is deployed horizontally in the working position, the forces of the arrowhead will be transmitted to the cylinder via the connecting rod and the three-point lever. To improve the lifespan of the cylinder and the entire mechanism, it is not necessary that they are solicited during the working phase of the crane, with the boom deployed horizontally.

The document (German utility model) DE 9316113 U1 discloses a boom and boom boom crane with a fold-and-unfold mechanism consisting of a ram, a three-point hinge lever and a connecting rod for pivoting the tip arrow between a working position aligned with the boom foot and a transport position folded over the boom foot. However, this document does not provides no operating clearance in the folding-unfolding mechanism and so it does not solve the previously discussed problems.

Moreover, considering always the working position of the boom, for the proper functioning of the crane it is necessary to realize the continuity of the lower chords of the elements of this arrow, so that the truck can roll without risk of derailment or even fall, and without suffering shocks to the passage of the carriage from one boom element to another. Or to fold the boom the respective lower members of the two boom members are spaced during folding, in other words the rolling path of the carriage is interrupted. It is also necessary to avoid here connections between the lower chords by splicing operations requiring human intervention on the boom.

The present invention provides solutions to these problems, and its purpose is therefore to provide a folding and unfolding device specially adapted to a collapsible tower crane boom, this device being designed not to be stressed when the boom is deployed to horizontally, and also to ensure the continuity of the tread of the carriage in the aligned working position of the arrow.

To this end, the object of the invention is a collapsible boom of a tower crane, with folding-unfolding mechanism, the boom being equipped with two tie-rods and consisting of at least two boom members with respective upper and lower chords, the boom elements being hinged together at their upper chords, while the lower chords constitute the rolling path of a carriage movable along the boom in the aligned working position, the folding-unfolding mechanism being composed thereof -Even a cylinder, a lever with three points of articulation and a connecting rod, the lever having a first point of articulation located on a first element of arrow, the cylinder connecting this first element of arrow to a second pivot point of the lever, and the connecting rod connecting the third point of articulation of the lever to the other arrow element, so that this other arrow element is p ivotable between a working position aligned with the first boom member and a transport position folded over the first boom member, the foldable tower crane boom being essentially characterized by the fact that in the folding mechanism- unfolding, an operating clearance is created at the second point of articulation of the lever, that is to say between the jack and the lever, so that that, in the aligned working position of the boom, the folding-unfolding mechanism is not stressed, the operating clearance being obtained by means of an oblong slot provided in the lever and traversed by a transverse axis connected to one end of the cylinder, the width of the light corresponding to the diameter of this axis. Advantageously, the oblong slot of the lever is inclined relative to a horizontal plane, with reference to the position occupied by the lever when the arrow is aligned and horizontal.

Thus, in the working position of the boom and the tower crane concerned, there is a clearance between the lever and the cylinder, so that the fold-unfolding mechanism of the boom is not biased. In addition, the provisions proposed by the invention are such that, during the unfolding and folding of the boom, shocks are prejudicial to the life of the mechanism and in particular the cylinder.

More precisely, when the boom is unfolded, when the arrowhead passes through the vertical intermediate position, the force in the jack changes direction, in other words the jack pushes the arrowhead into the "rising" phase of the tip. while in the "downward" phase, the jack is pulled, which means a reversal of the force in the connection between the jack and the lever, a reversal which could be accompanied by a rapid movement and a shock which are however avoided thanks to the inclined light which imposes the following operation:

During the thrust phase of the cylinder, the axis carried by the end of the cylinder is first supported at the highest point of the lever light, then, as the arrow tip pivots and rises, the thrust is exerted on a longitudinal side of the light, to a "vertical" position of the arrowhead, that is to say a position in which the center of gravity of the arrowhead is aligned vertically with the aforementioned axis. At this moment, the force in the cylinder is zero and said axis tends to descend into the light, under the effect of gravity. However, this downward movement is prevented by the presence of a mechanical stop provided on the first boom member, at the lower ribs substantially below the second pivot point of the lever, the abutment cooperating with the end considered cylinder. Then begins the traction phase, during which the weight of the arrowhead becomes the driving element, the axis located at the end of the cylinder then bearing on the other longitudinal side of the light.

In the extended working position of the boom, not only the folding-unfolding mechanism must not be solicited, but also, to avoid any hyperstatic structure here due to the fact that the boom is already supported by its two tie rods, we must also avoid any direct support between the close ends of the respective lower chords of the two boom elements, while ensuring the continuity of the tread of the carriage.

For this purpose, according to another aspect of the present invention, the respective ends of the lower chords of the first boom element and the other boom element, located in the hinge zone of these two elements, comprise respective end pieces of complementary shapes, one of the end pieces, integral with an arrow element, having a square or rectangular base section and having in its front part a notch oriented along a diagonal of its square or rectangular section, while the complementary end piece , secured to the other boom element, also has a square or rectangular base section and comprises a pin oriented along a diagonal of its square or rectangular section, the pin being adapted to engage with a game, in aligned position working of the arrow, in the notch of the first mouthpiece.

Thus, in the working position, that is to say when the boom is completely unfolded by means of the mechanism previously defined, the two complementary ends of the lower chords, which can also be designated respectively as a female end and a male end, fit one into the other. in the other without coming directly into contact with each other, but so as to form on their upper face and on their side face a raceway which, although interrupted, has vis-à-vis pebbles of the boom carriage a longitudinal continuity, to ensure the smooth running of the rollers of the boom carriage. It is recalled here that such a carriage usually comprises four support rollers, of horizontal axis, and four lateral guide rollers, of vertical axis. The configuration of the end pieces and their interlocking ensure the continuity of the lower chords of the jib foot and the jib tip, in a horizontal plane to guide the carrier rollers of the trolley, but also in a vertical plane for guiding the lateral rollers of the same carriage.

• Figure 1 est une vue de côté d'une telle grue à tour, la flèche étant presque entièrement repliée ;
• Figure 2 représente en vue de côté la même grue, avec sa flèche dépliée ;
• Figure 3 est une vue partielle à échelle agrandie de la flèche dans sa zone de pliage, montrant plus particulièrement le mécanisme de pliage-dépliage en position dépliée de travail ;
• Figure 4 montre le détail de l'articulation du levier au vérin, en faisant apparaître l'inclinaison de la lumière dans la position dépliée correspondant à la figure 3 ;
• Figure 5 est une vue similaire à la figure 3, mais montrant le mécanisme dans une autre configuration, en position intermédiaire verticale de l'élément de flèche ;
• Figure 6 est une vue de détail similaire à la figure 4, mais correspondant à la position intermédiaire de la figure 5 ;
• Figure 7 est une vue similaire aux figures 3 et 5, montrant le mécanisme dans la position entièrement repliée de la flèche ;
• Figure 8 est une vue en perspective montrant, de façon isolée, un embout femelle prévu pour l'extrémité d'une membrure inférieure d'un élément de flèche ;
• Figure 9 est une vue en perspective montrant, de façon isolée, un embout mâle prévu pour l'extrémité d'une membrure inférieure d'un élément de flèche ;
• Figure 10 est une vue en perspective montrant les embouts complémentaires des figures 8 et 9 emboîtés l'un dans l'autre, avec indication des surfaces de roulement résultant de cet emboîtement.

The invention will be better understood from the description which follows, with reference to the attached schematic drawing showing, for example, a tower crane with folding boom equipped with the mechanism in question:

• Figure 1 is a side view of such a tower crane, the boom being almost fully folded;
• Figure 2 represents in side view the same crane, with its unfolded arrow;
• Figure 3 is a partial view on an enlarged scale of the arrow in its folding zone, showing more particularly the folding-unfolding mechanism in unfolded working position;
• Figure 4 shows the detail of the articulation of the lever to the jack, showing the inclination of the light in the unfolded position corresponding to the figure 3 ;
• Figure 5 is a view similar to the figure 3 but showing the mechanism in another configuration, in the vertical intermediate position of the boom element;
• Figure 6 is a detail view similar to the figure 4 but corresponding to the intermediate position of the figure 5 ;
• Figure 7 is a view similar to Figures 3 and 5 , showing the mechanism in the fully folded position of the boom;
• Figure 8 is a perspective view showing, in isolation, a socket provided for the end of a lower chord of an arrow member;
• Figure 9 is a perspective view showing, in isolation, a spigot provided for the end of a lower chord of an arrow member;
• Figure 10 is a perspective view showing the complementary ends of Figures 8 and 9 nested one inside the other, with indication of the rolling surfaces resulting from this interlocking.

Referring to figures 1 and 2 , it is first recalled that a crane folding tower comprises a fixed base frame 2, on which is rotatably mounted a rotating frame 3, orientable about a vertical axis A. The crane comprises a mast 4, here realized in two mast elements 5 and 6 hinged together about a horizontal axis 7, which are a lower mast element 5 and an upper mast element 6. The lower mast element 5 is articulated by its base, around a horizontal axis 8, at the front of the rotating frame 3. At the top the upper mast element 6 is articulated, around a horizontal axis 9, an arrow 10 along which is movable a carriage 11, the arrow 10 here being composed of two main elements, respectively an arrow foot 12 and a second boom member 13, which is extended by a third shorter element 14 said dart. The crane further comprises mast struts 4, a retainer 16 of the boom 10, and a ballast (not shown) carried by the rear portion of the rotating frame 3.

As shown in figure 1 this is a crane whose second boom member 13 is foldable above the boom foot 12. For this purpose, the second boom member 13 is hinged to the boom foot 12 about an axis. horizontal 17 located at the respective upper chords 18 and 19 of these two boom members 12 and 13. The dart 14 is itself foldable against the second boom member 13, the boom 10 thus folding "snail".

In working position, illustrated on the figure 2 the three elements 12, 13 and 14 of the arrow 10 are aligned substantially horizontally. The arrow 10 is supported by means of two tie rods 20 and 21 which belong to the retaining device 16, the first tie 20 supporting the jib foot 12 while the second tie rod 21 supports the second jib element 13 extended by the jib 14. In this configuration, which corresponds to the working position of the crane, the respective lower chords 22 and 23 of the jib foot 12 and the jib member 13 (as well as the lower chords of the jib 14) form a raceway for the carriage 11.

In the region of the articulation between the jib foot 12 is of the next jib element 13, is placed a folding-unfolding mechanism of the jib 10, which mechanism is designated as a whole by the reference 24 and which is represented in more detail on Figures 3 to 7 .

In general, the folding-unfolding mechanism 24 consists of a hydraulic cylinder 25, a lever 26 with three pivot points and a connecting rod 27, which take place in the space requirement of the boom. 10.

The jack 25 has a jack body 28, one end of which is hinged about a horizontal axis 29, on the jib foot 12. The central axis of the jack 25 extends substantially in the longitudinal direction of the jib 12 The rod 30 of the ram 25 is directed forwards, the anterior end of the rod 30 carrying a cylinder head 31 which is articulated (in a manner specified below) to the lever 26.

The lever 26, located in a vertical plane, has three hinge points 32, 33 and 34, arranged in a triangle. By its first point of articulation 32, the lever 26 is pivotally mounted about a horizontal axis on the front end of the jib 12, substantially at the upper chord 18 of the jib 12.

The cylinder head 31 is articulated about a horizontal axis at the second pivot point 33 of the lever 26, this second pivot point 33 being located in the rear part of the lever 26.

The rod 27 connects the third hinge point 34 of the lever 26, located in the front portion of this lever 26, to a last hinge point 35 located at the rear end of the boom member 13.

With particular reference to figures 4 and 6 , we now detail the constitution of the second pivot point 33 of the lever 26, that is to say the connection between the cylinder head 31 and the lever 26:

The cylinder head 31 supports a transverse axis 36, while on the lever 26 is formed an oblong slot 37, through which the axis 36 passes, the width of the light 37 corresponding to the diameter of this axis 36. The light 37 is inclined relative to a horizontal plane, if one refers to the position occupied by the lever 26 when the arrow 10 is aligned and horizontal ( Figures 3 and 4 ).

More particularly, in horizontal working position of the boom, as shown in FIG. figure 4 there is a clearance J between the axis 36 connected to the cylinder 25 and the highest point of the light 37, so that the folding-unfolding mechanism 24 is not biased.

To fold the boom 10, the jack 25 is actuated in the direction of the output of its rod 30, the pin 36 connected to the cylinder head 31 then exerting a thrust on the lever 26. At the beginning of the push phase, the axis 36 bears at the highest point of the light 37, then the thrust of the axis 36 is exerted on the right side (with reference to the drawing) of the light 37. The lever 26 then pivots around its first point of articulation 32, in the opposite direction of clockwise (with reference to the drawing). The corresponding displacement of the third hinge point 34 of the lever 26 pushes the rod 27, which itself moves the boom member 13 by pivoting it upwards about the axis 17.

The boom element 13 is thus raised up to a vertical position ( figure 5 ), and more precisely a position in which the center of gravity of the boom member 13 (here supplemented by the dart 14) is in a vertical plane containing the axis 36 of the cylinder head 31. At this time, the force in the cylinder 25 is zero.

The axis 36 of the cylinder head 31 could then descend freely into the lumen 37, driven by its own weight and that of the jack 25, if this movement was not prevented by a mechanical stop 38 which holds the cylinder head 31 in its position, as shown on the figure 6 . In practice, the abutment 38 may consist of a bar added to the jib element 12 at the lower chords 22 of this element, and located in the median vertical plane of the jib 10, this plane containing the jack 25.

Then, the raised boom element 13 continues to rotate, gradually lowering above the boom foot 12. The weight of the element 13, to which is added the weight of the dart 14, then makes this motor element, which causes the continuation of the output of the cylinder rod 30, the axis 36 connected to the cylinder head 31 then bearing on the left side (with reference to the drawing) of the light 37. figure 1 shows the crane in a position where the boom 10 is almost fully folded, and the figure 7 illustrates the fully folded position of the boom 10, the boom member 13 being folded horizontally above the boom foot 12.

The inclination of the light 37 of the lever 26 depends on the dimensions of the various parts constituting the folding-unfolding mechanism 24. For a good operation of this mechanism 24, the light 37 must be perpendicular to the axis of the jack 25 when the force in this jack 25 is zero, that is to say with the vertical boom element 13, more precisely in the intermediate position for which the center of gravity of the boom element 13 is in the vertical plane containing the axis 36 of the cylinder head 31.

• d'une part, un embout femelle 39 (figure 8) fixé à l'extrémité avant de chaque membrure inférieure 22 du pied de flèche 12 ;
• d'autre part, un embout mâle 40 (figure 9) complémentaire de l'embout femelle 39 et fixé à l'extrémité arrière de chaque membrure inférieure 23 de l'élément de flèche 13.

Referring finally to Figures 8 to 10 the arrangements at the ends of the lower chords 22 and 23 of the boom elements 12 and 13, which are here constituted by square section tubes, will now be described. These provisions include:

• on the one hand, a female end piece 39 ( figure 8 ) attached to the front end of each lower chord 22 of the jib foot 12;
• on the other hand, a male end 40 ( figure 9 ) complementary to the female end piece 39 and attached to the rear end of each lower chord 23 of the boom member 13.

The female end piece 39 has a short portion 41 of square section, intended to be introduced and welded to the end of the square section tube forming the lower chord 22 of the jib foot 12, and a part 42 of square base section, but wider and longer, having in its front region a cut 43 inclined at 45 °, in other words oriented along a diagonal of the square section of the tip considered.

The spigot 40 has a short portion 44 of square section, to be inserted and welded to the end of the square section tube forming the lower chord 23 of the boom member 13, and a portion 45 to base section square, but wider and longer, which forms a pin 46 also oriented along a diagonal of the square section of the tip considered.

The pin 46 of the spigot 40 has a complementary configuration of the notch 43 of the socket 39, however with slightly smaller dimensions that provide a longitudinal and transverse play during the nesting (see below). Chamfers 47 and 48 are provided respectively at the free ends of the female end 39 at the inlet of the notch 43, and the male end 40 towards the end face of the post 46, to facilitate the reciprocal centering and guidance. two end pieces 39 and 40.

The square base section of the wide portion 42 of the female end piece 39 is equal to the outer section of the tube forming the corresponding lower chord 22, so that the female end piece 39 exactly extends the tread of the trolley 11 on the Similarly, the square base section of the wide portion 45 of the spigot 40 is equal to the outer section of the tube forming the corresponding lower chord 23 so that the spigot 40 extends exactly the way. rolling of the carriage 11 on the boom member 13.

At the end of the unfolding of the boom 10, when the boom element 13 aligns with the jib foot 12, the male end piece 40 integral with the jib element 13 approaches the female end piece 39 integral with the foot of arrow 12, and the pin 46 of the male end 40 engages in the corresponding notch 43 of the female end 39, until interlocking of the two ends 39 and 40 (see figure 10 ). A longitudinal clearance L then remains between the bottom of the notch 43 and the front face of the post 46.

However, despite the clearance L, the two end pieces 39 and 40 nested one inside the other constitute, on the upper face and on one of the lateral faces a longitudinally continuous rolling surface for the rollers of the carriage 11, which surface ensures the smooth running of these rollers. More particularly, there is formed here a horizontal continuous rolling surface 49, indicated by hatching, for the horizontal axis bearing rollers of the carriage, and a vertical continuous rolling surface 50, indicated by other hatching, for the lateral rollers. guiding the carriage, these other rollers being of vertical axis.

• En modifiant les formes ou les proportions des composants du mécanisme de pliage-dépliage, en particulier du levier à trois points d'articulation,
• En adaptant l'inclinaison de la lumière de ce levier,
• En fixant les embouts aux membrures inférieures par un procédé ou moyen autre que la soudure,
• En échangeant les embouts mâle et femelle,
• En disposant l'entaille et le tenon de ces embouts selon une orientation différente d'une inclinaison à 45°, en particulier si les membrures sont de section rectangulaire et non carrée,
• En remplaçant ou en complétant la butée mécanique fixe, destinée à l'axe de la tête de vérin, par un moyen élastique tel qu'un ressort, conçu pour maintenir l'axe de la tête de vérin à l'extrémité de la lumière lors du passage de l'élément de flèche en position verticale,
• En appliquant l'invention à une grue à tour avec flèche repliable possédant des éléments de flèche en nombre différent, par exemple deux éléments de flèche seulement, autrement dit en supprimant la fléchette de l'exemple illustré,
• En appliquant l'invention à une grue à tour avec un mât d'un type ou d'une structure différente de l'exemple illustré, par exemple un mât télescopique.

One would not depart from the scope of the invention, as defined in the appended claims:

• By modifying the shapes or the proportions of the components of the folding-unfolding mechanism, in particular of the lever with three points of articulation,
• By adapting the inclination of the light of this lever,
• By attaching the end caps to the lower chords by a method or means other than welding,
• By exchanging the male and female ends,
• By arranging the notch and the tenon of these tips in a different orientation than a 45 ° inclination, in particular if the ribs are rectangular and not square,
• By replacing or supplementing the fixed mechanical stop, intended for the axis of the cylinder head, by an elastic means such as a spring, designed to maintain the axis of the cylinder head at the end of the light when from the passage of the boom element to the vertical position,
• By applying the invention to a tower crane with folding boom having different number of boom elements, for example two boom elements only, ie by removing the dart of the illustrated example,
• By applying the invention to a tower crane with a mast of a type or structure different from the illustrated example, for example a telescopic mast.

Claims (7)

1. Foldable boom of a tower crane, with a folding/unfolding mechanism, the boom (10) being equipped with two ties (20, 21) and being composed of at least two boom elements (12, 13, 14) with respective upper chord members (18, 19) and lower chord members (22, 23), the boom elements (12, 13) being articulated to one another (17) in the area of their upper chord members (18, 19) while the lower chord members (22, 23) constitute the rolling path for a carriage (11) that can be displaced along the boom (10) in the aligned working position, the folding/unfolding mechanism (24) itself being composed of a cylinder (25), of a lever (26) having three points of articulation (32, 33, 34) and of a connecting rod (27), the lever (26) having a first point of articulation (32) located on a first boom element (12), the cylinder (25) connecting this first boom element (12) to a second point of articulation (33) of the lever (26), and the connecting rod (27) connecting the third point of articulation (34) of the lever (26) to the other boom element (13), so that this other boom element (13) is pivotable between a working position aligned with the first boom element (12) and a transport position folded back on top of this first boom element (13), characterised in that, in the folding/unfolding mechanism (24), an operating clearance (J) is created in the area of the second point of articulation (33) of the lever (26), that is to say between the cylinder (25) and the lever (26), so that, in the aligned working position of the boom (10), the fotding/unfolding mechanism (24) is not subjected to stress, the operating clearance (J) being obtained by means of an oblong opening (37) provided in the lever (26) and penetrated by a transverse pin (36) connected to one end of the cylinder (25), the width of the opening (37) corresponding to the diameter of this pin (36).
2. Crane boom according to claim 1, characterised in that the oblong opening (37) of the lever (26) is inclined relative to a horizontal plane, with reference to the position occupied by the lever (26) when the boom (10) is aligned and horizontal.
3. Crane boom according to claim 2, characterised in that the opening (37) is perpendicular to the axis of the cylinder (25) when the boom element (13) is vertical, more specifically in the intermediate position for which the centre of gravity of the boom element (13) is located in the vertical plane containing the pin (36) of the cylinder head (31).
4. Crane boom according to one of claims 1 to 3, characterised in that a mechanical stop (38) is provided on the first boom element (12), in the area of the lower chord members (22) substantially below the second point of articulation (33) of the lever (26), the stop (38) cooperating with the relevant end (31, 36) of the cylinder (25).
5. Crane boom according to claim 4, characterised in that the stop (38) consists of a bar added to the boom element (12) in the area of the lower chord members (22) of this element, and located in the median vertical plane of the boom (10), this plane containing the cylinder (25).
6. Crane boom according to one of claims 1 to 5, characterised in that the respective ends of the lower chord members (22, 23) of the first boom element (12) and of the other boom element (13), located in the zone of articulation of these two elements (12, 13), comprise respective end-pieces (39, 40) of complementary shape, one of the end-pieces (39), attached to one boom element (12), having a square or rectangular base section and having in its front part (42) a slot (43) oriented along a diagonal of its square or rectangular section, whereas the complementary end-piece (40), attached to the other boom element (13), also has a square or rectangular base section and comprises a tenon (46) oriented along a diagonal of its square or rectangular section, the tenon (46) being provided to engage with a clearance (L), in the aligned working position of the boom (10), in the slot (43) of the first end-piece (39) so as to form on the upper face of these end-pieces (39, 40) and on their side face a rolling path with longitudinal continuity (49, 50) for the rollers of the boom carriage (11).
7. Crane boom according to claim 6, characterised in that chamfers (47, 48) are provided respectively at the ends of the female end-piece (39), at the inlet of the slot (43), and of the male end-piece (40), towards the front face of the tenon (46), for the reciprocal centring and guiding of the two end-pieces (39, 40).

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